This document describes research on layer-by-layer assembly of ultrathin composite films from graphite oxide (GO) sheets and polycations. GO sheets with lateral dimensions of 150 nm to 9 μm were prepared from natural graphite and deposited as monolayers and multilayers on cationic surfaces through electrostatic self-assembly. Multilayer films were grown by alternating deposition of anionic GO sheets and cationic polyelectrolytes. The monolayers consisted of 11-14 Å thick GO sheets that partially or densely covered substrate surfaces. Multilayer films were invariably thicker than expected due to folding of the flexible GO sheets. The films showed potential for electronic and photonic applications by exhibiting diodelike behavior
The document provides an overview of geopolymers, including:
1) Geopolymers are inorganic materials that form long-range, covalently bonded networks, and were coined in 1978.
2) They have various uses such as fire-resistant coatings and encapsulating toxic waste.
3) Their microstructure is amorphous at room temperature but crystalline at over 500 degrees Celsius.
This document summarizes research on creating monolayer composite films of alumina particles and epoxy using a self-assembly process called fluid forming. Key points:
- Fluid forming uses a high-spreading fluid to propel ceramic particles across an air-water interface, compressing them into a dense, ordered monolayer on a substrate.
- Initial attempts using epoxy instead of mineral oil in fluid forming with alumina particles resulted in nonuniform, low density films.
- Replacing the solvent 2-propanol with a 4:1 mixture of 2-propanol and 1-butanol produced uniform, high density alumina/epoxy composite films via fluid forming.
We report research on electrodeposition of indium sulfide films, with In2S3 a less hazardous alternative to CdS buffer layers in solar cells. Numerous organic and aqueous/organic electrolytes of InCl3, NaCl, and elemental sulfur were investigated, including several glycols and amides. Temperatures ranged from 80-170°C, and deposition voltages from -0.6 to -1.2 V (Ag/AgCl with organic filling solution). Substrates included indium tin oxide-on-glass, molybdenum, and titanium, with indium or graphite anodes. Rapid stirring was used. Deposition was sluggish in all baths. Uniformity and adherence were only moderate, with irregular coverage and cracking-and-flaking sometimes evident. The best baths were ethylene glycol or 1, 2-propanediol-based, with golden-yellow films, nominally In2S3-xOx, depositing typically heavier around the substrate edges. With low temperatures and/or large currents, brown films more rich in indium sometimes formed. Cyclic voltammetry elucidated onset potentials, secondary reactions, and photoactivity, with the greatest anodic photocurrents arising from In2S3's n-type conductivity occurring with mixed ethylene glycol/propionic acid/water baths. Scanning electron microscope photographs indicated a compact small grain microstructure for yellow films. Energy dispersive X-ray analysis and photoelectron spectroscopy data indicate up to 15% oxygen content.
This document describes a new method for synthesizing robust free-standing nanomembranes of organic/inorganic interpenetrating networks. The method involves spin-coating reactive formulations containing both organic and inorganic precursors onto a sacrificial layer. Ultraviolet light induces polymerization of the organic components while residual humidity induces sol-gel formation of the inorganic network, creating an interpenetrating network. This allows simultaneous growth of the organic and inorganic networks during spin-coating. The films are then released by dissolving the sacrificial layer, resulting in macroscopically uniform nanomembranes around 35 nm thick with unprecedented mechanical strength and flexibility despite their nanoscale thickness.
Armenag Dekmezian is a chemist with expertise in polyolefin materials science and technology. He has over 30 years of experience working for ExxonMobil Chemical Company in roles such as section manager, supervisor of a polymer characterization laboratory, and technical research associate. He now works as a forensic expert providing analysis related to polyolefins. Dekmezian has a PhD in Chemistry from UCLA and has authored over 20 publications and holds over 40 patents related to polyolefins.
Neon is one of the least reactive elements in the periodic table. No neutral molecules containing neon have ever been synthesised and it is the only stable element not to have been previously observed in an organic crystal structure.
X-Ray Diffraction Analysis of the Microscopies of Some Corrosion-Protective B...IJMER
The document analyzes the microstructures of corrosion protective coatings produced from bitumens harvested in Nigeria using X-ray diffraction. The coatings were produced by bath dipping steel specimens in heated bitumen at 230°C. XRD analysis found the coatings contained different mineral phases constituting 3.75-4.847% of the coating. Coatings from the same bitumen source (KPB) varied in mineral composition, indicating microstructural variations. The KPB coatings exhibited the highest corrosion protection while coatings from Ondo S-A bitumen exhibited the lowest. The results provide information to improve bitumen composition and coating methods for better performance.
This document provides an overview of self-assembled monolayers (SAMs) of thiolates on metal surfaces as a form of nanotechnology. It discusses SAM preparation and characterization, as well as applications of SAMs on thin metal films and nanostructures. SAMs are formed when thiol molecules spontaneously adsorb onto metal surfaces like gold to form ordered, close-packed monolayers. SAMs allow the surface properties of materials to be modified and controlled at the nanoscale and have applications in fields like biochemistry, electronics, and materials science.
The document provides an overview of geopolymers, including:
1) Geopolymers are inorganic materials that form long-range, covalently bonded networks, and were coined in 1978.
2) They have various uses such as fire-resistant coatings and encapsulating toxic waste.
3) Their microstructure is amorphous at room temperature but crystalline at over 500 degrees Celsius.
This document summarizes research on creating monolayer composite films of alumina particles and epoxy using a self-assembly process called fluid forming. Key points:
- Fluid forming uses a high-spreading fluid to propel ceramic particles across an air-water interface, compressing them into a dense, ordered monolayer on a substrate.
- Initial attempts using epoxy instead of mineral oil in fluid forming with alumina particles resulted in nonuniform, low density films.
- Replacing the solvent 2-propanol with a 4:1 mixture of 2-propanol and 1-butanol produced uniform, high density alumina/epoxy composite films via fluid forming.
We report research on electrodeposition of indium sulfide films, with In2S3 a less hazardous alternative to CdS buffer layers in solar cells. Numerous organic and aqueous/organic electrolytes of InCl3, NaCl, and elemental sulfur were investigated, including several glycols and amides. Temperatures ranged from 80-170°C, and deposition voltages from -0.6 to -1.2 V (Ag/AgCl with organic filling solution). Substrates included indium tin oxide-on-glass, molybdenum, and titanium, with indium or graphite anodes. Rapid stirring was used. Deposition was sluggish in all baths. Uniformity and adherence were only moderate, with irregular coverage and cracking-and-flaking sometimes evident. The best baths were ethylene glycol or 1, 2-propanediol-based, with golden-yellow films, nominally In2S3-xOx, depositing typically heavier around the substrate edges. With low temperatures and/or large currents, brown films more rich in indium sometimes formed. Cyclic voltammetry elucidated onset potentials, secondary reactions, and photoactivity, with the greatest anodic photocurrents arising from In2S3's n-type conductivity occurring with mixed ethylene glycol/propionic acid/water baths. Scanning electron microscope photographs indicated a compact small grain microstructure for yellow films. Energy dispersive X-ray analysis and photoelectron spectroscopy data indicate up to 15% oxygen content.
This document describes a new method for synthesizing robust free-standing nanomembranes of organic/inorganic interpenetrating networks. The method involves spin-coating reactive formulations containing both organic and inorganic precursors onto a sacrificial layer. Ultraviolet light induces polymerization of the organic components while residual humidity induces sol-gel formation of the inorganic network, creating an interpenetrating network. This allows simultaneous growth of the organic and inorganic networks during spin-coating. The films are then released by dissolving the sacrificial layer, resulting in macroscopically uniform nanomembranes around 35 nm thick with unprecedented mechanical strength and flexibility despite their nanoscale thickness.
Armenag Dekmezian is a chemist with expertise in polyolefin materials science and technology. He has over 30 years of experience working for ExxonMobil Chemical Company in roles such as section manager, supervisor of a polymer characterization laboratory, and technical research associate. He now works as a forensic expert providing analysis related to polyolefins. Dekmezian has a PhD in Chemistry from UCLA and has authored over 20 publications and holds over 40 patents related to polyolefins.
Neon is one of the least reactive elements in the periodic table. No neutral molecules containing neon have ever been synthesised and it is the only stable element not to have been previously observed in an organic crystal structure.
X-Ray Diffraction Analysis of the Microscopies of Some Corrosion-Protective B...IJMER
The document analyzes the microstructures of corrosion protective coatings produced from bitumens harvested in Nigeria using X-ray diffraction. The coatings were produced by bath dipping steel specimens in heated bitumen at 230°C. XRD analysis found the coatings contained different mineral phases constituting 3.75-4.847% of the coating. Coatings from the same bitumen source (KPB) varied in mineral composition, indicating microstructural variations. The KPB coatings exhibited the highest corrosion protection while coatings from Ondo S-A bitumen exhibited the lowest. The results provide information to improve bitumen composition and coating methods for better performance.
This document provides an overview of self-assembled monolayers (SAMs) of thiolates on metal surfaces as a form of nanotechnology. It discusses SAM preparation and characterization, as well as applications of SAMs on thin metal films and nanostructures. SAMs are formed when thiol molecules spontaneously adsorb onto metal surfaces like gold to form ordered, close-packed monolayers. SAMs allow the surface properties of materials to be modified and controlled at the nanoscale and have applications in fields like biochemistry, electronics, and materials science.
1) The document describes a method for fabricating hierarchically structured graphene-TiO2 hybrid photoanodes through capillarity-assisted electrostatic assembly.
2) The assembly process involves fine-tuning the pH to electrostatically stabilize reduced graphene oxide sheets while making TiO2 nanoparticles positively charged, allowing them to deposit on the graphene sheets.
3) After assembly and annealing, the graphene sheets conform to the TiO2 nanoparticles and develop wrinkles and folds, forming bicontinuous networks that can transport charges through the photoanode more efficiently than plain TiO2 layers.
Yin Fang is a Ph.D. candidate in chemical engineering at the University of Florida. He has developed several novel photonic crystal and thin film technologies using stimuli-responsive shape memory polymers. These include pressure-sensitive elastic photonic crystals for fingerprint identification and vapor sensing, and tunable photonic crystals for filtration and displays. He holds patents on smart light-regulating coatings and chromogenic vapor sensors. Fang has published 15 journal articles and presented his work widely at conferences. He is skilled in materials characterization and microfabrication techniques.
This document describes the development of functionalized nanofibers for separating rhodium(III) and iridium(IV) chlorido species. Three quaternary diammonium-functionalized polyvinylbenzyl chloride nanofibers were synthesized using hexamethylenediamine quaternized with methyl, ethyl, or benzyl groups. Batch experiments showed the nanofibers followed Langmuir isotherm monolayer adsorption for both metal complexes. Column studies of a binary mixture found iridium loading capacities of 15.2, 9.7, and 42.9 mg/g for the different functionalized nanofibers. Computational methods helped explain the interaction
This document provides an overview of core/shell nanoparticles, including their classes, synthesis mechanisms, and applications. It discusses the four main classes of core/shell nanoparticles: inorganic/inorganic, inorganic/organic, organic/inorganic, and organic/organic. Two common approaches for synthesizing core/shell nanoparticles are described - using pre-synthesized core particles or synthesizing the core in-situ before adding the shell. The document outlines various techniques for synthesizing different types of core/shell nanoparticles and their mechanisms. Applications include modifying material properties, biomedical uses, and controlled drug release.
The document summarizes research on aluminum-doped zinc oxide (AZO) films grown by atomic layer deposition for use as transparent electrodes. Key findings:
1) AZO films with aluminum contents from 0.8-3% atomic had the lowest resistivities around 8x10-4 Ωcm, lower than previously reported for ALD AZO films.
2) Electrical properties depended on aluminum doping, with carrier concentration peaking at 6x1020 cm-3 for 3.4% Al, then decreasing due to compensation effects from intrinsic defects like zinc vacancies.
3) All films were highly transparent (>90% average) in the visible range, with optical bandgap increasing with
The document summarizes research on synthesizing Fe2TiO5–TiO2 heterostructures for efficient electrocatalytic hydrogen evolution. Key points:
- Hierarchically arranged nanostructures with interconnected nano-petals of thickness around 50 nm were obtained using a simple hydrothermal technique with natural ilmenite as the source material.
- The electrocatalytic properties of the synthesized heterostructures were enhanced following a cathodization technique. This led to an overpotential of 301 mV for 10 mA/cm2 hydrogen evolution compared to 928 mV without cathodization.
- The enhancement is attributed to defect-rich Fe2-xTiO5-x-TiO2-x heterostructures
Fabrication and electrical characteristic of quaternary ultrathin hf tiero th...Alexander Decker
This document describes the fabrication and electrical characterization of quaternary ultrathin HfTiErO thin films grown by RF sputtering for MOS devices. HfTiErO thin films with different Ti and Er contents were deposited on silicon substrates. The films were annealed at 500°C and 700°C. Atomic force microscopy showed the surface roughness decreased with annealing. X-ray photoelectron spectroscopy analysis showed the chemical compositions. MOS capacitors were fabricated and capacitance-voltage measurements showed the annealed films at 500°C had improved electrical properties like higher dielectric constant. The HfTiErO film with composition HfTi6Er4O annealed at 500°C achieved the best electrical performance of the
Structural characterization of TiO2 films grown on LaAlO3 and SrTiO3 substrat...Oleg Maksimov
The document summarizes a study that used transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS) to characterize the structural properties of TiO2 thin films grown on LaAlO3 (LAO) and SrTiO3 (STO) substrates using reactive molecular beam epitaxy (MBE). The TiO2 films grew epitaxially in the anatase polymorph and exhibited the expected crystallographic orientation relationship with the substrates. High-resolution TEM and EELS revealed an interfacial cubic TiOx phase present at the TiO2/STO interface, but not at the TiO2/LAO or TiO2/STO buffer layer interfaces. Growing the TiO2 film on a STO buffer layer eliminated the
A Nano Capacitor Including Graphene Layers Composed with Doped Boron and Nitr...CrimsonPublishersRDMS
A Nano Capacitor Including Graphene Layers Composed with Doped Boron and Nitrogen by Majid Monajjemi* in Crimson Publishers: Peer Reviewed Material Science Journals
Electrochemical Supercapacitive Performance of Sprayed Co3O4 ElectrodesIJERA Editor
Nanocrystalline cobalt oxide (Co3O4) thin film electrodes were fabricated by spray pyrolysis method on conducting fluorine doped tin oxide (FTO) substrates using ammonia complexed with cobalt chloride (CoCl2. 6H2O) solution. The structural and morphological properties of Co3O4electrodes were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM).The surface morphology study showed the film formation of porous surface with clusters. The electrochemical supercapacitive properties ofCo3O4 electrodes were evaluated using cyclic voltammetry and galvanostatic charge-discharge method. The Co3O4electrodes showed maximum specific capacitance of 168 F/g in 1 M aqueous KOH electrolyte at the scan rate of 20 mV/s. The maximum specific energy and specific power of the cell are 2.2Wh/kg and 0.23 kW/kg, respectively.
Graphene Supported Metal Oxide for Non-Enzymatic H2O2 Sensing - Crimson Publi...CrimsonPublishersRDMS
This document summarizes research on using graphene as a support material for metal oxides in producing sensors for detecting hydrogen peroxide. Graphene is well-suited as a support due to its large surface area, high conductivity, and ability to prevent metal oxide nanoparticle aggregation. Several studies are described that synthesized composites of graphene with various metal oxides like iron oxide, cobalt oxide, zinc oxide, and copper oxide. The graphene-metal oxide composites showed enhanced sensitivity, detection limits, stability, and electrochemical performance compared to metal oxides alone, due to the properties graphene provides as a support.
This document discusses composite materials for chromatographic column separations. It describes how composite materials made of organic and inorganic components can overcome limitations of conventional ion exchange resins by exhibiting improved mechanical strength, thermal and chemical stability, ion exchange capacity, and ability to be synthesized in granular form for column operations. Nanocomposites in particular are highlighted as having unusual property combinations and potential applications in areas like drug delivery, corrosion protection, and the automotive and electronics industries. The document outlines several applications of nanocomposites and their potential to enhance sensor performance and open new application horizons.
Synthesis and characterization of nanocompositessowmya sankaran
This document defines and discusses different types of nanocomposites. It begins by defining nanotechnology and some unique properties at the nanoscale. It then discusses different types of nanomaterials that can be used in nanocomposites like nanoparticles, nanotubes, and nanorods. The document outlines three main types of nanocomposites - metal matrix, ceramic matrix, and polymer matrix - and provides examples and processing methods for each type. It concludes by discussing several applications of nanocomposites in areas like food packaging, environmental protection, aerospace, automotive, and batteries.
IA Literature Review on Synthesis and Characterization of enamelled copper wi...Editor IJCATR
This paper discusses about the survey on the various magazines, conference papers and journals for understanding the
properties of enamelled copper wires mixed with nano fillers, fundamental methods for synthesis and characterization of carbon
nanotubes. From all these papers, it was noted that the research work carried out in an enamelled copper wires filled with nano fillers
has shown better results. It was also recorded that the research work was carried mostly with single metal catalysts and very little
amount of research work has been carried out on the synthesis of carbon nanotubes using bimetallic catalysts.
Self organization of nanostructured materialsNajiya Kpp
The document discusses self-organization of nanostructured materials. It begins with introducing self-organization as a spontaneous process where ordered structures can arise from local interactions between initially disordered components without external direction. It then describes different kinds of self-organization like micelle formation, lipid bilayers, and molecular beam epitaxy. Specific examples of self-organized nanostructures include ordered arrays of core-shell nanoparticles and nanostructures formed on interlayer surfaces of layered crystals. In conclusion, the document emphasizes that self-organization is an efficient method for constructing nanostructured materials and an area of significant research interest across many fields.
Hydrothermal synthesis and characterization of oneAlexander Decker
The document summarizes research on synthesizing and characterizing one-dimensional ceria nanorods for removing chromium ions from wastewater. Key points:
1) Ceria nanorods were synthesized via a hydrothermal method and characterized using techniques like SEM, TEM, XRD, and BET surface area analysis.
2) The ceria nanorods were 20-40nm in diameter and 200-300nm in length and had a high surface area of 78 m2/g, making them promising for chromium removal.
3) X-ray absorption spectroscopy (XAS) was used to investigate the oxidation states and local structure of ceria nanorods to better understand the surface reaction during chromium removal.
This document describes research into tungsten allylimido complexes as single-source precursors for tungsten nitride (WNx) and tungsten carbonitride (WNxCy) thin films deposited by chemical vapor deposition (CVD). The complexes Cl4(RCN)W(NC3H5) (3a, R = CH3 and 3b, R = Ph) were tested as precursors. Films deposited below 550°C contained amorphous β-WNxCy, while those deposited at higher temperatures were polycrystalline. Film growth rates ranged from 5 to 10 Å/min between 450-650°C. Cleavage of the N-C imido bond is implicated
National Basic Research Program of ChinaWentao Zhai
This document summarizes Wentao Zhai's research on developing porous materials using a non-surfactant sol-gel process and their biological applications. The research aimed to address challenges with immobilizing enzymes and living cells for applications like biocatalysis. Key accomplishments included developing a room temperature sol-gel process to encapsulate biomolecules, quantifying the effect of matrix nanostructure on cell metabolic kinetics, improving gel mechanical strength, and discovering new hierarchical nanostructures. However, challenges remained with preventing cell leakage from gels. The research was conducted as part of China's National Basic Research Program from 2010-2013.
The document is the 2006 yearbook for the Vidya Shilp Academy Alumni Association. It likely contains photos and information about alumni of Vidya Shilp Academy from that year, as well as updates on their accomplishments and events held by the alumni association. The yearbook serves as a way for alumni to stay connected with each other and see how their fellow alumni are doing years after graduation.
The document shows the percentage of promoters for each month from January to October, with percentages ranging from 0% to 100%. September had the highest percentage of promoters at 100%, while February and October both had 0% promoters. The percentages of promoters varied widely month to month.
The document is a yearbook from 2005 for the Vidya Shilp Academy Alumni Association. It likely contains photos and information about alumni of the school from that year as well as updates on their accomplishments. The yearbook serves to connect former students and teachers while celebrating the achievements of the academy's alumni from 2005.
1) The document describes a method for fabricating hierarchically structured graphene-TiO2 hybrid photoanodes through capillarity-assisted electrostatic assembly.
2) The assembly process involves fine-tuning the pH to electrostatically stabilize reduced graphene oxide sheets while making TiO2 nanoparticles positively charged, allowing them to deposit on the graphene sheets.
3) After assembly and annealing, the graphene sheets conform to the TiO2 nanoparticles and develop wrinkles and folds, forming bicontinuous networks that can transport charges through the photoanode more efficiently than plain TiO2 layers.
Yin Fang is a Ph.D. candidate in chemical engineering at the University of Florida. He has developed several novel photonic crystal and thin film technologies using stimuli-responsive shape memory polymers. These include pressure-sensitive elastic photonic crystals for fingerprint identification and vapor sensing, and tunable photonic crystals for filtration and displays. He holds patents on smart light-regulating coatings and chromogenic vapor sensors. Fang has published 15 journal articles and presented his work widely at conferences. He is skilled in materials characterization and microfabrication techniques.
This document describes the development of functionalized nanofibers for separating rhodium(III) and iridium(IV) chlorido species. Three quaternary diammonium-functionalized polyvinylbenzyl chloride nanofibers were synthesized using hexamethylenediamine quaternized with methyl, ethyl, or benzyl groups. Batch experiments showed the nanofibers followed Langmuir isotherm monolayer adsorption for both metal complexes. Column studies of a binary mixture found iridium loading capacities of 15.2, 9.7, and 42.9 mg/g for the different functionalized nanofibers. Computational methods helped explain the interaction
This document provides an overview of core/shell nanoparticles, including their classes, synthesis mechanisms, and applications. It discusses the four main classes of core/shell nanoparticles: inorganic/inorganic, inorganic/organic, organic/inorganic, and organic/organic. Two common approaches for synthesizing core/shell nanoparticles are described - using pre-synthesized core particles or synthesizing the core in-situ before adding the shell. The document outlines various techniques for synthesizing different types of core/shell nanoparticles and their mechanisms. Applications include modifying material properties, biomedical uses, and controlled drug release.
The document summarizes research on aluminum-doped zinc oxide (AZO) films grown by atomic layer deposition for use as transparent electrodes. Key findings:
1) AZO films with aluminum contents from 0.8-3% atomic had the lowest resistivities around 8x10-4 Ωcm, lower than previously reported for ALD AZO films.
2) Electrical properties depended on aluminum doping, with carrier concentration peaking at 6x1020 cm-3 for 3.4% Al, then decreasing due to compensation effects from intrinsic defects like zinc vacancies.
3) All films were highly transparent (>90% average) in the visible range, with optical bandgap increasing with
The document summarizes research on synthesizing Fe2TiO5–TiO2 heterostructures for efficient electrocatalytic hydrogen evolution. Key points:
- Hierarchically arranged nanostructures with interconnected nano-petals of thickness around 50 nm were obtained using a simple hydrothermal technique with natural ilmenite as the source material.
- The electrocatalytic properties of the synthesized heterostructures were enhanced following a cathodization technique. This led to an overpotential of 301 mV for 10 mA/cm2 hydrogen evolution compared to 928 mV without cathodization.
- The enhancement is attributed to defect-rich Fe2-xTiO5-x-TiO2-x heterostructures
Fabrication and electrical characteristic of quaternary ultrathin hf tiero th...Alexander Decker
This document describes the fabrication and electrical characterization of quaternary ultrathin HfTiErO thin films grown by RF sputtering for MOS devices. HfTiErO thin films with different Ti and Er contents were deposited on silicon substrates. The films were annealed at 500°C and 700°C. Atomic force microscopy showed the surface roughness decreased with annealing. X-ray photoelectron spectroscopy analysis showed the chemical compositions. MOS capacitors were fabricated and capacitance-voltage measurements showed the annealed films at 500°C had improved electrical properties like higher dielectric constant. The HfTiErO film with composition HfTi6Er4O annealed at 500°C achieved the best electrical performance of the
Structural characterization of TiO2 films grown on LaAlO3 and SrTiO3 substrat...Oleg Maksimov
The document summarizes a study that used transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS) to characterize the structural properties of TiO2 thin films grown on LaAlO3 (LAO) and SrTiO3 (STO) substrates using reactive molecular beam epitaxy (MBE). The TiO2 films grew epitaxially in the anatase polymorph and exhibited the expected crystallographic orientation relationship with the substrates. High-resolution TEM and EELS revealed an interfacial cubic TiOx phase present at the TiO2/STO interface, but not at the TiO2/LAO or TiO2/STO buffer layer interfaces. Growing the TiO2 film on a STO buffer layer eliminated the
A Nano Capacitor Including Graphene Layers Composed with Doped Boron and Nitr...CrimsonPublishersRDMS
A Nano Capacitor Including Graphene Layers Composed with Doped Boron and Nitrogen by Majid Monajjemi* in Crimson Publishers: Peer Reviewed Material Science Journals
Electrochemical Supercapacitive Performance of Sprayed Co3O4 ElectrodesIJERA Editor
Nanocrystalline cobalt oxide (Co3O4) thin film electrodes were fabricated by spray pyrolysis method on conducting fluorine doped tin oxide (FTO) substrates using ammonia complexed with cobalt chloride (CoCl2. 6H2O) solution. The structural and morphological properties of Co3O4electrodes were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM).The surface morphology study showed the film formation of porous surface with clusters. The electrochemical supercapacitive properties ofCo3O4 electrodes were evaluated using cyclic voltammetry and galvanostatic charge-discharge method. The Co3O4electrodes showed maximum specific capacitance of 168 F/g in 1 M aqueous KOH electrolyte at the scan rate of 20 mV/s. The maximum specific energy and specific power of the cell are 2.2Wh/kg and 0.23 kW/kg, respectively.
Graphene Supported Metal Oxide for Non-Enzymatic H2O2 Sensing - Crimson Publi...CrimsonPublishersRDMS
This document summarizes research on using graphene as a support material for metal oxides in producing sensors for detecting hydrogen peroxide. Graphene is well-suited as a support due to its large surface area, high conductivity, and ability to prevent metal oxide nanoparticle aggregation. Several studies are described that synthesized composites of graphene with various metal oxides like iron oxide, cobalt oxide, zinc oxide, and copper oxide. The graphene-metal oxide composites showed enhanced sensitivity, detection limits, stability, and electrochemical performance compared to metal oxides alone, due to the properties graphene provides as a support.
This document discusses composite materials for chromatographic column separations. It describes how composite materials made of organic and inorganic components can overcome limitations of conventional ion exchange resins by exhibiting improved mechanical strength, thermal and chemical stability, ion exchange capacity, and ability to be synthesized in granular form for column operations. Nanocomposites in particular are highlighted as having unusual property combinations and potential applications in areas like drug delivery, corrosion protection, and the automotive and electronics industries. The document outlines several applications of nanocomposites and their potential to enhance sensor performance and open new application horizons.
Synthesis and characterization of nanocompositessowmya sankaran
This document defines and discusses different types of nanocomposites. It begins by defining nanotechnology and some unique properties at the nanoscale. It then discusses different types of nanomaterials that can be used in nanocomposites like nanoparticles, nanotubes, and nanorods. The document outlines three main types of nanocomposites - metal matrix, ceramic matrix, and polymer matrix - and provides examples and processing methods for each type. It concludes by discussing several applications of nanocomposites in areas like food packaging, environmental protection, aerospace, automotive, and batteries.
IA Literature Review on Synthesis and Characterization of enamelled copper wi...Editor IJCATR
This paper discusses about the survey on the various magazines, conference papers and journals for understanding the
properties of enamelled copper wires mixed with nano fillers, fundamental methods for synthesis and characterization of carbon
nanotubes. From all these papers, it was noted that the research work carried out in an enamelled copper wires filled with nano fillers
has shown better results. It was also recorded that the research work was carried mostly with single metal catalysts and very little
amount of research work has been carried out on the synthesis of carbon nanotubes using bimetallic catalysts.
Self organization of nanostructured materialsNajiya Kpp
The document discusses self-organization of nanostructured materials. It begins with introducing self-organization as a spontaneous process where ordered structures can arise from local interactions between initially disordered components without external direction. It then describes different kinds of self-organization like micelle formation, lipid bilayers, and molecular beam epitaxy. Specific examples of self-organized nanostructures include ordered arrays of core-shell nanoparticles and nanostructures formed on interlayer surfaces of layered crystals. In conclusion, the document emphasizes that self-organization is an efficient method for constructing nanostructured materials and an area of significant research interest across many fields.
Hydrothermal synthesis and characterization of oneAlexander Decker
The document summarizes research on synthesizing and characterizing one-dimensional ceria nanorods for removing chromium ions from wastewater. Key points:
1) Ceria nanorods were synthesized via a hydrothermal method and characterized using techniques like SEM, TEM, XRD, and BET surface area analysis.
2) The ceria nanorods were 20-40nm in diameter and 200-300nm in length and had a high surface area of 78 m2/g, making them promising for chromium removal.
3) X-ray absorption spectroscopy (XAS) was used to investigate the oxidation states and local structure of ceria nanorods to better understand the surface reaction during chromium removal.
This document describes research into tungsten allylimido complexes as single-source precursors for tungsten nitride (WNx) and tungsten carbonitride (WNxCy) thin films deposited by chemical vapor deposition (CVD). The complexes Cl4(RCN)W(NC3H5) (3a, R = CH3 and 3b, R = Ph) were tested as precursors. Films deposited below 550°C contained amorphous β-WNxCy, while those deposited at higher temperatures were polycrystalline. Film growth rates ranged from 5 to 10 Å/min between 450-650°C. Cleavage of the N-C imido bond is implicated
National Basic Research Program of ChinaWentao Zhai
This document summarizes Wentao Zhai's research on developing porous materials using a non-surfactant sol-gel process and their biological applications. The research aimed to address challenges with immobilizing enzymes and living cells for applications like biocatalysis. Key accomplishments included developing a room temperature sol-gel process to encapsulate biomolecules, quantifying the effect of matrix nanostructure on cell metabolic kinetics, improving gel mechanical strength, and discovering new hierarchical nanostructures. However, challenges remained with preventing cell leakage from gels. The research was conducted as part of China's National Basic Research Program from 2010-2013.
The document is the 2006 yearbook for the Vidya Shilp Academy Alumni Association. It likely contains photos and information about alumni of Vidya Shilp Academy from that year, as well as updates on their accomplishments and events held by the alumni association. The yearbook serves as a way for alumni to stay connected with each other and see how their fellow alumni are doing years after graduation.
The document shows the percentage of promoters for each month from January to October, with percentages ranging from 0% to 100%. September had the highest percentage of promoters at 100%, while February and October both had 0% promoters. The percentages of promoters varied widely month to month.
The document is a yearbook from 2005 for the Vidya Shilp Academy Alumni Association. It likely contains photos and information about alumni of the school from that year as well as updates on their accomplishments. The yearbook serves to connect former students and teachers while celebrating the achievements of the academy's alumni from 2005.
This document contains Sreenu Prasad's resume. He has over 10 years of experience in full software development life cycles for enterprise applications using technologies like .NET, SQL Server, AngularJS, and more. Currently a senior software engineer at Capgemini, he has worked on projects for clients such as Warner Bros, Airbus, and Total. Sreenu Prasad holds an M.C.A. from the University of Madras and B.C.A. from SV University.
This document discusses how data can be understood geometrically through patterns and shapes. It explains that studying these "data shapes" is a type of geometry, not the high school variety. Different types of data can be visualized as points in multidimensional spaces. Matrix algebra and techniques like principal component analysis and linear programming describe geometric transformations and constraints on these data points. Thinking geometrically helps organize and clarify the underlying algebra and code needed to analyze data.
The document is the 2007 yearbook for the Vidya Shilp Academy Alumni Association. It likely contains photos and information about alumni from that year, as well as updates on their accomplishments and events held by the association. The yearbook aims to foster connections between former students and celebrate another year of the alumni network.
The document is a 2008 yearbook for the Vidya Shilp Academy Alumni Association. It likely contains profiles of alumni members, updates on their careers and lives, and information about events from the past year for the association. The yearbook serves as a record of the past year for the alumni group and a way to stay connected with former classmates.
More treasured memories (from the group photos folder)VSAAlumni
The document is about an alumni association for Vidya Shilp Academy. It discusses treasured memories from the school and organizing events to reconnect alumni members to share experiences and memories from their time at the academy. The alumni association aims to strengthen bonds between former students and support ongoing activities and programs at the school.
Our teachers at Vidya Shilp Academy's Alumni Association are dedicated to providing students with a strong educational foundation. The teachers ensure students learn important life skills and values along with their academic lessons. They help nurture well-rounded individuals who are prepared for success in their future careers and roles as community members.
1. The document provides 10 tips for saving diesel in tractors, including knowing your tractor maintenance needs, stopping diesel leaks, turning off the engine when stopped, driving in the correct gear, addressing smoke from the tractor, keeping the engine clean of dirt, preventing wheel slippage, using properly inflated tires, matching implement size to tractor capacity, and planning field routes efficiently.
2. It also provides 7 tips for saving diesel in lift irrigation pumps, such as using a foot valve with a wide opening, using large diameter rigid PVC pipes, minimizing bends and fittings, using standard bends, properly installing the pump near the water level, using short pipe lengths, and maintaining efficient belt transmission.
The 3-point hitch system is used on farming tractors to attach implements like plows and cultivators. It consists of a center link and two lift arms or links that connect to the implement. Category II implements should have their mast holes located 610 mm above the lower pins. The rockshaft position control lever raises and lowers the hitch to adjust the implement height, while the draft control lever controls the hitch position under load. Proper adjustment of the hitch links is needed to level the front-to-back and side-to-side position of the attached implement.
ho guys this is Pranav from Class 10th .This is a PPT for the students who are in search of a ppt on Salts and its application ... If you like it please hit the like button
The rotavator is used for primary and secondary tillage to a depth of 6 inches, conserving soil moisture. It prepares land for sowing without overturning soil. It eradicates weeds and mixes manure or fertilizer into soil. The rotavator enhances soil fertility by mixing crop residues and is efficient for puddling in dry or wet soils. It saves time and fuel compared to other tillage implements.
This document describes a study on developing a novel nanocomposite structure for dye-sensitized solar cells (DSSCs) consisting of zinc oxide (ZnO) nanorods coated with titanium dioxide (TiO2) nanoparticles. The ZnO nanorods provide fast electron transport while the TiO2 nanoparticles add high surface area for dye adsorption. Transient measurements show the composite film can transport electrons over 100 times faster than TiO2 nanoparticle films alone. When tested with an alternative redox couple that has fast recombination (ferrocene/ferrocenium), the ZnO-TiO2 films generate higher currents than TiO2 films, demonstrating their ability to better collect injected electrons. However, not all charges successfully transfer from TiO2 to Z
The fabrication of nanostructured layer-by-layer (LbL) films strives for molecular control of the film properties directly connected with modifications in the film architecture. In the present report, the photoinduced birefringence and formation of the surface-relief gratings in LbL films obtained with an azopolymer (PS119) are shown to be strongly affected by the generation of the dendrimer employed in the alternating layers. Stronger adsorption of PS119 occurred when polypropylenimine tetrahexacontaamine dendrimer (DAB) of higher generations is used, due to a larger number of sites available to interact with azochromophores in PS119. In contrast, the photoinduced birefringence for LbL films
made with the generation 1 dendrimer (DABG1) was higher, which can be explained by weaker interactions between
adjacent layers. Strong interactions in LbL films consisting of PS119 and generation 3 or 5 dendrimers restrict the
chromophore mobility, leading to a smaller birefringence. The interpretation is supported by the fact that surface-relief gratings with larger amplitudes were obtained for 35-bilayer films of DABG1/PS119 (31 nm) in comparison with films from DABG5/PS119 (5 nm). These gratings were formed with mass transport arising from a light-driven mechanism, as photoinscription was successful only with p-polarized light and not with s-polarized light.
The document discusses perovskite solar cells. It begins by defining perovskites and their crystal structure. It then discusses several important studies on perovskite solar cells that improved their efficiency over time, including studies published in 2012, 2013, 2014 and 2015 that achieved efficiencies up to 19.3%. It also reviews factors that affect the performance and stability of perovskite solar cells, such as humidity, UV light, annealing temperature, and the choice of electron transport material. In conclusion, it summarizes that perovskite solar cells have advantages over traditional silicon solar cells like easier processing, higher efficiency potential, flexibility and lower cost.
Influence of Manganese doping on Structural, optical and ethanol sensing of S...IRJET Journal
This document summarizes research on the influence of manganese doping on the structural, optical, and ethanol sensing properties of copper oxide thin films synthesized using successive ion layer adsorption and reaction technique. Key findings include:
- X-ray diffraction analysis showed manganese doping reduced grain size up to 5% doping due to increased microstrain, beyond which grain size increased.
- Optical studies found the band gap increased with doping up to 5% due to the Burstein-Moss effect, then decreased with further doping likely due to excess manganese in interstitial sites.
- The 5% doped film exhibited the highest sensitivity of 87% for detecting 1500 ppm ethanol at
One-step hydrothermal synthesis of graphene decorated V2O5 nanobelts for enha...suresh kannan
This document summarizes a study that synthesized graphene-decorated vanadium pentoxide (V2O5) nanobelts through a one-step hydrothermal method for use in supercapacitors. Graphene oxide acted as both a mild oxidant to form the V2O5 nanobelts and was reduced to graphene, enhancing conductivity. The graphene-decorated V2O5 nanobelts showed improved specific capacitance compared to other compositions due to pseudocapacitance from V2O5 and double layer capacitance from graphene. A vanadium-rich composite exhibited the best performance with high specific capacitance and capacity retention over 5000 cycles.
Electrodeposited nanostructured a-Fe2O3 thin films for solar water splitting:...North Breeze
This document describes a study on the effects of platinum (Pt) doping on the photoelectrochemical performance of nanostructured alpha-iron oxide (α-Fe2O3) thin films deposited via electrodeposition. Un-doped and Pt-doped α-Fe2O3 thin films were characterized using various techniques. The results showed that Pt doping increased the density of small nanoparticles in the films and enhanced the photocurrent density for water splitting by up to a factor of 1.4 compared to un-doped films. The highest photocurrent density of 0.56 mA/cm2 was achieved for a 3% Pt-doped film. Electrochemical impedance analysis also revealed that Pt d
This thesis examines the characterization of an aluminum-doped zinc oxide thin film for use in solar cells. The document provides background on renewable energy and solar cells. It then discusses zinc oxide thin films and their advantages over crystalline solar cells. The methodology section outlines the sol-gel process used to prepare the aluminum-doped zinc oxide films on glass substrates. Various experiments are described to characterize the film thickness, surface morphology, and electrical properties. The results and discussions section analyzes the measurement findings. In conclusion, the film properties are optimized by changing processing parameters.
Christina Engler conducted research on growing epitaxial cobalt oxide thin films via magnetron sputtering to study how crystal facets influence catalytic activity for CO2 hydrogenation. Several cobalt oxide films with varying crystal structures were deposited using different sputtering parameters. Characterization with XRD and Raman spectroscopy showed spinel structured films, mixed spinel and cubic polycrystalline films, and purely cubic films were produced. Future work will confirm epitaxial growth using WAXS and LEED, and test the films' catalytic activity for CO2 hydrogenation using PM-IRAS to detect adsorbed surface species.
This document summarizes an article that appeared in a journal published by Elsevier. The attached copy is provided to the author for non-commercial research and education purposes only. Other uses such as reproduction, distribution, selling, or posting to third party websites are prohibited without permission. Authors are generally allowed to post their article in Word or Tex format to their personal or institutional website. Further information about Elsevier's archiving and manuscript policies can be found at the provided URL.
This document summarizes restrictions on sharing and distributing an article from a journal published by Elsevier. It states that the attached copy is for the author's internal non-commercial use, including for instruction and sharing with colleagues. It prohibits other uses without permission, including reproduction, distribution, selling or licensing copies, or posting to personal, institutional or third party websites. It notes that in most cases authors can post their version of the article to their personal website or institutional repository.
This document summarizes restrictions on sharing and distributing an article from a journal published by Elsevier. It states that the attached copy is for the author's internal non-commercial use, including for instruction and sharing with colleagues. It prohibits other uses without permission, including reproduction, distribution, selling or licensing copies, or posting to personal, institutional or third party websites. It notes that in most cases authors can post their version of the article to their personal website or institutional repository.
Hot hole transfer from Ag nanoparticles to multiferroic YMn2O5 nanowires enab...Pawan Kumar
Plasmonic hot carriers with a nonthermal distribution of kinetic energies have opened up new avenues in photovoltaics, photodetection and photocatalysis. While several articles have reported ultrafast hot electron injection from coinage metals into n-type semiconductors across Schottky barriers and efficient subsequent utilization of injected hot electrons, reports of hot hole harvesting are comparatively rare due to the difficulty in forming Schottky junctions between p-type semiconductors and high work function metals. In this communication, we report the fabrication, characterization and theoretical calculations of a novel integrated multiferroic-plasmonic system comprising YMn2O5 nanowires decorated on their surface with Ag nanoparticles (NPs). A Schottky barrier for holes exists at the YMn2O5-Ag hetero-interface and hot holes were injected from Ag across this barrier. The synthesized hybrid along with bare Ag NPs were tested for Raman surface photocatalytic reduction of 4-NBT (4-nitrobenzenethiol) to DMAB (p, p′-dimercaptoazobenzene) where the composite demonstrated superior activity compared to the bare metal. Ultraviolet photoelectron spectroscopy (UPS) revealed a significantly reduced work function of the composite compared to the pristine Ag, indicative of more energetic hot electrons on the surface of the composite required for efficient photoreduction. Density functional theory (DFT)-based calculations revealed localization of molecular orbitals supportive of a possible hole transfer from YMn2O5 to Ag and a reorganization of electronic states beneficial for plasmon-induced charge carrier enhancement. DFT results also indicated a purely electronic contribution to the ferroelectric polarization of YMn2O5 over and above the ionic contribution, which originated from the magnetic polarization of O 2p states.
This document discusses the structural, optical, and electronic properties of ZnO nanoparticles. It begins by describing various synthesis methods for ZnO nanoparticles, including liquid-phase, gas-phase, and vapor-phase methods. It then discusses the wurtzite crystal structure of ZnO and properties that arise from its structure like polarity and piezoelectricity. The document also covers optical and electronic properties of ZnO like its large exciton binding energy and potential optoelectronic applications. Finally, it briefly mentions some applications of ZnO nanoparticles in areas like electronics, optics, sensors, and more.
Dr. Venkata Girish Kotnur of the University of Hyderabad presented a course on graphene. Graphene is a one atom thick sheet of carbon atoms arranged in a honeycomb lattice that was first isolated in 2004. It has exceptional properties such as being 200 times stronger than steel and more electrically conductive than silicon. Potential applications of graphene include flexible displays, DNA sequencing, water filtration, and energy storage. Challenges remain in reducing the cost of graphene and developing large-scale growth and production methods.
This document discusses a study on poly(vinyl chloride)/layered silicate nanocomposites. The study analyzed the effect of organoclay type (PGV or 1.31PS) and content on the electrical, antibacterial, and oxygen barrier properties of PVC compounds. Key findings include:
1) Dielectric properties (permittivity and loss) of PVC/1.31PS nanocomposites decreased with increasing organoclay content up to 2.5 phr, indicating improved electrical insulation properties, while PVC/PGV increased with content.
2) PVC/1.31PS (2.5 phr) showed significant resistance to Gram-positive and Gram
Carbon-cuprous oxide composite nanoparticles
were chemically deposited on surface of thin glass tubes of spent
energy saving lamps for solar heat collection. Carbon was
obtained from fly ash of heavy oil incomplete combustion in
electric power stations. Impurities in the carbon were removed by
leaching with mineral acids. The mineral free-carbon was then
wet ground to have a submicron size. After filtration, it was
reacted with concentrated sulfuric/fuming nitric acid mixture on
cold for 3-4 days. Potassium chlorate was then added drop wise on
hot conditions to a carbon slurry followed by filtration.
Nanocarbon sample was mixed with 5% by weight PVA to help
adhesion to the glass surface. Carbon so deposited was doped with
copper nitrate solution. After dryness, the carbon/copper nitrate
film was dipped in hydrazine hydrate to form cuprous oxide -
carbon composite, It was then roasted at 380-400 °C A heat
collector testing assembly was constructed of 5 glass coils
connected in series with a total surface area of 1250 cm2
. Heat
collection was estimated by water flowing in the glass coils that
are coated with the carbon/copper film,. Parameters affecting the
solar collection efficiency such as time of exposure and mass flow
rate of the water were studied. Results revealed that the prepared
glass coil has proven successful energy collector for solar heat.
The document provides an overview of geopolymers, including:
1) Geopolymers are inorganic materials that form long-range, covalently bonded networks, and were coined in 1978.
2) They have various uses such as fire-resistant coatings and encapsulating toxic waste.
3) Their microstructure is amorphous at room temperature but crystalline at over 500 degrees Celsius.
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
1. The document describes a new type of mixed matrix membrane composed of zeolitic imidazolate framework nanoparticles (ZIF-8) incorporated into a polyimide polymer matrix (Matrimid 5218).
2. ZIF-8 nanoparticles around 60 nm in size were directly mixed with the dissolved polymer by solution casting, producing transparent membranes with even dispersion of nanoparticles up to 30% by weight.
3. Gas permeation tests showed that the mixed matrix membranes had enhanced gas permeability compared to the pure polymer membrane, while maintaining similar gas selectivity, indicating their potential for industrial gas separation applications.
2. grown from graphite oxide (GO),7 which can subse-
quently be reduced electrochemically to make electroni-
cally conducting graphitic films. In their work, GO
nanoparticles were prepared from synthetic graphite.
They noted that the multilayer films consisted of
incompletely exfoliated platelets that were tens of
nanometers in their lateral dimensions. In this paper,
we revisit the assembly of GO/polycation thin films,
using GO prepared from natural crystals. We show that
exfoliated GO derived from these crystals is a mechani-
cally robust material that deposits conformally on
cationic surfaces as micron-sized, nanometer-thick sheets.
Graphite oxide is a pseudo-two-dimensional solid in
bulk form, with strong covalent bonding within the
layers. Weak interlayer contacts are made by hydrogen
bonds between intercalated water molecules.8-11 The
carbon sheets in GO contain embedded hydroxyl and
carbonyl groups, as well as carboxyl groups situated
mainly at the edges of the sheets.8,9,12 While there is no
consensus as to the precise structure of GO layers,
different structural models,9a,b,10 which correspond to an
ideal formula of C8O2(OH)2, have been advanced. A
recent study of the structure of GO argues from 13C and
1H NMR evidence for the presence of epoxy groups.13
Nakajima and co-workers have proposed that the carbon
layers in GO are linked together in pairs by sp3 C-C
bonds perpendicular to the sheets.10 According to Kli-
nowski et al.,13 the carbon layers in GO contain two
kinds of domains, aromatic regions with unoxidized
benzene rings and aliphatic regions with six-membered
carbon rings. The relative size of the domains, which
are randomly distributed, depends on the degree of
oxidation. In both models, the hydroxyl groups project
above and below the carbon grid. The phenolic hydroxyl
groups are acidic and, together with the carboxyl groups,
are responsible for the negative charge on the GO sheets
in aqueous suspensions.9,13 The surface charge density
of colloidal GO particles (degree of oxidation 85%) was
measured by Fendler and co-workers as 0.4 per 100 Å2.7
The GO interlayer distance is not constant and
depends strongly on the GO:H2O ratio.8-10,15 In very
dilute aqueous suspensions, the interlayer distance is
large, so interaction between the layers is sufficiently
weak that exfoliation occurs.8 Our previous research
showed that the number of layers in the GO colloidal
particles can be controlled by the dilution of the suspen-
sions.16,17 The adsorption capacity for Cu(II) ions, which
was for both aqueous suspensions16 and thin films
deposited from these suspensions on powder supports
(ZnO, Al2O3, fumed SiO2),17 increased with decreasing
GO concentration in the starting suspension. For ex-
ample, the adsorption capacity of GO films on SiO2
increased by a factor of 2.4 when the GO concentration
in the starting suspension was decreased from 1.0 to
0.3 g/L. This result shows that more complete exfoliation
provides increased access to the GO functional groups.
For samples prepared from the colloids with GO con-
centrations of 0.02-0.3 g/L, the maximum adsorption
capacity, 22-24 mmol/g, was obtained. This value is
close to the total quantity of oxygen-containing groups
in GO (25 mmol/g9) and gives indirect evidence that
dilute GO colloids are exfoliated as monolayers.
We report here a detailed study of the preparation
and characterization of GO/polycation films grown on
planar Si and Al2O3/Al supports. Using atomic force
microscopy (AFM), ellipsometry, and electrical mea-
surements, the following questions have been addressed:
What does the first layer of the sheets adsorbed on a
substrate look like microscopically?
Can we affect the quality of mono- and multilayer
films by varying the conditions of their deposition and
the chemical composition of the substrate surface?
What are the electronic properties of GO/polycation
films, and how are they influenced by the nature of the
polycation?
Experimental Section
Materials. GO was synthesized from natural graphite
powder (325 mesh, GAK-2, Ukraine) by the method of Hum-
mers and Offeman.18
It was found that, prior to the GO
preparation according to ref 18, an additional graphite oxida-
tion procedure was needed. Otherwise, incompletely oxidized
graphite-core/GO-shell particles were always observed in the
final product. The graphite powder (20 g) was put into an 80
°C solution of concentrated H2SO4 (30 mL), K2S2O8 (10 g), and
P2O5 (10 g). The resultant dark blue mixture was thermally
isolated and allowed to cool to room temperature over a period
of 6 h. The mixture was then carefully diluted with distilled
water, filtered, and washed on the filter until the rinse water
pH became neutral. The product was dried in air at ambient
temperature overnight. This preoxidized graphite was then
subjected to oxidation by Hummers’ method. The oxidized
graphite powder (20 g) was put into cold (0 °C) concentrated
H2SO4 (460 mL). KMnO4 (60 g) was added gradually with
stirring and cooling, so that the temperature of the mixture
was not allowed to reach 20 °C. The mixture was then stirred
at 35 °C for 2 h, and distilled water (920 mL) was added. In
15 min, the reaction was terminated by the addition of a large
amount of distilled water (2.8 L) and 30% H2O2 solution (50
mL), after which the color of the mixture changed to bright
yellow. The mixture was filtered and washed with 1:10 HCl
solution (5 L) in order to remove metal ions. The GO product
was suspended in distilled water to give a viscous, brown, 2%
dispersion, which was subjected to dialysis to completely
remove metal ions and acids. The resulting 0.5% w/v GO
dispersion, which is stable for a period of years, was used to
prepare exfoliated GO.
Exfoliation was achieved by dilution of the 0.5% GO disper-
sion (1 mL) with deionized water (24 mL), followed by 15 min
sonication. The resulting homogeneous yellow-brown sol,
which contained 0.2 g/L GO, was stable for a period of months
and was used for film preparation.
An aqueous solution (0.01 M) of poly(allylamine hydrochlo-
ride), PAH, (Aldrich, MW ) 50 000-65 000) was adjusted to
pH 7 with NH3 and was used for growth of polycation layers.
(7) (a) Kotov, N. A.; Dekany, I.; Fendler, J. H. Adv. Mater. 1996, 8,
637. (b) Cassagneau, T.; Fendler, J. H. Adv. Mater. 1998, 10, 877.
(8) (a) Thiele, H. Kolloid-Z 1948, 111, 15. (b) Croft, R. C. Quart.
Rev. 1960, 14, 1.
(9) (a) Scholz, W.; Boehm, H. P. Z. Anorg. Allg.Chem. 1969, 369,
327. (b) Clauss, A.; Boehm, H. P.; Hofmann, U. Z. Anorg. Allg.Chem.
1957, 291, 205.
(10) Nakajima, T.; Mabuchi, A.; Hagiwara, R. Carbon 1988, 26, 357.
(11) Karpenko, G.; Turov, V.; Kovtyukhova, N.; Bakai, E.; Chuiko,
A. Theor. Exp. Chem. (Russ.) 1990, 1, 102.
(12) Hadzi, D.; Novak, A. Trans. Faraday. Soc. 1955, 51, 1614.
(13) Lerf, A.; He, H.; Forster, M.; Klinowski, J. J. Phys. Chem. B
1998, 102, 4477.
(14) Hennig, Z. Progr. Inorg.Chem. 1959, 1, 125.
(15) Lagow, R. J.; Badachhape, R. B.; Wood, J. L.; Margrave, J. L.
J. Chem. Soc. Dalton 1974, 1268.
(16) Kovtjukhova, N. I.; Karpenko, G. A. Mater. Sci. Forum 1992,
91-93, 219.
(17) (a) Kovtyukhova, N. I.; Chuiko, A. A. Abstracts; Fall Meeting
of the Materials Research Society, 1994, Boston, C9.6. (b) Kovtyukhova,
N. I.; Buzaneva, E. V.; Senkevich, A. Carbon 1998, 36, 549. (18) Hummers, W.; Offeman, R. J. Am. Chem. Soc. 1958, 80, 1339.
772 Chem. Mater., Vol. 11, No. 3, 1999 Kovtyukhova et al.
3. An aqueous solution of doped polyaniline (PAN) was made
from a saturated solution of the emeraldine base form in
dimethylformamide. A 3 mL portion of this solution was slowly
added with stirring to 26 mL of water, which had been acidified
to pH 3.5 with aqueous HCl. The pH of the final PAN solution
was then adjusted to 2.5 by addition of aqueous HCl. The alu-
minum Keggin ion Al13O4(OH)24(H2O)12
7+ was prepared trom
Al13O4(OH)25(H2O)11(SO4)3‚x(H2O), which was available from
a previous study.5 Briefly, 0.102 g of the sulfate salt was added
to a solution of 0.042 g of BaCl2 in 200 mL of water and stirred
overnight. The resulting 0.3 mM solution of the chloride salt
of the aluminum Keggin ion was filtered using a 0.2 µm filter.
Polished (100) Si wafers were sonicated in CCl4 for 15 min
and then rinsed with 2-propanol and water. Their surface was
then hydroxylated by 30 min sonication in “piranha” solution
(4:1 concentrated H2SO4:30% H2O2) (CAUTION: piranha
solution reacts violently with organic compounds!) and was
rinsed sequentially with water, methanol, and 1:1 methanol/
toluene before the surface derivitization steps began.
Aluminum foil, Al-coated glass, both bearing a native oxide,
and ITO glass were cleaned by washing with hexane for 15
min prior to GO adsorption.
Multilayer GO/PAH Film Growth. Hydroxylated silicon
wafers were primed with one of three different types of cationic
monolayers in order to initiate the growth of the GO films.
This was achieved either by (1) reacting with 4-((dimethyl-
methoxy)silyl)butylamine (15 h treatment with a 5% toluene
solution under dry Ar, over KOH at ambient temperature) or
by (2) adsorbing a monolayer of aluminum Keggin ions (5 min
adsorption from aqueous solution of the chloride salt at 80 °C19
)
or by (3) adsorbing PAH (15 min adsorption from a 0.01 M
aqueous solution at pH 7 and ambient temperature). The
primed Si substrates (1, 2, and 3) are designated hereafter as
Si(NH2), Si(OH)/Al-Kg, and Si(OH)/PAH, respectively.
The primed substrates were immersed in an aqueous (pH
5) or aqueous ammonia (pH 9) GO sol (0.2 g/L) for 15 min and
then rinsed with deionized water and dried in flowing Ar. The
samples were then immersed in aqueous PAH solutions for
15 min, rinsed with deionized water, and dried in flowing Ar.
Multilayer GO/PAH films were grown by repeating these
adsorption cycles. Preliminary experiments had shown that
the thickness of a deposited layer (estimated by ellipsometry)
does not depend on the substrate/solution contact time in the
range from 2 min to 2 h. For electronic measurements,
multilayer (GO/PAH)14 and (GO/PAN)30 films were grown on
ITO in similar adsorption cycles. For comparison purposes, a
GO colloid film (ca. 90 nm thick) was prepared by dip-coating
the ITO/glass in the GO colloidal dispersion.
Characterization. Atomic force microscopy (AFM) images
of the layers deposited on Si substrates were obtained with a
Digital Instruments Nanoscope IIIa in tapping mode, using a
3045 JVW piezo tube scanner. The 125 µm etched Si cantile-
vers had a resonant frequency between 250 and 325 kHz, and
the oscillation frequency for scanning was set to ∼0.1-3 kHz
below resonance. Typical images were obtained with line scan
rates of 2 Hz while 256 × 256 pixel samples were collected.
Ellipsometric measurements were made with a Gaertner
model L2W26D ellipsometer. An analyzing wavelength of 632
nm was used, because GO absorbs minimally at this wave-
length. The incident angle was 70° and the polarizer was set
at 45°. Ellipsometric parameters were measured following each
GO or PAH adsorption step. Si substrates were dried in an
Ar stream before each measurement. The film thickness of the
GO/PAH multilayers was calculated using the Si refractive
indices, ns ) 3.875 and ks ) -0.018, determined from a blank
sample. The refractive index of GO/PAH films was estimated
as nf ) 1.540, kf ) 0.
Transmission electron microscope (TEM) images were ob-
tained with a JEOL 1200 EXII microscope at 120 kV ac-
celerating voltage. Samples were prepared by immersing a
copper grid in the GO sol and drying in air.
The elemental composition of GO was determined by using
a home-built mass spectrometer with laser probe (LMS). The
diameter of the crater for single laser impulse was 0.42-0.48
mm, and the depth was 1 µm. IR spectra were recorded using
a Perkin-Elmer 325 instrument. XPS spectra were obtained
using a Kratos Series 800 spectrometer with hν)1253.6 eV
and an analyzing window of 4 × 6 mm2
. The accuracy of the
measured core level binding energies (Eb) was 0.1 eV. For LMS,
IR, and XPS experiments, GO samples were prepared as films
by drying a droplet of the sol in air at ambient temperature.
X-ray powder diffraction (XRD) patterns were recorded with
a DRON-1 instrument using Cu KR radiation. Prior to the
measurement, the GO sample was dried in a vacuum over P2O5
for 24 h.
Electrical measurements of films deposited on ITO glass
were carried out using top Pt electrode contacts that were 10
µm in diameter and mechanically pressed into the film, using
a home-built parametric analyzer. The sensitivity of current
measurements was 0.01 nA. All measurements were carried
out in air at ambient temperature. The turn-on potential for
all thin film devices studied was taken as the potential at
which a current of 1.0 nA was observed. In regions where
current was more than 3 nA, every step of voltage increase
(typically 0.1 mV in both the forward and reversed directions)
was followed by repeating the measurement cycle to ensure
the reproducibility of the current measured at the lower
voltage. Measurements were considered irreversible (i.e., a
permanent change to a more conductive state occurred) when
the current recorded the second time at the lower voltage was
noticeably higher than that measured in the previous cycle.
Results and Discussion
Characterization of the GO Colloid. The XRD
pattern of GO prepared by preoxidation with persulfate
followed by oxidation with permanganate reveals a
sharp 002 reflection at 2θ ) 12.80°, which corresponds
to a c-axis spacing of 6.91 Å This value falls within the
range of 6.3-7.7 Å reported in the literature9a,10,20,21 for
GO prepared from natural graphite according to Hum-
mers’ method.18 No 002 diffraction peak from unreacted
graphite (d ) 3.35 Å) is observable in the XRD pattern.
The IR spectrum of GO prepared by this method is
essentially identical to that reported in the litera-
ture.9a,12,21 A band at 3420 cm-1 and a broad band
centered around 3220 cm-1 are attributed to O-H
stretching vibrations of the C-OH groups and water,
respectively; a band at 1730 cm-1 is assigned to CdO
stretching vibrations of the carbonyl and carboxyl
groups. Bands at 1365, 1425, and 1615 cm-1 are
assigned to the O-H deformations of C-OH groups and
water, respectively. A band at 1080 cm-1 is due to C-O
stretching vibrations.
Deconvolution of the C1s peak in the XPS spectrum
shows the presence of four types of carbon bonds: C-C
(284.8 eV), C-O (286.2 eV), CdO (287.7 eV), and O-Cd
O (288.5 eV). By integrating the area of the deconvolu-
tion peaks, the following approximate percentages were
obtained: C-C, 49.5; C-O, 31.4; CdO, 9.1; O-CdO,
2.9.
The LMS spectrum of GO prepared by this method
gave the following atomic composition (wt %): H, 2.3;
C, 45.2; O, 46.5; P, 3.3; K, 2.7; C:O ratio ) 1.3. The same
or nearly the same C:O ratio has been found previously
for GO samples prepared from natural graphite.21,22 It
is generally accepted that the conversion of graphite to
(19) Schoenherr, S.; Goerz, G.; Mueller, D.; Gessner, W. Z. Anorg.
Allg. Chem. 1981, 476, 188.
(20) Carr, K. E. Carbon 1970, 8, 245.
(21) Kyotani, T.; Suzuki, K.; Yamashita, H.; Tomita, A. Tanso 1993,
160, 255.
(22) Slabaugh, W. H.; Seiler, B. C. J. Phys. Chem. 1962, 66, 396.
Assembly of Ultrathin Composite Films Chem. Mater., Vol. 11, No. 3, 1999 773
4. GO is complete when the C:O ratio becomes 2.0. The
observed ratio C:O:H ) 4:3.1:2.5 is richer in O and H
than that calculated for C8O2(OH)2: 4:2:1; this can be
explained by the presence of intercalated/adsorbed
water and carboxyl groups, as shown by IR and XPS. It
should be noted that the ideal formulation does not take
into account the presence of carboxyl groups, which are
mainly situated on the edges of the sheets,8 or interca-
lated water, some amount of which is probably an
integral part of the GO structure.3 Allowing that 2.9%
of the carbon atoms are present as carboxyl groups (from
XPS) and assuming that the potassium ions are incor-
porated by ion-exchange, we calculate a formula of
C3.77O2.05H0.92K0.07‚0.73H2O, or C8O2.25(OH)1.95(OK)0.15‚
1.55H2O, which gives a C:O:H ratio of 4:2.95:2.5. The
remaining oxygen (2.05 wt %) is most probably bound
to phosphorus, an impurity introduced by the graphite
preoxidation step.
TEM images of the GO sol (Figure 1) reveal flexible,
wrinkled sheets of different lateral sizes ranging from
hundreds to thousands of nanometers. Flexible GO
particles were also observed by Hennig and Carr.14,20
No graphite particles are observed in these images.
AFM Images of the First Adsorbed GO Layer. Si
Substrates. AFM images (Figure 2a-c) of the GO films
deposited in one adsorption cycle from aqueous solution
show surface coverages of about 30% for Si(NH2), 85%
for Si(OH)/PAH, and 90% for Si(OH)/Al-Kg substrates.
The main features are 150-900-nm-wide islands, whose
size is close to that determined by TEM for the GO
sheets. In some cases, corrugations and the turned-in
edges of the sheets are seen. For the PAH-primed Si
substrate, the average roughness of the sheet-covered
part of the surface is 4.5 Å By comparison, the rough-
ness of the Si(OH)/PAH substrate was 6.2-Å, indicating
slight smoothing of the surface by the GO monolayer.
The height of the islands on Si(NH2) and Si(OH)/PAH,
10.6-14.1 Å, and the average roughness of their surface,
3.9-4.5 Å, are consistent with exposure of GO basal
planes covered by adsorbed H2O.8-10 Ellipsometric
measurements gave 11 and 14 Å thicknesses for GO
monolayers on Si(NH2) and Si(OH)/PAH. Considering
that the thickess of the priming layer is about 7 Å, and
that the GO sheets cover only part of the surface, these
results are in reasonable agreement with the island
heights measured by AFM.
According to Nakajima’s structural model,10 the thick-
ness of a GO monolayer depends on the content of
hydroxyl groups on its basal planes and can reach 8.2
Å for the completely hydroxylated monolayer. Assuming
the presence of completely hydroxylated GO carbon
layers in very dilute colloids, one can take the thickness
of a GO monolayer as 8.2 Å. By comparing this value
with the height of the islands in Figure 2, one can
conclude that the islands consist of a single GO sheet
covered by a layer of adsorbed water molecules. The
thickness of doubled GO layers can be estimated from
the thickness of two GO monolayers, 2 × 8.2 Å, plus
the distance between the layers, which is determined
by the thickness of the layer of weakly bound mobile
water molecules.11,13 This interlayer distance can be
estimated at about 3 Å, from the repeat distance along
the c-axis of well-hydrated GO samples, Ic )11 Å,9,14
minus the thickness of a GO monolayer, 8.2 Å. This
means the thickness of doubled GO layers should be
about 20 Å or more, if water adsorbed onto the top basal
plane is considered. This value is significantly greater
than the height of adsorbed islands (10.6-14.1 Å). The
height, 20.1 Å, of the GO islands adsorbed onto the Al-
Keggin-primed Si surface (Figure 2b) is roughly consis-
tent with the thickness of the Al-Keggin anchoring layer
(7 Å23) and a monolayer of GO sheets covered by
adsorbed H2O (10.6-14.1 Å).
An AFM image of the first GO layer adsorbed from
an aqueous ammonia suspension (pH 9) onto a Si(NH2)
substrate is shown in Figure 2d. In this case, the
adsorption process selects much larger sheets (900-
9000 nm) which cover about 60-65% area of the surface.
The dissociation of the GO hydroxyl groups (situated
mainly on the basal planes) occurs around pH 9 and
significantly increases the negative charge density on
the GO sheets. The increased attraction of the sheets
for the cationic surface results in higher coverage than
that observed at lower pH. This interaction is appar-
ently more effective for the larger sheets, which can
bridge over neutral regions of the incompletely primed
surface. Previous studies have shown that the amine
priming layer does not completely cover the surface, and
that it is only partially protonated at pH 9.5 The average
roughness of the sheets on the surface is 4.4 Å. The
height of the sheets, which are corrugated and some-
times have turned-in edges, is in the range of 19-23 Å.
The increased thickness may be due to a hydrated layer
of charge-compensating NH4
+ ions, which cover the
basal plane surface. The adsorption of a bilayer of sheets
(23) Johansson, G.; Lundgren, G.; Sillen, L. G.; Soderquist, R. Acta
Chem. Scand. 1960, 14, 769.
Figure 1. Transmission electron micrograph of colloidal
graphite oxide particles.
774 Chem. Mater., Vol. 11, No. 3, 1999 Kovtyukhova et al.
5. seems unlikely, since in basic media the exfoliation of
GO occurs more readily.8
Al2O3/Al Substrates. AFM images of the first GO
layer grown on Al-coated glass (Figure 3a) and alumi-
num foil (not shown) resemble those of the substrates,
except that corrugations similar to those seen in the
TEM image of GO and AFM images of the GO/Si have
appeared. Because both Al2O3/Al substrates are very
rough and because the flexible GO sheets conform to
the surface, it is not possible to determine the lateral
and vertical dimensions of the sheets. However, the
average roughness of the brighter area in the image,
which is presumed to have an adsorbed GO sheet, is
2.7 nm. By comparison, the substrate roughness is 3.5-
nm, again indicating a slight smoothing of the surface
by the GO sheets.
Characterization of GO/PAH Multilayers.
Ellipsometry. Figure 4 shows plots of film thickness,
determined by ellipsometry, versus the number of
adsorption cycles for GO/PAH multilayer films. The
films were grown on Si(NH2), Si(OH)/PAH, and Si(OH)/
Al-Kg substrates. The linearity of the film thickness
Figure 2. Tapping-mode AFM images of the first graphite oxide layer deposited from aqueous and aqueous ammonia sols on
primed Si substrates: (a) Si(NH2), GO sol pH 5, with the linescan showing the apparent height of sheet (14 Å) above the background;
(b) Si(OH)/Al-Kg, GO sol pH 5; (c) Si(OH)/PAH, GO sol pH 5; and (d) Si(NH2), GO sol pH 9.
Assembly of Ultrathin Composite Films Chem. Mater., Vol. 11, No. 3, 1999 775
6. plots indicates that on average the same amount of
material is deposited in each adsorption cycle. However,
for each the sample, the average increase in layer
thickness per PAH/GO bilayer is different and ranges
from 29 to 50 Å (Table 1). The lowest value, 29 Å per
PAH/GO bilayer, is found for GO grown from aqueous
ammonia solution (pH 9). The smaller layer pair thick-
ness in this case may arise from partial deprotonation
of the underlying PAH layer at this pH. Because the
surface charge density is lower, fewer anionic sheets are
bound by the polymer per unit area.
It should be noted that the measured thickness of the
GO/PAH layer pair (40-50 Å) is more than that
expected from the thickness of monolayer GO sheets
(10.6-14.1 Å, as estimated by AFM for the first depos-
ited GO layer, Figure 2a-c) and the thickness of single
PAH layer (5 Å24). This can be explained in part by
folding of the flexible GO sheets, which is apparent in
the AFM images of all GO monolayers except the low
coverage layer grown on Si(NH2). The multilayer ad-
sorption model proposed by Kleinfeld and Ferguson for
clay/polycation films1b may also be operative for GO/
PAH. In their model, each adsorption cycle deposits
about two layers of polyelectrolyte, but they rearrange
(possibly by folding in the present case) into alternating
single sheet/polycation films.
A plot of the thickness of a GO/PAH film grown from
aqueous solution onto Si(NH2) is linear only after the
third cycle. The average increase in thickness per PAH/
GO bilayer is 23 Å in the first two adsorption cycles and
49 Å in the following three adsorption cycles (Figure
4). This behavior is reminiscent of that observed by
Kleinfeld and Ferguson for clay/polycation films, which
nucleate in islands and completely cover the surface
only after several adsorption cycles.25 We conclude that
the GO/PAH film coverage is relatively complete after
adsorption of the second bilayer (the first adsorption
cycle covers ∼30% of the surface; Figure 2a). In subse-
quent adsorption cycles, the layer pair thickness is close
to that found for GO/PAH multilayers on Si(OH)/PAH.
In the latter case, the surface coverage is ∼85% after
the first adsorption cycle, as shown in Figure 2c.
AFM. AFM images of four or five bilayer GO/PAH
films on all three substrates were similar and did not
clearly resolve the sheet edges or the voids between
sheets. From these images, one can only conclude that
the multilayer films completely cover the surface. Figure
3b shows a typical image of a Si(OH)/Al-Kg/(GO/
PAH)3GO film. The average roughness of this film is
20 Å, which is consistent with a surface of loosely tiled
and folded sheets. Multilayer film roughness and thick-
ness parameters, determined by AFM and ellipsometry,
respectively, are summarized in Table 1.
For all the substrates under investigation (except for
very rough aluminum foil), GO/PAH multilayers depos-
ited from aqueous sols on Al(OH)x-terminated surfaces
(Si(OH)/Al-Kg and Al/Al2O3) are smoother than those
deposited on NH2-terminated surfaces (Si(NH2) and Si-
(OH)/PAH) (Table 1). Comparing the surface morphol-
ogies of the first GO layer and the multilayer films, one
can see that the more densely tiled first layer (∼90%,
Figure 2b), grown on the Keggin-primed surface, yields
a smoother and more compact multilayer film, whereas
the poorly tiled first layer (∼35%, Figure 2a) on Si(NH2)
yields the roughest multilayer surface. Again, this
behavior is consistent with the model proposed by
Kleinfeld and Ferguson for multilayer growth on is-
lands, which eventually coalesce into smoother films.25
(24) (a) Lvov, Yu.; Haas, H.; Decher, G.; Mohwald, H.; Kalachev,
A. J. Phys. Chem. 1993, 97, 12835. (b) Lvov, Yu.; Decher, G.; Mohwald,
H. Langmuir 1993, 9, 481, (c) Decher, G.; Hong, J.; Schmitt, J. Thin
Solid Films 1992, 210/211.
(25) Kleinfeld, E. R.; Ferguson, G. R. Chem. Mater. 1996, 8, 1575.
Figure 3. (a) Tapping-mode AFM image of the first graphite
oxide layer deposited from the aqueous sol onto Al-coated glass
and (b) image of a (GO/PAH)3GO film on Si(OH)/Al-Kg. Z range
is 15 nm in both images.
Figure 4. Ellipsometric measurements of the thickness of
multilayer GO/PAH films vs number of adsorption cycles: 1,
Si(OH)/PAH(GO/PAH)nGO; 2, Si(OH)/Al-Kg(GO/PAH)nGO; 3,
Si(NH2)(GO/PAH)nGO; 4, Si(NH2)(GO/PAH)nGO (pH 9). The
thicknesses at an abscissa value of 0.5 correspond to primer
cationic layers; points on the plots refer to films terminated
by a GO layer.
776 Chem. Mater., Vol. 11, No. 3, 1999 Kovtyukhova et al.
7. The most compact and smooth multilayer films are
grown from aqueous ammonia solution (pH 9), from
which very large (up to 9 µm wide) GO sheets are
adsorbed. Each of these sheets covers an area which
exceeds the area of voids between the sheets (see Figure
2d). Multilayer films grown on these large and smooth
islands have the best overall quality.
In this connection, it is important to emphasize that
the lateral dimensions of the GO sheets prepared by
preoxidation and oxidation of natural graphite, followed
by proper dispersion of the product GO, are significantly
larger than those previously used for layer-by-layer
assembly (50-150 nm)7. While there have now been
many studies of exfoliated lamellar compounds,4 it is
rare that one find sheets with lateral dimensions
exceeding 1-2 µm, even when the starting material
consists of relatively large single crystals. The fragmen-
tation of large individual sheets into submicron pieces
may arise from mechanical stress during the exfoliation
process. The factor that limits their lateral dimensions
is probably the density of defects in the sheets, which
apparently is quite low in GO prepared from natural
graphite. The other important point to note is that
complete oxidation is needed to make unilamellar GO
as opposed to a suspension of graphite core/GO shell
particles. This fact, and the higher dilution of the GO
dispersions used in this study, may be the reason that
the sheets in our monolayer films are thinner (10-14
Å) than those reported by Kotov et al. (18-27 Å).7
Multilayer films grown from unilamellar colloids of
zirconium phosphate, layered transition metal oxides,
and layered metal dichalcogenides typically have rough-
nesses on the order of the individual sheet thickness
(0.8-1.6 nm).5,6 In contrast, the relatively high rough-
ness of the GO/PAH multilayers is most probably due
to the flexibility of the GO sheets, which allows folding
and turning up of the edges of the sheets. However, in
the case of the relatively rough surface of the Al-coated
glass, adsorption of the large GO lamellae and multi-
layer (GO/PAH)4GO films results in smoothing of the
surface (Table 1).
Electronic Properties of GO/Polycation Films.
The electrical characteristics of GO/polycation multi-
layer films were investigated with both electronically
insulating (PAH) and conducting (PAN) polycations. For
comparison purposes, a restacked GO colloid containing
no polycations was also investigated. In all cases, the
films were grown on ITO glass, and the top contact was
Pt. ITO and Pt are respectively intermediate and high
work function contacts, and both GO and PAN are good
hole conductors. One would therefore expect that a
rectifying contact could form between the film and ITO
and that the forward bias direction would have the Pt
electrode positve and ITO negative.
All GO devices tested in this manner showed rectify-
ing behavior (Figure 5). (An ITO/Pt control experiment
gave the expected ohmic response). For the 60-nm-thick
ITO-(GO/PAH)14GO-Pt device (curve 2), the “forward”
(ITO(-)/Pt(+)) and “reverse” bias turn-on potentials
were 0.42 and 0.82 V, respectively. These potentials
correspond to electric fields, E, of 7.0 × 104 and 1.4 ×
105 V cm-1, respectively. When the conducting polymer
PAN is substituted for PAH (curve 1), the forward bias
turn-on potential is basically unaffected, but the reverse
bias turn-on potential decreases to 0.41 V. In this case
the electric fields required to obtain a current density
of 5 mA cm-2 were 4.8 and 4.4 × 104 V cm-1 in the
forward and reverse directions, respectively. These
fields are 1-2 orders of magnitude smaller than those
of single and bilayer polymer devices.26 For both devices,
the current follows the ln(I) ∼ E-1 law, as expected for
a tunneling-based charge injection mechanism. This is
similar to the behavior observed for most single and
bilayer polymer diode devices.
The resistivity of both the ITO-(GO/PAH)14GO-Pt
and ITO-(GO)x-Pt devices is on the order of 106 Ω cm,
and that of the thicker ITO-(GO/PAN)30GO-Pt device
is approximately 1 order of magnitude lower. The
(26) (a) Greenham, N. C.; Moratti, S. C.; Bradley, D. D. C.; Friend,
R. H.; Holmes, A. B. Nature 1998, 365, 628. (b) Vestweber, H.; Oberski,
J.; Greiner, A.; Heitz, W.; Mahrt, R. F.; Baessler, H. Adv. Mater. Opt.
Electron. 1993, 2, 197.
Table 1. Characterization of Multilayer GO/PAH Films by AFM and Ellipsometry
sample
average roughness of the
anchored substrate surface, Å
average roughness of
the film surface, Å
total film
thickness, Å
average increase in film
thickness per PAH/GO
bilayer, Å
Si(NH2)/(GO/PAH)3GO 3.8 27 137 23 (first, second)
49 (third, fourth)
Si(NH2)/(GO/PAH)3GOa 3.8 13 105 29
Si(OH)/PAH/(GO/PAH)3GO 6.2 26 176 51
Si(OH)/Al-Kg/(GO/PAH)3GO 4.3 20 130 38
Glass/Al/Al2O3/(GO/PAH)4GO 35.0 22
Al foil/Al2O3/(GO/PAH)4GO 48.0 58
a GO was adsorbed from aqueous ammonia solution (pH 9).
Figure 5. Current vs voltage characteristics of GO colloid and
GO/polycation multilayer films deposited on ITO-coated
glass: (1) 120-nm-thick ITO-(GO/PAN)30GO-Pt device; (2) 60-
nm-thick ITO-(GO/PAH)14GO-Pt; (3) 90-nm-thick ITO-
(GO)x-Pt. The positive direction on the voltage axis is ITO(+)/
Pt(-).
Assembly of Ultrathin Composite Films Chem. Mater., Vol. 11, No. 3, 1999 777
8. difference arises from the electronic conductivity of the
PAN layers, which mediate electron transfer between
GO layers. For both the GO/polycation and GO films,
an irreversible conversion to a more conductive state
occurs when the device is held at high current density.
For ITO-(GO/PAH)14GO-Pt and ITO-(GO/PAN)30GO-
Pt, this effect became noticeable at current densities of
17 and 70mA/cm2, respectively. A similar effect begins
at a current density of about 40 mA/cm2 with ITO-
(GO)x-Pt. At current densities above 470 mA/cm2, the
current gradually increases by 3 orders of magnitude
at constant voltage with the ITO-(GO/PAN)30GO-Pt
device. We tentatively ascribe this behavior to an
internal electrochemical reaction, which reduces GO to
a more conductive carbon-rich material. Apparently, the
PAN samples are more resistant to this effect, possibly
because the PAN itself acts as a reservoir of oxidizing
equivalents. Similar electrochemical effects have been
found with electrodes prepared from bulk GO27 and
were also observed by Kotov et al., in their study of GO/
poly(diallyldimethylammonium chloride) thin films.7
Conclusions
We have shown that the quality and morphology of
GO monolayer thin films depend on the source of
graphite, its degree of oxidation, and the conditions used
to prepare the GO colloid, as well as on the nature of
the surface-priming layer and the pH of the adsorbing
solutions. By properly controlling these parameters, one
can select intact, unilamellar GO sheets and achieve
reasonably dense (ca. 90%) coverage on a cationic
surface. GO sheets prepared in this manner from
natural graphite have larger lateral dimensions (1-9
µm) than any other lamellar inorganic colloid studied
to date. The thickness of an individual GO layer, which
can be fully exfoliated by means of preoxidation and
oxidation steps, followed by appropriate dilution, is on
the order of 10-14 Å
Multilayer GO/PAH films deposited in four or five
adsorption cycles completely cover the surface of cationic
substrates. The average roughness of these multilayer
films is lowest when the GO suspension contains large
sheets and when the coverage of the first layer of sheets
is highest. However, sequential adsorption of GO and
polycations invariably results in an average thickness
change per adsorption cycle that is 2-3 times the
monolayer thickness. This appears to occur because the
flexible GO sheets fold and overlap on the surface.
The electronic characteristics of GO multilayer films
contacted by ITO and Pt electrodes are consistent
with its hole-conducting properties. By interleaving GO
with poly(aniline), a hole-conducting polymer, the di-
odelike behavior of the films is retained, but the
conductivity is increased by approximately 1 order of
magnitude. Thin film GO devices are, however, ir-
reversibly changed at high current density, most prob-
ably because of electrochemical reduction of GO to
carbon.
Acknowledgment. This work was supported by
Civilian Research and Development Foundation (UC1-
338), and by the National Science Foundation (CHE-
9529202). Instrumentation for AFM experiments was
provided by National Science Foundation grant CHE-
9626326.
CM981085U(27) Touzain, P.; Yazami, R. J. Power Sources 1985, 14, 99.
778 Chem. Mater., Vol. 11, No. 3, 1999 Kovtyukhova et al.