This document summarizes a study on a nonvolatile resistive random access memory device based on the heterojunction of silver nanoparticles and aluminum oxide. The device structure consists of aluminum-aluminum oxide-silver nanoparticles-aluminum. Current-voltage measurements show the device transitions between two states in two steps - a major transition with a resistance ratio of 105 and a minor transition with a ratio of about 101. The memristor operates at low voltages with good uniformity. Scanning electron microscopy, X-ray diffraction and optical absorption characterization confirm the formation of aluminum oxide and silver nanoparticles.
TiO2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Dr...Pawan Kumar
The lack of active, stable, earth-abundant, and visible-light absorbing materials to replace
plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and costeffective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of
atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity
for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) a
large bandgap between optical and acoustic phonon modes (2) and no electronic bandgap, which
allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in
this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing
plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that
extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active
HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
A ruthenium trinuclear polyazine complex was synthesized and subsequently immobilized through
complexation to a graphene oxide support containing phenanthroline ligands (GO-phen). The developed
photocatalyst was used for the photocatalytic reduction of CO2 to methanol, using a 20 watt white cold
LED flood light, in a dimethyl formamide–water mixture containing triethylamine as a reductive
quencher. After 48 h illumination, the yield of methanol was found to be 3977.57 5.60 mmol gcat
1.
The developed photocatalyst exhibited a higher photocatalytic activity than graphene oxide, which
provided a yield of 2201.40 8.76 mmol gcat
1. After the reaction, the catalyst was easily recovered and
reused for four subsequent runs without a significant loss of catalytic activity and no leaching of the
metal/ligand was detected during the reaction.
Synthesis of flower-like magnetite nanoassembly: Application in the efficient...Pawan Kumar
A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported that proceeds via the reduction of iron (III) oxide under hydrogen atmosphere. The ensuing magnetic catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm and Mössbauer spectroscopy and explored for a simple yetbut efficient transfer hydrogenation reduction of a variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine hydrate. . The catalyst could be easily separated at the end of reaction using an external magnet and can be recycled up to 10 times without any loss in catalytic activity.
TiO2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Dr...Pawan Kumar
The lack of active, stable, earth-abundant, and visible-light absorbing materials to replace
plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and costeffective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of
atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity
for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) a
large bandgap between optical and acoustic phonon modes (2) and no electronic bandgap, which
allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in
this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing
plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that
extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active
HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
A ruthenium trinuclear polyazine complex was synthesized and subsequently immobilized through
complexation to a graphene oxide support containing phenanthroline ligands (GO-phen). The developed
photocatalyst was used for the photocatalytic reduction of CO2 to methanol, using a 20 watt white cold
LED flood light, in a dimethyl formamide–water mixture containing triethylamine as a reductive
quencher. After 48 h illumination, the yield of methanol was found to be 3977.57 5.60 mmol gcat
1.
The developed photocatalyst exhibited a higher photocatalytic activity than graphene oxide, which
provided a yield of 2201.40 8.76 mmol gcat
1. After the reaction, the catalyst was easily recovered and
reused for four subsequent runs without a significant loss of catalytic activity and no leaching of the
metal/ligand was detected during the reaction.
Synthesis of flower-like magnetite nanoassembly: Application in the efficient...Pawan Kumar
A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported that proceeds via the reduction of iron (III) oxide under hydrogen atmosphere. The ensuing magnetic catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm and Mössbauer spectroscopy and explored for a simple yetbut efficient transfer hydrogenation reduction of a variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine hydrate. . The catalyst could be easily separated at the end of reaction using an external magnet and can be recycled up to 10 times without any loss in catalytic activity.
Heterostructured nanocomposite tin phthalocyanine@mesoporous ceria (SnPc@CeO2...Pawan Kumar
Heterostructured tin phthalocyanine supported to mesoporous ceria was synthesized and used a
photocatalyst for CO2 reduction under visible light. The photoreduction CO2 activities of the
heterostructures were investigated in the presence of triethylamine as sacrificial agent. The developed
photocatalyst exhibited high catalytic activity for photoreduction of CO2 and after 24 hours of visible
light irradiation 2342 mmol g1 cat of methanol (fMeOH ¼ 0.0223 or 2.23%) and 840 mmol g1 cat of CO
(fCO ¼ 0.0026 or 0.26%) were obtained as the major reaction products. The methanol formation rate
(RMeOH) and CO formation rate (RCO) was found to be 97.5 mmol h1 g1 cat and 35.0 mmol h1 g1 cat
respectively. While under the identical experimental conditions mesoporous ceria (meso-CeO2) gave
only 316 mmol g1 cat of methanol (fMeOH ¼ 0.003 or 0.30%) and 126 mmol g1 cat CO (fCO ¼ 0.0004
or 0.04%) with product formation rate RMeOH ¼ 13.2 mmol h1 g1 cat and RCO ¼ 5.3 mmol h1 g1 cat.
Furthermore, the recovered catalyst showed consistent catalytic activity for at least five runs without any
significant loss in product yields
Photo-assisted oxidation of thiols to disulfides using cobalt ‘‘Nanorust’’ un...Pawan Kumar
Heterogeneous ‘‘Nanorust’’ containing cobalt oxide has been developed for the visible light assisted
oxidation of thiols to disulfides using molecular oxygen as an oxidant under alkaline free conditions and
therefore more environmentally friendly. Pyrolysis of heterogenized tetrasulfonated cobalt(II) phthalocyanine
(CoPcS) supported on mesoporous ceria (CeO2) transforms it into a novel heterogeneous ‘‘Nanorust’’
containing CoOx-C,N@CeO2 which exhibited higher catalytic activity than the homogeneous CoPcS as well
as the ceria immobilized CoPcS catalyst. Importantly, these catalysts could easily be recovered and recycled
for several runs, which makes the process greener and cost-effective.
Consistently High Voc Values in p-i-n Type Perovskite Solar Cells Using Ni3+-...Pawan Kumar
Leading edge p-i-n type halide perovskite solar cells (PSCs) severely underperform n-i-p PSCs. p-i-n type PSCs that use PEDOT:PSS hole transport layers (HTLs) struggle to generate open-circuit photovoltage values higher than 1 V. NiO HTLs have shown greater promise in achieving high Voc values albeit inconsistently. In this report, a NiO nanomesh with Ni3+ defect grown by the hydrothermal method was used to obtain PSCs with Voc values that consistently exceeded 1.10 V (champion Voc = 1.14 V). A champion device photoconversion efficiency of 17.75% was observed. Density functional theory modeling was used to understand the interfacial properties of the NiO/perovskite interface. The PCE of PSCs constructed using the Ni3+-doped NiO nanomesh HTL was ∼34% higher than that of conventional compact NiO-based perovskite solar cells. A suite of characterization techniques such as transmission electron microscopy, field emission scanning electron microscopy, intensity-modulated photocurrent spectroscopy, intensity-modulated photovoltage spectroscopy, time-resolved photoluminescence, steady-state photoluminescence, and Kelvin probe force microscopy provided evidence of better film quality, enhanced charge transfer, and suppressed charge recombination in PSCs based on hydrothermally grown NiO nanostructures.
Visible light assisted reduction of nitrobenzenes using Fe(bpy)3+2/rGOnanocom...Pawan Kumar
Visible-light-induced photocatalytic reduction of aromatic nitrobenzenes to the corresponding anilinesat room temperature using reduced graphene oxide (rGO) immobilized iron(II) bipyridine complex asphotocatalyst is described. The rGO-immobilized iron catalyst exhibited superior catalytic activity thanhomogeneous iron(II) bipyridine complex and much higher than metal free rGO photocatalysts. Theheterogeneous photocatalyst was found to be robust and could easily be recovered and reused for severalruns without any significant loss in photocatalytic activity.
Synthesis of flower-like magnetite nanoassembly: Application in the efficient...Pawan Kumar
A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported
that proceeds via the reduction of iron(III) oxide under a hydrogen atmosphere. The ensuing magnetic
catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm, and
Mössbauer spectroscopy and explored for a simple yet efficient transfer hydrogenation reduction of a
variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine
hydrate. The catalyst could be easily separated at the end of a reaction using an external magnet and
can be recycled up to 10 times without any loss in catalytic activity.
Nanostructured composite materials for CO2 activationPawan Kumar
The increasing energy crisis and the worsening global climate caused by the excessive
utilization of the fossil fuel have boosted tremendous research about CO2 capture, storage and
utilization. Among these approaches, utilization of carbon dioxide to produce valuable chemicals
is preferred than dumping it. Particularly, utilization of CO2 as feedstock for the photocatalytic
conversion into valuable products is a viable approach for harvesting solar radiation as an energy
source and to mitigate increasing CO2 concentration. Artificial photosynthesis by using
nanostructured materials as photocatalyst has immense potential to convert carbon dioxide into
renewable fuels such as methanol/CO etc. The present chapter focuses on the synthesis, characterization and application of various nanostructured materials for CO2 activation including
photoreduction of CO2 to valuable products.
Mixed-Valence Single-Atom Catalyst Derived from Functionalized GraphenePawan Kumar
Single-atom catalysts (SACs) aim at bridging the gap between homogeneous and heterogeneous catalysis. The challenge is the development of materials with ligands enabling coordination of metal atoms in different valence states, and preventing leaching or nanoparticle formation. Graphene functionalized with nitrile groups (cyanographene) is herein employed for the robust coordination of Cu(II) ions, which are partially reduced to Cu(I) due to graphene-induced charge transfer. Inspired by nature's selection of Cu(I) in enzymes for oxygen activation, this 2D mixed-valence SAC performs flawlessly in two O2-mediated reactions: the oxidative coupling of amines and the oxidation of benzylic CH bonds toward high-value pharmaceutical synthons. High conversions (up to 98%), selectivities (up to 99%), and recyclability are attained with very low metal loadings in the reaction. The synergistic effect of Cu(II) and Cu(I) is the essential part in the reaction mechanism. The developed strategy opens the door to a broad portfolio of other SACs via their coordination to various functional groups of graphene, as demonstrated by successful entrapment of FeIII/FeII single atoms to carboxy-graphene.
C3N5: A Low Bandgap Semiconductor Containing an Azo-linked Carbon Nitride Fra...Pawan Kumar
Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of the melem hydrazine precursor. Characterization revealed that in the C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence lifetime imaging, Raman, FTIR, TGA, KPFM, XPS, NMR and EPR clearly show that the properties of C3N5 are distinct from pristine carbon nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5 outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with MAxFA1–xPb(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7%. C3N5 was also shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Because of its electron-rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbon based materials. C3N5 coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion at much low laser intensity (1.0 mW) than g-C3N4, which showed sluggish performance even at high laser power (10.0 mW). The relatively narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature-resistant semiconductor for optoelectronic applications while its electron-rich character and intra sheet cavity make it an attractive supramolecular adsorbent for environmental applications.
Vapor growth of binary and ternary phosphorus-based semiconductors into TiO2 ...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12) were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO2 nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP@TiO2 emerged to be the most active among the polyphosphide@TiO2 materials. The improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge transfer resistance which facilitated better charge separation from inorganic phosphides to TiO2.
This work studied the effect of applying pulse current
(ton=off=1s) on the electrodeposition of silver nanoparticles on
carbon sphere surface as a substrate. The electrolyte is made of 0.1
M KNO3, 0.1 M KCN and 0.01M AgNO3. The pH value has been
adjusted in the alkaline region of 9.1 with the help of K(NO3)
addition. Experiments were carried out at room temperature for
periods up to 12 minutes. The cell is fitted with a mechanical stirrer
to keep the electrolyte in a dynamic state. Product(s) was
characterized with the help of SEM and EDX and field emission.
Results obtained show that silver nanoparticles has successfully
electrodeposited under pulse current conditions with a particle size
of 100–400 nm after 2 minutes. Deposition takes place on certain
accessible sites of the carbon surface of the substrate forming a
monolayer of scattered silver nanoparticles. Formation of macro
particles with larger diameter and multilayer in thickness takes
place with continuous deposition of silver nanoparticles on the
formerly deposited silver. Pulse current helps management of the
monolayer deposition as compared to the steady DC application
with respect to particle diameter and number of layers.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo), exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.
Electron transfer between methyl viologen radicals and graphene oxidekamatlab
Methyl viologen radicals are capable of transferring electrons to graphene oxide and partially restore the sp2 network. The reduced graphene oxide serves as a scaffold to anchor Ag nanoparticles. The growth of these silver nanoparticles is dictated by the ability of RGO to store and shuttle electrons. The RGO/Ag nanocomposites discussed in the present work offer new opportunities to design next generation photocatalysts.
Visit our website, KamatLab.com, for the latest news, publications, and research from our group.
Photocatalytic degradation of some organic dyes under solar light irradiation...Iranian Chemical Society
Nanoparticles of the ZnO and TiO2 were synthesized and the physicochemical properties of the compounds were characterized by IR, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD patterns of the ZnO and TiO2 nanoparticles could be indexed to hexagonal and rutile phase, respectively. Aggregated nanoparticles of ZnO and TiO2 with spherical-like shapes were observed with particle diameter in the range of 80-100 nm. These nanoparticles were used for photocatalytic degradation of various dyes, Rhodamine B (RhB), Methylene blue (MB) and Acridine orange (AO) under solar light irradiation at room temperature. Effect of the amount of catalyst on the rate of photodegradation was investigated. In general, because ZnO is unstable, due to incongruous dissolution to yield Zn(OH)2 on the ZnO particle surfaces and thus leading to catalyst inactivation,the catalytic activity of the system for photodegradation of dyes decreased dramatically when TiO2 was replaced by ZnO.
Heterostructured nanocomposite tin phthalocyanine@mesoporous ceria (SnPc@CeO2...Pawan Kumar
Heterostructured tin phthalocyanine supported to mesoporous ceria was synthesized and used a
photocatalyst for CO2 reduction under visible light. The photoreduction CO2 activities of the
heterostructures were investigated in the presence of triethylamine as sacrificial agent. The developed
photocatalyst exhibited high catalytic activity for photoreduction of CO2 and after 24 hours of visible
light irradiation 2342 mmol g1 cat of methanol (fMeOH ¼ 0.0223 or 2.23%) and 840 mmol g1 cat of CO
(fCO ¼ 0.0026 or 0.26%) were obtained as the major reaction products. The methanol formation rate
(RMeOH) and CO formation rate (RCO) was found to be 97.5 mmol h1 g1 cat and 35.0 mmol h1 g1 cat
respectively. While under the identical experimental conditions mesoporous ceria (meso-CeO2) gave
only 316 mmol g1 cat of methanol (fMeOH ¼ 0.003 or 0.30%) and 126 mmol g1 cat CO (fCO ¼ 0.0004
or 0.04%) with product formation rate RMeOH ¼ 13.2 mmol h1 g1 cat and RCO ¼ 5.3 mmol h1 g1 cat.
Furthermore, the recovered catalyst showed consistent catalytic activity for at least five runs without any
significant loss in product yields
Photo-assisted oxidation of thiols to disulfides using cobalt ‘‘Nanorust’’ un...Pawan Kumar
Heterogeneous ‘‘Nanorust’’ containing cobalt oxide has been developed for the visible light assisted
oxidation of thiols to disulfides using molecular oxygen as an oxidant under alkaline free conditions and
therefore more environmentally friendly. Pyrolysis of heterogenized tetrasulfonated cobalt(II) phthalocyanine
(CoPcS) supported on mesoporous ceria (CeO2) transforms it into a novel heterogeneous ‘‘Nanorust’’
containing CoOx-C,N@CeO2 which exhibited higher catalytic activity than the homogeneous CoPcS as well
as the ceria immobilized CoPcS catalyst. Importantly, these catalysts could easily be recovered and recycled
for several runs, which makes the process greener and cost-effective.
Consistently High Voc Values in p-i-n Type Perovskite Solar Cells Using Ni3+-...Pawan Kumar
Leading edge p-i-n type halide perovskite solar cells (PSCs) severely underperform n-i-p PSCs. p-i-n type PSCs that use PEDOT:PSS hole transport layers (HTLs) struggle to generate open-circuit photovoltage values higher than 1 V. NiO HTLs have shown greater promise in achieving high Voc values albeit inconsistently. In this report, a NiO nanomesh with Ni3+ defect grown by the hydrothermal method was used to obtain PSCs with Voc values that consistently exceeded 1.10 V (champion Voc = 1.14 V). A champion device photoconversion efficiency of 17.75% was observed. Density functional theory modeling was used to understand the interfacial properties of the NiO/perovskite interface. The PCE of PSCs constructed using the Ni3+-doped NiO nanomesh HTL was ∼34% higher than that of conventional compact NiO-based perovskite solar cells. A suite of characterization techniques such as transmission electron microscopy, field emission scanning electron microscopy, intensity-modulated photocurrent spectroscopy, intensity-modulated photovoltage spectroscopy, time-resolved photoluminescence, steady-state photoluminescence, and Kelvin probe force microscopy provided evidence of better film quality, enhanced charge transfer, and suppressed charge recombination in PSCs based on hydrothermally grown NiO nanostructures.
Visible light assisted reduction of nitrobenzenes using Fe(bpy)3+2/rGOnanocom...Pawan Kumar
Visible-light-induced photocatalytic reduction of aromatic nitrobenzenes to the corresponding anilinesat room temperature using reduced graphene oxide (rGO) immobilized iron(II) bipyridine complex asphotocatalyst is described. The rGO-immobilized iron catalyst exhibited superior catalytic activity thanhomogeneous iron(II) bipyridine complex and much higher than metal free rGO photocatalysts. Theheterogeneous photocatalyst was found to be robust and could easily be recovered and reused for severalruns without any significant loss in photocatalytic activity.
Synthesis of flower-like magnetite nanoassembly: Application in the efficient...Pawan Kumar
A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported
that proceeds via the reduction of iron(III) oxide under a hydrogen atmosphere. The ensuing magnetic
catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm, and
Mössbauer spectroscopy and explored for a simple yet efficient transfer hydrogenation reduction of a
variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine
hydrate. The catalyst could be easily separated at the end of a reaction using an external magnet and
can be recycled up to 10 times without any loss in catalytic activity.
Nanostructured composite materials for CO2 activationPawan Kumar
The increasing energy crisis and the worsening global climate caused by the excessive
utilization of the fossil fuel have boosted tremendous research about CO2 capture, storage and
utilization. Among these approaches, utilization of carbon dioxide to produce valuable chemicals
is preferred than dumping it. Particularly, utilization of CO2 as feedstock for the photocatalytic
conversion into valuable products is a viable approach for harvesting solar radiation as an energy
source and to mitigate increasing CO2 concentration. Artificial photosynthesis by using
nanostructured materials as photocatalyst has immense potential to convert carbon dioxide into
renewable fuels such as methanol/CO etc. The present chapter focuses on the synthesis, characterization and application of various nanostructured materials for CO2 activation including
photoreduction of CO2 to valuable products.
Mixed-Valence Single-Atom Catalyst Derived from Functionalized GraphenePawan Kumar
Single-atom catalysts (SACs) aim at bridging the gap between homogeneous and heterogeneous catalysis. The challenge is the development of materials with ligands enabling coordination of metal atoms in different valence states, and preventing leaching or nanoparticle formation. Graphene functionalized with nitrile groups (cyanographene) is herein employed for the robust coordination of Cu(II) ions, which are partially reduced to Cu(I) due to graphene-induced charge transfer. Inspired by nature's selection of Cu(I) in enzymes for oxygen activation, this 2D mixed-valence SAC performs flawlessly in two O2-mediated reactions: the oxidative coupling of amines and the oxidation of benzylic CH bonds toward high-value pharmaceutical synthons. High conversions (up to 98%), selectivities (up to 99%), and recyclability are attained with very low metal loadings in the reaction. The synergistic effect of Cu(II) and Cu(I) is the essential part in the reaction mechanism. The developed strategy opens the door to a broad portfolio of other SACs via their coordination to various functional groups of graphene, as demonstrated by successful entrapment of FeIII/FeII single atoms to carboxy-graphene.
C3N5: A Low Bandgap Semiconductor Containing an Azo-linked Carbon Nitride Fra...Pawan Kumar
Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of the melem hydrazine precursor. Characterization revealed that in the C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence lifetime imaging, Raman, FTIR, TGA, KPFM, XPS, NMR and EPR clearly show that the properties of C3N5 are distinct from pristine carbon nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5 outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with MAxFA1–xPb(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7%. C3N5 was also shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Because of its electron-rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbon based materials. C3N5 coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion at much low laser intensity (1.0 mW) than g-C3N4, which showed sluggish performance even at high laser power (10.0 mW). The relatively narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature-resistant semiconductor for optoelectronic applications while its electron-rich character and intra sheet cavity make it an attractive supramolecular adsorbent for environmental applications.
Vapor growth of binary and ternary phosphorus-based semiconductors into TiO2 ...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12) were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO2 nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP@TiO2 emerged to be the most active among the polyphosphide@TiO2 materials. The improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge transfer resistance which facilitated better charge separation from inorganic phosphides to TiO2.
This work studied the effect of applying pulse current
(ton=off=1s) on the electrodeposition of silver nanoparticles on
carbon sphere surface as a substrate. The electrolyte is made of 0.1
M KNO3, 0.1 M KCN and 0.01M AgNO3. The pH value has been
adjusted in the alkaline region of 9.1 with the help of K(NO3)
addition. Experiments were carried out at room temperature for
periods up to 12 minutes. The cell is fitted with a mechanical stirrer
to keep the electrolyte in a dynamic state. Product(s) was
characterized with the help of SEM and EDX and field emission.
Results obtained show that silver nanoparticles has successfully
electrodeposited under pulse current conditions with a particle size
of 100–400 nm after 2 minutes. Deposition takes place on certain
accessible sites of the carbon surface of the substrate forming a
monolayer of scattered silver nanoparticles. Formation of macro
particles with larger diameter and multilayer in thickness takes
place with continuous deposition of silver nanoparticles on the
formerly deposited silver. Pulse current helps management of the
monolayer deposition as compared to the steady DC application
with respect to particle diameter and number of layers.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo), exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.
Electron transfer between methyl viologen radicals and graphene oxidekamatlab
Methyl viologen radicals are capable of transferring electrons to graphene oxide and partially restore the sp2 network. The reduced graphene oxide serves as a scaffold to anchor Ag nanoparticles. The growth of these silver nanoparticles is dictated by the ability of RGO to store and shuttle electrons. The RGO/Ag nanocomposites discussed in the present work offer new opportunities to design next generation photocatalysts.
Visit our website, KamatLab.com, for the latest news, publications, and research from our group.
Photocatalytic degradation of some organic dyes under solar light irradiation...Iranian Chemical Society
Nanoparticles of the ZnO and TiO2 were synthesized and the physicochemical properties of the compounds were characterized by IR, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD patterns of the ZnO and TiO2 nanoparticles could be indexed to hexagonal and rutile phase, respectively. Aggregated nanoparticles of ZnO and TiO2 with spherical-like shapes were observed with particle diameter in the range of 80-100 nm. These nanoparticles were used for photocatalytic degradation of various dyes, Rhodamine B (RhB), Methylene blue (MB) and Acridine orange (AO) under solar light irradiation at room temperature. Effect of the amount of catalyst on the rate of photodegradation was investigated. In general, because ZnO is unstable, due to incongruous dissolution to yield Zn(OH)2 on the ZnO particle surfaces and thus leading to catalyst inactivation,the catalytic activity of the system for photodegradation of dyes decreased dramatically when TiO2 was replaced by ZnO.
Dosimetric evaluation of the MLCs for irregular shaped radiation fieldsIOSR Journals
The three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and image-guided radiotherapy (IGRT) are the most advanced techniques in radiotherapy, which use irregular fields–using multileaf collimators in a linear accelerator. The accuracy of these techniques depends on dosimetric characteristics of the multileaf collimators. There is an option for optimizing the jaws to the irregular MLC field to reduce the scattered radiation and intra- and inter-leaf radiation leakage beyond the field. In this study, ,80 leaf MLC system has been taken to compare and differentiate their characteristics with 6-MV, and 10-MV photon beams.
The MLC system in Elekta linear accelerator is used as a separate unit, that is, The dosimetric characteristics include dose rates, percentage depth doses, surface dose, dose in the build-up region, penumbra, and width of 50% dose levels
Bayesian Estimation of Above-Average Performance in Tertiary Institutions: A ...IOSR Journals
Bayesian approach for parameter estimation has the capacity to yield more precise estimates than methods based on sampling theory. There are several common Bayesian models; in this study we applied Empirical Bayes (EB) model called Beta-binomial model. The study is motivated by the need to beam searchlight on universities, faculties or fields of study with graduates who may not be eligible for further educational pursuits. This study provides means of assessment or a basis of evaluation of students’ performances among faculties or fields of study and overall performance of a university. This study uses Bayesian methods of inference to estimate the proportion of above-average performance of graduates from the various faculties in University of Lagos. The model adopted generated results which are of smaller variances compared with variances of sample Proportions, showing that the posterior proportions generated are more efficient estimators. This is further evidenced in narrow widths of the computed confidence intervals. The overall result shows that the proportion of above-average performance of graduates of University of Lagos, who are eligible for further educational pursuits (i.e. higher degrees), is approximately 72% of the university graduates
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
Un doped and doped with Al ZnS thin Films have been fabricated by vacuum evaporation
technique under the vacuum of 10-5 Torr on glass substrate at room temperature and with different
ratio of Al concentration of thickness (0.8µm). The optical properties were revealed by UV-Visible
transmittance spectra and the band gap energy was determined. Transmission spectra indicate a high
transmission coefficient (¨95%). The results showed that films have direct optical transition, and the
values of energy gap were found to decrease with doping concentrations. Also the optical constants
such as absorption coefficient, refractive index, extinction coefficient and dielectric constant have
been calculated. The effect of doping concentration on the electrical properties has been studied
The main objective of this project is to be produce copper reinforced metal matrix composite (MMC) layers using micron sized AlN particles via friction stir processing (FSP) in order to enhance surface mechanical properties. Micro structural evaluation using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) indicated that an increase in traverse speed and a decrease in rotational speed cause a reduction in the grain size of different groove width (0,0.4,0.8,1.2 mm) of stir zone (SZ) for the specimens friction stir processed (FSPed) without AlN particles. It was found that upon addition of AlN particles, wear properties were improved. This behavior was further supported by SEM images of wear surfaces. Results demonstrated that the micro composite produced by FSP exhibited enhanced wear resistance and higher average friction coefficient in comparison with pure copper. Tensile properties and fracture characteristics of the specimens FSPed with and without AlN particles and pure copper were also evaluated. According to the results, the MMC layer produced by FSP showed higher strength and lower elongation than pure copper while a remarkable elongation was observed for FSPed specimen without AlN particles and been greatly developed by the use of AlN.
A micro-electromechanical system (MEMS) gyroscope is commonly used to monitor the angular rate of a moving body due to its benefits. The most promising advantages include its small size, low cost, and a high degree of integration. MEMS gyroscope has different fabrication processes and micromachining techniques. LIGA (Lithography-Galvanoformung-Abformung), bulk micromachining, surface micromachining, Silicon-on-glass (SOG) and Deep Reactive Ion Etching (DRIE) are the known fabrication techniques for MEMS gyroscope. This paper systematically reviewed the fabrication techniques used to fabricate the MEMS gyroscope. The current review paper also focuses on the performance of MEMS gyroscope which included several recent developments. For the conclusion of results, the variable typically used is the rate of turn (°/s) for MEMS angular rate sensors with respect to bandwidth frequency. Finally based on the review some analysis on fabrication technology, key principles, and performance parameters are discussed.
Influence of Thickness on Electrical and Structural Properties of Zinc Oxide ...paperpublications3
Abstract: Zinc Oxide (ZnO) thin films were prepared on corning (7059) glass substrates at a thickness of 75.5 and 130.5nm by RF sputtering technique. The deposition was carried out at room temperature after which the samples were annealed in open air at 1500C. The electrical and structural properties of these films were studied. The electrical properties of the films were monitored by four-point probe method while the structural properties were studied by X-ray diffraction (XRD). It was found that the electrical resistance of the films decreases with increase in the thickness of the films. The XRD analysis of the films showed that the films have a peak located at 〖34.31^0-34.35〗^0with hkl (002). Other parameters calculated include the stress ( ) and the grain size (D).
Annealing and Microstructural Characterization of Tin-Oxide Based Thick Film ...Anis Rahman
Abstract. The sheet resistance of tin oxide based thick-film resistors exhibits two regions of temperature dependence,
described by hopping (23°C-200°C) and diffusion mechanisms (200°C-350°C), respectively.
Annealing these samples causes the sheet resistance to increase in both regions. In the post-annealed samples,
the hopping conduction range is extended by 50°C (23°C-250°C) while the hopping parameter, To, is decreased by
more than 50%. The activation energy of diffusion (0.60 eV) is the same for both pre- and post annealed samples, but
the magnitude of resistance in the diffusion controlled region is increased significantly as a result of annealing. These
changes are explained in terms of a net decrease in the concentration of tin ions in the glass matrix. From a careful
microstructural study it was found that a conduction path composed of tin-oxide grains or their clusters in contact
with each other does not exist in the present system. HREM micrographs showed the presence of nanocrystalline
tin-oxide particles in the glass phase separating the tin-oxide grain clusters. Estimated average separation between
the nanocrystals in 4 nm, consistent with a variable-range hopping conduction via the dissolved tin ions in the glass
matrix.
Similar to Aluminum Oxide-Silver Nanoparticle Interfaces for Memristive Applications (20)
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
NO1 Uk best vashikaran specialist in delhi vashikaran baba near me online vas...Amil Baba Dawood bangali
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Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
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Aluminum Oxide-Silver Nanoparticle Interfaces for Memristive Applications
1. IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE)
e-ISSN: 2278-1676,p-ISSN: 2320-3331, Volume 10, Issue 1 Ver. II (Jan – Feb. 2015), PP 62-67
www.iosrjournals.org
DOI: 10.9790/1676-10126267 www.iosrjournals.org 62 | Page
Aluminum Oxide-Silver Nanoparticle Interfaces for Memristive
Applications
Bindu Sharma, M. K. Rabinal *
(Department of Physics, Karnatak University Dharwad-580003, Karnatak, India)
Abstract: In the present work, a facile approach to construct a nonvolatile resistive random access memory
device based on the heterojunction of silver nanoparticles and aluminum oxide is reported. The device structure
consisting of Aluminum-Aluminum oxide-Silver Nanoparticles-Aluminum is used to study the charge transport.
The current-voltage measurements of this device clearly show the transition from one state to other in two
different steps. Initially, a major transition with the resistance ratio as high as 105
is obtained for the device
whereas the minor transition has resulted one order difference in between its low conducting state and high
conducting state. The prepared memristor is found to operate at low operational voltages with better uniformity.
Keywords: Charge transport, Nonvolatile resistive memristor, Silver nanoparticles heterojunction with
aluminum oxide, SEM and XRD.
I. Introduction
The resistive random access memory (ReRAM) devices based on transition metal oxides have been
studied since from 1962 [1], these are two terminal structures that take a transition from low conducting state
(off) to high conducting state (on) at a well defined critical voltage. A great attention has been revived towards
this field only after the first practical ReRAM device based on titanium oxide [2]. Since then a variety of oxides
including simple binary oxide to complex oxides has been investigated exhibiting unipolar/bi-polar non-volatile
resistive switching [3-9]. Today, the field has gained a tremendous importance both in the research as well as in
semiconductor industries due to its interesting properties such as simple structure, small size, low power
consumption, high write/erase speed, good endurance and high scalability [10, 11]. It has been predicted that the
phenomenon might manifest well at nano-meter length scale therefore, a great attention has been paid to utilize
various nanoparticles of metals, metal oxides and semiconductors in their different morphological forms to
constitute these devices.
The various forms of nanomaterials utilized for this purpose are nanowires, quantum dots, nanocrystal,
nanocubes, nanodots, nanoislands, and nanorods etc. [9, 12-18]. Attractive performance parameters such as fast
switching speed (~ 5 ns), excellent scalability (<10 nm cell size), long endurance (>1012
cycles), and stable data
retention (>10 years) has been reported in case of nanomaterials, exhibiting better compatibility with the
complementary metal-oxide semiconductor (CMOS) technology [13, 15,]. Hence, the nanotechnology has not
only empowered to reduce the particle size but it has also provided a platform for exploring its potential as a
strong competitor towards current Flash memory devices [19, 20]. Thus, taking advantage of this field towards
ReRAM device fabrication is highly desirable for future electronics. Despite of a better advancement of the field
in terms of its performance parameters, the field is still hampered due to lack of understanding in terms of
switching and conduction mechanisms in nanoscale vicinity that control the electrical switching [14, 16].
In this communication, we report a ReRAM device based on the silver nanoparticle (AgNPs) and
aluminum oxide (Al2O3) heterojunctions, prepared by simple chemical routes for resistive switching application.
Basically, the device has shown non volatile resistive switching whereby the transition from one state to other is
achieved in two different steps (major and minor). In case of major transition, the resistive ratio is observed as
high as 105
whereas it is only ~ 101
for minor transition case.
II. Experimental Methods
2.1 Materials
All commercially available reagents and anhydrous solvents were used without further purification.
Ammonium fluoride (anhydrous), sodium borohydride (NaBH4) (AR) and acetone (AR) were purchased from
sd-fine chemicals, India. Silver nitrate (AgNO3) and high purity aluminum wire (for evaporation of top metal
contact) were taken from Sigma Aldrich. Aluminum plate of thickness 1 mm was purchased from local source.
All reactions were carried out under open air. Prior to use, aluminum plate was well cleaned and rinsed with
triple distilled water.
2.2 Formation of Aluminum Oxide Thin Film
In the present work, thin film of aluminum oxide was grown on a conducting aluminum substrate by a
2. Aluminum Oxide-Silver Nanoparticle Interfaces for Memristive Applications
DOI: 10.9790/1676-10126267 www.iosrjournals.org 63 | Page
dip chemical coating method. The formation of thin layer was carried out in an aqueous solution of 500 mM
ammonium fluoride at room temperature. Complete dissolution of ammonium fluoride was attained by
sonicating in ultrasonication bath. The film was grown by dipping vertically a well cleaned aluminum substrate
having dimension (length = 4 cm, breadth = 2 cm and thickness = 0.1 cm) in 6 ml of prepared solution taken in
10 ml beaker. The oxidative reaction between the solution and substrate was confirmed from the bubble
formation originated at the surface of substrate and it was allowed for a maximum time of 8 minutes. After the
completion of process, substrate was taken out from the solution bath, rinsed well with distilled water and then
dried under table lamp. A thin layer of oxide film was clearly observed on the substrate which was then utilized
for the construction of nonvolatile memory device.
2.3 Synthesis of Silver Nanoparticles
The nanoparticles of silver were prepared by a well known chemical method of sodium borohydride
reduction. In a typical synthesis, 1 mM aqueous solution of silver nitrate was prepared in 10 ml solution. In a
separate beaker, 25 mM sodium borohydride was prepared in 5 ml distilled water. Both these solutions were
well sonicated for few minutes for complete dissolution of precursors. Now, 50 μl of sodium borohydride was
added to silver nitrate solution along with the continuous stirring. With the addition of sodium borohydride, the
transparent solution of silver nitrate started turning to light orange colour which was confirming the temporal
evolution of nanoparticles formation. This was repeatedly washed to purify the colloidal solution. These
nanoparticles were found stable for many days and were utilized in the same form to construct heterojunction
with aluminum oxide film to fabricate ReRAM device.
2.4 Device Fabrication and Measurements
The aluminum oxide film grown on aluminum substrate was used for ReRAM device fabrication.
Heterojunction of aluminum oxide with silver nanoparticles (AgNPs) was formed by drop casting its thin layer
with 200 μl of prepared AgNPs solution in open air. This solution was spread on the entire region of grown
aluminum oxide film (length = 1.8 cm, breadth = 2 cm) which resulted into 250 nm thick film. Above this layer,
aluminum contacts with an area of 1 mm2
were formed by evaporating pure aluminum using metal evaporator
under a shadow mask at a high pressure of 10-4
torr. With this the device constituted metal- metal oxide- AgNPs
-metal heterostructure. The resistive switching behavior of this device was studied by utilizing evaporated Al
contact as top electrode whereas the Al substrate as bottom electrode. The electrical contacts to these electrodes
were made through two thin tungsten probes with diameter 0.7 mm of conductivity setup which were further
connected to BNC connectors by using Keithley 2636 A source meter. All the charge transport measurements
were carried out in cyclic voltage sweep mode with biased sweeping voltage applied to the evaporated Al
electrode positive and bottom contact as negative, the voltage was zero to positive, positive to zero, zero to
negative and negative to zero sequence. A schematic cross-section of our Al/Aluminum oxide-AgNPs/Al
prototypes is shown in fig. 1.
Fig. 1: Typical schematic cross-sectional view of Al/Al2O3-AgNPs/Al resistive random access memory device.
2.5 Characterization
The formation of AgNPs was confirmed from XRD, optical absorption and scanning electron
microscopic (SEM) measurements, whereas, aluminum oxide film was studied under SEM instrument for
morphological growth and elemental analysis. The morphological and elemental analysis was performed using
Ultra 55, field emission scanning electron microscope (Carl Zeiss), with EDAX instrument. X-ray diffraction
pattern was recorded with Philips X’pert powder diffractometer with Cu kα1 radiation (kα1 = 1.54056 Å). The
sample subjected to XRD analysis was prepared by depositing and drying thick film of silver nanoparticles on
glass slide. Optical absorption analysis was done using Analytikjena sepcord 200 plus spectrophotometer in the
wavelength range 190 – 1100 nm.
Al
Al Substrate
Al2O3 Film
AgNPs Film
Al
3. Aluminum Oxide-Silver Nanoparticle Interfaces for Memristive Applications
DOI: 10.9790/1676-10126267 www.iosrjournals.org 64 | Page
III. Results And Discussion
In order to observe the growth and morphological behavior of aluminum oxide film grown on
conducting aluminum substrate, scanning electron microscopy was performed. The obtained results are provided
in fig. 2 (a) and (b) for two different resolutions. The lower resolution image of fig. 2(a) confirms the oxidative
growth of aluminum oxide on conductive aluminum substrate whereas fig. 2(b) represents higher resolution
image consisting of spherically shaped nanoparticles. This confirms that aluminum oxide film has grown in
terms of spherical shaped particles with an average size of nearly 40 nm. Since a dense growth of the oxide film
can be clearly seen in these micrographs therefore here, we stress that the measured size is an only estimation
and to get the exact size high resolution transmission electron microscopy (HRTEM) is must but in the present
case, it is out of our scope. Further, the elemental analysis of this film was also carried out to study chemical
composition. Carbon tape on metal stub was used as a substrate. Image was scanned at three different places of
the sample with a magnification of 2 µm. The EDS analysis of these films confirms that it is stoichiometric in
nature that is Al2O3.
Fig. 2: Scanning electron micrographic (SEM) images of aluminum oxide film grown on conducting aluminum
substrate (a) at low resolution and (b) at high resolution.
Powder X-ray diffraction studies were employed to access the crystallinity of synthesized silver nanoparticles
and the obtained behavior is shown in fig. 3(a). The pattern was recorded in the range 2θ = 10o
to 90o
whereas it
is given for 30o
to 90o
in the spectrum. The resultant diffraction pattern clearly shows five well resolved
diffraction peaks corresponding to (111), (200), (220), (311) and (222) diffraction planes of silver nanoparticles.
The obtained peak values are at 2θ = 38.13o
, 44.25 o
, 64.63 o
, 77.60 o
and 81.62o
, these are attributed to FCC
crystalline structure of silver. These values are highly consistent with the Joint Committee on Powder
Diffraction Standards (JCPDS 04-0784) and are confirmed from reported results [21]. Further, all the peaks
confirm that the as synthesized nanoparticles are crystalline in nature. The crystalline size of these is estimated
to be 42 nm ± 0.8 from (111) diffraction peak using Debye Scherrer formula, d=kλ/(βcos(θ)); where k is
Scherrer’s constant taken as 0.9, λ is wavelength of radiation, β is full width half maxima and θ is Bragg angle.
This result is further confirmed from scanning electron microscopic measurements. The micrographic image
shown in fig. 3(b) clearly shows that silver nanoparticles are spherical in nature.
Fig. 3: (a) X-ray diffraction spectrum and (b) Scanning electron micrographic image of silver nanoparticles.
4. Aluminum Oxide-Silver Nanoparticle Interfaces for Memristive Applications
DOI: 10.9790/1676-10126267 www.iosrjournals.org 65 | Page
The particle size was estimated by taking average of nearly 30 different sized nanoparticles and is
calculated as ~ 51 nm which is in good agreement with the estimated size from XRD analysis. The increase in
particle size in case of microscopic analysis in comparison with XRD is an obvious result as Debye-Scherrer
formula provides the size of the single crystal domain with in which there is periodicity of lattice but the actual
nanocrystal always possess wrapping of crystalline domain by disordered non-crystalline layers of its own.
Next, the optical absorption spectrum was recorded for the prepared silver nanoparticles in their
colloidal form. The obtained spectrum after normalization is shown in fig. 4. The spectrum clearly shows a
sharp surface Plasmon resonance (SPR) peak centered at the wavelength value of 405 nm with a dip at 320 nm,
this behavior is typically observed with sodium borohydride reduction in case of silver nanoparticles formation
[22, 23]. Further, the peak resonant energy calculated for this SPR peak is 3.07 eV with full width half
maximum of only 154 nm.
Fig. 4: Optical absorption spectrum of silver nanoparticles recorded in colloidal form.
The charge transport properties of Al/Al2O3-AgNPs/Al device are shown in fig. 5(a) and 5(b). The
measurements were carried out in voltage sweep mode in an ordered sequence of 0 V→ +2 V→ 0 V→ -2 V→ 0
V with a constant scan step of 0.04 V. The resultant I-V curves in fig. 5 (a) are indicating that the device has
taken transition to high conducting state in two different steps. The major transition has been taken during first
voltage sweep where the device was found initially in a low conducting state (with current ~ 10-11
A), it
remained low until a reverse bias with an appropriate voltage of – 1.87 V is applied. At this voltage, the device
has switched abruptly from low conducting state (with current ~ 8.96 x 10-10
A) to high conducting state (with
current ~ 3.85 x 10-5
A), these states are known as off and on states of device respectively. The resistance ratio
(ROff/ROn) for these two states is found to be a large nearly equal to 105
. The second transition which is
considerably minor in comparison with the first one was taken by the device when it is scanned after the major
transition.
Fig. 5: I-V characteristics of Al/Al2O3-AgNPs/Al resistive random access memory device (a) semi logarithmic
plot, and (b) expanded view of minor transition taken by the device between two more conducting states.
5. Aluminum Oxide-Silver Nanoparticle Interfaces for Memristive Applications
DOI: 10.9790/1676-10126267 www.iosrjournals.org 66 | Page
This time the device was switched from the state which was previously set by first voltage sweep to
even more high conducting state. For this voltage cycle, the device has shown bipolar resistive switching
behavior and the difference between the two states in this case was observed to be nearly of one order in
magnitude. With the further repetition of number of voltage sweep cycles, the device was found to be switched
alternatively in either of polarities between these conducting states. The expanded view of these behaviors can
be seen clearly in fig. 5(b). The repeatability of these measurements can also be seen from the same graph, it is
evident that they are quite reproducible.
Next, in order to check the switching mechanism behind this kind of charge transport behavior, the
obtained I-V curves were plotted in double logarithmic scale and the obtained results are given in fig. 6(a) and 6
(b). The set process representing the major transition of the device, shown in fig. 6(a) shows that in case of low
conducting state, the current response is almost consistent with the ohmic model except slight deviation near
low voltage region (< 0.28 V) and threshold region. This is attributed to the thermally generated free electrons at
the interface or in the nanoparticles layer from the electron injection. Near to threshold region and after taking
the transition, in the high conducting state, device has shown accordance with space charge limited conduction
behavior (1< slope < 2). This behavior shows that the injected electrons from the Al electrode can possibly
capture and fill the trapping sites in the oxide film. The electrons are able to flow effectively and continuously
through the heterojunction and the current increases sharply around five orders of magnitude as a high
conducting state.
Fig. 6: Double logarithmic graph representing set/reset operations of the device (a) first set operation, and (b)
second set operation. The inset of the fig. 6(b) represents reset operation of the device.
Fig. 6(b) provides the set and reset operations of minor transition taken by the device. From both the
graphs it is clear that high conducting and low conducting states during set and reset operations exhibit the same
transport mechanisms. For low conducting state, device shows the space charge limited conduction and is
almost similar to the high conducting state of major transition. For low conducting state of present case, the
device follows the ohm law behavior. Thus as an overall, the device takes transition from ohms behavior to
space charge limited current during major transition and then back to ohms law. This kind of transition in two
different steps shows that the obtained behavior is a result from the efficient hopping of charge carriers in the
film.
IV. Conclusions
In summary, we have constructed a resistive random access memory device by utilizing silver and
aluminum oxide nanoparticles as memristive elements for charge storage. Simple chemical routes have been
employed for nanoparticles synthesis. Dip coating and drop casting techniques were followed for heterojunction
formation between the two phases, whereas thermal evaporation technique was employed for creating the top
metal contacts. Characteristic nonvolatile resistive switching behavior with low operating voltage was observed
for the device. The transition from low to high conducting state was achieved in two different steps. The first
step has resulted into major transition with large Off/On ratio of 105
whereas second transition was observed
with one order difference in two conducting states. Here, as our study is focused on a single sized AgNPs, it can
also be extended to various other nanoparticles using their different size and morphology. Such studies are
crucially important in the design and development of potential memristive devices.
6. Aluminum Oxide-Silver Nanoparticle Interfaces for Memristive Applications
DOI: 10.9790/1676-10126267 www.iosrjournals.org 67 | Page
Acknowledgements
Financial support in the form of Research Fellowship in Science for Meritorious Students by
University Grant Commission, Govt. of India, is gratefully acknowledged by one of the author B. Sharma.
Authors also thank the members of MNCF, Indian Institute of Science, Bangalore, India for SEM and EDS
measurements whereas SSCU unit of same institute is greatly acknowledged for XRD analysis.
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