The document summarizes the synthesis of tungsten disulfide (WS2) nanosheets using chemical vapor deposition (CVD) with a gas-phase sulfur reactant. It is observed that the WS2 grows laterally and that domains coalesce over time. The number of layers can be controlled by adjusting the reaction time. Additionally, a graphene/WS2 heterostructure is shown to have properties suitable for photo detection.
Invited lecture of the Simposium N "Surface Engineering - functional coatings and modified surfaces" at the XIII SBPMat (Brazilian MRS) meeting, in João Pessoa (Brazil). The lecture took place on September 29th, 2014.
The speaker was Christopher Muratore, "Wright Brothers Institute Endowed Chair Professor" at the Department of Chemical and Materials Engineering from University of Dayton (USA).
Invited lecture of the Simposium N "Surface Engineering - functional coatings and modified surfaces" at the XIII SBPMat (Brazilian MRS) meeting, in João Pessoa (Brazil). The lecture took place on September 29th, 2014.
The speaker was Christopher Muratore, "Wright Brothers Institute Endowed Chair Professor" at the Department of Chemical and Materials Engineering from University of Dayton (USA).
Branislav K. Nikoli
ć
Department of Physics and Astronomy, University of Delaware, U.S.A.
PHYS 624: Introduction to Solid State Physics
http://www.physics.udel.edu/~bnikolic/teaching/phys624/phys624.html
The driving engine for the exponential growth of digital information processing systems is scaling down the transistor dimensions. For decades, this has enhanced the device performance and density. However, the International Technology Roadmap for Semiconductors (ITRS) states the end of Moore’s law in the next decade due to the scaling challenges of silicon-based CMOS electronics, e.g. extremely high power density. The forward-looking solutions are the utilization of emerging materials and devices for integrated circuits, e.g. carbon-based materials. The presentation of my Ph.D. work focuses on graphene, one atomic layer of carbon sheet, experimentally discovered in 2004. Since fabrication technology of emerging materials is still in early stages, transistor modeling has been playing an important role for evaluating futuristic graphene-based devices and circuits. The device has been simulated by solving a quantum transport model based on non-equilibrium Green’s function (NEGF) approach, which fully treats short channel-length electrostatic effects and the quantum tunneling effects, leading to the technology exploration of graphene nanoribbon field effect transistors (GNR FETs) for the future. This research presents a comprehensive study of the width-dependence performance of the GNR FETs and the scaling of its channel length down to 2.5 nanometer, investigating its potential use beyond-CMOS emerging technology.
This presentation summarizes history and recent development of perovskite solar cells. If you have any questions or comments, you can reach me at agassifeng@gmail.com
Los días 22 y 23 de junio de 2016 organizamos en la Fundación Ramón Areces un simposio internacional sobre 'Materiales bidimensionales: explorando los límites de la física y la ingeniería'. En colaboración con el Massachusetts Institute of Technology (MIT), científicos de este prestigioso centro de investigación mostraron las propiedades únicas de materiales como el grafeno, de solo un átomo de espesor, y al mismo tiempo más resistente que el acero y mucho más ligero.
In this presentation, you will be familiar with VSM and Magnetic characterization of materials, especially ferromagnetic materials via their magnetic hysteresis loop.
(If visualization is slow, please try downloading the file.)
Part 2 of a tutorial given in the Brazilian Physical Society meeting, ENFMC. Abstract: Density-functional theory (DFT) was developed 50 years ago, connecting fundamental quantum methods from early days of quantum mechanics to our days of computer-powered science. Today DFT is the most widely used method in electronic structure calculations. It helps moving forward materials sciences from a single atom to nanoclusters and biomolecules, connecting solid-state, quantum chemistry, atomic and molecular physics, biophysics and beyond. In this tutorial, I will try to clarify this pathway under a historical view, presenting the DFT pillars and its building blocks, namely, the Hohenberg-Kohn theorem, the Kohn-Sham scheme, the local density approximation (LDA) and generalized gradient approximation (GGA). I would like to open the black box misconception of the method, and present a more pedagogical and solid perspective on DFT.
Branislav K. Nikoli
ć
Department of Physics and Astronomy, University of Delaware, U.S.A.
PHYS 624: Introduction to Solid State Physics
http://www.physics.udel.edu/~bnikolic/teaching/phys624/phys624.html
The driving engine for the exponential growth of digital information processing systems is scaling down the transistor dimensions. For decades, this has enhanced the device performance and density. However, the International Technology Roadmap for Semiconductors (ITRS) states the end of Moore’s law in the next decade due to the scaling challenges of silicon-based CMOS electronics, e.g. extremely high power density. The forward-looking solutions are the utilization of emerging materials and devices for integrated circuits, e.g. carbon-based materials. The presentation of my Ph.D. work focuses on graphene, one atomic layer of carbon sheet, experimentally discovered in 2004. Since fabrication technology of emerging materials is still in early stages, transistor modeling has been playing an important role for evaluating futuristic graphene-based devices and circuits. The device has been simulated by solving a quantum transport model based on non-equilibrium Green’s function (NEGF) approach, which fully treats short channel-length electrostatic effects and the quantum tunneling effects, leading to the technology exploration of graphene nanoribbon field effect transistors (GNR FETs) for the future. This research presents a comprehensive study of the width-dependence performance of the GNR FETs and the scaling of its channel length down to 2.5 nanometer, investigating its potential use beyond-CMOS emerging technology.
This presentation summarizes history and recent development of perovskite solar cells. If you have any questions or comments, you can reach me at agassifeng@gmail.com
Los días 22 y 23 de junio de 2016 organizamos en la Fundación Ramón Areces un simposio internacional sobre 'Materiales bidimensionales: explorando los límites de la física y la ingeniería'. En colaboración con el Massachusetts Institute of Technology (MIT), científicos de este prestigioso centro de investigación mostraron las propiedades únicas de materiales como el grafeno, de solo un átomo de espesor, y al mismo tiempo más resistente que el acero y mucho más ligero.
In this presentation, you will be familiar with VSM and Magnetic characterization of materials, especially ferromagnetic materials via their magnetic hysteresis loop.
(If visualization is slow, please try downloading the file.)
Part 2 of a tutorial given in the Brazilian Physical Society meeting, ENFMC. Abstract: Density-functional theory (DFT) was developed 50 years ago, connecting fundamental quantum methods from early days of quantum mechanics to our days of computer-powered science. Today DFT is the most widely used method in electronic structure calculations. It helps moving forward materials sciences from a single atom to nanoclusters and biomolecules, connecting solid-state, quantum chemistry, atomic and molecular physics, biophysics and beyond. In this tutorial, I will try to clarify this pathway under a historical view, presenting the DFT pillars and its building blocks, namely, the Hohenberg-Kohn theorem, the Kohn-Sham scheme, the local density approximation (LDA) and generalized gradient approximation (GGA). I would like to open the black box misconception of the method, and present a more pedagogical and solid perspective on DFT.
Changing the World in Healthcare, Education, and Energy through Science, Tech...Mohamed Labadi
Changing the World in Healthcare, Education, and Energy through Science, Technology, and Social Entrepreneurship & Innovation!
“Global health and global education problems & challenges are a single-point failure for humanity.”
Dr. John D. Schmisseur presents an overview of his program, Energy, Power and Propulsion Sciences, at the AFOSR 2013 Spring Review. At this review, Program Officers from AFOSR Technical Divisions will present briefings that highlight basic research programs beneficial to the Air Force.
Dr. Jim Hwang presents an overview of his program, GHz-THz Electronics, at the AFOSR 2013 Spring Review. At this review, Program Officers from AFOSR Technical Divisions will present briefings that highlight basic research programs beneficial to the Air Force.
This research, presented at the 2014 APS March Meeting in Denver, Colorado, characterizes magnetic phase transitions in the manganese-doped dichalcogenide TaS2.
지난 세기, 인류는 원자의 발견과 양자물리학의 발전을 통해 우리 삶을 바꾸는 새로운 물질들을 찾아낸 바 있습니다. 우리가 사용하는 문명의 이기 뒤에는 과학자들의 쉼없는 노력에서 탄생한 물질이 큰 역할을 하기도 합니다. 이 강연에서는 과학자들이 새로운 물질을 찾기 위한 여러 노력을 탄소 나노 물질의 합성과 그 성질에 관한 연구과정을 예로 들어 설명하려고 합니다.
Los días 22 y 23 de junio de 2016 organizamos en la Fundación Ramón Areces un simposio internacional sobre 'Materiales bidimensionales: explorando los límites de la física y la ingeniería'. En colaboración con el Massachusetts Institute of Technology (MIT), científicos de este prestigioso centro de investigación mostraron las propiedades únicas de materiales como el grafeno, de solo un átomo de espesor, y al mismo tiempo más resistente que el acero y mucho más ligero.
Plasmon Enhanced Internal Quantum Efficiency of CdSe/ZnS Quantum Dotsijrap
The effects of surface plasmon oscillations on the radiative recombination rate and internal quantum efficiency of silver coated CdSe/ZnS quantum dots imbedded in quartz matrix is studied theoretically and
numerically. The analysis is carried out by introducing the local field enhancement factor for the description of the dielectric function of the quantum dots together with the modified Drude model for the metal-coat that takes into account the effects of interband transitions and the size dependent damping
parameter. It is found out that the internal quantum efficiency of photoluminescence emission of the metalcoated CdSe/ZnS quantum dots is enhanced by about 5-folds compared with the quantum dots without metal-coat. Moreover, increasing the metal fraction of the coated CdSe/ZnS quantum dots from 0.80 to 0.92 results in a significant increase of the intensity that is accompanied by a blue-shift of the quantum efficiency curves. The results obtained can be utilized in the design and fabrication of optoelectronic devices that require high intensity of photoluminescence emission.
A study of micro structural, magnetic and electrical properties of La-Co-Sm n...IJECEIAES
A Lanthanum (La 3+ ) doped Samarium-Cobalt nanoferrites (La_x,Co_0.2,Sm_0.2,Fe_(2-x) O_4, where x=0.0,0.5,1.0) have been synthesized by sol-gel method in citrate media. Obtained spinal ferrites micro structure properties have been investigated by XRD, FTIR, SEM-EDX, and TEM-SAED techniques. All the samples are nano in size with significant hysteresis. Micro structural analysis by XRD confirms the obtained samples showing the single phase cubic spinal structures with an average crystal size found from 12 nm to 25 nm, while the average particles sizes identified from TEM analysis are ranging from 21.5nm-26.8 nm (~23.4nm) and from 20.5 nm to 28(~26.4nm) nm for x=0.5,1.0. The lattice parameter found to be a= 8.402, 8.423, 8.467Å for the respective values of x= 0.0, 0.05, and 1.0. Electrical properties show increase in dc resistivity with increase in La ion concentration. Finally, it was concluded that the doping of Lanthanum ion (La 3+ ) in the ferrites structure is found to influencing the structural and electrical properties without scarifying the ferromagnetic character.
Structure, microstructure and dielectric study of (ba0.6 sr0.4)(zr0.6ti0.4)o3...eSAT Publishing House
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.
This to demonstrate the laser ablation of hard materials to form a thin film for optical sensors. The work was done at DIllard University , New Orleans LA by Professor Abdalla Darwish. any comment e-mail adarwish@bellsouth.net.
The effect of oxygen flow rate on metal–insulator transition (MIT) characteri...Pawan Kumar
Vanadium dioxide (VO2), because of its unique metal–insulator phase transion around room temperature, has enormous potential for applications in thermochromic, electrochromic, microbolometery, and non-volatile switches. However, obtaining phase-pure VO2 has been challenging due to its narrow window of thermodynamic stability. Pulsed laser deposition (PLD) is considered to be one of the most promising technique to deposit phase-pure VO2 thin films. While optimizing PLD processing parameters, (such as oxygen pressure (PO2), substrate temperature (Ts), laser energy (EL), target-substrate distance (dT-S), and laser repetition rate (RR)) is crucial, and their effects have been reported, the effect of gas flow rate (QO2) has been largely neglected. Since the QO2 and PO2 of the PLD system are intertwined at the outset, most reports are focused only on either QO2 or PO2. We report on the effect of gas flow rate under constant PO2, on the quality of the VO2 thin films. Controlling flow rate affected the resistivity contrast between the metallic and insulator phases, the temperature ranges of the transition, and the width of hysteresis. We anticipate that this study will help set the standard for obtaining high quality VO2 thin films.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Study the effect of nickel and aluminium doped ZnO photoanode in DSSCTELKOMNIKA JOURNAL
Dye sensitized solar cells (DSSC) is one of the promising candidates which are efficient, low-cost, and clean hybrid molecular solar cell devices. Zinc oxide (ZnO) has been widely used as the phoanode in DSSC due to its excellent charge conduction mechanism, yet still suffers from poor cell efficiency. In this study, aluminium doped ZnO (ZnO:Al) and Ni doped ZnO (ZnO:Ni) were studied as photoanode material in DSSC using solar cell capacitance simulator (SCAPS) simulation, and the electrolyte liquid considered a single solid p-type layer as hole transporting materials. Both studied photoanodes have demonstrated better cell performance than pure ZnO photoanode due to the small amount of aluminium (Al) and nikel (Ni) impurities added have enhanced the physiochemical properties of ZnO films. A power conversion efficiency (PCE) of 3.96% was obtained at 3 mol% ZnO:Al photoanode with optimized key parameters. These simulation results proved an opportunity to improve the performance of the DSSCs via doping engineering into the ZnO photonaode.
1. Layer-modulated synthesis of
uniform tungsten disulfide
nanosheet using gas-phase
precursors.
Jusang Park*
School of Electrical and Electronics Engineering,
Yonsei University, 262 Seongsanno, Seodaemun-gu,
Seoul, Korea
2. 2D material family
New materials for
advanced application
: Beyond graphene
Transition metal
dichalcogenides
(TMDC)
We can choose all
kinds of properties
for everything :
semiconductor,
ferromagnetic, or
nonmagnetic
metals…
New era for atomic nanosheet technology !
3. Thermal decomposition of thiosalts
Transition metal oxides with chalcogen
Transport and recrystallization from TMD
Vapor Phase Deposition
→The precursor(NH4)2MoS4 was dipcoated on SiO2/Si
→Two-step annealing process
→The facilitated nucleation by seeding the substrate
with graphene-like species
S. Wu, C. Huang et al,ACS Nano, 7, 2768–2772,(2013)
Y.-H. Lee, L. Yu er al,Nano Lett.13,1852–1857,(2013)
Liu K-K et al, Nano Lett. 12, 1538–1544, (2012)
→Vapour–solid (VS) growth method for synthesizing a
high optical quality MoS2 monolayer.
4. Growth of CVD WS2
• Initial growth of CVD WS2 Time dependent lateral growth of WS2
Precursor
H2S Gas
Vacuum furnace
Pump out
<SEM>
<Previous CVD method>
Lee Y-H et al, Adv. Mater, 24, 2320–2325, (2012)
<Gas Phase CVD WS2>
WCl6 Tube furnace
Growth temperature : 700 °C
5. Time dependent Layer Control
<Optical Microscopy>
<AFM>
Number of layer dependent on the cycle number of ALD WO3
6. Coalescence of CVD WS2
Coalescence of two or more domains
Seed for the growth of second WS2 layer
Sina Najmaei et al, Nat Mat, 12, 754–759, (2013)
<AFM>
CVD 10 min Transferred WS2
200 nm
Seed for second
layer of WS2
200 nm
First WS2
SiO2
CVD 10 min Transferred WS2
Seed for second
layer of WS2
7. Raman of CVD WS2
<Raman, laser excitation λ = 633 nm>
Raman spectra for the 1L, 2L and 4L WS2 nanosheets
Relative Raman peak intensities and peak distances of the E1
2g and A1g modes
Dependent on the number of layer
8. Optical Property of CVD WS2
<PL>
PL spectra for the 1L, 2L and 4L WS2 nanosheets
Indirect to direct band gap transition with reducing
number of layer
I peak from PL spectrum of 2L and 4L WS2
<Electronic structure of WS2>
Zeng, H. et al, Sci, Rep. 3, 1608, (2013)
9. Chemical Composition of CVD WS2
CVD WS2 show good stoicheometry with no Cl contamination (from WCl6)
1L WS2
W 33.6
S 66.4
Cl <1%
4L WS2
W 33.1
S 67
Cl <1%
CVD grown 1L WS2
CVD grown 4L WS2
<XPS>
10. Large Area Uniformity of CVD WS2
Color dependency on the number of layers
Large-area uniformity on 1 cm X 7 cmSiO2
<Raman analysis>
11. Atomic Arrangement of CVD WS2
<HRTEM> <Inversed FFT><TEM>
Low-magnification TEM image for a 1L WS2 nanosheet on a TEM grid
HRTEM image of 1L WS2 nanosheet at a selected region and (inset) the SAED pattern
Inverse FFT by applying a mask
(100) and (110) crystal directions
Lattice spacing: 0.26 nm and 0.16 nm for the (100) and (110) planes
12. Graphene/WS2 Photo-Detector
• △Id/Id @ Vg=0 V -> 4% with monochromatic green light (~550 nm) @ 1 W/m2
• Lower than exfoliated few-layer MoS2 with CVD graphene photo-detector (~ 7% @ 0.6
W/m2)
<Transfer curve> <Output curve><OM image>
Si++/SiO2
Unpublished Data
Transferred CVD Gr
aphene on WS2
20 µm
1L WS2
Kallol Roy et al, Nat nanotech, 8, 826–830, (2013)
13. Graphene/WS2 Photo-Detector
• Photo-excited electron injection to hole doped graphene resulting in
reduced hole channel current when Vg « VT
• CVD WS2 based photo-detector can be fabricated large area
Kallol Roy et al, Nat nanotech, 8, 826–830, (2013)
Vg « VT Vg > VT
EF
WS2
SiO2
P++
Si
(back
-gate)
EF
WS2
SiO2
P++
Si
(back
-gate)
14. Summary
CVD WS2 nanosheets are
synthesized using gas phase S
reactant
Lateral growth and coalescence of
two or more domains are observed
Number of layer can be controlled
by reaction time
Graphene/WS2 hetero-structure
shows properties of photo
detecting
