scholarly journals Influence of Mn, Fe, Co, and Cu Doping on the Photoelectric Properties of 1T HfS2 Crystals

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 173
Author(s):  
Der-Yuh Lin ◽  
Yu-Tai Shih ◽  
Wei-Chan Tseng ◽  
Chia-Feng Lin ◽  
Hone-Zern Chen
Keyword(s):  
Electron Microscopy ◽  
Activation Energy ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Vital Role ◽  
Chemical Vapor Transport ◽  
Time Resolved ◽  
Cu Doping ◽  
Photoelectric Properties ◽  
Co Doped

Doping plays a vital role in the application of transition-metal dichalcogenides (TMDCs) because it can increase the functionality of TMDCs by tuning their native characteristics. In this study, the influence of Mn, Fe, Co, and Cu doping on the photoelectric properties of HfS2 was investigated. Pristine, Mn-, Fe-, Co-, and Cu-doped HfS2 crystals were grown using the chemical vapor transport method. Scanning electron microscopy images showed that the crystals were layered and transmission electron microscopy, X-ray diffraction, and Raman spectroscopy measurements confirmed that the crystals were in the 1T-phase with a CdI2-like structure. The bandgap of pristine HfS2 obtained from the absorption and photoconductivity spectra was approximately 1.99 eV. As the dopant changed from Mn, Fe, and Co, to Cu, the bandgap gradually increased. The activation energies of the samples were determined using temperature-dependent current-voltage curves. After doping, the activation energy decreased, and the Co-doped HfS2 exhibited the smallest activation energy. Time-resolved photoresponse measurements showed that doping improved the response of HfS2 to light; the Co-doped HfS2 exhibited the best response. The photoresponsivity of HfS2 as a function of the laser power and bias voltage was measured. After doping, the photoresponsivity increased markedly; the Co-doped HfS2 exhibited the highest photoresponsivity. All the experimental results indicated that doping with Mn, Fe, Co, and Cu significantly improved the photoresponsive performance of HfS2, of which Co-doped HfS2 had the best performance.

scholarly journals High Optical Response of Niobium-Doped WSe2-Layered Crystals

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1161 ◽  
Author(s):  
Hung-Pin Hsu ◽  
Der-Yuh Lin ◽  
Jhin-Jhong Jheng ◽  
Pin-Cheng Lin ◽  
Tsung-Shine Ko
Keyword(s):  
Chemical Vapor ◽  
Vapor Transport ◽  
Chemical Vapor Transport ◽  
Near Band Edge ◽  
Frequency Dependent ◽  
Time Resolved ◽  
Niobium Doped ◽  
Layered Crystals ◽  
Transport Method ◽  
Vapor Transport Method

The optical properties of WSe2-layered crystals doped with 0.5% niobium (Nb) grown by the chemical vapor transport method were characterized by piezoreflectance (PzR), photoconductivity (PC) spectroscopy, frequency-dependent photocurrent, and time-resolved photoresponse. With the incorporation of 0.5% Nb, the WSe2 crystal showed slight blue shifts in the near band edge excitonic transitions and exhibited strongly enhanced photoresponsivity. Frequency-dependent photocurrent and time-resolved photoresponse were measured to explore the kinetic decay processes of carriers. Our results show the potential application of layered crystals for photodetection devices based on Nb-doped WSe2-layered crystals.

Controlled growth and characterization of monolayer MoS2 by using metal-organic chemical vapor deposition

2021 ◽  
Vol 66 (1) ◽  
pp. 49-56
Author(s):  
Quyen Do Le ◽  
Duc Nguyen Anh
Keyword(s):  
Electron Microscopy ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Inorganic Materials ◽  
Organic Chemical ◽  
Sio2 Substrate ◽  
Metal Organic ◽  
Organic Chemical Vapor Deposition

Recently, novel physical properties originating from quantum confinement endow the twodimensional (2D) transition metal dichalcogenides, such as MoS2, or WSe2 to attract a great deal of attention. However, the synthesis of 2D-TMDC has to be still limited, in which the precursors are almost based on high vapor pressure inorganic materials, that produce a smallscale film, and it is mainly performed only on conventional Si\SiO2 substrate. In this work, we successfully synthesize the atomic thickness of 2D-MoS2 films by using metal-organic chemical vapor deposition (MOCVD) on several kinds of substrate, namely silicon (Si), silicon dioxide (SiO2), graphite foil, or fluorine-doped tin oxide (FTO). The morphology of samples is observed by field emission scanning electron microscopy (FE-SEM), and scanning transmission electron microscopy (STEM). The lattice vibrational and optical properties are investigated by Raman and photoluminescence (PL) spectroscopies, respectively. With the same MOCVD growing condition, as-obtained samples exhibit the hexagonal configuration (2H phase), whereas the surface morphology and the thickness show a discrepancy, depending on the substrates.

scholarly journals PbI2 Single Crystal Growth and Its Optical Property Study

Crystals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 589 ◽  
Author(s):  
Lin ◽  
Guo ◽  
Dai ◽  
Lin ◽  
Hsu
Keyword(s):  
Band Gap ◽  
Chemical Vapor ◽  
Band Gap Energy ◽  
Chemical Vapor Transport ◽  
X Ray Diffraction ◽  
X Ray ◽  
Gap Energy ◽  
Photoelectric Properties ◽  
Metal Semiconductor Metal ◽  
Excitonic Transition

In this work, we used the chemical vapor transport (CVT) method to grow PbI2 crystals using iodine as a self-transporting agent. The crystals’ structure, composition, and uniformity were confirmed by X-ray diffraction (XRD) and electron probe microanalysis (EPMA) measurements. We investigated the band gap energy using absorption spectroscopy measurements. Furthermore, we explored the temperature dependence of the band gap energy, which shifts from 2.346 eV at 300 K to 2.487 eV at 20 K, and extracted the temperature coefficients. A prototype photodetector with a lateral metal–semiconductor–metal (MSM) configuration was fabricated to evaluate its photoelectric properties using a photoconductivity spectrum (PC) and persistent photoconductivity (PPC) experiments. The resonance-like PC peak indicates the excitonic transition in absorption. The photoresponse ILight/IDark-1 is up to 200%.

Conductivity Mechanisms in Acceptor Doped KTaO3 Crystals

1990 ◽  
Vol 210 ◽  
Author(s):  
T. Scherban ◽  
S.Q. Fu ◽  
A.S. Nowick
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Oxygen Vacancy ◽  
Ionic Conduction ◽  
Electron Hole ◽  
Cu Doping ◽  
Hole Conduction ◽  
Protonic Conductors ◽  
Dry Conditions ◽  
Co Doped

AbstractThe electrical conductivity of perovskite—structured KTaO3 crystals acceptor doped with Co, Cu or Fe was investigated after treatments in oxidizing and reducing atmospheres under both wet and dry conditions. Isotope effect measurements (using H2O vs. D2O) show that, after treatments in wet gases of low P(O2), all the crystals are primarily protonic conductors, through a process of proton hopping with an activation energy close to 0.84 eV. Electron hole conduction dominatesat high P(O2) in the case of Fe and Cu doping. For Co—doped crystals, the conductivity is independent of P(O2) up to 1 atm., indicating that ionic conduction predominates. There is no evidence of oxygen vacancy migration, leading to the conclusion that the activation energy for that process Is relatively high.

scholarly journals Unveiling defect-mediated carrier dynamics in monolayer semiconductors by spatiotemporal microwave imaging

2020 ◽  
Vol 117 (25) ◽  
pp. 13908-13913
Author(s):  
Zhaodong Chu ◽  
Chun-Yuan Wang ◽  
Jiamin Quan ◽  
Chenhui Zhang ◽  
Chao Lei ◽  
...  
Keyword(s):  
Carrier Transport ◽  
Electrical Response ◽  
Transition Metal Dichalcogenides ◽  
Chemical Vapor ◽  
Strongly Correlated ◽  
Trap States ◽  
Time Resolved ◽  
Metal Dichalcogenides ◽  
Microwave Signals ◽  
The Time Domain

The optoelectronic properties of atomically thin transition-metal dichalcogenides are strongly correlated with the presence of defects in the materials, which are not necessarily detrimental for certain applications. For instance, defects can lead to an enhanced photoconduction, a complicated process involving charge generation and recombination in the time domain and carrier transport in the spatial domain. Here, we report the simultaneous spatial and temporal photoconductivity imaging in two types of WS2monolayers by laser-illuminated microwave impedance microscopy. The diffusion length and carrier lifetime were directly extracted from the spatial profile and temporal relaxation of microwave signals, respectively. Time-resolved experiments indicate that the critical process for photoexcited carriers is the escape of holes from trap states, which prolongs the apparent lifetime of mobile electrons in the conduction band. As a result, counterintuitively, the long-lived photoconductivity signal is higher in chemical-vapor deposited (CVD) samples than exfoliated monolayers due to the presence of traps that inhibits recombination. Our work reveals the intrinsic time and length scales of electrical response to photoexcitation in van der Waals materials, which is essential for their applications in optoelectronic devices.

Microstructures and Kinetics of Tungsten Coating Deposited by Chemical Vapor Transport

2019 ◽  
Vol 815 ◽  
pp. 70-80
Author(s):  
Fang Wang ◽  
Yun Peng Hao ◽  
Xiao Dong Yu ◽  
Zhi Hua Nie ◽  
Xiu Chen Zhao ◽  
...  
Keyword(s):  
Activation Energy ◽  
Work Function ◽  
Control Mechanism ◽  
Chemical Vapor ◽  
Growth Direction ◽  
Vapor Transport ◽  
Chemical Vapor Transport ◽  
Tungsten Coating ◽  
Polycrystalline Tungsten ◽  
System Pressure

Chemical vapor transport deposition (CVTD) is an effective method for preparing large tungsten coatings for space thermionic reactors. In this study, a high-density, high-work-function polycrystalline tungsten coating was prepared using a WCl6 transport agent in a concentric tube-type closed transport system. The relationship between the kinetics and the microstructures of the CVTD polycrystalline tungsten coating at the substrate temperature of 1593 K-1793 K and system pressure of 15.93 Pa-106.8 Pa was studied, which provided a basis for the preparation of high-quality tungsten coatings. At a low temperature or a low pressure, the activation energy was approximately 2 kJ/mol, the deposition rate was almost independent of the temperature changes, and the control mechanism was mass transport limited. The tungsten coating had nodules on the surface with pores in the grain boundaries and grew preferentially along <111>. At a high temperature and a high pressure, the apparent activation energy was approximately 90 kJ/mol, the value of order was approximately 1, and the control mechanism in this process range was surface limited. The tungsten coating exhibited a hexagonal pyramidal structure, and the growth direction was preferred along <110>. The average work function of the tungsten coating prepared at a temperature of 1673 K and a system pressure of 106.80 Pa was as high as 5.20 eV.

Microtubule nucleation sequence studied by time-resolved x-ray scattering and electron microscopy

1983 ◽  
Vol 41 ◽  
pp. 766-767
Author(s):  
Eva-Maria Mandelkow ◽  
Eckhard Mandelkow ◽  
Joan Bordas
Keyword(s):  
Electron Microscopy ◽  
Dynamic Equilibrium ◽  
Time Resolved ◽  
X Ray ◽  
Additional Information ◽  
X Ray Scattering ◽  
Low Concentrations ◽  
Microtubule Growth ◽  
Ray Patterns ◽  
Ray Scattering

When a solution of microtubule protein is changed from non-polymerising to polymerising conditions (e.g. by temperature jump or mixing with GTP) there is a series of structural transitions preceding microtubule growth. These have been detected by time-resolved X-ray scattering using synchrotron radiation, and they may be classified into pre-nucleation and nucleation events. X-ray patterns are good indicators for the average behavior of the particles in solution, but they are difficult to interpret unless additional information on their structure is available. We therefore studied the assembly process by electron microscopy under conditions approaching those of the X-ray experiment. There are two difficulties in the EM approach: One is that the particles important for assembly are usually small and not very regular and therefore tend to be overlooked. Secondly EM specimens require low concentrations which favor disassembly of the particles one wants to observe since there is a dynamic equilibrium between polymers and subunits.

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