In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant is hydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless number...In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant is hydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers for heat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phase heat and mass transfer, respectively. A simplified model has been established to simulate gas-phase temperature and H concentration distributions between the filament and the substrate. Examination of the relative importance of homogeneous and heterogeneous production of H atoms indicates that filament-surface decomposition of molecular hydrogen is the dominant source of H and gas-phase reaction plays a negligible role. The filament-surface dissociation rates of H2 for various filament temperatures were calculated to match H-atom concentrations observed in the literature or derived from power consumption by filaments. Arrhenius plots of the filament-surface hydrogen dissociation rates suggest that dissociation of H2 at refractory filament surface is a catalytic process, which has a rather lower effective activation energy than homogeneous thermal dissociation. Atomic hydrogen, acting as an important heat transfer medium to heat the substrate, can freely diffuse from the filament to the substrate without recombination.展开更多
About φ45 mm LiAlO2 single crystal was grown by Czochralski （Cz） technique. However, the full-width at half-maximum （FWHM） value was high to 116.9 arcsec. After three vapor transport equilibration （VTE） process...About φ45 mm LiAlO2 single crystal was grown by Czochralski （Cz） technique. However, the full-width at half-maximum （FWHM） value was high to 116.9 arcsec. After three vapor transport equilibration （VTE） processes, we can obtain high-quality LiAlO2 slice with the FWHM value of 44.2 arcsec. ZnO films were fabricated on as-grown slices and after-VTE ones by pulsed laser deposition （PLD）. It was found that ZnO films on the two slices have similar crystallinity, optical transmittance and optical band gap at room temperature. These results not only show that LAO substrate is suitable for ZnO growth, but also prove that the crystal quality of LAO substrate slightly affects the structural and optical properties of ZnO film.展开更多
We report a novel two-step ambient pressure chemical vapor deposition(CVD)pathway to grow high-quality Mo S_(2)monolayer on the Si O_(2)substrate with large crystal size up to 110μm.The large specific surface area of...We report a novel two-step ambient pressure chemical vapor deposition(CVD)pathway to grow high-quality Mo S_(2)monolayer on the Si O_(2)substrate with large crystal size up to 110μm.The large specific surface area of the pre-synthesized Mo O_(3)flakes on the mica substrate compared to Mo O_(3)powder could dramatically reduce the consumption of the Mo source.The electronic information inferred from the four-probe scanning tunneling microscope(4P-STM)image explains the threshold voltage variations and the n-type behavior observed in the two-terminal transport measurements.Furthermore,the direct van der Pauw transport also confirms its relatively high carrier mobility.Our study provides a reliable method to synthesize high-quality Mo S_(2)monolayer,which is confirmed by the direct 4P-STM measurement results.Such methodology is a key step toward the large-scale growth of transition metal dichalcogenides(TMDs)on the Si O_(2)substrate and is essential to further development of the TMDs-related integrated devices.展开更多
This paper introduces a feasible process to achieve the molybdenum disulfide atomic layers using chemical vapor deposition(CVD) method,with molybdenum thin film and solid sulfur as precursors.And some improvements wer...This paper introduces a feasible process to achieve the molybdenum disulfide atomic layers using chemical vapor deposition(CVD) method,with molybdenum thin film and solid sulfur as precursors.And some improvements were made to reduce the amount of metastable MoS_(2)-3 R.The morphology of the acquired MoS_(2) layers,existing as triangular flakes or large-area continuous films,can be controlled by adjusting the synthesis time and reacting temperature.The characterization results show that the monolayer MoS_(2) flakes reveal a(002)-oriented growth on SiO_(2)/Si substrates,and its crystalline domain size is approximately 30 μm,and the thickness is 0.65 nm.Since the synthesis of MoS_(2)-3 R is restrained,the electronic transport properties of MoS_(2) with different layers were investigated,revealing that those properties equal with those of MoS_(2) samples prepared by exfoliation methods.展开更多
Thickness and component distributions of large-area thin films are an issue of in-ternational concern in the field of material processing. The present work employs experiments and direct simulation Monte Carlo (DSMC) ...Thickness and component distributions of large-area thin films are an issue of in-ternational concern in the field of material processing. The present work employs experiments and direct simulation Monte Carlo (DSMC) method to investigate three-dimensional low-density, non-equilibrium jets of yttrium and titanium vapor atoms in an electron-beams physical vapor deposition (EBPVD) system furnished with two or three electron-beams, and obtains their deposition thickness and component distributions onto 4-inch and 6-inch mono-crystal silicon wafers. The DSMC results are found in excellent agreement with our measurements, such as evaporation rates of yttrium and titanium measured in-situ by quartz crystal reso-nators, deposited film thickness distribution measured by Rutherford backscat-tering spectrometer (RBS) and surface profilometer and deposited film molar ratio distribution measured by RBS and inductively coupled plasma atomic emission spectrometer (ICP-AES). This can be taken as an indication that a combination of DSMC method with elaborate measurements may be satisfactory for predicting and designing accurately the transport process of EBPVD at the atomic level.展开更多
文摘In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant is hydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers for heat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phase heat and mass transfer, respectively. A simplified model has been established to simulate gas-phase temperature and H concentration distributions between the filament and the substrate. Examination of the relative importance of homogeneous and heterogeneous production of H atoms indicates that filament-surface decomposition of molecular hydrogen is the dominant source of H and gas-phase reaction plays a negligible role. The filament-surface dissociation rates of H2 for various filament temperatures were calculated to match H-atom concentrations observed in the literature or derived from power consumption by filaments. Arrhenius plots of the filament-surface hydrogen dissociation rates suggest that dissociation of H2 at refractory filament surface is a catalytic process, which has a rather lower effective activation energy than homogeneous thermal dissociation. Atomic hydrogen, acting as an important heat transfer medium to heat the substrate, can freely diffuse from the filament to the substrate without recombination.
文摘About φ45 mm LiAlO2 single crystal was grown by Czochralski （Cz） technique. However, the full-width at half-maximum （FWHM） value was high to 116.9 arcsec. After three vapor transport equilibration （VTE） processes, we can obtain high-quality LiAlO2 slice with the FWHM value of 44.2 arcsec. ZnO films were fabricated on as-grown slices and after-VTE ones by pulsed laser deposition （PLD）. It was found that ZnO films on the two slices have similar crystallinity, optical transmittance and optical band gap at room temperature. These results not only show that LAO substrate is suitable for ZnO growth, but also prove that the crystal quality of LAO substrate slightly affects the structural and optical properties of ZnO film.
基金Project supported by the National Natural Science Foundation of China(Grant No.61888102)the National Natural Science Foundation of China(Grant No.12004417)+5 种基金the National Key Research and Development Program of China(Grant Nos.2018YFA0305800 and 2019YFA0308500)the National Natural Science Foundation of China(Grant No.U2032206)Chinese Academy of Sciences(Grant Nos.XDB36000000,YSBR-003,and 112111KYSB20160061)Strategic Priority Research Program of Chinese Academy of Sciences(CAS)(Grant Nos.XDB30000000 and XDB28000000)Youth Innovation Promotion Association of CAS(Grant No.Y201902)CAS Project for Young Scientists in Basic Research(Grant No.YSBR-003)。
文摘We report a novel two-step ambient pressure chemical vapor deposition(CVD)pathway to grow high-quality Mo S_(2)monolayer on the Si O_(2)substrate with large crystal size up to 110μm.The large specific surface area of the pre-synthesized Mo O_(3)flakes on the mica substrate compared to Mo O_(3)powder could dramatically reduce the consumption of the Mo source.The electronic information inferred from the four-probe scanning tunneling microscope(4P-STM)image explains the threshold voltage variations and the n-type behavior observed in the two-terminal transport measurements.Furthermore,the direct van der Pauw transport also confirms its relatively high carrier mobility.Our study provides a reliable method to synthesize high-quality Mo S_(2)monolayer,which is confirmed by the direct 4P-STM measurement results.Such methodology is a key step toward the large-scale growth of transition metal dichalcogenides(TMDs)on the Si O_(2)substrate and is essential to further development of the TMDs-related integrated devices.
基金financially supported by the National Natural Science Foundation of China (Nos.50835002 and 51105102)。
文摘This paper introduces a feasible process to achieve the molybdenum disulfide atomic layers using chemical vapor deposition(CVD) method,with molybdenum thin film and solid sulfur as precursors.And some improvements were made to reduce the amount of metastable MoS_(2)-3 R.The morphology of the acquired MoS_(2) layers,existing as triangular flakes or large-area continuous films,can be controlled by adjusting the synthesis time and reacting temperature.The characterization results show that the monolayer MoS_(2) flakes reveal a(002)-oriented growth on SiO_(2)/Si substrates,and its crystalline domain size is approximately 30 μm,and the thickness is 0.65 nm.Since the synthesis of MoS_(2)-3 R is restrained,the electronic transport properties of MoS_(2) with different layers were investigated,revealing that those properties equal with those of MoS_(2) samples prepared by exfoliation methods.
基金the National Natural Science Foundation of China (Grant Nos. 90205024, 10502051 and 10621202)
文摘Thickness and component distributions of large-area thin films are an issue of in-ternational concern in the field of material processing. The present work employs experiments and direct simulation Monte Carlo (DSMC) method to investigate three-dimensional low-density, non-equilibrium jets of yttrium and titanium vapor atoms in an electron-beams physical vapor deposition (EBPVD) system furnished with two or three electron-beams, and obtains their deposition thickness and component distributions onto 4-inch and 6-inch mono-crystal silicon wafers. The DSMC results are found in excellent agreement with our measurements, such as evaporation rates of yttrium and titanium measured in-situ by quartz crystal reso-nators, deposited film thickness distribution measured by Rutherford backscat-tering spectrometer (RBS) and surface profilometer and deposited film molar ratio distribution measured by RBS and inductively coupled plasma atomic emission spectrometer (ICP-AES). This can be taken as an indication that a combination of DSMC method with elaborate measurements may be satisfactory for predicting and designing accurately the transport process of EBPVD at the atomic level.
