Ternary Ti-B-N coatings were synthesized on AISI 304 and Si wafer by plasma-enhanced chemical vapor deposition (PECVD) technique using a gaseous mixture of TiCl4,BCl3,H2,N2,and Ar.By virtue of X-ray diffraction analys...Ternary Ti-B-N coatings were synthesized on AISI 304 and Si wafer by plasma-enhanced chemical vapor deposition (PECVD) technique using a gaseous mixture of TiCl4,BCl3,H2,N2,and Ar.By virtue of X-ray diffraction analysis,X-ray photoelectron spectroscopy,scanning electron microscope,and high-resolution transmission electron microscope,the influences of B content on the microstructure and properties of Ti B N coatings were investigated systematically.The results indicated that the microstructure and mechanical properties of Ti-B-N coatings largely depend on the transformation from FCC-TiN phase to HCP-TiB2 phase.With increasing B content and decreasing N content in the coatings,the coating microstructure evolves gradually from FCC-TiN/a-BN to HCP-TiB2 /a-BN via FCC-TiN+HCP-TiB2/a-BN.The highest microhardness of about 34 GPa is achieved,which corresponds to the nanocomposite Ti-63%B-N (mole fraction) coating consisting of the HCP-TiB2 nano-crystallites and amorphous BN phase.The lowest friction-coefficient was observed for the nanocomposite Ti-41%B-N (mole fraction) coating consisting of the FCC-TiN nanocrystallites and amorphous BN展开更多
InGaAs high electron mobility transistors （HEMTs） on InP substrate with very good device performance have been grown by mental organic chemical vapor deposition （MOCVD）. Room temperature Hall mobilities of the 2-D...InGaAs high electron mobility transistors （HEMTs） on InP substrate with very good device performance have been grown by mental organic chemical vapor deposition （MOCVD）. Room temperature Hall mobilities of the 2-DEG are measured to be over 8 700 cm^2/V-s with sheet carrier densities larger than 4.6× 10^12 cm^ 2. Transistors with 1.0 μm gate length exhibits transconductance up to 842 mS/ram. Excellent depletion-mode operation, with a threshold voltage of-0.3 V and IDss of 673 mA/mm, is realized. The non-alloyed ohmic contact special resistance is as low as 1.66×10^-8 Ω/cm^2, which is so far the lowest ohmic contact special resistance. The unity current gain cut off frequency （fT） and the maximum oscillation frequency （fmax） are 42.7 and 61.3 GHz, respectively. These results are very encouraging toward manufacturing InP-based HEMT by MOCVD.展开更多
We directly grow a lattice matched GalnP/GalnAs/GalnNAs/Ge （1.88 eVil .42 eVil .05 eV/0.67eV） four-junction （4J） solar cell on a Ge substrate by the metal organic chemical vapor deposition technology. To solve the...We directly grow a lattice matched GalnP/GalnAs/GalnNAs/Ge （1.88 eVil .42 eVil .05 eV/0.67eV） four-junction （4J） solar cell on a Ge substrate by the metal organic chemical vapor deposition technology. To solve the current limit of the GalnNAs sub cell, we design three kinds of anti-reflection coatings and adjust the base region thickness of the GalnNAs sub cell. Developed by a series of experiments, the external quantum efficiency of the GalnNAs sub cell exceeds 80%, and its current density reaches 11.24 mA/cm2. Therefore the current limit of the 4J solar cell is significantly improved. Moreover, we discuss the difference of test results between 4J and GalnP/GalnAs/Ge solar cells under the 1 sun AMO spectrum.展开更多
Nearly lattice-matched InAIGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostruct...Nearly lattice-matched InAIGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostructure. The electron mobility is 1668.08cm2/V.s together with a high two-dimensional-electron-gas density of 1.43 × 10^13 cm-2 for the InAlCaN/CaN heterostructure of 2Onto InAlCaN quaternary barrier. High electron mobility transistors with gate dimensions of 1 × 50 μm2 and 4μm source-drain distance exhibit the maximum drain current of 763.91 mA/mm, the maximum extrinsic transconductance of 163.13 mS/mm, and current gain and maximum oscillation cutoff frequencies of 11 GHz and 21 GHz, respectively.展开更多
An ultrahigh vacuum chemical vapor deposition (UHV/CVD) system is developed and the details of its construction and operation are reported. Using high purity SiH4 and GeH4 reactant gases, the Si0.82Ge0.18 layer is dep...An ultrahigh vacuum chemical vapor deposition (UHV/CVD) system is developed and the details of its construction and operation are reported. Using high purity SiH4 and GeH4 reactant gases, the Si0.82Ge0.18 layer is deposited at 550℃. With the measurements by double crystal X-ray diffraction (DCXRD), transmission electron microscopy (TEM) and Rutherford backscattering spectroscppy (RBS) techniques, it is shown that the crystalline quality of the SiGe layer is good, and the underlying SiGe/Si heterointerface is sharply defined.展开更多
Thin strain-relaxed Si0.81Ge0.19 films (95 nm) on the Ar+ ion implanted Si substrates with different ener- gies (30 keV,40 keV and 60 keV) at the same implanted dose (3×1015cm-2) were grown by ultra high vacuum c...Thin strain-relaxed Si0.81Ge0.19 films (95 nm) on the Ar+ ion implanted Si substrates with different ener- gies (30 keV,40 keV and 60 keV) at the same implanted dose (3×1015cm-2) were grown by ultra high vacuum chemi- cal vapor deposition (UHVCVD). Rutherford backscattering/ion channeling (RBS/C),Raman spectra as well as atomic force microscopy (AFM) were used to characterize these SiGe films. Investigations by RBS/C demonstrate that these thin Si0.81Ge0.19 films were epitaxially grown on the Ar+ ion implanted Si substrates,although there existed lots of crystal defects. The relaxation extent of Si0.81Ge0.19 films on the Ar+ implanted Si substrates is larger than that in the unimplanted case,which were verified by Raman spectra. Considering the relaxation extent of strain,surface roughness and crystal defects in these SiGe films,the thin relaxed SiGe film on the 30 keV Ar+ implanted Si substrate is optimal.展开更多
Deposition of diamond thin films on tungsten wire substrate with the gas mixture of acetone and hydrogen by using bias-enhanced hot filament chemical vapor deposition（CVD）with the tantalum wires being optimized arra...Deposition of diamond thin films on tungsten wire substrate with the gas mixture of acetone and hydrogen by using bias-enhanced hot filament chemical vapor deposition（CVD）with the tantalum wires being optimized arranged is investigated.The self-supported diamond tubes are obtained by etching away the tungsten substrates.The quality of the diamond film before and after the removal of substrates is observed by scanning electron microscope（SEM）and Raman spectrum.The results show that the cylindrical diamond tubes with good quality and uniform thickness are obtained on tungsten wires by using bias enhanced hot filament CVD.The compressive stress in diamond film formed during the deposition is released after the substrate etches away by mixture of H2O2 and NH4 OH.There is no residual stress in diamond tube after substrate removal.展开更多
Atomic-layer MoS_2 ultrathin films are synthesized using a hot filament chemical vapor deposition method. A combination of atomic force microscopy（AFM）, x-ray diffraction（XRD）, high-resolution transition electron ...Atomic-layer MoS_2 ultrathin films are synthesized using a hot filament chemical vapor deposition method. A combination of atomic force microscopy（AFM）, x-ray diffraction（XRD）, high-resolution transition electron microscopy（HRTEM）, photoluminescence（PL）, and x-ray photoelectron spectroscopy（XPS） characterization methods is applied to investigate the crystal structures, valence states, and compositions of the ultrathin film areas. The nucleation particles show irregular morphology, while for a larger size somewhere, the films are granular and the grains have a triangle shape. The films grow in a preferred orientation（002）. The HRTEM images present the graphene-like structure of stacked layers with low density of stacking fault, and the interlayer distance of plane is measured to be about 0.63 nm. It shows a clear quasihoneycomb-like structure and 6-fold coordination symmetry. Room-temperature PL spectra for the atomic layer MoS_2 under the condition of right and left circular light show that for both cases, the A1 and B1 direct excitonic transitions can be observed. In the meantime, valley polarization resolved PL spectra are obtained. XPS measurements provide high-purity samples aside from some contaminations from the air, and confirm the presence of pure MoS_2. The stoichiometric mole ratio of S/Mo is about 2.0–2.1, suggesting that sulfur is abundant rather than deficient in the atomic layer MoS_2 under our experimental conditions.展开更多
The hydrophobic films of TixOy-CmHn. deposited from mixture gases of titanium isopropoxide （TTIP） and oxygen by plasma enhanced chemical vapor deposition （PECVD） were investigated. The films were investigated by s...The hydrophobic films of TixOy-CmHn. deposited from mixture gases of titanium isopropoxide （TTIP） and oxygen by plasma enhanced chemical vapor deposition （PECVD） were investigated. The films were investigated by scanning electron microscope （ SEM ）, transmission electron microscope （ TEM ）, Fourier transform infrared spectrometer （ FTIR）, X-Ray diffraction （ XRD ）, element analysis （ EA ）, ultraviolet visible spectrometer （ UV-Vis）, and water contact angle （WCA）. The results reveal that the surface of the films is formed by mierosized papillaes aggregated by inorganic and organic phases of complex nanoparticles with size from 50 nm to 200 nm when the discharge power is increased from 40 W to 150 W. All fdms demonstrate the strong broad of Ti-O-Ti stretching vibration at 400 -800cm-1, -CH bending vibration at 1 388 cm -1, and broadening -OH stretching vibration at 3 000-3500 cm-1 With the increase of the discharge power, the asdeposited film changes from amorphous to crystallization. The WCA of the film can be as high as 160°, indicating the hydrophobicity. The films show a similar ultraviolet absorption property as the bulk TiO2 film. The composition of the composition of film deposited at 150 W can be formulated as Tio.302-C1.5H3. Therefore, the composition formula of this hydrophobic film could be expressed as TiO2-C5H10O4.7. It is believed that the complex micro/nano structures of TiO2 and C5H10O4.7 residues are responsible for the observed hydrophobicity and the ultraviolet absorption property of the film.展开更多
ZrC coatings were deposited on graphite substrates by low pressure chemical vapor deposition（LPCVD） with the Br2-Zr-C3H6-H2-Ar system. The effects of deposition time on the microstructures and growth behavior of ZrC...ZrC coatings were deposited on graphite substrates by low pressure chemical vapor deposition（LPCVD） with the Br2-Zr-C3H6-H2-Ar system. The effects of deposition time on the microstructures and growth behavior of ZrC coatings were investigated. ZrC coating grew in an island-layer mode. The formation of coating was dominated by the nucleation of ZrC in the initial 20 minutes, and the rapid nucleation generated a fine-grained structure of ZrC coating. When the deposition time was over 30 min, the growth of coating was dominated by that of crystals, giving a column-arranged structure. Energy dispersive X-ray spectroscopy showed that the molar ratio of carbon to zirconium was near 1：1 in ZrC coating, and X-ray photoelectron spectroscopy showed that ZrC was the main phase in coatings, accompanied by about 2.5mol% ZrO2 minor phase.展开更多
Hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared by high- pressure radio-frequency (13.56 MHz) plasma enhanced chemical vapor deposition (rf-PECVD) with a screened plasma. The deposition rate ...Hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared by high- pressure radio-frequency (13.56 MHz) plasma enhanced chemical vapor deposition (rf-PECVD) with a screened plasma. The deposition rate and crystallinity varying with the deposition pressure, rf power, hydrogen dilution ratio and electrodes distance were systematically studied. By optimizing the deposition parameters the device quality μc-Si:H films have been achieved with a high deposition rate of 7.8 /s at a high pressure. The Voc of 560 mV and the FF of 0.70 have been achieved for a single-junction μc-Si:H p-i-n solar cell at a deposition rate of 7.8 /s.展开更多
Optical emission spectroscopy （OES） was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition （CVD）. C2 radical was ...Optical emission spectroscopy （OES） was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition （CVD）. C2 radical was determined as the main carbon radical in this plasma atmosphere. The deposition parameters, such as substrate temperature, anode-substrate distance, methane concentration, and gas flow rate, were inspected to find out the influence on the gas phase. A strong dependence of the concentrations and distribution of radicals on substrate temperature was confirmed by the design of experiments （DOE）. An explanation for this dependence could be that radicals near the substrate surface may have additional ionization or dissociation and also have recombination, or are consumed on the substrate surface where chemical reactions occur.展开更多
Catalyst-free and scalable synthesis of graphene on various glass substrates at low temperatures is of paramount significance to numerous applications such as low-cost transparent electronics and state-of-the-art disp...Catalyst-free and scalable synthesis of graphene on various glass substrates at low temperatures is of paramount significance to numerous applications such as low-cost transparent electronics and state-of-the-art displays. However, systematic study within this promising research field has remained scarce thus far. Herein, we report the direct growth of graphene on various glasses using a low-temperature plasma-enhanced chemical vapor deposition method. Such a facile and scalable approach guarantees the growth of uniform, transfer-free graphene films on various glass substrates at a growth temperature range of 400-600 ℃. The morphological, surface wetting, optical, and electrical properties of the obtained graphene can be tailored by controlling the growth parameters. Our uniform and high-quality graphene films directly integrated with low-cost, commonly used glasses show great potential in the fabrication of multi-functional electrodes for versatile applications in solar cells, transparent electronics, and smart windows.展开更多
The plasma-enhanced chemical vapor deposition(PECVD)technique is well suited for fabricating optical filters with continuously variable refractive index profiles;however,it is not clear how the optical and structural ...The plasma-enhanced chemical vapor deposition(PECVD)technique is well suited for fabricating optical filters with continuously variable refractive index profiles;however,it is not clear how the optical and structural properties of thin films differ when deposited on different substrates.Herein,silicon nitride films were deposited on silicon,fused silica,and glass substrates by PECVD,using silane and ammonia,to investigate the effects of the substrate used on the optical properties and structures of the films.All of the deposited films were amorphous.Further,the types and amounts of Si-centered tetrahedral Si–SivN4-v bonds formed were based upon the substrates used;Si–N4 bonds with higher elemental nitrogen content were formed on Si substrates,which lead to obtaining higher refractive indices,and the Si–SiN3 bonds were mainly formed on glass and fused silica substrates.The refractive indices of the films formed on the different substrates had a maximum difference of0.05(at 550 nm),the refractive index of SiNx films formed on silicon substrates was 1.83,and the refractive indices of films formed on glass were very close to those formed on fused silica.The deposition rates of these SiNx films are similar,and the extinction coefficients of all the films were lower than 10-4.展开更多
For nanotube-based electronics to become a viable alternative to silicon technology,high-density aligned carbon nanotubes are essential.In this paper,we report the combined use of low-pressure chemical vapor depositio...For nanotube-based electronics to become a viable alternative to silicon technology,high-density aligned carbon nanotubes are essential.In this paper,we report the combined use of low-pressure chemical vapor deposition and stacked multiple transfer to achieve high-density aligned nanotubes.By using an optimized nanotube synthesis recipe,we have achieved high-density aligned carbon nanotubes with density as high as 30 tubes/μm.In addition,a facile stacked multiple transfer technique has been developed to further increase the nanotube density to 55 tubes/μm.Furthermore,high-performance submicron carbon nanotube field-effect transistors have been fabricated on the high-density aligned nanotubes.Before removing the metallic nanotubes by electrical breakdown,the devices exhibit on-current density of 92.4μA/μm and normalized transconductance of 13.3μS/μm.Moreover,benchmarking with the aligned carbon nanotube transistors in the literature indicates that our devices exhibit the best performance so far,which is attributed to both the increased nanotube density and scaling down of channel length.This study shows the great potential of using such high-density aligned nanotubes for high performance nanoelectronics and analog/RF applications.展开更多
For ZnO/diamond structured surface acoustic wave （SAW） filters, performance is sensitively dependent on the quality of the ZnO films. In this paper, we prepare highly-oriented and fine grained polycrystalline ZnO th...For ZnO/diamond structured surface acoustic wave （SAW） filters, performance is sensitively dependent on the quality of the ZnO films. In this paper, we prepare highly-oriented and fine grained polycrystalline ZnO thin films with excellent surface smoothness on the smooth nucleation surfaces of freestanding CVD diamond films by metal organic chemical vapour deposition （MOCVD）. The properties of the ZnO films are characterized by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, and photoluminescence （PL） spectrum. The influences of the deposition conditions on the quality of ZnO films are discussed briefly. ZnO/freestanding thick-diamond-film layered SAW devices with high response frequencies are expected to be developed.展开更多
Bismuth vanadate （BiVO4） has been identified as one of the excellent visible-light-responsive photoanode for use in the photoelectrochemical water splitting. Recently intense research efforts have been devoted to th...Bismuth vanadate （BiVO4） has been identified as one of the excellent visible-light-responsive photoanode for use in the photoelectrochemical water splitting. Recently intense research efforts have been devoted to the development of highly efficient BiVO4 photoanode. Herein, we reported a low-cost and scalable method for preparing nanostructured BiVO4 film. A much enhanced photocurrent （1.5 mAocm 2） was obtained for such film, which was 6.5 times higher than that of planar film at 1.23 V [vs. RHE （Reversible Hydrogen Electrode）]. The method provides an eco-friendly, reproducible and facile way to scale up on different substrates with attractive potential.展开更多
Mulitipe stoichiometric ratio of two-dimensional(2D)transition metal dichalcogenides(TMDCs)attracted considerable interest for their unique chemical and physical properties.Here we developed a chemical vapor depositio...Mulitipe stoichiometric ratio of two-dimensional(2D)transition metal dichalcogenides(TMDCs)attracted considerable interest for their unique chemical and physical properties.Here we developed a chemical vapor deposition(CVD)method to controllably synthesize ultrathin NiS and NiS2 nanoplates.By tuning the growth temperature and the amounts of the sulfur powder,2D nonlayered NiS and NiS2 nanoplates can be selectively prepared with the thickness of 2.0 and 7.0 nm,respectively.X-ray diffraction(XRD)and transmission electron microscopy(TEM)characterization reveal that the 2D NiS and N1S2 nanoplates are high-quality single crystals in the hexagonal and cubic phase,respectively.Electrical transport studies show that electrical conductivities of the 2D NiS and N1S2 nanoplates are as high as 4.6 x 10^5 and 6.3 x 10^5 S·m^-1,respectively.The electrical results demonstrate that the synthesized metallic NiS and NiS2 could serve as good electrodes in 2D electronics.展开更多
基金funded by a grant from the National Core Research Center(NCRC)Program through the National Research Foundation of Korea funded by the Ministry of Education,Science and Technology(No.2012-0000-957)by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy,Republic of Korea
文摘Ternary Ti-B-N coatings were synthesized on AISI 304 and Si wafer by plasma-enhanced chemical vapor deposition (PECVD) technique using a gaseous mixture of TiCl4,BCl3,H2,N2,and Ar.By virtue of X-ray diffraction analysis,X-ray photoelectron spectroscopy,scanning electron microscope,and high-resolution transmission electron microscope,the influences of B content on the microstructure and properties of Ti B N coatings were investigated systematically.The results indicated that the microstructure and mechanical properties of Ti-B-N coatings largely depend on the transformation from FCC-TiN phase to HCP-TiB2 phase.With increasing B content and decreasing N content in the coatings,the coating microstructure evolves gradually from FCC-TiN/a-BN to HCP-TiB2 /a-BN via FCC-TiN+HCP-TiB2/a-BN.The highest microhardness of about 34 GPa is achieved,which corresponds to the nanocomposite Ti-63%B-N (mole fraction) coating consisting of the HCP-TiB2 nano-crystallites and amorphous BN phase.The lowest friction-coefficient was observed for the nanocomposite Ti-41%B-N (mole fraction) coating consisting of the FCC-TiN nanocrystallites and amorphous BN
基金Project(Z132012A001)supported by the Technical Basis Research Program in Science and Industry Bureau of ChinaProject(61201028,60876009)supported by the National Natural Science Foundation of China
文摘InGaAs high electron mobility transistors （HEMTs） on InP substrate with very good device performance have been grown by mental organic chemical vapor deposition （MOCVD）. Room temperature Hall mobilities of the 2-DEG are measured to be over 8 700 cm^2/V-s with sheet carrier densities larger than 4.6× 10^12 cm^ 2. Transistors with 1.0 μm gate length exhibits transconductance up to 842 mS/ram. Excellent depletion-mode operation, with a threshold voltage of-0.3 V and IDss of 673 mA/mm, is realized. The non-alloyed ohmic contact special resistance is as low as 1.66×10^-8 Ω/cm^2, which is so far the lowest ohmic contact special resistance. The unity current gain cut off frequency （fT） and the maximum oscillation frequency （fmax） are 42.7 and 61.3 GHz, respectively. These results are very encouraging toward manufacturing InP-based HEMT by MOCVD.
文摘We directly grow a lattice matched GalnP/GalnAs/GalnNAs/Ge （1.88 eVil .42 eVil .05 eV/0.67eV） four-junction （4J） solar cell on a Ge substrate by the metal organic chemical vapor deposition technology. To solve the current limit of the GalnNAs sub cell, we design three kinds of anti-reflection coatings and adjust the base region thickness of the GalnNAs sub cell. Developed by a series of experiments, the external quantum efficiency of the GalnNAs sub cell exceeds 80%, and its current density reaches 11.24 mA/cm2. Therefore the current limit of the 4J solar cell is significantly improved. Moreover, we discuss the difference of test results between 4J and GalnP/GalnAs/Ge solar cells under the 1 sun AMO spectrum.
基金Supported by the National Science and Technology Major Project of China under Grant No 2013ZX02308-002the National Natural Sciences Foundation of China under Grant Nos 61574108,61334002,61474086 and 61306017
文摘Nearly lattice-matched InAIGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostructure. The electron mobility is 1668.08cm2/V.s together with a high two-dimensional-electron-gas density of 1.43 × 10^13 cm-2 for the InAlCaN/CaN heterostructure of 2Onto InAlCaN quaternary barrier. High electron mobility transistors with gate dimensions of 1 × 50 μm2 and 4μm source-drain distance exhibit the maximum drain current of 763.91 mA/mm, the maximum extrinsic transconductance of 163.13 mS/mm, and current gain and maximum oscillation cutoff frequencies of 11 GHz and 21 GHz, respectively.
文摘An ultrahigh vacuum chemical vapor deposition (UHV/CVD) system is developed and the details of its construction and operation are reported. Using high purity SiH4 and GeH4 reactant gases, the Si0.82Ge0.18 layer is deposited at 550℃. With the measurements by double crystal X-ray diffraction (DCXRD), transmission electron microscopy (TEM) and Rutherford backscattering spectroscppy (RBS) techniques, it is shown that the crystalline quality of the SiGe layer is good, and the underlying SiGe/Si heterointerface is sharply defined.
基金Partially supported by the National Natural Sciences Foundation of China (No.10075072)
文摘Thin strain-relaxed Si0.81Ge0.19 films (95 nm) on the Ar+ ion implanted Si substrates with different ener- gies (30 keV,40 keV and 60 keV) at the same implanted dose (3×1015cm-2) were grown by ultra high vacuum chemi- cal vapor deposition (UHVCVD). Rutherford backscattering/ion channeling (RBS/C),Raman spectra as well as atomic force microscopy (AFM) were used to characterize these SiGe films. Investigations by RBS/C demonstrate that these thin Si0.81Ge0.19 films were epitaxially grown on the Ar+ ion implanted Si substrates,although there existed lots of crystal defects. The relaxation extent of Si0.81Ge0.19 films on the Ar+ implanted Si substrates is larger than that in the unimplanted case,which were verified by Raman spectra. Considering the relaxation extent of strain,surface roughness and crystal defects in these SiGe films,the thin relaxed SiGe film on the 30 keV Ar+ implanted Si substrate is optimal.
基金Selected from Proceedings of the 7th International Conference on Frontiers of Design and Manufacturing(ICFDM'2006)This project is supported by National Natural Science Foundation of China(No.50475026,No.50275095,No.50575135).
文摘Deposition of diamond thin films on tungsten wire substrate with the gas mixture of acetone and hydrogen by using bias-enhanced hot filament chemical vapor deposition（CVD）with the tantalum wires being optimized arranged is investigated.The self-supported diamond tubes are obtained by etching away the tungsten substrates.The quality of the diamond film before and after the removal of substrates is observed by scanning electron microscope（SEM）and Raman spectrum.The results show that the cylindrical diamond tubes with good quality and uniform thickness are obtained on tungsten wires by using bias enhanced hot filament CVD.The compressive stress in diamond film formed during the deposition is released after the substrate etches away by mixture of H2O2 and NH4 OH.There is no residual stress in diamond tube after substrate removal.
基金Project supported by the Natural Science Foundation of Zhejiang Province,China(Grant Nos.LY16F040003 and LY16A040007)the National Natural Science Foundation of China(Grant Nos.51401069 and 11574067)
文摘Atomic-layer MoS_2 ultrathin films are synthesized using a hot filament chemical vapor deposition method. A combination of atomic force microscopy（AFM）, x-ray diffraction（XRD）, high-resolution transition electron microscopy（HRTEM）, photoluminescence（PL）, and x-ray photoelectron spectroscopy（XPS） characterization methods is applied to investigate the crystal structures, valence states, and compositions of the ultrathin film areas. The nucleation particles show irregular morphology, while for a larger size somewhere, the films are granular and the grains have a triangle shape. The films grow in a preferred orientation（002）. The HRTEM images present the graphene-like structure of stacked layers with low density of stacking fault, and the interlayer distance of plane is measured to be about 0.63 nm. It shows a clear quasihoneycomb-like structure and 6-fold coordination symmetry. Room-temperature PL spectra for the atomic layer MoS_2 under the condition of right and left circular light show that for both cases, the A1 and B1 direct excitonic transitions can be observed. In the meantime, valley polarization resolved PL spectra are obtained. XPS measurements provide high-purity samples aside from some contaminations from the air, and confirm the presence of pure MoS_2. The stoichiometric mole ratio of S/Mo is about 2.0–2.1, suggesting that sulfur is abundant rather than deficient in the atomic layer MoS_2 under our experimental conditions.
基金Foundation items: National Natural Science Foundations of China (No.10835004,No.10775031)Science and Technology Commission of Shanghai Municipality,China (No. 10XD1400100)
文摘The hydrophobic films of TixOy-CmHn. deposited from mixture gases of titanium isopropoxide （TTIP） and oxygen by plasma enhanced chemical vapor deposition （PECVD） were investigated. The films were investigated by scanning electron microscope （ SEM ）, transmission electron microscope （ TEM ）, Fourier transform infrared spectrometer （ FTIR）, X-Ray diffraction （ XRD ）, element analysis （ EA ）, ultraviolet visible spectrometer （ UV-Vis）, and water contact angle （WCA）. The results reveal that the surface of the films is formed by mierosized papillaes aggregated by inorganic and organic phases of complex nanoparticles with size from 50 nm to 200 nm when the discharge power is increased from 40 W to 150 W. All fdms demonstrate the strong broad of Ti-O-Ti stretching vibration at 400 -800cm-1, -CH bending vibration at 1 388 cm -1, and broadening -OH stretching vibration at 3 000-3500 cm-1 With the increase of the discharge power, the asdeposited film changes from amorphous to crystallization. The WCA of the film can be as high as 160°, indicating the hydrophobicity. The films show a similar ultraviolet absorption property as the bulk TiO2 film. The composition of the composition of film deposited at 150 W can be formulated as Tio.302-C1.5H3. Therefore, the composition formula of this hydrophobic film could be expressed as TiO2-C5H10O4.7. It is believed that the complex micro/nano structures of TiO2 and C5H10O4.7 residues are responsible for the observed hydrophobicity and the ultraviolet absorption property of the film.
基金Founded by the National Natural Science Foundation of China(No.91216302)the National Program on Key Basic Research Project of the People's Republic of China(No.2015CB655200)
文摘ZrC coatings were deposited on graphite substrates by low pressure chemical vapor deposition（LPCVD） with the Br2-Zr-C3H6-H2-Ar system. The effects of deposition time on the microstructures and growth behavior of ZrC coatings were investigated. ZrC coating grew in an island-layer mode. The formation of coating was dominated by the nucleation of ZrC in the initial 20 minutes, and the rapid nucleation generated a fine-grained structure of ZrC coating. When the deposition time was over 30 min, the growth of coating was dominated by that of crystals, giving a column-arranged structure. Energy dispersive X-ray spectroscopy showed that the molar ratio of carbon to zirconium was near 1：1 in ZrC coating, and X-ray photoelectron spectroscopy showed that ZrC was the main phase in coatings, accompanied by about 2.5mol% ZrO2 minor phase.
基金Supported by the National Natural Science Foundation of China (Grant No. 50662003)the State Development Program for Basic Research of China (Grant No. G2000028208)
文摘Hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared by high- pressure radio-frequency (13.56 MHz) plasma enhanced chemical vapor deposition (rf-PECVD) with a screened plasma. The deposition rate and crystallinity varying with the deposition pressure, rf power, hydrogen dilution ratio and electrodes distance were systematically studied. By optimizing the deposition parameters the device quality μc-Si:H films have been achieved with a high deposition rate of 7.8 /s at a high pressure. The Voc of 560 mV and the FF of 0.70 have been achieved for a single-junction μc-Si:H p-i-n solar cell at a deposition rate of 7.8 /s.
基金the National High-Tech Research and Development Program of China (No.2002AA305508)the National Natural Science Foundation of China (No.50472095)+1 种基金the Scientific Research Foundation for the Returned Overseas Chinese Scholars (No.2003-14)Beijing Novel Project (No. 2003A13).]
文摘Optical emission spectroscopy （OES） was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition （CVD）. C2 radical was determined as the main carbon radical in this plasma atmosphere. The deposition parameters, such as substrate temperature, anode-substrate distance, methane concentration, and gas flow rate, were inspected to find out the influence on the gas phase. A strong dependence of the concentrations and distribution of radicals on substrate temperature was confirmed by the design of experiments （DOE）. An explanation for this dependence could be that radicals near the substrate surface may have additional ionization or dissociation and also have recombination, or are consumed on the substrate surface where chemical reactions occur.
基金Acknowledgements This work was financially supported by the National Basic Research Program of China （Nos. 2013CB932603, 2012CB933404, 2011CB921903, and 2013CB934600）, the National Natural Science Foundation of China （Nos. 51432002, 51290272, 51121091, 51~201, and 11222434）, the Ministry of Education （No. 20120001130010） and the Beijing Municipal Sdence and Technology Planning Project （No. Z151100003315013）.
文摘Catalyst-free and scalable synthesis of graphene on various glass substrates at low temperatures is of paramount significance to numerous applications such as low-cost transparent electronics and state-of-the-art displays. However, systematic study within this promising research field has remained scarce thus far. Herein, we report the direct growth of graphene on various glasses using a low-temperature plasma-enhanced chemical vapor deposition method. Such a facile and scalable approach guarantees the growth of uniform, transfer-free graphene films on various glass substrates at a growth temperature range of 400-600 ℃. The morphological, surface wetting, optical, and electrical properties of the obtained graphene can be tailored by controlling the growth parameters. Our uniform and high-quality graphene films directly integrated with low-cost, commonly used glasses show great potential in the fabrication of multi-functional electrodes for versatile applications in solar cells, transparent electronics, and smart windows.
基金supported by the Project of Innovative Team of Advanced Optical Manufacturing and Detection(No.2017KCT-08-02)。
文摘The plasma-enhanced chemical vapor deposition(PECVD)technique is well suited for fabricating optical filters with continuously variable refractive index profiles;however,it is not clear how the optical and structural properties of thin films differ when deposited on different substrates.Herein,silicon nitride films were deposited on silicon,fused silica,and glass substrates by PECVD,using silane and ammonia,to investigate the effects of the substrate used on the optical properties and structures of the films.All of the deposited films were amorphous.Further,the types and amounts of Si-centered tetrahedral Si–SivN4-v bonds formed were based upon the substrates used;Si–N4 bonds with higher elemental nitrogen content were formed on Si substrates,which lead to obtaining higher refractive indices,and the Si–SiN3 bonds were mainly formed on glass and fused silica substrates.The refractive indices of the films formed on the different substrates had a maximum difference of0.05(at 550 nm),the refractive index of SiNx films formed on silicon substrates was 1.83,and the refractive indices of films formed on glass were very close to those formed on fused silica.The deposition rates of these SiNx films are similar,and the extinction coefficients of all the films were lower than 10-4.
基金the Focus Center Research Program(FCRP)-Center on Func-tional Engineered Nano Architectonics(FENA)Joint King Abdulaziz City for Science and Technology(KACST)/California Center of Excellence on Nano Science and Engineering for Green and Clean Tech-nologiesthe National Science Foundation(Nos.CCF-0726815 and CCF-0702204).
文摘For nanotube-based electronics to become a viable alternative to silicon technology,high-density aligned carbon nanotubes are essential.In this paper,we report the combined use of low-pressure chemical vapor deposition and stacked multiple transfer to achieve high-density aligned nanotubes.By using an optimized nanotube synthesis recipe,we have achieved high-density aligned carbon nanotubes with density as high as 30 tubes/μm.In addition,a facile stacked multiple transfer technique has been developed to further increase the nanotube density to 55 tubes/μm.Furthermore,high-performance submicron carbon nanotube field-effect transistors have been fabricated on the high-density aligned nanotubes.Before removing the metallic nanotubes by electrical breakdown,the devices exhibit on-current density of 92.4μA/μm and normalized transconductance of 13.3μS/μm.Moreover,benchmarking with the aligned carbon nanotube transistors in the literature indicates that our devices exhibit the best performance so far,which is attributed to both the increased nanotube density and scaling down of channel length.This study shows the great potential of using such high-density aligned nanotubes for high performance nanoelectronics and analog/RF applications.
文摘For ZnO/diamond structured surface acoustic wave （SAW） filters, performance is sensitively dependent on the quality of the ZnO films. In this paper, we prepare highly-oriented and fine grained polycrystalline ZnO thin films with excellent surface smoothness on the smooth nucleation surfaces of freestanding CVD diamond films by metal organic chemical vapour deposition （MOCVD）. The properties of the ZnO films are characterized by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, and photoluminescence （PL） spectrum. The influences of the deposition conditions on the quality of ZnO films are discussed briefly. ZnO/freestanding thick-diamond-film layered SAW devices with high response frequencies are expected to be developed.
基金This work was financially supported by the National Natural Science Foundation of China （Nos. 21373083 and 21573068）, the Program of Shanghai Subject Chief Scientist （No. 15XD 1501300）, the Specialized Research Fund for the Doctoral Program of Higher Education, the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry Fundamental Research Funds for the Central Universities （No. WD1313009）, 111 Project （No. B14018） and the Science and Technology Commission of Shanghai Municipality （No. 14JC 1490900）.
文摘Bismuth vanadate （BiVO4） has been identified as one of the excellent visible-light-responsive photoanode for use in the photoelectrochemical water splitting. Recently intense research efforts have been devoted to the development of highly efficient BiVO4 photoanode. Herein, we reported a low-cost and scalable method for preparing nanostructured BiVO4 film. A much enhanced photocurrent （1.5 mAocm 2） was obtained for such film, which was 6.5 times higher than that of planar film at 1.23 V [vs. RHE （Reversible Hydrogen Electrode）]. The method provides an eco-friendly, reproducible and facile way to scale up on different substrates with attractive potential.
基金We acknowledge the support from the National Natural Science Foundation of China(No.51872086)the Hunan Key Laboratory of Two-Dimensional Materials(No.2018TP1010)+1 种基金the Strategic Priority Research Program of Chinese Academy of Science(No.XDB30000000)the National Key Research and Development Program of Ministry of Science and Technology(No.2018YFA0703704).
文摘Mulitipe stoichiometric ratio of two-dimensional(2D)transition metal dichalcogenides(TMDCs)attracted considerable interest for their unique chemical and physical properties.Here we developed a chemical vapor deposition(CVD)method to controllably synthesize ultrathin NiS and NiS2 nanoplates.By tuning the growth temperature and the amounts of the sulfur powder,2D nonlayered NiS and NiS2 nanoplates can be selectively prepared with the thickness of 2.0 and 7.0 nm,respectively.X-ray diffraction(XRD)and transmission electron microscopy(TEM)characterization reveal that the 2D NiS and N1S2 nanoplates are high-quality single crystals in the hexagonal and cubic phase,respectively.Electrical transport studies show that electrical conductivities of the 2D NiS and N1S2 nanoplates are as high as 4.6 x 10^5 and 6.3 x 10^5 S·m^-1,respectively.The electrical results demonstrate that the synthesized metallic NiS and NiS2 could serve as good electrodes in 2D electronics.
