Deposition of diamond inside the trenches or microchannels by chemical vapor deposition (CVD) is limited by the diffusion efficiency of important radical species for diamond growth (H, CH3) and the pore depth of t...Deposition of diamond inside the trenches or microchannels by chemical vapor deposition (CVD) is limited by the diffusion efficiency of important radical species for diamond growth (H, CH3) and the pore depth of the substrate template. By ultrasonic seeding with nanodiamond suspension, three-dimensional (3D) penetration structure diamond was successfully deposited in cylindrical microchannels of Cu template by hot-filament chemical vapor deposition. Micro-Raman spectroscopy and scanning electron microscopy (SEM) were used to characterize diamond film and the effects of microchannel depth on the morphology, grain size and growth rate of diamond film were comprehensively investigated. The results show that diamond quality and growth rate sharply decrease with the increase of the depth of cylindrical microchannel. Individual diamond grain develops gradually from faceted crystals into micrometer cluster, and finally to ballas-type nanocrystalline one. In order to modify the rapid decrease of diamond quality and growth rate, a new hot filament apparatus with a forced gas flow through Cu microchannels was designed. Furthermore, the growth of diamond film by new apparatus was compared with that without a forced gas flow, and the enhancement mechanism was discussed.展开更多
Natural rutile and gaseous chlorine with carbon as reductant were used to prepare titanium tetrachloride. Thermodynamics and kinetics of chlorination of Kenya natural rutile particles in a batch-type fluidized bed wer...Natural rutile and gaseous chlorine with carbon as reductant were used to prepare titanium tetrachloride. Thermodynamics and kinetics of chlorination of Kenya natural rutile particles in a batch-type fluidized bed were studied at 1173-1273 K. Thermodynamic analysis of this system revealed that the equation of producing CO was dominant at high temperatures. Based on the gas-solid multi-phase reaction theory and a two-phase model for the fluidized bed, the mathematical description for the chlorination reaction of rutile was proposed. The reaction parameters and the average concentration of gaseous chlorine in the emulsion phase were estimated. The average concentration of emulsion phase in the range of fluidized bed was calculated as 0.3 mol/m^3. The results showed that the chlorination of natural rutile proceeded principally in the emulsion phase, and the reaction rate was mainly controlled by the surface reaction.展开更多
The characteristics of hot filament chemical vapor deposition(HFCVD) diamond films are significantly influenced by the deposition parameters, such as the substrate temperature, total pressure and carbon concentratio...The characteristics of hot filament chemical vapor deposition(HFCVD) diamond films are significantly influenced by the deposition parameters, such as the substrate temperature, total pressure and carbon concentration. Orthogonal experiments were introduced to study the comprehensive effects of such three parameters on diamond films deposited on WC-Co substrates. Field emission scanning electron microscopy, atomic force microscopy and Raman spectrum were employed to analyze the morphology, growth rate and composition of as-deposited diamond films. The morphology varies from pyramidal to cluster features with temperature decreasing. It is found that the low total pressure is suitable for nano-crystalline diamond films growth. Moreover, the substrate temperature and total pressure have combined influence on the growth rate of the diamond films.展开更多
A series of boron-doped polycrystalline diamond films were prepared by hot filament (HF) chemical vapor deposition on Nb substrates. The effects of B/C ratio of reaction gas on film morphology, growth rate, chemical...A series of boron-doped polycrystalline diamond films were prepared by hot filament (HF) chemical vapor deposition on Nb substrates. The effects of B/C ratio of reaction gas on film morphology, growth rate, chemical bonding states, phase composition and electrochemical properties of each deposited sample were studied by scanning electron microscopy, Raman spectra, X-ray diffraction, microhardness indentation, and electrochemical analysis. Results show that the average grain size of diamond and the growth rate decrease with increasing the B/C ratio. The diamond films exhibit excellent adhesion under Vickers microhardness testing (9.8 N load). The sample with 2% B/C ratio has a wider potential window and a lower background current as well as a faster redox reaction rate in H2SO4 solution and KFe(CN)6 redox system compared with other doping level electrodes.展开更多
A positive grid bias and a negative substrate bias voltages are applied to the self-made hot filament chemical vapor deposited (HFCVD) system. The high quality nanocrystalline diamond (NCD) film is successfully de...A positive grid bias and a negative substrate bias voltages are applied to the self-made hot filament chemical vapor deposited (HFCVD) system. The high quality nanocrystalline diamond (NCD) film is successfully deposited by double bias voltage nucleation and grid bias voltage growth. The Micro-Raman XRD SEM and AFM are used to investigate the diamond grain size, microstructure, surface morphology, and nucleation density. Results show that the obtained NCD has grain size of about 20 nm. The effect of grid bias voltage on the nucleation and the diamond growth is studied. Experimental results and theoretical analysis show that the positive grid bias increases the plasma density near the hot filaments, enhances the diamond nucleation, keeps the nanometer size of the diamond grains, and improves the quality of diamond film.展开更多
In HFCVD system the substrate temperature is a key factor which deeply affects the quality of diamond films. Th e magnitude and the variation of the substrate temperature must be limited in a suitable range to depo...In HFCVD system the substrate temperature is a key factor which deeply affects the quality of diamond films. Th e magnitude and the variation of the substrate temperature must be limited in a suitable range to deposit diamond films of uniform thickness over large areas. In this paper, the hot filament parameters are investigated on the basi s of GAs to realize a good substrate temperature profile. Computer simulations d emonstrate that on parameters optimized by GAs a uniform substrate temperatur e field can be formed over a relatively large circle area with R s=10 cm.展开更多
The effects of Si doping on morphology, components and structure characteristics of CVD diamond films were studied. Si-doped CVD diamond films were deposited on Si substrate by adding tetraethoxysilane (TEOS) into a...The effects of Si doping on morphology, components and structure characteristics of CVD diamond films were studied. Si-doped CVD diamond films were deposited on Si substrate by adding tetraethoxysilane (TEOS) into acetone as source of reactant gas. The morphology and microstructure of diamond films were characterized by scanning electron microcopy (SEM). The crystalline quality of diamond films was studied by Raman spectroscopy and X-ray diffractometry (XRD). The surface roughness of the films was evaluated with surface profilometer. The results suggest that Si doping tends to reduce the crystallite size, enhance grain refinement and inhibit the appearance of (11 I) facets. Raman spectra indicate that Si doping can enhance the formation of sp2 phase in diamond films. Moreover, Raman signal of SiC was detected, which suggests the existence of Si in the diamond films. Smooth fine-grained diamond (SFGD) film was synthesized at Si to C ratio of 1%.展开更多
Amorphous Si O2(a-Si O2) films were synthesized on WC-Co substrates with H2 and tetraethoxysilane(TEOS) via pyrolysis of molecular precursor.X-ray diffraction(XRD) pattern shows that silicon-cobalt compounds for...Amorphous Si O2(a-Si O2) films were synthesized on WC-Co substrates with H2 and tetraethoxysilane(TEOS) via pyrolysis of molecular precursor.X-ray diffraction(XRD) pattern shows that silicon-cobalt compounds form at the interface between a-Si O2 films and WC-Co substrates.Moreover,it is observed by transmission electron microscope(TEM) that the a-Si O2 films are composed of hollow mirco-spheroid a-Si O2 particles.Subsequently,the a-Si O2 films are used as intermediate films and chemical vapor deposition(CVD) diamond films are deposited on them.Indentation tests were performed to evaluate the adhesion of bi-layer(a-Si O2 + diamond) films on cemented carbide substrates.And the cutting performance of bi-layer(a-Si O2 + diamond) coated inserts was evaluated by machining the glass fiber reinforced plastic(GFRP).The results show that a-Si O2 interlayers can greatly improve the adhesive strength of diamond films on cemented carbide inserts;furthermore,thickness of the a-Si O2 interlayers plays a significant role in their effectiveness on adhesion enhancement of diamond films.展开更多
The influence of intermetallic Al-Mn particles on the corrosion behavior of in-situ formed Mg-Al layered double hydroxide(Mg-Al-CO32--LDH)steam coating on AZ31 Mg alloy was investigated.The alloy was pretreated with H...The influence of intermetallic Al-Mn particles on the corrosion behavior of in-situ formed Mg-Al layered double hydroxide(Mg-Al-CO32--LDH)steam coating on AZ31 Mg alloy was investigated.The alloy was pretreated with H3PO4,HCl,HNO3or citric acid(CA),followed by hydrothermal treatment,for the fabrication of Mg-Al-LDH coating.The microstructure,composition and corrosion resistance of the coated samples were investigated.The results showed that the surface area fraction of Al-Mn phase exposed on the surface of the alloy was significantly increased after CA pretreatment,which promotes the growth of the Mg-Al-LDH steam coating.Further,the LDH-coated alloy pretreated with CA possessed the most compact surface and the maximum coating thickness among all the coatings.The corrosion current density of the coated alloy was decreased by three orders of magnitude as compared to that of the bare alloy.展开更多
Boron-doped diamond(BDD)films were deposited on the tungsten carbide substrates at different substrate temperatures ranging from 450 to 850°C by hot filament chemical vapor deposition(HFCVD)method.The effect of d...Boron-doped diamond(BDD)films were deposited on the tungsten carbide substrates at different substrate temperatures ranging from 450 to 850°C by hot filament chemical vapor deposition(HFCVD)method.The effect of deposition temperature on the properties of the boron-doped diamond films on tungsten carbide substrate was investigated.It is found that boron doping obviously enhances the growth rate of diamond films.A relatively high growth rate of 544 nm/h was obtained for the BDD film deposited on the tungsten carbide at 650°C.The added boron-containing precursor gas apparently reduced activation energy of film growth to be 53.1 kJ/mol,thus accelerated the rate of deposition chemical reaction.Moreover,Raman and XRD analysis showed that heavy boron doping(750 and 850°C)deteriorated the diamond crystallinity and produced a high defect density in the BDD films.Overall,600-700°C is found to be an optimum substrate temperature range for depositing BDD films on tungsten carbide substrate.展开更多
In this study,the original tourmaline and beryl mineral samples have been collected from a Brazilian pegmatite.The objective of this study was to examine the adsorption behavior of Brazilian ciclosilicate samples,towa...In this study,the original tourmaline and beryl mineral samples have been collected from a Brazilian pegmatite.The objective of this study was to examine the adsorption behavior of Brazilian ciclosilicate samples,towards divalent metals(Pb 2+,Mn 2+,and Zn 2+) in ethanol solution has been studies by a batch technique.The ciclosilicate samples were characterized by elemental analysis,Fourier transform infrared spectroscopy,helium picnometry,mercury porosity,and nitrogen adsorption-desorption.The Langmuir expression for adsorption isotherm was applied in order to determine the adsorption capacity to form a monolayer and the constant related to the adsorption intensity.In aqueous solution there was a significant adsorption increase with the temperature and pronounced synergistic effects were observed.The maximum number of moles adsorbed was determined to be 12.48 and 11.49 mmol/g for systems Pb 2+ /beryl and Pb 2+ /tourmaline,respectively.The energetic effects caused by metal cations adsorption were determined through calorimetric titrations.Thermodynamics indicated the existence of favorable conditions for such Pb 2+-,Mn 2+-,and Zn 2+-OH interactions.展开更多
We investigate the effects of etching gases on the synthesis of nano crystalline diamonds grown on silicon substrate at the substrate temperature of 550℃ and the reaction pressure of 4 kPa by hot filament chemical va...We investigate the effects of etching gases on the synthesis of nano crystalline diamonds grown on silicon substrate at the substrate temperature of 550℃ and the reaction pressure of 4 kPa by hot filament chemical vapor deposition method, in which CH4 and H2 act as a source and diluting gases, respectively. N2, H2, and NH3 were used as the etching gases, respectively. Results show that the optimum conditions can be obtained only for the case of H2 gas. The crystal morphology and crystallinity of the samples have been examined by scanning electron microscopy and X-ray diffraction, respectively.展开更多
A low turn-on field electron emission from diamond-like carbon films has been observed for the first time to author’s knowledge.Carbon films were prepared by microwave plasma chemical vapor deposition (CVD).Special p...A low turn-on field electron emission from diamond-like carbon films has been observed for the first time to author’s knowledge.Carbon films were prepared by microwave plasma chemical vapor deposition (CVD).Special pretreatment ceramic substrates were used. The characteristics of the film have been identified by using X-ray diffraction(XRD),and Raman spectrum. The field emission experiment has been performed in a vacuum chamber with a base pressure of about 10 -5 Pa. The turn-on field of 1.2 V/μm,and the current density of 1.25 mA/cm 2 at electric field of 6 V/μm were obtained.展开更多
The main goal of this work is to explore the possibility of using Au-modified hydroxyapatite(HA) as a potential sensor material. Tube-like HA structure was fabricated with the aid of a Nafion N-117 cation exchange mem...The main goal of this work is to explore the possibility of using Au-modified hydroxyapatite(HA) as a potential sensor material. Tube-like HA structure was fabricated with the aid of a Nafion N-117 cation exchange membrane and gold(Au) nanoparticles were added by a hydrothermal method. The morphology, structure and composition were characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS). The gas sensing properties were also investigated. Results show that Au nanoparticles are dispersed into the HA powder, which is tube-like, with rough inner and outer surfaces. Compared with pure HA, Au-modified HA exhibits improved sensing properties for NH_3. 5%(mass fraction) Au-modified HA shows the highest response with relatively short response/recovery time. The response is up to 79.2% when the corresponding sensor is exposed to 200×10^(-6) NH_3 at room temperature, and the response time and recovery time are 20 s and 25 s, respectively. For lower concentration, like 50×10^(-6), the response is still up to 70.8%. Good selectivity and repeatability are also observed. The sensing mechanism of high response and selectivity for NH_3 gas was also discussed. These results suggest that Au-HA composite is a promising material for NH_3 sensors operating at room temperature.展开更多
Diamond films were deposited on high-speed steel substrates by hot filament chemical vapor deposition (HFCVD) method. To minimize the early formation of graphite and to enhance the diamond film adhesion, a WC-Co coa...Diamond films were deposited on high-speed steel substrates by hot filament chemical vapor deposition (HFCVD) method. To minimize the early formation of graphite and to enhance the diamond film adhesion, a WC-Co coating was used as an interlayer on the steel substrates by high velocity oxy-fuel spraying. The effects of methane content on nucleation, quality, residual stress and adhesion of diamond films were investigated. The results indicate that the increasing methane content leads to the increase in nucleation density, residual stress, the degradation of quality and adhesion of diamond films. Diamond films deposited on high-speed steel (HSS) substrate with a WC-Co interlayer exhibit high nucleation density and good adhesion under the condition of the methane content initially set to be a higher value (4%, volume fraction) for 30 min, and then reduced to 2% for subsequent growth at pressure of 3 kPa and substrate temperature of 800 ℃.展开更多
A Ti interlayer with thickness about 300 nm was sputtered on Cu microchannels, followed by an ultrasonic seeding with nanodiamond powders. Adherent diamond film with crystalline grains close to thermal equilibrium sha...A Ti interlayer with thickness about 300 nm was sputtered on Cu microchannels, followed by an ultrasonic seeding with nanodiamond powders. Adherent diamond film with crystalline grains close to thermal equilibrium shape was tightly deposited by hot-filament chemical vapor deposition(HF-CVD). The nucleation and growth of diamond were investigated with micro-Raman spectroscope and field emission scanning electron microscope(FE-SEM) with energy dispersive X-ray detector(EDX). Results show that the nucleation density is found to be up to 1010 cm-2. The enhancement of the nucleation kinetics can be attributed to the nanometer rough Ti interlayer surface. An improved absorption of nanodiamond particles is found, which act as starting points for the diamond nucleation during HF-CVD process. Furthermore, finite element simulation was conducted to understand the thermal management properties of prepared diamond/Cu microchannel heat sink.展开更多
The activity and adsorption behavior of oxygen on rutile TiO_(2)(110)(RTiO_(2)(110))were investigated using the temperature programmed desorption(TPD)method with methanol(CH_(3)OH)as the probe molecule.By controlling ...The activity and adsorption behavior of oxygen on rutile TiO_(2)(110)(RTiO_(2)(110))were investigated using the temperature programmed desorption(TPD)method with methanol(CH_(3)OH)as the probe molecule.By controlling the coverage of molecular O_(2)on the surface via increasing or decreasing O_(2)exposure,two chemisorbed O_(2)species on the surface are confirmed,one at the bridging oxygen vacancy(Ov)site(O_(2)^(2-)/Ov)and the other at the five-fold coordinated titanium(Ti_(5c))site(O^(2-)/Ti_(5c)).At low O_(2)exposure,O^(2-)/Ov is the main species on the surface,which only leads to the O-H bond cleavage of CH_(3)OH,producing methoxy groups(CHgO).However,after the Ov sites are nearly filled by O_(2)at about 0.1 L O_(2)exposure,O_(2)/Tisc species begins to appear on R-TiO_(2)(110)surface,resulting in the formation of formaldehyde(CH_(2)O)via the reaction of O_(2)/Tisc species with CH_(3)OH or CH3O to break the C-H bond at low surface temperature.Moreover,the yield of CH_(2)O increases linearly with that of H_(2)O.In addition,when the 1 L O_(2)covered surface is irradiated with 355 nm UV irradiation to desorb and dissociate O_(2)/Ti_(5c)species,the yield of CH_(2)O decreases linearly with that of H_(2)O.Further analysis suggests that the charge state of O_(2)/Ti_(5c)may not change as the exposure of O_(2)changes on the R-TiO_(2)(110)surface,and O_(2)is most likely to adsorb on the Ti_(5c)sites in the form of O_(2)^(2-),not O_(2)^(-),The result not only advances our understanding on the adsorption state of O_(2)on TiO_(2),but also provides clues for low temperature C-H bond activation with O_(2)on TiO_(2).展开更多
Previous reports about the growth of large graphene single crystals on polycrystalline metal substrates usually adopted the strategy of suppressing the nucleation by lowering the concentration of the feedstock, which ...Previous reports about the growth of large graphene single crystals on polycrystalline metal substrates usually adopted the strategy of suppressing the nucleation by lowering the concentration of the feedstock, which greatly limited the rate of the nucleation and the sequent growth. The emerging liquid metal catalyst possesses the characteristic of quasi-atomically smooth surface with high diffusion rate. In principle, it should be a naturally ideal platform for the lowdensity nucleation and the fast growth of graphene. However,the rapid growth of large graphene single crystals on liquid metals has not received the due attention. In this paper, we firstly purposed the insight into the rapid growth of large graphene single crystals on liquid metals. We obtained the millimeter-size graphene single crystals on liquid Cu. The rich free-electrons in liquid Cu accelerate the nucleation, and the isotropic smooth surface greatly suppresses the nucleation.Moreover, the fast mass-transfer of carbon atoms due to the excellent fluidity of liquid Cu promotes the fast growth with a rate up to 79 μm s^-1. We hope the research on the growth speed of graphene on liquid Cu can enrich the recognition of the growth behavior of two-dimensional(2 D) materials on the liquid metal. We also believe that the liquid metal strategy for the rapid growth of graphene can be extended to various 2 D materials and thus promote their future applications in the photonics and electronics.展开更多
基金Project(21271188) supported by the Nature Science Foundation of China
文摘Deposition of diamond inside the trenches or microchannels by chemical vapor deposition (CVD) is limited by the diffusion efficiency of important radical species for diamond growth (H, CH3) and the pore depth of the substrate template. By ultrasonic seeding with nanodiamond suspension, three-dimensional (3D) penetration structure diamond was successfully deposited in cylindrical microchannels of Cu template by hot-filament chemical vapor deposition. Micro-Raman spectroscopy and scanning electron microscopy (SEM) were used to characterize diamond film and the effects of microchannel depth on the morphology, grain size and growth rate of diamond film were comprehensively investigated. The results show that diamond quality and growth rate sharply decrease with the increase of the depth of cylindrical microchannel. Individual diamond grain develops gradually from faceted crystals into micrometer cluster, and finally to ballas-type nanocrystalline one. In order to modify the rapid decrease of diamond quality and growth rate, a new hot filament apparatus with a forced gas flow through Cu microchannels was designed. Furthermore, the growth of diamond film by new apparatus was compared with that without a forced gas flow, and the enhancement mechanism was discussed.
基金Projects(51374064,51004033,51074044)supported by the National Natural Science Foundation of ChinaProject(2012AA062303)supported by High-tech Research and Development Program of China
文摘Natural rutile and gaseous chlorine with carbon as reductant were used to prepare titanium tetrachloride. Thermodynamics and kinetics of chlorination of Kenya natural rutile particles in a batch-type fluidized bed were studied at 1173-1273 K. Thermodynamic analysis of this system revealed that the equation of producing CO was dominant at high temperatures. Based on the gas-solid multi-phase reaction theory and a two-phase model for the fluidized bed, the mathematical description for the chlorination reaction of rutile was proposed. The reaction parameters and the average concentration of gaseous chlorine in the emulsion phase were estimated. The average concentration of emulsion phase in the range of fluidized bed was calculated as 0.3 mol/m^3. The results showed that the chlorination of natural rutile proceeded principally in the emulsion phase, and the reaction rate was mainly controlled by the surface reaction.
基金Project(2012ZX04003-031)supported by the National Science and Technology Major Project,China
文摘The characteristics of hot filament chemical vapor deposition(HFCVD) diamond films are significantly influenced by the deposition parameters, such as the substrate temperature, total pressure and carbon concentration. Orthogonal experiments were introduced to study the comprehensive effects of such three parameters on diamond films deposited on WC-Co substrates. Field emission scanning electron microscopy, atomic force microscopy and Raman spectrum were employed to analyze the morphology, growth rate and composition of as-deposited diamond films. The morphology varies from pyramidal to cluster features with temperature decreasing. It is found that the low total pressure is suitable for nano-crystalline diamond films growth. Moreover, the substrate temperature and total pressure have combined influence on the growth rate of the diamond films.
基金Project(21271188)supported by the National Natural Science Foundation of ChinaProject(2012M521541)supported by the China Postdoctoral Science Foundation,China+2 种基金Project(2012QNZT002)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(20110933K)supported by the State Key Laboratory of Powder Metallurgy,ChinaProject(CSUZC2013016)supported by the Open-End Fund for Valuable and Precision Instruments of Central South University,China
文摘A series of boron-doped polycrystalline diamond films were prepared by hot filament (HF) chemical vapor deposition on Nb substrates. The effects of B/C ratio of reaction gas on film morphology, growth rate, chemical bonding states, phase composition and electrochemical properties of each deposited sample were studied by scanning electron microscopy, Raman spectra, X-ray diffraction, microhardness indentation, and electrochemical analysis. Results show that the average grain size of diamond and the growth rate decrease with increasing the B/C ratio. The diamond films exhibit excellent adhesion under Vickers microhardness testing (9.8 N load). The sample with 2% B/C ratio has a wider potential window and a lower background current as well as a faster redox reaction rate in H2SO4 solution and KFe(CN)6 redox system compared with other doping level electrodes.
文摘A positive grid bias and a negative substrate bias voltages are applied to the self-made hot filament chemical vapor deposited (HFCVD) system. The high quality nanocrystalline diamond (NCD) film is successfully deposited by double bias voltage nucleation and grid bias voltage growth. The Micro-Raman XRD SEM and AFM are used to investigate the diamond grain size, microstructure, surface morphology, and nucleation density. Results show that the obtained NCD has grain size of about 20 nm. The effect of grid bias voltage on the nucleation and the diamond growth is studied. Experimental results and theoretical analysis show that the positive grid bias increases the plasma density near the hot filaments, enhances the diamond nucleation, keeps the nanometer size of the diamond grains, and improves the quality of diamond film.
文摘In HFCVD system the substrate temperature is a key factor which deeply affects the quality of diamond films. Th e magnitude and the variation of the substrate temperature must be limited in a suitable range to deposit diamond films of uniform thickness over large areas. In this paper, the hot filament parameters are investigated on the basi s of GAs to realize a good substrate temperature profile. Computer simulations d emonstrate that on parameters optimized by GAs a uniform substrate temperatur e field can be formed over a relatively large circle area with R s=10 cm.
基金Project(51275302)supported by the National Natural Science Foundation of ChinaProject(BC2012124)supported by Technical Innovation Funds for the Sci-Tech Enterprise of Jiangsu Province,China
文摘The effects of Si doping on morphology, components and structure characteristics of CVD diamond films were studied. Si-doped CVD diamond films were deposited on Si substrate by adding tetraethoxysilane (TEOS) into acetone as source of reactant gas. The morphology and microstructure of diamond films were characterized by scanning electron microcopy (SEM). The crystalline quality of diamond films was studied by Raman spectroscopy and X-ray diffractometry (XRD). The surface roughness of the films was evaluated with surface profilometer. The results suggest that Si doping tends to reduce the crystallite size, enhance grain refinement and inhibit the appearance of (11 I) facets. Raman spectra indicate that Si doping can enhance the formation of sp2 phase in diamond films. Moreover, Raman signal of SiC was detected, which suggests the existence of Si in the diamond films. Smooth fine-grained diamond (SFGD) film was synthesized at Si to C ratio of 1%.
基金Project(20130073110036)supported by the Research Fund for the Doctoral Program of Higher Education of China
文摘Amorphous Si O2(a-Si O2) films were synthesized on WC-Co substrates with H2 and tetraethoxysilane(TEOS) via pyrolysis of molecular precursor.X-ray diffraction(XRD) pattern shows that silicon-cobalt compounds form at the interface between a-Si O2 films and WC-Co substrates.Moreover,it is observed by transmission electron microscope(TEM) that the a-Si O2 films are composed of hollow mirco-spheroid a-Si O2 particles.Subsequently,the a-Si O2 films are used as intermediate films and chemical vapor deposition(CVD) diamond films are deposited on them.Indentation tests were performed to evaluate the adhesion of bi-layer(a-Si O2 + diamond) films on cemented carbide substrates.And the cutting performance of bi-layer(a-Si O2 + diamond) coated inserts was evaluated by machining the glass fiber reinforced plastic(GFRP).The results show that a-Si O2 interlayers can greatly improve the adhesive strength of diamond films on cemented carbide inserts;furthermore,thickness of the a-Si O2 interlayers plays a significant role in their effectiveness on adhesion enhancement of diamond films.
基金supported by the National Natural Science Foundation of China(Nos.51601108 and 52071191)the Natural Science Foundation of Shandong Province,China(No.ZR2020ME011)。
文摘The influence of intermetallic Al-Mn particles on the corrosion behavior of in-situ formed Mg-Al layered double hydroxide(Mg-Al-CO32--LDH)steam coating on AZ31 Mg alloy was investigated.The alloy was pretreated with H3PO4,HCl,HNO3or citric acid(CA),followed by hydrothermal treatment,for the fabrication of Mg-Al-LDH coating.The microstructure,composition and corrosion resistance of the coated samples were investigated.The results showed that the surface area fraction of Al-Mn phase exposed on the surface of the alloy was significantly increased after CA pretreatment,which promotes the growth of the Mg-Al-LDH steam coating.Further,the LDH-coated alloy pretreated with CA possessed the most compact surface and the maximum coating thickness among all the coatings.The corrosion current density of the coated alloy was decreased by three orders of magnitude as compared to that of the bare alloy.
基金Project(51375011)supported by the National Natural Science Foundation of ChinaProject(15cxy49)supported by the Shanghai Municipal Education Commission,ChinaProject(16PJ025)supported by the Shanghai Pujiang Program,China
文摘Boron-doped diamond(BDD)films were deposited on the tungsten carbide substrates at different substrate temperatures ranging from 450 to 850°C by hot filament chemical vapor deposition(HFCVD)method.The effect of deposition temperature on the properties of the boron-doped diamond films on tungsten carbide substrate was investigated.It is found that boron doping obviously enhances the growth rate of diamond films.A relatively high growth rate of 544 nm/h was obtained for the BDD film deposited on the tungsten carbide at 650°C.The added boron-containing precursor gas apparently reduced activation energy of film growth to be 53.1 kJ/mol,thus accelerated the rate of deposition chemical reaction.Moreover,Raman and XRD analysis showed that heavy boron doping(750 and 850°C)deteriorated the diamond crystallinity and produced a high defect density in the BDD films.Overall,600-700°C is found to be an optimum substrate temperature range for depositing BDD films on tungsten carbide substrate.
基金The authors are indebted to CNPq for fellowships and CAPES for financial support
文摘In this study,the original tourmaline and beryl mineral samples have been collected from a Brazilian pegmatite.The objective of this study was to examine the adsorption behavior of Brazilian ciclosilicate samples,towards divalent metals(Pb 2+,Mn 2+,and Zn 2+) in ethanol solution has been studies by a batch technique.The ciclosilicate samples were characterized by elemental analysis,Fourier transform infrared spectroscopy,helium picnometry,mercury porosity,and nitrogen adsorption-desorption.The Langmuir expression for adsorption isotherm was applied in order to determine the adsorption capacity to form a monolayer and the constant related to the adsorption intensity.In aqueous solution there was a significant adsorption increase with the temperature and pronounced synergistic effects were observed.The maximum number of moles adsorbed was determined to be 12.48 and 11.49 mmol/g for systems Pb 2+ /beryl and Pb 2+ /tourmaline,respectively.The energetic effects caused by metal cations adsorption were determined through calorimetric titrations.Thermodynamics indicated the existence of favorable conditions for such Pb 2+-,Mn 2+-,and Zn 2+-OH interactions.
文摘We investigate the effects of etching gases on the synthesis of nano crystalline diamonds grown on silicon substrate at the substrate temperature of 550℃ and the reaction pressure of 4 kPa by hot filament chemical vapor deposition method, in which CH4 and H2 act as a source and diluting gases, respectively. N2, H2, and NH3 were used as the etching gases, respectively. Results show that the optimum conditions can be obtained only for the case of H2 gas. The crystal morphology and crystallinity of the samples have been examined by scanning electron microscopy and X-ray diffraction, respectively.
基金The National Advanced Material Com mittee of China
文摘A low turn-on field electron emission from diamond-like carbon films has been observed for the first time to author’s knowledge.Carbon films were prepared by microwave plasma chemical vapor deposition (CVD).Special pretreatment ceramic substrates were used. The characteristics of the film have been identified by using X-ray diffraction(XRD),and Raman spectrum. The field emission experiment has been performed in a vacuum chamber with a base pressure of about 10 -5 Pa. The turn-on field of 1.2 V/μm,and the current density of 1.25 mA/cm 2 at electric field of 6 V/μm were obtained.
基金Project(51272289) supported by the National Natural Science Foundation of China
文摘The main goal of this work is to explore the possibility of using Au-modified hydroxyapatite(HA) as a potential sensor material. Tube-like HA structure was fabricated with the aid of a Nafion N-117 cation exchange membrane and gold(Au) nanoparticles were added by a hydrothermal method. The morphology, structure and composition were characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS). The gas sensing properties were also investigated. Results show that Au nanoparticles are dispersed into the HA powder, which is tube-like, with rough inner and outer surfaces. Compared with pure HA, Au-modified HA exhibits improved sensing properties for NH_3. 5%(mass fraction) Au-modified HA shows the highest response with relatively short response/recovery time. The response is up to 79.2% when the corresponding sensor is exposed to 200×10^(-6) NH_3 at room temperature, and the response time and recovery time are 20 s and 25 s, respectively. For lower concentration, like 50×10^(-6), the response is still up to 70.8%. Good selectivity and repeatability are also observed. The sensing mechanism of high response and selectivity for NH_3 gas was also discussed. These results suggest that Au-HA composite is a promising material for NH_3 sensors operating at room temperature.
基金Project(1343-74236000005) supported by the Innovation Foundation for Postgraduates of Hunan Province, ChinaProject(ZKJ2008001) supported by the Open Fund for Valuable Instruments of Central South University, ChinaProject(2008112048) supported by the Open Fund of State Key Laboratory of Metallurgy, China
文摘Diamond films were deposited on high-speed steel substrates by hot filament chemical vapor deposition (HFCVD) method. To minimize the early formation of graphite and to enhance the diamond film adhesion, a WC-Co coating was used as an interlayer on the steel substrates by high velocity oxy-fuel spraying. The effects of methane content on nucleation, quality, residual stress and adhesion of diamond films were investigated. The results indicate that the increasing methane content leads to the increase in nucleation density, residual stress, the degradation of quality and adhesion of diamond films. Diamond films deposited on high-speed steel (HSS) substrate with a WC-Co interlayer exhibit high nucleation density and good adhesion under the condition of the methane content initially set to be a higher value (4%, volume fraction) for 30 min, and then reduced to 2% for subsequent growth at pressure of 3 kPa and substrate temperature of 800 ℃.
基金Project(21271188) supported by the National Natural Science Foundation of China
文摘A Ti interlayer with thickness about 300 nm was sputtered on Cu microchannels, followed by an ultrasonic seeding with nanodiamond powders. Adherent diamond film with crystalline grains close to thermal equilibrium shape was tightly deposited by hot-filament chemical vapor deposition(HF-CVD). The nucleation and growth of diamond were investigated with micro-Raman spectroscope and field emission scanning electron microscope(FE-SEM) with energy dispersive X-ray detector(EDX). Results show that the nucleation density is found to be up to 1010 cm-2. The enhancement of the nucleation kinetics can be attributed to the nanometer rough Ti interlayer surface. An improved absorption of nanodiamond particles is found, which act as starting points for the diamond nucleation during HF-CVD process. Furthermore, finite element simulation was conducted to understand the thermal management properties of prepared diamond/Cu microchannel heat sink.
基金This work was supported by the National Natural Science Foundation of China(No.21973010)Liaoning Revitalization Talents Program(No.XLYC1907032)The authors thank Qing Guo at Southern University of Science and Technolog for many insightful discussions。
文摘The activity and adsorption behavior of oxygen on rutile TiO_(2)(110)(RTiO_(2)(110))were investigated using the temperature programmed desorption(TPD)method with methanol(CH_(3)OH)as the probe molecule.By controlling the coverage of molecular O_(2)on the surface via increasing or decreasing O_(2)exposure,two chemisorbed O_(2)species on the surface are confirmed,one at the bridging oxygen vacancy(Ov)site(O_(2)^(2-)/Ov)and the other at the five-fold coordinated titanium(Ti_(5c))site(O^(2-)/Ti_(5c)).At low O_(2)exposure,O^(2-)/Ov is the main species on the surface,which only leads to the O-H bond cleavage of CH_(3)OH,producing methoxy groups(CHgO).However,after the Ov sites are nearly filled by O_(2)at about 0.1 L O_(2)exposure,O_(2)/Tisc species begins to appear on R-TiO_(2)(110)surface,resulting in the formation of formaldehyde(CH_(2)O)via the reaction of O_(2)/Tisc species with CH_(3)OH or CH3O to break the C-H bond at low surface temperature.Moreover,the yield of CH_(2)O increases linearly with that of H_(2)O.In addition,when the 1 L O_(2)covered surface is irradiated with 355 nm UV irradiation to desorb and dissociate O_(2)/Ti_(5c)species,the yield of CH_(2)O decreases linearly with that of H_(2)O.Further analysis suggests that the charge state of O_(2)/Ti_(5c)may not change as the exposure of O_(2)changes on the R-TiO_(2)(110)surface,and O_(2)is most likely to adsorb on the Ti_(5c)sites in the form of O_(2)^(2-),not O_(2)^(-),The result not only advances our understanding on the adsorption state of O_(2)on TiO_(2),but also provides clues for low temperature C-H bond activation with O_(2)on TiO_(2).
基金supported by the National Natural Science Foundation of China(21673161)the Sino-German Center for Research Promotion(1400)
文摘Previous reports about the growth of large graphene single crystals on polycrystalline metal substrates usually adopted the strategy of suppressing the nucleation by lowering the concentration of the feedstock, which greatly limited the rate of the nucleation and the sequent growth. The emerging liquid metal catalyst possesses the characteristic of quasi-atomically smooth surface with high diffusion rate. In principle, it should be a naturally ideal platform for the lowdensity nucleation and the fast growth of graphene. However,the rapid growth of large graphene single crystals on liquid metals has not received the due attention. In this paper, we firstly purposed the insight into the rapid growth of large graphene single crystals on liquid metals. We obtained the millimeter-size graphene single crystals on liquid Cu. The rich free-electrons in liquid Cu accelerate the nucleation, and the isotropic smooth surface greatly suppresses the nucleation.Moreover, the fast mass-transfer of carbon atoms due to the excellent fluidity of liquid Cu promotes the fast growth with a rate up to 79 μm s^-1. We hope the research on the growth speed of graphene on liquid Cu can enrich the recognition of the growth behavior of two-dimensional(2 D) materials on the liquid metal. We also believe that the liquid metal strategy for the rapid growth of graphene can be extended to various 2 D materials and thus promote their future applications in the photonics and electronics.