Pressure Chemical Vapor Deposition Method Research Articles

Synthesis and magnetotransport studies of CrO2–Al2O3 composite films

CrO2–Al2O3 composite films were deposited on Si(100) substrates by the atmospheric pressure chemical vapor deposition method using CrO3 and AlBr3 as precursors. The CrO2–Al2O3 composite films consist of large CrO2 grains and Al2O3 nanoparticles. The composition of the films was controlled by adjusting the temperature of CrO3 during deposition. The CrO2–Al2O3 composite film with Al2O3 content of 0.38 (molar fraction) shows insulator–metal transition. Below 120K, it is insulator and the temperature dependence of its resistance can be well explained by the fluctuation-induced tunneling model; above 175K, it is metallic. It shows large intergrain tunneling magnetoresistance at low temperature, which reaches −15.2% at 5K and 50kOe. While at high temperature the intergrain tunneling magnetoresistance in the film nearly disappears, and the film shows a small linear magnetoresistance, which should be due to the double-exchange mechanism in CrO2.

Hierarchical SnO2 architectures: controllable growth on graphene by atmospheric pressure chemical vapour deposition and application in cataluminescence gas sensor

A facile catalyst-free atmospheric pressure chemical vapour deposition (APCVD) method for the growth of hierarchical SnO2 architectures on graphene is demonstrated. SnO2 2D nanorod arrays, flower@column composites, dendrite structures, and nanoparticles grown on graphene, named as SnO2/graphene architectures, were synthesized on Thermally-Reduced Graphene Oxide (TRGO) and Chemically-Reduced Graphene Oxide (CRGO), respectively. According to characterizations, the rutile SnO2 architectures had large-area uniformity and high crystallinity, which were highly densely and uniformly grown on graphene. A self-catalyzed vapor–solid (VS) and a self-catalyzed vapor–liquid–solid (VLS) mechanisms were proposed based on the detailed observation on the growth behaviour of the SnO2/graphene materials. The synthesized SnO2/graphene materials were directly used to construct gas sensors for methanol detection based on the cataluminescence (CTL) emission. Further study indicated that the SnO2/graphene materials showed enhanced CTL response to methanol and a morphology-dependent CTL performance. And then a fast and highly effective gas sensor for selective detection of methanol was designed based on the SnO2/graphene nanoparticles. The linear range of the methanol gas sensor was 6.3–88.5 μg mL−1, and the detection limit was 5.2 μg mL−1 (S/N = 3).

Complex Boron Redistribution in P+ Doped-polysilicon / Nitrogen Doped Silicon Bi-layers during Activation Annealing

Abstract We have investigated and modeled the complex phenomenon of boron (B) redistribution process in strongly doped silicon bilayers structure. A one-dimensional two stream transfer model well adapted to the particular structure of bi- layers and to the effects of strong-concentrations has been developed. This model takes into account the instantaneous kinetics of B transfer, trapping, clustering and segregation during the thermal B activation annealing. The used silicon bi-layers have been obtained by low pressure chemical vapor deposition (LPCVD) method, using in-situ nitrogen- doped-silicon (NiDoS) layer and strongly B doped polycrystalline-silicon (P+) layer. To avoid long redistributions, thermal annealing was carried out at relatively lowtemperatures (600 °C and 700 °C) for various times ranging between 30 minutes and 2 hours. The good adjustment of the simulated profiles with the experimental secondary ion mass spectroscopy (SIMS) profiles allowed a fundamental understanding about the instantaneous physical phenomena giving and disturbing the complex B redistribution profiles-shoulders kinetics.

Size and Density of Graphene Domains Grown with Different Annealing Times

Single crystals of hexagonal graphenes were successfully grown on Cu foils using the atmospheric pressure chemical vapor deposition (CVD) method. We investigated the effects of reaction parameters, such as the growth temperature and annealing time, on the size, coverage, and density of graphene domains grown over Cu foil. The mean size of the graphene domains increased significantly with increases in both the growth temperature and annealing time, and similar phenomena were observed in graphene domains grown by low pressure CVD over Cu foil. From the comparison of micro Raman spectroscopy in the graphene films grown with different annealing times, we found that the nucleation and growth of the domains were strongly dependent on the annealing time and growth temperature. Therefore, we confirmed that when reaction time was same, the number of layers and the degree of defects in the synthesized graphene films both decreased as the annealing time increased.

SYNTHESIS AND MORPHOLOGY OF SILICON NANOPARTICLES BY DEPOSITION TIME VARYING LPCVD METHOD TO DEMONSTRATE THE VARIATION OF HEIGHT, DENSITY AND SIZE

The confinement of the modern day semiconductor dev ices is fast propelling the growth of nanoparticles as an excellent constituent of such device and the characteristics like quantum si ze confinement and coulomb blockade effect of the sis accelerating their application in this field. But before the fabrication of devices with the nanoparticles, their morphol ogical and electrical characteristics needs to be studied in order to hav e a sense about the efficiency of such a device. In this experiment, Silicon nanoparticles have been deposited on SiO 2 substrate by thermal decomposition of silane using Low Pressure Chemical Vapor Deposition (LPCVD) Method with varying deposition t imes. Then, the morphology of the sample, the size as well as distribution of the nanoparticles is investigated using Atomic Force Mi croscopy (AFM) and the Scanning Probe Image Process or (SPIP). It shows that all the characteristics of the nanoparticles like h eight, density and size of the nanoparticles change with the varying deposition time. The size of the nanoparticles varied between 2-10nm whereas the height and density varied between 1-3n m and 2X10 11 /cm 2 3.5X10 11 /cm 2 respectively.

Large-scale and low cost synthesis of graphene as high capacity anode materials for lithium-ion batteries

Graphene has emerged as an intriguing and attractive functional material for a wide range of applications, owing to its unique physical, chemical and mechanical properties. Herein, we report large-scale production of high quality single crystalline graphene sheets based on the ambient pressure chemical vapor deposition (APCVD) method using acetylene (C2H2) as the carbon source and coral-like iron with body-centered-cubic structure as the catalyst. The process can be scaled up for large quantity production at a low cost. The optimum APCVD temperature has been identified to be 850°C, which is much lower than that catalyzed by other metals. Transmission electron microscopy (TEM), atomic force microscopy, Raman spectroscopy and X-ray photoemission spectroscopy characterizations show the single crystalline and high quality nature of the as-prepared graphene produced by the bottom-up APCVD approach. A new horizontal “dissolution–deposition–growth” mechanism is proposed and verified by high resolution TEM. When applied as anode materials in lithium ion batteries, graphene sheets exhibited a high lithium storage capacity and an excellent cyclability. The capability of preparing crystalline graphene on a large scale with low cost opens an avenue for technological applications of graphene in many fields.

Synthesis of multi-layer graphene films on copper tape by atmospheric pressure chemical vapor deposition method

Graphene films were successfully synthesized by atmospheric pressure chemical vapor deposition (APCVD) method. Methane (CH4) gas and copper (Cu) tapes were used as a carbon source and a catalyst, respectively. The CVD temperature and time were in the range of 800–1000 °C and 10 s to 45 min, respectively. The role of the CVD temperature and time on the growth of graphene films was investigated in detail via scanning electron microscopy (SEM) and Raman spectroscopy techniques. The results of SEM images and Raman spectra show that the quality of the graphene films was improved with increasing of CVD temperature due to the increase of catalytic activity.

Fabrication of large area hexagonal boron nitride thin films for bendable capacitors

Highly reliable and bendable dielectrics are desired in flexible or bendable electronic devices for future applications. Hexagonal boron nitride (h-BN) can be used as bendable dielectric due to its wide band gap. Here, we fabricate high quality h-BN films with controllable thickness by a low pressure chemical vapor deposition method. We demonstrate a parallel-plate capacitor using h-BN film as the dielectric. The h-BN capacitors are reliable with a high breakdown field strength of ∼9.0 MV/cm. Tunneling current across the h-BN film is inversely exponential to the thickness of dielectric, which makes the capacitance drop significantly. The h-BN capacitor shows a best specific capacitance of 6.8 μF/cm2, which is one order of magnitude higher than the calculated value. Open image in new window

Tailoring of textured transparent conductive SnO2:F thin films

In order to optimize the light trapping, textured SnO2:F (FTO) films have been successfully deposited and optimized on glass in large scale using atmospheric pressure chemical vapor deposition (APCVD) method on an industrial production line. The microstructures, optical and electrical properties of the films were investigated as a function of the total flow rate and fluorine doping concentration. The as-deposited FTO polycrystalline films possessed the tetragonal rutile structure of SnO2. Enhanced light trapping has been achieved with the increased surface roughness of the films by manipulating the total flow rate of monobutyltin trichloride (MBTC) and trifluoro acetic acid (TFA), while the corresponding high transmittance and conductivity remained stable. The optimized film with haze value of 10.9%, a figure of merit at the level of∼10−3 and sheet resistance of∼11Ωsq−1, showed good potential to improve the efficiency of silicon thin film solar cells.

Preparation and magnetic properties of submicron CrO2 thin film on poly-crystal TiO2 film

The submicron chromium dioxide(CrO2) thin film was fabricated on a poly-crystal titania(TiO2) film using Si wafers as substrates by atmospheric pressure chemical vapor deposition(CVD) method. X-Ray diffraction patterns show that the CrO2 films were pure rutile structure. Scanning electron microscopy(SEM) images indicate that the CrO2 films consisted of submicron grains with a grain size of 250–750 nm. The magnetic researches reveal that the magnetic easy axis is parallel to the films, and at room temperature, the CrO2 films show linear magnetoresistance.

Effect of glass tempering on microstructure and functional properties of SnO2:F thin film prepared by atmosphere pressure chemical vapor deposition

The low-emission glass was prepared via depositing fluorine-doped tin oxide thin film on glass substrate by atmospheric pressure chemical vapor deposition method. The as-deposited low-emission glass was found to present a SnO2:F/SiCxOy/glass sandwich structure via focused ion beam technique and transmission microscopic measurement. After tempering process at ~650°C with varied periods, the electrical and optical properties of the SnO2:F thin film remained stable for less than 10min, but decreased dramatically when the tempering period exceeded 10min, which was mainly due to the oxygen chemisorptions and fluorine ion diffusion. It was observed that the SnO2:F thin films presented uniform polycrystalline nature of cassiterite structure throughout the tempering process. The study has therefore suggested the appropriate tempering conditions for the SnO2:F low-emission glass, and provided a critical guidance for further energy-saving glass applications.

Zinc Oxide Thin Films Prepared by Atmospheric Pressure Chemical Vapor Deposition Using Zinc Chloride

Thin films of zinc oxide are deposited on silicon by Atmospheric Pressure Chemical Vapor Deposition (APCVD) method using zinc chloride precursor. The effect of time deposition on the structural, morphological, electrical, and optical properties of these films are investigated. The best films exhibiting appropriate properties for heterostructure solar cells application are obtained in the temperature range of 450 to 500°C. The X-ray diffraction spectra show the pattern of ZnO having an hexagonal structure with (002) preferred orientation. The morphology of the ZnO thin films shows nanorods with hexagonal symmetry normal to the substrate. Hall measurements indicate that decreased resistivity and increased conductivity resulted from the improvement of grain size and crystal quality. Under the optimal growth condition, ZnO thin films exhibit the lowest resistivity of 1.3×10-2 Ω.cm and average transmittance above 90% in the range 380-850 nm.

Controllable growth of millimeter-size graphene domains on Cufoil

As chemical vapor deposition (CVD) graphene is polycrystalline, its electrical and mechanical properties can be improved significantly by increasing the size of the single-crystal domains of graphene. In this report, round-shape millimeter-size graphene domains were prepared on copper (Cu) foil by the atmospheric pressure chemical vapor deposition (APCVD) method using controllable reduction of methane (CH4). The influences of the flow mass of CH4 and the growth temperature of the graphene nucleation density were also studied in detail. The results demonstrated that the initial nucleation density increased with the increase of CH4 and the decrease of growth temperature. The measurements of optical microscopy and Raman spectra indicated that the graphene domains were monolayers with high crystal quality and good uniformity.

The study of the effects of cooling conditions on high quality graphene growth by the APCVD method

The effects of cooling conditions on graphene growth by the atmospheric pressure chemical vapor deposition (APCVD) method on platinum are investigated. It is found that the cooling conditions are the key to better control of the coverage, thickness and uniformity of the graphene films. A series of experiments were carried out with different cooling rates and gas atmospheres. Various characterization techniques (SEM, Raman, AFM and TEM) were applied to examine the graphene morphology and quality. A "three competitive reactions" mechanism is proposed to explain the cooling condition effects. Based on optimized growth conditions, a high-coverage, single-layer graphene film could be grown on Pt using the APCVD method. Back-gated field effect transistors were fabricated and the measured carrier mobility is about 1600 cm(2) V(-1) s(-1).

Performance improvement of p-type silicon solar cells with thin silicon films deposited by low pressure chemical vapor deposition method

It is known that surface passivation plays a significant role in upgrading solar cell performance. In this study, silicon thin films deposited by LPCVD (low pressure chemical vapor deposition) are used to passivate the surface of solar-grade p-type crystalline silicon solar cells for the first time. Intrinsic amorphous silicon films and poly-silicon films were obtained on the front and rear surfaces of solar wafers at the deposition temperatures of 560°C and 620°C, respectively. Both kinds of silicon films proved to be effective in improving the open-circuit voltage owing to surface passivation for crystalline silicon solar cells. Optical spectral responses in the short and long wavelength ranges (e.g. the range 300–600nm and the range 850–1100nm, respectively) also showed an improvement in photogenerated current resulting from reduced surface recombination rates on the front and back surface.

Microstructural and functional stability of large-scale SnO2:F thin film with micro-nano structure

The large-scale homogeneous fluorine-doped tin oxide (SnO2:F) thin film was successfully deposited on glass by atmospheric pressure chemical vapor deposition (APCVD) method on an industrial production line. XRD, SEM and TEM were employed to investigate the film morphological and microstructural variation. It was observed for the first time that the as-deposited SnO2:F thin film presented a typical micro-nano structure, of which the micro-sized grains (100–300nm) were assembled by nano-sized crystallites (<10nm). It was found that the post-heating for 20min at ∼580°C or above induced splitting phenomenon of the micro-sized polyhedron-like grains into the smaller ones. Meanwhile, the increased grain boundaries due to such process were found to lead a dramatic decrease in the Hall mobility and distinguishable increase in the sheet resistance. Therefore, it was confirmed that such large-scale low-emission glass can serve with good functional properties below 580°C.

Analysis of Chlorine Ions in Antimony-Doped Tin Oxide Thin Film Using Synchrotron Grazing Incidence X-ray Diffraction

Antimony-doped tin oxide (SnO2:Sb, ATO) films have been deposited on glass substrates using atmospheric pressure chemical vapor deposition (APCVD) method. The precursors are mixed with SnCl4, SbCl5, and O2 to prepare the films. This study used synchrotron grazing incidence X-ray diffraction (GIXRD) to investigate the film microstructure. Our results show that the precursors of chlorine ions were involved in the doping mechanism, causing the microstructure of films to change slightly. The film has an average transmittance between 85.8 and 82.1% within a visible spectral range from 400 to 800 nm. The minimal resistivity was 6.1×10-4 Ω cm after doping. The synchrotron GIXRD data show that the chlorine ions caused the lattice constant change. A possible mechanism was proposed to explain the enhancement in electrical property due to chlorine dopants.

Quasi-vertical multi-tooth thin film transistors based on low-temperature technology (T ⩽ 600 °C)

A new concept of vertical thin film transistor (TFT), called thin film transistor comb (TFTC), is proposed based on polycrystalline silicon (polysilicon) deposited at low temperature (T⩽600°C). This structure, compatible with glass substrates, is designed to have up to 4 teeth and enables to get a high channel width W with a short channel length L. The channels of TFTC are made of a non-intentionally doped (NID) polysilicon layer between two in situ heavily-doped polysilicon layers; all these three layers are deposited by low pressure chemical vapor deposition (LPCVD) method. Electrical characteristics of TFTC show relatively high on-currents (ION) correlated with the geometric parameters. However, high off-currents (IOFF) are also observed due to the large overlapping area between drain and source regions.

Complex boron redistribution kinetics in strongly doped polycrystalline-silicon/nitrogen-doped-silicon thin bi-layers

We have investigated the complex behaviour of boron (B) redistribution process via silicon thin bi-layers interface. It concerns the instantaneous kinetics of B transfer, trapping, clustering and segregation during the thermal B activation annealing. The used silicon bi-layers have been obtained by low pressure chemical vapor deposition (LPCVD) method at 480 °C, by using in-situ nitrogen-doped-silicon (NiDoS) layer and strongly B doped polycrystalline-silicon (P+) layer. To avoid long-range B redistributions, thermal annealing was carried out at relatively low-temperatures (600 °C and 700 °C) for various times ranging between 30 min and 2 h. To investigate the experimental secondary ion mass spectroscopy (SIMS) doping profiles, a redistribution model well adapted to the particular structure of two thin layers and to the effects of strong-concentrations has been established. The good adjustment of the simulated profiles with the experimental SIMS profiles allowed a fundamental understanding about the instantaneous physical phenomena giving and disturbing the complex B redistribution profiles-shoulders. The increasing kinetics of the B peak concentration near the bi-layers interface is well reproduced by the established model.

Synthesis and optical properties of three-dimensional nanowall ZnO film prepared by atmospheric pressure chemical vapor deposition

Without template, three-dimensional nanowall ZnO films were synthesized in an atmospheric pressure chemical vapor deposition (APCVD) system by adjusting zinc species concentration. In the high ordered film, the vertical nanosheets were assembled along three directions angled approximately 120°. The extremely strong ZnO (0002) peaks in X-ray diffraction patterns testified the preferred (0001) orientation and high crystalline quality of the films. The low transmittances of nanowall films were attributed to the strong inner reflection and scattering. These results show that the simplified APCVD method is potential in synthesizing uniform nanowall ZnO films.