Papers by Keyword: Boron Doping

Abstract: In this work, a complementary microstructural and optical approach is used to define processing conditions favorable for the formation of deep boron-related acceptor centers that may provide a pathway for achieving an intermediate band behavior in highly B-doped 3C-SiC. The crystallinity, boron solubility and precipitation mechanisms in sublimation-grown 3C-SiC crystals implanted to 1-3 at.% B concentrations were investigated by STEM. The revealed defect formation and boron precipitation trends upon thermal treatment in the range 1100-2000°C have been cross-correlated with the optical characterization results provided by imaging PL spectroscopy. We discuss optical activity of the implanted B ions in terms of both shallow acceptors and deep D-centers, a complex formed by a boron atom and a carbon vacancy, and associate the observed spectral developments upon annealing with the strong temperature dependence of the D-center formation efficiency, which is further enhanced by the presence of implantation-induced defects.

Abstract: An epitaxial growth technique for 4H-SiC with B doping was developed to control the carrier lifetimes of the epilayers. A linear relationship was observed between the B doping concentration and the flow rate of tri-ethyl-boron, which was used as the B doping source. A room temperature photoluminescence spectrum of a N-and B-doped epilayer showed a broad B-related peak at 2.37 eV instead of a band-edge luminescence, which indicates that the carrier recombination path was changed by the B doping. The minority carrier lifetime decreased (< 30 ns at 250°C) with increasing B doping concentration. The thermal stability of the short carrier lifetime was compared with a conventional carrier lifetime reduction method, namely an electron irradiation technique. After thermal annealing at 1700°C, the carrier lifetime of the electron irradiated epilayer recovered while that of the B-doped epilayer remained, indicating that the carrier lifetime controlled by the B doping technique was more stable against the thermal processes.

Abstract: Diamond deposition on carbon substrates is difficult, because atomic hydrogen needed for the diamond growth, attacks the graphitic and amorphous carbon of the substrate. To reduce the etching effect, the duration till diamond layer formation should be short.By controlling the diamond deposition conditions, boron addition and seeding with diamond prior to the deposition, the formation of diamond coatings is possible.Diamond coated carbon substrates are of high interest for electrochemical applications because they show electrical conductivity and are chemically inert in a wide range. Boron doped diamond shows high overvoltage for hydrogen and oxygen and allows electrochemical reactions in water without decomposing it. Diamond was deposited on glassy carbon and electro-graphite.

Abstract: Boron-BiVO₄ samples were synthesized by sol-gel method. They were characterized by UV-vis diffuse reflectance spectroscopy, X-ray diffraction. Photocatalytic activity of the obtained BiVO₄ samples was investigated through degrading methylene blue (MB). The results reveal that boron-BiVO₄ catalysts have monoclinic scheelite structure. The BiVO₄ and Co-BiVO₄ photocatalysts were responsive to visible light. Co-BiVO₄ photocatalyst showed higher photocatalytic activity than pure BiVO₄, resulting in the significantly improved efficiency of degradation of MB.

Abstract: Undoped and B-doped silicon-based nanowires (SiNWs) were synthesized by vapor-liquid-solid growth, and SiNW devices using Au electrodes were prototyped using focused ion beam (FIB) processing. Needle-shaped thin SiNWs were formed at a substrate temperature between 1170 and 1313 °C. The average and minimum diameters of the B-doped SiNWs were 72 nm and 52 nm, respectively. According to the current-voltage characteristics, SiNW devices have ohmic properties, and the estimated resistivity of the undoped and B-doped SiNWs are about 3.8 × 10³ Ωcm and 1.7 × 10³ Ωcm, respectively.

Abstract: Doping can lead to residual strain and change of elastic properties in silicon. Residual strain makes silicon wafer exhibit curvature, which are used for fabricate MEMS structure. The boron doping profile is not uniform through depth, which makes doped silicon become a inhomogeneous material or Functionally Graded Material. For boron-doped circular single crystal silicon wafer, a analytical method which based on functionally graded plate mechanics theory, is proposed to calculate its curvature. Example was used to verify the analytical method through 3D finite element simulation.

Abstract: Catalytic graphitization of polyacrylonitrile-based carbon fiber by doping boric acid was reported in this paper. The microstructure and mechanical properties of polyacrylonitrile-based carbon fibers with and without doping boric acid after heat treatment of 1300°C,1500°C,1800°C, 2100°C,2300°C,2400°Cand 2500°Cwas investigated by X-ray diffraction (XRD) and mechanical testing. The results showed that the tensile modulus of the carbon fibers either boron modified or not, increased obviously with increasing temperatures, and that of the modified carbon fibers was much higher than the unmodified fibers at all temperatures, reaching 404Gpa when the fiber was graphitized at 2500°C. The tensile strength of the modified carbon fibers was lower than the unmodified ones after being graphitized at temperatures below 2300°C, but increased to 2.69 GPa and 2.46 GPa respectively after the fibers were treated at 2300°C and 2500°C, which were higher than that of unmodified fibers treated under the same conditions, indicatinging that the mechanism of boron catalytic graphitization changed at the temperatures higher than 2300°C. It also showed that the interlayer spacing (d₀₀₂) decreased, while the crystallite size (L_c) and the orientation increased with increasing temperatures.

Abstract: Boron doping titanium pillared montmorillonite (B-Ti-mont) were prepared by the sol-gel technique using sodic montmorillonite (Na-mont) as a substrate. Several technics such as XRD, SEM, UV-vis diffuse reflection spectra were used to characterize the samples. The results showed that all of the samples were of anatase, the absorption in the visible light region was strengthened after doped with boron. The basic skeleton of montmorillonite did not change after doping. The photocatalyst with the boron mole content of 5% displayed the best photocatalytic performance.

Abstract: The boron-doped nanocrystalline diamond films were prepared on Si(100) substrates by microwave plasma chemical vapor deposition in gas mixture of CH4/H2/trimethylboron (TMB) with B/C ratio in the range of 0-1900ppm. The dependencies of surface morphology, microstructure, phase composition and field electron emission properties on the B/C ratio were systematically investigated by scanning electron microscope, X-ray diffractometer, visible and UV Raman spectroscopy. The results show that the diamond grains gather together forming ball-like clusters with inhomogeneous size, the doped boron atoms can promote the growth of plane (111) surface and terminate the diamond growth sites, resulting in the reduction of growth rate with the increase of B/C ratio in the gas mixture. The two peaks located at approximately 500 and 1220cm-1 resulted from Fano interference were observed in the visible Raman spectra for the heavily boron-doped nanocrystalline diamond film, and the sp2/sp3 ratio of carbon bonds increased with B/C ratio increasing in gas mixture. The field electron emission performances of the boron-doped nanocrystalline diamond films were obviously dependent on B/C ratio in the gas mixture, and boron doping can improve their field electron emission properties remarkably. The low turn-on electric field of 7.6V/μm was achieved for the boron-doped nanocrystalline diamond film deposited at B/C ratio of 1900ppm.

Abstract: In order to investigate the effects of doping boron on the self-cleaning properties of TiO2 thin films, sol-gel method was employed to prepare TiO2 films with various amount of boron on the glass substrates. Atomic Force Microscope (AFM) and X-ray diffraction (XRD) were carried out to investigate the effects of boron on the microstructure and crystallization behavior of the thin films. The photocatalytic activity and the hydrophilicity of the films were also measured. The results showed that the photocatalytic activity of TiO2 films was improved by doping boron, and its hydrophilicity wasn’t destroyed. This can be ascribed to the enhancement of the surface energy, which was caused by the reduction of the crystal grain size of TiO2.