The Experts below are selected from a list of 114 Experts worldwide ranked by ideXlab platform
Ting Yang - One of the best experts on this subject based on the ideXlab platform.
-
Textural and chemical properties of zinc chloride activated carbons prepared from pistachio-nut shells
Materials Chemistry and Physics, 2006Co-Authors: Ting YangAbstract:Abstract The effects of activation temperature on the textural and chemical properties of the activated carbons prepared from pistachio-nut shells using zinc chloride activation under both inert nitrogen gas atmosphere and vacuum condition were studied. Relatively low temperature of 400 °C was beneficial for the development of pore structures. Too high an activation temperature would lead to sintering of volatiles and shrinkage of the carbon structure. The microstructures and microcrystallinity of the activated carbons prepared were examined by scanning electron microscope and powder X-ray diffraction techniques, respectively, while Fourier transform infrared spectra determined the changes in the surface functional groups at the various stages of preparation.
-
effects of vacuum pyrolysis conditions on the characteristics of activated carbons derived from pistachio nut shells
Journal of Colloid and Interface Science, 2004Co-Authors: Aik Chong Lua, Ting YangAbstract:Abstract Preparation of effective adsorbents from pistachio-nut shells was carried out. Optimization of the vacuum pyrolysis parameters prior to activation was carried out to study the effects of vacuum pyrolysis temperature, hold time, and heating rate on the properties of chars and activated carbons, while CO2 activation conditions were fixed at a temperature of 900 °C, an activation time of 30 min, a heating rate of 10 °C/min, a CO2 flow rate of 100 cm3/min, and a nitrogen flow rate of 150 cm3/min. The optimum vacuum pyrolysis conditions for preparing activated carbons with high surface area and pore volume were identified. The microstructure and microcrystallinity of the activated carbons prepared were examined by scanning electron microscopy and powder X-ray diffraction techniques respectively while the Fourier transform infrared spectra determined any changes in the surface functional groups produced during different preparation stages. Experimental results show that it is feasible to prepare activated carbons with high BET surface area from pistachio-nut shells.
A.k. Barua - One of the best experts on this subject based on the ideXlab platform.
-
the role of hydrogen dilution and radio frequency power in the formation of microcrystallinity of n type si h thin film
Journal of Applied Physics, 1993Co-Authors: S. C. Saha, A.k. BaruaAbstract:Phosphorus doped n‐type hydrogenated microcrystalline silicon (μc‐Si:H) films have been prepared at low power densities suitable for application in solar cells by the usual radio‐frequency plasma enhanced chemical vapor deposition method (rf‐PECVD, 13.56 MHz). For this purpose hydrogen (H2) dilution in the silane (SiH4) and phosphine (PH3) gas mixture and rf power densities have been varied carefully to produce a plasma condition conducive to the growth of microcrystallinity. The structural properties of the films have been studied by Raman spectroscopy, x‐ray diffractometry, transmission electron microscopy, and infrared vibrational spectroscopy. The electrical and optical characterizations have been done by dark conductivity, dark conductivity activation energy, and optical absorption measurements, respectively. Effects of variations of hydrogen dilution and rf power density on the electrical and structural properties of the films have been investigated thoroughly. Film with highest conductivity (32.6 S...
-
role of hydrogen dilution and diborane doping on the growth mechanism of p type microcrystalline silicon films prepared by photochemical vapor deposition
Journal of Applied Physics, 1992Co-Authors: Sukriti Ghosh, Swati Ray, A.k. BaruaAbstract:Boron‐doped microcrystalline hydrogenated silicon (μc‐Si:H) films were grown from a gas mixture of silane, diborane, and hydrogen employing mercury sensitized photochemical vapor deposition. At a low diborane doping ratio (1.1×10−3) hydrogen dilution of source gases resulted in films exhibiting a maximum conductivity of 7.4 S cm−1. For a higher doping ratio (10−2) the value of conductivity remained almost unchanged (10−5–10−6 S cm−1) with hydrogen dilution indicating nonexistence of microcrystallinity under such conditions. Transmission electron microscopy of B‐doped μc‐Si:H films revealed formation of crystallites possessing different crystallographic orientations, e.g., (111), (220), and (311) along with other planes. X‐ray spectra confirmed a large number of crystallites with (220) orientations.
J Yang - One of the best experts on this subject based on the ideXlab platform.
-
amorphous silicon alloy materials and solar cells near the threshold of microcrystallinity
MRS Proceedings, 1999Co-Authors: J Yang, S. GuhaAbstract:One of the most effective techniques used to obtain high quality amorphous silicon alloys is the use of hydrogen dilution during film growth. The resultant material exhibits a more ordered microstructure and gives rise to high efficiency solar cells. As the hydrogen dilution increases, however, a threshold is reached, beyond which microcrystallites begin to form rapidly. In this paper, they review some of the interesting features associated with the thin film materials obtained from various hydrogen dilutions. They include the observation of linear-like objects in the TEM micrograph, a shift of the principal Si TO band in the Raman spectrum, a sharp, low temperature peak in the H{sub 2} evolution spectrum, a shift of the wagging mode in the IR spectrum, and a narrowing of the Si(111) peak in the X-ray diffraction pattern. These spectroscopic tools have allowed them to optimize deposition conditions to near the threshold of microcrystallinity and obtain desired high quality materials. Incorporation of the improved materials into device configuration has significantly enhanced the solar cell performance. Using a spectral-splitting, triple-junction configuration, the spectral response of a typical high efficiency device spans from below 350 nm to beyond 950 nm with a peak quantum efficiency exceeding 90%;more » the triple stack generates a photocurrent of 27 mA/cm{sup 2}. This paper describes the effect of the improved materials on various solar cell structures, including a 13% active-area, stable triple-junction device.« less
-
structural defect and device behavior of hydrogenated amorphous si near and above the onset of microcrystallinity
Applied Physics Letters, 1999Co-Authors: Subhendu Guha, Yoram Lubianiker, D. L. Williamson, J.d. Cohen, J Yang, A. Harv MahanAbstract:High-hydrogen-diluted films of hydrogenated amorphous Si (a-Si:H) 0.5 μm in thickness and optimized for solar cell efficiency and stability, are found to be partially microcrystalline (μc) if deposited directly on stainless steel (SS) substrates but are fully amorphous if a thin n layer of a-Si:H or μc-Si:H is first deposited on the SS. In these latter cases, partial microcrystallinity develops as the films are grown thicker (1.5–2.5 μm) and this is accompanied by sharp drops in solar cell open circuit voltage. For the fully amorphous films, x-ray diffraction (XRD) shows improved medium-range order compared to undiluted films and this correlates with better light stability. Capacitance profiling shows a decrease in deep defect density as growth proceeds further from the substrate, consistent with the XRD evidence of improved order for thicker films.
Aik Chong Lua - One of the best experts on this subject based on the ideXlab platform.
-
effects of vacuum pyrolysis conditions on the characteristics of activated carbons derived from pistachio nut shells
Journal of Colloid and Interface Science, 2004Co-Authors: Aik Chong Lua, Ting YangAbstract:Abstract Preparation of effective adsorbents from pistachio-nut shells was carried out. Optimization of the vacuum pyrolysis parameters prior to activation was carried out to study the effects of vacuum pyrolysis temperature, hold time, and heating rate on the properties of chars and activated carbons, while CO2 activation conditions were fixed at a temperature of 900 °C, an activation time of 30 min, a heating rate of 10 °C/min, a CO2 flow rate of 100 cm3/min, and a nitrogen flow rate of 150 cm3/min. The optimum vacuum pyrolysis conditions for preparing activated carbons with high surface area and pore volume were identified. The microstructure and microcrystallinity of the activated carbons prepared were examined by scanning electron microscopy and powder X-ray diffraction techniques respectively while the Fourier transform infrared spectra determined any changes in the surface functional groups produced during different preparation stages. Experimental results show that it is feasible to prepare activated carbons with high BET surface area from pistachio-nut shells.
Guanglin Kong - One of the best experts on this subject based on the ideXlab platform.
-
gap states of hydrogenated amorphous silicon near and above the threshold of microcrystallinity with subtle boron compensation
Applied Physics Letters, 2001Co-Authors: Shuran Sheng, Xianbo Liao, Guanglin KongAbstract:The effects of hydrogen dilution, subtle boron compensation, and light-soaking on the gap states of hydrogenated amorphous silicon films (a-Si:H) near and above the threshold of microcrystallinity have been investigated in detail by the constant photocurrent method and the improved phase-shift analysis of modulated photocurrent technique. It is shown that high hydrogen dilution near the threshold of microcrystallinity leads to a more ordered network structure and to the redistribution of gap states; it gives rise to a small peak at about 0.55 eV and a shoulder at about 1.2 eV below the conduction band edge, which are associated with the formation of microcrystallites embedded in the amorphous silicon host matrix. A concurrent subtle boron compensation is demonstrated to prevent excessive formation of microcrystallinity, and to help promote the growth of the ordered regions and reduce the density of gap defect states, particularly those associated with microcrystallites. Hydrogen-diluted and appropriately boron-compensated a-Si:H films deposited near the threshold of microcrystallinity show the lowest density of the defects in both the annealed and light-soaked states, and hence, the highest performance and stability. (C) 2001 American Institute of Physics.
