Growth of 0.55eV-GaInAsSb Quaternary Alloy Films for a Thermophotovoltaic Device by Liquid Phase Epitaxy

Lattice matched Ga_(1-x)In_xAs_ySb_(1-y) quaternary alloy films for thermophotovoltaic cells were successfully grown on n-type GaSb substrates by liquid phase epitaxy. Mirror-like surfaces for the epitaxial layers were achieved and evaluated by atomic force microscopy. The composition of the Ga_(1-x)In_xAs_ySb_(1-y) layer was characterized by energy dispersive X-ray analysis with the result that x = 0.2, y = 0.17. The absorption edges of the Ga_(1-x)In_xAs_ySb_(1-y) films were determined to be 2. 256μm at room temperature by Fourier transform infrared transmission spectrum analysis, corresponding to an energy gap of 0.55eV. Hall measurements show that the highest obtained electron mobility in the undoped p-type samples is 512cm2~/(V·s) and the carrier density is 6. 1×10~(16)cm~(-3) at room temperature. Finally, GaInAsSb based thermophotovoltaic cells in different structures with quantum efficiency values of around 60% were fabricated and the spectrum response characteristics of the cells are discussed.

Improvement of CMOS SOS devices characteristics by a modified solid phase epitaxy

CMOS/SOS devices have lower carriers mobility and higher channel leakage current than bulk silicon CMOS devices. These mainly results from the defects of heteroepitaxial silicon film, especially from the defects near Si-Sapphire interface. This paper describes the experiment results of CMOS/SOS devices characteristics improved by a better epitaxial silicon quality which is obtained by a modified solid phase epitaxy.

Improvement of thin silicon on sapphire (SOS) film materials and device performances by solid phase epitaxy

The increased emphasis on sub-micron CMOS/SOS devices has placed a demand for high quality thin silicon on sapphire (SOS) films with thickness of the order 100-200 nm. It is demonstrated that the crystalline quality of as-grown thin SOS films by the CVD method can be greatly improved by solid phase epitaxy (SPE) process: implantation of self-silicon ions and subsequent thermal annealing. Subsequent regrowth of this amorphous layer leads to a greater improvement in silicon layer crystallinity and channel carrier mobility, evidenced, respectively, by double crystal X-ray diffraction and electrical measurements. We concluded that the thin SPE SOS films are suitable for application to high-performance CMOS circuitry. (C) 2000 Elsevier Science S.A. All rights reserved.

Rare Earth Pyrophosphates: Effective Catalysts for the Production of Acrolein from Vapor-phase Dehydration of Glycerol

Vapor-phase dehydration of glycerol to produce acrolein was investigated at 320 A degrees C over rare earth (including La, Ce, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb, Lu) pyrophosphates, which were prepared by precipitation method. The most promising catalysts were characterized by means of XRD, FT-IR, TG-DTA, BET and NH3-TPD measurements. The excellent catalytic performance of rare earth pyrophosphate depends on the appropriate surface acidity which can be obtained by the control of pH value in the precipitation and the calcination temperature, e.g. Nd-4(P2O7)(3) precipitated at pH = 6 and calcined at 500 A degrees C in the catalyst preparation.

Vapor phase beckmann rearrangement of cyclohexanone oxime over rare earth pyrophosphates

A new application of rare earth pyrophosphates in vapor phase Beckmann rearrangement of cyclohexanone oxime was investigated. The rare earth phosphates were characterized by means of XRD, FT-IR, NH3-TPD and water contact angle measurement. It was found that the weak surface acidity and appropriate surface hydrophobicity should be two key factors in the excellent performance of these catalysts.

Preparation of methyl tert-butyl ether (MTBE) over heteropoly acids immobilized on activated carbon (HPA/C) in the vapor phase

Heteropolyacids (HPAs) supported on the activated carbon (SiW12/C and PW12/C) have been used to study the formation of methyl tert-butyl ether (MTBE). Compared to the conventional commercial catalysts, Amberlyst-15 resin and HZSM-5, HPAs supported catalysts have been proved to have much higher catalytic activity under lower temperature, especially selectivity to MTBE is up to 100%. It may be due to the high acid strength of HPAs as well as the specialty of heteropolyanion.

Vapor phase esterification catalyzed by immobilized dodecatungstosilicic acid (SiW12) on activated carbon

The vapor phase esterification of acetic acid with ethanol and n-butanol catalyzed by SiW12 supported on activated carbon was studied in a flow fixed-bed reactor in the range of 358 to 433 K. The effects of the reaction temperature, liquid hourly space velocity (LHSV) as well as the molar ratio on the catalytic activity have been investigated. The kinetic studies showed that the rate of esterification was dependent on the partial pressures of the reactants and the addition of argon, an inert diluent in the system when the total pressure was kept at 1 atm. Also the alcohol structure has a profound effect on not only the rate of esterification, but also on the mechanism of esterification changing from a dual site mechanism for ethanol to a single site mechanism for n-butanol.

Neutral and Charged 1-Butyl-3-methylimidazolium Triflate Clusters: Equilibrium Concentration in the Vapor Phase and Thermal Properties of Nanometric Droplets

Ground state energy, structure, and harmonic vibrational modes of 1-butyl-3-methylimidazolium triflate ([bmim][Tf]) clusters have been computed using an all-atom empirical potential model. Neutral and charged species have been considered up to a size (30 [bmim][Tf] pairs) well into the nanometric range. Free energy computations and thermodynamic modeling have been used to predict the equilibrium composition of the vapor phase as a function of temperature and density. The results point to a nonnegligible concentration of very small charged species at pressures (P ~ 0.01 Pa) and temperatures (T 600 K) at the boundary of the stability range of [bmim][Tf]. Thermal properties of nanometric neutral droplets have been investigated in the 0 T 700 K range. A near-continuous transition between a liquidlike phase at high T and a solidlike phase at low T takes place at T ~ 190 K in close correspondence with the bulk glass point Tg ~ 200 K. Solidification is accompanied by a transition in the dielectric properties of the droplet, giving rise to a small permanent dipole embedded into the solid cluster. The simulation results highlight the molecular precursors of several macroscopic properties and phenomena and point to the close competition of Coulomb and dispersion forces as their common origin.

Effect of humidity and solvent vapor phase on cellulose esters films

In the present study the effect of relative humidity (RH) during spin-coating process on the structural characteristics of cellulose acetate (CA), cellulose acetate phthalate (C-A-P), cellulose acetate butyrate (CAB) and carboxymethyl cellulose acetate butyrate (CMCAB) films was investigated by means of atomic force microscopy (AFM), ellipsometry and contact angle measurements. All polymer solutions were prepared in tetrahydrofuran (THF), which is a good solvent for all cellulose esters, and used for spin-coating at RH of (35 +/- A 5)%, (55 +/- A 5)% or (75 +/- A 5)%. The structural features were correlated with the molecular characteristics of each cellulose ester and with the balance between surface energies of water and THF and interface energy between water and THF. CA, CAB, CMCAB and C-A-P films spin-coated at RH of (55 +/- A 5)% were exposed to THF vapor during 3, 6, 9, 60 and 720 min. The structural changes on the cellulose esters films due to THF vapor exposition were monitored by means of AFM and ellipsometry. THF vapor enabled the mobility of cellulose esters chains, causing considerable changes in the film morphology. In the case of CA films, which are thermodynamically unstable, dewetting was observed after 6 min exposure to THF vapor. On the other hand, porous structures observed for C-A-P, CAB and CMCAB turned smooth and homogeneous after only 3 min exposure to THF vapor.

Vapor phase composition as an indicator of thermal stability of the Sm, Eu, and Yb chlorides

The Sm, Eu, and Yb tri- and dichlorides were investigated by Knudsen effusion mass spectrometry. It was found out by the analysis of mass spectra and ionization efficiency curves that the vapor composition is complex due to the partial high temperature decomposition/disproportionation of the samples. Up to five vapor species were identified for both LnCl3 (LnCl3, LnCl2, Ln2Cl4, Ln2Cl5, and Ln2Cl6) and LnCl2 (LnCl3, LnCl2, LnCl, Ln, and Ln2Cl4). The quantitative evaluation of vapor composition was made. It indicates that the disproportionation of SmCl2 and EuCl2 is negligible in the temperature range studied whereas that of YbCl2 and the decomposition of SmCl3 and YbCl3 cannot be neglected.