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A.SH. Hussein Z. Hassan S.M. Thahab Abu Hassan M.A. Abid C.W. Chin 《Physica B: Condensed Matter》2011,406(6-7):1267-1271
We have studied the structural properties of undoped and Si-doped AlxGa1?xN/GaN/AlN on Si (1 1 1) substrate prepared by plasma-assisted molecular beam epitaxy (PA-MBE) using high-resolution X-ray diffraction (HR-XRD) and atomic force microscopy (AFM). In comparison with undoped AlGaN, the roughness and dislocation density on the surface of the AlGaN layer decrease with Si doping. Full width half maximum (FWHM) of the undoped and Si-doped samples were equal to 0.69° and 0.52°, respectively. This indicates that the Si doping improves the crystalline quality of the AlxGa1?xN layer compared with the undoped one. Raman scattering measurement reveals that the optical phonon modes of A1(LO) and E2(H) of the AlGaN show a one-mode and two-modes behavior, respectively. The Fourier-transform infrared reflectance (FTIR) investigation confirms the one-mode (two-mode) behavior of the LO (TO) phonon in our samples. This is in good agreement with Raman measurement. Finally, the barrier height (ΦB) of undoped and Si-doped AlxGa1?xN samples was found to be 0.86 and 0.74 eV, respectively. 相似文献
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James WH Buchanan EG Guo L Gellman SH Zwier TS 《The journal of physical chemistry. A》2011,115(43):11960-11970
Resonant two-photon ionization (R2PI), IR-UV holeburning (IR-UV), and resonant ion-dip infrared spectroscopy (RIDIRS) have been used to record mass-selected, single-conformation ultraviolet and infrared spectra of three simple diamide derivatives of γ-amino acids as isolated molecules cooled in a supersonic expansion. This work builds on an earlier study of Ac-γ(2)-hPhe-NHMe (James, W. H., III, et al. J. Am. Chem. Soc. 2009, 131, 14243), which showed that this methyl-capped γ-peptide forms amide-stacked conformations that are similar in stability to H-bonded conformations containing a C9 ring and more stable than C7 H-bonded ring structures. Among the γ-peptides discussed here, Ac-γ(2)-hPhe-N(Me)(2) contains an additional methyl group relative to the previously studied Ac-γ(2)-hPhe-NHMe and therefore lacks the amide NH group responsible for C9 ring formation. Three conformations of Ac-γ(2)-hPhe-N(Me)(2) are observed, all of which are amide-stacked structures. In a second new molecule, Ac-γ(2)-hPhe-NH(iPr), the C-terminal NHMe group of Ac-γ(2)-hPhe-NHMe is replaced with an NH(iPr) group. Three conformations of Ac-γ(2)-hPhe-NH(iPr) are observed, all of which are C9 H-bonded structures. The dramatic difference between C-terminal NHMe and NH(iPr) reveals the delicate balance of noncovalent forces within these γ-peptides. The third molecule we examined is a gabapentin-derived diamide (designated 1), which contains a phenylacyl group at the N-terminus and an N(Me)(2) group at the C-terminus; the latter precludes C9 H bonding. Comparison of 1 with Ac-γ(2)-hPhe-N(Me)(2) allows us to examine the impact of the backbone substitution pattern (monosubstitution at carbon-2 vs disubstitution at carbon-3) on the competition between the C7 H-bonded and the amide-stacked conformation. In this case, only C7 rings are observed. The different gas-phase behaviors observed among the molecules analyzed here offer insight on the intrinsic conformational propensities of the γ-peptide backbone, information that provides a foundation for future foldamer design efforts. 相似文献
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Metal/superconductor/semiconductor (Ag/Hg-1212/CdSe) hetero-nanostructures have been fabricated using pulse-electrodeposition
technique and are characterized by X-ray diffraction (XRD), full-width at half-maximum (FWHM) and scanning electron microscopy
(SEM) studies. The junction capacitance of Ag/Hg-1212, Hg-1212/CdSe and Ag/Hg-1212/CdSe heterojunctions is measured in dark
and under laser irradiation at room temperature. The nature of the junction formed and built-in-junction potentials were determined.
The increase in carrier concentration across the junction due to photo-irradiation has been observed. 相似文献
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One of the innovative technological directions for the high-temperature superconductors has been persued by fabricating the
heteroepitaxial multilayer structures such as superconductor-semiconductor heterostructures. In the present investigation,
metal/superconductor/semiconductor (Ag/Tl-2223/CdSe) hetero-nanostructures have successfully been fabricated using dc electrodeposition
technique and were characterized by X-ray diffraction (XRD), full-width at half-maximum (FWHM) and scanning electron microscopy
(SEM) studies. The measurement of junction capacitance as a function of biasing voltage was used for the estimation of junction
built-in-potential (V
D) and to study the charge distribution in a heterojunction. The Mott-Schottky plots were measured for each junction in dark
and under the photo-irradiation. The effect of laser irradiation on C-V characteristics of hetero-nanostructure has been studied. 相似文献
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SHUbarICHI NOSÉ 《Molecular physics》2013,111(1):191-198
A molecular dynamics simulation method which can generate configurations belonging to the canonical (T, V, N) ensemble or the constant temperature constant pressure (T, P, N) ensemble, is proposed. The physical system of interest consists of N particles (f degrees of freedom), to which an external, macroscopic variable and its conjugate momentum are added. This device allows the total energy of the physical system to fluctuate. The equilibrium distribution of the energy coincides with the canonical distribution both in momentum and in coordinate space. The method is tested for an atomic fluid (Ar) and works well. 相似文献
30.
Jiang Wang Brian P. Cary Peyton D. Beyer Samuel H. Gellman Daniel J. Weix 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(35):12209-12213
Synthesis of the C?C bonds of ketones relies upon one high‐availability reagent (carboxylic acids) and one low‐availability reagent (organometallic reagents or alkyl iodides). We demonstrate here a ketone synthesis that couples two different carboxylic acid esters, N‐hydroxyphthalimide esters and S‐2‐pyridyl thioesters, to form aryl alkyl and dialkyl ketones in high yields. The keys to this approach are the use of a nickel catalyst with an electron‐poor bipyridine or terpyridine ligand, a THF/DMA mixed solvent system, and ZnCl2 to enhance the reactivity of the NHP ester. The resulting reaction can be used to form ketones that have previously been difficult to access, such as hindered tertiary/tertiary ketones with strained rings and ketones with α‐heteroatoms. The conditions can be employed in the coupling of complex fragments, including a 20‐mer peptide fragment analog of Exendin(9–39) on solid support. 相似文献