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Polar and non-polar ZnMgO were synthesized on different crystallographic planes (C-, R- and M-planes) of sapphire (Al 2 O 3 ) substrates by metal organic chemical vapor deposition, respectively. Under the same experimental condition, polar ZnMgO nanorods were obtained on C-Al 2 O 3 substrate whereas non-polar ZnMgO thin films were obtained on R- and M-Al 2 O 3 substrates. The surface morphology was significantly influenced by the competition of the preferable growth directions on different sapphire substrates. On C-Al 2 O 3 substrate, ZnMgO nanorods were vertically well-aligned with typical lengths in the range 330–360 nm. On R- and M-Al 2 O 3 substrates, however, ZnMgO thin films with flat surfaces were obtained, whose thickness were 150 and 20 nm, respectively. Under the same condition, the C-ZnMgO deposited on C-Al 2 O 3 substrate has the maximum growth velocity (11 nm/nim), followed by A-ZnMgO deposited on R-Al 2 O 3 substrate (5 nm/min), and the M-ZnMgO deposited on M-Al 2 O 3 substrate has the minimum one (0.67 nm/min). The Near-Band-Edge (NBE) emission in Photoluminescence (PL) spectra shows a clear blueshift and a slight broadening compared with that of pure ZnO samples, which suggest that the Mg content has successfully incorporated into ZnO. The different energy blueshifts (67 meV and 98 meV) of the NBE emission demonstrate that A-ZnMgO deposited on R-Al 2 O 3 substrate has higher Mg incorporation efficiency than C-ZnMgO on C-Al 2 O 3 substrate.

The crystalline, surface, and optical properties of the (1 0 1¯ 3¯) semipolar GaN directly grown on m-plane sapphire substrates by hydride vapor phase epitaxy (HVPE) were investigated. It was found that the increase of V/III ratio led to high quality (1 0 1¯ 3¯) oriented GaN epilayers with a morphology that may have been produced by step-flow growth and with minor evidence of anisotropic crystalline structure. After etching in the mixed acids, the inclined pyramids dominated the GaN surface with a density of 2×105 cm−2, revealing the N-polarity characteristic. In the low-temperature PL spectra, weak BSF-related emission at 3.44 eV could be observed as a shoulder of donor-bound exciton lines for the epilayer at high V/III ratio, which was indicative of obvious reduction of BSFs density. In comparison with other defect related emissions, a different quenching behavior was found for the 3.29 eV emission, characterized by the temperature-dependent PL measurement.

A GaN film with a thickness of 250@mm was grown on a GaN/sapphire template in a vertical hydride vapor phase epitaxy (HVPE) reactor. The full-width at half-maximum (FWHM) values of the film were 141 and 498arcsec for the (002) and (102) reflections, respectively. A sharp band-edge emission with a FWHM of 20meV at 50K was observed, which corresponded to good crystalline quality of the film. Some almost circular-shaped hillocks located in the spiral growth center were found on the film surface with dimensions of 100@mm, whose origin was related to screw dislocations and micropipes. Meanwhile, large hexagonal pits also appeared on the film surface, which had six triangular {101@?1} facets. The strong emission in the pits was dominated by an impurity-related emission at 377nm, which could have been a high-concentration oxygen impurity.

High quality ZnO films have been successfully grown on a Si (100) substrate by metal organic chemical vapour deposition with a γ-Al2O3 buffer. The crystal structure, surface morphology and optical properties of the ZnO films were characterized by x-ray diffraction, Raman spectroscopy, atomic force microscopy and photoluminescence (PL) spectroscopy. The properties of the films with the Al2O3 buffer were improved in comparison with those of as-grown ZnO films. It is shown that the ZnO films with the γ-Al2O3 buffer grown on Si (100) substrates have a highly-preferential c-axis (0002) orientation, a narrow (0002) peak, smooth surface morphology and better PL spectral properties. This demonstrates that the use of γ-Al2O3/Si as a ZnO substrate is beneficial for reducing the residual stress for further growth of ZnO films, compared with the growth on bulk Si substrates.

We describe the growth of GaN on Si(111) substrates with AlxGa1-xN/AlN buffer layer by ammonia gas source molecular beam epitaxy (NH3-GSMBE). The influence of the AlN and AlxGa1-xN buffer layer thickness and the Al composition on the crack density of GaN has been investigated. It is found that the optimum thickness is 120 and 250 nm for AlN and AlxGa1-xN layers, respectively. The optimum Al composition is between 0.3 < x < 0.6. (c) 2005 Elsevier B.V. All rights reserved.

The resistive transitions of (Bi, Pb) 2 Sr 2 Ca 2− x Pr x Cu 3 O y silver sheathed tapes with x =0.0, 0.001, 0.002 have been measured under applied magnetic fields oriented perpendicular to tape plane (H∥c) from 0 to 7 T. The transitions can be well agreed with the thermally activated flux creep model by Anderson: R ( T , H )= R 0 exp[− U ( H )/ k B T ] in the low resistance range. Under lower applied magnetic field the calculated activation energies U ( H ) of flux motion increased drastically in the samples with proper amount of Pr-ion defects, for example, U is about 29,000 K for tape with x =0.001 at 0.025 T while that is 4200 K for that without ion defects. For our samples, U are all well fitted with the law of U /(1− T irr / T c0 )∝1/ H α . With the doped Pr-ion defects, the data α are obviously increased from 0.67 to 1–1.22. The markedly changed α indicated the flux creep according to varied manners in different samples.

The relationship of the threading dislocations (TDs) and InGaN-based quantum well (QW) optical characteristics is studied by temperature-dependent photoluminescence, high-resolution X-ray diffraction and atomic force microscopic. It is found that TDs deteriorate the QW interfacial abruptness, and can enhance the localization effect. Temperature-dependent photoluminescence measurements give evidence that the TDs act as nonradiative recombination (NR) centers in InGaN active layer. According to these results, it is inferred that the influence of TD on the optical properties of InGaN-based QW depends on the competition of localization induced by TDs and the NR effect of TDs.

Raman spectroscopy was used to study the evolution of host lattice recrystallization in Mn+-implanted GaAs. A high dose of Mn+-ions (> 10(15) cm(-2)) was introduced into semi-insulating GaAs by the combinatorial implantation method. Subsequent thermal annealing at 920 degreesC was carried out to re-grow the implantation-induced amorphous layers. The dependence of the recrystallization behavior on the Mn content was systematically observed. The lattice orientation of recrystallized layers in the surface changed after high-dose implantation (> 1.6 x 10(15) cm(-2)) and annealing. The size of the recrystallized crystallites decreased with increasing Mn+ dose, as indicated by images from atomic force microscopy. The decrease in the phonon frequency-of the Raman lines with the size reduction of microcrystals was in good agreement with the spatial correlation model. However, at higher doses (> 7 x 10(16) cm(-2)), a blue shift of the frequency was observed due to the compressive stress exerted on the microcrystals.

The hydrogen-enhanced recrystallization during thermal annealing in N+-implanted GaAs has been studied by combinatorial implantation process. Raman spectroscopy was used to study the crystallization properties of a set of hydrogenated cells on the N+-implanted GaAs wafer. A whole competitive process between H+ implantation-induced damage and recovery in the regrowth process of amorphous GaAs was observed within the proton dose region of 1.6×1015 to 1.1×1017 cm-2. In H+ dose region of 2.1×1016 to 5.4×1016 cm-2, H-enhanced recovery of crystal dominates the regrowth process. The crystal quality is better than that of unhydrogenated cell of N+-implanted GaAs in the H+ dose range from 4.7×1016 to 8.1×1016 cm-2. It is suggested that the vacancy supersaturation produced during hydrogen irradiation is dominantly responsible for the enhancement of thermal regrowth in the N+-implanted GaAs. Both the crystallization and amorphization process are clearly observed in different proton implantation dose regions.

The electrodeposition of Tl on Au(100) has been investigated using surface X-ray scattering. At potentials prior to Tl bulk deposition, Tl adatoms form a c( p × 2) close-packed monolayer on the unreconstructed Au(100) surface in both acid and alkaline solutions. The Tl monolayer uniaxially compresses over a 0.25 V wide potential range and the nearest-neighbor-separation of Tl attains a minimum value of 3.34A. This is close to the value obtained on Au(111) prior to bulk Tl deposition. From the specular X-ray reflectivity, a 2.55AAu Tl layer spacing is obtained for the c( p × 2) monolayer. Bulk deposition of Tl at potentials negative of the reversible Nernst potential results in the formation of imperfectly-aligned hexagonal-close-packed crystallites on top of the c( p × 2) monolayer. At potentials positive to the stripping of the c( p × 2) monolayer, a (2 × 2) diffraction pattern is observed in perchloric and sulfuric acid solutions but not in alkaline solutions. Real space models are proposed.

Molecular beam epitaxy has been employed to grow Ga x In 1− x As 1− y Sb y PIN detectors operating at 2.0 to 2.6 μm on (100)-oriented GaSb substrates. The epitaxial layers were characterized by X-ray double-crystal diffraction, Fourier transform infrared spectroscopy, electron microprobe analysis, and Hall effect measurements. The background hole concentration and mobility at room temperature are (4–5) × 10 16 cm −3 , 254 cm 2 /V·s and 9 × 10 15 cm −3 , 970 cm 2 /V·s for GaInAsSb and GaSb, respectively. For a PIN mesa front-illuminated photodetector, a maximum external quantum efficiency of 65% without anti-reflection coating and a peak detectivity D λ ∗ at 2.5 μm of 3.0 × 10 9 cm Hz 1/2 / W with a cut-off wavelength of 2.6 μm at room temperature have been achieved.

Electrical properties and donor ionization energy level E D in Te-doped n-Al x Ga 1-x As 0.003 Sb 0.97 (0

GaN epilayers were grown on (0001) sapphire substrates by NH3-MBE and RF-MBE (radio frequency plasma). The polarities of the epilayers were investigated by in-situ RHEED, chemical solution etching and AFM surface examination. By using a RF-MBE grown GaN layer as template to deposit GaN epilayer by NH3-MBE method, we found that not only Ga-polarity GaN films were repeatedly obtained, but also the electron mobility of these Ga-polarity films was significantly improved with a best value of 290 cm2/V.s at room temperature. Experimental results show it is an easy and stable way for growth of high quality Ga-polarity GaN films.

Recent diggings in Brittany provide us with new Gaulish coins for a further study about their value and dating. The elemental analysis gives a good idea of the great variety in the monetary alloys used in Gallia in the second part of the first century B.C. Each coin was analyzed by surface and volume techniques. For some samples the discrepancy between the two types of analysis is large for Ag-rich alloys: a surface enrichment in silver is observed.

Silica inverse opal photonic crystals (PCs) were fabricated by using a sacrificial polymer template method, and were characterized by scanning electron microscopy and reflection spectra. The fluorescence of tricolor fluorescent powders has been enhanced obviously by silica inverse opals as the emission wavelengths of the tricolor fluorescent powders are in the range of stop bands of the inverse opal PCs, which demonstrates that the PCs will be efficient and selective reflection mirrors. A promising application of the strategy would be in novel effective lighting devices.

Examen de l'influence de la tension negative de polarisation du substrat sur la microstructure des films d'alliage Al/Cu formes par pulverisation ionique magnetron d'aluminium sur des substrats de cuivre

Advantages of X-ray fluorescence with the use of Synchrotron Radiation are emphasized (intensity, polarization, tunability of energy). The experimental set-up and the fast computer system for the data reduction without standards are presented. The results are in good agreement with standard references. Examples of applications are presented: old coins and potteries were studied in archaeological domain; metal alloys were analyzed; element composition of bulk samples of volcanic rocks, sublimates and aerosols were determined.