摘要:

In order to overcome dissipation due to impurity segregation at grain boundaries, niobium cavities are submitted to a purification annealing (1300 °C±200 °C under vacuum) during which titanium is evaporated onto the Nb surface. The resulting titanium layer acts as a solid state getter reacting with light impurities (H, C, N, O), thereby removing these impurities from the bulk of the niobium. Preferential titanium diffusion along grain boundaries have been studied using proton-induced x-ray emission. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364025

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Although the AlxGa1−xAs alloy system has been extensively investigated, there are still considerable uncertainties in measuring the value ofx. Here a new AlxGa1−xAs calibration structure, grown by molecular beam epitaxy, has been used to establish unambiguous alloy compositions. Such “standard’’ AlxGa1−xAs layers were measured by high-resolution x-ray diffraction, photoluminescence, and Raman spectroscopy to determine the compositional variations of the measured physical parameters. The phenomenological equations derived from these measurements can now be used to establish the Al content of unknown alloys with confidence. In addition, the results show that Vegard’s law does not hold for the variation of the AlxGa1−xAs lattice constant withx. The small quadratic term has very important implications for a correct analysis of x-ray results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364012

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A thick (260 nm) pseudomorphic metastablen-type Ge0.06Si0.94layer grown by molecular beam epitaxy on ann-type Si(100) substrate was implanted at room temperature with 70 keV BF2+ions to a dose of 3×1013cm−2, so that ap−njunction was formed in the GeSi layers. The samples were subsequently annealed for 10–40 s in a lamp furnace with a nitrogen ambient, or for 30 min in a vacuum-tube furnace. The samples were characterized by 2 MeV4Hebackscattering/channeling spectrometry, double-crystal x-ray diffractometry, transmission electron microscopy, and by Hall effect measurements using the van der Pauw sample geometry. Samples annealed for either 40 s or 30 min at 800 °C exhibit full electrical activation of the boron in the GeSi epilayer without losing their strain. The Hall mobility of the holes is lower than that ofp-type Si doped under the same experimental conditions. These results can be attributed to the Hall factor of heavily dopedp-type GeSi films which is less than unity while the Hall factor of a heavily dopedp-type Si orn-type GeSi film is close to unity. When annealed at 900 °C, the strain in both implanted and unimplanted layers is partly relaxed after 30 min, whereas it is not visibly relaxed after 40 s. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364026

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Dual-energy carbon implantation(1×1016/cm2at 150 and at 220 keV) was performed on 260-nm-thick undoped metastable pseudomorphic Si(100)/Ge0.08Si0.92with a 450-nm-thickSiO2capping layer, at either room temperature or at 100 °C. After removal of theSiO2the samples were measured using backscattering/channeling spectrometry and double-crystal x-ray diffractometry. A 150-nm-thick amorphous layer was observed in the room temperature implanted samples. This layer was found to have regrown epitaxially after sequential annealing at 550 °C for 2 h plus at 700 °C for 30 min. Following this anneal, tensile strain, believed to result from a large fraction of substitutional carbon in the regrown layer, was observed. Compressive strain, that presumably arises from the damaged but nonamorphized portion of the GeSi layer, was also observed. This strain was not significantly affected by the annealing treatment. For the samples implanted at 100 °C, in which case no amorphous layer was produced, only compressive strain was observed. For samples implanted at both room temperature and 100 °C, the channelled backscattering yield from the Si substrate was the same as that of the virgin sample. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364027

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Gas source molecular beam epitaxy growth of TlInP (thallium indium phosphide) on (100) InP substrate is described. TlInP is an important constituent material of newly proposed novel infrared optical device material, TlInGaP, which can be lattice-matched to InP. Reflection high-energy electron diffraction reveals the (2×2), (2×4), and (4×2) streak patterns corresponding to the P-excess, P-stabilized and group-III rich surfaces, respectively. However, facet pattern emerges in the low temperature (380 °C) growth. This pattern is consistent with the scanning electron microscopy image; hatched pattern along the [011] direction, which is caused by insufficient migration of group III adatoms on the surface. Double crystal x-ray diffraction rocking curves for TlP on InP and TlInP on InP samples clearly show the peak from TlP and TlInP as well as that from InP substrate. The peak position is changed with Tl/In flux ratio. Photoluminescence emission is observed for TlInP grown on InP. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364013

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The molecular beam epitaxy of InSb/Si structures was accomplished using group IIa fluoride buffer layers. InSb growth was initiated by opening the In and Sb shutters simultaneously at substrate temperatures between 300 °C and 400 °C, producing In-terminated InSb(111)-A surfaces on CaF2/Si(111) substrates. Reflection high-energy electron diffraction, electron channeling, and high resolution x-ray diffraction measurements indicated that the InSb layers were of good crystalline quality. Electron mobilities at room temperature were as high as 65 000 cm2/V s for an 8-&mgr;m-thick InSb layer grown on CaF2/Si(111). On CaF2/Si(001) substrates, the InSb layers grew in the (111) orientation with two domains 90° apart. These InSb layers and ones grown on BaF2/CaF2/Si(111) substrates exhibited inferior electrical and structural properties compared to structures grown on CaF2/Si(111) substrates. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364028

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Layers of AlBN were grown on sapphire by organometallic vapor-phase epitaxy at 1050 °C using triethylboron, trimethylaluminum, and ammonia as precursors. It is shown that boron is readily incorporated into the layers and its concentration in the solid phase can be as high as 40&percent;. However, single phase Al1−xBxN films can only be grown for compositions not exceedingx=0.01. For higher boron concentrations in the solid the second B-rich phase is formed. This phase was identified as wurtzite BN based on the results of transmission electron microscopy and x-ray diffraction. The growth of this thermodynamically unfavorable phase becomes possible, most probably, because it occurs within the framework provided by wurtzite AlN islands first formed on the surface and setting up the sites for lateral growth of wurtzite BN. That leads to formation of columnar structure of AlN and BN crystallites oriented in the basal plane and existing side by side. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364066

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Homoepitaxial chemical vapor deposited (CVD)13C diamond films were grown on ⟨100⟩ diamond substrates predamaged by implantation with 620 keV Xe ions. The structural quality of the overgrown films was analyzed by plain-view and cross-sectional micro-Raman spectroscopy. Implantation doses below 2×1014cm−2, for which no damage detectable by Raman spectroscopy was observed in the substrate, had no effect on the quality of the overgrown films. For doses around 4×1014cm−2, a pronounced predamage of the diamond substrate was found which had a strong degrading effect on the quality of the overgrown layer resulting in a drastic increase of the width of the optic zone-center phonon and in the appearance of Raman scattering from sp2-bonded carbon. Higher implantation doses up to 1×1015cm−2resulted in a complete etch removal of the predamaged graphitic surface layer during the initial phase of CVD growth, which thus had no effect on the quality of the film produced by the subsequent overgrowth. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364029

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The stress distribution in heteroepitaxial chemical vapor deposited diamond films has been investigated by Raman spectroscopy. A new method for stress determination based on polarized confocal micro-Raman is presented and used for the measurement of the stress evolution across the film thickness in the center of the sample. The presence of highly inhomogeneous stresses at a microscopic scale is first demonstrated. The interface appears to be under compressive stress which rapidly decreases and then stabilizes, but remains compressive. The strain tensor is also shown to vary. Near the interface, the common assumption of biaxial stress in the plane of the film has been confirmed. Near the growth surface, the stress tensor appears to be more complicated. Grain boundaries are suggested to be mainly responsible for the intrinsic stress generation when the grain boundary density is high. Inhomogeneous impurity distribution could be related to stress inhomogeneities near the growth surface, where the grain boundary density becomes small. Agreement has been obtained between micro- and macro-Raman stress measurements. The average stress (over film thickness) as determined by macro-Raman is shown to increase by 30&percent;–40&percent; from the sample center to the edge. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364006

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A fine-scale model is developed for the removal of an adhesive layer by a uniform stress. The initial motivation of this modeling project was a description of the removal of a layer of filter cake from cylindrical filters by backpulse cleaning. The model includes the bonding forces of adhesion between the layer and a substrate, as well as the forces of cohesion between imaginary “gridblocks’’ within the layer. For stresses greater than a threshold value, some of the layer is removed, with the fraction removed depending upon the stress, the average adhesive and cohesive forces, and the distribution of these forces about their average. The cohesive forces reduce the threshold well below the average strength of the adhesive force, because they increase the stress near broken adhesive bonds. The cohesive forces also sharpen the threshold in the cleaning pressure significantly, so that the threshold is very much sharper than the distribution of adhesive strengths. For moderate filter cake thickness (moderately strong cohesive forces), the threshold becomes steplike, with no cleaning just below the threshold and complete cleaning at the threshold and above. The model also provides the pressure dependence of the size and shape distributions for the fragments of the filter cake layer removed from the filter, enabling the model to address questions of cleaning efficiency, “patchy cleaning,’’ re-entrainment, and trapping of large cake-fragments in the filter vessel. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365272

出版商:AIP    

年代:1997

数据来源: AIP