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Solid state reaction between nanocrystalline Cu and Sn films was investigated at room temperature by depth profiling with secondary neutral mass spectrometry and by X-ray diffraction. A rapid diffusion intermixing was observed leading to the formation of homogeneous Cu 6Sn5 layer. There is no indication of the appearance of the Cu3Sn phase. This offers a way for solid phase soldering at low temperatures, i.e. to produce homogeneous Cu6Sn5 intermediate layer of several tens of nanometers during reasonable time (in the order of hours or less). From the detailed analysis of the growth of the planar reaction layer, formed at the initial interface in Sn(100 nm)/Cu(50 nm) system, the value of the parabolic growth rate coefficient at room temperature is 2.3 x 10-15 cm2/s. In addition, the overall increase of the composition near to the substrate inside the Cu film was interpreted by grain boundary diffusion induced solid state reaction: the new phase formed along the grain boundaries and grew perpendicular to the boundary planes. From the initial slope of the composition versus time function, the interface velocity during this reaction was estimated to be about 0.5 nm/h.

Microstructure changes during annealing of nano-crystalline silver and amorphous silicon multilayers (Ag/a-Si) have been studied by X-ray diffraction and transmission electron microscopy. The dc-magnetron sputtered Ag/a-Si multilayers remained stable even after annealing at 523K for 10h, and microstructural changes occurred only above 600K. The degradation of Ag/a-Si multilayers can be described by the increase of size of Ag grains, formation of grooves and pinholes at Ag grain boundaries and by the diffusion of silicon atoms through the silver grain boundaries and along the Ag/a-Si interfaces. This results in thinning of a-Si layers, and in formation of Ag granulates after longer annealing times.

Over the last years several experimental and theoretical studies of diffusion kinetics on the nanoscale have shown that the time evolution differs from the classical Fickian law (kc=0.5). However, all work was based on crystalline samples or models, so far. In this letter, we report on the diffusion kinetics of a thin amorphous-Si layer into amorphous-Ge to account for the rising importance of amorphous materials in nanodevices. Employing surface sensitive technics, the initial kc was found at 0.7+-0.1. Moreover, after some monolayers of Si dissolved into the Ge, kc changes to the generally expected classical Fickian law with kc=0.5.

It is shown that the well-known blue-shift of the fundamental absorption edge in as-deposited compositionally modulated amorphous Si/Ge and As6Se94/Se80Te20 multilayers (with periods of 4-8 nm) is further enhanced due to the thermal or laser-induced intermixing of adjacent layers. The laser-induced intermixing process, as supported by experiments and model calculations, can be attributed to both the local heating and photo-effects in As6Se94/Se80Te20 multilayers, while only the thermal effects were observed for Si/Ge multilayers. Structural transformations, based on this enhanced interdiffusion, provides good capability for spatially patterning optoelectronic devices and digital information recording.

Thermal annealing of Si/Si1-xSbx/Si amorphous thin film tri-layer samples (x=18 and 24 at%Sb) under 100 bar Ar pressure results in an interesting pattern formation. In pictures, taken by means of cross-sectional transmission electron microscopy (TEM), stripe-shaped contrast, with three maxima, parallel with the interfaces can be seen. Secondary neutral mass spectrometer (SNMS) measurements revealed that the regions with different contrasts correspond to Sb-rich and Sb-depleted regions. Furthermore, the Sb concentration peaks in the Sb-rich regions, especially at longer annealing times, are different: the peak developed at the Si/SiSb interface closer to the free surface decays faster than that of the inner one closer to the substrate. The pattern formation is interpreted by segregation-initiated spinodal-like decomposition, while the difference of the Sb concentration peaks is explained by the resultant Sb transport to and evaporation from the free surface. The possible role of formation of nanocrystalline grains, in the explanation of the fast transport under pressure as compared to vacuum is also discussed., Comment: This work was presented on JVC-10 conference

Amorphous silicon materials and its alloys become extensively used in some technical applications involving large area of the microelectronic and optoelectronic devices. However, the amorphous-crystalline transition, segregation and diffusion processes still have numerous unanswered questions. In this work we study the Sb diffusion into an amorphous Si film by means of Secondary Neutral Mass Spectrometry (SNMS). Amorphous Si/Si1-xSbx/Si tri-layer samples with 5 at% antimony concentration were prepared by DC magnetron sputtering onto Si substrate at room temperature. Annealing of the samples were performed at different temperature in vacuum (p<10-7 mbar) and 100 bar high purity (99.999%) Ar pressure. During annealing a rather slow mixing between the Sb-alloyed and the amorphous Si layers was observed. Supposing concentration independent diffusion, the evaluated diffusion coefficients are in the range of ~10-21 m2s-1 at 823 K., Comment: This work was presented on JVC-11 conference

Thermal stability of hydrogenated amorphous Si/Ge multilayers has been investigated by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Small-Angle X-Ray Diffraction (SAXRD) techniques. Amorphous H-Si/Ge multilayers were prepared by RF sputtering with 1.5 and 6 ml/min H2 flow-rate. It is shown by Elastic Recoil Detection Analysis (ERDA) that the hydrogen concentration increased by increasing H2 flow-rate. Annealing of the samples was carried out at 400 and 450 oC for several hours. It has been observed that samples prepared with 6 ml/min flow-rate at both annealing temperatures underwent significant structural changes: the surface of the samples was visibly roughened, gas bubbles were formed and craters were created. The decay of the periodic structure of Si and Ge layers in these types of multilayers was faster than in non-hydrogenated samples. Samples prepared with 1.5 ml/min flow-rate have similar behaviour at 450 oC, but at 400 oC the decay of the first order SAXRD peaks was slower than in case of the non-hydrogenated multilayers. Qualitatively the observed behaviour can be explained by the fast desorption of the saturated hydrogen, leading to the formation of bubbles and craters at 450 oC, as well as, at 400oC in the sample with lower H-content, by the possible passivation of the dangling bonds resulting in a slowing down of the diffusion intermixing.

The overall quality of multilayer thin films prepared by electrodeposition is strongly influenced by the surface and interface roughness which increases with the layer number. For that very reason the reliable analysis of the first few layers can be necessary. However, in depth profiling methods based on sputtering techniques the first layer is always found at the bottom of the sputtered crater. Since the depth resolution decreases during sputtering, the analysis of the first few layers are difficult. In order to circumvent this problem, we used reverse Secondary Neutral Mass Spectrometry (SNMS) depth profiling method for electrodeposited multilayered films. We prepared thin film samples in two ways. First, Co/Cu multilayer stacks were electrodeposited on Si/Cr/Cu substrates and SNMS depth profiling was carried out from the direction of the topmost layer. Secondly, elecrodeposited Co/Cu multilayer stacks were coated with a few microns thick Ni layer and detached from the Si substrate in order to study the film structure from the side of the substrate. Using this latter method, we were able to analyze the first and, probably, the most even layers of the thin film structure with high resolution.

Electromagnetic properties of doped perovskites depend sensitively on the doping level. Both the superconducting transition temperature of Bi2Sr2Ca(Pr)Cu2O8+d compounds and the magnetic and electronic transport properties of La(Sr)Co(Fe)O3 perovskites change dramatically with the doping level. Apart from doping, oxygen deficiency is influenced by the details of preparation processes such as calcination and sintering. Simultaneous determination of constituents is of crucial importance from sample characterization point of view. Quantitative analysis of perovskite oxides can be performed by Secondary Neutral Mass Spectrometry (SNMS) which is a suitable technique to measure the chemical composition of almost any sample because the flux of atoms sputtered from the sample is representative of the stoichiometry of the top-most layers. The composition and oxygen content of Bi2Sr2Ca0.86Pr0.14Cu2O8.4 and La1-xSrxCo0.975Fe0.025O3-d, where 0

This work is devoted to experimental study of influence of superconductivity (S) on ferromagnetism (FM) (inverse proximity effects) with the help of Polarized Neutron Reflectivity. Combining meausurements of specular and diffuse intensities it is possible to obtain full picture of magnetization change in S/FM layered systems like magnetization rotation, domain state formation, inducing of magnetization in S layer, etc. To increase weak magnetic signal we propose to use enhanced neutron standing wave regime (e.g. waveguides). In previous work we have made calculation to increase enhcanced factor. Here we present results of preparation sets of S/FM samples and attestation of their structural, magnetic, superconducting and neutron waveguide properties., Comment: This work was presented on workshop 3-7 dec 2008, http://hungary.jinr.ru. Contains 4 pages and 3 figures

We report on the fabrication and characterization of a micromechanical oscillator consisting only of a free-standing dielectric Bragg mirror with high optical reflectivity and high mechanical quality. The fabrication technique is a hybrid approach involving laser ablation and dry etching. The mirror has a reflectivity of 99.6%, a mass of 400ng, and a mechanical quality factor Q of approximately 10^4. Using this micromirror in a Fabry Perot cavity, a finesse of 500 has been achieved. This is an important step towards designing tunable high-Q high-finesse cavities on chip., Comment: 3 pages, 2 figures

We demonstrate passive feedback cooling of a mechanical resonator based on radiation pressure forces and assisted by photothermal forces in a high-finesse optical cavity. The resonator is a free-standing high-reflectance micro-mirror (of mass m=400ng and mechanical quality factor Q=10^4) that is used as back-mirror in a detuned Fabry-Perot cavity of optical finesse F=500. We observe an increased damping in the dynamics of the mechanical oscillator by a factor of 30 and a corresponding cooling of the oscillator modes below 10 K starting from room temperature. This effect is an important ingredient for recently proposed schemes to prepare quantum entanglement of macroscopic mechanical oscillators., Comment: 11 pages, 9 figures, minor corrections

By employing two different spectroscopic techniques we have mapped out the variable ISM dust extinction endemic to globular cluster M4. We derive an average E(B-V) reddening of 0.33 +/- 0.01 and R = 3.4 +/- 0.4, both in good agreement with previous studies of M4. For individual stars in the most heavily reddened regions of M4, we find E(B-V) values significantly higher than those inferred by studies of interstellar gas; for heavily reddened regions, the gas measured in column density measurements may not completely trace the dust., Comment: 4 pages, 1 figure, to appear in Revista Mexicana de Astronomia y Astrofisica Serie de Conferencias: ``The Seventh Texas-Mexico Conference on Astrophysics: Glows, Flows & Blows'' April 6-8, 2000, Austin, Texas

We present a chemical composition analysis of 36 giants in the nearby mildy metal-poor (<[Fe/H]> = -1.18) "CN-bimodal" globular cluster M4. Confronted with a cluster that has large and variable interstellar extinction across the cluster face, we combined traditional spectroscopic abundance methods with modifications to line-depth ratio techniques to determine the atmospheric parameters of our stars. We derive a total-to-selective extinction ratio of 3.4 and an average reddening of 0.33 which is significantly lower than that estimated by using the dust maps made by Schlegel et al. (1998). Abundance ratios for Sc, Ti, V, Ni, & Eu are typical of halo field and cluster stars. However, Si, Al, Ba, & La are overabundant with respect to what is seen in other globular clusters of similar metallicity. Superimposed on the primordial abundance distribution is evidence for the existence of proton-capture synthesis. We recover some of the C, N, O, Na, Mg, & Al abundance swings and correlations found in other more metal-poor globular clusters but the range of variation is muted. The Al enhancements appear to be from the destruction of 25,26Mg, not 24Mg. The C+N+O abundance sum is constant to within the observational errors, and agrees with the C+N+O total that might be expected for M4 stars at birth. The M4 AGB stars have C,N,O abundances that show less evidence for proton- capture nucleosynthesis than is found in the less-evolved stars of the RGB. Deeply-mixed stars of the RGB, subsequent to the helium core flash, might take up residence on the blue end of the HB, and thus fail to evolve back to the AGB but reasons for skepticism concerning this scenario are noted., Comment: 46 pages, 19 figures, 9 tables, accepted by AJ

We have serendipitously discovered an extremely lithium-rich star on the red giant branch of the globular cluster M3 (NGC 5272). An echelle spectrum obtained with the Keck I HIRES reveals a Li I 6707 Angstrom resonance doublet of 520 milli-Angstrom equivalent width, and our analysis places the star among the most Li-rich giants known: log[epsilon(Li)] ~= +3.0. We determine the elemental abundances of this star, IV-101, and three other cluster members of similar luminosity and color, and conclude that IV-101 has abundance ratios typical of giants in M3 and M13 that have undergone significant mixing. We discuss mechanisms by which a low-mass star may be so enriched in Li, focusing on the mixing of material processed by the hydrogen-burning shell just below the convective envelope. While such enrichment could conceivably only happen rarely, it may in fact regularly occur during giant-branch evolution but be rarely detected because of rapid subsequent Li depletion., Comment: 7-page LaTeX file, including 2 encapsulated ps figures + 1 table; accepted for publication in the Astrophysical Journal Letters

We present new VI photometry for the halo globular cluster M30 (NGC 7099), and compute luminosity functions (LFs) in both bands for samples of about 15,000 hydrogen-burning stars from near the tip of the red giant branch (RGB) to over four magnitudes below the main-sequence (MS) turnoff. We confirm previously observed features of the LF that are at odds with canonical theoretical predictions: an excess of stars on subgiant branch (SGB) approximately 0.4 mag above the turnoff and an excess number of RGB stars relative to MS stars. Based on subdwarfs with Hipparcos-measured parallaxes, we compute apparent distance moduli of (m-M)_{V} = 14.87+/-0.12 and 14.65+/-0.12 for reddenings of E(V-I)=0.06 and 0.02 respectively. The implied luminosity for the horizontal branch (HB) at these distances is M_V(HB)=0.11 and 0.37 mag. The two helium indicators we have been able to measure (R and Delta) both indicate that M30's helium content is high relative to other clusters of similar metallicity. M30 has a larger value for the parameter Delta V_{TO}^{HB} than any of the other similarly metal-poor clusters for which this quantity can be reliably measured. This suggests that M30 has either a larger age or higher helium content than all of the other metal-poor clusters examined. The color-difference method for measuring relative ages indicates that M30 is coeval with the metal-poor clusters M68 and M92., Comment: 38 pages text, 20 figures, accepted for ApJ