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15 Nov 2005

Volume 98, Issue 10, Articles (10xxxx)

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SiOxFy passivation layer in silicon cryoetching

X. Mellhaoui, R. Dussart, T. Tillocher, P. Lefaucheux, P. Ranson, M. Boufnichel, and L. J. Overzet

J. Appl. Phys. 98, 104901 (2005); http://dx.doi.org/10.1063/1.2133896 (10 pages) | Cited 24 times

Online Publication Date: 21 November 2005

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The SiOxFy passivation layer created on structure sidewalls during silicon cryoetching is investigated. This SiOxFy passivation layer formation strongly depends on O2 content, temperature and bias. It is a fragile layer, which mostly disappears when the wafer is warmed up to ambient temperature. A mass spectrometer was used to analyze the desorbed species during the warm-up and using this instrument allowed us to find a large signal increase in SiF3+ between −80 °C and −50 °C. SiF4 etching products can participate in the formation of the passivation layer as it is shown by a series of test experiments. SiF4/O2 plasmas are used to form a thin SiOxFy layer on a cooled silicon wafer. Thickness and optical index of this thin film can be determined by in situ spectroscopic ellipsometry. It is shown that the passivation layer spontaneously desorbs when the silicon wafer temperature increases in good agreement with the mass spectrometry analysis. Two physical mechanisms are proposed to explain the SiOxFy passivation layer buildup involving either the etching products or the SiFx sites created during etching. In both cases, oxygen radicals react at the surface to form the SiOxFy layer.
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81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.65.Rv Passivation
68.43.Mn Adsorption kinetics
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Thermal stability and atomic ordering of epitaxial Heusler alloy Co2FeSi films grown on GaAs(001)

M. Hashimoto, J. Herfort, H.-P. Schönherr, and K. H. Ploog

J. Appl. Phys. 98, 104902 (2005); http://dx.doi.org/10.1063/1.2136213 (6 pages) | Cited 11 times

Online Publication Date: 28 November 2005

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The thermal stability and the atomic ordering of single-crystal Heusler alloy Co2FeSi layers grown by molecular beam epitaxy on GaAs(001) have been studied. We found that the Co2FeSi layers have a long-range atomic order and crystallize in a partly disordered L21 structure in the low growth temperature (TG) regime. The long-range atomic order of the layers is further improved with increasing TG up to 350 °C. However, the increase of TG induces an interfacial reaction between the Co2FeSi layer and the GaAs substrate. The analysis of the in-plane magnetic anisotropy reveals that the interface perfection is improved up to TG = 200 °C and deteriorated due to an interfacial reaction above 200 °C.
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68.60.Dv Thermal stability; thermal effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films

Emergence of asymmetry in constructal tree flow networks

Louis Gosselin and Adrian Bejan

J. Appl. Phys. 98, 104903 (2005); http://dx.doi.org/10.1063/1.2133899 (7 pages) | Cited 7 times

Online Publication Date: 30 November 2005

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In this paper, we demonstrate that asymmetry in fluid distribution tree networks emerges from power requirement minimization, under global volume constraint. We have discovered several levels of asymmetry in optimal trees: different pipe lengths at the same level of branching, different mass flow rates at junctions or bifurcations, and different main branches to build the optimal dendrite. The emergence of asymmetry in optimal tree networks (man-made or natural) is a result of the optimization: it is not an assumption or a modeling feature. The constructal method that we used to discover asymmetry is predictive, and this distinguishes it from descriptive methods such as fractal geometry.
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89.20.Kk Engineering
47.60.-i Flow phenomena in quasi-one-dimensional systems
02.60.Pn Numerical optimization

Wave-solid interactions in laser-shock-induced deformation processes

Y. Fan, Y. Wang, S. Vukelic, and Y. L. Yao

J. Appl. Phys. 98, 104904 (2005); http://dx.doi.org/10.1063/1.2134882 (11 pages) | Cited 29 times

Online Publication Date: 30 November 2005

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A model was developed for material deformation processes induced by laser-generated shock waves. The processes include laser peen forming (LPF) and laser shock peening (LSP) of metals. Numerical solutions of the model using finite element method were implemented in two steps: (1) explicit step, devoted to shock wave propagation, and (2) implicit step, calculating relaxation of material. A series of LPF and LSP experiments was conducted to validate the model. The residual stress measurements by synchrotron x-ray diffraction and deformation measurements by profilometry showed that the experimental and numerical results were in good agreement. It is the first time to numerically and experimentally study the novel process of micro-scale LPF. An important aspect of the work is that the numerical results were further analytically explored to gain improved understanding of wave-solid interaction including shock wave attenuation and shock velocity variation.
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62.50.-p High-pressure effects in solids and liquids
47.40.Nm Shock wave interactions and shock effects
46.40.-f Vibrations and mechanical waves
52.38.-r Laser-plasma interactions
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
46.35.+z Viscoelasticity, plasticity, viscoplasticity
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