595,436 research outputs found
Multi-layer light-weight protective coating and method for application
A thin, light-weight, multi-layer coating is provided for protecting metals and their alloys from environmental attack at high temperatures. A reaction barrier is applied to the metal substrate and a diffusion barrier is then applied to the reaction barrier. A sealant layer may also be applied to the diffusion barrier if desired. The reaction barrier is either non-reactive or passivating with respect to the metal substrate and the diffusion barrier. The diffusion barrier is either non-reactive or passivating with respect to the reaction barrier and the sealant layer. The sealant layer is immiscible with the diffusion barrier and has a softening point below the expected use temperature of the metal
Collective Diffusion of Colloidal Hard Rods in Smectic Liquid Crystals: Effect of Particle Anisotropy
We study the layer-to-layer diffusion in smectic-A liquid crystals of
colloidal hard rods with different length-to-diameter ratios using computer
simulations. The layered arrangement of the smectic phase yields a hopping-type
diffusion due to the presence of permanent barriers and transient cages.
Remarkably, we detect stringlike clusters composed of inter-layer rods moving
cooperatively along the nematic director. Furthermore, we find that the
structural relaxation in equilibrium smectic phases shows interesting
similarities with that of out-of-equilibrium supercooled liquids, although
there the particles are kinetically trapped in transient rather than permanent
cages. Additionally, at fixed packing fraction we find that the barrier height
increases with increasing particle anisotropy, and hence the dynamics is more
heterogeneous and non-Gaussian for longer rods, yielding a lower diffusion
coefficient along the nematic director and smaller clusters of inter-layer
particles that move less cooperatively. At fixed barrier height, the dynamics
becomes more non-Gaussian and heterogeneous for longer rods that move more
collectively giving rise to a higher diffusion coefficient along the nematic
director.Comment: 24 pages, 10 figure
The kinetics of titanium monosilicide growth studied by three-wavelength ellipsometry
Thin titanium layers (approximately 10 nm) have been grown on top of a clean Si(111) substrate. Heating these layers initiates a solid state reaction, yielding an amorphous monosilicide phase at about 350 °C. The kinetics of the solid state reaction has been followed using three-wavelength ellipsometry (340, 450 and 550 nm). A very coarse two-layer model has been applied in the analyses of the measured data: a top layer of pure titanium is consumed by a second layer of TiSi. The dielectric constants of titanium and TiSi are known and the layer thicknesses d1 and d2 have been fitted to the six ellipsometrical angles measured. These analyses reveal a diffusion-limited growth mechanism exhibiting two growth rates: a rapid initial rate followed by a slower final rate. The diffusion coefficient D of the rapid process and its activation energy Ea could be obtained: D = 2 × 10−15cm2s−1atT 370 °CandEa = 0.62 eV The two growth rates have been attributed to silicon diffusion along the grains and diffusion into the grains.\ud
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Diffusion behavior of delta-doped Si in InAlAs/InP heterostructures
Diffusion behavior of delta-doped Si in InAlAs and InP was studied by using secondary ion mass spectroscopy. A significant broadening of the profile due to postgrowth annealing was observed in In0.52Al0.48As. In contrast, the depth profile of delta-doped Si in InP was scarcely changed by annealing. This indicates that the diffusion coefficient of delta-doped Si in InP is much smaller than that in In0.52Al0.48As. Suppression of Si diffusion by using a delta-doped InP layer as the carrier supply layer (CSL) improves the thermal stability of the InP-HEMT structures
Dynamical Heterogeneities and Cooperative Motion in Smectic Liquid Crystals
Using simulations of hard rods in smectic-A states, we find non-gaussian
diffusion and heterogeneous dynamics due to the equilibrium periodic smectic
density profiles, which give rise to permanent barriers for layer-to-layer
diffusion. This relaxation behavior is surprisingly similar to that of
non-equilibrium supercooled liquids, although there the particles are trapped
in transient (instead of permanent) cages. Interestingly, we also find
stringlike clusters of up to 10 inter-layer rods exhibiting dynamic
cooperativity in this equilibrium state.Comment: 10 pages, 4 figure
Diffusion of Mn interstitials in (Ga,Mn)As epitaxial layers
Magnetic properties of thin (Ga,Mn)As layers improve during annealing by
out-diffusion of interstitial Mn ions to a free surface. Out-diffused Mn atoms
participate in the growth of a Mn-rich surface layer and a saturation of this
layer causes an inhibition of the out-diffusion. We combine high-resolution
x-ray diffraction with x-ray absorption spectroscopy and a numerical solution
of the diffusion problem for the study of the out-diffusion of Mn interstitials
during a sequence of annealing steps. Our data demonstrate that the
out-diffusion of the interstitials is substantially affected by the internal
electric field caused by an inhomogeneous distribution of charges in the
(Ga,Mn)As layer.Comment: 11 pages, 5 figure
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