2,686 research outputs found
Solid state studies in ceramic alloys Quarterly progress report, 1 Jun. - 31 Aug. 1969
Solid state characteristics of ceramic alloy
Use of Hydration Inhibitors to Improve Bond Durability of Aluminum Adhesive Joints
An investigation is conducted of the mechanisms by which nitrilotris methylene phosphonic acid (NTMP) and related compounds are adsorbed onto oxidized aluminum surfaces to inhibit hydration and increase the durability of adhesive bonds formed with inhibitor-treated panels. P - O - Al bonds are identified as the basis of adsorption, and it is found that water initially adsorbed onto the etched aluminum surfaces is displaced by the NTMP. The hydration of the NTMP-treated surfaces occurs in three stages, namely the reverisble physisorption of water, the slow dissolution of NTMP followed by rapid hydration of the freshly exposed Al2O3 to AlOOH and further hydration of the surface to Al(OH)3. Five properties of an ideal inhibitor are identified
Solid state studies in ceramic alloys Quarterly progress report no. 2, 1 Dec. 1965 - 28 Feb. 1966
Electron microscope study of boron-doped titanium carbide sample
Solid State Studies in Ceramic Alloys Quarterly Progress Report No. 1, 31 Aug. - 30 Nov. 1965
Effect of trace amounts of boron on defect structure of titanium carbide crystal
Bonding, structure and mechanical behavior of vanadium carbide single crystals
Bonding, structure, and mechanical behavior of vanadium carbide single crystal
Crossover in the scaling of island size and capture zone distributions
Simulations of irreversible growth of extended (fractal and square) islands
with critical island sizes i=1 and 2 are performed in broad ranges of coverage
\theta and diffusion-to-deposition ratios R in order to investigate scaling of
island size and capture zone area distributions (ISD, CZD). Large \theta and
small R lead to a crossover from the CZD predicted by the theory of Pimpinelli
and Einstein (PE), with Gaussian right tail, to CZD with simple exponential
decays. The corresponding ISD also cross over from Gaussian or faster decays to
simple exponential ones. For fractal islands, these features are explained by
changes in the island growth kinetics, from a competition for capture of
diffusing adatoms (PE scaling) to aggregation of adatoms with effectively
irrelevant diffusion, which is characteristic of random sequential adsorption
(RSA) without surface diffusion. This interpretation is confirmed by studying
the crossover with similar CZ areas (of order 100 sites) in a model with
freezing of diffusing adatoms that corresponds to i=0. For square islands,
deviations from PE predictions appear for coverages near \theta=0.2 and are
mainly related to island coalescence. Our results show that the range of
applicability of the PE theory is narrow, thus observing the predicted Gaussian
tail of CZD may be difficult in real systems.Comment: 9 pages, 7 figure
Capture-zone scaling in island nucleation: phenomenological theory of an example of universal fluctuation behavior
In studies of island nucleation and growth, the distribution of capture
zones, essentially proximity cells, can give more insight than island-size
distributions. In contrast to the complicated expressions, ad hoc or derived
from rate equations, usually used, we find the capture-zone distribution can be
described by a simple expression generalizing the Wigner surmise from random
matrix theory that accounts for the distribution of spacings in a host of
fluctuation phenomena. Furthermore, its single adjustable parameter can be
simply related to the critical nucleus of growth models and the substrate
dimensionality. We compare with extensive published kinetic Monte Carlo data
and limited experimental data. A phenomenological theory sheds light on the
result.Comment: 5 pages, 4 figures, originally submitted to Phys. Rev. Lett. on Dec.
15, 2006; revised version v2 tightens and focuses the presentation,
emphasizes the importance of universal features of fluctuations, corrects an
error for d=1, replaces 2 of the figure
Growth of Patterned Surfaces
During epitaxial crystal growth a pattern that has initially been imprinted
on a surface approximately reproduces itself after the deposition of an integer
number of monolayers. Computer simulations of the one-dimensional case show
that the quality of reproduction decays exponentially with a characteristic
time which is linear in the activation energy of surface diffusion. We argue
that this life time of a pattern is optimized, if the characteristic feature
size of the pattern is larger than , where is the surface
diffusion constant, the deposition rate and the surface dimension.Comment: 4 pages, 4 figures, uses psfig; to appear in Phys. Rev. Let
Spatio-temporal distribution of nucleation events during crystal growth
We consider irreversible second-layer nucleation that occurs when two adatoms
on a terrace meet. We solve the problem analytically in one dimension for zero
and infinite step-edge barriers, and numerically for any value of the barriers
in one and two dimensions. For large barriers, the spatial distribution of
nucleation events strongly differs from , where is the
stationary adatom density in the presence of a constant flux. The probability
that nucleation occurs at time after the deposition of the second
adatom, decays for short time as a power law [] in and
logarithmically [] in ; for long time it decays
exponentially. Theories of the nucleation rate based on the assumption
that it is proportional to are shown to overestimate by a
factor proportional to the number of times an adatom diffusing on the terrace
visits an already visited lattice site.Comment: 4 pages, 3 figures; accepted for publication on PR
Scaling of island size and capture zone distributions in submonolayer growth
Island size and capture zone distributions (ISDs, CZDs) are studied
numerically in submonolayer growth with various critical island sizes and
shapes. CZDs scaled by the variance show excellent agreement with the Wigner
surmise, confirming the Pimpinelli-Einstein approach for large CZs / large
island dynamics. The ISD decay as exp(-s^x), with x=4, x approx 2.4 and 2 for
point, fractal, and square islands, respectively. A scaling approach explains
the values of x from the Gaussian decay of CZD and the efficiency of islands to
capture diffusing adatoms.Comment: 12 pages, 3 figure
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