Grain-boundary grooving and agglomeration of alloy thin films with a slow-diffusing species

We present a general phase-field model for grain-boundary grooving and agglomeration of polycrystalline alloy thin films. In particular, we study the effects of slow-diffusing species on grooving rate. As the groove grows, the slow species becomes concentrated near the groove tip so that further grooving is limited by the rate at which it diffuses away from the tip. At early times the dominant diffusion path is along the boundary, while at late times it is parallel to the substrate. This change in path strongly affects the time-dependence of grain boundary grooving and increases the time to agglomeration. The present model provides a tool for agglomeration-resistant thin film alloy design. keywords: phase-field, thermal grooving, diffusion, kinetics, metal silicidesComment: 4 pages, 6 figure

Effect of grain shape on the agglomeration of polycrystalline thin films

Grain-boundary grooving is a general phenomenon occurring in all polycrystalline materials at the intersection between the grain-boundary and the interface or free surface. It has been studied theoretically for some time. Grain-boundary grooving in the context of faceted interfaces in particular has attracted some attention. However, these works did not consider the case of thin films and the consequences on agglomeration of the shape of the interface. In this Letter, we compare the agglomeration of thin films with rounded and faceted interfaces. The shape of the grains can dramatically affect the agglomeration of polycrystalline thin films by grain-boundary grooving. Anisotropy plays a central role in the stability against agglomeration of faceted films. Even a small difference between the interface energies of the facets can destabilize faceted grains or, on the contrary, it can make them perfectly stable at any thickness. keywords: grain-boundary grooving, dihedral angle, faceting, energy, silicide, theory, model.Comment: 3 pages, 3 figure

Pavement grooving at John F. Kennedy International Airport

Pavement grooving at Kennedy Airpor

Restoration of Fricitonal Characteristics on Older Portland Cement Concrete Pavement:Final Report for Iowa Highway Research Board Project HR-224, June 1986

Safety i s a very important aspect o f the highway program. The Iowa DOT initiated an inventory o f the friction values of all paved primary roadways i n 1969. This inventory, with an ASTM E-274 test unit, has continued to the present time. The t e s t i n g frequency varies based upon traffic volume and the previous friction value. Historically , the state o f Iowa constructed a substantial amount o f pcc pavement during the 1928-30 period t o "get Iowa out o f the mud". Some of that pavement has never been resurfaced and has been subjected to more than 50 years o f wear. The textured surface has been worn away and has subsequently polished. Even though some pavements from 15 t o 50 years old continue t o function structurally , because of the loss of friction , they do not provide the desired level o f safety to the driver. As a temporary measure, "Sl ippery -When -Wet " signs have been posted on many older pcc roads due to friction numbers below t h e desirable level. These signs warn the motorist of the current conditions. An economical method of restoring the high quality frictional properties i s needed

Interplay between grain boundary grooving, stress, and dealloying in the agglomeration of NiSi1-xGex films

Germanosilicides, especially those formed on compressive substrates, are less stable than silicides against agglomeration. By studying the solid-state reaction of Ni thin film on strained Si0.8Ge0.2(001), we show that nickel germanosilicide is different from nickel silicide and nickel germanide in several respects: the grains are smaller and faceted, the groove angle is sharper, and dealloying takes place. The germanium out-diffusion creates a stress in the film which favors grooving and agglomeration.Comment: 13 pages, 4 figure

Runway grooving project at Chicago Midway Airport

Runway grooving project at Chicago Midway Airpor

Optimization of Al/AlOx/AlAl/AlO_x/Al-Layer Systems for Josephson Junctions from a Microstructure Point of View

$Al/AlO_x/Al$-layer systems are frequently used for Josephson junction-based superconducting devices. Although much work has been devoted to the optimization of the superconducting properties of these devices, systematic studies on influence of deposition conditions combined with structural analyses on the nanoscale are rare up to now. We have focused on the optimization of the structural properties of $Al/AlO_x/Al$-layer systems deposited on Si(111) substrates with a particular focus on the thickness homogeneity of the $AlO_x$-tunnel barrier. A standard high-vacuum electron-beam deposition system was used and the effect of substrate pretreatment, different Al-deposition temperatures and Al-deposition rates was studied. Transmission electron microscopy was applied to analyze the structural properties of the $Al/AlO_x/Al$-layer systems to determine the thickness homogeneity of the $AlO_x$ layer, grain size distribution in the Al layers, Al-grain boundary types and the morphology of the $Al/AlO_x$ interface. We show that the structural properties of the lower Al layer are decisive for the structural quality of the whole $Al/AlO_x/Al$-layer system. Optimum conditions yield an epitaxial Al(111) layer on a Si(111) substrate with an Al-layer thickness variation of only 1.6 nm over more than 10 $\mu m$ and large lateral grain sizes up to 1 $\mu m$. Thickness fluctuations of the $AlO_x$-tunnel barrier are minimized on such an Al layer which is essential for the homogeneity of the tunnel current. Systematic variation of the Al-deposition rate and deposition temperature allows to develop an understanding of the growth mechanisms

General-aviation pilot reactions to and opinons on grooved runways

Survey of airline pilot reactions to grooved runway

Plastic (wire-combed) grooving of a slip-formed concrete runway overlay at Patrick Henry Airport: An initial evaluation

A wire-comb technique is described for transversely grooving the surface of a freshly laid (plastic state) slip-formed concrete overlay installed at Patrick Henry Airport. This method of surface texturing yields better water drainage and pavement skid resistance than that obtained with an older conventional burlap drag concrete surface treatment installed on an adjacent portion of the runway