Abstract
This paper presents information about the formation of terraces (often composed of relatively wide faces and relatively narrow steps between them) on samples of polycrystalline palladium. These have been formed via simple heat treatments, involving holding at 1200°C for periods ranging from a few minutes to several hours, followed by quenching by jets of inert gas. These treatments are such that the terraces are created, and survive the cooling, without significant formation of surface oxide. The crystallographic anisotropy of the surface energy is the driving force for terrace formation, with low surface energy planes tending to be preferentially exposed. Information is presented regarding the surface topography of the terraces and of the grain boundary regions, which have mainly been explored using AFM. Typically, the step heights are of the order of 50nm and the widths of the faces between them are around 1μm, although there are quite substantial local variations in these figures. It is shown that a degree of control is possible via the grain structure and texture of the sample, as well as via the processing conditions during the terracing treatment.
Highlights
In tissue engineering, physical cues such as topographical features, in the nanometer scale, have been recognized as important for cellular function at the substrate/cell interface
In catalytic reactions, terraced nanomaterials have received a lot of attention over classical catalysts, which is highly related to their exposed crystallographic planes, as the atoms at different planes have different surface energy and surface charges
It is well established that the surfaces of a range of material systems tend to reconstruct, by forming terrace structures, to minimize their surface energy even if this involves an increase in the total surface area
Summary
Physical cues such as topographical features, in the nanometer scale, have been recognized as important for cellular function at the substrate/cell interface (see reviews [1,2]). A typical terrace structure would contain a “face” which is expected to expose the lowest energy plane available Presumably it would not in general be possible for the entire grains to be composed entirely of these faces, since this would require a great deal of atomic movement, and for most grain orientations, this would lead to large inclinations between the surfaces of neighbouring grains and substantially greater overall surface area than if the whole sample were flat. Laue microdiffraction and scanning electron microscopy, terraces were found to expose one {100} plane and two {111} planes Such observations have sometimes been interpreted in the light of theoretical studies on the expected anisotropy of the surface energy e.g. Guidelines for control of the resultant terrace structures are presented
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