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Full-Text Articles in Condensed Matter Physics
Origin Of The 〈11/20〉 Atomic Short-Range Order In Au-Rich Au-Fe Alloys, M. F. Ling, J. B. Staunton, Duane D. Johnson, F. J. Pinski
Origin Of The 〈11/20〉 Atomic Short-Range Order In Au-Rich Au-Fe Alloys, M. F. Ling, J. B. Staunton, Duane D. Johnson, F. J. Pinski
Duane D. Johnson
We have calculated the atomic short-range order (ASRO) and paramagnetic susceptibility in high-temperature, chemically disordered Au75Fe25 and Au90Fe10, using a density-functional-based, electronic-structure method. For both alloys, we obtain 〈11/20〉-type ASRO, in excellent agreement with experiments performed on samples that have been fast quenched from high temperature. We also identify the underlying electronic mechanism responsible for this unusual ordering behavior. During annealing at high temperatures, we suggest that aligning local moments via an external magnetic field will produce interesting AuFe alloys with 〈100〉-type ASRO.
Van Hove Singularity Induced L11 Ordering In Cupt, J. F. Clark, F. J. Pinski, Duane D. Johnson, P. A. Sterne, J. B. Staunton, B. Ginatempo
Van Hove Singularity Induced L11 Ordering In Cupt, J. F. Clark, F. J. Pinski, Duane D. Johnson, P. A. Sterne, J. B. Staunton, B. Ginatempo
Duane D. Johnson
We describe an ordering mechanism that arises due to coupling between electronic states at van Hove singularities. This novel mechanism, which naturally leads to ordered structures with small unit cells, couples states near the Fermi energy which are localized at high-symmetry points in k space, in contrast to the conventional mechanism which relies on large parallel sheets of Fermi surface. Using first-principles calculations of the electronic structure of ordered and disordered alloys, we show that this mechanism drives the unusual short- and long-range order found in fcc CuPt.
Commensurate And Incommensurate Ordering Tendencies In The Ternary Fcc Cu-Ni-Zn System, J. D. Althoff, Duane D. Johnson, F. J. Pinski
Commensurate And Incommensurate Ordering Tendencies In The Ternary Fcc Cu-Ni-Zn System, J. D. Althoff, Duane D. Johnson, F. J. Pinski
Duane D. Johnson
We show that Fermi-surface (FS) nesting drives both the incommensurate and commensurate ordering tendencies of the fcc ternary Cu-Ni-Zn system. Surprisingly, commensurate order persists over a wide range of composition, despite its origins. For Cu2NiZn, we discuss how FS nesting and the other effects of alloying lead to ordering tendencies consistent with the experimentally observed order-disorder transformations. All calculations are based on a first-principles theory of the atomic short-range order in alloys with an arbitrary number of components.
Characterization Of Piezoceramic Crosses With Large Range Scanning Capability And Applications For Low Temperature Scanning Tunneling Microscopy, J. A. Helfrich, Shireen Adenwalla, J. B. Ketterson, G. A. Zhitomirsky
Characterization Of Piezoceramic Crosses With Large Range Scanning Capability And Applications For Low Temperature Scanning Tunneling Microscopy, J. A. Helfrich, Shireen Adenwalla, J. B. Ketterson, G. A. Zhitomirsky
Shireen Adenwalla Papers
We have developed a large amplitude piezoceramic scanner which should have numerous applications. Scanning tunneling microscopy (STM) and other scanning probe microscopies predominantly use piezoceramics for the scanning elements. Similarly adaptive optics, high resolution lithography, and micromanipulators are other examples of research which regularly utilize piezoceramic scanners. We present a new geometry for a piezoceramic scanner which allows for both high resolution (~nanometers) and large amplitude (~400 µm) displacements. The cross-shaped geometry makes it possible to produce extremely long pieces with very high tolerances. We have shown its effectiveness by using it as the major component of a low temperature …