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Equilibrium segregation to terraces and steps
A48 Surface Science 150 (1985) 289-301 North-tiolland, Amsterdam EQUILIBRIUM Paul WYNBLATT
SEGREGATION
289 TO TERRACES
AND
STEPS
and Daniel A. STEIGERWALD
Department of Metallurgwal Engineering and Materials Science. Carnegie .. Mellon Unit'er~tty. Pittsburgh. Penn,~vh,ania 15213. USA Received 10 July 1984; accepted for publication 18 October 1984 A method based on empirical interatomic potentials has been developed to calculate energies of segregation to low index (001) surfaces as well as to [110] and [100] steps on a (001) surface in simple (AB) binary alloys. The Baskes and Melius potentials have been used to model the A - A and B - B atomic interactions and a procedure has been outlined to derive an A - B interaction from the pure metal potentials. This approach has been used to compute the energy of segregation of gold, in an infinitely dilute nickel-gold alloy, to both terraces and steps. The results obtained are consistent with previous measurements of the anisotropy of surface segregation in that alloy.
302 INHOMOGENEOUS
Surface Science 150 (1985) 302- 318 North-Holland, Amsterdam STRAINS
IN SMALL
PARTICLES
L.D. MARKS
Department of Physics, Arizona State Universi(v. Tempe, Arizona 85287, USA Received 12 July 1984; accepted for publication 23 October 1984 This paper considers the evidence for strains in small particles. Firstly, the dynamical electron diffraction theory for dark field imaging of small particles is briefly reviewed, considering primarily the effects of strain on wedge crystals and identifying the fingerprint of strain contrast effects under strong beam conditions. Evidence included herein and from published papers by other authors clearly shows inhomogeneous strain effects in both multiply twinned particles and single crystals. Considering these results and earlier reports of lattice parameter changes, there are problems with the uniqueness of these analyses, and the strains in the small single crystals are thought more likely to be due to interfacial stresses or contaminants than any intrinsic particle effect; there are so m a n y different origins of this type of strain that we cannot with confidence isolate a unique source. It is emphasised that the uniqueness of any interpretation of experimental results from small particles must be very carefully considered.
Surface Science 150 (1985) 319-338 North-Holland, Amsterdam
319
ADSORPTION AND DECOMPOSITION
OF
H20
ON
A K-COVERED
PI(I 1 I) SURFACE M. KISKINOVA
*, G . P I R U G
and H.P. BONZEL
**
lnstitut fur Grenzfli~chenforschung und Vakuumphysik. Kernforschungsanlage Ji~lich GmbH, Postfach 1913, D-5170 Jiilich, Fed. Rep. of Germany Received 19 July 1984; accepted for publication 16 October 1984 The adsorption of H 2 0 on clean and K-covered Pt(111) was investigated by utilizing Auger, X-ray and ultra-violet photoemission spectroscopies. The adsorption on Pt(111) at 100-150 K was
SEGREGATION
289 TO TERRACES
AND
STEPS
and Daniel A. STEIGERWALD
Department of Metallurgwal Engineering and Materials Science. Carnegie .. Mellon Unit'er~tty. Pittsburgh. Penn,~vh,ania 15213. USA Received 10 July 1984; accepted for publication 18 October 1984 A method based on empirical interatomic potentials has been developed to calculate energies of segregation to low index (001) surfaces as well as to [110] and [100] steps on a (001) surface in simple (AB) binary alloys. The Baskes and Melius potentials have been used to model the A - A and B - B atomic interactions and a procedure has been outlined to derive an A - B interaction from the pure metal potentials. This approach has been used to compute the energy of segregation of gold, in an infinitely dilute nickel-gold alloy, to both terraces and steps. The results obtained are consistent with previous measurements of the anisotropy of surface segregation in that alloy.
302 INHOMOGENEOUS
Surface Science 150 (1985) 302- 318 North-Holland, Amsterdam STRAINS
IN SMALL
PARTICLES
L.D. MARKS
Department of Physics, Arizona State Universi(v. Tempe, Arizona 85287, USA Received 12 July 1984; accepted for publication 23 October 1984 This paper considers the evidence for strains in small particles. Firstly, the dynamical electron diffraction theory for dark field imaging of small particles is briefly reviewed, considering primarily the effects of strain on wedge crystals and identifying the fingerprint of strain contrast effects under strong beam conditions. Evidence included herein and from published papers by other authors clearly shows inhomogeneous strain effects in both multiply twinned particles and single crystals. Considering these results and earlier reports of lattice parameter changes, there are problems with the uniqueness of these analyses, and the strains in the small single crystals are thought more likely to be due to interfacial stresses or contaminants than any intrinsic particle effect; there are so m a n y different origins of this type of strain that we cannot with confidence isolate a unique source. It is emphasised that the uniqueness of any interpretation of experimental results from small particles must be very carefully considered.
Surface Science 150 (1985) 319-338 North-Holland, Amsterdam
319
ADSORPTION AND DECOMPOSITION
OF
H20
ON
A K-COVERED
PI(I 1 I) SURFACE M. KISKINOVA
*, G . P I R U G
and H.P. BONZEL
**
lnstitut fur Grenzfli~chenforschung und Vakuumphysik. Kernforschungsanlage Ji~lich GmbH, Postfach 1913, D-5170 Jiilich, Fed. Rep. of Germany Received 19 July 1984; accepted for publication 16 October 1984 The adsorption of H 2 0 on clean and K-covered Pt(111) was investigated by utilizing Auger, X-ray and ultra-violet photoemission spectroscopies. The adsorption on Pt(111) at 100-150 K was