Ralf VaneslowRalf Vanselow

Professor Emeritus

Phone: 414-229-
e-mail: rvans@uwm.edu

Degree(s):

Ph.D., Technische Universität Berlin, Germany

Research Description:

Professor Vanselow's research program is concerned with the investigation of solid surfaces by means of field-electron (FEM) and field-ion microcopy (FIM). Included are studies of surface segregation, face specific adsorption and adsorbate dissociation on metal single crystal planes, nucleation, epitaxial growth, surface migration, and surface roughening on ultrapure metal surfaces.

Using a combination of FEM and very high resolution AES, the surface segregation of Pt impurities (in particular, C and Si) have been studied in detail. The temperature ranges in which segregation occurs, crystal areas in which impurities precipitate, as well as the chemical nature of the impurities, could all be determined. The adsorption and dissociation of CO has been studied on Pt and Rh.

The most recent investigations deal with roughening transitions. In their pioneering paper on surface roughening transitions, Burton and Cabrera predicted in 1949 an accelerated crystal growth at temperatures above the transition temperature, Tc. Two years later, however, they had to qualify their prediction: "The existence of a transition temperature will not have any influence on the kinetics of growth of the crystal surface. It would if the crystal were perfect". This modification was necessary because of the proposed dominance of spiral growth in the case of real crystals. Yet, the statement also implied that the effect of roughening transitions on growth kinetics could be observed if perfect (dislocation free) surface conditions could be generated in the measured surface area.

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Fig. 1. Drastic growth rate increases on tantalum at 800K and 860K caused by roughening transitions.

Such conditions can be obtained on the sample crystals of FEM's. The number of dislocations in these rounded microcrystallites is so small that the probability of their interference with the growth of a specific surface area (hk1) is minimal. Studying with FEM the vapour self-growth in the vicinal areas of Ta{110} and Ta{100} as a function of crystal temperature, precipitous increases of the growth rate could indeed be discovered at 800K and 860K, the respective transition temperatures. The measurements were carried out on clean, thermally rounded Ta microcrystallites and later extended to Rh{111} and Rh[110}.

Selected Publications:

"Accelerated Vapor Growth Caused by Roughening Transitions in the Vicinal Areas of Rh{111} and Rh{110}.", R. Vanselow and X.Q.D. Li, Surface Sci. 301, L229-L234 (1994).

"Roughening Transitions in the vicinal Areas of Ta{110} and Ta {100} Observed during Vapour Growth on Clean, Thermally Rounded Ta Crystallities", R. Vanselow and X.Q.D. Li, Surface Sci. 281, L326 (1993).

"Thermal Roughening of FEM-Clean Pt{110} and Its Vicinal Areas," R. Vanselow, Surface Sci. 279, L213 (1992).

"The Work Function of Kinked Areas on Clean, Thermally Rounded Pt and Rh Crystallites: Its Dependence on the Strucutre of Terraces and Edges," R. Vanselow and X.Q.D. Li, Surface Sci. 264, L200 (1992).

"CO Dissociation Activities of Clean Pt{430}, {320}, {520}, {310}, {410} and {210}: A Comparison with the Predictions of Banholzer's Orbital Symmetry Model," R. Vanselow, Catal. Letters 10, 19 (1991).

Chemistry and Physics of Solid Surfaces, Vol. VIII, R. Vanselow and R. Howe, Springer Verlag, Berlin Heidelberg New York Tokyo (1990).