Direct observation of atomic exchange during surface self-diffusion

Some metallic adsorbed atoms on fcc metal surfaces can exchange with substrate atoms well below the room temperature. For homogeneous systems, the atomic exchange is a mechanism for self-diffusion. For heterogeneous systems, it is a mechanism for point alloy formation of only the top surface layer but it will also induce self-diffusion. We present experimental evidence found from FIM, HREELS and LEIS studies. These experiments and their relations to available theories and molecular dynamic simulations of this phenomenon are also mentioned. In addition, we present evidence for the ascending motion of step edge atoms to the upper terrace for the Ir (111) surface, and the result of a measurement of the potential barrier height of the ascending motion and the dissociation energy of step edge atoms to the lower terrace.

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DIRECT OBSERVATION OF RAPID SELF‐DIFFUSION ALONG DISLOCATIONS IN ALUMINUM

Applied Physics Letters ◽

10.1063/1.1755125 ◽

1967 ◽

Vol 11 (8) ◽

pp. 259-261 ◽

Cited By ~ 18

Author(s):

T. E. Volin ◽

R. W. Balluffi

Keyword(s):

Direct Observation ◽

Self Diffusion

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Direct Observation of the Self-Diffusion Mechanism on the Ag(100) Surface

Physical Review Letters ◽

10.1103/physrevlett.81.4680 ◽

1998 ◽

Vol 81 (21) ◽

pp. 4680-4683 ◽

Cited By ~ 15

Author(s):

M. F. Roşu ◽

C. R. Laurens ◽

A. Falepin ◽

M. A. James ◽

M. H. Langelaar ◽

...

Keyword(s):

Direct Observation ◽

Diffusion Mechanism ◽

The Self ◽

Self Diffusion

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Surface Self-Diffusion on Pt(001) by an Atomic Exchange Mechanism

Physical Review Letters ◽

10.1103/physrevlett.65.939.2 ◽

1990 ◽

Vol 65 (7) ◽

pp. 939-939 ◽

Cited By ~ 3

Author(s):

G. L. Kellogg ◽

Peter J. Feibelman

Keyword(s):

Exchange Mechanism ◽

Self Diffusion ◽

Atomic Exchange

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Direct Observation of Heat Exchanger Deposits by Cross Sectioning

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100061835 ◽

1967 ◽

Vol 25 ◽

pp. 364-365

Author(s):

R. W. Anderson ◽

D. L. Senecal

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Heat Exchanger ◽

Direct Observation ◽

Cross Sections ◽

Preparation Method ◽

Specimen Preparation ◽

Flowing Water ◽

Transmission Electron ◽

Deposit Layer

A problem was presented to observe the packing densities of deposits of sub-micron corrosion product particles. The deposits were 5-100 mils thick and had formed on the inside surfaces of 3/8 inch diameter Zircaloy-2 heat exchanger tubes. The particles were iron oxides deposited from flowing water and consequently were only weakly bonded. Particular care was required during handling to preserve the original formations of the deposits. The specimen preparation method described below allowed direct observation of cross sections of the deposit layers by transmission electron microscopy.The specimens were short sections of the tubes (about 3 inches long) that were carefully cut from the systems. The insides of the tube sections were first coated with a thin layer of a fluid epoxy resin by dipping. This coating served to impregnate the deposit layer as well as to protect the layer if subsequent handling were required.

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Application of a Simple Cold Stub to the Direct Observation of Frozen Hydrated Sand

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100071508 ◽

1973 ◽

Vol 31 ◽

pp. 212-213

Author(s):

John M. Wehrung ◽

Richard J. Harniman

Keyword(s):

United States ◽

Surface Water ◽

Direct Observation ◽

Controlled Study ◽

Clay Particles ◽

Organic Debris ◽

Rock Formations ◽

Water Tables ◽

Permeable Rock ◽

Natural Means

Water tables in aquifer regions of the southwest United States are dropping off at a rate which is greater than can be replaced by natural means. It is estimated that by 1985 wells will run dry in this region unless adequate artificial recharging can be accomplished. Recharging with surface water is limited by the plugging of permeable rock formations underground by clay particles and organic debris.A controlled study was initiated in which sand grains were used as the rock formation and water with known clay concentrations as the recharge media. The plugging mechanism was investigated by direct observation in the SEM of frozen hydrated sand samples from selected depths.

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Direct Observation of the Diffusionless β → β + ω Transformation in Titanium Alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100064669 ◽

1971 ◽

Vol 29 ◽

pp. 122-123

Author(s):

N. E. Paton ◽

D. de Fontaine ◽

J. C. Williams

Keyword(s):

Electron Microscope ◽

Titanium Alloys ◽

Direct Observation ◽

Dark Field ◽

X Ray Diffraction ◽

Resistivity Measurements ◽

Selected Area Electron Diffraction ◽

Ti Alloys ◽

Thin Foils ◽

Field Device

The electron microscope has been used to study the diffusionless β → β + ω transformation occurring in certain titanium alloys at low temperatures. Evidence for such a transformation was obtained by Cometto et al by means of x-ray diffraction and resistivity measurements on a Ti-Nb alloy. The present work shows that this type of transformation can occur in several Ti alloys of suitable composition, and some of the details of the transformation are elucidated by means of direct observation in the electron microscope.Thin foils were examined in a Philips EM-300 electron microscope equipped with a uniaxial tilt, liquid nitrogen cooled, cold stage and a high resolution dark field device. Selected area electron diffraction was used to identify the phases present and the ω-phase was imaged in dark field by using a (101)ω reflection. Alloys were water quenched from 950°C, thinned, and mounted between copper grids to minimize temperature gradients in the foil.

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A New 1000kv Electron Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100062415 ◽

1969 ◽

Vol 27 ◽

pp. 100-101

Author(s):

J.L. Williams ◽

K. Heathcote ◽

E.J. Greer

Keyword(s):

Electron Microscope ◽

Direct Observation ◽

High Voltage ◽

Three Dimensional ◽

Dimensional Structure ◽

Specimen Thickness ◽

Voltage Electron ◽

High Voltage Electron Microscope ◽

Dynamic Experiments ◽

Conventional Instrument

High Voltage Electron Microscope already offers exciting experimental possibilities to Biologists and Materials Scientists because the increased specimen thickness allows direct observation of three dimensional structure and dynamic experiments on effectively bulk specimens. This microscope is designed to give maximum accessibility and space in the specimen region for the special stages which are required. At the same time it provides an ease of operation similar to a conventional instrument.

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Direct Observation of Monolayer Zones in Al-wt 4% Cu

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100178823 ◽

1990 ◽

Vol 48 (1) ◽

pp. 14-15

Author(s):

B. Jouffrey ◽

D. Dorignac ◽

A. Bourret

Keyword(s):

Solid Solution ◽

Synchrotron Radiation ◽

Direct Observation ◽

Supersaturated Solid Solution ◽

Original Model ◽

X Ray ◽

Image Position

Since the early works on GP zones and the model independently proposed by Preston and Guinier on the first steps of precipitation in supersaturated solid solution of aluminium containing a few percent of copper, many works have been performed to understand the structure of different stages in the sequence of precipitation.The scheme which is generally admitted can be drawn from a work by Phillips.In their original model Guinier and Preston analysed a GP zone as composed of a single (100) copperrich plane surrounded by aluminum atomic planes with a slightly shorter distance from the original plane than in the solid solution.From X-ray measurements it has also been shown that GP1 zones were not only copper monolayer zones. They could be up to a few atomic planes thick. Different models were proposed by Guinier, Gerold, Toman. Using synchrotron radiation, proposals have been recently made.

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