Surface compositions and composition profiles of AgAu (100), (110), and (111) surfaces determined quantitatively by Auger electron spectroscopy

Surface segregation from gold alloys

“…For the Ag-Au (62,69) and Pd-Au (68) alloys a number of experimental studies indicate that no surface segregation occurs, in contradiction with other experimental data for Ag-Au alloys (57,75,76,83,84), PdAu alloys (79), and Pt-Au alloys (81,85) as well as most theoretical models. This absence of segregation may be due to a lack of thermodynamic equilibrium (69) or substantial preferential sputtering of Au atoms from the surface (68).…”

“…Both these methods, however, may leave the surface with a number of defects or in a condition that does either thermodynamic or chemical not represent where vX is the pre-exponential function (dependent on the equilibrium. Most alloys containing gold that have been used in surface segregation studies were prepared by melting the constituent metals together (26, 54, 56-57, 62-63, 67-68, 73-77), polishing, typically using diamond or alumina grit down to 1 pm grit size or less (51,54,56,57,77,78), chemically treating (74,75,79), and annealing (56,62,63,67,68,73,74,76,79). Chemical treatments were often combined with the annealing of the gold alloy samples since the samples were not always annealed in just vacuum (63,73), or argon (62,74,76,77), but in hydrogen (68,75,77,80) and oxygen (79,81) as well.…”

“…The segregation (76), or absence of segregation (75), in Ag-Au alloys at the selvedge is a controversy that may be resolved by theory. Selvedge segregation has been observed in Cu-Ni alloys (23,87,88) and present theories have not satisfactorily predicted this phenomenon.…”

“…Selvedge segregation has been observed in Cu-Ni alloys (23,87,88) and present theories have not satisfactorily predicted this phenomenon. For some gold-silver alloys, there is an observed depletion from the second layer of silver (75), while silver segregates to the surface. Since silver is enriched at the first layer, this corresponds to the oscillatory profile expected for ordering alloys (see Section 2.2 and Figure 2 for the regular solution model with Il < 0).…”

“…Since silver is enriched at the first layer, this corresponds to the oscillatory profile expected for ordering alloys (see Section 2.2 and Figure 2 for the regular solution model with Il < 0). There exists evidence that Ag-Au alloys are ordered alloys (75), but there is also evidence indicating these alloys are clustering alloys (76) if the regular solution model is used as an indication of their behaviour.…”