SHOCKLEY-TYPE SURFACE STATES ON THE (111) AND (110) SURFACES OF Cu-BASED ALLOYS WITH NOBLE AND TRANSITION METAL IMPURITIES

Abstract

We have investigated Shockley-type surface states (SSS's) on ideal semi-infinite surfaces of randomly disordered alloys, Cu 70 Ni 30, Cu 80 Ni 20, Cu 90 Ni 10, Cu 85 Pd 15, Cu 95 Pd 5, and Cu 90 Au 10 using a Green's function approach. In particular, the binding energies and disorder induced smearings of the [Formula: see text]-centered SSS's on the (111) surfaces and the [Formula: see text]-centered SSS's on the (110) surfaces of these alloys are presented. Our theoretical predictions are in good accord with the available angle-resolved photoemission measurements, although the experimental results in this regard for well-characterized alloy surfaces appear to be limited to the (111) surfaces of CuPd and CuAu solid solutions. The binding energy of the SSS's is found to decrease roughly linearly with decreasing e/a ratio, but significant deviations from such a rigid-band behavior are noted for various impurities. The SSS's investigated in this article lie in the [Formula: see text] gap in the bulk alloy electronic spectrum, and their character (changes in binding energy on alloying, and disorder induced smearing) is correlated with that of the L2′ bulk level.