Thin film quantum size effects: II. The effect of defect structure at the film / substrate interface

Abstract

We have investigated the effect of atomic impurities and structural defects at the film/substrate interface on the quantum size oscillations observed in retarding potential measurements of the sample current versus normally incident electron energy for thin epitaxial (111) Cu and Ag films on W(110). The quantum size oscillations are sensitive to the structural order of the film/substrate interface itself and are capable of providing a relative indication of interface structural perfection. The quantum size effect (QSE) amplitude is significantly reduced for small amounts of carbon at the Cu/W interface, while oxygen on the substrate surface severely inhibits epitaxial growth. Using the W(110) LEED (00) beam width as an index of substrate surface roughness produced by mild ion bombardment prior to film deposition, we find that the QSE amplitude decreases linearly by 70% for monatomic step atom densities ranging from 1% to 3% at the Cu/W interface. The QSE measurements further indicate that annealing does not measurably improve the structure of the Cu/W interface via a reduction in open-volume defect density before islanding of the film occurs.