Temperature-dependent vacancy formation during the growth of Cu on Cu(001)

X-ray diffraction measurements show that a large number of vacancies are incorporated in thin Cu films grown on Cu(001) at low temperatures. At any given deposition temperature between 110 and 160 K, the vacancy concentration c(v), obtained from reflectivity data, does not change with the coverage Theta, for 2.5 MLless than or equal toThetaless than or equal to20 ML. However, c(v) is temperature dependent: for 15-ML-thick films, grown at different temperatures, it monotonically decreases with increasing T from c(v)approximate to2% at 110 K to zero at T=160 K. A different "c(v) vs T" dependence is observed for films grown at 110 K and then annealed at progressively higher temperatures. Here c(v)approximate to2% persists over a broad temperature interval (between 110 and 200 K) and c(v) exhibits a slower decrease upon heating, reaching zero at 300 K.