  This Letter reports an anomaly of film porosity dependence on deposition rate
during physical vapor deposition - the porosity increases as deposition rate
decreases. Using glancing angle deposition of Cu on SiO2 substrate, the authors
show that the Cu film consists of well separated nanorods when the deposition
rate is 1 nm/second, and that the Cu films consists of a more uniform (or lower
porosity) film when the deposition rate is 6 nm/second; all other deposition
conditions remain the same. This anomaly is the result of interplay among
substrate non-wetting, density of Cu nuclei on the substrate, and the minimum
diameter of nanorods.
