  A sputter deposition source for use in ultrahigh vacuum (UHV) is described
and some properties of the source are analyzed. The operating principle is
based on the design developed by Mayr et al. [Rev. Sci. Instrum. 84, 094103
(2013)], where electrons emitted from a filament ionize argon gas, and the
Ar$^+$ ions are accelerated to the target. In contrast to the original design,
two grids are used to direct a large fraction of the Ar$^+$ ions to the target,
and the source has a housing cooled by liquid nitrogen to reduce
contaminations. The source has been used for deposition of zirconium, a
material that is difficult to evaporate in standard UHV evaporators. At an Ar
pressure of $9\times 10^{-6}$ mbar in the UHV chamber and moderate emission
current, a highly reproducible deposition rate of $\approx 1$ monolayer in 250
s was achieved at the substrate (at a distance of $\approx 50$ mm from the
target). Higher deposition rates are easily possible. X-ray photoelectron
spectroscopy shows a high purity of the deposited films. Depending on the grid
voltages, the substrate gets mildly sputtered by Ar$^+$ ions; in addition, the
substrate is also reached by electrons from the negatively biased sputter
target.
