COMPUTER-CONTROLLED PREPARATION OF THIN TUNGSTEN LAYERS

Tungsten layers of 1-6 mg/cm(2) with diameters of 10 mm are needed as heavy-ion targets and as flat or domed windows for in-beam ion sources . They are prepared by a high-vacuum evaporation-deposition process ca rried out in a computer-controlled apparatus. The tungsten, placed in the water-cooled crucible of an electron-beam gun, is gradually healed and evaporates at about its melting point (T-m = 3643 K). The tungste n is deposited onto 9 mg/cm(2) copper backings which are preheated by the thermal radiation from the evaporant. The deposition rate is contr olled by a quartz crystal monitor. After the high-vacuum deposition pr ocess, the copper backings are removed by selective etching and the se lf-supported tungsten foils are characterized by their areal mass. The features of the commercially available evaporation unit used are disc ussed by way of this deposition process.