Sputter shadowing improved by using a tungsten target.

This work builds upon a previous paper (W. Colquhoun, 1984, J. Ultrastruct. Res. 87, 97) in which a sputter shadowing device was briefly described. The device allowed TEM specimens to be shadowed in a conventional sputter coater. Images obtained by sputter shadowing with a standard Au/Pd target were of good quality but were slightly inferior to the best that could be obtained by e--beam evaporation of tungsten. Here we show that construction and use of a tungsten target greatly improves the quality of the sputter shadowed deposit. Images of DNA and ribosomal subunits contrasted by sputter shadowing with tungsten are shown. The DNA images indicate that sputter shadowing with tungsten is a gentle contrasting technique. The sputter shadowed images of the 30 S ribosomal subunits show the major features of the particle revealed by evaporation shadowing using the most sophisticated of methods in that technology. Advantages of sputter shadowing are discussed and a rationale for the improved grain obtained by sputtering tungsten is suggested.