Specimen heating during sputter‐coating

Abstract

It is possible to sputter thin films of gold on to surfaces of frozen biological specimens at very low temperatures ( < 120 K) without untoward effects from heating. This is achieved by using permanent magnets to confine the plasma and thus to minimize the energy required to give a reasonable sputtering yield. The system described uses only 250 V at 12-15 mA to give 15 nm films within 2-3 min. It is shown, from theory portraying 'worst-case' conditions, that the specimen temperature could not increase by more than 6.0 K at equilibrium. Practical results support the theoretical assumptions. Similar considerations have been applied to sputtering at normal ambient temperature where it is shown that appropriate design of simple apparatus and selection of operational conditions can give adequate films in a reasonable time with negligible (< 3 K) temperature rise above the starting temperature.

Very low voltage sputter coating

“…Earlier studies by Echlin et al (1980Echlin et al ( , 1982, Echlin (1981), Robards et al (1981 and Nockolds et al (1982) have shown that there is a decrease in thin film particle size and hence an increased spatial resolution on specimens, if sputter coating is carried out at decreased cathode voltages. The earlier studies were carried out in the range 400-2000 V (Echlin et al, 1982), 250-760 V (Robards et al, 1981) and 200-350 V (Nockolds et al, 1982) and in all instances it was found that as the cathode voltage was lowered there was also a decrease in the potential thermal load into the specimen. These procedures allowed thermolabile specimens such as low melting point hydrocarbon waxes, plastic films and frozen hydrated specimens to be coated without any apparent damage to the samples.…”

Ion beam‐sputtered and magnetron‐sputtered thin films on cytoskeletons: A high‐resolution tem study

“…This can in turn distort the morphology of the specimens as demonstrated with polymer substrates (Bodo and Sundgren 1986). According to some authors (Echlin 1978, Ingram 1976, Robards 1981, another source of heat damage is radiation from the target. This heat, which is of long wavelength, could only damage a specimen which is placed quite close to the target.…”