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

Abstract

A comparison of ion beam‐sputtered and magnetron‐sputtered thin platinum (Pt) and tungsten (W) films was made. Cytoskeletons from detergent extracted glioma cells grown on gold grids were coated with Pt or W at thicknesses of 1, 1.5, and 2.5 nm. Transmission electron micrographs were taken at high magnification and the granularity of the metal films was evaluated both on the Formvar film and the filaments of the cytoskeleton. In order to make a comparison between the two deposition methods, the metal deposition rate must be equal when corresponding thicknesses are made. Since ion beam sputtering generally is a slower process than magnetron sputtering, an increased target to specimen distance was necessary with the latter technique. This resulted in a coarser granularity of the W films as compared with the ion beam sputtered. The Pt, however, showed no marked difference between the two techniques at equal deposition rates. The study also demonstrated that varying the deposition rate caused differences in the granularity of the magnetron‐sputtered Pt and W films, even if the voltage of the target was kept constant. Decreasing the target to specimen distance which increased the deposition rate resulted in a finer granularity of both the Pt and the W films. At the highest deposition rate the granularity of both the Pt and W films was comparable with the granularity of the ion beam‐sputtered films.

Preservation and visualization of molecular structure in detergent‐extracted whole mounts of cultured cells

“…Increasing the deposition rate increases the number of initial metal atoms that can serve as nucleation sites, thus resulting in a decreased grain size (Lewis and Anderson, 1978;Muller, 1985). We have clearly demonstrated this relationship experimentally using magnetron and ion beam sputter coating (Lindroth and Sundgren, 1989). Decreasing the target to specimen distance in a magnetron sputter coater while keeping other parameters such as vacuum conditions and current constant, increases the deposition rate while decreasing the granularity of Pt and W films.…”

“…(Panayi et al, 1977;Echlin, 1978Echlin, ,1981Echlin and Kaye, 1979;Peters, 1980Peters, , 1986cNockolds et al, 1982;Lindroth and Sundgren, 1989). Potential contaminants include oilbackstreaming from both the rotary pump and the oil diffusion pump, hydrocarbons and water present in the Argon gas, and water from various sources (Peters, 1980Nockolds et al, 1982).…”

“…The method that we use to visualize detergent-extracted cells by EM is to sputter coat thein with a very thin film of metal (Bell et al, 1987a;Lindroth et al, 1987;Lindroth and Sundgren, 1989). This approach has several advantages: it permits us to examine the same or similarly prepared samples by TEM, SEM, and STEM; is not limited to thin areas (as is negative staining); it permits observation throughout the entire thickness of the extracted cell (unlike negative staining or replication); and it can be combined with immunocytochemistry and immunogold labeling.…”

“…The resulting irregularity of the metal coat can obscure underlying structures and reduces the ability of the microscope to resolve fine structural details. (Peters, 1986c;Lindroth and Sundgren, 1989).…”

“…Because the mobility of deposited metal atoms is related to their melting point, to form metal films that are fine-grained one must use metals such as tungsten (W), tantalum (Ta), and niobium (Nb) which, because of their high melting points are called refractory metals. Unlike the low melting point metals such as Au, AufPd, and Pt which can be deposited by vacuum-evaporation, refractory metals have to be deposited with other methods such as electron beam evaporation (Slayter, 19801, Penning sputtering (Peters, 1980, 1985a,b, 1986a, magnetron sputtering (Nockolds et al, 1982;Bell et al, 1987aBell et al, , 1988Lindroth et al, 1987Lindroth et al, , 1988Lindroth and Sundgren, 1989) or ion beam sputtering (Jacopic et al, 1978;Geller et al, 1979;Franks et al, 1980;Clay and Peace, 1981;Evans and Franks, 1981; Kemmenoe and Bullock, 1983;Lindroth and Sundgren, 1989). The two most widely used methods for depositing refractory metals and the ones with which we have experience are magnetron and ion beam sputtering.…”