Construction of a Cooling and Heating Substrate Holderfor the Preparation of Thin Films for Electron MicroscopyPHILIPP OTT AND JOHN RALPH GUNTER*Division of Chemical Electron Microscopy, Institute for Inorganic Chemistry, University of Zurich, CH-8057 Zurich, Switzerland

ABSTRACT The PVD preparation of thin, oriented films for electron microscopy of materialswith high adatom mobilities on the substrates requires cooling of the substrate holder. Theconstruction of such a holder for cooling the substrate to 250 and heating it to 500°C is described.Microsc. Res. Tech. 45:132–133, 1999. r 1999 Wiley-Liss, Inc.

INTRODUCTIONWe have recently been interested in preparing thin

films of tellurium as highly oriented or even singlecrystalline as possible. However, it has earlier beenshown by different authors (Saito et al., 1981; Weidmannand Anderson, 1971) that deposition of tellurium onrocksalt only yields polycrystalline or dendritic crystal-lites of tellurium. Tellurium adatoms have been demon-strated to have very high mobilities (Kalin, 1995;Weidmann and Anderson, 1971) on heated substrates.Therefore, we tried to cool the substrates during theevaporation. As no cooling holder was commerciallyavailable, we built such an attachment, able to bothcool the substrate to 250, and to heat it to 500°C,alternatively. With this holder, single crystalline tellu-rium films with thicknesses between 200 and 800 Å

were obtained by physical vapor deposition (PVD) onsingle crystals of sodium chloride (001).

CONSTRUCTION OF A SUBSTRATE HOLDERFOR COOLING AND HEATING

In order to get a usable substrate cooling and heatingholder for vacuum evaporation, an important require-ment is to be able to change its temperature sufficientlyfast, and, therefore, a material with a low heat capacityhas to be chosen. Figure 1 shows the construction ofsuch a holder. With the sandwich construction shown, it

*Correspondence to: John R. Gunter, Division of Chemical Electron Micros-copy, Institute for Inorganic Chemistry, University of Zurich, Winterthurer-strasse 190, CH-8057 Zurich, Switzerland.

Received 16 July 1998; accepted in revised form 2 November 1998

Fig. 1. Construction of the substrate holder (measures in mm).

MICROSCOPY RESEARCH AND TECHNIQUE 45:132–133 (1999)

r 1999 WILEY-LISS, INC.

is possible to renounce a gasket between the coolingtubes and the holder. The cooling tubes are made fromstainless steel and the sandwich plates of the holder ofaluminum. The two resistive heating devices have acapacity of 100 W each at 230 V. The upper temperatureis limited by the melting point (660°C) of aluminum.The lowest temperature depends on the cooling deviceattached to the tubes used for pumping through thecooling media (cooled nitrogen gas, ethanol, or liquidnitrogen).

RESULTS OF AN APPLICATIONTO TELLURIUM THIN FILMS

Thin films of tellurium were prepared in a newlyconstructed high vacuum coating system with a turbo-molecular pump and a liquid nitrogen cooled baffle.Thin tellurium films were deposited onto NaCl crystals(001), which were cleaved in air and treated with waterand chlorine gas to improve epitaxy (Safran et al.,1991). The substrate was mounted on the special holderdescribed above.

Before the deposition of the tellurium, the substratewas preheated to 70°C. Then it was cooled down to18°C. At this temperature, tellurium (99.99%) wassublimated onto the NaCl substrate. The depositionwas made in a vacuum of 5 3 1027 mbar. The films wereprepared in a thickness range of 200–800 Å. Thedeposition rate was 1.5 nm/s, monitored with an oscillat-ing quartz crystal. The films were wet stripped inwater, collected on copper grids covered with holeycarbon film, and investigated in the transmission elec-tron microscope (Fig. 2). In this way, single crystallinetellurium films could be prepared for the first time. Ottand Gunter are preparing a detailed report of theseresults for publication.

REFERENCESKalin W. 1995. Ph.D. Thesis, University of Zurich.Safran G, Geszti O, Barna PB, Gunter JR. 1991. Thin solid films.

198:333–338.Saito Y, Sato M, Shiojiri M. 1981. Thin solid films. 79:257–266.Weidmann EJ, Anderson JC. 1971. Thin solid films. 7:265–276.

Fig. 2. Electron micrograph of a single crystalline tellurim film (inset: diffraction pattern).

133COOLING AND HEATING SUBSTRATE HOLDER