A new UHV variable temperature STM for gas adsorption studies

A new UHV variable temperature STM has been constructed. A "beetle type" STM is coupled with a Liquid Helium cryostat, allowing us to vary the sample temperature in the range 60-500 K. The base pressure in the UHV chamber is 10(-10) mbar. The STM is able to obtain atomic resolution on metal surfaces such as Ag(110). The Z-piezo parameters to correct the intrinsic distortion have been calculated. This apparatus is used to study gas adsorption on metal surfaces. As an example, we present recent results on the O-2-Ag(110) system. At room temperature, we observe the well known (n x 1) structures, with the Ag-O rows growing along the <001> direction. At low temperatures, the O-2 molecules are first randomly adsorbed on the surface, but at increasing coverage they are organised in short rows (approximate to 50 Angstrom) along the <1(1) over bar0$> direction. (C) 1997 Elsevier Science Ltd.