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 × 1) structures, with the Ag-O rows growing along the ＜ O01 ＞ 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 (≈ 50 #) along the ＜110 ＞ direction. # 1997 Elsevier Science Ltd. All rights reserved
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