Ultrathin-film differential-thermal-analysis apparatus with simultaneous photoemission measurements

We developed an apparatus of differential thermal analysis (DTA) capable of simultaneous surface specific ultraviolet (UV) photoemission measurements to investigate thin-film phase transitions. The apparatus was installed in a vacuum chamber of 10(-6) Torr range for thermal isolation and the measure ments of UV photoemission. As a sample substrate, we used a thin (10 mu m) copper sheet supported by two wires for optimal thermal resistivity. The pe rformance of the apparatus was examined using a 650-Angstrom-thick pentacon tane (n-C50H102) film, which may exhibit a unique monolayer phase transitio n known as surface freezing. We observed two anomalies of DTA curve around the bulk melting temperature, one of which is apparently due to the bulk me lting. Since the temperature dependence of the surface specific UV photoemi ssion measurements showed corresponding changes in photoemission current, w e could conclude that the other phase transition peak originates from the s urface freezing effect. This demonstrates that our DTA-UV apparatus is suff iciently sensitive to examine such monolayer phase transitions. (C) 2000 Am erican Institute of Physics. [S0034-6748(00)05103-0].