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 measurements of UV photoemission. As a sample substrate, we used a thin (10 μm) copper sheet supported by two wires for optimal thermal resistivity. The performance of the apparatus was examined using a 650-Å-thick pentacontane (n-C50H102) film, which may exhibit a unique monolayer phase transition 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 melting. Since the temperature dependence of the surface specific UV photoemission measurements showed corresponding changes in photoemission current, we could conclude that the other phase transition peak originates from the surface freezing effect. This demonstrates that our DTA-UV apparatus is sufficiently sensitive to examine such monolayer phase transitions.
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