A differential thermal analysis and ultraviolet photoemission study on surface freezing of n-alkanes

The surface-freezing effect of pentacontane (n-C50H102) and tetratetracontane (n-C44H90) films evaporated on a copper substrate has been investigated by differential thermal analysis (DTA) simultaneously with measurements of surface-specific ultraviolet (UV) photoemission. Two anomalies in the DTA curve were observed near the bulk melting temperature, one of which has been attributed to bulk melting. Since the temperature dependence of the surface-specific UV photoemission measurement showed a corresponding stepwise increase and decrease in the photoemission current at the two anomalies observed in the DTA, we have concluded that the other phase transition peak originates from surface freezing.