Time-dependent melting and superheating of lead crystallites

Reflection high-energy electron-diffraction study of melting and solidification of Pb on graphite

“…1 Spiller deposited 5 and 50 Å of Pb on to a graphite substrate at 470 K in a low vacuum of 10 Ϫ7 Torr. Spiller found some irregularly shaped particles without sharp corners, in the 50-Å thin film, to superheat by 2 K. 2 The superheating we observe is much larger than that observed in fully annealed Pb layers previously investigated by SEM. This difference can be attributed to the localized heating effects of the electron beam of the SEM and sample preparation.…”

“…[1][2][3] Métois and Heyraud were able to produce a large number of polyhedral Pb crystallites on graphite in an ultrahigh vacuum scanning electron microscope ͑UHV-SEM͒. Of these, the sharp edged Pb crystallites with extensive ͕111͖ facets were seen to superheat by 3 K. The formation of ͕111͖ facets near the melting point were confirmed by SEM studies.…”

“…This difference can be attributed to the localized heating effects of the electron beam of the SEM and sample preparation. The electron-beam intensity of the SEM is much higher than that of the RHEED beam, thus localized heating due to this beam is significant, being as high as 40 K. 2 Spiller estimates the temperature rise to be 0.5 K on account of the high thermal conductivity of the substrate, neglecting the interface mismatch between the substrate and the film, the presence of domain boundaries, and defects in thin-film layers that may contribute to a decrease in the thermal conductivity. Thus, there may be a difference between the measured and the real values, and that this could explain the discrepancy between our results and those obtained previously.…”

“…This result is in agreement with results obtained by Spiller and Pavlovska, Faulian, and Bauer. 2,21 In SEM observations, Spiller showed that at 598 K, some liquid particles were present. Pavlovska, Faulian, and Bauer observed a bright ring surrounding the ͕111͖ facet above 580 K that shrank and disappeared at T m .…”

“…Of these, the sharp edged Pb crystallites with extensive ͕111͖ facets were seen to superheat by 3 K. The formation of ͕111͖ facets near the melting point were confirmed by SEM studies. 1,4 Spiller observed superheating of irregularly shaped Pb microcrystallites by 2 K. These were obtained by depositing 5-and 50-Å thick films of Pb onto a graphite substrate at 470 K. 2 The sample was prepared in a low vacuum (10 Ϫ7 Torr) and observed in situ using SEM. Recent theoretical calculations predicted that surface superheating is related to the partial wetting angle of the surface, and the tilt angle of the melted regions in a vicinal surface undergoing nonmelting induced faceting.…”