Time-resolved valence band photoelectron spectroscopy of liquid AuSn

Abstract

The solid-liquid-solid-phase transitions of a Au 50 Sn 50 alloy have been investigated by means of the recently developed method of time-resolved photoelectron spectroscopy, using dye laser pulses to melt the sample surface on a microsecond scale. Starting at a temperature of the liquid sample just above the melting point (740 K), the laser pulse heating allowed us to obtain, for the first time, valence band spectra of an alloy at temperatures of up to 1620 K, distinctly above the vapour pressure limit of steady-state photoelectron spectroscopy. The photoemission results of the liquid at different temperatures are compared with data from the corresponding amorphous alloy, prepared by vapour condensation at liquid-nitrogen temperature. By increasing the temperature of the disordered phase, the Au 5d band is found to shift continuously toward a lower binding energy, showing a linear behaviour over the whole temperature range. Our measurements confirm earlier results obtained with conventional photoemission within a restricted temperature range. The results presented here clearly show the potential of the new technique to investigate the electronic structure of alloys at conditions under which standard photoemission experiments cannot be performed.

Electronic structure of liquid tungsten studied by time-resolved photoelectron spectroscopy

“…Another effect which has to be considered when discussing differences in the electronic structure of transition metals over a broad range of temperatures are intrinsic thermal binding energy shifts of valence band and core electron states due to mass density changes caused by the large temperature variations. d-band and core state binding energy shifts have been observed and determined before in Au, Au-Sn alloys and in Pd-Bi alloys [9,22,24]. For W we have found a binding energy shift of −0.35 meV/K for the peak located near 1.8 eV (fig.…”

“…Our approach to study liquid transition metals by PES is a dynamic method based on melting of a surface layer by laser pulses combined with simultaneous continuous irradiation with UV or X-ray irradiation and time-resolved counting of photoelectrons [7][8][9][10]. This method makes it possible to study samples with very high vapor pressures and evaporation rates.…”

“…No theoretical studies to the liquid phase of W have been published so far to our knowledge. TR-PES has been applied previously to liquid Si and Ge [7], liquid Au-Sn alloys [9] and some transition metals [10].…”

Electronic structure of liquid transition metals studied by time resolved photoelectron spectroscopy

“…It is this condition which restricts the study of liquid metals to vapour pressures below 10 −4 Pa at the melting point for liquid metals. In order to circumvent the vapour pressure limit and to reach extremely high temperatures a new dynamic experimental method has been developed: surface heating by laser pulses combined with time resolved photoelectron spectroscopy (TR-PES) [18][19][20][21]. This method enables third generation experiments on high melting transition metals such as W in the liquid state [22] and measurements on liquid metals with corresponding equilibrium vapour pressures of 100 Pa have been performed.…”