Abstract
We report a photoelectron spectroscopic study of the valence bands of double hexagonal-close-packed (dhcp) α-La(0001) films epitaxially grown on W(110) at room temperature. The La 5d photoemission cross section in the photon energy region from 20 eV to 130 eV was obtained and the valence-band structure of α-La was determined. Except for 4f-related structures, the valence-band structures of dhcp α-La and dhcp β-Ce were found to resemble each other. From the band structure, the crystal structure of the La film was confirmed. No evidence for the existence of a 5d-like surface state near the Fermi energy at the point of the surface Brillouin zone was obtained and a 6s band bottom was identified.
Highlights
The unusual physical properties of the various phases of metallic La have been the subject of many experimental and theoretical investigations [1]-[8]
La exists in three different phases at atmospheric pressure: double hexagonal-close-packed α phase below 609 K, fcc β phase between 609 K and 1138 K, and bcc γ phase between 1138 K and its melting point (1191 K)
The electronic structure of well-ordered and atomically clean dhcp α-La(0001) epitaxially grown on a W(110) surface has been studied by means of photoelectron spectroscopy
Summary
The unusual physical properties of the various phases of metallic La have been the subject of many experimental and theoretical investigations [1]-[8]. The temperature dependence of the thermal-expansion coefficient is quite anomalous for fcc β-La: it becomes negative at ~40 K, and reaches its largest negative value at ~18 K These remarkable properties have led to speculations and suggestions about their electronic origin that a mechanism involving 4f electrons is responsible and the electronic wave functions at the Fermi level contain a significant admixture of 4f character. Several photoemission experiments have been done to determine _the valence-band electronic structure of La [11]-[14], suggesting the existence of a surface state near EF at the Γ point of the surface Brillouin zone (SBZ). It cannot be denied that there has been relatively little theoretical effort given to determine the electronic structure of La, there are a large number of papers [15]-[22] This is no doubt related to the scarcity of experimental data available for comparison. Photon-energy (hν) dependence of the intensities of the photoemission peaks is measured to characterize the energy bands of La and the 5d6s valenceband structures of La(0001) film are determined
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