Low‐energy electron diffraction study of atomic structure of Sc–O/W(100) surface acting as Schottky emitter at high temperatures

Abstract

Low-energy electron diffraction (LEED) was used to investigate the atomic structure of an Sc-O/W(100) surface acting as a Schottky emitter in order to elucidate a marked reduction in the work function of the Sc-O/W(100) Schottky emitter surface. The results of our LEED observation of the Sc-O/W(100) surface at room temperature revealed that a p(2 × 1) and p(1 × 2) double-domain structure is formed on the surface. This reconstructed structure exhibited no changes when heated to 1400 K, and continued to remain stable even when held at 1400 K. These results strongly suggest that the p(2 × 1) and p(1 × 2) double-domain structure is formed by scandium-oxygen electric dipoles on the W(100) surface, leading to a marked reduction in the work function of the Sc-O/W(100) surface at the operating temperature of the Sc-O/W(100) Schottky emitter.

Self‐recovery function of p(1×1)‐Sc‐O/W(100) system used as Schottky emitter

“…15,16 The low-work-function Zr-O/W(100) surface is realized only at high temperature and the work function at room temperature is close to that of clean W(100). 15,16 We have confirmed already that the p 2 ð 1 -p 1 ð 2 structure of the Sc-O/W(100) surface prepared by heating at ¾1500 K shows negligible change between room temperature and ¾1500 K. 9 Taking this into account, the present results strongly suggest that the p 1 ð 1 structure of the Sc-O/W(100) surface prepared by heating at ¾1700 K is maintained also at both room temperature and ¾1500 K, resulting in the realization of the low-work-function Sc-O/W(100) surface at both room temperature and ¾1500 K.…”

“…The corresponding LEED pattern indicates that Sc atoms are deposited randomly on the W(100) surface without the formation of a reconstructed surface structure. 9 By oxygen exposure at step (iii), an amorphous or polycrystalline layer of Sc-O is formed 9 and the O KLL peak intensity increases. By heating at ¾1500 K for 3 min (step (iv)), the p 2 ð 1 -p 1 ð 2 doubledomain structure is formed.…”

Self-recovery function of Sc–O/W() system as Schottky emitter

“…The results strongly suggested that the superior characteristics of the Sc-O/W(1 0 0) system used as an emitter are due to the decrease of the work function caused by the formation of Sc-O electric dipoles aligning into the p(2 · 1)-p(1 · 2) double domain structure [9][10][11]. It was also confirmed that the surface properties, i.e., the atomic arrangement, composition and chemical bonding state of the Sc-O/W(1 0 0) surface, are very stable at the operating temperature of the Sc-O/W(1 0 0) emitter.…”

“…Ions were irradiated onto the surface to homogeneously cover the whole of the sample surface. Sc-O/W(1 0 0) surface showing the markedly low work function was prepared by the same procedure as that reported previously [8][9][10][11]: LEED pattern showing the p(2 · 1)-p(1 · 2) double domain structure disappears and only a slightly weak p(1 · 1) pattern is observed. These results indicate that the Sc-O/W(1 0 0) surface is damaged by the 0.5 keV Ar þ bombardment at RT.…”

“…Regarding the Sc-O/W(1 0 0) Schottky emitter, the authors have carried out the surface characterization of the Sc-O/W(1 0 0) system at the operating temperature of the emitter using Auger electron spectroscopy (AES), ion scattering spectroscopy (ISS), low-energy electron diffraction (LEED) and work function measurement [8][9][10][11]. The results strongly suggested that the superior characteristics of the Sc-O/W(1 0 0) system used as an emitter are due to the decrease of the work function caused by the formation of Sc-O electric dipoles aligning into the p(2 · 1)-p(1 · 2) double domain structure [9][10][11].…”