D. E. Eastman

The band edge of amorphous SiO2 by photoinjection and photoconductivity measurements

Abstract Photoconductivity measurements indicate an interband gap of 9.0 eV in amorphous SiO2. Correspondingly, a gap of 8.9 ± 0.2 eV is seen in photoinjection measurements which are insensitive to band edge selection rules.

An ellipsoidal mirror display analyzer system for electron energy and angular measurements

Abstract A new electron imaging analyzer is described which consists of a retarding field ellipsoidal mirror low pass energy filter, a retarding field spherical grid high pass filter, and an area detector which consists of a CEMA multiplier, phosphor screen, and data acquisition system. This analyzer system energy analyzes and directly displays and measures all angular (momentum) directions within a ∼85° cone (∼1.8 sr). Angular resolutions of δθ ⋍ 2° and energy resolutions ΔE ⪅ 100 meV are obtained for angle-resolved photoemission measurements using synchrotron radiation. It has a very high throughput when used as an angle-integrated analyzer, with a resolution ΔE ⪅ 0.2 eV which can be achieved for a wide range of energies through the use of a spherical pre-retard lens. Descriptions are given of the ellipsoidal mirror design, system design, and system performance.

Photoemission energy level measurements of sorbed gases on titanium

Abstract Energy distributions at hν =21.2 eV show the energy levels and level widths of sorbed gases (H 2 , N 2 , CO, CO 2 and O 2 ) on Ti. CO and CO 2 appear to dissociate into Ti/0 + Ti/C upon adsorption. Exposure to ⪆ 10 −4 Torr sec of H 2 and O 2 results in the formation of Ti compounds on the surface.

Geometric structure and electronic states of copper films on a ruthenium (0001) surface

Abstract Auger electron spectroscopy (AES), combined with thermal desorption mass spectroscopy (TDS), work function (Δφ) measurements and energy-dependent angular resolved UV photoemission using synchrotron radiation were used to investigate the geometric and electronic properties of submonolayer and monolayer copper films grown by vapor deposition on a clean Ru(0001) substrate. A pronounced influence of the deposition temperature on the morphology of the Cu films was established in that lower temperatures favor an island growth mechanism (Stranski-Krastanov or Volmer-Weber type), whereas higher deposition temperatures lead to a more uniform spreading and a layer-by-layer growth (Frank-van der Merwe type). For Cu films grown under the latter conditions angular resolved photoemission reveals the existence of two-dimensional Cu bands even before the monolayer has reached completion; the experimentally determined band dispersions agree quite well with recent theoretical calculations.

Electronic properties of the clean and hydrogen-covered TiC(111) Ti-terminated polar surface

Abstract A polar TiC(111)-Ti(1 × 1) surface has been prepared by ion bombardment and annealing of TiC(111). The hexagonal array of exposed titanium atoms gives rise to surface properties similar to those of metallic Ti(0001). Angle-resolved photoemission spectra indicate a strong titanium-derived surface state just below EF at Γ , which is rapidly quenched by hydrogen adsorption. As on Ti(0001), hydrogen is found to chemisorb readily, resulting in a (1 × 1) overlayer and a hydrogen 1s-induced level at 6.8 eV below EF at Γ with a ∼1 eV dispersion width. These results have important implications for the use of refractory metal compounds in catalysis and electrocatalysis.

Application of synchrotron radiation to x‐ray lithography

Synchrotron radiation from the German electron synchrotron DESY in Hamburg has been used for x‐ray lithography. Replications of different master patterns (for magnetic bubble devices, Fresnel zone plates, etc.) were made using various wavelengths and exposures. High‐quality lines down to 500 A wide have been reproduced using very soft x rays. The sensitivities of x‐ray resists have been evaluated over a wide range of exposures. Various critical factors (heating, radiation damage, etc.) involved with x‐ray lithography using synchrotron radiation have been studied. General considerations of storage ring sources designed as radiation sources for x‐ray lithography are discussed, together with a comparison with x‐ray tube sources. The general conclusion is that x‐ray lithography using synchrotron radiation offers considerable promise as a process for forming high‐quality‐submicron images with exposure times as short as a few seconds.

Surface core-level shifts and surface valence change in mixed-valent YbAl2

Abstract High-resolution photoemission studies show that about two surface layers of mixed-valent YbAl2 are divalent. These layers exhibit large surface core-level shifts of Δs1=0.92 eV for the topmost and Δs2=0.35 eV for an underlying surface layer, allowing a separation of the divalent part of the spectrum into bulk and surface contributions. In this way, a mean valence of 2.4±0.1 can be derived for bulk YbAl2. The observed Δs1/Δs2 ratio is consistent with a recent theoretical prediction.

Photoemission from physisorbed Co on clean and Xe-covered Al(111)

Abstract Molecular-orbital energy shifts are observed in photoemission from weakly physisorbed CO on clean and Xe-covered Al(111) surfaces. These shifts in ionization potentials are mainly due to final-state relaxation effects, which can be described approximately by a point-charge image-potential model. Differential distance- and orbital-dependent energy shifts suggest that CO molecules lie flat on the substrates. CO is adsorbed on Al(111) with a heat of formation of 0.21 eV/molecule.

Schottky barriers on diamond (1 1 1)

Abstract We have measured Schottky barrier heights OB = 1.3 eV for Au and OB = 1.5 eV for Al on (p-type) diamond(1 1 1)−(1 × 1) using photoelectron spectroscopy with synchroton radiation. These barrier heights yield a barrier index of S = 0.2, which is closer to the values for Si and Ge (S ∼ 0.1) than to the value S = 0.4 calculated for jellium on an ideal diamond(1 1 1) surface. After reacting Al with the diamond surface by annealing to 800° C, we find that OB decreases by 0.24 to 1.25 eV.

Photoemission studies of d-band structure in Sc, Y, Gd, Ti, Zr, Hf, V, Nb, Cr and Mo

Abstract Photoemission optical densities of states (ODSs) of a number of transition metals are presented and compared with energy band densities of states. The ODSs summarize observed band widths and dominant structure of the d -bands, and generally show good correlation with band densities of states. Metals with the same valence and crystal structure tend to show common features.