M. del Giudice

Quantitative analysis of synchrotron radiation photoemission core level data

Abstract A procedure for quantitative analysis of photoemission core level energy distribution curves is presented which includes the determination of the Fermi level, the background function, and phonon broadening, as well as properties unique to evolving metal/semiconductor interfaces. The fitting algorithm based on a non-linear least squares routine is discussed in detail. Core level data are represented by computer-generated Lorentzian (or Doniach-Sunjic) lineshapes convoluted with Gaussians. An approximation to the convolution representation using summations of a Lorentzian (or Doniach-Sunjic) with a Gaussian is presented and its limitations are discussed. Constraints on the fitting parameters are discussed in light of the physical descriptions of clean surfaces, interfaces, and the photoemission process. The Si2 p and As3 d (in GaAs) core levels are considered as prototype shallow core levels. This quantitative analysis has been used successfully on a wide range of group IV, III-V and II-VI semiconductors as well as a number of metals.

Photoemission study of 5f localization in UPd3−x(Pt,Rh)x

Photoemission measurements in the two systems UPd3−x(Pt,Rh)x show that the 5f spectra are consistent with localized 5f electrons (peak in spectral weight is below EF for all x within the double hexagonal DO24 phase) while at both phase transitions the 5f peaks lock in at EF consistent with intinerancy. A satellite 5f peak which we attribute to d screening is observed in both localized and itinerant systems.

Photoemission study of 5f localization in UPd/sub 3-//sub x/(Pt,Rh)/sub x/

Photoemission measurements in the two systems UPd3−x(Pt,Rh)x show that the 5f spectra are consistent with localized 5f electrons (peak in spectral weight is below EF for all x within the double hexagonal DO24 phase) while at both phase transitions the 5f peaks lock in at EF consistent with intinerancy. A satellite 5f peak which we attribute to d screening is observed in both localized and itinerant systems.

Electron spectroscopy in narrow band f-electron compounds☆

Abstract We show by the combined means of high-resolution photoemission measurements at low temperatures on uranium and cerium compounds (including heavy fermions) and systematic resonant data on a series of uranium narrow-band compounds, that the “two-peaked” f-electron spectrum commonly found in cerium compounds is also found in uranium compounds. The 5f spectra consist of a superposition of features consistent with the band structure ground state plus a 5f satellite due to poorly-screened final state effects.

Systematics of electronic structure and local bonding for metal/GaAs(110) interfaces

We present high‐resolution synchrotron radiation core level photoemission results which reveal the evolving electronic structures and morphologies of metal/GaAs interfaces for the metals Ce, Sm, Ti, V, Cr, Fe, Co, Cu, and Au. By studying a wide range of overlayer metals we sought to identify common interface characteristics and discriminate between chemical and morphological effects. Quantitative fitting of the Ga and As 3d core level emission provided insight into the stages of interface development. Our results indicate that Ga is found in solution at these interfaces with chemical shifts from −0.40 eV for Au to −1.78 eV for Ce (relative to Ga in GaAs). In contrast, the results for As indicate well‐defined local chemical environments and, in some cases, the possibility of surface segregation. A direct correlation between overlayer electronegativity and core level shifts is observed.

Modeling of interface reaction products with high‐resolution core‐level photoemission

High‐resolution photoemission studies make it possible to distinguish different atomic configurations at evolving interfaces by monitoring chemical shifts. Hence, it is possible to determine the coverage at which reactions are triggered and are effectively completed, the species that outdiffuses into the metal overlayer, and the bonding of surface‐segregated species. Core‐level deconvolutions and plots of the concentration of substrate, reacted, and segregated species as a function of coverage are discussed for Ce/Si(111), Ce/GaAs(110), and Cr/GaAs(110). Our results show that distinct Ce/As and Ce/Si species form but that no distinct Cr/Ga bonding configuration is established at the interface.

Band dispersion, photoemission satellites, and Fermi liquid behavior at T ⪢ TK in 5f heavy fermion systems

Abstract We present UV photoemission spectroscopy (UPS) data on the alloy system UPd 3− x Pt x . In the double hexagonal phase ( x E F and a satellite at≈−1.0 to −1.5 eV). This satellite structure carries over into the itinerant phase ( x > 2.4) except that the low-binding energy features are now locked in at E F and show evidence for energy dispersion already at room temperature. This is consistent with well-defined bands. It would appear that Fermi liquid behavior already exists at room temperature. There is evidence for satellite formation even in well-behaved narrow band systems (USn 3 ), so that apart from satellite intensity they are spectroscopically indistinguishable from heavy fermions.

High‐resolution electron energy loss spectroscopy as a probe of surface morphology and electronic states at metal/semiconductor interfaces

The covering and consumption of sp3 hybridized Si atoms in reactions between a metal and Si(111) are monitored by the use of a chemical probe—atomic hydrogen. The surface vibrational spectrum of H on Cu/Si(111) has been measured at various stages of interface growth. The presence of Si atoms with dangling bonds results in covalent bonding with free H atoms, as seen in the Si–H stretching and bending modes in the HREELS spectrum. As Cu is deposited, the morphology of the surface layer can be deduced by observing the disappearance of Si–H vibrational excitations and correlating with Si 2p photoelectron line shape and attenuation behavior. The picture which emerges from this analysis is that Cu atoms form clusters from 0 to 3 A and that at 3 A the clusters disrupt the surface and trigger outdiffusion of Si. Atomic hydrogen also constitutes a powerful probe of surface electronic states. Previous Auger electron diffraction measurements on the annealed 1 ML Cu/Si(111) interface showed that the surface reconstru...

V/Ge(111): Temperature dependent intermixing studied with high resolution photoemission and quantitative modeling

High resolution, temperature dependent core level photoemission results for the V/Ge(111) interface show the interplay between atomic diffusion and trapping in the boundary layer. Room temperature results show strong intermixing, and core level analysis allows us to identify well‐defined chemical environments for Ge atoms (chemical shifts of −0.5 and −0.95 eV). Through modeling of the interface, we have determined the composition and extent of each reacted species. Studies at higher temperature showed that the extent and composition of the reacted overlayer could be varied. Indeed, by increasing the substrate temperature, we could produce an overlayer which became chemically homogeneous by 475 K. In this range, we find a diffusion activation energy of 5 kcal/mol which controls the width of the reacted layer.