Photoelectron yield of small silver and gold particles suspended in gas up to a photon energy of 10 eV

The photoelectric yieldY of clean Ag and Au particles suspended in He-gas has been measured up to photon energieshv=10 eV.Y shows strong deviations from the bulk in the case of Ag but not in the case of Au. Surface adsorbates generate dramatic changes inY, pointing to the decisive role of the surface electron density profile on the optical properties.     

Scattering of Li+ from LEED characterized W(110) and Si (111) surfaces at energies between 2 and 20 eV

Energy and angular distributions of Li⁺ ions scattered from W(110) and Si(111) surfaces have been measured for a wide range of scattering angles and for beam energies between 2 and 20 eV. The collision process can be explained in terms of binary collisions with single surface atoms, if the influence of the attractive part of the interaction potential is taken into account. A square well approximation for the potential makes it possible to predict the form of the energy spectrum as well as the behaviour of the angular distribution of the scattered particles for both systems. The influence of adsorbed atoms and molecules on the scattering behaviour has been investigated. Exposure of the W surface to H₂, O₂ and CO shows that surface coverages exceeding 10% of a monolayer very drastically influence the scattering. The results from the clean surfaces indicate that sufficiently precise measurements of the energy spectra of the scattered particles can yield very detailed information about the form of the interaction potential. The form of the energy spectra also contains information as to the extent of vibrational excitation of the surface atoms.     

Intensity analysis of XPS spectra to determine oxide uniformity: Application to SiO2/Si interfaces

A simple method of determining oxide uniformity is derived which requires no knowledge of film thickness, escape depth, or film composition. The method involves only the measurement of oxide and substrate intensities and is illustrated by analysis of XPS spectral data for thin SiO₂ films grown both thermally and by low-temperature chemical vapor deposition on monocrystalline Si. A region 20–30 Å thick is found near the SiO₂/Si interface on thermally oxidized samples which has an inelastic mean free path 35% less than that found in the bulk oxide. This is interpreted as being due to lattice mismatch resulting in a strained region which is structurally, but not stoichiometrically, distinct from the bulk oxide.     

Contributions of high-spin resonances to the reaction γp → ηp for photon energies above 2 GeV

Based on new experimental data obtained for photon energies in the range 2–3 GeV, the contributions and properties of heavy high-spin resonances to the amplitude of the process γp → ηp obtained by an earlier constructed model have been corrected. It has been shown that this process is related to the G₁₇(2190) and H₁₉(2220) resonances. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 87–90, March, 2006.     

Relative partial photoionization cross-section of methylacetylene to the X2E ion state over the photon energy range 11–26 eV

Relative partial cross-sections for photoionization to the X²E ground state of the methylacetylene ion over the photon energy range 11–26 e V have been determined using synchrotron radiation. The observed cross-sections show a broad resonance feature similar to the results for photoionization to the X²II_u ground state of the acetylene ion. An explanation involving autoionization from a π^* (e) excited state is proposed.     

Generalized oscillator strengths for two transitions in CO2 at incident electron energies of 300, 400 and 500 eV

Generalized oscillator strengths have been obtained for two transitions in CO₂ from inelastic electron scattering determinations as a function of angle. Excitation energies for the two transitions are 11.04 and 11.38 eV, respectively. This spectral region was studied previously by Lassettre and Shiloff¹ but at a resolution too low to resolve the two transitions. In the present experiments the two are clearly resolved. Results are compared with the previous experiments of Foo et al.². Since substantial discrepancies are found both with the previous results of Lassettre and Shiloff and that of Foo et al., the accuracy of angular trends has been checked by comparing elastic scattering with the accurate determinations of Bromberg.⁶ Agreement is good. Multiple scattering is shown to be absent by varying the pressure. Generalized oscillator strengths are compared with the theoretical calculations of McKoy and collaborators. The change in the shape of the CO₂ spectrum in the region of 7–10 eV excitation energy is also studied.     

R-matrix formulation and phase shifts for n-He and p-He scattering for energies up to 20 MeV

An R-matrix formulation for a single level with a background approximation has been used to analyse n-⁴He and p-⁴He elastic scattering data below the inelastic thresholds near 22 MeV. For every partial wave a single level and a distant pole contribution constant with energy has been employed. Simple relations between neutron and proton scattering parameters have been sought to possibly derive more dependable values for neutron phase shifts and analysing powers at energies where little experimental information exists. The R-matrix parameters corresponding to ⁵He and ⁵Li ground and 1st excited states, phase shifts up to 20 MeV and neutron analysing powers up to 15 MeV are given in tabular form and are compared to results of earlier analyses. Differences in n-⁴He phase shifts are discussed and shown to be due to a scarcity of accurate neutron scattering data above 11 MeV. Some typical fits to n-⁴He scattering data are shown.     

Disorder broadening of E2 optical spectra in GeSi alloys

he E₂ transitions in GeSi alloys are analyzed quantitatively using low-field electroreflectance data. The model of M₁ saddle point transitions is found to be in fair agreement with differentiated electroreflectance spectra in the whole composttion range. The broadening parameter of pure Ge and Si increases by 0.035 eV in the alloy with equal content of both components.     

Raman spectra of a coupled LO phonon-damped plasmon mode in n-GaAs

It is shown that recently observed spectra of Raman scattering from a coupled longitudinal optical (LO) phonon-damped plasmon mode in n-GaAs can be reproduced theoretically by taking into account the Landau damping of the mode itself as well as a distribution of wave number of laser light due to the attenuation of light near the surface.     

Ground-based photon path measurements from solar absorption spectra of the O2 A-band

High-resolution solar absorption spectra obtained from Table Mountain Facility (TMF, 34.38°N, 117.68°W, 2286 m elevation) have been analyzed in the region of the O₂ A-band. The photon paths of direct sunlight in clear sky cases are retrieved from the O₂ absorption lines and compared with ray-tracing calculations based on the solar zenith angle and surface pressure. At a given zenith angle, the ratios of retrieved to geometrically derived photon paths are highly precise (0.2%), but they vary as the zenith angle changes. This is because current models of the spectral lineshape in this band do not properly account for the significant absorption that exists far from the centers of saturated lines. For example, use of a Voigt function with Lorentzian far wings results in an error in the retrieved photon path of as much as 5%, highly correlated with solar zenith angle. Adopting a super-Lorentz function reduces, but does not completely eliminate this problem. New lab measurements of the lineshape are required to make further progress.     

Size dependence of the plasmon peak position in electron stimulated photon emission spectra of Ag clusters supported on amorphous carbon film

The plasmon energy of Ag clusters produced on an amorphous carbon substrate by gas-aggregation technique has been measured. It has been determined from the plasmon peak position in the light emission spectrum obtained during bombardment of Ag clusters by low-energy electrons. For Ag cluster films with maximum of the cluster size distribution at 30, 8 and 2.5 nm, the plasmon energy comprised 3.76, 4.13 and 4.28 eV (the wavelength was 330, 300 and 290 nm), respectively. The blue shift of the plasmon energy is probably related to the effect of confounding of collective and single-particle excitations.     

Electron scattering from levels in 208Pb with excitation energies up to 6.2 MeV and spins up to J = 10

Spectra of electrons scattered inelastically from ²⁰⁸Pb have been measured in the region of excitation energies up to 6.2 MeV. The measured form factors are indicative for spins of the excited states up to J = 10.     

Fundamental reflectivity spectra of Hg1−xMnxTe mixed crystals in the 1.7 to 3.5 eV energy range

The room temperature reflectivity coefficient R(E) for the mixed crystals Hg_1?xMn_xTe (x up to 0.57) in the energy range 1.7 to 3.5 eV was investigated. Two distinct maxima E₁ and E₁ + Δ₁ connected with the transitions in the critical points on the [111] direction of the Brillouin zone for the samples with x up to 0.3 and the more diffused structure of R(E) for the samples with x > 0.3 was observed. A quadratic dependence of E₁ and E₁ + Δ₁ transition energy vs alloy composition with x up to 0.3 was found, with bowing coefficient c = 1.21 ± 0.02 and 1.06 ± 0.02 respectively. The energy variation of an additional shoulder probably connected with the e₁ transitions at L point of the Brillouin zone is also reported.     

UHV-MOCVD growth of TiO2 on SiOx/Si(1 1 1): Interfacial properties reflected in the Si 2p photoemission spectra

Metal–organic chemical vapour deposition growth of titanium oxide on moderately pre-oxidised Si(1 1 1) using the titanium(IV) isopropoxide precursor has been studied for two different growth modes, reaction-limited growth at 300 °C and flux-limited growth at 500 °C. The interfacial properties have been characterized by monitoring synchrotron radiation excited Si 2p photoemission spectra. The cross-linking from oxidised Si to bulk Si after TTIP exposure has been found to be very similar to that of SiO_x/Si(1 1 1). However, the results show that the additional oxidation of Si most probably causes a corrugation of the SiO_x/Si interface. Those conclusions are valid for both growth modes. A model is introduced in which the amorphous interface region is described as (TiO₂)_x(SiO₂)_y where x and y changes linearly and continuously over the interface. The model quantifies how (TiO₂)_x(SiO₂)_y mixing changes the relative intensities of the signals from silicon oxide and silicon. The method can be generalised and used for the analyses of other metal-oxides on silicon.     

Simulation of range profiles for boron implantation into SiO2/Si and Si3N4/SiO2/Si targets

The simple method of profile combination is shown to be applicable to the simulation of boron profiles in SiO₂/Si and Si₃N₄/Si layered targets. This is demonstrated by comparison with range distributions calculated by more sophisticated theoretical methods, i.e. TRIM Monte Carlo simulations and the algorithm of Christel et al., and with experimental data. The method of profile combination can also be applied to layered targets with a crystalline silicon substrate.     

Strain-induced photoreflectance spectra in the vicinity of the E 0 transition in GaAs/Si and InP/Si heterostructures

A study is reported of the structure of photoreflectance (PR) spectra in the vicinity of the E ₀ transition from thin (d=1–5 μm) n-GaAs and n-InP films (n=10¹⁶–10¹⁷ cm⁻³) grown epitaxially on Si(001) substrates. A quantitative analysis of the spectra involving multi-component fitting shows that the electronic optical transition from the {3/2;±1/2} subband provides a dominant contribution to the intermediate-field electromodulation component in both systems. The splitting observed in the GaAS/Si PR spectra near the main peak are accounted for not by the strain-induced valence-band splitting but rather by a spectral superposition of the intermediate-field component due to the {3/2;±1/2} subband with a low-energy excitonic component. The analytically established transition energy E ₀ ^3/2;±1/2 is used to calculate biaxial strains in epitaxial films. Fiz. Tverd. Tela (St. Petersburg) 41, 725–731 (April 1999)