Zr Mζ Research Articles

Oxynitridation of cubic silicon carbide (100) surfaces

The interaction of nitric oxide (NO) on Si-rich β-SiC(100) 3×2 surface reconstruction is investigated by photoemission spectroscopy using Al Kα (1486.6 eV) and Zr Mζ (151.4 eV) x-ray lines at Si 2p, C 1s, N 1s and O 1s core levels. NO exposures are performed at sample temperatures ranging from 25 to 1000 °C. The initial sticking coefficient of the NO molecules is found to be already significant at room temperature, with a dissociative adsorption resulting in Si oxynitride products as SiOxNy. The amount of oxynitride is significantly increased at surface temperatures of 500 °C and above. In addition, temperature is found to favor the formation nitrogen-rich SiOxNy oxynitride products. Thermal oxynitridation on the 3×2 reconstruction results in a SiOxNy/β-SiC(100) interface.

Electronic and Structural Properties of the 6H–SiC(0001) Surfaces

The atomic and electronic structures of clean 6H–SiC(0001) surfaces have been investigated by means of LEED and photoelectron spectroscopies (XPS, XAES and UPS). First a clean surface having the (3 × 3) structure has been obtained by heating the sample at 800°C under a low Si flux. Successive annealings in UHV have produced two other stable reconstructions, namely the [Formula: see text] and the [Formula: see text]. The various surface structures show distinctive core-level and Auger line shapes, which are characteristic of the composition of the surface layer, as checked by the XPS intensities by two different excitation sources (Mg Kα and Zr Mζ), while UPS spectra show sizeable differences in the character of the valence bands. The evaluation of the atomic composition is able to sort between different models proposed in the literature.

Characterization of a Zr Mζ ( hν = 151.6 eV) source for soft X-ray photoemission spectroscopy

The Mζ emission of a Zr anode ( hν = 151.6 eV) is characterized for use in soft X-ray photoemission spectroscopy. The Fermi edge spectrum of Al is recorded as a function of the resolution of the electron energy analyzer. Least-squares fits are performed using a Fermi-Dirac function convoluted with a gaussian-broadened lorentzian representing the combined effects of the Zr Mζ natural linewidth (0.77 eV), inhomogeneous broadening of the Mζ spectrum and finite analyzer resolution. The empirical system resolution function thus determined is deconvoluted from core-level or valence-band data for Au, Al and GaN, resulting in enhanced resolution. Least-squares fits of the resolution-enhanced core levels with gaussian-broadened lorentzian (GaN Ga3d) or Doniach-Šunjić (Al2p) functions are performed and lineshape parameters obtained.

Investigation of semiconductor surfaces using soft-X-ray photoelectron spectroscopy.

A soft X-ray photoelectron spectroscopy with Zr Mζ radiation is used to investigate semiconductor surfaces. Zr Mζ photons of 151.4eV energy have good surface sensitivity, because Si2p photoelectron energy was about 50eV where the escape depth reaches minimum (0.5nm). The surface sensitivity was 10times higher than these in conventional techniques, and this result was in good agreement with that of theoretical calculation according to the difference of electron escape depth. Thanks to this high surface sensitivity, the Surface Core Level Shift (SCLS) was found to be -0.5eV in Si (100) 2×1 surface. We also used this technique to study the oxygen adsorbed surfaces layers at room temperature on Si (100) 2×1. The significant difference in photoelectron spectra was observed after annealing above 650°C.

Soft X-ray photoelectron spectroscopy studies of the initial oxidation of Al xGa 1−xAs(100) surfaces

Core level shifts and intensity ratios of the spectra of Zr Mζ excited photoelectrons were used to describe the oxide growth on Al x Ga 1− x As(100) surfaces with different x values. The chemisorption of oxygen at exposures up to 10 9 L was studied at room temperature. In highly surface sensitive experiments (λ ⋍ 0.6 nm) we could show that oxygen interacts first with the aluminium atoms. During the further oxidation an outdiffusion of aluminium takes place leading to the formation of a surface aluminium oxide layer which hinders the oxidation of the other semiconductor elements.

Photoemission on AB semiconductor material. Cd3As2, Zn3As2, Cd3P2, Zn3P2 crystals and thin films

AbstractThe density of valence states of sputter‐annealed Cd3As2, Zn3As2, (Cd0.54Zn0.46)3As2, Cd3P2, and Zn3P2 crystals as well as in situ UHV deposited Cd3As2 and Zn3P2 thin films are determined with UV (He/Ne I, II) and X‐ray (Zr Mζ, Al/Mg Kα) photoemission. Some AB valence electron density of states data reported in literature and measured by X‐ray emission and UP/XP spectroscopy are verified by the experiments. All AB materials studied provide UPS/XPS curves, which are qualitatively similar to those reported for AIIBVI compounds.

Oxidation of etched silicon in air at room temperature; Measurements with ultrasoft X-ray photoelectron spectroscopy (ESCA) and neutron activation analysis

The oxide growth rate for p-type Si〈100〉 crystals after HF etching in air at room temperature was measured for exposures betwen 3 min and ≈ 10 3 min after etching. The oxide thicknesses were determined with traditional Al Kα excited XPS and two nontraditional methods — especially suited for very thin layers: Zr Mζ excited XPS and neutron activation analysis (NAA). The oxide thicknesses (mainly SiO x with x < 2) lie between 0.1 and 0.55 nm with a logarithmic growth rate of ≈ 0.2 nm/decade.

Relative intensities in x-ray photoelectron spectra. Part VI. The spectra of He(I), He(II), Y Mζ and Zr Mζ

The 2 s- and 2 p-electron photoionization cross-sections at photon energies up to 190 eV have been calculated, using the RPAE method for averaged configurations of the C, N, O and Ne atoms. The RPAE method ensures a more accurate relation between the cross-sections, 2 s/2 p, than that obtained using the Hartree—Fock method. Within the framework of the Gelius—Siegbahn model, but with the use of theoretical atomic cross-sections, we have calculated the photoionization cross-sections for He(I), He(II), Y Mζ, Zr Mζ for CH 4, C 2H 6, C 3H 8, C 2H 4, C 2H 2, NH 3, H 2O, CN −, N 2, CO, CO 2, N 2O and NO 2 − molecules. For CO, N 2, CO 2, N 2O and H 2O molecules, a comparison is made between the theoretical and experimental cross-sections for hν < 60 eV. The calculated absolute and relative values of the molecular-orbital cross-sections are in reasonable agreement with experiment, especially at hν ⩾ 40 eV. The calculations correctly reproduce the change in intensities under the transition He(I) → He(II). We have shown that our calculations have a significant advantage over those performed using the PW and OPW approximations. It is shown for NO, N 2, CO, H 2O, CH 4, NH 3 and N 2O molecules that the total photoionization cross-section calculated taking into account the real structure of the molecular orbitals is in better agreement with the experimental photoabsorption cross-section than is the sum of the cross-sections for the atoms in a molecule.

Investigation of surfaces by means of the Zr Mζ radiation

Photoelectron spectra excited by Zr Mζ radiation of the valence electrons of films of copper and indium and of clean silicon as well as the Si 2p level of clean silicon and of silicon after reaction in ammonia were investigated. The results show up a disagreement between theory and experiment for the Cu 3d/Cu 3p cross-section ratio, for the interpretation of the valence band of silicon and for the electron escape depth in SiO 2. The reaction of NH 3 with Silicon (111) gives information about the formation of an interfacial region between thermally-grown nitride films and the Si substrates.

Photoelectron spectra of acetylene with HeI, HeII, Zr Mζ, and Mg Kα radiation sources

Valence level photoelectron spectra of gaseous acetylene excited by HeI (21.217 eV), HeII (40.8 eV), Zr Mζ (151.4 eV) with Mg Kα (1253.6 eV) radiations have been obtained. With one exception, the 3σg band under Mg Kα excitation, all of the expected valence level excitations are observed in each case. The best measured orbital ionization potentials are 1πu (11.41 eV), 3σg (16.76 eV), 2σu (18.71 eV), and 2σg (23.65 eV). All values except that for 1πu are adiabatic values. Relative photoionization probabilities (cross sections) have been determined for each of the radiations and compared to those estimated theoretically. The low calculated cross sections for 3σg excitation with Mg Kα radiation provides an explanation for the lack of an observable band due to this ionization in the photoelectron spectrum. A prominent ’’shake-up’’ peak is observed at 27.6 eV in both the Mg Kα and Zr Mζ excited valence shell photoelectron spectra although it is more pronounced in the former. Similarly the C1s core spectrum shows several ’’shake-up’’ peaks which have been assigned with the aid of CNDO calculations.

Photoelectron spectroscopy with Zr Mζ (151 eV) radiation. A study of the variation of relative photoionization cross sections of molecules containing first row atoms (C, N, O) with exciting radiation from HeI to Mg Kα limits

Relative perpendicular photoionization intensities for the noble gases Ne and Ar and the molecules CH4, NH3, H2O, CO, N2, and CO2 have been measured with HeI (21.2 eV), HeII (α, 40.8 eV and β, 48.4 eV) resonance lines and Zr Mζ (151 eV) and Mg Kα (1253.6 eV) soft x rays using the same instrument for all measurements. New valence shell spectra of NH3, CO, and CO2 obtained with Zr Mζ radiation are illustrated. The experimental values are compared to values calculated for each radiation by the method of Ellison [J. Chem. Phys. 61, 507 (1974)]. Reasonable success was achieved by the theory which appears to falter most seriously with the inner valence orbitals of dominant 2s atomic character. This failure is most likely due to the improper treatment of the Cooper minimum. Attempts to improve the agreement between observed and calculated relative intensities by inclusion of multiple electron processes (’’shake up’’ transitions) are discussed.

Photoelectron spectra of alkali halides by use of zirconium Mζ and other X-rays

Abstract The photoelectron spectra of eight kinds of alkali halide, in the solid phase, were observed by stimulation with Zr Mζ, Al Kα and other X-ray lines. The ratios of the photoionization cross-sections of the 2s and 2p levels or those of the 3s and 3p levels were estimated from the observed intensifies of the photoelectron peaks. Observations are given about the photon energy dependence of these ratios. It is also shown that comparison of the spectra from different stimulating radiations provides information which is useful for the analysis of structures in the loss-band region.

Valence orbital photoelectron spectroscopic studies of free molecules with zirconium M? soft X-ray excitation

Zirconium Mζ X-rays (151.4 eV) have been used to produce valence shell photoelectron spectra of the noble gases Ne and Ar and the molecules CH4, N2 and H2O. This radiation, which appears to be free of nearby satellites, gives good count rates and clean spectra. Since the orbitals with a large proportion of p character have a higher cross-section for photoemission with Zr Mζ than with Mg Kα, the spectra show prominent peaks for molecular orbitals with dominant p components whereas Mg Kα spectra emphasize those orbitals which have dominant s character.

Relative intensities in photoelectron spectroscopy of atoms and molecules

The relative intensities of photoelectron lines is discussed. The relationship of observed intensities to angle of observation is considered as are the errors introduced by ignoring the fact that different lines may have different angular distributions. Tables of theoretical results for the angular distribution asymmetry parameter, β, are presented for incident Al Kα, Mg Kα, and Zr Mζ radiation for all atomic ground state subshells of non-zero angular momentum. The application of these results to molecules is discussed.