Angle-dependent valence photoemission from adsorbed molecular nitrogen a comparison of measurements and model calculations

He I and He II photoelectron spectra for N₂ adsorbed on W (110) have been measured at three different polar emission angles. The behaviour of the adsorbate-induced features with angle is compared to the angle- dependence of dipole matrix elements for oriented N₂, Ni-N₂, and Ni₉-N₂ clusters obtained by SCF-Xa-SW calculations. The agreement is very good for He I and acceptable for He II, if the N₂ axis is assumed normal to the “surface” and the assignment of peaks proposed earlier is used. For He II the use of the big cluster is important to arrive at good agreement.     

Charged particle oscillator and hollow cathode He(II) lamps for high resolution photoelectron studies: C 2 s spectrum of CH 4 and Hg 5 d5/2 spectrum of (CH 3) 2Hg

Charged particle oscillator and hollow cathode He discharge lamps are described, and the performances of the two lamps in the same spectrometer are compared. Both lamps give high percentages of He(II) radiation, but the hollow cathode lamp gives higher overall He(I) and He(II) intensifies and has greater long term stability. The observed resolution for He(II) studies (～ 25 meV) is the same for both lamps. The C 2 s spectrum of CH ₄ and the Hg 5 d_5/2 spectrum of (CH ₃) ₂Hg demonstrate the performance of the hollow cathode lamp. In the CH ₄ spectrum, a vibrational progression is observed, and attributed to the totally symmetric stretching mode. The linewidth of individual components increases at higher binding energy. The high resolution of the (CH ₃) ₂Hg spectrum enables us to identify additional peaks not previously seen in this spectrum. The Hg 5 d orbital energy-ordering for Me ₂Hg is reassigned.     

Calibration of electron-energy spectrometers

Relative photoionization cross-sections of strong peaks in the He(I) photoelectron spectra of N₂, CO, CO₂, and O₂, are tabulated. These data have been measured with an electron energy analyzer whose relative luminosity has been calibrated to an accuracy of ± 5 ‰ Thus, the tables will be useful for calibrating the transmission of other analyzers for electron energies below 9 eV. Correction for angular distribution effects is discussed.     

Thermoluminescence and electron spin resonance after room-temperature X-ray irradiation of NaCl:Mn2+

A parallel investigation of thermoluminescence (TL) and electron spin resonance (ESR) spectra on room-temperature (RT) X-irradiated NaCl:Mn²⁺ has been performed. The TL spectra in the range 20–300°C consist of five glow peaks, numbered from I to V. Temperatures at maximum height are 41°, 68°, 118°, 152° and 216°C, respectively. Peaks I, II and IV obey first-order kinetics, whereas peaks III and V fit second-order behavior. The wavelength spectrum for all glow peaks consists of two bands centered at 595 and 400 nm. The 595 nm emission is attributed to hole capture by Mn⁺ and subsequent deexcitation of Mn²⁺. The 400 nm emission is produced as a consequence of hole-F center recombination.The correlation of TL glow peaks to various defects has been investigated. Peak II is clearly related to manganese-vacancy dipoles and peak I can be roughly associated to free cation vacancies. Peak IV appears to relate to large Mn-aggregates, whereas peak V is intrinsic and not related to impurities.On the other hand, ESR data indicate that each glow peak in the 595 nm emission is associated to the annihilation of a given Mn-center; Peak I to Mn⁰C, peak II to Mn⁰C and Mn⁺, peak III to Mn⁺ and peaks IV and V to Mn⁰-D.     

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

The 2s- and 2p-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, 2s/2p, 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 CH₄, C₂H₆, C₃H₈, C₂H₄, C₂H₂, NH₃, H₂O, CN^?, N₂, CO, CO₂, N₂O and NO₂^? molecules. For CO, N₂, CO₂, N₂O and H₂O 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, N₂, CO, H₂O, CH₄, NH₃ and N₂O 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.     

Angular distribution of the photoelectron spectrum of CO2, COS,CS2, N2O,H2O,and H2S

The photoelectron spectra of the triatomic molecules CO₂, COS, CS₂, N₂O, H₂O, and H₂S have been measured as a function of the angle θ between the direction of the incoming photon and outgoing photoelectron. The photoelectron spectra have been measured with a double-focusing electrostatic electron spectrometer to which has been attached a chamber containing a gas discharge lamp that can be freely rotated. (The photon source used was the 21.22 eV He I resonance line). From the dependence of intensity as a function of θ the angular parameter β was determined for each ionization band observed in the photoelectron spectra. A correlation was noted between the values of β and the molecular orbitals relative to the contributions of oxygen and sulfur atomic orbitals. Individual β values were also obtained for most of the vibrational bands seen in the photoelectron spectra. In most cases the vibrational structure showed little or no change in the angular parameter for a given electronic state. In certain cases, however, such as the fourth ionization band in CS₂, CO₂, and COS, rather sizeable changes in β were observed for the different vibrational bands.     

He(I) and He(II) photoelectron spectra of glycine and related molecules

Photoelectron spectra obtained by He(I) and He(II) excitation of glycine, sarcosine and glycine methyl ester are presented. The p-type bands in the He(I) spectrum of glycine are interpreted in terms of localized molecular orbitals; the C 2s bands are identified in the He(II) spectrum. He(I) spectra of some N-acetylamino acids and of a variety of α-and ω-substituted amino acids are also reported.     

Configuration interaction calculations of the satellite peaks observed in the core and valence photoelectron spectra of N2

Configuration interaction calculations are used to interpret satellite peaks observed in the X-ray and He (II) photoelectron spectra of N₂. Using a basis containing diffuse atomic functions, the X-ray peaks are assigned to states involving transitions to valence and Rydberg type orbitals. The three satellites in the He (II) spectrum are correlated with states involving occupancy of the 1π_g and 4σ_g molecular orbitals.     

Ultraviolet photoemission from polymeric sulfur nitride polycrystalline films and single crystals

The (SN)_x valence band structure, for polycrystalline films as well as for single crystal samples, has been studied using He I and He II resonance radiation. In angle-resolved photoemission energy distributions from single crystals, structure in the spectra is selectively enhanced offering a possibility of assigning the photoemission as originating from particular regions of the Brillouin Zone. The observed onset of photoemission 0.2 eV below the Fermi edge is discussed.     

Semi-empirical calculations and the assignment of valence photoelectron spectra of large molecules : Phenalen-9-amino-1-imine.

The He(I) photoelectron spectrum of phenalen-9-amino-1-imine (C₁₃H₁₀N₂) has been assigned using the SPINDO and HAM/3 semi-empirical methods. The molecular orbital patterns and properties suggested by the calculations are compared for the low energy region (7–12 ev).     

Thin layers of aluminium: A molecular orbital study

Molecular beam epitaxy has been used to prepare thin layers (200 nm thickness) of aluminium grown either on aluminium or gallium arsenide substrates; their He(I) and He(II) photoelectron spectra have been recorded. The quasirelativistic CNDO/1 method has been applied to investigate the band structure of {Al}₁₇₂, {Al}₂₈₄ and {Al}₄₂₄ clusters obtained by a duplication of the unit cell: the DOS profiles and their projections were generated. These data were correlated with the periodic crystal orbitals of the EHT quality. The first excitation energy serves as a better estimate of the vanishing energy gap showing thus a metallic character of aluminium.     

Penning ionization electron spectroscopy and photo-electron spectroscopy of molecular solids. II. Ammonia and water

The Penning ionization electron spectra (PIES) and ultraviolet photoelectron spectra (UPS) of ammonia and water molecules condensed on a cold metal substrate have been measured using thermal He*(2³S, 2¹S) metastable atoms and He(I) (58.4 nm) photons. The shifts of the observed positions of the PIES peaks relative to those of the UPS peaks in the condensed phase are roughly equal to the corresponding shifts in the gas phase. The relative intensities of the 3a₁ and 1e orbital peaks are reversed in the PIES and UPS for both gaseous and condensed ammonia; the origin of this reversal is interpreted as the difference between the interactions with metastable atoms and photons. On the other hand, the relative intensities of the 3a₁ orbital peak in the PIES and UPS for condensed water decrease as compared to the gas-phase spectra. This implies participation of the 3a₁ orbital of water in the hydrogen bonding.     

Electron energy loss spectra of the silicon 2p, 2s, carbon 1s and valence shells of tetramethylsilane

Inner shell excitation spectra of tetramethylsilane, (CH₃)₄Si, have been measured in the silicon 2s, 2p (L_I,II,III-shell) and carbon is (K-shell) regions using electron energy-loss spectroscopy at an impact energy of 2.5 keV and a scattering angle of ~1°. The high-resolution valence shell spectrum has also been observed at an impact energy of 3 keV and a zero degree scattering angle. The silicon 2p spectra are compared and contrasted with published photoabsorption spectra of SiF₄, SiH₄, and other related Si-containing molecules with varying ligands.     

Use of the 447 nm He I line to determine electron concentrations

The helium 447 nm complex line has been excited in a wall-stabilized arc fed at atmospheric pressure by pure He, He-H₂, He-Ne-H₂ or He-Ar-H₂ mixtures. Photoelectric endon observations of the central part of the arc channel were made with high spatial (1/600) and spectral (53,000) resolution.A collection of 88 helium 447 nm line profiles, of which 75 were recorded simultaneously with H_β and Ne I or Ar II line profiles, yielded information about the electron concentration (2 X 10²⁰-2 X 10²² m^-3), temperature and relative ion composition of the plasma. Plots have been made of the forbidden to allowed peak separations (S), forbidden to allowed relative intensities of the peaks (F/A) and dips (i.e. the minimum intensities between lines) to allowed peak intensities (D/A) as functions of electron concentration, temperature and ionic composition in different plasmas.The peak separations depend only on the electron concentration. Other characteristic line-profile parameters (F/A and D/A) show weak ion motion with a strong electron-concentration influence. We propose simple formulae, which may be useful for practical determinations of the electron concentrations in helium-containing plasmas with an accuracy of ±15% and without taking into account either the chemical composition of the plasma or the temperature.     

Behavioral studies of gain and saturation energy density in a N2 laser with corona preionization

By the use of an oscillator-amplifier (OSC-AMP) TE N₂ laser system, both operating with corona preionizers, the laser parameters (small-signal gain g ₀ and saturation energy density E _s) have been measured at different N₂ gas pressure and for different states of the AMP preionizer. The details of our measurements are presented. In addition, the effect of He buffer gas on the laser parameters has also been investigated; it was found that both laser parameters remain almost constant up to 150 Torr of He gas pressure, indicating that He mainly affects the discharge uniformity. Finally, with the variation of the N₂ laser gain values in the literature, we found that the g ₀-N₂-laser parameter depends strongly on the length of the laser channel. Based on the most recent measurements, a graph showing this dependency is introduced.     

A comparison between shake-up and UV charge-transfer transitions

The He(II) spectra of the unsubstituted metallocenes {M(η-C₅H₅)₂}, M  V, Cr, Mn, Fe, Co, Ni and Ru, and of {Mn(η-C₅H₄Me)₂} are reported; both He(I) and He(II) spectra of some decamethylmetallocenes {M(η-C₅Me₅)₂}, where M  Mg, V, Cr, Mn, Fe, Co and Ni, are also given. Intensity changes between the He(I) and He(II) spectra are shown to provide a reliable guide to band assignment. A ligand field treatment of the decamethylmanganocene cation, including limited configuration interaction, gives values for Δ₂, B and C; these values are also in good agreement with the photoelectron spectra of {M(η-C₅Me₅)₂} where M  V, Cr and Fe. Overlap between the ligand and metal “d” band structures prevents complete assignment in the cases of Co and Ni.     

Calculation of the wave functions of the ground and weakly excited states of helium II

The wave functions of the ground (Ψ₀) and the first excited (Ψ_k) states of He II in the second-order approximation, i.e., up to the first two corrections to the corresponding solutions for a weakly nonideal Bose gas, are determined by the collective variable method, which was proposed by Bogolyubov and Zubarev and developed in the studies by Yukhnovskii and Vakarchuk. The functions Ψ₀ and Ψ_k = ψ_kΨ₀ are determined as the eigenfunctions of the N-particle Schrödinger equation from a system of coupled equations for Ψ₀, Ψ_k, and the quasiparticle spectrum E(k) of helium II. The results consist in the following: (1) these equations are solved numerically for a higher order approximation compared with those investigated earlier (the first-order approximation), and (2) Ψ₀ and ψ_k are derived from a model potential of interaction between He⁴ atoms (rather than from the structure factor as earlier) in which the potential barrier is joined with the attractive potential found from experiment. The height V ₀ of the potential barrier is a free parameter. Except for V ₀, the model does not have any free parameters or functions. The calculated values of the structure factor, the ground-state energy E ₀, and the quasiparticle spectrum E(k) of He II are in agreement with the experimental values for V ₀ ≈ 100 K. The second-order correction to the logarithm of Ψ₀ significantly affects the value of E ₀ and provides the asymptotics E(k → 0) = ck, while the second-order correction to ψ_k slightly affects the E(k). The second-order corrections to Ψ₀ and ψ_k have a smaller effect on the results compared with the first-order corrections, whereby the theory is in agreement with experiment; therefore, one may assume that the truncated Ψ₀ and ψ_k well describe the microstructure of He II. Thus, the series for Ψ₀ and Ψ_k can be truncated in spite of the fact that the expansion parameter is not very small (～1/2).     

Measurement of Ar(I) and Ar(II) transition probabilities in LTE ARC plasmas

The transition probabilities of two Ar(I) lines and one Ar(II) line have been measured in emission on wall-stabilized argon arc plasmas (0·5×10⁵?p, Nm^-2?3×10⁵; 10,000?T, K?20,000; 10²²?N_e, m^-3?5×10²³) using the “method of best fit (MBF)”. The results (without line-wing correction) are for Ar(I) at 714·7 nm, A_nm=5·66×10⁵ s^-1±5%; for Ar(I) at 430·0 nm, A_nm=3·40×10⁵ s^-1±5%; for Ar(II) at 480·6 nm, A_nm=8·82×10⁷ s^-1±7%. These values were not influenced by deviations from LTE, which have been observed at electron number densities n_e?10²³ m^-3. The small uncertainties were achieved after careful corrections of different sources of error.     

A Structural and Ellipsometric Investigation of Thin Gallium Oxide Layers Deposited on Si by Means of Laser Deposition

The morphology of Ga₂O₃ layers deposited on a silicon substrate by pulse laser deposition is studied using scanning electron microscopy in the thickness range of 30–200 nm. Using spectroscopic ellipsometry in the wavelength range from 250 to 900 nm, the thickness of layers and dispersion of their optical parameters (complex pseudodielectric function ε, refractive and absorptive indices) have been determined and the fraction of voids has been estimated in the scope of the Bruggeman effective medium approximation. In the spectrum of the imaginary part ε₂, there is observed an increase in values in the region of energy E = 4.8 eV corresponding to the direct interband transition in the Ga₂O₃ structure. X-ray structure analysis showed the presence of peaks typical for the β-Ga₂O₃ structure. The results of the investigations can be used for the formation of wide-bandgap gallium oxide layers in developing devices of power electronics and in creating optoelectronic devices for the UV range.     

On the He(I) and Ne(I) photoelectron spectra of OCS

The He(I) (58.43 nm) and Ne(I) (73.59–74.37 nm) photoelectron spectra of carbonyl sulphide have been reinvestigated at an improved resolution and a high signal-to-noise ratio; deconvolution of the data was carried out to aid interpretation of the spectra. Improved values are deduced for the vibrational wavenumbers and the ionization energies. The spin—orbit components of the Ã²Π II level are well resolved and a value of 135 cm^?1 (17 ± 5 meV) is proposed for the splitting. Perturbations in the relative intensities are observed in the Ne(I) spectrum; they suggest that the autoionizing Rydberg state located around 73.7 nm is excited by the 73.59 nm Ne(I) line and contributes to populate, with different probabilities, the ionic levels of lower energy, and particularly the X?²Π state.