Atomic compound states in rare gases: Bound-state energies

Bound state energy of the compound states of the rare gases has been computed in the Hartree-Fock approximation. Results obtained for neon and xenon well agree with the experimental data and their usual interpretation. Different behaviour is shown by argon and krypton.     

Auger parameter of hafnium in elemental hafnium and in hafnium oxide

X-ray photoelectron spectroscopy has been used to determine the Auger parameters in elemental hafnium and in hafnium oxide (HfO₂). The zirconium L_α line has been used as a source of excitation to study the 3d core levels of hafnium, the 1s core level of oxygen, and the X-ray excited MNN Auger region of hafnium and KVV Auger region of oxygen. The Auger parameters for hafnium and oxygen have been determined from these spectral data. In case of oxygen, the Auger parameter has been compared with the corresponding value in water. The change in the Auger parameter is observed to be negative for hafnium and positive for oxygen. We have shown that the opposite signs of the Auger parameters in binary systems can be utilized to determine the direction of charge transfer between the constituents. This is consistent with the chemical shift due to charge transfer. This chemical shift in the core level has been evaluated by subtracting the relaxation shift from the experimentally observed core level shift. It is found to be positive for the 3d_5/2 core level of hafnium in the oxide indicating a charge transfer from hafnium to oxygen in the oxide. The observations are consistent with Pauling’s electronegativity criterion.     

Atomic squeezing in three level atoms

The conditions under which squeezing occurs, in a system of atoms and photons, are modelled by describing atom–photon interactions in three atomic levels. The time evolution of the spin population is calculated for different initial conditions. The effect of the use of coherent states, in the photon sector of the initial condition, is discussed. It is found that (i) the use of coherent states does not suffice for the transfer of spin between the atoms and the laser field, (ii) the interactions between the atomic levels and the radiation field must be non-symmetric, and (iii) that the squeezing is washed-out if the number of atoms is increased.     

Experimental transition probabilities and improved level energies in Yb III

Radiative lifetimes of nine out of the twelve 4f¹³6p levels in Yb III have been measured, seven of these for the first time. A Penning discharge lamp is introduced as a continuous plasma source, in which the lifetimes are determined with the time-resolved laser-induced fluorescence technique by pumping from metastable 5d and 6s levels. Spectra of the same source are recorded with a Fourier-transform spectrometer, which are used to derive branching fractions of the 6p and 7s levels. Combined with the lifetimes, the branching fractions are used to determine 81 experimental transition probabilities. Wavelengths of 142 Yb III transitions are measured and the uncertainties of corresponding Ritz wavenumbers are improved by an order of magnitude from the prior values. The energy of the 5d (5/2,5/2)^○ ₀ level has been shifted 144.20 cm^-1 to the higher value 45421.045 cm^-1. Much emphasis is put on data treatment and error analysis. Electronic supplementary material Supplementary Online Material     

Luminescence of hafnium dioxide films produced from hafnium dipivaloylmethanate

A technique is developed for measuring luminescence spectra of hafnium dioxide using a hydrogen lamp as an excitation source. The luminescence spectra of the as-grown and annealed hafnium dioxide films prepared by chemical deposition from volatile hafnium dipivaloylmethanate on the Si(111) substrates are measured at room temperature. Intense luminescence at λ ≌ 280 nm is characteristic of nanocrystallites of monoclinic modification. The band gap width is found to be ≌ 5.76 eV. It is shown that the film composition significantly deviates from the stoichiometric one. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 63–67, April, 2007.     

Linear regge trajectories and hadronic level degeneracy at high energies

The statistical bootstrap condition for hadronic systems at rest implies an asymptotic density of states increasing exponentially in the total energy. We show that if for a given system the squared energies of all possible subsystems are constrained to lie on linear Regge trajectories, such a behaviour of the level density indeed follows. This result is then used to clarify common features of dual and statistical bootstrap approaches.     

Systematic for parity distribution in nuclear level density near neutron separation energies

The correct form of nuclear level density function ρ(U,J,π)$\rho (U,J,\pi )$ is required to calculate nuclear cross-sections needed for various applications ranging from reactor designing, nuclear astrophysics, etc., to transmutation of nuclear waste. The asymmetrical statistical distribution of parity of nuclear levels at low energies poses an intriguing problem leading to larger uncertainties in the calculated values of cross-sections. On the basis of high resolution data available on individual resonance parameters (Eo,Jπ,Γn)$(E_o,J^{\pi },{\Gamma }_n)$ for s- and p-wave neutrons, mass and energy dependence formulae for the parity distribution in the nuclear level density have been proposed which supports the fact of equipartition of parities at high excitation energies.     

Determination of localized level energies by a statistics of the fermi-level

For a very large number of samples of a semiconducting material, which is not intentionally doped, the Fermi-level coincides approximately with the respective energy levels of the accidential impurities and defects. Based on this fact, the energies of localized levels were determined from a statistic of the Fermi-level in CdSe platelets. These energies agree very well with most of the values obtained with different methods by other authors.     

Adsorbate-induced surface resonances on tungsten at energies above the vacuum level

In angle-resolved secondary electron emission normal to a W(110) surface, spectral structure, due to adsorbate-induced (i.e. “extrinsic”) surface resonances lying above the vacuum level, is resolved when the energy of the emitted electron corresponds to a gap in the energy bands of the substrate. Results are presented for ordered monolayers of O₂ and CO. The adsorbate resonances are interpreted in terms of excited two-dimensional Bloch states produced by the lattice periodicity of the adsorbate.     

Stabilization energies of charged multiexciton complexes calculated at configuration interaction level

Recombination and stabilization energies of multiexcitons confined in positively and negatively charged semiconductor InGaAs/GaAs quantum dot (QD) samples have been studied by employing large-scale configuration interaction (CI) calculations. The CI calculations show that at most six electrons or two holes can be confined in the QD. Multiply charged multiexciton complexes with up to five excess electrons or two excess holes are also found to be stable, even when a few electron–hole pairs are present in the QD. The chemical potential functions for charged QD samples do not possess the pronounced stepped form as obtained for the corresponding neutral multiexciton complexes. The negatively and the positively charged excitons (negative and positive trions) lie lower in energy as compared to a neutral exciton and a single non-interacting charge carrier in the lowest single-particle state of another quantum dot. The other charged multiexciton complexes studied are not confined with respect to the corresponding neutral multiexciton and a non-interacting charge carrier. To include the contributions from the heavy-hole light-hole (HH–LH) coupling, a perturbative treatment of the band-mixing effects was implemented. The perturbation-theory calculations show that the HH–LH coupling does not shift the energies in the present InGaAs/GaAs QD sample.     

Atomic level analysis of biomolecules by the scanning atom probe

Utilizing the unique features of the scanning atom probe (SAP) the binding states of the biomolecules, leucine and methionine, are investigated at atomic level. The molecules are mass analyzed by detecting a single atom and/or clustering atoms field evaporated from a specimen surface. Since the field evaporation is a static process, the evaporated clustering atoms are closely related with the binding between atoms forming the molecules. For example, many thiophene radicals are detected when polythiophene is mass analyzed by the SAP. In the present study the specimens are prepared by immersing a micro cotton ball of single walled carbon nanotubes (SWCNT) in the leucine or methionine solution. The mass spectra obtained by analyzing the cotton balls exhibit singly and doubly ionized carbon ions of SWCNT and the characteristic fragments of the molecules, CH₃, CHCH₃, C₄H₇, CHNH₂ and COOH for leucine and CH₃, SCH₃, C₂H₄, C₄H₇, CHNH₂ and COOH for methionine.     

Rotational bands in odd hafnium nucleides

Rotational bands up to high-spin members in odd-neutron Hf nucleides are studied by in-beam spectroscopy using (α, xn) reactions on isotopically enriched Yb targets. The $\text{1}\text{2}{}^{\mathrm{?}}$ [521], $\text{5}\text{2}{}^{\mathrm{?}}$ [512], and the $\text{7}\text{2}{}^{\mathrm{+}}$ mixed positive-parity (mainly $\text{7}\text{2}{}^{\mathrm{+}}$ [633]) bands were observed in ¹⁷³Hf and ¹⁷⁵Hf while the $\text{7}\text{2}{}^{\mathrm{?}}$ [514], $\text{9}\text{2}{}^{\mathrm{+}}$ (mainly $\text{9}\text{2}{}^{\mathrm{+}}$[624]), and the $\text{3}\text{QP}\text{(K =}\text{23}\text{2}$⁺) bands were studied in ¹⁷⁷Hf. The analysis of the band structure within the Nilsson model is extended to also include adjacent odd Hf nuclei making it possible to follow these bands through five isotopes of Hf.     

The synthesis of hafnium nanomaterials by alkali metal reduction of hafnium tetrachloride

Hafnium tetrachloride was reduced in organic solvents with lithium powder, sodium–potassium alloy, or lithium hydride/Et₃B. All reductions required sonochemical agitation to proceed at an appreciable rate, with the notable exception of the reaction of HfCl₄ with Li in diethyl ether. Activation of C–H bonds occurred in all reactions, which resulted in carbon-containing products. HfCl₄ was reduced on a 50-g scale with LiH/Et₃B, and a 10-g scale with Li powder in pentane. All the solid products from the reductions were converted to nanomaterials by annealing under vacuum from 500 to 1,000 °C, which also resulted in the sublimation of the alkali metal salts. The nanomaterials contain a mixture of products with the α-Hf (hexagonal) structure (crystallite size 8–250 nm) and the HfC (FCC) structure (crystallite size 3–80 nm), with the amount of hafnium in the bulk annealed product varying from 88 to 99 wt%. When toluene, pentane, or triethylamine solvents were used, the presence of amorphous graphitic or carbonaceous material was also detected by solid state ¹³C NMR. Thermally annealed products were additionally characterized by electron microscopy and thermal analysis under Ar/O₂, and have BET surface areas ranging from 2.7 to 155 m²/g.     

Electric quadrupole interaction in hafnium sulphates

A coincidence system is developed which gives a time resolution of =0,8 ns for the 133–482 keV -ray cascade of¹⁸¹Hf. It is applied to the study of EQI in hafnium sulphate salts. In the case of Hf(SO₄)₂ the interaction strength of _Q = 157.8 ± 0.5 MHz is obtained, together with the assymetry parameter =0.531±0.005 and the field distribution parameter =0.003±0.001. The data are compared with point-charge model calculations.A similar set of EQI data is also derived for another unstable and unidentified hafnium sulphate structure.     

Electron binding energies in the study of adsorption by photoelectron spectroscopy: The reference level problem

There has been much discussion in the literature concerning the definition of a suitable reference level for electron binding energies in solids and adsorbed species. The reference level in molecular photoelectron spectroscopy is the vacuum level at infinity; and, in order to calculate the total energy of the system, it is also the appropriate reference level for electron binding energies in solids. We show that for solids and adsorbates the vacuum level is not a chemically useful reference level. This is because the absolute binding energy is affected by electrostatic potentials which are unrelated to the local chemical bonding. It is concluded that there is no experimental energy level, to which adsorbate binding energies can be referenced, which allows one to make an absolute measurement of binding energy shifts due to surface interaction. Approaches to obtaining chemically meaningful binding energies from the photoelectron spectra of adsorbates are discussed.     

Evaluation of nuclear shell correction energies for realistic level schemes by temperature smearing method

Calculations of shell correction energies by the temperature smearing method for realistic single particle level schemes of finite depth potentials are described and discussed. It is found that the method provides unique values of the shell correction energies for the various shapes relevant in the fission of actinide nuclei including those shapes where breakdown of the usual Gaussian energy smearing procedure was observed.     

四能级原子系统中量子相干增强的Kerr非线性效应的研究

应用密度矩阵方程计算了四能级原子系统中三阶非线性极化率随信号光和探针光频率失谐的变化关系。结果表明，由于量子干涉对信号光强度的敏感性，使四能级原子介质的交叉Kerr非线性作用大大增强，与三能级系统相比，四能级原子介质的Kerr非线性系数可增强两个数量级。