Energy band structure of silver azide (AgN3)

The self-consistent energy band structure of silver azide (AgN₃) is calculated within the density-functional approximation with a mixed basis and a norm-conserving pseudopotential. The energy band diagram is displayed and the origin of the bands is analyzed by a comparison with the molecular states of N ₃ ^– . The role of the d states of silver, which are partially responsible for the formation of a wide anionic-cationic top valence band, is pointed out. The obtained results agree with experimental data and exhibit similarities with the band structures of silver halides.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 38–40, February, 1992.     

Explosive luminescence of silver azide

Spectroscopic-kinetic investigations of the luminescence accompanying the explosive decomposition of silver azide are performed. A new phenomenon is observed: predetonation luminescence. A comparison of the predetonation luminescence spectrum with the band structure is in agreement with a model in which the exothermic reaction 2N ₃ ⁰ →N₆ provides the energy for the explosion. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 2, 101–103 (25 July 1997)     

Rate constant of capture of electron charge carriers on a screened repulsive center

The rate constant of capture of electron charge carriers on a screened repulsive center are performed. Approximate expressions for the potential barrier width, the capture cross section, and rate constant are derived. It is shown that the increase in the concentration of free charge carriers in silver azide from 10¹⁶ to 10²⁰ cm^?3 results in an increase in the capture rate constant by four orders of magnitude. It is also shown that, with increasing concentration of free carriers, the temperature dependence of the rate constant weakens and the effective activation energy of capture in silver azide decreases from 0.18 to 0.01 eV.     

Lead azide pre-explosive luminescence

Pre-explosive luminescence of lead azidePb(N ₃)₂ in the range from 400 to 1000 nm was investigated both experimentally and theoretically. A theoretical investigation of the electron structure for a lead azide crystal was made using the Hartree-Fock method. The rated density of states and experimental pre-explosive luminescence spectrum of lead azide were analyzed in detail. The probable location of the hole quasi-local state in the valence band was determined. Kemerovo State University, Michigan Technological University. Translated from Izvestiya Vysschikh Uchebnych Zavedenii, Fizika, No. 3, pp. 17–21, March, 2000.     

Energieverlustmessungen mit 60 keV Elektronen an amorphem und polykristallinem Selen und Tellur und Bestimmung optischer Konstanten

The energy loss functions Im—(1/?) of amorphous and polycrystalline Selenium and Tellurium are determined from energy loss spectra of 60 keV electrons in the energy range up to 30 eV. The optical constants ?₁ and ?₂ are calculated from the energy loss function by Kramers Kronig analysis. The energy difference in the position of the volume plasma loss of amorphous and polycrystalline foils is compared with the calculated change in free electron plasma energy resulting from density change. Characteristic structure dependence of the optical constants are found to be similar for Selenium and Tellurium. They are discussed in terms of the results of band structure calculations.     

Effect of a dielectric shell of a silver nanoparticle on the spectral position of the plasmon resonance of the nanoparticle in photochromic glass

The behavior of the spectral position of the absorption band of colloidal silver in photochromic glass is analyzed in relation to the variation in the refractive index of a thin layer of the medium (shell) that surrounds silver nanoparticles. It is shown that the appearance of a shell with a high refractive index leads to a long-wavelength shift in the plasmon absorption band of silver nanoparticles. These results make it possible to explain particular features of the absorption spectrum of photothermorefractive glasses.     

Electronic structure of PbI2 from photoelectron spectra and the exciton problem

The valence band density of states for PbI₂ is determined from X-ray and u.v. induced photoelectron spectra. It is shown that the band derived from Pb 6s states is at 8 eV binding energy and not at the top of the valence bands as suggested by band structure and charge density calculations. A rigid shift in the predominantly iodine 5p derived bands to lower binding energy brings the band structure calculations into essential agreement with experiment. Pb 5d core level binding energies determined here are used to derive core level exciton energies of 0.7 eV from published reflectivity spectra.     

Symmetric and Anti-Symmetric Lamb Waves in a Two-Dimensional Phononic Crystal Plate

It is weft known that Lamb waves in a plate with a mirror plane can be separated into two uncoupled sets： symmetric and anti-symmetric modes. Based on this property, we present a revised plane wave expansion method （PWE） to calculate the band structure of a phononie crystal （PC） plate with a mirror plane. The developed PWE method can be used to calculate the band structure of symmetric and anti-symmetric modes separately, by which the depending relationship between the partial acoustic band gap （PABG）, which belongs to the symmetric and anti-symmetric modes alternatively, and the position of the scatterers can be determined. As an example of its application, the band structure of the Lamb modes in a two-dimensional PC plate with two layers of void circular inclusions is investigated. The results show that the band structure for the symmetric and anti-symmetric modes can be changed by the position of the scatterers drastically, and larger PABGs will be opened when the scatterers are inserted into the area of the plate, where the elastic potential energy is concentrated.     

Relaxation of electronically excited products of solid-state reactions in the crystal lattice

The mechanisms of deactivation of electronically excited products of decomposition of silver azide (nitrogen molecules) are examined. A model of dipole interaction with the electron subsystem of the crystal is used to estimate the rate constants of deactivation with formation of electron-hole pairs (∼10⁹ s⁻¹) and energy transfer to a band hole (∼10⁻¹² cm³ s⁻¹). The values obtained confirm the basic postulate underlying the models of solid-phase chain reactions: the preferential formation of electronic excitations of the crystal lattice during the deactivation of excited decomposition products.     

Density of Electronic States in the Conduction Band of Ultrathin Films of Naphthalenedicarboxylic Anhydride and Naphthalenetetracarboxylic Dianhydride on the Surface of Oxidized Silicon

The results of examination of the electronic structure of the conduction band of naphthalenedicarboxylic anhydride (NDCA) films in the process of their deposition on the surface of oxidized silicon are presented. These results were obtained using total current spectroscopy (TCS) in the energy range from 5 to 20 eV above the Fermi level. The energy position of the primary maxima of the density of unoccupied states (DOUS) of an NDCA film was determined based on the experimental TCS data and calculated data and compared with the position of the DOUS maxima of a naphthalenetetracarboxylic dianhydride (NTCDA) film. The theoretical analysis involved calculating the energies and the spatial distribution of orbitals of the molecules under study at the B3LYP/6-31G(d) DFT (density functional theory) level and correcting the obtained energies in accordance with the procedure that was proven effective in earlier studies of the conduction band of films of small conjugated organic molecules. It was found that the DOUS maxima of the NTCDA film in the studied energy interval from 5 to 20 eV above the Fermi level are shifted toward lower electron energies by 1–2 eV relative to the corresponding DOUS maxima of the NDCA film Subdivision of the Ufa Federal Research Centre of the.

     

Sensitized Fluorescence of Silver Nanoparticles in the Presence of Pyrene

The fluorescence of pyrene adsorbed onto the surface of the cetyltrimethylammonium-coated silver nanoparticles was studied. Pyrene molecules adsorbed on freshly prepared silver particles were found to be in close proximity to silver surface thus providing the possibility of energy transfer from excited pyrene to silver cores of the particles. In that case along with the expected fluorescence of pyrene we observed the fluorescence of the silver nanoparticles induced by the excited pyrene molecules. In due course the restructuring of the cetyltrimethylammonium layer resulted in moving of pyrene molecules away from silver surface and simultaneous disappearance of the silver nanoparticles fluorescence band. These data strongly support the recent hypothesis of fluorophore-plasmon coupled emission.     

硅铝酸银分子筛吸附氖原子的第一性原理计算

采用基于第一性原理的密度泛函理论(DFT)和局域密度近似(LDA)方法,优化计算硅铝酸银分子筛吸附Ne原子体系的几何结构,能量,电子能带和电荷密度分布。结果表明,硅铝酸银为层状的周期结构,具有直径为a=5.390 Å的孔道。在分子晶体孔道的轴线上,桥O原子附近(I)和表面Ag+离子附近(II)的能量均有利于对Ne原子的吸附。尽管Ne(I)的能量最低,但是SiO4四面体排斥产生的能垒在动力学上不利于Ne原子的吸附。电子能带和电荷分布显示,Ne(II)原子主要受库仑极化的影响,其电子能带的能量较高,Ne(I)原子与桥O原子之间的共价作用能够降低对应的电子能带能量。     

硅铝酸银分子筛吸附氖原子的第一性原理计算

采用基于第一性原理的密度泛函理论(DFT)和局域密度近似(LDA)方法,优化计算硅铝酸银分子筛吸附Ne原子体系的几何结构,能量,电子能带和电荷密度分布。结果表明,硅铝酸银为层状的周期结构,具有直径为a=5.390 Å的孔道。在分子晶体孔道的轴线上,桥O原子附近(I)和表面Ag+离子附近(II)的能量均有利于对Ne原子的吸附。尽管Ne(I)的能量最低,但是SiO4四面体排斥产生的能垒在动力学上不利于Ne原子的吸附。电子能带和电荷分布显示,Ne(II)原子主要受库仑极化的影响,其电子能带的能量较高,Ne(I)原子与桥O原子之间的共价作用能够降低对应的电子能带能量。     

The external photoeffect and a simple band scheme of AVB 3 VII iodide crystals

The external photoeffect was measured on AsI₃, SbI₃ and BiI₃ crystals grown in the gaseous phase from very pure parent materials. The energy necessary for transferring an electron from the top of the valence band to the zero energy level was determined from the position of the long wave-length threshold of photoemission in the first approximation. This energy was approximately the same for all Vb metal iodide crystals, i.e. 5.8 eV. The electron affinities of crystals were determined from the known forbidden band width and from the results of measurements, and a simple band scheme of the crystals was proposed.The fine structure of the spectrum was successfully investigated on BiI₃ crystals, from which it was possible to conclude the existence of exciton levels.Finally, the relations between the forbidden band width, the difference of the electronegativities corresponding to the various compounds and the melting point of A^VB^VII crystals were discussed.The authors' thanks are due to Dr. F. J. Vilesov from the Department of Physics of A. A. danov State University in Leningrad (USSR) for the possibility of measuring the photoelectrical work function.     

Electronic structure of CuN3(I)

Self-consistent calculations of the electronic structure of monovalent copper azide CuN₃(I) are carried out in the framework of the density functional theory in the basis set of pseudoatomic orbitals. The specific features of the band structure and the effect of Cu d states on the formation of the energy spectrum of CuN₃(I) are considered. The structure of chemical bonding is analyzed using electron density maps.     

Study of the local atomic structure of a silver aluminum alloy by the method of extended electron energy loss fine structure (EELFS)

Extended energy loss fine structure spectra are obtained for electrons at the Al K and Ag M _4,5 edges for an Al-20 wt %Ag solid solution after high-temperature aging, as well as for the pure alloy components. The analysis layer depth was ～20 Å. Radial distribution functions for the atoms are determined by Fourier transforming these spectra with a correction for the phase shift and the method of regularization. For pure aluminum and silver it is found that the position of the first coordinate spheres does not differ from bulk interatomic distances. For the binary alloy it was shown that the state of the sample corresponds to a decomposed solid solution with inclusions of a phase enriched with silver against an aluminum host background. The interatomic Al-Al distances in the binary alloy correspond to the length of a pure aluminum bond. The partial distances to the first two coordination spheres for the pairs Ag-Ag, Ag-Al are the same and equal the interatomic distances of the γ-phase Ag₂Al.     

Femtosecond optical diagnostics of interlevel energy relaxation in the band gap of silver iodide nanocrystals

The kinetics of the relaxation processes in silver iodide nanocrystals synthesized in a nanoporous silicate glass matrix and excited by femtosecond laser pulses has been experimentally studied. A short-lived characteristic transmission band is found to be formed in the spectral range of exciton absorption of nanocrystals. The specific features of photoexcited-carrier relaxation, which are due to the energy redistribution of captured carriers over levels in the band gap of silver iodide nanocrystals, are considered. The energy transfer relaxation rates are estimated and possible mechanisms of the energy transfer are discussed.     

The exact solutions of Kane equations which have position-dependence band gap in an external non-uniform electric field

The energy spectrum of electrons in narrow band gap semiconductor nanocrystals which have position dependence band gap in an external non-uniform electric field which compensate the position dependence of the band edge of the valence band potential are studied theoretically taking into account the non-parabolicity of electrons in dispersion laws. The exact solutions of the Kane equations with strong spin–orbital interaction are determined with and without magnetic field via the band gap changes as a function of the position. The position dependence of the band gap is taken parabolically.     

光照对HF/Fe(NO3)3溶液中制备硅纳米线的作用研究

以不同掺杂浓度的单晶n型硅为衬底、金属银为催化剂、硝酸铁作为氧化剂制备硅纳米线, 系统研究了光照对不同硝酸铁浓度条件下用化学腐蚀法制备硅纳米线的作用. 研究发现, 不同掺杂浓度的硅衬底, 光照对硅纳米线长度的影响明显不同. 通过对比硅纳米线的长度, 发现光照对硅纳米线的形成兼具促进和溶解作用, 并分别从能带结构、电化学表征和光致发光等方面对这两种作用的形成机理进行了深入讨论.     

Photoelectron spectroscopy studies of the band structure of silver halides

X-ray photoelectron spectroscopy has been used to probe the valence bands of the silver halides. Previous ultraviolet photoemission and optical absorption experiments together with the theoretical band structure calculations form the basis for interpretation of the spectra. Density of states maxima from the halogen p levels are clearly resolved from those of the silver 4d states. Additional splittings due to k space symmetry are observable and in the case of AgCl and AgBr, give excellent conformation of existing band structure calculations. The role of spin-orbit coupling is shown to be unimportant in determining the primary shape of the photoelectron spectrum. The spectrum of AgF shows the inversion of silver 4d and halogen 2p levels suggested by the optical absorption spectra and predicted by several recent band calculations. A new interpretation is proposed for the AgF optical spectrum in which the observed excitons are due to the forbidden Γ₁₂→ Γ₁ and Γ_25′ → Γ₁ tr the high temperature body centered cubic structure. These spectra clearly show the broadening of the I 5p levels which causes the band gap to decrease above the transition temperature.