ESR of Ni doped amorphous chalcogenide semiconductors

ESR signals with g = 2.08 and 2.13 due to Ni were observed for evaporated (Ge_0.32Se_0.32Te_0.32As_0.4) 100_-xNi_x and $\text{(Ge}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Se}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{100}{}_{\mathrm{-x}}\text{Ni}{}_{\mathrm{x}}$ films respectively. The large increase of the electrical conductivity by the addition of Ni is discussed in connection with the ESR signal. Bulk glasses prepared by melt-quenching are also investigated for comparison.     

Silver-compensated germanium center in α-quartz

A synthetic germanium-doped crystal of α-quartz was subjected to an electro-diffusion process $\text{ca. 600}\text{V}\text{cm}$, 625°K), in which Ag⁺ ions were introduced along the crystal's optic axis (c). A 9800MHz electron paramagnetic resonance spectrum at room temperature, taken after room temperature x-irradiation, revealed the presence of a silver-compensated germanium center A_Ge?Ag with large, almost isotropic ¹⁰⁷Ag and ¹⁰⁹Ag hyperfine splittings (26.078, 30.112 mT for magnetic field B∥c). Measurement of the spin-Hamiltonian (i.e. matrices $\text{g}$, $\text{A}{}^{73}{}_{\mathrm{<mtext>Ge</mtext>}}$, $\text{A}{}^{107}{}_{\mathrm{<mtext>Ag</mtext>}}$ and $\text{A}{}^{109}{}_{\mathrm{<mtext>Ag</mtext>}}\text{)}$ discloses that a suitable model for the observed center utilizes germanium, substituted for silicon, with the accompanying silver interstitial in a nearby c-axis channel, and with electronic structure in which an appreciable admixture Ge⁴⁺?Ag⁰ to Ge³⁺?Ag⁺ exists. Estimates of the unpaired electron orbital are presented.     

Selenium dioxide: Rotational analysis and Franck-Condon calculations for the 3130 Å 1B2-X̃1A1 absorption system

Band contour analyses of the absorption bands of ⁷⁸Se¹⁶O₂ and ⁸⁰Se¹⁶O₂ at 2949 Å, assigned to the 1₀³ transition (King and McLean, in press), show that they are type A, with transition moment directed in-plane and parallel to the line joining the oxygen nuclei. The electronic transition responsible for the B absorption system of the molecule is therefore ${}^1\text{B}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1$ under the C_2v point group. The contour analysis gives the excited state bond angle as 101.0°, and the bond length as 1.74 Å. The latter value is confirmed by Franck-Condon calculations. There is therefore an increase in bond length and a decrease in bond angle upon electronic excitation. This agrees with the predictions of molecular orbital theory.     

Selenium dioxide: Analysis of the 419-nm absorption system

The C absorption systems in the region 370–500 nm of the three isotopic species ⁷⁸Se¹⁶O₂, ⁸⁰Se¹⁶O₂, and ⁷⁸Se¹⁸O₂ have been comparatively studied in the vapor phase. The 0₀⁰ band is at 23840, 23840, and 23842 cm^?1, respectively. The vibrational structure consists of long progressions in the bending mode ν′₂(a₁) ～ 200 cm^?1, which are based on the origin band and on vibronic origins in which all three normal modes can be active. Most bands are severely overlapped, so that detailed rotational analyses are not possible. Band contour analysis of the 2₀²3₁⁰ band indicates that the transition is ${}^3\text{B}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1$, which acquires intensity by both spin-orbit and spin-vibronic coupling mechanisms. The estimated bond length and angle in the triplet state are 1.69 Å and 100°, respectively, the latter representing a large decrease from the ground state value of 114°.     

Pressure dependence of superconductivity in the pseudo-one-dimensional compound Tl2Mo6Se6

Measurements of the temperature and pressure dependences of the resistivity of the pseudo-one-dimensional ternary compound Tl₂Mo₆Se₆ are presented. We find that the conductivity parallel to the highly conducting c-axis is enhanced by pressure and the superconducting transition temperature T_c is suppressed by pressure at a rate $\text{?T}{}_{\mathrm{c}}\text{?P}\text{=?7.6×10}{}^{\mathrm{?5}}$ kbar^?1. These results are discussed in relation to the current models of transport in one-dimensional conductors.     

Anomalous transient photocurrent in disordered semiconductors: Theory and experiment

Anomalous transient photocurrents are theoretically and experimentally studied in amorphous As₂Se₃. At high photogeneration rates a maximum of photocurrent I_ph(t) is formed by two asymptotes I_ph ～ t^α and $\text{I}{}_{\mathrm{ph}}\text{～ t}{}^{\mathrm{<mtext>?(1?\alpha )</mtext><mtext>2</mtext>}}$. At intermediate generation level the portion of a quasi-stationary current occurs between the two asymptotics due to monomolecular recombination, though the current decay towards the steady state is still governed by bimolecular recombination. At low generation rates the transition into steady-state is determined by monomolecular recombination alone.     

Small angle X-ray scattering evidence for the absence of voids in chalcogenide glasses

Small angle X-ray scattering measurements show no evidence for the presence of voids in chalcogenide glasses, in contrast to the situation found in deposited films of Ge and Si. This result and the observation of a diffraction peak near $\text{k = 1.2}\text{A}\text{?}{}^{\mathrm{?1}}$ are found to be consistent with the existence of a layer structure in glassy As₂S₃ and As₂Se₃.     

Structure,vibrational study and conductivity of the trihydrated uranyl bis(dihydrogenophosphate): UO2(H2PO4)2·3H2O

The X-ray structure (293 K) of UO₂(H₂PO₄)₂·3H₂O has been refined (R = 0.062): M_r = 518g, space group: P2₁/c (Z = 4); $\text{a = 10.816(1)}\text{A}\text{?}$, $\text{b = 13.896(2)}\text{A}\text{?}$, $\text{c = 7.481(1)}\text{A}\text{?}$, β = 105.65(1)^°, $\text{V = 1082.7(2)}\text{A}\text{?}{}^3$; D_c = 3.17 Mg m^?3. The structure consists of infinite chains along the (101) axis with U atoms bridged by two H₂PO₄ groups. The U atom is surrounded by a pentagonal bipyramid of oxygen atoms, one of them being an equatorial water molecule. The cohesion between the chains is ensured by hydrogen bonds involving the two last water molecules. An assignment of IR and Raman bands with isotopic substitution spectra is proposed. A phase transition at 128 K was made evident by DSC and spectroscopy. The room-temperature phase is characterized by a high disorder of the OH bond orientation while in the low-temperature phase H₂O and POH species appear well oriented. The conductivity seems to occur by proton transfer and protonic-species rotation at the POH-water molecular interface between the chains. ac conductivity has been determined by means of the complex-impedance method ($\text{σ}{}_{\mathrm{<mtext>RT</mtext>}}\text{～ (3?12) × 10}{}^{\mathrm{?5}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$; E ～ 0.20 eV).     

ESR and photoacoustic spectra of V2O5−MO2 (M = Se, Te, Ge) glasses

ESR spectra of V₂O₅?MO₂ (M = Ge, Se, Te) glasses are investigated in the range 298–498 K. The spectra at 298 K are characteristic of V⁴⁺ with the 3d¹ electron localized on a single ${}^{51}\text{V}\text{(I =}\text{7}\text{2}$) in the glass network. At higher temperature, the hyperfine structure progressively broadens, leading eventually to a broad, single ESR peak. These results are consistent with thermally-induced electron hopping from V⁴⁺ to V⁵⁺. Photoacoustic spectra of the glass at 298 K are characteristic of V⁴⁺ in a distorted octa environment. A correlation of ESR and PAS data suggests that covalency increased as M is charged from Ge through Te to Se.     

A study of valency changes of vanadium ions in Al2O3 by γ irradiation

The effect of γ irradiation at 300 K on the concentrations of vanadium ions V³⁺, V⁴⁺ and V²⁺ in Al₂O₃ has been studied quantitatively, using three techniques: optical absorption (V³⁺), low temperature thermal conductivity measurements (V⁴⁺) and EPR (V²⁺). Several single crystals of Al₂O₃ doped with vanadium in a large range of concentration $\text{(2.8 × 10}{}^{18}\text{? 1.3 × 10}{}^{20}\text{at.}\text{cm}{}^3\text{)}$ have been measured. The evolution of the respective concentrations by γ irradiation as a function of the total vanadium content C is quite different in the two regions $\text{C< 1.2 × 10}{}^{19}\text{at.}\text{cm}{}^3$ and C larger than this value. A consistent analysis of the results has nevertheless been achieved, leading to the determination of the absolute concentrations of the three ions in the as-received and γ irradiated states for all samples with $\text{C<4.2 × 10}{}^{19}\text{at.}\text{cm}{}^3$ (room temperature annealing is observed above this value). The concentrations of V⁴⁺ and V²⁺ ions are always small, but V⁴⁺ ions are more stable: they are present in the as-received state at a level of 1% of the total concentration and a maximum value of $\text{/}\text{?}\text{2.3 × 10}{}^{18}\text{at.}\text{cm}{}^3$ is observed in the γ irradiated state; on the other hand there are less than 4.7 × 10¹⁵V²⁺ ions per cm³ in the as-received state and the maximum value is only $\text{4.2 × 10}{}^{17}\text{at.}\text{cm}{}^3$. Charge transfer between V ions only is not sufficient to explain the experimental results and other defects must be involved in the γ irradiation effect.     

Iron diffusion and electrical conductivity in magnesio-wüstite solid solutions (Mg,Fe)O

Diffusion of ⁵⁹Fe and electrical conductivity in magnesio-wüstite solid solution (Mg_xFe_1?x)O with x = 0.26 and 0.5 have been measured as a function of temperature and oxygen partial pressure. For both solid solutions, the results show that at 1100°C the diffusivity D of ⁵⁹Fe is directly proportional to $\text{p}{}_{\mathrm{o2}}{}^{\mathrm{<mtext>1</mtext><mtext>6</mtext>}}$, whereas the electrical conductivity σ is directly proportional to $\text{p}{}_{\mathrm{o2}}{}^{\mathrm{<mtext>1</mtext><mtext>3.4</mtext>}}$. At a given temperature and oxygen partial pressure, the value of D decreases with an increase in MgO concentration in the solid solution. The results are discussed in terms of the coexistence of variously ionized cation vacancies and their change in concentration with MgO additions.     

Field-driven reversible doping of a polydiacetylene crystal (DCH)

The dark conductivity of crystalline DCH contacted with a J₂ saturated 0.5 n NaJ electrolytic solution is found to be determined by field-driven, 3eversible doping by J^?/J^?₃ ions penetrating the crystal at negative bias. The maximum conductivity is about $\text{10}{}^{\mathrm{?3}}\text{(Ω cm)}{}^{\mathrm{?1}}$ at a doping level of ≈ 10^?3 mol per base mole DCH.     

Dielectric susceptibility and correlation length of one-dimensional CDW with impurties. II. weak disorder

Dependence of static dielectric susceptibility and correlation length of charge density waves (CDW) with weak defects on parameter of incommensurability with lattice is investigated. In almost commensurate phase (h?h_ch_c), $\text{χ ～ (h?h}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{In}{}^{\mathrm{<mtext>-4</mtext><mtext>3</mtext>}}\text{h}{}_{\mathrm{c}}\text{/h?h}{}_{\mathrm{c}}$ and R_c ～ (h ? h_c)^{$\text{2}\text{3}$}. In${}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{h}{}_{\mathrm{c}}\text{/h ? h}{}_{\mathrm{c}}$. Far from commensurability $\text{(h?h}{}_{\mathrm{c}}\text{) χ～ (a+h}{}^2{}_{\mathrm{c}}\text{/h}{}^2\text{)}{}^{\mathrm{<mtext>-2</mtext><mtext>3</mtext>}}$, $\text{R}{}_{\mathrm{c}}\text{～ (a + h}{}^2{}_{\mathrm{c}}\text{/h}{}^2\text{)}{}^{\mathrm{<mtext>-2</mtext><mtext>3</mtext>}}$, where a is the dimensionless ratio of random potential intensities, corresponding to backward and forward scattering impurities.     

Structure of positive parity states in 29P and two-step processes in (p,t) reactions

From a study of (p,t) reactions on ³¹P and ³⁰Si it is suggested that in ²⁹P the states with $\text{J}{}^{\mathrm{\pi }}\text{=}\text{1}\text{2}{}_1{}^{\mathrm{+}}$ and $\text{1}\text{2}{}_2{}^{\mathrm{+}}$, the pair $\text{3}\text{2}{}_2{}^{\mathrm{+}}$, $\text{5}\text{2}{}_1{}^{\mathrm{+}}$, and the pair $\text{7}\text{2}{}_3{}^{\mathrm{+}}$, $\text{9}\text{2}{}_1{}^{\mathrm{+}}$ are related by weak coupling of a s${}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ proton with the states 0₁⁺, 0₂⁺, 2₁⁺ and 4₁⁺ respectively of ²⁸Si. Completely atypical L = 2 angular distributions have been obtained for the $\text{3}\text{2}{}_1{}^{\mathrm{+}}$ and $\text{5}\text{2}{}_2{}^{\mathrm{+}}$ states in ²⁹P and it is suggested that this is due to contribution by two-step processes.     

Analysis of the 2770-Å emission system in I2

A weak emission spectrum of I₂ near 2770 Å is reanalyzed and found to to minate on the A(1u³Π) state. The assigned bands span v″ levels 5–19 and v′ levels 0–8. The new assignment is corroborated by isotope shifts, band profile simulations, and Franck-Condon calculations. The excited state is an ion-pair state, probably the 1g state which tends toward $\text{I}{}^{\mathrm{?}}\text{(}{}^1\text{S) +}\text{I}{}^{\mathrm{+}}\text{(}{}^3\text{P}{}_1\text{)}$. In combination with other results for the A state, the analysis yields the following spectroscopic constants: T″_e = 10 907 cm^?1, $\text{D}$″_e = 1640 cm^?1, ω″_e = 95 cm^?1, $\text{R″}{}_{\mathrm{e}}\text{= 3.06}\text{A}\text{?}$; T′_e = 47 559.1 cm^?1, ω′_e = 106.60 cm^?1, $\text{R′}{}_{\mathrm{e}}\text{= 3.53}\text{A}\text{?}$.     

Energy available for the double beta-decay of 76Ge

The Manitoba II high-resolution mass spectrometer has been used to determine the atomic mass difference ${}^{76}\text{Ge}\text{?}{}^{76}\text{Se}\text{= 2040.71 ± 0.52}\text{keV}$. This result, which is superior in precision and accuracy to previous values, should facilitate current searches for the neutrinoless double beta-decay of ⁷⁶Ge.     

Electronic conductivity of AgI using D.C. polarization and charge transfer techniques

A Study of electronic conductivity using the d.c. polarization technique has been carried out in α and β-AgI which shows the former is a hole and the latter an electron conductor. Activation energies of undoped and Cu-doped single crystals and polycrystalline β-AgI were found to be 0.46 eV, 0.34 eV and 0.44 eV respectively and can be related to electron trap depths. The electron transference number ($\text{σ}{}_{\mathrm{\theta }}\text{σ}{}_{\mathrm{t}}$) for polycrystalline β-AgI was found to be 0.008 at 306 K. The activation energy for hole conduction in α-AgI was determined to be 0.97 eV in agreement with previous XPS studies.Transient measurements have also been conducted using the charge transfer technique in double cells of polycrystalline β-AgI. The carrier concentration C_θ and electron mobility μ_θ, have thus been estimated to be 1.8 × $\text{10}{}^{15}\text{cm}{}^3$ and 5.14 × 10^?5$\text{cm}{}^2\text{V}$?sec. respectively at 306 K, while the double layer capacitance was 0.496 $\text{μF}\text{cm}{}^2$.     

3Σu−-3Σu+ coupling in the O2B3Σu− predissociation

The role of $\text{B}{}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{?}}\text{-2}{}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$ spin-orbit mixing in the O₂ Schumann-Runge predissociation is investigated. The $\text{2}{}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$ state is found to cross the $\text{B}{}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{?}}$ state near 2.0 Å with an interaction matrix element of approximately 55 cm^?1. This state contributes to the widths of the Bv ≥ 6 levels, but introduces only small level shift perturbations. When the partial widths due to the ${}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{?}}\text{-}{}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$ interaction are added to the previously calculated widths due to the ⁵Π_u, ³Π_u, and ¹Π_u states, reasonable agreement is obtained with experimental measurements on O¹⁶O¹⁶ and O¹⁸O¹⁸. The possibility of non-Lorentzian line profiles and the dependence of the width on rotational quantum number is investigated. The approximation of the spin-orbit matrix element by its value at the crossing point is shown to be a good approximation for calculating the second difference perturbations.     

Excitation intensity dependence of shallow donor bound exciton luminescence in n-GaAs

Luminescence measurements were performed on high purity epitaxial n-GaAs $\text{(}\text{1 × 10}{}^{14}\text{cm}{}^3\text{< n <}\text{3 × 10}{}^{15}\text{cm}{}^3\text{)}$ for various excitation intensities I₀ in the range $\text{8 mW}\text{cm}{}^2\text{< I}{}_0\text{<}\text{4 W}\text{cm}{}^2$. The luminescence line corresponding to the radiative decay of the shallow donor bound exciton, (D⁰, X), broadens with increasing I₀ and appears as a doublet for $\text{I}{}_0\text{? 1}\text{W}\text{cm}{}^2$, while the two-electron replica of the (D⁰, X) remains a single narrow line. The doublet structure of the (D⁰, X) at elevated excitation levels is due to missing luminescence intensity in the center of the line as a consequence of low (D⁰, X) concentration in a layer extending 1–2 μm from the sample surface into the bulk. The low concentration of (D⁰, X) is attributed to capture of (D⁰, X) quanta into surface states, extending to lower energies from the Fermi level fixed by the shallow donors. Comparison of the present results with luminescence spectra obtained by various authors reveals, that unexplained spectral features in the (D⁰, X) region of n-GaAs reported in the literature are a consequence of high excitation intensity and correspond to the effect reported here. In partly compensated p-GaAs with donor concentrations as given above, the (D⁰, X) did not transform into a doublet structure even at $\text{W}\text{cm}{}^2$ excitation intensity.     

Stark mixing spectroscopy in cesium

We present a new technique for selectively populating excited states which are inaccessible by dipole excitation from the ground state. The method uses a static electric field to introduce a component of a dipole-allowed state into the state of interest. We have applied the method to cesium to measure lifetimes and a Stark mixing coefficient. The results are $\text{τ(6}{}^2\text{D}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)=64(2) ns}$, $\text{τ(7}{}^2\text{D}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)=92.5(15) ns}$, and <6²D_{$\text{5}\text{2}$}|;ez |7²P_{$\text{3}\text{2}$}>/(E_7P?E_6D)=0.7(3)×10^?3 where is in kV/cm. 141