Ligand field splitting of d orbitals in nine-coordinated sites of capped antiprism structure: Application to monazite

The splitting of the energy levels of d¹ ions in a field of nine ligands arranged in a capped antiprism is calculated for both the regular and distorted structure. In the regular capped antiprism, the ground state is found to be the degenerate state dxy, dx²-y²; in the distorted structure, the ground state is dx²-y². The results are consistent with experimental ESR data on the V⁴⁺: CePO₄ system.     

Effect of F-inclusion in nm-thick MgO tunnel barrier

We investigated the electrical characteristics of MgO tunnel barriers while we add F during oxidation process of nm-thick Mg layer. Specifically we measured dI/dV and d²I/dV² data of MgO tunnel barriers as we add F. When comparing the data of magnesium oxyfluoride tunnel barriers to those of aluminum oxyfluoride data, we have found that effect of F-inclusion in MgO is different from that in AlO_x; F-inclusion in MgO barrier makes the barrier more symmetric while F-inclusion in AlO_x barrier makes the barrier more asymmetric. However, the d²I/dV² data of MgO did not change much even after F-inclusion, suggesting a very small amount of F-doping can make significant change in oxidation process of nm-thick Mg layer. We believe this result from the fact the oxidation process of nm-thick Mg layer is reaction-limited while the oxidation process of Al layer is diffusion-limited.     

Preparation and properties of binary metal monolayers: II. Pb and Sn on Al(100)

The growth modes, structures and thermal properties of binary monolayers of lead and tin on the (100) face of aluminium have been investigated by LEED and AES. Monolayers of pure lead and pure tin were also examined. Dense binary layers were formed by successive vapour deposition of the two elements. The compositions were accurately determined by AES. For the pure monolayers sharp changes in the sticking probability at half-monolayer coverage (detectable by AES) lead to accurate determinations of the densities of the complete monolayers. The LEED pattern for the pure lead monolayer can be interpreted in terms of a pseudo-hexagonal arrangement while that for tin shows intensity features that favour an arrangement of dense atomic chains. For the binary layers the apparent mesh parameter varies continuously as a function of composition between the values for the pure monolayers. Different variations in parameter are found, depending on which element is deposited first. It is deduced that the binary layers are formed of intimate mixtures of the coincidence meshes of the pure monolayer structures together with disordered regions. Each binary layer is characterized by a temperature for complete thermal desordering T_d. For tin-rich layers there are significant differences between values of T_d for “tin-first” and “lead-first” layers. A sharp minimum in T_d is observed for the composition Sn₄Pb.     

Low-temperature transport properties of individual SnO2 nanowires

Stannic oxide (SnO₂) nanowires have been prepared by Chemical vapor deposition (CVD). The low-temperature transport properties of a single SnO₂ nanowire have been studied. It is found that the transport of the electrons in the nanowires is dominated by the Efros-Shklovskii variable-range hopping (ES-VRH) process due to the enhanced Coulomb interaction in this semiconducting nanowire. The temperature dependence of the resistance follows the relation lnR∼T^−1/2. On the I-V and dI/dV curves of the nanowire a Coulomb gap-like structure at low temperatures appears.     

A novel investigation of tin-doped ferrihydrite nanoparticles

Tin-doped ferrihydrite was synthesized and characterized with powder X-ray diffraction and ⁵⁷Fe and ¹¹⁹Sn Mössbauer spectroscopy to obtain diagnostic and structural information. Samples were prepared with doping concentrations (molar percentages) of 0, 10, 25, 40, 50, 60, 75, and 90% tin. As Sn concentration increases, the 110 reflection plane of ferrihydrite shifts to higher d-values, while the 300 plane d-values increase, reach a maximum and then sharply drop. The δ (isomer shift) and Δ (quadrupole splitting) values for ⁵⁷Fe Mössbauer spectra increase, while the Γ (line width) values stay constant. In ¹¹⁹Sn Mössbauer spectra, δ values decrease with increasing tin substitution while Δ and Γ values increase. After 50% Sn has been substituted, the ferrihydrite becomes oversaturated with surface tin and a secondary tin structure is proposed to develop.     

Hall mobility of hot electrons in CdS

Photo-Hall effect of hot electrons in a pure single crystal of CdS was observed, for the first time. The measurement was carried out for electric fields up to 4,300 V/cm in magnetic fields up to 40 kOe at 4.2 K. The saturation of the drift velocity V_d of electrons due to optical phonon emission was observed. The saturated value of V_d is found to be about 1.7 × 10⁷ cm/sec.     

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.     

Theoretical studies of the optical and EPR spectra for V in Y2O3 crystal

In this paper, we give an alternative suggestion that both the observed optical and electron paramagnetic resonance (EPR) spectra of Yttrium oxide (Y₂O₃):V³⁺ are attributed to V³⁺ ions at the S₆ site of Y₂O₃. This suggestion is different from the opinion in the previous paper that the optical and EPR spectra are attributed to V³⁺ ions at the C₂ and S₆ sites, respectively. From the suggestion, the optical band positions and spin-Hamiltonian parameters are calculated by diagonalizing the complete energy matrix for 3d² ions in trigonal symmetry. The results are in good agreement with the experimental values, suggesting that both the observed optical and EPR spectra in Y₂O₃:V³⁺ may be due to V³⁺ at S₆ site of Y₂O₃ crystal.     

Perturbation of the Laplacian supported by null sets,with applications to polymer measures and quantum fields

We discuss hamiltonians in L²(R^d, dx) of the form H = ?Δ + V, with V a potential supported by a zero measure set C. In particular if C is a path of a brownian motion b such that V(x) = ∫₀¹λ(x, ω)δ(x-b(s, ω)) ds, we show that H exists as a nontrivial, self-adjoint, lower bounded perturbation of ?Δ when d ?5. We must choose λ to be an infinitesimal, negative function for d = 4,5, but for d ? 3 any bounded real-valued function λ will do. The connection with Edward's model of polymers as well as with quantum fields of the ?_d⁴-type is also discussed. The proofs use methods of nonstandard analysis.     

Nanometer-scale characterization and manipulation of ferroelectric films using scanning probe microscopy

Ferroelectric domain structures in Pb(Ni_0.04Zr_0.28Ti_0.68)O₃ and SrBi₂Ta₂O₉ ferroelectric thin films have been non-destructively observed using various scanning probe microscopy (SPM) modes. Using the SPM, it has been shown that it is possible to not only image but also manipulate the local domain structure on a nanometer scale by biasing the SPM tip. In addition, the SPM was applied to measure dC/dV–V spectra on individual ferroelectric grains. The examples illustrate the possibility of using an SPM-based datastorage read/write system.     

Theory of inelastic tunneling spectroscopy of a single molecule - Competition between elastic and inelastic current

A theory of inelastic electron tunneling spectroscopy of a single molecule with scanning tunneling microscope is presented using the Keldysh Green’s function method for an adsorbate-induced resonance coupled to the molecular vibration. It is found that the correction to the tunneling current is expressed in terms of the transmission probability; the correction is negative for the elastic part of the current and positive for the inelastic one. The differential conductance (dI/dV) exhibits an increase or decrease at the threshold corresponding to the opening of inelastic channel depending on the sign of the correction, and the size of this conductance jump is scaled with the vibrational damping due to electron-hole pair excitation. The lineshape of d²I/dV²-spectra calculated using a renormalized adsorbate Green’s function evolves from an antisymmetric dip to a peak through the derivative-like one as the position of the adsorbate resonance recedes from the Fermi level of the substrate.     

M4,5N4,5N4,5 auger electron spectrum of Ba metal

The Al Kα excited M_4,5N_4,5N_4,5 Auger spectrum of Ba has been measured from the metallic sample evaporated on a Ag substrate. The spectrum has been decomposed into individual line components after the background subtraction. The decomposed spectrum has been compared with the theoretical spectrum calculated for the 4d^?2 final state configuration in the mixed coupling scheme applying jj-coupling for the initial state and intermediate coupling for the final state. The most prominent structure of the spectrum shows the two 4d-hole coupling, but the structure which is caused by the Auger transitions M_,45N_2,3V has also been observed. The screening of the core holes in Ba metal seems to be produced by (5d6s) electrons. The simple excited atom model HF-calculations give an Auger kinetic energy shift (metal-free atom) of 16.7 eV, which is comparable to the experimental value 14–18 eV.     

Vibrational spectra and ring-puckering of 2-cyclopenten-1-ones

The mid-infrared, far-infrared, and Raman spectra of 2-cyclopenten-1-one and 2-cyclopenten-1-one-5, 5-d₂ have been recorded. Assignments for each of the thirty vibrational fundamentals have been made for the two molecules. Several ring-puckering transitions were observed in the far-infrared spectrum of each molecule. From these were determined potential functions which establish the planarity of the ring system. The potential functions in reduced form derived for the hyride and deuteride are V = 15.0(Z⁴ + 8.0Z²) cm^?1 and V = 14.2(Z⁴ + 8.8Z²) cm^?1, respectively.     

On the determination of α2F(ω) in metals by measuring I–V characteristics of “wide” (non-ballistic) point-contact junctions

For metals with small electron and phonon mean free paths (alloys, deformed or amorphous materials), there exists a possibility of determining α²F(ω) by measuring the V dependence of $\text{d}{}^2\text{I}\text{d}\text{V}{}^2$ or $\text{d}{}^3\text{I}\text{d}\text{V}{}^3$ of wide (d ? 10³ Å) point contacts (PC) and then inverting the linear equation relating these quantities to α²F(ω). The procedure is elaborated numerically and tested successfully for model electron-phonon interaction spectra.     

Study of the electron paramagnetic resonance spectra of Zn(antipyrine)2(NO3)2:VO

In this work, a full ligand-field energy matrix (10×10) diagonalization treatment for 3d¹ ions in tetragonal symmetry is developed on the basis of the two-s.o.-coupling-parameter model. Spin Hamiltonian parameters (g factors g_∥, g_⊥ and hyperfine structure constants A_∥, A_⊥) of the tetragonal V⁴⁺ center in Zn(antipyrine)₂(NO₃)₂ are calculated from the complete energy matrix diagonalization method and the perturbation theory method. The calculated results from both methods are not only close to each other but also in good agreement with the experimental values. Furthermore, the compressed defect structure of V⁴⁺ center is discussed.     

Large deviations and Lifshitz singularity of the integrated density of states of random Hamiltonians

We consider the integrated density of states (IDS) ρ_∞(λ) of random Hamiltonian H_ω=?Δ+V_ω, V_ω being a random field on ? ^d which satisfies a mixing condition. We prove that the probability of large fluctuations of the finite volume IDS |Λ|^?1ρ(λ, H_Λ(ω)), Λ ? ? ^d , around the thermodynamic limit ρ_∞(λ) is bounded from above by exp {?k|Λ|},k>0. In this case ρ_∞(λ) can be recovered from a variational principle. Furthermore we show the existence of a Lifshitztype of singularity of ρ_∞(λ) as λ → 0⁺ in the case where V_ω is non-negative. More precisely we prove the following bound: ρ_∞(λ)≦exp(?kλ^?d/2) as λ → 0⁺ k>0. This last result is then discussed in some examples.     

Point contact spectroscopy in Ga single crystals

The current-voltage characteristics of point contacts in Ga single crystals have been measured in the liquid helium temperature range. At least six singular structures were found in energy range between 6 to 31 mV of the spectra d²V/dI². They are in good agreement with the structure of the phonon density-of-states determined from the inelastic neutron scattering experiment by Reichardt et al. The obtained spectra were used to estimate the electron-phonon coupling parameter.     

EPR parameters and local lattice structure study of V ions in CdCl2 and CsMgCl3 crystals

The local lattice structure and EPR parameters (D, g_‖, g_⊥) have been studied systematically on the basis of the complete energy matrix for a d³ configuration ion in a trigonal ligand field. By simulating the calculated optical and EPR spectra data to the experimental results, the local distortion parameters (ΔR, Δθ) are determined for V²⁺ ions in CdCl₂ and CsMgCl₃ crystals, respectively. The results show that the local lattice structure of CdCl₂:V²⁺ system exhibits a compression distortion (ΔR=−0.0868 Å) while that of CsMgCl₃:V²⁺ system exists an elongation distortion (ΔR=0.0165 Å). The different distortion may be ascribed to the fact that the radius of V²⁺ ion is smaller than that of Cd²⁺ ion or larger than that of Mg²⁺ ion. Moreover, the relationships between EPR parameter D and local structure parameters (R, θ) as well as the orbital reduction factor k and g‐factors (g_‖, g_⊥) are discussed.     

Motional narrowing in the electron-spin-resonance-spectrum of pentavalent vanadium-compounds

The activation energy of the hopping frequency of the vanadium-3d ¹-electron is derived from the temperature dependence of the ESR linewidth in the following semiconducting, pentavalent vanadium-compounds: Na_xV₂O₅, Li_xV₂O₅ (x <0.02), V₂O₅ weakly doped with WO₃ or MoO₃ (E _a ≈0.07 eV). In V₂MoO₈, vanadium-3d ₁-electrons are responsible for the electronic conductivity, too.