Isomer shift of the electrically split 6.2 keV nuclear transition of Ta181 in CuTaS3

The isomer shift of the 6.2 keV nuclear transition of Ta181 in CuTaS₃RAIN was investigated by nuclear gamma resonance spectroscopy. Relative to tantalum metal the isomer shift in CuTaS₃ corresponds to +37.95±0.1 mm/s. The z component of the electric field gradient at the nuclear site of Ta181 was found to be V_zz = (−1.29±0.01)·10¹⁸ v/cm². The close correlation between the isomer shift in CuTaS₃ and the electronegativity of the Ta-ligands is pointed out.     

Deexcitation of Cd 53P1 atoms in collisions with ground state atoms and molecules

Collisions of excited Cd 5³P₁ atoms were investigated using atomic fluorescence spectroscopy. Cadmium vapor, together with a quenching gas, was irradiated in a quartz fluorescence vessel with Cd 3261 Å resonance radiation and the intensity of the resulting resonance fluorescence was monitored in relation to the gas pressures. The experiments yielded the following cross sections Q₁₀ (in A²) for collisional transfer 5³P₁→5³P₀: CdAr=2×10^?3, CdN₂=8.0, CdH₂=7.0, CdCO=15.6. The cross sections Q for collisional deexcitation to the ground state (quenching) in A² are CdN₂ = 2.6×10^?2, CdH₂ = 11.0, CdCO = 3.4, CdCO₂ = 26.     

Superconductivity and electron-phonon interaction in TaV alloys

The electron-phonon coupling in TaV alloys is estimated from resistive measurements. It decreases rapidly with increasing V in Ta in qualitative agreement with the observed transition temperature, T_c. A calculation of T_c from the strong-coupling equation gives good agreement with observed values for a constant Coulomb pseudo-potential and one adjustable parameter.     

ITC experiment on LiDMg2+ and LiHCa2+ crystals

In ITC curves of LiDMg²⁺ and LiHCa²⁺ two peaks were observed low temperature peak disappeared after a special thermal treatment. The high temperature peak when analysed by the usual method leads to an unexpected value of the pre-exponential factor of the Arrhenius relation. This is attributed to the questionable validity of the Arrhenius relation in a temperature region T ? θ_D.     

Powder spectra of 181Ta NMR in 2HTaS2

Powder spectra of ¹⁸¹Ta NMR in a swept field for the transitions between degenerate PQR states are discussed. Spin-echo signals of ¹⁸¹Ta in 2HTaS₂ powder have been observed at 4.2 K with line shapes that can clearly be associated with two inequivalent Ta sites, having well-defined asymmetry parameter (η) with values of 0.00 and 0.52 (± 0.02), one of which has the local charge density deviating strongly from the axial symmetry.     

Preparation of amorphous films of superionic conducting glasses in systems AgIAg2MoO4 and AgIAg2OB2O3

Thermal evaporation, flash evaporation and rf-sputtering techniques were applied to the preparation of amorphous films of superionic conducting glasses in the systems AgIAg₂MoO₄ and AgIAg₂OB₂O₃. The flash-evaporated films were amorphous and showed very high conductivities, about 2 × 10^?2S/cm for the AgIAg₂MoO₄ and about 5 × 10^?3S/cm for the AgIAg₂OB₂O₃ at room temperature, and gave a Ag⁺ transport number of unity. The thermal evaporation method produced crystalline-phase included films. The rf-sputtered films were amorphous by X-ray diffraction and the transport number of Ag⁺ ions was smaller than unity (about 0.9). Thus flash evaporation was concluded to be the most suitable method for preparing amorphous films of superionic conducting glasses.     

Gamma-gamma angular correlation study of oxygen motion in yttria-stabilized zirconia

The nuclear quadrupole relaxation of ¹⁸¹Ta in ZrO₂9 mole% Y₂O₃ has been measured by time differential angular correlations between 350 and 1150°C. The results are consistent with a distribution of the activation energy controlling the local motion of oxygen vacancies.     

X-ray study of c-axis parameters in disordered stage II Agχ TiS2

X-ray measurements have been performed on disordered Stage II Ag_χ TiS₂ crystals with χ = 0.18 and 0.19. The c-axis structure was determined using the 00.l reflections for 4 ?l? 29. A principal result is that the intercalation of Ag⁺ between S layers produces unequal TiS distances in the adjacent TiS₂. The charge transfer to the Ti layer produces an expanded TiS distance adjacent to the Ag layer. The TiS distance away from the Ag ions is accordingly contracted. This effective (indirect) repulsive interaction between Ag⁺ and Ti may provide a mechanism for staging in these materials by keeping the Ag layers as far apart as possible.     

Molecular and atomic adsorption states of oxygen on Cu(111) at 100–300 K

Adsorption states of oxygen on Cu(111) at 100–300 K were investigated by means of HREELS. Two molecular species were characterized by different OO stretching frequencies (v(OO)) at 610 cm⁻¹ and 820–870 cm⁻¹, which are assigned to the peroxo-like species (O²⁻₂) adsorbed in a bridged form and the one in a bidentate form bound on an atop site, respectively. The bridged peroxo species is preferred at the low coverage and the atop peroxo species becomes dominant at the higher coverage. In addition to the peaks due to the molecular oxygen, a peak assigned to v(CuO) of atomic oxygen was observed at 370 cm⁻¹ at the high coverage. The frequency of this mode was higher than the frequency reported for Cu(111) exposed to oxygen above 300 K, indicating that the adsorption state of atomic oxygen formed at 100 K is different from that above 300 K. The v(OO) modes became faint after annealing to 170 K because of O₂ dissociation. The v(CuO) mode of the atomic oxygen formed at 100 K remained up to 230 K and disappeared after annealing to 300 K. No desorption of O₂ was detected on annealing to 300 K. It was also found that vibrational spectra for adsorbed NH₃ are influenced by the adsorption states of atomic oxygen on Cu(111).     

Molecular electronics and spintronics devices produced by the plasma oxidation of photolithographically defined metal electrode

Tunnel junction based molecular devices, which utilize the two metal electrodes of a metal–insulator–metal tunnel junction as the two electrical leads to connect with molecular channels, can overcome the long standing fabrication challenges for developing futuristic molecular devices. However, producing an ultrathin insulator is the most challenging step in this tunnel junction based molecular device fabrication. A simplified molecular device approach was developed by avoiding the need of depositing a new material on the bottom electrode for growing ultrathin insulator. This paper discusses the new approach for insulator growth by one-step oxidation of a tantalum (Ta) bottom electrode, in the pholithographically defined region, i.e., ultrathin tantalum oxide (TaO _x ) insulator was grown by oxidizing bottom Ta metal electrode itself. Organometallic molecular clusters (OMCs) were bridged across 1–3 nm TaO _x along the perimeter of a tunnel junction to establish the highly efficient molecular conduction channels. OMC transformed the asymmetric transport profile of TaO _x based tunnel junction into symmetric one. A TaO _x based tunnel junction with the top ferromagnetic (NiFe) electrode exhibited the transient current suppression by several orders. Further studies by independent research groups will be needed to strengthen the current suppression phenomenon, and to realize the full potential of TaO _x based molecular devices.     

Underlayer dependence of electric field effect on magnetic anisotropy and its volatility in CoFeB/MgO structures

We report the dependence of voltage-controlled magnetic anisotropy (VCMA) effect and its volatility on an underlayer (UL) in CoFeB/MgO structures. For a sample with Ta or Pt UL, the VCMA effect occurs when the applied gate voltage (V_g) exceeds a critical value, and it persists even after removing V_g. This is in contrast to the volatile VCMA effect and its linear dependence on V_g in a sample with W UL. Furthermore, we demonstrate that the volatility of the VCMA effect can be modified by introducing a Ta/W bilayer, enabling arbitrary control of the magnetic properties via VCMA effect.     

Laser-induced Raman scattering in calcium titanate

The Raman spectrum of polycrystalline calcium titanate prepared by a liquid mix technique and heated to 800°C has been recorded at room temperature using an argon-ion laser as exciter. The observed spectrum was interpreted on the basis of factor-group C_2V. Not all of the Raman active modes predicted by factor group analysis were observed and this could be due to: over-lapping of bands, or very low polarizabilities of some of the modes or masking of the weak bands by intense bands. The band at 639 cm^?1 is tentatively assigned to the TiO symmetric stretching vibration (γ₁) and the bands at 495 and 471 cm^?1 to torsional modes. The bands in the region 180–340 cm^?1 are assigned to the OTiO bending modes and the 155 cm^?1 band to the Ca(TiO₃) lattice mode. The observed Raman bands are compared with the available infrared absorption data and, as expected, some coincidences in frequencies are seen for this compound with a noncentrosymmetric structure.     

The influence of covalency on anion-anion interionic potentials in NiO

Hartree-Fock self-consistent field cluster calculations were performed to investigate the short-range anion-anion interionic potential V₂₂ in NiO. The cluster consisted of two oxygen ions and ten surrounding Ni ions embedded in a matrix of point charges; the Ni²⁺ ions were represented by pseudopotentials. V₂₂ was extracted from calculations of the total cluster electronic energy as a function of the OO separation when one of the O ions is displaced from its lattice site towards the other O ion. The results indicate that covalency is mainly responsible for the anomalously large attractive terms in semiempirically derived OO interionic potentials.     

Electrical conductivity in amorphous Si(O or H)-Au films

SiO films obtained by sputtering in an ArO mixture with an oxygen partial pressure less than 3% are similar to a-Si films: the resistivity is proportional to exp (T₀/T)^{$\text{1}\text{4}$} and T₀ increases with oxygen content and decreases with increasing Au concentration (? 3.7 at.%). On the other hand, above an oxygen partial pressure of 5% one obtains insulating amorphous SiO₂ films. Conductivity appears in such films for Au? 13 at.% (? the percolation threshold) and then the resistivity is proportional to exp (T₀/T)^{$\text{1}\text{2}$}. The same behavior is observed when oxygen is replaced by hydrogen.     

Mixed cationic effect in the Li/AgB2O3P2O5 glasses

Electrical conductivity data have been determined for a series of x Ag₂O(1 − x)Li₂OB₂O₃P₂O₅ glasses. The progressive substitution of Li⁺ by Ag⁺ considerably decreases the ionic conductivity which shows a minimum at Ag/(Ag + Li) = 0.4. This behaviour becomes intense as the temperature is lowered. This mixed cationic effect is further characterised by activation energy and conductivity relaxation time going to a maxima where conductivity minima occurs. ac conductivity and electric modulus response of those glasses are discussed.     

Electronic structure and bond multiplicity in compounds of the type M2Rh2Ac4Cl2

The electronic structure of the binuclear complex Rh₂Ac₄Cl₂^2? was analysed using X-ray and X-ray photoelectron spectra. The closeness of the structure of Rh₂Ac₄Cl₂^2? to two boundary structures ClRhRhCl (I) and Cl… RhRh… Cl (II) has been studied. The correlation between Rh₂Ac₄ Cl₂^2? and RhCl₆^3? has shown that structure I is more in agreement with the experimental data than structure II. The structure of the K-edge of the spectra provides support for weakening of the RhCl bond.     

Determination of Oxygen partial free energy for non-stoichiometric TiO by E.M.F. measurements: Thermodynamics of TiO at 1323 K

The equilibrium oxygen partial pressures with non-stoichiometric TiO and the two phase regions TiOTi₂O₃ and Ti₂OTiO have been determined at 1323 K by electromotive force measurements with ThO₂Y₂O₃ solid electrolyte. These pressures are included between 10^?25.6atm and 10^?34.3atm. The results take into account the PO₂ dependence of the ionic transference number of our electrolytes. This dependence has been determined down to 10^?35 atm by using a UUO₂ reference electrode and applying a model proposed earlier by Schmalzried for the conductivity of ThO₂Y₂O₃.We had previously measured ΔH(O₂) for the same range of composition and at the same temperature. Hence a set of new thermodynamic data relative to ΔG(O₂), ΔH(O₂) and ΔS(O₂) is available for TiO at 1323 K.     

Light emission from a-Si:C:O:H films fabricated by C2F6 and O2/C2F6 plasma treating silicone oil liquid

Amorphous Si:C:O:H films were fabricated at low temperature by C₂F₆ and O₂/C₂F₆ plasma treating silicone oil liquid. The a-Si:C:O:H films fabricated by C₂F₆ plasma treatment exhibited white photoluminescence at room temperature, while that by O₂/C₂F₆ plasma treatment exhibited blue photoluminescence. Fourier transformed infrared spectroscopy and Raman spectroscopy studies showed that the sp³ and sp² hybridized carbons, SiC bond, SiO bond and carbon-related defects in a-Si:C:O:H films correlated with photoluminescence. It is suggested that the blue emission at 469 nm was related to the sp³ and sp² hybridized carbons, SiC bond, carbon dangling bonds as well as SiO short chains and small clusters, while the light emitting at 554 nm was related to the carbon-related defects.     

The 290-nm absorption system of propiolyl fluoride

The vapor-phase absorption spectrum of propiolyl fluoride HCCCOF and deuterio-propiolyl fluoride has been examined under medium resolution in the region from 303 to 260 nm. While considerable vibrational structure is evident, all bands are found to be rotationally diffuse. The electronic transition is identified as the singlet-singlet $\text{π}{}^1\text{← n}$ transition analogous to the 382-nm system of propynal. The evidence for a nonplanar excited-state geometry is discussed. The principal excited-state vibrational frequencies identified are 158 (ν′₉), 396 (ν′₈), and 1222 cm^?1 (ν′₃) for HCCCOF. The corresponding values for DCCCOF are 150, 390, and 1217 cm^?1, respectively. The triplet ← singlet system involving the same electron promotion has not been found.     

EPR of cadmium ferric voltaite above the ferrimagnetic transition

A single isotropic EPR line of Fe³⁺ in synthetic cadmium ferric voltaite, (NH₄)₂Cd₅Fe₃Al(SO₄)₁₂ · 18H₂O, was observed in a wide temperature range from 295 to 1.57°K. The ferrimagnetic transition temperature of CdFe voltaite was determined to be ～ 0.7°K using the temperature dependence of the g-factor and the line width. The cubic crystal field parameter, a, for Fe³⁺ in CdFe voltaite is extracted from the EPR line width measurement using the exchange-narrowed line width model of Anderson and Weiss. The parameter a for Fe³⁺ in CdFe voltaite at 4.2°K is 157 × 10^-4cm^-1 which is consistent with the corresponding values for Fe³⁺ in other cubic structures.