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The ability to manipulate the electronic transport properties and electronic states in transition metal chalcogenides greatly expands the range of their application. Here, we investigate the effect of applied stress on the electrical conductivity of quasi-two-dimensional ZrTe2 and several intercalated AgxZrTe2 and CuxZrTe2 crystals using pressure-dependent measurements of their Seebeck coefficients (thermoelectric powers) at room temperature. The pristine ZrTe2 crystal is characterized by p-type semimetal conductivity, and the pressure dependence of its thermopower exhibits a broad wave-like maximum at about 2 GPa. Potentially, this feature is related to a charge density wave transition. The electrical conductivity in all the intercalated crystals is of n-type, but an applied pressure of about 1.5–3 GPa, dependent on crystal composition, reversibly inverts it to p-type. At pressures above 6 GPa, thermopower curves for all samples demonstrate a nearly identical and degenerate pressure behavior, thereby suggesting metallization of the samples. We verify the reproducibility of the above features by multiple pressure cycling of the samples up to 9 GPa. We, therefore, experimentally show that slightly intercalated ZrTe2 crystals with n-type conductivity can be utilized as stress-controlled n-/p-switches of the conductivity type. We give and discuss simple examples of how the above n–p conductivity inversions could be potentially implemented in various modules for next-generation nanoelectronic devices. [ABSTRACT FROM AUTHOR]

A comprehensive study of the crystal and electronic structure of TiSe2 intercalated with two 3d metals, Cu and Ni, is presented. It is found that the intercalation of Cu into NixTiSe2 at room temperature leads to the displacement of the Ni atoms from the octahedral to tetrahedral sites with respect to the Se sublattice. This effect is explained by the charge transfer from Cu to the TiSe2-derived conduction band, which makes the chemical bond of Ni with the lattice more stable. This is because the hybridization between Ni 3d and Se 4p, 4s states is stronger than that between Ni 3d and Ti 3d in mono-intercalated NixTiSe2. Therefore, it is possible to control the type of the coordination of the intercalated transition metal atom by changing the concentration of doped electrons. [ABSTRACT FROM AUTHOR]

In this article, the design approach for a ${V}$ -band miniaturized oscillator with a pseudospark-based high-current-density sheet electron beam source is presented. The hollow cathode electron gun has been designed and developed. In the experiment, the ~10-A current in the hollow-cathode phase has been measured. The high-frequency structure comprised of a truncated sine waveguide slow wave structure (TSW SWS) with wideband-matched output couplers has been designed, optimized, and simulated. The simulations show good transmission characteristics of the structure. The operation of a backward-wave oscillator with the designed TSW SWS driven by a 10-A, 40-kV sheet electron beam has been investigated by using 3-D particle-in-cell simulations. The maximal output power of 70 kW has been attained in the simulation. Frequency tuning within the 10-GHz frequency band has been demonstrated. [ABSTRACT FROM AUTHOR]

The effect of atomic ordering in the cobalt sublattice on the electronic structure of the CoxTiSe2 intercalation compounds has been studied using a complex of spectral techniques – XPS, XAS, and ResPES, along with theoretical calculations of the total and partial densities of states. It has been found that the cobalt intercalation significantly affects the character of the chemical bond inside the host lattice. No signs of the direct overlapping of the Co 3d orbitals in the ordered material were observed. It has been found that the reason for the ordering of the cobalt atoms is a Co 3d/Ti 3d/Se 4p hybridization. [ABSTRACT FROM AUTHOR]

Crystal and electronic structure, optical absorption and transmission spectra, temperature dependences of conductivity and magnetic susceptibility were studied for copper intercalated ZrSe2 in the copper concentration range of 0 ≤ x ≤ 0.3. The electronic structure of CuxZrSe2 single crystals was studied at room temperature using X-ray Absorption Near Edge Structure spectroscopy (XANES), resonant photoelectron spectroscopy (ResPES) and optical absorption. The partial and total densities of states were calculated to determine the atomic contributions to the valence band. The competition between the occupation of octahedral and tetrahedral sites in the van der Waals gap by copper was found. The contribution of both positions to the formation of the chemical bond between copper and the ZrSe2 lattice with the domination of the Cu–Se interaction was determined. It was found that the intercalation of copper in the concentration range of x = 0–0.2 resulted in the formation of the localized impurity states in the Se 4p/Zr 4d band gap but not in the charge transfer to the conduction band. As the copper concentration increased above x = 0.2, the semiconductor-to-metal transition occurred due to the reaching of the conduction band by the Fermi level. The Se 4p/Zr 4d band gap was found to be a direct one in the whole studied concentration range. Some inconsistencies in the conductivity and spectral data along with the DOS calculation results were explained by the Frenkel defects in the ZrSe2 lattice. [ABSTRACT FROM AUTHOR]

The spectroscopic characteristics of potassium yttrium tungstate crystal (KYW), codoped with ytterbium and thulium ions, have been investigated from the point of view of up-conversion blue lasing from 1G4 multiplet. An overall 3H6 multiplet splitting of ∼530 cm-1 for the trivalent thulium ion in the KYW host was obtained. A decay time of ∼112 μs for the 1G4→3H6 blue luminescence in the material doped by 1 at. % of thulium was measured. The value of peak emission cross section for this transition is estimated to be (1.8±0.3)×10-20 cm2. Strong cross-relaxation quenching was found to be one of the main channels of nonradiative losses from the 1G4 and 3H4 multiplets. The cross-relaxation rate was significantly higher at higher concentration of thulium. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]