Electrical and optical properties of MoSe2 films prepared by r.f. magnetron sputtering

The electrical resistivity of MoSe₂ films prepared by r.f. magnetron sputtering was measured between 300 and 10 K. The main sputtering parameter governing the physical properties of the films was found to be the substrate temperature T_sub. The room temperature resistivity of the as-sputtered films increased from $\text{1.7 × 10}{}^{-1}\text{Ω}\text{cm}$(T_sub = -70 °C) to $\text{1.4 × 10}{}^1\text{Ω}\text{cm}\text{(T}{}_{\mathrm{<mtext>sub</mtext>}}\text{= 150 °}\text{C}\text{)}$. A check of the thermo-electrical response showed that the majority charge carriers are holes except for films deposited at T_sub = 150 °C which are n type. Hall effect measurements indicated very low Hall mobilities (3–5 cm² V^-1 s^-1). Thermal annealing increased the room temperature resistivities by more than one order of magnitude for the specimens sputtered at a low substrate temperature. The optical properties were weakly influenced by the process conditions. The optical gap was determined to be 1.06 eV.     

Photoelectrochemical study of TiS3 in aqueous solution

TiS₃ single crystals have been grown by chemical vapor transport. They were characterized by X-ray diffraction and measurement of their electronic transport properties. A photoelectrochemical study shows both anodic and cathodic dark currents and anodic photocurrents. Flat band potentials and anodic corrosion p$\text{o}$te$\text{n}$tials in acidic and basic solutions and in the presence of an $\text{I}{}^{\mathrm{?}}{}_3\text{I}{}^{\mathrm{?}}$ redox couple have been determined from the onset of photocurrent and from the Schottky-Mott plot of capacitance. The flat band potential ex$\text{h}$ibits a pH dependence but is almost independent of the presenc$\text{e}$ o$\text{f}$ I^? in solution. The stability of this material in a 1N H₂SO₄+ 1N $\text{I}{}^{\mathrm{?}}{}_3\text{I}{}^{\mathrm{?}}$ solution has been observed for a period of fourteen days with a photocurrent of approximately $\text{1}\text{mA}\text{cm}{}^2$. A particular photocorrosion mechanism is reported. The reaction starts at the edges of the layer and proceeds toward the interior. These mechanisms are discussed in relation to the existence of two types of S atoms in the structure: sulfur dimers and S^2? ions.     

Electronic and spin configurations of Co3+ and Ni3+ ions in oxides of K2NiF4 structure: A magnetic susceptibility study

In La₄LiCoO₈, Li⁺ and Co³⁺ ions are ordered in two dimensions and Co³⁺ ions undergo transitions from the low-spin to the intermediate as well as the high-spin states. Both Sr₄TaCoO₈ and Sr₄NbCoO₈ exhibit low to intermediate-spin state transitions of Co³⁺ ions. In the system LaSr_1?xBa_xNiO₄, the e_g electrons are essentially in extended states forming a band. With increase in x, the band width decreases accompanying an increase in unit cell volume; high-spin Ni³⁺ ions are formed to a small extent with increasing x, but there is no spin-state transition. In LaSrAl_1?xNi_xO₄, at small x, there is a small proportion of high-spin Ni³⁺; when x ≈ 0.6, there is an abrupt decrease in the $\text{c}$/$\text{a}$ ratio, signalling the formation of the band. In LnSrNiO₄, the $\text{c}$/$\text{a}$ ratio decreases sharply between Ln = La and Nd; this is likely to be accompanied by a broadening of the band.     

Thermal expansion of corundum structure Rh2O3

The directional thermal expansion coefficients of the corundum structure form of Rh₂O₃ were determined from room temperature to 850°C by x-ray diffraction methods. Rh₂O₃ has a lower thermal expansion and is less anisotropic in thermal expansion than alumina. The directional thermal expansion coefficients of Rh₂O₃ expressed in second degree polynominal form are: $\text{“α}{}_{\mathrm{<mtext>a</mtext>}}\text{” = 5.350 ×10}{}^{\mathrm{?6}}\text{+ 1.281 ×10}{}^{\mathrm{?9}}\text{T}\text{? 1.133 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$ and $\text{“α}{}_{\mathrm{<mtext>c</mtext>}}\text{” = 5.246 ×10}{}^{\mathrm{?6}}\text{+ 6.369 ×10}{}^{\mathrm{?9}}\text{T}\text{? 7.480 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$.     

Properties of aluminum-based cermet thin film resistors

A family of novel aluminum-aluminum oxide cermet resistance thin films has been deposited by the controlled oxidation of thermally decomposing triethyl aluminum vapor. Film resistivity can be varied, controllably, from 10^?2 to 10⁴ Ωcm. Over the range $\text{10}{}^{\mathrm{?1}}\text{?10}{}^3\text{Ωcm}$, the temperature coefficient of resistivity decreases monotonically from zero to ?1200 ppm/°C. High value resistors having surface resistivities from $\text{1 kΩ/sq. to 1000 MΩ/sq}$. have been fabricated by conventional aluminum metallization patterning techniques and they are compatible with silicon wafer processing technology.     

Copper doped zinc oxide Y2BaZnO5: ERS and optical investigation

In copper doped Y₂BaZnO₅ oxides, copper exhibits a distorted square pyramidal coordination which is consistant with the values of g and A tensors obtained from O band ERS spectrum for a sample containing about 1 % Cu. Three values for g and A are observed, g₁ = 2.049₅, g₂ = 2.051₅, g₃ = 2.275, $\text{¦}\text{A}{}_1\text{¦ = 13 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$, $\text{¦}\text{A}{}_2\text{¦ = 10 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$ and $\text{¦}\text{A}{}_3\text{¦ = 147.5 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$. Since $\text{g}{}_1\text{?}\text{g}{}_2$ an approximate C_4v point symmetry can be assumed for copper. The electronic spectrum shows three bands at 11700, 14500 and 20500 cm^?1 which can be assigned to the transitions A₁ → B₁, B₂ → B₁ and E → B₁ respectively. The orbital reduction parameters are calculated and the bonding covalency is discussed.     

Nouveaux conducteurs ioniques caracterises par une structure a tunnels entrecroises

The ionic conductivity of pyrochlores A_1+α(Ta_1+αW_1?α)O₆ was investigated for A = Na and T1. The thallium compounds are rather good conductors (0.34 ≤ ΔE ≤ 0.40 eV and $\text{5 10}{}^{\mathrm{?8}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 5.5 10}{}^{\mathrm{?5}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$); the sodium oxides are poor conductors (0.76 eV ≤ ΔE ≤ 1.48 eV and $\text{10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{500}\text{K}\text{≤ 10}{}^{\mathrm{?5}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$). The differences between these two classes of pyrochlores are explained in terms of structure. New non-stoechiometric oxides T1_12+x(M_30+xW_3?x)O₉₀, with M = Ta, Nb, and 0 ≤ x ≤ 3, were isolated. They are, like pyrochlores, characterized by an intersecting tunnel structure, which is an intergrowth of pyrochlore and A₂M₇O₁₈ structures. These oxides show ionic conduction properties which are very close to those of pyrochlores: the tantalum oxides are better conductors (0.30 eV ≤ ΔE ≤ 0.37 eV ; $\text{3.6 10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 1.4 10}{}^{\mathrm{?6}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$) than the niobium oxides (0.36 eV ≤ ΔE ≤ 0.42 eV ; $\text{10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 3.8 10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$). The evolution ofionic conduction properties of all these compounds is discussed.     

Crystal chemistry of α-(Zn,M)2V2O7 solid solutions correlation between preference for five-coordination and extension of solid solubility

Solid solutions of $\text{M}$₂V₂O₇ in α-Zn₂V₂O₇ have been prepared and equilibrated at 600°C ($\text{M}\text{=}\text{Mg, Ca, Mn, Co, Ni, Cu, Zn, and Cd}$). The crystal structure of α-Zn₂V₂O₇ contains only one type of metal site, which is five-coordinated by a somewhat distorted trigonal bipyramid ZnO₅ (Gopal & Calvo, 1973). The solubility range is largest for Cu²⁺ and Co²⁺ which can substitute for about 35% of the zinc atoms. The cations can be arranged in the following sequence with respect to their solubility in α-Zn₂V₂O₇, which accords well with these ions' preference for five-coordination:

$\text{Zn}{}^{\mathrm{2+}}\text{>> (Cu}{}^{\mathrm{2+}}\text{,Co}{}^{\mathrm{2+}}\text{) > Mg}{}^{\mathrm{2+}}\text{>(Ni}{}^{\mathrm{2+}}\text{, Mn}{}^{\mathrm{2+}}\text{) > Cd}{}^{\mathrm{2+}}$

     

Concentration quenching of Nd3+ fluorescence in ordered perovskite oxides and fluorides

New ordered perovskite-type fluorides, Rb₂KNdF₆ and Cs₂KNdF₆, have been synthesized and their luminescence properties investigated. Their neodymium emission shows weak self-quenching. This results both from the isolation of the neodymium in discrete NdF₆ octahedra and from the weak absorption associated with the ${}^4\text{I}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$ transitions in the region of the ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$ emission, which restricts cross-relaxation via the intermediate ${}^4\text{I}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$ levels. In contrast the emission of neodymium, substituted for lanthanum in the homologous Ba₂LaNbO₆ oxide, shows a strong concentration self-quenching.     

Vaporization reactions of manganese gallium sulfide

The vaporization of manganese gallium sulfide was investigated in the temperature range 500–975°. Manganese gallium sulfide was found to vaporize incongruently by the reaction:

$\text{3}\text{MnGa}{}^2\text{S}{}^4\text{(s) =}\text{Mn}{}^3\text{Ga}{}^2\text{S}{}^6\text{(s) + 2}\text{Ga}{}^2\text{S}\text{(g) + 2}\text{S}{}^2\text{(g)}$

and

$\text{Mn}{}^3\text{Ga}{}^2\text{S}{}^6\text{(s) = 3}\text{MnS(s)}\text{+}\text{Ga}{}^2\text{S}\text{(g) +}\text{S}{}^2\text{(g)}$

Approximate vapor pressures were measured by the Knudsen effusion technique. Lattice parameters, density, and chemical analysis of the new ternary compound Mn₃Ga₂S₆ are reported.     

Concentration quenching of Tb3+ luminescence in LaOBr and Gd2O2S phosphors

The concentration quenching of trivalent terbium ${}^5\text{D}{}_{\mathrm{3,4}}\text{→}{}^7\text{F}{}_{\mathrm{J}}$ emissions from UV-excited (La, Tb) OBr and (Gd, Tb)₂O₂S phosphors was studied. The activation concentration x was varied from 5·10^?5 to 0.2 for (La_1?xTb_x) OBr and from 10^?3 to 0.1 for (Gd_1?xTb_x)₂O₂S. ${}^5\text{D}{}_3\text{→}{}^7\text{F}{}_{\mathrm{J}}$ emissions (blue) were observed to quench first and the Tb³⁺ concentration giving rise to maximum intensity was 0.003 in (La, Tb) OBr and between 0.005 and 0.01 in (Gd, Tb)₂O₂S. The optimum concentration for ${}^5\text{D}{}_4\text{→}{}^7\text{F}{}_{\mathrm{J}}$ (green) emissions was 0.05 in (La, Tb) OBr and 0.03 in (Gd, Tb)₂O₂S. Dipole-dipole and dipole-quadrupole interactions are possible mechanisms for the quenching of emissions from the ⁵D₃ and ⁵D₄ levels.A method for determining the Tb³⁺ concentration in these phosphors, based on the intensity ratios of the ${}^5\text{D}{}_3\text{→}{}^7\text{F}{}_{\mathrm{J}}$ and ${}^5\text{D}{}_4\text{→}{}^7\text{F}{}_{\mathrm{J}}$ transitions, is also presented.     

The preparation,characterisation and ion exchange properties of an amorphous titanium phosphate

An amorphous titanium phosphate has been synthesized and characterized by chemical analysis, thermal analysis (DTA and TGA), i,r. spectroscopy and X-ray diffraction of the product calcined at 1000 °C. It was assigned the molecular formula Ti₄O₂(HPO₄)₃(H₂PO₄)₂(OH)₄·3H₂O. Its exchange capacity in the processes $\text{H}{}^{\mathrm{+}}\text{Na}{}^{\mathrm{+}}$ and $\text{H}{}^{\mathrm{+}}\text{Cu}{}^{\mathrm{2+}}$ has been determined.     

Flux-pinning by superconductor-normal boundaries

It is shown that flux-pinning by Nb₃Sn-Cu interfaces in in-situ superconducting composites can lead to a pinning function of the form $\text{F}{}_{\mathrm{p}}\text{∝ b}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1 ? b)}{}^2$, as is found experimentally.     

Verres fluores au tetrafluorure de zirconium proprietes optiques d'un verre dope au Nd3+

Glass formation has been observed in the ZrF₄BaF₂NaF system around the composition 50 % ZrF₄, 25 % BaF₂, 25 % NaF. A Nd³⁺ doped glass obtained by dissolving NdF₃ in the previous material has been studied. Absorption spectra in the region ${}^4\text{I}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{→}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, I.R. fluorescence spectra and lifetime measurement of the ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ level show a good protection of Nd³⁺ against the fluorescence quenching.     

Distribution coefficients in (YSmLuCa)3(FeGe)5O12 film growth

The composition of bubble garnet films has been analyzed by Inductively Coupled Plasma Emission Spectroscopy (ICP) to determine the distribution coefficients for different growth conditions. Under typical growth conditions, the distribution coefficients, k, of each element are as follows: k^Y = 2.15, k^Sm = 1.56, k^Lu = 1.32, k^Ca = 0.45, k^Fe = 0.98, k^Ge = 1.10. As the supercooling temperature (growth rate) increases, k^Ca, which is the smallest and deviates most from 1.0, changes in the direction approaching 1.0. For charge compensation, k^Ge also increases, consequently, k^Fe must decrease. Also k^Y, which is the largest, $\text{k}{}^{\mathrm{Sm}}\text{k}{}^{\mathrm{Y}}$ and $\text{k}{}^{\mathrm{Lu}}\text{k}{}^{\mathrm{Y}}$ change in the direction approaching 1.0. On the other hand, as the melt parameter R₁ (≡ $\text{Fe}{}_2\text{O}{}_3\text{Σ}\text{Ln}{}_2\text{O}{}_3$) increases, k^Fe decreases, and k^Y, k^Sm and k^Lu increase, whereas $\text{k}{}^{\mathrm{Sm}}\text{k}{}^{\mathrm{Y}}$ and $\text{k}{}^{\mathrm{Lu}}\text{k}{}^{\mathrm{Y}}$ remain constant at 0.73 and 0.61, respectively.     

Proton conduction in zeolites

Protonic conduction in zeolites is optimized. The approach is based on a vehicle-mechanism for the transport process. The parameters controlling protonic conduction are discussed. Fully hydrated “NH₄-zeolite A” has a room temperature conductivity of $\text{2×10}{}^{\mathrm{?3}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$. The material was successfully used in oxygen concentration cells (e.g. MnO₂/NH₄-zeolite A/Zn).     

Formation of thin SiO2 films by high dose oxygen ion implantation into silicon and their investigation by IR techniques

The ion dose dependence of the infrared transmission spectra of SiO₂ layers formed by high dose ion implantation into silicon was investigated for ion doses ranging from $\text{10}{}^{16}\text{to}\text{2 × 10}{}^{18}\text{(}{}^{16}\text{O}{}_2\text{)}{}^{\mathrm{+}}\text{30}\text{kV ions cm}{}^{-2}$. The annealing temperature dependence of these spectra is also reported.The passivation properties of the SiO₂ layers and their dependence on annealing were investigated and monitored by IR techniques. It was found that an SiO₂ layer that is formed by implantation with 1 × 10¹⁸ ions cm^-2 and annealed at temperatures higher than 550 °C but not more than 800 °C is similar in its IR and passivation properties to thermally grown SiO₂ films.     

Relations for hydration enthalpies of metalion-hydrates and stability constants of metal-dibenzoylmethane chelate complexes

Absolute hydration enthalpy (H) for cations relates well to lgK_Σ, the sum of the logarithms of the individual step chelation constants for metal-dibenzoylmethane complexes. The products $\text{d}{}^2$H and $\text{d}{}^2$lgK_Σ, where $\text{d}$ is the bond length, are essentially constant for a given cation valence (v) and increases as v². These relations fit a simple electrostatic model wherein the polarization of coordinating chelate or hydrate oxygen atoms is proportional to cation charge.     

Synthesis and electrical properties of Ln2(V43W23)O7 pyrochlores

Mixed oxides of the type $\text{Ln}{}_2\text{(V}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{W}{}^{\mathrm{6+}}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)O}{}_7$, Ln=GdLu, Y have been synthesized in vacuum via solid state reactions of the constituent oxides at 1150–1300°C. The compounds, which crystallize in cubic pyrochlore structure ($\text{a ～ 10.2}\text{A}\text{?}$), have been characterized by X-ray, density and wet chemical analysis. Electrical resistivity and Seebeck coefficient measurements show the phases to be p-type extrinsic semiconductors with low energies of activation possibly exhibiting hopping-type behavior.     

Growth and characterisation of epitaxial Gax In1−x Asy P1−y

Epitaxial layers of the quatternary semiconducting compounds Ga_x In_1?x As_y P_1?y have been grown on (111)B InP substrates by liquid phase epitaxy. Undoped compounds of this general formula with $\text{y}\text{?2}\text{x}$ are lattice matched to InP. Both cathodoluminescence (CL) and photoluminescence (PL) measurements on a range of nominally undoped and doped samples that (a) are lattice matched and (b) of varying degrees of lattice mismatch allow the selection of optimum material characteristics for subsequent fabrication into light emitting diodes. n-type material ($\text{ca}\text{2 × 10}{}^1{}^8\text{cm}{}^{\mathrm{?3}}\text{Sn}$) appears best suited for such devices.