Thermal properties of oxygen-, phosphorus-, and halogen-free dimethylgold(III) diethyldithiocarbamate complex (CH 3 ) 2 AuS 2 CN(C 2 H 5 ) 2 (gold, dimethyl(diethylcarbamodithioato -S,S′)-) having excellent storage stability and the mechanism of its decomposition to elemental gold were studied. Saturated vapor pressure was found to be~10
10−1 Torr at 50-90°C. Decomposition of the vapor on the surface starts at T=210°C. The temperature dependence of gas phase composition was studied using the original mass spectrometric technique, it was established that the decomposition of the compound on the surface in vacuum follows three main pathways. Two of them result in the formation of elemental gold, saturated C2-C4 alkanes and (1) protonated ligand or (2) methylated ligand. The third one results in elemental gold and gaseous products: C2-C3 alkylmercaptanes and CH 3 SCN(C 2 H 5 ) 2 . The formation of gold as a sole solid product within the temperature range 210-240°C was confirmed by X-ray photoelectron spectroscopy analysis. It was shown that the compound exhibits the best combination of volatility, thermal, and storage stability among volatile organogold complexes and thus it may be a promising precursor for obtaining gold films by chemical vapor deposition.
Using metal-organic (MO)CVD, gold films and arrays of gold nanoparticles are obtained from volatile organometallic dimethylgold(III) complexes with O, N, S donor ligands. As precursors, such compounds as (CH 3 ) 2 Au(OAc), (CH 3 ) 2 Au(piv), (CH 3 ) 2 Au(OQ), (CH 3 ) 2 Au(SQ), (CH 3 ) 2 Au(thd), and (CH 3 ) 2 Au(dtc) were used. Deposition processes are carried out within a low pressure (LP)CVD reactor with additional vacuum ultraviolet (VUV) stimulation, with and without a hydrogen reactant gas. The influence of precursor structure on the morphology of the deposited layers is demonstrated. The use of precursor (CH 3 ) 2 Au(OQ) results in obtaining ultra-thin continuous gold film $3 nm thick. It is established that with hydrogen reactant gas injected into the system, the amount of impurities in the film decreases. With the VUV stimulation, the gold content in the films amounts to almost 100%; in addition, the morphology of coatings is observed to change significantly. According to the X-ray diffraction (XRD) phase analysis, gold crystallites in the films grow mainly in the [111] direction.
The thermoelectric properties of a series of the polycrystalline samples of titanium dichalcogenides with partial substitution of Ti for Nb and S for Se were investigated. It was found that sintering of the samples improved the thermoelectric efficiency (ZT), and the maximum ZT was achieved at sintering temperature of 600°C. A further increase in the sintering temperature (850°C and 950°C) led to the recrystallization of the samples, as a result, the Seebeck coefficient sharply decreased and electrical conductivity dramatically increased. The temperature dependences of electrical conductivity σ(T) in the temperature range from 4.2 to 300 K and Seebeck coefficient S(T) in the temperature range from 77 to 300 K were investigated in order to determine the nature of the observed improvements in thermoelectric properties due to double substitutions and sintering. Two‐dimensionalization of electron transport properties of Ti1−xNbxS2−ySey solid solutions was found. The Fermi energy EF2D was estimated using the temperature dependences of Seebeck coefficient. The relationship between the Fermi energy EF2D and figure of merit ZT was established. The effect of sintering on parameters σ(T), S(T), charge carrier concentration (n2D), mobility (µ), and thermal conductivity (k) was found. The optimal value of Fermi energy EF2D in terms of figure of merit ZT = 0.31 at room temperature (T = 300 K) was found for Ti0.98Nb0.02S1.3Se0.7 sample sintered at 600°C.
Dipivaloylmethane was used as a precursor to deposit MgO layers on polished silicon (100) plane in a hot-wall pulsed MO CVD reactor. A detailed investigation of the thermal parameters of the precursor was carried out to optimize the conditions for film deposition experiments. Temperature dependencies of vapour pressure were measured using the flow procedure and Knudsen's method with the mass spectrometric identification of the composition of the gas phase. The processes of Mg(thd) 2 decomposition in vacuum, in oxygen and in water vapour were investigated by means of high-temperature mass spectrometry. The major products of precursor decomposition were established; the mechanism of its decomposition was proposed. Investigation of the deposition of MgO layers was carried out within the substrate temperature range 350-450 о С, source temperature 190÷210 о C in the presence of oxygen. The resulting layers were characterized using AFM, ellipsometry, XRD. The morphology, structure and secondary electron emission of MgO films were investigated.
Phase formation study of the Na2MoO4–Cs2MoO4–CoMoO4 system resulted in new cesium‐containing alluaudite‐related phases. The solid solution Na4–2x‐yCsyCo1+x(MoO4)3 (0 ≤ x, y ≤ 0.30), based on the alluaudite‐type Na4–2xCo1+x(MoO4)3, and triple molybdate Na10(Cs4‐xNax)Co5(MoO4)12 (0 ≤ x ≤ 0.30) were found, and their structures were solved. In the structure of Na3.21Cs0.37Co1.21(MoO4)3 (a = 13.0917(8) Å, b = 13.5443(8) Å, c = 7.1217(4) Å, space group C2/c, β = 112.331(2), Z = 4), the cesium ions partially substitute the Na+ in the channels running along the c‐axis. The structure of Na10(Cs3.77Na0.23)Co5(MoO4)12 (a = 13.6572(3) Å, b = 11.5063(3) Å, c = 27.9898(5) Å, space group Pbca, Z = 4) was proved to be the aristotype for the pseudo orthorhombic Na25Cs8R5(MoO4)24 (R = Fe, Sc, In). The compounds contain alluaudite‐like layers of MoO4 tetrahedra and pairs of edge‐shared (Co, Na)O6 or (R, Na)O6 and NaO6 octahedra, which are connected by bridging MoO4 tetrahedra to form 3D frameworks differing from the alluaudite type. The frameworks contain channels along the c‐axis filled by Cs+ and Na+ ions. Bond valence sum (BVS) maps show that the alluaudite‐related molybdates can have a 2D sodium‐ion conductivity at elevated temperatures in contrast to the alluaudite‐type cathode material Na2+2xFe2‐x(SO4)3 with a 1D conductivity. The measured ionic conductivity of Na4–2xCo1+x(MoO4)3, Na4–2x‐yCsyCo1+x(MoO4)3, and Na10Cs4Co5(MoO4)12 reaches 10–3–10–2 S cm–1 at 500 °C.
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