Combination of Solid-State and Electrochemical Impedance Spectroscopy To Explore Effects of Porosity in Sol-Gel-Derived BaTiO3 Thin Films.

BaTiO3 thin films were deposited onto polycrystalline Pt using a dip-coating technique, with annealing temperatures of 750-900 °C. To avoid film imperfections such as cracking or pinholes, key conditions, including aging periods, water content, and stirring speeds, were refined to produce a pinhole-free, uniform film with some porosity. Whereas those coated a single time short circuited during electrical characterization, this could be avoided in films produced by multiple coating cycles. The effective permittivity of a 600 nm BaTiO3 film was measured at 290 by fitting solid-state impedance data in the frequency range of 100 Hz to 1 MHz. Electrochemical impedance with an aqueous electrolyte allowed evaluation of the porosity, which remained fairly constant between 1 and 5 coating cycles. Using this method, it was possible to estimate the effective permittivity of the BaTiO3 itself as 374 and hence to evaluate the increase in the effective permittivity that could be achieved by minimizing porosity.

Synthesis and properties of MoCl4 complexes with thio- and seleno-ethers and their use for chemical vapour deposition of MoSe2 and MoS2 films.

Treatment of trans-[MoCl4(MeCN)2] with L (L = Me2S, Me2Se, THT, ½MeSCH2CH2SMe) in CH2Cl2 solution, or reaction of MoCl5 with excess L' (L' = nBu2S, nBu2Se, ½MeSCH2CH2SMe, ½iPrSCH2CH2SiPr, ½MeSCH2CH2CH2SMe, ½MeSeCH2CH2CH2SeMe) in MeCN, produces the Mo(iv) complexes, [MoCl4(L)2] and [MoCl4(L')2], respectively, in good yield. The new complexes have been characterised by IR and UV-vis spectroscopy, elemental analysis and magnetic measurements, whilst crystal structure analyses of trans-[MoCl4(Me2S)2], cis-[MoCl4{RS(CH2)2SR}] (R = Me, iPr) and cis-[MoCl4{MeS(CH2)3SMe}] confirmed their identities and distorted octahedral geometries. The potential of [MoCl4(nBu2E)2] (E = S, Se) as the first examples of molybdenum halide derived single source CVD precursors for the growth of MoE2 thin films was first probed by TGA, which showed multi-step decomposition processes, with the masses of the final residues consistent with MoSe2 (E = Se) and MoCl4 (E = S), respectively. Low pressure CVD experiments conducted at 750 °C (E = S) and 525 °C (E = Se) gave silvery and golden yellow films, respectively. Grazing incidence and in plane XRD data confirmed these to be 2H-MoE2, whilst the texture of the MoSe2 was investigated using pole figure measurements. SEM and EDX data, optical and Raman data on the films are also reported.