Indium-zinc-oxide thin films produced by low-cost chemical solution deposition: Tuning the microstructure, optical and electrical properties with the processing conditions.

Indium-zinc-oxide (IZO) films were prepared by spin coating an ethanol-ethylene-glycol precursor solution with a Zn/(In + Zn) ratio of 0.36 on glass. The effects of temperature on the structure, microstructure, electrical, and optical properties of the IZO thin films were investigated by thermal analysis, Fourier-transform infrared spectroscopy, X-ray diffraction, electron and atomic-force microscopy, X-ray photoelectron spectroscopy and variable-angle spectroscopic ellipsometry. The prepared IZO thin films heated at 500, 600, and 700 °C in air were transparent, without long-range ordering, and with an RMS surface roughness of less than 1 nm. The lowest electrical resistivity at room temperature, 0.0069 Ωcm, was observed for the 115-nm-thick IZO thin film heated at 600 °C in air and subsequently post-annealed in Ar/H2. The thin film exhibited a microstructure characterized by grains typically 20 nm in size and had no organic residues. This film exhibits uniaxial optical anisotropy due to its ultra-thin lamellae with a high electron density. The ordinary refractive index was fitted as a Tauc-Lorentz-Urbach function, which is typical of an indirect absorption edge occurring in amorphous semiconductor materials. The principal absorption peak with an onset at about 2.8 eV and a Tauc gap energy of ∼2.6 eV is similar to those observed for In2O3. The described process of chemical solution deposition and subsequent curing is promising for the low-cost fabrication of IZO thin films for transparent electronics, and can be used to tune the structure and microstructure of IZO thin films, as well as their electrical and optical properties.

Building organosilica hybrid nanohemispheres via thiol-ene click reaction on alumina thin films deposited by atomic layer deposition (ALD).

The present work shows a surface-induced preparation of sub-100 nm organosilica nanohemispheres on atomic layer deposited (ALD) Al2O3 thin films, which was achieved by cooperative condensation/hydrolysis and thiol-ene click chemical reactions. The two-step synthetic approach consists of an initial silanization of the Al2O3 film with vinyltrimethoxysilane (VTMS), followed by a photo-promoted growth of surface-bound nanoparticles in the presence of (3-mercaptopropyl)trimethoxysilane (MPTMS). Characterization by means of FE-SEM, XPS and EDS points towards the growth of the nanohemispherical structures being governed by an initial nucleation of thiolated organosilica seeds in solution as a result of self-condensation of MPTMS and oxidation of thiols to disulfides. Once bound to the vinyl terminated Al2O3via photo-assisted thiol-ene coupling, these seeds promote area-selective growth of the nanoparticles through binding of further MPTMS from the solution. After an additional ALD deposition of ZnO, the resulting thin hybrid film exhibits enhanced hydrophobicity when compared to ZnO films deposited directly on Al2O3 under the same processing conditions.

Resolution of microscopic protonation enthalpies of polyprotic molecules by means of cluster expansions.

Cluster expansion techniques are used to obtain microconstants and microenthalpies of protonation reactions. The approach relies on the analysis of macroscopic protonation constants and protonation enthalpies within a homologous series. Various linear aliphatic polyamines are considered, including 3,4-tri (spermidine), 3,4,3-tet (spermine), and 2,2,2,2-pent. Besides the full resolution of the microscopic protonation equilibria, one obtains information on the temperature dependence of the microstate probabilities. We find that the concentrations of the dominant microspecies increase with increasing temperature. Due to the large negative protonation enthalpies that are typical for amines, higher temperatures generally favor the less protonated species.

Effects of heat treatment on the aggregation and charging of Stöber-type silica.

Colloidal silica is known to be stable at high salt concentrations and low pH, where silica is basically uncharged. This observation is in qualitative disagreement with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), which predicts rapid aggregation (or coagulation) under these conditions. This study reports a very different behaviour for Stöber-type silica heated at 800 degrees C, as these particles follow DLVO theory quantitatively. Unheated samples behave approximatively according to DLVO theory, but they show systematic deviations, in particular, featuring higher stability at low pH. The heat treatment also substantially modifies the charging properties, as heated particles show titratable surface charge densities in the range expected for the water-silica interface, while much higher charge densities are observed for the unheated samples. The electrophoretic mobilities, on the other hand, are hardly influenced by the heat treatment. We suspect that the suspension stability of the unheated particles is influenced by the presence of a hairy-layer of polysilicilic acid chains on the surface.