Interfaces play an important role in solar cell heterostructures, especially when film thicknesses decrease. In this work, we use XPS, transmission electron microscopy (TEM) and density functional theory (DFT) to study both the film and the film-Si interface of electron beam deposited indium tin oxides (ITO) and pulsed laser deposition (PLD) deposited ZnO on p-Si (100). Vacuum evaporation of ITO resulted in a film that contained elemental Sn and In which oxidized after annealing at 300• C for 30 min. Ar etching of the HF-treated Si substrate in the PLD deposition chamber caused an increase of the interfacial oxide thickness independently of the deposition temperature as a result of Ar etching-induced dangling bonds. Deposition as well as annealing at elevated temperature also increases the interfacial oxide thickness for both ITO-Si and ZnO-Si systems. Copyright
Low temperature optical response of a single grain boundary in superconducting YBa2Cu3O7−δ thin filmThe introduction of a temperature dependence to the effective penetration depth as calculated in the strong-coupling limit of the coupled grain model is discussed. Assuming a phenomenological Gorter-Casimir behavior for the intrinsic penetration depth of YBa,CuaO,-8 (YBCO) and a simple model for the temperature-dependent intergrain critical current density, the coupled grain model is' found to predict a kinetic inductance which accurately fits the relative phase velocity,. v,+(T)/u4(Ta), measured on coplanar YBCO transmission lines. This indicates that the coupled grain model provides an adequate physical interpretation of the empirical penetration depth proposed by, e.g., Rauch et aI. [J. Appl. Phys. 73, 1866(1993] and suggests that the kinetic inductance is strongly influenced by -boundaries between grains with minor relative misaligmnent. The average grain size and critical current density of the grain boundaries were estimated at , a=140-240 nm andJ~(0)=3.5X1010-1X10" Am-', respectively. We argue that the coupled grain model may prove suitable for implementation in microwave circuit design software, as thin film preparation techniques mature in the sense of providing samples with highly reproducible properties.7408
The interfacial microstructure of three differently prepared silver contacts on c-axis oriented YBa2Cu3O7−δ (YBCO) thin films was examined using high-resolution transmission electron microscopy (HRTEM). For contacts prepared in situ by Ag sputter deposition on films maintained at elevated temperature and ex situ by Ag vapor deposition on films annealed in ultrahigh vacuum prior to metallization, regions of atomically sharp YBCO(001)/Ag interfaces were observed. In contrast, the cross-section HRTEM images of contacts prepared by in situ Ag deposition at room temperature reveal an amorphous interfacial zone, typically 20 Å thick. Scattered Y2O3 precipitates are found at the YBCO surface of all three contacts. The data suggest that intrinsic reactions between Ag and YBCO(001) are negligible, and that the amorphous interface layer for in situ contacts to cold films must be ascribed to reactions with gaseous impurities in the sputter chamber ambient. In conclusion, we strongly emphasize the importance of using ultrahigh purity process gases in order to avoid formation of a resistive interfacial barrier.
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