The agglomeration behavior of Cu and Au films each with a thickness of 5 and 50 nm, deposited on thermally grown SiO 2 by dc magnetron sputtering, was investigated with scanning electron microscopy. The size of Cu islands formed by agglomeration increased with increasing annealing temperature. Also, the agglomeration of Cu films seem to follow the grain boundary grooving process. On the other hand, Au islands have an identical size at different annealing temperatures. Au films were observed to agglomerate via nucleation of voids followed by the fractal growth of voids. The fractal dimension was determined to be 1.7 indicating that the fractal growth of voids can be described with a diffusion limited aggregation model. Finally, the kinetics of agglomeration of the Au films was described with an Avrami-type equation.

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The stability and efficiency of organic solar cells (OSCs) were improved using thermally stable fluorine-doped tin oxide (FTO) as the bottom electrode and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and TiO2 as the buffer layers. The TiO2 layer between FTO and the P3HT:PCBM active layer improved the interface characteristics for a better charge transfer. The PEDOT:PSS layer retarded the oxygen diffusion to the active layer. A maximum power conversion efficiency of 4.3% was obtained for the inverted structure of FTO/TiO2/P3HT:PCBM/PEDOT:PSS/Ag with a stable performance, and the cell retained over 65% of its initial efficiency after 500 h. Additionally, the OSCs were fabricated using all-solution based vacuum-free processes with screen printing for the Ag electrode and the results were comparable to the device that used an evaporated Ag electrode.

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The nucleation behavior of Ru deposited by atomic layer deposition (ALD) using bis(ethylcyclopentadienyl)ruthenium precursor and O2 reactant is investigated as a function of the number of ALD cycles. The substrates are thermally grown SiO2, NH3 plasma-treated SiO2, and chemical vapor deposited SiNx. The nucleation of Ru strongly depends on the substrate and is much enhanced on the nitride substrates. Transmission electron microscopy analysis reveals that the maximum density of the nuclei is 5.7×1010cm−2 on the SiO2 surface at 500 ALD cycles, 1.2×1012cm−2 on SiNx at 160 ALD cycles, and 2.3×1012cm−2 on NH3 plasma-nitrided SiO2 at 110 ALD cycles. Although the kinetics of Ru nucleation is different on the various substrates, the overall nucleation process in each case consists of an initial slow nucleation stage and a subsequent fast nucleation stage before the coalescence of the nuclei occurs. Considering the adsorption of Ru precursor on the substrate and the surface diffusion of deposited Ru during an ALD cycle, we suggest a model for describing the nucleation of an ALD film at the initial stage with a low surface coverage based on the atomistic nucleation theory of a thin film. The proposed model shows that the density of the nuclei is proportional to the (i+2)th power of the number of ALD cycles and (i+1)th power of the density of atoms deposited per ALD cycle, where i is the critical nuclei size. By applying the proposed model to the experimental results, the critical nuclei size i is found to be 1. The amounts of Ru atoms deposited per ALD cycle on the NH3 plasma-nitrided SiO2 and SiNx are 70 and 24 times larger, respectively, than that on the SiO2 surface. This model quantitatively describes the nucleation kinetics in the ALD system and is verified by a comparison with the experimental results of Ru on various substrates.