Thin films of photoactive Cu1.8S have been deposited by atomic layer deposition (ALD) using Cu(thd)2 and H2S as the precursors. This is a first step in the construction of nanoporous heterojunctions of TiO2/Cu1.8S. The ALD process can be divided into two temperature regimes: below 175 °C, adsorption of the complete Cu(thd)2 molecule occurs, followed by an exchange reaction with H2S yielding CuS; above 175 °C, Cu(thd)2 reduces upon adsorption and slowly decomposes yielding Cu1.8S. The slow decomposition of Cu(thd)2 ensures that smooth and homogeneous films can be obtained up to 280 °C. Flat film solar cell devices of TiO2/Cu1.8S have an open‐circuit voltage of about 200 mV and a short‐circuit current of 30 μA cm–2 at 2.8 kW m–2.
Laser-induced chemical vapor deposition of silicon carbonitride thin films has been investigated using a continuous wave CO2 laser in parallel configuration with the substrate. The reactant gases in this process, hexamethyl disilazane and ammonia, are rapidly heated by CO2 laser radiation due to their absorption of the laser energy. Polymerlike silicon carbonitride films or agglomerated nanosized particles are formed depending on process conditions. Dense, smooth films or nanostructured deposits have been synthesized at low substrate temperatures (Ts<300 °C) on quartz, copper, and silicon and can be obtained with controlled microstructures. Surface morphology, composition, and type of chemical bonding have been studied with electron microscopy and spectroscopic analysis and are correlated to the most important laser process parameters. X-ray photoelectron spectroscopy and reflectance Fourier transform infrared spectroscopy show that the deposits consist of Si–N, Si–C, and Si–O bonds, linked together in a x-ray amorphous, polymerlike structure. The nitrogen content is about 40% and can be varied by adding ammonia to the reactant gas flow. The layers are readily contaminated with oxygen after exposure to air, caused by hydrolysis and/or oxidation.
Thin films of Cu x S are deposited by both chemical vapor deposition (CVD) and atomic layer deposition (ALD) using copper bis-tetramethylheptanedionate, Cu(thd) 2 , and H 2 S as the precursors. Single-phase CuS and Cu 1.8 S can be deposited using both techniques, while in CVD also mixed phases can be formed. Comparing the ALD process with the CVD process leads to a better understanding of the reaction chemistry of both processes. The main factor is the decomposition of Cu(thd) 2 at 175 °C, which leads to a phase transition from CuS to Cu 1.8 S in ALD and deposition of mixed phases in CVD. Consequently, the phase transition is sharp in ALD and gradual in CVD. At temperatures higher than 250 °C, decomposition of Cu(thd) 2 occurs in the gas phase, leading to a transition from a reaction-limited regime to a thermodynamic regime in CVD and to loss of uniformity and homogeneity in ALD.
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