Chemistry Colloquium

Recent results in studies of the formation of compound and metal nanofilms by electrochemical atomic layer deposition (ALD) will be discussed. ALD is the deposition of materials an atomic layer at a time using surface limited reactions. Electrochemical surface limited reactions are generally referred to as underpotential deposition or UPD. By combining UPD and ALD, electrochemical ALD is created. Historically most electrochemical ALD has been performed in the creation of compound semiconductor thin films. More recently a number of elemental deposits have been formed by electrochemical ALD, and a surface limited reaction referred to here as a surface limited redox replacement or SLRR. Recent work on the formation of compound for photovoltaics, thermoelectrics, and for phase change memory may be discussed. In addition, recent work on the growth of Pt and Ru nanofilms for fuel cell electrodes may be described. Deposit characterization involves electron beam microprobe analysis (EPMA) for deposit stoichiometry. Glancing angle X-ray diffraction for structural characterization, while scanning tunneling microscopy (STM) was used to characterize the surface morphology. Optical characterization involves reflection absorption studies as well as photoelectrochemical studies. Optimization studies involve systematic investigation of the conditions which result in the formation of one compound or elemental monolayer with each deposition cycle. In general, deposits formed at a rate of one monolayer per cycle or less show the best structure, stoichiometry and morphology. Nano templates can be used to form nanoclusters, rods or wires, depending on the number of cycles performed. Superlattices can be formed by alternating some finite number of cycles for the growth of one compound with a similar number of cycles of another. X-ray diffraction can then be used to characterize the period of the superlattice.