The growth of Pt nanofilms on well-defined Au(111) electrode surfaces, using electrochemical atomic layer epitaxy (EC-ALE), is described here. EC-ALE is a deposition method based on surface-limited reactions. This report describes the first use of surface-limited redox replacement reactions (SLR(3)) in an EC-ALE cycle to form atomically ordered metal nanofilms. The SLR(3) consisted of the underpotential deposition (UPD) of a copper atomic layer, subsequently replaced by Pt at open circuit, in a Pt cation solution. This SLR(3) was then used a cycle, repeated to grow thicker Pt films. Deposits were studied using a combination of electrochemistry (EC), in-situ scanning tunneling microscopy (STM) using an electrochemical flow cell, and ultrahigh vacuum (UHV) surface studies combined with electrochemistry (UHV-EC). A single redox replacement of upd Cu from a PtCl(4)(2-) solution yielded an incomplete monolayer, though no preferential deposition was observed at step edges. Use of an iodine adlayer, as a surfactant, facilitated the growth of uniformed films. In-situ STM images revealed ordered Au(111)-(square root 3 x square root 3)R30 degrees-iodine structure, with areas partially distorted by Pt nanoislands. After the second application, an ordered Moiré pattern was observed with a spacing consistent with the lattice mismatch between a Pt monolayer and the Au(111) substrate. After application of three or more cycles, a new adlattice, a (3 x 3)-iodine structure, was observed, previously observed for I atoms adsorbed on Pt(111). In addition, five atom adsorbed Pt-I complexes randomly decorated the surface and showed some mobility. These pinwheels, planar PtI(4) complexes, and the ordered (3 x 3)-iodine layer all appeared stable during rinsing with blank solution, free of I(-) and the Pt complex (PtCl(4)(2-)).

Au͑111͒ single-crystal substrates were used in studies of Cu nanofilm formation by electrochemical atomic layer deposion ͑ALD͒. Cu undepotential deposition ͑UPD͒ was used to deposit the first Cu atomic layer on a Au͑111͒ substrate, modified with an atomic layer of I atoms. By definition, Cu UPD results in the formation of an atomic layer, thus, to deposit subsequent Cu, surface-limited redox replacement ͑SLRR͒ was used. The SLRR involved initial formation of Pb UPD on the Cu-coated surface just described. This Pb UPD-coated surface was then exposed to CuSO 4 at open-circuit potential ͑OCP͒, where the Pb atoms were exchanged for Cu. In the ultrahigh-vacuum electrochemical ͑UHV-EC͒ studies presented here, two Pb UPD potentials were investigated: −0.400 and −0.440 V. UHV-EC studies involved use of a surface analysis instrument with optics for low-energy electron diffraction and Auger, and to which was attached an ante-chamber containing a Pyrex glass electrochemical H-cell. In this way, surface analysis was performed without transfer of the deposit through air and the contamination which would result. In addition, studies of the first few cycles of redox replacement were investigated using electrochemical in situ scanning tunnel microscopy ͑STM͒, with a flow cell for solution exchange to prevent loss of potential control.

A Au(111) single crystal, cleaned by Ar ion bombardment and annealed in a UHV chamber, was used as a substrate for studies of Cu deposition by electrochemical ALD. The first Cu atomic layer was deposited at an underpotential, by UPD, of 0.050 V versus Ag/AgCl on an I modified Au(111) substrate. The subsequent layers were formed using the redox replacement of Pb UPD with Cu in what is referred to as a surface limited redox replacement (SLRR). Two potentials for Pb UPD were investigated, -0.400 V and -0.440 V, with each deposit lasting 2 minutes. Subsequent immersion in the Cu 2+ solution was for 10 second, at open circuit. The resulting Cu thin films were analyzed using Auger electron spectroscopy and low energy electron diffraction (LEED). As a final step, total Cu coverages were determined for the resulting nanofilms by anodic stripping, and Cu replacement efficiencies were determined.

This paper describes the electrodeposition of Tellurium (Te) atomic layer on n-type GaAs(100) substrates. As-received n-GaAs(100) substrates were treated in 10 % HF and ultraviolet (UV) ozone cleaned. The substrate was then transferred to the ultrahigh vacuum (UHV) electrochemistry chamber and cleaned by Ar+ ion bombardment. The clean substrate was then transferred into the attached electrochemistry ante-chamber, and immersed in a tellurite solution. A number of deposition potentials were investigated. The resulting Auger peak height ratios, Te/Ga, were plotted versus the Te deposition potential. From the Auger ratio plot, below -0.8 V, a reduction feature was observed, at −0.9 V, due to the reduction of Te to Telluride ion (Te0 + 2e− → Te2−). At potentials of -0.9 and below, only a surface limited atomic layer of Te was left on the GaAs surface. An initial investigation of In deposition on this Te coated GaAs surface was also performed.

The electrodeposition of tellurium (Te) and indium (In) atomic layers on n-type GaAs(100) substrates is described. As-received n-GaAs(100) substrates were treated in 10% HF and ultraviolet (UV) ozone cleaned. The substrates were then transferred to an ultrahigh vacuum (UHV) chamber and cleaned by Ar + ion bombardment. The clean substrate was then transferred into an attached electrochemistry ante-chamber and immersed in a telluride solution, where a number of deposition potentials were investigated. The resulting Auger peak height ratios, Te/Ga, were plotted versus the Te deposition potential. From the Auger ratios, it was evident that bulk Te was formed between -0.4 and -0.8 V, while below -0.8 V, a reduction feature was observed corresponding to the reduction of Te to the telluride ion (Te 0 + 2ef Te 2-). Below -0.9 V, only a surface-limited atomic layer of Te was left on the GaAs surface. Indium deposition on this Te-coated GaAs surface was also performed, and electrodeposited adlayer thicknesses were calculated from the Auger data. Indium electrodeposited directly on the GaAs surface resulted in 3D nucleation and growth of widely spaced In clusters. Electrodeposition of In on an atomic layer of Te on the GaAs surface resulted in layerby-layer growth. Alternation of atomic layers of Te and In resulted in formation of indium telluride nanofilms, probably In 2 Te 3 , by electrochemical atomic layer deposition (ALD). Deposits with up to three cycles were performed.