Atomic level studies of electrochemical reactions used in electrochemical atomic layer epitaxy (EC-ALE) : cadmium, lead, tellurium, cadmium telluride, mercury, mercury telluride, sulfur, sodium thiosulfate, and sodium ethane thiolate
Lay, Marcus David
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Electrochemical scanning tunneling microscopy (EC-STM), thin-layer electrochemistry (TLEC) and ultra-high vacuum emersion techniques (UHV-EC) have been used to elucidate structural changes at the atomic level during the first few atomic layers during electrochemical atomic layer epitaxy (EC-ALE) cycles. This Dissertation will demonstrate data and knowledge acquired in this endeavor for the following systems: Cd, Pb, Te, CdTe, Hg, HgTe, S, Na2S2O3, and C2H5SNa. These layers can be used to form Cd-containing compound semiconductors such as CdTe, CdSe, or CdS, using EC-ALE. Ordered sulfur atomic layers were formed on Au(111) from alkaline solutions of sulfide, thiosulfate, and thiourea. A range of electrode potentials were found where the same 1/3rd monolayer ( 3X 3)R30° sulfur layer can form, which can be used in an EC-ALE cycle to form compound semiconductors such as: ZnS, CdS, and CuInS2. A flow cell STM has been built in this group and is being used for studies of CdTe and CdSe growth by EC-ALE. Studies of the atomic layers formed on Au(111) single crystal surfaces will be described, as well as the alternated deposition of atomic layers of elements to form compound semiconductors. The impetus for these studies was to determine the ideal conditions for growing II-VI compound semiconductor thin films. In each EC-ALE cycle, aqueous precursors for a compound’s elements are alternately flowed in to the cell at specific potentials, and atomic layers are deposited (upd). Thin film growth is just the reapplication of the cycle the desired number of times.