Electrochemical control of the thermal stability of atomically thin Ag films on Au(111)

• Published in: Surface science 2018-11, Vol.677, p.316-323
• Main Authors: Phillips, Jesse A., Harville, Lauren K., Morgan, Heather R., Jackson, Lauren E., LeBlanc, Gabriel, Iski, Erin V.
• Format: Article
• Language: English
• Subjects: AgCl; Chemical reactions; Control stability; EC-STM; Gold; Heat treatment; Organic chemistry; Physical properties; Reduction; Scanning tunneling microscopy; Silver; Silver chloride; Surface chemistry; Thermal stability; Thin films; Underpotential deposition; Unit cell; UPD
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2018.08.006

•EC-STM and CVs are used to investigate the UPD of AgCl and AgBr on Au(111).•Two different chemical mechanisms by which the Ag monolayer is formed on the Au(111) surface are proposed.•The amount of Ag on the surface depends on the mechanism employed to deposit the layer as indicated by EC-STM images.•Electrochemical parameters can be used to impart specific properties to the Ag film, including extreme thermal stability. Alterations of a surface even on the nanoscale can have a significant impact on the physical properties and subsequent applications of a bulk system. Using Electrochemical Scanning Tunneling Microscopy (EC-STM) to perform an investigation of AgCl and AgBr deposition, evidence suggests multiple chemical mechanisms for the formation of a single, atomically-thin Ag layer on Au(111). Ag deposition has been extensively studied on Au(111). However, few reports provide a detailed mechanism of surface adsorption from Ag solutions. The electrochemical phenomena of Underpotential Deposition (UPD) was used to deposit up to a monolayer of Ag on the Au surface. Cyclic voltammograms (CVs) indicated two UPD peaks of +0.87 V (region 1) and +0.38 V (region 2) vs Ag/AgCl in the AgCl system and one peak at +0.87 V (region 1) in the AgBr system. The presence of two UPD peaks in the AgCl system suggests two different chemical reactions as the deposition mechanism of Ag on Au(111), region 1 representing a reduction of Ag+ as a dissociated cation, which was also seen in the AgBr system, and region 2 representing a reduction of AgCl as a solvated undissociated unit. According to EC-STM images, region 1 deposition resulted in a (4 × 4) packing of the Ag atoms, while deposition in region 2 produced a more closely packed surface with a corresponding (1 × 1) unit cell. A detailed understanding of the nature of these deposition processes is necessary to the fundamental characterization of these atomically thin-metal layers, as well as their subsequent applications. Importantly, relevant applications may include exploiting the thermal stability of the Ag layers, which was drastically affected by the deposition parameters. Deposition of Ag in region 1 resulted in a layer that was thermally unstable after a heat treatment at 1000 K, while the opposite was true from the deposition in region 2. It is proposed that the origin of stability is derived from both the Ag source and the electrochemical deposition conditions. [Display omitted]