Self-Assembled Monolayers on Pt(111):  Molecular Packing Structure and Strain Effects Observed by Scanning Tunneling Microscopy

• Published in: Journal of the American Chemical Society Vol. 128; no. 17; pp. 5745 - 5750
• Main Authors: Lee, Sangyeob, Park, Jung, Ragan, Regina, Kim, Sehun, Lee, Zonghoon, Lim, Do Kyung, Ohlberg, Douglas A. A, Williams, R. Stanley
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 03.05.2006
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electrical properties of specific thin films; Electron, ion, and scanning probe microscopy; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Physics; Polymers; organic compounds; Scanning probe microscopy: scanning tunneling, atomic force, scanning optical, magnetic force, etc; Structure of solids and liquids; crystallography; Molecular packing; Scanning tunneling microscopy; Platinum; Transition elements; Monolayers; Gas solid interface; Alkanethiol; Crystal faces; Experimental study; IV characteristic; Electrical characteristic
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja058037c

Self-assembled monolayers (SAMs) of octanethiol and benzeneethanethiol were deposited on clean Pt(111) surfaces in ultrahigh vacuum (UHV). Highly resolved images of these SAMs produced by an in situ scanning tunneling microscope (STM) showed that both systems organize into a super-structure mosaic of domains of locally ordered, closely packed molecules. Analysis of the STM images indicated a ( × )R30° unit cell for the octanethiol SAMs and a 4( × )R30° periodicity based on 2 × 2 basic molecular packing for the benzeneethanethiol SAMs under the coverage conditions investigated. SAMs on Pt(111) exhibited differences in molecular packing and a lower density of disordered regions than SAMs on Au(111). Electron transport measurements were performed using scanning tunneling spectroscopy. Benzeneethanethiol/Pt(111) junctions exhibited a higher conductance than octanethiol/Pt(111) junctions.