Direct Covalent Grafting of Conjugated Molecules onto Si, GaAs, and Pd Surfaces from Aryldiazonium Salts

• Published in: Journal of the American Chemical Society Vol. 126; no. 1; pp. 370 - 378
• Main Authors: Stewart, Michael P, Maya, Francisco, Kosynkin, Dmitry V, Dirk, Shawn M, Stapleton, Joshua J, McGuiness, Christine L, Allara, David L, Tour, James M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14.01.2004
• Subjects: Adsorption and desorption kinetics; evaporation and condensation; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Solid-fluid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Chemisorption; Atomic force microscopy; Gallium arsenides; Liquid solid interface; Liquid solid adsorption; Organic adsorbate; Electron transfer; Palladium; Inorganic adsorbent; Experimental study; Photoelectron spectroscopy; Molecular orientation; Transition elements; n type semiconductor; Adsorption structure; Silicon; Diazonium compounds; III-V semiconductors
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0383120

Using aryldiazonium salts that are air-stable and easily synthesized, we describe here a one-step, room-temperature route to direct covalent bonds between π-conjugated organic molecules on three material surfaces:  Si, GaAs, and Pd. The Si can be in the form of single crystal Si including heavily doped p-type Si, intrinsic Si, heavily doped n-type Si, on Si(111) and Si(100), and on n-type polycrystalline Si. The formation of the aryl−metal or aryl−semiconductor bond attachments was confirmed by corroborating evidence from ellipsometry, reflectance FTIR, XPS, cyclic voltammetry, and AFM analyses of the surface-grafted monolayers. A data-encompassing explanation for the mechanism suggests a diazonium activation by reduction at the open circuit potential, with aryl radical secondary products bonding to the surface. The synthetic details are included for preparing the surface-grafted monolayers and the precursor diazonium salts. This spontaneous diazonium activation reaction offers an attractive route to highly passivating, robust monolayers and multilayers on many surfaces that allow for strong bonds between carbon and surface atoms with molecular species that are near perpendicular to the surface.