Nathir Al-Rawashdeh
Jordan University of Science & Technology, Jordan
Title: A comprehensive characterization of self-assembled monolayers of aromatic selenol on Au(111): solvent effects, immersion time effects, and structure
Biography
Biography: Nathir Al-Rawashdeh
Abstract
Self-assembled monolayers (SAMs) formed by adsorption of 1,2-dibenzyldiselane (DBDSe) and 1,2-diphenyldiselane (DPDSe) on Au(111) substrates at room temperature (RT) and 345 K have been characterized using scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRRAS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and low-energy electron diffraction (LEED). Upon adsorption, the Se-Se bonds in DBDSe and DPDSe are cleaved on gold surface to form phenylmethaneselenolate (BSe) and benzeneselenolate (PSe) species, respectively. Although both the PSe and BSe species differ only in their molecular structure with an additional methyl group in BSe, the resulting films reveal noteworthy dissimilarities concerning their adlayer SAM structure and surface morphology. The molecular adlayer structure and orientation of PSe and BSe species were found to depend significantly on the immersion time (IT). For BSe SAMs, the IR data exhibited vibrational modes verifying the adsorption of BSe species on gold surface only for SAMs prepared for ITs longer than 1 h. Furthermore, acquiring STM-images showing individual BSe molecules or any type of order was only achievable for SAMs prepared for 24 h of IT at RT. With increasing the IT, the SAMs exhibited structural changes to a lower density of molecular packing structure. The spectroscopic data also confirmed this structural variation by suggesting upright orientation for PSe-SAMs prepared after short ITs and strongly inclined adsorption geometry for SAMs prepared after long ITs.