Self-Assembled Monolayers of Thiols Adsorbed on Au/ZnO-Functionalized Silica Nanosprings: Photoelectron Spectroscopy-Analysis and Detection of Vaporized Explosives

Self-assembled monolayers (SAMs) of thiols of l-cysteine, 6-mercaptohexanol, 4-mercaptobenzoic acid, dl-thioctic acid and 11-(1-pyrenyl)-1-undecathiol, which have been selected for their propensity to interact with vaporized explosives, have been attached from solution onto gold decorated ZnO-coated nanosprings. X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) have been used to investigate the surface electronic structure of the SAMs coated nanosprings. On the basis of XPS analysis, it has been determined that the packing densities of l-cysteine, 6-mercaptohexanol, 4-mercaptobenzoic acid, dl-thioctic acid and 11-(1-pyrenyl)-1-undecathiol on gold (zinc oxide) are 5.42 × 1014 (2.83 × 1014), 3.26 × 1014 (2.54 × 1014), 9.50 × 1013, 2.55 × 1014 (1.12 × 1014), and 5.23 × 1013 molecules/cm2, respectively. A single S 2p core level doublet is observed for 4-mercaptobenzoic acid and 11-(1-pyrenyl)-1-undecathiol, which is assigned to the S–Au bond. The S 2p core level for l-cysteine, 6-mercaptohexano...