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

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• 作者：Blaise-Alexis Fouetio Kengne ; Saswata Karmakar ; Mamta Kaura ; V.V.R. Sai ; Giancarlo Corti ; Ishwar B. Niraula ; Alexander Larin ; Jessica Hall ; Dewayne Sowell ; Patrick J. Hrdlicka ; Vladimir Dobrokhotov ; David N. McIlroy
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2014
• 出版时间：August 27, 2014
• 年：2014
• 卷：6
• 期：16
• 页码：13355-13366
• 全文大小：655K
• ISSN：1944-8252

文摘

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 脳 10¹⁴ (2.83 脳 10¹⁴), 3.26 脳 10¹⁴ (2.54 脳 10¹⁴), 9.50 脳 10¹³, 2.55 脳 10¹⁴ (1.12 脳 10¹⁴), and 5.23 脳 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鈥揂u bond. The S 2p core level for l-cysteine, 6-mercaptohexanol, and DL-thioctic acid consist of two doublets, where one is S鈥揂u bond and the other is the S鈥揨n bond. Analysis of the C/S ratios agrees well with the stoichiometry of the respective thiols. UPS analysis shows that the hybridization of S 3p states and Au d-bands produces antibonding and bonding states, above and below the Au d-bands, which is characteristic of molecular chemisorption on Au nanoparticles. Gas sensors were constructed with thiolated nanosprings and their responsiveness to ammonium nitrate at 100鈥?50 掳C was tested. Nanosprings sensors functionalized with 4-mercaptobenzoic acid and 6-mercaptohexanol showed the strongest responses by a factor of 4 to 5 relative to the less responsive thiols. The response to ammonium nitrate can be correlated to the packing density and ordering of the SAMs.

Keywords:

nanosprings; thiols; chemisorption; photoemission; analytes