Adsorption of Alkylthiol Self-Assembled Monolayers on Gold and the Effect of Substrate Roughness: A Comparative Study Using Scanning Tunneling Microscopy, Cyclic Voltammetry, Second-Harmonic Generation, and Sum-Frequency Generation

Autor(es)

Uehara, T. M. ^[1] ; de Aguiar, H. B. ^[1] ; Bergamaski, K. ^{[1, 2]} ; Miranda, P. B. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP - Brazil

^[2] Univ Fed Sergipe, Dept Quim, BR-49100000 Sao Cristovao, Sergipe - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Journal of Physical Chemistry C; v. 118, n. 35, p. 20374-20382, SEP 4 2014.
• Citações Web of Science: 16

Resumo

Self-assembled monolayers (SAMs) of allcylthiols on gold have called considerable attention due to several applications in the modification and control of surface properties, such as wettability, tribology, and biocompatibility. Therefore, understanding the adsorption and molecular structure of these SAMs is crucial to optimize their quality for a given application. Although many studies in this area have been performed, the effects of substrate morphology on the quality of long chain allcylthiols on gold have not been satisfactorily clarified. This study focuses on the adsorption and conformation of SAMs of 1-hexadecanethiol (C16SH) as a function of adsorption time, substrate roughness, and morphology. The adsorption of C16SH on atomically flat Au surfaces was analyzed via cyclic voltammetry (CV), scanning tunneling microscopy (STM), and second-harmonic generation (SHG), while the molecular conformation and orientation were characterized via sum-frequency generation (SFG) vibrational spectroscopy. We show that CV and STM are much more sensitive to defects in the monolayer than SFG spectroscopy, while SHG is useful to monitor the final stages of adsorption (defect healing). However, SFG spectroscopy suggests that the disordered regions observed in STM are not due to flat-lying molecules but to conformationally disordered upright alkylthiols. Finally, the formation of a nearly perfect monolayer is only obtained at long adsorption times for very flat substrates, with the packing and organization of the alkyl chains depending strongly on the roughness of the gold surface. These findings may have important implications to the preparation of high-quality SAMs for sensitive applications and also highlight the advantages and drawbacks of each technique for assessing the quality of SAMs. (AU)

• Processo FAPESP: 05/02284-0 - Estudo in situ da adsorcao de polieletrolitos em substratos solidos atraves da espectroscopia vibracional por soma de frequencia (sfg).
• Beneficiário: Kleber Bergamaski
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 10/00486-2 - Estudo da Interação de Nanotubos e Nanopartículas com Modelos de Membranas Celulares e Aplicações
• Beneficiário: Thiers Massami Uehara
• Modalidade de apoio: Bolsas no Brasil - Doutorado