Displacement processes of pre-covered cyclohexanethiol (CHT) self-assembled monolayers (SAMs) by 4-fluorobenzenethiol (4-FBT) on Au(111) were examined as a function of displacement time by scanning tunneling microscopy (STM) and water static contact angle (CA) measurements. STM imaging revealed that the adsorption of 4-FBT on Au(111) in a 1 mM ethanol solution at room temperature for 24 h generated disordered SAMs, whereas well-ordered 4-FBT SAMs with a (4√6 × √3)R5° packing structure were formed over the entire Au(111) surfaces via the displacement of pre-covered CHT SAMs by 4-FBT molecules. The CA measurements also showed that CA values increase with increasing displacement time, reflecting that the displacement reaction took place and the resulting SAMs had greater hydrophobicity compared with CHT SAMs. In this study, we found that the displacement technique using CHT SAMs as a molecular template is very useful in obtaining 4-FBT SAMs with a high degree of structural order and large ordered domains.
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Displacement processes of pre-covered cyclohexanethiol (CHT) self-assembled monolayers (SAMs) by 4-fluorobenzenethiol (4-FBT) on Au(111) were examined as a function of displacement time by scanning tunneling microscopy (STM) and water static contact angle (CA) measurements. STM imaging revealed that the adsorption of 4-FBT on Au(111) in a 1 mM ethanol solution at room temperature for 24 h generated disordered SAMs, whereas well-ordered 4-FBT SAMs with a (4√6 × √3)R5° packing structure were formed over the entire Au(111) surfaces via the displacement of pre-covered CHT SAMs by 4-FBT molecules. The CA measurements also showed that CA values increase with increasing displacement time, reflecting that the displacement reaction took place and the resulting SAMs had greater hydrophobicity compared with CHT SAMs.
View Article and Find Full Text PDFSpontaneous desorption and phase transitions of self-assembled alkanethiol and alicyclic thiol monolayers chemisorbed on Au(111) in ultrahigh vacuum at room temperature.
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March 2013
Flucto-Order Functions Research Team, RIKEN-HYU Collaboration Research Center, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) were used to examine the surface structure and adsorption conditions of hexanethiol (HT) and cyclohexanethiol (CHT) self-assembled monolayers (SAMs) on Au(111) as a function of storage period in ultrahigh vacuum (UHV) conditions of 3×10(-7) Pa at room temperature (RT). STM imaging revealed that after storage for 7 days, HT SAMs underwent phase transitions from c(4×2) phase to low coverage 4×√3 phase. This transition is due to a structural rearrangement of hexanethiolates that results from the spontaneous desorption of chemisorbed HT molecules on Au(111) surface.
View Article and Find Full Text PDFMolecular-scale investigation of structural changes in cyclohexanethiol self-assembled monolayers on Au(111).
J Nanosci Nanotechnol
December 2009
Department of Chemistry, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea.
Two-dimensional ordered structures of cyclohexanethiol (CHT) self-assembled monolayers (SAMs) on Au(111) formed from different solution concentrations were investigated using scanning tunneling microscopy (STM). Molecular-scale STM imaging clearly revealed the 2D phase transitions of CHT SAMs from a (2 x 4 square root of 2)R20 degrees structure to a (5 x 2 square root of 3)R35 degrees structure via a intermediate phase of a (5 x square root of 15)R25 degrees structure depending on solution concentration used for SAM fabrication. The (5 x 2 square root of 3)R35 degrees phase was observed for high concentrations, after deposition at low temperature or after long-time immersion.
View Article and Find Full Text PDFUltrafast excitation of molecular adsorbates on flash-heated gold surfaces.
J Phys Chem A
November 2009
School of Chemical Sciences, University of Illinois at Urbana-Champaign, Chemical and Life Sciences Laboratory, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
An ultrafast flash-thermal conductance technique is used to study energy transfer from a flash-heated polycrystalline Au(111) surface to adsorbed thiolate self-assembled monolayers (SAMs). The focus is on understanding energy transfer processes to parts of SAM molecules situated within a few carbon atoms of the Au surface, by probing specific SAM functional groups with vibrational sum-frequency generation (SFG) spectroscopy. The SFG intensity drop after flash-heating for benzenethiol (BT) CH-stretch transitions shows a substantial overshoot lasting several tens of picoseconds before BT and Au equilibrate at a higher temperature estimated at 600 degrees C.
View Article and Find Full Text PDFFast displacement and structural transition of cyclohexanethiol self-assembled monolayers by octanethiols on Au (111).
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September 2008
Department of Chemistry, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Republic of Korea.
Displacement of cyclohexanethiols (CHTs) self-assembled monolayers (SAMs) by octanethiols on Au (111) (OTs) was examined by scanning tunneling microscopy (STM) and contact angle measurements. We revealed that the fast displacement of CHT by OT takes place within a few minutes, and then displacement proceeds slowly to form the closely packed OT SAMs. The main driving force for the unusual fast displacement is due to the large increase of chemical interactions between the sulfur and gold atoms, and the van der Waals interactions between alkyl chains after displacement of CHT by OT.
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