Unique Ordered Domains of Biphenylthiol Self-Assembled Monolayers on Au(111)

Abstract

The surface structure and adsorption conditions of biphenylthiol (BPT) self-assembled monolayers (SAMs) on Au(111) were examined using scanning tunneling microscopy (STM) and X-ray photoelectron microscopy (XPS). STM imaging revealed that the structural order of BPT SAMs formed in a 0.01 mM ethanol solution at 60 degrees C decreases with increasing immersion time. Interestingly, BPT SAMs formed after 30 min have unique ordered domains containing well-ordered (square root of 3 x square root of 3)R30 degrees structures and bright rows that are connected by small aggregated domains with a periodicity of approximately 10 angstroms, results that have never been observed for other thiol SAM systems. Distances between the bright rows were 20-35 angstroms. The bright small domains contained five or six BPT molecules each, which may have originated from differences in the adsorption orientations of biphenyl groups that were induced by localized interactions between them. XPS measurements for BPT SAMs on Au(111) showed the two sulfur peaks at 161.2 and 162.2 eV, implying the formation of chemisorbed monolayers. Our results are anticipated to be useful for understanding the formation and structure of BPT SAMs on gold surfaces.

Improved Structural Quality of Aromatic Thiol Self-Assembled Monolayers on Au(111) by Microwave Irradiation

“…Note that these islands have usually been observed in SAM formation with various aromatic thiols in which the thiol group was attached directly to the aromatic ring such as for BT, BPT, and substituted benzenethiols. 8,9,14,16 The observation of Au adatom islands released from the top gold layer during adsorption of aromatic thiols was suggested to result from their low surface mobility.…”

Structural Investigation of 4-Methylbenzenethiol Self-Assembled Monolayers on Au(111) by Scanning Tunneling Microscopy

“…Structural order of aromatic thiol SAMs on Au(111) was considerably enhanced by increasing the number of phenyl ring in the molecular backbone [9][10][11] and by inserting the alkyl spacer between the phenyl ring and the sulfur atom.…”

“…[6][7][8][9][10][11][12][13][14][15][16] However, there have been very few reports on the structure and orientation of SAMs of 4-alkylbenzenethiols with a nonpolar sustituent.…”

“…10 4-MBT SAMs were prepared by dipping the Au(111) substrate in a 1 mM ethanol solution of 4-MBT at room temperature or 75 °C for 2 h. STM measurements were carried out using a NanoScope E (Veeco, Santa Barbara, CA) with a commercial Pt/Ir (80:20) tip under ambient conditions. Imaging parameters were in the range of 300-500 mV for the bias voltage and in the range of 0.30-0.60 nA for the tunneling current between the tip and the sample.…”

“…The similar structure was often observed for other aromatic thiol SAMs. 9,10,12,15 It was suggested that the formation of gold adatom islands is due to a low mobility of gold adatoms emerged from the first gold layer during the chemisorption of aromatic thiols on gold surfaces. Therefore, higher deposition temperature can increase a mobility of gold adatoms and a diffusion rate of adsorbing molecules on the gold surfaces, resulting in the formation of high quality SAMs with a structural order and without such gold a datom islands.…”