Potential-Induced Structural Change in a Self-Assembled Monolayer of 4-Methylbenzenethiol on Au(111)

Seo, Kyoungja; Borguet, Eric

doi:10.1021/jp064493r

Cited by 55 publications

(67 citation statements)

References 56 publications

(162 reference statements)

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“…The molecular packing structure for 4-MBT SAMs can be referred to as a (2√3 × √11.5)R30° structure, which is comparable to the previously observed structures: 4 × √3 and 2√3 × √3 structures. 17 This structural discrepancy between our and their results is due to different SAM preparation conditions because they prepared SAMs in a 0.05 mM ethanol solution at RT for 5 min and STM observation was performed under electrochemical environments (0.1 M HClO 4 at 0.4 V). On the other hand, the surface structures of 4-MBT SAMs with a nonpolar substituent were completely different from those of fluorobenzenethiol (4-FBT) SAMs with a polar substituent even if 4-FBT SAMs were prepared using same preparation conditions.…”

contrasting

confidence: 67%

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

Kang¹,

Noh²

2014

Bulletin of the Korean Chemical Society

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Self-assembled Monolayers (SAMs) Formed by the Spontaneous Adsorption of Organic Thiols on Metal Surfaces offer a powerful route for potential applications in a variety of fields such as corrosion inhibition, lubrication, sensors, biointerface, and nanopatterning. [1][2][3][4] Recently, SAMs of aromatic thiols have drawn considerable attention due to their practical applications in molecular electronic devices. 5,6 It has been demonstrated that the work function of metal electrodes in electronic devices can be easily tuned by introducing the SAMs of ω-functionalized aromatic thiols with different functional group 5-8 and the performance of SAMmodified devices was strongly dependent on the molecular orientation of adsorbed molecules.8 Therefore, it is essential to understand the surface structure and molecular orientation of aromatic thiol SAMs as well as to control two-dimensional (2D) structure of SAMs for the development of electronic devices. Structural order of aromatic thiol SAMs on Au(111) was considerably enhanced by increasing the number of phenyl ring in the molecular backbone 9-11 and by inserting the alkyl spacer between the phenyl ring and the sulfur atom.12,13 High-resolution scanning tunneling microscopy (STM) imaging revealed that the adsorption of benzenethiol (BT) on Au(111) at 50°C led to the formation of well-ordered SAMs showing the (2 × 3√2)R30° structure, 9,12 while fluorinated benzenethiol SAMs have quite different packing strcutures.14,15 So far, numerous reports have mainly focused on the surface structure, molecular orientation, self-assembled process and physical property of SAMs formed by various aromatic thiols. 6-16 However, there have been very few reports on the structure and orientation of SAMs of 4-alkylbenzenethiols with a nonpolar sustituent. 17The main purpose of this work is to elucidate how much the alkyl substituent of benzenethiol at 4-position affects the formation and structure of SAMs. To explore this question, we examined 4-methylbenzenethiol (4-MBT) SAMs prepared in a 1 mM ethanol solution using STM, and revealed for the first time that 4-MBP molecules on Au(111) at 75 ºC form 2D ordered SAMs describing a (2√3 × √11.5)R30°s tructure.Atomically flat Au(111) substrates were prepared by thermal evaporation of gold onto mica as described previously.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.STM images in Figure 1 show the surface structures of 4-MBT SAMs on Au(111) formed after immersion in a 1 mM ethanol solution at room temperature and 75 °C for 2 h. The adsorption of 4-MBT molecules on Au(111) at room temperature yielded to the disordered SAMs containing gold adatom islands (bri...

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contrasting

confidence: 67%

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

Kang¹,

Noh²

2014

Bulletin of the Korean Chemical Society

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“…An obvious choice therefore in our case is the 1068 cm 1 Raman band and we utilize the average intensity from 100 sample points in Eqn (1). Taking 1.3 ð 10 15 molecules/cm 2 for a monolayer of 4-MBT on gold,33 we find that approximately 6.47 ð 10 14 moles (9.3 ð 10 10 molecules) of 4-MBT are exited in the laser spot (100 µm diameter). The determination of N ref is more challenging and different methodologies have been reported to estimate it.…”

mentioning

confidence: 94%

Surface‐enhanced Raman scattering from gold‐coated germanium oxide nanowires

Khan

Hogan

Shanker

2008

J Raman Spectroscopy

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We utilized bulk-synthesized nanowires (NWs) of germanium dioxide as nanoscale structures that can be coated with noble metals to allow the excitation of surface plasmons over a broad frequency range. The NWs were synthesized on substrates of silicon using gold-catalyst-assisted vapor-liquid-solid (VLS) growth mechanism in a simple quartz tube furnace setup. The resulting NWs have diameters of ∼100-200 nm, with lengths averaging ∼10-40 µm and randomly distributed on the substrate. The NWs are subsequently coated with thin films of gold, which provide a surface-plasmon-active surface. Surfaceenhanced Raman scattering (SERS) studies with near-infrared (NIR) excitation at 785 nm show significant enhancement (average enhancement >10 6 ) with good uniformity to detect submonolayer concentrations of 4-methylbenzenethiol (4-MBT), trans-1,2-bis(4-pyridyl)ethylene (BPE), and 1,2-benzendithiol (1,2-BDT) probe molecules. We also observed an intense, broad continuum in the Raman spectrum of NWs after metal coating, which tended to diminish with the analyte monolayer formation.

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“…In this technique, the tunneling current is monitored by applying different tip and sample potentials (E tip = E sample ), where the potential difference (E tip − E sample ) defines the bias voltage. Unlike the typical STM measurements in vacuum, air, and inert solvents, the potential profile created by mixing the tip and sample double layers might change the sample states during EC-STM imaging [19]. Recently, the electron transfer between potential-controlled electrodes through electroactive molecules has attracted considerable attention in the field of molecular electronics, because electron transfer rates can be controlled by simply applying appropriate potentials (electrochemical gate effect) [20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Force Curve Measurements between n-Decanethiol Self-Assembled Monolayers in Inert Solvent and in Electrochemical Environment

Yokota

Yamada

Kawai

2009

e-J. Surf. Sci. Nanotechnol.

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It was revealed that electrostatic forces between electrodes under the applied bias are almost completely suppressed by an electrochemical potential control. The force operating between n-decanethiol self-assembled monolayers (SAMs) on gold was examined by atomic force microscopy in liquid n-dodecane and in an aqueous solution of HClO4. In inert n-dodecane, the bias voltage was simply applied between the tip and the sample, and the force curve exhibited a long-range attractive force in accordance with the simple capacitance model. Meanwhile under the independent control of the tip and sample potentials in HClO4, the force curve did not depend on the applied potentials due to the small double-layer capacitance.

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Potential-Induced Structural Change in a Self-Assembled Monolayer of 4-Methylbenzenethiol on Au(111)

Cited by 55 publications

References 56 publications

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

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

Surface‐enhanced Raman scattering from gold‐coated germanium oxide nanowires

Force Curve Measurements between n-Decanethiol Self-Assembled Monolayers in Inert Solvent and in Electrochemical Environment

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