Dodecanethiol Self-assembled Monolayers Research Articles

Two-Dimensional Crystal Structure of a Quaterthiophene−Alkanethiol Self-Assembled Monolayer on Gold

We investigated the fine structure of a self-assembled monolayer of dodecanethiol functionalized by alpha-quaterthiophene on gold (alpha-4TC 12H 24SH). The molecular orientation, quantified using polarization modulation infrared reflection-absorption spectroscopy, was studied as a function of the adsorption time. The alpha-4T moieties arrange in the upright position on the surface as the adsorption time increases, while the alkyl chain organization remains poor. Here we quantify the orientation of the self-assembled monolayer and, more significantly, reveal through surface X-ray diffraction that after a long incubation period (12 h) the alpha-4T on the gold surface adopts a 2D crystal structure.

Study of the solvent effect on the quality of dodecanethiol self-assembled monolayers on polycrystalline gold

This paper reports the study of the solvent (tetrachloromethane, toluene, tetrahydrofuran, acetone, N, N-dimethylformamide, acetonitrile, ethanol, ethanol–water mixture (1:1, v:v) and neat dodecanethiol liquid) effect on the quality of self-assembled monolayers of dodecanethiol (C 12SH-SAMs) on polycrystalline gold. The quality of the C 12SH-SAMs was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the results show that highly dense and well-ordered C 12SH-SAMs can be prepared from ethanol–water mixture and neat dodecanethiol liquid. The property parameters of the solvents, such as polarity, solubility parameter, molecular diameter, octanol–water partition coefficients and viscosity were correlated with their ability to influence the quality of the C 12SH-SAMs.

Dipyrromethene–dodecanethiol self-assembled monolayers deposited onto gold electrodes

In the work presented, a dipyrromethene with a thiol group has been applied to gold electrode modification. The blocking behaviour of mixed dipyrromethene-thiol (DPT)/dodecanethiol (DDT) self-assembled monolayers (SAMs) has been studied as a function of pH using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It has been shown that hydrogen-bonding between adjacent ligands affects the pH properties of SAMs studied. In the modification solution, an optimum ratio dipyrromethene-thiol/dodecanethiol was found to get the strongest pH response of SAM. The dipyrromethene-thiol/dodecanethiol SAMs have been characterized also by FTIR and wettability contact angle measurements. The possible application of the mixed dipyrromethene-thiol/dodecanethiol SAMs presented will be discussed.

Extracellular biosynthesis of monodispersed gold nanoparticles by a SAM capping route

Monodispersed gold nanoparticles capped with a self-assembled monolayer of dodecanethiol were biosynthesized extracellularly by an efficient, simple, and environmental friendly procedure, which involved the use of Bacillus megatherium D01 as the reducing agent and the use of dodecanethiol as the capping ligand at 26 °C. The kinetics of gold nanoparticle formation was followed by transmission electron microscope (TEM) and UV-vis spectroscopy. It was shown that reaction time was an important parameter in controlling the morphology of gold nanoparticles. The effect of thiol on the shape, size, and dispersity of gold nanoparticles was also studied. The results showed that the presence of thiol during the biosynthesis could induce the formation of small size gold nanoparticles (<2.5 nm), hold the shape of spherical nanoparticles, and promote the monodispersity of nanoparticles. Through the modulation of reaction time and the use of thiol, monodispersed spherical gold nanoparticles capped with thiol of 1.9 ± 0.8 nm size were formed by using Bacillus megatherium D01.

Rapid formation of well-ordered self-assembled monolayers of dodecanethiol on polycrystalline gold by microwave irradiation

This article reports a rapid method of preparing self-assembled monolayers of dodecanethiol (C 12SH-SAMs) on polycrystalline gold by microwave irradiation (MWI, 650 W, duty cycle is 10%). The qualities of C 12SH-SAMs were characterized by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that the C 12SH-SAMs formed by MWI in 120 s (C 12SH-SAMs MWI,120 s ) have low ionic permeability (the differential capacitance C d values are independent of the scan rate and phase angle at 1 Hz Φ 1 Hz = 89 ± 0.9°), excellent electrochemical blocking ability towards the redox probe (the current i MWI,120 s obtained from CV is lowest when compared to other SAMs and charge transfer resistance R ct = (1.15 ± 0.19) × 10 6 Ω cm 2), and high surface coverage (99.996 ± 0.001%).

Room-temperature ionic liquid as a new solvent to prepare high-quality dodecanethiol self-assembled monolayers on polycrystalline gold

This paper reports a new solvent, room-temperature ionic liquid (RTIL), for the preparation of dodecanethiol self-assembled monolayers (C 12SH-SAMs) on polycrystalline gold. The quality of C 12SH-SAMs was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). From CV experiments, we find that the differential capacitance C d values of the C 12SH-SAM prepared in RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF 6) containing 10 μL neat C 12SH for 24 h (C 12SH-SAMs [BMIM]PF6,10 μL,24 h ) are independent of the scan rate, the effective thickness d eff value and the average cant angle φ value of this monolayer are 18 ± 1 Å and 27 ± 4°, respectively. The difference value of the current density at −0.2 and 0.5 V (Δ i p) is only 0.73 ± 0.18 μA cm −2. EIS experiments show that the phase angle value at 1 Hz Φ 1 Hz , the charge transfer resistance R ct value and surface coverage θ value of this C 12SH-SAM are 88.2 ± 0.7°, 3.44 ± 1.91 MΩ cm 2 and 99.998 ± 0.001%, respectively. These results indicate that high-quality C 12SH-SAMs can be formed in [BMIM]PF 6. In addition, the rate of formations of high-quality C 12SH-SAMs in RTIL can be substantially improved by ultrasound.

Rapid formation of high-quality self-assembled monolayers of dodecanethiol on polycrystalline gold under ultrasonic irradiation

Self-assembled monolayers of dodecanethiol (C 12SH-SAMs) on polycrystalline gold were prepared under ultrasonic irradiation at 100 W (the actual ultrasonic power intensity is about 0.1 W cm −2 including the heat loss) for different time and investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV experiments show that the differential capacitance C d values of the C 12SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm −2) for 15 min are independent of the scan rate, the thickness d value of this monolayer is 17.5 Å, the tilt angle φ value of the molecules in this monolayer from the gold surface normal was calculated to be 30° and the difference value of the current density at −0.2 and 0.5 V (Δ i p) is only 0.69 μA cm −2. From the EIS experiments, we find that the phase angle value at 1 Hz Φ 1 Hz of the C 12SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm −2) for 15 min is 89°, the charge transfer resistance R ct value of this monolayer is 1.40 × 10 6 Ω cm 2 and the surface coverage θ value of this monolayer was calculated to be 99.997% from R ct. These results indicate that the C 12SH-SAM of almost defect-free structure and very low ionic permeability can be formed under ultrasonic irradiation at 100 W (0.1 W cm −2) in a short time (15 min).

Real-Time Measurements of Conductance Switching and Motion of Single Oligo(phenylene ethynylene) Molecules

Real-time conductance switching and place-exchange up and down substrate step edges have been measured for oligo(phenylene ethynylene) (OPE) molecules inserted into host dodecanethiolate self-assembled monolayers (SAM). These measurements were obtained by placing a scanning tunneling microscopy tip over individual nitro-functionalized OPE molecules and recording apparent height versus time. In addition, real-time measurements for the host SAM were acquired and indicated small motions for the monolayer−substrate system.

Electro-oxidation of altertoxin I (ATX-I) at gold electrodes modified by dodecanethiol self-assembled monolayers

Abstract The adsorptive accumulation of ATX-I, a mycotoxin produced by the fungi the Alternaria alternate genus, onto polycrystalline gold electrodes modified by a self-assembled monolayer (SAM) of 1-dodecanethiol (DDT) from unstirred solutions of the pure commercial reagent in 20% acetone (Ac) + 80% pH 7 phosphate buffer solutions (PBS) has been studied by cyclic (CV) and square wave voltammetries (SWV). The influence of different experimental conditions on the adsorptive process has been analyzed. The specific interaction of ATX-I with these modified gold electrodes was adequately described by a Freundlich adsorption isotherm. Electrochemical impedance spectroscopy (EIS) measurements were used to assess the state of the adsorbed thiol molecules, demonstrating that optimum conditions for analytical detection require the presence of defects in the monolayer, where analyte accumulation and charge transfer rate are enhanced with respect to well ordered monolayers. SWV was employed to generate the calibration curves. For a signal-to-noise ratio of 3:1, a detection limit of 4 × 10 −8 mol dm −3 (14 ppb) was calculated at a frequency ( f ) of 40 Hz.

Molecular Self-Assembly at Bare Semiconductor Surfaces: Investigation of the Chemical and Electronic Properties of the Alkanethiolate−GaAs(001) Interface

High-resolution X-ray photoelectron spectroscopy (HRXPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and Raman scattering have been used to characterize the bonding and electronic properties of the interfaces formed by ambient-temperature, solution self-assembly of octadecanethiol and dodecanethiol under oxygen-free conditions on GaAs(001) surfaces. The combination of HRXPS and ToF-SIMS shows that both monolayers form direct S−[GaAs] attachment to the bare substrate with dominant As−S bonding and some fraction of Ga−S bonding, but the densely packed octadecanethiolate self-assembled monolayers (SAMs) are significantly more effective in protecting the interface from oxide regrowth compared to the less dense dodecanethiolate SAMs. Raman scattering measurements of the GaAs LO phonon modes indicate that the formation of these direct, oxide-free S−[GaAs] interfaces does not induce any significant changes in the GaAs surface electronic states, whereas control experiments with inorganic sulfide t...

Scanning Tunneling Microscopy-Based Replacement Lithography on Self-Assembled Monolayers: Comparison of Gold, Palladium, and Platinum Substrates

Self-assembled monolayers of dodecanethiol on gold, palladium, and platinum can be locally replaced with a different thiol under the action of a scanning tunneling microscopy tip at elevated bias. This process is characterized and the bias dependence of the degree of replacement for each metal substrate is illustrated. Replacement on gold substrates occurs at lower applied potentials than on platinum substrates, provided care has been taken to remove surface oxides.

Sensitive determination of fluphenazine at a dodecanethiol self-assembled monolayer-modified gold electrode, and its electrocatalysis to phenylephrine

Fluphenazine, an important tranquilizer, was found to undergo effective accumulation on dodecanethiol (DDT) self-assembled monolayer modified gold electrode (i.e. DDT/Au) and generated two anodic peaks at about 0.7 and 0.79 V (vs. SCE) in 0.05 M Na2B4O7 (pH = 9.3) buffer solution. Sensitive and quantitative measurement of fluphenazine based on the former anodic peak was established under optimum conditions. The peak current was linear to fluphenazine concentration in the range from 5 × 10−7 to 5 × 10−5 M, with a detection limit of 5 × 10−9 M. This method was successfully applied to the determination of fluphenazine in drug tablets and proved to be reliable compared with UV spectrophotometry. In the presence of fluphenazine, the electrochemical oxidation of phenylephrine was catalyzed. The DDT self-assembled monolayer was characterized by Fourier transform infrared spectroscopy, surface Raman spectroscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and electrochemical probing.

Influence of Nanobubbles on the Adsorption of Nanoparticles

A quartz crystal microbalance was used to study the influence of nanobubbles on the adsorption of polystyrene nanoparticles onto surfaces coated with gold, or coated with dodecanethiol or mercaptoundecanoic acid self-assembled monolayers (SAMs). Adsorption of the nanoparticles onto the surface causes the resonant frequency of the quartz crystal to decrease. We found that particles were adsorbed onto the gold-coated quartz crystal in air-rich water, but not in degassed water. This finding supports the long-standing hypothesis that nanobubbles play a key role in the long-range attractive force between hydrophobic surfaces in aqueous solutions. When the experiments were conducted using quartz crystals coated with a hydrophobic dodecanethiol SAM, the nanoparticles were adsorbed onto the surface even in degassed water due to the short-range hydrophobic interactions between the nanoparticles and the dodecanethiol molecules. In contrast, the nanoparticles were adsorbed to a lesser degree onto the hydrophilic mercaptoundecanoic acid-coated crystals due to electrostatic repulsive forces.

Copper Protection by a Self-Assembled Monolayer of Alkanethiol: Comparison with Benzotriazole

Self-assembled monolayers (SAMs) formed by the adsorption of alkanethiols onto copper is a simple method for producing coatings that can protect the metal against oxidation and corrosion. However, a contradiction regarding the influence of oxygen on the SAMs formation and barrier properties is still present. In this work the SAMs of dodecanethiol (DT) were formed on the copper substrates from ethanolic solutions of DT with and without the presence of dissolved oxygen. The protecting properties of monolayers were studied in a sodium acetate solution with a pH of 6 using cyclic voltammetry and electrochemical impedance spectroscopy. The effect of exposing samples, prepared in the deoxygenated solutions, to air was also studied to examine the decrease in the protecting properties of the SAMs against copper corrosion. The protection efficiency of the DT SAMs was compared with those of benzotriazole, which is known as the best inhibitor for copper corrosion.

Synthesis of dodecanethiol monolayer-stabilized nickel nanoparticles

Nickel nanoparticles surface-capped with self-assembled monolayer of dodecanethiol were prepared by the controlled reduction of nickel chloride (NiCl 2·6H 2O) in the presence of dodecanethiol of different concentrations as the ligand and hydrazinium hydroxide as the reductant. The morphology and structure of the resulting surface-capped nickel nanoparticles were analyzed by means of transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transformation infrared spectroscopy and thermogravimetric analysis. It was found that dodecanethiol played a critical role in controlling the radius and dispersibility of the surface-capped Ni nanoparticles. Namely, the nickel nanoparticles prepared in the absence of the surface-capping agent were liable to aggregate, while those prepared in the presence of decanethiol with a large enough concentration had a very small grain size. It was supposed that the surface-capped nickel nanoparticles with significantly increased stability and dispersibility as compared to the non-surface-capped nickle nanoparticles could be used as a kind of novel nanoscale lubricating additives.

STM Study of Mixed Alkanethiol/Biphenylthiol Self-Assembled Monolayers on Au(111)

A method is presented for depositing mixed self-assembled monolayers (SAMs) of dodecanethiol (C12) and 4'-methyl-1,1'-biphenyl-4-butane (H3C-C6H4-C6H4-(CH2)4-SH, BP4) by insertion of BP4 into a closely packed SAM of dodecanethiol on Au(111). Insertion takes place at defect sites such as domain boundaries or etch pits in the gold surface that are characteristic of C12 monolayers on gold. With a lower probability, insertion also occurs beside defect sites inside dodecanethiol domains. Insertion at defect sites results in domains of BP4, whereas insertion into C12 domains leads to isolated BP4 molecules. The isolated BP4 molecules are shown not to move at room temperature. By comparing the apparent height of the isolated BP4 molecules and BP4 domains, it is proposed that the isolated molecules have the same conformation as in the full-coverage phase. A simple two-layer model is proposed to characterize the current transport through BP4. The decay constant beta for the phenylene groups is deduced from the apparent STM heights of the inserted BP4 islands compared to the STM heights of the C12 closely packed monolayers.

Two-Site Adsorption Model for the (√3 × √3)-R30° Dodecanethiolate Lattice on Au(111) Surfaces

The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au(111) surfaces, formed from the liquid phase, have been studied by grazing incidence X-ray diffraction (GIXRD), scanning tunneling microscopy (STM), and electrochemical techniques. STM images show that the surface structure consists of (square root 3 x square root 3)-R30 degrees domains with only a few domains of the c(4 x 2) lattice. The best fitting of GIXRD data for the (square root 3 x square root 3)-R30 degrees lattice is obtained with alkanethiolate adsorption at the top sites, although good fittings are also obtained for the fcc and hcp hollow sites. On the basis of this observation, STM data, electrochemical measurements, and previously reported data, we propose a two-site model that implies the formation of incoherent domains of alkanethiolate molecules at top and fcc hollow sites. This model largely improves the fitting of the GIXRD data with respect to those observed for single adsorption sites and, also, for the other possible two-site combinations. The presence of alkanethiolate molecules adsorbed at the less favorable top sites could result from the adsorption pathway that involves an initial physisorption step which, for steric reasons, takes place at on top sites. Once the molecules are chemisorbed, the presence of energy barriers for alkanethiolate surface diffusion, arising mostly from chain-chain interactions, "freezes" some of them at the on top sites, hindering their movement toward fcc hollow sites. By considering the length of the hydrocarbon chain and the adsorption time, the two-site model could be a tool to explain most of the controversial results on this matter reported in the literature.

Enhanced surface evolution induced by the molecular desorption in dodecanethiol self-assembled monolayer on Au(1 1 1)

The evolution of the surface structure in dodecanethiol self-assembled monolayer on Au(1 1 1) substrate has been studied with ultra high vacuum scanning tunneling microscopy at several temperatures. The structure of substrate Au(1 1 1) surface changed suddenly at a temperature of 110 °C. The enhanced mobility of the substrate gold atoms at this temperature is attributed to the desorption of the dodecanethiol molecules.

Stochastic and photochromic switching of diarylethenes studied by scanning tunnellingmicroscopy

We investigate switching of photochromic, thiophene-substituted diarylethene switches ongold. For this, the conjugated isomer is inserted in a dodecanethiol self-assembledmonolayer. This layer is subsequently scanned by tunnelling microscopy. First, we studythe statistics of stochastic switching events, using two different counting methods. Onemethod monitors reversible switching, whereas the other counts irreversible switchingevents. For each STM bias voltage, we observe a saturation to a dynamic equilibrium of‘on’ and ‘off’ state molecules. This equilibrium shifts to the ‘off’-side when the voltage biasis increased. Second, we separate light-induced switching from stochastic switching. In thisway, we demonstrate photochromic switching of single molecules, from the conjugated tothe non-conjugated form. The switching times we measure are comparable tothose found for conjugated switches self-assembled on gold colloids in solution.

Adsorption behaviors of poly(amido amine) dendrimers with an azacrown core and long alkyl chain spacers on solid substrates

Adsorption behaviors of functional poly(amido amine) dendrimers with an azacrown core and long alkyl chain spacers were investigated on gold and self-assembled monolayer (SAM) by means of time course attenuated total reflection–surface enhanced infrared absorption and surface plasmon resonance spectroscopies. While 1.5th and 2.5th generation (G1.5 and G2.5) ester-terminated dendrimers were slightly adsorbed on all substrates examined, the adsorption of G2 amine-terminated dendrimer increased in the order dodecanethiol SAM < bare gold < 3-mercaptopropionic acid (MPA) SAM. The time course results also revealed that the G2 dendrimer displayed the steep increase of adsorption on the bare gold, followed by the slight progress of adsorption. G2 dendrimers adsorbed on MPA SAM involved their subsequent conformational rearrangement, while the adsorption equilibrium was quickly attained for G3 dendrimer on the MPA SAM. It was supported that G3 dendrimer was adsorbed with the perpendicularly extended structure on the MPA SAM substrate, and G2 dendrimer varied its conformation from the globular structure to the extended one perpendicular to the substrate.