Dodecanethiol Self-assembled Monolayers Research Articles

Spatial variations of conductivity of self-assembled monolayers of dodecanethiol on Au/mica and Au/Si substrates

Determining the conductivity of molecular layers is a crucial step in advancing towards applications in molecular electronics. A common test bed for fundamental investigations on how to acquire this conductivity are alkanethiol layers on gold substrates. A widely used approach in measuring the conductivity of a molecular layer is conductive atomic force microscopy. Using this method, we investigate the influence of a rougher and a flatter gold substrate on the lateral variation of the conductivity. We find that the roughness of the substrate crucially defines this variation. We conclude that it is paramount to adequately choose a gold substrate for investigations on molecular layer conductivity.

Unraveling the Radiation Damage of n-Dodecanethiol Self-Assembled Monolayers on Au(100) and Au(111): A Prerequisite to Understand the Oriented Attachment of Au Nanoparticles

Unraveling the Radiation Damage of <i>n</i>-Dodecanethiol Self-Assembled Monolayers on Au(100) and Au(111): A Prerequisite to Understand the Oriented Attachment of Au Nanoparticles

Mechanistic Framework for the Formation of Different Sulfur Species by Electron Irradiation of n-Dodecanethiol Self-Assembled Monolayers on Au(111) and Au(100)

The electron induced damage in self-assembled monolayers (SAMs) of n-dodecanethiolate on Au(111) and Au(100) single-crystalline surfaces is investigated in situ by X-ray photoelectron spectroscopy....

Layer-by-layer growth of molecular self-assembled monolayers /sputtered gold thin films/graphene oxide on glass substrate

In the present study, 1-dodecanethiol self-assembled monolayers (SAMs) on graphene oxide (GO) –Au (Gold) thin films as molecular templates for the selective deposition of multilayer films was performed. Thus, heterostructured GO/Au/DDT and DDT/Au/GO thin film are fabricated by sputtering Au target onto modified GO structure or self-assembled 1-dodecanethiol (DDT) arrays. It has been shown that a new device concept can be made by completing the glass substrate with the surface heterostructures; i.e. layer GO sheet or DDT with Au nanoparticles (Au NPs). In the light of the performed study, the layer-by-layer assembling of DDT on the GO sheet-Au thin films template has been proved for the distinct conjugation. Also, Optical and morphological characterizations are coherent with the instantaneous nucleation and growth model over the modified DDT-Au NPs-GO or GO-Au NPs-DDT thin films in the aspect of surface roughness, the phonon transport, and other multilayer films properties. As a consequence, the multilayer films of DDT-capped Au thin films and GO sheets have shown a better hybrid nanostructure with higher consistency, hierarchy and surface area. In addition, this work will present a new perspective for template preparation based on nanostructured thin films due to its unique properties resulting from nanoscale properties.

Inhibition Effect of Three-Dimensional (3D) Nanostructures on the Corrosion Resistance of 1-Dodecanethiol Self-Assembled Monolayer on Copper in NaCl Solution.

A novel and simple method to improve the corrosion resistance of copper by constructing a three-dimensional (3D) 1-dodecanethiol self-assembled monolayer (SAM) in 3.5% NaCl solution is reported in this study. Several drops of 1% H3PO4 solution are thinly and uniformly distributed on copper surface to form a 3D nanostructure constituted by Cu3(PO4)2 nanoflowers. The anticorrosion properties of 1-dodecanethiol SAM on copper surface and on copper surface that is treated with H3PO4 solution were evaluated. Results demonstrated that 1-dodecanethiol SAM on bare copper surface exhibits good protection capacity, whereas a copper surface that is pretreated with H3PO4 solution can substantially enhance the corrosion resistance of 1-dodecanethiol SAM.

Nonlinear optical response of a gold surface in the visible range: A study by two-color sum-frequency generation spectroscopy. I. Experimental determination

We experimentally determine the effective nonlinear second-order susceptibility of gold over the visible spectral range. To reach that goal, we probe by vibrational two-color sum-frequency generation spectroscopy the methyl stretching region of a dodecanethiol self-assembled monolayer adsorbed on a gold film. The sum-frequency generation spectra show a remarkable shape reversal when the visible probe wavelength is tuned from 435 to 705 nm. After correcting from Fresnel effects, the methyl stretching vibrations serve as an internal reference, allowing to extract the dispersion of the absolute phase and relative amplitude of the effective nonlinear optical response of gold in the visible range.

Hydrogen Oxidation-Selective Electrocatalysis by Fine Tuning of Pt Ensemble Sites to Enhance the Durability of Automotive Fuel Cells.

A simple, inexpensive approach is proposed for enhancing the durability of automotive proton exchange membrane fuel cells by selective promotion of the hydrogen oxidation reaction (HOR) and suppression of the oxygen reduction reaction (ORR) at the anode in startup/shutdown events. Dodecanethiol forms a self-assembled monolayer (SAM) on the surface of Pt particles, thus decreasing the number of Pt ensemble sites. Interestingly, by controlling the dodecanethiol concentration during SAM formation, the number of ensemble sites can be precisely optimized such that it is sufficient for the HOR but insufficient for the ORR. Thus, a Pt surface with an SAM of dodecanethiol clearly effects HOR-selective electrocatalysis. Clear HOR selectivity is demonstrated in unit cell tests with the actual membrane electrode assembly, as well as in an electrochemical three-electrode setup with a thin-film rotating disk electrode configuration.

Hydrogen Oxidation Reaction-Selective Electrocatalysis Via Fine Tuning of Platinum Ensemble Sites Using Dodecanethiol to Enhance the Durability of Automotive Fuel Cells

We suggest a simple, inexpensive approach for enhancing the durability of automotive proton exchange membrane fuel cells by selective promotion of the hydrogen oxidation reaction (HOR) and suppression of the oxygen reduction reaction (ORR) at the anode in startup/shutdown events. Dodecanethiol forms a self-assembled monolayer (SAM) on the surface of Pt particles, thus decreasing the number of Pt ensemble sites. Interestingly, by controlling the dodecanethiol concentration during SAM formation, we can precisely tune the number of ensemble sites to an optimum such that it is sufficient for the HOR but insufficient for the ORR. Thus, a Pt surface with an SAM of dodecanethiol clearly shows HOR-selective electrocatalysis. We demonstrate clear HOR selectivity in unit cell tests with the actual membrane electrode assembly as well as in an electrochemical three-electrode setup with a thin film rotating disk electrode configuration.

Nanomolar Level Determination of Octyl Gallate in Fats and Oils

Monitoring of synthetic phenolic antioxidants in food is very important due to their potential harmfulness to human beings. Octyl gallate (OG) is a commonly used phenolic antioxidant as a preservative in food stuff such as margarine, lard, sunflower oil etc. Herein, a glassy carbon electrode (GCE) chemically modified with gold nanoparticles (AuNPs) followed by self-assembled monolayer of dodecane thiol (DDT) was fabricated and employed for the determination of OG. An anodic peak corresponds to the oxidation of OG was observed at a potential of 0.22 V at DDT/AuNPs/GCE by square wave voltammetry. Based on this, a novel electrochemical sensor was developed for the determination of OG in oils and fats. Linear calibration graph was obtained within the range 1.2 to 0.2 μM. The detection limit was found to be 8.3 nM which is remarkably lower than those reported previously. The applicability of the method was demonstrated by analyzing OG in commercially available food samples such as margarine, butter and sunflower oil.

Superhydrophobic SAM Modified Electrodes for Enhanced Current Limiting Properties in Intrinsic Conducting Polymer Surge Protection Devices.

Surface interface engineering using superhydrophobic gold electrodes made with 1-dodecanethiol self-assembled monolayer (SAM) has been used to enhance the current limiting properties of novel surge protection devices based on the intrinsic conducting polymer, polyaniline doped with methanesulfonic acid. The resulting devices show significantly enhanced current limiting characteristics, including current saturation, foldback, and negative differential effects. We show how SAM modification changes the morphology of the polymer film directly adjacent to the electrodes, leading to the formation of an interfacial compact thin film that lowers the contact resistance at the Au-polymer interface. We attribute the enhanced current limiting properties of the devices to a combination of lower contact resistance and increased Joule heating within this interface region which during a current surge produces a current blocking resistive barrier due to a thermally induced dedoping effect caused by the rapid diffusion of moisture away from this region. The effect is exacerbated at higher applied voltages as the higher temperature leads to stronger depletion of charge carriers in this region, resulting in a negative differential resistance effect.

Argon ion irradiation induced morphological instability of bare and thiol-functionalized Au(111) surfaces.

Ar ion irradiation-induced changes in the morphology of bare and 1-dodecanethiol self-assembled monolayer (SAM) covered Au(111) surfaces have been investigated systematically. The changes were followed by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) measurements while varying the ion charge (Ar(+),Ar(4+)), energy (10-40 keV) and fluency (10(12)-10(13) ions per cm(2)). The impact of flame-annealing of the Au(111) surface on subsequent ion bombardment was considered and more prominent related surface morphology changes were noted. The irradiation of Au(111) surfaces generated Au vacancy and adatom islands and caused roughening of step edges. The size and abundance of these islands and the level of deformation on the step edges depended strongly on the ion energy and fluency. In case of the SAM functionalized surface, the gold vacancy islands present on the surface already from the SAM formation were modified, step edges roughened and gold adatom islands formed. Similarly to the bare surface, the level of surface deformation increased as a function of ion energy and fluency. The Ar(4+) irradiation caused on the average slightly larger vacancy islands on the SAM modified surfaces than the Ar(+) irradiation. Irradiation to fluency of 10(12) ions per cm(2) mostly maintained standing-up orientation of the thiolates whereas irradiation to higher fluency resulted in reduced surface coverage and flat-lying molecules. As a general trend the DDT covered surfaces were more susceptible for irradiation-induced surface morphology changes than the unmodified Au surfaces.

Optical imaging beyond the diffraction limit by SNEM: effects of AFM tip modifications with thiol monolayers on imaging quality.

Tip-enhanced nanoscale optical imaging techniques such as apertureless scanning near-field optical microscopy (a-SNOM) and scanning near-field ellipsometric microscopy (SNEM) applications can suffer from a steady degradation in performance due to adhesion of atmospheric contaminants to the metal coated tip. Here, we demonstrate that a self-assembled monolayer (SAM) of ethanethiol (EtSH) is an effective means of protecting gold-coated atomic force microscopy (AFM) probe tips from accumulation of surface contaminants during prolonged exposure to ambient air. The period over which they yield consistent and reproducible results for scanning near-field ellipsometric microscopy (SNEM) imaging is thus extended. SNEM optical images of a microphase separated polystyrene-block-poly (methylmethacrylate) (PS-b-PMMA) diblock copolymer film, which were captured with bare and SAM-protected gold-coated AFM probes, both immediately after coating and following five days of storage in ambient air, were compared. During this period the intensity of the optical signals from the untreated gold tip fell by 66%, while those from the SAM protected tip fell by 14%. Additionally, gold coated AFM probe tips were modified with various lengths of alkanethiols to measure the change in intensity variation in the optical images with SAM layer thickness. The experimental results were compared to point dipole model calculations. While a SAM of 1-dodecanethiol (DoSH) was found to strongly suppress field enhancement we find that it can be locally removed from the tip apex by deforming the molecules under load, restoring SNEM image contrast.

SELF-ASSEMBLING BEHAVIOR AND INHIBITION EFFECT OF DODECANETHIOL SELF-ASSEMBLED MONOLAYERS ON COPPER SURFACE

The self-assembling behavior and inhibition effect of dodecanethiol self-assembled monolayers (SAMs) on copper surface were investigated by atomic force microscopy (AFM) and electrochemical methods. The assembling process was monitored by AFM phase images. The assembling time influences the corrosion protection efficiency of dodecanethiol SAMs. Surface friction significantly decreases when the copper surface is covered by SAMs.

Vibrational Sum‐Frequency Generation Activity of a 2,4‐Dinitrophenyl Phospholipid Hybrid Bilayer: Retrieving Orientational Parameters from a DFT Analysis of Experimental Data

The vibrational nonlinear activity of films of 2,4-dinitrophenyl phospholipid (DNP) at the solid interface is measured by sum-frequency generation spectroscopy (SFG). Hybrid bilayers are formed by a Langmuir-Schaefer approach in which the lipid layer is physisorbed on top of a self-assembled monolayer of dodecanethiol on Pt with the polar heads pointing out from the surface. The SFG response is investigated in two vibrational frequency domains, namely, 3050-2750 and 1375-1240 cm(-1). The first region probes the CH stretching modes of DNP films, and the latter explores the vibrational nonlinear activity of the 2,4-dinitroaniline moiety of the polar head of the lipid. Analysis of the CH stretching vibrations suggests substantial conformational order of the aliphatic chains with only a few gauche defects. To reliably assign the detected SFG signals to specific molecular vibrations, DFT calculations of the IR and Raman activities of molecular models are performed and compared to experimental solid-state spectra. This allows unambiguous assignment of the observed SFG vibrations to molecular modes localized on the 2,4-dinitroaniline moiety of the polar head of DNP. Then, SFG spectra of DNP in the 1375-1240 cm(-1) frequency range are simulated and compared with experimental ones, and thus the 1,4-axis of the 2,4-dinitrophenyl head is estimated to have tilt and rotation angles of 45±5° and 0±30°, respectively.

The Relationship Between Contact Mechanics and Adhesion in Nanoscale Contacts Between Non-Polar Molecular Monolayers

Atomic and friction force microscopy were employed to examine adhesion and friction between dodecanethiol self-assembled monolayers in pure media as well as in two-component heptane/acetone mixtures. In media that did not contain hydrogen bond donors, the pull-off forces were found to be in very good agreement with theoretic predictions based on the Lifshitz theory. As the hydrogen bond donor ability of the medium increased, the adhesion energy was found to be increasingly underestimated by the model, illustrating the importance of the medium–medium interactions outside the contact area in determining the adhesive properties of the contact at the nanoscale. Exceptionally, in n-octanol, the pull-off forces were considerably lower than predicted and a dual slope linear friction–load relation was observed. These observations were rationalized by the formation of physisorbed layers of octanol on the surfaces. The friction–load relationship in the other media was found to be dependent on the magnitude of adhesion. For weakly adhering systems, the friction–load relationship was linear, but as adhesion increased, a sublinear relationship was observed. The data were rationalized by treating the friction as the sum of an adhesion-dependent shear term characterized by a surface shear strength τ and a molecular plowing term characterized by a coefficient of friction μ. Thus, Amontons’ law appears to describe the limiting case of very weak adhesion where viscoelastic plowing is primarily responsible for energy dissipation, while a sublinear friction–load relationship emerges in other situations due to the dissipation of energy in shearing adhesive contacts.

Self-assembled thiolate functionalized gold nanoparticles template toward tailoring the morphology of electrochemically deposited silver nanostructure

The evolution of silver particles’ morphologies synthesized by electrochemical deposition on highly oriented pyrolytic graphite (HOPG) substrate modified by self-assembled gold nanoparticle (Au NP) was studied. It was found that for a convenient potential, controlling only the temperature causes a change in the deposited silver morphology from dendrite to plate. Interestingly, different average sizes of plate were obtained by varying the deposition time. X-ray diffraction (XRD) measurements show that plates grow preferentially along the (111) direction. The surface mobility of thiolate covered Au NP surfaces was believed to be the cause of the temperature-induced morphology evolution of deposited silver. Scanning electrochemical microscopy (SECM) was used to probe charge transfer between ferricyanide electroactive ionic species and electrodeposited silver particles modified by self-assembled monolayer (SAM) of dodecanethiol. The observed phenomena indicate that the electron transfer (ET) process is affected by the properties of the dodecanethiol SAM on deposited silver particles.

Grating-coupled surface plasmon resonance in conical mounting with polarization modulation

A grating-coupled surface plasmon resonance (GCSPR) technique based on polarization modulation in conical mounting is presented. A metallic grating is azimuthally rotated to support double-surface plasmon polariton excitation and exploit the consequent sensitivity enhancement. Corresponding to the resonance polar angle, a polarization scan of incident light is performed, and reflectivity data are collected before and after functionalization with a dodecanethiol self-assembled monolayer. The output signal exhibits a harmonic dependence on polarization, and the phase term is used as a parameter for sensing. This technique offers the possibility of designing extremely compact, fast, and cheap high-resolution plasmonic sensors based on GCSPR.

Antibody Adsorption and Orientation on Hydrophobic Surfaces

The orientation of a monoclonal, anti-streptavidin human IgG1 antibody on a model hydrophobic, CH(3)-terminated surface (1-dodecanethiol self-assembled monolayer on gold) was studied by monitoring the mechanical coupling between the adsorbed layer and the surface as well as the binding of molecular probes to the antibodies. In this study, the streptavidin antigen was used as a probe for the Fab portions of the antibody, while bacteria-derived Protein G' was used as a probe for the Fc region. Bovine serum albumin (BSA) acted as a blocking protein. Monolayer coverage occurred around 468 ng/cm(2). Below 100 ng/cm(2), antibodies were found to adsorb flat-on, tightly coupled to the surface and unable to capture their antigen, whereas the Fc region was able to bind Protein G'. At half-monolayer coverage, there was a transition in the mechanism of adsorption to allow for vertically oriented antibodies, as evidenced by the binding of both Protein G' and streptavidin as well as looser mechanical coupling with the surface. Monolayer coverage was characterized by a reduced level in probe binding per antibody and an even less rigid coupling to the surface.

Corrosion Protection of Copper by Self-Assembled Monolayers Modified in Aqueous Micellar Solution

Dodecanethiol self-assembled monolayers (SAMs) were formed on copper in aerated and deaerated aqueous micellar solutions of cetyltrimethyl ammonium bromide (CTAB), respectively. The corrosion inhibition effect was investigated in 0.51 mol/L NaCl solution using electrochemical impedance spectroscopy and polarization curves. The surface covered with SAMs was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy. The inhibition efficiency of the SAMs formed in aerated solution and deaerated solution is 99.955% and 99.60%, respectively. During the self-assembly process in aerated solution, CTAB molecules are trapped into dodecanethiol SAMs. The mechanism involved is proposed and discussed.

Variable temperature STM study of Co deposition on a dodecanethiol self assembled monolayer

The present scanning tunneling microscopy study reports on the growth processes of Co vapor-deposited on a dodecanethiol (DDT) self-assembled monolayer (SAM)/Au(111). We observe strongly modified surface and depth diffusions of Co adatoms depending on the growth temperature. Co deposited at 300K shows an extremely incomplete regime of condensation on the organic layer. Besides, Co penetrates the DDT monolayer and resides at the DDT/Au(111) interface as 2D clusters. This phenomenon takes place through defects in the SAM which are transient channels. In contrast, Co deposited at 50K shows a complete condensation and nucleates on defects of the SAM layer as 3D islands sitting most likely on top of the DDTs. These results are of interest in the growing field of organic spintronics where the quality of the organic/ferromagnetic interface is a key issue.