Thiol Adsorption Research Articles

Effect of thiol adsorption on the electrical resistance of copper ultrathin films

The impact of thiol adsorption on thin copper films, covered with a copper oxide layer, was investigated using electrical resistance measurements at various stages: during film growth, aging, exposure to air, and immersion in thiol solutions. Thin copper films (20 nm) were thermally evaporated, with variations in substrate temperature (RT, 330 and 390 K). Films deposited at 330 K exhibited the smallest percolation thickness and aging rates due to their compact morphology, showcasing lower surface roughness and correlation length. Exposure to air led to the formation of a Cu2O layer on the film surface. Subsequent immersion in a dodecanethiol solution in ethanol resulted in a resistance increase, ranging from 0.1 % to 0.4 %. This change was dependent on the substrate temperature, with the largest difference observed at 330 K. This observation suggests that samples grown at this temperature exhibited the highest electron-surface scattering. Moreover, by depositing a chromium surfactant layer, the impact of this scattering mechanism was amplified, leading to a resistance increase of up to 1.2 %. Mayadas-Shatzkes theory provided a good description of these resistance changes. The negatively charged S-head of the adsorbed thiols alters the electric field experienced by conduction electrons in the Cu2O/Cu interface, modifying the electron-surface scattering.

Thiol-based defect healing of WSe2 and WS2

Recent research on two-dimensional (2D) transition metal dichalcogenides (TMDCs) has led to remarkable discoveries of fundamental phenomena and to device applications with technological potential. Large-scale TMDCs grown by chemical vapor deposition (CVD) are now available at continuously improving quality, but native defects and natural degradation in these materials still present significant challenges. Spectral hysteresis in gate-biased photoluminescence (PL) measurements of WSe2 further revealed long-term trapping issues of charge carriers in intrinsic defect states. To address these issues, we apply here a two-step treatment with organic molecules, demonstrating the “healing” of native defects in CVD-grown WSe2 and WS2 by substituting atomic sulfur into chalcogen vacancies. We uncover that the adsorption of thiols provides only partial defect passivation, even for high adsorption quality, and that thiol adsorption is fundamentally limited in eliminating charge traps. However, as soon as the molecular backbone is trimmed and atomic sulfur is released to the crystal, both bonds of the sulfur are recruited to passivate the divalent defect and the semiconductor quality improves drastically. Time-dependent X-ray photoelectron spectroscopy (XPS) is applied here together with other methods for the characterization of defects, their healing, leading energies and occupation. First-principles calculations support a unified picture of the electronic passivation of sulfur-healed WSe2 and WS2. This work provides a simple and efficient method for improving the quality of 2D semiconductors and has the potential to impact device performance even after natural degradation.

Effect of Heat and Plasma Treatment on Carboranethiol Self-Assembled Monolayers on Copper

Carborane (C2B10H12) molecules are unique precursors for self-assembled monolayer (SAM) applications. These 3D, icosahedral (12-vertex) molecules allow for the formation of well-ordered layers, potentially with fewer defects than traditional linear alkyl SAMs, and are amenable to cross-linking via labile H atoms with a variety of mechanisms including heat, plasma, and radiation (e.g., UV, e-beam). We have investigated the deposition of SAMs of 1,2-dithiol-ortho-carborane (O) and 9-thiol-meta-carborane (M) on copper from the vapor phase in ultrahigh-vacuum conditions, along with the effect of thermal (150–400 °C) and plasma (N2, H2, Ar, O2) postgrowth treatment. Both films show rapid deposition in the vapor phase with approximate monolayer or few layer coverage, as well as a mixture of physisorption (thiol adsorption) and chemisorption (thiolate binding). Both films additionally show notable stability to thermal treatment up to 400 °C, with only gradual (not abrupt) decrease in boron coverage and minor changes in chemical composition/makeup; however, with the monothiol derivative M showing greater loss of boron and greater oxidation. Nitrogen (N2) plasma treatment leads to partial nitrogenation of boron, while hydrogen (H2) and argon (Ar) plasma treatments lead to partial oxidation of boron, with some parasitic growth (increase in B coverage) especially for the dithiol derivative O. Oxygen (O2) plasma treatment shows an aggressive oxidation (of boron, carbon, sulfur, and copper), but appears to passivate the layers (i.e., the boron oxide based layer formed remains stable and does not change with further plasma exposure). Both heat and plasma treatments reduce copper oxide at the interface and increase thiolate binding (thus conceivably stabilizing the films). Indeed, exposure to N2 plasma appears to further stabilize the films toward heat treatment. These findings highlight that these carboranethiol SAMs represent a robust option for various functional and protective layer applications, and that heat and plasma may be used to further stabilize these films, to modify their properties, or as part of a more complex fabrication scheme.

In situ reversible tuning of chemical interface damping in mesoporous silica-coated gold nanorods via direct adsorption and removal of thiol.

Chemical interface damping (CID) is a recently proposed plasmon decay channel in gold nanoparticles. However, thus far, a very limited number of studies have focused on controlling CID in single gold nanoparticles. Herein, we describe a new simple method for reversible tuning of CID in single gold nanorods coated with a mesoporous silica shell (AuNRs@mSiO2). We used 1-alkanethiols with two different carbon chain lengths (1-butanethiol and 1-decanethiol) as adsorbates to induce CID. In addition, NaBH4 solution was used to remove the attached thiol from the AuNR surface. We confirmed the adsorption and removal of 1-alkanethiols on single AuNRs@mSiO2 and the corresponding changes in localized surface plasmon resonance (LSPR) peak wavelengths and linewidths. Furthermore, we investigated the effect of immersion time in NaBH4 solution on thiol removal from AuNRs@mSiO2. Therefore, the LSPR properties and CID can be controlled, thereby paving the way for in situ reversible tuning of CID by repeated adsorption and desorption of thiol molecules on single AuNRs@mSiO2.

Composite ligand shells on gold nanoprisms - an ensemble and single particle study.

The attachment of thiolated molecules onto gold surfaces is one of the most extensively used and robust ligand exchange approaches to exploit the nanooptical features of nanoscale and nanostructured plasmonic materials. In this work, the impact of thiol adsorption on the optical properties of wet-chemically synthesized gold nanoprisms is studied both at the ensemble and single particle level to investigate the build-up of more complex ligand layers. Two prototypical ligands with different lengths have been investigated ((16-mercaptohexadecyl)trimethylammonium bromide - MTAB and thiolated polyethylene glycol - mPEG-SH). From ensemble experiments it is found that composite ligand layers are obtained by the sequential addition of the two thiols, and an island-like surface accumulation of the molecules can be anticipated. The single particle experiment derived chemical interface damping and resonance energy changes further support this and show additionally that when the two thiols are used simultaneously, a higher density, intermixed layer is formed. Hence, when working with more than a single type of ligand during surface modification, sequential adsorption is preferred for the combination of accessible essential surface functionalities, whereas for high overall loading the simultaneous use of the different ligand types is favourable.

Gold nanostructured membranes to concentrate low molecular weight thiols, a proof of concept study

Thiols are very important molecules in the biomedical field involved for example in redox homeostasis. Their detection and quantification remain difficult due to their poor stability (oxidation) linked to their strong reactivity towards other thiols (by the formation of S-S bonds) or other interfering molecules in the medium. Cellulose membranes with immobilized gold nanoparticles (AuNP) were developed to capture and quantify thiols in simple and complex matrices. This device was first optimized and characterized in terms of nanostructuration and thiol adsorption. N-Acetylcysteine (NAC) and reduced glutathione (GSH), chosen as model molecules, were filtered through the device demonstrating a maximal adsorption capacity of 270 and 60 nmol respectively. In a second step, the adsorbed species were subjected to ligand exchange using a more reactive thiol, dithiothreitol. The results showed release rates of approximately 90% for NAC and GSH. Finally, the amount of endogenous GSH in rat plasma was determined without any pretreatment. For the first time to our knowledge, a nanostructured device for the capture, selective and sensitive quantification of thiols is proposed. This device is easy to handle and overcomes matrix effects. Moreover, the very large concentration factor induced by this technology will be a valuable asset to decrease the quantification limits of analytical methods.

Strain mapping in symmetrical core-shell gold nanorods from HRTEM images

Strain distribution, interface type and the causes of strain in gold core-shell nanorods were studied by employing high-resolution electron transmission microscope (HRTEM) and Geometric Phase Analysis (GPA). Anisotropic Strain distributions in gold core-shell nanorods were affected by l-cysteine (Cys) concentration and AA/Au3+ ratio which determines shell growth kinetics. Strain circles were generated at the core-shell interfaces of gold nanorods. The {002} strain distributions of gold nanorods were very sensitive to the increase of Cys concentration and AA/Au3+ ratio. Strain distributions with high strain values on {111} planes were more significant than that on {002} planes. This state was related to the preferential adsorption of thiols on {111} planes. The core-shell interface of gold nanorods was determined to be a mix of distorted coherent interface and semi-coherent interface, which was mainly produced via the slip of {111} planes along <110> slip direction. The gold shell covered the whole core at the growth conditions of different Cys concentrations and AA/Au3+ ratios provided in this work via seed-mediated symmetric epitaxial growth. The strain at the core-shell interface was mainly generated by Au–S bonds and lattice distortion.

Highly efficient adsorption of thiol compounds by ZSM-5 zeolites: Governing mechanisms

Abstract The adsorption of thiol compounds (tert-butyl mercaptan and benzenethiol) on different zeolites was systematically investigated using batch experiments to reveal the governing mechanisms of this process. For this purpose, the absorption performances of a series of zeolites with different pore size distributions (ZSM-5 and Y- and β-zeolites) and surface hydrophobicities (adjusted by the Si/Al ratio) were investigated. Among the tested zeolites, ZSM-5 exhibited a significantly higher adsorption affinity to thiols, because its pore size is suitable for invoking a micropore filling effect to enhance the adsorption. Hydrophobic interaction was another key mechanism governing the adsorption of thiols on zeolites. Furthermore, pore ion exchanging of ZSM-5 by Cu(II) could effectively improve the adsorption capacity of zeolites because of the high coordination affinity of Cu(II) toward the sulfydryl in thiols. The adsorption capacity of ZSM-5 was strongly pH dependent and sharply decreased at the pKa values of the thiols. The presence of dissolved humic acid had negligible influence on thiol compounds adsorption because of the size exclusive effect of zeolites for humic acid. Moreover, all the tested zeolites exhibited a high adsorption affinity to thiols in the presence of coexisting ions (e.g., 0.02–0.20 mol/L Na+, Ca2+). The used zeolites displayed stable thiol compounds adsorption behaviors after 10 regeneration cycles. These results reflected the high potential for applying ZSM-5 zeolites in an actual water body.

Thiol adsorption on metal oxide nanoparticles.

The adsorption of 2-naphthalenethiol (2-NPT) and methanethiol (MT) on 13 different metal oxide nanoparticles, of approximately 30 nm average primary particle size, has been investigated. In the case of 2-NPT, which is fluorescent, a screening method to assess adsorption was developed that consists of mixing the nanoparticles with a dilute ethanolic solution of 2-NPT and performing several cycles of centrifuging and rinsing with ethanol. Fluorescence measurements on the re-dispersed particle suspensions were then used to diagnose whether or not adsorption had occurred. Complementary experiments were performed by mounting powder samples of each of the metal oxide nanoparticles onto sample stubs and performing X-ray photoelectron spectroscopy (XPS) before and after in situ dosing with MT. In both cases, adsorption was observed only on ZnO, TiO2, and In2O3. Adsorption did not occur on Al2O3, CeO2, Fe2O3, Gd2O3, Ho2O3, NiO, SiOx, WO3, Y2O3, and ZrO2. Density functional theory (DFT) calculations were performed using small metal oxide clusters, assuming that dissociative adsorption occurs by replacement of a hydroxyl group attached to a metal site and the formation of water. The theoretical and experimental results generally agree, suggesting that this is indeed the adsorption mechanism for most of the nanoparticles. The agreement also suggests that the size and geometry of the nanoclusters play a minor role and that the relative strengths of the metal-sulfur and metal-hydroxyl bonds dictate thiol adsorption. This work has important implications related to the functionalization of metal oxide nanoparticles and surfaces.

Shedding Light on the Interfacial Structure of Low-Coverage Alkanethiol Lattices

A comprehensive description of the self-assembly process of alkanethiols on Au(111) is presented, focused on the initial formation of the lying down phases. Low-coverage monolayers are prepared by the disintegration of Au144(RS)60 nanoclusters on the reconstructed (22 × ?3)-Au(111) surface. The method provides a limited number of thiols together with a large excess of gold adatoms. Scanning tunneling microscopy and density functional theory calculations were employed to study the transition between low to high thiolate coverage phases. The process involves different lattices and surface transformations, including thiyl radicals on the herringbone reconstruction, radical-induced herringbone lifting, and the formation of energetically similar metastable phases formed by RS-Au-RS moieties. Results also show that the transition is slow, and different surface structures can coexist on the same sample. Along the process, the first source of Au adatoms to form the RS-Au-SR moieties is the lifting of the herringbone reconstruction because of the lower energetic cost to extract the extra Au atom. However, for hexanethiol (and shorter alkanethiols) at low coverage, additional Au adatoms must be taken from terraces leading to vacancy islands. This process can be entirely suppressed by growing the lying down phases in the presence of an excess of Au adatoms. Taken together, our results shed light on the elusive initial steps of thiol adsorption on clean reconstructed Au, showing that the RS-Au-SR staple motif is also present at the interface of low-coverage self-assembled monolayers.

Self-assembly of octanethiol on oxide-free cobalt electrode from aqueous solution under electrochemical control

Self-assembly of alkanethiols on Co surface from organic solution has met with limited success due to the presence of the native oxides. A way needs to be found to remove any oxide and form perfect self-assembled monolayers (SAMs). We report the development of electrochemical approach for formation of alkanethiol self-assembled monolayers on base metals in aqueous solutions. For formation of octanethiol (OT) SAMs on oxide-free cobalt surfaces, we combine the surface renewal technique with in situ electrochemical procedure of removing the native oxide, thiol adsorption, and electrochemical control of SAMs properties in one aqueous solution. The use of aqueous thiol-containing media results in removing any oxide by electrochemical reduction, accelerated monolayer formation under electrochemical control, and investigating SAMs surface coverage and monolayer integrity by voltammetry. In this work, we study the influence of different factors on self-assembly process such as the surface pretreatment, adsorption time, the presence of dissolved oxygen, solution pH, and potential cycling on polycrystalline cobalt microelectrode from aqueous 0.1 M NaClO4 solutions of 0.1 mM OT. We obtain the high-quality self-assembled monolayers which are stable in wide range of potentials and show blocking characteristics toward the following Faradaic processes: Co surface oxidation and O2 and H+ reduction.

Interfacial charge-transfer transitions in ZnO induced exclusively by adsorption of aromatic thiols.

Interfacial charge-transfer transitions (ICTTs) between organic compounds and inorganic semiconductors have recently gained increasing interest as a new visible light absorption mechanism for optical biosensing via direct visualization, surface enhanced Raman scattering (SERS), and circular dichroism (CD) and also as a direct charge separation mechanism for photoenergy conversions such as photocatalytic reactions. So far, ICTTs have been observed with various organic compounds, while inorganic materials are almost limited to titanium oxides such as TiO2. Although SERS via ICTTs has been reported with several kinds of inorganic semiconductors, their ICTT bands have not been observed directly except for TiO2. From these viewpoints, the direct observation of ICTT bands in inorganic semiconductors other than TiO2 is an important issue. In this study, we demonstrate ICTTs in ZnO induced by the adsorption of aromatic thiols. ICTTs take place from the HOMO of the adsorbed thiol compounds to the conduction band of ZnO via a Ti-S linkage. Notably, ZnO selectively shows ICTTs with aromatic thiols, but almost no ICTT with oxygen-linkage-type organic compounds such as phenol. In addition, the wide-range control of ICTTs was achieved by the chemical modification of aromatic thiols. Our research not only opens up a new way for the research of ICTTs but also supports the reported ICTT-based SERS in ZnO.

Quantum model for the effect of thiols adsorption on resistivity of gold ultrathin films

The predominant role of surface scattering, in electronic transport through nanoscale thin films, was examined by measuring and modeling the change in resistivity induced by the adsorption of thiols on the surface. For this purpose, gold ultrathin films on sapphire, using chromium as surfactant, were prepared through thermal evaporation, seeking to maximize the surface induced dispersion. A maximum resistivity increase of 13.5% was observed, in an 8 nm Au/Cr/Sapphire sample. This is the highest reported value for such films to date. The morphology of the samples was measured by STM and characterized through height-difference correlation function. A fractal self-affine representation of the surface was found, and it was modified to account the thiol effect: the scattering center due to the adsorption of a molecule was modeled as a void in the surface. This change was related to the electrical transport of the film through two quantum models: the Palasantzas and Barnas (PB) theory and the Sheng, Xing and Wang theory, extended by Munoz et al. (mSXW). For our samples, the mSXW theory did not predict a resistivity change, while the PB theory provides a good description of the experimental resistivity increase due to thiols adsorption as function of thickness.

Aromatic versus aliphatic thiols on Au(111) surface: a DFT exploration of adsorption registry and electronic structure

ABSTRACTSelf-assembled monolayers (SAMs) on metal surfaces have inspired many interesting applications, such as chemical and biological sensors, molecular electronics, magnetism and protective coatings. In this respect, SAMs having different head and tail groups have been synthesised which allow the modification of the material properties by tuning intermolecular, monolayer–metal and/or monolayer–solvent interactions. In this respect, we investigate the adsorption of thiols having aromatic, p-mercaptobenzonitrile (pPhCN) or aliphatic, 2-azidoethanthiol (N3S), tail groups on Au(111) surface by means of Density Functional Theory (DFT). Monomer and dimer adsorption configurations of both pPhCN and N3S molecules as well as the modification of the electronic structures upon adsorption are studied. Our results show that different adsorption mechanisms are observed for the molecules under consideration. While monomer and dimer structures of the pPhCN prefer to adsorb laterally on the surface, for N3S vertical arrangement of the molecules enhances the molecular immobilisation. Although, dominant contributions to the adsorption energy of the laterally adsorbed pPhCN are through S–Au chemical bond, phenyl ring–surface and cyano N–surface interactions, π–π stacking of the rings contributes to the stabilisation of the complex in addition to the S–Au chemical bond in the case of vertical attachment. For N3S, on the other hand, only S–Au chemical bond determines the adsorption strength. S–Au interactions result in broad molecular orbital redistribution of the S atoms of both molecules, due to the rehybridisation of S and Au states. Density of cyano-N and cyano-C states present in the pPhCN is affected by the orientation of the rings with respect to each other. In the case of 2N3S, instead, the distribution of the tail group molecular orbitals is not modified by the adsorption.

Comparative Study of the Adsorption of Thiol and Isocyanide Molecules on a Silver Surface by in Situ Surface-Enhanced Raman Scattering

We report an investigation of the adsorption of thiol and isocyanide molecules on colloidal Ag nanocubes through surface-enhanced Raman scattering (SERS). Specifically, we collect SERS spectra in situ at different time points from a mixture of Ag nanocubes and ligand molecules at a specific concentration. We demonstrate that 4-nitrothiophenol could readily bind to the Ag surface through strong thiol–Ag interaction. We also observe red shifts for the SERS peaks as the concentration decreases, suggesting a change to the molecular orientation relative to the surface. Likewise, 4-aminothiophenol also adsorbs onto Ag quickly, but gives much weaker SERS signals relative to 4-nitrothiophenol because the electron-donating amine group would retard the chemical enhancement of SERS. Different from thiols, 1,4-phenylene diisocyanide binds to Ag surface through a relatively weak, σ-donation bond. With an increase in concentration, molecules tend to adsorb on the nanocubes with the benzene ring tilting away from the su...

The Pressure Gap for Thiols: Methanethiol Self-Assembly on Au(111) from Vacuum to 1 bar

Functionalizing noble metal surfaces with (bio)organic molecules is a vibrant field of research, with key applications in medicine, catalysis, and molecular electronics. Control over the molecular self-assembly is essential to creating functional devices. Here, we exploit our high-pressure, high-temperature scanning tunneling microscope (STM) to relate the effects of controllable parameters (temperature and pressure) to atomic-scale assembly mechanisms. Using methanethiol self-assembly on Au(111) as a model system, we monitor the formation and assembly of the ubiquitous (CH3S)2Au “staple” motif into row structures at pressures of up to 1 bar. We observe a pressure-induced transition from the usual 1/3 monolayer (ML) saturation coverage in vacuum to 3/8 ML at 1 bar, thus providing the first evidence for a pressure gap effect for thiol adsorption. Complementing our experiments, we employed dispersion-corrected density functional theory computations to model the formed surface adlayers, corresponding STM images, and underlying equilibrium thermodynamics.

Tailoring the Strength of Nanoporous Gold by Self-Assembled Monolayers of Alkanethiols

Because of the large specific surface area, the properties of nanoporous metals and in particular their mechanical properties are sensitive to chemical modifications of their surfaces. Here, we exploit self-assembled monolayers (SAMs) to modify a surface of nanoporous gold and study their effect on plastic behavior. The SAMs investigated here (i) are made from alkanethiols, which consist of a sulfur headgroup that strongly binds to metal substrates, a hydrocarbon chain, and an end group, and (ii) are known to spontaneously self-organize into well-ordered, dense two-dimensional molecular films on the surface of coinage metals. Alkanethiols with various chain lengths and terminal groups were used to prepare SAMs on bulk nanoporous gold, and compression tests were performed on the SAM-modified and nonmodified macroscopic samples. Our experiments reveal a substantial, up to 50%, increase of the flow stress due to thiol adsorption. We attribute the strengthening to the adsorption locking of dislocation end poi...

The synthesis of thiol-modified cellulose composites for the chelation of ions from water

A thiol-cellulose composite was prepared and used as an adsorbent for the extraction of copper ions from water. Two particular reaction paths were developed and investigated for thiol coupling efficiency and adsorption capacity. Reaction path “FCys,” which utilized N-(9-fluorenylmethyloxycarbonyl)-S-(trityl)-L-cysteine, possessed a maximum adsorption capacity of 454 μg/g. Reaction path “Cys” involved the coupling of cysteine onto microcrystalline cellulose using 1,1′ carbonyldiimidazole as a linkage agent under mild reaction conditions. For this reaction, the calculated maximum adsorption capacity was 3333 μg/g. Fitting the resulting data indicated that the adsorption behavior followed the Langmuir isotherm model. An ultraviolet-visible spectrophotometer verified the success of the coupling reaction, while an inductively-coupled mass spectrometer measured the copper concentration. The results reveal that the synthesized composite acts as an effective adsorbent for copper ions.

Super Bright Luminescent Metallic Nanoparticles.

It is found that, by curing the surface defects that quench photoexcited carriers, luminescence efficiency of metallic nanoparticles can be dramatically increased. For Ag nanoparticles, as much as 300 times increase in photoexcitation induced luminescence is observed upon surface adsorption of ethanethiol. The same treatment increases Au nanoparticle luminescence efficiency by a factor of 3. A model based on the elimination of surface defects by the sulfur-metal bond formed upon thiol adsorption can quantitatively account for the observations, which also indicate that nanoparticles without proper surface treatment typically have low luminescence quantum yields.

Spherical Nucleic Acids: Adding a New Dimension to Nucleic Acids and Clinical Chemistry.

Featured Article: Mirkin CA, Letsinger RL, Mucic RC, Storhoff JJ. A DNA-based method for rationally assembling nanoparticles into macroscopic materials. Nature 1996;382:607–9.2 Spherical nucleic acids, or SNAs (1), were first introduced in our 1996 paper in Nature featured here. The original nanoconstructs were composed of gold nanoparticles modified with a layer of DNA at a density high enough to force the strands upright, forming a shell that adopted the spherical shape of the nanoparticle template. Since then, many other core and nucleic acid compositions have been synthesized and explored. SNAs were born from an idea I had after attending a seminar on colloidal crystallization. Researchers were exploring ways of engineering such crystals on the basis of electrostatic and simple small-molecule interactions between particles. I imagined a new type of chemistry in which the interactions between nanoparticles could be programed using sequence-specific DNA interactions—a system in which the particles could be viewed as atoms and the DNA as programmable bonds between them, offering an almost limitless number of possibilities for controlling the assembly of particles into hierarchical materials, crystals in particular. To test this concept, I asked then-Northwestern graduate students Bobby Mucic and James Storhoff to seek out Bob Letsinger, the pioneer of oligonucleotide synthesis, and learn how to make strands of DNA that could be chemically immobilized on gold. Soon after, Bobby and James synthesized two sets of gold particles, each approximately 13 nm in diameter, with DNA strands linked to their surfaces via thiol adsorption on gold; …