Alkanethiol Molecules Research Articles

Carbonate-Terminated Self-Assembled Monolayers for Mimicking Nanoscale Polycarbonate Surfaces

Two carbonate-terminated alkanethiol molecules having different positional isomers of a six-membered cyclic carbonate group, 3-COC12SH and 2-COC12SH, were synthesized and used to generate self-assembled monolayers (SAMs) on gold to serve as mimics of the surfaces of commercially available poly(propylene carbonate) (PPC) and poly(ethylene carbonate) (PEC). The adsorbate molecules were characterized using 1H and 13C nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The corresponding SAMs on gold were characterized by ellipsometry, contact angle goniometry, polarization-modulation infrared reflection-adsorption spectroscopy, and X-ray photoelectron spectroscopy. The contact angle data showed that the wettabilities of both SAMs were largely similar to each other and to the PEC samples for a wide range of contacting probe liquids (with water correlating particularly well with PEC and both SAMs). As a whole, the wettability data suggest that the carbonate-terminated SAMs can serve as mimics of nanoscale polycarbonate surfaces and can be used to investigate the interfacial properties of polycarbonates without interference from the surface reconstruction.

Planar aromatic anchors control the electrical conductance of gold|molecule|graphene junctions.

The synthesis of a family of alkanethiol molecules with planar aromatic head groups, designed to anchor molecules effectively to graphene electrodes, is reported. Characterisation of self-assembled monolayers of these molecules on a gold surface via conductive atomic force microscopy shows that when an aromatic head group is present, the conductance G graphene obtained using a graphene coated probe is higher than the conductance G Pt obtained using a platinum (Pt) probe. For Pt probe and graphene probe junctions, the tunnelling decay constant of benzyl ether derivatives with an alkanethiol molecular backbone is determined as β = 5.6 nm-1 and 3.5 nm-1, respectively. The conductance ratio G graphene/G Pt increases as the number of rings present in the aromatic head unit, n, increases. However, as the number of rings increases, the conductance path length increases because the planar head groups lie at an angle to the plane of the electrodes. This means that overall conductance decreases as n increases. Density functional theory-based charge transport calculations support these experimental findings. This study confirms that planar aromatic head groups can function as effective anchoring units for graphene electrodes in large area molecular junctions. However, the results also indicate that the size and geometry of these head groups must be considered in order to produce effective molecular designs.

Effect of halogenation on the electronic transport properties of aromatic and alkanethiolate molecules

Quantum transport calculations are conducted using nonequilibrium Green’s functional formalism to study the effect of halogenation on the electronic transport properties of aromatic S(C6H5)2X and alkanethiolate S(CH2)11X molecules (with X = H, F, Cl, Br, or I) sandwiched between gold electrodes. In terms of conductance, both molecules show the same dependence on the halogen terminal groups despite their different electronic nature. For example, fluorination results in a reduction of the current by almost an order of magnitude, whereas iodine substitution leads to larger current as compared to the reference system (i.e. hydrogen termination). Regarding the asymmetry in the current–voltage characteristics, halogenation reduces the rectification level for the aromatic molecule with the smallest asymmetry for iodine termination. However, in the case of alkanethiolate molecule, halogen substitution increases the current rectification except for fluorination. A physical explanation of these results is obtained from the analysis of the behavior of the density of states, transmission spectra and transmission eigenstates. These findings are of practical importance in exploring the potential of halogenation for creating functional molecular self-assemblies on metallic substrates.

Feasibility for SERS-based discrimination of gallbladder cancer from polyp by indirect recognition of components in bile

The aqueous solution extracted from raw bile juice is composed primarily of bile salts, with lower levels of bilirubin and its derivatives. Among them, the bilirubin and bilirubin-derived metabolites are the only surface-enhanced Raman scattering (SERS)-active components. An analytical scheme indirectly responsive and able to utilize all bile components, including SERS-inactive bile salts, was explored for SERS-based discrimination of gallbladder (GB) polyp and GB cancer. Initially, the surface of a SERS substrate (Au nanodendrite on Ni foil (AuND@NiF)) was covered with an alkanethiol molecule to generate a SERS signal and attract bile components by mutual interaction. For more effective recognition of bile components, 4 independent substrates covered with 4 different alkanethiols with various functional groups (SH(CH2)2CH3, SH(CH2)2NH2, SH(CH2)2COOH, and SH(CH2)2OH) were prepared. The SERS peaks of each substrate clearly varied on interaction with pure bile components as well as aqueous bile samples, and the SERS peaks in each substrate were individually characteristic. When the principal component (PC) scores of spectra obtained using the SH(CH2)2CH3- and SH(CH2)2OH-covered substrates were combined, the k-Nearest Neighbor-based discrimination accuracy was 100%, superior to those (90.6–96.9%) using individual substrates. The use of complementary bile component-induced spectral information provided by the two substrates was responsible for accurate discrimination. On the other hand, when bare AuND@NiF recognizing only SERS-active bilirubin derivatives was used, discrimination was unsatisfactory (accuracy: 75.0%).

Substrate roughness influence on the order of nanografted Self-Assembled Monolayers

Adjacent patches of alkanethiol molecules whose chain lengths range from 11 to 15 carbon atoms are fabricated by nanografting within a Self-Assembled Monolayer matrix. Atomic Force Microscopy and Electrostatic Force Microscopy are employed to investigate their structural and electronic properties, highlighting the key role of the substrate roughness. In particular, the topographic phase signal allows to establish an odd–even dependence of the local stiffness versus the alkyl chain length, while the electrostatic force signal provides evidence that the conformational order versus the alkyl chain length follows an asymmetric parabolic trend induced by the substrate roughness.

Molecular-Scale Insights into Electrochemical Reduction of CO2 on Hydrophobically Modified Cu Surfaces.

Depressing the competitive hydrogen evolution reaction (HER) to promote current efficiency toward carbon-based chemicals in the electrocatalytic CO2 reduction reaction (CO2RR) is desirable. A strategy is to apply the hydrophobically molecular-modified electrodes. However, the molecular-scale catalytic process remains poorly understood. Using alkanethiol-modified hydrophobic Cu as an electrode and CO2-saturated KHCO3 as an electrolyte, we reveal that H2O, rather than HCO3-, is the major H+ source for the HER, determined by differential electrochemical mass spectrometry with isotopic labeling. As a result, using in situ Raman, we find that the hydrophobic molecules screen the cathodic electric field effect on the reorientation of interfacial H2O to a "H-down" configuration toward Cu surfaces that corresponds to the decreased content of H-bonding-free water, leading to unfavorable H2O dissociation and thus decreased H+ source for the HER. Further, density functional theory calculations suggest that the absorbed alkanethiol molecules alter the electronic structure of Cu sites, thus decreasing the formation energy barrier of CO2RR intermediates, which consequently increases the CO2RR selectivity. This work provides a molecular-level understanding of improved CO2RR on hydrophobically molecule-modified catalysts and presents general references for catalytic systems having H2O-involved competitive HER.

Effect of cavitation intensity control on self-assembling of alkanethiols on gold in room temperature ionic liquids

This study investigates the effect of cavitation intensity on self-assembling of alkanethiol molecules on gold in room temperature ionic liquids (RTILs) under low frequency ultrasound irradiation (20 kHz). The use of RTILs, with low vapor pressure, enabled cavitation activity to be controlled up to quenching through pressure decrease within an argon-saturated atmosphere. This control possibility was used to acquire deeper insights into the role of cavitation on self-assembling processes. It was shown by electrochemical, contact angles and Polarization Modulation - Infrared Reflection Absorption Spectroscopy (PM-IRRAS) measurements that cavitation activates orientation and organization of self-assembled monolayers (SAM). X-ray Photoelectron Spectroscopy (XPS) revealed that, even if chemical adsorption of molecules is highly activated under ultrasound irradiation, it is not dependent on acoustic cavitation intensity.

Self Assembled Monolayers and Carbon Nanotubes: A Significant Tool’s for Modification of Electrode Surface

A compromising and well-organized model system is needed for investigating the molecular behaviour of biomolecules as many transduction processes and biological recognition occur at biological surfaces. The application of techniques in interfacial surfaces like one molecule thick films has made a feasible and significant tool for modern scientific studies. Self Assembling Monolayers (SAMs) technology is a very useful means for producing monomolecular films of various biological molecules on different substrates. Carbon Nanotubes (CNTs) have length-to-diameter aspect ratio property which provides a large surface-to-volume ratio, making it an intensely capable material for biomolecular attachments. The incorporation of Carbon Nanotubes (CNTs) with biological systems forming functional assemblies has shown an explored area of research. Organo-sulfur mainly alkanethiol (CnH2n+1–SH) molecules get adsorbed onto CNTs. This phenomenon has grabbed a lot of attention because Self Assembling Monolayers (SAMs) of organo-sulfur compound acts as an example system for understanding important chemical, physical or biological processes.

Interaction of the (2√3 × 3)rect. Adsorption-Site Basis and Alkyl-Chain Close Packing in Alkanethiol Self-Assembled Monolayers on Au(111): A Molecular Dynamics Study of Alkyl-Chain Conformation.

We show that the adsorption site basis of the (2√3 × 3)rect. phase of n-alkanethiol self-assembled monolayers plays a key role in determining the molecular conformation of the close-packed alkyl chains. Ten proposed reconstructed Au–S interfaces are used to explore the minimized energy alkyl-chain packing of n-decanethiol molecules using molecular dynamics with the all-atom description. In this comparative study, all models have the same alkyl-chain surface density of four molecules per unit cell; thus, differences are due to the headgroup spacing within the 4-molecule basis as opposed to the average surface density. We demonstrate for the first time the 4-molecule-basis twist structure driven by the packing of alkanethiol molecules in a large simulation box (100 molecules, 25 unit cells) using molecular dynamics. Our results validate the prediction put forward by Mar and Klein that to achieve the 4-molecule-basis twist symmetry observed by the experiment, the headgroups must deviate from the high-symmetry (√3 × √3)R30° sites. The key structural parameters: tilt, twist, and end-group height, as well as their spatial order, are compared with experimental results, which we show is a highly sensitive approach that can be used to vet proposed Au–S interfacial models.

Electrochemical Detection of Endotoxins from Gram-Negative Bacteria Using Immobilized TLR4 Immunoproteins

Diagnostic platforms utilizing biorecognition elements, such as antibodies and DNA molecules, have been demonstrated as useful tools for the rapid detection of pathogens. However, these bioelements are extremely specific to a particular microorganism, which for the purpose of detection, requires prior knowledge of the infection to utilize the proper receptor. In order to circumvent this challenge, our group has been developing biosensors using a family of immunoproteins belonging to the non-specific innate immune system, the Toll-Like Receptor (TLR) immunoproteins, which are programmed to recognize chemical markers from a broad source of microorganisms. This makes them ideal for the first line of detection against an unknown pathogen. For example, TLR4 proteins are selective against endotoxins found in the cell walls of Gram-negative bacteria but not in Gram-positive bacteria. Here we show the results obtained from a Gram-negative bacteria sensor based on TLR4 tethered on the surface of a self-assembled monolayer (SAM) of alkyl thiols on a Au electrode.The TLR4 biosensor assembly involves a multi-step process, starting with the co-adsorption of three alkanethiols onto Au. The resulting SAM possesses distinct characteristics derived from each alkanethiol molecule. A hydroxyl-terminated alkanethiol serves as an anti-fouling agent and a spacer, a ferrocene- (Fc-) terminated alkanethiol is the redox active molecule assisting in charge transfer mediation, and an alkanethiol with a nitrilotriacetic acid- (NTA-) motif permits the chelation of Ni2+ cations, which then immobilizes the TLR4 immunoprotein via its His-tagged recombined C-terminus. Additionally, the desired surface orientation of the TLR4 ligand-recognition sites is also achieved using this anchoring method.1 In nature, TLR4 is a transmembrane monomer that undergoes dimerization once bound to lipopolysaccharide (LPS) endotoxin.2 It is believed that the recombinant TLR4 in our sensors behaves similarly and that dimerization results in an increase in charge transfer resistance (RCT ) with the addition of endotoxin.The sensor assembly process was monitored using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. CVs were recorded in 200 mM phosphate buffer (PB) pH 7 while tracking the Fc redox chemistry. Similarly, EIS was performed in an electrolyte containing 5 mM ferrocyanide (ferroCN) dissolved in the same buffer. The addition of ferroCN as a second redox probe allows us to monitor the charge transfer mediation between the SAM-bound Fc and the solution-phase ferroCN ions.3 During sensor assembly, CVs showed a peak shift to higher potentials, while EIS showed higher RCT values with the transition from unmodified SAM to TLR4 modification. Both techniques indicated successful assembly. Overall, the sensors show a stable RCT signal prior to LPS exposure. During sensor testing, the amount of LPS added to the sensor was monitored using EIS, tracking the RCT value, as described above. The addition of LPS resulted in a linear RCT change with logarithmic changes in the LPS concentration in the range of 0.01-100 ug/mL, while at higher concentrations, the response deviated from linearity. Early results estimated a limit of detection of 1 ug/mL LPS.Finally, the TLR4-endotoxin interaction has been characterized using the fluorescence-based microscale thermophoresis (MST) technique. In an MST experiment, a fluorophore-labeled molecule is subjected to a pulse of IR laser to heat a focused point in a solution inside a glass capillary, thus inducing microscopic temperature gradients and thermophoresis-induced migration away from that point.4 In our MST experiments, LPS concentrations from 1-2000 ug/mL were combined with a fixed 20 nM fluorescently-labelled TLR4 protein in order to determine their binding affinity. The MST binding curves of TLR4 with endotoxin allowed the determination of the dissociation constant, Kd, which was found to be ca. 11 uM.

Molecular Approach to Electrochemically Switchable Monolayer MoS2 Transistors.

As Moore's law is running to its physical limit, tomorrow's electronic systems can be leveraged to a higher value by integrating "More than Moore" technologies into CMOS digital circuits. The hybrid heterostructure composed of two-dimensional (2D) semiconductors and molecular materials represents a powerful strategy to confer new properties to the former components, realize stimuli-responsive functional devices, and enable diversification in "More than Moore" technologies. Here, an ionic liquid (IL) gated 2D MoS2 field-effect transistor (FET) with molecular functionalization is fabricated. The suitably designed ferrocene-substituted alkanethiol molecules not only improve the FET performance, but also show reversible electrochemical switching on the surface of MoS2 . Field-effect mobility of monolayer MoS2 reaches values as high as ≈116 cm2 V-1 s-1 with Ion /Ioff ratio exceeding 105 . Molecules in their neutral or charged state impose distinct doping effect, efficiently tuning the electron density in monolayer MoS2 . It is noteworthy that the joint doping effect from IL and switchable molecules results in the steep subthreshold swing of MoS2 FET in the backward sweep. These results demonstrate that the device architecture represents an unprecedented and powerful strategy to fabricate switchable 2D FET with a chemically programmed electrochemical signal as a remote control, paving the road toward novel functional devices.

The electronic and transport properties of MoS2 combined with thiol-based molecules: A first principles study

Using first-principles calculations, we investigate the electronic and transport properties of MoS2 combined with thiol-based molecules. The calculated results indicate alkane thiol molecule with anchor group NH2 is more likely to be captured by S vacancy. Charges transfer from the molecule to MoS2, leading the Fermi level of MoS2 closes to its conduction band. The defect states vanish in the repaired MoS2, nevertheless, the unexpected extra flat bands dominated by the molecular states arise. Electron transmission spectrums calculations show that the thiol-based molecules can significantly degrade the transmission ability of MoS2.

Low energy electron interactions with 1-decanethiol self-assembled monolayers on Au(111)

Understanding the interaction of low energy electrons with organic thin films is important for the development of a wide range of technological applications. In this study, the interaction of 80 eV electrons with self-assembled monolayers (SAMs) of 1-decanethiol grown on Au(111) via vapor phase deposition was explored for both the lying down (striped) phase and the standing up phase. Low-energy electron diffraction measurements performed at 100 K show that the SAM loses its crystalline structure within about 3 min for the lying down phase and approximately 30 s for the standing up phase. For the standing up phase, temperature programed desorption measurements reveal two desorption features for the hydrocarbon fragments of the SAM, one centered around 130 °C and a second near 220 °C. For the lying down phase, only the higher temperature desorption feature is observed. For both phases, desorption peaks for S and H2S that are centered around 250 °C were observed, suggesting that there is a high probability for the alkane chain of the 1-decanethiol molecule to detach from the sulfur head group before desorbing from the surface. For the standing up phase, exposing the SAM to the electron beam results in a near complete attenuation of the two peaks associated with the cracking fragments of the alkane chain. However, for the lying down phase, the intensities and positions of all of the desorption peaks were similar to the unexposed SAMs, which indicates that the cross section for electron beam damage for the lying down phase is much lower than that for the standing up phase. Ex situ x-ray photoelectron spectroscopy reveals a chemical shift of almost 0.5 eV for the C-1s emission after electron exposure for the standing up phase, whereas the shift for the lying down phase was less than 0.1 eV. These results indicate that exposure of alkanethiol SAMs to 80 eV electrons results in both disordering of the SAM and decomposition of the alkanethiol molecule SAMs. For the standing up phase, the rate of decomposition is much higher than the lying down phase. The lower decomposition rate for the lying down phase is primarily attributed to the quenching of excess charge in this phase since the entire molecule is in direct contact with the metallic substrate.

Protection of silver and gold LSPR biosensors in corrosive NaCl environment by short alkanethiol molecules; characterized by extinction spectrum, helium ion microscopy and SERS.

We investigated the utility of localized surface plasmon resonance sensors in a biologically relevant environment containing NaCl. Our sensors are fabricated by depositing gold or silver on a monolayer of adsorbed monodisperse SiO2 nanospheres. While silver nanostructures are rather unstable in air and water as assessed by drifts in the extinction peak, even gold nanostructures have been found to drift at elevated NaCl concentrations. In an attempt to protect these nanostructures against NaCl, we modified them with alkanethiols with different lengths in the vapor phase and found that shorter chain alkanethiols such as 1-butanethiol are particularly effective against even 250 mM NaCl, rather than longer-chain alkanethiols more suitable for robust SAM formation. A vapor phase treatment method, in contrast to widely used solution phase treatment methods, was selected with the intention of reducing the solvent effect, i.e. destruction of intricate nanostructures upon contact with a solvent when nanostructures have been prepared in a vacuum system. Moreover, the treatment with 1-butanethiol led to an enhanced sensitivity as expressed by peak shift in nm per refractive index unit, nm per RIU. We show the results of evaluating alkanethiol-protected silver and gold nanostructures by extinction spectroscopy, helium ion microscopy and surface-enhanced Raman spectroscopy. The vapor phase treatment method with short chain alkanethiols is an effective way to protect intricate gold and silver nanostructures prepared in a vacuum system.

Structures and properties of alkanethiol-modified graphene oxide/solution-polymerized styrene butadiene rubber composites: Click chemistry and molecular dynamics simulation

Alkanethiol-modified graphene oxides (GOs) containing alkanethiol (CxGO) molecules with varying chain lengths were synthesized through click chemistry. Then, CxGO/solution-polymerized styrene butadiene rubber (CxGO/SSBR) composites with different CxGO loadings were prepared by a solution-mixing method. By combining experiment and molecular dynamics (MD) simulation, we investigated the relationship between the microstructures and properties of the CxGO/SSBR composites. Results showed that the 1-heptanethiol-modified GO (C7GO)/SSBR composite had the smallest fractional free volume and the least mobility of the polymer chains. Moreover, the 1-octadecanethiol-modified GO (C18GO)/SSBR composite displayed the largest binding energy (Ebinding). Thermal stability, gas barrier, dynamic, and static mechanical properties were improved by introducing CxGO. The long chain length of CxGO indicated that the composites had good performance. We believe that these results provide a basis for the design and fabrication of high-performance GO/SSBR composites.

Acid-enhanced conformation changes of yeast cytochrome c coated onto gold nanoparticles, a FT-IR spectroscopic analysis

Under conditions with or without linker molecules, the effects of acidic pH on the conformation of yeast iso-1-cytochrome c coated onto gold nanoparticles (AuNPs) in correlation with color changes of a Cyt c-coated AuNPs solution/suspension were examined by Fourier transform infrared (FT-IR) spectroscopy and correlated to color change. The results of detailed secondary structural analysis revealed that although the color changes coincide with acid-induced conformational changes in Cyt c coated onto AuNPs, the pH-related conformational unfolding of Cyt c coated onto AuNPs differed dramatically from that of its counterpart in solution. For Cyt c free in solution, the acid-induced unfolding did not occur until the pH was below 3.0, whereas for Cyt c coated onto AuNPs via C102 coordination near the C-terminal, a partial unfolding was observed even at near neutral pH which continuously intensified as pH decreased. Insertion of a short alkanethiol (3-mercaptoproprionic acid, 3-MPA) molecule between Cyt c and AuNP, which changes the interaction mode from a thiol coordination between Cyt c and AuNP to an electrostatic interaction between Cyt c and 3-MPA, which stabilized the conformation of Cyt c significantly, but did not prevent the acid-induced aggregation of Cyt c-3MPA-AuNPs.

Oxide removal and stabilization of bismuth thin films through chemically bound thiol layers.

Bismuth has been identified as a material of interest for electronic applications due to its extremely high electron mobility and quantum confinement effects observed at nanoscale dimensions. However, it is also the case that Bi nanostructures are readily oxidised in ambient air, necessitating additional capping steps to prevent surface re-oxidation, thus limiting the processing potential of this material. This article describes an oxide removal and surface stabilization method performed on molecular beam epitaxy (MBE) grown bismuth thin-films using ambient air wet-chemistry. Alkanethiol molecules were used to dissolve the readily formed bismuth oxides through a catalytic reaction; the bare surface was then reacted with the free thiols to form an organic layer which showed resistance to complete reoxidation for up to 10 days.

Self-Assembled Molecular Films of Alkanethiols on Graphene for Heavy Metal Sensing

We report a comparative study involving the formation of self-assembled molecular films by two types of alkanethiols (1-octadecanethiol and 1-dodecanethiol) on graphene grown via chemical vapor deposition, for heavy metal sensing applications. Scanning tunneling microscopy measurements confirm that the alkanethiol molecules can form localized, ordered molecular films on single-layer graphene despite the presence of structural and chemical irregularities. To test and compare the sensory characteristics associated with graphene functionalized by 1-octadecanethiol and 1-dodecanethiol, graphene-based field effect transistors are fabricated via photolithography on silicon dioxide substrates. Devices based on graphene functionalized with 1-octadecanethiol are successfully employed to demonstrate the detection of mercury and lead ions at the 10 ppm level via Dirac point shifts, with a notable difference in response associated with the use of different heavy metal ions. On the other hand, devices based on graphene functionalized with 1-dodecanethiol exhibit p-type character, before and/or after exposure to heavy metal ions, complicating their use in heavy metal sensing in a straightforward fashion via Dirac point shifts.

Controlled growth of ZnO nanorods via self-assembled monolayer

A simple method to achieve tailored growth of ZnO nanorods by employing self-assembled monolayer of alkanethiol molecules on a conductive substrate is introduced. Defects or pinholes in self-assembled monolayer are used to define the nucleation sites of ZnO during electrochemical deposition. The density of ZnO nanorods is tuned by the quality of self-assembled monolayer. A corresponding growth model for the growth of ZnO on self-assembled monolayer-modified substrate is proposed. The dimensions and the nucleation density of ZnO nanorods are tailored by systematically varying the quality of self-assembled monolayer and the parameters of electrochemical deposition. Furthermore, it is shown that this method also allows for laterally patterned growth of ZnO nanorods via microcontact printing of self-assembled monolayer. Electrochemical deposition of ZnO on Au surface results in dense coverage of ZnO nanorods. Self-assembled monolayers are applied on Au to tune the density of ZnO nanorods. The pinholes in self-assembled monolayer are used to define the nucleation site of ZnO.

Patterning of supported gold monolayers via chemical lift-off lithography.

The supported monolayer of Au that accompanies alkanethiolate molecules removed by polymer stamps during chemical lift-off lithography is a scarcely studied hybrid material. We show that these Au–alkanethiolate layers on poly(dimethylsiloxane) (PDMS) are transparent, functional, hybrid interfaces that can be patterned over nanometer, micrometer, and millimeter length scales. Unlike other ultrathin Au films and nanoparticles, lifted-off Au–alkanethiolate thin films lack a measurable optical signature. We therefore devised fabrication, characterization, and simulation strategies by which to interrogate the nanoscale structure, chemical functionality, stoichiometry, and spectral signature of the supported Au–thiolate layers. The patterning of these layers laterally encodes their functionality, as demonstrated by a fluorescence-based approach that relies on dye-labeled complementary DNA hybridization. Supported thin Au films can be patterned via features on PDMS stamps (controlled contact), using patterned Au substrates prior to lift-off (e.g., selective wet etching), or by patterning alkanethiols on Au substrates to be reactive in selected regions but not others (controlled reactivity). In all cases, the regions containing Au–alkanethiolate layers have a sub-nanometer apparent height, which was found to be consistent with molecular dynamics simulations that predicted the removal of no more than 1.5 Au atoms per thiol, thus presenting a monolayer-like structure.