Self-assembled Monolayer Layer Research Articles

Surface functionalization enabling highly effective phase-change heat transfer of R1234yf: A molecular dynamics study

Phase-change heat transfer has been demonstrated to be an effective thermal management approach for high-power electronics and power generators. In this work, we propose a strategy using surface functionalization to enhance the phase-change heat transfer of an environmentally friendly refrigerant, i.e., hydrofluoroolefins (HFO)-based R1234yf. Using molecular dynamics simulations, we find that the evaporation (condensation) heat transfer coefficient (HTC) at self-assembled monolayer (SAM) functionalized gold (Au) surfaces can be increased by ∼7 (∼5) times compared to that at the planar Au surfaces. The improvement in phase-change heat transfer of R1234yf at functionalized Au surfaces arises from the high thermal conductance across functionalized Au/R1234yf interfaces and the strong vibrational couplings between SAM molecules and R1234yf molecules. On the one hand, the introduced SAM layer can increase the interfacial thermal conductance (ITC) between Au and R1234yf owing to the strong bonding between Au and the SAM molecules, as well as the strong vibrational couplings at low-frequency modes (0–6 THz) among Au, SAM, and R1234yf. On the other hand, the thermal energy exchange during the evaporation (condensation) process can be improved by surface functionalization through the vibrational couplings between SAM and R1234yf at high frequency (∼12 and ∼30 THz) regions. This dual vibrational coupling will then allow the SAM layer to work as an intermedia to bridge the vibrations between Au and R1234yf molecules, which in return benefits the phase-change heat transfer. By further characterizing the evaporation and condensation processes, we find that the evaporation rate of R1234yf is increased by ∼50% at most at the wall superheat <70 K when the Au surfaces are functionalized using SAMs. When the wall superheat is above 70 K (i.e., 100 K for the planar Au surface), the evaporation of R1234yf becomes like film evaporation in which clusters of R1234yf molecules move off the surface together, which limits the enhancement (i.e., ∼100% at most) of evaporation HTC at the functionalized Au surfaces. At the same time, the condensation rate at functionalized Au surfaces is found to be increased by 15%–100% compared to that of the planar Au surfaces. By elucidating the mechanisms governing phase-change heat transfer on functionalized surfaces, our results provide an efficient strategy to enhance the cooling efficiency of the HFO refrigerants, which may benefit the design of surfaces with high phase-change heat transfer capabilities.

Functionalizing self-assembled monolayers to reduce interface scattering in ruthenium/dielectric for next-generation microelectronic interconnects

As the number of transistor increases in modern devices, the resistivity of metal lines increases with the downscaling of the vias dimension due to the increased in surface scattering of electrons. Herein, we evaluated the electrical performance and the adhesion strength of the Ru/SiO2 substrate upon functionalizing with benzyliminetriethoxysilane (BITES) and aminoproyltriethoxysilane (APTES) self-assembled monolayers (SAMs)s at the Ru/SiO2 interface. The covalent bonding and retention of the SAM film on the SiO2 surface were characterized via angle-resolved X-ray Photoelectron Spectroscopy (AR-XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (Tof-SIMS), respectively. According to the Fuchs–Sondheimer (FS) model and scratch test, the specularity parameter and the adhesion strength of the Ru/BITES/SiO2 simultaneously improved after thermal annealing compared to the non-functionalized Ru/SiO2 substrate. The effect of different SAM’s terminal groups (amine and benzylimine) on the electron scattering behavior was investigated based on the formation of an interface dipole upon chemisorption of organic molecules on the metal film. Our results indicate that SAM with the benzylimine terminal group formed a larger positive dipole at the SAM layer of the Ru/BITES/SiO2 interface compared to the Ru/APTES/SiO2, leading to an increased in specular electron scattering events and, thus an enhanced electrical performance of the Ru/BITES/SiO2.

Comparing nanobody and aptamer-based capacitive sensing for detection of interleukin-6 (IL-6) at physiologically relevant levels

A major societal challenge is the development of the necessary tools for early diagnosis of diseases such as cancer and sepsis. Consequently, there is a concerted push to develop low-cost and non-invasive methods of analysis with high sensitivity and selectivity. A notable trend is the development of highly sensitive methods that are not only amenable for point-of-care (POC) testing, but also for wearable devices allowing continuous monitoring of biomarkers. In this context, a non-invasive test for the detection of a promising biomarker, the protein Interleukin-6 (IL-6), could represent a significant advance in the clinical management of cancer, in monitoring the chemotherapy response, or for prompt diagnosis of sepsis. This work reports a capacitive electrochemical impedance spectroscopy sensing platform tailored towards POC detection and treatment monitoring in human serum. The specific recognition of IL-6 was achieved employing gold surfaces modified with an anti-IL6 nanobody (anti-IL-6 VHH) or a specific IL-6 aptamer. In the first system, the anti-IL-6 VHH was covalently attached to the gold surface using a binary self-assembled-monolayer (SAM) of 6-mercapto-1-hexanol (MCH) and 11-mercaptoundecanoic acid. In the second system, the aptamer was chemisorbed onto the surface in a mixed SAM layer with MCH. The analytical performance for each label-free sensor was evaluated in buffer and 10% human serum samples and then compared. The results of this work were generated using a low-cost, thin film eight-channel gold sensor array produced on a flexible substrate providing useful information on the future design of POC and wearable impedance biomarker detection platforms.

Defect Mapping and Densification in Self-Assembled Monolayers of Octadecyltrichlorosilane on SiO&lt;sub&gt;2&lt;/sub&gt;

Self-assembled monolayers (SAMs) can be used for surface functional control to assist with pattern collapse prevention and as a protective layer to enable Area Selective Deposition (ASD). To be successful, these applications require the formation of a high-density, defect-free, so-called well-packed SAM at the nm scale. In this paper, we describe a method to map the nm scale defects of octadecyltrichlorosilane (ODTS) SAMs using a post-etching AFM analysis of the surface of the substrate and used this technique to develop a process to form high-density, defect-free SAM layer at the nm scale. This was achieved by optimizing the water concentration in the solvent for the precursor solution and annealing after SAM formation.

Impact of pretreatment and thiol modifiers on the partial oxidation of glutaraldehyde using Pd/Al2O3

Oxidative conversion of biomass-derived compounds to value-added chemicals is challenging due to the tendency of multi-functional reactants to overoxidize. Catalyst performance can be sensitive to both synthesis and pretreatment conditions. Additionally, coating the catalyst with self-assembled monolayers (SAMs) has shown promise in modulating activity and selectivity. Here, the liquid-phase partial oxidation of glutaraldehyde (GA) to glutaric semialdehyde (GSA) was investigated as a model reaction using a Pd/Al2O3 catalyst, with and without various thiolate SAM modifiers. Reductive pretreatment of the catalyst showed enhancement in the activity and a shortening of an apparent induction period relative to the untreated catalyst. The selectivity for GSA was further found to be sensitive to the identity of the SAM layers, with hydrophilic thioglycerol (TG) and thiolactic acid (TLA) coatings showing an enhancement in selectivity to GSA; the TG coating raised selectivity from ∼ 60 % (on uncoated catalyst and catalysts coated with hydrophobic thiols) to ∼ 80 % at identical conversion (∼ 30 %). However, the TG coating exhibited lower catalytic rates compared to UC and hydrophobically coated materials. Morphological and electronic causes were ruled out with various materials characterization techniques. Density functional theory (DFT) calculations suggested that hydrogen bonding stabilizes adsorption of GSA compared to the uncoated Pd surface. However, a large stabilization of glutaric acid (GAC) adsorption for TG-coated Pd was also predicted, likely leading to accumulation of this overoxidation product and lower overall rates. Inhibition of the rate of GA partial oxidation by GAC adsorption was then corroborated experimentally. Finding ways to stabilize the less-oxidized intermediates with more specificity is thus suggested as a strategy to improve rate and selectivity.

Factors Affecting the Hydrophobic Property of Stearic Acid Self-Assembled on the TiO2 Substrate.

The self-assembled monolayer (SAM) on inorganic metal oxides is highly applicable in making different kinds of surface phenomena such as superhydrophobicity, functional group-modified surfaces, corrosion resistance, and so on. The formation of stearic acid SAMs on the TiO2 substrate depends on a few factors, and the cleanability of the substrate surface can be considered as the critical criterion for the formation of the SAM layer. The solvent, concentration of the adsorbate, immersion time, and temperature can be identified as other factors that are crucial for growing a uniform and highly dense monolayer. SAM layers always build up spontaneously on a suitable substrate, but the growth rate and arrangement can be changed by varying the external factors. These factors highly affect the chemisorption of stearic acid molecules onto the TiO2 substrate and building a well-ordered pattern on the surface without defects. This study mainly focuses on identifying the critical conditions of the external factors in obtaining a high-performance superhydrophobic surface. The crystal structure and surface morphologies of the substrate materials are characterized by powder X-ray diffraction and scanning electron microscopy, and the surface wettability is characterized by contact angle measurements. High superhydrophobicity is observed at the optimum conditions of the factors. Ethanol is used as the solvent; the temperature is about 40 °C; and 600 ppm of stearic acid is the critical concentration in obtaining a superhydrophobic surface with 100 min of immersion time, while the contact angle is 151.38°. Simultaneously, if the concentration is 1000 ppm and the immersion time is 120 min, the surface shows high superhydrophobicity with a contact angle of 162.06°. These critical conditions are found to be adequate for building well-ordered stearic acid SAMs on the TiO2 substrate.

Achieving High-Performance Molecular Rectification through Fast Screening Alkanethiol Carboxylate-Metal Complexes Electroactive Units

Achieving High-Performance Molecular Rectification through Fast Screening Alkanethiol Carboxylate-Metal Complexes Electroactive Units

Binding of Sulfate-Terminated Surfactants with Different Alkyl Chain Lengths to Viologen Sites Covalently Embedded in the Interior of a Self-Assembled Monolayer on a Au Electrode

We investigated the binding of anionic surfactants of lower concentrations than their critical micelle concentrations (cmcs) to the cationic redox-active viologen site in the interior of a self-assembled monolayer (SAM) on a polycrystalline Au electrode. We embedded the viologen site in the midway of the alkyl chain to facilitate the ion-pairing binding, which depends on the oxidation state of the viologen. We found that the binding of anionic surfactants and inorganic anions causes a negative shift of the formal potential of the redox couple of the viologen radical cation/viologen dication in line with the binding equilibrium. In contrast, the anion binding was weak and trivial when viologens are located at the SAM surface, indicative of the enhancement of the binding by the electrostatic interaction in the microenvironment with the low dielectric constant. The negative shift of the formal potential of viologen in the interior was greater for the surfactants with longer alkyl chain lengths, indicative of the efficacy of the alkyl chain-chain interaction. The chain-length-dependent potential shift followed the linear Traube rule but with a smaller slope than that in the original rule. We also demonstrated that the conjugated layer of the viologen SAM with dodecyl sulfate at a lower concentration than the cmc completely blocks the direct electron transfer (ET) from the Au electrode to solution-phase Fe(CN)63- but allows mediated ET around the formal potential of the viologen.

OLED application of π-conjugated phenylimino carboxylic acid organic semiconductor material

The organic semiconductor materials which form Self-Assembled Monolayers (SAMs) on Indium Tin Oxide (ITO) surface have been synthesized and used in Organic Light Emitting Diode (OLED) applications. The synthesized molecules are bonded chemically to the hydrophilic and rough ITO surface and formed a new hydrophobic and smother surface of ITO by the effect of SAM formation. The synthesized SAM molecule is 4″, 4″″-[biphenyl-4,4″-diylbis(phenylimino)]dibiphenyl-4-carboxylic acid (MZ-187) that contains carboxylic acid head group to bond to ITO surface. The formation on ITO surface is analyzed by cyclic voltammetry (CV) and atomic force microscopy (AFM). Two configurations, ITO/SAM(MZ-187)/HTL/EML/LiF/Al (MZ187-OLED) and ITO/HTL/EML/LiF/Al (bare-OLED), are fabricated to investigate the effect of SAM layer on the performance of the OLED device. Current–voltage (I–V) characterization of OLED devices are carried out and the luminescence of the devices are measured by integrating sphere under nitrogen gas in a glow box system. The quantum efficiency is calculated to determine how to affects the SAM layers on OLEDs performance. As a consequence, it is determined that the OLED device containing MZ-187 SAM layer, a similar structure with N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD), is exhibited a better OLED performance compare to the device without SAM layer.

Complementary electrochemical ICP-MS flow cell and in-situ AFM study of the anodic desorption of molecular adhesion promotors

Molecular adhesion promoters are a central component of modern coating systems for the corrosion protection of structural materials. They are interface active and form ultrathin corrosion inhibiting and adhesion-promoting layers. Here we utilize thiol-based self-assembled monolayers (SAMs) as model system for demonstrating a comprehensive combinatorial approach to understand molecular level corrosion protection mechanisms under anodic polarization. Specifically, we compare hydrophilic 11-Mercapto-1-undecanol and hydrophobic 1-Undecanethiol SAMs and their gold-dissolution inhibiting properties. We can show that the intermolecular forces (hydrophobic vs hydrophilic effects) control how SAM layers perform under oxidative conditions. Specifically, using in situ electrochemical AFM and a flow cell coupled to an ICP-MS a complementary view on both corrosion resistance, as well as on changes in surface morphology/adhesion of the SAM is possible. Protection from oxidative dissolution is higher with hydrophobic SAMs, which detach under micelle formation, while the hydrophilic SAM exhibits lower protective effects on gold dissolution rates, although it stays intact as highly mobile layer under anodic polarization. The developed multi-technique approach will prove useful for studying the interfacial activity and corrosion suppression mechanism of inhibiting molecules on other metals and alloys.

Interfacial Acid-Base Equilibria and Electric Fields Concurrently Probed by In Situ Surface-Enhanced Infrared Spectroscopy.

Understanding how applied potentials and electrolyte solution conditions affect interfacial proton (charge) transfers at electrode surfaces is critical for electrochemical technologies. Herein, we examine mixed self-assembled monolayers (SAMs) of 4-mercaptobenzoic acid (4-MBA) and 4-mercaptobenzonitrile (4-MBN) on gold using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS). Measurements as a function of the applied potential, the electrolyte pD, and the electrolyte concentration determined both the relative surface populations of acidic and basic forms of 4-MBA, as well as the local electric fields at the SAM-solution interface by following the Stark shifts of 4-MBN. The effective acidity of the SAM varied with the applied potential, requiring a 600 mV change to move the pKa by one unit. Since this is ca. 10× the Nernstian value of 59 mV/pKa, ∼90% of the applied potential dropped across the SAM layer. This emphasizes the importance of distinguishing applied potentials from the potential experienced at the interface. We use the measured interfacial electric fields to estimate the experienced potential at the SAM edge. The SAM pKa showed a roughly Nernstian dependence on this estimated experienced potential. An analysis of the combined acid-base equilibria and Stark shifts reveals that the interfacial charge density has significant contributions from both SAM carboxylate headgroups and electrolyte components. Ion pairing and ion penetration into the SAM also influence the observed surface acidity. To our knowledge, this study is the first concurrent examination of both effective acidity and electric fields, and highlights the relevance of experienced potentials and specific ion effects at functionalized electrode surfaces.

Molecular bridge-mediated ultralow-power gas sensing

We report the electrical detection of captured gases through measurement of the quantum tunneling characteristics of gas-mediated molecular junctions formed across nanogaps. The gas-sensing nanogap device consists of a pair of vertically stacked gold electrodes separated by an insulating 6 nm spacer (~1.5 nm of sputtered α-Si and ~4.5 nm ALD SiO2), which is notched ~10 nm into the stack between the gold electrodes. The exposed gold surface is functionalized with a self-assembled monolayer (SAM) of conjugated thiol linker molecules. When the device is exposed to a target gas (1,5-diaminopentane), the SAM layer electrostatically captures the target gas molecules, forming a molecular bridge across the nanogap. The gas capture lowers the barrier potential for electron tunneling across the notched edge region, from ~5 eV to ~0.9 eV and establishes additional conducting paths for charge transport between the gold electrodes, leading to a substantial decrease in junction resistance. We demonstrated an output resistance change of >108 times upon exposure to 80 ppm diamine target gas as well as ultralow standby power consumption of <15 pW, confirming electron tunneling through molecular bridges for ultralow-power gas sensing.

Effects of Experimental Conditions on the Signaling Fidelity of Impedance-Based Nucleic Acid Sensors.

Electrochemical impedance spectroscopy (EIS), an extremely sensitive analytical technique, is a widely used signal transduction method for the electrochemical detection of target analytes in a broad range of applications. The use of nucleic acids (aptamers) for sequence-specific or molecular detection in electrochemical biosensor development has been extensive, and the field continues to grow. Although nucleic acid-based sensors using EIS offer exceptional sensitivity, signal fidelity is often linked to the physical and chemical properties of the electrode-solution interface. Little emphasis has been placed on the stability of nucleic acid self-assembled monolayers (SAMs) over repeated voltammetric and impedimetric analyses. We have studied the stability and performance of electrochemical biosensors with mixed SAMs of varying length thiolated nucleic acids and short mercapto alcohols on gold surfaces under repeated electrochemical interrogation. This systematic study demonstrates that signal fidelity is linked to the stability of the SAM layer and nucleic acid structure and the packing density of the nucleic acid on the surface. A decrease in packing density and structural changes of nucleic acids significantly influence the signal change observed with EIS after routine voltammetric analysis. The goal of this article is to improve our understanding of the effect of multiple factors on EIS signal response and to optimize the experimental conditions for development of sensitive and reproducible sensors. Our data demonstrate a need for rigorous control experiments to ensure that the measured change in impedance is unequivocally a result of a specific interaction between the target analyte and nucleic recognition element.

Hysteresis Modulation on Van der Waals-Based Ferroelectric Field-Effect Transistor by Interfacial Passivation Technique and Its Application in Optic Neural Networks.

2D semiconductor-based ferroelectric field effect transistors (FeFETs) have been considered as a promising artificial synaptic device for implementation of neuromorphic computing systems. However, an inevitable problem, interface traps at the 2D semiconductor/ferroelectric oxide interface, suppresses ferroelectric characteristics, and causes a critical degradation on the performance of 2D-based FeFETs. Here, hysteresis modulation method using self-assembly monolayer (SAM) material for interface trap passivation on 2D-based FeFET is presented. Through effectively passivation of interface traps by SAM layer, the hysteresis of the proposed device changes from interface traps-dependent to polarization-dependent direction. The reduction of interface trap density is clearly confirmed through the result of calculation using the subthreshold swing of the device. Furthermore, excellent optic-neural synaptic characteristics are successfully implemeted, including linear and symmetric potentiation and depression, and multilevel conductance. This work identifies the potential of passivation effect for 2D-based FeFETs to accelerate the development of neuromorphic computing systems.

Improvement of memory characteristics for an organic charge trapping memory by introduction of PS tunneling layer

Abstract An organic charge trapping memory was fabricated employing (3-aminopropyl) triethoxysilane (APTES) self-assembled monolayer (SAM) as the charge trapping layer, and pentacene as the active layer. In the initial trial, APTES SAM is directly in contact with the active layer, which shows inferior memory characteristics exhibiting as small memory window, low reading currents ratio in WRER test, and short retention time. By introducing a thin Polystyrene (PS) tunneling layer between APTES SAM and active layer, all aspects of memory characteristics have been ameliorated, including enlarged memory window, much increased reading currents ratio in WRER test, and much longer retention time. Interestingly, the programming efficiency is not affected by the introduction of the PS tunneling layer, showing a short programming time of less than 1 μs. However, with further increase of PS tunneling layer thickness, the reading current ratio in WRER test and the programming efficiency is slightly decreased. In addition, the retention time is also slightly shorter in terms of thicker PS tunneling layer. Nevertheless, the comprehensive improvement of the memory characteristics by introducing PS tunneling layer enables the potential applications of a nonvolatile memory device.

Density Functional Theory Study of Pd Aggregation on a Pyridine-Terminated Self-Assembled Monolayer.

By using density functional theory calculations, the initial steps towards Pd metal cluster formation on a pyridine‐terminated self‐assembled monolayer (SAM) consisting of 3‐(4‐(pyridine‐4‐yl)phenyl)propane‐1‐thiol on an Au(1 1 1) surface are investigated. Theoretical modelling allows the investigation of structural details of the SAM surface and the metal/SAM interface at the atomic level, which is essential for elucidating the nature of Pd–SAM and Pd–Pd interactions at the liquid/solid interface and gaining insight into the mechanism of metal nucleation in the initial stage of electrodeposition. The structural flexibility of SAM molecules was studied first and the most stable conformation was identified, planar molecules in a herringbone packing, as the model for Pd adsorption. Two binding sites are found for Pd atoms on the pyridine end group of the SAM. The strong interaction between Pd atoms and pyridines illustrates the importance of SAM functionalisation in the metal nucleation process. Consistent with an energetic driving force of approximately −0.3 eV per Pd atom towards Pd aggregation suggested by static calculations, a spontaneous Pd dimerisation is observed in ab initio molecular dynamic studies of the system. Nudged elastic band calculations suggest a potential route with a low energy barrier of 0.10 eV for the Pd atom diffusion and then dimerisation on top of the SAM layer.

QCM Sensors Combining Highly Nanostructured Metal-Blacks Sublayers and Active Self-Assembled Monolayers

Introduction Quartz Crystal Microbalance (QCM) sensors are characterized by many potential applications. They are being widely used as biosensors, in pharmacological applications, for combustion control, environmental pollution monitoring, etc. [1]. Regardless the specific application, the recognition resolution of quartz chips is usually determined and restrained according to the Sauerbray equation (For example for 10 MHz QCM, the change of resonance frequency in 1 Hz corresponds to 4.4 ng/cm2 of adsorbed mass per surface). This fact is crucial mainly for gas sensor application where we need to detect concentration down to ppm or even ppb levels. However, there are some possibilities on how to enhance the QCM sensor properties and amplify their sensitivity, for instance by increasing the specific surface area of QCM electrodes, and thus providing more bonding sites for the analyte [2]. In this contribution, we propose a novel method that uses nanostructured materials called metal-blacks as a sublayer for the increase of active sensor surface, in combination with self-assembled monolayers (SAMs) that serves as a receptor layer. Metal-Blacks Metal-blacks – MBs are highly nanoporous and nanostructured materials with a large surface area. Their name originates in black colour, caused by the absorption of incident light on their surface. The incident light penetrates into the pores and channels where it undergoes multiple reflections in cavities and where it is almost completely absorbed. Due to the very large surface area, MBs are ideal materials for enhancement of QCM gas sensors properties [3]. Experimental The nanostructured layers of black gold (BAu) and black palladium (BPd) were prepared by evaporation from a tungsten boat at an elevated pressure of 200 Pa. Prepared layers of MBs were then characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SAMs of zinc octacarboxylphthalocyanine ZnPc(COOH)8 were prepared by two-step grafting method, where ZnPc(COOH)8 is covalently bonded to the molecule of aminothiophenol, which serves as an surface anchor via its gold/palladium-sulfur bond. The preparation procedure was as follows. At first, the QCM electrodes with MB layers were degreased in a sonicated ethanol bath during a few minutes and then dried under a nitrogen flow. Second, the QCM samples were cleaned by UV-ozone treatment and immediately immersed into 10-4 M solution of aminothiophenol in ethanol/DMF solvent for 24h. Third, after the 24h incubation time, the samples were moved into 10-4 M solution of the macrocycles and left there for another 24h. In the end, the samples were carefully rinsed with the solvent to eliminate adsorbed molecular overlayers and subsequently washed with ethanol in order to remove solvent residues and dried under nitrogen flux.Once prepared, QCM sensor impedance spectra were obtained by impedance analyzer Agilent 4294A. Responses towards different analytes (EtOH, CH4, H2O, NO2, toluene, acetaldehyde) were measured in a glass chamber that enables the measurement of up to 6 sensors at the same time. Sensors were measured at a constant gas flow and room temperature. The sensor resonant frequencies were measured by oscillattor circuits in connection with an NI PCI-6602 card used as a precise counter Results and Conclusions In this contribution, we have proved that highly nanoporous and nanostructured materials (such as metal-blacks), which have a large specific surface area, provide more binding sites for analytes and, hence, increase the response of the QCM sensors. As an example measurement, we present the response of QCMs with BAu towards ethanol vapours (Fig. 1). The curves illustrate that the response of the sensor with the BAu electrode is 10-times bigger than the one of the standard QCM (152Hz/15Hz). For the combined layer (BAu + ZnPc(COOH)8), the response amplification is not so large but it is still significant. In this case, the response is 3-times bigger than the one from the QCM with ZnPc(COOH)8 only (without BAu). However, in contrast with QCM with just bare BAu, the surface modification with SAMs layers influences the sensor selectivity. The combined layers of MBs and SAMs then result in a selective sensor with increased sensitivity. According to the presented results metal-blacks are promising materials that can significantly boost the sensitivity of QCM sensors and still preserve the selectivity of its active layers.

Electrochemical Immunosensor for Human IgE Using Ferrocene Self-Assembled Monolayers Modified ITO Electrode.

The immunoglobulin E (IgE) level in serum is an important factor in the examination of allergy. Ferrocene (Fc)-modified self-assembled monolayers (SAMs) were placed on an indium tin oxide (ITO) electrode as a sensing layer for the detection of human IgE. The Fc moiety in the SAMs facilitated the electron transfer through the organic SAMs layer and electrocatalytic signal amplification. The electrochemical measurement was accomplished after the sandwich type immobilization of the receptor antibody, target human IgE, and enzyme conjugated secondary antibody. The enzyme product, p-aminophenol, was quantitatively analyzed by redox cycling via Fc. In addition, the electrochemical impedance spectroscopy (EIS) was investigated for the detection of IgE. The limit of detection (LOD), limit of quantification (LOQ), and dynamic range of the electrochemical sensor were 3 IU/mL, 10 IU/mL, and from 10 IU/mL to 100 IU/mL, respectively.

Low temperature platinum chemical vapor deposition on functionalized self-assembled monolayers

The reaction pathways of Pt CVD using (COD)PtMe2 – xClx (x = 0, 1, 2) have been investigated on functionalized self-assembled monolayers (SAMs) as models for organic substrates. Residual gas analysis for (COD)PtMe2 and (COD)PtMeCl is consistent with the loss of methyl radicals as the initial step in deposition, while for (COD)PtCl2, the first step is the loss of a chlorine radical. It is further shown using x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry that the deposition process leads to chemical damage of the SAM layer and little Pt deposition. Using this understanding, it is demonstrated that the Pt CVD rate can be controlled using a radical trap. In the presence of 1,4-cyclohexadiene, a well-known alkyl radical trap, Pt deposition was increased by 5× to 10×, creating a room-temperature effective Pt CVD process.

Redox Control of Charge Transport in Vertical Ferrocene Molecular Tunnel Junctions

Summary Controlling charge transport through molecular tunnel junctions is of crucial importance for exploring basic physical and chemical mechanisms at the molecular level and realizing the applications of molecular devices. Here, through a combined experimental and theoretical investigation, we demonstrate redox control of cross-plane charge transport in a vertical gold/self-assembled monolayer (SAM)/graphene tunnel junction composed of a ferrocene-based SAM. When an oxidant/reductant or electrochemical control is applied to the outside surface of the neutral single-layer graphene top electrode, reversible redox reactions of ferrocene groups take place with charges crossing the graphene layer. This leads to counter anions on the outer surface of graphene, which balance the charges of ferrocene cations in the oxidized state. Correspondingly, the junctions switch between a high-conductance, neutral state with asymmetrical characteristics and a low-conductance, oxidized state with symmetrical characteristics, yielding a large on/off ratio (>100).