SAM Layer Research Articles

HaloTag-Modified, Ferrocene Labeled Self-Assembled Monolayers for Protein Sensing.

Ferrocene (Fc)-based disulfide molecules of various lengths with amino acid scaffolds and alkane or oligo(phenylene-ethynylene) (OPE) bridges are used in a mixed SAM with a di-(ethylene oxide) terminal mercaptoundecanol diluent (PEG2). The relative height of the Fc redox reporter in the SAM is compared to determine if there are protective effects like antifouling and specific detection. The HaloTag-binding motif is used as a proof-of-concept to investigate the electrochemical response to the HaloTag protein due to its known covalent and fast linkage. When the Fc-SAMs are exposed to the HaloTag protein, there are an antifouling nature and more specific detection for the engulfed Fc-based molecules (C6tBu/Halo). The further out the Fc is from the SAM layer, the more nonspecific adsorption is detected. The double layer capacitance (CDL) has the smallest change for the C6tBu control (ΔCDL = -0.1 μF cm-2) showing antifouling properties and produces a large change (ΔCDL = 0.9 μF cm-2) as well as a shift in oxidation potential when the active C6Halo is exposed to the HaloTag protein (ΔE1/2 = 50 ± 10 mV). The remaining Fc molecules are partially in or outside the PEG2 layer, allowing more ion penetration/mobility even when the HaloTag protein is bound. Generally, a more disordered environment was observed for the Fc-based molecules when adding the HaloTag ligand, which is evident from a larger Efwhm and higher CDL. Desorption of the SAMs with sodium iodide (NaI) showed retention of the HaloTag protein bound with the corresponding ligand, whereas negative controls did not. Self-assembled monolayers for MALDI mass spectrometry (SAMDI-MS) were used as an orthogonal detection technique to show the qualitative binding of the HaloTag protein to the electrode. Together, these results provide insight into the antifouling and detection methods of engulfing the redox molecules in the SAM diluent.

Perovskite Solar Cells Consisting of PTAA Modified with Monomolecular Layer and Application to All‐Perovskite Tandem Solar Cells with Efficiency over 25%

AbstractThis study is on the enhancement of the efficiency of wide bandgap (FA0.8Cs0.2PbI1.8Br1.2) perovskite solar cells (PSCs) used as the top layer of the perovskite/perovskite tandem solar cell. Poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA) and the monomolecular layer called SAM layer are effective hole collection layers for APbI3 PSCs. However, these hole transport layers (HTL) do not give high efficiencies for the wide bandgap FA0.8Cs0.2PbI1.8Br1.2 PSCs. It is found that the surface‐modified PTAA by monomolecular layer (MNL) improves the efficiency of PSCs. The improved efficiency is explained by the improved FA0.8Cs0.2PbI1.8Br1.2 film quality, decreased film distortion (low lattice disordering) and low density of the charge recombination site, and improves carrier collection by the surface modified PTAA layer. In addition, the relationship between the length of the alkyl group linking the anchor group and the carbazole group is also discussed. Finally, the wide bandgap lead PSCs (Eg = 1.77 eV) fabricated on the PTAA/monomolecular bilayer give a higher power conversion efficiency of 16.57%. Meanwhile, all‐perovskite tandem solar cells with over 25% efficiency are reported by using the PTAA/monomolecular substrate.

Impedimetric CRISPR-dCas9 Based Biosensor System for Sickle Cell Anemia Mutation

Sickle cell anemia is one of the single point mutation diseases with symptoms such as stroke, lethargy, chronic anemia, and increased mortality, and it causes red blood cells to become sickle-shaped. In the study, a biosensor system was developed to detect this mutation quickly and cost-effectively. This biosensor system was prepared by forming a SAM layer with 4-Aminothiophenol (4-ATP) on the gold electrode, and coating it with amino graphene. It was then modified with SG-RNA with the sequence of the target mutation after CRISPR-dCas9 immobilization. The nanomaterial used in the preparation of the biosensor increased the sensitivity of the method by increasing the surface area. The biosensor prepared in this way was optimized and made to perform DNA analysis. As a measurement method, electrochemical impedance spectroscopy (EIS) was used. Electrochemical measurements were carried out in 50 mM pH 7.0 phosphate buffer solution, which includes 5 mM Fe(CN)64- /3- and 10 mM KCl, as redox probe solution by CV and EIS in this redox probe solution. EIS parameters were 10,000–0.05 Hz frequency, 10 mV AC and 180 mV DC potentials, and CV parameters were between - 0.2 to 0.5 V potential, 100 mV/s scan rate for 5 cycles. The DNA measurement time of the biosensor system was determined by the chronoimpedance measurements taken by applying a frequency of 500 Hz under 200 mV DC current. Measurement time of the biosensor was found to be 100 seconds. With the CRISPR-Cas9 based electrochemical biosensor system, which gives faster results compared to the measurement methods in the literature, a linear measurement between 40 pM and 1000 pM with a length of 400 base pairs was taken.

Zirconia nanotube coatings - UV-resistant superhydrophobic surfaces

Surface modifications influence material interactions such as wettability, imparting hydrophobicity or hydrophilicity. Mainstream research focused on enhancing product shelf-life directs attention towards superhydrophobic surfaces (SHS). SHS offer several benefits for out-door applications such as self-cleaning, anti-soiling, anti-mist etc. Recently, such surfaces were created by hydrophobization of anodized titania, which although effective lacked a long-term stability of their hydrophobic modifications due to it being susceptible to UV-mitigated degradation. In light of this situation, ZrO2-nanotubes are evaluated with regard to their application as transparent UV-stable superhydrophobic coatings. Nanostructured oxide surfaces are created via single-step electrochemical anodization. The absence of HF acid-based pre-etching steps offer a safe and alternatively a green synthesis route. Anodized oxides are modified using octadecylphosphonic acid (OPA) self-assembled monolayers, demonstrate superhydrophobicity and are at par with conventionally employed coatings such as PTFE, PFDPA and PTES. The OPA-coatings are evaluated for their mechanical stability under a jet of water, chemical stability under indirect sunlight irradiation in air/water and direct UV exposure. Zirconia nanotubular films were evaluated for optical transparency using light microscopy and surface wettability of the different zirconia-composites was compared to the model system - titania. Structural and compositional differences of the SAM layer upon time dependent decay were analyzed with X-ray photoelectron spectroscopy.

Immunosensing prostate-specific antigen: Faradaic vs non-Faradaic electrochemical impedance spectroscopy analysis on interdigitated microelectrode device

This work explores Electrochemical Impedance Spectroscopy (EIS) detection for a highly-sensitive quantification of prostate-specific antigen (PSA) in Faradaic (f-EIS) and non-Faradaic modes (nf-EIS). Immobilization of monoclonal antibody specific to PSA (anti-PSA) was performed using 1-ethyl-3-dimethylaminopropylcarbodiimide hydrochloride and N-hydroxysuccinimide crosslinking agents in order to conjugate carboxylic (-COOH) terminated group of 16-Mercaptoundecanoic acid with amine (-NH3+) on anti-PSA epitope. This approach offers simple and efficient approach to form a strong, covalently bound thiol-gold (SAu) for a reliable SAM layer formation. Studies on the topographic of pristine Au-IDE surface were performed by Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy techniques, meanwhile a 3-dimensional optical surface profiler, Atomic Force Microscopy and X-ray Photoelectron Spectroscopy techniques were used to validate the successful functionalization steps on the sensor transducer surface. Detection of PSA in f-EIS mode was carried out by measuring the response in charge transfer resistance (Rct) and impedance change (Z), meanwhile in nf-EIS mode, the changes in device capacitance was monitored. In f-EIS mode, the sensor reveals a logarithmic detection of PSA in a range of 100 ng/ml down to 0.01 ng/ml in Phosphate Buffered Saline with a recorded sensitivity of 2.412 kΩ/log10 ([PSA] ng/ml) and the limit of detection (LOD) down to 0.01 ng/ml. The nf-EIS detection mode yields a logarithmic detection range of 5000 ng/ml down to 0.5 ng/ml, with a sensitivity of 8.570 nF/log10 ([PSA] ng/ml) and an LOD of 0.5 ng/ml. The developed bio-assay yields great device stability, specificity to PSA and repeatability of detection that would pave its way for the future development into portable lab-on-chip bio-sensing system.

A MoS2–Au nanoparticle-modified immunosensor for T3 biomarker detection in clinical serum samples

A label-free and highly sensitive impedimetric sensor was developed based on electrodeposited molybdenum disulfide (MoS2)-gold (Au) nanoparticles for the detection of total triiodothyronine (T3) in human serum samples. The first step was the electrodeposition of MoS2 and Au on ITO substrates followed by the formation of a monolayer of dithiobis(succinimidyl propionate) (DSP) for binding of T3 antibodies (anti-T3) through coordination of amine coupling to form Au–MoS2/anti-T3 electrode transducers. The resulting film was characterized by SEM-EDS, XRD, FT-IR spectroscopy and electrochemical methods. The electrode kinetics of both MoS2 and Au–MoS2 electrodes were examined through impedance and cyclic voltammetry techniques. The impedance sensor was applied for the label-free detection and quantification of T3 via impedimetric measurements. The T3 binding on the SAM layer on the hybrid electrodes was examined through electrochemical impedance spectroscopy (EIS), and the relative change in the charge transfer resistance was used to quantify T3 in both serum and PBS samples. A linear quantification of T3 was obtained in the range of 0.01–100 ng/mL with a detection limit of 2.5 pg/mL. Also, to test the selectivity, Au–MoS2/anti-T3 electrodes were incubated with similar types of thyroid biomarkers (TSH and cortisol), which did not exhibit non-specific reactions with the transducer surface. Moreover, the sensor has been applied to real samples from healthy individuals and patients diagnosed with cancer and was compared with conventionally available methods.

Interfacial engineering of a ZnO electron transporting layer using self-assembled monolayers for high performance and stable perovskite solar cells

The SAM layer which formed hydrogen-bonding to the methylammonium of the perovskite induced dipole moments at the interface, resulting in energy band bending and increased built-in voltage, and consequently, improved charge transfer of the PSC.

Self-Healing Effect of Wet-Processed Organic SAM Diffusion Barrier Layer Using Polymer Capped Palladium Nanoclusters

In ultra-large scale integrated circuits (ULSIs), aluminum (Al) has been replaced by copper (Cu) as the interconnect material due to Cu has higher resistance to electromigration and lower electrical conductivity [1]. Unfortunately, Cu has high mobility in silicon (Si) and silicon dioxide (SiO2), thus impacting interconnect reliability and leading to inferior electrical performance or device failure. Therefore, it is necessary to form a good copper diffusion barrier between Si/SiO2 and Cu layer. In the past few decades, inorganic materials such as tantalum (Ta) or tantalum nitride (TaN) based compounds or metal-alloys has been successfully introduced as the diffusion barrier industrially. However, from the ULSI roadmap revealed by the International Technology Roadmap for Semiconductors report (ITRS), the necessary diffusion barrier thickness for the line-width of 22 nm is less than 2 nm [2], which challenges the current Ta or TaN technology by using the conventional vapor-phase deposition. Recently, a few reports use the organo-silane compounds such as 3-aminopropyltrimethoxysilane (APTMS) as the diffusion barrier to substitute inorganic Ta or TaN barrier layer [3-5], and show promising result. However, forming SAM is known to very sensitive to process conditions, particularly when SAM is prepared by wet-soaking. Imperfect SAM cannot block Cu diffusion efficiently and thus fails to compete with inorganic counterparts. In this study, we developed an all-wet, self-healing process to converge the copper diffusion blocking property on a Cu/SAM/SiO2 substrate. In particular, a 3-[2-(2-aminoethylamino)ethylamino] propyl-trimethoxysilane (ETAS) layer was deposited on SiO2 surface via wet soaking process. Then a 200 nm Cu film was electroless plated onto ETAS-treated SiO2 with the help of a home-made poly(vinyl alcohol)-capped palladium (PVA-Pd) nanoparticle catalysts. By varying ETAS soaking time and the ratio of PVA:Pd in the process, the sheet resistance of the Cu/SAM/SiO2 substrate after rapid thermal annealing (RTA) was investigated. As shown in Fig.1, it can be seen the sheet resistance increased rapidly after RTA over 300 oC in the case of no ETAS treatment, indicating the formation of copper silicide because of the absence of diffusion barrier layer. It is also found in the case of 30 minutes ETAS treatment (approaching SAM[6]) and 1:1 PVA to Pd ratio (ETAS-30-1xPVA-Pd), no copper silicide formation up to 500 oC. Interestingly, in 1 minute ETAS (ETAS-1) soaking samples, which is considered islandish ETAS coating rather than SAM, the PVA:Pd ratio affects the effectiveness of Cu diffusion barrier significantly. The more the PVA, the better Cu diffusion blocking capability is. Finally, in the sample processed by 1 minute islandish ETAS treatment and PVA:Pd ratio of 2 (ETAS-1-2xPVA-Pd), the Cu diffusion blocking capability is identical to the case of ETAS SAM, evidencing PVA can mend the imperfect SAM layer and thus converging the overall performance. Our study provides a simple and controllable process to utilize organic compound as the alternative for Ta or TaN diffusion barrier layer in fine line ULSI fabrication. REFERENCES [1] S. P. Murarka, Mater. Sci. Eng., 19 (1997) 87. [2] International Technology Roadmap for Semiconductors,2013 edition. [3] A. M. Caro, S. Armini, O. Richard, G. Maes, G. Borghs, C. M. Whelan and Y. Travaly, Adv. Funct. Mater., 20 (2010) 1125. [4] W. K. Han, G. H. Hwang, S. J. Hong, C. S. Yoon, J. S. Park, J. K. Cho and S. G. Kang, Appl. Surf. Sci., 255 (2009) 6082. [5] Y. Chung, S. Lee, C. Mahata, J. Seo, S. M. Lim, M. S. Jeong, H. Jung, Y. C. Joo, Y. B. Park, H. Kimd and T. Lee, RSC Adv., 4 (2014) 60123. [6] C. W. Hsu, W. Y. Wang, K. T. Wang, H. A. Chen and T. C. Wei, Sci. Rep., 7 (2017) 1. Figure 1

Transparent polymer-based SERS substrates templated by a soda can

This paper demonstrates the reproducible fabrication of transparent Surface Enhanced Raman Scattering (SERS) substrates, fabricated by employing an aluminium soda can to template nanostructures on a flexible thermoplastic polymer surface, followed by deposition of a silver over layer. Electron microscopy and finite element modelling simulations strongly suggested the SERS response arose at regions of high electromagnetic field strength occurring between metallic clusters following illumination by monochromatic radiation. The sensors exhibited rapid, quantitative and high sensitivity, for example, 5 × 10−10 M (204 pg/mL) crystal violet detection in 10 min using a simple drop and dry method. We also show detection of glucose employing a chemically modified silver surface bearing a pre-deposited SAM layer. Furthermore, the transparent substrates permitted back excitation and collection through the substrate with corresponding spectra exhibiting clear and well-defined spectral SERS peaks. Finally, we present the detection of trace amounts of melamine in complex media solution (milk and infant formula). We benchmark the sensor performance using commercial analytical instrumentation (MS-MS) and show comparable sensitivity between the SERS substrates and MS-MS.

Development of novel paper based electrochemical immunosensor with self-made gold nanoparticle ink and quinone derivate for highly sensitive carcinoembryonic antigen

In this study, a low cost and robust paper based electrochemical immunosensor was developed using self-made gold nanoparticle electrode for rapid and selective detection of Carcinoembryonic antigen (CEA). The working and counter electrode were printed using gold nanoparticle ink while the reference electrode was made using commerical silver ink. A simple mercapto-amine functionalised receptor (R1) based on moiety Quinone compound was formed on the paper based screen-printed gold (Au) electrode (P-SPGE) for highly selective sensing of CEA. A self-assembled monolayer principle (SAM) was exploited to fabricate the sensitive and selective immunosensor electrodes. In electrode fabrication, SAM layer was accomplished using covalent linkage of thiol in the R1 compound on the P-SPGE surface. Immobilised amine served as a layer for further binding of biological components. CEA levels were examined quantitatively using differential pulse voltammetry (DPV) and limit of detection (LoD) was calculated as 0.33ngmL−1. The performance of P-SPGE was compared with the commercial screen-printed Au electrode. A novel P-SPGE functionalised with R1 exhibited the tremendous performance for CEA detection in a linear concentration range of 1.0ngmL−1–100.0ngmL−1. The performance of this electrochemical immunosensor were carried out using different proteins.

Development of a Simple Isatin‐Based Electrochemical Immunosensor on a Screen‐Printed Gold Electrode for Highly Sensitive Detection of Carcinoembryonic Antigen

AbstractIn this study, an electrochemical immunosensor was designed to exploit for the detection of Carcinoembryonic antigen (CEA) based on simple mercapto‐amine functionalised Isatin compound (R1) on the screen‐printed gold (Au) electrode. Isatin is an endogenous inhibitor with monoamine oxidase B and it has been modified with mercapto‐amine for the functionalization. The self‐assembled monolayer principle (SAM) was utilized to fabricate the sensitive and selective immunosensor electrodes. In electrode fabrication, SAM layer was achieved using covalent linkage of mercapto unit in the Isatin compound on the screen‐printed Au electrode surface. Immobilised amine served as a layer for further binding of biological components. CEA levels were investigated quantitatively using differential pulse voltammetry (DPV) and limit of detection (LoD) was calculated as 0.29 ng mL−1 in a linear concentration range of 50.0 pg mL−1‐100.0 ng mL−1. The performance of this immunosensor were carried out using different proteins and human serum and the selectivity was compared with commercial cystamine.

Selective CO2 Reduction with Catalyst-Assembled Electrodes in an Aqueous Solution

Suppression of CO2 emission is an urgent and important issue to be solved global warming problem. When one recycles emitted CO2 from burned fossil fuels as useful carbon resources, such as CO, the overall amount of emitted CO2 in air will be reduced by keeping the usefulness of carbon-containing fuels and materials as key chemicals in industries without increase of CO2 emission. On the design of CO2 reduction catalysts, overpotential (η), turnover frequency (TOF), and robustness are major issues for highly efficient catalytic reaction. Our strategy is based on mimicking the active site structures of metalloenzyms, carbon monoxide dehydrogenases (CODHs), which contain Ni-Fe bimetallic center in a Fe-S cluster.1 These enzymes can convert CO2-to-CO at a quite low η, < 100 mV.2 However, the enzymes easily lose their activity due to the lack of their robustness. On the other hand, reported metal complexes applied for CO2 reduction, different from the enzymes, involve single metal ion in their active centers and require relatively higher η than those of the enzymes. On this context, we have developed efficient electrocatalysts and their reaction systems, which fulfill all essential requisites for catalytic CO2 reduction. We applied the bimetallic motif in the enzymes for the structures of CO2 reduction catalysts and synthesized Fe porphyrin dimers by linking two Fe porphyrins through a phenylene group.3 As expected, the catalytic activity is very sensitive on the Fe-Fe separation. As the results, we demonstrated homogeneous catalytic CO2-to-CO reaction with Fe meso-tris(perfluorophenyl)porphyrin dimer bearing o-phnylene linker in very high TOF, 25,000 s-1, at η = 0.42 V and 93% CO selectivity in a wet DMF. Controlled potential electrolysis under the same conditions keeps current density, ≈1 mA cm-2 for 12 h without any loss of the activity.4 Since CO2-to-CO reaction couples with water splitting, heterogeneous electrocatalytic system is important. When one uses a coordination catalyst-assembled electrode in an aqueous solution, following issues should be solved: 1. When one modifies a flat electrode with a coordination catalyst, catalyst coverage on the electrode is limited. In order to increase current density or reaction velocity, the surface coverage should be several orders higher than the modified flat electrode. 2. The standard reduction potential of proton is less negative than those of many CO2 reduction reaction. Thus, an electrode protected by a suitable material is required in order to avoid preferential proton reduction over CO2. To overcome these issues, we use (1) nano tin oxide-sintered film on an electrode in order to increase the electrode surface area and (2) co-modification of a SAM layer for the protection of the metal oxide surface from water. By application of these methods, we attained selective CO2 reduction over hydrogen formation at zero overpotential in an aqueous solution in ten times higher current density than one with the ordinary flat electrode. References J.-H. Jeoung and H. Dobbek, Science, 2007, 318, 1461; J. Fesseler, J.-H. Jeoung, and H. Dobbek, Angew. Chem. Int. Ed., 2015, 54, 8560.W. Shin et al., J. Am. Chem. Soc., 2003, 125, 14688.E. A. Mohamed, Z. N. Zaharan, and Y. Naruta, Chem. Commun, 2015, 51, 16900.Z. N. Zahran, E. A. Mohamed, and Y. Naruta, Sci. Reports, 2016, 6, 24533.

Rapid Recovery Process of Plasma Damaged Porous Low-k Dielectrics by Wet Surface Modifying Treatment

A rapid repair process of plasma damaged SiCOH in combination with post-etch residue removal has been developed. The carbon depletion layer caused by plasma dry etching was repaired by subsequent surface modifying SAM treatment, which resulted in replenishment of carbon not only on the surface but also a few nm toward the bulk. This repairing technique provides a high-quality hydrophobic surface under conditions of low temperature and short process time. In addition, the SAM layer can be expected to act as an adhesion promotor with metal materials.

Synergic Effects of Randomly Aligned SWCNT Mesh and Self‐Assembled Molecule Layer for High‐Performance, Low‐Bandgap, Polymer Solar Cells with Fast Charge Extraction

Currently, most of the promising organic solar cells (OSCs) are based on low bandgap polymer donors with deep‐lying highest occupied molecular orbit (HOMO) levels, which impose the challenges for device architecture design. In terms of fast charge extraction and suppression of bimolecular recombination, elaborate interface design in low bandgap OSCs is of significance to further boost their ultimate efficiency. In this work, a facile solution‐processed functionalized single wall carbon nanotube (f‐SWCNT) mesh/self‐assembled molecule (SAM) hybrid structure is reported as hole transport layer (HTL) in low bandgap OSCs. The effectiveness of such hybrid HTL originates from two aspects: (i) SAM layer can effectively realize Ohmic contact between f‐SWCNT and low bandgap polymer donors with deep‐lying HOMO levels due to the reduction of interface energy barrier; (ii) f‐SWCNT mesh can provide fast hole extraction pathways to quickly sweep out photogenerated charges. As a consequence of synergic effects of such hybrid HTL, both photocurrent and fill factor are greatly enhanced due to the reduced bimolecular recombination. Together with careful light management by using ZnO optical spacer, a high efficiency of 10.5% has been achieved. This work offers an excellent choice for large‐scale processable and effective HTL toward the application in low bandgap OSCs with deep‐lying energy levels.

P.155L: Late‐News Poster: Surface Monolayer Stabilized Vertically Aligned Liquid Crystals for Display Applications

AbstractThe surface monolayer stabilized vertically aligned liquid crystal (VA‐LC) mode is presented for television applications. Photo‐reactive self‐assembled monolayer (PR‐SAM) is formed on inorganic oxide surfaces. The SAM layer on oxide surfaces initially induce a homeotropic alignment of nematic LCs. Subsequent polymerization of the photo‐reactive SAM under applied electric field efficiently stabilizes LC alignment and induces a stable pretilt of LC molecules for four different directions in each pixel of the fishbone‐patterned VA‐cells. As results, improved electro‐optic characteristics, such as faster grey‐to‐grey response time, lower threshold voltage and enhanced brightness, are obtained after the polymerization‐induced stabilization of the photo‐reactive SAM.

Midland Blotting: A Rapid, Semi-Quantitative Method for Biosensor Surface Characterization

Biosensor performance and readout are critically dependent upon sensor surface characteristics. It is vital that key steps in sensor construction, such as base layer polymer/Self-Assembled Monolayer (SAM) deposition and bioreceptor tethering, are controlled tightly in order to achieve high sensitivity, specificity and reproducibility. Here, we present a rapid, semi-quantitative method by which key biosensor surface features can be characterised using chemiluminescence. This technique, which we have termed midland blotting, permits the detection of biosensor surface components through the attachment of a HorseRadish Peroxidase (HRP)-conjugated reagent to the target of interest. Upon addition of luminol-based substrate, HRP generates a reagent which emits light when it decays. The light signal is proportional to the bound HRP on the sensor surface. We show here that midland blotting allows the measurement and validation of various important surface features including: (1) availability of functional groups on the polymer or SAM layer; (2) bioreceptor tethering and (3) analyte binding. Midland blotting is rapid, cost-effective and allows for much faster optimisation of biosensor surface design. This method also provides a simple way of troubleshooting and can explain sensor performance when combined with readout data. In this report, we have focussed on midland blotting for electrochemical immunosensors as a proof of concept, but this technique is readily applicable to all biosensor systems.

Charge trapping at organic/self-assembly molecule interfaces studied by electrical switching behaviour in a crosspoint structure

Charge trapping at organic/self-assembly molecule (SAM) interfaces is studied by the electrical switching behaviour in a crosspoint structure, where interfacial charge trapping tunes the potential barrier of the SAM layer. The sample with rubrene exhibits the write-once read-many-times memory effect, which is due to the interfacial charges trapped at deep states. On the other hand, the sample with 2-amino-4,5-dicyanoimidazole presents recyclable conduction transition, which results from the trapped charges distributed at shallow states. Moreover, the percentage of the charges trapped at shallow states can be estimated from electrical transition levels.

Photolithographic Fabrication of Micro-Patterned, Nanoscale Prussian Blue (PB) Arrays for Electrocatalytic Analysis of Ascorbic Acid

A micro-patterned Prussian Blue (PB) array of nanometer thickness was fabricated using soft photolithography and voltammetric deposition for electrocatalytic detection of biomolecules. A self-assembled alkylthiol monolayer on gold was photooxidized by UV irradiation with a TEM mask, generating an imprinted pattern into which a PB microarray was subsequently deposited. Cyclic voltammetric and microscopic characterization indicates that the PB arrays demonstrate improved electrochemical stability as compared to conventional PB films, particularly at neutral pH, allowing scores of potential cyclings with little film deterioration. The PB film thickness in the array can be conveniently controlled by varying deposition time. Facile electron transfer was observed on the array electrode and the effect of the SAM layer on electrochemical response was investigated. The use of PB arrays for electrocatalytic analysis of biologically significant molecules was demonstrated with ascorbic acid (AA). The calibration curve for AA shows a linear relationship over the concentration range of 1.0 x 10(-5) to 8 x 10(-7) M with a correlation coefficient of 0.99. The detection limit was determined to be 1 x 10(-8) M, which is about 100 times lower than the reported value on a conventional PB electrode. The method developed here provides a new functional surface for bioanalysis using electrocatalytic principles.

Interfacial friction of thin PDMS network films

This study focuses on developing dry, surface-tethered polymeric lubricant coatings capable of significantly decreasing friction and wear of nano- and micrometer scale machines. Vinyl-terminated polydimethylsiloxane chains are spin-coated with a crosslinking agent and platinum catalyst onto silicon wafers functionalized with a self-assembling monolayer containing reactive vinyl groups. Lateral force microscopy (LFM) measurements employing a bead probe are used to quantify the coefficient of friction (COF) and adhesion characteristics of the PDMS-SAM surface tethered networks. The combined polymer network and SAM layer manifest extremely low friction coefficients, μ = 4 × 10−3, which is nearly one order of magnitude lower than the friction coefficient of the bare silicon substrate. The lowest friction forces are measured using silicon substrates covered with nanometer thick, peroxide crosslinked PDMS networks; though poorly crosslinked, these networks display COFs as much as ten-times lower than a solitary SAM coating layer. Micrometer thick end-linked optimal networks also manifest attractive interfacial friction properties, with COFs approximately three times larger than the thinner, imperfect networks. These observations are discussed in terms of the structure of the polymer networks and the role of adhesion forces on interfacial friction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1773–1787, 2008

Formation of Au nano-patterns on various substrates using simplified nano-transfer printing method

For future device applications, fabrication of the metal nano-patterns on various substrates, such as Si wafer, non-planar glass lens and flexible plastic films become important. Among various nano-patterning technologies, nano-transfer print method is one of the simplest techniques to fabricate metal nano-patterns. In nano-transfer printing process, thin Au layer is deposited on flexible PDMS mold, containing surface protrusion patterns, and the Au layer is transferred from PDMS mold to various substrates due to the difference of bonding strength of Au layer to PDMS mold and to the substrate. For effective transfer of Au layer, self-assembled monolayer, which has strong bonding to Au, is deposited on the substrate as a glue layer. In this study, complicated SAM layer coating process was replaced to simple UV/ozone treatment, which can activates the surface and form the –OH radicals. Using simple UV/ozone treatments on both Au and substrate, Au nano-pattern can be successfully transferred to as large as 6 in. diameter Si wafer, without SAM coating process. High fidelity transfer of Au nano-patterns to non-planar glass lens and flexible PET film was also demonstrated.