Use Of Self-assembled Monolayers Research Articles

Location-Selective Work Function Engineering by Self-Assembled Monolayers.

Control over specific interfaces in devices represents a key challenge for modern organic electronics and photovoltaics. Such control is frequently gained by the use of self-assembled monolayers (SAMs), which, by selection of a proper anchoring group, are generally discriminative with respect to different materials but are not selective between different areas of the same material. In particular, selective tailoring of the work function may be useful for different functional devices in a circuit. Here we demonstrate an approach for solving this problem, opening a way to function-selective electrostatic engineering of chemically identical areas, such as source and drain electrodes in a specific type of organic transistor and, more importantly, the electrodes in different types of organic devices, such as p- and n-channel transistors, located on the same circuitry board. The approach is based on the ultraviolet-light-promoted exchange reaction of SAMs on gold, a standard electrode material in organic electronics.

A modified Prussian blue biosensor with improved stability based on the use of self-assembled monolayers and polydopamine for quantitative L-glutamate detection.

Aminiature L-glutamate (L-Glu)biosensor is describedbased on Prussian blue (PB) modification with improved stability by using self-assembled monolayers (SAMs) technology and polydopamine (PDA). A gold microelectrode (AuME) was immersed in NH2(CH2)6SH-ethanol solution, forming well-defined SAMs via thiol-gold bonding chemistry which increased the number of deposited Prussian blue nanoparticles (PBNPs) and confined them tightly on the AuME surface. Then, dopamine solution was dropped onto the PBNPs surface and self-polymerized into PDA to protect the PB structure from destruction. The PDA/PB/SAMs/AuME showed improved stability through CV measurements in comparison with PB/AuME, PB/SAMs/AuME, and PDA/PB/AuME. The constructed biosensor achieved a high sensitivity of 70.683 nAµM-1cm-2 in the concentrationrange 1-476µM L-Gluwith a low LOD of 0.329µM and performed well in terms of selectivity, reproducibility, and stability. In addition, the developed biosensor was successfully applied to the determination of L-Glu in tomato juice, and the results were in good agreement with that of high-performance liquid chromatography (HPLC). Due to its excellent sensitivity, improved stability, and miniature volume, the developed biosensor not only has a promising potential for application in food sample analysis but also provides a good candidate for monitoring L-Glu level in food production.

Synthetic Chemistry and Microelectrode Arrays: Building Stable Platforms for Point of Care Diagnostics

Molecular diagnostics typically require three main components. A molecular interaction that identifies a specific target, a device that detects, quantifies, and records that interaction, and an interface between the two. The interface is critical because it provides a means to fix molecular recognition elements to the surface of the device. For a "point-of-care" application, the interface must be stable both in terms of chemistry and time while still allowing the signal from the molecular interaction to be sensed and recorded by the device. For the use of a microelectrode array as the detection device, construction of the interface must also allow for individual molecular recognition elements to be placed by individual, addressable electrodes in the array.Because of the need for stability and synthetic flexibility, we made the choice to move away from the use of self-assembled monolayers as the interface for developing microelectrode arrays as point-of-care devices. To that end, we have employed diblock copolymers to coat the surface of microelectrode arrays, a change that has offered increased stability of the surface and enabled the use of a broad array of synthetic methods for functionalizing the electrodes in the array. In this talk, we show how the use of a diblock copolymer in conjunction with Cu(I)- and Cu(II)-mediated reactions can be used to functionalize a microelectrode array with multiple DNA-aptamers for the multiplex detection of metabolites. The resulting surface is stable for over 30 weeks (and counting), allows for the detection of multiple metabolites in the same experiment, and retains the detection sensitivity obtained with a self-assembled monolayer.One of the goals of the talk will also be to illustrate for the synthetic community the role that it can play in developing new tools for molecular diagnostics. After all, it is the surface on a microelectrode array that in the long-run defines what an array can be used for and the quality of the resulting analytical experiments. The construction of those surfaces is a synthetic chemistry challenge that moving forward will require both new synthetic methods and new approaches for characterization of the products generated from the new methods. One approach for characterization will be discussed in the context of the Cu(I)- and Cu(II)-mediated reactions employed in the current study.

Self-Assembled Monolayers Derived from Positively Charged Adsorbates on Plasmonic Substrates for MicroRNA Delivery: A Review

MicroRNA (miRNA) has emerged as a promising alternative therapeutic treatment for cancer, but its delivery has been hindered by low cellular uptake and degradation during circulation. In this review, we discuss the various methods of delivering miRNA, including viral and non-viral delivery systems such as liposomes and nanoparticles. We also examine the use of nanoparticles for miRNA-based diagnostics. We focus specifically on non-viral delivery systems utilizing coinage metals in the form of nanoparticles and the use of self-assembled monolayers (SAMs) as a method of surface modification. We review the use of SAMs for the conjugation and delivery of small noncoding ribonucleic acid (ncRNA), particularly SAMs derived from positively charged adsorbates to generate charged surfaces that can interact electrostatically with negatively charged miRNA. We also discuss the effects of the cellular uptake of gold and other plasmonic nanoparticles, as well as the challenges associated with the degradation of oligonucleotides. Our review highlights the potential of SAM-based systems as versatile and robust tools for delivering miRNA and other RNAs in vitro and in vivo and the need for further research to address the challenges associated with miRNA delivery and diagnostics.

Effect of alkanethiol chain length on the oxidation resistance of self-assembled monolayer passivated Ge(100) surfaces

• The resistance to oxidation is dependent on the length of thiol chain • Oxidation resistance increases with increasing chain length. • Acceptable oxidation resistance down the C4 chain length. • Van der Waals interactions are significant for SAM stability. The use of self-assembled monolayers (SAMs) of heteroalkanes as passivation layers to protect against oxidation has been studied on a variety of materials. However, typically heteroalkanes with C8 and longer have been used, since the contributing van der Waals between the carbon chains is a significant stabilising force and the longer the chain the greater the force. The industry requirement for passivating semiconducting materials is that they remain oxide free for a queue time of 24 h. The remit of this study is to explore whether passivation using shorter chain alkanethiols, which would be beneficial for reducing carbon, will work to prevent re-oxidation over this time frame. A series of 1-alkanethiols, with chain lengths from C2 to C12 are used to create SAMs on Ge(100) and a study of the re-oxidation of the passivated Ge upon exposure to ambient conditions is undertaken in an effort to determine how chain length effects oxidation resistance of the passivated Ge. X-ray photoelectron spectroscopy is used, complimented by water contact angle measurements to show that the longer thiol molecules outperform their shorter-chain counterparts at inhibiting re-oxidation over 168 h of exposure to ambient. Nonetheless, Ge surfaces passivated by the short-chain thiols, down to C4, still display acceptable resistance to re-oxidation. Finally, a detailed summary of density functional theory simulations whereby the most stable SAM structures and coverages are explored.

Concept of Embedded Dipoles as a Versatile Tool for Surface Engineering.

ConspectusControlling the physical and chemical properties of surfaces and interfaces is of fundamental relevance in various areas of physical chemistry and a key issue of modern nanotechnology. A highly promising strategy for achieving that control is the use of self-assembled monolayers (SAMs), which are ordered arrays of rodlike molecules bound to the substrate by a suitable anchoring group and carrying a functional tail group at the other end of the molecular backbone. Besides various other applications, SAMs are frequently used in organic electronics for the electrostatic engineering of interfaces by controlling the interfacial level alignment. This is usually achieved by introducing a dipolar tail group at the SAM–semiconductor interface. Such an approach, however, also changes the chemical character of that interface, for example, affecting the growth of subsequent layers. A strategy for avoiding this complication is to embed polar groups into the backbones of the SAM-forming molecules. This allows disentangling electronic interface engineering and the nucleation of further layers, such that both can be optimized independently. This novel concept was successfully demonstrated for both aliphatic and aromatic SAMs on different application-relevant substrates, such as gold, silver, and indium tin oxide. Embedding, for example, ester and pyrimidine groups in different orientations into the backbones of the SAM-forming molecules results in significant work-function changes. These can then be fine-tuned over a wide energy range by growing mixed monolayers consisting of molecules with oppositely oriented polar groups. In such systems, the variation of the work function is accompanied by pronounced shifts of the peaks in X-ray photoelectron spectra, which demonstrates that electrostatically triggered core-level shifts can be as important as the well-established chemical shifts. This illustrates the potential of X-ray photoelectron spectroscopy (XPS) as a tool for probing the local electrostatic energy within monolayers and, in systems like the ones studied here, makes XPS a powerful tool for studying the composition and morphology of binary SAMs. All these experimental observations can be rationalized through simulations, which show that the assemblies of embedded dipolar groups introduce a potential discontinuity within the monolayer, shifting the energy levels above and below the dipoles relative to each other. In molecular and monolayer electronics, embedded-dipole SAMs can be used to control transition voltages and current rectification. In devices based on organic and 2D semiconductors, such as MoS2, they can reduce contact resistances by several orders of magnitude without adversely affecting film growth even on flexible substrates. By varying the orientation of the embedded dipolar moieties, it is also possible to build p- and n-type organic transistors using the same electrode materials (Au). The extensions of the embedded-dipole concept from hybrid interfaces to systems such as metal–organic frameworks is currently underway, which further underlines the high potential of this approach.

Enhancing Structural Properties and Performance of Graphene-Based Devices Using Self-Assembled HMDS Monolayers.

The performance of graphene devices is often limited by defects and impurities induced during device fabrication. Polymer residue left on the surface of graphene after photoresist processing can increase electron scattering and hinder electron transport. Furthermore, exposing graphene to plasma-based processing such as sputtering of metallization layers can increase the defect density in graphene and alter the device performance. Therefore, the preservation of the high-quality surface of graphene during thin-film deposition and device manufacturing is essential for many electronic applications. Here, we show that the use of self-assembled monolayers (SAMs) of hexamethyldisilazane (HMDS) as a buffer layer during the device fabrication of graphene can significantly reduce damage, improve the quality of graphene, and enhance device performance. The role of HMDS has been systematically investigated using surface analysis techniques and electrical measurements. The benefits of HMDS treatment include a significant reduction in defect density compared with as-treated graphene and more than a 2-fold reduction of contact resistance. This surface treatment is simple and offers a practical route for improving graphene device interfaces, which is important for the integration of graphene into functional devices such as electronics and sensor devices.

Reinforced Room-Temperature Spin Filtering in Chiral Paramagnetic Metallopeptides.

Chirality-induced spin selectivity (CISS), whereby helical molecules polarize the spin of electrical current, is an intriguing effect with potential applications in nanospintronics. In this nascent field, the study of the CISS effect using paramagnetic chiral molecules, which could introduce another degree of freedom in controlling the spin transport, remains so far unexplored. To address this challenge, herein we propose the use of self-assembled monolayers (SAMs) of helical lanthanide-binding peptides. To elucidate the effect of the paramagnetic nuclei, monolayers of the peptide coordinating paramagnetic or diamagnetic ions are prepared. By means of spin-dependent electrochemistry, the CISS effect is demonstrated by cyclic voltammetry and electrochemical impedance measurements for both samples. Additionally, an implementation of the standard liquid-metal drop electron transport setup has been carried out, and this process helped to demonstrate the peptides' suitability for solid-state devices. Remarkably, the inclusion of a paramagnetic center in the peptide increases the spin polarization as was independently proved by different techniques. These findings permit the inclusion of magnetic biomolecules in the CISS field and pave the way to their implementation in a new generation of (bio)spintronic nanodevices.

Effect of Octadecylamine Surfactant on DNA Interactions with Graphene Surfaces.

Understanding of how to integrate DNA molecules with graphene materials is important for the development of biosensors and biomolecular logic circuits. For some of these applications, controlling DNA structural conformation on the graphene substrate is critically important and can be achieved through the use of self-assembled monolayers. Here, we performed all-atom molecular dynamics simulations to understand how various 1-octadecylamine (ODA) coatings of the graphene surface affect the conformation of double-stranded DNA (dsDNA) on the surface. The simulation results demonstrated that dsDNA structures become more stable as ODA concentration increases due to the formation of DNA-ODA hydrogen bonds and reduction of DNA-surface interactions, which aid in retaining internal DNA interactions. Specifically, the interaction of ODA molecules with DNA prevents nucleobases from forming π-π stacking interactions with the surface. Some dsDNA conformations, such as sharp kinks or unwinding, can occur more frequently in DNA with A-T sequences due to weaker pairing interactions than with G-C sequences. Furthermore, our results conclude that both DNA sequence and ODA concentration play an essential role in experimentally observed conformational changes of DNA on the graphene surface.

Self-assembled Zn phthalocyanine as a robust p-type selective contact in perovskite solar cells.

The use of self-assembled monolayers (SAMs) as selective charge extracting layers in perovskite solar cells is a great approach to replace the commonly used charge selective contacts, as they can easily modify the interface to enhance the final solar cell performance. Here, we report a novel synthetic approach of the commonly known zinc phtalocyanine (ZnPc) molecule TT1, widely employed in dye-sensitized solar cells and previously used in perovskite solar cells. TT1 is used as a p-type selective contact, and it demonstrates its ability to form SAM on top of the indium tin oxide (ITO) transparent electrode, obtaining higher efficiencies compared to Pedot:PSS based perovskite solar cells. The differences observed, with an enhanced open-circuit voltage and overall efficiency in TT1 devices are correlated with differences in energetics rather than recombination kinetics.

Profiling Protein Tyrosine Phosphatase Specificity with Self-Assembled Monolayers for Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry and Peptide Arrays.

The opposing activities of phosphatases and kinases determine the phosphorylation status of proteins, yet kinases have received disproportionate attention in studies of cellular processes, with the roles of phosphatases remaining less understood. This Research Article describes the use of phosphotyrosine-containing peptide arrays together with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to directly profile phosphatase substrate selectivities. Twenty-two protein tyrosine phosphatases were characterized with the arrays to give a profile of their specificities. An analysis of the data revealed that certain residues in the substrates had a conserved effect on activity for all enzymes tested, including the general rule that inclusion of a basic lysine or arginine residue on either side of the phosphotyrosine decreased activity. This insight also provides a new perspective on the role of a R1152Q mutant in the insulin receptor, which is known to exhibit a lower phosphorylation level and which this work suggests may be due to an increased activity toward phosphatase enzymes. The use of self-assembled monolayers for matrix-assisted laser desorption/ionization mass spectrometry (SAMDI-MS) to provide a rapid and quantitative assay of phosphatase enzymes will be important to gaining a more complete understanding of the biochemistry and biology of this important enzyme class.

(Invited) PEALD and ALE for Area Selective Deposition

Advanced CMOS scaling relies on novel structure and design, as well as material developments, which leads to challenging integration issues. Innovation in gap filling technologies, area selective deposition (ASD) and etch processes should help in reaching this scaling specification. Criteria for an adequate area selective deposition process are: growth only on specific regions, high throughput compatible with industrial demands and no so-called mushroom profiles into adjacent features. Several approaches are currently being investigated for the development of ASD processes, among which ASD by surface deactivation with the use of self-assembled monolayers (SAM) or block copolymers, processing temperatures promoting inherent selectivity, and spatial ALD or selective ALD based on ABC-type cycles [1-3]. The original approach developed in our group consists in taking benefit from an in situ etching step inserted in a standard ALD cycle [4, 5]: this so-called deposition/etch approach is already being used for Si epitaxy by the incorporation of HCl in the gas phase. In this presentation, a short introduction on challenges and opportunities for ASD in high volume manufacturing will be presented. A brief state of the art of ASD strategies with their inherent pros and cons will be provided, to open up a discussion on different deposition/etch approaches for Area Selective Deposition, as illustrated in the figure 1. This figure highlights the benefits of developing isotropic as well as anisotropic etching for ASD. Indeed, isotropic plasma etching relies mainly on radical (ie chemical) etching, whereas anisotropic etching can be induced by an appropriate Ion etching process or plasma Atomic Layer Etching (ALE) development. The PEALD/ALE strategy entails a precise energy control of ions flowing from the plasma onto the substrate (with an energy range between 0 and 50 eV). Therefore, a specific design must be conceived for PEALD tool, consistent with this issue. In our work, a low power RF biasing waveform has been applied to the substrate holder in the Flexal deposition tool from Oxford Instruments. Benefits and drawbacks of this deposition/etch approach will be discussed in terms of throughput, etching impact (contamination, roughness…) and process drift. Finally, two examples will be given illustrating a versatile route for topographically selective deposition, either on sidewalls, as needed for spacer fabrication, [6] or on top and bottom of trenches only. This second example will be discussed in regards of surface selective deposition of dielectrics on metal. [1] A. J. M. Mackus et al, Chem. Mater. 31 (2019) 2-12 [2] G. N. Parsons, J. Vac. Sci. Technol. A 37 (2019) 020911 [3] R. Chen, H. Kim, P. C. McIntyre, and S. F. Bent, Appl. Phys. Lett. 84 (2004) 4017 [4] R. Vallat et al, J. Vac. Sci. Technol. A 35 (2017) 01B104 [5] R. Vallat et al, J. Vac. Sci. Technol. A 37 (2019) 020918 [6] A. Chaker et al, Appl. Phys. Lett. 114 (2019) Figure 1

Mimicking the endothelial glycocalyx through the supramolecular presentation of hyaluronan on patterned surfaces.

The glycocalyx is the immediate pericellular matrix that surrounds many cell types, including endothelial cells (ECs), and is typically composed of glycans (glycosaminoglycans, proteoglycans, and glycoproteins). The endothelial glycocalyx is rich in hyaluronic acid (HA), which plays an important role in the maintenance of vascular integrity, although fundamental questions about the precise molecular regulation mechanisms remain unanswered. Here, we investigate the contribution of HA to the regulation of endothelial function using model surfaces. The peptide sequence GAHWQFNALTVR, previously identified by phage display with strong binding affinity for HA and named Pep-1, was thiolated at the N-terminal to form self-assembled monolayers (SAMs) on gold (Au) substrates, and microcontact printing (μCP) was used to develop patterned surfaces for the controlled spatial presentation of HA. Acetylated Pep-1 and a scrambled sequence of Pep-1 were used as controls. The SAMs and HA-coated surfaces were characterized by X-ray photoelectron spectroscopy (XPS), contact angle measurements, and quartz crystal microbalance with dissipation (QCM-D) monitoring, which confirmed the binding and presence of thiolated peptides on the Au surfaces and the deposition of HA. Fluorescence microscopy showed the localization of fluorescently labelled HA only on areas printed with Pep-1 SAMs. Cell culture studies demonstrated that low molecular weight HA improved the adhesion of human umbilical vein endothelial cells (HUVECs) to the substrate and also stimulated their migration. This research provides insight into the use of SAMs for the controlled presentation of HA with defined size in cultures of HUVECs to study their functions.

Peptide Arrays: Development and Application.

This review identifies the important approaches to peptide arrays and discusses the various technical options that must be considered. Of the five important approaches that are now practiced and commercially available, it is clear that no single approach offers advantages for all applications. Instead, the variations of peptide arrays enable the study of a wide range of applications. For example, the approaches based on in situ synthesis can prepare the highest density arrays and do so at relatively low reagent costs (though with varying expense in the synthesis hardware). The approaches that prepare arrays by immobilizing presynthesized peptides have the primary benefits of compatibility with a broader range of surface chemistries (that may not be sufficiently stable toward the conditions for in situ synthesis). The use of self-assembled monolayers, for example, brings the important benefits of chemistries that prevent the nonspecific adsorption of protein, give excellent control over the densities of peptides in the array, and are uniquely compatible with the use of SAMDI mass spectrometry to perform a broad range of label-free assays.

Biosensor Experiments in Undergraduate Laboratories

This talk will describe a junior/senior level undergraduate laboratory for analytical or physical chemistry that can be used to demonstrate the use of self-assembled monolayers (SAM) to produce biosensors. The laboratory has the students form SAMs on the surface of the electrode and then examine how they pack onto a surface. The laboratory experiment will also introduce students to electrochemical techniques, instrumentation and surface analysis techniques. This experiment uses both chronocoulometry to determine the surface area of an electrode as well as using reductive desorption to determine the surface coverage and packing of the SAM. Use of these SAM modified electrodes as biosenors is also discussed.

Selective Ru ALD as a Catalyst for Sub-Seven-Nanometer Bottom-Up Metal Interconnects

Integrating bottom-up area-selective building-blocks in microelectronics has a disruptive potential because of the unique capability of engineering new structures and architectures. Atomic layer deposition (ALD) is an enabling technology, yet understanding the surfaces and their modification is crucial to leverage area-selective ALD (AS-ALD) in this field. The understanding of general selectivity mechanisms and the compatibility of plasma surface modifications with existing materials and processes, both at research and production scale, will greatly facilitate AS-ALD integration in microelectronics. The use of self-assembled monolayers to inhibit the nucleation and growth of ALD films is still scarcely compatible with nanofabrication because of defectivity and downscaling limitations. Alternatively, in this Research Article, we demonstrate a straightforward H2 plasma surface modification process capable of inhibiting Ru ALD nucleation on an amorphous carbon surface while still allowing instantaneous nucleation and linear growth on Si-containing materials. Furthermore, we demonstrate how AS-ALD enables previously inaccessible routes, such as bottom-up electroless metal deposition in a dual damascene etch-damage free low-k replacement scheme. Specifically, our approach offers a general strategy for scalable ultrafine 3D nanostructures without the burden of subtractive metal patterning and high cost chemical mechanical planarization processes.

Development and validation of a maleimide-based enzyme-linked immunosorbent assay for the detection of tetrodotoxin in oysters and mussels

The recent detection of tetrodotoxins (TTXs) in puffer fish and shellfish in Europe highlights the necessity to monitor the levels of TTXs in seafood by rapid, specific, sensitive and reliable methods in order to protect human consumers. A previous immunoassay for TTX detection in puffer fish, based on the use of self-assembled monolayers (SAMs) for the immobilization of TTX on maleimide plates (mELISA), has been modified and adapted to the analysis of oyster and mussel samples. Changing dithiol for cysteamine-based SAMs enabled reductions in the assay time and cost, while maintaining the sensitivity of the assay. The mELISA showed high selectivity for TTX since the antibody did not cross-react with co-occurring paralytic shellfish poisoning (PSP) toxins and no interferences were observed from arginine (Arg). Moreover, TTX-coated maleimide plates stored for 3 months at −20°C and 4°C were stable, thus when pre-prepared, the time to perform the assay is reduced. When analyzing shellfish samples, matrix effects and toxin recovery values strongly depended on the shellfish type and the sample treatment. Blank oyster extracts could be directly analyzed without solid-phase extraction (SPE) clean-up, whereas blank mussel extracts showed strong matrix effects and SPE and subsequent solvent evaporation were required for removal. However, the SPE clean-up and evaporation resulted in toxin loss. Toxin recovery values were taken as correction factors (CFs) and were applied to the quantification of TTX contents in the analysis of naturally-contaminated shellfish samples by mELISA. The lowest effective limits of detection (eLODs) were about 20 and 50µg/kg for oyster extracts without and with SPE clean-up, respectively, and about 30µg/kg for mussel extracts with both protocols, all of them substantially below the eLOD attained in the previous mELISA for puffer fish (230µg/kg). Analysis of naturally-contaminated samples by mELISA and comparison with LC-MS/MS quantifications demonstrated the viability of the approach. This mELISA is a selective and sensitive tool for the rapid detection of TTX in oyster and mussel samples showing promise to be implemented in routine monitoring programs to protect human health.

Correcting defects in area selective molecular layer deposition

Area selective deposition, as used with atomic layer deposition and molecular layer deposition (MLD), is a rapidly emerging field of study due to its potential applications in micro- and nanoelectronic devices. Previous studies have shown successful area selective MLD of nanoscale organic thin films using self-assembled monolayers (SAMs) as blocking layers. In this report, the authors expand upon the use of SAMs by implementing an etching process for the removal of the SAM resist once the MLD film has been deposited. This process has the benefit of removing unwanted deposits, which improves MLD selectivity on a dielectric by 380-fold over using a SAM layer alone and enables twice the amount of polymer film to be selectively deposited compared to that in previous reports. Although the etching leaves intact the polymer film in unblocked regions, the clean removal of the polymer film is limited at pattern interfaces. This effect is attributed to intermolecular interactions, such as polymer entanglement and hydrogen bonding between the chains.

Use of self-assembled monolayers for selective metal removal and ultrathin gate dielectrics in MoS2 field-effect transistors

We demonstrate a simple and rapid method for the fabrication of multilayer molybdenum disulfide (MoS2) field-effect transistors (FETs) by exploiting various functions of an octadecylphosphonic acid (ODPA)-based self-assembled monolayer (SAM). The SAM is used both for selective metal removal in patterning to simplify the fabrication process and as an ultrathin gate dielectrics in the device. The low voltage operation of the MoS2 FETs was observed with a low gate leakage current and small hysteresis. In addition, selective metal removal can effectively narrow the spacing between the gate and contact electrodes, resulting in improved device characteristics. This approach also makes it possible to transfer thinner and smaller MoS2 flakes. This study suggests intriguing applications of the SAM for the fabrication of functional electronic devices.

Self-Assembled Monolayers as Patterning Tool for Organic Electronic Devices.

The patterning of functional materials represents a crucial step for the implementation of organic semiconducting materials into functional devices. Classical patterning techniques such as photolithography or shadow masking exhibit certain limitations in terms of choice of materials, processing techniques and feasibility for large area fabrication. The use of self-assembled monolayers (SAMs) as a patterning tool offers a wide variety of opportunities, from the region-selective deposition of active components to guiding the crystallization direction. Here, we discuss general techniques and mechanisms for SAM-based patterning and show that all necessary components for organic electronic devices, i.e., conducting materials, dielectrics, organic semiconductors, and further functional layers can be patterned with the use of self-assembled monolayers. The advantages and limitations, and potential further applications of patterning approaches based on self-assembled monolayers are critically discussed.