Silane Self-assembled Monolayers Research Articles

Fluorinated silane self-assembled monolayer modification of V2O5 for enhanced hole injection and device efficiency

This study introduces a new approach to enhance hole injection in organic light-emitting diodes (OLEDs) by modifying the energy band alignment. This enhancement is achieved by incorporating gap states near the Fermi level through the application of a 1H,1H,2H,2H-perfluorooctyltriethoxysilane self-assembled monolayer (F8SAM) coating on V2O5. Compared to thermally evaporated V2O5, the F8SAM coating induces greater oxygen deficiency, reducing the V2O5 (V5+) content from 84.2 % to 76.9 % and increasing the VO2 (V4+) content from 15.7 % to 23.0 %. This modification causes both the highest occupied molecular orbital and gap state levels to move closer to the Fermi level, facilitated by increased oxygen vacancies, high carrier concentration, and delocalized free electrons. The alteration in the gap state provides a more accessible pathway for efficient hole injection, as confirmed in optoelectronic green light devices, which demonstrate a wavelength of 530 ± 5 nm. Significantly, devices incorporating a double-layer hole-injection layer exhibit a 5-fold increase in maximum luminance, a 1.6-fold increase in current efficiency, and a 1.7-fold increase in power efficiency compared to devices with an unmodified V2O5 film. The enhanced performance is attributed to the well-aligned F8SAM on V2O5, which increases the density of hole states and thereby improves device performance. This study demonstrates a practical method for modulating the cation valence state of V2O5, offering a pathway toward improved hole injection and, consequently, more efficient and functional OLED devices.

A healable amino silane self-assembled monolayer incorporating polymer capped palladium nanoclusters and its application as the copper diffusion barrier layer on silicon wafer

Self-assembled monolayers (SAMs) with short organic chains terminated with specific functional groups are attractive for modifying surface properties for a variety of applications, including being a copper diffusion barrier layer on Si wafer. However, SAM formation is process-sensitive and ideal SAM is difficult to obtain, both of which need to carefully deal with before practical use. Herein we developed a system to achieve seamless electroless deposited copper (ELD Cu) film on an amino-terminated silane SAM modified Si wafer with the help of a bifunctional polyvinyl alcohol-capped Pd nanocluster (PVA-Pd) catalyst. The PVA-Pd acts as a catalyst for ELD Cu as well as a healing agent to fix defects of the amino silane SAM. The sheet resistance, cross-sectional morphology analysis and adhesion of ELD Cu on the Si wafer are extensively studied. By controlling the abundancy of PVA in PVA-Pd, the diffusion barrier property of a flawed amino-terminated silane SAM remains reliably effective even after a 500 °C rapid thermal annealing (RTA), evidencing the superior healing function of PVA. The whole thickness of the PVA-Pd/amino-terminated silane SAM before and after RTA is 〜6 nm and 〜2 nm, respectively, which is applicable for advanced microelectronic manufacturing.

Simultaneous Enhancement of Efficiency and Operational-Stability of Mesoscopic Perovskite Solar Cells via Interfacial Toughening.

The combined effects of compact TiO2 (c-TiO2 ) electron-transport layer (ETL) are investigated without and with mesoscopic TiO2 (m-TiO2 ) on top, and without and with an iodine-terminated silane self-assembled monolayer (SAM), on the mechanical behavior, opto-electronic properties, photovoltaic (PV) performance, and operational-stability of solar cells based on metal-halide perovskites (MHPs). The interfacial toughness increases almost threefold in going from c-TiO2 without SAM to m-TiO2 with SAM. This is attributed to the synergistic effect of the m-TiO2 /MHP nanocomposite at the interface and the enhanced adhesion afforded by the iodine-terminated silane SAM. The combination of m-TiO2 and SAM also offers a significant beneficial effect on the photocarriers extraction at the ETL/MHP interface, resulting in perovskite solar cells (PSCs) with power-conversion efficiency (PCE) of over 24% and 20% for 0.1 and 1cm2 active areas, respectively. These PSCs also have exceptionally long operational-stability lives: extrapolated T80 (duration at 80% initial PCE retained) is ≈18000 and 10000h for 0.1 and 1cm2 active areas, respectively. Postmortem characterization and analyses of the operational-stability-tested PSCs are performed to elucidate the possible mechanisms responsible for the long operational-stability.

Nanoplasmonic Au:CuO thin films functionalized with APTES to enhance the sensitivity of gas sensors

Carbon monoxide (CO) is a highly flammable and toxic gas to humans and animals, that’s why its detection and monitoring are crucial. A promising technique to develop a robust and cheap gas sensor, operating at room temperature, is Localized Surface Plasmon Resonance (LSPR) sensing. However, LSPR sensing of inorganic gas molecules, such as CO, is challenging due to their extremely small differences in refractive indices. In this work, a nanoplasmonic thin film, composed of Au NPs semi-embedded in a CuO matrix (Au:CuO) was functionalized with a silane self-assembled monolayer (APTES molecule) that enhanced the sensitivity of the film to a mixture of CO (50 ppm) in Argon. Three different concentrations of APTES (0.1 %, 1.0 %, and 5.0 %) were silanized on Au:CuO thin film surface, and all the functionalized Au:CuO thin films showed better sensing results than bare Au:CuO thin film. The functionalized Au:CuO thin film with 0.1 % of APTES revealed the best sensing characteristics. Its sensitivity was almost 3 times higher than that of the unmodified Au:CuO thin film. Au:CuO thin films functionalized with APTES are potentially relevant to developing sensitive and selective LSPR sensors for the detection of inorganic gases such as CO, in harsh environments.

Scaffold-Enforced Nanoscale Crystalline Order Supersedes Interfacial Interactions in Driving CsPbI3 Perovskite Phase Stability

The equilibrium phase of cesium lead iodide (CsPbI3) is a high-density, low-symmetry, yellow crystalline solid below 320 °C, above which it transitions to the optoelectronically functional, black, perovskite phase. Several reports have achieved lowered phase transition temperatures and increased metastability of perovskite-phase CsPbI3 and attributed the effect variably to reduced size, surface-induced strain, and/or external additives. While theory supports that both reduced size and substrate-induced strain can tilt the competition between surface and bulk energies to favor the perovskite phase, there has not been a study of the relative influence of size and interfacial interactions on these dynamics. In this study, we selectively varied crystalline domain size by embedding CsPbI3 in open nanoporous titania scaffolds composed of particles ranging from 20 to 200 nm and measured the influence on phase transition behavior. We modified the surface of the scaffold using polar, ionizable, and nonpolar silane self-assembled monolayers (SAMs) to systematically test the extent to which the chemical identity of the interface impacts the surface energy contribution to the phase stability in the perovskite-scaffold composite. While structural and functional consequences were observed for different interfacial chemistries, there was no significant influence on phase equilibrium, and the disruption of long-range crystalline order alone was found to be sufficient to depress the phase transition temperature by more than 250 °C compared to bulk.

Bottom gate top contact organic transistors using thiophene and furan flanked diketopyrrolopyrrole polymers and its comparative study

Herein, two donor–acceptor conjugated polymers based on dithieno[3,2-b:2′,3′-d]thiophene (DTT) and thiophene-flanked diketopyrrolopyrrole (DPP) or furan-flanked DPP, namely PDPPT-DTT and PDPPF-DTT were synthesised, characterised and evaluated for their electrical performance in transistor devices for comparison. The influence of the heteroatoms (thiophene and furan) flanked DPP on their thermal, optical, electronic structure and charge carrier transport properties were investigated. The absorption spectra of polymer PDPPT-DTT are broader and red-shifted (26–30 nm) compared with that of polymer PDPPF-DTT, indicating the resonance energy of thiophene is greater than furan, which may allow for different electron localization and result in the difference of optical properties. In addition, energy levels of polymers were slightly affected by the aromatic remote end-groups (thiophene to furan) in DPP-based molecule. Hole transport properties of copolymers were investigated by fabricating the field-effect transistors in the bottom gate top contact (BGTC) configurations for three different self-assembled monolayers (SAMs)/gate dielectric interfaces and different annealing temperatures of polymeric active layer. The BGTC organic thin film transistor (OFET) devices having PDPPT-DTT and PDPPF-DTT thin film annealed at 200 °C exhibit the hole mobility of 0.18 and 0.20 cm2 V−1 s−1, respectively. The OFET devices with trichloro(octyl)silane SAM, fabricated and characterized in ambient environment (temperature ∼25 °C, humidity ∼50%), were found to retain 90% of their performance up to 1000 h.

Can solid surface energy be a predictor of ice nucleation ability?

Surface energy is one of the most important properties of materials that dictate many behaviors such as the spreading of water and ice nucleation. It is commonly thought that low surface energy leads to hydrophobicity and delays ice formation. Conventional studies mainly focus on rough surfaces where surface energy is amplified/reduced accordingly and it remains elusive to clearly decouple the effect of surface energy on ice nucleation. Here we experimentally construct the atomically smooth surfaces of halogen chemistry by varying silane self-assembled monolayers with exactly the same aliphatic chain but varied end groups of F, Cl, Br and I. By analyzing ice nucleation rate and free energy barrier based on the measured freezing temperature/delay time and the classical nucleation theory, we demonstrate that the ice nucleation efficiencies of various halogen chemistry surfaces increase in the order of Br, F, I and Cl, which is inconsistent with the surface energy sequence. The results indicate that solid surface energy is not a secure predictor of ice nucleation ability. By further analyzing the surface potentials of different halogen chemistry surfaces, we find that surface polarity plays a key role in ice nucleation maybe through impacting the orientation of interfacial water.

Controlling surface effects in extremely high aspect ratio gold plasmonic electrodes

Nanofabrication is key to many technological advances, especially the challenge of merging nanophotonics with electronics. Here, we investigate the fabrication process of plasmonic interdigitated gold electrodes having a very high aspect ratio (i.e. long and thin geometries) and a large surface area. Stringent stability issues that arise when these structures are fabricated using inorganic adhesion layers, such as titanium or chromium, on silica substrates are highlighted. We ascribe these problems to thermodynamical non-equilibrium states of freshly deposited gold and, in particular, discuss the role of surface energy in determining the structural properties of high aspect ratio gold nanostructures. We then show that the use of organic silane self-assembled monolayers improves the long term stability of these structures and, finally, characterize the fabricated electrodes. This technology can unleash the potential of hybrid optoelectronic circuits where current and light are manipulated with the same component.

Robust silane self-assembled monolayer coatings on plasma-engineered copper surfaces promoting dropwise condensation

Dropwise condensation is well known to result in better heat transfer performance owing to efficient condensate/droplet removal, which can be harnessed in various industrial heat/mass transfer applications such as power generation and conversion, water harvesting/desalination, and electronics thermal management. The key to enhancing condensation via the dropwise mode is thin low surface energy coatings (<100 nm) with low contact angle hysteresis. Ultrathin (<5 nm) silane self-assembled monolayers (or SAMs) have been widely studied to promote dropwise condensation due to their minimal thermal resistance and scalable integration processes. Such thin coatings typically degrade within an hour during condensation of water vapor. After coating failure, water vapor condensation transitions to the inefficient filmwise mode with poor heat transfer performance. We enhance silane SAM quality and durability during water vapor condensation on copper compared to state-of-the-art silane coatings on metal surfaces. We achieve this via (i) surface polishing to sub-10 nm levels, (ii) pure oxygen plasma surface treatment, and (iii) silane coating integration with the copper substrate in an anhydrous/moisture-free environment. The resulting silane SAM has low contact angle hysteresis (≈20°) and promotes efficient dropwise condensation of water for >360 hours without any visible sign of coating failure/degradation in the absence of non-condensable gases. We further demonstrate enhanced heat transfer performance (≈5-7× increase over filmwise condensation) over an extended period of time. Surface characterization data post-condensation leads us to propose that in the absence of non-condensable gases in the vapor environment, the silane SAM degrades due to reduction and subsequent dissolution of copper oxide at the oligomer-substrate interface. The experiments also indicate that the magnitude of surface subcooling (or condensation rate) affects the rate of coating degradation. This work identifies a pathway to durable dropwise promoter coatings that will enable efficient heat transfer in industrial applications.

Elucidating the Mechanism of Condensation-Mediated Degradation of Organofunctional Silane Self-Assembled Monolayer Coatings.

Dropwise condensation is favorable for numerous industrial and heat/mass transfer applications due to the enhanced heat transfer performance that results from efficient condensate removal. Organofunctional silane self-assembled monolayer (SAM) coatings are one of the most common ultrathin low surface energy materials used to promote dropwise condensation of water vapors because of their minimal thermal resistance and scalable synthesis process. These SAM coatings typically degrade (i.e., condensation transitions from the efficient dropwise mode to the inefficient filmwise mode) rapidly during water vapor condensation. More importantly, the condensation-mediated coating degradation/failure mechanism(s) remain unknown and/or unproven. In this work, we develop a mechanistic understanding of water vapor condensation-mediated organofunctional silane SAM coating degradation and validate our hypothesis through controlled coating synthesis procedures on silicon/silicon dioxide substrates. We further demonstrate that a pristine organofunctional silane SAM coating resulting from a water/moisture-free coating environment exhibits superior long-term robustness during water vapor condensation. Our molecular/nanoscale surface characterizations, pre- and post-condensation heat transfer testing, indicate that the presence of moisture in the coating environment leads to uncoated regions of the substrate that act as nucleation sites for coating degradation. By elucidating the reasons for formation of these degradation nuclei and demonstrating a method to suppress such defects, this study provides new insight into why low surface energy silane SAM coatings degrade during water vapor condensation. The proposed approach addresses a key bottleneck (i.e., coating failure) preventing the adoption of efficient dropwise condensation methods in industry, and it will facilitate enhanced phase-change heat transfer technologies in industrial applications.

Hydrophobic/Oleophilic Structures Based on MacroPorous Silicon: Effect of Topography and Fluoroalkyl Silane Functionalization on Wettability.

The effect of the morphology and chemical composition of a surface on the wettability of porous silicon structures is analyzed in the present work. Hydrophobic and superhydrophobic macroporous substrates are attractive for different potential applications. Herein, different hydrophobic macroporous silicon structures were fabricated by the chemical etching of p-type silicon wafers in a solution based on hydrofluoric acid and coated with a fluoro silane self-assembled monolayer. The surface morphology of the final substrate was characterized using a scanning electron microscope. The wettability was assessed from contact angle measurements using water and organic solvents that present low surface energy. The experimental data were compared with the classical wetting states theoretical models described in the literature. Perfluoro-silane functionalized macroporous silicon surfaces presented systematically higher contact angles than untreated silicon substrates. The influence of porosity on the surface wettability of macoporous silicon structures has been established. These results suggest that the combination of etching conditions with a surface chemistry modification could lead to hydrophobic/oleophilic or superhydrophobic/oleophobic structures.

Robust Silane Self-Assembled Monolayer Coatings on Plasma-Engineered Copper Surfaces Promoting Dropwise Condensation

Robust Silane Self-Assembled Monolayer Coatings on Plasma-Engineered Copper Surfaces Promoting Dropwise Condensation

Functional Microarray Platform with Self-Assembled Monolayers on 3C-Silicon Carbide.

Currently available bioplatforms such as microarrays and surface plasmon resonators are unable to combine high-throughput multiplexing with label-free detection. As such, emerging microelectromechanical systems (MEMS) and microplasmonics platforms offer the potential for high-resolution, high-throughput label-free sensing of biological and chemical analytes. Therefore, the search for materials capable of combining multiplexing and label-free quantitation is of great significance. Recently, interest in silicon carbide (SiC) as a suitable material in numerous biomedical applications has increased due to its well-explored chemical inertness, mechanical strength, bio- and hemocompatibility, and the presence of carbon that enables the transfer-free growth of graphene. SiC is also multifunctional as both a wide-band-gap semiconductor and an efficient low-loss plasmonics material and thus is ideal for augmenting current biotransducers in biosensors. Additionally, the cubic variant, 3C-SiC, is an extremely promising material for MEMS, being a suitable platform for the easy micromachining of microcantilevers, and as such capable of realizing the potential of real time miniaturized multiplexed assays. The generation of an appropriately functionalized and versatile organic monolayer suitable for the immobilization of biomolecules is therefore critical to explore label-free, multiplexed quantitation of biological interactions on SiC. Herein, we address the use of various silane self-assembled monolayers (SAMs) for the covalent functionalization of monocrystalline 3C-SiC films as a novel platform for the generation of functionalized microarray surfaces using high-throughput glycan arrays as the model system. We also demonstrate the ability to robotically print high throughput arrays on free-standing SiC microstructures. The implementation of a SiC-based label-free glycan array will provide a proof of principle that could be extended to the immobilization of other biomolecules in a similar SiC-based array format, thus making potentially significant advances to the way biological interactions are studied.

Leak-free integrated microfluidic channel fabrication for surface plasmon resonance applications

In this paper, we describe a novel fabrication method of a microfluidic integrated surface plasmon resonance (SPR) gold chip based on a (3-mercaptopropyl) trimethoxy silane (MPTMS) self-assembled monolayer. This monolayer was formed at the surface of a microfluidic chip made of polydimethylsiloxane (PDMS). Its presence was confirmed by contact angle and Fourier transform infrared spectroscopy measurements on the modified PDMS surface. A basic, but nevertheless appropriate, 4-channel microfluidic system was made on PDMS and reported on a gold SPR sensor. Sealing tests were carried-out by injecting continuous flows of solutions under gradient pressure up to 1.8 bar. Bonding strength of chemical and corona binding were measured and compared. The test of the integrated microfluidic SPR sensor on an SPR bench validated its functionality and proved as well that no leakage is observed between the different microfluidic channels.

Impact of Silane Monolayers on the Adsorption of Streptavidin on Silica and Its Subsequent Interactions with Biotin: Molecular Dynamics and Steered Molecular Dynamics Simulations.

Protein adsorption on surfaces is used in analytical tools as an immobilization mean to trap the analyte to be detected. However, protein adsorption can lead to a conformational change in the protein structure, resulting in a loss of bioactivity. Here, we study adsorption of a streptavidin-biotin complex on amorphous SiO2 surfaces functionalized with five different silane self-assembled monolayers by all-atom molecular dynamics simulations. We find that the streptavidin global conformational change, as well as the nature of residues with high mobility, depends on the alkyl chain length and head-group charge of silane molecules. Effects on interactions with biotin are further investigated by steered molecular dynamics (SMD) simulations, which mimics atomic force microscopy (AFM) with the biotin attached on the tip. We show the combined effects of adsorption-induced global conformational changes and of the position of residues with high mobility on the streptavidin-biotin rupture force. By comparing our results to experimental and SMD rupture forces obtained in water, without any surface, we conclude that silane with uncharged and short alkyl chains allows streptavidin immobilization, while keeping biotin interactions better than silanes with long alkyl chains or charged head groups.

Superhydrophobic Self-Assembled Silane Monolayers on Hierarchical 6082 Aluminum Alloy for Anti-Corrosion Applications

In this work, a two-stage methodology to design super-hydrophobic surfaces was proposed. The first step consists of creating a rough nano/micro-structure and the second step consists of reducing the surface energy using octadecyltrimethoxysilane. The surface roughening was realized by three different short-term pretreatments: (i) Boiling water, (ii) HNO3/HCl etching, or (iii) HF/HCl etching. Then, the surface energy was reduced by dip-coating in diluted solution of octadecyltrimethoxysilane to allow the formation of self-assembled silane monolayers on a 6082-T6 aluminum alloy surface. Super-hydrophobic aluminum surfaces were investigated by SEM-EDS, FTIR, profilometry, and contact and sliding angles measurements. The resulting surface morphologies by the three approaches were structured by a dual hierarchical nano/micro-roughness. The surface wettability varied with the applied roughening pretreatment. In particular, an extremely high water contact angle (around 180°) and low sliding angle (0°) were evidenced for the HF/HCl-etched silanized surface. The results of electrochemical tests demonstrate a remarkable enhancement of the aluminum alloy corrosion resistance through the proposed superhydrophobic surface modifications. Thus, the obtained results evidenced that the anti-wetting behavior of the aluminum surface can be optimized by coupling an appropriate roughening pretreatment with a self-assembled silane monolayer deposition (to reduce surface energy) for anticorrosion application.

Silver Electroless Finishing of Selective Laser Melting 3D-Printed AlSi10Mg Artifacts

Additive manufactured selective laser melting (AM-SLM) parts often need post-printing coatings. The current research presents a method for surface finishing of AM-SLM AlSi10Mg parts coated by electroless silver plating. Such coating can be applied as a decorative film on printed replicas of antique artifacts. For this purpose, silver was deposited for the first time on AlSi10Mg printed disk-shaped specimens and coins, making their appearance close to the original artifact. The silver was plated with and without adhesion-promoting silane self-assembled monolayers. Dimensions and mass measurements, pilling test, light microscopy, optical profilometer, SEM–EDS examination, XRD analysis, and FIB-SEM technique were applied to characterize the coated samples. The results displayed good silver quality with a satisfactory appearance. The roughness of the plated samples was slightly reduced as the thickness of the silver layer was increased. The developed coating can be adapted for different applications, including printed replicas of coins in museum exhibitions.

Monolayer Arrays of Nanoparticles on Block Copolymer Brush Films.

Two-dimensional arrays of nanoparticles (NPs) have widespread applications in optical coatings, plasmonic sensors, and nanocomposites. Current bottom-up approaches that use homogeneous NP templates, such as silane self-assembled monolayers or homopolymers, are typically plagued by NP aggregation, whereas patterned block copolymer (BCP) films require specific compositions for specific NP distributions. Here, we show, using polystyrene- b-poly(4-vinylpyridine) (PS- b-P4VP) and gold NPs (AuNPs) of various sizes, that a nanothin PS- b-P4VP brushlike coating (comprised of a P4VP wetting layer and a PS overlayer), which is adsorbed onto flat substrates during their immersion in very dilute PS- b-P4VP tetrahydrofuran solutions, provides an excellent template for obtaining dense and well-dispersed AuNPs with little aggregation. These non-close-packed arrays have similar characteristics regardless of immersion time in solution (about 10-120 s studied), solution concentration below a critical value (0.1 and 0.05 mg/mL studied), and AuNP diameter (10-90 nm studied). Very dilute BCP solutions are necessary to avoid deposition, during substrate withdrawal, of additional material onto the adsorbed BCP layer, which typically leads to patterned surfaces. The PS brush coverage depends on immersion time (adsorption kinetics), but full coverage does not inhibit AuNP adsorption, which is attributed to PS molecular rearrangement during exposure to the aqueous AuNP colloidal solution. The simplicity, versatility and robustness of the method will enable applications in materials science requiring dense, unaggregated NP arrays.

Ferrocenealkylsilane molecular rectifiers

We developed four new ferrocene containing alkylated silane self-assembled monolayers (SAMs), and evaluated their electrical properties in a metal/SAM/metal configuration. The ferrocenyl silanes used in this work can be prepared in one to two simple chemical steps from readily available ferrocene carboxaldehyde. We found that the molecular diodes obtained from these molecules can exhibit current rectification ratios as high as 150. The ease of processing coupled with the excellent rectification behavior makes these compounds very attractive for molecular electronics applications.

A method of conserving ancient iron artefacts retrieved from shipwrecks using a combination of silane self-assembled monolayers and wax coating

Iron artefacts corrode severely in a marine environment, and require further conservation after retrieval. This research proposes a novel conservation method, based on a bi-layered concept: a thin silane self-assembled monolayer serving as nano-scale barrier, covered by a thicker waxlayer, which is applied by dipping the object into a suitable solution. An accelerated corrosion test was performed, using modern cast iron and steel samples, and repeated on archaeological wrought iron artefacts retrieved from shipwrecks. This protection, which can be easily applied, was found to improve the corrosion resistance of the artefacts.