Self-assembled Thin Films Research Articles

Nanostructure Formation in Glycerolipid Films during Enzymatic Hydrolysis: A GISAXS Study.

Responsive nanostructured films from food-grade lipids can be valuable for food, pharmaceutical, and biotechnological science. Lyotropic liquid crystalline structures that respond to enzymes in their environment can, for instance, be innovated as drug delivery platforms or biosensors. However, the structural changes that such films undergo during enzymatic reactions with lipase are not yet understood. This work demonstrates the preparation of mesostructured lipid films from the food-grade lipids glycerol monooleate (GMO) and triolein on silicon wafers and their digestion with pancreatic lipase using time-resolved synchrotron grazing incidence small-angle X-ray scattering (GISAXS). The film structure is compared with the corresponding GMO/triolein bulk phases in excess water. Increasing the GMO/triolein ratio in the film makes it possible to modulate the structure of the films from oil coatings to inverse hexagonal and inverse bicontinuous cubic films. Pancreatic lipase triggered swelling of the internal film nanostructure and eventually structural transformation inside the film. Orientation and reorientation of the internal film structure relative to the silicon wafer surface were observed during the preparation of the films and their digestion. The findings contribute to the understanding of self-assembly in thin films and guide the development of enzyme-responsive coatings for the functional modification of various substrates.

Highly stable, low voltage, flexible photodetector in UV-visible region from self-assembled organic small molecule

The fabrication of a high-performance, low voltage operated flexible organic photodetector (OPD) based on solution self-assembled crystalline thin film of a small molecule, viz, 6,13 bis(tri-isopropylsilylethynyl) pentacene (Tips pentacene) is reported. The OPD demonstrated excellent photodetection ability under range of visible light as well as under UV light, with low illumination intensity. Under 590 nm illumination (5.6 µW/cm2), the device showcased photo to dark current ratio (Iphoto/Idark), ca. 25, photoresponsivity (P) of 89 mA/W, detectivity of 1.81×1010 jones at 1 V bias and response times of 0.04/0.2 sec. Photocurrent modulation of the OPD has been realized by varying the channel width, incident wavelength, applied bias and the illumination intensity. The OPD exhibited excellent photodetection ability under different tensile bending, with roughly 55 % decline in Iphoto/Idark value and 30 % decline in R value under bending radius of 7.5 mm. The OPD could withstand thousands of repeated bending/folding cycles, and regain its initial photoresponse characteristics, if put at rest for 2 hours. The excellent device performances with its precise tuning via various input stimuli suggests that present OPD have great potential for future low cost, low energy and wearable optoelectronics.

Interfacially Self-Assembled Mutifunctional Protein Thin Films for Accelerated Wound Healing.

The design of mutifunctional protein films for large-area spatially ordered arrays of functional components holds great promise in the field of biomedical applications. Herein, interfacial electrostatic self-assembly was employed to construct a large-scale protein thin film by inducing electrostatic interactions between three bovine serum albumin (BSA)-coated nanoclusters and cetyltrimethylammonium bromide (CTAB), leading to their spontaneous organization and uniform distribution at the oil-water interface. This protein film demonstrated excellent multienzyme functions, high antibacterial activity, and pH-responsive drug release capability. Therefore, it can accelerate the wound closure process through a synergistic effect that includes reducing local blood glucose levels, regulating cellular oxidative stress, eradicating bacteria, and promoting cell proliferation.

A Self-Assembled Multiphasic Thin Film as an Oxygen Electrode for Enhanced Durability in Reversible Solid Oxide Cells.

The implementation of nanocomposite materials as electrode layers represents a potential turning point for next-generation of solid oxide cells in order to reduce the use of critical raw materials. However, the substitution of bulk electrode materials by thin films is still under debate especially due to the uncertainty about their performance and stability under operando conditions, which restricts their use in real applications. In this work, we propose a multiphase nanocomposite characterized by a highly disordered microstructure and high cationic intermixing as a result from thin-film self-assembly of a perovskite-based mixed ionic-electronic conductor (lanthanum strontium cobaltite) and a fluorite-based pure ionic conductor (samarium-doped ceria) as an oxygen electrode for reversible solid oxide cells. Electrochemical characterization shows remarkable oxygen reduction reaction (fuel cell mode) and oxygen evolution activity (electrolysis mode) in comparison with state-of-the-art bulk electrodes, combined with outstanding long-term stability at operational temperatures of 700 °C. The disordered nanostructure was implemented as a standalone oxygen electrode on commercial anode-supported cells, resulting in high electrical output in fuel cell and electrolysis mode for active layer thicknesses of only 200 nm (>95% decrease in critical raw materials with respect to conventional cathodes). The cell was operated for over 300 h in fuel cell mode displaying excellent stability. Our findings unlock the hidden potential of advanced thin-film technologies for obtaining high-performance disordered electrodes based on nanocomposite self-assembly combining long durability and minimized use of critical raw materials.

Self-Assembled Ti3C2TX MXene Thin Films for High-Performance Ammonia Sensors

MXenes have emerged as a fascinating material for RT gas-sensing applications due to their outstanding properties. This work reports the design and fabrication of a high-performance ammonia sensor based on MXenes material. To improve its sensing performance, a MXenes nanosheets thin film with a thickness of ≈ 10 nm was prepared using a scalable self-assembled method. Specifically, we employed the controlled and enhanced interfacial self-assembled method to fabricate a continuous and conductive MXene ultra-thin film. The morphology and the structure of the produced MXene materials and their films were characterized by combining multi-characterization tools. Altoghether, these highlight the uniform and continuous deposition of the MXene nanosheets film on the glass substrate. The electrical characterization indicates a sheet resistance value of 4.82 × 105 Ω/sq. The fabricated devices present good RT sensing performances for NH3 detection, ranging from 1 to 20 ppm. This demonstrates the outstanding sensitivity of MXene with a value of 1.92 % for the lowest concentration (1 ppm), a fast response (179 s) and a recovery time of (612 s), which is related to the high quality of the ultra-thin MXene sensiting layer. Moreover, the sensors demonstrate high degree of stability and excellent reproducibility, make them suitable candidate for practical applications like environmental monitoring.

Supercapacitive performance of self-assembled thin film of liquid catocene/basal plane pyrolytic graphite electrode

Reasonable design of electrode material with low cost, lightweight, and excellent electrochemical properties is of great significance for future large-scale energy storage applications. Herein, we report the electrochemical and supercapacitive behaviour of the liquid redox of catocene, 2,2’-bis(ethyl-ferroceneyl) propane, self-assembled on a basal plane pyrolitic graphite electrode in comparison to the solid ferrocene thin film in aqueous sodium sulfate electrolyte. The modified electrode surfaces were evaluated to assess the iron content and the formation of thin film using scanning electron microscopy, laser-induced breakdown spectroscopy, and attenuated total reflectance method. Also, the supercapacitive performances of the related modified electrodes were assessed and compared using cyclic voltammetry and galvanostatic charge-discharge in a three-electrode system and an asymmetric two-electrode supercapacitor system. Electro­chemical results showed that the electrode processes are diffusion-controlled with battery-like behaviour, and the liquid catocene exhibits more effective interaction with the graphite surface in comparison to solid ferrocene. The catocene surface coverage on graphite is nearly 50-75 % higher than ferrocene, leading to improved interaction and charge transfer resistance, observed in electrochemical impedance spectroscopy studies. In galvanostatic charge-discharge evaluations, the supercapacitor based on catocene modified electrode shows a specific capacitance of 141.2 F g-1 at a current density of 1.0 A g-1, with a specific energy density of 56.7 Wh kg-1 at a power density of 2.9 kW kg-1.

Multifunctional corrosion inhibition of brass by interface engineering based on ternary layer-by-layer self-assembly with trivalent cerium captured

A nanoscale ternary layer-by-layer self-assembly (LbL) thin film was fabricated on brass via a simple dipping method. Dual driving force of intermolecular interactions and coordination realized the high homogeneous dispersion of Ce3+, thereby improving the controlled distribution and release of inhibitors. Compared to previous nanometer-thick conversion coatings, ternary LbL film exhibited excellent multifunctional corrosion protection. The maximum strengthening reached 496.8 % in impendence, and corrosion inhibition efficiency remained 95.0 % after a 10-day exposure in 3.5 wt% NaCl. These improvements originated from dynamic barrier effect by crosslinked gel film of PA/PAH and the surface passivation through interface deposition of Ce species.

PH effect in Langmuir–Blodgett self-assembly of MoS2 and WS2 thin films

We reported Langmuir–Blodgett films of molybdenum disulphide and tungsten disulfide and studied the formation of MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Mo}}{\ ext{S}}_{2}$$\\end{document} and WS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{WS}}_{2}$$\\end{document} layers. The effect of the subphase pH is investigated. Also, the influence of the subphase conditions on the number of layers was reported. By varying the pH of the buffer solution subphase, the solvent-to-nanoparticle interaction is changed and the compression of the layer during deposition is influenced. The stacking of the MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Mo}}{\ ext{S}}_{2}$$\\end{document} and WS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{WS}}_{2}$$\\end{document} crystalline structure under the influence of subphase pH and the material concentration were investigated. Langmuir layers assembly is a useful method to manipulate the distribution of WS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{WS}}_{2}$$\\end{document} and MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Mo}}{\ ext{S}}_{2}$$\\end{document}. Successful deposition of dichalcogenides at the air–water interface on silicon substrate was performed using Balance Langmuir–Blodgett technique. The characterization of WS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{WS}}_{2}$$\\end{document} and films MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Mo}}{\ ext{S}}_{2}$$\\end{document} with X-ray diffraction, Raman spectroscopy, atomic force microscopy and scanning electron microscopy was carried out.

Orientation transitions and chiral assemblies of para-terphenyl molecules on Cd(0001).

The interplay between orientation transition and chiral self-assemblies of para-terphenyl (P3P) molecules on the Cd(0001) surface has been investigated using low temperature scanning tunneling microscopy and density functional theory calculations. Three distinct molecular orientations have been discerned from the self-assembled thin films of P3P. At the low coverage, flat-lying molecules appear in the homochiral domains with the incommensurate registry to the substrate. With the coverage increasing, the incoming molecules are incorporated into the first layer with edge-on orientation and form the self-assembled zigzag chains. The alternative arrangement of zigzag chains with opposite chirality leads to the formation of a c(4 × 2) superstructure, in which the tilted molecules exhibit orientational frustration and fuzzy noises. The analysis of the tunneling spectra reveals that the electronic structure of P3P layers is contingent upon the hybridization between the electronic states of P3P molecules and the Cd(0001) surface. These results provide important insights into the interplay between orientational transition and chiral assembly of P3P molecules on metal substrates.

A novel method to enhance the superconducting properties of Bi2Sr2CaCu2O8+δ superconducting thin films by self-assembly NiO nanorods

The utilization of Bi-based superconductors in magnetic field environments is limited due to their anisotropic structure and lack of efficient magnetic flux pinning sites. Therefore, to enhance the performance of Bi-based superconductors in a magnetic field, this study presents the preparation of Bi2212 high-temperature superconducting thin films with varying NiO doping levels on SrTiO3 (STO) single crystal substrates with different concentrations of NiO seed layers via the self-assembly method. Additionally, phase purity, crystal structure, surface morphology, and transport properties were thoroughly analyzed. According to the results, the NiO seed layers prepared on the STO substrates presented epitaxial growth characteristics, with the NiO second phase in the Bi2212 matrix growing epitaxially along the seed layers. As NiO doping slightly broadens the phase formation temperature range of Bi2212 superconducting thin films, the self-assembly method can be utilized to prepare NiO nanorods with epitaxial growth in Bi2212 thin films. Notably, the self-assembled NiO-doped Bi2212 thin film demonstrated higher critical current carrying capacity, with its Jc reaching 6.28 × 104 A/cm2 at 10 K in self-field. This provides a technical reference for improving the performance of high-temperature superconducting thin films under a high magnetic field.

Enhancing catalytic activity through self-assembled hydrogen-bonded organic framework-based catalysts at liquid/liquid interface for 4-nitrophenol reduction and energy challenges in methanol fuel cell

Hydrogen-bonded organic frameworks (HOFs) are pure organic framework structures endowed with appropriate flexibility and porosity, which have attracted special attention in the field of energy and water, air, and soil remediation. In this study, six HOF-based materials were synthesized as thin film at the liquid/liquid (toluene/water) interface and characterized by FT-IR, Raman, UV–Vis, PXRD, ICP, AFM, SEM, TGA, and BET techniques. The self-assembled HOF-based thin films were employed as catalysts for the 4-nitrophenol removal from water medium and, for the first time, for methanol oxidation of fuel cell, with satisfying results. Simultaneous in situ catalyst formation and 4-nitrophenol reduction occurred in the case of Pt(0)@HOF thin film, but an extraordinary removal (not reduction) occurred in the presence of Pt(0)-trimesic acid thin film by formation of a new HOF from trimesic acid and 4-nitrophenol. Successful reduction of 4-nitrophenol occurred also in the presence of freshly prepared Pt(0)-trimesic acid, Pt(0)-melamine and Pt(0)@HOF catalysts (ex situ strategy). The chemical and thermal stability of HOF structure was improved by the interpenetration of ZIF-8 crystal structure, by increasing the hydrogen bonding and π-π stacking in the presence of 2-methylimidazole. The interpenetration of ZIF-8 to the crystal structure of HOF caused a significant decrease of the pore diameter of the structure. These pores acted as specific sites for the guest molecules, and their dimensions did not permit 4-nitrophenol to penetrate into the cavity of structures whereas allowed methanol penetration into these cavities due to its smaller size.

Influence of chitosan’s purification methodology on the formation of layer-by-layer films

Concern for the environment for the development of new biodegradable materials has been constant in scientific circles. With this in mind, this work proposes a study on the formation of self-assembled thin films using chitosan (Qt), a biodegradable material. This polyelectrolyte has several purification methodologies, but we did not identify any studies on the effect of these methodologies on film formation. Thus, after the purification process and characterization of the three forms of chitosan purification, films were produced using the layer-by-layer (LBL) technique. The growth of the films was monitored using the UV-vis technique. Spectroscopy in the Infrared region showed positions in the main bands present in chitosan and sodium nitroprusside (NP) in the formed films. Two semi-reversible processes were found for the QtN/NP and QtAc/NP films, related to the reduction of iron oxide present in the NP. The effect of pH (4.0, 7.0 and 10) on the electrochemical processes indicated that the charge transfer occurs more efficiently at pH 7.0.

Homogeneous and Nanogranular Prussian Blue to Enable Long-Term-Stable Electrochromic Devices.

The increasing demand for the state-of-the-art electrochromic devices has received great interest in synthesizing Prussian blue (PB) nanoparticles with a uniform diameter that exhibit excellent electrochromism, electrochemistry, and cyclability. Herein, we report the controllable synthesis of sub-100 nm PB nanoparticles via the coprecipitation method. The diameter of PB nanoparticles can be modulated by adjusting the reactant concentration, the selection of a chelator, and their purification. The self-assembled nanogranular thin films, homogeneously fabricated by using optimized PB nanoparticles with an average diameter of 50 nm as building blocks via the blade coating technique enable excellent performance with a large optical modulation of 80% and a high coloration efficiency of 417.79 cm2 C-1. It is also demonstrated by in situ and ex situ observations that the nanogranular PB thin films possess outstanding structural and electrochemical reversibility. Furthermore, such nanogranular PB thin films can enjoy the enhanced long-term cycling stability of the PB-WO3 complementary electrochromic devices having a 91.4% optical contrast retention after 16,000 consecutive cycles. This work provides a newly and industrially compatible approach to producing a complementary electrochromic device with extraordinary durability for various practical applications.

Self-assembled graphene oxide thin films deposited by atmospheric pressure plasma and their hydrogen thermal reduction

This work uses an atmosphere-pressure plasma jet to obtain thin, homogeneous graphene oxide coatings. The films consisted of self-assembled graphene oxide (GO) layers, which were reduced by heat treatment under a reductive hydrogen atmosphere to obtain a reduced graphene oxide film. The electrochemical and photoelectrochemical analyses show that electrical conductivity increases after the reduction process; meanwhile, this process eliminates the p-type photoactivity of the graphene oxide film. The reduced graphene oxide X-ray diffraction pattern revealed the elimination of the signal at 2θ = 11° initially found in the graphene oxide film. The C1s and O1s high-resolution XPS analyses of the reduced graphene oxide film reveal a pronounced increase in the graphitic-like carbon (sp2), whereas a decrease in the organic-like carbon (sp3) and oxygenated species, such as C-OH, C-O-C, CO, and OCOH, initially found in the graphene oxide film.

Photoconductivity in self-assembled CuO thin films

Self-assembly is the most promising low-cost and high-throughput methodology for nanofabrication. This paper reports the optimization of a self-assembly process at room temperature for the growth of copper oxide (CuO) based nanostructures over a copper substrate using aqueous potassium hydroxide (KOH) solution as the oxidizing agent. The monoclinic phase of CuO nanostructures grown over the copper substrate was confirmed from the X-ray diffraction (XRD) and micro-Raman analysis. The overall chemical composition of nanostructures was confirmed to be that of CuO from its oxidation state using X-ray photoelectron spectroscopy (XPS). Photodetectors were engineered with the structure Cu/CuO/Ag. The photodetectors exhibited a response to both ultraviolet and visible light illumination. The optimized Cu/CuO/Ag structure exhibits a responsivity of ~ 1.65 µA/W, with an ON:OFF ratio of ~ 69 under a bias voltage of 0.01 V. The temporal dependence of photo-response for the optimized photodetector displayed the persistent nature of photoconduction indicating a delay in charge carrier recombination which could potentially be exploited for photovoltaic applications.

Transparent Structures for ZnO Thin Film Paper Transistors Fabricated by Pulsed Electron Beam Deposition.

Thin film transistors on paper are increasingly in demand for emerging applications, such as flexible displays and sensors for wearable and disposable devices, making paper a promising substrate for green electronics and the circular economy. ZnO self-assembled thin film transistors on a paper substrate, also using paper as a gate dielectric, were fabricated by pulsed electron beam deposition (PED) at room temperature. These self-assembled ZnO thin film transistor source-channel-drain structures were obtained in a single deposition process using 200 and 300 µm metal wires as obstacles in the path of the ablation plasma. These transistors exhibited a memory effect, with two distinct states, "on" and "off", and with a field-effect mobility of about 25 cm2/Vs in both states. For the "on" state, a threshold voltage (Vth on = -1.75 V) and subthreshold swing (S = 1.1 V/decade) were determined, while, in the "off" state, Vth off = +1.8 V and S = 1.34 V/decade were obtained. A 1.6 μA maximum drain current was obtained in the "off" state, and 11.5 μA was obtained in the "on" state of the transistor. Due to ZnO's non-toxicity, such self-assembled transistors are promising as components for flexible, disposable smart labels and other various green paper-based electronics.

Self-assembled thin films as alternative surface textures in assistive aids with users who are blind.

Current tactile graphics primarily render tactile information for blind users through physical features, such as raised bumps or lines. However, the variety of distinctive physical features that can be created is effectively saturated, and alternatives to these physical features are not currently available for static tactile aids. Here, we explored the use of chemical modification through self-assembled thin films to generate distinctive textures in tactile aids. We used two silane precursors, n-butylaminopropyltrimethoxysilane and n-pentyltrichlorosilane, to coat playing card surfaces and investigated their efficacy as a tactile coating. We verified the surface coating process and examined their durability to repeated use by traditional materials characterization and custom mesoscale friction testing. Finally, we asked participants who were both congenitally blind and braille-literate to sort the cards based on touch. We found that participants were able to identify the correct coated card with 82% accuracy, which was significantly above chance, and two participants achieved 100% accuracy. This success with study participants demonstrates that surface coatings and surface modifications might augment or complement physical textures in next-generation tactile aids.

Effects of alumina priming on the electrical properties of ZnO nanostructures derived from vapor-phase infiltration into self-assembled block copolymer thin films

Alumina priming, typically used for vapor-phase infiltration (VPI) of weakly reactive precursors, increases both ZnO VPI fidelity and its electrical conductivity, as demonstrated in the ZnO nanostructures derived from self-assembled block copolymers.

Self-brushing for nanopatterning: achieving perpendicular domain orientation in block copolymer thin films.

The self-assembly of thin films of block copolymers (BCPs) with perpendicular domain orientation offers a promising approach for nanopatterning on a variety of substrates, which is required by advanced applications such as ultrasmall transistors in integrated circuits, nanopatterned materials for tissue engineering, and electrocatalysts for fuel cell applications. In this study, we created BCPs with an A-b-(B-r-C) architecture that have blocks with equal surface energy (γair) and that can bind to the substrate, effectively creating a non-preferential substrate coating via self-brushing that enables the formation of through-film perpendicular domains in thin films of BCPs. We employed a thiol-epoxy click reaction to functionalize polystyrene-block-poly(glycidyl methacrylate) with a pair of thiols to generate an A-b-(B-r-C) BCP and tune γair of the B-r-C block. The secondary hydroxyl and thiol ether functionality generated by the click reaction was utilized to bind the BCP to the substrates. Scanning electron microscopy revealed that perpendicular orientation was achieved by simply annealing a thin film of the BCP on the bare substrate without the usual extra step of coating a random copolymer brush on the substrate. The self-brushing capability of the BCP was also examined on gold, platinum, titanium, aluminum nitride, and silicon nitride surfaces. These results demonstrate that self-brushing is a promising approach for achieving perpendicular domain orientation in thin films of BCP for nanopatterning on a variety of useful surfaces.

Self-assembly of thiophene-based luminescent thin films on flexible substrates.

Luminescent organic thin films are widely used in optoelectronic devices for sensing, imaging and data processing. Herein, the transition to a flexible form is accompanied by a number of challenges associated with a limited endurance and bending-dependent properties. Here we report a study on the growth of thin films based on thiophene-based luminescent molecular crystals (MC) on a flexible polypropylene (PP) substrate of a various thicknesses (400 μm to 50 μm). The resulting flexible thin films demonstrate the stability of their luminescent properties under mechanical bending (up to 100 times) at ambient conditions, which pave the way for large scale production of planar optoelectronic components.