Arbitrary Substrates Research Articles

Polarization‐Driven‐Orientation Selective Growth of Single‐Crystalline III‐Nitride Semiconductors on Arbitrary Substrates (Adv. Funct. Mater. 14/2022)

Arbitrary Substrates In article number 2113211, Xuelin Yang, Bing Huang, Bo Shen, and co-workers propose a strategy of polarization-driven-orientation selective growth and demonstrate that single-crystalline GaN can in principle be achieved on polycrystalline diamond or other substrates by utilizing a composed buffer layer consisting of graphene and polycrystalline physical-vapor-deposited AlN. This strategy can be extended to the growth of any emergent single-crystalline semiconductor films on any arbitrary freestanding substrates by choosing appropriate 2D materials with matched crystal structures.

Rapid Assembly of Magnetoplasmonic Photonic Arrays for Brilliant, Noniridescent, and Stimuli-Responsive Structural Colors.

There are usually trade-offs between maximizing the color saturation and brightness and minimizing the angle-dependent effect in structural colors. Here, a magnetic field-induced assembly for the rapid formation of scalable, uniform amorphous photonic arrays (APAs) featuring unique structural colors is demonstrated. The magnetic field plays a fundamental role in photonic film formation, making this assembly technology versatile for developing structural color patterns on arbitrary substrates. The synergistic combination of surface plasmonic resonance of the Ag core and broadband light absorption of high refractive index (RI) Fe3 O4 shell in hybrid magnetoplasmonic nanoparticles (MagPlas NPs) enables breaking the trade-offs to produce brilliant, noniridescent structural colors with high tunability and responsiveness. These features enable the fabrication of various types of highly sensitive and reliable colorimetric sensors for naked-eye detection without sophisticated instruments. Furthermore, large-scale structural color patterns are effortlessly achieved, demonstrating the high potential of the present approach for full-spectrum displays, active coatings, and rewritable papers.

All-dielectric multi-resonant bullseye antennas.

Integrated devices that generate multiple optical resonances in the same volume can enhance on-chip nonlinear frequency generation, nonlinear spectroscopy, and quantum sensing. Here, we demonstrate circular Bragg antennas that exhibit multiple spatially overlapping, polarization-selective optical resonances. Using templated atomic layer deposition of TiO2, these devices can be fabricated on arbitrary substrates, making them compatible with a wide range of nonlinear materials and sensing targets, and couple efficiently to underlying films. In this work, we detail the design, simulation, and fabrication of all-dielectric multi-resonant bullseye antennas and characterize their performance using polarized broadband reflection spectroscopy.

In situ synergistic strategy of sacrificial intermedium for scalable-manufactured and controllable layered double hydroxide film

Layered double hydroxides (LDHs), a class of two-dimensional (2D) brucite-like layers, have been effectively applied in diverse fields. However, the current synthesis methods restrict the in situ scaling-up and tunable production of LDH-based materials. Inspired by the growing characteristic of “Bryophyllum pinnatum”, a sacrificial co-sputtered Zn−Al transition layer was introduced for the first time to in situ grow a scalable-manufactured and thickness-controllable LDH film on arbitrary substrate materials with flexible shapes through “partial dissolution” and “solution infiltration” processes. Diverse LDH films could be tailored by the creative regulation of the component, structure and surface state of the transition layer. Results showed that the as-prepared LDH film had strong mechanical robustness under harsh abrasion conditions due to its large thickness and multi-level microstructure. Moreover, a series of galvanic couple model experiments based on Zn/Al single-metal transition layers were designed to solve the real-time monitoring issue in the complex hydrothermal solution. This work not only develops a new strategy to design and grow in situ LDH films with multifaceted features, but also reveals sophisticated LDH formation mechanisms. Hence, the findings of this study may broaden the practical application of LDH-based materials toward advanced and smart devices.

A versatile technique for micro and nano structuring of conductive thin metal layers using electric field assisted dissolution

A simple, versatile technique for structuring conductive thin metal films is proposed. Over the last years, glass poling and electric field assisted dissolution of metal nanoparticles and films have been the basis of new approaches for fabrication of micro and nanostructures on glass. Here we demonstrate how the sequential combination of glass poling and electric field assisted dissolution can be used to circumvent the necessity of glass as supporting substrate. In short, a patterned electrode is applied to selectively modify by glass poling an auxiliary glass substrate that is later used to induce indirect electric field assisted dissolution of a metal layer deposited on an arbitrary substrate. The proposed method is verified by microstructuring conductive thin metal layers (Ag and Cu) deposited on silicon wafers. This technique enables transferring the pattern from a primary electrode onto conductive thin metal film using inexpensive equipment and the process duration is independent on the pattern area. The primary electrode can be used many times to fabricate selectively modified auxiliary glass substrates and the only limitation on the substrate supporting the final metal microstructure is to be able to sustain moderately elevated temperature and electric field for couple of hours. This method turns out to reproduce the original pattern better than other approaches based on glass poling. Overall, the proposed method significantly expands the application range of glass poling and electric field assisted dissolution as competitive structuring techniques.

Synthesis of Thin Film of a Three‐Dimensional Covalent Organic Framework as Anti‐counterfeiting Label

Comprehensive SummaryFilm plays a key role in the sustainable development of our society. Freestanding thin films of two‐dimensional covalent organic frameworks (COFs) have been produced by interface, spin coating, microwave‐assisted synthesis, and screen printing methods and are applied in nanofiltration, molecular separation, photochemical sensing, anion transport, heat conduction, and proton conduction. On the other hand, the synthesis of their three‐dimensional (3D) analogues and subsequent integration in devices remains challenging. Herein, self‐supporting thin films of a three‐dimensional COF with tunable thickness was created by a stearic acid mediated synthesis methodology on water surface at room temperature in air. The film could be transferred onto arbitrary substrate, and when supported on indium tin oxide glass, it exhibited irreversible electrochromism. The optical feature made it act as a one‐time anti‐counterfeiting label in an electrochemical device. This work will inspire the synthesis of thin films of 3D COFs as well as other 3D materials, and boost their property and application exploration.

Template‐Assisted Self‐Assembly of Colloidal Silicon Nanoparticles for All‐Dielectric Nanoantenna

AbstractA solution‐based bottom‐up process to produce one‐ and two‐dimensional arrays of densely packed spherical nanoparticles (NPs) of crystalline silicon (Si), having the lowest order Mie resonance in the visible range, is developed. First, an agglomeration‐free solution of Si NPs with a narrow size distribution is prepared. By using grooves fabricated on the surface of a polymer as a template, arrays of Si NPs with different shapes are formed by a template‐assisted self‐assembly method, and then they are transferred to an arbitrary substrate. To demonstrate proper formation of Si NP arrays, polarization‐resolved scattering spectra are measured for different size linear arrays, i.e., a monomer to a pentamer, of Si NPs placed on a silica substrate. The observed spectra are well‐reproduced by the numerical simulations. When the polarization direction of incident light is parallel to the array axis, the scattering spectra are strongly modified from that of a Si NP monomer due to near‐field coupling of the electric dipole (ED) modes. In a Si NP tetramer, the peak of the ED mode overlaps with that of the magnetic dipole (MD) mode and strong forward scattering is observed at the MD peak wavelength due to the Kerker effect.

Galvanic-Replacement-Assisted Surface-Initiated Atom Transfer Radical Polymerization for Functional Polymer Brush Engineering.

Here we present a facile and robust strategy, namely, galvanic-replacement-assisted surface-initiated Cu(0)-mediated atom transfer radical polymerization (gr-SI-Cu0ATRP, or gr-SI-Cu0CRP) for polymer brush engineering under ambient conditions. In gr-SI-Cu0ATRP, highly active and nanostructured Cu(0) surfaces are obtained by a simple galvanic replacement on zinc/aluminum surfaces in dilute Cu2+ solution. Polymer brush growth rate is extremely high (up to ∼904 nm in 30 min polymerization); meanwhile, both nano Cu(0) surfaces and Cu2+ solution can be reused multiple times without losing grafting efficiency. We also demonstrate that the gr-SI-Cu0ATRP is advantageous for polymer brush engineering on arbitrary substrates, including flexible (polyethylene terephthalate), curved (polycarbonate), and porous (anodic aluminum oxide), and endow the substrates with various functionalities, for example, anti-icing, antifogging, and ion selectivity.

Synergistic enhancement of hydrogel adhesion via tough chemical bonding and physical entanglements

Herein, excellent hydrogel–solid adhesion over 1500 J/m2 was achieved with the synergy of energy dissipation, covalent bonds, and topological entanglements using self-assembled monolayers. Phosphonic acids were densely deposited on arbitrary substrates, followed by direct coating with polyacrylamide. Two functional end-groups of phosphonic acids based on an alkenyl group were introduced to chemically bond with the hydrogel network. The covalent bonding between the alkenyl group and the hydrogel drastically enhances the adhesion to substrates. In addition, the long alkyl chain improved the interfacial adhesion energy to 1500 J/m2. Infrared absorbance analysis demonstrated that longer alkyl chains formed more densely packed self-assembled monolayers, leading to a higher supply of chemically reactive sites to the hydrogels. Moreover, the tendency of the adhesion energy of the swollen hydrogel proves that the long alkyl chain is physically tangled with hydrogel networks, resulting in stronger adhesion.

The first progress of plasma-based transition metal dichalcogenide synthesis: a stable 1T phase and promising applications.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted attention as polymorphs depending on their phases (1T and 2H) when applying typical synthesis methods. The 2H phase is generally synthesised through chemical vapour deposition (CVD) on a wafer-scale at high temperatures, and many synthesis methods have been reported owing to their thermodynamic stability and semiconductor properties. By contrast, although the 1T phase is meta-stable with an octahedral coordination, thereby limiting the use of synthesis methods, the recent structural advantage in terms of the hydrogen evolution reaction (HER) has been emphasised. Despite this demand, no large-area thin-film synthesis method for 1T-TMDs has been developed. Among several strategies of synthesizing metallic-phase (1T) TMDs, chemical exfoliation (alkali metal intercalation) is a major strategy and others have been used for electron-beam irradiation, laser irradiation, defects, plasma hot electron transfer, and mechanical strain. Therefore, we suggest an innovative synthesis method using plasma-enhanced CVD (PECVD) for both the 1T and 2H phases of TMDs (MoS2 and WS2). Because ions and radicals are accelerated to the substrate within the sheath region, a high-temperature source is not needed for vapour ionisation, and thus the process temperature can be significantly lowered (150 °C). Moreover, a 4-inch wafer-scale of a thin film is an advantage and can be synthesised on arbitrary substrates (SiO2/Si wafer, glassy carbon electrode, Teflon, and polyimide). Furthermore, the PECVD method was applied to TMD-graphene heterostructure films with a graphene-transferred substrate, and for the first time, sequential metal seed layer depositions of W (1 nm) and Mo (1 nm) were sulfurized to MoS2-WS2 vertical heterostructures with Ar + H2S plasma. We considered the prospects and challenges of the new PECVD method in the development of practical applications in next-generation integrated electronics, HER catalysts, and flexible biosensors.

In situ growth of laser-induced graphene micro-patterns on arbitrary substrates.

In this article we report a new laser processing method, combining the in situ graphitization of polyimide with simultaneous transfer of the graphene patterns to arbitrary substrates. The synthesis conditions are similar to those normally used for the well-known laser-induced graphene method. The approach is based on the enclosure of polyimide sheets between microscope glass slides. Graphene patterns have been successfully generated on glass and on PDMS, as well as graphene decorated with metals and oxides. In order to illustrate the usefulness of the proposed approach, the method was applied to the fabrication of hybrid supercapacitors, which exhibited very good electrochemical performance.

Direct fabrication of high-quality vertical graphene nanowalls on arbitrary substrates without catalysts for tidal power generation.

The non-catalytic preparation of high-quality vertical graphene nanowalls (VGN) and graphene-based high output power hydrovoltaic effect power generation devices has always been difficult to achieve. In this work, we successfully prepared VGN with defect density, few layers and submicron domain size on a variety of substrates without catalysts through reasonable adjustment of growth conditions by the hot-wire chemical vapor deposition (HWCVD) method. The Raman test of the VGN prepared under optimal conditions showed that its ID/IG value was less than 1, and I2D/IG was more than 2.8. The deposition pressure was a key factor affecting the crystallization quality of the VGN. A suitable deposition pressure of 500 Pa could screen the active carbon clusters involved in the growth of nanowalls. The VGN prepared had excellent electrical properties and output of dropping-ion-droplet nano-power generation devices. Because of the larger crystal domain area and smaller contact angle of the VGN, the maximum output power exhibited at 100 Pa was 15.7 μW, which exceeded the value produced by other reported hydrovoltaic energy harvesting devices. All of them confirmed that VGN with improved quality had high application prospects in nano-energy devices.

Novel Fabrication Technology for Clamped Micron-Thick Titanium Diaphragms Used for the Packaging of an Implantable MEMS Acoustic Transducer.

Micro-Electro-Mechanical Systems (MEMS) acoustic transducers are highly sophisticated devices with high sensing performance, small size, and low power consumption. To be applied in an implantable medical device, they require a customized packaging solution with a protecting shell, usually made from titanium (Ti), to fulfill biocompatibility and hermeticity requirements. To allow acoustic sound to be transferred between the surroundings and the hermetically sealed MEMS transducer, a compliant diaphragm element needs to be integrated into the protecting enclosure. In this paper, we present a novel fabrication technology for clamped micron-thick Ti diaphragms that can be applied on arbitrary 3D substrate geometry and hence directly integrated into the packaging structure. Stiffness measurements on various diaphragm samples illustrate that the technology enables a significant reduction of residual stress in the diaphragm developed during its deposition on a polymer sacrificial material.

Fast Peel-Off Ultrathin, Transparent, and Free-Standing Films Assembled from Low-Dimensional Materials Using MXene Sacrificial Layers and Produced Bubbles.

Ultrathin, transparent, and free-standing films assembled from low-dimensional nanomaterials (LDMs) are promising for various applications, including transparent heaters and membranes. However, the intact separation of the assembled films, especially those with controlled ultrathin thickness from deposited substrates, is a tremendous challenge, particularly for fast peeling off via self-detaching. Herein, we propose a versatile method to rapidly peel off ultrathin assembled LDM films, including three types of carbon nanotubes, vermiculite, Ag nanowires, and carbon nanotube@graphene, by dissolving the MXene interlayer from the layer-by-layer filtered MXene/LDM Janus films using diluted H2 O2 . The MXene sacrificial interlayers play dual roles, including physical isolation of LDM films from filter membranes and the production of bubbles that buoy ultrathin LDM films, making them free-standing. The integrality and self-detaching rate of the LDM films are determined by the loading and reactivity of the MXene interlayers. The intact LDM films can self-detach in 80 s by dissolving the optimized MXene interlayer and producing bubbles. The as-made free-standing ultrathin LDM films can be transferred to arbitrary substrates and exhibit outstanding performance as transparent heaters. This scalable method provides an efficient and versatile method to produce ultrathin, transparent, and free-standing LDM films and finds new applications for the growing MXene family.

Carbon Dioxide Sensing with Langmuir–Blodgett Graphene Films

Graphene has become a material of choice for an increasing number of scientific and industrial applications. It has been used for gas sensing due to its favorable properties, such as a large specific surface area, as well as the sensitivity of its electrical parameters to adsorption processes occurring on its surface. Efforts are ongoing to produce graphene gas sensors by using methods that are compatible with scaling, simple deposition techniques on arbitrary substrates, and ease of use. In this paper, we demonstrate the fabrication of carbon dioxide gas sensors from Langmuir–Blodgett thin films of sulfonated polyaniline-functionalized graphene that was obtained by using electrochemical exfoliation. The sensor was tested within the highly relevant concentration range of 150 to 10,000 ppm and 0% to 100% at room temperature (15 to 35 °C). The results show that the sensor has both high sensitivity to low analyte concentrations and high dynamic range. The sensor response times are approximately 15 s. The fabrication method is simple, scalable, and compatible with arbitrary substrates, which makes it potentially interesting for many practical applications. The sensor is used for real-time carbon dioxide concentration monitoring based on a theoretical model matched to our experimental data. The sensor performance was unchanged over a period of several months.

Wafer scale synthesis of organic semiconductor nanosheets for van der Waals heterojunction devices

Organic semiconductors (OSC) are widely used for consumer electronic products owing to their attractive properties such as flexibility and low production cost. Atomically thin transition metal dichalcogenides (TMDs) are another class of emerging materials with superior electronic and optical properties. Integrating them into van der Waals (vdW) heterostructures provides an opportunity to harness the advantages of both material systems. However, building such heterojunctions by conventional physical vapor deposition (PVD) of OSCs is challenging, since the growth is disrupted due to limited diffusion of the molecules on the TMD surface. Here we report wafer-scale (3-inch) fabrication of transferable OSC nanosheets with thickness down to 15 nm, which enable the realization of heterojunction devices. By controlled dissolution of a poly(acrylic acid) film, on which the OSC films were grown by PVD, they can be released and transferred onto arbitrary substrates. OSC crystal quality and optical anisotropy are preserved during the transfer process. By transferring OSC nanosheets (p-type) onto prefabricated electrodes and TMD monolayers (n-type), we fabricate and characterize various electronic devices including unipolar, ambipolar and antiambipolar field-effect transistors. Such vdW p-n heterojunction devices open up a wide range of possible applications ranging from ultrafast photodetectors to conformal electronics.

Near-Equilibrium Growth of Chemically Stable Covalent Organic Framework/Graphene Oxide Hybrid Materials for the Hydrogen Evolution Reaction.

Facile synthesis and post-processing of covalent organic frameworks (COFs) under mild synthetic conditions are highly sought after and important for widespread utilizations in catalysis and energy storage. Here we report the synthesis of the chemically stable aza-fused COFs BPT-COF and PT-COF by a liquid-phase method. The process involves the spontaneous polycondensation of vicinal diamines and vicinal diketones, and is driven by the near-equilibrium growth of COF domains at a very low monomer concentration. The method permits in situ assembly of COFs and COF-GO hybrid materials and leads to the formation of a uniform conducting film on arbitrary substrates on vacuum filtration. When used as electrocatalysts, the as-prepared membranes show a fast hydrogen evolution reaction (HER) with a low overpotential (45 mV at 10 mA cm-2 ) and a small Tafel slope (53 mV dec-1 ), which are the best among metal-free catalysts. Our results may open a new route towards the preparation of highly π-conjugated COFs for multifunctional applications.

Near‐Equilibrium Growth of Chemically Stable Covalent Organic Framework/Graphene Oxide Hybrid Materials for the Hydrogen Evolution Reaction

AbstractFacile synthesis and post‐processing of covalent organic frameworks (COFs) under mild synthetic conditions are highly sought after and important for widespread utilizations in catalysis and energy storage. Here we report the synthesis of the chemically stable aza‐fused COFs BPT‐COF and PT‐COF by a liquid‐phase method. The process involves the spontaneous polycondensation of vicinal diamines and vicinal diketones, and is driven by the near‐equilibrium growth of COF domains at a very low monomer concentration. The method permits in situ assembly of COFs and COF‐GO hybrid materials and leads to the formation of a uniform conducting film on arbitrary substrates on vacuum filtration. When used as electrocatalysts, the as‐prepared membranes show a fast hydrogen evolution reaction (HER) with a low overpotential (45 mV at 10 mA cm−2) and a small Tafel slope (53 mV dec−1), which are the best among metal‐free catalysts. Our results may open a new route towards the preparation of highly π‐conjugated COFs for multifunctional applications.

Releasable AlGaN/GaN 2D Electron Gas Heterostructure Membranes for Flexible Wide‐Bandgap Electronics

AbstractThe development of transferrable free‐standing semiconductor materials and their heterogeneous integration to arbitrary substrates open up new possibilities in improving device performance, exploring nonconventional manufacturing approaches, and offering a pathway to soft, conformal, and flexible electronics. In this work, flexible AlGaN/GaN high‐electron mobility transistors (HEMTs) are demonstrated, which are transfer‐printed from AlGaN/GaN on insulator to a flexible substrate using a novel releasing strategy based on the fast, facile, and reliable transfer process. Flexible AlGaN/GaN HEMTs possess good electrical performance such as the maximum saturated drain current density and transconductance of 110 mA mm−1 and 42.5 mS mm−1, respectively. Moreover, a significant piezoelectric behavior is observed when the device is under strain, resulting from the piezoelectric‐induced polarization at the heterostructure interface. Owing to an additional strain‐induced piezoelectric effect by the mechanical bending, the performance of AlGaN/GaN HEMT can be further improved. The results demonstrate that the device has great potential in applications for the next‐generation flexible electronics, such as wearable systems, intelligent microinductor systems, and smart systems that can sense or feedback external mechanical stimuli.

Liquid-Metal-Assisted Deposition and Patterning of Molybdenum Dioxide at Low Temperature.

Molybdenum dioxide (MoO2), considering its near-metallic conductivity and surface plasmonic properties, is a great material for electronics, energy storage devices and biosensing. Yet to this day, room-temperature synthesis of large area MoO2, which allows deposition on arbitrary substrates, has remained a challenge. Due to their reactive interfaces and specific solubility conditions, gallium-based liquid metal alloys offer unique opportunities for synthesizing materials that can meet these challenges. Herein, a substrate-independent liquid metal-based method for the room temperature deposition and patterning of MoO2 is presented. By introducing a molybdate precursor to the surrounding of a eutectic gallium-indium alloy droplet, a uniform layer of hydrated molybdenum oxide (H2MoO3) is formed at the interface. This layer is then exfoliated and transferred onto a desired substrate. Utilizing the transferred H2MoO3 layer, a laser-writing technique is developed which selectively transforms this H2MoO3 into crystalline MoO2 and produces electrically conductive MoO2 patterns at room temperature. The electrical conductivity and plasmonic properties of the MoO2 are analyzed and demonstrated. The presented metal oxide room-temperature deposition and patterning method can find many applications in optoelectronics, sensing, and energy industries.