Simple and Reliable Lift-Off Patterning Approach for Graphene and Graphene-Ag Nanowire Hybrid Films

Recent Advances in 1D Nanostructure Assembly and Direct Integration Methods for Device Applications

In recent years, 1D nanostructure-based devices have achieved widespread usage in various fields, such as sensors, energy harvesters, transistors, and electrodes owing to their exceptional and distinct properties. The pioneering work of Dr. R. S. Wagner at Bell Laboratories in 1964 introduced the vapor-liquid-solid (VLS) process, a powerful synthesis method. Since then, numerous synthesis techniques, including sol-gel, hydrothermal, chemical vapor deposition (CVD), physical vapor deposition (PVD), and more, have been developed. These methods have enabled researchers to effectively control the shape (length and diameter) and material properties of nanowires. However, it was only about two decades ago that nanowires started to be widely utilized as key components in functional devices, primarily due to the lack of proper integration methods. Although dozens of integration techniques have been developed, none have emerged as a predominant choice, with each method presenting its own set of advantages and limitations. Therefore, this work aims to categorize these methods based on their working principles and provide a comprehensive summary of their pros and cons. Additionally, state-of-the-art devices that capitalize on the integration of 1D nanomaterials are introduced.

Block Copolymer-Directed Facile Synthesis of N-Doped Mesoporous Graphitic Carbon for Reliable, High-Performance Zn Ion Hybrid Supercapacitor

Ordered mesoporous carbons (OMCs) are promising materials for cathode materials of a Zn ion hybrid capacitor (Zn HC) due to their high surface area and interconnected porous structure. Graphitization of the framework and nitrogen doping have been used to improve the energy storage performance of the OMCs by enhancing electrical conductivity, pseudocapacitive reaction sites, and surface affinity toward aqueous electrolytes. Thus, when both methods are simultaneously implemented to the OMCs, the Zn HC would have improved energy storage performance. Herein, we introduce a facile synthetic method for N-doped mesoporous graphitic carbon (N-mgc) by utilizing polystyrene-block-poly(2-vinlypyridine) copolymer (PS-b-P2VP) as both soft-template and carbon/nitrogen sources. Co-assembly of PS-b-P2VP with Ni precursors for graphitization formed a mesostructured composite, which was converted to N-doped graphitic carbon through catalytic pyrolysis. After selective removal of Ni, N-mgc was prepared. The obtained N-mgc exhibited interconnected mesoporous structure with high nitrogen content and high surface area. When N-mgc was employed as a cathode material in Zn ion HC, excellent energy storage performance was achieved: a high specific capacitance (43 F/g at 0.2 A/g), a high energy density of 19.4 Wh/kg at a power density of 180 W/kg, and reliable cycle stability (>3000 cycles).

Self-assembly, alignment, and patterning of metal nanowires

Armed with the merits of one-dimensional nanostructures (flexibility, high aspect ratio, and anisotropy) and metals (high conductivity, plasmonic properties, and catalytic activity), metal nanowires (MNWs) have stood out as a new class of nanomaterials in the last two decades. They are envisaged to expedite significantly and even revolutionize a broad spectrum of applications related to display, sensing, energy, plasmonics, photonics, and catalysis. Compared with disordered MNWs, well-organized MNWs would not only enhance the intrinsic physical and chemical properties, but also create new functions and sophisticated architectures of optoelectronic devices. This paper presents a comprehensive review of assembly strategies of MNWs, including self-assembly for specific structures, alignment for anisotropic constructions, and patterning for precise configurations. The technical processes, underlying mechanisms, performance indicators, and representative applications of these strategies are described and discussed to inspire further innovation in assembly techniques and guide the fabrication of optoelectrical devices. Finally, a perspective on the critical challenges and future opportunities of MNW assembly is provided.

Fabrication Technologies for the On-Chip Integration of 2D Materials

With compact footprint, low energy consumption, high scalability, and mass producibility, chip-scale integrated devices are an indispensable part of modern technological change and development. Recent advances in 2D layered materials with their unique structures and distinctive properties have motivated their on-chip integration, yielding a variety of functional devices with superior performance and new features. To realize integrated devices incorporating 2D materials, it requires a diverse range of device fabrication techniques, which are of fundamental importance to achieve good performance and high reproducibility. This paper reviews the state-of-art fabrication techniques for the on-chip integration of 2D materials. First, an overview of the material properties and on-chip applications of 2D materials is provided. Second, different approaches used for integrating 2D materials on chips are comprehensively reviewed, which are categorized into material synthesis, on-chip transfer, film patterning, and property tuning/modification. Third, the methods for integrating 2D van der Waals heterostructures are also discussed and summarized. Finally, the current challenges and future perspectives are highlighted.

Evolution of Graphene Patterning: From Dimension Regulation to Molecular Engineering

The realization that nanostructured graphene featuring nanoscale width can confine electrons to open its bandgap has aroused scientists' attention to the regulation of graphene structures, where the concept of graphene patterns emerged. Exploring various effective methods for creating graphene patterns has led to the birth of a new field termed graphene patterning, which has evolved into the most vigorous and intriguing branch of graphene research during the past decade. The efforts in this field have resulted in the development of numerous strategies to structure graphene, affording a variety of graphene patterns with tailored shapes and sizes. The established patterning approaches combined with graphene chemistry yields a novel chemical patterning route via molecular engineering, which opens up a new era in graphene research. In this review, the currently developed graphene patterning strategies is systematically outlined, with emphasis on the chemical patterning. In addition to introducing the basic concepts and the important progress of traditional methods, which are generally categorized into top-down, bottom-up technologies, an exhaustive review of established protocols for emerging chemical patterning is presented. At the end, an outlook for future development and challenges is proposed.

Highly transparent and conductive electrodes enabled by scalable printing-and-sintering of silver nanowires

Silver nanowires (Ag NWs) have good promised for flexible and transparent electronics. However, It remains an open question on how to achieve large-scale printing of Ag NWs with high optical transparency, electrical conductivity, and mechanical durability for practical applications, though extensive research has been conducted for more than a decade. In this work, we propose a possible solution that integrates screen printing of Ag NWs with flash-light sintering (FLS). We demonstrate that the use of low-concentration, screen-printable Ag NW ink enables large-area and high-resolution patterning of Ag NWs. A critical advantage comes from the FLS process that allows low-temperature processing, short operational time, and high output rate-characteristics that fit the scalable manufacturing. Importantly, we show that the resultant Ag NW patterns feature low sheet resistance (1.1-9.2 Ohm sq^-1), high transparency (75.2-92.6%), and thus a remarkable figure of merit comparable to state of the art. These outstanding properties of Ag NW patterns, together with the scalable fabrication method we propose, would facilitate many Ag NW-based applications, such as transparent heaters, stretchable displays, and wearable devices; here, we demonstrate the novel design of flexible and transparent radio frequency 5G antennas.

Solution-based, flexible, and transparent patterned reduced graphene oxide electrodes for lab-on-chip applications

The fabrication of patterned reduced graphene oxide (rGO) thin films by dispersion of graphene oxide (GO) solution on different substrates is demonstrated. The GO films are deposited on substrates and patterned using plasma-enhanced liftoff techniques. The substrate is initially treated with oxygen plasma to increase surface energy and enhance wettability thus increasing the bond between the GO flakes and the substrate. The GO film is then deposited on the substrate from a GO aqueous solution via a spin coating approach. Photolithography is then used to pattern the GO film. Finally, the GO film is chemically reduced to rGO using hydroiodic acid. The fabrication method is found to be very compatible with polymer substrates. In addition, the developed patterned rGO electrodes are employed in manipulating living cells in a microfluidic device using dielectrophoresis.

Advances in nanomaterials for electrochromic devices

This review article systematically highlights the recent advances regarding the design, preparation, performance and application of new and unique nanomaterials for electrochromic devices.