Xingxing Zhang

The doping of three‐dimensional (3D) graphene has emerged as a topic of interest because of attempts to combine its large available surface area and superior catalytic, structural, chemical, and biocompatible characteristics that can be induced by doping. This review provides an overview of the scalable chemical‐vapor‐deposition‐based growth of doped 3D graphene materials and their applications in various contexts.

Abstract

Graphene doping principally commenced to compensate for its inert nature and create an appropriate bandgap. Doping of 3D graphene has emerged as a topic of interest because of attempts to combine its large available surface area—arising from its interconnected porous architecture—with superior catalytic, structural, chemical, and biocompatible characteristics that can be induced by doping. In light of the latest developments, this review provides an overview of the scalable chemical vapor deposition (CVD)‐based growth of doped 3D graphene materials as well as their applications in various contexts, such as in devices used for energy generation and gas storage and biosensors. In particular, single‐ and multielement doping of 3D graphene by various dopants (such as nitrogen (N), boron (B), sulfur (S) and phosphorous (P)), the doping configurations of the resultant materials, an overview of recent developments in the field of CVD, and the influence of various parameters of CVD on graphene doping and 3D morphologies are focused in this paper. Finally, this report concludes the discussion by mentioning the existing challenges and future opportunities of these developing graphitic materials, intending to inspire the unveiling of more exciting functionalized 3D graphene morphologies and their potential properties, which can hopefully realize many possible applications.

Various theoretical and experimental researches regarding the mechanism of degradation and passivation strategies are proposed and reported to overcome the problem of the ambient instability of phosphorene. Here, not only an extensive summary of these passivation strategies but also an overview of the fabrication methods, challenges, and suitable applications of phosphorene are provided.

Abstract

Phosphorene as a rising star is a monolayer or few‐layer form of black phosphorus (BP), which is used as a 2D material, in addition to graphene. This monoelemental 2D material has gained considerable attention in the fields of electronics, optoelectronics, and biomedicine due to its extraordinary physical properties. However, as both theoretical and experimental works show, the intrinsic instability of phosphorene under ambient conditions is a major challenge in practical applications. Various theoretical and experimental researches regarding the mechanism of the degradation and passivation strategies are proposed and reported to overcome the problem of the ambient instability of phosphorene. These strategies have enabled researchers to conduct fundamental studies on phosphorene's extraordinary properties. Here, not only an extensive summary of these passivation strategies but also an overview of the fabrication methods, challenges, and suitable applications of phosphorene are provided.

X‐ray photoemission electron microscopy reveals the resistive‐switching mechanism in brownmillerite SrFeO_2.5 memristive devices. The resistance change is caused by a reversible phase transition between an insulating brownmillerite SrFeO_2.5 and a conductive perovskite SrFeO_{3− δ} phase. Devices with out‐of‐plane oriented oxygen vacancy channels promote localized phase transitions, while devices with in‐plane vacancy channels show nonlocalized phase transitions.

Abstract

Redox‐based memristive devices are one of the most attractive candidates for future nonvolatile memory applications and neuromorphic circuits, and their performance is determined by redox processes and the corresponding oxygen‐ion dynamics. In this regard, brownmillerite SrFeO_2.5 has been recently introduced as a novel material platform due to its exceptional oxygen‐ion transport properties for resistive‐switching memory devices. However, the underlying redox processes that give rise to resistive switching remain poorly understood. By using X‐ray absorption spectromicroscopy, it is demonstrated that the reversible redox‐based topotactic phase transition between the insulating brownmillerite phase, SrFeO_2.5, and the conductive perovskite phase, SrFeO₃, gives rise to the resistive‐switching properties of SrFeO _x memristive devices. Furthermore, it is found that the electric‐field‐induced phase transition spreads over a large area in (001) oriented SrFeO_2.5 devices, where oxygen vacancy channels are ordered along the in‐plane direction of the device. In contrast, (111)‐grown SrFeO_2.5 devices with out‐of‐plane oriented oxygen vacancy channels, reaching from the bottom to the top electrode, show a localized phase transition. These findings provide detailed insight into the resistive‐switching mechanism in SrFeO _x ‐based memristive devices within the framework of metal–insulator topotactic phase transitions.

Recent advancements in the laser fabrication of graphene‐based flexible electronic devices are comprehensively reviewed. Various laser processing technologies that enable preparation, processing, and modification of graphene and its derivatives are summarized. An overview of typical laser‐fabricated flexible electronic devices based on graphene‐related materials is presented.

Abstract

Recent years have witnessed the rise of graphene and its applications in various electronic devices. Specifically, featuring excellent flexibility, transparency, conductivity, and mechanical robustness, graphene has emerged as a versatile material for flexible electronics. In the past decade, facilitated by various laser processing technologies, including the laser‐treatment‐induced photoreduction of graphene oxides, flexible patterning, hierarchical structuring, heteroatom doping, controllable thinning, etching, and shock of graphene, along with laser‐induced graphene on polyimide, graphene has found broad applications in a wide range of electronic devices, such as power generators, supercapacitors, optoelectronic devices, sensors, and actuators. Here, the recent advancements in the laser fabrication of graphene‐based flexible electronic devices are comprehensively summarized. The various laser fabrication technologies that have been employed for the preparation, processing, and modification of graphene and its derivatives are reviewed. A thorough overview of typical laser‐enabled flexible electronic devices that are based on various graphene sources is presented. With the rapid progress that has been made in the research on graphene preparation methodologies and laser micronanofabrication technologies, graphene‐based electronics may soon undergo fast development.

Large‐size 1T‐VSe₂ monolayers are successfully produced at high yield by electrochemical exfoliation of bulk crystal. To guard against air‐induced degradation, thiol molecules are introduced to passivate the VSe₂ flakes, allowing the observation of robust room‐temperature ferromagnetism in monolayer VSe₂.

Abstract

Among van der Waals layered ferromagnets, monolayer vanadium diselenide (VSe₂) stands out due to its robust ferromagnetism. However, the exfoliation of monolayer VSe₂ is challenging, not least because the monolayer flake is extremely unstable in air. Using an electrochemical exfoliation approach with organic cations as the intercalants, monolayer 1T‐VSe₂ flakes are successfully obtained from the bulk crystal at high yield. Thiol molecules are further introduced onto the VSe₂ surface to passivate the exfoliated flakes, which improves the air stability of the flakes for subsequent characterizations. Room‐temperature ferromagnetism is confirmed on the exfoliated 2D VSe₂ flakes using a superconducting quantum interference device (SQUID), X‐ray magnetic circular dichroism (XMCD), and magnetic force microscopy (MFM), where the monolayer flake displays the strongest ferromagnetic properties. Se vacancies, which can be ubiquitous in such materials, also contribute to the ferromagnetism of VSe₂, although density functional theory (DFT) calculations show that such effect can be minimized by physisorbed oxygen molecules or covalently bound thiol molecules.

Research on the integration of graphene with group‐IV elementary semiconductors, which can complement and enhance the intrinsic properties of the semiconductor through graphene's superior and unique properties, is actively under way. The recent progress in the direct growth of graphene on the Si and Ge surface and its applications are comprehensively summarized.

Abstract

Since the first development of large‐area graphene synthesis by the chemical vapor deposition (CVD) method in 2009, CVD‐graphene has been considered to be a key material in the future electronics, energy, and display industries, which require transparent, flexible, and stretchable characteristics. Although many graphene‐based prototype applications have been demonstrated, several important issues must be addressed in order for them to be compatible with current complementary metal‐oxide‐semiconductor (CMOS)‐based manufacturing processes. In particular, metal contamination and mechanical damage, caused by the metal catalyst for graphene growth, are known to cause severe and irreversible deterioration in the performance of devices. The most effective way to solve the problems is to grow the graphene directly on the semiconductor substrate. Herein, recent advances in the direct growth of graphene on group‐IV semiconductors are reviewed, focusing mainly on the growth mechanism and initial growth behavior when graphene is synthesized on Si and Ge. Furthermore, recent progress in the device applications of graphene with Si and Ge are presented. Finally, perspectives for future research in graphene with a semiconductor are discussed.

Heterostructures composed of a 2D layered material (2DLM) and complex transition metal oxides (TMO) provide a new platform for the design, realization, and examination of artificial materials that are physically intriguing and technologically useful. An overview is presented for some of the examples, where various functional properties emerge at the novel 2DLM/TMO heterostructures.

Abstract

The marriage between a 2D layered material (2DLM) and a complex transition metal oxide (TMO) results in a variety of physical and chemical phenomena that cannot be achieved in either material alone. Interesting recent discoveries in systems such as graphene/SrTiO₃, graphene/LaAlO₃/SrTiO₃, graphene/ferroelectric oxide, MoS₂/SrTiO₃, and FeSe/SrTiO₃ heterostructures include voltage scaling in field‐effect transistors, charge state coupling across an interface, quantum conductance probing of the electrochemical activity, novel memory functions based on charge traps, and greatly enhanced superconductivity. In this context, various properties and functionalities appearing in numerous different 2DLM/TMO heterostructure systems are reviewed. The results imply that the multidimensional heterostructure approach based on the disparate material systems leads to an entirely new platform for the study of condensed matter physics and materials science. The heterostructures are also highly relevant technologically as each constituent material is a promising candidate for next‐generation optoelectronic devices.

Two-dimensional (2D) materials are appealing for energy storage devices due to their intriguing chemical and physical properties. Herein, a promising anode material for both half/full cells is well prepared by constructing bi-continuous porous structure in Fe 2 O 3 nanosheets (bp-Fe 2 O 3 ) through a target construction method. Notably, the obtained bp-Fe 2 O 3 exhibits a unique wrinkled layer structure composed by ultrasmall Fe 2 O 3 nanoparticles, which can well shorten the charge diffusion pathway. Furthermore, the wrinkled layer structure and the presence of pores in the bp-Fe 2 O 3 sample are able to accommodate the volume variation during deep lithiation–delithiation processes, and enable electrolyte easy penetration to the whole electrode, thus significantly improving the electrochemical performance. Benefiting from the favorable electrode framing together with fast lithiation dy...