Yongna Zhang’s research while affiliated with Chongqing Institute of Green and Intelligent Technology and other places

In this paper, we propose a graphene-based radar cross section (RCS) tunable antenna that utilizes metal mesh and graphene, both of which are optically transparent. The graphene sandwich structure is introduced to replace traditional components like diodes, micro-electro-mechanical systems (MEMS), and varactors, acting as an electromagnetic wave controller and significantly simplifying the device's complexity. By applying different voltages, the electrical properties of graphene are altered, enabling the regulation of reflection, transmission, and absorption of electromagnetic waves. This not only modifies the antenna's pattern but also achieves a substantial reduction in out-of-band RCS. The radiation and scattering mechanism of the antenna is carefully elaborated. The numerical and experimental results match well, which validates the effectiveness of the proposed method. The optical transmittance of the device is 27.9% at 550 nm, and the out-of-band RCS reduction is 10.01 dB at 3.83 GHz. The transparent, RCS tunable antenna proposed has significant potential applications in optical and microwave stealth technology.

Graphene plasmonic modulators can manipulate the mid‐infrared light in transmission mode, which is currently challenging for traditional liquid crystal and digital micromirror devices, opening up a new avenue for infrared scene projection, infrared optical communication, and hyper spectra imaging. Nevertheless, their efficiencies are not high enough due to the single‐layer atomic thickness and low free carrier density of graphene. Here, it is demonstrated that the modulation efficiency can be significantly improved by enhancing the asymmetric light‐plasmon coupling. A general theoretical model is established to describe the modulation behaviors of the modulator, revealing the critical role of the asymmetric coupling rate. By using dielectric environment engineering and graphene structure design experimentally to enhance the asymmetric coupling rate from 0.45×10 ¹² to 7.05×10 ¹² s ⁻¹ , the modulation efficiency has been improved from 4% to 41% at 1530 cm ⁻¹ , while maintaining the bandwidth as large as 230 cm ⁻¹ . The modulator outperforms previous transmission‐type graphene plasmonic modulators in both efficiency and bandwidth, presenting great potential in next‐generation infrared integrated photonics platforms.

Graphene nanowalls (GNWs) have emerged as a promising material in the field of photodetection, thanks to their exceptional optical, electrical, mechanical, and thermodynamic properties. However, the lack of a comprehensive review in this domain hinders the understanding of GNWs' development and potential applications. This review aims to provide a systematic summary and analysis of the current research status and challenges in GNW-based photodetectors. We begin by outlining the growth mechanisms and methods of GNWs, followed by a discussion on their physical properties. Next, we categorize and analyze the latest research progress in GNW photodetectors, focusing on photovoltaic, photoconductive, and photothermal detectors. Lastly, we offer a summary and outlook, identifying potential challenges and outlining industry development directions. This review serves as a valuable reference for researchers and industry professionals in understanding and exploring the opportunities of GNW materials in photodetection.

Twin crystals, the formation energy of which is much smaller than that of ordinary grain boundaries, widely exist in the annealed copper and are hard to eliminate. The study of the effects of twin boundaries on graphene growth is of great significance to the understanding of graphene epitaxy. However, there are few studies on the effects of twin boundaries on the graphene growth process. Here, this article experimentally demonstrates that graphene islands are subjected to different compressive strains from the opposite copper crystal plane after growing across the twin boundary. Further results reveal that graphene can grow across different twin boundaries, such as atom steps, narrow valleys, and even micron‐scale ridges, without forming linear defect. Therefore, strain‐induced graphene doping can be manipulated with the type of twin boundaries and the location on the twin crystals. The transition region where the degree of doping changes monotonically across the twin boundary further confirms the different spatial doping phenomena of graphene islands. This work provides a new perspective for understanding the effect of twin boundaries on the graphene epitaxy, which is expected to have a potential impact on growing high‐quality graphene on twinned copper substrates.

Single-crystal Cu not only has high electrical and thermal conductivity, but can also be used as a promising platform for the epitaxial growth of two-dimensional materials. Preparing large-area single-crystal Cu foils from polycrystalline foils has emerged as the most promising technique in terms of its simplicity and effectiveness. However, the studies on transforming polycrystalline foil into large-area single-crystal foil mainly focus on the influence of annealing temperature and strain energy on the recrystallization process of copper foil, while studies on the effect of annealing atmosphere on abnormal grain growth behavior are relatively rare. It is necessary to carry out more studies on the effect of annealing atmosphere on grain growth behavior to understand the recrystallization mechanism of metal. Here, we found that introduction of ethanol in pure argon annealing atmosphere will cause the abnormal grain growth of copper foil. Moreover, the number of abnormally grown grains can be controlled by the concentration of ethanol in the annealing atmosphere. Using this technology, the number of abnormally grown grains on the copper foil can be controlled to single one. This abnormally grown grain will grow rapidly to decimeter-size by consuming the surrounding small grains. This work provides a new perspective for the understanding of the recrystallization of metals, and a new method for the preparation of large-area single-crystal copper foils.

A helium ion beam (HIB) is ideal for milling monolayer graphene in nanopore applications, but the optimizing irradiation parameter requires a comprehensive microscopic understanding of the interaction between helium ions and the suspended graphene. In this work, we investigate the influence of the substrate hole shape on the interaction between helium ions and suspended monolayer graphene on a substrate with periodic structures of different shapes. Raman spectroscopy is used to correlate the dose of HIB irradiation with engineered defects on freestanding monolayer graphene. Raman characteristics of the suspended monolayer graphene are related to the pore size and shape of the supporting substrate upon helium ion irradiation. These provide insights into the influence of the substrate hole shape on the interaction between helium ions and a freestanding graphene membrane. Our results can be used to analyze ion-membrane interactions in the other suspended monolayer two-dimensional materials for sub-nanometer precision nanopore fabrication.

Non-through and through nanopores were introduced to study the Raman band shift of suspended graphene by the substrate edge and the helium ion beam irradiation during the fabrication of nanopore in graphene. Before the ion beam irradiation, there is a blue-shift in the G band and G’ band of suspended graphene on the micro-scale non-through and through holes edge because of the n-type mixing for suspended graphene from the translocation. After different doses of the helium ion irradiation, G’ band Raman of suspended graphene on through are blue-shift, and the G band positions are red-shift. Helium ion irradiation introduces n-type doping during the graphene nanopore fabrication. The observed Raman shifts help us to gain more intrinsic properties of the graphene nanopore. Thus, Raman spectroscopy can be used as a quantitative diagnostic tool to character graphene-based nanopore.

Batch production of continuous and uniform graphene films is critical for the application of graphene. Chemical vapor deposition (CVD) has shown great promise for mass producing high-quality graphene films. However, the critical factors affected the uniformity of graphene films during the batch production need to be further studied. Herein, we propose a method for batch production of uniform graphene films by controlling the gaseous carbon source to be uniformly distributed near the substrate surface. By designing the growth space of graphene into a rectangular channel structure, we adjusted the velocity of feedstock gas flow to be uniformly distributed in the channel, which is critical for uniform graphene growth. The monolayer graphene film grown inside the rectangular channel structure shows high uniformity with average sheet resistance of 345 Ω sq-1 without doping. The experimental and simulation results show that the placement of the substrates during batch growth of graphene films will greatly affect the distribution of gas-phase dynamics near the substrate surface and the growth process of graphene. Uniform graphene films with large-scale can be prepared in batches by adjusting the distribution of gas-phase dynamics.