Table of contents

The two-dimensional (2D) materials are regarded as the ideal solid lubricants at micro- and nano-scale. Besides the experiments and analytical models, the atomistic simulations are important tools to investigate the frictional properties of 2D materials. This review will focus the recent atomistic simulation studies on frictional properties 2D materials with a particular emphasis on the density functional theory (DFT) calculations and molecular dynamics (MD) simulations. Starting from the proper calculation of long range dispersion forces, the correlations between the physical characteristics (e.g. electronic charge redistribution, interfacial commensurability, chemical modification, moiré superlattice, layer effect, atomic contact quality, defect, external fields, humidity and temperature) and frictional properties of 2D materials are reviewed for both the interlayer and surface sliding. Meanwhile, recent MD simulations about the phononic energy dissipation in friction of 2D materials are summarized. At last, some shortcomings in current simulation techniques are summarized and it is suggested that the atomistic simulations combined with machine learning will be a more powerful strategy to investigate the frictional properties of 2D materials.

Over the past two decades, metamaterial absorbers have undergone significant advancements, evolving from microwave single-frequency designs to multi-frequency and broadband absorption, extending into the terahertz band. These absorbers have transitioned from unadjustable to adjustable and multifunctional configurations, enabled by the integration of adjustable materials, mechanical structures, and semiconductor devices. This article provides a comprehensive review of the progress achieved in the microwave to terahertz frequency range over the last five years. Key aspects covered include the absorbing mechanism of metamaterials in the microwave frequency band, with absorption efficiencies exceeding 90% for specific frequency ranges. The development of adjustable absorbers allows for frequency tunability within ±10% of the central frequency, while multifunctional absorbers enable concurrent control over absorption and reflection properties. In the terahertz regime, advanced electromagnetic simulations have led to absorber designs with bandwidths exceeding 50% of the central frequency, resulting in absorption efficiencies above 80% over the entire bandwidth. Integration of gallium nitride-based gallium nitride high electron mobility transistors provides fast switching speeds below 100 ns, facilitating rapid reconfiguration of absorber functionalities. These advancements in metamaterial absorbers offer promising prospects for intelligent and integrated designs in future applications.

The integration of two-dimensional materials into spintronics represents a frontier in the development of novel computational devices. In this work, by utilizing ab initio many-body theory, we investigate the spin dynamics within the Co-doped γ-graphyne structure, with a particular emphasis on the role of cobalt atoms as magnetic centers. The result reveals that each cobalt atom on the γ-graphyne hosts states with enough spin-density localization to facilitate both local spin flips and global spin transfers. The spin-dynamic processes in our study are characterized by ultrafast time scales and high fidelities, demonstrating efficient spin control in the system. Building upon these spin-dynamic processes, we theoretically construct a spin-based Reset-Set latch, thus demonstrating the feasibility of sophisticated logic operations in our system. Such spin-based devices exhibit the advantages of nano-spintronics over conventional-electronic approaches, offering lower energy consumption, faster operational speeds, and greater potential for miniaturization. The results highlight the efficacy of γ-graphyne nanoflakes doped with cobalt atoms as spin-information processing units, signifying a pivotal advancement in the incorporation of graphyne-based materials into sophisticated spintronic devices. This research paves the way for their application in areas such as data storage, quantum computing, and the development of complex logic-processing architectures.

Analytical calculations of interaction forces between permanent magnets are essential for the fast and accurate modeling of magnetic springs and bearings. Whereas extensive research has been conducted on interaction forces between cuboidal magnets, there is a lack of research on force calculations between other prismatic magnets in existing literature. This paper newly develops a semi-analytical method for force calculation between two magnets with rhombus-shaped cross-sections. The method is based on interaction force between two rectangular magnetically charged surfaces which are inclined toward each other. Under a Cartesian coordinate system, two components of the force between inclined rectangular magnetically charged surfaces are presented with fully analytical expressions, whereas the other component is expressed with one numerical integral. By applying these expressions repeatedly, the force between two magnets with rhombus-shaped cross-sections is derived. Moreover, a test rig is constructed to validate this semi-analytical method. Furthermore, the method can be extended to force calculations between prismatic magnets with arbitrary-shaped cross-sections, which allows a simple and fast modeling of many magnetic applications.

Recently, the optical vortex (OV) has gained increasing interest since the potential for applications of the orbital angular momentum (OAM) carried by optical vortex beams. However, generation is currently limited single static circular intensity profile, greatly constraining the breadth of achievable spatiotemporal dynamics. Here, we propose a novel phase distribution to generate a dynamic propagation OV with a customized topological charge (TC ⩾ 10) based on Fibonacci series annular subzone (FSAS) by tailoring the local phase gradient along the azimuthal direction. We describe the generation of the FSAS vortex phase. The Fibonacci vortex beam (FVB) have customization TC, multi-singularity intensity distributions. Furthermore, such optical fields exhibit the spatial dynamic rotation and self-focusing have yielded fascinating phenomena. The simulation results are agreed with the experimental results, which provide an important basis for the generation of OV with spatial dynamic propagation. These results contribute to the advanced complex light manipulation with spatial dynamic propagation and pave the way to achieve a new laser with the structured light based on modified phase control.

Radiation susceptibility of electronic devices is commonly studied as a function of radiation energetics and device physics. Often overlooked is the presence or magnitude of the electrical field, which we hypothesize to play an influential role in low energy radiation. Accordingly, we present a comprehensive study of low-energy proton irradiation on gallium nitride high electron mobility transistors (HEMTs), turning the transistor ON or OFF during irradiation. Commercially available GaN HEMTs were exposed to 300 keV proton irradiation at fluences varying from 3.76 × 10¹² to 3.76 × 10¹⁴ cm², and the electrical performance was evaluated in terms of forward saturation current, transconductance, and threshold voltage. The results demonstrate that the presence of an electrical field makes it more susceptible to proton irradiation. The decrease of 12.4% in forward saturation and 19% in transconductance at the lowest fluence in ON mode suggests that both carrier density and mobility are reduced after irradiation. Additionally, a positive shift in threshold voltage (0.32 V and 0.09 V in ON and OFF mode, respectively) indicates the generation of acceptor-like traps due to proton bombardment. high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy analysis reveal significant defects introduction and atom intermixing near AlGaN/GaN interfaces and within the GaN layer after the highest irradiation dose employed in this study. According to in-situ Raman spectroscopy, defects caused by irradiation can lead to a rise in self-heating and a considerable increase in (∼750 times) thermoelastic stress in the GaN layer during device operation. The findings indicate device engineering or electrical biasing protocol must be employed to compensate for radiation-induced defects formed during proton irradiation to improve device durability and reliability.

Infrared (IR) detectors play crucial roles in various applications. A significant milestone in advancing the next-generation low-cost silicon technology is the enhancement of hyperdoped black silicon (b-Si) photodetectors, particularly within the IR wavelength range. In this study, highly selenium (Se)-doped b-Si photodetectors. Through the optimization of laser parameters and the application of SiO₂ passivation, significant enhancements were achieved in responsivity (R), external quantum efficiency, and specific detectivity (D*) within the long-wave IR range, culminating in a D* of 1.3 × 10¹² Jones at 9.5 μm. Additionally, the Se: b-Si photodetectors maintain a D* of approximately 1.3 × 10¹¹ Jones at critical optical telecommunications wavelengths of 1.3 μm and 1.5 μm. These results significantly contribute to the advancement of IR photodetector technology and provide a foundation for the development of highly efficient, low-cost, and broadband IR detectors for Si photonic applications.

Photonic nanojets (PNJs) and photonic hooks (PHs) are two significant effects in Mesotronics. However, it is difficult to analyze and control the two phenomena generated by diffraction-based structures, such as rectangles and right-angled trapezoids, using diffraction theory. This work focuses on the modulation of incident fields by edge diffraction and the reconstruction of energy distribution, and proposes a model based on energy flows and energy reconstruction, called the 'energy-based model', to analyze the formation of PNJs and PHs through such structures. This model reveals that the morphology of PNJ and PH originates from the contributions of different regions of the incident energy, especially the crucial influence of edge diffraction, and successfully clarifies the modulation mechanism of the near-field and far-field regions of PNJ, as well as the tailoring mechanism of the two arms of PH. On the one hand, the model provides reasonable and intuitive explanations for the control of energy flow paths resulting from edge diffraction in rectangles and their variants with different parameters on the generation of PNJs and PHs. On the other hand, it also serves as a basis for reverse design. By adjusting energy flow and energy reconstruction through alterations in incident conditions or structural shapes, PHJs and PHs can be tailored easily and flexibly. The model is also been validated to be applicable in explaining many reported works. The results indicate that the 'energy-based model', which describes the energy flow paths resulting from edge diffraction, offers intuitive, convenient, and predictive advantages in analyzing the morphological variations of PNJs and PHs generated by diffraction-based structures, such as rectangles, trapezoids, and their variants. This provides a valuable reference for relevant research on Mesotronics.

The first asymmetric mode (A1 mode) lamb wave resonator (LWR) with a resonant frequency of 6 GHz based on Z-cut lithium niobate (LN) films is presented. An asymmetric electrode structure with different-sized electrode pads in the center and edged regions has been proposed, which can be used to optimize the distribution of the electric field and decrease acoustic impedance mismatch to improve the target mode. Experiment results reveal that LWRs with an asymmetric electrode structure can successfully enhance the A1 mode, achieving a high effective electromechanical coefficient ($k_{{\text{eff}}}^2$) of 26%, a quality factor (Q) of 1123, and an excellent figure-of-merit (FOM = $k_{{\text{eff}}}^2$Q) of 262. It demonstrates that asymmetric electrode structure provides a new way to suppress the spurious modes for LWRs and shows a great application prospect in wide-bandwidth and low-loss filters used in the sub-6 G frequency range.

Density functional theory calculations have been employed for the theoretical studies of the geometric structures and electronic characteristics of PdGe_n (n = 1−11) clusters. An analysis of the second- order energy differences indicates that PdGe₇ and PdGe₁₀ clusters possess superior thermodynamic stability. PdGe₁₀ displays the highest chemical stability and the lowest chemical activity, due to its largest energy gap value (E_g). Vertical ionization potential and vertical electron affinity exhibit the decreasing and increasing trends, respectively, with the increase of the number n of Ge atoms. PdGe₁₀ presents the highest electronegativity among these clusters. The analysis on the adsorption properties of PdGe_n (n = 7,10) clusters for gas molecules (e.g. CO, NO, NO₂, NH₃, SO₂ and H₂S) yields the adsorption structures, adsorption energies, Mulliken charge transfer and the changes in the electronic properties. All the listed gas molecules chemically adsorb onto PdGe₇. PdGe₁₀ has a better adsorption performance for NO₂, while its adsorption ability for CO is poorer. The potentiality of PdGe_n (n = 7, 10) clusters as gas sensors is also evaluated and reveals that NO adsorption significantly affects the electronic properties, especially conductivity, of the systems. PdGe₁₀ has an appropriate NO adsorption capacity and significant charge transfer, with the adsorption energy of −0.278 eV and the recovery time of about 10⁻⁹s, indicating its fast response and hence good potentiality as the NO sensor. In contrast, PdGe₇ has a higher adsorption capability towards NO with a lower adsorption energy of −1.16 eV, leading to the difficulty in desorption and a longer recovery time of over 12 h.

The dielectric-magnetic matching effect emerges from the presence of dual dielectric relaxation and multiple magnetic resonances. This phenomenon becomes a strategic approach in the quest to enhance microwave absorption performance by optimizing magnetic components. Herein, binary and ternary ferromagnetic alloy with tunable components embedded in carbon skeleton (core/shell) nanocapsules has been successfully fabricated by one step metal-organic chemical vapor deposition. The core/shell structure design introduces numerous interfaces that amplify dielectric loss stemming from polarization. It is important to emphasize that modifying the composition of magnetic core in these nanocapsules effectively regulates the impedance matching characteristics. As a result, the CoFeNi/C nanocapsules demonstrate an optimal reflection loss (RL_min) of −53.6 dB at a thickness of 2.55 mm, alongside an effective absorption bandwidth of 5.92 GHz at a thickness of 2.05 mm, with a filling ratio as low as 20 wt%. This study has provided valuable insights into a promising avenue for fabricating dielectric-magnetic nanocomposites with outstanding microwave attenuation capabilities through the manipulation of composited elements.

The magnetocaloric effect in the cryogenic temperature regime has gained enormous attention due to its application in the field of cryogenic refrigeration technology, which is required for quantum computing, space sciences and basic research activities. In this context, Gd- and Dy-based frustrated systems are considered as promising cryogenic magnetocaloric materials. Hence, in this paper the magnetic and magnetocaloric properties of GdTaO₄, GdNbO₄ and DyNbO₄ are comprehensively investigated. Structural analysis suggests that these compounds crystallize in a monoclinic structure, wherein magnetic ions form an elongated diamond geometry. Analysis of magnetization, heat capacity and field-dependent magnetic entropy changes confirms the presence of short-range magnetic correlations in these compounds. Additionally, a remarkably large magnetic entropy change and relative cooling power are noted. The mechanical efficiency is found to be comparable to (or even better than) those reported for good magnetic refrigerants. Our study suggests that GdTaO₄, GdNbO₄ and DyNbO₄ can be regarded as promising cryogenic magnetic refrigerant materials.

We propose a lamina-shaped metamaterial absorber based on the coherently coupled weak resonances of high-order Helmholtz resonators in this work. Such an ultra-thin lamina metamaterial can achieve broadband tunable absorption (maximal absorption >0.9), which exhibits near-perfect ventilation performance (ventilated area ratio >0.8, ratio of wind velocity >0.95). Benefiting from coherently coupled weak resonances between units with different structure parameters, the lamina metamaterial presents a broadband absorption (506–659 Hz with 2 × 3 units and 480–679 Hz with 2 × 4 units). The ultra-thin and simple structure shape of this sound absorption metamaterial lamina leads to not only an efficient ventilation performance but also high potential value in various scenarios of ventilated sound absorption, especially in ventilation tubes with high noise.

To improve the performance of energy storage devices, research into anode materials is essential. This study explores the potential of two-dimensional (2D) materials, particularly silicon carbide (Si₂C), to enhance the efficacy of lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (KIBs). Our first-principles calculations indicate that Si₂C achieves storage capacities of 174.7 mAh g⁻¹ for LIBs, 436.8 mAh g⁻¹ for SIBs, and 349.4 mAh g⁻¹ for KIBs. The exceptional performance of Si₂C comes from its high conductivity, large surface area, high capacitance, synergistic atomic radius and electronegativity effects. Furthermore, this study delves into the diffusion kinetics of Li/Na/K-ions in Si₂C, revealing extremely low energy barriers and uncovering the fundamental principles behind its superior electrochemical performance. This research emphasizes Si₂C's potential in energy storage, highlighting its capacity and diffusion advantages for Li/Na/K-ion batteries.