Explore the vast range of titles available.

It is the nature of crystals to exist in different polymorphs. The recent emergence of two-dimensional (2D) materials has evoked the discovery of a number of new crystal phases that are different from their bulk structures at ambient conditions, and revealed novel structure-dependent properties, which deserve in-depth understanding and further exploration. In this contribution, we review the recent development of crystal phase control in 2D materials, including group V and VI. transition metal dichalcogenides (TMDs), group IVA metal chalcogenides and noble metals. For each group of materials, we begin with introducing the various existing crystal phases and their structure-related properties, followed by a detailed discussion on factors that influence these crystal structures and thus the possible strategies for phase control. Finally, after summarizing the whole paper, we present the challenges and opportunities in this research direction.

Time-domain backprojection algorithms are widely used in state-of-the-art synthetic aperture radar (SAR) imaging systems that are designed for applications where motion error compensation is required. These algorithms include an interpolation procedure, under which an unknown SAR range-compressed data parameter is estimated based on complex-valued SAR data samples and backprojected into a defined image plane. However, the phase of complex-valued SAR parameters estimated based on existing interpolators does not contain correct information about the range distance between the SAR imaging system and the given point of space in a defined image plane, which affects the quality of reconstructed SAR scenes. Thus, a phase-control procedure is required. This paper introduces extensions of existing linear, cubic, and sinc interpolation algorithms to interpolate complex-valued SAR data, where the phase of the interpolated SAR data value is controlled through the assigned a priori known range time that is needed for a signal to reach the given point of the defined image plane and return back. The efficiency of the extended algorithms is tested at the Nyquist rate on simulated and real data at THz frequencies and compared with existing algorithms. In comparison to the widely used nearest-neighbor interpolation algorithm, the proposed extended algorithms are beneficial from the lower computational complexity perspective, which is directly related to the offering of smaller memory requirements for SAR image reconstruction at THz frequencies.

Flexible and diverse manipulation of electromagnetic (EM) waves in half space (reflection or transmission) has facilitated strong aspiration toward full-space wave control. However, it remains challenging to achieve independent amplitude and phase control, which seriously hinder the real-world applications. Herein, an innovative strategy of trifunctional metasurface is proposed to independently and simultaneously manipulate the amplitude and phase of circular polarized waves in full space. The multifunctional design is composed of double-layer anisotropic metasurface sandwiched with a bandpass frequency selective surface, with a frequency-direction multiplexed paradigm for on-demand control of both amplitude and phase across three independent channels. To validate the concept, a multifunctional metadevice is designed and verified by simulations and experiments, showcasing arbitrary near-field and far-field power modulation in full space. Lateral and axial bifocal metalenses with desired intensity distribution are designed in two reflection channels at 9 GHz, while multibeam generator with desired spatial scatterings and power allocations is designed in transmissive channel at 13 GHz. The finding paves the way for attaining multifunctional metadevices with amplitude and phase modulation in full space, which have potential applications in high-quality imaging and high-capacity communication systems.

This study presents a generalized design strategy for novel terahertz‐wave polarization space‐division multiplexing meta‐devices, functioning as multi‐polarization generators, modulators, and analyzers. It introduces the spin‐decoupled phase control method by combining gradient phase design with circular polarization multiplexing techniques, enabling exceptional flexibility in controlling the polarization directions and spatial distributions of multiple output beams. The meta‐device M‐4D is significantly demonstrated as proof of concept, which converts an incident linearly polarized wave into four beams with distinct polarization angles. Additionally, the advanced meta‐devices M‐2B and M‐4B are designed to generate two‐vector and four‐vector Bessel beams with tunable spatial polarization distributions. These meta‐devices demonstrate dynamic multi‐polarization beam modulation, validated through simulations and experiments. The proposed method significantly expands the design methodology for multi‐beam polarization control using all‐dielectric metasurfaces and holds promising potential for applications in imaging, sensing, particle manipulation, communication, and information processing. Moreover, it holds potential for adaptation to other spectral ranges. This study introduces spin‐decoupled phase control engineering for terahertz‐wave polarization space‐division multiplexing meta‐devices. It enables the generation of distinct polarization and vector Bessel beams, utilizing gradient grating phase design and circular polarization multiplexing. The approach enhances polarization control flexibility, with applications in terahertz imaging, communication, and processing, and potential extension across the electromagnetic spectrum.

An in-band low radar cross section (RCS) microstrip patch antenna based on a phase control metasurface is proposed. As the size of the phase control metasurface changes, it will have different phase adjustments to the incident electromagnetic wave. Two kinds of phase control metasurfaces with a 90° reflection phase difference are arranged in a checkerboard configuration and loaded above a microstrip array antenna. The metal of the microstrip array antenna can fully reflect the electromagnetic wave, so the incident wave passes through the metasurface again and forms a reflected wave with a phase difference of 180° ± 37° when passing through the phase control metasurfaces of different sizes. Thus, the microstrip array antenna can achieve in-band RCS reduction. The metamaterial forms a transmission window in the microstrip patch array antenna band to maintain the radiation performance. Finally, a reasonable agreement is obtained between the measured and simulated results.

Mode (de)multiplexers (MDMs) serve as critical foundational elements within systems for facilitating high-capacity communication, relying on mode conversions achieved through directional coupler (DC) structures. However, DC structures are challenged by dispersion issues for broadband mode coupling, particularly for high-order modes. In this work, based on the principles of phase control theory, we have devised an approach to mitigate the dispersion challenges, focusing on a thin-film lithium niobate-on-onsulator (LNOI) platform. This solution involves integrating a customized inverse-dispersion section into the device architecture, offsetting minor phase shifts encountered during the mode coupling process. By employing this approach, we have achieved broadband mode conversion from TE0 to TE1 and TE0 to TE2 within a 300 nm wavelength range, and the maximum deviations were maintained below −0.68 dB and −0.78 dB, respectively. Furthermore, the device exhibited remarkably low crosstalk, reaching down to −26 dB.

In this letter, an investigation of the use of a covariance matrix adaptation evolution strategy (CMA‐ES) algorithm is conducted as the phase‐locking method for multi‐channel coherent beam combining (CBC) for the first time. A comprehensive numerical analysis is carried out on the operational performances of the CMA‐ES based phase‐locking algorithm implemented into 7‐ and 19‐channel CBC systems in a filled‐aperture format. Through numerical simulations it can be verified that the CMA‐ES algorithm can readily lead to over 0.90 of normalised beam combining efficiency with appropriate algorithm parameter sets, which can also be optimised by a combinatorial study. The proposed CMA‐ES based phase‐locking algorithm is a feasible option for novel phase‐locking technique for a CBC system particularly when the local extremum issue becomes severe such as in CBC under turbulent atmospheric conditions.

Battery charging is a fundamental application of Wireless Power Transfer (WPT) systems that requires effective implementation of Constant Current (CC) and Constant Voltage (CV) power conduction modes. DC-DC converters used in WPT systems utilize large inductors and capacitors that increase the size and volume of the system in addition to causing higher DC losses. This work proposes a novel single-switch active rectifier for phase controlled WPT systems that is smaller in volume and weight as compared to conventional WPT topologies. The proposed method simplifies the control scheme using improved Digital Phase Control (DPC) and Analog Phase Control (APC) to realize the CC and CV power transfer modes. Furthermore, it prevents forward voltage losses in Silicon Carbide (SiC) switches and shoot through states with improved switching patterns. Simulation studies and experimental results are added to verify the effectiveness of the proposed methodology.

Coherent control is an ingenious tactic to steer a system to a desired optimal state by tailoring the phase of an incident ultrashort laser pulse. A relevant process is the two-photon–induced photoluminescence (TPPL) of nanoantennas, as it constitutes a convenient route to map plasmonic fields, and has important applications in biological imaging and sensing. Unfortunately, coherent control of metallic nanoantennas is impeded by their ultrafast femtosecond dephasing times so far limiting control to polarization and spectral optimization. Here, we report that phase control of the TPPL in resonant gold nanoantennas is possible. We show that, by compressing pulses shorter than the localized surface plasmon dephasing time (<20 fs), a very fast coherent regime develops, in which the two-photon excitation is sensitive to the phase of the electric field and can therefore be controlled. Instead, any phase control is gone when using longer pulses. Finally, we demonstrate pure phase control by resorting to a highly sensitive closed-loop strategy, which exploits the phase differences in the ultrafast coherent response of different nanoantennas, to selectively excite a chosen antenna. These results underline the direct and intimate relation between TPPL and coherence in gold nanoantennas, which makes them interesting systems for nanoscale nonlinear coherent control.

Phase control plays an important role in the precise synthesis of inorganic materials, as the phase structure has a profound influence on properties such as conductivity and chemical stability. Phase-controlled preparation has been challenging for the metallic-phase group-VI transition metal dichalcogenides (the transition metals are Mo and W, and the chalcogens are S, Se and Te), which show better performance in electrocatalysis than their semiconducting counterparts. Here, we report the large-scale preparation of micrometre-sized metallic-phase 1T′-MoX2 (X = S, Se)-layered bulk crystals in high purity. We reveal that 1T′-MoS2 crystals feature a distorted octahedral coordination structure and are convertible to 2H-MoS2 following thermal annealing or laser irradiation. Electrochemical measurements show that the basal plane of 1T′-MoS2 is much more active than that of 2H-MoS2 for the electrocatalytic hydrogen evolution reaction in an acidic medium.