A Highly Efficient Heterogeneous Processor for SAR Imaging.

The expansion and improvement of synthetic aperture radar (SAR) technology have greatly enhanced its practicality. SAR imaging requires real-time processing with limited power consumption for large input images. Designing a specific heterogeneous array processor is an effective approach to meet the power consumption constraints and real-time processing requirements of an application system. In this paper, taking a commonly used algorithm for SAR imaging-the chirp scaling algorithm (CSA)-as an example, the characteristics of each calculation stage in the SAR imaging process is analyzed, and the data flow model of SAR imaging is extracted. A heterogeneous array architecture for SAR imaging that effectively supports Fast Fourier Transformation/Inverse Fast Fourier Transform (FFT/IFFT) and phase compensation operations is proposed. First, a heterogeneous array architecture consisting of fixed-point PE units and floating-point FPE units, which are respectively proposed for the FFT/IFFT and phase compensation operations, increasing energy efficiency by 50% compared with the architecture using floating-point units. Second, data cross-placement and simultaneous access strategies are proposed to support the intra-block parallel processing of SAR block imaging, achieving up to 115.2 GOPS throughput. Third, a resource management strategy for heterogeneous computing arrays is designed, which supports the pipeline processing of FFT/IFFT and phase compensation operation, improving PE utilization by a factor of 1.82 and increasing energy efficiency by a factor of 1.5. Implemented in 65-nm technology, the experimental results show that the processor can achieve energy efficiency of up to 254 GOPS/W. The imaging fidelity and accuracy of the proposed processor were verified by evaluating the image quality of the actual scene.

Surface and Interface Regulation of MXenes: Methods and Properties.

Since the discovery of Ti3 C2 Tx in 2011, 2D transition metal carbides, nitrides, and carbonitrides, known as MXenes, have been attracting great attention as the emerging member of 2D materials. The surface terminations, intercalants, and the interfaces between MXenes and other substances are of importance for tuning the properties of MXenes. For instance, surface termination of MXenes can change the density of states at the Fermi levels to make MXenes electronically tunable. Different terminations can lead to band opening and changes in behavior from metallic to semiconducting, as well as dramatic changes in the work function of MXenes. On the other hand, electron transfer occurring at the interface between MXenes and other substances due to the physical interaction/chemical bonding, changes the electron configuration of MXenes and realizes the functionalization. In this review, the most up-to-date progress of the surface and interface regulation of MXenes is comprehensively summarized, introducing the effect of various synthesis methods on the surface and interface chemistry, the routes on tuning the surface and interface chemistry, and the related potential applications. Finally, the perspective of the future research directions and challenges on surface and interface regulation is outlined.

Simultaneously tuning interlayer spacing and termination of MXenes by Lewis-basic halides.

The surface and interface chemistry are of significance on controlling the properties of two-dimensional transition metal carbides and nitrides (MXenes). Numerous efforts have been devoted to the regulation of Ti3C2Tx MXene, however, tuning interlayer spacing and surface halogen termination of other MXenes (besides Ti3C2Tx) is rarely reported while demanded. Here we propose a Lewis-basic halides treatment, which is capable of simultaneously engineering the interlayer spacing and surface termination of various MXenes. Benefited from the abundant desolvated halogen anions and cations in molten state Lewis-basic halides, the -F termination was substituted by nucleophilic reaction and the interlayer spacing was enlarged. Ti3C2Tx MXene treated by this method showed a high specific capacity of 229 mAh g-1 for Li+ storage, which is almost 2 times higher than pristine one. Considering the universality, our method provides an approach to regulating the properties of MXenes, which may expand their potential applications in energy storage, optoelectronics and beyond.

High-temperature stability in air of Ti3C2Tx MXene-based composite with extracted bentonite.

Although Ti3C2Tx MXene is a promising material for many applications such as catalysis, energy storage, electromagnetic interference shielding due to its metallic conductivity and high processability, it's poor resistance to oxidation at high temperatures makes its application under harsh environments challenging. Here, we report an air-stable Ti3C2Tx based composite with extracted bentonite (EB) nanosheets. In this case, oxygen molecules are shown to be preferentially adsorbed on EB. The saturated adsorption of oxygen on EB further inhibits more oxygen molecules to be adsorbed on the surface of Ti3C2Tx due to the weakened p-d orbital hybridization between adsorbed O2 and Ti3C2Tx, which is induced by the Ti3C2Tx/EB interface coupling. As a result, the composite is capable of tolerating high annealing temperatures (above 400 °C for several hours) both in air or humid environment, indicating highly improved antioxidation properties in harsh condition. The above finding is shown to be independent on the termination ratio of Ti3C2Tx obtained through different synthesis routes. Utilized as terahertz shielding materials, the composite retains its shielding ability after high-temperature treatment even up to 600 °C, while pristine Ti3C2Tx is completely oxidized with no terahertz shielding ability. Joule heating and thermal cycling performance are also demonstrated.

Emerging Topochemical Strategies for Designing Two-Dimensional Energy Materials.

The unique properties of two-dimensional (2D) materials make them increasingly attractive in various fields, especially for energy harvesting, conversion, or storage. Simultaneously, numerous synthetic methods have been rapidly developed. Recently, topochemical strategies were demonstrated, and they show tremendous promising potential for synthesizing 2D materials due to their simplicity, scalability, and high efficiency. Considering the suitability of material structures and their synthesis methods, as well as the relationship between material properties and applications, it is necessary for researchers to comprehensively review and determine the prospects of 2D materials based on topological chemical synthesis methods and their related applications. Therefore, in this review, we systematically summarize and analyze the representative topochemical strategies for synthesizing 2D materials, including salt-templating methods for non-layered 2D materials, molten Lewis acid etching strategy for novel MXenes, and the chalcogen vapors etching and substituting strategy for phase-controlled 2D materials and so on, with the application of these 2D materials in energy-related fields including batteries, supercapacitors, and electrocatalysis. At the end of the paper, the corresponding perspective was also illustrated, and we expect that this could provide a reference for the future research in the field.

Nacre-inspired composite films with high mechanical strength constructed from MXenes and wood-inspired hydrothermal cellulose-based nanofibers for high performance flexible supercapacitors.

Two dimensional MXenes with fascinating characteristics of high electrical conductivity, high density and electroactivity show promising applications in various fields. However, the direct applications of MXenes have been limited due to their inferior mechanical properties and easy restacking. Herein, a kind of nacre-like composite film constructed with Ti3C2Tx, cellulose nanofiber (HCNF) and sodium lignosulfonate (Lig) obtained through the hydrothermal process, named Ti3C2Tx/HCNF@Lig, has been successfully synthesized. The hydrothermal cellulose nanofiber (HCNF) film shows an enhanced mechanical strength (114 MPa) compared to that of the CNF film (95 MPa). Wood-inspired HCNF@Lig composite films present an enhanced mechanical tensile strength of up to 133 MPa. Nacre-like deformable Ti3C2Tx/HCNF@Lig(3@1) composite films exhibit high conductivity (up to 1.75 × 105 S m-1) and mechanical properties (up to 258 MPa). The electrodes of Ti3C2Tx/HCNF@Lig(3@1)97/3 composite film assembled flexible solid-state supercapacitors possess an excellent volumetric specific capacitance of 748.96 F cm-3. The corresponding deformable supercapacitors show an excellent energy density of 16.2 W h L-1 and outstanding electrochemical cycling stability. The as-prepared nacre-like Ti3C2Tx/HCNF@Lig composite films with high mechanical properties and electrochemical performance are expected to be practically applied in flexible/wearable energy storage devices.