Polarized detection has been brought into operation for optics applications in the visible band. Meanwhile, an advanced requirement in short-wave near-infrared (SW-NIR) (700-1100 nm) is proposed. Typical IV-VI chalcogenides-2D GeSe with anisotropic layered orthorhombic structure and narrow 1.1-1.2 eV band gap-potentially meets the demand. Here we report the unusual angle dependences of Raman spectra on high-quality GeSe crystals. The polarization-resolved absorption spectra (400-950 nm) and polarization-sensitive photodetectors (532, 638, and 808 nm) both exhibited well-reproducible cycles, distinct anisotropic features, and typical absorption ratios α/α ≈ 1.09 at 532 nm, 1.26 at 638 nm, and 3.02 at 808 nm (the dichroic ratio I/I ≈ 1.09 at 532 nm, 1.44 at 638 nm, 2.16 at 808 nm). Obviously, the polarized measurement for GeSe showed superior anisotropic response at around 808 nm within the SW-NIR band. Besides, the two testing methods have demonstrated the superior reliability for each other. For the layer dependence of linear dichroism, the GeSe samples with different thicknesses measured under both 638 and 808 nm lasers identify that the best results can be achieved at a moderate thickness about 8-16 nm. Overall, few-layer GeSe has capacity with the integrated SW-NIR optical applications for polarization detection.

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Some gamma-ray bursts (GRBs) have a tera–electron volt (TeV) afterglow, but the early onset of this has not been observed. We report observations with the Large High Altitude Air Shower Observatory of the bright GRB 221009A, which serendipitously occurred within the instrument field of view. More than 64,000 photons >0.2 TeV were detected within the first 3000 seconds. The TeV flux began several minutes after the GRB trigger, then rose to a peak about 10 seconds later. This was followed by a decay phase, which became more rapid ~650 seconds after the peak. We interpret the emission using a model of a relativistic jet with half-opening angle ~0.8°. This is consistent with the core of a structured jet and could explain the high isotropic energy of this GRB.

As Moore's law approaches its end, two dimensional (2D) materials are intensely studied for their potentials as one of the "More than Moore' (MM) devices. However, the ultimate performance limits and the optimal design parameters for such devices are still unknown. One common problem for the 2D material based device is the relative weak on-current. In this study, two dimensional Schottky-Barrier Field-Effect Transistors (SBFETs) consisted with in-plane hetero-junctions of 1T metallic-phase and 2H semiconducting-phase Transition-Metal Dichalcogenide (TMD) are studied following the recent experimental synthesis of such devices at much larger scale. Our ab initio simulation reveals the ultimate performance limits of such devices, and offers suggestions for better TMD materials. Our study shows that the Schottky-Barrier heights (SBH) of the in-plane 1T/2H contacts are smaller than the SBH of out-of-plane contacts, and the contact coupling is also stronger in the in-plane contact. Due to the atomic thickness of the mono-layer TMD, the average subthreshold swing (SS) of the in-plane TMD-SBFETs are found to be close to the limit of 60mV/dec, and smaller than that of out-of-plane TMD-SBFET device. Different TMDs are considered, and it is found that the in-plane WTe 2-SBFET provides the best performance, and it can satisfy the performance requirement of sub-10nm high performance (HP) Transistor outlined by International Technology Roadmap for Semiconductors (ITRS), thus could be developed into a viable sub-10nm MM device in the future.

Large scale (up to 30 μm in lateral size) atomically thin hexagonal ZrS2 nanoflakes were prepared on traditional substrates (silica, sapphire) through a temperature dependent growth process.

Monolayer Schottky barrier (SB) field-effect transistors based on the in-plane heterojunction of 1T/1T'-phase (metallic) and 2H-phase (semiconducting) transition-metal dichalcogenides (TMDs) have been proposed following the recent experimental synthesis of such devices. By using density functional theory and ab initio simulations, intrinsic device performance, sub-10 nm scaling, and performance boosting of MoSe, MoTe, WSe, and WTe, SB field-effect transistors are systematically investigated. We find that the Schottky barrier heights (SBHs) of these in-plane 1T(1T')/2H contacts are proportional to their band gaps: the bigger band gap corresponds to bigger SBH. For four TMDs, the SBH of 1T/2H contact is always smaller than that of 1T'/2H contact. The WTe SB field-effect transistor can provide the best performance and satisfy the requirement of the high-performance transistor outlined by the International Technology Roadmap for Semiconductors down to a 6 nm gate length. In addition, the replacement of suitable 1T-TMD on the source/drain regions can modulate conduction band SB, leading to the 8.8 nm WSe SB field-effect transistor also satisfying the requirement. Moreover, the introduction of the underlap can increase the effective channel length and reduce the coupling between the source/drain and the channel, leading to the 5.1 nm WTe SB field-effect transistor also satisfying the International Technology Roadmap for Semiconductors high-performance requirement. The underlying physical mechanisms are discussed, and it is concluded that the in-plane SB engineering is the key point to optimize such two-dimensional devices.

The optimization of the atomic and molecular clusters with a large number of atoms is a very challenging topic. This article proposes a parallel differential evolution (DE) optimization scheme for large-scale clusters. It combines a modified DE algorithm with improved genetic operators and a parallel strategy with a migration operator to address the problems of numerous local optima and large computational demanding. Results of Lennard-Jones (LJ) clusters and Gupta-potential Co clusters show the performance of the algorithm surpasses those in previous researches in terms of successful rate, convergent speed, and global searching ability. The overall performance for large or challenging LJ clusters is enhanced significantly. The average number of local minimizations per hit of the global minima for Co clusters is only about 3-4% of that in previous methods. Some global optima for Co are also updated. We then apply the algorithm to optimize the Pt clusters with Gupta potential from the size 3 to 130 and analyze their electronic properties by density functional theory calculation. The clusters with 13, 38, 54, 75, 108, and 125 atoms are extremely stable and can be taken as the magic numbers for Pt systems. It is interesting that the more stable structures, especially magic-number ones, tend to have a larger energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. It is also found that the clusters are gradually close to the metal bulk from the size N > 80 and Pt38 is expected to be more active than Pt75 in catalytic reaction.

Germanium selenide (GeSe) is an isoelectronic analogue of phosphorene, which has been studied widely in recent experiments. In this paper, we have investigated tunable electronic structures and transport properties of 2D and quasi-1D GeSe by using a self-consistent ab initio approach. The calculated band structures show stretching and compression in the zigzag direction and stretching in the armchair direction, and all can enlarge the band gap of 2D GeSe nanosheet. However, the compression in the armchair direction will reduce the band gap of the 2D GeSe nanosheet. In addition, appropriate compressions in both directions can change the 2D GeSe nanosheet from indirect band gap to direct band gap. When the 2D GeSe nanosheet is cut into a quasi-1D nanoribbon, the band structures can be modulated by the ribbon width and the passivation. The unpassivated zigzag GeSe nanoribbons are metals regardless of the ribbon width. The H-passivated zigzag GeSe nanoribbons are semiconductors with direct band gaps, and the band gaps decrease with increasing ribbon width. The unpassivated armchair GeSe nanoribbons are semiconductors with direct band gaps, and H-passivated armchair GeSe nanoribbons are semiconductors with indirect band gaps. Their band gaps all decrease with increasing ribbon width. In addition, we find that the in-plane contact structure of the unpassivated zigzag GeSe nanoribbon and H-passivated zigzag GeSe nanoribbon can lead to the formation of a Schottky barrier, which results in rectifying current–voltage characteristics.