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<jats:p> <jats:italic>The hydrogenation of two-dimensional (2D) systems can efficiently modify the physical and chemical properties of materials. Here we report a systematic study on the hydrogenation of 2D semiconductor Sn<jats:sub>2</jats:sub>Bi on Si(111) by scanning tunneling microscopy experiments and first principle calculations. The unique butterfly-like and trench-like features were observed for single H adsorption sites and hydrogen-saturated surfaces respectively, from which the bridge-site adsorption geometry can be unambiguously determined. The structural model was further confirmed by the theoretical calculations, which is in good agreement with the experimental observation. In addition, the hydrogenation is found to vanish the flat band of Sn<jats:sub>2</jats:sub>Bi and increase the band gap obviously.</jats:italic> </jats:p>

<jats:p> <jats:italic>We theoretically and experimentally show that, with water being adsorbed, the graphene oxide (GO) is converted to a spontaneously dynamic covalent material under ambient conditions, where the dominated epoxy and hydroxyl groups are mediated by water molecules to spontaneously break/reform their C–O bonds to achieve dynamic oxygen migration. This dynamic material presents structural adaptivity for response to biomolecule adsorption. Both density functional theory calculations and ab initio molecular dynamics simulations demonstrate that this spontaneously dynamic characteristics is attributed to the adsorption of water molecules, which sharply reduces the barriers of these oxygen migration reactions on GO to the level less than or comparable to the hydrogen bonding energy in liquid water</jats:italic>.</jats:p>

<jats:p> <jats:italic>Time-periodic laser driving can create nonequilibrium states not accessible in equilibrium, opening new regimes in materials engineering and topological phase transitions. We report that black phosphorus (BP) exhibits spatially nonuniform topological Floquet–Dirac states under laser illumination, mimicking the “gravity” felt by fermionic quasiparticles in the same way as that for a Schwarzschild black hole (SBH). Quantum tunneling of electrons from a type-II Dirac cone (inside BH) to a type-I Dirac cone (outside BH) emits an SBH-like Planck radiation spectrum. The Hawking temperature T<jats:sub>H</jats:sub> obtained for a fermionic analog of BH in the bilayer BP is approximately 3 K, which is several orders of magnitude higher than that in previous works. Our work sheds light on increasing T<jats:sub>H</jats:sub> from the perspective of engineering 2D materials by time-periodic light illumination. The predicted SBH-like Hawking radiation, accessible in BP thin films, provides clues to probe analogous astrophysical phenomena in solids</jats:italic>.</jats:p>

<jats:p> <jats:italic>We use femtosecond time-resolved optical reflectivity to study the photoexcited quasiparticle (QP) dynamics in the iron-based 112 type superconducting (SC) samples Ca</jats:italic> <jats:sub>0.82</jats:sub> <jats:italic>La</jats:italic> <jats:sub>0.18</jats:sub> <jats:italic>Fe</jats:italic> <jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub> <jats:italic>Ni<jats:sub>x</jats:sub>As</jats:italic> <jats:sub>2</jats:sub>, <jats:italic>with x</jats:italic> = 0 <jats:italic>and 0.024. In the parent sample, a fast and a slow relaxation emerge at temperatures below the magnetic-structure (MS) transition T</jats:italic> <jats:sub>ms</jats:sub> ≈ 50 <jats:italic>K and the SC transition T</jats:italic> <jats:sub>c</jats:sub> ≈ 33 <jats:italic>K, respectively. The latter obviously corresponds to an SC QP dynamics, which is further confirmed in the x</jats:italic> = 0.024 <jats:italic>sample with T</jats:italic> <jats:sub>c</jats:sub> ≈ 25 <jats:italic>K. The former suggests that a partial of photoexcited QP relaxation through a pesudogap (PG) channel, which is absent in the doped x</jats:italic> = 0.024 <jats:italic>sample without the MS transition</jats:italic>.</jats:p>

<jats:p> <jats:italic>We study the influence of Cr doping on magnetic properties of α-RuCl</jats:italic> <jats:sub>3</jats:sub> <jats:italic>single crystals in detail. With increasing Cr content, the c-axial lattice parameter increases gradually, implying that the Cr doping may weaken the interlayer interactions. The magnetism of Ru</jats:italic> <jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub> <jats:italic>Cr<jats:sub>x</jats:sub>Cl</jats:italic> <jats:sub>3</jats:sub> <jats:italic>single crystals evolves from a long-range AFM order to a possible spin-glass state with Cr doping. The appearance of a possible spin-glass state can be explained by the introduction of FM interaction by Cr</jats:italic> <jats:sup>3+</jats:sup> <jats:italic>ions, which competes with the AFM interaction between Ru</jats:italic> <jats:sup>3+</jats:sup> <jats:italic>ions. Moreover, the larger magnetic moment of Cr</jats:italic> <jats:sup>3+</jats:sup> <jats:italic>ion with S</jats:italic> = 3/2 <jats:italic>than Ru</jats:italic> <jats:sup>3+</jats:sup> <jats:italic>ion with J</jats:italic> <jats:sub>eff</jats:sub> = 1/2 <jats:italic>also results in a monotonic increase of the effective moment of Ru</jats:italic> <jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub> <jats:italic>Cr<jats:sub>x</jats:sub>Cl</jats:italic> <jats:sub>3</jats:sub> <jats:italic>single crystal</jats:italic>.</jats:p>

<jats:p> <jats:italic>Equipped with multiple and unique features, a terahertz absorber exhibits great potential for use in the development of communication, military, and other fields where achieving perfect broadband absorption has always been a challenge. We present a metamaterial terahertz (THz) absorber comprising a cross-dipole patch, four symmetric square patches and an asymmetric open-loop patch with a good perfect absorption rate for TE and TM polarizations. The average absorption of more than 96% occurs in the frequency range from 2.4 THz to 3.8 THz, in which the absorptance peak can reach 99.9%, as indicated by simulated results. Our design has broad potential applications in THz couplers, as well as in fields like biology and security.</jats:italic> </jats:p>

<jats:p> <jats:italic>A simple one-dimensional subwavelength plasmonic grating can support symmetry protected bound states in the continuum (BICs), but not necessarily for the non-symmetry protected BICs. By dimerizing the lattice, non-symmetry protected BIC can be supported on the dimerized grating and can be tuned readily. The mechanism for the BICs in the dimerized grating is interpreted in the viewpoint of interference between the electromagnetic multipoles.</jats:italic> </jats:p>

<jats:p> <jats:italic>A new extended solid nitrogen, referred to as post-layered-polymeric nitrogen (PLP-N, or Panda-N), was observed by further heating the layered-polymeric nitrogen (LP-N) to above 2300 K at 161 GPa. The new phase is found to be very optically transparent and exhibits ultra-large <jats:italic>d</jats:italic>-spacings ranging from 2.8 to 4.9 Å at 172 GPa, suggesting a lower-symmetry large-unit-cell 2D chain-like or 0D cluster-type structure with wide bandgap. However, the observed x-ray diffraction pattern and Raman scattering data cannot match any predicted structures in the published literature. This finding further complicates the phase diagram of nitrogen and also highlights the path dependence of the high-pressure dissociative transition in nitrogen. In addition, the phase transition from cubic gauche nitrogen (cg-N) to LP-N is observed at 157 GPa and 2000 K.</jats:italic> </jats:p>

<jats:p> <jats:italic>By vacuum sputtering and annealing processes of gold (Au) films on boron-doped diamond (BDD) surfaces, Au-nanoparticles/BDD (AuNP/BDD) composite substrates were prepared as surface-enhanced Raman scattering (SERS) substrates. The SERS performances of the substrate were investigated using methylene blue molecule as a probe. With the AuNPs having an average diameter of 20 nm, high performance of SERS was achieved at an enhancement factor of</jats:italic> 9 × 10<jats:sup>5</jats:sup>, <jats:italic>arising from the synergistic effect of electromagnetic enhancement from AuNPs and chemical enhancement from diamond. The AuNP/BDD substrate is demonstrated to be highly sensitive, reproducible, stable, and reusable for the SERS examination. Due to the facile preparation process and controllable surface morphology, the AuNP/BDD substrates are favorable as a high performance SERS platform performed in practical applications</jats:italic>.</jats:p>

<jats:p> <jats:italic>Two-dimensional (2D) materials are playing more and more important roles in both basic sciences and industrial applications. For 2D materials, strain could tune the properties and enlarge applications. Since the growth of 2D materials on substrates is often accompanied by strain, the interaction between 2D materials and substrates is worthy of careful attention. Here we demonstrate the fabrication of strained monolayer silver arsenide (AgAs) on Ag(111) by molecular beam epitaxy, which shows one-dimensional stripe structures arising from uniaxial strain. The atomic geometric structure and electronic band structure are investigated by low energy electron diffraction, scanning tunneling microscopy, x-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy and first-principle calculations. Monolayer AgAs synthesized on Ag(111) provides a platform to study the physical properties of strained 2D materials.</jats:italic> </jats:p>