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The giant second‐order nonlinearity of SnS with ferroelectric stacking is reported. Based on theoretical calculations, the susceptibility of second harmonic generation (SHG) from SnS with ferroelectric stacking is up to 1354 pm V−1, which is three orders of magnitude higher than the values of traditional nonlinear crystals such as BBO and KTP. The SHG from ferroelectric SnS few layers is experimentally measured and its intensity is found to be 131 times larger than that of a MoS2 monolayer under the same experimental conditions, with a photon energy of 1.55 eV. The SHG susceptibility is determined to be on the order of 100 pm V−1. Numerous SnS flakes are systematically investigated using polarization‐resolved SHG. Micrometer‐sized flakes with a single domain are found, and their SHG anisotropic patterns fit well with the theoretical calculations derived from first‐principles methods. The variation in SHG anisotropic patterns, attributed to SHG interference from multiple domains, is investigated both theoretically and experimentally. Additionally, the impact of stacking disorder on the SHG anisotropic pattern is explored. It is demonstrated that polarization‐resolved SHG microscopy is a valuable tool for identifying domains in SnS flakes and examining stacking disorder. [ABSTRACT FROM AUTHOR]

Electrochemical reduction in aqueous graphene oxide (GO) dispersion has emerged as an alternative route to producing a reduced GO (rGO) membrane on Au mesh. Under scanning electron microscopy, an interesting pattern formed by distinct differences was discovered from the deoxidization evolution. Scanning transmission X-ray microscopy shows the chemical composition coordination mixing of C–OH, C–O–C, HO–C O, and C O bonds at nanoscale resolution. The electrochemical reduction of C–OH, new bonding of C–O–C, and structure recovery of C C were obtained from GO transformation into the rGO membrane. In Kelvin probe force microscopy, the same pattern of rGO was also observed for the diversity of work functions ranging from 5.55 to 5.70 eV compared with the uniform distribution of GO of 5.78 eV. Density functional theory calculations predicted that the work function variation originated from the dependence of O atom number and functional group species. A high (low) diversity in work function values was ascribed to the C–O–C (HO–C O) bond even with increasing oxygen numbers, accounting for the peak variation. Controlling the work function holds great significance for photovoltaic behavior and band alignment in photoelectric devices. Thus, growing large-area rGO membranes offers a new route to obtaining membranes for applications requiring transparent materials. [Display omitted] • Large-area and suspended membrane synthesized from the aqueous graphene oxide dispersion. • Electrochemical reduction of C–OH, interlayer connection of C–O–C, lattice reconstruct of C=C bond after the electrochemical reduction. • Work function variation studied by kelvin probe force microscopy and density function theory calculation. • Chemical composition and work function modulation for the transparent optical and electronics devices. [ABSTRACT FROM AUTHOR]

We have studied in-situ cleaved (0001) surfaces of the magnetic Weyl semimetal Mn3Sn by low-temperature scanning tunneling microscopy and spectroscopy (STM/S). It was found that freshly cleaved Mn3Sn surfaces are covered with unknown clusters, and the application of voltage pulses in the tunneling condition was needed to achieve atomically flat surfaces. STM topographs taken on the flat terrace show a bulk-terminated 1 × 1 honeycomb lattice with the Sn site brightest. First-principles calculations reveal that the brightest contrast at the Sn site originates from the surrounding surface Mn d orbitals. Tunneling spectroscopy performed on the as-cleaved and voltage-pulsed surfaces show a prominent semimetal valley near the Fermi energy. [ABSTRACT FROM AUTHOR]

We have investigated the adsorption and thermal reaction processes of NO with silicene spontaneously formed on the ZrB2/Si(111) substrate using synchrotron radiation x-ray photoelectron spectroscopy (XPS) and density-functional theory calculations. NO is dissociatively adsorbed on the silicene surface at 300 K. An atomic nitrogen is bonded to three Si atoms most probably by a substitutional adsorption with a Si atom of silicene (N≡Si3). An atomic oxygen is inserted between two Si atoms of the silicene (Si—O—Si). With increasing NO exposure, the two-dimensional honeycomb silicene structure gets destroyed, judging from the decay of typical Si 2p spectra for silicene. After a large amount of NO exposure, the oxidation state of Si becomes Si4+ predominantly, and the intensity of the XPS peaks of the ZrB2 substrate decreases, indicating that complicated silicon oxinitride species have developed three-dimensionally. By heating above 900 K, the oxide species start to desorb from the surface, but nitrogen-bonded species still exist. After flashing at 1053 K, no oxygen species is observed on the surface; SiN species are temporally formed as a metastable species and BN species also start to develop. In addition, the silicene structure is restored on the ZrB2/Si(111) substrate. After prolonged heating at 1053 K, most of nitrogen atoms are bonded to B atoms to form a BN layer at the topmost surface. Thus, BN-covered silicene is formed on the ZrB2/Si(111) substrate by the adsorption of NO at 300 K and prolonged heating at 1053 K. [ABSTRACT FROM AUTHOR]

Indium selenide (InSe) is an emerging van der Waals material, which exhibits the potential to serve in excellent electronic and optoelectronic devices. One of the advantages of layered materials is their application to flexible devices. How strain alters the electronic and optical properties is, thus, an important issue. In this work, we experimentally measured the strain dependence on the angle-resolved second harmonic generation (SHG) pattern of a few layers of InSe. We used the exfoliation method to fabricate InSe flakes and measured the SHG images of the flakes with different azimuthal angles. We found the SHG intensity of InSe decreased, while the compressive strain increased. Through first–principles electronic structure calculations, we investigated the strain dependence on SHG susceptibilities and the corresponding angle-resolved SHG pattern. The experimental data could be fitted well by the calculated results using only a fitting parameter. The demonstrated method based on first–principles in this work can be used to quantitatively model the strain-induced angle-resolved SHG patterns in 2D materials. Our obtained results are very useful for the exploration of the physical properties of flexible devices based on 2D materials. [ABSTRACT FROM AUTHOR]

Abstract: The photonic laser propulsion (PLP) system can produce continuous and constant thrust. This paper reviews its basics and then studies its application in the two-body interplanetary trajectory. This study also derives the equations of motion (EOM) for a spacecraft in an inertial frame and rotational frame for the two-body problem, and uses the Jacobi integral to investigate the spatial restrictions on trajectory. This study proposes a constraint on the smallest thrust at the launching stage, and finds the in-plane and out-of-plane equilibria. Numerical simulations confirm the validity of the derivations. The results of this paper are directly applicable to future PLP thrust missions, and particularly interplanetary travel. [Copyright &y& Elsevier]

Purpose – The purpose of this paper is to examine the effect of work characteristics on members' self-efficacy and collective efficacy, and the subsequent effect on police officers' performance. Design/methodology/approach – A multilevel model is adopted to analyze quantitative data obtained by using 812 police officers and 54 chiefs of police stations in Taiwan as the research objects. Findings – The authors found that work characteristics affected members' self-efficacy and collective efficacy, which further affected the individual- and group-level performance and the contextual effect of social work characteristics (SWCs) and collective efficacy on self-efficacy and individual performance. The authors also confirmed the cross-level moderation of social characteristics on the relationship between motivational work characteristics (MWCs) and self-efficacy, and between self-efficacy and individual performance. Research limitations/implications – A limitation was the characteristics of the sample, which consisted of mostly first-line uniformed police officers in Taiwan. From the perspective of managerial implications, it is felt that police organizations should beef up the training on police officers' collective efficacy, such as building group spirit, improving members' sense of responsibility, and building up trust with the organization. Originality/value – The findings prove that the study of work design is particularly important for enhancing the management effectiveness of police organization, because it explains the causes of a number of organizational behaviors as well as a number of important results that influence the police organization (e.g. efficacy and performance). [ABSTRACT FROM AUTHOR]

Three types of fermions play a fundamental role in our understanding of nature: Dirac, Majorana and Weyl. Whereas Dirac fermions have been known for decades, the latter two have not been observed as any fundamental particle in high-energy physics, and have emerged as a much-sought-out treasure in condensed matter physics. A Weyl semimetal is a novel crystal whose low-energy electronic excitations behave as Weyl fermions. It has received worldwide interest and is believed to open the next era of condensed matter physics after graphene and three-dimensional topological insulators. However, experimental research has been held back because Weyl semimetals are extremely rare in nature. Here, we present the experimental discovery of the Weyl semimetal state in an inversion-symmetry-breaking single-crystalline solid, niobium arsenide (NbAs). Utilizing the combination of soft X-ray and ultraviolet photoemission spectroscopy, we systematically study both the surface and bulk electronic structure of NbAs. We experimentally observe both the Weyl cones in the bulk and the Fermi arcs on the surface of this system. Our ARPES data, in agreement with our theoretical band structure calculations, identify the Weyl semimetal state in NbAs, which provides a real platform to test the potential of Weyltronics. [ABSTRACT FROM AUTHOR]

Theories involving highly energetic spin fluctuations are among the leading contenders for explaining high-temperature superconductivity in the cuprates. These theories could be tested by inelastic neutron scattering (INS), as a change in the magnetic scattering intensity that marks the entry into the superconducting state provides a precise quantitative measure of the spin-interaction energy involved in the superconductivity. However, the absolute intensities of spin fluctuations measured in neutron scattering experiments vary widely, and are usually much smaller than expected from fundamental sum rules, resulting in ‘missing’ INS intensity. Here, we solve this problem by studying magnetic excitations in the one-dimensional related compound, Sr2CuO3, for which an exact theory of the dynamical spin response has recently been developed. In this case, the missing INS intensity can be unambiguously identified and associated with the strongly covalent nature of magnetic orbitals. We find that whereas the energies of spin excitations in Sr2CuO3 are well described by the nearest-neighbour spin-1/2 Heisenberg Hamiltonian, the corresponding magnetic INS intensities are modified markedly by the strong 2p–3d hybridization of Cu and O states. Hence, the ionic picture of magnetism, where spins reside on the atomic-like 3d orbitals of Cu2+ ions, fails markedly in the cuprates. [ABSTRACT FROM AUTHOR]