Molybdenum Nanoscrews: A Novel Non-coinage-Metal Substrate for Surface-Enhanced Raman Scattering

Optical and scintillation properties of hybrid manganese(II) bromides with formamidinium and acetamidinium cations

In recent years, hybrid manganese(II) halides (HMHs) have attracted wide attention due to their impressive optical properties, low toxicity, and facile synthetic processibility. Being effective reabsorption-free phosphors, these compounds demonstrate the potential to be used as low-cost solution-processable scintillators. However, most of the HMHs studied to date contain bulk organic cations and, as a result, are characterized by low density and low X-ray stopping power. For this reason, we studied manganese(II) bromides with compact organic cations such as formamidinium (FA+) and acetamidinium (AcA+). In particular, we synthesized four new phases, two of which are characterized by octahedral coordination of manganese ions ((FA)MnBr3 and (AcA)MnBr3) and red emission, whereas the other two have tetrahedrally coordinated Mn2+ ions ((FA)3MnBr5 and (AcA)2MnBr4) and green emission. Photoluminescence (PL) and radioluminescence measurements demonstrated high PL quantum yields and reasonable scintillation light yields of acetamidinium-based compounds. In addition, unlike most known HMH-based scintillators, the discovered materials have a relatively high density due to the small fraction of the volume occupied by organic cations, so their X-ray attenuation coefficients are comparable to the well-known oxide scintillators.

Microwave synthesis of molybdenene from MoS2

Dirac materials are characterized by the emergence of massless quasiparticles in their low-energy excitation spectrum that obey the Dirac Hamiltonian. Known examples of Dirac materials are topological insulators, d-wave superconductors, graphene, and Weyl and Dirac semimetals, representing a striking range of fundamental properties with potential disruptive applications. However, none of the Dirac materials identified so far shows metallic character. Here, we present evidence for the formation of free-standing molybdenene, a two-dimensional material composed of only Mo atoms. Using MoS2 as a precursor, we induced electric-field-assisted molybdenene growth under microwave irradiation. We observe the formation of millimetre-long whiskers following screw-dislocation growth, consisting of weakly bonded molybdenene sheets, which, upon exfoliation, show metallic character, with an electrical conductivity of ~940 S m-1. Molybdenene when hybridized with two-dimensional h-BN or MoS2, fetch tunable optical and electronic properties. As a proof of principle, we also demonstrate applications of molybdenene as a surface-enhanced Raman spectroscopy platform for molecular sensing, as a substrate for electron imaging and as a scanning probe microscope cantilever.

Self-assembly of Au nanocrystals into large-area 3-D ordered flexible superlattice nanostructures arrays for ultrasensitive trace multi-hazard detection

Plasmonic nanoparticles that self-assemble into highly ordered superlattice nanostructures hold substantial promise for facilitating ultra-trace surface-enhanced Raman scattering (SERS) detection. Herein, we propose a boiling-point evaporation method to synthesize ordered monocrystal-like superlattice Au nanostructures (OML-Au NTs) with a polyhedral morphology. Combined with thermal nanoimprint technology, OML-Au NTs were directly transferred to impact-resistant polystyrene (IPS) flexible SERS substrates, the obtained flexible substrates (donated as OML-Au NTs/IPS) detection limit for R6G molecules as low as 10^-13 M. These results were confirmed by simulating the electromagnetic field distribution of ordered/unordered two-dimensional single-layer and three-dimensional aggregated gold nanostructures. The OML-Au NTs/IPS substrates were successfully used to detect and quantify three commonly-used agricultural pesticides, achieving detection limits as low as 10^-11 M and 10^-12 M, and in situ real-time detection limit reached 0.24 pg/cm² for thiram on apple peels, which was 3 orders of magnitude lower than the current detection limit. In addition, the Raman intensity from multiple locations showed a relative standard deviation lower than 7 %, exhibiting the reliability necessary for practical applications. As a result, this research demonstrates a highly reproducible method to enable the development of plasmonic nanomaterials with flexible superstructures.

Pyramid-Shaped Single-Crystalline Nanostructure of Molybdenum with Excellent Mechanical, Electrical, and Optical Properties

Specific geometric morphology and improved crystalline properties are of great significance for the development of materials in micro-nano scale. However, for high-melting molybdenum (Mo), it is difficult to get high-quality structures exhibiting a single-crystalline nature and preconceived morphology simultaneously. In this paper, a pyramid-shaped single-crystalline Mo nanostructure was prepared through a thermal evaporation technique, as well as a series of experimental controls. Based on detailed characterizations, the growth mechanism was demonstrated to follow a sequential process that includes MoO₂ decomposition and Mo deposition, single-crystalline islands formation, layered nucleation, and competitive growth. Furthermore, the product was measured to show excellent physical properties. The prepared nanostructures exhibited strong nano-indentation hardness, elastic modulus, and tensile strength in mechanical measurements, which are much higher than those of the Mo bulks. In the measurement of electronic characteristics, the individual structures indicated very good electrical transport properties, with a conductance of ∼0.16 S. The prepared film with an area of 0.02 cm² showed large-current electron emission properties with a maximum current of 33.6 mA and a current density of 1.68 A cm^-2. Optical properties of the structures were measured to show obvious electromagnetic field localization and enhancement, which enabled it to have good surface enhanced Raman scattering (SERS) activity as a substrate material. The corresponding structure-response relationships were further discussed. The reported physical properties profit from the basic features of the Mo nanostructures, including the micro-nano scale, the single-crystalline nature in each grain, as well as the pyramid-shaped top morphology. The findings may provide a potential material for the research and application of micro-nano electrons and photons.