Density Functional Study on Adsorption of NO on AuSe (010) Surface

Quasi one-dimensional van der Waals gold selenide with strong interchain interaction and giant magnetoresistance

The atomic structure of quasi one-dimensional (1D) van der Waals materials can be regarded as the stacking of atomic chains to form thin flakes or nanoribbons, which substantially differentiates them from typical two-dimensional (2D) layered materials and 1D nanotube/nanowire array. Here we present our studies on quasi 1D gold selenide (AuSe) that possesses highly anisotropic crystal structure, excellent electrical conductivity, giant magnetoresistance, and unusual reentrant metallic behavior. The low in-plane symmetry of AuSe gives rise to its high anisotropy of vibrational behavior. In contrast, quasi 1D AuSe exhibits high in-plane electrical conductivity along the directions of both atomic chains and perpendicular one, which can be understood as a result of strong interchain interaction. We found that AuSe exhibits a near quadratic nonsaturating giant magnetoresistance of 1841% with the magnetic field perpendicular to its in-plane. We also observe unusual reentrant metallic behavior, which is caused by the carrier mismatch in the multiband transport. Our works help to establish fundamental understandings on quasi 1D van der Waals semimetallic AuSe and identify it as a new candidate for exploring giant magnetoresistance and compensated semimetals.

Colloidal and Deposited Products of the Interaction of Tetrachloroauric Acid with Hydrogen Selenide and Hydrogen Sulfide in Aqueous Solutions

The reactions of aqueous gold complexes with H2Se and H2S are important for transportation and deposition of gold in nature and for synthesis of AuSe-based nanomaterials but are scantily understood. Here, we explored species formed at different proportions of HAuCl4, H2Se and H2S at room temperature using in situ UV-vis spectroscopy, dynamic light scattering (DLS), zeta-potential measurement and ex situ Transmission electron microscopy (TEM), electron diffraction, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Metal gold colloids arose at the molar ratios H2Se(H2S)/HAuCl4 less than 2. At higher ratios, pre-nucleation “dense liquid” species having the hydrodynamic diameter of 20–40 nm, zeta potential −40 mV to −50 mV, and the indirect band gap less than 1 eV derived from the UV-vis spectra grow into submicrometer droplets over several hours, followed by fractional nucleation in the interior and coagulation of disordered gold chalcogenide. XPS found only one Au+ site (Au 4f7/2 at 85.4 eV) in deposited AuSe, surface layers of which partially decomposed yielding Au0 nanoparticles capped with elemental selenium. The liquid species became less dense, the gap approached 2 eV, and gold chalcogenide destabilized towards the decomposition with increasing H2S content. Therefore, the reactions proceed via the non-classical mechanism involving “dense droplets” of supersaturated solution and produce AuSe1−xSx/Au nanocomposites.