The synthesis of monolayer gold has so far been limited to free-standing several-atoms-thick layers, or monolayers confined on or inside templates. Here we report the exfoliation of single-atom-thick gold achieved through wet-chemically etching away Ti ₃ C ₂ from nanolaminated Ti ₃ AuC ₂ , initially formed by substituting Si in Ti ₃ SiC ₂ with Au. Ti ₃ SiC ₂ is a renown MAX phase, where M is a transition metal, A is a group A element, and X is C or N. Our developed synthetic route is by a facile, scalable and hydrofluoric acid-free method. The two-dimensional layers are termed goldene. Goldene layers with roughly 9% lattice contraction compared to bulk gold are observed by electron microscopy. While ab initio molecular dynamics simulations show that two-dimensional goldene is inherently stable, experiments show some curling and agglomeration, which can be mitigated by surfactants. X-ray photoelectron spectroscopy reveals an Au 4 f binding energy increase of 0.88 eV. Prospects for preparing goldene from other non-van der Waals Au-intercalated phases, including developing etching schemes, are presented.

The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni₁-xCx (0.05 ⩽ x⩽0.62) thin films have been investigated by high-resolution x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and soft x-ray absorption spectroscopy. By using x-ray as well as electron diffraction, we found carbon-containing hcp-Ni (hcp-NiCy phase), instead of the expected rhombohedral-Ni₃C. At low carbon content (4.9 at%), the thin film consists of hcp-NiCy nanocrystallites mixed with a smaller amount of fcc-NiCx. The average grain size is about 10-20 nm. With the increase of carbon content to 16.3 at%, the film contains single-phase hcp-NiCy nanocrystallites with expanded lattice parameters. With a further increase of carbon content to 38 at%, and 62 at%, the films transform to x-ray amorphous materials with hcp-NiCy and fcc-NiCx nanodomain structures in an amorphous carbon-rich matrix. Raman spectra of carbon indicate dominant sp(2) hybridization, consistent with photoelectron spectra that show a decreasing amount of C-Ni phase with increasing carbon content. The Ni 3d-C 2p hybridization in the hexagonal structure gives rise to the salient double-peak structure in Ni 2p soft x-ray absorption spectra at 16.3 at% that changes with carbon content. We also show that the resistivity is not only governed by the amount of carbon, but increases by more than a factor of two when the samples transform from crystalline to amorphous.

We measured the Mn ${\mathit{L}}_{\mathrm{\alpha },\mathrm{\beta }}$ x-ray fluorescence spectra of MnO excited by selected photon energies near the ${\mathit{L}}_{2,3}$ absorption edges. The resulting resonant inelastic x-ray scattering spectra probe low-lying electronic excited states, due to dd and charge-transfer excitations. Using a two-step model and a purely atomic approximation, we reproduce both energies and varying intensities of dd excitations relative to the electronic recombination peak. Our results show that strongly varying line shapes in resonant x-ray emission need not be due to channel interference effects. © 1996 The American Physical Society.

Unambiguous evidence for resonant photoemission in Ni is presented. Interference effects are identified at the $2p$ edges for the valence band and the 6 eV satellite. A rapid transition from a resonant Raman to an Auger-like regime shows that the core-excited states above threshold are not localized enough to significantly enhance the photoemission intensity, implying a large fraction of incoherent intensity. The results indicate that the appearance of interference effects does not require strong localization of the intermediate state.

We have performed ab initio calculations for the cubic inverse-perovskite ${\text{Sc}}_{3}E\text{N}$ $\left(E=\text{Al},\text{Ga},\text{In}\right)$ systems to study their electronic band-structures and elastic properties. In this study, we used the accurate augmented plane wave plus local orbital method to find the equilibrium structural parameters and to compute the full elastic tensors. The obtained single-crystal elastic constants were used to quantify the stiffness of the Sc-based ternary nitrides and to appraise their mechanical stability. The site-projected density of states, Fermi surfaces, and the charge-density plots have also been used to analyze the chemical bonding between the ${\text{Sc}}_6\text{N}$ cluster and the surrounding metallic lattice of either Al, Ga, or In atoms. Our calculations show that ${\text{Sc}}_3\text{GaN}$ has the largest covalent Sc-N bonding-type character with the highest Young, shear, and bulk moduli. Compared with the other two isoelectronic systems, it also behaves as the most brittle material with a relatively large elastic anisotropy.