Bi8Te3, the 11-Atom Layer Member of the Tetradymite Homologous Series

Bi8Te3 is a member of the tetradymite homologous series, previously shown to be compositionally and structurally distinct from hedleyite, Bi7Te3, yet inadequately characterized structurally. The phase is identified in a sample from the Hedley district, British Columbia, Canada. Compositions are documented by electron probe microanalysis and structures are directly imaged using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). Results confirm that Bi8Te3 has an 11-atom layer structure, in which three Bi-Bi pairs are placed adjacent to the five-atom sequence (Te-Bi-Te-Bi-Te). Bi8Te3 has trigonal symmetry (space group R3¯m) with unit cell dimensions of a = ~4.4 Å and c = ~63 Å calculated from measurements on representative electron diffraction patterns. The model is assessed by STEM simulations and EDS mapping, all displaying good agreement with the HAADF STEM imaging. Lattice-scale intergrowths are documented in phases replacing Bi8Te3, accounting for the rarity of this phase in nature. These results support prior predictions of crystal structures in the tetradymite homologous series from theoretical modeling and indicate that other phases are likely to exist for future discovery. Tetradymite homologues are mixed-layer compounds derived as one-dimensional superstructures of a basic rhombohedral sub-cell. Each member of the series has a discrete stoichiometric composition and unique crystal structure.

Scanning Tunneling Microscopy Observation of WSe2 Surface

The surface structure of the WSe2 were studied using scanning tunneling microscopy. Exfoliation method in an ultra-high-vacuum chamber method is used to obtain a clean surface of WSe2 samples with atomically smooth terraces and multi-layer steps. Atomic-resolution images revealed two types of atomic defects of surface or near surface. These defects have been identified as the defects in the tungsten atom layer just below the topmost selenium layer.

Amorphizing noble metal for single-atom-layer catalysis

The authors have requested that this preprint be withdrawn due to erroneous posting.

Amorphizing noble metal for single-atom-layer catalysis

Rational design of noble catalysts with a potential to leverage efficiency at the atomic scale is vital for industrial applications. Such an ultimate atom-utilization efficiency can be achieved when all noble atoms exclusively contribute to catalysis. Here, we demonstrate a scalable synthesis of freestanding amorphous PtSex (where 1.2 < x < 1.3) layers acting as single-atom-layer of Pt catalysts with an unprecedentedly high atom-utilization efficiency (~ 30 wt%) at the monolayer limit. The amorphous PtSex behaviors a fully-activated surface accessible to catalytic reactions. The catalytic performance of the amorphous layer is featured by a nearly 100% current density relative to a pure Pt surface and reliable production of sustained high-flux hydrogen over a 2-inch sized wafer sample as a proof-of-concept. Furthermore, an electrolyser using the PtSex amorphous layer as a cathode is demonstrated to generate a high current density of 1000 mA cm− 2. Such an amorphization strategy is potentially extendable to other noble metals, including Pd, Ir, Os, Rh, and Ru elements, demonstrating the universality of single-atom-layer catalysts.

Sample Preparation Using Graphene-Oxide-Derived Nanomaterials for the Extraction of Metals

Graphene oxide is a compound with a form similar to graphene, composed of carbon atoms in a sp2 single-atom layer of a hybrid connection. Due to its significant surface area and its good mechanical and thermal stability, graphene oxide has a plethora of applications in various scientific fields including heterogenous catalysis, gas storage, environmental remediation, etc. In analytical chemistry, graphene oxide has been successfully employed for the extraction and preconcentration of organic compounds, metal ions, and proteins. Since graphene oxide sheets are negatively charged in aqueous solutions, the material and its derivatives are ideal sorbents to bind with metal ions. To date, various graphene oxide nanocomposites have been successfully synthesized and evaluated for the extraction and preconcentration of metal ions from biological, environmental, agricultural, and food samples. In this review article, we aim to discuss the application of graphene oxide and functionalized graphene oxide nanocomposites for the extraction of metal ions prior to their determination via an instrumental analytical technique. Applications of ionic liquids and deep eutectic solvents for the modification of graphene oxide and its functionalized derivatives are also discussed.

The Comprehensive Study of Low Thermospheric Sodium Layers during the 24th Solar Cycle

The low thermospheric sodium layer (LTSL) is the separate sodium atom layer above 105 km. Based on 11,607 h of lidar observations from Yanqing (40.5° N, 116.0° E) from 2010 to 2016, we found 38 LTSLs wherein the peak densities were more than five percent above those of the main sodium layers. This work presents the peak altitudes, peak local times and peak densities of the LTSLs as well as the long-term characteristics of the seasonal and inter-annual variations of LTSLs. We analyzed the correlation between the LTSL and sporadic E layer (Es). The seasonal variation trends of the occurrences of LTSL and Es are similar, and the results showed that 95% of the LTSLs were accompanied by Es. We also found that 69% of the LTSL cases exhibited apparent downward phase progressions, while the descending rates of the LTSLs are consistent with the phase speeds of the tide.