S. B. Liu

Hexane-Driven Icosahedral to Cuboctahedral Structure Transformation of Gold Nanoclusters

Whether and how nanoclusters possessing a rich diversity of possible geometric configurations can transform from one structural type to another are critical issues in cluster science. Here we demonstrate an icosahedral-to-cuboctahedral structural transformation of Au nanoclusters driven by changing the chemical environment. For icosahedral Au(13) clusters protected by a mixture of dodecanethiol and triphenylphosphine ligands, solvent exchange of ethanol by hexane leads to quick selective desorption of the thiolate layers from the cluster surface. The surviving Au cores then undergo a much slower energy-minimization process via structural rearrangement, stabilized in the cuboctahedral structure and protected by triphenylphosphine in the hexane environment. In response to the dramatically changed atomic structure, the character of the electronic structure of the Au clusters is converted from semiconducting to metallic. This work addresses the structure-property correlation and its strong dependence on the chemical environment for metal nanoclusters.

Unidirectional Thermal Diffusion in Bimetallic Cu@Au Nanoparticles

Understanding the atomic diffusions at the nanoscale is important for controlling the synthesis and utilization of nanomaterials. Here, using in situ X-ray absorption spectroscopy coupled with theoretical calculations, we demonstrate a so far unexplored unidirectional diffusion from the Au shell to the Cu core in thermally alloying Cu@Au core@shell architecture of ca. 7.1 nm. The initial diffusion step at 423 K is found to be characterized by the formation of a diffusion layer composed of a Au-dilute substitutional CuAu-like intermetallic compound with short Cu-Au bond length (2.61 Å). The diffusion further happens by the migration of the Au atoms with large disorder into the interior Cu matrix at higher temperatures (453 and 553 K). These results suggest that the structural preference of a CuAu-like compound, along with the nanosized effect, plays a critical role in determining the atomic diffusion dynamics.

Test of high time resolution MRPC with different readout modes for the BESIII upgrade

In order to further enhance the particle identification capability of the Beijing Spectrometer (BESIII), it is proposed to upgrade the current end-cap time-of-flight (eTOF) detector with multi-gap resistive plate chamber (MRPC). The prototypes, together with the front end electronics (FEE) and time digitizer (TDIG) module have been tested at the E3 line of Beijing Electron Positron Collider (BEPCII) to study the difference between the single and double-end readout MRPC designs. The time resolutions (sigma) of the single-end readout MRPC are 47/53 ps obtained by 600 MeV/c proton/pion beam, while that of the double-end readout MRPC is 40 Ps (proton beam). The efficiencies of three MRPC modules tested by both proton and pion beam are better than 98%. For the double-end readout MRPC, no incident position dependence is observed

Biomembrane derived porous carbon film supported Au nanoparticles for highly reproducible surface-enhanced Raman scattering

A surface-enhanced Raman scattering (SERS) substrate based on porous carbon film supported Au nanoparticles (NPs) has been successfully fabricated by using an eggshell membrane as template. The as-prepared substrate exhibited excellent sensitivity toward Rhodamine 6G (R6G) at a low concentration of 1 × 10−9 M and great reproducibility with a small relative standard deviation (RSD) (16.3%) in the intensity of the main Raman peaks of the R6G. The good SERS signals could be due to the strong electromagnetic field coupling induced by the densely assembled Au NPs and the absence of surfactant. The high reproducibility and sensitivity in SERS was also found in the detection of Sudan dye at a low concentration of 1 × 10−8 M with a RSD of less than 20%. The results not only provide a facile and green approach to an ultrasensitive SERS substrate but also represented a new strategy to utilize daily consumption waste and turned them into useful materials for inspection of the environment pollutants and food safety.

Synthesis and Characterization of Cu-Pt Bimetallic Nanoparticles

Pt-based alloys have recently triggered a lot of attentions due to their important potential industrial applications. They provide great opportunities for the development of low-cost and high-performance fuel-cell catalysts. Many studies have already pointed out the excellent physico-chemical properties of Pt-based alloys, intimately related to their internal structure. Great efforts have been spent to characterize shape, homogeneity, dispersion, alloying extent and kinetic growth of Pt-based nano-particles. Here, we present Cu-Pt bimetallic nano-particles synthesized by the thermal decomposition method under oleylamine and OE coordination. HRTEM images show that Cu-Pt nanostructures having size of about 1.2 nm includes about 35 atoms capped by the surfactant with OA. Accurate structural information of this system has been obtained by XRD and XAFS. A charge transfer mechanism has been observed and Pt occupied Cu sites in these Cu-Pt nanoparticles.

In-situ observation of Cu-Pt core-shell nanoparticles in the atomic scale by XAFS

Bimetallic nanoparticles play an important role in potential industrial applications, such as catalysis, optoelectronics, information storage and biological labeling. Herein, homogeneous Cu-Pt core-shell nanoparticles with the averaged size of 8 nm have been synthesized by chemical methods. Cu atoms diffusion process, which motivated by heating, was observed in-situ by using temperature-dependent x-ray absorption fine-structure (XAFS) spectroscopy. Results show that Cu diffuse gradually from Cu core to Pt shell in these nanoparticles with increasing temperature. We also found the surface ligand (O) bonded Pt at the room temperature and were removed gradually by heating the sample. The analysis of the diffusion process in bimetallic nanoparticles will provide important guideline for their designing and tuning.

Synthesis and magnetic properties of samarium hydroxide nanocrystals

Samarium hydroxide (Sm(OH)3) is an important samarium compound with many potential applications in electronics, optics and catalysis. Based on a facile hydrothermal method assisted by oleic acid surface modifications we synthesized Sm(OH)3 nanocrystals with various morphologies. In this system, by adding the oleic acid surfactant both crystallization and grain size of nanocrystals can be tuned. Furthermore, the paramagnetic resonance and magnetic measurements point out that rod-like Sm(OH)3 samples are non-magnetic, while Sm(OH)3 disc-like samples exhibit weak ferromagnetism. The correlation between magnetism and morphology in Sm(OH)3 nanocrystals is associated with the surfactant-induced surface modification as well as with the changes in the localization of electrons in Sm 5d orbitals, in agreement with X-ray absorption spectroscopy data.