Shu Xiao

Evaporative Self-Assembly of Gold Nanorods into Macroscopic 3D Plasmonic Superlattice Arrays.

Millimeter-scale 3D superlattice arrays composed of dense, regular, and vertically aligned gold nanorods are fabricated by evaporative self-assembly. The regular organization of the gold nanorods into a macroscopic superlattice enables the production of a plasmonic substrate with excellent sensitivity and reproducibility, as well as reliability in surface-enhanced Raman scattering. The work bridges the gap between nanoscale materials and macroscopic applications.

Pre-Lithiation of Li(Ni1-x-yMnxCoy)O2 Materials Enabling Enhancement of Performance for Li-Ion Battery

Transition metal oxide materials Li(NixMnyCoz)O2 (NMCxyz) based on layered structure are potential cathode candidates for automotive Li-ion batteries because of their high specific capacities and operating potentials. However, the actual usable capacity, cycling stability, and first-cycle Coulombic efficiency remain far from practical. Previously, we reported a combined strategy consisting of depolarization with embedded carbon nanotube (CNT) and activation through pre-lithiation of the NMC host, which significantly improved the reversible capacity and cycling stability of NMC532-based material. In the present work we attempt to understand how pre-lithiation leads to these improvements on an atomic level with experimental investigation and ab initio calculations. By lithiating a series of NMC materials with varying chemical compositions prepared via a conventional approach, we identified the Ni in the NMC lattice as the component responsible for accommodating a double-layered Li structure. Specifically, much better improvements in the cycling stability and capacity can be achieved with the NMC lattices populated with Ni(3+) than those populated with only Ni(2+). Using the XRD we also found that the emergence of a double-layer Li structure is not only reversible during the pre-lithiation and the following delithiation, but also stable against elevated temperatures up to 320 °C. These new findings regarding the mechanism of pre-lithiation as well as how it affects the reversibility and stability of NMC-based cathode materials prepared by the conventional slurry approach will promote the possibility of their application in the future battery industry.

Discharge current modes of high power impulse magnetron sputtering

Based on the production and disappearance of ions and electrons in the high power impulse magnetron sputtering plasma near the target, the expression of the discharge current is derived. Depending on the slope, six possible modes are deduced for the discharge current and the feasibility of each mode is discussed. The discharge parameters and target properties are simplified into the discharge voltage, sputtering yield, and ionization energy which mainly affect the discharge plasma. The relationship between these factors and the discharge current modes is also investigated.

Controllable Formation of (004)-Orientated Nb:TiO2 for High-Performance Transparent Conductive Oxide Thin Films with Tunable Near-Infrared Transmittance

A niobium-doped titanium dioxide (Nb:TiO2, NTO) film is a promising candidate material for indium-free transparent conductive oxide (TCO) films. It is challenging and interesting to control (004)-oriented growth to decrease resistivity. In this work, NTO films with different fractions of preferential (004) orientation (η(004)) were controllably prepared by direct current sputtering. Notably, the direction of local-ordering of ions-packing could be adjusted by slightly changing the angle between the sputtering source and the glass substrate, which is identified as a key factor to determine the growth direction of a columnar crystal as well as the η(004) of films. Hall effect measurements indicate that NTO films with the highest η(004) present the lowest resistivity (6.4 × 10-4 Ω cm), which originates from super-high carrier concentration (2.9 × 1021 cm-3) and mobility (3.4 cm2 V-1 s-1). The corresponding low sheet resistance (10.3 Ω sq-1) makes it a potential material for commercial TCO films. We also observe that films with higher η(004) show lower transmittance in the near-infrared region.

Origin of Initial Current Peak in High Power Impulse Magnetron Sputtering and Verification by Non-Sputtering Discharge*

A non-sputtering discharge is utilized to verify the effect of replacement of gas ions by metallic ions and consequent decrease in the secondary electron emission coefficient in the discharge current curves in high-power impulse magnetron sputtering (HiPIMS). In the non-sputtering discharge involving hydrogen, replacement of ions is avoided while the rarefaction still contributes. The initial peak and ensuing decay disappear and all the discharge current curves show a similar feature as the HiPIMS discharge of materials with low sputtering yields such as carbon. The results demonstrate the key effect of ion replacement during sputtering.

Gold Nanorods: Evaporative Self‐Assembly of Gold Nanorods into Macroscopic 3D Plasmonic Superlattice Arrays (Adv. Mater. 13/2016)

On page 2511, X.-F. Yu, P. K. Chu, and co-workers demonstrate the successful fabrication of millimeter-scale three-dimensional superlattice arrays consisting of dense, regular, and vertically aligned gold nanorods by the evaporative self-assembly method. The excellent performance in surface-enhanced Raman scattering indicates applications in plasmonic substrates.