Polycrystalline Few-Layer Graphene as a Durable Anticorrosion Film for Copper.

Corrosion of metals in atmospheric environments is a worldwide problem in industry and daily life. Traditional anticorrosion methods including sacrificial anodes or protective coatings have performance limitations. Here, we report atomically thin, polycrystalline few-layer graphene (FLG) grown by chemical vapor deposition as a long-term protective coating film for copper (Cu). A six-year old, FLG-protected Cu is visually shiny and detailed material characterizations capture no sign of oxidation. The success of the durable anticorrosion film depends on the misalignment of grain boundaries between adjacent graphene layers. Theoretical calculations further found that corrosive molecules always encounter extremely high energy barrier when diffusing through the FLG layers. Therefore, the FLG is able to prevent the corrosive molecules from reaching the underlying Cu surface. This work highlights the interesting structures of polycrystalline FLG and sheds insight into the atomically thin coatings for various applications.

Solid-State Lithium Batteries with Ultrastable Cyclability: An Internal-External Modification Strategy.

A commonly used strategy to tackle the unstable interfacial problem between Li1.3Al0.3Ti1.7(PO4)3 (LATP) and lithium (Li) is to introduce an interlayer. However, this strategy has a limited effect on stabilizing LATP during long-term cycling or under high current density, which is due in part to the negative impact of its internal defects (e.g., gaps between grains (GBs)) that are usually neglected. Here, control experiments and theoretical calculations show clearly that the GBs of LATP have higher electronic conductivity, which significantly accelerates its side reactions with Li. Thus, a simple LiCl solution immersion method is demonstrated to modify the GBs and their electronic states, thereby stabilizing LATP. In addition to LiCl filling, composite solid polymer electrolyte (CSPE) interlayering is concurrently introduced at the Li/LATP interface to realize the internal-external dual modifications for LATP. As a result, electron leakage in LATP can be strictly inhibited from its interior (by LiCl) and exterior (by CSPE), and such dual modifications can well protect the Li/LATP interface from side reactions and Li dendrite penetration. Notably, thus-modified Li symmetrical cells can achieve ultrastable cycling for more than 3500 h at 0.4 mA cm-2 and 1500 h at 0.6 mA cm-2, among the best cycling performance to date.

Raman Spectroscopy of Multi-Layer Graphene epitaxially Grown on 4H-SiC by Joule Heat Decomposition.

We developed a Joule heating decomposition (JHD) method, which applied direct current on the SiC for the epitaxial growth of multi-layer graphene (MLG) films on Si-terminated (0001) face of the high doping 4H-SiC substrate. By this JHD method, the growth time for preparing MLG was only several minutes. Raman spectroscopy was employed to study the influence of the temperature caused by the Joule heating on the quality and the uniformity of the sample. Then, other properties, such as the strain, the layer's number, and the electric characteristics, of the MLG were studied in details. It was found that the quality of the MLG was substantially dependent on the growth temperature (operation current) and the growth time, while the layer's number was only dependent on the growth temperature but not the growth time. Finally, less-defect and homogeneous MLG (~ 45 layers) with an area of ~ 12 × 5 mm2 could be obtained at a heating temperature of ~ 1470 °C with duration time of 5 min. By using the linear transmission line method, the specific contact resistance of Au and MLG was 5.03 × 10-5 Ω cm2, and the sheet resistance was 52.36 Ω/sq, respectively.

Tuning the Surface Morphologies and Properties of ZnO Films by the Design of Interfacial Layer.

Wurtzite ZnO films were grown on MgO(111) substrates by plasma-assisted molecular beam epitaxy (MBE). Different initial growth conditions were designed to monitor the film quality. All the grown ZnO films show highly (0001)-oriented textures without in-plane rotation, as illustrated by in situ reflection high-energy electron diffraction (RHEED) and ex situ X-ray diffraction (XRD). As demonstrated by atomic force microscopy (AFM) images, "ridge-like" and "particle-like" surface morphologies are observed for the ZnO films grown in a molecular O2 atmosphere with and without an initial deposition of Zn adatoms, respectively, before ZnO growth with oxygen plasma. This artificially designed interfacial layer deeply influences the final surface morphology and optical properties of the ZnO film. From room-temperature photoluminescence (PL) measurements, a strong defect-related green luminescence band appears for the ZnO film with a "particle-like" morphology but was hardly observed in the films with flat "ridge-like" surface morphologies. Our work suggests that the ZnO crystallinity can be improved and defect luminescence can be reduced by designing interfacial layers between substrates and epilayers.