Zeitschriftenaufsätze

In the studies presented here, the subsequent growth of graphene on hexagonal boron nitride (h-BN) is achieved by the thermal decomposition of molecular precursors and the catalytic assistance of metal substrates. The epitaxial growth of h-BN on Pt(111) is followed by the deposition of a temporary Pt film that acts as a catalyst for the fabrication of the graphene sheet. After intercalation of the intermediate Pt film underneath the boron-nitride mesh, graphene resides on top of h-BN. Scanning tunneling microscopy and density functional calculations reveal that the moiré pattern of the van-der-Waals-coupled double layer is due to the interface of h-BN and Pt(111). While on Pt(111) the graphene honeycomb unit cells uniformly appear as depressions using a clean metal tip for imaging, on h-BN they are arranged in a honeycomb lattice where six protruding unit cells enframe a topographically dark cell. This superstructure is most clearly observed at small probe-surface distances. Spatially resolved inelastic electron tunneling spectroscopy enables the detection of a previously predicted acoustic hybrid phonon of the stacked materials. Its' spectroscopic signature is visible in surface regions where the single graphene sheet on Pt(111) transitions into the top layer of the stacking.

The origin of excellent lithium storage ability and high irreversible capacity is probably the least understood component for transition-metal oxalates as anode materials in lithium-ion batteries. Considerable efforts have been put into understanding their electrochemical reaction mechanisms, but these insights have mostly been unilateral and unsystematic. Herein, the interface characteristic between iron oxalate anode and electrolyte and detailed conversion process were investigated to explore the source of irreversible Li+ storage. In particular, a gelatinous "organic" layer identified oxygen, fluorine and phosphorus as the main chemical elements can be re-oxidized and exhibits an obviously reversible conversion between sedimentation and decomposition during its initial lithiation process, despite the general belief that it shows similar electrochemically inert to solid-electrolyte interphase (SEI). Meanwhile, this special interface layer leads to higher ability of Li+ ions diffusion and smaller charge-transfer resistance, which is the vital role for excellent rate capability. Furthermore, ex situ FTIR analysis confirms the formation and residue of new intermediate compound of Li2Fe(C2O4)2, thus making a part of initial irreversible capacity. It is also found that the iron oxalate electrode with larger capacitive contribution still has more widely application in energy storage of supercapacitors in future.

The transfer of an ultrathin membrane onto arbitrary substrates is important in different practical fields. Conventional wet-transfer methods inevitably induce wrinkle defects as a result of the large contact angle of the trapped droplet between the membrane and the substrate. Here, we demonstrate a gas flow-assisted method (GFAM) to transfer centimeter (cm)-scale ultrathin membranes onto arbitrary substrates (including a curved substrate) without wrinkles. GFAM makes use of contact angle hysteresis to bulge the trapped droplet between the substrate and the ultrathin membrane and simultaneously stretch the ultrathin membrane during rapid dewetting driven by gas flow. Moreover, GFAM can be easily fulfilled by using compressed air for seconds. Compared with conventional hydrophilic treatments or organic liquid wetting, this method has no durability concern and does not change the surface nature of substrates. Taking a widely used ultrathin anodic aluminum oxide (AAO) membrane as an example, we successfully demonstrate the application of a large-area wrinkle-free ultrathin AAO membrane to defect-free ordered nanostructure array fabrication and investigate the micro-scale details of macro-scale wrinkles generated by the conventional ways. In addition, its corresponding superiority over the defective counterpart is further studied in optical sensing. This method is highly valuable for promoting the simplicity of large-area ultrathin membrane transfer in practice.