Nanopatterned High-Frequency Supporting Structures Stably Eliminate Substrate Effects Imposed on Two-Dimensional Semiconductors.

Despite the outstanding physical and chemical properties of two-dimensional (2D) materials, due to their extremely thin nature, eliminating detrimental substrate effects such as serious degradation of charge-carrier mobility or light-emission yield remains a major challenge. However, previous approaches have suffered from limitations such as structural instability or the need of costly and high-temperature deposition processes. Herein, we propose a new strategy based on the insertion of high-density topographic nanopatterns as a nanogap-containing supporter between 2D materials and substrate to minimize their contact and to block the substrate-induced undesirable effects. We show that well-controlled high-frequency SiO x nanopillar structures derived from the self-assembly of Si-containing block copolymer securely prevent the collapse or deformation of transferred MoS2 and guarantee excellent mechanical stability. The nanogap supporters formed below monolayer MoS2 lead to dramatic enhancement of the photoluminescence emission intensity (8.7-fold), field-effect mobility (2.0-fold, with a maximum of 4.3-fold), and photoresponsivity (12.1-fold) compared to the sample on flat SiO2. Similar favorable effects observed for graphene strongly suggest that this simple but powerful nanogap-supporting method can be extensively applicable to a variety of low-dimensional materials and contribute to improved device performance.

Engineering Nanoscale Interfaces of Metal/Oxide Nanowires to Control Catalytic Activity.

The interfacial effect between a metal catalyst and its various supporting transition metal oxides on the catalytic activity of heterogeneous catalysis has been extensively explored; engineering interfacial sites of metal supported on metal oxide has been found to influence catalytic performance. Here, we investigate the interfacial effect of Pt nanowires (NWs) vertically and alternatingly stacked with titanium dioxide (TiO2) or cobalt monoxide (CoO) NWs, which exhibit a strong metal-support interaction under carbon monoxide (CO) oxidation. High-resolution nanotransfer printing based on nanoscale pattern replication and e-beam evaporation were utilized to obtain the Pt NWs cross-stacked on the CoO or TiO2 NW on the silicon dioxide (SiO2) substrate with varying numbers of nanowires. The morphology and interfacial area were precisely determined by means of atomic force microscopy and scanning electron microscopy. The cross-stacked Pt/TiO2 NW and Pt/CoO NW catalysts were estimated with CO oxidation under 40 Torr CO and 100 Torr O2 from 200 to 240 °C. Higher catalytic activity was found on the Pt/CoO NW catalyst than on Pt/TiO2 NWs and Pt NWs, which indicates the significance of nanoscale metal-oxide interfaces. As the number of nanowire layers increased, the catalytic activity became saturated. Our study demonstrates the interfacial role of nanoscale metal-oxide interfaces under CO oxidation, which has intriguing applications in the smart design of catalytic materials.