This review intertwines current engineering strategies tailoring the carrier injection and carrier transport of two-dimensional transition metal dichalcogenides toward efficient electronic devices.

This article presents a comprehensive review of the current research addressing the surface effects on physical properties and potential applications of nanostructured ZnO. Studies illustrating the transport, photoluminescence (PL), and photoconductivity properties of ZnO with ultrahigh surface-to-volume (S/V) ratio are reviewed first. Secondly, we examine recent studies of the applications of nanostructured ZnO employing the surface effect on gas/chemical sensing, relying on a change of conductivity via electron trapping and detrapping process at the surfaces of nanostructures. Finally, we comprehensively review the photovoltaic (PV) application of ZnO nanostructures. The ultrahigh S/V ratios of nanostructured devices suggest that studies on the synthesis and PV properties of various nanostructured ZnO for dye-sensitized solar cells (DSSCs) offer great potential for high efficiency and low-cost solar cell solutions. After surveying the current literature on the surface effects on nano-structured ZnO, we conclude this review with personal perspectives on a few surface-related issues that remain to be addressed before nanostructured ZnO devices can reach their ultimate potential as a new class of industrial applications.

The interaction between chemisorbed oxygen adatoms (O2(ad)−) and oxygen vacancies associated with the formation/rupture of conductive filaments dominates the switching yield of ZnO, which is also confirmed by the fact that the reduction of SET/RESET voltage with the temperature. The pronounced surface effect-induced conductivity lowering due to O2(ad)− chemisorption leads to increased resistance of high resistance state (HRS). The current decay of the HRS with increased temperatures/times is owing to the severe O2(ad)− chemisorption as Joule heating is continuously applied. The statistical analysis for over 400 cells provides essential evidence for evaluating the surface effect on resistive switching.

Organic semiconductors demonstrate several advantages over conventional inorganic materials for novel electronic and optoelectronic applications, including molecularly-tunable properties, flexibility, low-cost, and facile device integration. However, before organic semiconductors can be used for the next generation of devices, such as ultrafast photodetectors (PDs), it is necessary to develop new materials that feature both high mobility and ambient stability. Toward this goal, we demonstrate a highly stable PD based on organic single crystal [PtBr2(5,5′-bis(CF3CH2OCH2)-2,2′-bpy)] (or "Pt complex (1o)") as the active Revised Manuscript Furthermore, the device features a maximum photoresponsivity of 1×10 3 A/W, a detectivity of 1.1×10 12 cm Hz-1/2 W-1 at 5 V, and a record fast response/recovery time of 80/90 μs, which has never been previously achieved in other organic PDs. Our findings strongly support and promote the use of single crystal Pt complex (1o) in the next generation of organic optoelectronic devices.

Organic-inorganic perovskites have arrived at the forefront of solar technology due to their impressive carrier lifetimes and superior optoelectronic properties. By having the cm-sized perovskite single crystal and employing device patterning techniques, and the transfer length method (TLM), we are able to get the insight into the metal contact and carrier transport behaviors, which is necessary for maximizing device performance and efficiency. In addition to the metal work function, we found that the image force and interface charge pinning effects also affect the metal contact, and the studied single crystal CH 3 NH 3 PbBr 3 features Schottky barriers of 0.17 eV, 0.38 eV, and 0.47 eV for Au, Pt, and Ti electrodes, respectively. Furthermore, the surface charges lead to the thermally activated transport from 207 K to 300 K near the perovskite surface. In contrast, from 120 K to 207 K, the material exhibited three-dimensional (3D) variable range hopping (VRH) carrier transport behavior. Understanding these fundamental contact and transport properties of perovskite will enable future electronic and optoelectronic applications. Graphical abstract3

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CitationEffect of ultraviolet illumination on metal oxide resistive memory 2014, 105 (25):253111 Applied Physics Letters

We demonstrated a nanocontacting scheme using a focus ion beam (FIB) system without further heat treatment for ZnO nanowires. This scheme includes Ga ion surface modification and direct-write Pt deposition induced by Ga ion, leading to an Ohmic nanocontact with a specific contact resistance as low as 2.5 × 10(-6)Ω cm(2). Temperature-dependent measurements show that the transport of the FIB-Pt contact on the ZnO nanowire with local surface modification is governed by field emission tunneling. Taking advantage of area-selected and room-temperature processes, Ga ion surface modification and direct-write Pt deposition using a FIB system demonstrates a feasible Ohmic scheme.