Knowing and controlling the resistivity of an individual nanowire (NW) is crucial for the production of new sensors and devices. For ZnO NWs this is poorly understood; a 10(8) variation in resistivity has previously been reported, making the production of reproducible devices almost impossible. Here, we provide accurate resistivity measurements of individual NWs, using a four-probe scanning tunnelling microscope (STM), revealing a dependence on the NW dimensions. To correctly interpret this behaviour, an atomic level transmission electron microscopy technique was employed to study the structural properties of the NWs in relation to three growth techniques: hydrothermal, catalytic and non-catalytic vapour phase. All NWs were found to be defect free and structurally equivalent; those grown with a metallic catalyst were free from Au contamination. The resistivity measurements showed a distinct increase with decreasing NW diameter, independent of growth technique. The increasing resistivity at small NW diameters was attributed to the dominance of surface states removing electrons from the bulk. However, a fundamental variance in resistivity (10(2)) was observed and attributed to changes in occupied surface state density, an effect which is not seen with other NW materials such as Si. This is examined by a model to predict the effect of surface state occupancy on the measured resistivity and is confirmed with measurements after passivating the ZnO surface. Our results provide an understanding of the primary influence of the reactive nature of the surface and its dramatic effect on the electrical properties of ZnO NWs.

The ability to control the properties of electrical contacts to nanostructures is essential to realize operational nanodevices. Here, we show that the electrical behavior of the nanocontacts between free-standing ZnO nanowires and the catalytic Au particle used for their growth can switch from Schottky to Ohmic depending on the size of the Au particles in relation to the cross-sectional width of the ZnO nanowires. We observe a distinct Schottky to Ohmic transition in transport behavior at an Au to nanowire diameter ratio of 0.6. The current-voltage electrical measurements performed with a multiprobe instrument are explained using 3-D self-consistent electrostatic and transport simulations revealing that tunneling at the contact edge is the dominant carrier transport mechanism for these nanoscale contacts. The results are applicable to other nanowire materials such as Si, GaAs, and InAs when the effects of surface charge and contact size are considered.

In this work we report on a universal methodology for connecting organic nanowires and nanosheets formed by p-conjugated molecules via metal nanoparticles. We present a brief study on the electrical characteristics of the thus connected nanowires carried out in a four-tip-STM manipulation and measurement system (4TMMS; STM ¼ scanning tunneling microscopy) under ultrahigh vacuum (UHV) conditions.The recent developments in organic semiconducting nanostructures have permitted important advances in the fabrication of low-cost, large-area, flexible optic and microelectronic devices.[1] In fact, over the last few years the use of p-conjugated molecules as building blocks for such organic nanostructures has received special attention and interest.[1] Within the class of p-conjugated molecules, the families of metallo porphyrins, metallo phthalocyanines, and perylenes are promising materials for varying applications such as vapor (gas) nanosensors and as active components for photonic devices, organic field effect transistors (OFETs), phototransistors, and solar cells.[2] It has been realized that the fabrication of hybrid organic!inorganic materials comprising semiconducting organic nanowires and metal particles opens new routes in the design of devices' functionality.[3] Such hybrid materials may provide a ideal model system for the study of organic!inorganic nanomaterials. Despite this promising prospect, only very few works exist regarding the formation of organic semiconducting nanofibers!metal particles hybrid systems. [3b-d,f ] In this Communication, we present a significant step forward in the fabrication of nanowire-metal-nanowire junctions by using metal nanoparticle-decorated organic nanowires as a base for the growth of secondary nanowires in such a way that a new route for the fabrication of connected organic single-crystal nanowires is demonstrated.First, we describe the organic/inorganic hybrid nanostructures prepared by decorating single-crystal organic nanowires with metal particles in a one-step dry process at room temperature. In a second step we demonstrate an unprecedented class of heterostructured nanowires formed by connection through metal nanoparticles of different organic nanostructures. Finally, the electrical conductivity of these connected nanowires is studied in a 4TMMS. [4] Preparation of Hybrid and Connected Nanowires: Recently, we have reported a universal method for the growth of squared nanowires and nanobelts formed by p-conjugated molecules on metal and non-metal substrates.[5] This protocol is based on physical vapor deposition (PVD) of the organic molecules on substrates at controlled temperatures. A high density of supported single-crystalline organic nanowires can be obtained by this methodology.[5]The preparation of the silver-decorated organic nanowires is carried out by direct current (DC) sputtering of silver at room temperature on the as-grown nanowires. DC sputtering is a versatile technique for producing metal thin films and nanoparticles (silver, gold, copper, etc.)....

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Modulation of effective Schottky barrier height of nickel silicide on silicon using pre-silicide ammonium sulfide treatment