Electrical transport measurements were conducted on semiconducting nanowires and three distinct current-voltage (I-V) characteristics were observed, i.e., almost symmetric, almost rectifying, and almost linear. These I-V characteristics were modeled by treating the transport in the nanowire as in a metal-semiconductor-metal structure involving two Schottky barriers and a resistor in between these barriers, and the transport is shown to be dominated by the reverse-biased Schottky barrier under low bias and by the semiconducting nanowire at large bias. In contrast to the conventional Schottky diode, the reverse current in the nano-Schottky barrier structure is not negligible and the current is largely tunneling rather than thermionic. Experimental I-V curves are reproduced very well using our model, and a method for extracting nanowire resistance, electron density, and mobility is proposed and applied to ZnO, CdS, and Bi2S3 nanowires.

A simple one-step hydrothermal method for large-scale synthesis of ultralong single-crystalline Bi2S3 nanowires was reported, and the nanowires were comprehensively characterized. The diameters of the nanowires are about 60 nm, and their lengths range from tens of microns to several millimeters. The structure of the nanowires was determined to be of the orthorhombic phase, the growth direction was along [001], and the growth mechanism was investigated based on extensive high-resolution transmission electron microscopy observations. Optical absorption experiments revealed that the Bi2S3 nanowires are narrow-band semiconductors with a band gap E(g) approximately 1.33 eV. Electrical transport measurements on individual nanowires gave a resistivity of about 1.2 ohms cm and an emission current of 3.5 microA at a bias field of 35 V/microm. This current corresponds to a current density of about 10(5) A/cm2, which makes the Bi2S3 nanowire a potential candidate for applications in field-emission electronic devices.

A quantitative metal-semiconductor-metal (MSM) model and a Matlab based program have been developed and used to obtain parameters that are important for characterizing semiconductor nanowires (NWs), nanotubes (NTs) or nanoribbons (NRs). The use of the MSM model for quantitative analysis of nonlinear current-voltage curves of one-dimensional semiconducting nanostructures is illustrated by working through two examples, i.e., an amorphous carbon NT and a ZnO NW, and the obtained parameters include the carrier density, mobility, resistance of the NT(NW), and the heights of the two Schottky barriers formed at the interfaces between metal electrodes and semiconducting NT(NW).

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Carbon nanotube (CNT) and nanowire materials are important building materials for nanotechnology. These materials may be synthesized via a range of physical and chemical methods, and new nanotube and nanowire materials are produced every day. Measurements on individual nanostructures remain, however, difficult and it is even more challenging to control the property of these nanomaterials via structure modification at near atomic resolution. A very promising and perhaps the best method to tackle this problem is to combine the scanning tunnelling microscope (STM) with electron microscope (EM) so that manipulation and structure modification may be made via a highly controllable fashion on individual nanostructure [1][2][3].CNT can be cut, manipulated and used to form complicated patterns such as PKU as shown in Fig. 1. This operation requires a correlated manipulation of the CNT by two independent nanomanipulators [1], and in principle complicated CNT circuit may be constructed this way and its electric characteristics may be measured at each step of the pattern construction. While it is very convenient to carry out manipulation and measurement on nanostructure in a scanning electron microscope (SEM) either on or above a substrate, the resolution of the SEM is limited and the vacuum level is typically not as good as in a transmission electron microscope (TEM). The higher resolution and vacuum level in a TEM has been utilized for revealing the importance of the CNT tip structure on its electron field emission characteristics [4] and effects of deformation on the conductance of the CNT [5]. Figure 2 shows a typical bending experiment on a multi-walled CNT (~40nm in diameter) and the corresponding current passing through the CNT while it was under deformation. Experiments of this type show clearly that the conductance of the large diameter multi-walled CNT is not easily affected by deformation etc. and these CNTs may in principle be used in the fabrication of novel nanoelectronic circuit as interconnects [5].A quantitative analysis of the electric transport property of the semiconducting nanowire also requires the detailed structure of the contact and nanowire. Two terminal I-V characteritics may be measured inside TEM as shown in Fig. 3, and the diameter, length etc. of the nanowire may readily be obtained from TEM imaging and varied during experiments providing valuable input for the quantitative analysis of the transport property of the nanowires [6].

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