The elastic modulus of ZnO nanowires was measured using a resonance method based on laser Doppler effect and their fracture strains were determined via two-point bending with the aid of optical nanomanipulation. The elastic moduli of ZnO nanowires with diameters of 78 to 310 nm vary from 123 to 154 GPa, which are close to the bulk value of 140 GPa and independent of the diameters and surface defects. However, the fracture strains of the ZnO nanowires depend significantly on their diameters, increasing from 2.1% to 6.0% with the decrease in diameter from 316 to 114 nm. Post-mortem TEM analysis of the ends of the fractured nanowires revealed that fracture initiated at surface defects. The Weibull statistical analysis demonstrated that a greater defect depth led to a smaller fracture strain. The surface-defect dominated fracture should be an important consideration for the design and application of nanowire-based nanoelectromechanical systems.

A scanning tunneling microscope (STM) has been developed, dedicated for use on artificially fabricated nanostructures at low temperatures. With this STM mesoscopic phenomena can be studied, combining the unique possibilities of scanning tunneling microscopy and artificially fabricated nanostructures for investigating the physics in this regime. The STM is vibration insensitive, has reliable coarse approach mechanisms in three dimensions, and operates at low temperatures. In order to be able to position the tip above the structure of interest, also a searching strategy has been developed. In this article we describe design and operation of the STM and demonstrate searching.

A thermal resonant method was developed to accurately determine the temperature-dependent Young's moduli of nanowires. In this method, the frequency spectra of a [0001]-oriented ZnO nanowire cantilever at elevated temperatures were measured using scanning laser Doppler vibrometry. The temperature-dependent Young's moduli were derived from the resonant frequencies using Euler-Bernoulli beam theory. It was found that the modulus of ZnO nanowires decreased linearly with the increase of temperature from 300 to 650 K, independent of the nanowire diameter ranged from 101 to 350 nm. The temperature coefficient that defines the linear relationship between the dimensionless modulus and temperature is -´--( ) 1.087 0.018 10 K , 4 1 which agrees with that of - ´--( ) 1.266 0.549 10 K , 4 1 being calculated using molecular dynamics with a partially charged rigid ion model.

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