Sunday, February 05, 2012

High frequency impedance spectroscopy on ZnO nanorod arrays.

High frequency impedance spectroscopy on ZnO nanorod arrays.

The radio-frequency (rf)-to-microwave impedance spectra of solution grown ZnO nanorods have been measured from 0.1 to 50 GHz using vector network analysis. To increase interaction with rf/microwave fields, the nanorods were assembled by dielectrophoresis into arrays on coplanar waveguides. 

The average complex impedance frequency response per nanorod in an array was accurately modeled as a simple three-element circuit composed of the inherent nanorod resistance in series with a parallel resistor-capacitor representing the contact. 

The nanorod resistance dominates at high frequencies while the contact impedance dominates at low frequencies, permitting a quantitative separation of contact effects from nanorod properties. The average inherent resistivity of a nanorod was found to be ∼10-2 Ω cm, indicating the nanorods were unintentionally highly doped. Accuracy of the inherent resistance measurement was limited by the highly conductive nature of the nanorods used and the upper limit of the experimental frequency range. Determination of the nanorod resistance becomes more accurate for higher resistivity nanorods, so high frequency impedance spectroscopy will provide an increasingly valuable electrical characterization technique as the ability to synthesize more intrinsic (i.e., lower unintentional dopant density) ZnO nanorods improves.

Scrymgeour, D. A., Highstrete, C., Lee, Y., Hsu, J. P., & Lee, M. (2010). High frequency impedance spectroscopy on ZnO nanorod arrays. Journal Of Applied Physics107

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