Multidimensional SPM applied for nanoscale conductance mapping
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Ilja Grishin and Oleg V. Kolosov Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom
Bryan D. Hueya) Department of Materials Science and Engineering, University of Connecticut, Storrs, Connecticut 06269-3136 (Received 29 August 2013; accepted 19 November 2013)
A new approach has been developed for nanoscale conductance mapping (NCM) based on multidimensional atomic force microscopy (AFM) to efficiently investigate the nanoscale electronic properties of heterogeneous surfaces. The technique uses a sequence of conductive AFM images, all acquired in a single area but each with incrementally higher applied voltages. This generates a matrix of current versus voltage (I–V) spectra, providing nanoscale maps of conductance and current nonlinearities with negligible spatial drift. For crystalline and amorphous phases of a GeSe chalcogenide phase change film, conductance and characteristic amorphous phase “turn-on” voltages are mapped with results providing traditional point-by-point I–V measurements, but acquired hundreds of times faster. Although similar to current imaging tunneling spectroscopy in a scanning tunneling microscope, the NCM technique does not require conducting specimens. It is therefore a promising approach for efficient, quantitative electronic investigations of heterogeneous materials used in sensors, resistive memories, and photovoltaics.
I. INTRODUCTION
For several decades, the electronic properties of materials have been characterized with various atomic force microscopy (AFM)1-based approaches targeting optimization of the designs and performance of a wide range of electronic devices. Such electronic investigations are especially relevant to micro- and nanoelectromechanical systems (MEMS/NEMS),2–6 organic and ceramic photovoltaics,7–9 oxide semiconductors,10–14 phase change memories,15–20 and other systems.21–28 In these devices, the nanoscale spatial distribution in the local electronic response is critical for their operation, but its characterization is increasingly difficult to achieve as dimensions diminish and complexity rises. Of course, scanning tunneling microscopy (STM) can be utilized for current or conductance detection in circumstances where specimens are sufficiently conducting, but specialized surface preparation and/or vacuum environment is often required.29 Therefore, AFM-based measurements have become more commonplace,30–33 as they are more compatible with lower conductivity specimens than STM necessitates and/or samples where only particular regions are conducting. Two main approaches have emerged. In first, the AFM maps currents with nanoscale resolution by scanning an area with a fixed a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.365 J. Mater. Res., Vol. 28, No. 24, Dec 28, 2013
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voltage and recording the current, pixel-by-pixel.2,26,32,34 Such individual images are excellent at qualitatively identifying heterogeneities, especially as they can be dire
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