NU 2005-060

Inventors

Mark Hersam*

Liam Pingree

Short Description

A conductive atomic force microscopy (cAFM) adjunct that is capable of quantitatively measuring the magnitude and phase of alternating current flow through the tip/sample junction with a five order of magnitude improvement in sensitivity

Abstract

Northwestern scientists have developed a conductive atomic force microscopy (cAFM) adjunct that is capable of quantitatively measuring the magnitude and phase of alternating current flow through the tip/sample junction with a five order of magnitude improvement in sensitivity. This technology called bridge enhanced nanoscale impedance microscopy (BE-NIM) offers significant improvement in sensitivity and spatial resolution for the study of electronic behavior in nanomaterials and biological samples. While macroscopic impedance spectroscopy techniques have been employed to characterize alternating current charge transport for a variety of materials systems and devices, they only reveal an ensemble average of the underlying contributions of individual pathways, defects, film thickness variations, electrochemical reactions, and failure mechanisms. Scanning probe impedance measurement techniques based on the conductive Atomic Force Microscope (cAFM) has enabled probing current flow and resistivity variations on conductive surfaces with nanoscale spatial resolution; however, fringe capacitance (1-100 picoF) between the sample and the probe imposes a serious detection limit. In an effort to improve the sensitivity of nanoscale impedance microscopy, BE-NIM offers a variable resistor/capacitor (RC) bridge circuit to cancel the spurious contribution to the AC current flow caused by fringe capacitance. This addition significantly improves the detection limit of NIM by at least five orders of magnitude, enabling the detection of impedance values that are typical for many nanostructures, nano-electrochemical cells, and biological systems.

Applications

• Study of electrical properties of nanomaterials and biological samples

Advantages

• Greater spatial resolution
• Greater sensitivity

Publications

Pingree L and Hersam M (2005) Bridge enhanced nanoscale impedance microscopy. Appl Phys Lett. 87: 233117.

IP Status

Issued US Patent No. 7,705,617