Date of Completion

7-11-2014

Embargo Period

7-10-2014

Keywords

AFM, Phase Change Materials, NCM, UFM, Amorphous, Crystalline

Major Advisor

Bryan D. Huey

Associate Advisor

Ramamurthy Ramprasad

Associate Advisor

George A. Rossetti, Jr.

Field of Study

Materials Science and Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Atomic Force Microscopy (AFM) has become an indispensable tool for imaging the properties of surfaces at the nanoscale. With traditional AFM variations, quantitative mapping of surface properties is possible, but typically at the expense of spatial and/or temporal resolution. Accordingly, several new multiparametric AFM techniques have been developed to overcome these drawbacks in order to detect, understand, and ultimately enhance materials properties.

The first approach has been developed for Nanoscale Conductance Mapping (NCM), to efficiently investigate the nanoscale electronic properties of heterogeneous surfaces. The technique employs a sequence of conductive atomic force microscopy 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 akin to traditional point-by-point I-V measurements, but acquired hundreds of times faster and with better spatial resolution. The methodology of the NCM technique has also been applied to spatially map the performance parameters for electro-mechanical (PMN-PT ferroelectrics) and nanotribology (SiO2/Au) measurements.

The second approach has been developed for Ultrasonic Force Microscopy (UFM), which employs high frequency vibrations to map the nanomechanical properties of stiff materials and subsurface features. Unfortunately, UFM critically depends on the usually poorly characterized high frequency behavior of AFM cantilevers. Leveraging automated multidimensional measurements, spectroscopic UFM (sUFM) is introduced to investigate a range of common experimental parameters. The data-rich sUFM signatures allow efficient optimization of ultrasonic-AFM based measurements, leading to best practices recommendations. Diverse materials such as Si, Cr, photoresist, and phase change memory films are specifically investigated.

In summary, multiparametric AFM techniques provide a means to efficiently investigate the nanoscale properties of heterogeneous surfaces with nanoscale resolution, with direct applicability to improving the performance of data storage systems, MEMS/NEMS, energy harvesting, and other semiconducting devices.

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