Fringe Field Corrections in nvCPD Probe Tip Applications
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This thesis addresses the fabrication, evaluation, and analysis of the probe tip of a non-vibrating contact potential difference sensor. The non-vibrating contact potential difference (nvCPD) probe measures the work function variation on a conducting surface and recent experiments performed to measure the size of surface features have shown poor correlation between actual and calculated probe tip dimensions. In order to address this deficiency, experiments were done and an analytical model was developed, including fringe electrical fields, that predicts the shape of the nvCPD probe signal as a function of probe tip geometry, work function variation, and experimental parameters. Probe tips were constructed with varying geometric properties and experiments using these probe tips were compared to a model. There was good correlation of the nvCPD probe output for a known work function change and probe tip geometry. The effective area of the probe tip resulting from electrical field fringing is expected to increase with dielectric thickness to a finite value, based on pre-existing electrostatic models for a shielded parallel plate capacitor. The minimum fringe field obtained in these experiments was for a 3.18mm diameter probe tip with a dielectric thickness of 0.20mm. The fringe field diameter was 3.38mm at a fly height of 0.60mm, representing an effective probe tip area increase of 13%.