Nanomechanical Resonators towards Single Spin Sensitivity
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Ultrasensitive force detectors are required for progress towards single atom imaging using magnetic resonance force microscopy (MRFM). MRFM is a scanned probe imaging technique, with potential for atomic-scale, non-destructive and sub-surface imaging. To achieve the goal of single atom imaging, technical development towards realization of high magnetic field gradients as well as force detectors with very high sensitivity are necessary. Given values of field gradients that can be achieved at present (typically of the order of 10 5 T/m), force sensitivity of an atto-newton (10-18 N/√Hz) at low temperatures (0.3 - 4 K) is required for single spin sensitivity. This has been achieved using optical interferometry; however, optical interferometers corrupt measurements by heating the cantilevers and inducing decoherence of spins in the sample. Thus, there is a need to develop a light-free technique to measure cantilever motion with high sensitivity. In this dissertation, a design for ultrasensitive force detection using capacitive sensing is developed. Thermomechanical noise and position detection sensitivity constraints are addressed. The fabrication of an ultra-thin, nanomechanical force sensing cantilever with an integrated sense electrode for capacitive detection (double cantilever architecture) is accomplished. Gallium Arsenide field effect transistors with potential for integration onto the double cantilever chips are fabricated and characterized at low temperatures. Measurement techniques for capacitive detection are explored and lay the groundwork for future research towards the development of integrated nanomechanical force detectors towards single spin sensitivity for magnetic resonance force microscopy.