Damping of a nanomechanical oscillator strongly coupled to a quantum dot

We present theoretical and experimental results on the mechanical damping of an atomic force microscope cantilever strongly coupled to a self-assembled InAs quantum dot. When the cantilever oscillation amplitude is large, its motion dominates the charge dynamics of the dot which in turn leads to nonlinear, amplitude-dependent damping of the cantilever. We observe highly asymmetric lineshapes of Coulomb blockade peaks in the damping that reflect the degeneracy of energy levels on the dot, in excellent agreement with our strong coupling theory. Furthermore, we predict that excited state spectroscopy is possible by studying the damping versus oscillation amplitude, in analogy to varying the amplitude of an ac gate voltage.Comment: 4+ pages, 4 figure

High aspect ratio cantilever tips for non-contact electrostatic force microscopy

This work focuses on the atomic force microscope: its hardware, modes of operation, and applications.The construction of a x-y sample positioner, equipped with position dependent capacitive sensor, is presented. The implementation of a temperature-controlled laser for cantilever detection, via interferometry, is also discussed.Two modes of atomic force microscopy are used. Amplitude modulation mode images are done in vacuum using Q-control to reduce the apparent Q-factor of the cantilever. Frequency modulation mode is used to obtain non-contact images and force curves above a quantum dot or gold sample. The former leads to detection of single electron charging events from a buried 2D electron gas to the surface layer of the sample. The latter was done to determine the geometric behaviour and capacitance of high-aspect ratio cantilever tips; a method for which is presented where the height, cone angle, radius of curvature and angle to the sample can be controlled