Piezoelectric and Magnetoelastic Strain in the Transduction and Frequency Control of Nanomechanical Resonators

Stress and strain play a central role in semiconductors, and are strongly manifested at the nanometer-scale regime. Piezoelectricity and magnetostriction produce internal strains that are anisotropic and addressable via a remote electric or magnetic field. These properties could greatly benefit the nascent field of nanoelectromechanical systems (NEMS), which promises to impact a variety of sensor and actuator applications. The piezoelectric semiconductor GaAs is used as a platform for probing novel implementations of resonant nanomechanical actuation and frequency control. GaAs/AlGaAs heterostructures can be grown epitaxially, are easily amenable to suspended nanostructure fabrication, have a modest piezoelectric coefficient roughly twice that of quartz, and if appropriately doped with manganese, can form dilute magnetic compounds. In ordinary piezoelectric transducers there is a clear distinction between the metal electrodes and piezoelectric insulator. But this distinction is blurred in semiconductors. An integrated piezoelectric actuation mechanism is demonstrated in a series of suspended anisotype GaAs junctions, notably pin diodes. A dc bias was found to alter the resonance amplitude and frequency in such devices. The results are in good agreement with a model of strain based actuation encompassing the diode’s voltage-dependent carrier depletion width and impedance. A bandstructure engineering approach is employed to control the actuation efficiency by appropriately designing the doping level and thickness of the GaAs structure. Actuation and frequency are also sensitively dependent on the device’s crystallographic orientation. This combined tuning behavior represents a novel type of depletion-mediated electromechanical coupling in piezoelectric semiconductor nanostructures. All devices are actuated piezoelectrically, whereas three techniques are demonstrated for sensing: optical interferometry, piezoresistance and piezoelectricity. Finally, a nanoelectromechanical GaMnAs resonator is used to obtain the first measurement of magnetostriction in a dilute magnetic semiconductor. Resonance frequency shifts induced by field-dependent magnetoelastic stress are used to simultaneously map the magnetostriction and magnetic anisotropy constants over a wide range of temperatures. Owing to the central role of carriers in controlling ferromagnetic interactions in this material, the results appear to provide insight into a unique form of magnetoelastic behavior mediated by holes

55th Annual Rocky Mountain Conference on Magnetic Resonance

Final program, abstracts, and information about the 55th annual meeting of the Rocky Mountain Conference on Magnetic Resonance, co-endorsed by the Colorado Section of the American Chemical Society and the Society for Applied Spectroscopy. Held in Denver, Colorado, July 28 - August 1, 2013

Implantable Nanofluidic Membrane and Smart Electronic System for Drug Release Control

L'abstract è presente nell'allegato / the abstract is in the attachmen

Molecular thin films and nanostructures for the formation of oxides

Metal oxide thin films have a wide range of applications, for example in so-called “plastic electronics” as semiconductors and contacts. However, their synthesis traditionally involves a high temperature step which is not compatible with plastic substrates, and the morphology can be difficult to tailor to different applications. Recently a new method to form oxide films from molecular precursors using only processes close to room temperature has been developed. The procedure relied on irradiating metal phthalocyanines (MPcs) using vacuum ultra-violet (VUV) radiation produced by an excimer lamp (λ =172 nm). In this thesis, we extend the procedure to the fabrication of functional oxides and aim to elucidate the mechanisms of degradation at the nanoscale. The first chapter explores the degradation mechanisms of MPcs. The influence atmosphere is assessed by varying the O concentration and overall pressure in the irradiation process. The existence of O radicals and excited species are found to play a major role in the kinetics of the reaction. An optimized atmosphere for the degradation of the films is obtained. The second chapter explores whether the technique is applicable to new morphologies. Films with flat topography like zinc porphyrin highlight the importance of grain boundaries and the diffusion of reactive species between grains as one of the main reasons to promote film degradation, while nanowires show shape retention. Blends of Zn1- XCoXPc show similar degradation mechanisms to pure films. The CoPc concentration in the blend influences the reaction rate. The final chapter is a study of the elemental composition of irradiated films with energy-dispersive X-ray spectroscopy and secondary ion mass spectrometry. It shows formation of a thin layer of metal oxide as a result of exposure to VUV light on the phthalocyanine thin films