Probing local thermodynamical properties of a nanomechanical resonator in a scanning electron microscope

Chardin, Clément (2024) Probing local thermodynamical properties of a nanomechanical resonator in a scanning electron microscope. PhD thesis, University of Nottingham.

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Micro and nano-mechanical devices have attracted increasing interest from scientists and engineers over the last few years because of their promising fundamental and technical applications. Their extremely low masses make them very sensitive to noises and forces, making them perfectly suited to act as detectors of weak forces or for testing new physics and potentially bringing quantumness towards the macroscopic world. Both the fabrication processes for producing nanomechanical resonators and the detection schemes used to monitor their motion have greatly improved recently. In particular, unprecedented sensitivities have been achieved with optomechanical detection systems and ultra-high mechanical quality factors.

In this thesis, we explore a detection method based on the interaction between a nanomechanical resonator, in the form of an InAs nanowire, and the electron beam inside a SEM. Although SEMs were first used as nanomechanical motion sensors more than 20 years ago, there has been a renewed interest in their use in the last few years as the back-action mechanisms are better understood thanks to related work on optomechanical systems and the potential of the technique has been demonstrated more clearly. This work extends the SEM measurement technique to provide "hyper-spectral images", i.e. local information on the dynamics of the resonator obtained by tracking several mechanical modes simultaneously as the SEM beam is moved across and along the nanowire. This new technique provides important new insights into unique features of the SEM-mechanical system: we describe how it can be used to study three aspects of the interplay between the dynamics of the nanowires, the heating supplied by the electron beam and the structural properties of the resonator. Firstly, we show that the SEM is a strong source of heating, causing a remarkably strong temperature gradient inside the nanowire, driving it far from equilibrium. Secondly, we explored the properties of self-sustaining oscillations in the nanowire which the SEM can induce in much more detail than has been possible before. Finally, we also investigated the severe irreversible structural changes of the nanowire that the SEM beam causes via etching. Theoretical modelling provided valuable insights into the observed behaviours, but could not capture all of the features. Most significantly, the experiments and modelling together provide valuable evidence that localised defects within the wire can play an important role in mediating its response to the SEM. This could lead to the SEM being used to detect structural defects inside nanowires.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Armour, Andrew
Verlot, Pierre
Keywords: Nanomechanics, Thermodynamics, Optomechanics, Scanning Electron Microscope, Electromechanics, Dynamical Back-action
Subjects: Q Science > QC Physics > QC251 Heat
Q Science > QC Physics > QC770 Nuclear and particle physics. Atomic energy. Radioactivity
Q Science > QH Natural history. Biology > QH201 Microscopy
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 77277
Depositing User: Chardin, Clement
Date Deposited: 28 Mar 2024 14:15
Last Modified: 28 Mar 2024 14:15

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