Stochastic fluctuations at the nanoscale assessed by scanning probe microscopy

Gehrig, Jeffrey Carl. Stochastic fluctuations at the nanoscale assessed by scanning probe microscopy. 2019, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: http://edoc.unibas.ch/diss/DissB_13497

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The first description of a process due to random fluctuations was published in 1827 by the botanist Robert Brown, when he observed the erratic motion of plant pollen immersed in water. This random walk motion, referred to as Brownian motion, is a result of the forces of the surrounding liquid molecules acting on the Brownian particle. In an isothermal system, no net motion can be achieved and thermal fluctuations will give rise to dissipation, required by the second law of thermodynamics. However, systems at thermal equilibrium are microscopically dynamic and molecules can explore the thermally accessible microstates. Such local variations in metastable systems allow transitions, which is relevant for activation events in chemical reactions, or changes in molecular orientation and position (diffusion) of surface adsorbates.
In this thesis, the stochastic motion of the molecular rotating fluctuator dibutylsulfide (DBS) was studied. Scanning Tunneling Microscopy (STM) was used to measure the stochastic hopping of the molecule between the different metastable positions. A statistical analysis of these data allowed to obtain energy barrier and transition entropy maps that govern the dynamics of the molecule on the surface.
Stochastic fluctuations of the interaction force between two bodies in close proximity also lead to non-contact friction or energy dissipation. A 3D measurement of a surface oxygen adsorbate with an oxygen-functionalized cantilever tip is performed with Atomic Force Microscopy (AFM). Forces in the repulsive regime are measured. Furthermore, dissipation is seen, which can be related to the stochastic friction force mechanism.
Advisors:Hug, Hans-Josef and Meyer, Ernst
Faculties and Departments:05 Faculty of Science > Departement Physik > Former Organization Units Physics > Experimentalphysik (Hug)
UniBasel Contributors:Hug, Hans Josef and Meyer, Ernst
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:13497
Thesis status:Complete
Number of Pages:1 Online-Ressource (III, 134 Seiten)
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edoc DOI:
Last Modified:14 Feb 2020 05:30
Deposited On:13 Feb 2020 14:44

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