Thermoelektrische Effekte auf der Nanometerskala

• Antragsteller: Professor Dr. Frank Cichos
• Fachliche Zuordnung: Physikalische Chemie von Molekülen, Flüssigkeiten und Grenzflächen, Biophysikalische Chemie
• Förderung: Förderung von 2013 bis 2019
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 242631004

• Erstellungsjahr: 2019

Zusammenfassung der Projektergebnisse

Our experiments have been devoted to the detection of thermo-electric effects and the interactions of heated metal nanostructures in electrolyte solutions. With the help of dedicated experiments, we could detect for the first time the thermo-osmotic flow field around a single heated gold nanoparticle at a glass surface. The interfacial thermo-osmotic flow strongly depends on the physico-chemical properties of the interface. These thermo-osmotic flows have also been shown to be responsible for the flow field generated by a single self-thermophoretic Janus particle. In experiments confining the flow field of a single immobilized Janus particle we find evidence, that the flow field has additional effects of a thermoosmotic flow at the substrate boundaries confining the Janus particle flow field. These additional thermo-osmotic flows are suggested to be responsible for an accumulation of passive colloidal particles around phoretic particles as observed in many recent experiments. We have for the first time measured the alignment of a single Janus particle within an external temperature field. Our results show an active rotation of the Janus particle in the external temperature field of a single heated gold nanoparticle. The alignment has been analyzed theoretically and simple predictions are derived which reveal that the rotation can be only calculated from the boundary temperature at the gold cap of the Janus particle. The rotational and translational motion of the Janus particle in the temperature field contain the sum and the difference of the thermoosmotic mobility coefficients of gold and polymer. Our results show that the thermo-osmotic mobility of gold is important for the alignment. Finally, we have addressed possible thermoelectric effects in the interaction of a gold nanoparticle and a locally heated gold film. We find good agreement for an attraction of the gold nanoparticle by electrostatic and van der Waals forces (DLVO). A thermo-osmotic slip flow at the gold surface is able to trap a single gold nanoparticle in the heated spot. No particular dependence of the thermo-osmotic slip velocity on the salt ion concentration and the specific type of the salt ions has been observed. From those results we conclude that the thermo-electric contribution is weak.

Projektbezogene Publikationen (Auswahl)

• Single Molecules Trapped by Dynamic Inhomogeneous Temperature Fields. Nano Lett. 15, 5499 (2015)
  M. Braun, A.P. Bregulla, K. Günther, M. Mertig, F. Cichos
  
• Size Dependent Efficiency of Photoohoretic Swimmers. Faraday Discuss. 184, 381 (2015)
  A.P. Bregulla, F. Cichos
  
• Polarization of Thermophoretic Swimmers in External Temperature Fields. Proc. SPIE 9922, 99221L (2016)
  A.P. Bregulla, F. Cichos
  
• Thermo-Osmotic Flow in Thin Films. Phys. Rev. Lett. 116, 188303 (2016)
  A.P. Bregulla, A. Würger, K. Günther, M. Mertig, F. Cichos
  
• Thermoelectric Fields Hold Nanoparticles. Nat. Photonics 12, 191 (2018)
  F. Cichos
  
• Thermophoretic Trap for Single Amyloid Fibril and Protein Aggregation Studies. Nat. Methods 16, 611 (2019)
  M. Fränzl, T. Thalheim, J. Adler, D. Huster, J. Posseckardt, M. Mertig, F. Cichos