Mikk Vahtrus will defend his PhD thesis "Structure-dependent mechanical properties of individual one-dimensional metal-oxide nanostructures" (physics) on 21 February 2019.
Prof. Ergo Nõmmiste, Institute of Physics, University of Tartu
Dr. Sergei Vlassov, Institute of Physics, University of Tartu
Prof. Irina Hussainova, Tallinna University of Technology
Prof. Alexey Romanov, ITMO University, St Petersburg, Russiab
Global demand for more powerful and versatile technologies has driven the research for novel materials with superior properties and diverse functionality. One of the possible solutions lies with nanomaterials. Not only is the size of nanoobjects advantageous but also as the dimensions of the material are reduced under 100 nm, superior and even novel electrical, magnetic, thermal and mechanical properties emerge. One of the most interesting nanomaterials is one dimensional nanostructures (1D NS) – object that is up to several tens to hundred micrometers long but has a diameter below 100 nm. Due to the properties and shape of 1D NS, they could be potentially used as building blocks for electronic switches, transistors, diodes, solar cells, supercapacitors, sensors etc. At the same time, the properties of 1D NS have not been fully studied and the size-depended properties truly understood. Therefore, it is imperative to investigate the properties of single 1D NS before they can be used in real-word applications. In most potential applications, 1D NS would be subjected to continues deformations, which means that knowing the mechanical properties of 1D NS is one of the most crucial parameters from the application point of view. The measurement of mechanical properties of 1D NS is very challenging due to the small size of 1D NS. Novel measurement devices and methods have to be developed, which allow to contact, manipulate and measure the single 1D NS. Scanning electron microscope (SEM) and atomic force microscope (AFM) are the main tools which help to connect the real-word to the nanoscale. Measurements of 1D NS can be conducted by combining these microscopes with cutting edge devices. In the current thesis, different factors that could affect the structure and therefore the mechanical properties of metal oxide 1D NS (1D MONS) were investigated separately, using SEM and AFM. Cantilever beam bending and three-point bending techniques were applied. Structural properties of the 1D MONS were characterized by powder XRD, SEM and TEM. It was shown how small change in synthesis method, addition of another material, heating or covering 1D MONS with a layer of another material can significantly change the mechanical properties of 1D MONS. In author’s opinion these results will give a fundamental basis for the application of 1D MONS in future devices.