У оквиру семинара Центра за физику чврстог стања и нових материјала у среду, 7. новембра 2018. године у 14:30 часова, у читаоници „Др Драган Поповић“, проф. др Војислав Крстић (Department of Physics, Friedrich-Alexander-Universität, Erlangen, Germany) одржаће предавање:
Local Electronic Confinement in Graphene: From Raman Response of Covalent Derivatives to Optics with Electrons
Local electronic confinement is a key-ingredient for the successful control of electronic and optoelectronic properties of any material. In graphene however, due to its specific hexagonal lattice structure (two triangular sublattices) and the circumstance to be made of carbon atoms, electronic confinement can have many different flavours than just the localisation of electrons. Here we address two manifestations of electronic confinement, one mainly chemistry driven, the other driven by physical interactions:
Covalent functionalization of graphene is a continuously progressing field of research. However, in virtually all optical responses, an unresolved enhancement in peak intensity with increase of sp3 carbon content is observed. To elucidate this general phenomenon we present a phenomenological model  which takes into account the circumstance that upon covalent functionalization confined π-conjugated domains (photoluminescent) surrounded by sp3 carbon regions in graphene monolayers are formed.[2,3] Our model, underpinned by combined Raman measurements and an in-situ dry electrostatic doping technique, incorporates the modulation of the Raman intensities through the photoluminescence active domains, and correlates the individual D- and G-mode intensities to the degree of functionalization. Through this, evaluations of Raman spectra using our model circumvent the ambiguities and information loss encountered when using the ratio of D- and G-mode intensities. Physical confinement involves the use of potential barriers and wells in contrast to altering chemical bonds. However, the use of electrostatic potentials for confinement of the relativistic electrons in graphene is not efficient due to the Klein paradox. Nevertheless, the introduction of local electrostatic potentials is theoretically predicted to have a confining action in form of a caustic motion of electrons within the potential . We will show that this effectively results in a guiding of electrons through scattering, which is the electronic analogue of the well-known Mie scattering .
1. P. Vecera, S. Eigler, M. Koleśnik-Gray, V. Krstić, A. Vierck, J. Maultzsch, R. A. Schäfer, F. Hauke, A. Hirsch, Scientific Reports 7, 45165, DOI: 10.1038/srep45165 (2017)
2. J. Robertson, E.P. O’Reilly, Phys. Rev. B 35, 2946-2957 (1987).
3. F. Demichelis, S. Schreiter, A. Tagliaferro, Phys. Rev. B 51, 2143-2147 (1995).
4. R.L. Heinisch, F.X. Bronold, H. Fehske, Phys. Rev. B 87, 155409 (2013).
5. J.M. Caridad, S. Connaughton, C. Ott, H.B. Weber, V. Krstić, Nature Communications 7, 12894, DOI: 10.1038/NCOMMS12894 (2016)