Depolarizációs források és hatásuk vékonyrétegek spektroszkópiai ellipszometriai vizsgálatára

A doktori disszertációm témája a spektroszkópiai ellipszometria, ezen belül is a depolarizáló tulajdonságú minták vizsgálata. Az ellipszometriai mérési módszer azon alapul, hogy ha a vizsgálandó mintát ismert polarizációs állapotú fénnyel megvilágítjuk, akkor a mintáról való visszaverődés során a polarizációs állapot a mintára jellemző módon fog megváltozni. Ennek detektálásával következtetni tudunk a minta számos tulajdonságára, leggyakrabban a szerkezetre és az optikai jellemzőkre. Ha a minta vagy a mérőeszköz egyes tulajdonságai olyan módon befolyásolják a mérést, hogy a visszaverődő fény nem jellemezhető egy tiszta polarizációs állapottal, akkor depolarizáció megjelenéséről beszélhetünk. A depolarizáció különböző forrásokból eredhet, azonban minden esetben lerontja a mérés pontosságát és körültekintő kiértékelést követel meg a kezelése. Doktori munkám fő feladata a depolarizáció különféle típusainak vizsgálata, illetve az egyes típusok esetén a kiértékelést megkönnyítő eljárások megadása volt

Monitoring of evolving laser induced periodic surface structures

Laser induced periodic surface structures (LIPSS) are generated on titanium and silicon nitride surfaces by multiple femtosecond laser pulses. An optical imaging system is used to observe the backscattered light during the patterning process. A characteristic fringe pattern in the backscattered light is observed and evidences the surface modification. Experiments are complemented by finite difference time domain numerical simulations which clearly show that the periodic surface modulation leads to characteristic modulations in the coherently scattered light field. It is proposed that these characteristic fringe pattern can be used as a very fast and low-cost monitor of LIPSS formation formation during the manufacturing process. © 2019 by the authors

Ultrasensitive Probing of Plasmonic Hot Electron Occupancies

Non-thermal and thermal carrier populations in plasmonic systems raised significant interest in contemporary fundamental and applied physics. Although the theoretical description predicts not only the energies but also the location of the generated carriers, the experimental justification of these theories is still lacking. Here, we demonstrate experimentally that upon the optical excitation of surface plasmon polaritons, a non-thermal electron population appears in the topmost domain of the plasmonic film directly coupled to the local fields. The applied all-optical method is based on spectroscopic ellipsometric determination of the dielectric function, allowing us to obtain in-depth information on surface plasmon induced changes of the directly related electron occupancies. The ultrahigh sensitivity of our method allows us to capture the signatures of changes induced by electron-electron scattering processes with ultrafast decay times. These experiments shed light on the build-up of plasmonic hot electron population in nanoscale media

Growth of CNT forests on titanium substrates : effect of catalyst ration and hydrogen on the incorporation of nitrogen into carbon nanotube structure

For better electrical contacts of potential devices, growth of vertically aligned carbon nanotubes (CNT forests) directly onto conductive substrates is an emerging challenge. Here, we report a systematic study on the CCVD synthesis of carbon nanotube forests on titaniumbased substrates. As a crucial issue, the effect of the presence of an insulating layer (alumina) on the growing forest was investigated. Other important parameters, such as the influence of water vapor or the Fe-Co catalyst ratio, and the incorporation of nitrogen into carbon nanotube were also studied during the synthesis. As-prepared CNT forests were characterized by various techniques: scanning and transmission electron microscopies, Raman spectroscopy, energy-dispersive X-ray spectroscopy, spectroscopic ellipsometry

Growth of CNT Forests on Titanium Based Layers, Detailed Study of Catalysts

For better electrical contacts of potential devices, growth of vertically aligned carbon nanotubes (CNT forests) directly onto conductive substrates is an emerging challenge. Here, we report a systematic study on the CCVD synthesis of carbon nanotube forests on titanium based substrates. As a crucial issue, the effect of the presence of an insulating layer (alumina) on the growing forest was investigated. Other important parameters, such as the influence of water vapor or the Fe-Co catalyst ratio, were also studied during the synthesis. As-prepared CNT forests were characterized by various techniques: scanning and transmission electron microscopies, Raman spectroscopy, spectroscopic ellipsometry. CNT forests grown directly onto the conductive substrate were also tested as electrodes in hybrid halide perovskite photodetectors and found to be effective in detecting light of intensity as low as 3 nW