Browsing by Author "Yavuz, Koray"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Open Access Ablation-cooled material removal at high speed with femtosecond pulse bursts(OSA, 2015) Kerse, Can; Kalaycıoğlu, Hamit; Elahi, Parviz; Akçaalan, Önder; Yavaş, S.; Aşık, M. D.; Kesim, Deniz Koray; Yavuz, Koray; Çetin, Barbaros; İlday, Fatih ÖmerWe report exploitation of ablation cooling, a concept well-known in rocket design, to remove materials, including metals, silicon, hard and soft tissue. Exciting possibilities include ablation using sub-microjoule pulses with efficiencies of 100-mJ pulses.Item Restricted Bir müze otel olarak Pera Palas(Bilkent University, 2013) Yazıcı, Elifnur; Kondel, Gülizar; Yavuz, Koray; Özdemir, Ömer; Yıldızhan, YağmurItem Open Access Crystal growth and investigations on the effects of hydrogen doping of VO2(2019-03) Yavuz, KorayVanadium Dioxide(VO2) has been studied extensively for its interesting electronic structure that allows it to go through Metal-Insulator Transition(MIT) at 65 C. The nature of this phenomena is not entirely clear and more research is needed to firmly establish the science behind it and to realize possible applications; such as ultra-fast electrical and optical switching, sensor devices and Mott-Field Effect Transistors. One of the important experiments to understand the electronic structure of a material is Hall-effect measurements but due to acicular (needle like) nature of VO2 crystals, this subject is only studied either on millimeter sized samples which are not suitable for many device applications or on poly crystalline thin films that are under non-uniform stress due to the substrate effects which gives unsatisfactory results when performing experiments. This thesis suggest a new method of chemical vapour deposition(CVD) growth for low aspect ratio VO2 crystals that have lengths between 50-100 m and thicknesses between 40- 170 nm. These crystals can be mechanically removed from the substrate and transferred to use in different applications such as Hall-effect measurements or Transmission Electron Microscope(TEM) studies. Additionaly this work shows some aspects of the surface chemistry of the widely used Silica, Si, quartz and Sapphire substrates; relating with the control of oxygen saturation on the surface. Another VO2 growth method for c-plane sapphire that leads to considerably more crystal yield is shown. Hydrogenation of the VO2 crystals suppresses the MIT so understanding this phenomena might help us better understand the effects lying behind the transition. To study this phenomena a crystal is doped only from half by blocking the passage of hydrogen to other half so the interplay between the insulating phase and hydrogenated conductive phase can be observed. As the analysis tool, TEM is used on this sample. Using a two-terminal device of a VO2 crystal, the effects of hydrogenation on the electronic properties have also been studied. Overall this thesis introduces a new method for CVD growth of VO2 which is used in various applications such as Hall-effect experiments, two terminal devices and TEM studies. To control the growth process the interplay between oxygen and surface chemistry of sapphire, silica, Si and quartz substrates have been investigated. With these studies a better understanding of the mechanics of growth is intended.Item Open Access Ultrafast micromachining of Cu and Si at ultra-high repetition rates with pulse bursts(IEEE, 2016) Kerse, Can; Kalaycıoğlu, Hamit; Elahi, Parviz; Yavuz, Koray; Mirza I.; Bulgakova N.M.; İlday, F. ÖmerWe report a novel ultrafast burst mode fiber laser system, which can deliver pulses at ultra-high repetition rates in order to systematically investigate micromachining efficiency on copper and silicon samples. © 2015 IEEE.