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Technological challenges in the fabrication of MoS.sub.2./sub./diamond heterostructures
Varga, Marián ; Sojková, M. ; Hrdá, J. ; Hutar, P. ; Parsa Saeb, S. ; Vanko, G. ; Pribusova Slusna, L. ; Ondič, Lukáš ; Fait, Jan ; Kromka, Alexander ; Hulman, M.
Nowadays, 2D materials are one of the most studied classes of materials. In addition to the most famous graphene, progress has been achieved in studying and using fundamental properties of transition metal dichalcogenides (TMD). Complementary, diamond as a representative of 3D materials has gained a reputation as an extremely versatile material due to its extraordinary combination of physical/chemical/electrical/optical properties. Besides these particular forms of 2D and 3D materials, their heterostructures have become very attractive due to new phenomena and functions (bandgap engineering, enhanced charge transport, optical interaction, etc.). However, individual technological procedures are still minimally investigated and described. Here, we will demonstrate a proof-of-concept for the preparation of MoS2/diamond heterostructures, where two different strategies were employed: a) growth of MoS2 layers on diamond films, and b) growth of diamond films on Si/MoS2 substrates.
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Enhanced growth rate of diamond films at low temperature in focused microwave plasma system
Babčenko, Oleg ; Bydžovská, Irena ; Fait, Jan ; Shagieva, Ekaterina ; Ondič, Lukáš ; Kromka, Alexander
The low temperature (< 500 °C) diamond film deposition on fused silica in two different focused microwave plasma systems, i.e. a multimode clamshell cavity (MCC) and a rotational ellipsoid cavity (REC) reactor, was investigated. During the experiments, the methane to hydrogen ratio, in the hydrogen-rich process gas mixture, varied from 1 % to 15 % for MCC and from 1 % to 9 % for REC. The grown films were analyzed by scanning electron microscopy and Raman shift measurements. The outcomes of the study and enhanced diamond growth at low temperatures is advantageous for overcoating of fused silica as well as thermally sensitive substrates, e.g. optical elements, photonic crystals, sensors, etc.
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Kerr microscopy of magnetic microstructures
Hovořáková, Kristýna ; Schmoranzerová, Eva (advisor) ; Ondič, Lukáš (referee)
The main objective of the thesis was to construct a wide-field Kerr microscope to study all-optical helicity-dependent (AOHDS) switching in FePt nanograins. The wide- field Kerr microscope was successfully implemented into AOHDS experiments, was fully characterized and optimized for maximum image contrast. The real-time imaging and resolution of 2, 5µm enables the study of a wide range of magnetic materials and their dynamics. Moreover, a new light source, the High Lumen Density MODULE from CRY- TUR, spol. s r.o., was tested for future application in Kerr microscopy. The technical solution enabled to form a collimated beam with low divergence required for Kerr mi- croscopy. From the switching experiments on FePt nanograins, we observed a strong non-magnetic contribution to the magnetic signal, not reported in previous works. The experiments have also shown that the switching intensity depends on the laser spot size and total laser power, suggesting that the FePt grains are not entirely isolated. The grains' ensemble exhibits a more complex behavior than anticipated. 1
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Time-resolved measurement of optical gain in silicon based nanostructures
Ondič, Lukáš
2 Title: Time-resolved measurement of optical gain in silicon based nanostructures Author: Bc. Lukáš Ondič Department: Department of Chemical Physics and Optics Supervisor: Prof. RNDr. Ivan Pelant, DrSc., Institute of Physics, Academy of Sci- ences of the Czech Republic Supervisor's email address: pelant@fzu.cz Abstract: The aim of this work is to study the optical properties of the mate- rial based on oxidized silicon nanocrystals (Si-ncs) embedded at high densities in SiO2-based matrix. These materials seem to be very promising on the way towards silicon laser. Using our preparation technique - modified electrochemical etching and post-etching in H2O2 - we obtain small Si-ncs with the mean core size of 2-3 nm, in- corporated at high densities of ∼ 1019 Si-ncs/cm3 into an SiO2-based matrix. In this work, we focused on studying their photoluminiscence (PL) properties and measuring the net optical gain of these samples. Therefore, we investigated their time-resolved and steady-state PL emission spectra which revealed two emission bands - the F-band (∼ 435 nm) with ns decay-time and the S-band (∼ 600 − 620 nm) with µs decay- time. Moreover, we observed a "green" emission band (∼ 500 nm) present only during the pulsed excitation and immediately after. We performed time-resolved gain spec- troscopy using...
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Sum-frequency generation in far-UV spectral region
Martínek, Miroslav ; Kozák, Martin (advisor) ; Ondič, Lukáš (referee)
Nonlinear optics is the area of high field optics, where the dependence of polarization of matter on the electric field of optical radiation cannot be considered as linear. This has important implications for practise, since the superposition principle is no longer valid in nonlinear optics. Thus it is possible to influence light, propagating through material, by another intensive radiation. Nonlinear optical phenomena are important especially for laser technology because they allow to generate light at different wavelengths using various interactions. This thesis is focused on the study of the sum-frequency generation in the far ultraviolet (UV) region of the spectrum. As the radiation source the femtosecond laser system was used. The aim of the study was to theoretically describe generation by nonlinear wave equation and to calculate the dependence of phase-matching angle on generated wavelength. Theoretical results were then verified experimentally in the laboratory. Also the energy of generated pulses and sum-frequency generation efficiency were measured for pulses in spectral region 215-250 nm. The generated pulses will further serve to excite electron-hole pairs in the diamond.
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Silicon nanocrystals, photonic structures and optical gain
Ondič, Lukáš ; Herynková, Kateřina (advisor) ; Oswald, Jiří (referee) ; Lauret, Jean-Sebastien (referee)
Silicon nanocrystals (SiNCs) of sizes below approximately 5 nm are a material with an efficient room-temperature photoluminescence (PL) and optical gain. Optical gain is a pre- requisite for obtaining stimulated emission from a pumped material, and the achievement of stimulated emission (and lasing) from Si-based nanostructures is of particular interest of the field of silicon photonics. The aim of this work was (i) to investigate fundamental optical properties of SiNCs, (ii) to design and prepare a photonic crystal with enhanced light ex- traction efficiency and (iii) to explore a possibility of enhancing optical gain of light-emitting SiNCs by combining them with a two-dimensional photonic crystal. First, free-standing oxide (SiOx/SiO2)-passivated SiNCs were prepared by electrochemical etching of a Si wafer. Their optical properties were studied by employing time-resolved spectroscopy, also at cryogenic temperatures. The fast blue-green emission band of these SiNCs was linked with the quasi- direct recombination of hot electrons and holes in the vicinity of the Γ-point. Furthermore, the spectral shift of the slow orange-red band (of these SiNCs) as a function of temperature was explained on the basis of an interplay between tensile strain and bulk Si temperature-induced indirect bandgap shift. The...
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Time-resolved measurement of optical gain in silicon based nanostructures
Ondič, Lukáš
2 Title: Time-resolved measurement of optical gain in silicon based nanostructures Author: Bc. Lukáš Ondič Department: Department of Chemical Physics and Optics Supervisor: Prof. RNDr. Ivan Pelant, DrSc., Institute of Physics, Academy of Sci- ences of the Czech Republic Supervisor's email address: pelant@fzu.cz Abstract: The aim of this work is to study the optical properties of the mate- rial based on oxidized silicon nanocrystals (Si-ncs) embedded at high densities in SiO2-based matrix. These materials seem to be very promising on the way towards silicon laser. Using our preparation technique - modified electrochemical etching and post-etching in H2O2 - we obtain small Si-ncs with the mean core size of 2-3 nm, in- corporated at high densities of ∼ 1019 Si-ncs/cm3 into an SiO2-based matrix. In this work, we focused on studying their photoluminiscence (PL) properties and measuring the net optical gain of these samples. Therefore, we investigated their time-resolved and steady-state PL emission spectra which revealed two emission bands - the F-band (∼ 435 nm) with ns decay-time and the S-band (∼ 600 − 620 nm) with µs decay- time. Moreover, we observed a "green" emission band (∼ 500 nm) present only during the pulsed excitation and immediately after. We performed time-resolved gain spec- troscopy using...
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