Molecular beam epitaxy of CuMnAs

We present a detailed study of the growth of the tetragonal polymorph of antiferromagnetic CuMnAs by the molecular beam epitaxy technique. We explore the parameter space of growth conditions and their effect on the microstructural and transport properties of the material. We identify its typical structural defects and compare the properties of epitaxial CuMnAs layers grown on GaP, GaAs and Si substrates. Finally, we investigate the correlation between the crystalline quality of CuMnAs and its performance in terms of electrically induced resistance switching.Comment: 10 pages, 8 figures and supplementary materia

Investigation of new materials for second harmonic generation

V této bakalářské práci se zabýváme studiem optických vlastností materiálů cíleně připravovaných pro účinné generování druhé harmonické frekven- ce (SHG) pro použití v optoelektronice. Konkrétně jde o měření první hyperpo- larizibility. Využívat budeme nekoherentního jevu, hyper-Rayleighova rozptylu. Vzhledem k nekoherentnosti tohoto jevu je efekt velmi slabý. Je třeba použít silný zdroj světla, pulzní laser a citlivé detekční zařízení, fotonásobič. Vzorky se připravují ve spolupracujících chemických laboratořích Přírodovědecké fakul- ty Univerzity Karlovy v Praze. Dále nás bude zajímat zastoupení dvoufotonové fluorescence ve výsledné intenzitě, kvůli zaměnitelnosti s SHG.In these bachelor thesis optical properties of materials are studied. This materials are purposefully prepared for effective second harmonic generation (SHG) and for its usage in optoelectronics. Specificely we will measure the first hyperpolarizibility. Non-coherent phenomenon of hyper-Rayleigh scattering will be used. Considering its incoherence, the effect is very weak. It's necessary to use a strong source of light, pulse laser and a sensitive detection device, photomultiplier. Samples are prepared in cooperating chemical laboratories of Faculty of Science of Charles University in Prague. Additionally, we will discuss participation of two-photon fluorescence in output intensity because of its interchangeability with SHG.Department of Chemical Physics and OpticsKatedra chemické fyziky a optikyFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Laser spectroscopy of materials for spintronics

In these diploma thesis magnetically ordered materials are studied with the prospect of their application in spintronics. Specifically, we investigated metallic alloy FeRh, which undergoes a magnetic phase transition from antife- romagnetic phase to feromagnetic one around 100◦ C. This phenomenon can be readily used in memory devices. Laser spectroscopy is used as a nondestructive method without need of any electrical contacts. Magnetic properties of FeRh are studied by magnetooptical effects including quadratic magnetic linear dichroism. The measured polarization rotations are of the order of miliradians, therefore, the detection is realized by an optical bridge. At first, we concentrated on discrimina- ting of various magnetooptical effects from each other. The second part is focused on the phase transition induced by different means. Firstly, by heating the whole sample, secondly by illuminating the sample locally by continuous laser

Investigation of new materials for second harmonic generation

In these bachelor thesis optical properties of materials are studied. This materials are purposefully prepared for effective second harmonic generation (SHG) and for its usage in optoelectronics. Specificely we will measure the first hyperpolarizibility. Non-coherent phenomenon of hyper-Rayleigh scattering will be used. Considering its incoherence, the effect is very weak. It's necessary to use a strong source of light, pulse laser and a sensitive detection device, photomultiplier. Samples are prepared in cooperating chemical laboratories of Faculty of Science of Charles University in Prague. Additionally, we will discuss participation of two-photon fluorescence in output intensity because of its interchangeability with SHG

Investigation of new materials for second harmonic generation

In these bachelor thesis optical properties of materials are studied. This materials are purposefully prepared for effective second harmonic generation (SHG) and for its usage in optoelectronics. Specificely we will measure the first hyperpolarizibility. Non-coherent phenomenon of hyper-Rayleigh scattering will be used. Considering its incoherence, the effect is very weak. It's necessary to use a strong source of light, pulse laser and a sensitive detection device, photomultiplier. Samples are prepared in cooperating chemical laboratories of Faculty of Science of Charles University in Prague. Additionally, we will discuss participation of two-photon fluorescence in output intensity because of its interchangeability with SHG

Anti-Reflection Nanostructures on Tempered Glass by Dynamic Beam Shaping

Reflectivity and surface topography of tempered glass were modified without any thermal damage to the surroundings by utilizing 1.7 ps ultrashort pulsed laser on its fundamental wavelength of 1030 nm. To speed up the fabrication, a dynamic beam shaping unit combined with a galvanometer scanning head was applied to divide the initial laser beam into a matrix of beamlets with adjustable beamlets number and separation distance. By tuning the laser and processing parameters, reflected intensity can be reduced up to 75% while maintaining 90% of transparency thus showing great potential for display functionalization of mobile phones or laptops

Large-Beam Picosecond Interference Patterning of Metallic Substrates

In this paper, we introduce a method to efficiently use a high-energy pulsed 1.7 ps HiLASE Perla laser system for two beam interference patterning. The newly developed method of large-beam interference patterning permits the production of micro and sub-micron sized features on a treated surface with increased processing throughputs by enlarging the interference area. The limits for beam enlarging are explained and calculated for the used laser source. The formation of a variety of surface micro and nanostructures and their combinations are reported on stainless steel, invar, and tungsten with the maximum fabrication speed of 206 cm2/min. The wettability of selected hierarchical structures combining interference patterns with 2.6 µm periodicity and the nanoscale surface structures on top were analyzed showing superhydrophobic behavior with contact angles of 164°, 156°, and 150° in the case of stainless steel, invar, and tungsten, respectively

Investigation of Multiparameter Laser Stripping of AlTiN and DLC C Coatings

The lifetime and properties of cutting tools and forming moulds can be prolonged and enhanced by the deposition of hard, thin coatings. After a certain period of usage, the coating will deteriorate. Any remaining coating must be removed prior to successful recoating. Laser stripping is a fast and environmentally friendly coating removal method. In this paper, we present laser removal of two types of coatings deposited on a 1.2379 tool steel substrate, namely, an AlTiN coating with high hardness and a DLC C coating with a small coefficient of friction (COF). A powerful nanosecond laser was employed to remove the coating from the substrate with high efficiency, along with suitable residual surface roughness. Measurements were taken of surface roughness, removed depth, and working time on a stripped area of 1 cm2. The samples were evaluated under a microscope, with a 3D profilometer, and by EDS chemical analysis. Successful removal of the coating was confirmed by optical analysis, but detailed chemical characterisation showed that about 30% of the coating element may remain on the surface. Moreover, a working time of less than 7.5 s per cm2 was obtained in this study. In addition, it was shown that the application of a second low energy, high frequency laser beam pass leads to remelting of the peaks of the material and reduced surface roughness