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Optimal X-ray detection for thin samples in low-energy STEM
Rozbořil, Jakub ; Oral, Martin ; Radlička, Tomáš
In many applications it is desirable to perform energy-dispersive X-ray spectroscopy (EDS) on very thin samples at low primary beam energies in a STEM. Thin samples, or lamellae, with the thickness of about 10 nm, are mostly prepared in focused ion beam instruments (FIBs), and they are used to evaluate experiments in the development of thin films and coatings, in the semiconductor industry, and in other applications. EDS then provides a map of different chemical elements or compounds in the sample, obtained by scanning the electron beam in a raster. Often the qualitative composition is known as a limited set of materials and only their distribution on the sample is to be determined. For large batches of samples fast measurements are desired to maximize utilization of expensive equipment. In this study we found a method to minimize the time needed to reliably acquire an elemental map by determining the optimal detector placement and the minimal necessary primary electron dose per pixel.
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Electrostatic Deflection and Correction Systems
Badin, Viktor ; Oral, Martin (referee) ; Zlámal, Jakub (advisor)
The aim of this master's thesis is to explore and study dynamic aberration correction options in electron-beam lithography systems. For the calculations, the thesis uses the optical column of the BS600 electron-beam writer. The thesis focuses on corrections of the third order field curvature, astigmatism, and distortion aberrations of the currently used magnetic deflection system and a newly designed electrostatic deflection system. The parameters of the two deflection and correction systems were compared.
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Technologie bodového svařování
Oral, Martin
Bachelor thesis describes the technology of resistance spot welding. Outset, the work focuses on the historical development of a resistance welding, basic characteristics and principles of pot welding. It focuses description of the main parts of spot welders, more structure, properties and functions when making connections. The last part focuses on the shortcomings of the technology and the methods used to control the quality and strength of welded parts.
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Computations in Charged Particle Optics
Oral, Martin ; Radlička, Tomáš
The design of modern electron microscopes could not be possible without appropriate software tools. With the sub-nanometer resolution in SEM, and the sub-ångström resolution in TEM, one can see that the simulations involved in designing the instruments need to be tremendously accurate. A simulation starts with the computation of the electric and magnetic fields generated by various optical elements. That is followed by determinig the paraxial properties, aberrations and accurate particle trajectories (ray tracing). The distributions of the fields are mostly detemined with the Finite Element Method (FEM), the Boundary Element Method (BEM) or the Finite Difference Method (FDM). As the field data are at the input of all the subsequent calculations, they need to be very accurate, especially in the region close to the optical axis. Current expertise includes a set of rules that need to be applied in generating a FEM or BEM mesh. Advanced field interpolation techniques are necessary for accurate aberration analysis and particle tracing with high-order integration methods. Specialized software has been developped for the use in charged particle optics which aids the user in getting meaningful and accurate results. For instance, the EOD (Electron Optical Design) is a comprehensive package for particle optical sumulations. Field data produced by SIMION and Comsol need a specialized post-processing before their use in accurate ray tracing. Presented will be different methods of computing the optical aberrations, intensity distribution and probe size (resolution) on basic as well as more advanced examples (electron and ion optical columns, deflection systems, ToF spectrometers etc.) that were solved in the EOD and using custom programs.
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Fast simulation of ToF spectrometers
Oral, Martin
A fast simulation method was developed for analysis of time-of-flight spectrometers and it has been successfully used to optimize parameters of a real instrument. In the general case, the function of a time-of-flight spectrometer is best modeled using the Monte Carlo method, That involves calculation of a high number of ion trajectories, which is time consuming. We have found a way to reduce the calculation time greatly by introducing a simplification and using pre-computed data independent on the ion mass and charge. The procedure makes it computationally feasible to run iterative optimizations. By comparing the results with those of a realistic simulation on a selected case, we have verified that there is no noticeable influence on the results.
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Ray tracing, aberration coefficients and intensity distribution
Oral, Martin
In particle optics paraxial ray tracing (solution of the paraxial trajectory equation) provides the basic imaging properties of an optical system and real ray tracing (solution of the equation of motion with time as the parameter) gives the complete particle paths including all aberrations. While there are methods of computing the aberration coefficients directly, for example by evaluating the aberration integrals, ray tracing can also be used for this purpose.
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Programy pro elektronově optický návrh
Lencová, Bohumila ; Oral, Martin
The paper gives a brief overview of computational method used in the Institute of Scientific Instruments of AS CR for the design of electron optical devices. New possibilities of the software are then illustrated on the computations of spot profile in a scanning electron microscope with low energy and Wien filter.
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Determination of exact charged-particle trajectories and aberrations of systems in particle optics
Oral, Martin
The paper describes a method of calculation of aberration coefficients by regression (fitting). A prerequisite for the calculation is knowledge of an analytical expression of optical aberrations, which is used not only for fitting, but also for a fast computation of particle positions behind an optical system, e. g. for evaluation of a beam profile. The method is illustrated on computation of current density profiles in a deflected ion beam.
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The assessment of accurate trajectories of charged particles and errors of systems in particle optics
Oral, Martin
The work is supposed to deal with the design of a sufficiently effective method of computation of trajectories in particle-optical systems in general cases of non-adjusted optical systems (i.e. with errors in adjustment). Contemporarily, a method of computation in systems without these errors in adjustment by geometrical aberration theory of the 3rd order and chromatic theory of the 1st is developed, while it is principally possible to use aberration theories of higher orders (for achieving of higher exactness). It is necessary to include 'non-adjustment' of the optical system in the calculations. The neighbouring project is the computation of profiles of particles beams after processing by the optical system, in which the results of the main topic of the work have been exploited.
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Calculation of the beam profile
Oral, Martin
The beam profile provides local current density distribution of a particle beam. From the known distribution we can optimize the axial position of the specimen in a SEM, understand image aberrations or find optimum function of electron or ion analyzers. Graphical plot of the profile as a function of the z coordinate shows what is happening with the beam when it passes through the optical system. The first attempts of graphical presentationof the beam aberrations and profiles based on aberration theory are discussed in the recent diploma thesis.
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