Nanomaterials have the remarkable characteristic of displaying physical properties different from their bulk counterparts. An additional degree of complexity and functionality arises when oxide nanoparticles interact with metallic nanostructures. In this context the Raman spectra due to plasmonic enhancement of iron oxide nanocrystals are here reported showing the activation of spin-waves. Iron oxide nanoparticles on gold and silver tips are found to display a band around 1584 cm−1 attributed to a spin-wave magnon mode. This magnon mode is not observed for nanoparticles deposited on silicon (111) or on glass substrates. Metal–nanoparticle interaction and the strongly localized electromagnetic field contribute to the appearance of this mode. The localized excitation that generates this mode is confirmed by tip-enhanced Raman spectroscopy (TERS). The appearance of the spin-waves only when the TERS tip is in close proximity to a nanocrystal edge suggests that the coupling of a localized plasmon with spin-waves arises due to broken symmetry at the nanoparticle border and the additional electric field confinement. Beyond phonon confinement effects previously reported in similar systems, this work offers significant insights on the plasmon-assisted generation and detection of spin-waves optically induced. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Οι πηγές πλάσματος επαγωγικής ζεύξης (Inductively Coupled Plasma Sources – ICP’s), παρέχουν πλάσμα υψηλής πυκνότητας ηλεκτρονίων σε χαμηλή πίεση και έχουν ευρεία εφαρμογή στη σύγχρονη βιομηχανία ημιαγωγών και την κατεργασία επιφανειών. Σε πολύ χαμηλές πιέσεις, (~mTorr), οι εκκενώσεις πλάσματος παρουσιάζουν ιδιαίτερη συμπεριφορά όσον αφορά τη διείσδυση του ηλεκτρομαγνητικού πεδίου και την αλληλεπίδραση κύματος-σωματιδίου: Η ανώμαλη επιδερμική διείσδυση (anomalous skin effect) και η συντονισμένη αλληλεπίδραση κύματος-σωματιδίου όταν υπερτίθεται στατικό μαγνητικό πεδίο (resonant wave-particle interaction) είναι δύο φαινόμενα τυπικά σε αυτές τις εκκενώσεις. Η κατανόηση και μαθηματική ανάλυση αυτών των ιδιαίτερα περίπλοκων φαινομένων, ώστε να προσομοιωθούν με ακρίβεια αλλά και χωρίς χρονοβόρες υπολογιστικά διαδικασίες οι πηγές πλάσματος επαγωγικής ζεύξης, αποτελεί μια σύγχρονη επιστημονική και υπολογιστική πρόκληση. Στα πλαίσια αυτά, στην παρούσα διατριβή τέθηκε ως στόχος η αξιοποίηση της υπάρχουσας επιστημονικής γνώσης στον τομέα της υπολογιστικής προσομοίωσης πλάσματος, για την ανάπτυξη ταχύτατων προσομοιώσεων των πηγών πλάσματος επαγωγικής ζεύξης, διασφαλίζοντας ταυτόχρονα την εξαγωγή έγκυρων συμπερασμάτων: Η προσέγγιση αυτή συνίσταται στη διατύπωση υπόθεσης (μοντέλου), τον έλεγχό της σε σχέση με υπάρχοντα δεδομένα και την επαναδιατύπωσή της μέχρις ότου το μοντέλο να κριθεί επαρκές. Αρχικά αναπτύχθηκε ένα ρευστοδυναμικό μοντέλο πλάσματος βασισμένο στην υπόθεση ψευδουδετερότητας και αμφιπολικής διάχυσης των φορέων φορτίου, προκειμένου να προσομοιωθεί η ενισχυμένης μαγνητικής διαπερατότητας πηγή επαγωγικής ζεύξης MaPE–ICP. Τα αποτελέσματα της προσομοίωσης συγκρίνονται με τα πειραματικά στοιχεία προηγούμενων ερευνητών για εκκενώσεις Αργού και εξετάζεται η ικανότητα του ρευστοδυναμικού μοντέλου να παρέχει μια στοιχειώδη ποσοτική περιγραφή πλάσματος επαγωγικής ζεύξης σε χαμηλή πίεση. Η αξιοπιστία του ρευστοδυναμικού μοντέλου εξελίσσεται περεταίρω, με την ενσωμάτωση μιας αποτελεσματικής αριθμητικής επίλυσης της κινητικής εξίσωσης Boltzmann για τα ηλεκτρόνια. Τα αποτελέσματα της υβριδικής προσομοίωσης για εκκένωση Αργού πίεσης 30 mTorr στον αντιδραστήρα MaPE–ICP συγκρίνονται τόσο με αντίστοιχα πειραματικά δεδομένα όσο και με τα προηγούμενα αποτελέσματα της ρευστοδυναμικής προσομοίωσης και εξετάζεται η βελτίωση της ποιοτικής συμφωνίας όσον αφορά την επίδραση των παραμέτρων με ιδιαίτερο ενδιαφέρον. Στη συνέχεια αναπτύχθηκε ένα ρευστοδυναμικό μοντέλο εκκενώσεων αίγλης τύπου ECWR (Electron Cyclotron Wave Resonance) βασισμένο σε προκαθορισμένες οριακές συνθήκες για το ηλεκτρομαγνητικό πεδίο. Προσομοιώθηκε ένα διάκενο με πλάσμα Αργού σε πίεση 15 mTorr (μονοδιάστατο μοντέλο) και τα αποτελέσματα ελέγχθηκαν έναντι αναλυτικής θεωρίας, πειραματικών δεδομένων και αποτελεσμάτων προσομοίωσης Particle In Cell/Monte Carlo (PIC/MC). Επιπρόσθετα, τα αποτελέσματα προσομοίωσης για μια εκκένωση Αργού σε πίεση 1 mTorr εντός κυλινδρικού αντιδραστήρα τύπου ECWR (δισδιάστατο μοντέλο), συγκρίνονται με τα αποτελέσματα προσομοίωσης και πειραματικά στοιχεία. Τέλος, το μοντέλο έχει επεκταθεί για να περιλάβει την διάδοση του πλάσματος που παράγεται από μια τυπική πηγή πλάσματος τύπου ECWR σε μια περιοχή διάχυσης. Τα αποτελέσματα για εκκένωση Αργού πίεσης 5 mTorr συγκρίνονται με τα αντίστοιχα αποτελέσματα ενός μοντέλου σφαιρικής διάχυσης πλάσματος και εν προκειμένω εξετάζεται η πλήρης επεκτασιμότητα του εισαχθέντος ρευστοδυναμικού μοντέλου ECWR σε διεργασίες πλάσματος. / Inductively Coupled Plasma Sources (ICP’s) are capable of producing high density-low pressure plasmas in a variety of applications for the semiconductor and material processing industry. In the mTorr range, ICP discharges exhibit an extraordinary behaviour concerning the electromagnetic field propagation and wave-particle interaction: Anomalous skin effect and resonant wave-particle interaction within a superimposed static magnetic field consist two of the most typical phenomena. The efficient comprehension and mathematical description of such a complex gas discharge in order to fast and accurately simulate ICP sources, is still a challenging task. Within this context, the thesis focuses on evaluating the existing scientific knowledge in plasma computational modeling in order to develop not only rapidly converging but reliable ICP simulations: The implementation methodology consists on formulating an hypothesis (model) and repetitively inquiring its accuracy by checking the simulation results against existing experimental and/or other simulation data. The continuation of the model re-formulation process depends on the accuracy of the simulation results. Initally a simulation of a Magnetic Pole Enhanced (MaPE)-ICP plasma source was developed, under the assumptions of plasma quasineutrality and ambipolar diffusion. The simulation results were checked against the experimental data of previous workers for Argon discharges and the ability of the model to provide an elementary quantitative description of low pressure ICP sources was scrutinized. The validity of the fluid model was enhanced with the incorporation of a time effective numerical solution of the Boltzmann transport equation for electrons. Simulation results of the hybrid model were compared to the previous fluid simulation results and existing experimental data, for a 30 mTorr Argon discharge in the MaPE–ICP reactor. The major improvements of the qualitative agreement in regard to the effect of parameters with particular interest are discussed. Moreover, a fluid model of ECWR (Electron Cyclotron Wave Resonance) discharges, based on predefined boundary conditions for the electromagnetic field, was developed: The simulation results for a 15 mTorr Argon plasma within a slab (1-dimensional model) were checked against the particle in cell/Monte Carlo (PIC/MC) simulation results that can be found in the literature and also compared to the analytical theory and experimental data. In addition, the model was further developed to simulate realistic geometries as a cylindrical ECWR reactor (2-D) and the data were also compared to both simulation results and experimental data of other researchers. Finally, the model was extended in order to simulate plasma propagation from a typical ECWR plasma source to a diffusion region. The simulation results for an Argon plasma generated from a cylindrical ECWR source in a processing chamber at 5 mTorr were presented in order to verify the feasibility of model application in ECWR plasma processes.

The work focuses on outlet of the electrical power from power plants operating in urban areas. After a short analysis of the general possibility of leading out electric power from power plants of various types, thesis continues to describe of outlet electrical power from PPC Červený Mlýn. Subsequently, are calculated short-circuit conditions in the main switching station. It follows an analysis of power lines. The last part dealt with the issue of reliability of sources in connection with random transition processes in the electrical network and the light of the operational reliability of electrical power equipment.

Master’s thesis is focused on making the acquaintance of EMC issues and ways of electromagnetic field scanner RS321 utilization for pre-compliance measurements. First part contains analysis of available equipment’s influence on measurement results on the basis of gathered specification. Next part includes an example measurement used as operational manual for scanner and its controlling program. The most important part is correction evaluation for performed EMI measurement of signal generator using its EMC certification protocol and application of gained correction curve on independent EMI measurement of device tested by EMC testing laboratory. Other possibilities of scanner utilization are mentioned in the next chapters. Last part of the thesis contains suitability evaluation of EMC scanner on the basis of findings from performed measurements.

e main goal of this thesis is mechanical torque analysis of induction machine based on magnetic circuit saturation, oversaturated areas classification and the possibility of oversaturated areas reduction of their influence on machine properties. Whole problem is solved by finite element method in ANSYS program. Work is divided into the description and creating of electromagnetic model, a method of the induction machine equivalent circuit parameters determination, the electromagnetic field calculation by finite element method, experimental measurement using LabVIEW program with measurement accessories (PCIe card National Instruments), data processing program in DIAdem, results analysis of calculations in terms of magnetic circuit saturation, the influence of magnetic circuit material based on electromagnetic field distribution and the magnetic flux density along the air gap including spectral analysis using MATLAB and the electromagnetic torque and its parasitic torque components calculation.

Nanomaterials have the remarkable characteristic of displaying physical properties different from their bulk counterparts. An additional degree of complexity and functionality arises when oxide nanoparticles interact with metallic nanostructures. In this context the Raman spectra due to plasmonic enhancement of iron oxide nanocrystals are here reported showing the activation of spin-waves. Iron oxide nanoparticles on gold and silver tips are found to display a band around 1584 cm−1 attributed to a spin-wave magnon mode. This magnon mode is not observed for nanoparticles deposited on silicon (111) or on glass substrates. Metal–nanoparticle interaction and the strongly localized electromagnetic field contribute to the appearance of this mode. The localized excitation that generates this mode is confirmed by tip-enhanced Raman spectroscopy (TERS). The appearance of the spin-waves only when the TERS tip is in close proximity to a nanocrystal edge suggests that the coupling of a localized plasmon with spin-waves arises due to broken symmetry at the nanoparticle border and the additional electric field confinement. Beyond phonon confinement effects previously reported in similar systems, this work offers significant insights on the plasmon-assisted generation and detection of spin-waves optically induced. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Raman spectroscopy is a powerful analytical method that allows deposited and/or immobilized cells to be evaluated without complex sample preparation or labeling. However, a main limitation of Raman spectroscopy in cell analysis is the extremely weak Raman intensity that results in low signal to noise ratios. Therefore, it is important to seize any opportunity that increases the intensity of the Raman signal and to understand whether and how the signal enhancement changes with respect to the substrate used. Our experimental results show clear differences in the spectroscopic response from cells on different surfaces. This result is partly due to the difference in spatial distribution of electric field at the substrate/cell interface as shown by numerical simulations. We found that the substrate also changes the spatial location of maximum field enhancement around the cells. Moreover, beyond conventional flat surfaces, we introduce an efficient nanostructured silver substrate that largely enhances the Raman signal intensity from a single yeast cell. This work contributes to the field of vibrational spectroscopy analysis by providing a fresh look at the significance of the substrate for Raman investigations in cell research.