Rozprawy doktorskie na temat „Hard Electron Energy Spectrum”

Questa tesi descrive lo studio di elettroni e positroni nella radiazione cosmica. Nuove misure della frazione di positroni al top dell’atmosfera tra 200 MeV e 3.0 GeV, nonché lo spettro di elettroni fino a 20 GeV, sono presentati. La misura è stata effettuata con l’esperimento PAMELA da Luglio 2006 a Dicembre 2008, periodo di minima attività solare e polarità negativa. PAMELA fornisce le prime osservazioni a lungo termine della frazione di positroni di bassa energia durante questo particolare stato della eliosfera. La grande statistica collezionata permette di studiare la variazione del flusso di particelle a Terra in funzione dell’energia e del tempo, e di investigare effetti dipendenti dal segno della carica. Durante circa 860 giorni di raccolta dati circa 16000 positroni e 178000 elettroni sono stati identificati. Le maggiore fonte di fondo, costituite da protoni e pioni localmente prodotti, sono state studiate. Lo spettro di elettroni derivato mostra chiaramente l’effetto della modulazione solare sotto qualche GeV. La frazione di positroni è risultata in accordo con le predizioni di modelli teorici che descrivono il trasporto di particelle nell’eliosfera che tengono conto di effetti di drift.
This thesis describes the study of electrons and positrons in the cosmic radiation. New measurements of the positron fraction at the top of the atmosphere between 200 MeV and 3.0 GeV are presented, together with the electron spectrum up to 20 GeV. The measurement was conducted with the space borne PAMELA experiment from July 2006 to December 2008, that is a period of minimum solar activity and negative solar magnetic field polarity. PAMELA provides the first long term observation of the low energy positron abundance during this particular solar and heliospheric state. The great amount of collected statistics allows to study the variation of the particle intensity at Earth with energy and time, and to investigate effects depending on the particles sign of charge. During approximately 860 days of data collection about 16300 positrons and 178000 electrons were identified. The major sources of background, constituted by cosmic protons and locally produced pions, have been studied. The derived electron spectrum clearly shows the effect of the solar modulation below few GeV. The detected positron fraction has been found to be in accordance with predictions from theoretical models that describe the transport of particles in the heliosphere taking drift effects into account.

Philosophiae Doctor - PhD
The main aim of this study was to prepare band gap-engineered graphene quantum dot (GQD) structures which match the different energies of the visible region in the solar spectrum. These band gap-engineered graphene quantum dot structures were used as donor materials in rainbow Schottky junction solar cells, targeting all the energies in the visible region of the solar spectrum for improved solar-to-electricity power conversion efficiency. Structural characterisation of the prepared nanomaterials under solid-state nuclear magnetic resonance spectroscopy (SS-NMR) showed appearance of bands at 40 ppm due to the presence of sp3 hybridised carbon atoms from the peripheral region of the GQD structures. Other bands were observed at 130 ppm due to the presence of polycyclic aromatic carbon atoms from the benzene rings of the GQD backbone, and around 180 ppm due to the presence of carboxylic acid carbons from oxidation due to moisture. Fourier-transform infrared resonance (FTIR) spectroscopy further confirmed the presence of aromatic carbon atoms and oxidised carbons due to the presence of C=O, C=C and -OH functional groups, concurrent with SS-NMR results.
2023-12-01

Dieses Dokument präsentiert eine Messung des CKM Matrixelementes Vub in inklusiven semileptonischen B nach Xu e nu Ereignissen, auf einem Datensatz von 471 Millionen BB Ereignissen, aufgezeichnet vom BABAR Detektor. Inklusive B nach Xu e nu Zerfälle wurden selektiert indem hochenergetische Elektronen (Positronen) rekonstruiert wurden. Untergrundunterdrückung wurde erreicht indem Ereignisse selektiert wurden mit Elektron- (Positron-) Energien in der Nähe des kinematischen Endpunktes von B nach Xu e nu Zerfällen. Ein Veto für B nach Dstern e nu wurde angewendet um den Untergrund weiter zu reduzieren. Dieses Veto benutzt Dstern Mesonen die mit einer Partiellen Rekonstruktionstechnik rekonstruiert wurden.
This document presents a measurement of the CKM matrix-element Vub in inclusive semileptonic B to Xu e nu events on a dataset of 471 million BB events recorded by the BABAR detector. Inclusive B to Xu e nu decays are selected by reconstructing a high energetic electron (positron). Background suppression is achieved by selecting events with electron (positron) energies near the kinematical allowed endpoint of B to Xu e nu decays. A B to Dstar e nu veto is applied to further suppress background. This veto uses Dstar mesons which have been reconstructed with a partial reconstruction technique.

This investigation is primarily concerned with the low loss, or plasmon region of an electron energy loss spectrum. Specifically, why these spectra have the shape and form that they do; what the significance of the material is in determining the shape and form of these spectra; what can be done with plasmon excited electrons; and how all of this fits in with the current theory of plasmon excitation. In particular, the concept of plasmon scattering being an energy transfer process of a coupled wave in the material is explored. This gives rise to slightly different explanations of the plasmon scattering process to the status quo. Multiple scattering is typically pictured as a combination of separate and independent, elastic and inelastic scattering events interactively contributing to a final exit wave function. However, this investigation explores the idea of the elastic and inelastic components being a coupled event, and what the consequences of this idea are from a conceptual point of view. The energy transfer process itself, does not deviate from a virtual particle exchange description that is consistent with the standard model. However, the two significant points made throughout the chapters are one: that the elastic and inelastic scattering events are coupled rather than separate, and two: that each succussive higher order scattering event in multiple scattering scenarios, are dependant and connecte d rather than independent.

The main goal of this thesis is to combine electron tomography and electron energy loss spectroscopy (EELS) in the TEM, in order to obtain chemical and electronic information in 3D in the nanoscale. Tomography in the TEM has been discussed and the advantages and disadvantages of HAADF STEM tomography have been analyzed. - A Fe3O4 nanocube sample has been considered to illustrate the acquisition, alignment, tilt axis assessment, reconstruction and visualization processes. - HAADF STEM tomography has been used to reconstruct the shape of a series of Cu2O nanoparticles. For one of the samples, the facets of the Cu2O nanoparticles, octahedral in shape, have been found to correspond to {111} planes. The physics and the data analysis methods of core-loss EELS have been briefly summarized. Two relevant contributions have been made: - The effects of beam precession on EELS have been investigated. A signal enhancement due to electron beam precession in the TEM when in zone axis conditions has been discovered for the first time. - A homemade software, Oxide Wizard, for valence state determination of transition metals has been developed and applied to map the Mn oxidation state of a MnOx/FeOy nanoparticle. EELS spectrum imaging and electron tomography have been combined to recover chemical information in 3D for FexCo(3-x)O4@Co3O4 mesoporous nanoparticles. - The samples have been first characterized by HAADF STEM tomography and EELS. - EELS chemical information is, of course, limited to 2D maps, while only structural information is be recovered in 3D form HAADF tomography. . An EELS-SI tilt series has been acquired at 80 kV and low acquisition times, resulting in a very noisy dataset. - Principal component analysis (PCA) has been used to separate the noise from the signal. - Quantifications of the O, Fe and Co signals have been reconstructed, and the shape of the particle recovered. - From the noise clean dataset, components with physical meaning (iron oxide, cobalt oxide and thickness) have been extracted using independent component analysis (ICA), and reconstructed in 3D. - A new kind of signal with chemical and thickness information has been obtained by combining the thickness component with the quantification results. This signal is able to properly reconstruct the chemical structure of the sample in 3D, detecting a higher presence of iron in the surface, and an even distribution of Fe inside of the particle. . Another EELS-SI tilt series has been acquired at 80 kV and low acquisition times with enough spatial resolution to resolve the porous structure. - The noise has been reduced using PCA. - Four signals extracted from the spectrum have been reconstructed: the integrated edge intensities for oxygen, iron and cobalt, and the integrated background prior to the oxygen edge. EELS-SI tomography has been applied to reconstruct CoFe2O4 (CFO) nanocolumns embedded in a BiFeO3 (BFO) matrix grown on LaNiO3 buffered LaAlO3 substrate (BFO-CFO//LNO/LAO). - The nanocomposite sample has been prepared in a nanoneedle shape by means of focused ion beam (FIB). This preparation has the advantage of keeping the thickness of the sample constant throughout the tilting experiment. The nanoneedle contains an island of CFO in a matrix of BFO, as well as the LNO/LAO substrate. - The noise has been discarded using PCA. - The oxygen, iron and lanthanum edges intensities have been extracted and reconstructed. A new kind of data hypercube, the Spectrum Volume, has been proposed. Just as a Spectrum Image contains a spectrum per pixel, a Spectrum Volume is to contain a spectrum per voxel. EELS-SI tomography has been applied to successfully acquire a spectrum volume (SV) of the (BFO-CFO//LNO/LAO) system. - PCA has been used to discard the noise and Bayesian linear unmixing (BLU) has been used to extract independent components (eigenspectra). - Each eigenspectrum has a 2D weighting map for each tilt; weighting maps have been reconstructed into 3D weighting volumes. - Full single spectra for any point in the reconstructed space can now be recovered as a weighed sum of eigenspectra, using the 3D weighting distributions. This approach is used to extract single spectra, spectrum lines and spectrum images from the inside of the sample. In the context of this thesis, tomography and EELS-SI have been combined to successfully recover chemical information in 3D at the nanoscale, and a new kind of data hypercube, the Spectrum Volume, has been proposed and experimentally recovered.
En el microscopi electrònic de transmissió (TEM), es poden obtenir imatges d’una mostra des de diferents angles i posteriorment reconstruir aquestes imatges en tres dimensions (3D). Per altra banda, les interaccions dels electrons del feix amb els electrons de la mostra poden ser analitzades mitjançant l’espectroscòpia de pèrdues d’energia dels electrons (EELS), obtenint així informació química de la mostra. L’objectiu d’aquesta tesi és la combinació de l’espectroscòpia EELS amb la tomografia electrònica per obtenir informació química en 3 dimensions a la nanoescala. S’han explicat les bases de la tomografia electrònica i el procediment de la reconstrucció ha estat il•lustrat amb una mostra de nanocubs d’òxid de ferro. Posteriorment, s’ha aplicat a una sèrie de nanopartícules de Cu2O per tal de descriure’n la forma. També s’ha explicat la física en què es basa l’EELS, fent especial atenció als llindars d’altes pèrdues d’energia. A continuació, s’ha mostrat l’augment del senyal obtingut amb precessió electrònica al TEM quan la mostra es troba en condicions d’eix de zona. Seguint amb les aplicacions d’EELS, s’ha explotat la possibilitat de caracteritzar els estats d’oxidació dels metalls de transició mitjançant un programa propi, escrit per a Digital Micrograph i anomenat Oxide Wizard. Una vegada la tomografia electrònica i l’espectroscòpia de pèrdues d’energia dels electrons han estat explicades, s’ha procedit a reconstruir informació extreta d’EELS en 3D. S’han realitzat una sèrie d’experiments amb partícules mesoporoses que han demostrat la utilitat d’aplicar l’anàlisi multivariable per tal de reduir el soroll de les dades i extreure’n els components. Finalment, s’ha dissenyat un experiment en el qual ha estat possible recuperar l’espectre corresponent a cada unitat d’espai com la combinació d’espectres propis en una mostra preparada en forma de nanoagulla. Els espectres recuperats corresponen a la contribució de cada unitat de volum als espectres projectats. Aquest nou tipus de dades permet extreure espectres de l’interior d’una mostra. Finalment, doncs, s’ha pogut combinar amb èxit la tomografia electrònica i EELS per obtenir informació química en tres dimensions a la nanoescala.

Etude chimique, microscopique et electrique des differents types de precipitation du carbone dans le silicium polycristallin. Mise en evidence de deux types de precipitation. Pour montrer que l'activite electrique des defauts cristallins est essentiellement liee a la presence d'impuretes, une nouvelle methode a ete elaboree qui presente une resolution spatiale du signal meilleure que l'ebic. L'ensemble de ces etude a permis de conclure sur l'influence du carbone sur les proprietes electriques du materiau

La caractérisation et modélisation de « nanohorns » monofeuillets (SWNH) et de forêts de nanotubes par microscopie analytique sont présentées ainsi que leurs applications pour le traitement du cancer. Dans une première partie, nous introduirons les méthodes de microscopie et de spectroscopie utilisées dans nos expériences. Nous étudierons ensuite le processus de croissance de forêts de nanotubes de carbone monofeuillets (dans le contexte d’une collaboration avec l'AIST au Japon). Les SWNH, leur structure, propriétés de remplissage et de fonctionnarisation seront analysés et une nouvelle méthode sera présentée pour l'étude de la porosité de matériaux inorganique en EELS. Des calculs ab-initio seront aussi utilisés pour étudier l'effet des défauts dans les parois des SWNH sur les phénomènes d'oxydation et de remplissage des SWNH. Finalement, nous étudierons les possibles applications de SWNH dans le domaine pharmaceutique, et en particulier pour les traitements cancéreux
In this manuscript, we will expose the characterization and modelling of Single Wall Nanohorns (SWNH) and Nanotube Forests by analytical microscopy and the functionalization of SWNH for drug delivery applications. Firstly, we will introduce the microscopy and spectroscopy methods used for our experiments. We will then study the growth process of Single Wall Carbon Nanotubes (SWCNT) forests (within the framework of a collaboration with AIST, Japan). SWCH, their structure, modifications and filling properties will be analysed in details. An original method will be presented to study the porosity of inorganic material with EELS. Ab initio calculation will also be used to explore the effect of the defects present in the SWNH wall on the oxidation and filling process. We will study the potentialities of Single Wall Carbon nanohorns as Drug Delivery Systems and particularly as anticancer drug carriers

On etudie par microscopie (meb, met, eels, edx) et par analyse par sonde ionique (sims) les composites prepares par impregnation de fibres de sic par depot chimique en phase vapeur de si::(3)n::(4) ou sic. On etudie l'influence du substrat sur la microstructure des depots, puis on caracterise la microstructure et la composition chimique de fibres elementaires de sic revetues par cvd de c et de sic. L'analyse des fibres revetues et tout particulierement de l'interface fibre/matrice montre la complementarite des methodes eels et sims pour caracteriser les composites a fibres longues

En spectroscopie de perte d’énergie des électrons (EELS), l’échantillon à analyser est soumis à un faisceau d’électron et une détection de l’énergie perdue au cours de la traversée du matériau renseigne sur la composition chimique du composé. Pour des échantillons particulièrement sensibles aux dégâts d'irradiation électronique, comme par exemple des matériaux organiques, on cherche à limiter la dose totale d'électrons reçue par l'échantillon tout en obtenant un rapport signal-sur-bruit satisfaisant. Avec le développement récent de modules d’échantillonnage adaptés aux microscopes en transmission à balayage (STEM), l’acquisition initialement réalisée ligne par ligne est devenue hautement paramétrable. Ainsi, il est désormais possible de visiter un ensemble de positions spatiales quelconques au cours de l’acquisition. De nombreux travaux ont proposé de s’appuyer sur ces avancées techniques pour permettre une acquisition optimisée pour des échantillons sensibles. Pour une dose d’électron globale équivalente à un échantillonnage standard, ces stratégies consistent à visiter moins de positions spatiales, et donc à procéder à un échantillonnage partiel. Par conséquent, une dose d’électron par position spatiale plus élevée est autorisée, ce qui permet d’augmenter le rapport signal-sur-bruit de chaque spectre mesuré. En contrepartie, une étape de post-traitement est nécessaire pour reconstruire l’ensemble de l’image, en particulier les spectres associés aux positions spatiales non visitées au cours de l’acquisition. Parmi les techniques de reconstruction utilisées dans la littérature, les méthodes d’interpolation sont rapides mais peu précises ; elles sont d’un intérêt tout particulier pour visualiser l’image complète au cours de l’acquisition. Au contraire, les techniques par apprentissage de dictionnaire sont très performantes, mais coûteuses tant en mémoire qu’en temps de calcul, et sont donc privilégiées pour raffiner l’image reconstruite après l’expérimentation. En définitive, peu de travaux ont cherché à combler ce fossé. L’objectif principal de cette thèse est de proposer des algorithmes de reconstruction rapides et performants en imagerie EELS. Ils devront, comme pour les méthodes d’interpolation, être suffisamment rapides pour visualiser l’image reconstruite au cours de l’acquisition. D’autre part, ces méthodes devront également afficher de meilleures performances que celles données par l’interpolation, voire proches de celles des techniques par apprentissage de dictionnaire. Pour cela, des méthodes par moindres carrés régularisés sont envisagées dans le cas d’échantillons spatialement lisses et d’échantillons cristallins périodiques. Les algorithmes proposés sont ensuite testés en s’appuyant sur des données synthétiques et réelles. L’intérêt de l’approche par acquisition partielle et les performances par rapport à d’autres méthodes de reconstruction sont étudiés
In electron energy loss spectroscopy (EELS), the sample to be analyzed is exposed to an electron beam, and the measure of the energy loss after passing through the material informs about the chemical composition. For samples particularly sensitive to electronic irradiation damages, such as organic materials, the experimenter is constrained to reduce the total electron dose received by the sample while obtaining a satisfying signal-to-noise ratio. With the recent development of sampling modules adapted to scanning transmission electron microscopes (STEM), the initial raster acquisition (i.e., line-by-line) has become highly configurable. Henceforth, it is now possible to visit any set of spatial positions during the acquisition. Based on these technical advances, a lot of works proposed optimized acquisition schemes for preserving sensitive samples. For a global electron dose equivalent to standard sampling, these strategies consist in visiting less spatial positions, i.e., to perform partial sampling. As a consequence, a higher electron dose per spatial position is allowed, which permits to increase the signal-to-noise ratio for each sampled spectrum. Yet, a post-processing step is required to infer the missing spectra. Among the reconstruction techniques used in the literature, the interpolation methods are fast but rather inaccurate ; they are particularly efficient for displaying the full image along the acquisition process. On the contrary, the dictionary learning-based methods are very performant, but are memory and computation demanding. They are chosen in priority to refine the reconstructed image after experimenting. Finally, only a few works attempt to fill this gap. The main objective of this Ph.D. thesis is to propose fast and accurate reconstruction algorithms for STEM-EELS imaging. Similarly to the interpolation methods, they should be fast enough to visualize the reconstructed image along the acquisition. Meanwhile, they should also achieve better reconstruction performances than those reached by interpolation, close to those of dictionary learning-based methods. To that end, regularized least square methods are proposed in the context of spatially smooth samples or of periodic crystalline samples. The proposed algorithms are then tested based on synthetic as well as real data experiments. The interest of partial-sampling based methods and the performances with respect to other reconstruction methods are evaluated

Examen des possibilites offertes par l'esca pour l'etude des polarites des liaisons, la distribution des cgarges et les transferts de charge intramoleculaires dans les composes organiques. Etude des correlations energie de liaison - charge atomique afin d'estimer les charges portees par les heteroatomes des merocyanines etudiees. Etude des problemes poses par l'analyse esca des composes organiques et des effets de la polarisation electrique du porte-echantillon

The widely popular and successful standard fireball model for Gamma Ray Burst (GRB) afterglows is based on ultra-relativistic external shocks sweeping up matter around the explosion site to accelerate electrons up to GOV energies and boost the magnetic field to values close a few Gauss in its downstream. According to the model, the afterglow radiation is the synchrotron emission from these electrons gyrating around the enhanced magnetic field. A contribution from inverse Compton scattering may also appear in the total flux at higher frequencies. The synchrotron spectrum is characterized by 'breaks' which arise due to various physical processes. The spectral slope changes due to the synchrotron self-absorption below a frequency Va. The synchrotron peak frequency (I'm) corresponds to the emission by electrons at the lower limit of the power law distribution of energies and the cooling break 14 corresponds to the electron energy above which synchrotron radiation loss becomes very significant. Apart from these, the light curves exhibit achromatic slope changes due to dynamical processes within the fireball. The ejected matter is collimated and initially undergoes a radial expansion. Later, the lateral expansion of the jet takes over and this is reflected as an achromatic break (jet break) in the light curve. The next achromatic change of slope marks the transition of the fireball into the non-relativistic regime. The spectrum of afterglow radiation itself evolves with time, reflecting the expansion of the fireball, hence a data set well sampled in both spectral and in temporal domain is essential for useful study. Multiband modelling of GRB afterglow (AG) light curves is at present the best available tool to understand the true nature of the explosion and its surroundings. Apart from that, detailed modelling also holds the key to the secrets of particle acceleration processes in collision less shocks. By modelling the well-sampled data set of an afterglow, the energy content (Etot) of the jet, its angle of collimation (00), the density profile of the ambient medium (n(r) where r is the distance from the site of the explosion) and some relevant parameters of shock microphysics (p, the power law index of the distribution of electrons which are radiating via synchrotron mechanism, G, the fraction of energy in those electrons and that in downstream magnetic field) can be obtained. Afterglow data of the nearby (z 0.16, one of the nearest GRBs) GRB 030329 was unprecedentedly rich in both optical and radio bands (but unfortunately poor in x-rays) which enabled detailed and well constrained modelling attempts. The rigorous monitoring campaign revealed an unexpected behavior of the radio flux, for which one explanation was that that the early optical emission and the late radio emission arose in two different jets. However, our detailed modelling using the rich data set allowed us to propose a new mechanism in which the initial outflux of energy is 'refreshed' by a later episode of injection. The standard fireball model uses certain simplistic assumptions owing to our lack of knowledge of the shock acceleration process. One common assumption is that of a universal spectrum of the accelerated electrons, a steep non thermal energy distribution with power law of index 2.2. It owes its origin to theoretical simulations of shock acceleration which often produce a steep (p > 2) spectrum. This also fits many observed cases of such energy distributions. Further, this assumption leads to a simplification in theoretical models, since the upper cut off energy of the distribution plays virtually no role. The presence of harder, p < 2 spectrum, in a minority of cases, has hence not received a fair share of attention. Calculations to derive the physical parameters of the burst in such cases are often not done consistently. Early attempts to model GRB afterglows with hard electron energy spectrum had several loopholes. In this thesis, we have done these calculations consistently and applied them to a few afterglows with good temporal and spectral coverage. Apart from multiband modelling, this thesis also presents late time observations of the GRB030329 afterglow in low frequency radio bands. Radio observations have always been special since they allow the estimation of the self-absorption frequency, thus giving a direct clue to the size of the fireball. Afterglows are long lived in low radio frequencies (< 1 GHz) while they quickly decay below visibility in all other bands, even at high radio frequencies (say 15 GHz). Hence monitoring at low radio frequencies is the only way to study the late time evolution including the transition from relativistic to non-relativistic dynamics. GRB030329 had one such rare bright radio afterglow and we followed it up in low frequencies (1280 MHz and 610 MHz) using the Giant Meter wave Radio Telescope (GMRT). The follow up campaign is continuing thanks to the slow evolution in low radio frequencies. This afterglow has hence become the longest (N 1000 days) observed, beating the earlier record of 500-day long observations of Radio afterglow of GRB970508. It also is the only one which is seen in frequencies below 1 GHz. This thesis is organized in the following manner: Chapter 1 gives a general introduction to GR13s and their afterglows. After describing the properties of the burst and the afterglow, we proceed to explain the standard fireball model in detail. The dynamics of the external shock and the profile of the bulk Lorentz factor (I") vs. r is described. We explain the jet break (tj) and non-relativistic transition (tnr), two major developments in the life of the fireball. We then give a detailed description of the synchrotron radiation mechanism, which is the source of afterglow radiation. The spectral breaks (va, I'm and 14) and their time evolution is explained. We conclude this chapter by listing a few unanswered questions relevant to this thesis. In Chapter 2, we present the theoretical modifications required for the standard model to accommodate electron energy spectra with power-law indices less than 2. The energy spectrum requires a new parameter 7i, which is the Lorentz factor corresponding to the upper cut-off of the hard energy distribution. Above 'i, the distribution either terminates or steepens (double slope electron distribution) to a value of p larger than 2. The functional form of this cut-off is decided by the particle acceleration processes, which are at present poorly understood. We therefore parameterized the temporal evolution of in terms of the bulk Lorentz factor of the shock. We discuss two possible origins for the cut off. As a result of this cut-off in the energy spectrum, a new break Vi is introduced in the radiation spectrum, which is the synchrotron frequency corresponding to 7i. Apart from that, the expressions for l.'m and va differ from the standard scenario. We have calculated the shock dynamics using the method adopted by Huang et. al. 2000, which allows a smooth transition from ultra-relativistic to nonrelativistic regime of the fireball. Using this profile of I' vs. observed time, we calculated the synchrotron spectral evolution from a double slope electron energy distribution semi-analytically. The self-Compton emission also is calculated. For ultra-relativistic and non-relativistic regimes, analytical solutions are presented for both ISM n(r) r0] and stellar wind driven [n(r) ambient medium density profiles. The way one identifies potential candidates which could have an underlying hard electron energy spectrum, is by looking at the light curve decay index past the jet break. The choice is confirmed by the optical and x-ray spectral indices. According to the standard model, the flux in higher frequencies, past jet break, decay as a power-law of index p; the spectrum below 14 should have a slope of (p — 1)/2 and above it should fall as pp. The value of p one thus obtains from all these methods is expected to be consistent. In chapter 3, we chose three such afterglows (GRB010222, GRB020813 and GRB041006), which show shallow decay of fluxes in the optical as well as in x-ray bands and relatively flat spectra. Out of a dozen such afterglows, these three have well sampled multi-band light curves. We fitted the data set with the model and estimated the physical parameters. For we have estimated the contribution of the associated supernova by subtracting the afterglow model from the total emission. We found the contribution from Compton emission to be negligible in all these cases. Interestingly, all these afterglows had relatively low cooling frequency, which could perhaps be due to some unknown relation to the acceleration mechanism itself. Chapter 4 and 5 are devoted to GRB030329, one of the best monitored afterglows till date. The 4th Chapter focuses on the radio observations of the afterglow done with the GMRT at low frequencies. To begin with, we give a brief introduction to the interferometric techniques and the instrument. GMRT, an interferometric array with 30 elements, each of diameter 45 meters has an excellent sensitivity at low frequencies which allowed it to detect and monitor the afterglow for a long time. We then present observations in 1280 MHz and 610 MHz bands during the second year of the afterglow Thanks to this long coverage, we were able to pin-point the location of va and the transition of the fireball to the Newtonian regime. Chapter 5 describes the multiband modelling of this afterglow. The evolution of the afterglow was complex. While the afterglow flux in optical as well as in x-ray exhibited a jet break around half a day, the radio flux past 0.5 days did not follow the expectations from a jet which has already entered the lateral expansion regime. Instead, it showed an achromatic steepening around 10 days. Hence, a novel suggestion of two co-aligned jets, one narrow and one wide, together giving rise to the observed flux has emerged (Berger et. al. 2003). We test the predictions of this conjecture and get a refined set of parameters, prompted primarily by the additional data from GMRT. We then proceed to suggest a different scenario in which the initial jet which gave rise to the x ray and optical flux is reenergized by the central engine during its lateral expansion that makes it once again collimated, now to a wider opening angle. This new jet enters a lateral expansion phase around 10 days, resulting in the jet break seen in radio bands. One peculiarity of this GRB was its association with a supernova (SN2003dh) which dominated the optical flux beyond a week. The refined afterglow flux calculation allowed us to subtract the afterglow contribution from the total optical flux and compare the resulting supernova contribution with the stereotype SN1998bw. While being similar in light curve, SN2003dh is fainter compared to a redshifted SN1998bw. The contribution of this thesis lies in presenting a consistent modelling platform for 'hard' electron energy spectra as well as in the low frequency campaign of GRB030329 afterglow and the interpretation of its evolution. Chapter 6 concludes the thesis along with a few suggestions for future directions.

碩士
中原大學
電子工程研究所
102
In the semiconductor industry, non-volatile memory (NVM) applications are extensive, and the relative markets have been well developed. For developing semiconductor NVM devices, the effect and improvement of reliability characteristics play important roles. This work is aimed at investigating the surface states and energy profile of single-side non-overlapped implantation (SNOI) MOSFETs which use the drain-side spacer region to store charges by hot carrier injection. To extract the interface state of energy distribution and trap density, we used the two-level charge pumping method and three-level charge pumping methods for investigating SNOI devices. Based on the charge pumping measurement results, the interface trap and trap energy can be found. Finally, by using the charge pumping method, the energy distribution will shift about 60meV to the shallow site, and the interface trap density will increase to about 2.5x1010 (cm-2eV-1) after the program process.

碩士
國立臺灣大學
物理研究所
99
Since plasmons have strong near-fields, they can break the limit of optical diffraction and become an important mechanism for developments of optical instruments. In order to explore the characteristics of plasmons, in this thesis we simulate the plasmon modes in spherical and cylindrical nanomaterials excited by fast electron beams. In addition, the variations of mode eigenfrequencies as a function of incident electron speed, location, and direction were carefully studied. An exotic mode of Cherenkov radiation was also carefully investigated and cannot be tackled without the thorough relativistic consideration of the calculations. Comparison between electron-beam experiments and calculations were also briefly discussed.

Early processes following photon absorption by the photosynthetic pigment-protein complex photosystem I (PS I) have been the subject of decades of research, yet many questions remain in this area of study. Among the trickiest to investigate is the role of the PS I reaction center’s (RC’s) two accessory (A_‑1) chlorophyll (Chl) cofactors as primary electron donors or acceptors, oxidizing the special pair (P₇₀₀) of Chls or reducing a nominal primary electron acceptor (A₀) Chl in the first electron transfer step. Such processes, which occur on a picosecond timescale, have long been studied via ultrafast spectroscopy, though difficulty lies in distinguishing among signals from early processes, which have similar lifetimes and involve many identical pigments. In this work, we used steady-state and ultrafast optical pump-probe spectroscopies on PS I trimers from wildtype and mutant strains of the cyanobacterium Synechocystis sp. PCC 6803 in which an asparagine amino acid residue near A_‑1 had been replaced with methionine on one or both sides of the RC. We also conducted an identical set of experiments on mutants in which A₀ was similarly targeted, as well as studied the effects on the A₀ absorption spectrum of a third category of mutations in which a peripheral H‑bond to A₀ was lost. Steady-state absorption spectroscopy revealed that many of these mutations caused mild Chl deficiencies in the light-capturing antenna of PS I without necessarily preventing organisms’ growth. More importantly, we determined that contrary to certain hypotheses, A_‑1 is the most likely true first electron acceptor, as reasoned from observing rapid triplet state formation in double A_‑1 mutants. We also concluded from non-additive detrimental effects of single-side mutations that if one RC branch is damaged at the level of A₀ or A_‑1, electron transfer may be redirected along the intact branch. This may help explain the conservation of two functional RC branches in PS I over many generations of natural selection, despite the additional cost to organisms of manufacturing both.