The adiabatic approximation is a natural approach for the description of phenomena induced by low frequency laser radiation because the ratio of the laser frequency to the characteristic frequency of an atom or a molecule is a small parameter. Since the main aim of this work is the study of ionization phenomena, the version of the adiabatic approximation that can account for the transition from a bound state to the continuum must be employed. Despite much work in this topic, a universally accepted adiabatic approach of bound-free transitions is lacking. Hence, based on Savichev's modified adiabatic approximation [Sov. Phys. JETP 73, 803 (1991)], we first of all derive the most convenient form of the adiabatic approximation for the problems at hand. Connections of the obtained result with the quasiclassical approximation and other previous investigations are discussed. Then, such an adiabatic approximation is applied to single-electron ionization and non-sequential double ionization of atoms in a strong low frequency laser field. The momentum distribution of photoelectrons induced by single-electron ionization is obtained analytically without any assumptions on the momentum of the electrons. Previous known results are derived as special cases of this general momentum distribution. The correlated momentum distribution of two-electrons due to non-sequential double ionization of atoms is calculated semi-analytically. We focus on the deeply quantum regime -- the below intensity threshold regime, where the energy of the active electron driven by the laser field is insufficient to collisionally ionize the parent ion, and the assistance of the laser field is required to create a doubly charged ion. A special attention is paid to the role of Coulomb interactions in the process. The signatures of electron-electron repulsion, electron-core attraction, and electron-laser interaction are identified. The results are compared with available experimental data. Two-electron correlated spectra of non-sequential double ionization below intensity threshold are known to exhibit back-to-back scattering of the electrons, viz., the anticorrelation of the electrons. Currently, the widely accepted interpretation of the anticorrelation is recollision-induced excitation of the ion plus subsequent field ionization of the second electron. We argue that there exists another mechanism, namely simultaneous electron emission, when the time of return of the rescattered electron is equal to the time of liberation of the bounded electron (the ion has no time for excitation), that can also explain the anticorrelation of the electrons in the deep below intensity threshold regime. Finally, we study single-electron molecular ionization. Based on the geometrical approach to tunnelling by P. D. Hislop and I. M. Sigal [Memoir. AMS 78, No. 399 (1989)], we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single active electron models of molecular tunnelling ionization (i.e., theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short range interactions and ``almost'' linear in the case of long range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the proven statements are discussed.

This thesis describes a research of suppression of superconducting gap in a superconducting island of a Ferromagnetic-Superconducting-Ferromagnetic Single-Electron-Transistor due to the fringing magnetic fields produced by the ferromagnetic leads. The devices are working below the critical temperature of the superconducting gap. A model is proposed to explain how the fringing magnetic field produced by the leads is strong enough to suppress the superconducting gap. The peak of the fringing magnetic field produced by one lead reaches 5000 oe. It is observed an inverse tunneling magneto resistance during the suppression of the superconducting gap, obtaining a maximum absolute value 500 times greater than the TMR in the normal state where the efficiency of the spin injection is low. It is concluded that the suppression of the superconducting gap is due to fringing magnetic field and not to the spin accumulation because the low efficiency of the spin injection. It is suggested a new geometry to reduce the effect of the fringing magnetic field so it can be obtained a suppression of the superconductivity due to the spin accumulation. It is described the qualitatively behavior of the IV characteristic when the suppression of the superconductivity is due to spin accumulation.

The low-energy properties of quantum dot systems are dominated by the Kondo effect. We study the dependence of the characteristic energy scale of the effect, the Kondo temperature, on the gate voltage, which controls the number of electrons in the strongly blockaded dot. We show that in order to obtain the correct Kondo temperature as a function of the gate voltage, it is crucial to take into account the presence of many energy levels in the dot. The dependence turns out to be very different from that in the conventional single-level Anderson impurity model. Unlike in the latter, the Kondo temperature cannot be characterized by a single parameter, such as the ratio of the tunneling-induced width of the energy levels in the dot and the charging energy.

The adiabatic approximation is a natural approach for the description of phenomena induced by low frequency laser radiation because the ratio of the laser frequency to the characteristic frequency of an atom or a molecule is a small parameter. Since the main aim of this work is the study of ionization phenomena, the version of the adiabatic approximation that can account for the transition from a bound state to the continuum must be employed. Despite much work in this topic, a universally accepted adiabatic approach of bound-free transitions is lacking. Hence, based on Savichev's modified adiabatic approximation [Sov. Phys. JETP 73, 803 (1991)], we first of all derive the most convenient form of the adiabatic approximation for the problems at hand. Connections of the obtained result with the quasiclassical approximation and other previous investigations are discussed. Then, such an adiabatic approximation is applied to single-electron ionization and non-sequential double ionization of atoms in a strong low frequency laser field. The momentum distribution of photoelectrons induced by single-electron ionization is obtained analytically without any assumptions on the momentum of the electrons. Previous known results are derived as special cases of this general momentum distribution. The correlated momentum distribution of two-electrons due to non-sequential double ionization of atoms is calculated semi-analytically. We focus on the deeply quantum regime -- the below intensity threshold regime, where the energy of the active electron driven by the laser field is insufficient to collisionally ionize the parent ion, and the assistance of the laser field is required to create a doubly charged ion. A special attention is paid to the role of Coulomb interactions in the process. The signatures of electron-electron repulsion, electron-core attraction, and electron-laser interaction are identified. The results are compared with available experimental data. Two-electron correlated spectra of non-sequential double ionization below intensity threshold are known to exhibit back-to-back scattering of the electrons, viz., the anticorrelation of the electrons. Currently, the widely accepted interpretation of the anticorrelation is recollision-induced excitation of the ion plus subsequent field ionization of the second electron. We argue that there exists another mechanism, namely simultaneous electron emission, when the time of return of the rescattered electron is equal to the time of liberation of the bounded electron (the ion has no time for excitation), that can also explain the anticorrelation of the electrons in the deep below intensity threshold regime. Finally, we study single-electron molecular ionization. Based on the geometrical approach to tunnelling by P. D. Hislop and I. M. Sigal [Memoir. AMS 78, No. 399 (1989)], we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single active electron models of molecular tunnelling ionization (i.e., theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short range interactions and ``almost'' linear in the case of long range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the proven statements are discussed.

Un effort mondial existe actuellement dans le but de réaliser un ordinateur quantique. Un tel dispositif permettrait d'implémenter des algorithmes plus rapides que les algorithmes classiques pour certaines tâches (recherche dans des bases de données, factorisation d'entiers). Il permettrait également de simuler des systèmes quantiques de manière beaucoup plus efficace qu'un ordinateur classique. L'obtention de ce gain en puissance nécessite d'intriquer un grand nombre de bits quantiques (qubits). Celle ci suppose de pouvoir déplacer un qubit d'un point à un autre de l'espace. Dans cette thèse, nous démontrons une première étape vers le déplacement d'un qubit de spin électronique : un électron unique est déplacé, à la demande, entre deux boîtes quantiques distantes de quelques microns. Le transport est réalisé à l'aide d'une onde acoustique de surface qui entraîne l'électron. Le transfert a été réalisé avec une efficacité de 90 % et déclenché à la nanoseconde. Ces résultats ouvrent la voie à la réalisation d'expériences d'optique quantique électronique avec une détection évènement par évènement. L'envoi d'un électron sur deux initialement présents ouvre la voie à la génération de paires d'électrons distants et intriqués.

Reductive electron transfer has been successfully utilized to facilitate the first enantioselective desymmetrisation of malonate derivatives. Selective monoreduction of cyclic 1,3-diesters through the combined use of SmI2-Et3N and chiral non-racemic diols has granted rapid access to enantioenriched β-hydroxy acids containing challenging quaternary centres – an abundant motif in many drug molecules. Unique radical anions generated from the single electron reduction of cyclic 1,3-diesters have been exploited in cyclisation cascades. Capture of acyl-type radical anions by both alkene and alkyne acceptors have permitted the construction of complex bicyclic architectures in a single synthetic operation. The reductive cyclisation cascade of lactones has also been demonstrated, using SmI2-H2O to achieve a challenging domino 5-exo-trig/6-exo-trig cyclisation event. This process generates highly decorated carbo[5.4.0]bicyclic scaffolds with complete diastereocontrol.

The MAO-B catalyzed metabolic bioactivation of the parkinsonian inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to generate the neurotoxic 1-methyl-4-phenylpyridinium species (MPP+) is well documented. The N-cyclopropyl analog (CPTP) of MPTP is a mechanism based inactivator of MAO-B which presumably is processed by a single electron transfer (SET) pathway to generate a bioalkylating species. These results have prompted us to study how the cytochromes P450, the major liver drug metabolizing oxidases, interact with N-cyclopropyl analogs of MPTP. HPLC with diode array detection and LC-electrosprary ionization mass spectrometry (LC-ESI/MS) based methods have been developed for metabolite detection and characterization. From the UV spectral data and pseudomolecular ion species observed by LC-ESI/MS, we have identified N-oxide, C-hydroxylated, and pyridinium metabolites. For the trans-1-(2-phenylcyclopropyl) analog, cinnamaldehyde and p-hydroxycinnamaldehyde also were characterized. Incubation of CPTP and its derivatives with cDNA expressed human hepatic cytochrome P450 has shown that CYP2D6 catalyzes the formation of cinnamaldehyde, the N-descyclopropyl, pyridinium and hydroxylated products. CYP3A4 is responsible for the formation of the N-descyclopropyl and pyridinium species and cinnamaldehyde but it does not mediate any hydroxylation reactions. Since both the a-carbon oxidation and N-descyclopropylation transformations are mediated by a single enzyme (either CYP2D6 or CYP3A4), we propose a common intermediate for both pathways, namely the cyclopropylaminyl radical cation generated by the SET pathway. This intermediate partitions between the a-carbon oxidation pathway leading to the dihydropyridinium and pyridinium species and the ring opening pathway leading to the N-descyclopropyl metabolite and aldehyde species. The phenyl substituent on the cyclopropyl ring stabilizes the ring opened distonic radical cation and favors the ring opening pathway and results in the formation of less of the pyridinium species. The proton and methyl substituents on the cyclopropyl ring favor the a-carbon oxidation pathway and increased amounts of the pyridinium species are formed. / Master of Science

No description available.

Single electron transistors (SET) have attracted significant attention as a potential building block for post CMOS nanoelectronic devices. However, lack of reproducible and parallel fabrication approach and room temperature operation are the two major bottlenecks for practical realization of SET based devices. In this thesis, I demonstrate large scale single electron transistors fabrication techniques using solution processed single wall carbon nanotubes (SWNTs) and studied their electron transport properties. The approach is based on the assembly of individual SWNTs via dielectrophoresis (DEP) at the selected position of the circuit and formation of tunnel barriers on SWNT. Two different techniques: i) metal-SWNT Schottky contact, and ii) mechanical templating of SWNTs were used for tunnel barrier creation. Low temperature (4.2K) transport measurement of 100 nm long metal-SWNT Schottky contact devices show that 93% of the devices with contact resistance (RT) > 100 K? show SET behavior. Majority (90%) of the devices with 100 K? < RT < 1 M?, show periodic, well-de?ned Coulomb diamonds with a charging energy ~ 15 meV, represents single electron tunnelling through a single quantum dot (QD), defined by the top contact. For high RT (> 1M?), devices show multiple QDs behaviors, while QD was not formed for low RT ( < 100 K?) devices. From the transport study of 50 SWNT devices, a total of 38 devices show SET behavior giving an yield of 76%. I also demonstrate room temperature operating SET by using mechanical template technique. In mechanical template method individual SWNT is placed on top of a Al/Al2O3 local gate which bends the SWNT at the edge and tunnel barriers are created. SET devices fabricated with a template width of ~20 nm shows room temperature operation with a charging energy of ~150 meV. I also discussed the detailed transport spectroscopy of the devices.

No description available.