This thesis deals with theoretical studies of the electronic structure of molecules used in the context of molecular electronics. Both studies with model Hamiltonians and first principle calculations have been performed. The materials studied include molecular crystals of pentacene and DNA, which are used as active material in field-effect transistors and as tentative molecular wires, respectively. The molecular magnet compound TCNE and surface modification by means of chemisorption of TDAE on gold are also studied. Molecular crystals of pentacene are reported to have the highest field-effect mobility values for organic thin film field-effect transistors. The conduction process in field-effect transistors applications occurs in a single layer of the molecular crystal. Hence, in studies of transport properties molecular crystals of pentacene can be considered as a two dimensional system. An open question of these system is if the charge transport is bandlike or if as a result of disorder is a hopping process. We address this question in two of the included papers, paper I and paper II. The conducting properties of DNA are of interest for a broad scientific community. Biologist for understanding of oxidatively damaged DNA and physicist and the electronics community for use as a molecular wire. Some reports on the subject classifies DNA as a conductor while other report insulating behavior. The outcome of the investigations are heavily dependent on the type of DNA being studied, clearly there is a big difference between the natural and more or less random sequence in, e.g., λ-DNA and the highly ordered syntethic poly(G)-poly(C) DNA. It has been suggested that long-range correlation would yield delocalized states, i.e., bandlike transport, in natural DNA, especially in the human chromosome 22. In paper III we show that this is not the case. In general our results show that DNA containing an approximately equal amount of the four basis is an insulator in a static picture. An emerging research field is spintronics. In spintronic devices the spin of the charge carrier is as important as the charge. One can envision a device where spin alone is the carrier of information. In realizing spintronic devices, materials that are both magnetic and semiconducting are needed. Systems that exhibit both these properties are organic-based magnets. In paper IV the electronic structure of the molecular magnet compound TCNE is studied, both experimentally and theoretically. The injection of carriers from metal contacts to organic semiconductors is central to the performance of organic based devices. The interface between the metal contact and the organic material has been pointed out to be one of the device parameters that most significantly influences the device performance. This relates to the process of injection of charge carriers in to the organic material. In some contact and organic material combinations the energy barrier for charge injection can be very high. The barrier can be reduced by modify the interface dipole, this is achieved by a monolayer of adsorbed molecules at the interface. The molecule TDAE chemisorbed on gold is studied in paper V.

Plasmonic nanoparticles support surface plasmon resonances that are sensitive to the environment. Factors contributing to the refractive index sensitivity are explored systematically through simulation, theory, and experiment. Particles small with respect to the wavelength of light and with size parameters much less than 1 have optical properties accurately predicted by quasi-electrostatic theory while particles with larger size parameters necessitate electrodynamics. A theory is developed that captures the effects of geometry on the refractive index sensitivity with a single factor, plasmon band location, and, although based on electrostatic theory, well predicts the sensitivity of particles whose properties are beyond the electrostatic limit. This theory is validated by high quality simulations for compact particles with shape parameters approaching 1 and, therefore, electrodynamic in nature, as well as higher aspect ratio particles that are electrostatic. Experimentally observed optical spectra for nanorods immobilized on glass and subjected to changes in n of the medium are used to calculate the sensitivity of the particles, found to be well matched by a variation on the homogeneous plasmon band theory. The separate electrostatic and electrodynamic components of plasmon band width, are explored and the overall width is found to affect the observability of the aforementioned sensitivity similarly within each particle class. The extent of the sensing volume around a spherical particle is explored and found to vary with particle size for small particles. Through simulation of oriented dielectric layers, it is shown particles are most sensitive to material located in regions of highest field enhancement. Variations on seed-mediated growth of gold nanorods results in spectra exhibiting a middle peak, intermediate to the generally accepted longitudinal and transverse modes. Simulated optical properties and calculated field enhancement illustrates the correlation between geometry and optical properties and allows for identification of the middle peak. / Dissertation

<p>Quantum Dot Infrared Photodetectors (QDIPs) are important alternatives to conventional infrared photodetectors with high potential to provide required detector performance, such as higher temperature operation and multispectral response, due to the 3-D quantum confinement of electrons, discrete energy levels, and intrinsic response to perpendicular incident light due to selection rules. However, excessive dark current density, which causes QDIPs to underperform theoretical predictions, is a limiting factor for the advancement of QDIP technologies. The purpose of this dissertation research is to achieve a better understanding of dopant incorporation into the active region of QDIPs, which is directly related to dark current control and spectral response. From this dissertation research, doping related dipole fields are found to be responsible for excessive dark current in QDIPs. </p><p>InAs/GaAs QDIPs were grown using solid source molecular beam epitaxy (MBE) with different doping conditions. The QDIPs were optically characterized using photoluminescence and Fourier transform infrared (FT-IR) spectroscopy. Devices were fabricated using standard cleanroom fabrication procedures. Dark current and capacitance measurements were performed under different temperature to reveal electronic properties of the materials and devices. A novel scanning capacitance microscopy (SCM) technique was used to study the band structure and carrier concentration on the cross section of a quantum dot (QD) heterostructure. In addition, dark current modeling and bandstructure calculations were performed to verify and better understand experimental results.</p><p>Two widely used QDIP doping methods with different doping concentrations have been studied in this dissertation research, namely direct doping in InAs QD layer, and modulation doping in the GaAs barrier above InAs QD layer. In the SCM experiment, electron redistribution has been observed due to band-bending in the modulation-doping region, while there is no band-bending observed in directly doped samples. A good agreement between the calculated bandstructure and experimental results leads to better understanding of doping in QD structures. The charge filling process in QDs has been observed by an innovative polarization-dependent FT-IR spectroscopy. The red-shift of QD absorbance peaks with increasing electron occupation supports a miniband electronic configuration for high-density QD ensembles. In addition, the FT-IR measurement indicates the existence of donor-complex (DX) defect centers in Si-doped QDIPs. The existence of DX centers and related dipole fields have been confirmed by dark current measurements to extract activation energies and by photocapacitance quenching measurements. </p><p>With the understanding achieved from experimental results, a further improved dark current model has been developed based on the previous model originally established by Ryzhii and improved by Stiff-Roberts. In the model described in this dissertation, two new factors have been considered. The inclusion of background drift current originating from Si shallow donors in the low bias region results in excellent agreement between calculated and measured dark currents at different temperatures, which has not been achieved by previous models. A very significant effect has been observed in that dark current leakage occurs due to the dipole field caused by doping induced charge distribution and impact-ionized DX centers. </p><p>Last but not least, QDIPs featuring the dipole interface doping (DID) method have been designed to reduce the dark current density without changing the activation energy (thus detection wavelength) of QDIPs. The DID samples involve an InAs QD layer directly-doped by Si, as well as Be doping in the GaAs barrier on both sides of the QD layer. The experimental result shows the dark current density has been significantly reduced by 104 times without any significant change to the corresponding activation energy. However, the high p-type doping in the GaAs barrier poses a challenge in that the Fermi level is reduced to be well below the QD energy states. High p-type doping is reported to reduce the dark current, photocurrent and the responsivity of the devices. </p><p>To conclude, it is significant to identify to effect of Si-induced defect centers on QDIP dark currents. The subsequent study reveals doping induced dipole fields can have significant effects on QDIP device performance, for example, causing charge leakage from QDs and reducing activation energy, thereby increasing dark current density. The DID approach developed in this work is a promising approach that could help address these issues by using controlled dipole fields to reduce dark current density without changing the minimum detectable energy of QDIPs.</p> / Dissertation

In this thesis the entanglement properties of atom-atom, atom-photon, and photon-photon are investigated. The recent developments of quantum computation as well as quantum information and communication have attracted much interest in the generation of these entanglements in the laboratory. To generate atom-photon entanglement, I discuss a model system in the cavity QED setup. By using a four-level atom and two resonant cavity modes, we can generate atom-photon entanglement almost deterministically. An extension of the above model to a six-level atom and again two resonant cavity modes can generate entangled photon pairs by appropriately adjusting system parameters. I then investigate the atom-atom entanglement in a 1D harmonic trap. I show the dependence of the pair entanglement on the scattering length and temperature, as well as the particle symmetry requirement (bosons or fermions). Among many peculiar properties in a 1D system, we briefly discuss the Fermi-Bose duality". While the entanglement properties of a single-channel model have recently been obtained for 1D and 3D systems, I thus study the entanglement of a multi-channel process in a cylindrical harmonic trap. I discuss the dependence of entanglement on the trap geometry. Finally I present detailed studies of the spin mixing between two Rb87 atoms in a single lattice site. The topic is emphasized on various motional state approximations and dipolar effect. Various motional state approximations can cause up to 20% error to experimental data. I also find that the dipolar interaction can lead to an experimentally observable frequency shift in a cylindrical harmonic trap with very large aspect ratio. The spin mixing of spin-2 manifold has also been discussed.

In this thesis, two novel broadband slot mobile phone antenna designs respectively for penta-band WWAN operation and eight-band LTE/WWAN operation are presented. The antennas are suitable to be mounted near the bottom edge of the system ground plane of the mobile phone. Good radiation characteristics for the antennas are obtained, and the two antennas respectively occupy a small printed area of 50 ¡Ñ 4 mm2 and 53 ¡Ñ 4 mm2. The first design uses a C-shaped strip connected to the bottom edge of the system ground plane to make the structure of the system ground plane close to a symmetric shorted dipole antenna. This makes it promising to excite a chassis mode to enhance the operating bandwidth of the antenna. The second one uses a microstrip feedline having a chip-inductor-loaded branch. The novel microstrip feedline can lead to more uniform distribution of the electric fields excited in the slot such that enhanced bandwidth of the antenna¡¦s lower band is obtained. Further, since the chip inductor performs like a low-pass filter, the original bandwidth of the antenna¡¦s upper band is not affected. Additionaly, the impedance matching of the lower frequencies of the upper band can be improved, which enhances the upper-band bandwidth of the antenna. Effects of the user¡¦s head and hand on the proposed antenna are also studied, and the simulated SAR and HAC issues are also analyzed in this thesis.

Applicability of the Hartree-Fock (HF) based random phase approximation (RPA) with several Skyrme effective interactions to the description of the isoscalar giant monopole (ISGMR) and the isoscalar giant dipole resonance (ISGDR) in 90Zr, 116Sn, 144Sm and 208Pb nuclei has been investigated. The existing Skyrme interactions SL1, SkM*, SGII, Sly4 and Sk255 were used. Hartree-Fock description of the ground state properties of all nuclei of interest was obtained using these Skyrme interactions. Transition strength distributions for the ISGMR and the ISGDR in nuclei of interest were calculated using coordinate space representation for the RPA in the Green’s function formalism with discretized continuum. A method of projecting out the spurious state contribution from the transition strength distribution and the transition density of the ISGDR was employed to eliminate spurious state mixing, due to a not fully selfconsistent description of the particle-hole interaction within the RPA. Differential cross sections of 240 MeV alpha-particles inelastic scattering on all nuclei of interest were calculated using the folding model within the distorted wave Born approximation (DWBA). Optical potentials were obtained by folding HF ground state densities with a alpha-nucleon density dependent Gaussian interaction. Parameters of the interaction were obtained by fitting experimental angular distribution of alpha-nucleus elastic scattering. The inelastic differential cross sections were calculated using both collective and microscopic transition densities. Possible underestimations of the energy weighted sum rule for the case of the ISGDR are reported. An alternative description for the ISGDR in nuclei based on the Fermi liquid drop model (FLDM) with the collisional Fermi surface distortion was investigated. The FLDM dispersion relation was obtained from the linearized Landau-Vlasov equation. Centroid energies, E0 and E1, and widths, gamma-0 and gamma-1, of the ISGMR and ISGDR, respectively, were calculated as functions of the damping parameter using appropriate boundary conditions. Comparison of the theoretical ratios of the ISGDR and ISGMR centroid energies, E1/E0, to the experimental values resulted in a damping parameter equal to 0.5, however, systematic overestimation of energy of the ISGMR and ISGDR by 2.0-2.5 MeV was observed. The applicability of the HF-RPA to the description for the ISGDR in nuclei is confirmed.

Abstract Whether an Open Area Test Site (OATS) is qualified is based on the Normalized Site Attenuation (NSA). The purpose is to eliminate the influence of Antenna Factor (AF). Usually the AF provided by the manufacturer adopts the Standard Site Method (SSM) and is quoted from measurements at a 10-m range. In practice, the AF varies with the measurement conditions. This uncertainly will translate into error in NSA measurements. Currently radiated electromagnetic interference measurement mostly adopts the broadband antennas, and LPDA is one of the antennas used extensively. However, the AF provided by the manufacturer does not consider shifts in the phase center of LPDA with frequency. In the meantime the radiation pattern of LPDA is different from that of a short dipole. The investigation of this thesis will focus on these two parts. In determining the phase center of LPDA antenna we adopt the average shift of phase center to improve the AF. The numerical simulation results show that such an arrangement can result in improvement. We also use the method of PCPM (Phase Center and Pattern Matching) to modify the AF under different conditions of measurement when a ground plane is present. Our study, by using the numerical simulation and measurement, shows that this indeed improves the variation of AF over that obtained by SSM. In addition, efforts are also made to have a detailed discussion in mutually coupling effects between the LPDA antenna and the ground plane, in order to distinguish the impact on AF due to the coupling of the LPDA antenna and its image. Our numerical simulation results indicate that it does not have a significant effect.

In this thesis, the study mainly focuses on the terrestrial DTV signal reception antenna. These antennas are designed based on the use of planar dipole antenna, but with different techniques in order to overcome the narrow-bandwidth problem of conventional dipole antenna. In ¡§Broadband Three-arm Dipole Planar Antenna for DTV Signal Reception,¡¨ a metal plate is added for achieving wideband operation. In ¡§End-fed Modified Dipole Antenna for DTV Signal Reception,¡¨ two arms of different lengths are extended in the same direction to wideband operation. In ¡§Internal DTV Antenna for Folder-Type Mobile Phone,¡¨ two system ground planes are regarded as the two arms of the dipole. With the use of an internal matching circuit, good impedance matching can be obtained for receiving DTV signal over a wide bandwidth.

A six-band antenna design for the mobile phone is presented. The required bandwidth for DTV/GSM850/900/DCS/PCS/UMTS operation is achieved by using two antennas. For DTV/GSM850/900 operation, we propose a novel antenna by using the concept of the dipole antenna and an internal matching portion to excite the half- and one-wavelength resonant modes of the antenna. With the internal matching portion, the frequency ratio of the two resonant modes can be controlled, thereby making the two resonant modes formed into a very wide operating band. For DCS/PCS/UMTS operation, a novel monopole slot antenna is used. The lower-edge frequency of the slot antenna depends on its length and the required bandwidth can be achieved by adjusting its tuning section. Effects of casing and human body on the proposed mobile phone antenna are also discussed. It is found that the radiation efficiency of DTV/GSM bands is larger than that of DCS/PCS/UMTS bands in this design. However, overall the operating bands, the antenna performances are greatly affected when the human effects are taken into considerations.

In this study, optical behavior of metal nanoparticles having dimensions smaller than the wavelength of visible light is studied experimentally and numerically. Gold (Au) and silver (Ag) nanoparticles are studied due to their superior optical properties when compared to other metals. A compact code based on Discrete Dipole Approximation (DDA) is developed to compute extinction efficiencies of nanoparticles with various different properties such as material, dimension and geometry. To obtain self consistent nanoparticle arrays with well defined geometries and dimensions, Electron Beam Lithography (EBL) technique is mainly used as the manufacturing method. Dose parameters required to produce nanoparticles with dimensions down to 50 nm over substrates with different electrical conductivities are determined. Beam current is found to affect the doseV size relation. The use of thin Au films as antistatic layer for e-beam patterning over insulating substrates is considered and production steps, involving instabilities due to contaminants introduced to the system during additional removal steps, are clarified. 4 nm thick Au layer is found to provide sufficient conductivity for e-beam patterning over insulating substrates. An optical setup capable of performing transmittance and reflectance measurements of samples having small areas patterned with EBL is designed. Sizes of the metal nanoparticles are determined by scanning electron microscope (SEM) and spectral data obtained using the optical setup is analyzed to find out the parameters affecting the localized surface plasmon resonances (LSPR). Arrays of particles with diameters between 50 &ndash / 200 nm are produced and optically analyzed. Size and shape of the nanoparticles are found to affect the resonance behavior. Furthermore, lattice constants of the particle arrays and surrounding medium are also shown to influence the reflectance spectra. Axes with different lengths in ellipsoidal nanoparticles are observed to cause distinguishable resonance peaks when illuminated with polarized light. Peak intensities obtained from both polarizations are observed to decrease under unpolarized illumination. Binary systems consisting of nanosized particles and holes provided better contrast for transmitted light.