Quantum-mechanical calculations of vibrationally resolved cross sections for non-dissociative charge transfer of O3+ with H-2

Charge transfer due to collisions of ground state O3+ (2s(2)2p P-2) ions with molecular hydrogen is investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) method, and electronic and vibrational state-selective cross sections along with the corresponding differential cross sections are calculated for projectile energies of 100, 500, 1000 and 5000 eV/u at the orientation angles of 25 degrees,45 degrees and 89 degrees. The adiabatic potentials and radial coupling matrix elements utilized in the QMOCC calculations were obtained with the spin-coupled valence-bond approach. The infinite order sudden approximation (IOSA) and the vibrational sudden approximation (VSA) are utilized to deal with the rotation of H-2 and the coupling between the electron and the vibration of H-2. It is found that the distribution of vibrationally resolved cross sections with the vibrational quantum number upsilon' of H-2(+) (upsilon') varies with the increment of the projectile energy; and the electronic and vibrational stateselective differential cross sections show similar behaviors: there is a highest platform within a very small scattering angle, beyond which the differential cross sections decrease as the scattering angle increases and lots of oscillating structures appear, where the scattering angle of the first structure decreases as E-P(-1/2) with the increment of the projectile energy E-P; and the structure and amplitude of the differential cross sections are sensitive to the orientation of molecule H-2, which provides a possibility to identify the orientations of molecule H-2 by the vibrational state-selective differential scattering processes.

Charge carrier transporting, photoluminescent, and electroluminescent properties of zinc(II)-2-(2-hydroxyphenyl)benzothiazolate complex

Zinc(II)-2-(2-hydroxyphenyl)benzothiazolate complex is an excellent white-light-emitting material. Despite some studies devoted to this complex, no information on the real origin of the unusually broad electroluminescent (EL) emission is available. Therefore, we investigate photoluminescent and EL properties of the zinc complex. Orange phosphorescent emission at 580 nm was observed for the complex in thin film at 77 K, whereas only fluorescent emission was obtained at room temperature. Molecular orbitals, excitation energy, and emission energy of the complex were investigated using quantum chemical calculations. We fabricated the device with a structure of ITO/F16CuPc(5.5 nm)/Zn-complex/Al, where F16CuPc is hexadecafluoro copper phthalocyanine. The EL spectra varied strongly with the thickness of the emissive layer. We observed a significant change in the emission spectra with the viewing angles. Optical interference effects and light emission originating both from fluorescence and from phosphorescence can explain all of the observed phenomena, resulting in the broad light emission for the devices based on the Zn complex. We calculated the charge transfer integral and the reorganization energy to explain why the Zn complex is a better electron transporter than a hole transporter.

Investigation of charge-carrier injection characteristics in NPB/Alq3 heterojunction devices

The effect of copper phthalocyanine (CuPc) and LiF interfacial layers on the charge-carrier injection in NN'-di(naphthalene-l-yl)N,N'-diphenyl-benzidine (NPB)/tris(8-hydroxyquinoline) aluminium (Alq(3)) organic heterojunction devices have been studied through the analysis of current-voltage characteristics. The investigation clearly demonstrated that the hole injection into NPB from anode is Fowler-Nordheim (FN) tunneling and the electron injection into Alq3 from cathode is Richardson-Schottky (RS) thermionic emission. The barrier heights obtained from the FN and RS models proved that the band alignments for charge-carrier injection are greatly improved by the CuPc and LiF interfacial layers, which should fully clarify the role of the interfacial layer on the improvement of device performance.

Studies on charge transfer across the micro-liquid/liquid interface supported at a double-barrel micropipette

In this paper, the charge transfer across the micro-liquid/liquid interface supported at the orifice of a double-barrel micropipette, namely, a theta-pipette, is reported. Simple ion transfer(TMA(+)), facilitated ion transfer (potassium ion transfer facilitated by DB18C6), and electron transfer (ferrocene and ferri/ferrocyanide system) have been investigated by cyclic voltammetry. The experimental results show that a very thin aqueous film, linking both barrels filled with the aqueous solution and the organic solution respectively, can spontaneously be formed on the outer glass surface of such a double-barrel micropipette to construct a micro-liquid/liquid interface, which provides the asymmetry of diffusion field. Such device is demonstrated experimentally which can be employed as one of the simplest electrochemical cells to investigate the charge transfer across the liquid/liquid interface.

THEORY OF STEADY-STATE CURRENT AT MULTIPLE MICROCYLINDER ELECTRODES COUPLED WITH A PARALLEL PLANAR ELECTRODE

A novel device of multiple cylinder microelectrodes coupled with a parallel planar electrode was proposed. The feedback diffusion current at this device was studied using bilinear transformation of coordinates in the diffusion space, where lines of mass flux and equiconcentration are represented by orthogonal circular functions. The derived expression for the steady-state current shows that as the gap between cylindrical microelectrodes and planar electrode diminishes, greatly enhanced currents can be obtained with high signal-to-noise ratio. Other important geometrical parameters such as distance between adjacent microcylinders, cylinder radius, and number of microcylinders were also discussed in detail.

PREPARATION AND CHARACTERIZATION OF A MULTICYLINDER MICROELECTRODE COUPLED WITH A CONVENTIONAL GLASSY-CARBON ELECTRODE AND ITS APPLICATION TO THE DETECTION OF DOPAMINE

A multi-cylinder microelectrode coupled with a conventional glassy carbon disc electrode (MCM/GC) was prepared and characterized using cyclic voltammetry and chronoamperometry. It was demonstrated that in the same way as one observed a steady-state current at closely spaced microelectrodes when redox recycling takes place, the same effect can be obtained with the MCM/GC device. The experimental results obtained with K3Fe(CN)6 solutions were compared with a previously developed theory. Further, it was demonstrated that with a carbon fibre MCM/GC device, the voltammetric behaviour of dopamine is greatly improved by virtue of redox recycling, hence giving high sensitivity. The steady-state collection current was linearly related to dopamine concentration in the range 1 X 10(-4) to 5 x 10(-7) Mol l-1, and the detection limit was 2 x 10(-7) mol l-1. The influence of coexisting ascorbic acid was also investigated. This device was applied successfully in the determination of dopamine hydrochloride in pharmaceutical preparations.

Computational modeling of defects in nanoscale device materials

This PhD thesis concerns the computational modeling of the electronic and atomic structure of point defects in technologically relevant materials. Identifying the atomistic origin of defects observed in the electrical characteristics of electronic devices has been a long-term goal of first-principles methods. First principles simulations are performed in this thesis, consisting of density functional theory (DFT) supplemented with many body perturbation theory (MBPT) methods, of native defects in bulk and slab models of In0.53Ga0.47As. The latter consist of (100) - oriented surfaces passivated with A12O3. Our results indicate that the experimentally extracted midgap interface state density (Dit) peaks are not the result of defects directly at the semiconductor/oxide interface, but originate from defects in a more bulk-like chemical environment. This conclusion is reached by considering the energy of charge transition levels for defects at the interface as a function of distance from the oxide. Our work provides insight into the types of defects responsible for the observed departure from ideal electrical behaviour in III-V metal-oxidesemiconductor (MOS) capacitors. In addition, the formation energetics and electron scattering properties of point defects in carbon nanotubes (CNTs) are studied using DFT in conjunction with Green’s function based techniques. The latter are applied to evaluate the low-temperature, low-bias Landauer conductance spectrum from which mesoscopic transport properties such as the elastic mean free path and localization length of technologically relevant CNT sizes can be estimated from computationally tractable CNT models. Our calculations show that at CNT diameters pertinent to interconnect applications, the 555777 divacancy defect results in increased scattering and hence higher electrical resistance for electron transport near the Fermi level.

Hand-held spectroscopic device for in vivo and intraoperative tumor detection: contrast enhancement, detection sensitivity, and tissue penetration.

Surgery is one of the most effective and widely used procedures in treating human cancers, but a major problem is that the surgeon often fails to remove the entire tumor, leaving behind tumor-positive margins, metastatic lymph nodes, and/or satellite tumor nodules. Here we report the use of a hand-held spectroscopic pen device (termed SpectroPen) and near-infrared contrast agents for intraoperative detection of malignant tumors, based on wavelength-resolved measurements of fluorescence and surface-enhanced Raman scattering (SERS) signals. The SpectroPen utilizes a near-infrared diode laser (emitting at 785 nm) coupled to a compact head unit for light excitation and collection. This pen-shaped device effectively removes silica Raman peaks from the fiber optics and attenuates the reflected excitation light, allowing sensitive analysis of both fluorescence and Raman signals. Its overall performance has been evaluated by using a fluorescent contrast agent (indocyanine green, or ICG) as well as a surface-enhanced Raman scattering (SERS) contrast agent (pegylated colloidal gold). Under in vitro conditions, the detection limits are approximately 2-5 × 10(-11) M for the indocyanine dye and 0.5-1 × 10(-13) M for the SERS contrast agent. Ex vivo tissue penetration data show attenuated but resolvable fluorescence and Raman signals when the contrast agents are buried 5-10 mm deep in fresh animal tissues. In vivo studies using mice bearing bioluminescent 4T1 breast tumors further demonstrate that the tumor borders can be precisely detected preoperatively and intraoperatively, and that the contrast signals are strongly correlated with tumor bioluminescence. After surgery, the SpectroPen device permits further evaluation of both positive and negative tumor margins around the surgical cavity, raising new possibilities for real-time tumor detection and image-guided surgery.

Cold-Atom-Induced Control of an Optomechanical Device

We consider a cavity with a vibrating end mirror and coupled to a Bose-Einstein condensate. The cavity field mediates the interplay between mirror and collective oscillations of the atomic density. We study the implications of this dynamics and the possibility of an indirect diagnostic. Our predictions can be observed in a realistic setup that is central to the current quest for mesoscopic quantumness.

Determination of absolute ion yields from a MALDI source through calibration of an image-charge detector

MALDI (matrix-assisted laser desorption/ionization) is one of the most important techniques used to produce large biomolecular ions in the gas phase. Surprisingly, the exact ionization mechanism is still not well understood and absolute values for the ion yields are scarce. This is in part due to the unknown efficiencies of typical detectors, especially for heavy biomolecular ions. As an alternative, charged particles can be non-destructively detected using an image-charge detector where the output voltage signal is proportional to the total charge within the device. In this paper, we report an absolute calibration which provides the voltage output per detected electronic charge in our experimental arrangement. A minimum of 3 x 10(3) ions were required to distinguish the signal above background noise in a single pass through the device, which could be further reduced using filtering techniques. The calibration results have been applied to raw MALDI spectra to measure absolute ion yields of both matrix and analyte ions.

Observation of K-Shell Soft X Ray Emission of Nitrogen Irradiated by XUV-Free Electron Laser FLASH at Intensities Greater than 10(16) W/cm(2)

In the past few years, the development of light sources of the 4(th) generation, namely XUV/X-ray Free Electron Lasers provides to the scientific community outstanding tools to investigate matter under extreme conditions never obtained in laboratories so far. As theory is at its infancy, the analysis of matter via the self-emission of the target is of central importance. The characterization of such dense matter is possible if photons can escape the medium. As the absorption of K-shell X-ray transitions is minimal, it plays a key role in this study. We report here the first successful observation of K-shell emission of Nitrogen at 430 eV using an XUV-Free Electron Laser to irradiate solid Boron Nitride targets under exceptional conditions: photon energy of 92 eV, pulse duration of similar to 20 fs, micro focusing leading to intensities larger than 10(16) W/cm(2). Using a Bragg crystal of THM coupled to a CCD, we resolved K-shell line emission from different charge states. We demonstrate that the spectroscopic data allow characterization of electron heating processes when X-ray radiation is interacting with solid matter. As energy transport is non-trivial because the light source is monochromatic, these results have an important impact on the theory. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Resistance of Staphylococcus aureus to the cationic antimicrobial agent poly(2-(dimethylamino ethyl)methacrylate) (pDMAEMA) is influenced by cell-surface charge and hydrophobicity

Cationic antimicrobial agents may prevent device-associated infections caused by Staphylococcus epidermidis and Staphylococcus aureus. This study reports that the cationic antimicrobial polymer poly(2-(dimethylamino ethyl)methacrylate) (pDMAEMA) was more effective at antagonizing growth of clinical isolates of S. epidermidis than of S. aureus. Importantly, mature S. epidermidis biofilms were significantly inactivated by pDMAEMA. The S. aureus isolates tested were generally more hydrophobic than the S. epidermidis isolates and had a less negative charge, although a number of individual S. aureus and S. epidermidis clinical isolates had similar surface hydrophobicity and charge values. Fluorescence spectroscopy and flow cytometry revealed that fluorescently labelled pDMAEMA interacted strongly with S. epidermidis compared with S. aureus. S. aureus Delta dltA and Delta mprF mutants were less hydrophobic and therefore more susceptible to pDMAEMA than wild-type S. aureus. Although the different susceptibility of S. epidermidis and S. aureus isolates to pDMAEMA is complex, influenced in part by surface hydrophobicity and charge, these findings nevertheless reveal the potential of pDMAEMA to treat S. epidermidis infections.

Orientation effects in copper phthalocyanine films studied by electron paramagnetic resonance spectroscopy

The metallo-phthalocyanines (MPcs) are an interesting group of organic semiconductor materials for applications such as large area solar cells due to their optoelectronic properties coupled with the possibility of easily and cheaply fabricating thin films of MPcs [1, 2]. As for organic semiconductors in general, many of the interesting properties of the MPcs such as magnetism, light absorption and charge transport, are highly anisotropic [2, 3]. To maximise the efficiency of a device based on these materials it is therefore important to study their molecular orientation in films and to assess the influence of different growth conditions and substrate treatments.
X-ray diffraction is a well established and powerful technique for studying texture (and hence molecular orientation) in crystalline materials, but it cannot provide any information about amorphous or nanocrystalline films. In electron paramagnetic resonance (EPR) spectroscopy the signal comes from the spin of unpaired electrons in the material. This technique therefore does not require the sample to be crystalline. It works for any sample with paramagnetic centres such as the MPcs where the unpaired electrons are contributed by the metal. In this paper we present a continuous-wave X-band EPR study using the anisotropy of the EPR spectrum of CuPc [4] to determine the orientation effects in different types of CuPc films. From these measurements we gain insight into the molecular arrangement of films with different spin concentrations, and apply our technique to the study of molecular orientation in photovoltaic cells.

Orientation effects in copper phthalocyanine films studied by EPR

Organic semiconductors have already found commercial applications in for example displays with organic light-emitting diodes (OLEDs) and great advances are also being made in other areas, such as organic field-effect transistors and organic solar cells. [1] The organic semicondutor group of materials known as metal phthalocyanines (MPc’s) is interesting for applications such as large area solar cells due to their optoelectronic properties coupled with the possibility of easily and cheaply fabricating thin films of MPc’s. [1, 2]

Many of the properties of organic semiconductors, such as magnetism, light absorption and charge transport, show orientational anisotropy. [2, 3] To maximise the efficiency of a device based on these materials it is therefore important to study the molecular orientation in films and to assess the influence of different growth conditions and substrate treatments. X-ray diffraction is a well established and powerful technique for studying texture (and hence molecular orientation)_in crystalline materials, but cannot provide any information about amorphous or nanocrystalline films. In this paper we present a continuous wave X-band EPR study using the anisotropy of the CuPc EPR spectrum [4] to determine the orientation effects in different types of CuPc films. From these measurements we also gain insight into the molecular arrangement of films of CuPc mixed with the isomorphous H2Pc and with C60 in films typical of real solar cell systems.

Nonlinearly coupled localized plasmon resonances: Resonant second-harmonic generation

The efficient resonant nonlinear coupling between localized surface plasmon modes is demonstrated in a simple and intuitive way using boundary integral formulation and utilizing second-order optical nonlinearity. The nonlinearity is derived from the hydrodynamic description of electron plasma and originates from the presence of material interfaces in the case of small metal particles. The coupling between fundamental and second-harmonic modes is shown to be symmetry selective and proportional to the spatial overlap between polarization dipole density of the second-harmonic mode and the square of the polarization charge density of the fundamental mode. Particles with high geometrical symmetry will convert a far-field illumination into dark nonradiating second-harmonic modes, such as quadrupoles. Effective second-harmonic susceptibilities are proportional to the surface-to-volume ratio of a particle, emphasizing the nanoscale enhancement of the effect.