Linear and nonlinear transport in a small charge-tunable open quantum ring

We experimentally study the Aharonov-Bohm-conductance oscillations under external gate voltage in a semiconductor quantum ring with a radius of 80 nm. We find that, in the linear regime, the resistance-oscillation plot in the voltage-magnetic-field plane corresponds to the quantum ring energy spectra. The chessboard pattern assembled by resistance diamonds, while loading the ring, is attributed to a short electron lifetime in the open configuration, which agrees with calculations within the single-particle model. Remarkably, the application of a small dc current allows observing strong deviations in the oscillation plot from this pattern accompanied by a magnetic-field symmetry break. We relate such behavior to the higher-order-conductance coefficients determined by electron-electron interactions in the nonlinear regime.

THE FLUID SYSTEMS FOR THE SLD CHERENKOV RING IMAGING DETECTOR

We describe the design and operation of the fluid delivery, monitor and control systems for the SLD barrel Cherenkov Ring Imaging Detector (CRID). The systems deliver drift gas (C2H6+TMAE), radiator gas (C5F12+N2) and radiator liquid (C6F14). MeasUred critical quantities such as electron lifetime in the drift gas and ultra-violet (UV) transparencies of the radiator fluids, together with the operational experience, are also reported.

Efficient Dye-Sensitized Solar Cells Based on the Combination of ZnO Nanorods and Microflowers

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Stepped light-induced transient measurements of photocurrent and voltage in dye-sensitized solar cells based on ZnO and ZnO:Ga

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Células solares de ZnO:Ga nanocristalino sensibilizado por corante

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Enhanced iron gettering by short, optimized low-temperature annealing after phosphorus emitter diffusion for industrial silicon solar cell processing

The introduction of a low-temperature (LT) tail after P emitter diffusion was shown to lead to considerable improvements in electron lifetime and solar cell performance by different researchers. So far, the drawback of the investigated extended gettering treatments has been the lack of knowledge about optimum annealing times and temperatures and the important increase in processing time. In this manuscript, we calculate optimum annealing temperatures of Fe-contaminated Si wafers for different annealing durations. Subsequently, it is shown theoretically and experimentally that a relatively short LT tail of 15 min can lead to a significant reduction of interstitial Fe and an increase in electron lifetime. Finally, we calculate the potential improvement of solar cell efficiency when such a short-tail extended P diffusion gettering is included in an industrial fabrication process.

Calculation of the hyperfine structure transition energy and lifetime in the one-electron Bi^82+ ion

We calculate the energy and lifetime of the ground state hyperfine structure transition in one-electron Bi^82+ . The influence of various distributions of the magnetic moment and the electric charge in the nucleus ^209_83 Bi on energy and lifetime is studied.

Composite electrode of carbon nanotubes and vitreous carbon for electron field emission

In this work, the electron field emission behaviour of electrodes formed by carbon nanotubes (CNTs) grown onto monolithic vitreous carbon (VCarbon) substrates with microcavities is presented. Scanning electron microscopy was used to characterize the microstructure of the films. Tungsten probes, stainless steel sphere, and phosphor electrodes were employed in the electron field emission study. The CNT/VCarbon composite represents a route to inexpensive excellent large area electron emission cathodes with fields as low as 2.1 V mu m(-1). In preliminary lifetime tests for a period of about 24 h at an emission current of about 4 mA cm(-2), there is an onset degradation of the emission current of about 28%, which then stabilizes. Electron emission images of the composites show the cavity of the samples act as separate emission sites and predominantly control the emission process. The emission of CNTs/VCarbon was found to be stable for several hours. (c) 2008 American Institute of Physics.

Electron and photon induced processes in SF5CF3

The photo-absorption cross section of trifluoromethyl sulphur pentafluoride, SF5CF3 has been measured using synchrotron radiation in the range of 4–11 eV (310 nm > l > 110 nm) and comparison made with electron energy loss spectroscopy (EELS). The measured VUV cross sections are used to derive the photolysis rate of SF5CF3 in the terrestrial atmosphere. It is estimated that the lifetime for this molecule is the order of a 1000 years and the calculated global warming potential (GWP) is found to be between 17000 and 18100, making it one of the most potent global warming gases in the terrestrial atmosphere.

Electron driven reactions in sulphur containing biological prototypes

The interaction of ionising radiation with living tissues may direct or indirectly generate several secondary species with relevant genotoxic potential. Due to recent findings that electrons with energies below the ionisation threshold can effectively damage DNA, radiation-induced damage to biological systems has increasingly come under scrutiny. The exact physico-chemical processes that occur in the first stages of electron induced damage remain to be explained. However, it is also known that free electrons have a short lifetime in the physiological medium. Hence, electron transfer processes studies represent an alternative approach through which the role of "bound" electrons as a source of damage to biological tissues can be further explored. The thesis work consists of studying dissociative electron attachment (DEA) and electron transfer to taurine and thiaproline. DEA measurements were executed in Siedlce University with Prof. Janina Kopyra under COST action MP1002 (Nanoscale insights in ion beam cancer therapy). The electron transfer experiments were conducted in a crossed atom(potassium)-molecule beam arrangement. In these studies the anionic fragmentation patterns were obtained. The results of both mechanisms are shown to be significantly different, unveiling that the damaging potential of secondary electrons can be underestimated. In addition, sulphur atoms appear to strongly influence the dissociation process, demonstrating that certain reactions can be controlled by substitution of sulphur at specific molecular sites.

First results of experimental and theoretical investigations on sextet states of doubly-excited five-electron ions

In continuation of our previous work on doubly-excited ions with three and four electrons we present the first results on optical transitions in the term system of doubly-excited ions with five electrons. Transitions between such sextet states were identified in beam-foil spectra of the ions nitrogen, oxygen and fluorine. Assignments were first established by comparison with Multi-Configuration Dirac-Fock calculations. Later assignments were aided by Multi-Configuration Hartree-Fock calculations (see the contribution by G. Miecznik et al. in this issue). Decay curves were recorded for all six candidate lines. The lifetime results are compared to theoretical values which confirm most of the assignments qualitatively.

An optical study of multiple NEIAL events driven by low energy electron precipitation

Optical data are compared with EISCAT radar observations of multiple Naturally Enhanced Ion-Acoustic Line (NEIAL) events in the dayside cusp. This study uses narrow field of view cameras to observe small-scale, short-lived auroral features. Using multiple-wavelength optical observations, a direct link between NEIAL occurrences and low energy (about 100 eV) optical emissions is shown. This is consistent with the Langmuir wave decay interpretation of NEIALs being driven by streams of low-energy electrons. Modelling work connected with this study shows that, for the measured ionospheric conditions and precipitation characteristics, growth of unstable Langmuir (electron plasma) waves can occur, which decay into ion-acoustic wave modes. The link with low energy optical emissions shown here, will enable future studies of the shape, extent, lifetime, grouping and motions of NEIALs.

Direct probing of photoinduced electron transfer in a self- assembled biomimetic [2Fe2S]-hydrogenase complex using ultrafast vibrational spectroscopy

A pyridyl-functionalized diiron dithiolate complex, [μ-(4-pyCH2−NMI-S2)Fe2(CO)6] (3, py = pyridine(ligand), NMI = naphthalene monoimide) was synthesized and fully characterized. In the presence of zinc tetraphenylporphyrin (ZnTPP), a self-assembled 3·ZnTPP complex was readily formed in CH2Cl2 by the coordination of the pyridyl nitrogen to the porphyrin zinc center. Ultrafast photoinduced electron transfer from excited ZnTPP to complex 3 in the supramolecular assembly was observed in real time by monitoring the ν(CO) and ν(CO)NMI spectral changes with femtosecond time-resolved infrared (TRIR) spectroscopy. We have confirmed that photoinduced charge separation produced the monoreduced species by comparing the time-resolved IR spectra with the conventional IR spectra of 3•− generated by reversible electrochemical reduction. The lifetimes for the charge separation and charge recombination processes were found to be τCS = 40 ± 3 ps and τCR = 205 ± 14 ps, respectively. The charge recombination is much slower than that in an analogous covalent complex, demonstrating the potential of a supramolecular approach to extend the lifetime of the chargeseparated state in photocatalytic complexes. The observed vibrational frequency shifts provide a very sensitive probe of the delocalization of the electron-spin density over the different parts of the Fe2S2 complex. The TR and spectro-electrochemical IR spectra, electron paramagnetic resonance spectra, and density functional theory calculations all show that the spin density in 3•− is delocalized over the diiron core and the NMI bridge. This delocalization explains why the complex exhibits low catalytic dihydrogen production even though it features a very efficient photoinduced electron transfer. The ultrafast porphyrin-to-NMIS2−Fe2(CO)6 photoinduced electron transfer is the first reported example of a supramolecular Fe2S2-hydrogenase model studied by femtosecond TRIR spectroscopy. Our results show that TRIR spectroscopy is a powerful tool to investigate photoinduced electron transfer in potential dihydrogen-producing catalytic complexes, and that way to optimize their performance by rational approaches.

Photo-induced electron trapping in indirect bandgap AlxGa1-xAs : Si at low temperature

A variation of photoconductivity excitation with wavelength is applied to Si-doped Al0.56Ga0.44As (indirect bandgap material) for a wide range of temperature. The lower the temperature the lower the photocurrent below 70 K. In the range 13-30 K there is a decrease in the photoconductivity spectrum slightly above the bandgap transition energy, followed by another increase in the conductivity. We interpret these results in the light of existing models and confirm the trapping by the X-valley effective mass state. which is responsible for attenuation of persistent photoconductivity below 70 K. A DX0 intermediate state which has non-negligible lifetime is proposed as responsible for the decrease in the photoconductivity with about 561 nm of wavelength of exciting light, in the investigated 13-30 g range.

Measurement of the t(t)over-bar production cross section in p(p)over-bar collisions at root s=1.96 TeV using lepton plus jets events with lifetime b-tagging

We present a measurement of the top quark pair (t (t) over bar) production cross section (sigma(t (t) over bar)) in pp collisions at root s = 1.96 TeV using 230 pb(-1) of data collected by the DO experiment at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), missing transverse energy, and jets in the final state. We employ lifetime-based b-jet identification techniques to further enhance the t F purity of the selected sample. For a top quark mass of 175 GeV, we measure sigma(t (t) over bar) 8.6(-1.5)(+1.6) (stat. + syst.) +/- 0.6(lumi.) pb, in agreement with the standard model expectation. (c) 2005 Published by Elsevier B.V.