pinecone/core-2020-05-10-deduplication huggingface dataset:
Strong exciton‐photon coupling and its polarization dependence in a metal‐mirror microcavity with oriented PIC J‐aggregates

We present a study of strong exciton-photon coupling and its dependence on incident light polarization in a metal-metal mirror microcavity containing PIC J-aggregates. Rabi-splitting energies between upper and lower polariton branches are estimated as 94 meV and 69 meV for s- and p-polarized incident light, respectively. These large values are due to large oscillator strength of Frenkel excitons in the PIC J-aggregates and strong confinement of light attributed to the metallic microcavity as well. As for the effective thickness of the active layer for s-polarized light, a good agreement is obtained between Lfiteff = 201 nm deduced from the experimental data and Lcalceff = 207 nm calculated from the summation of the measured thickness of active layer with the estimated penetration depths into silver mirrors. We also discuss the difference in the polarization dependences of Rabi-splitting energy, quantitatively. It is concluded that the polarization dependence is mainly due to an alignment of the J-aggregates in the active layer and is not affected so much by anisotropy of the penetration depths into the silver mirrors
InP-quantum dots in Al0.20Ga0.80InP with different barrier
  configurations

Systematic ensemble photoluminescence studies have been performed on type-I
InP-quantum dots in Al0.20Ga0.80InP barriers, emitting at approximately 1.85 eV
at 5 K. The influence of different barrier configurations as well as the
incorporation of additional tunnel barriers on the optical properties has been
investigated. The confinement energy between the dot barrier and the
surrounding barrier layers, which is the sum of the band discontinuities for
the valence and the conduction bands, was chosen to be approximately 190 meV by
using Al0.50Ga0.50InP. In combination with 2 nm thick AlInP tunnel barriers,
the internal quantum efficiency of these barrier configurations can be
increased by up to a factor of 20 at elevated temperatures with respect to
quantum dots without such layers.Comment: physica status solidi (c) (Proceedings of QD 2008
Optical Properties and Modal Gain of InGaN Quantum Dot Stacks

We present investigations of the optical properties of stacked InGaN quantum
dot layers and demonstrate their advantage over single quantum dot layer
structures. Measurements were performed on structures containing a single layer
with quantum dots or threefold stacked quantum dot layers, respectively. A
superlinear increase of the quantum dot related photoluminescence is detected
with increasing number of quantum dot layers while other relevant GaN related
spectral features are much less intensive when compared to the
photoluminescence of a single quantum dot layer. The quantum dot character of
the active material is verified by microphotoluminescence experiments at
different temperatures. For the possible integration within optical devices in
the future the threshold power density was investigated as well as the modal
gain by using the variable stripe length method.Comment: 9 Pages, 4 Figure
Erbium-doped nanocrystalline silicon thin films produced by RF sputtering: annealing effect on the ER emission

In order to improve the transparent contact layer in amorphous silicon solar cells fabricated on low-temperature plastic substrates, Al and Ga doped ZnO films were deposited at room temperature on plastic and glass and their optical, electronic and structural properties were correlated and optimized. Aiming to explore light trapping effects, plastic substrates were laser textured and their haze and total transmittance and reflectance were compared with those of untextured substrates. Although the haze increased dramatically, from 1.7 to 78.9 %, the total transmittance of PET coated with ZnO:Ga decreased from 83.9 %, in the untextured substrate, to 58.5 %  in the textured PET. The haze in reflected light of PET coated with Al increased from 4.3% to 66.2% after texturing but the total reflectance decreased from 70.1 % to 36.8 %. Therefore the untextured substrates were used in the solar cells. a-Si:H solar cells were deposited at a substrate temperature of 150ºC on plastic, in the superstrate p-i-n configuration, and on stainless steel, in the substrate n-i-p configuration. The efficiency is ~5% in both types of devices, limited by low Jsc and low fill factor.Fundação para a Ciência e Tecnologia (FCT) - Pluriannual Contracto com CFUM, FCT/CNRS bi-lateral project n° 2079
Carbon nanotube based sensors and fluctuation enhanced sensing

Trabajo presentado al 23rd International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 23)and E-MRS 2009 Spring Meeting, Symposium N – Carbon Nanotubes and Graphene.-- et al.Drop-cast thin films of multi-walled carbon nanotubes are used as gas sensors in a four-probe measurement setup. The novelty of the approach is that the sensor information is extracted from the noise of the dc resistance data using Fluctuation Enhanced Sensing (FES). We investigate the effects of measurement duration, gate voltage and frequency window on the chemical selectivity of the MWCNT-FES sensor. The selectivity of the device is superior to those of conventional gas sensors, and preliminary experiments indicate that it may also be possible to extract quantitative information from the noise.The financial support of the European\ud
Commission (FP6 STREP #17310 „SANES”), TEKES (projects: 52467 and 52468), Academy of Finland (projects: 120853, 128626 and 128908) and the Hungarian Scientific Research Fund (OTKA) through project NNF-78920 is acknowledged. YP and\ud
AR acknowledge funding by the Spanish MEC (FIS2007-65702-C02-01), "Grupos Consolidados UPV/EHU del Gobierno Vasco" (IT-319-07) and e-I3 ETSF project (Contract Number 211956).\ud
Computational resources for theoretical support are provided by the SGI/IZO-SGIker UPV/EHU (Arina cluster).). K.K. and G.T. thank the support (research fellow and researcher posts) received\ud
from the Academy of Finland. N.H. acknowledges the postgraduate student post received from the NGS-Nano.Peer reviewe
Raman study of doped-ZnO thin films grown by rf sputtering

A Raman spectroscopy study of doped versus undoped ZnO layers is presented. The layers were grown by RF magnetron sputtering and the doping with Al, Sb and Mn was achieved by ion implantation with subsequent annealing. First-order Raman response measured under λ=488 nm
excitation is discussed. It is shown that doping with any of the impurities used in this work produces a strong enhancement of the longitudinal optical (LO) phonon band, which is attributed to the intra-band Fröhlich mechanism. In addition, doping with Mn results in an extra mode located at 530 cm-1,
tentatively attributed to a local vibrational mode of Mn substituting Zn in the lattice sites.FCT through project PTDC/FIS/72843/200
Porous Silicon for Light Management in Silicon Solar Cells

In the present work possibilities of utilizing porous silicon (PS) to enhance absorption in silicon solar cells are investigated. Silicon solar cells produce energy by converting the incoming solar radiation to electricity and the efficiency of this technology will naturally depend on the amount of light that can be absorbed by the solar cell. Antireflection coatings are used on the surface of solar cells to increase the fraction of light that enters the cell. In addition texture and rear side reflectors can be used to ‘trap’ the light within the cell.<br>
PS is a versatile, nanostructured material commonly made by electrochemical etching of silicon. The porosity of PS can be controlled by the etching parameters applied during formation, and because the porosity is closely related to the refractive index, PS is a highly interesting material for optical applications. In this work we show that thin, complex multilayer PS structures can be tailored to give very low reflectances over a broad wavelength range. The versatile optical properties of PS are also utilized to fabricate a variety of colored coatings that retain very low reflectance. Therefore, PS could be an exiting material for use in efficient designer cells, desirable for applications where the visual impression is important. PS can also be used to make highly reflective structures simply by altering the electrochemical etching parameters. Such structures can be used as rear side reflectors in solar cells.
This work also presents detailed investigations of the fabrication process, structure, optical properties, and oxidation of the multilayered PS structures. In particular, spectroscopic ellipsometry is extensively utilized in the characterization of these multilayers, providing accurate in-depth modeling of optical and structural properties. In addition, reflectometry, scanning and transmission electron microscopy, and x-ray photoelectron spectroscopy is utilized in order to unveil the secrets of this complex material
Electrical characterization of hydrogen-vacancy-related defects in monocrystalline silicon

Electrical characterization of point defects in silicon (Si) is carried out to study fundamental defects present in Si solar cell structures. The interactions between various defect complexes is investigated, while paying special attention to the interactions with hydrogen. As hydrogen is readily incorporated during manufacturing processes, it is important to learn about the defect dynamics of hydrogen related defects Firstly, hydrogen implantation into p- and n-type based pn-junctions has been investigated in order to learn about the fundamental nature of the defect reactions between vacancy related defects and hydrogen. Samples have been electrically characterized by capacitance–voltage (CV), deep level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS), which reveals the presence of multiple hydrogen-related levels. A firm correlation between the reported donor and acceptor states of the vacancy–oxygen–hydrogen (VOH) complex is established in p-type samples, providing data on formation and annealing of both states. In the n-type samples, there is a rapid formation of a hydrogen-related level at E<sub>c</sub> − 0.36 eV, at the expense of VO, without any formation of VOH after heat treatments at 200 C. This complex is not observed in the p-type samples, leading to the conclusion that the formation barrier for VOH must be higher in n-type than in p-type material. Further, an observation of a hydrogen-related defect in p-type samples, achieved by MCTS, provides preliminary data that may challenge the accepted model for the di–vacancy–hydrogen complex (V<sub>2</sub>H). The level observed in p-type samples,corresponds to a well-known DLTS peak in hydrogen contaminated n-type Si and is often ascribed to the acceptor level of V<sub>2</sub>H. However, the theoretically predicted single donor level of V2H is not observed in the investigated samples, thereby urging additional studies on the validity of the model of V<sub>2</sub>H. Finally, a study of interfaces between tin doped indium oxide (ITO) and silicon has been conducted. Thin films of ITO were sputtered onto crystalline pand n-type Si wafers, and a lithography process was applied to make individual diodes of various areas. By combining current–voltage (IV), CV and DLTS with secondary ion mass spectrometry (SIMS), a clear understanding of the composition and behavior of the interface is achieved. Heat treatments of the samples up to 600 C provide information of the defect evolution and the subsequent change in properties of the junction. The ITO/n-Si samples are found to be rectifying at all investigated temperatures, while the ITO/p-Si samples are rectifying up to 400 C, after which the junctions are transformed into an Ohmic behavior. Correlating these observations with the DLTS measurements reveals that the dominant hole traps anneal out as the rectification of the ITO/p-Si samples is at its highest. Likewise, the annealing of the dominant electron trap is followed by a significant increase in the rectification of the ITO/n-Si samples
Electrical studies of Fe-related defect complexes in silicon

Iron (Fe) is an important impurity in solar-grade silicon which contributes substantially in degrading the efficiency of solar cells. The degradation is mainly caused by the Fe atoms situating at an unperturbed tetrahedral interstitial sites (Fei) in the silicon crystal, consequently acting as a recombination center. By altering the position and the neighbouring environment at which the Fe atoms reside, there are opportunities in minimizing or neutralizing the electrical activity of Fe. Furthermore, utilizing the high mobility of Fe, one can increase the performance of a device by accumulating the Fe atoms from critical regions into regions where Fe can be tolerated. These approaches can help in realizing high efficient solar cells based on cheap and highly Fe-contaminated silicon. In this work, we have investigated the interaction between Fe and defects relevant to solar cells, using mainly electrical characterization methods such as capacitance-voltage measurement, deep level transient spectroscopy and admittance spectroscopy.
From the study of potential hydrogen passivation of Fe, hydrogen was introduced through wet chemical etching and further driven to a defined region. Using depth profiles, it is found that incorporation of hydrogen stimulates the dissociation of the iron-boron (Fe-B) pair, releasing and resulting in the unwanted Fei. At the same time, no passivation of Fe by hydrogen has been observed.
On the investigation of the mechanism of phosphorus gettering of metal impurities, vacancies have been generated through proton-irradiation. The resulting irradiation-induced defects were examined for reactions with Fe after heat treatments. Based on the evolution of defect concentrations by isochronal annealings, it is found that Fe interacts with the divacancy and the vacancy-oxygen complexes, forming deep levels of 0.28 eV and 0.34 eV above the valence band edge (EV), respectively.
In the search for substitutional Fe to investigate its electrical activity and thermal stability, measurements were performed around the projected range of Fe-implantations after rapid thermal annealing. A shallow acceptor is uncovered with an energy level position of EV +0.06 eV and a defect concentration closely following the calculated concentration of the Fe-implantation dose. However, chemical analysis with secondary ion-mass spectrometry shows out-diffusion of Fe from the region around the projected range after annealing. This suggests that the formation of the shallow acceptor is only assisted/promoted by Fe without Fe being a part of the final complex
High-rate deposition of nano-crystalline silicon thin films on plastics

Nanocrystalline silicon (nc-Si:H) is commonly used in the bottom cell of tandem solar cells. With an indirect bandgap, nc-Si:H requires thicker (∼1 µm) films for efficient light harvesting than amorphous Si (a-Si:H) does. Therefore, thin-film high deposition rates are crucial for further cost reduction of highly efficient a–Si:H based photovoltaic technology. Plastic substrates allow for further cost reduction by enabling roll-to-roll inline deposition. In this work, high nc-Si:H deposition rates on plastic were achieved at low substrate temperature (150 °C) by standard Radio-frequency (13.56 MHz) Plasma Enhanced Chemical Vapor Deposition. Focus was on the influence of deposition pressure, inter-electrode distance (1.2 cm) and high power coupled to the plasma, on the hydrogen-to-silane dilution ratios (HD) necessary to achieve the amorphous-to-nanocrystalline phase transition and on the resulting film deposition rate. For each pressure and rf-power, there is a value of HD for which the films start to exhibit a certain amount of crystalline fraction. For constant rf-power, this value increases with pressure. Within the parameter range studied the deposition rate was highest (0.38 nm/s) for nc-Si:H films deposited at 6 Torr, 700 mW/cm2 using HD of 98.5 %. Decreasing the pressure to 3 Torr (1.5 Torr) and rf-power to 350 mW/cm2 using HD – 98.5 % deposition rate is 0.12 nm/s (0.076 nm/s). Raman crystalline fraction of these films is 72, 62 and 53 % for the 6, 3 and 1.5 Torr films, respectively.Fundação para a Ciência e a Tecnologia (FCT)DREBM/PICS_CNRS/201
Surface study of organopalladium molecules on S-terminated GaAs

Organopalladium species ({Pd}) immobilized on an Sterminated GaAs substrate (S/GaAs) effectively catalyzes C-C bond formation in the Mizoroki-Heck reaction with cycle durability. However, the immobilizing mechanism of {Pd} is unknown. In this study, we deposited Pd(OCOCH3)2 on S/GaAs in two different methods, namely dry-physical vapor-deposition and wetchemical deposition, and compared the catalytic activities in the Mizoroki-Heck reaction. Also, S-termination and {Pd}-immobilization on GaAs grains were performed by the wet-chemical method to monitor the change in the surface chemical structure during the preparation process with diffuse reflectance Fourier transform infrared spectroscopy (FT-IR). FT-IR measurements implied that the immobilization of catalytic active {Pd} was related to the OH groups on the S-terminated surface. {Pd}-S/GaAs prepared dryphysically showed poor catalytic activity, because {Pd} was not immobilized under absence of OH groups
Photoluminescence properties of CdSe/ZnS/TOPO nanocrystals in full- and half-microcavity structures

We report a recent study on photoluminescence (PL) properties of CdSe/ZnS/TOPO nanocrystals (NCs) in a planar full microcavity composed of top and bottom two metal (Ag) mirrors, and also in a similar structure but without top mirror, i.e. half-microcavity, respectively. Angular-dependencies of PL spectra and PL decay curves have been measured to investigate PL modifications due to light-matter coupling in the microcavities. Obtained results indicate that PL dynamics are drastically changed depending on the microcavity structures. In the full-microcavity, PL emission is directed at particular angles and its decay-time is shortened, both of which can be described in terms of so-called Purcell effect, i.e. the interaction between photon-modes and confined excitons in the NCs. As for the half-microcavity, anomalous PL band appears at low energy side of a main PL band associated with the confined excitons. The origin of the anomalous PL will be interpreted as due to the interaction between specific photon-modes in the half-microcavity structure and excitons associated with surface states
Effect of temperature and frequency of dynamic loading in the viscoelastic properties of aluminium alloy 7075-T6

The viscoelastic response of a material offers an alternative\ud
method for analyzing its microstructure, phase transformations\ud
and fatigue behaviour. In this work, the viscoelastic\ud
properties of commercial aluminium alloy (AA)\ud
7075-T6 are studied with a Dynamic-Mechanical Analyzer\ud
(DMA), and results are combined with Transmission\ud
Electron Microscopy (TEM) and Differential Scanning\ud
Calorimetry (DSC) data. In accordance with this\ud
analysis, we propose an analytical model for the storage\ud
modulus E’ as a function of temperature, frequency of\ud
the dynamic loading and the concentration of Guinier-\ud
Preston Zones (GPZ). The latter parameter is obtained as\ud
a function of temperature after integration and fitting of\ud
the model. It is shown that the proposed model fits the\ud
experimental data for the storage modulus reasonably\ud
well in the prescribed region, and that this fact supports\ud
the hypothesis that the change in the storage modulus\ud
slope at about 130-160 ºC is due to GPZ decompositionPostprint (published version
Nonlinear optical response of hole-trion systems in quantum dots in
  tilted magnetic fields

We discuss, from a theoretical point of view, the four wave mixing
spectroscopy on an ensemble of p-doped quantum dots in a magnetic field
slightly tilted from the in-plane configuration. We describe the system
evolution in the density matrix formalism. In the limit of coherent ultrafast
optical driving, we obtain analytical formulas for the single system dynamics
and for the response of an inhomogeneously broadened ensemble. The results are
compared to the previously studied time-resolved Kerr rotation spectroscopy on
the same system. We show that the Kerr rotation and four wave mixing spectra
yield complementary information on the spin dynamics (precession and damping).Comment: 4 pages, 2 figures, conference NOEKS1
Phonon-assisted decoherence and tunneling in quantum dot molecules

We study the influence of the phonon environment on the electron dynamics in
a doped quantum dot molecule. A non-perturbative quantum kinetic theory based
on correlation expansion is used in order to describe both diagonal and
off-diagonal electron-phonon couplings representing real and virtual processes
with relevant acoustic phonons. We show that the relaxation is dominated by
phonon-assisted electron tunneling between constituent quantum dots and occurs
on a picosecond time scale. The dependence of the time evolution of the quantum
dot occupation probabilities on the energy mismatch between the quantum dots is
studied in detail.Comment: 4 pages, 2 figures, conference proceeding NOEKS10, to be published in
  Phys. Stat. So
Phase separation of multicomponent excitonic Bose-Einstein condensates

For the observation of Bose-Einstein condensation, excitons in cuprous oxide
are regarded as promising candidates due to their large binding energy and long
lifetime. High particle densities may be achieved by entrapment in a stress
induced potential. We consider a multi-component gas of interacting para- and
orthoexcitons in cuprous oxide confined in a three-dimensional potential trap.
Based on the Hartree-Fock-Bogoliubov theory, we calculate density profiles as
well as decay luminescence spectra which exhibit signatures of the separation
of the Bose-condensed phases.Comment: 4 pages, 1 figure, presented at NOEKS 10, Paderborn, August 201
High quality factor of AlN microdisks embedding GaN quantum dots

International audienceWe report the observation of high quality (Q) factor whispering gallery modes for GaN/AlN quantum dot based microdisks. Room temperature photoluminescence measurements show a large number of high Q modes on the whole PL spectral range. For the first time we report Q values up to 6000 for nitride based cavities. We attribute this improvement of the Q factor to the etching quality and to the relatively low cavity loss by inserting dots into the microdisks. The uniformity of the resonant modes with respect to a wide range of energies allows us to identify the different radial mode families
Well-arrayed ZnO nanostructures formed by multi-annealing processes at low temperature

A novel process of multi-annealing was proposed for forming well-arrayed ZnO nanostructures on as-deposited ZnO thin films that were prepared on quartz glass using a radio frequency (rf) magnetron sputtering at low temperature. It was found that the formation and morphology of ZnO nanostructures were strongly dependent on the reducing gas annealing processes. Oxygen ambient annealing between two reducing annealing processes had the effect of introducing more oxygen into the ZnO thin film, as well as improving the crystallinity of the ZnO nanostructures. An intense photoluminescence peak centered at 504 nm was observed in the well-arrayed ZnO nanostructures, due to the large amount of oxygen vacancies which existed on the larger surface area of ZnO nanostructures formed after the multi-annealing processes at a low temperature of 430 ℃. These results show that multi-annealing processes are very effective in forming well-arrayed and controllable ZnO nanostructures