pinecone/core-2020-05-10-deduplication huggingface dataset:
Effect of QW growth temperature on the optical properties of blue and green InGaN/GaN QW structures

In this paper we report on the impact that the quantum well growth temperature has on the internal quantum efficiency and carrier recombination dynamics of two sets of InGaN/GaN multiple quantum well samples, designed to emit at 460 and 530 nm, in which the indium content of the quantum wells within each sample set was maintained. Measurements of the internal quantum efficiency of each sample set showed a systematic variation, with quantum wells grown at a higher temperature exhibiting higher internal quantum efficiency and this variation was preserved at all excitation power densities. By investigating the carrier dynamics at both 10 K and 300 K we were able to attribute this change in internal quantum efficiency to a decrease in the non-radiative recombination rate as the QW growth temperature was increased which we attribute to a decrease in incorporation of the point defects.This work was carried out with the financial support of the United Kingdom Engineering and Physical Sciences Research Council under Grant Nos. EP/I012591/1 and EP/H011676/1.This is the final version of the article. It first appeared from Wiley via https://doi.org/10.1002/pssc.20151018
Effect of electron blocking layers on the conduction and valence band profiles of InGaN/GaN LEDs

In this paper we investigate the effect of including an electron blocking layer between the quantum well active region and the p-type layers of a light emitting diode has on the conduction and valence band profile of a light emitting diode. Two light emitting diode structures with nominally identical quantum well active regions one containing an electron blocking layer and one without were grown for the purposes of this investigation. The conduction and valence band profiles for both structures were then calculated using a commercially available Schrödinger-Poisson calculator, and a modification to the electric field across the QWs observed. The results of these calculations were then compared to photoluminescence and photoluminescence time decay measurements. The modification in electric field across the quantum wells of the structures resulted in slower radiative recombination in the sample containing an electron blocking layers. The sample containing an electron blocking layer was also found to exhibit a lower internal quantum efficiency, which we attribute to the observed slower radiative recombination lifetime making radiative recombination less competitive.This work was carried out with the financial support of the United Kingdom Engineering and Physical Sciences Research Council under Grant Nos. EP/I012591/1 and EP/H011676/1.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/pssc.20151018
Field- and irradiation-induced phenomena in memristive nanomaterials

The breakthrough in electronics and information technology is anticipated by the development of emerging memory and logic devices, artificial neural networks and brain-inspired systems on the basis of memristive nano-materials represented, in a particular case, by a simple 'metal-insulator-metal' (MIM) thin-film structure. The present article is focused on the comparative analysis of MIM devices based on oxides with dominating ionic (ZrOx, HfOx) and covalent (SiOx, GeOx) bonding of various composition and geometry deposited by magnetron sputtering. The studied memristive devices demonstrate reproducible change in their resistance (resistive switching - RS) originated from the formation and rupture of conductive pathways (filaments) in oxide films due to the electric-field-driven migration of oxygen vacancies and/or mobile oxygen ions. It is shown that, for both ionic and covalent oxides under study, the RS behaviour depends only weakly on the oxide film composition and thickness, device geometry (down to a device size of about 20x20 mu m(2)). The devices under study are found to be tolerant to ion irradiation that reproduces the effect of extreme fluences of high-energy protons and fast neutrons. This common behaviour of RS is explained by the localized nature of the redox processes in a nanoscale switching oxide volume. Adaptive (synaptic) change of resistive states of memristive devices is demonstrated under the action of single or repeated electrical pulses, as well as in a simple model of coupled (synchronized) neuron-like generators. It is concluded that the noise-induced phenomena cannot be neglected in the consideration of a memristive device as a nonlinear system. The dynamic response of a memristive device to periodic signals of complex waveform can be predicted and tailored from the viewpoint of stochastic resonance concept. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Is polaron effect important for resonant Raman scattering in self-assembled quantum dots?

While the diagonal (or intra-level) interaction of a confined exciton with optical phonons in selfassembled quantum dots (SAQD’s) is rather weak, the non-diagonal one can lead to a considerable change of the exciton spectrum and the formation of a polaron. An impact of this effect on resonant inelastic
light scattering is studied theoretically. The polaron spectrum is obtained by numerical diagonalisation of the exciton–phonon interaction Hamiltonian in a truncated Hilbert space of the non-interacting excitons
and phonons. Based on this spectrum, the probability of the multi-phonon Raman scattering is calculated, which is compared to that obtained within the standard perturbation theory approach (where phonon emission
and absorption are irreversible). It is shown that there are two major effects of the polaron formation: (i) the intensity of the two-phonon (2 LO) peak, relative to that of the fundamental 1 LO one is strongly increased and (ii) the resonant behaviour of the 1 LO peak differs considerably from the perturbation theory predictions. With the correct theoretical interpretation, resonant Raman scattering in SAQD’s opens the possibility of accessing the (renormalised) exciton spectrum and exciton–phonon coupling constantsFundação para a Ciência e a Tecnologia (FCT
Adhesion hysteresis in dynamic atomic force microscopy

The effects of adhesion hysteresis in the dynamic-dissipation curves measured in amplitude-modulation atomic force microscopy\ud
are discussed. Hysteresis in the interaction forces is shown to modify the dynamics of the cantilever leading to different power dissipation curves in the repulsive and attractive regimes. Experimental results together with numerical simulations show that power dissipation, as measured in force\ud
microscopy, is not always proportional to the energy dissipated in the tip–sample interaction process.This work has been supported by the Spanish M.E.C. (Projects CTQ2005-07993-C0202/BQU, NAN2004-09125-C07-02 and FIS2006-11170-C02-02) and by the EU IP “Molecular Imaging” (LSHG-CT-2003-503259). M.K., M.F. and M.L. acknowledge financial support from the MEC.Peer reviewe
Electronic structure of superconducting gallium-doped germanium from
  ab-initio calculations

Using ab-initio calculations, we study the electronic structure of
gallium-doped germanium, which was found recently to be a superconductor, with
a critical temperature of 0.5 Kelvins, and a particularly low density of Cooper
pairs. The calculations of the electronic properties reveal that no sign of an
impurity band is observed, and that the Fermi level lies in the valence band of
Germanium. Moreover, the calculation of the phonon frequencies shows that a new
mode associated to the Ga atom is appearing, around 175$ cm-1.Comment: Submitted to physica status solidi - Rapid Research Letter
Conductance Through a Redox System in the Coulomb Blockade Regime:
  Many-Particle Effects and Influence of Electronic Correlations

We investigate the transport characteristics of a redox system weakly coupled
to leads in the Coulomb blockade regime. The redox system comprises a donor and
acceptor separated by an insulating bridge in a solution. It is modeled by a
two-site extended Hubbard model which includes on-site and inter-site Coulomb
interactions and the coupling to a bosonic bath. The current voltage
characteristics is calculated at high temperatures using a rate equation
approach. For high voltages exceeding the Coulomb repulsion at the donor site
the calculated transport characteristics exhibit pronounced deviations from the
behavior expected from single-electron transport. Depending on the relative
sizes of the effective on-site and inter-site Coulomb interactions on one side
and the reorganization energy on the other side we find negative differential
resistance or current enhancement
Adjustable and negative thermal expansion from multilayered systems

A construct in the form of a multi-layered system built from conventional materials having different mechanical and thermal properties is proposed. This construct can exhibit pre-determined values of thermal expansion which could also be negative. It is shown that for maximising negative thermal expansion (NTE) there should be a combination of thin layers of stiff materials having a high positive coefficient of thermal expansion (CTE) bonded with thicker layers of a soft material having low CTE values and, more importantly, having Poisson's ratio as high as possible.peer-reviewe
Physical mechanisms of boron diffusion gettering of iron in silicon

We have studied the boron diffusion gettering (BDG) of iron in single crystalline silicon. The results show that iron is gettered efficiently by electrically inactive boron, which leads to gettering efficiencies comparable to phosphorus diffusion gettering (PDG). In addition we discuss the different physical mechanisms behind BDG. We also consider the possibilities of using boron diffusion gettering in solar cell fabrication and discuss the role of boron and iron concentration in the optimization of gettering efficiency.Peer reviewe
Metamaterial inspired enhanced far-field transmission through a subwavelength nano-hole

In the present study, we first demonstrate the polarization and orientation dependent transmission response of split ring resonators at the infrared and visible band. Then, we numerically demonstrate a configuration for the enhancement of power passing through an electrically small hole. By using deep subwavelength optical split ring resonator antennas and couplers we achieved a 400-fold enhanced transmission from a subwavelength aperture area of the electrical size Λ 2/25. The power was transmitted to the far field with 3.9 dBi directivity at 300 THz. (© 2010 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim) Transmission through a subwavelength aperture at the optical regime is quite low. The Letter by Alici and Ozbay shows how it can be enhanced and transferred to the far field by using a metamaterial inspired configuration composed of nano-scale split ring resonator antennas and couplers. A 400-fold power enhancement was achieved. © 2010 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim
Plasmonic modes of gold nano-particle arrays on thin gold films

Regular arrays of metal nanoparticles on metal films have tuneable optical
resonances that can be applied for surface enhanced Raman scattering or
biosensing. With the aim of developing more surface selective geometries we
investigate regular gold nanoparticle arrays on 25nm thick gold films, which
allow to excite asymmetric surface plasmon modes featuring a much better field
confinement compared to the symmetric modes used in conventional surface
plasmon resonance setups. By optical extinction spectroscopy we identify the
plasmonic modes sustained by our structures. Furthermore, the role of thermal
treatment of the metal structures is investigated, revealing the role of
modifications in the crystalline structure of gold on the optical properties.Comment: 8 pages, 3 figure
First evidence of resistive switching in polycrystalline GaV4S8 thin layers

Recently a new type of reversible and non-volatile resistive\ud
switching was discovered in single crystals of Mott insulators AM4X8 (A = Ga, Ge; M = V, Nb, Ta; X = S, Se). Here we report on the first synthesis of thin layers (thicknesses in the 100 to 1000 nm range) of GaV4S8 by RF magnetron sputtering process. Energy dispersive spectroscopy, X-ray diffraction and TEM analyses attest the high quality of polycrystalline GaV4S8 thin layers. Electrical measurements demonstrate that deposited GaV4S8 thin films exhibit a non-volatile reversible resistive switching at room temperature with writing/erasing times of ~10 μs and a memory window (Rhigh – Rlow)/ Rlow > 33%
Lateral IBIC characterization of single crystal synthetic diamond detectors

In order to evaluate the charge collection efficiency (CCE) profile of single-crystal diamond devices based on a p-type/intrinsic/metal configuration, a lateral Ion Beam Induced Charge (IBIC) analysis was performed over their cleaved cross sections using a 2 MeV proton microbeam. CCE profiles in the depth direction were extracted from the cross-sectional maps at variable bias voltage. IBIC spectra relevant to the depletion region extending beneath the frontal Schottky electrode show a 100% CCE, with a spectral resolution of about 1.5%. The dependence of the width of the high efficiency region from applied bias voltage allows the constant residual doping concentration of the active region to be evaluated. The region where the electric field is absent shows an exponentially decreasing CCE profile, from which it is possible to estimate the diffusion length of the minority carriers by means of a drift-diffusion model. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
The configurational energy gap between amorphous and crystalline silicon

The crystallization enthalpy of pure amorphous silicon (a-Si) and hydrogenated a-Si was measured by differential scanning calorimetry (DSC) for a large set of materials deposited from the vapour phase by different techniques. Although the values cover a wide range (200-480 J/g), the minimum value is common to all the deposition techniques used and close to the predicted minimum strain energy of relaxed a-Si (240 ± 25 J/g). This result gives a reliable value for the configurational energy gap between a-Si and crystalline silicon. An excess of enthalpy above this minimum value can be ascribed to coordination defects
The Effects of Post-Thermal Annealing on the Emission Spectra of
  GaAs/AlGaAs Quantum Dots grown by Droplet Epitaxy

We fabricated GaAs/AlGaAs quantum dots by droplet epitaxy method, and
obtained the geometries of the dots from scanning transmission electron
microscopy data. Post-thermal annealing is essential for the optical activation
of quantum dots grown by droplet epitaxy. We investigated the emission energy
shifts of the dots and underlying superlattice by post-thermal annealing with
photoluminescence and cathodoluminescence measurements, and specified the
emissions from the dots by selectively etching the structure down to a lower
layer of quantum dots. We studied the influences of the degree of annealing on
the optical properties of the dots from the peak shifts of the superlattice,
which has the same composition as the dots, since the superlattice has uniform
and well-defined geometry. Theoretical analysis provided the diffusion length
dependence of the peak shifts of the emission spectra
Au/TiO2 nanorod-based Schottky-type UV photodetectors

Cataloged from PDF version of article.TiO2 nanorods (NRs) were synthesized on fluorine-doped tin oxide (FTO) pre-coated glass substrates using hydrothermal growth technique. Scanning electron microscopy studies have revealed the formation of vertically-aligned TiO2 NRs with length of similar to 2 mu m and diameter of 110128 nm, homogenously distributed over the substrate surface. 130 nm thick Au contacts using thermal evaporation were deposited on the n-type TiO2 NRs at room temperature for the fabrication of NR-based Schottky-type UV photodetectors. The fabricated Schottky devices functioned as highly sensitive UV photodetectors with a peak responsivity of 134.8 A/W (lambda = 350 nm) measured under 3 V reverse bias. (c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Momentum-space instantons and maximally localized flat-band topological
  Hamiltonians

Recently, two-dimensional band insulators with a topologically nontrivial
(almost) flat band has been studied extensively, which can realize integer and
fractional quantum Hall effect in a system without an orbital magnetic field.
Realizing a topological flat band generally requires longer range hoppings in a
lattice Hamiltonian. It is natural to ask what is the minimal hopping range
required.% for a topological flat-band Hamiltonian. In this paper, we prove
that the mean hopping range of the flat-band Hamiltonian with Chern number
$C_1$ and total number of bands $N$ has a universal lower bound of
$\sqrt{4|C_1|/\pi N}$. Furthermore, for the Hamiltonians that reach this lower
bound, the Bloch wavefunctions of the topological flat band are instanton
solutions of a $CP(N-1)$ non-linear $\sigma$ model on the Brillouin zone torus,
which are elliptic functions up to a normalization factor.Comment: 3 pages, 1 figur
Topological phase transitions in bulk

We consider the analogy between the topological phase transition which occurs
as a function of spatial coordinate on a surface of a non-trivial insulator,
and the one which occurs in the bulk due to the change of internal parameters
(such as crystal field and spin-orbit coupling). In both cases the system
exhibits a Dirac cone, which is the universal manifestation of topological
phase transition, independently on the type of driving parameters. In
particular, this leads to a simple way of determining the topological class
based solely on the bulk information even for the systems with translational
symmetry broken by atomic disorder or by strong electron correlations. Here we
demonstrate this on example of the zinc-blende related semiconductors by means
of the {\it ab-initio} fully-relativistic band structure calculations involving
the coherent potential approximation (CPA) technique.Comment: Phys. Status Solidi RRL, DOI 10.1002/pssr.2012064xx (2012), submitte
Topological insulators and thermoelectric materials

Topological insulators (TIs) are a new quantum state of matter which have
gapless surface states inside the bulk energy gap. Starting with the discovery
of two dimensional TIs, the HgTe-based quantum wells, many new topological
materials have been theoretically predicted and experimentally observed.
Currently known TI materials can possibly be classified into two families, the
HgTe family and the Bi2Se family. The signatures found in the electronic
structure of a TI also cause these materials to be excellent thermoelectric
materials. On the other hand, excellent thermoelectric materials can be also
topologically trivial. Here we present a short introduction to topological
insulators and thermoelectrics, and give examples of compound classes were both
good thermoelectric properties and topological insulators can be found.Comment: Phys. Status Solidi RRL, accepte
Fabrication and characterization of semiconducting half Heusler YPtSb
  thin films

The semiconducting half Heusler compound YPtSb was predicted theoretically to
be capable of changing into topological insulator under proper strain. In this
work, p type semiconducting half-Heusler YPtSb thin films were prepared by
magnetron co-sputtering method from a specially designed target for the first
time. Textured structure with (111) plane paralleling with (001) of MgO
substrate was observed when YPtSb thin films were grown on MgO (100) substrate
at 600{\deg}C.Electrical measurements show that the resistivity of YPtSb films
decreases with increasing temperature, indicating a semiconductor-like
behavior. The carrier density is as high as 1.15 X 10^21 cm-3 at 300 K. The
band gap of YPtSb thin films obtained by infrared spectroscopy is around 0.1 -
0.15 eV, which is well in agreement with the theoretical prediction and the
value measured in bulk YPtSb.Comment: Phys. Status Solidi RRL, DOI 10.1002/pssr.2012064xx (2012), accepte
Topological insulators from the Perspective of first-principles
  calculations

Topological insulators are new quantum states with helical gapless edge or
surface states inside the bulk band gap.These topological surface states are
robust against the weak time-reversal invariant perturbations, such as lattice
distortions and non-magnetic impurities. Recently a variety of topological
insulators have been predicted by theories, and observed by experiments.
First-principles calculations have been widely used to predict topological
insulators with great success.
  In this review, we summarize the current progress in this field from the
perspective of first-principles calculations. First of all, the basic concepts
of topological insulators and the frequently-used techniques within
first-principles calculations are briefly introduced. Secondly, we summarize
general methodologies to search for new topological insulators. In the last
part, based on the band inversion picture first introduced in the context of
HgTe, we classify topological insulators into three types with s-p, p-p and
d-f, and discuss some representative examples for each type.Comment: 10 pages, 7 figure
Circular dichroism in angle-resolved photoemission spectroscopy of topological insulators

Topological insulators are a new phase of matter that exhibits exotic surface electronic properties. Determining the spin texture of this class of material is of paramount importance for both fundamental understanding of its topological order and future spin-based applications. In this article, we review the recent experimental and theoretical studies on the differential coupling of left-circularly versus right-circularly polarized light to the topological surface states in angle-resolved photoemission spectroscopy. These studies have shown that the polarization of light and the experimental geometry play a veryimportant role in both photocurrent intensity and spin polarization of photoelectrons emitted from the topological surface states. A general photoemission matrix element calculation can quantitatively explain the observations and is also applicable to topologically trivial systems with strong spin–orbit coupling. These experimental and theoretical investigations suggest that optical excitation with circularly polarized light is a promising route towards mapping the spin–orbit texture and manipulating the spin orientation in topological and other spin–orbit coupled materials.

The circular-dichroic angle-resolved photoemission spectrum of Bi2Se3 as obtained by the difference between spectra taken with left-circularly vs. right-circularly polarized light using a time-of-flight electron spectrometer.United States. Dept. of Energy (Office of Basic Energy Sciences, Grant number DE-FG02-08ER46521)United States. Dept. of Energy (Office of Basic Energy Sciences, Grant number DE-SC0006423)United States. Army Research Office ((ARO- DURIP) Grant number W911NF-09-1-0170)Alfred P. Sloan Foundatio
Tapered Yagi-Uda Nanoantennas for Broadband Unidirectional Emission

We demonstrate experimentally the operation of tapered Yagi-Uda nanoantennas
for broadband unidirectional emission enhancement. The measured transmittance
spectra show that, in comparison to untapered reference structures, the tapered
nanoantennas exhibit distinct wide-band spectral resonances. The performed
full-vectorial numerical calculations are in good qualitative agreement with
the measured spectra, further revealing how the near-field profiles of the
tapered nanoantennas are directly reflecting their broadband characteristics