pinecone/core-2020-05-10-deduplication huggingface dataset:
Nonequilibrium valley polarization in graphene nanoconstrictions

We recently shown, using tight-binding calculations, that nonequilibrium
valley polarization can be realized in graphene, when the current is injected
through "valley filter": a ballistic point contact with zigzag edges. Here we
demonstrate, that the effect is surprisingly robust against changing the
crystallographic orientation of the filter axis. Namely, the output current
remains polarized unless a point contact has perfect armchair edges, at which
two subblattices are equally represented. The polarization is inverted when the
filter orientation crosses the amchair line and, subsequently, dominating
subblattice index of terminal atoms changes. In a bended graphene strip, the
valley-polarized current can be directed towards one edge providing a
theoretical possibility to observe a zero-magnetic-field analogue of the
well-known Hall effect. For the valley valve, build of two valley filters in
series and controlled elecrostatically by a gate voltage, the
conductance-to-gate characteristic is inverted when $\pi/3$ vertex is placed
between two filters.Comment: 10 pages, 7+1 figures, presented on the conference TNT2007 "Trends in
  Nanotechnology", San Sebastian (Spain), September 3-7, 2007. Submitted to
  special edition of phys. stat. sol. (a
Indium tin oxide thin films prepared by ion beam assisted deposition technique at different ion beam currents

Indium tin oxide (ITO) films have been deposited onto glass substrates at room temperature by ion beam assisted deposition technique (IBAD) at different ion beam currents (80 mA – 120 mA). The effect of the ion beam current on films properties has been studied. The films prepared at low ion beam current (80 mA) show an almost amorphous structure. As the ion beam current is increased, films show a preferred orientation along the (222) direction. AFM measurements show that the surface RMS roughness of the film increases as the current goes up. The optical properties have been studied by measuring the transmittance. It has been found that the film prepared at 100 mA current has the highest transmittance. The optical constants of the films have been calculated by fitting the transmittance. The Hall measurements also showed that the film prepared at 100 mA current has one of the lower electrical resistivities. FTIR measurements show that the film prepared at 100 mA current has the highest infra-red reflectance. All the measurements show the 100 mA ion beam current can produce good quality ITO films.Fundação para a Ciência e a Tecnologia (FCT) - SFRH-BSAB-514
Sample Size Effects on the Transport Characteristics of Mesoscopic
  Graphite Samples

In this work we investigated correlations between the internal microstructure
and sample size (lateral as well as thickness) of mesoscopic, tens of nanometer
thick graphite (multigraphene) samples and the temperature $(T)$ and field
$(B)$ dependence of their electrical resistivity $\rho(T,B)$. Low energy
transmission electron microscopy reveals that the original highly oriented
pyrolytic graphite material -- from which the multigraphene samples were
obtained by exfoliation -- is composed of a stack of $\sim 50 $nm thick and
micrometer long crystalline regions separated by interfaces running parallel to
the graphene planes. We found a qualitative and quantitative change in the
behavior of $\rho(T,B)$ upon thickness of the multigraphene samples, indicating
that their internal microstructure is important.} {The overall results indicate
that the metallic-like behavior of $\rho(T)$ at zero field measured for bulk
graphite samples is not intrinsic of ideal graphite. The results suggest that
the interfaces between crystalline regions may be responsible for the
superconducting-like properties observed in graphite. Our transport
measurements also show that reducing the sample lateral size as well as the
length between voltage electrodes decreases the magnetoresistance, in agreement
with recently published results. The magnetoresistance of the multigraphene
samples shows a scaling of the form ($(R(B) - R(0))/R(0))/T^\alpha = f(B/T)$
with a sample dependent exponent $\alpha \sim 1$, which applies in the whole
temperature 2 K $\le T \le 270$K and magnetic field range $B \le 8 $T.Comment: 11 pages, 11 figure
Ion beam induced charge (IBIC) irradiation damage study in synthetic single crystal diamond using 2.6 MeV protons

We have studied the effects of irradiation induced damage on the detector response of a synthetic single crystal diamond radiation detector. Before introducing radiation damage, the spatial variation of the detector response was investigated using a highly focused 2.6 MeV proton beam. A very uniform response close to 100% charge collection efficiency (CCE) over the whole contact area was found at applied electric field strengths as low as 0.4 V μm–1. At lower biases, time dependent polarisation phenomena were observed and clearly reduced the average signal amplitude. Subsequently, the 2.6 MeV proton beam has been used to introduce radiation damage within selected areas. The ion beam induced charge imaging was repeated to probe the modified regions. Even at an applied electric field of 2.6 V μm–1, no signal above the analogue threshold of the system was observed in the areas which had received a dose larger then 5 × 1014 cm–2, whereas more than 90% CCE was reached in the area with 1012 protons cm–2. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Deep levels in homoepitaxial boron-doped diamond films studied by capacitance transient spectroscopies

International audienceDeep level transient spectroscopies (DLTS) applied to Schottky junctions made on homoepitaxial boron-doped diamond films show the existence of two traps. A deep acceptor, negatively charged and strongly attractive for holes, 1.57 eV above the valence band edge displays the characteristic features of a complex defect due to interacting centers and impurities, also displaying some evolutions after thermal cycles, possibly due to hydrogen effusion or diffusion. It is tentatively ascribed to association of a boron atom, a vacancy and several hydrogen atoms. A deep donor, 1.13 eV above the valence band edge, able to compensate the boron acceptors, is attributed to a defect correlated with dislocations. It could be due to the positively charged carbon vacancy. These conclusions are drawn from the Fourier transform-DLTS results coupled with isothermal time domain algorithms allowing the discrimination of multiple emission rates with high resolution
Structural and photoluminescence studies of erbium implanted nanocrystalline silicon thin films

Hydrogenated amorphous and nanocrystalline silicon thin films deposited by Hot Wire (HW) and Radio-Frequency Plasma-Enhanced (RF) Chemical Vapor Deposition were Er-bium-implanted. Their pre-implantation structural properties and post-implantation optical properties were studied and cor-related. After one-hour annealing at 150ºC in nitrogen atmos-phere only amorphous films showed photoluminescence (PL) activity at 1.54 μm, measured at 5 K. After further annealing at 300oC for one hour, all the samples exhibited a sharp PL peak positioned at 1.54 m, with a FWHM of ~5 nm. Amorphous films deposited by HW originated a stronger PL peak than corresponding films deposited by RF, while in na-nocrystalline films PL emission was much stronger in sam-ples deposited by RF than by HW. There was no noticeable difference in Er3+ PL activity be-tween films implanted with 1x1014 atoms/cm2 and 5x1015 at-oms/cm2 Er doses.FCT for a post-doctorate grant (SFRH/BPD/14919/2004
Semimagnetic semiconductor oxides as materials for transparent electronics and spintronics

Zinc oxide-based semimagnetic semiconductor (SMS) ZnMnO, ZnMnFeO and ZnMnSnO thin films were deposited on sapphire and glass substrate by pulsed laser deposition (PLD) and RF sputtering techniques. Further, ZnMnO nanocrystals embedded in polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) matrices were prepared by chemical method employing zinc acetate and manganese acetate as precursors. The morphology of the thin films was studied using atomic force microscopy (AFM). Large variety of the morphology images was obtained depending on the film composition and growth conditions. The most interesting feature was observed for the ZnMnSnO films, in which the formation of clusters including nanowire-like structures was shown. Optical transmission spectra suggest that metalsMn, Fe and Sn substitute for Zn2+ ions in the ZnO lattice, resulting in the increase in the band gap energy.Magneto-optical Faraday rotation measurements confirm ferromagnetic ordering in ZnMnFeO thin films and paramagnetic behaviour for the other films.The work has been supported in part
by the Ministry of Education and Science of Ukrain
Anti-stokes cooling in semiconductor nanocrystal quantum dots : a feasibility study

In this review, we discuss the feasibility of laser cooling of
semiconductor nanocrystal quantum dots by phonon-assisted
anti-Stokes photoluminescence. Taking into account recent
experimental advances, in particular, the development of
semiconductor nanocrystals with very high quantum yield, we analyze in detail how the various physical processes in
nanocrystals might help or hinder the cooling process. Possible
experimental approaches to achieve efficient optical cooling are
also discussed.Science Foundation Ireland - 02/IN.1/I47;
00/PI.1/C077A.2; 07/IN.1/B186
Charge Carrier Dissociation and Recombination in Polymer Solar Cells

In polymer:fullerene solar cells, the origin of the losses in the
field-dependent photocurrent is still controversially debated. We contribute to
the ongoing discussion by performing photo-induced charge extraction
measurements on poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C$_{61}$ butyric
acid methyl ester solar cells in order to investigate the processes ruling
charge carrier decay. Calculating the drift length of photogenerated charges,
we find that polaron recombination is not limiting the photocurrent for
annealed devices. Additionally, we applied Monte Carlo simulations on blends of
conjugated polymer chain donors with acceptor molecules in order to gain
insight into the polaron pair dissociation. The dissociation yield turns out to
be rather high, with only a weak field dependence. With this complementary view
on dissociation and recombination, we stress the importance of accounting for
polaron pair dissociation, polaron recombination as well as charge extraction
when considering the loss mechanisms in organic solar cells.Comment: 6 pages, 7 figue
Hydrogen effects on crystallinity, photoluminescence, and magnetization of indium tin oxide thin films sputter-deposited on glass substrate without heat treatment

Indium tin oxide (ITO) thin films were sputter deposited by using working gas containing hydrogen on glass substrate without any heat treatments. The films demonstrated X-ray diffraction due to polycrystalline ITO, blue-green photoluminescence (PL) due to oxygen defects in nano-structured ITO crystals, and paramagnetic behaviour in temperature dependence of magnetization overlapped with diamagnetic signal from the substrate. The carrier density n of the films was of the order of 1020 cm−3, and varied as an inverse of V-character with the hydrogen concentration [H] in the gas. The n value peaked at [H] = 1%. Spectral features at ≈430 and ≈470 nm of the PL emission were invariant with [H]. The order of the density of electrons N with spins obeying the Curie law was 1023 cm−3, and the variation in N with [H] was almost parallel to that in n with [H]
Electronic and optical properties\ud
 of group IV 2-dimensional materials

The microscopic study of complex systems has reached a high level of accuracy that allows for a deep understanding of their structure, electronic properties, and optical spectra. The theoretical investigation of surfaces is nowadays routinely done within density functional theory, for ground state properties, and, with a larger computational load, within many-body perturbation theory, for excited states properties. In this paper we present and discuss examples of calculations for group IV two-dimensional systems such as a clean silicon surface, a tin–germanium interface, graphene, and graphane, pointing out the importance of a pertinent treatment of many-body effects
Theoretical study of hydrogen microstructure in models of hydrogenated
  amorphous silicon

We study the distribution of hydrogen and various hydride configurations in
realistic models of a-Si:H for two different concentration generated via
experimentally constrained molecular relaxation approach (ECMR) [1]. The
microstructure corresponding to low (< 10%) and high (> 20%) concentration of H
atoms are addressed and are compared to the experimental results with
particular emphasis on the size of H clusters and local environment of H
atoms.The linewidths of the nuclear magnetic resonance (NMR) spectrum for the
model configurations are calculated in order to compare to the experimental NMR
data. Our study shows the presence of isolated hydrogen atoms, small and
relatively large clusters with average proton-proton neighbor distance in the
clusters around 1.6 to 2.4 Angstrom that have been observed in multiple quantum
NMR experiments.Comment: 5 pages, 5 figure
Detection of volatile organic compounds using a polythiophene derivative

Conjugated polymers have been subject of great interest in\ud
the recent literature from both fundamental point of view\ud
and applied science perspective. Among the several types\ud
of conjugated polymers used in recent investigations, polythiophene\ud
and its derivatives have attracted considerable\ud
attention over the past 20 years due to their high mobility\ud
and other remarkable solid-state properties. They have\ud
potential applications in many fields, such as microelectronic\ud
devices, catalysts, organic field-effect transistors, chemical\ud
sensors, and biosensors. They have been studied as gas and\ud
volatile organic compounds (VOCs) sensors using different\ud
principles or transduction techniques, such as optical\ud
absorption, conductivity, and capacitance measurements.\ud
In this work, we report on the fabrication of gas sensors\ud
based on a conducting polymer on an interdigitated gold\ud
electrode. We use as active layer of the sensor a polythiophene\ud
derivative: poly (3-hexylthiophene) (P3HT) and analyzed its\ud
conductivity as response for exposure to dynamic flow of\ud
saturated vapors of six VOCs [n-hexane, toluene, chloroform,\ud
dichloromethane, methanol, and tetrahydrofuran (THF)].\ud
Different responses were obtained upon exposure to all VOCs,\ud
THF gave the higher response while methanol the lower\ud
response. The influenceFAPESPCNPq/INEO (Brazil)LNLS (Brazil
Mechanisms of doping graphene

We distinguish three mechanisms of doping graphene. Density functional theory
is used to show that electronegative molecule like F4-TCNQ and electropositive
metals like K dope graphene p- and n-type respectively. These dopants are
expected to lead to a decrease in carrier mobility arising from Coulomb
scattering but without any hysteresis effects. Secondly, a novel doping
mechanism is exhibited by Au which dopes bilayer graphene but not single layer.
Thirdly, electrochemical doping is effected by redox reactions and can result
in p-doping by humid atmospheres and n-doping by NH3 and toluene.Comment: submitted to Physica Status Solid
Study on the giant positive magnetoresistance and Hall effect in ultrathin graphite flakes

In this paper, we report on the electronic transport properties of mesoscopic, ultrathin graphite flakes with a thickness corresponding to a stack of 150 graphene layers. The graphite flakes show an unexpectedly strong positive magnetoresistance (PMR) already at room temperature, which scales in good approximation with the square of the magnetic field. Furthermore, we show that the resistivity is unaffected by magnetic fields oriented in plane with the graphene layers. Hall effect measurements indicate that the charge carriers are p-type and their concentration increases with increasing temperature while the mobility is decreasing. The Hall voltage is non-linear in higher magnetic fields. Possible origins of the observed effects are discussed. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheimstatus: publishe
Novel Multifunctional Materials Based on Oxide Thin Films and Artificial
  Heteroepitaxial Multilayers

Transition metal oxides show fascinating physical properties such as high
temperature superconductivity, ferro- and antiferromagnetism, ferroelectricity
or even multiferroicity. The enormous progress in oxide thin film technology
allows us to integrate these materials with semiconducting, normal conducting,
dielectric or non-linear optical oxides in complex oxide heterostructures,
providing the basis for novel multi-functional materials and various device
applications. Here, we report on the combination of ferromagnetic,
semiconducting, metallic, and dielectric materials properties in thin films and
artificial heterostructures using laser molecular beam epitaxy. We discuss the
fabrication and characterization of oxide-based ferromagnetic tunnel junctions,
transition metal-doped semiconductors, intrinsic multiferroics, and artificial
ferroelectric/ferromagetic heterostructures - the latter allow for the detailed
study of strain effects, forming the basis of spin-mechanics. For
characterization we use X-ray diffraction, SQUID magnetometry, magnetotransport
measurements, and advanced methods of transmission electron microscopy with the
goal to correlate macroscopic physical properties with the microstructure of
the thin films and heterostructures.Comment: 21 pages, 21 figures (2 figures added, typos corrected
Oxygen annealing for deuterium doped indium tin oxide thin films

Deuterium-doped indium tin oxide films, fabricated by dc plasma deposition in sputter gas consisting of deuterium and argon, were annealed at 300 °C for 40 min in flowing oxygen gas by using tubular gold image furnace. On oxygen annealing, the optical transparency of the film deposited at the gas pressure ratio of deuterium to argon of 3.6% increased from ≈30 to 60% at the wavelength of 600 nm, although that of the films deposited at the ratios of 1 and 1.5% slightly decreased from 88 to 80% and from 85 to 77%, respectively. The resistivity of the films at room temperature, ranged from 2 × 10−4 to 1.4 × 10−3 Ω cm corresponding to the gas pressure ratio from 1 to 3.6%, was almost the same before and after the annealing for each film. A change in morphology toward a smoother surface by the oxygen annealing was apparent especially for the film with the gas pressure ratio of 3.6%. Agglomeration of randomly oriented grains with diameters of <100–200 nm observed before the annealing disappeared on annealing. A smoother surface is responsible for higher transparency of the annealed films that contained densely populated hydroxyl bond before the annealing.Oxygen annealing at 300 °C enlarged the optical transmittance (left panel) but decreased the population of hydrogen-bonded oxygen (right panel) of the indium tin oxide thin film fabricated by dc plasma deposition in sputter gas containing deuterium of 3.6%
Pressure effects in PrT2B2C (T = Co, Ni, Pt): Applied and chemical
  pressure

High-pressure electrical resistivity, r(T), measurements on intermetallic
Pr(Co, Ni, Pt)2B2C compounds were performed down to 2K. At room pressure the
r(T) in a-b direction curves for the non superconducting Pr(Co, Ni)2B2C
compounds exhibit magnetic correlations at about 10 and 4 K, respectively. At
low temperatures, PrCo2B2C shows a large spin-dependent electron scattering in
comparison to PrNi2B2C. Under applied pressure the magnetic scattering tends to
be suppressed more effectively in PrCo2B2C than in PrNi2 B2C. The low
temperature behavior of r(T,P) for PrNi2B2C and PrCo2B2C suggests a spin
fluctuations mechanism. In the other hand PrPt2B2C compound shows
superconductivity at about 6 K and under pressure its superconducting
transition temperature tends to be degraded at a rate dTc/dP = -0.34 K/GPa, as
expected in compounds with transition metals. The experimental results in Co,
Ni and Pt based compounds are analyzed from the point of view of the external
and chemical internal pressure effects
Electron transport properties in Al0.25Ga0.75N/AIN/GaN hetrostructures with different InGaN back barrier layers and GaN channel thickness grown by MOCVD

Cataloged from PDF version of article.The electron transport properties in Al0.25Ga0.75N/AlN/GaN/InxGa1-xN/GaN double heterostructures with various indium compositions and GaN channel thicknesses were investigated. Samples were grown on c-plane sapphire substrates by MOCVD and evaluated using variable temperature Hall effect measurements. In order to understand the observed transport properties, various scattering mechanisms, such as acoustic phonon, optical phonon, interface roughness, background impurity, and alloy disorder, were included in the theoretical model that was applied to the temperature-dependent mobility data. It was found that low temperature (T < 160 K) mobility is limited only by the interface roughness scattering mechanism, while at high temperatures (T > 160 K), optical phonon scattering is the dominant scattering mechanism for AlGaN/AlN/GaN/InGaN/GaN heterostructures. The higher mobility of the structures with InGaN back barriers was attributed to the large conduction band discontinuity obtained at the channel/buffer interface, which leads to better electron confinement. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Colorimetry and efficiency of white LEDs : Spectral width dependence

The potential colour rendering capability and efficiency of white LEDs constructed by a combination of individual red, green and blue (RGB) LEDs are analysed. The conventional measurement of colour rendering quality, the colour rendering index (CRI), is used as well as a recently proposed colour quality scale (CQS), designed to overcome some of the limitations of CRI when narrow-band emitters are being studied. The colour rendering performance is maximised by variation of the peak emission wavelength and relative intensity of the component LEDs, with the constraint that the spectral widths follow those measured in actual devices. The highest CRI achieved is 89.5, corresponding to a CQS value of 79, colour temperature of 3800 K and a luminous efficacy of radiation (LER) of 365 lm/W. By allowing the spectral width of the green LED to vary the CRI can be raised to 90.9, giving values of 82.5 and 370 lm/W for the CQS and LER, respectively. The significance of these values are discussed in terms of optimising the possible performance of RGB LEDs
Growth and magnetic properties of bulk electron doped 'LA IND. 0.7''CE IND. 0.3''MN''O IND. 3' manganites

We report on the growth of bulk samples (composite fibers) of the nominal composition La0.7Ce0.3MnO3 (LCMO) manganites (with Curie temperature TC,max = 300 K) by using the laser heated pedestal growth (LHPG) technique. Samples composition was verified through scanning electron microscopy with energy dispersive X-ray (EDX) analysis. The magnetic behavior of the fibers was probed by magnetization measurements. In addition to a weak ferromagnetic transition at TC0 = 45 K (due to MnO2 impurities), two more transitions with TC1 = 126 K and TC2 = 180 K were identified and linked to regions with cerium concentration of x = 0.063 and 0.13, respectively.FAPESPCAPESCNP