pinecone/core-2020-05-10-deduplication huggingface dataset:
Magnetic relaxation in a model of interacting nanoparticles in terms of
  microscopic energy barriers

Monte Carlo simulations are used to study the magnetic relaxation of a system
of single domain particles with dipolar interactions modeled by a chain of
Heisenberg classical spins. We show that the so-called $T\ln(t/\tau_0)$ method
can be extended to interacting systems and how, from the computed master
relaxation curves, the effective energy barrier distributions responsible for
the relaxation can be obtained. A transition from a quasi-logarithmic to
power-law behavior of the relaxation as the interaction strength is in-creased
is found. By direct computation of the effective energy barriers of the system,
we show that this is due to the appearance of an increasing number of small
energy barriers caused by the reduction of the anisotropy energy barriers as
the local dipolar fields increase.Comment: Contribution to SCM 2004 (2nd Seeheim Conference on Magnetism), to be
  published in Physica Status Solidi. 5 pages, 3 figure
Ag buffer layer effect on magnetization reversal of epitaxial Co films

[[abstract]]Nano-sized Ag(111) islands were first prepared by using molecular beam epitaxy technique on diluted-hydrofluoric acid etched Si(111) substrate. Epitaxial Co films were then grown onto the Ag films at 100 蚓 to decrease interdiffusion. The Ag buffer layer designed to form isolated islands with {111} sidewalls on the Si(111) substrate, and provided Co films (111) texture growth to study the correlation between magnetic properties of Co films and Ag buffer layer effect. It reveals that the Ag rough surface acts as a pinning source and Ag {111} sidewalls also plays an important role on the magnetoresistance transition of Co films.[[fileno]]2020336010012[[department]]材料科學工程學
Thermally stimulated currents in layered Ga4SeS3 semiconductor

Cataloged from PDF version of article.Thermally stimulated current (TSC) measurements are carried out on nominally undoped Ga4SeS3 layered semiconductor samples with the cur-rent flowing along the c-axis in the temperature range of 10 to 150 K. The results are analyzed according to various methods, such as curve fitting, initial rise and Chen's methods, which seem to be in good agreement with each other. Experimental evidence is found for the presence of three trapping centers in Ga4SeS3 with activation energies of 70, 210 and 357 meV. The calculation yielded 7.9 x 10(-21), 7.0 x 10(-19) and 1.5 x 10(-13) cm(2) for the capture cross section, and 1.6 x 10(10), 6.5 x 10(10) and 1.2 x 10(11) cm(-3) for the concentration of the traps studied. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Electronic conductivity and structural distortion at the interface between insulators SrTiO3 and LaAlO3

When insulator LaAlO3 is grown by epitaxy onto a TiO2-terminated {100} surface of insulator SrTiO3, the resulting system has a metallic character. This phenomenon has been associated with an electrostatic frustration at the interface, as {100} surfaces of SrTiO3 are neutral while those of LaAlO3 are polar, but its microscopic mechanism is not quite understood. Here, we present a structural characterisation of this interface by aberration-corrected transmission electron microscopy. The unit cells at the interface appear elongated: we discuss this distortion in terms of electrostatic charge and extra carriers at the interface
Density functionals and half-metalicity in La2/3Sr1/3MnO3

The electronic structure and equilibrium geometry of La2/3Sr1/3MnO3 are
studied theoretically by means of density functional calculations. The doping
is treated by introducing holes and a compensating jellium background. The
results for the local density approximation (LDA) agree with previous LDA
calculations, with an equilibrium volume 5.3% too small and with both majority
and minority spin states present at the Fermi level for the relaxed system. The
generalised gradient approximation (GGA) offers a qualitatively improved
description of the system, with a more realistic volume, and a half-metallic
behaviour for the relaxed structure, which enables studies needing theoretical
relaxation.The ideal MnO2-terminated (001) surface is then described with
explicit doping.Comment: 5 pages, 3 Encapsulated Postscript figures. Submitted to the
  Proceedings of TNT 2005, Oviedo, Spai
Kondo effect in nanostructures

Kondo effect arises whenever a coupling to the Fermi gas induces transitions
within the otherwise degenerate ground state multiplet of an interacting
system. Both coupling to the Fermi gas and interactions are naturally present
in any nanoscale transport experiment. At the same time, many nanostructures
can easily be tuned to the vicinity of a degeneracy point. This is why the
Kondo effect in its various forms often influences the low temperature
transport in meso- and nanoscale systems.
  In this short review we discuss the basic physics of the Kondo effect and its
manifestations in the low-temperature electronic transport through a single
electron transistor
Symmetry breaking and Wigner molecules in few-electron quantum dots

We discuss symmetry breaking in two-dimensional quantum dots resulting from
strong interelectron repulsion relative to the zero-point kinetic energy
associated with the confining potential. Such symmetry breaking leads to the
emergence of crystalline arrangements of electrons in the dot. The so-called
Wigner molecules form already at field-free conditions. The appearance of
rotating Wigner molecules in circular dots under high magnetic field, and their
relation to magic angular momenta and quantum-Hall-effect fractional fillings,
is also discussed. Recent calculations for two electrons in an elliptic quantum
dot, using exact diagonalization and an approximate generalized-Heitler-London
treatment, show that the electrons can localize and form a molecular dimer for
screened interelectron repulsion. The calculated singlet-triplet splitting (J)
as a function of the magnetic field (B) agrees with cotunneling measurements;
its behavior reflects the effective dissociation of the dimer for large B.
Knowledge of the dot shape and of J(B) allows determination of two measures of
entanglement (concurrence and von Neumann entropy for indistinguishable
fermions), whose behavior correlates also with the dissociation of the dimer.
The theoretical value for the concurrence at B=0 agrees with the experimental
estimates.Comment: LATEX, 12 pages with 6 figures. Invited talk at TNT2005 (Trends in
  Nanotechnology). To download a file with figures of higher quality, click
  http://www.prism.gatech.edu/~ph274cy/ (go to publication #74
Comparison between ab-initio and phenomenological modeling of the
  exchange couplings in diluted magnetic semiconductors: the case of
  $Zn_{1-x}Cr_{x}Te$

Using a recently developed semi-analytical method (Self-Consistent Local RPA
or SC-LRPA) we study the stability of the ferromagnetic phase in diluted
magnetic systems where the exchange coupling between magnetic impurities are of
RKKY form. A short discussion of the relevance of these calculations with
respect to the ferromagnetism observed in diluted ferromagnetic materials is
provided. Then, within a two step approach, we study ferromagnetism in
$Zn_{1-x}Cr_{x}Te$. In the first step of our study, we calculate the magnetic
couplings between Mn impurities within the LDA. In the second step, we
diagonalize the resulting effective Heisenberg Hamiltonian using the SC-LRPA.
We also compare, when available, our calculations with Monte Carlo simulations
and experimental measurements.Comment: Proceedings of the International Conference MSM05, Agadir Maroc
  September 2005'', to appear in Physica Status Solid
Surface potential of chalcopyrite films measured by KPFM

Atomic force microscopy is widely used to characterize the surface topography of a variety of samples.  Kelvin probe force microscopy  KPFM  additionally allows determining images of the surface potential  with nanometer resolution. The KPFM technique will be introduced and studies on surfaces of chalcopyrite  semiconductors for solar cell absorbers will be presented. It is shown that operation in ultra high vacuum   UHV  is required to obtain meaningful work function values. Different methods for obtaining UHV clean  surfaces are presented and KPFM studies on these are compared. Surfaces where prepared by in vacuum  deposition, inert gas transfer, in vacuum decapping of a protective Se cap and a peel off method. Finally,  a sputter annealing cycle also allows to obtain well suited surfaces for KPFM studies. Employing KPFM,  variations in the local surface potential at grain boundaries of polycrystalline CuGaSe2 films were observed.  A potential drop indicates the presence of charged defects at grain boundaries. Furthermore, different  electronic activity was found for different grain boundaries, as concluded from studies under illumination.  Using laterally resolved surface photovoltage, a Cu2 amp; 8722;xSe impurity phase could be observed in CuGaSe
Electronic structure and exchange constants in magnetic semiconductors
  digital alloys: chemical and band-gap effects

First-principles simulations have been performed for [001]-ordered Mn/Ge and
Mn/GaAs "digital alloys", focusing on the effects of i) a larger band-gap and
ii) a different semiconducting host on the electronic structure of the magnetic
semiconductors of interest. Our results for the exchange constants in Mn/Ge,
evaluated using a frozen-magnon scheme, show that a larger band-gap tends to
give a stronger nearest-neighbor ferromagnetic coupling and an overall enhanced
in-plane ferromagnetic coupling even for longer-ranged coupling constants. As
for the chemical effects on the exchange constants, we show that Mn/GaAs shows
a smaller nearest-neighbor ferromagnetic coupling than Mn/Ge, but exchange
constants for higher Mn-Mn distance show an overall increased ferromagnetic
behavior in Mn/GaAs. As a result, from the magnetic-coupling point of view, the
two systems behave on average rather similarly
Zero-resistance States Induced by Bichromatic Microwaves

We have studied the bichromatic photoresistance states of a two dimensional
electron gas in the regime of microwave induced resistance oscillations. Zudov
and coworkers found clear experimental evidence of zero-resistance states by
measuring the bichromatic resistance in a bidimensional gas of electrons. They
found that the bichromatic resistance closely replicates the superposition of
the two monochromatic components provided that both contributions are positive.
However, the superposition principle is no longer valid if one of the two
contributions give rice to a zero-resistance state. The experiments by Zudov
and coworkers confirm that negative resistance states are rapidly driven into
zero-resistance states through A. V. Andreev's symmetry breaking. In this work
we present a model for the bichromatic-photoconductivity of a two dimensional
electron system subjected to a uniform magnetic field. Our model includes both
components of the microwave radiation, a uniform magnetic field and impurity
scattering effects. The conductivity is calculated from a Kubo-like formula.
Our calculations reproduce the main features of Zudov's experimental results.Comment: 4 pages, 1 figur
Formation of atomic-sized contacts controlled by electrochemical methods

Electrochemical methods have recently become an interesting tool for fabricating and characterizing nanostructures at room temperature. Simplicity, low cost and reversibility are some of the advantages of this technique that allows to work at the nanoscale without requiring sophisticated instrumentation. In our experimental setup, we measure the conductance across a nanocontact fabricated either by dissolving a macroscopic gold wire or by depositing gold in between two separated gold electrodes. We have achieved a high level of control on the electrochemical fabrication of atomic-sized contacts in gold. The use of electrochemistry as a reproducible technique to prepare nanocontacts will open several possibilities that are not feasible with other methodologies. It involves, also, the possibility of reproducing experiments that today are made by more expensive, complicated or irreversible methods. As example, we show here a comparison of the results when looking for shell effects in gold nanocontacts with those obtained by other techniques.This work is part of the research program of the “Stichting FOM”. C.U. and R.C. acknowledge support of the Spanish MEC through FIS2004-02356 and Generalitat Valenciana through ACOMP06/138. C.U. and V.C. acknowledge financial support through the “Ramón y Cajal” program of the Spanish MCyT
Characterization of InAs quantum wires on (001)InP: toward the realization of VCSEL structures with a stabilized polarization

International audienceWe propose a new type of long-wavelength vertical cavity surface emitting laser (VCSEL) which consists of quantum wires (QWires) layers of InAs/InGaAsP grown on InP(001) and dielectrics Bragg mirrors, in order to control the in plane polarization of output power. QWires and quantum wells growth are performed by molecular beam epitaxy. QWires present a strong photoluminescence dependence to the polarization in contrast to the quantum wells, a polarization rate of 33% is measured. The optically pumped VCSEL is fabricated by metallic bonding, which allows the deposition of two dielectrics Bragg mirrors. The VCSEL with an active region based on InGaAs/InGaAsP quantum wells exhibits a lasing emission at 1.578 µm at room temperature under continuous wave operation. The VCSEL with an active region based on quantum wires shows a luminescence at 1.53 µm strongly polarized along the direction [1-10] which is promising for the stabilization of in plane polarization of VCSEL emission
Visible and infrared photoluminescence from erbium-doped silicon nanocrystals produced by rf sputtering

Erbium-doped low-dimensional Si films with different microstructures were deposited by reactive magnetron sputtering on glass substrates by varying the hydrogen flow rate during deposition. Amorphous, micro- and nanocrystalline samples, consisting of Si nanocrystalls embedded in silicon-based matrices with different structures, were achieved with optical properties in the visible and IR depending on nanocrystalline fraction and matrix structure and chemical composition. Structural characterization was performed by X-ray diffraction in the grazing incidence geometry and Raman spectroscopy. The chemical composition was studied using RBS/ERD techniques. Spectroscopic ellipsometry was combined with the previous techniques to further re-solve the film microstructure and composition. In particular, the distribution along the film thickness of the volume fractions of nanocrystalline/amorphous silicon and SiOx phases has been obtained.
In this contribution we discuss visible and infrared photoluminescence as a function of sample microstructure and of the oxygen/ hydrogen concentration ratio present in the matrix.FCT (POCTI/CTM/39395)INTAS Project #03-51-648
Radiation hardness of diamond and silicon sensors compared

The radiation hardness of silicon charged particle sensors is compared with
single crystal and polycrystalline diamond sensors, both experimentally and
theoretically. It is shown that for Si- and C-sensors, the NIEL hypothesis,
which states that the signal loss is proportional to the Non-Ionizing Energy
Loss, is a good approximation to the present data. At incident proton and
neutron energies well above 0.1 GeV the radiation damage is dominated by the
inelastic cross section, while at non-relativistic energies the elastic cross
section prevails. The smaller inelastic nucleon-Carbon cross section and the
light nuclear fragments imply that at high energies diamond is an order of
magnitude more radiation hard than silicon, while at energies below 0.1 GeV the
difference becomes significantly smaller.Comment: 6 pages, 4 figurs, invited talk at the Hasselt Diamond Workshop, Feb.
  200
Diamond thin Film Detectors for Beam Monitoring Devices

Diamonds offer radiation hard sensors, which can be used directly in primary
beams. Here we report on the use of a polycrystalline CVD diamond strip sensor
as beam monitor of heavy ion beams with up to 2.10^9 lead ions per bunch. The
strips allow for a determination of the transverse beam profile to a fraction
of the pitch of the strips, while the timing information yields the
longitudinal bunch length with a resolution of the order of a few mm.Comment: 6 pages, 7 figures, to appear in the Proceedings of the Hasselt
  Diamond Workshop (Hasselt, Belgium, Feb. 2006), v4: accidentally submitted
  figure, appearing at end, remove
High gain observed in X-ray induced currents in synthetic single crystal diamonds

Diamond is considered as tissue equivalent, due to its low atomic number, which makes it a particular attractive material for medical radiation dosimetry applications. X-ray dosimeters made of natural single crystal diamonds are commercially available and routinely used, with typical gain values of about 0.5. The selection of suitable natural diamonds for this purpose is time and cost intensive. We report an X-ray induced current study in synthetic single crystal diamonds. Similar to natural diamond dosimeters, the devices had to be pre-irradiated before use to achieve a reproducible performance. We compare two chemical vapour deposited (CVD) samples grown by Element Six Ltd (UK). D1 was a high purity sample contacted in a sandwich structure with an asymmetric contact pair. Sample D2 was cut vertically and contained some nitrogen rich layers. It was contacted with two Ohmic contacts, which partly covered the high temperature/high pressure substrate material. Particle spectroscopy suggests better charge transport in D1 compared to D2, most likely caused by the lower purity. In contrast to this, large gain values up to 6 x 104 and a sensitivity of similar to 30 mC/Gy were measured at field strengths of 2 kV/cm in D2, and only 7 mu C/Gy in D1, despite their comparable volumes. We deduce that the gain observed in these devices is affected by the electrical properties of the metal-diamond contacts. The response time of the high gain device was in the order of minutes, which is longer than expected by a purely photoconductive process. Long persistent currents have been reported before in diamond under UV irradiation and modifications of gain and response time by surface treatment of UV detectors are known in the literature, highlighting the influence of the surface and contact interface on the device operation. Our results indicate that synthetic single crystal diamond provides a promising material for high sensitivity tissue-equivalent X-ray dosimeters. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Ferrimagnetism and antiferromagnetism in half-metallic Heusler alloys

Half-metallic Heusler alloys are among the most promising materials for
future applications in spintronic devices. Although most Heusler alloys are
ferromagnets, ferrimagnetic or antiferromagnetic (also called fully-compensated
ferrimagnetic) alloys would be more desirable for applications due to the lower
external fields. Ferrimagnetism can be either found in perfect Heusler
compounds or achieved through the creation of defects in ferromagnetic Heusler
alloys.Comment: To be considered for the proceedings of the International Conference
  on Nanoscale Magnetism (ICNM 07
Stiffening and Hydrophilisation of SOG Low-k Material Studied by Ellipsometric Porosimetry, UV Ellipsometry and Laser-induced Surface Acoustic Waves

In this paper we evaluate the correlation between UV light absorption of SOG (spin-on glass) low dielectric constant (low-k) films and chemical changes induced by an excimer UV source at several wavelengths: 172 rim, 222 ran, and 308 nm. Low-k absorption in the UV range was measured by nitrogen purged UV ellipsometry. It is shown that imprevenient of mechanical properties is accompanied by degradation (hydrophilisation) of low-k films. Changes in hydrophobic properties were evaluated by water-source ellipsometric porosimetry (WEP). The Young's moduli of the films were measured by laser-induced surface acoustic waves (LAwaves).status: publishe
Diffusion simulation of Cr-Fe bcc systems at atomic level using a random walk alogorithm

This paper proposes a model to simulate the diffusion\ud
of impurities in bcc atomic lattices. It works with threedimensional\ud
volume divided in small cubic elements\ud
(voxels), containing more than one atomic cell each.\ud
Once the domain is discretized, impurities jump for one\ud
voxel to another according to certain probability that\ud
takes into account the composition and geometry of the\ud
target voxel.\ud
In present work, model was applied to prismatic volume,\ud
and in order to deduce the relationship between the\ud
atomic jumping frequency and the temperature two different\ud
cases were studied. One consists of a Fe matrix\ud
with Cr impurities, and the other, is based on a Cr matrix\ud
with Fe impurities. Results obtained from these simulations\ud
were compared with profiles obtained by Dictra\ud
software.\ud
Results for the atomic jumping frequencies were fitted to\ud
Arrhenius type equation, as shown in following expressions.\ud
JCr = 3.396 × 1018exp(−306421\ud
RT\ud
)\ud
JFe = 1.096 × 1019exp(−411729\ud
RT\ud
)\ud
From these equations it is possible to obtain an activation\ud
energy for the atomic jumping phenomenon of » 306\ud
and » 411 kJ/mol for the Fe-matrix and Cr-matrix systems\ud
respectively. These energies match the empirical\ud
measured values for the diffusion of Cr and Fe impurities,\ud
250 and 407 kJ/mol respectively.\ud
Results obtained in this work assure that the proposed\ud
model is suitable for simulating the three-dimensional\ud
diffusion of substitutional impurities in Cr and Fe bcc\ud
systems. It could be easily expanded to other bcc matrix\ud
systems.Spanish Ministry of Science and Education (ENE2006-15170-\ud
C0-02) for the financial support.Peer reviewe
Band structure effects on the Be(0001) acoustic surface plasmon energy dispersion

22 pp.-- PACS nrs.: 71.15.Mb, 71.45.Gm, 73.20.At, 73.20.Mf.-- Pre-print version available at: http://arxiv.org/abs/0806.2364.We report first-principles calculations of acoustic surface plasmons on the (0001) surface of Be, as obtained in the random-phase approximation of many-body theory. The energy dispersion of these collective excitations has been obtained along two symmetry directions. Our results show a considerable anisotropy of acoustic surface plasmons, and underline the capability of experimental measurements of these plasmons to map the electron-hole excitation spectrum of the quasi two-dimensional Shockley surface state band that is present on the Be(0001) surface.V.M.S., J.M.P, E.V.C, and P.M.E. acknowledge partial support from the University of the Basque Country (9/UPV 00206.215-13639/2001), the Basque Unibertsitate eta Ikerketa Saila, and the Spanish Ministerio de Educación y Ciencia (MEC) (FIS 2004-06490-C03-01 and CSD2006-53). B.D. and K.P. acknowledge the National\ud
Science Foundation; L.V., L.S., and M.R. Compagnia di San Paolo; P.H. the Danish Natural Science Research Council; D.F. the Programa Ramón y Cajal and Comunidad de Madrid.Peer reviewe