10,129 research outputs found
Detecting swift heavy ion irradiation effects with graphene
In this paper we show how single layer graphene can be utilized to study
swift heavy ion (SHI) modifications on various substrates. The samples were
prepared by mechanical exfoliation of bulk graphite onto SrTiO, NaCl and
Si(111), respectively. SHI irradiations were performed under glancing angles of
incidence and the samples were analysed by means of atomic force microscopy in
ambient conditions. We show that graphene can be used to check whether the
irradiation was successful or not, to determine the nominal ion fluence and to
locally mark SHI impacts. In case of samples prepared in situ, graphene is
shown to be able to catch material which would otherwise escape from the
surface.Comment: 10 pages, 3 figure
Damage in graphene due to electronic excitation induced by highly charged ions
Graphene is expected to be rather insensitive to ionizing particle radiation.
We demonstrate that single layers of exfoliated graphene sustain significant
damage from irradiation with slow highly charged ions. We have investigated the
ion induced changes of graphene after irradiation with highly charged ions of
different charge states (q = 28-42) and kinetic energies E_kin = 150-450 keV.
Atomic force microscopy images reveal that the ion induced defects are not
topographic in nature but are related to a significant change in friction. To
create these defects, a minimum charge state is needed. In addition to this
threshold behaviour, the required minimum charge state as well as the defect
diameter show a strong dependency on the kinetic energy of the projectiles.
From the linear dependency of the defect diameter on the projectile velocity we
infer that electronic excitations triggered by the incoming ion in the
above-surface phase play a dominant role for this unexpected defect creation in
graphene
Zamke za nositelje naboja u stupnjevanim InGaAS fotodiodama s velikim sadržajem indija
Carrier traps in In0.82Ga0.18As, introduced during manufacturing of photodiodes by vapour phase epitaxy (VPE), have been studied by electrical measurements. Two groups of localized energy levels associated with traps were found in photodiodes annealed at higher temperature after fabrication: the first, at Ec- 0.14 eV, and the second located deeper, close to the middle of the energy gap. Electrically activated dislocations by association with some impurities are responsible for the occurrence of the deeper levels.Električnim mjerenjima istražena su svojstva zamki za nositelje naboja koje nastaju pri izradi fotodioda iz In0.82Ga0.18As metodom epitaksijalnog rasta iz parne faze (VPE). U fotodiodama, koje su naknadno napuštane nakon izrade na povišenoj temperaturi, zapažene su dvije skupine lokaliziranih nivoa zamki: jedan plići na Ec − 0, 14 eV i druge dublje nešto ispod sredine zabranjenog energijskog pojasa. Ustanovljeno je da su električki aktivirane dislokacije primjesama odgovorne za pojavu dubljih nivoa
Conditional generation of sub-Poissonian light from two-mode squeezed vacuum via balanced homodyne detection on idler mode
A simple scheme for conditional generation of nonclassical light with
sub-Poissonian photon-number statistics is proposed. The method utilizes
entanglement of signal and idler modes in two-mode squeezed vacuum state
generated in optical parametric amplifier. A quadrature component of the idler
mode is measured in balanced homodyne detector and only those experimental runs
where the absolute value of the measured quadrature is higher than certain
threshold are accepted. If the threshold is large enough then the conditional
output state of signal mode exhibits reduction of photon-number fluctuations
below the coherent-state level.Comment: 7 pages, 6 figures, REVTe
Optimized Dynamical Decoupling for Time Dependent Hamiltonians
The validity of optimized dynamical decoupling (DD) is extended to
analytically time dependent Hamiltonians. As long as an expansion in time is
possible the time dependence of the initial Hamiltonian does not affect the
efficiency of optimized dynamical decoupling (UDD, Uhrig DD). This extension
provides the analytic basis for (i) applying UDD to effective Hamiltonians in
time dependent reference frames, for instance in the interaction picture of
fast modes and for (ii) its application in hierarchical
DD schemes with pulses about two perpendicular axes in spin space. to
suppress general decoherence, i.e., longitudinal relaxation and dephasing.Comment: 5 pages, no figure
Structural phase transitions in epitaxial perovskite films
Three different film systems have been systematically investigated to
understand the effects of strain and substrate constraint on the phase
transitions of perovskite films. In SrTiO films, the phase transition
temperature T was determined by monitoring the superlattice peaks
associated with rotations of TiO octahedra. It is found that T depends
on both SrTiO film thickness and SrRuO buffer layer thickness. However,
lattice parameter measurements showed no sign of the phase transitions,
indicating that the tetragonality of the SrTiO unit cells was no longer a
good order parameter. This signals a change in the nature of this phase
transition, the internal degree of freedom is decoupled from the external
degree of freedom. The phase transitions occur even without lattice relaxation
through domain formation. In NdNiO thin films, it is found that the
in-plane lattice parameters were clamped by the substrate, while out-of-plane
lattice constant varied to accommodate the volume change across the phase
transition. This shows that substrate constraint is an important parameter for
epitaxial film systems, and is responsible for the suppression of external
structural change in SrTiO and NdNiO films. However, in SrRuO films
we observed domain formation at elevated temperature through x-ray reciprocal
space mapping. This indicated that internal strain energy within films also
played an important role, and may dominate in some film systems. The final
strain states within epitaxial films were the result of competition between
multiple mechanisms and may not be described by a single parameter.Comment: REVTeX4, 14 figure
Data taking strategy for the phase study in
The study of the relative phase between strong and electromagnetic amplitudes
is of great importance for understanding the dynamics of charmonium decays. The
information of the phase can be obtained model-independently by fitting the
scan data of some special decay channels, one of which is . To find out the optimal data taking strategy for a scan experiment
in the measurement of the phase in , the
minimization process is analyzed from a theoretical point of view. The result
indicates that for one parameter fit, only one data taking point in the
vicinity of a resonance peak is sufficient to acquire the optimal precision.
Numerical results are obtained by fitting simulated scan data. Besides the
results related to the relative phase between strong and electromagnetic
amplitudes, the method is extended to analyze the fits of other resonant
parameters, such as the mass and the total decay width of .Comment: 13 pages, 7 figure
Quantum recoil effects in finite-time disentanglement of two distinguishable atoms
Starting from the requirement of distinguishability of two atoms by their
positions, it is shown that photon recoil has a strong influence on finite-time
disentanglement and in some cases prevents its appearance. At near-field inter
atomic distances well localized atoms, with maximally one atom being initially
excited, may suffer disentanglement at a single finite time or even at a series
of equidistant finite times, depending on their mean inter atomic distance and
their initial electronic preparation.Comment: 13 pages, 1 figure, submitted to Physical Review on august 2
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