466 research outputs found
Films of Ni–7 at% V, Pd, Pt and Ta–Si–N as diffusion barriers for copper on Bi2Te3
Films of Ni–7 at% V, Pt, Pd, and Ta40Si14N46, each approximately 100 nm thick, were magnetron-deposited and interposed between about 250 nm thick copper overlayers and Bi2Te3 single-crystalline substrates. The samples were then annealed in vacuum up to 350 degrees C. The performance of the metal and the tantalum-silicon-nitride films as diffusion barriers for in-diffusion of Cu and out-diffusion of Bi and Te was evaluated by 2.0 MeV 4He backscattering spectrometry and x-ray diffraction. The Ni–7 at% V, Pd and Pt films all fail to prevent interdiffusion of Cu and Bi2Te3 after a few hours of annealing at 200 degrees C.
However, the Ta40Si14N46 barrier preserves the integrity of the contact after 250 degrees C for 50 h and 350 degrees C for 1 h anneals. These results confirm the superior characteristics of the metal-silicon-nitride films as diffusion barriers
Synthesis and characterization of attosecond light vortices in the extreme ultraviolet
Infrared and visible light beams carrying orbital angular momentum (OAM) are
currently thoroughly studied for their extremely broad applicative prospects,
among which are quantum information, micromachining and diagnostic tools. Here
we extend these prospects, presenting a comprehensive study for the synthesis
and full characterization of optical vortices carrying OAM in the extreme
ultraviolet (XUV) domain. We confirm the upconversion rules of a femtosecond
infrared helically phased beam into its high-order harmonics, showing that each
harmonic order carries the total number of OAM units absorbed in the process up
to very high orders (57). This allows us to synthesize and characterize
helically shaped XUV trains of attosecond pulses. To demonstrate a typical use
of these new XUV light beams, we show our ability to generate and control,
through photoionization, attosecond electron beams carrying OAM. These
breakthroughs pave the route for the study of a series of fundamental phenomena
and the development of new ultrafast diagnosis tools using either photonic or
electronic vortices
Laboratory validation of the dual-zone phase mask coronagraph in broadband light at the high-contrast imaging THD-testbed
Specific high contrast imaging instruments are mandatory to characterize
circumstellar disks and exoplanets around nearby stars. Coronagraphs are
commonly used in these facilities to reject the diffracted light of an observed
star and enable the direct imaging and spectroscopy of its circumstellar
environment. One important property of the coronagraph is to be able to work in
broadband light.
Among several proposed coronagraphs, the dual-zone phase mask coronagraph is
a promising solution for starlight rejection in broadband light. In this paper,
we perform the first validation of this concept in laboratory.
First, we recall the principle of the dual-zone phase mask coronagraph. Then,
we describe the high-contrast imaging THD testbed, the manufacturing of the
components and the quality-control procedures. Finally, we study the
sensitivity of our coronagraph to low-order aberrations (inner working angle
and defocus) and estimate its contrast performance. Our experimental broadband
light results are compared with numerical simulations to check agreement with
the performance predictions.
With the manufactured prototype and using a dark hole technique based on the
self-coherent camera, we obtain contrast levels down to between 5
and 17 in monochromatic light (640 nm). We also reach contrast
levels of between 7 and 17 in broadband
( nm, nm and %), which demonstrates the excellent chromatic performance of the dual-zone
phase mask coronagraph.
The performance reached by the dual-zone phase mask coronagraph is promising
for future high-contrast imaging instruments that aim at detecting and
spectrally characterizing old or light gaseous planets.Comment: 9 pages, 16 figure
Probing single-photon ionization on the attosecond time scale
We study photoionization of argon atoms excited by attosecond pulses using an
interferometric measurement technique. We measure the difference in time delays
between electrons emitted from the and from the shell, at
different excitation energies ranging from 32 to 42 eV. The determination of
single photoemission time delays requires to take into account the measurement
process, involving the interaction with a probing infrared field. This
contribution can be estimated using an universal formula and is found to
account for a substantial fraction of the measured delay.Comment: 4 pages, 4 figures, under consideratio
Imaging orbitals with attosecond and Ångström resolutions: toward attochemistry? Imaging orbitals with attosecond and Ångström resolutions: toward attochemistry?
International audienceThe recently developed attosecond light sources make the investigation of ultrafast processes in matter possible with unprecedented time resolution. It has been proposed that the very mechanism underlying the attosecond emission allows the imaging of valence orbitals with Ångström space resolution. This controversial idea together with the possibility of combining attosecond and Ångström resolutions in the same measurements has become a hot topic in strong-field science. Indeed , this could provide a new way to image the evolution of the molecular electron cloud during , e. g. a chemical reaction in ' real time '. Here we review both experimental and theoretical challenges raised by the implementation of these prospects. In particular , we show how the valence orbital structure is encoded in the spectral phase of the recombination dipole moment calculated for Coulomb scattering states , which allows a tomographic reconstruction of the orbital using first-order corrections to the plane-wave approach. The possibility of disentangling multi-channel contributions to the attosecond emission is discussed as well as the necessary compromise between the temporal and spatial resolutions. (Some figures may appear in colour only in the online journal
Testing of Milliwatt Power Source Components
A milliwatt power source (MPS) has been developed to satisfy the requirements of several potential solar system exploration missions. The MPS is a small power source consisting of three major components: a space qualified heat source (RHU), a thermopile (thermoelectric converter or TEC) and a container to direct the RHU heat to the TEC. Thermopiles from Hi-Z Technology, Inc. of San Diego and the Institute of Thermoelectricity of Chernivtsi Ukraine suitable for the MPS were tested and shown to perform as expected, producing 40 mW of power with a temperature difference of about 170°C. Such thermopiles were successfully life tested for up to a year. A MPS container designed and built by Swales Aerospace was tested with both a TEC simulator and actual TEC. The Swales unit, tested under dynamic vacuum, provided less temperature difference than anticipated, such that the TEC produced 20 mW of power with heat input equivalent to a RHU
Production of positronium chloride: A study of the charge exchange reaction between Ps and Cl
We present cross sections for the formation of positronium chloride (PsCl) in
its ground state from the charge exchange between positronium (Ps) and chloride
(Cl) in the range of 10 meV - 100 eV Ps energy. We have used theoretical
models based on the first Born approximation in its three-body formulation. We
simulated the collisions between Ps and Cl using ab-initio methods at both
mean-field and correlated levels extrapolated to the complete basis set limit.
We have investigated Ps excited states up to . The results suggest that
the channel Ps() is of particular interest for the production of PsCl in
the ground state, and shows that an accurate treatment of the electronic
correlation leads to a significant change in the global shape of the PsCl
production cross section with respect to the mean-field level.Comment: 13 Pages, 7 Figures, 3 Table
Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. II. Concept validation with ZELDA on VLT/SPHERE
Warm or massive gas giant planets, brown dwarfs, and debris disks around
nearby stars are now routinely observed by dedicated high-contrast imaging
instruments on large, ground-based observatories. These facilities include
extreme adaptive optics (ExAO) and state-of-the-art coronagraphy to achieve
unprecedented sensitivities for exoplanet detection and spectral
characterization. However, differential aberrations between the ExAO sensing
path and the science path represent a critical limitation for the detection of
giant planets with a contrast lower than a few at very small
separations (<0.3\as) from their host star. In our previous work, we proposed a
wavefront sensor based on Zernike phase contrast methods to circumvent this
issue and measure these quasi-static aberrations at a nanometric level. We
present the design, manufacturing and testing of ZELDA, a prototype that was
installed on VLT/SPHERE during its reintegration in Chile. Using the internal
light source of the instrument, we performed measurements in the presence of
Zernike or Fourier modes introduced with the deformable mirror. Our
experimental and simulation results are consistent, confirming the ability of
our sensor to measure small aberrations (<50 nm rms) with nanometric accuracy.
We then corrected the long-lived non-common path aberrations in SPHERE based on
ZELDA measurements. We estimated a contrast gain of 10 in the coronagraphic
image at 0.2\as, reaching the raw contrast limit set by the coronagraph in the
instrument. The simplicity of the design and its phase reconstruction algorithm
makes ZELDA an excellent candidate for the on-line measurements of quasi-static
aberrations during the observations. The implementation of a ZELDA-based
sensing path on the current and future facilities (ELTs, future space missions)
could ease the observation of the cold gaseous or massive rocky planets around
nearby stars.Comment: 13 pages, 12 figures, A&A accepted on June 3rd, 2016. v2 after
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