352 research outputs found
Multiple wavelengths reflectance microscopy to study the multi-physical behavior of MEMS
International audienceIn order to characterize surface chemomechanical driving micro-electro-mechanical systems (MEMS) behavior, we propose herein a method to simultaneously obtain a full kinematic field describing the surface displacement and a map of its chemical modification from optical measurements. Using a microscope, reflected intensity fields are recorded for two different illumination wavelengths. Decoupling the wavelength-independent and -dependent contributions to the measured relative intensity changes then yields the sought fields. This method is applied to the investigation of the electro-elastic coupling, providing images of both the local surface electrical charge density and the device deformation field
Radiative quantum efficiency in an InAs/AlSb intersubband transition
The quantum efficiency of an electroluminescent intersubband emitter based on
InAs/AlSb has been measured as a function of the magnetic field up to 20T. Two
series of oscillations periodic in 1/B are observed, corresponding to the
elastic and inelastic scattering of electrons of the upper state of the
radiative transitions. Experimental results are accurately reproduced by a
calculation of the excited state lifetime as a function of the applied magnetic
field. The interpretation of these data gives an exact measure of the relative
weight of the scattering mechanisms and allows the extraction of material
parameters such as the energy dependent electron effective mass and the optical
phonon energy.Comment: 4 pages, 5 figure
The effect of inelastic processes on tunneling
We study an electron that interacts with phonons or other linear or nonlinear
excitations as it resonantly tunnels. The method we use is based on mapping a
many-body problem in a large variational space exactly onto a one-body problem.
The method is conceptually simpler than previous Green's function approaches,
and allows the essentially exact numerical solution of much more general
problems. We solve tunneling problems with transverse channels, multiple sites
coupled to phonons, and multiple phonon degrees of freedom and excitations.Comment: 12 pages, REVTex, 4 figures in compressed tar .ps forma
Demonstration and frequency noise characterization of a 17 m quantum cascade laser
We describe the properties of a continuous-wave room-temperature quantum
cascade laser operating at the long wavelength of 17 m. Long wavelength
mid-infrared quantum cascade lasers offer new opportunities for chemical
detection, vibrational spectroscopy and metrological measurements using
molecular species. In particular, probing low energy vibrational transitions
would be beneficial to the spectroscopy of large and complex molecules,
reducing intramolecular vibrational energy redistribution which acts as a
decoherence channel. By performing linear absorption spectroscopy of the v2
fundamental vibrational mode of N2O molecules, we have demonstrated the
spectral range and spectroscopic potential of this laser, and characterized its
free-running frequency noise properties. Finally, we also discuss the potential
application of this specific laser in an experiment to test fundamental physics
with ultra-cold molecules
Singularities and Topology of Meromorphic Functions
We present several aspects of the "topology of meromorphic functions", which
we conceive as a general theory which includes the topology of holomorphic
functions, the topology of pencils on quasi-projective spaces and the topology
of polynomial functions.Comment: 21 pages, 1 figur
Chiral tunneling and the Klein paradox in graphene
The so-called Klein paradox - unimpeded penetration of relativistic particles
through high and wide potential barriers - is one of the most exotic and
counterintuitive consequences of quantum electrodynamics (QED). The phenomenon
is discussed in many contexts in particle, nuclear and astro- physics but
direct tests of the Klein paradox using elementary particles have so far proved
impossible. Here we show that the effect can be tested in a conceptually simple
condensed-matter experiment by using electrostatic barriers in single- and
bi-layer graphene. Due to the chiral nature of their quasiparticles, quantum
tunneling in these materials becomes highly anisotropic, qualitatively
different from the case of normal, nonrelativistic electrons. Massless Dirac
fermions in graphene allow a close realization of Klein's gedanken experiment
whereas massive chiral fermions in bilayer graphene offer an interesting
complementary system that elucidates the basic physics involved.Comment: 15 pages, 4 figure
Acoustic Phonon-Assisted Resonant Tunneling via Single Impurities
We perform the investigations of the resonant tunneling via impurities
embedded in the AlAs barrier of a single GaAs/AlGaAs heterostructure. In the
characteristics measured at 30mK, the contribution of individual donors
is resolved and the fingerprints of phonon assistance in the tunneling process
are seen. The latter is confirmed by detailed analysis of the tunneling rates
and the modeling of the resonant tunneling contribution to the current.
Moreover, fluctuations of the local structure of the DOS (LDOS) and Fermi edge
singularities are observed.Comment: accepted in Phys. Rev.
OJEDA, FERNANDO [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201
HERNÁNDEZ, ANTONIA E HIJA [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201
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