646 research outputs found
1.55 μm direct bandgap electroluminescence from strained n-Ge quantum wells grown on Si substrates
Electroluminescence from strained n-Ge quantum well light emitting diodes grown on a silicon substrate are demonstrated at room temperature. Electroluminescence characterisation demonstrates two peaks around 1.55 μm and 1.8 μm, which correspond to recombination between the direct and indirect transitions, respectively. The emission wavelength can be tuned by around 4% through changing the current density through the device. The devices have potential applications in the fields of optical interconnects, gas sensing, and healthcare
Si/SiGe bound-to-continuum quantum cascade emitters
Si/SiGe bound-to-continuum quantum cascade emitters designed
by self-consistent 6-band k.p modeling and grown by low energy
plasma enhanced chemical vapour deposition are presented
demonstrating electroluminescence between 1.5 and 3 THz. The
electroluminescence is Stark shifted by an electric field and
demonstrates polarized emission consistent with the design.
Transmission electron microscopy and x-ray diffraction are also
presented to characterize the thick heterolayer structure
miR-SEA: miRNA Seed Extension based Aligner Pipeline for NGS Expression Level Extraction
The advent of Next Generation Sequencing (NGS) technology has enabled a new major approach for micro RNAs (miRNAs) expression profiling through the so called RNA-Sequencing (RNA-Seq).
Different tools have been developed in the last years in order to detect and quantify miRNAs, especially in pathological samples, starting from the big amount of data deriving from RNA sequencing. These tools, usually relying on general purpose alignment algorithms, are however characterized by different sensitivity and accuracy levels and in the most of the cases provide not overlapping predictions. To overcome these limitations we propose a novel pipeline for miRNAs detection and quantification in RNA-Seq sample, miRNA Seed Extension Aligner (miR-SEA), based on an experimental evidence concerning miRNAs structure. The proposed pipeline was tested on three Colorectal Cancer (CRC) RNA-Seq samples and the obtained results compared with those provided by two well-known miRNAs detection tools showing good ability in performing detection and quantification more adherent to miRNAs structure
Mid-Infrared Plasmonic Platform Based on n-Doped Ge-on-Si: Molecular Sensing with Germanium Nano-Antennas on Si
CMOS-compatible, heavily-doped semiconductor
films are very promising for applications in mid-infrared
plasmonic devices because the real part of their dielectric
function is negative and broadly tunable in this wavelength
range. In this work we investigate n-type doped germanium
epilayers grown on Si substrates. We design and realize Ge nanoantennas
on Si substrates demonstrating the presence of localized
plasmon resonances, and exploit them for molecular sensing in
the mid-infrared
Optical spin injection and spin lifetime in Ge heterostructures
We demonstrate optical orientation in Ge/SiGe quantum wells and study their
spin properties. The ultrafast electron transfer from the center of the
Brillouin zone to its edge allows us to achieve high spin-polarization
efficiencies and to resolve the spin dynamics of holes and electrons. The
circular polarization degree of the direct-gap photoluminescence exceeds the
theoretical bulk limit, yielding ~37% and ~85% for transitions with heavy and
light holes states, respectively. The spin lifetime of holes at the top of the
valence band is found to be ~0.5 ps and it is governed by transitions between
heavy and light hole states. Electrons at the bottom of the conduction band, on
the other hand, have a spin lifetime that exceeds 5 ns below 150 K. Theoretical
analysis of the electrons spin relaxation indicates that phonon-induced
intervalley scattering dictates the spin lifetime.Comment: 5 pages, 3 figure
Linear coupling of modes in 2D radially stratified astrophysical discs
We investigate mode coupling in a two dimensional compressible disc with
radial stratification and differential rotation. We employ the global radial
scaling of linear perturbations and study the linear modes in the local
shearing sheet approximation. We employ a three-mode formalism and study the
vorticity (W), entropy (S) and compressional (P) modes and their coupling
properties. The system exhibits asymmetric three-mode coupling: these include
mutual coupling of S and P-modes, S and W-modes, and asymmetric coupling
between the W and P-modes. P-mode perturbations are able to generate potential
vorticity through indirect three-mode coupling. This process indicates that
compressional perturbations can lead to the development of vortical structures
and influence the dynamics of radially stratified hydrodynamic accretion and
protoplanetary discs.Comment: 10 pages, 10 figures, MNRAS (accepted
Revealing the sub-AU asymmetries of the inner dust rim in the disk around the Herbig Ae star R CrA
Models predict that in the innermost AU of the disk around Herbig Ae/Be star,
the dust disk forms a "puffed-up" inner rim, which should result in a strongly
asymmetric brightness distribution for disks seen under intermediate
inclination. Using the VLTI/AMBER long-baseline interferometer, we obtained 24
near-infrared (H- and K-band) spectro-interferometric observations on the
Herbig Ae star R CrA. In the derived visibility function, we detect the
signatures of an extended (25 mas) and a compact component (5.8 mas), with the
compact component contributing about 2/3 of the total flux. The brightness
distribution is highly asymmetric, as indicated by the strong closure phases
(up to 40 deg) and the detected position angle dependence of the visibilities
and closure phases. To interpret these asymmetries, we employ geometric as well
as physical models, including a binary model, a skewed ring model, and a
puffed-up inner rim model with a vertical or curved rim shape. Our curved
puffed-up rim model can reasonably well reproduce the interferometric
observables and the SED simultaneously and suggests a luminosity of 29 L_sun
and the presence of relatively large (> 1.2 micron) Silicate dust grains.
Perpendicular to the disk, two bow shock-like structures appear in the
associated reflection nebula NGC 6729, suggesting that the resolved sub-AU size
disk is the driving engine of a large-scale outflow. Detecting, for the first
time, strong non-localized asymmetries in the inner regions of a Herbig Ae
disk, our study supports the existence of a puffed-up inner rim in YSO disks.Comment: 17 pages; 15 figures; Accepted by A&
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