108 research outputs found
Voltage controlled spin injection in a (Ga,Mn)As/(Al,Ga)As Zener diode
The spin polarization of the electron current in a
p-(Ga,Mn)As-n-(Al,Ga)As-Zener tunnel diode, which is embedded in a
light-emitting diode, has been studied theoretically. A series of
self-consistent simulations determines the charge distribution, the band
bending, and the current-voltage characteristics for the entire structure. An
empirical tight-binding model, together with the Landauer- Buttiker theory of
coherent transport has been developed to study the current spin polarization.
This dual approach allows to explain the experimentally observed high magnitude
and strong bias dependence of the current spin polarization.Comment: Submitted to Phys. Rev. B Rapid Communication
Low-loss singlemode PECVD silicon nitride photonic wire waveguides for 532-900 nm wavelength window fabricated within a CMOS pilot line
PECVD silicon nitride photonic wire waveguides have been fabricated in a CMOS pilot line. Both clad and unclad single mode wire waveguides were measured at lambda = 532, 780, and 900 nm, respectively. The dependence of loss on wire width, wavelength, and cladding is discussed in detail. Cladded multimode and singlemode waveguides show a loss well below 1 dB/cm in the 532-900 nm wavelength range. For singlemode unclad waveguides, losses < 1 dB/cm were achieved at lambda = 900 nm, whereas losses were measured in the range of 1-3 dB/cm for lambda = 780 and 532 nm, respectively
High spatial resolution nanoslit SERS for single-molecule nucleobase sensing
Solid-state nanopores promise a scalable platform for single-molecule DNA analysis. Direct, real-time identification of nucleobases in DNA strands is still limited by the sensitivity and the spatial resolution of established ionic sensing strategies. Here, we study a different but promising strategy based on optical spectroscopy. We use an optically engineered elongated nanopore structure, a plasmonic nanoslit, to locally enable single-molecule surface enhanced Raman spectroscopy (SERS). Combining SERS with nanopore fluidics facilitates both the electrokinetic capture of DNA analytes and their local identification through direct Raman spectroscopic fingerprinting of four nucleobases. By studying the stochastic fluctuation process of DNA analytes that are temporarily adsorbed inside the pores, we have observed asynchronous spectroscopic behavior of different nucleobases, both individual and incorporated in DNA strands. These results provide evidences for the single-molecule sensitivity and the sub-nanometer spatial resolution of plasmonic nanoslit SERS
Long-Read Sequencing to Unravel Complex Structural Variants of CEP78 Leading to Cone-Rod Dystrophy and Hearing Loss
Inactivating variants as well as a missense variant in the centrosomal CEP78 gene
have been identified in autosomal recessive cone-rod dystrophy with hearing loss
(CRDHL), a rare syndromic inherited retinal disease distinct from Usher syndrome.
Apart from this, a complex structural variant (SV) implicating CEP78 has been reported
in CRDHL. Here we aimed to expand the genetic architecture of typical CRDHL
by the identification of complex SVs of the CEP78 region and characterization of
their underlying mechanisms. Approaches used for the identification of the SVs are
shallow whole-genome sequencing (sWGS) combined with quantitative polymerase
chain reaction (PCR) and long-range PCR, or ExomeDepth analysis on whole-exome
sequencing (WES) data. Targeted or whole-genome nanopore long-read sequencing
(LRS) was used to delineate breakpoint junctions at the nucleotide level. For all SVs
cases, the effect of the SVs on CEP78 expression was assessed using quantitative
PCR on patient-derived RNA. Apart from two novel canonical CEP78 splice variants
and a frameshifting single-nucleotide variant (SNV), two SVs affecting CEP78 were
identified in three unrelated individuals with CRDHL: a heterozygous total gene deletion
of 235 kb and a partial gene deletion of 15 kb in a heterozygous and homozygous
state, respectively. Assessment of the molecular consequences of the SVs on patientâs
materials displayed a loss-of-function effect. Delineation and characterization of the 15-kb deletion using targeted LRS revealed the previously described complex CEP78
SV, suggestive of a recurrent genomic rearrangement. A founder haplotype was
demonstrated for the latter SV in cases of Belgian and British origin, respectively. The
novel 235-kb deletion was delineated using whole-genome LRS. Breakpoint analysis
showed microhomology and pointed to a replication-based underlying mechanism.
Moreover, data mining of bulk and single-cell human and mouse transcriptional datasets,
together with CEP78 immunostaining on human retina, linked the CEP78 expression
domain with its phenotypic manifestations. Overall, this study supports that the CEP78
locus is prone to distinct SVs and that SV analysis should be considered in a genetic
workup of CRDHL. Finally, it demonstrated the power of sWGS and both targeted
and whole-genome LRS in identifying and characterizing complex SVs in patients with
ocular diseases
Near-field interactions between metal nanoparticle surface plasmons and molecular excitons in thin-films: part I: absorption
In this and the following paper (parts I and II, respectively), we systematically study the interactions between surface plasmons of metal nanoparticles (NPs) with excitons in thin-films of organic media. In an effort to exclusively probe near-field interactions, we utilize spherical Ag NPs in a size-regime where far-field light scattering is negligibly small compared to absorption. In part I, we discuss the effect of the presence of these Ag NPs on the absorption of the embedding medium by means of experiment, numerical simulations, and analytical calculations, all shown to be in good agreement. We observe absorption enhancement in the embedding medium due to the Ag NPs with a strong dependence on the medium permittivity, the spectral position relative to the surface plasmon resonance frequency, and the thickness of the organic layer. By introducing a low index spacer layer between the NPs and the organic medium, this absorption enhancement is experimentally confirmed to be a near field effect In part II, we probe the impact of the Ag NPs on the emission of organic molecules by time-resolved and steady-state photoluminescence measurements
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
Spin dynamics in semiconductors
This article reviews the current status of spin dynamics in semiconductors
which has achieved a lot of progress in the past years due to the fast growing
field of semiconductor spintronics. The primary focus is the theoretical and
experimental developments of spin relaxation and dephasing in both spin
precession in time domain and spin diffusion and transport in spacial domain. A
fully microscopic many-body investigation on spin dynamics based on the kinetic
spin Bloch equation approach is reviewed comprehensively.Comment: a review article with 193 pages and 1103 references. To be published
in Physics Reports
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