6 research outputs found
Raman shifts in MBEâgrown SixGe1âââxâââySny alloys with large Si content
We examine the Raman shift in siliconâgermaniumâtin alloys with high silicon content grown on a germanium virtual substrate by molecular beam epitaxy. The Raman shifts of the three most prominent modes, SiâSi, SiâGe, and GeâGe, are measured and compared with results in previous literature. We analyze and fit the dependence of the three modes on the composition and strain of the semiconductor alloys. We also demonstrate the calculation of the composition and strain of SixGe1âââxâââySny from the Raman shifts alone, based on the fitted relationships. Our analysis extends previous results to samples lattice matched on Ge and with higher Si content than in prior comprehensive Raman analyses, thus making Raman measurements as a local, fast, and nondestructive characterization technique accessible for a wider compositional range of these ternary alloys for silicon-based photonic and microelectronic devices.Deutsche Forschungsgemeinschaft
http://dx.doi.org/10.13039/501100001659Peer Reviewe
Stark verbesserte Empfindlichkeit von CMOS-kompatiblen plasmonischen Titannitrid-Nanoloch-Arrays fĂŒr die Brechungsindex-Messungen unter nicht-senkrechtem Lichteinfall
Titanium nitride (TiN) is a complementary metal-oxide-semiconductor (CMOS) compatible material with large potential for the fabrication of plasmonic structures suited for device integration. However, the comparatively large optical losses can be detrimental for application. This work reports a CMOS compatible TiN nanohole array (NHA) on top of a multilayer stack for potential use in integrated refractive index sensing with high sensitivities at wavelengths between 800 and 1500â
nm. The stack, consisting of the TiN NHA on a silicon dioxide (SiO2) layer with Si as substrate (TiN NHA/SiO2/Si), is prepared using an industrial CMOS compatible process. The TiN NHA/SiO2/Si shows Fano resonances in reflectance spectra under oblique excitation, which are well reproduced by simulation using both finite difference time domain (FDTD) and rigorous coupled-wave analysis (RCWA) methods. The sensitivities derived from spectroscopic characterizations increase with the increasing incident angle and match well with the simulated sensitivities. Our systematic simulation-based investigation of the sensitivity of the TiN NHA/SiO2/Si stack under varied conditions reveals that very large sensitivities up to 2305â
nm per refractive index unit (nm RIUâ1) are predicted when the refractive index of superstrate is similar to that of the SiO2 layer. We analyze in detail how the interplay between plasmonic and photonic resonances such as surface plasmon polaritons (SPPs), localized surface plasmon resonances (LSPRs), Rayleigh Anomalies (RAs), and photonic microcavity modes (Fabry-PĂ©rot resonances) contributes to this result. This work not only reveals the tunability of TiN nanostructures for plasmonic applications but also paves the way to explore efficient devices for sensing in broad conditions.Titannitrid (TiN) ist ein CMOS-kompatibles Material mit groĂem Potenzial fĂŒr die Herstellung plasmonischer Strukturen, die sich fĂŒr die Bauelementintegration eignen. Die vergleichsweise groĂen optischen Verluste können sich jedoch nachteilig auf die Anwendung auswirken. In dieser Arbeit wird ein CMOS-kompatibles TiN-Nanoloch-Array (NHA) auf einem Mehrschichtstapel vorgestellt, das fĂŒr die integrierte Brechungsindexmessung mit hoher Empfindlichkeit bei WellenlĂ€ngen zwischen 800 und 1500 nm eingesetzt werden kann. Der Stapel, bestehend aus dem TiN NHA auf einer Siliziumdioxid (SiO2)-Schicht mit Si als Substrat (TiN NHA/SiO2/Si), wurde in einem industriellen CMOS-kompatiblen Prozess hergestellt. Das TiN NHA/SiO2/Si zeigt Fano-Resonanzen in den Reflexionsspektren bei schrĂ€gem Einfallswinkel, die durch Simulationen sowohl mit Finite-Differenzen-Zeitbereichsmethoden (FDTD) als auch Rigorous Coupled Wave Analysis (RCWA) gut reproduziert werden. Die aus den spektroskopischen Charakterisierungen abgeleiteten Empfindlichkeiten nehmen mit zunehmendem Einfallswinkel zu und stimmen gut mit den simulierten Empfindlichkeiten ĂŒberein. Unsere systematische simulationsbasierte Untersuchung der Empfindlichkeit des TiN NHA/SiO2/Si-Stapels unter verschiedenen Bedingungen zeigt, dass sehr groĂe Empfindlichkeiten bis zu 2305 nm RIU-1 vorhergesagt werden, wenn der Brechungsindex des Dielektrikums oberhalb des NHAs Ă€hnlich dem der SiO2-Schicht ist. Wir analysieren im Detail, wie das Zusammenspiel zwischen plasmonischen und photonischen Resonanzen wie OberflĂ€chenplasmonpolaritonen (SPPs), lokalisierten OberflĂ€chenplasmonenresonanzen (LSPRs), Rayleigh-Anomalien (RAs) und photonischen MikrokavitĂ€tsmoden (Fabry-PĂ©rot-Resonanzen) zu diesem Ergebnis beitrĂ€gt. Diese Arbeit zeigt nicht nur die Abstimmbarkeit von TiN-Nanostrukturen fĂŒr plasmonische Anwendungen, sondern ebnet auch den Weg fĂŒr die Erforschung effizienter GerĂ€te fĂŒr die Erkennung unter verschiedensten Bedingungen
Strong Optical Coupling of Lattice Resonances in a Top-down Fabricated Hybrid MetalâDielectric Al/Si/Ge Metasurface
Optical metasurfaces
enable the manipulation of the lightâmatter
interaction in ultrathin layers. Compared with their metal or dielectric
counterparts, hybrid metasurfaces resulting from the combination of
dielectric and metallic nanostructures can offer increased possibilities
for interactions between modes present in the system. Here, we investigate
the interaction between lattice resonances in a hybrid metalâdielectric
metasurface obtained from a single-step nanofabrication process. Finite-difference
time domain simulations show the avoided crossing of the modes appearing
in the wavelength-dependent absorptance inside the Ge upon variations
in a selected geometry parameter as evidence for strong optical coupling.
We find good agreement between the measured and simulated absorptance
and reflectance spectra. Our metasurface design can be easily incorporated
into a top-down optoelectronic device fabrication process with possible
applications ranging from on-chip spectroscopy to sensing
Raman shifts in MBEâgrown Si x Ge 1 â x â y Sn y alloys with large Si content
We examine the Raman shift in siliconâgermaniumâtin alloys with high silicon content grown on a germanium virtual substrate by molecular beam epitaxy. The Raman shifts of the three most prominent modes, SiâSi, SiâGe, and GeâGe, are measured and compared with results in previous literature. We analyze and fit the dependence of the three modes on the composition and strain of the semiconductor alloys. We also demonstrate the calculation of the composition and strain of SixGe1âââxâââySny from the Raman shifts alone, based on the fitted relationships. Our analysis extends previous results to samples lattice matched on Ge and with higher Si content than in prior comprehensive Raman analyses, thus making Raman measurements as a local, fast, and nondestructive characterization technique accessible for a wider compositional range of these ternary alloys for silicon-based photonic and microelectronic devices.Deutsche Forschungsgemeinschaft
http://dx.doi.org/10.13039/501100001659Peer Reviewe
Mutations in the SPG7 gene cause chronic progressive external ophthalmoplegia through disordered mitochondrial DNA maintenance
Despite being a canonical presenting feature of mitochondrial disease, the genetic basis of progressive external ophthalmoplegia remains unknown in a large proportion of patients. Here we show that mutations in SPG7 are a novel cause of progressive external ophthalmoplegia associated with multiple mitochondrial DNA deletions. After excluding known causes, whole exome sequencing, targeted Sanger sequencing and multiplex ligation-dependent probe amplification analysis were used to study 68 adult patients with progressive external ophthalmoplegia either with or without multiple mitochondrial DNA deletions in skeletal muscle. Nine patients (eight probands) were found to carry compound heterozygous SPG7 mutations, including three novel mutations: two missense mutations c.2221G>A; p.(Glu741Lys), c.2224G>A; p.(Asp742Asn), a truncating mutation c.861dupT; p.Asn288*, and seven previously reported mutations. We identified a further six patients with single heterozygous mutations in SPG7, including two further novel mutations: c.184-3C>T (predicted to remove a splice site before exon 2) and c.1067C>T; p.(Thr356Met). The clinical phenotype typically developed in mid-adult life with either progressive external ophthalmoplegia/ptosis and spastic ataxia, or a progressive ataxic disorder. Dysphagia and proximal myopathy were common, but urinary symptoms were rare, despite the spasticity. Functional studies included transcript analysis, proteomics, mitochondrial network analysis, single fibre mitochondrial DNA analysis and deep re-sequencing of mitochondrial DNA. SPG7 mutations caused increased mitochondrial biogenesis in patient muscle, and mitochondrial fusion in patient fibroblasts associated with the clonal expansion of mitochondrial DNA mutations. In conclusion, the SPG7 gene should be screened in patients in whom a disorder of mitochondrial DNA maintenance is suspected when spastic ataxia is prominent. The complex neurological phenotype is likely a result of the clonal expansion of secondary mitochondrial DNA mutations modulating the phenotype, driven by compensatory mitochondrial biogenesis