Quantum Rings in Electromagnetic Fields

This is the author accepted manuscript. The final version is available from Springer via the DOI in this recordThis chapter is devoted to optical properties of so-called Aharonov-Bohm quantum rings (quantum rings pierced by a magnetic flux resulting in AharonovBohm oscillations of their electronic spectra) in external electromagnetic fields. It studies two problems. The first problem deals with a single-electron AharonovBohm quantum ring pierced by a magnetic flux and subjected to an in-plane (lateral) electric field. We predict magneto-oscillations of the ring electric dipole moment. These oscillations are accompanied by periodic changes in the selection rules for inter-level optical transitions in the ring allowing control of polarization properties of the associated terahertz radiation. The second problem treats a single-mode microcavity with an embedded Aharonov-Bohm quantum ring which is pierced by a magnetic flux and subjected to a lateral electric field. We show that external electric and magnetic fields provide additional means of control of the emission spectrum of the system. In particular, when the magnetic flux through the quantum ring is equal to a half-integer number of the magnetic flux quanta, a small change in the lateral electric field allows for tuning of the energy levels of the quantum ring into resonance with the microcavity mode, thus providing an efficient way to control the quantum ring-microcavity coupling strength. Emission spectra of the system are discussed for several combinations of the applied magnetic and electric fields

Clinical-grade Detection of Microsatellite Instability in Colorectal Tumors by Deep Learning

Background and Aims: Microsatellite instability (MSI) and mismatch-repair deficiency (dMMR) in colorectal tumors are used to select treatment for patients. Deep learning can detect MSI and dMMR in tumor samples on routine histology slides faster and cheaper than molecular assays. But clinical application of this technology requires high performance and multisite validation, which have not yet been performed. Methods: We collected hematoxylin and eosin-stained slides, and findings from molecular analyses for MSI and dMMR, from 8836 colorectal tumors (of all stages) included in the MSIDETECT consortium study, from Germany, the Netherlands, the United Kingdom, and the United States. Specimens with dMMR were identified by immunohistochemistry analyses of tissue microarrays for loss of MLH1, MSH2, MSH6, and/or PMS2. Specimens with MSI were identified by genetic analyses. We trained a deep-learning detector to identify samples with MSI from these slides; performance was assessed by cross-validation (n=6406 specimens) and validated in an external cohort (n=771 specimens). Prespecified endpoints were area under the receiver operating characteristic (AUROC) curve and area under the precision-recall curve (AUPRC). Results: The deep-learning detector identified specimens with dMMR or MSI with a mean AUROC curve of 0.92 (lower bound 0.91, upper bound 0.93) and an AUPRC of 0.63 (range, 0.59–0.65), or 67% specificity and 95% sensitivity, in the cross-validation development cohort. In the validation cohort, the classifier identified samples with dMMR with an AUROC curve of 0.95 (range, 0.92–0.96) without image-preprocessing and an AUROC curve of 0.96 (range, 0.93–0.98) after color normalization. Conclusions: We developed a deep-learning system that detects colorectal cancer specimens with dMMR or MSI using hematoxylin and eosin-stained slides; it detected tissues with dMMR with an AUROC of 0.96 in a large, international validation cohort. This system might be used for high-throughput, low-cost evaluation of colorectal tissue specimens

Surface wave sensors based on nanometric layers of strongly absorbing materials Citation for published version (APA): Surface wave sensors based on nanometric layers of strongly absorbing materials

Abstract: We demonstrate the excitation of guided modes in thin layers of strongly absorbing chalcogenide glasses. These modes are similar to surface plasmon polaritons in terms of resonance width and shift with changes in the permittivity of the surrounding medium. We exploit these characteristics to demonstrate a high sensitivity chalcogenide glass refractive index sensor that outperforms gold surface plasmon resonance sensors at short wavelengths in the visible. This demonstration opens a new range of possibilities for sensing using different materials

Atomic-scale structure of self-assembled In(Ga)As quantum rings in GaAs

We present an atomic-scale analysis of the indium distribution of self-assembled In(Ga)As quantum rings (QRs) which are formed from InAs quantum dots by capping with a thin layer of GaAs and subsequent annealing. We find that the size and shape of QRs as observed by cross-sectional scanning tunneling microscopy (X-STM) deviate substantially from the ring-shaped islands as observed by atomic force microscopy on the surface of uncapped QR structures. We show unambiguously that X-STM images the remaining quantum dot material whereas the AFM images the erupted quantum dot material. The remaining dot material shows an asymmetric indium-rich crater-like shape with a depression rather than an opening at the center and is responsible for the observed electronic properties of QR structures. These quantum craters have an indium concentration of about 55% and a diameter of about 20 nm which is consistent with the observed electronic radius of QR structures. © 2005 American Institute of Physics

Formation of columnar (In,Ga)As quantum dots on GaAs(100)

Columnar (In,Ga)As quantum dots (QDs) with homogeneous composition and shape in the growth direction are realized by molecular-beam epitaxy on GaAs(100) substrates. The columnar (In,Ga)As QDs are formed on InAs seed QDs by alternating deposition of thin GaAs intermediate layers and monolayers of InAs with extended growth interruptions after each layer. The height of the columnar (In,Ga)As QDs is controlled by varying the number of stacked GaAs/InAs layers. The structural and optical properties are studied by cross-sectional scanning tunneling microscopy, atomic force microscopy, and photoluminescence spectroscopy. With increase of the aspect ratio of the columnar QDs, the emission wavelength is redshifted and the linewidth is reduced

InGaAs-AlAsSb quantum cascade lasers emitting at 4.4 μm

We report the first realization of 1no53Ga0.47As/AlAs056 Sbo.44 quantum cascade lasers grown on InP substrates. Stable optical and electrical characteristics as well as good structural quality of epitaxial layers demonstrate the significant potencial of this system. ©2005 Optical Society of Americ

InGaAs-AlAsSb quantum cascade lasers emitting at 4.4 µm

We report the first realization of In0.53Ga0.47 As/AlAs0.56Sb0.44 quantum cascade lasers grown on InP substrates. Stable optical and electrical characteristics as well as good structural quality of epitaxial layers demonstrate the significant potential of this syste

Relaxation of a strained quantum well at a cleaved surface. Part II: Effect of cubic symmetry

In a previous paper [J. H. Davies, D. M. Bruls, J. W. A. M. Vugs, and P. M. Koenraad, J. Appl. Phys. 91, 4171 (2002). Part I.] we compared theory and experiment for the relaxation at a cleaved surface of a strained quantum well of InGaAs in GaAs. The measurements were taken with a scanning tunneling microscope and the analytic calculation used classical elastic theory for a linear, isotropic, homogeneous medium. Qualitative agreement was good but the theory gave only about 80% of the observed displacement. We have therefore extended the calculation to explore the effect of cubic symmetry and the orientation of the cleaved surface. The strain suppression method reduces the problem to the response of a half space to traction on its surface. We have calculated this for orthotropic symmetry, which includes the common orientations of orthorhombic, tetragonal, hexagonal, and cubic crystals. Anisotropy has no effect on the shape of the relaxed surface but the magnitude of relaxation changes. For cubic material there is no effect on the strain along the direction of growth if the cleaved surface is a {001} plane and a reduction of a few percent for a {011} plane, which is the case of experimental interest. The outward relaxation is reduced by about 20% due to cubic symmetry for a {001} plane because the shear stiffness of GaAs is higher than in the isotropic model, and is a further 10% smaller for a {011} plane. Thus the results for cubic symmetry lie further from the measurements than those calculated for isotropic material. Interfacial forces may contribute to this discrepancy but we suggest that nonlinear elasticity is probably responsibl

(In,Ga)As sidewall quantum wires on shallow-patterned InP (311) A

(In,Ga)As sidewall quantum wires (QWires) are realized by chemical beam epitaxy along [01-1] mesa stripes on shallow-patterned InP (311)A substrates. The QWires exhibit strong lateral carrier confinement due to larger thickness and In composition compared to the adjacent quantum wells, as determined by cross-sectional scanning-tunneling microscopy and microphotoluminescence (micro-PL) spectroscopy. The PL of the (In,Ga)As QWires with InP and quaternary (Ga,In)(As,P) barriers reveals narrow linewidth, high efficiency, and large lateral carrier confinement energies of 60–70 meV. The QWires are stacked in growth direction with identical PL peak emission energy. The PL emission energy is not only controlled by the (In,Ga)As layer thickness but also by the patterned mesa height. Stacked (In,Ga)As QWires with quaternary barriers exhibit room temperature PL emission at 1.55 µm in the technologically important wavelength region for telecommunication applications. ©2005 American Institute of Physic