Controlled tuning of whispering gallery modes of GaN/InGaN microdisk cavities

Controlled tuning of the whispering gallery modes of GaN/InGaN {\mu}-disk cavities is demonstrated. The whispering gallery mode (WGM) tuning is achieved at room temperature by immersing the {\mu}-disks in water and irradiating with ultraviolet (UV) laser. The tuning rate can be controlled by varying the laser excitation power, with a nanometer precision accessible at low excitation power (~ several {\mu}W). The selective oxidation mechanism is proposed to explain the results and supported by theoretical analysis. The tuning of WGMs in GaN/InGaN {\mu}-disk cavities may have important implication in cavity quantum electrodynamics and the development of efficient light emitting devices

Linking archaeology and paleoenvironment: Mid-Holocene occupational sequences in the Varamin Plain (Iran)

Early human habitation of the arid to semiarid Central Iranian Plateau was strongly connected to the availability of water and associated natural hazards, such as flooding and drought events. In this geoarchaeological study, we focus on the occupation at the prehistoric site of Ajor Pazi within the formerly active fluvial environment of the Varamin Plain. Through radiocarbon and luminescence-dated sediment cross-sections, we apply multivariate statistics to sedimentological characteristics of bulk samples collected during a rescue excavation in 2018. Based on facies interpretations, we differentiate depositional processes and present their implications for the environs of Ajor Pazi. Our results show evidence of settlement activities between 6.4 and 5.6 ka cal B.P. (4.4–3.6 ka cal. B.C.E.). Phases of reduced geomorphodynamics can be distinguished when soil-forming processes take place. Our findings provide insights into the hitherto scarcely explored Transitional Chalcolithic II period during which the site of Ajor Pazi emerged and began to shape its environs

Fabrication of Thin, Luminescent, Single-crystal Diamond Membranes

The formation of single-crystal diamond membranes is an important prerequisite for the fabrication of high-quality optical cavities in this material. Diamond membranes fabricated using lift-off processes involving the creation of a damaged layer through ion implantation often suffer from residual ion damage, which severely limits their usefulness for photonic structures. The current work demonstrates that strategic etch removal of the most highly defective material yields thin, single-crystal diamond membranes with strong photoluminescence and a Raman signature approaching that of single-crystal bulk diamond. These optically-active membranes can form the starting point for fabrication of high-quality optical resonators.Comment: To appear in AP

Optical and microstructural studies of atomically flat ultrathin In-rich InGaN/GaN multiple quantum wells

Optical and microstructural properties of atomically flat ultrathin In-rich (UTIR) InGaN/GaN multiple quantum well were investigated by means of photoluminescence (PL), time-resolved PL (TRPL), and cathodoluminescence (CL) experiments. The sample exhibits efficient trapping of the photoexcited carriers into quantum wells (QWs) and the effect of internal electric field in the QWs was found negligible by excitation power-dependent PL and TRPL. These phenomena were attributed to the nature of UTIR InGaN QWs, indicating the potential of this system for application in optoelectronic devices. Variation of TRPL lifetime across the PL band and spatially resolved monochromatic CL mapping images strongly suggest that there is micrometer-scale inhomogeneity in effective band gap in UTIR InGaN/GaN QWs, which is originated from two types of localized areas.open141

Coupling of silicon-vacancy centers to a single crystal diamond cavity

Optical coupling of an ensemble of silicon-vacancy (SiV) centers to single-crystal diamond microdisk cavities is demonstrated. The cavities are fabricated from a single-crystal diamond membrane generated by ion implantation and, electrochemical liftoff followed by homo-epitaxial overgrowth. Whispering gallery modes which spectrally overlap with the zero-phonon line (ZPL) of the SiV centers and exhibit quality factors ~2200 are measured. Lifetime reduction from 1.8 ns to 1.48 ns is observed from SiV centers in the cavity compared to those in the membrane outside the cavity. These results are pivotal in developing diamond integrated photonics networks

Single-cell scattering and auto-fluorescence-based fast antibiotic susceptibility testing for gram-negative and gram-positive bacteria

In this study, we assess the scattering of light and auto-fluorescence from single bacterial cells to address the challenge of fast (<2 h), label-free phenotypic antimicrobial susceptibility testing (AST). Label-free flow cytometry is used for monitoring both the respiration-related auto-fluorescence in two different fluorescence channels corresponding to FAD and NADH, and the morphological and structural information contained in the light scattered by individual bacteria during incubation with or without antibiotic. Large multi-parameter data are analyzed using dimensionality reduction methods, based either on a combination of 2D binning and Principal Component Analysis, or with a one-class Support Vector Machine approach, with the objective to predict the Susceptible or Resistant phenotype of the strain. For the first time, both Escherichia coli (Gram-negative) and Staphylococcus epidermidis (Gram-positive) isolates were tested with a label-free approach, and, in the presence of two groups of bactericidal antibiotic molecules, aminoglycosides and beta-lactams. Our results support the feasibility of label-free AST in less than 2 h and suggest that single cell auto-fluorescence adds value to the Susceptible/Resistant phenotyping over single-cell scattering alone, in particular for the mecA+ Staphylococcus (i.e., resistant) strains treated with oxacillin

Etude optique de boîtes quantiques uniques non polaires de GaN/AlN

We studied by optical spectroscopy the electronic properties of GaN/AlN quantum dots (QDs) grown by molecular beam epitaxy along the non-polar direction [11-20] (a axis). In this orientation a strong reduction of the internal electric field effects present in the [0001] axis (c axis) heterostructures is expected. This could be experimentally verified through time resolved and time integrated photoluminescence (PL) experiments performed on ensembles of dots.By making a UV dedicated microPL setup we could isolate the first a-plane GaN single QDs spectra. Local charge effects responsible for PL line broadening (spectral diffusion) could be displayed and partly controlled by a vertically applied electric field.The temperature dependence of the single quantum dot lines allowed us to study the coupling between the confined exciton and the acoustic phonons. The modeling of this mechanism so as the decay time values indicate that the lateral localization of the exciton is stronger than that imposed by the dot.Nous avons étudié par spectroscopie optique les propriétés électroniques de boîtes quantiques (BQs) de GaN/AlN crûes en épitaxie par jets moléculaires selon la direction non-polaire [11-20] (axe a). Dans cette orientation on attend une forte réduction des effets du champ électrique interne existant dans les hétérostructures d'axe [0001] (axe c), ce que nous avons vérifié expérimentalement par des expériences de photoluminescence (PL) résolue et intégrée en temps d'un ensemble de boîtes.La réalisation d'un montage de microPL optimisé pour l'UV nous a permis d'isoler les premiers spectres de BQs uniques de GaN plan a. Des effets de charges locales responsables de l'élargissement des raies de PL (diffusion spectrale) ont pu être mises en évidence et partiellement contrôlés par l'application d'un champ électrique vertical.La dépendance en température des raies de BQs uniques nous a permis d'étudier le couplage de l'exciton confiné avec les phonons acoustiques. La modélisation de ce mécanisme ainsi que les valeurs des temps de déclin indiquent que la localisation latérale de l'exciton est plus forte que celle imposée par la boîte

Etude optique de boîtes quantiques uniques non polaires de GaN/AlN

We studied by optical spectroscopy the electronic properties of GaN/AlN quantum dots (QDs) grown by molecular beam epitaxy along the non-polar direction [11-20] (a axis). In this orientation a strong reduction of the internal electric field effects present in the [0001] axis (c axis) heterostructures is expected. This could be experimentally verified through time resolved and time integrated photoluminescence (PL) experiments performed on ensembles of dots.By making a UV dedicated microPL setup we could isolate the first a-plane GaN single QDs spectra. Local charge effects responsible for PL line broadening (spectral diffusion) could be displayed and partly controlled by a vertically applied electric field.The temperature dependence of the single quantum dot lines allowed us to study the coupling between the confined exciton and the acoustic phonons. The modeling of this mechanism so as the decay time values indicate that the lateral localization of the exciton is stronger than that imposed by the dot.Nous avons étudié par spectroscopie optique les propriétés électroniques de boîtes quantiques (BQs) de GaN/AlN crûes en épitaxie par jets moléculaires selon la direction non-polaire [11-20] (axe a). Dans cette orientation on attend une forte réduction des effets du champ électrique interne existant dans les hétérostructures d'axe [0001] (axe c), ce que nous avons vérifié expérimentalement par des expériences de photoluminescence (PL) résolue et intégrée en temps d'un ensemble de boîtes.La réalisation d'un montage de microPL optimisé pour l'UV nous a permis d'isoler les premiers spectres de BQs uniques de GaN plan a. Des effets de charges locales responsables de l'élargissement des raies de PL (diffusion spectrale) ont pu être mises en évidence et partiellement contrôlés par l'application d'un champ électrique vertical.La dépendance en température des raies de BQs uniques nous a permis d'étudier le couplage de l'exciton confiné avec les phonons acoustiques. La modélisation de ce mécanisme ainsi que les valeurs des temps de déclin indiquent que la localisation latérale de l'exciton est plus forte que celle imposée par la boîte

Sedimentological data sets from the prehistoric site of Ajor Pazi (northern Iran)

During a rescue excavation in 2018, 136 sedimentary bulk samples were collected from sediment cross-sections at the prehistoric site of Ajor Pazi (northern Iran). This study aimed to understand the prehistoric human-environmental interactions in an active fluvial fan setting. Using radiocarbon and luminescence-dated sedimentary cross sections, we applied multivariate statistics to sedimentological characteristics (magnetic susceptibility, grain size, remission, total organic and total inorganic carbon, and X-ray fluorescence) interpreted in terms of depositional facies. Based on numerical and material dating and facies interpretation, the first settlement activities must have occurred between 6.4 - 5.6 ka cal. BP (4.4 - 3.6 ka cal. BCE), which archaeologically falls into the Transitional Chalcolithic II period

Growth of (101¯1 ) semipolar GaN-based light-emitting diode structures on silicon-on-insulator

The growth and characterization of (101¯1 ) semipolar GaN buffer, InGaN multiple quantum wells (MQWs), and light-emitting diode (LED) structure on patterned silicon-on-insulator (SOI) substrates, implementing the aspect ratio technique (ART), are reported. The early growth stages of GaN result in continuous and uniform stripes with small height variations that cause the formation of chevrons. Three coalescence strategies are tested to improve surface morphology and optical quality. Scanning electron microscopy identifies no crack formation but undulations of the surface. A roughness of ≈10 nm is measured by atomic force microscopy on large areas. The impact of MQW growth temperature shows similar surface morphology in terms of undulations and roughness. Room temperature photoluminescence spectra show wavelength emission redshifting when decreasing the MQW growth temperature. Room-temperature cathodoluminescence (CL) highlights first the presence of threading dislocations (TDs) in between the coalescence boundary despite the use of the ART technique. Second, CL shows a spatially homogeneous emission wavelength of around 485 nm only perturbed by lower-wavelength emission (455 nm) arising from the chevrons. Blue LED structures exhibit uniform emission wavelength at 450 nm, having a crack-free surface, and roughness of ≈5 nm. These results pave the way for the fabrication of semipolar micro-LEDs on SOI substrates.Published versio