Photoacoustic detection of circular dichroism in a square array of nano-helices

A novel nano-structured material has been assembled by means of a focused ion beam technique. This artificial material is composed of a square array of nano-helices built upon a multilayered substrate. Optical measurements of circular dichroism of a sample are confirmed by photo-acoustic investigations, which allow to directly study the helix-field interaction apart from the dielectric substrate. The study is consistent with 3D numerical simulations, and demonstrates to be an efficient tool of investigation for the entire class of these novel structured materials

Direct quantitative measurement of compositional enrichment and variations in InyGa1−yAs quantum dots

Assessment of the composition of quantum dots on the nanoscale is crucial for a deeper understanding of both the growth mechanisms and the properties of these materials. In this letter, we discuss a direct method to obtain a quantitative evaluation of the In variation across nanometer-sized InGaAs quantum dots embedded in a GaAs matrix, by means of electron energy-loss spectroscopy in a scanning transmission electron microscope

Polarization Response in InAs Quantum Dots: Theoretical Correlation between Composition and Electronic Properties

III-V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two layer composition model, mimicking In segregation and In-Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response.Comment: 8 pages, 6 figures; accepted for publication in IOP Nanotechnology journa

Ground state of excitons and charged excitons in a quantum well

A variational calculation of the ground state of a neutral exciton and of positively and negatively charged excitons (trions) in single quantum well is presented. We study the dependance of the correlation energy and of the binding energy on the well width and on the hole mass. Our results are are compared with previous theoretical results and with avalaible experimental data.Comment: 8 pages, 5 figures presented to OECS

Four conjectures in Nonlinear Analysis

In this chapter, I formulate four challenging conjectures in Nonlinear Analysis. More precisely: a conjecture on the Monge-Amp\`ere equation; a conjecture on an eigenvalue problem; a conjecture on a non-local problem; a conjecture on disconnectedness versus infinitely many solutions.Comment: arXiv admin note: text overlap with arXiv:1504.01010, arXiv:1409.5919, arXiv:1612.0819

PCI Express Over Optical Links for Data Acquisition and Control

PCI Express is a new I/O technology for desktop, mobile, server and communications platforms designed to allow increasing levels of computer system performance. The serial nature of its links and the packet based protocols allows an easy geographical decoupling of a peripheral device. We have investigated the possibility of using an optical physical layer for the PCI Express, and we have built a bus adapter which can bridge remote busses (> 100m) to a single host computer without even the need of a specialized driver, given the legacy PCI compatibility of the PCI Express hardware. This adapter has been made tolerant to harsh environmental conditions, like strong magnetic fields or radiation fluxes, as the data acquisition needs of high energy physics experiments often require

Bubble concentration on spheres for supercritical elliptic problems

We consider the supercritical Lane-Emden problem (P_\eps)\qquad -\Delta v= |v|^{p_\eps-1} v \ \hbox{in}\ \mathcal{A} ,\quad u=0\ \hbox{on}\ \partial\mathcal{A} where $\mathcal A$ is an annulus in \rr^{2m}, $m\ge2$ and p_\eps={(m+1)+2\over(m+1)-2}-\eps, \eps>0. We prove the existence of positive and sign changing solutions of (P_\eps) concentrating and blowing-up, as \eps\to0, on $(m-1)-$dimensional spheres. Using a reduction method (see Ruf-Srikanth (2010) J. Eur. Math. Soc. and Pacella-Srikanth (2012) arXiv:1210.0782)we transform problem (P_\eps) into a nonhomogeneous problem in an annulus \mathcal D\subset \rr^{m+1} which can be solved by a Ljapunov-Schmidt finite dimensional reduction

Stress-driven AlN cantilever-based flow sensor for fish lateral line system

In this work, we report on the fabrication and characterization of stress-driven aluminum nitride (AlN) cantilevers to be applied as flow sensor for fish lateral line system. The fabricated structures exploit a multilayered cantilever AlN/molybdenum (Mo) and a Nichrome 80/20 alloy as piezoresistor. Cantilever arrays are realized by using conventional micromachining techniques involving optical lithography and etching processes. The fabrication of the piezoresistive cantilevers is reported and the operation of the cantilever as flow sensor has been investigated by electrical measurement under nitrogen flowing condition showing a sensitivity to directionality and to low value applied forces

Aluminum Nitride piezo-MEMS on polyimide flexible substrates

In this work the micro-fabrication of flexible MicroElectroMechanical transducers based on the piezoelectric effect is reported. We developed the technological protocol to realize a piezoelectric transducer composed by a Molybdenum (Mo) top electrode, the Aluminum Nitride active layer and a Mo bottom electrode on a polymeric tape. The process starts from the DC sputtering deposition of the Molybdenum layer at room temperature on Kapton HN. The Molybdenum is chosen not only for its electrical properties but also because it enhances the crystal orientation of AlN. The next step is the deposition of AlN that occurs at high temperature, around 250^oC. Temperature and physical sputtering enhanced by applying a DC bias on the substrates are two important parameters to improve the crystal orientation of the film. These extreme growth conditions guarantee a very good crystal structure without damaging the Kapton substrate. Then a final Mo layer is sputtered at room temperature. SU8-25 thick photo resist is used to define the top electrode and the AlN layer, and in a second mask step the Mo bottom electrode. The developer, the PG remover and SU8 negative resist itself have shown a chemical compatibility with Kapton HN. We measured the piezoelectric response on a capacitor test structure: through the Dynamic Mechanical Analyzer we applied controlled forces, and at the same time, by an LCR meter we performed measurements of the capacitance

Microphotoluminescence spectroscopy of vertically stacked In x Ga 1 − x A s / G a A s quantum wires

Disorder and spectral broadening of vertically stacked InGaAs/GaAs V-grooved quantum wires have been investigated by means of microprobe luminescence. We show that the main spectral broadening mechanism originates from monolayer fluctuations at the bottom of the wire. A direct evidence of monolayer height islands of area 40\ifmmode\times\else\texttimes\fi{}40\mathrm{nm} formed at the bottom of the grooves is provided by atomic force microscopy. Lateral and vertical wire-to-wire fluctuations are found to be negligible on the micron scale