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Strain engineering allows the physical properties of materials and devices to be widely tailored, as paradigmatically demonstrated by strained transistors and semiconductor lasers employed in consumer electronics. For this reason, its potential impact on our society has been compared to that of chemical alloying. Although significant progress has been made in the last years on strained nanomaterials, strain fields (which are of tensorial nature, with six independent components) are still mostly used in a "scalar" and/or static fashion. Here we present a new class of strain actuators which allow the three components of the in-plane stress tensor in a nanomembrane to be independently and reversibly controlled. The actuators are based on monolithic piezoelectric substrates, which are micro-machined via femtosecond-laser processing. Their functionality is demonstrated by "programming" arbitrary stress states in a semiconductor layer, whose light emission is used as a local and sensitive strain gauge. The results shown in this work open a new route to investigate and make use of strain effects in materials and devices., 16 pages, 4 figures

[EN] Photoluminescence and time resolved photoluminescence from single metamorphic InAs/GaAs quantum dots (QDs) emitting at 1.3 micrometers have been measured by means of a novel fibre-based characterization set-up. We demonstrate that the use of a wavelength tunable fibre Bragg grating filter increases the light collection efficiency by more than one order of magnitude as compared to a conventional grating monochromator. We identified single charged exciton and neutral biexciton transitions in the framework of a random population model. The QD recombination dynamics under pulsed excitation can be understood under the weak quantum confinement potential limit and the interaction between carriers at the wetting layer and QD states., G Munoz-Matutano appreciates valuable help from Professor Miguel Andres (University of Valencia) and thanks the Spanish Juan de la Cierva program (JCI-2011-10686). We acknowledge the support of the FEDER actions UPVOV08-3E-008 and UPVOV10-3E-492, the PROMETEO2009/74 project from Generalitat Valenciana, the Spanish projects TEC2011-29120-C05-01-02-05, the Italian FIRB Project ‘Nanotecnologie e Nanodispositivi per la Societa` dell’Informazione’ and ‘SANDiE’ Network of Excellence of EC, Contract No. NMP4-CT-2004-500101.

We report on the design, the growth by MBE and the optical and morphological characterization of metamorphic InAs/InGaAs quantum dots (QD) with a density low enough to allow single dot characterization without the need of complex litographic steps to isolate single QDs. InAs sub-critical coverages were deposited on InxGa1-xAs metamorphic buffers (MBs) and the transition from 2D growth to 3D island nucleation was monitored by reflection high energy electron diffraction (RHEED). We discuss the fundamental differences of the sub-critical growth method compared with the Stranski-Krastanow one, also by considering available theoretical models. AFM confirmed that the density of QDs can be controlled down to 10(8) cm(-2) and showed that InGaAs surfaces have an effect on QD positioning uniformity. Optical properties were studied by ensemble PL at 10 K and by mu-PL at 4 K and single dot emission was detected in the whole range from 1000 to 1315 nm for structures grown on In0.15Ga0.85As MBs, allowing to identify most of the excitonic species at the ground state. In conclusion, our results show that the sub-critical QD growth technique can be successfully used to prepare low-density InAs QD structures on InxGa1-xAs (x >= 0.15) metamorphic buffers and that, based on advanced mu PL characterization, these nanostructures can be effective single photon sources emitting at 1300 nm, with the potential of emission extension towards 1550 nm.

Back in the seventies, only a few years after the invention of low-loss optical sensors, it became apparent that optical devices can not only reliably transmit data, but also provide remarkable sensing capabilities. These sensing capabilities combined with unique properties, such as total dielectric design, complete immunity to electromagnetic interference, small size, capability for distributed sensing, safety and good bio-compatibility attracted significant attention in both industry and academia. The rapid development of sensors based on semiconductor materials over the past two decades has been brought about in part by the application of integrated circuit technologies to fabricating precision micro-structures and devices, and by the great need for sensors that can provide the necessary performance requirements that many of today's electronic systems demand. Currently molecular sensing is being represented by traditional semiconductors (p-type, n-type), where the area/volume proportions of the material have determined values. Those values influence the structure stability, the absorption and the emission properties of the sensor device. In this communication we present our preliminary results on the preparation and characterization (AFM and XPS) of InAs Quantum Dot deposited on GaAs substrates1 and on their superficial functionalization with synthetic molecular receptors belonging to the class of calixarenes.2 The well-known recognition properties of the latter compounds together with the photosensing abilities of the InAs/GaAs QDs may indeed lead to the development of potential chemosensors (see Figure 1) which offer a better integration in the sensor circuit and an improvement of sensing properties. These novel devices will bring highly desirable properties such as: high structure stability, large area/volume proportion and an emission in a range of 1-5 ?m which is ideal for fibre optics transmission of information in the sensing.