Built-in tensile strain dependence on the lateral size of monolayer MoS2 synthesized by liquid precursor chemical vapor deposition.

Strain engineering is an efficient tool to tune and tailor the electrical and optical properties of 2D materials. The built-in strain can be tuned during the synthesis process of a two-dimensional semiconductor, such as molybdenum disulfide, by employing different growth substrates with peculiar thermal properties. In this work, we demonstrate that the built-in strain of MoS2 monolayers, grown on a SiO2/Si substrate by liquid precursor chemical vapor deposition, is mainly dependent on the size of the monolayer. In fact, we identify a critical size equal to 20 µm, from which the built-in strain increases drastically. The built-in strain is the maximum for a 60 µm sized monolayer, leading to 1.2% tensile strain with a partial release of strain close to the monolayer triangular vertexes due to the formation of nanocracks. These findings also imply that the standard method for evaluation of the number of layers based on the Raman mode separation can become unreliable for highly strained monolayers with a lateral size above 20 µm.

Titanium Dioxide Nanowires Grown on Titanium Disks Create a Nanostructured Surface with Improved In Vitro Osteogenic Potential.

Current biomedical research is centered on the study of nanomaterials and their effects in biological environments. In particular, there is an increasing interest on TiO2 nanostructures for biomedical applications such as drug delivery or implant materials. In this framework, we present a Chemical Vapour Deposition process to synthesize titanium dioxide nanowires (NWs) on a commercially pure titanium substrate and we test the material In Vitro as a culture substrate for murine osteoblast-like MC3T3-E1 cells. A physical-morphological, structural and optical-characterization of the inorganic samples is performed by Electron Microscopy techniques and X-ray Diffraction, showing that a mat of crystalline rutile TiO2 NWs is obtained over the commercial substrate. In Vitro biological tests are performed by seeding MC3T3-E1 cells on the material and studying cell morphology, the cellmaterial interface and the osteoblast gene expression. These experiments show good cell adhesion to the nano-structured surface and a higher degree of early osteoblastic differentiation compared to control titanium surfaces, indicating that the present nano-structured material has good osteogenic potential for biomedical applications.

Glioblastoma del nervio óptico detectado por PET/TC cerebral con 11C-Metionina / Optic nerve glioblastoma detected by 11C-Methionine brain PET/CT

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All-Optical Fiber Hanbury Brown &Twiss Interferometer to study 1300 nm single photon emission of a metamorphic InAs Quantum Dot.

New optical fiber based spectroscopic tools open the possibility to develop more robust and efficient characterization experiments. Spectral filtering and light reflection have been used to produce compact and versatile fiber based optical cavities and sensors. Moreover, these technologies would be also suitable to study N-photon correlations, where high collection efficiency and frequency tunability is desirable. We demonstrated single photon emission of a single quantum dot emitting at 1300 nm, using a Fiber Bragg Grating for wavelength filtering and InGaAs Avalanche Photodiodes operated in Geiger mode for single photon detection. As we do not observe any significant fine structure splitting for the neutral exciton transition within our spectral resolution (46 µeV), metamorphic QD single photon emission studied with our all-fiber Hanbury Brown &Twiss interferometer could lead to a more efficient analysis of entangled photon sources at telecom wavelength. This all-optical fiber scheme opens the door to new first and second order interferometers to study photon indistinguishability, entangled photon and photon cross correlation in the more interesting telecom wavelengths.

Time resolved emission at 1.3 µm of a single InAs quantum dot by using a tunable fibre Bragg grating.

Photoluminescence and time resolved photoluminescence from single metamorphic InAs/GaAs quantum dots (QDs) emitting at 1.3 µm 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.

Low density InAs/(In)GaAs quantum dots emitting at long wavelengths.

We present research carried out on molecular beam epitaxy grown InAs/(In)GaAs quantum dot structures for single-photon operation at long wavelengths. The optical and morphological properties of the structures are studied as functions of quantum dot growth parameters and of the InGaAs upper confining layer thickness and composition. We show that low growth rate, high growth temperature and reduced quantum dot coverage are very effective in reducing the quantum dot density but, owing to In desorption effects and quantum dot size reduction, this result is not always concomitant with the achievement of long wavelength emission. To this aim, we show that the use of InGaAs upper confining layers allows the redshift of quantum dot emission energy without affecting their density. Both the thickness and composition of the InGaAs layer have to be carefully chosen to provide a complete coverage of quantum dots and not to exceed the critical thickness for plastic relaxation. Our results led to the preparation of quantum dot structures with densities in the low 10(9) cm(-2) range, 1.33 microm emission at 10 K and full widths at half maximum of 22 meV.

The role of wetting layer states on the emission efficiency of InAs/InGaAs metamorphic quantum dot nanostructures.

We report on a photoluminescence and photoreflectance study of metamorphic InAs/InGaAs quantum dot strain-engineered structures with and without additional InAlAs barriers intended to limit the carrier escape from the embedded quantum dots. From: (1) the substantial correspondence of the activation energies for thermal quenching of photoluminescence and the differences between wetting layer and quantum dot transition energies and (2) the unique capability of photoreflectance of assessing the confined nature of the escape states, we confidently identify the wetting layer states as the final ones of the process of carrier thermal escape from quantum dots, which is responsible for the photoluminescence quenching. Consistently, by studying structures with additional InAlAs barriers, we show that a significant reduction of the photoluminescence quenching can be obtained by the increase of the energy separation between wetting layers and quantum dot states that results from the insertion of enhanced barriers. These results provide useful indications on the light emission quenching in metamorphic quantum dot strain-engineered structures; such indications allow us to obtain light emission at room temperature in the 1.55 microm range and beyond by quantum dot nanostructures grown on GaAs substrates.