Nanopatterning of colloidal nanocrystals emitters dispersed in a PMMA matrix by e-beam lithography

We report on the fabrication of periodic nanostructures embedding semiconductor colloidal nanocrystals (NCs) by directly exposing a polymer/NCs blend to electron beam lithography (EBL). Our technological approach for the fabrication of NCs-based photonic devices relies on the dispersion of CdSe/ZnS core/shell NCs into a layer of polymethilmethacrylate (PMMA) positive electron resist, which is patterned by means of an EBL process. The presence of NCs in the resist did not modify the peculiar behaviour of PMMA, which was selectively removed from the regions exposed to the electron beam. The morphology of the sample was assessed by scanning electron microscopy and atomic force microscopy measurements. The optical analysis of the samples after the dispersion of the NCs into the PMMA matrix and the exposure to the e-beam showed the successful localization of the colloidal NCs, whose emission properties were preserved

Action and non-action oriented body representations. insight from behavioural and grey matter modifications in individuals with lower limb amputation

Following current model of body representations, we aimed to systematically investigate the association between brain modifications, in terms of grey matter loss, and body representation deficits, in terms of alterations of the body schema (BS) and of non-action oriented body representations (NA), in individuals with lower limb amputation (LLA)

Determination of band-offset enhanced in InGaAsP -InGaAsP strained multiquantum wells by photocurrent measurements

We experimentally determine the band offset of strain-compensated InGaAsP-InGaAsP multiquantum-well (MQW) heterostructures, emitting at 1.55 mum, that were grown by metal-organic chemical vapor deposition. A band offset value of about 56% is found for the conduction band, which is higher than the value reported for the unstrained structure. The temperature dependence of the photoluminescence intensity shows that the unipolar detrapping of carriers in such MQWs is more efficient than the thermal activation of excitons. (C) 2005 American Institute of Physic

Local degradation of selectively oxidized AlGaAs/AlAs distributed Bragg reflectors in lateral-injection vertical-cavity surface-emitting lasers

We show the local degradation of a selectively oxidized top distributed Bragg reflector (DBR) in a lateral-junction vertical-cavity surface-emitting laser (LJ-VCSEL) working at room temperature in continuous-wave operation. The measurements were carried out by a scanning microluminescence system used in reflection mode. The injection of a few milliamps in continuous-wave operation at room temperature in the LJ-VCSEL induces damage both in the DBRs and in the active area. The submicron resolution maps of the reflected laser intensity, recorded from the top surface of the LJ-VCSEL, show a strong local change in the top DBR reflectivity before and after current injection. The μ-photoluminescence map, recorded after the device failure, shows that the radiative recombination is strongly decreased in the damaged area of the device

Energy harvesting technologies and devices from vehicular transit and natural sources on roads for a sustainable transport: state-of-the-art analysis and commercial solutions

The roads we travel daily are exposed to several energy sources (mechanical load, solar radiation, heat, air movement, etc.), which can be exploited to make common systems and apparatus for roadways (i.e., lighting, video surveillance, and traffic monitoring systems) energetically autonomous. For decades, research groups have developed many technologies able to scavenge energy from the said sources related to roadways: electromagnetism, piezoelectric and triboelectric harvesters for the cars’ stress and vibrations, photovoltaic modules for sunlight, thermoelectric solutions and pyroelectric materials for heat and wind turbines optimized for low-speed winds, such as the ones produced by moving vehicles. Thus, this paper explores the existing technologies for scavenging energy from sources available on roadways, both natural and related to vehicular transit. At first, to contextualize them within the application scenario, the available energy sources and transduction mechanisms were identified and described, arguing the main requirements that must be considered for developing harvesters applicable on roadways. Afterward, an overview of energy harvesting solutions presented in the scientific literature to recover energy from roadways is introduced, classifying them according to the transduction method (i.e., piezoelectric, triboelectric, electromagnetic, photovoltaic, etc.) and proposed system architecture. Later, a survey of commercial systems available on the market for scavenging energy from roadways is introduced, focusing on their architecture, performance, and installation methods. Lastly, comparative analyses are offered for each device category (i.e., scientific works and commercial products), providing insights to identify the most promising solutions and technologies for developing future self-sustainable smart roads

Radiative recombination dynamics in tetrapod-shaped CdTe nanocrystals: Evidence for a photoinduced screening of the internal electric field

We study the radiative recombination processes in CdTe tetrapod nanocrystals at 10K. Two intrinsic emission bands, namely the ground state (GS) and the excited state (EX), decay with three time constants, due to a power dependent Auger-like recombination process (tens of picoseconds), to the intrinsic emission of the two states (hundreds of picoseconds) and to emission from defect states (a few nanoseconds). The existence of an internal electric field originating from the e-h separation induced by the peculiar symmetry of the GS is demonstrated by a dynamical shift of the GS emission energy that is correlated to the EX population

High Q-factor colloidal nanocrystal-based vertical microcavity by hot embossing technology

We report on the fabrication and optical characterization of vertical hybrid microcavities in which a layer of colloidal nanocrystals dispersed in an organic matrix is embedded between two inorganic mirrors. The devices are fabricated by a technique based on the unconventional use of the hot embossing technology, which allows a very fine control of the cavity length. The technique exploits a λ -thick microstructured dielectric top mirror pressed onto the bottom one, previously coated with the active layer, to sandwich the cavity and precisely control its thickness. Room-temperature photoluminescence measurements show a Q factor as high as 146 for our devices

Picosecond photoluminescence decay time in colloidal nanocrystals : The role of intrinsic and surface states

Picosecond time-resolved photoluminescence measurements were performed on CdSe core and CdSe/ZnS core/shell colloidal quantum dots (QDs). Photoluminescence (PL) emission is observed to originate from intrinsic ±1U and ±1L bright states with lifetimes of 60 and 450 ps, respectively, and from a long living component with nanosecond lifetimes. The latter is attribuited to the emission from surface states (ss) approximately 16 and 13 meV below the ±1L state for core and core/shell QDs, respectively. We show that in the temperature range between 15 and 70 K the three recombination processes compete and they are thermally populated through different pathways (±1L → ±1U and ss → ±1L)

Photoconduction properties in aligned assemblies of colloidal CdSe/CdS nanorods.

We report on photoconduction and optical properties of aligned assemblies of core−shell CdSe/CdS nanorods prepared by a seeded growth approach. We fabricate oriented layers of nanorods by drop casting the nanorods from a solution on substrates with prepatterned, micrometer-spaced electrodes and obtain nanorod alignment due to the coffee stain effect. The photoconductivity of the nanorod layers can be improved significantly by an annealing process under vacuum conditions. The spectral response of the photocurrent shows distinct features that can be assigned to the electronic level structure of the core−shell nanorods and that relate well to the spectra obtained by absorption measurements. We study assemblies of nanorods oriented parallel and perpendicular to the applied electric field by the combined use of photocurrent and photoluminescence spectroscopy. We obtain consistent results which show that charge carrier separation and transport are more efficient for nanorods oriented parallel to the electric fi..

Intrinsic optical nonlinearity in colloidal seeded grown CdSe/CdS nanostructures: Photoinduced screening of the internal electric field

The assessment of the presence and the origin of an intrinsic internal electric field in novel colloidal CdSe/CdS nanoheterostructures is of fundamental importance in order to understand their optical properties, due to both their impact on the basic research fields, and their potential in technological applications. To this aim, a deep study of the carrier dynamics in spherical (quantum dots) and rod-shaped (nanorods) colloidal seeded grown CdSe/CdS nanocrystals via time-resolved photoluminescence spectroscopy has been carried out in this report. A transient, power-dependent redshift of the spectra is observed. An optical nonlinearity is also found by continuous-wave photoluminescence measurements on ensemble and single nanostructures, which is attributed to a photoinduced screening of an internal field. This internal field could originate from the intrinsic piezoelectric polarization, which is a typical effect in strained heterostructures with a lattice mismatch greater than 3.9%. Our theoretical calculations support the experimental results