El majúscul impacte d'allò minúscul

Tininess Makes a Huge Impact: Semiconducting and Metallic Nanoparticles.Defying the conventions of linguistic repetition, the prefi x nano springs up in all languages with unusual force. Nanostructure, nanofi ber, nanocrystals, nanowires, nanotubes, nanodevice ... These are just a few examples, although you won’t fi nd them in the dictionary. These words have retained some meaning of the root from which they are derived, but should inescapably be contemplated, at best, as distant metaphorical refl ections. The words nanoparticle and nanocrystal will be the focus of this article: What are nanoparticles? When is a nanoparticle a nanocrystal? When is the nanoparticle a quantum dot? What applications can we expect if they are semiconducting or metallic

Charge Transport in Trap-Sensitized Infrared PbS Quantum-Dot-Based Photoconductors: Pros and Cons

Control of quantum-dot (QD) surface chemistry offers a direct approach for the tuning of charge-carrier dynamics in photoconductors based on strongly coupled QD solids. We investigate the effects of altering the surface chemistry of PbS QDs in such QD solids via ligand exchange using 3-mercaptopropionic acid (MPA) and tetrabutylammonium iodide (TBAI). The roll-to-roll compatible doctor-blade technique was used for the fabrication of the QD solid films as the photoactive component in photoconductors and field-effect phototransistors. The ligand exchange of the QD solid film with MPA yields superior device performance with higher photosensitivity and detectivity, which is due to less dark current and lower noise level as compared to ligand exchange with TBAI. In both cases, the mechanism responsible for photoconductivity is related to trap sensitization of the QD solid, in which traps are responsible of high photoconductive gain values, but slow response times under very low incident optical power (100 pW), where traps are filled, both MPA- and TBAI-treated photodevices exhibit similar behavior, characterized by lower responsivity and faster response time, as limited by the mobility in the QD solid

Propagation length enhancement of surface plasmon polaritons in gold nano-/microwaveguides by the interference with photonic modes in the surrounding active dielectrics

In this work, the unique optical properties of surface plasmon polaritons (SPPs), i.e. subwavelength confinement or strong electric field concentration, are exploited to demonstrate the propagation of light signal at 600 nm along distances in the range from 17 to 150 μm for Au nanostripes 500 nm down to 100 nm wide (30 nm of height), respectively, both theoretically and experimentally. A low power laser is coupled into an optical fiber tip that is used to locally excite the photoluminescence of colloidal quantum dots (QDs) dispersed in their surroundings. Emitted light from these QDs is generating the SPPs that propagate along the metal waveguides. Then, the above-referred propagation lengths were directly extracted from this novel experimental technique by studying the intensity of light decoupled at the output edge of the waveguide. Furthermore, an enhancement of the propagation length up to 0.4 mm is measured for the 500-nm-wide metal nanostripe, for which this effect is maximum. For this purpose, a simultaneous excitation of the same QDs dispersed in poly(methyl methacrylate) waveguides integrated with the metal nanostructures is performed by end-fire coupling an excitation laser energy as low as 1 KW/cm2. The proposed mechanism to explain such enhancement is a non-linear interference effect between dielectric and plasmonic (super)modes propagating in the metal-dielectric structure, which can be apparently seen as an effective amplification or compensation effect of the gain material (QDs) over the SPPs, as previously reported in literature. The proposed system and the method to create propagating SPPs in metal waveguides can be of interest for the application field of sensors and optical communications at visible wavelengths, among other applications, using plasmonic interconnects to reduce the dimensions of photonic chips

MWP true time delay implemented in PbS-SU8 waveguides

Es presenta un nou tipus de dispositiu de retard en temps real de microones (TTD) basat en la dispersió de punts quàntics col·loïdals PbS (QD) en el fotoresist SU8 disponible comercialment. Amb aquest propòsit, els nanocompostos PbS-SU8 s’integren en una plataforma de silici en forma de guies d’ones de cresta. Quan aquestes estructures es bomben a longituds d’ona per sota de l’interval de banda dels PbS QD, es realitza un desplaçament de fase en un senyal de microones transmès òpticament (a 1550 nm) i, per tant, es produeix un retard temporal. A més, es milloren els resultats mitjançant la implementació d’una nova guia d’ones de doble capa de cresta composta per un nanocompost PbS-SU8 i una capa passiva SU8 que redueix les pèrdues degudes al feix de la bomba i, per tant, millorar l’excitació dels QD. El dispositiu resultant mostra avantatges potencials respecte a les tecnologies TTD actuals, ja que permet una ràpida sintonització del retard temporal controlant la potència de la bomba i un alt nivell d’integració a causa de la seva petita mida i el material utilitzat.JCI-2012-14805FPU 13/04675PROMETEO II/2013/012EU-NAVOLCHI project 288869TEC2011-29120-C05-01TEC2011-29120-C05-05A new kind of microwave true time delay (TTD) device based on the dispersion of PbS colloidal quantum dots (QDs) in the commercially available photoresist SU8 is presented. For this purpose PbS-SU8 nanocomposites are integrated on a silicon platform in the form of ridge waveguides. When these structures are pumped at wavelengths below the band-gap of the PbS QDs, a phase shift in an optically conveyed (at 1550 nm) microwave signal is performed and therefore a temporal delay is produced. Furthermore, results are improved by implementing a novel ridge bilayer waveguide composed by a PbS-SU8 nanocomposite and a SU8 passive layer that reduces the losses due to the pump beam, and hence to improve the excitation of the QDs. The resulting device shows potential benefits respect to the current TTD technologies since it allows a fast tunability of the temporal delay by controlling the pump power and a high level of integration due to its small size and the material used

Boosting Photoluminescence in MAPbBr3 Single Crystals through Laser-Based Surface Modification

Single crystals (SCs) of metal halide perovskites show promise in improving the good optoelectronic characteristics of their polycrystalline counterparts, yet the surface losses represent a substantial drawback in the form of nonradiative recombination. We show that blue CW laser treatment of MAPbBr3 perovskite SCs results in the crystal surface modification, which includes the formation of an upper PbBr2 film as well as an underlying layer of a crystalline perovskite, which demonstrates ≈75 meV extended band gap. As a result, photoluminescence improves up to 2 orders of magnitude after the treatment. We suggest that the extended-band gap MAPbBr3 has a distorted crystalline lattice formed due to tensile strain after the laser-induced partial decomposition of CH3NH3+ in the presence of O2. Formic acid and methylamine are formed as byproducts to passivate the distorted MAPbBr3 layer and protect perovskite structures from adverse influences of the environment such as water-induced degradation

Evaluación espectral y colorimétrica de puntos cuánticos como nuevos emisores de luz

Las nanopartículas semiconductoras (puntos cuánticos) son nanomateriales emisores de luz por luminiscencia a partir de una excitación UV, con prometedoras aplicaciones futuras en nano-biomedicina y nano-optoelectrónica. El comportamiento óptico básico de estos nanomateriales luminiscentes depende principalmente de su composición química, forma y tamaño. En este trabajo se realiza un análisis espectral y colorimétrico preliminar de dos variedades químicas de puntos cuánticos (CdSe y CdTe) en función diferentes variaciones en sus procesos de síntesis. Este análisis comprende el paso de los espectros de absorción/emisión relativa a valores colorimétricos convencionales usando espacios de representación del color recomendados por la Comisión Internacional de Iluminación y Color (CIE) con el fin de evaluar el rango de colores perceptibles, y, correlacionar la evolución de color con las variables implicadas en el proceso de sus síntesis.Ministerio de Ciencia e Innovación (proyectos DPI2008-06455-C02-02 y TEC-2008-06756-C03-03); Generalitat Valencia (proyecto PROMETEO/2009/074)