In this work, we study the optical emission from arrays of InGaN/GaN MQW nanofin and nanorod arrays with sizes ranging from a few micrometers down to sub-wavelength dimensions (i.e., nanometers). Such systems are of interest for developing arrays of single addressable nanoLEDs, which could be used to obtain a visible wavelength super-resolution microscope where the resolution is due to highly localized light spots with sub-wavelength LED-to-LED pitch.
We have used commercial full-wave Maxwell solvers (COMSOL, CST) to calculate the optical field emitted from a single nanoLED in a periodic array for a wavelength of 450 nm. Simulations on 11×11 nanoLED arrays with pitches of 200 nm up to 800 nm and diameters of down to 50 nm have been conducted, in which the dependency of the emission pattern on different structural parameters is studied. In case of small nanoLED array with very narrow pitch, a large optical cross-talk between the activated LED and its neighboring pixels was found. Moreover, in presence of cross-talks, test objects smaller than the LED pitch placed on its surface with influence of near field could potentially be resolved by evaluating the varied emission patterns obtained by different pixel activations. Routes to achieve higher localized optical fields and reduce optical cross-talk have been also investigated by modifying the nanoLED array structures (e.g., by introducing filling material among the LED pixels).
We present here some methods for the production of organized systems formed by carbon nanotubes and suitable for
nano-beams generation and handling. In particular methodologies based on Chemical Vapour Deposition (CVD),
chemically induced assembling and alignment by dielectrophoretic processes are examined and their capacity to produce
assembling of nanostructured materials with defined architecture is discussed
The importance of nanocomposites materials such as carbon nanotubes-polymers composites for the efficient realization
of innovative solar cells based on organic as well hybrid organic-inorganic solar cells is more and more evident. We
present a study on the realization of dye sensitized solar cells (DSSC) and sublimation deposited solar cells, considering
the impact of using nanocomposite materials in the different sections composing the cells. We discuss the effect of using
poly-3,4-ethylene dioxythiophene/poly(styrene sulfonate) (PEDOT/PSS)-Carbon nanotube (CNT) blend as counterelectrode
in DSSC on the cell efficiency and fill factor, also considering DSSC structures where low cost, innovative
dyes are used. Nanocomposites can be used as solution processed or electropolimerized electrodes, where accurate
control of nanotube dispersion is obtained through specific chemical treatment of Carbon nanotubes solubility. The use
of Carbon based nanostructured material is also investigated in terms of their positive impact on the realization of
organic solar cells on flexible substrates.
In the present research, purified commercially SWCNTs are used as gas sensing material in an interdigitated electrode platform for NH<sub>3</sub>, NO<sub>x</sub> and H<sub>2</sub>O detection. The SWCNT response to gas absorption is known to be dependent from different parameters and operational conditions, such as the relative orientation of the nanotubes and their organization between the electrodes, the temperature of the sensor, and moreover the voltage applied to a back gate contact. We show the sensor response for the various gas species considered and we analyze the sensor behavior with respect to the sensibility and to the detection velocity. Moreover we studied the effect on absorption/desorption gas processes by applying a gate voltage to the Si substrate beneath the interdigitated electrodes. The results indicate that the acceleration of the time response of the sensor for the detection of NH<sub>3</sub> is proportional to the gate voltage in the range 0 V - 40 V.
We have performed studies on the correlation between mechanical deformations and electrical conductance on a new interesting hybrid material, a Single Wall Carbon Nanotubes (SWCNTs)/Poly(3,4-ethylenedioxythiophene) (PEDOT) composite. Two are the synthesis techniques utilized to prepare the composite material in form of few hundreds of nm thick films: a spin coating deposition starting from an aqueous dispersion of SWCNTs and PEDOT, and an electrochemical de*position starting from a dispersion of SWCNTs and EDOT monomer. The composite conductance changes induced by a modulated periodic elongation via a coherent technique have been monitored by measuring the voltage variations of a Wheatstone bridge connected with the films. The measurements were performed on SWCNTs/PEDOT composites layered on a rigid substrate. The piezoresistivity gauge factor (GF) of the various samples was evaluated by comparing their responses to mechanical deformations to those of a commercial strain gauge, sticked on a substrate of the same kind. We found no significant piezoresistive effect in the hybrid material films deposited by means of spin coating while the effect is remarkable for the composites prepared by means of the electrochemical technique. In this case the gauge factor is found to be up to 3-4 times higher than that of the commercial strain gauge.
We reported the design and realization of a carbon nanotube-based integrated multielectrode device. Patterned Si/SiO<sub>2</sub>/Nb/Nb<sub>2</sub>O<sub>5</sub> multilayer was successfully realized by means of a few, common photolithographic processes with the minimum number of mask alignment steps. Such structure constitutes the patterned substrate of successive Hot Filament Chemical Vapour Deposition (HFCVD) process. Selective growth of highly oriented SWCNT arrays was obtained in the predefined locations while survival of the entire structure was achieved. Field emission measurements of such materials were carried out. Good and reproducible field emission behaviour has been observed in several realized structures.
This paper investigates the effect that Four Wave Mixing (FWM) has on Frequency Shift Keyed (FSK) optical signals. The paper will show how an optical FSK modulated signal can be implemented using a widely tunable laser. These lasers will have a bigger impact in future optical transmission systems due to their agile wavelength capabilities. Then measurements of FWM in a Semiconductor Optical Amplifier (SOA) and in Zero Dispersion Shifted Fiber (DSF) will be presented. SOAs are of crucial importance in modern & future transmission systems as many operations can be implemented using their highly nonlinear properties, such as wavelength conversion, pulse reshaping & format conversion can be implemented. While Zero DSF is less popular these days, due to its nonlinearities, nevertheless the fiber still forms the core of many networks and thus its ability to handle many different WDM signals without introducing potential interference needs to be investigated.
We have performed studies on the correlation between mechanical deformation and conductivity on a set of carbon samples constituted by 70% of single-walled carbon nanotubes. The samples, in form of slabs (6 × 5 mm, thickness: 400 mm), were obtained by compacting the nanotube material at 200 and 600 bar. The changes of conductivity have been monitored by measuring the current variations induced by a modulated periodic elongation of the slabs via a coherent technique. The mechanical deformations were produced by forces applied vertically at the center of each slab, horizontally placed on a sample holder. A piezoelectric actuator controlled by a lock-in amplifier was fixed to the sample holder. The modulation of the current induced by the mechanical deformation of the nanotube slabs is huge, and the amplitude of the modulation is almost linearly proportional to the elongation induced by the piezoelectric actuator. Such change of conductivity is more than an order of magnitude higher than the change obtained by piezoelectrical deformation of Si. The behaviour of the nanotube samples has been compared to that of a reference sample made of graphite compressed at 200 bar to form a slab with similar dimensions. In this case the change of conductivity was below the sensitivity of the lock-in amplifier, which was unable to lock to the periodicity of the mechanical deformation. We are currently addressing the problem to interpret the strong response of the nanotube slabs, which could be attributed either to a piezoresistive response of the sample or to the direct effect of the deformation on the hopping transport processes.