Paolo Visconti

Oligomer-based organic distributed feedback lasers by room-temperature nanoimprint lithography

Room-temperature nanoimprint lithography in air is used in order to pattern a nonthermoplastic, low-molar-mass thiophene-based pentamer with excellent gain properties. No degradation of the luminescence efficiency of the active medium was observed after patterning. In this way, we fabricated single-mode emission distributed feedback lasers having a threshold excitation fluence of 140 μJ/cm2. The lasing line is peaked at 637 nm and exhibits a linewidth of less than 0.7 nm and a well-behaved input-output characteristic in the whole range of pump fluences. These results demonstrate room-temperature nanoimprint lithography as powerful and straightforward fabrication technique for oligomer-based nanostructured optoelectronic devices.

Highly selective photoelectrochemical etching of nitride materials for defect investigation and device fabrication

Photoenhanced electrochemical (PEC) etching in an unstirred KOH solution under He–Cd laser illumination was used for delineating extended defects in GaN films. When a low-excitation intensity was employed, the process yielded threading vertical features at dislocation sites. Application of an external voltage or a higher-illumination intensity led to high-etch rates with smooth surfaces. Some highly resistive samples, for which no etching was obtained under normal etching conditions, could be etched with the application of a single-polarity external voltage. Finally, in a GaN sample with an AlN/GaN superstructure inside, high selectivity between AlN and GaN was achieved; in this case, the PEC process stopped at the thin AlN stop layer.

Holographic nanopatterning of the organic semiconductor poly(p-phenylene vinylene)

We report a flexible method for the patterning of organic semiconductors in the submicrometer range, which we have successfully applied to thin films of poly(p-phenylene vinylene) (PPV) prepared on a variety of substrates, such as quartz, indium–tin oxide coated glass, or inorganic dielectric mirrors. The method is based on holographic lithography performed by a corner cube interferometer of our own design and construction, followed by Ar-ion etching.

Electronic system for improvement of solar plant efficiency by optimized algorithm implemented in biaxial solar trackers

In this paper it is described an algorithm, implemented in a biaxial solar tracker, that can instantly calculate the sun position at the latitude and longitude of a set point. The algorithm can drive up to two engines which are able to change the position of a solar panel, in order to increase its efficiency, for tracking the sun in its movement from east to west (azimuth motion) and in its elevation up to solar noon (tilt motion). The whole system is adaptable to various types of structures as it involves a cycle of self-learning of the structure and consequently the adaptation of calculations to the tracker on which it is installed.

Emission properties of printed organic semiconductor lasers

We investigated the emission properties of a distributed-feedback resonator based on an organic semiconductor patterned by a novel printing technology. We observed the peak splitting of the photonic bandstructure of the periodic grating and extracted the effective refractive index of the outcoupled guided modes. The laser works at the second diffraction order, exhibiting narrow single-mode emission at 637 nm, with a threshold as low as 37 microJ/cm2. The results suggest that direct printing is a promising fabrication technique for optically confined integrated optoelectronics.

Intelligent system for monitoring and control of photovoltaic plants and for optimization of solar energy production

This paper describes an intelligent electronic system designed to monitor, both locally or remotely, a PV system in order to detect any theft or malfunction and to optimize energy production by efficient algorithm for driving the plants solar trackers. The system consists of several electronic boards; the CS097 sensing/processing board detects environmental parameters, temperature and solar radiation, calculates produced power and energy for monitoring efficiency and electricity production. The CS083/CS088 electrical boards work as alarm anti-theft system which detects a critical condition in case of electrical continuity loss or not-justified rapid variation of PV string voltage; the intelligent unit has dual operation mode that makes it capable of auto-adapting itself distinguishing between day and night. The designed CS012 board controls a biaxial solar tracker and instantly calculates the sun position at latitude and longitude of the installation site so following solar orbit.

Field-Emission Breakdown and Electromigration in Insulated Planar Nanoscopic Contacts

Planar nanoscopic contacts are observed to undergo early electrical breakdown. The authors show that the cause is high field emission capable of triggering electromigration. The phenomenon is well described by an empirical current-voltage law, well different from that usually found in nonflat field emitters; this is attributed to the particular geometry of the contacts. Although the mathematical form of the law is always the same, the intensity of breakdown current changes from sample to sample, ranging over several orders of magnitude; this is explained by the nanoscopic roughness of the emitting surfaces. They also show that the occurrence of breakdown may be dependent on the polarity of the applied voltage

Design of electronic programmable board with user-friendly touch screen interface for management and control of thermosolar plant parameters

This paper describes a programmable electronic unit for controlling the environmental parameters and managing the electrical functions of a civil/industrial thermo-solar plant. The control unit acquires data from five analog temperature sensors, processes this information and, on the basis of them, commands a series of external equipments (pumps, electric valves and power supplies) with dedicated relay outputs. In addition to, the designed electronic system has a display for graphical interface with users in order to ensure simple programming and managing and lastly its manageable even remotely. The electronic board, integrated with the display embedded system, allows the optimization of plant performances in order to maximize efficiency and energy saving; obviously, the system is designed in general purpose concept and, being widely programmable, its functionalities can be simply and quickly modified by user through the touch screen display.

Hardware Design and Software Development for a White LED-Based Experimental Spectrophotometer Managed by a PIC-Based Control System

In this paper, the design and testing of a PC-interfaced PIC-based control unit used to manage an absorption spectrophotometer, employing a white LED as light source, are described. LED technology allows to perform the absorption measurements reducing the analyte temperature variations and thus noise generation, which occur if a Xenon light source, usually employed, is used; also thanks to LED technology, the system results low cost, easy to use and with a low power consumption. The realized spectrophotometer can be used for atmospheric and industrial pollutant detection or for indoor air monitoring (e.g., in hospital rooms), being able to detect particulate matter, pesticides, volatile organic compounds as well as pollution produced by heavy metals. The realized system manages the different required functionalities, such as acquisition and processing, via firmware, of raw data provided by sensors, actuation of mechanical devices (stepper motor and solenoid valve), and synchronizing and controlling the data exchange between hardware sections, microcontroller, and PC. Both hardware and software sections were designed carrying out the appropriate tests to verify their proper operation. Results confirm the correct system functioning and interaction, via PC terminal, between user and the realized control unit.

Solar powered WSN for monitoring environment and soil parameters by specific app for mobile devices usable for early flood prediction or water savings

This paper describes the design and realization of a smart electronic system, based on a Wireless Sensor Network, for wide-area monitoring of availability level and rapid changes of the water presence in the monitored soil in order to guarantee flood prediction, water savings in the optimized farmland irrigation, waste reduction and optimal use of water resources where its availability is low. The designed sensor node, by means of the different embedded sensors, is capable of detecting environmental parameters, the solar radiation level and soil temperature and moisture (i.e. water volume content) values. The sensors communicate with a central processing unit located on board, used both as data processing unit and as Wi-Fi transceiver to receive/transmit the sensors data. The user near a sensor node, by a tablet or smartphone with an appropriate app, can collect information provided from sensors and share them with all users who use the same app on the Cloud, through peer to peer Wi-Fi or other internet connection.