Manel López

Field effect luminescence from Si nanocrystals obtained by plasma-enhanced chemical vapor deposition

Field effect induced luminescence has been achieved by alternate tunnel injection of electrons and holes into Si nanocrystals. The emitting device is a metal-oxide-semiconductor structure with a semitransparent polycrystalline Si contact ∼250nm thick and a silicon-rich silicon oxide layer of about 40nm deposited on a p-type Si substrate by plasma-enhanced chemical vapor deposition. The electroluminescence is optimized for a Si excess of 17% and annealing at 1250°C for 1h in nitrogen-rich atmosphere. The pulsed emission presents typical decay times of ∼5μs and external quantum efficiencies of ∼0.03%.

Studies on the synthesis of akuammiline-type alkaloids. Construction of the hexahydro-1,5-methanoazocino[3,4-b)indole fragment

Abstract A three step route to the title tetracyclic substructure of akuammiline-type alkaloids consisting in the nucleophilic addition of an ester α-anion to an N -alkylpyridinium salt, acid-induced cyclization of the resultant 1,4-dihydropyridine, and stereoselective elaboration of the ethylidene substituent is reported.

IEEE 802.15.4 based wireless monitoring of pH and temperature in a fish farm

In the last years the number of papers related to wireless sensor networks has increased substantially. Most of them focus in raising issues as routing algorithms, network lifetime, and more recently, Multiple Input Multiple Output wireless networks. In contrast with all those studies, we present a practical application of wireless networks: The sensing of the pH and temperature for a fish farm. The application requires two different kind of modules: the sensor itself and the wireless module. The sensor collect and transmit the information to a wireless module using a wired connection. Once the information reaches the wireless node, it is forwarded to the central unit through a wireless protocol. The central unit starts and manages the network, as well as stores all the received data. The sensor module includes an pH sensor based on a specially designed ISFET and a commercial temperature sensor. The wireless node collects the sensed data by means of an asynchronous wired serial polling communication. The use of this kind of protocol allows to connect a single master with multiple slaves. In our particular case, we have connected one master with four slaves using a transmission rate of 9600 b/s. The wireless transmission follows the standard IEEE 802.15.4, and implements the routing protocol based on the ZigBee standard. The number of nodes distributed in the fish farm has been limited to 30 while the maximum number of hops to 6. Moreover, between the MAC and the routing layer an energy management layer have been included. This layer reduces the power consumption of the wireless network using an RF activity duty cycle for the reception stage at the final end device of around 0.02%.

Microstructure of Czochralski silicon annealed at enhanced stress conditions

Abstract The microstructure of Czochralski silicon (Cz-Si, containing oxygen interstitials, O i ) treated at high temperatures–pressures (HT–HP) at (1230, 1400) K/(0.01–1.2) GPa was investigated by optical, photoluminescence (PL), X-ray (synchrotron) and related methods. Prior to the HT–HP treatment, Cz-Si was pre-annealed at (720–1000) K/10 5 Pa to create nucleation centres (NCs) for oxygen precipitation at HT. The samples pre-annealed at (720, 830) K and treated at 1230 K indicate pronounced O i precipitation with creation of dislocations, while different oxygen-related micro-defects were created in the samples pre-annealed at (920, 1000) K and treated at (1230, 1400 K)/HP. The observed effects are related to stabilisation of NCs and retarded oxygen diffusion at HT–HP.

Oxygen-related micro-defects in Czochralski silicon annealed at enhanced stress conditions

Abstract Effect of enhanced (up to 1.2 GPa) hydrostatic argon pressure on creation of oxygen-related micro-defects (such as oxygen clusters, OC’s, and precipitates, OP’s) in Cz–Si during high temperature–high pressure treatment, HT–HP, at up to 1400 K, was investigated by chemical selective etching, FTIR, and photoluminescence, PL, methods. Cz–Si contained interstitial oxygen, O i , with a concentration, c 0 , up to 1.1×10 18 cm 3 ; prior to the HT–HP treatment some samples were pre-annealed at (720, 830) K–10 5 Pa to create nucleation centres for O i precipitation. The HT–HP treatment results in decrease of c 0 , revealing defect-related PL bands and enhanced (in comparison to effect of annealing at 10 5 Pa) creation of oxygen-related micro-defects.

Organosilane-functionalization of nanostructured indium tin oxide films

Fabrication and organosilane-functionalization and characterization of nanostructured ITO electrodes are reported. Nanostructured ITO electrodes were obtained by electron beam evaporation, and a subsequent annealing treatment was selectively performed to modify their crystalline state. An increase in geometrical surface area in comparison with thin-film electrodes area was observed by atomic force microscopy, implying higher electroactive surface area for nanostructured ITO electrodes and thus higher detection levels. To investigate the increase in detectability, chemical organosilane-functionalization of nanostructured ITO electrodes was performed. The formation of 3-glycidoxypropyltrimethoxysilane (GOPTS) layers was detected by X-ray photoelectron spectroscopy. As an indirect method to confirm the presence of organosilane molecules on the ITO substrates, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were also carried out. Cyclic voltammograms of functionalized ITO electrodes presented lower reduction-oxidation peak currents compared with non-functionalized ITO electrodes. These results demonstrate the presence of the epoxysilane coating on the ITO surface. EIS showed that organosilane-functionalized electrodes present higher polarization resistance, acting as an electronic barrier for the electron transfer between the conductive solution and the ITO electrode. The results of these electrochemical measurements, together with the significant difference in the X-ray spectra between bare ITO and organosilane-functionalized ITO substrates, may point to a new exploitable oxide-based nanostructured material for biosensing applications. As a first step towards sensing, rapid functionalization of such substrates and their application to electrochemical analysis is tested in this work. Interestingly, oxide-based materials are highly integrable with the silicon chip technology, which would permit the easy adaptation of such sensors into lab-on-a-chip configurations, providing benefits such as reduced size and weight to facilitate on-chip integration, and leading to low-cost mass production of microanalysis systems.

A low-cost and miniaturized potentiostat for sensing of biomolecular species such as TNF-α by electrochemical impedance spectroscopy

Miniaturizing potentiostats, keeping their cost low and yet preserving full measurement characteristics (e.g. bandwidth, determination of capacitive/inductive contribution to sensors impedance and parallel screening) is still an unresolved challenge in bioelectronics. In this work, the combination of simple analogue circuitry together with powerful microcontrollers and a digital filter implementation is presented as an alternative to complex and incomplete architectures reported in the literature. A low-cost acquisition electronic system fully integrated with a biosensors platform containing eight gold working microelectrodes and integrated reference and counter electrodes was developed and validated. The manufacturing cost of the prototype was kept below 300 USD. The performance of the proposed device was benchmarked against a commercial impedance analyzer through the electrochemical analysis of a highly sensitive biosensor for the detection of tumor necrosis factor α (TNF-α) within the randomly chosen range of 266pg/mL to 666ng/mL in physiological medium (PBS). A strong correlation between the outputs of both devices was found in a critical range of frequencies (1-10Hz), and several TNF-α cytokine concentrations were properly discriminated. These results are very promising for the development of low-cost, portable and miniaturized electrochemical systems for point-of-care and environmental diagnosis.

System model of an image stabilization system

The Polarimetric and Helioseismic Imager (PHI) instrument is part of the remote instruments for the ESA Solar Orbiter (SO), which is scheduled to launch in 2017. PHI captures polarimetric images from the Sun to better understand our nearest star, the Sun. A set of images is acquired with different polarizations, and afterwards is processed to extract the Stokes parameters. As Stokes parameters require the subtraction of the image values, in order to get the desired quality it is necessary to have good contrast in the image and very small displacements between them. As a result an Image Stabilization System (ISS) is required. This paper is focused in the behavior and the main characteristics of this system. This ISS is composed of a camera, a tip-tilt mirror and a control system. The camera is based on a STAR1000 sensor that includes a 10 bits resolution high-speed Analog-to-Digital Converter (ADC). The control system includes a Correlation Tracking (CT) algorithm that determines the necessary corrections. The tip-tilt mirror is moved based on this corrections to minimize the effects of the spacecraft (S/C) drift and jitter with respect to the Sun. Due to its stringent requirements, a system model has been developed in order to verify that the required parameters can be satisfied. The results show that the ISS is feasible, although the margins are very small.

Software management of power consumption in WSN based on duty cycle algorithms

In battery-operated nodes of a wireless sensor network, energy is a scarce resource that should not be wasted. During the recent years, energy efficient algorithms and protocols to maximize network lifetime have attracted the attention of many researchers. As the radio transceiver is one of the elements of the node that has higher power consumption, a typical approach to save energy is to minimize the period of time it is active. That can be achieved by introducing a duty cycle in which the node periodically enables its radio for a short time to later return to an idle state. In this paper, we discuss the importance of the duty cycle window size and present an expression to determine it according to the particularities of the IEEE 802.15.4 specification. But, to obtain a more accurate expression, we show that it is necessary to consider the characteristics of a noisy channel, especially in industrial applications, where interferences cannot be underestimated. The proposed technique tries to minimize electromagnetic pollution in order not to disturb the normal operation of other radio devices in the environment. The results of a real implementation are also presented and its efficiency discussed in terms of boundary conditions.

Towards an IEEE 802.15.4 SDR transceiver

One of the goals of a software defined radio system is to be adaptable to send and receive data according to several specifications. That can be achieved if that system implements most of the communication operations, including physical layer tasks, in reconfigurable platforms. This paper introduces an all-digital transceiver based on the 868 MHz band of the IEEE 802.15.4 standard. The design consist of a transmitter with a bandpass delta-sigma modulator and an undersampling receiver. A Xilinx Virtex-5 FPGA is used to implement the proposed model.