Alberto J. Palma

Smartphone-Based Simultaneous pH and Nitrite Colorimetric Determination for Paper Microfluidic Devices

In this work, an Android application for measurement of nitrite concentration and pH determination in combination with a low-cost paper-based microfluidic device is presented. The application uses seven sensing areas, containing the corresponding immobilized reagents, to produce selective color changes when a sample solution is placed in the sampling area. Under controlled conditions of light, using the flash of the smartphone as a light source, the image captured with the built-in camera is processed using a customized algorithm for multidetection of the colored sensing areas. The developed image-processing allows reducing the influence of the light source and the positioning of the microfluidic device in the picture. Then, the H (hue) and S (saturation) coordinates of the HSV color space are extracted and related to pH and nitrite concentration, respectively. A complete characterization of the sensing elements has been carried out as well as a full description of the image analysis for detection. The results show good use of a mobile phone as an analytical instrument. For the pH, the resolution obtained is 0.04 units of pH, 0.09 of accuracy, and a mean squared error of 0.167. With regard to nitrite, 0.51% at 4.0 mg L(-1) of resolution and 0.52 mg L(-1) as the limit of detection was achieved.

A comprehensive model for Coulomb scattering in inversion layers

A comprehensive model for Coulomb scattering in inversion layers is presented. This model simultaneously takes into account the effects of: (i) the screening of charged centers by mobile carriers, (ii) the distribution of charged centers inside the structure, (iii) the actual electron distribution in the inversion layer, (iv) the charged‐center correlation, and (v) the effect of image charges. A Monte Carlo calculation to obtain the effective mobility of electrons in an n‐Si(100) inversion layer by using the model proposed for Coulomb scattering has been developed. The importance of correctly taking into account the effects above to study Coulomb scattering in inversion layers is pointed out.

Recent developments in handheld and portable optosensing—A review

Recent developments in portable and handheld opto-chemical analytical instrumentation over the last decade (2000-2010) are reviewed. First, the characteristics of typical portable/handheld instrumentation are discussed from different points of view: in situ operation, low energy consumption, ease of use, and self-contained devices. These advancements have improved or hastened improvements in the development of miniaturized optoelectronic and optical components, mainly solid-state devices such as different types of semiconductor lasers, light-emitting diodes, and photodiodes. A brief review of advances in these components is also presented. The numerous examples of portable instrumentation presented have been classified according to direct-recognition and reagent-based sensing, and within these, by absorption and emission-based systems. The conclusion discusses some key trends and future perspectives for this technology.

Physical model for trap-assisted inelastic tunneling in metal-oxide- semiconductor structures

A physical model for trap-assisted inelastic tunnel current through potential barriers in semiconductor structures has been developed. The model is based on the theory of multiphonon transitions between detrapped and trapped states and the only fitting parameters are those of the traps (energy level and concentration) and the Huang–Rhys factor. Therefore, dependences of the trapping and detrapping processes on the bias, position, and temperature can be obtained with this model. The results of the model are compared with experimental data of stress induced leakage current in metal-oxide-semiconductor devices. The average energy loss has been obtained and an interpretation is given of the curves of average energy loss versus oxide voltage. This allows us to identify the entrance of the assisted tunnel current in the Fowler–Nordheim regime. In addition, the dependence of the tunnel current and average energy loss on the model parameters has been studied.

Effects of the inversion-layer centroid on the performance of double-gate MOSFETs

The role of the inversion-layer centroid in a double-gate metal-oxide-semiconductor field-effect-transistor (DGMOSFET) has been investigated. The expression obtained for the inversion charge is similar to that found in conventional MOSFETs, with the inversion-charge centroid playing an identical role. The quantitative value of this magnitude has been analyzed in volume-inversion transistors and compared with the value obtained in conventional MOSFETs. The minority-carrier distribution has been found to be even closer to the interfaces in volume-inversion transistors with very thin films, and therefore, some of the advantages assumed for these devices are ungrounded. Finally, the overall advantages and disadvantages of double-gate MOSFETs over their conventional counterparts are discussed.

Direct and trap-assisted elastic tunneling through ultrathin gate oxides

The direct and assisted-by-trap elastic tunnel current in metal–oxide–semiconductor capacitors with ultrathin gate oxide (1.5–3.6 nm) has been studied. Bardeen’s method has been adapted to obtain the assisted tunnel current, in addition to the direct tunnel current. The dependence of the assisted current on the trap distribution in energy has also been analyzed. This allows us to obtain the trap distribution in energy from experimental current curves. Finally, we have analyzed the role of the image force, the inclusion of which can avoid a barrier height dependence on the oxide thickness.

Recent developments in computer vision-based analytical chemistry: A tutorial review

Chemical analysis based on colour changes recorded with imaging devices is gaining increasing interest. This is due to its several significant advantages, such as simplicity of use, and the fact that it is easily combinable with portable and widely distributed imaging devices, resulting in friendly analytical procedures in many areas that demand out-of-lab applications for in situ and real-time monitoring. This tutorial review covers computer vision-based analytical (CVAC) procedures and systems from 2005 to 2015, a period of time when 87.5% of the papers on this topic were published. The background regarding colour spaces and recent analytical system architectures of interest in analytical chemistry is presented in the form of a tutorial. Moreover, issues regarding images, such as the influence of illuminants, and the most relevant techniques for processing and analysing digital images are addressed. Some of the most relevant applications are then detailed, highlighting their main characteristics. Finally, our opinion about future perspectives is discussed.

A simple subthreshold swing model for short channel MOSFETs

Abstract A new approach to calculate the subthreshold swing of short channel bulk and silicon-on-insulator metal oxide semiconductor field effect transistors is presented. The procedure utilizes a channel-potential expression appropriate for submicron dimensions. The final result is similar to that used for long channels except for a factor λ which represents the short channel effects. Comparison with different published results reveals excellent quantitative agreement.

Fast prototyping of paper-based microfluidic devices by contact stamping using indelible ink

Here we present a fast and cheap prototyping technique for the realisation of paper-based microfluidic devices simply by using a stamp and indelible ink. The proposed mechanism involves contact stamping of indelible ink to laboratory filter paper using a PDMS stamp, which defines the microfluidic structure. It is a cleanroom and washing steps-free method which provides a reproducible method for the production of functional paper-based microfluidic devices in a single step in less than 10 s. The method is fully characterised and the concept has been applied, as a proof-of-principle, for the realisation of a low-cost colorimetric glucose sensor.

Design and Development of Sensing RFID Tags on Flexible Foil Compatible With EPC Gen 2

Taking advantage of the sensor interface capabilities of a radio frequency identification (RFID) chip, the integration of different types of sensors on printed ultrahigh frequency (UHF) RFID tags is investigated. The design, development, and testing of printed smart sensing tags compatible with the RFID standard electronic product code Gen 2 is presented. Two different strategies are employed to interface the sensors: 1) passive single-chip and 2) semipassive architectures. Both strategies provide sensor data by directly answering to the RFID reader inquiries or using a data logging mechanism to store the sensor data in the RFID chip memory. Temperature readout is measured using the embedded sensor in the RFID chip. Additionally, a light sensor and pressure sensor interfaced to a microcontroller are implemented in the passive and semipassive tags versions, respectively. For the employed RFID chip, two different UHF antennas are designed and printed using inkjet and screen printing to compare their radio frequency performances. Finally, the fabricated smart tags are fully validated through measurements in an anechoic chamber and their behaviors are compared with numerical simulation. The screen printed semipassive RFID tag with loop antenna shows a better reading range than the inkjet-printed one, whereas the passive tag can be considered as the most cost-effective system.