EWOD using nonaqueous liquids

Electrowetting on Dielectric (EWOD) has been studied for more than a decade and used for different applications but still there are few works on non-aqueous liquids such as mixtures of polyols. We have found that significant contact angle change can be achieved at voltages of 10 V and bellow and that the recovery, when the voltage is withdrawn, exceeds 92% in all the cases. The dynamic change of contact angle has been measured applying 2 Hz and 5 Hz square 10 V amplitude signal. The operation is stable but has a cut-off frequency in the range of frequency explored. Those results have been achieved using a glass substrate covered by an ITO electrode followed by a thin alumina layer and by a Teflon layer. We have also observed that the use of an HMDS layer followed by an ALD alumina layer prior to Teflon deposition provides better initial contact angle value, and that it can be achieved a significant contact angle change at lower voltages. Up to 1000 switch cycles have been performed and the contact angle change when using DI water rapidly becomes insignificant whereas with the polyol mixtures, although we have observed contact angle change degradation, it gets to a stable value thereafter.Peer ReviewedPostprint (updated version

Study of GaAs(Ti) thin films as candidates for IB solar cells manufacturing

Thin films of GaAs(Ti) have been deposited by sputtering on glass and n_GaAs substrates under different process conditions. Optical characteristics of these samples have been analyzed to study the potential of this material in intermediate Band solar cell manufacturing.Postprint (published version

Effect of dielectrophoretic force in the self-assembly process of electrosprayed nanoparticles

In this work the effect of the dielectrophoretic force (DEP) in the self-assembly process of nanoparticles electrosprayed onto a substrate, is examined. DEP force is originated by the electric field created by the electrospray gun and by the distortion of the field created by the effective dipole of each nanoparticle. It is also shown that the modulus of this force is large when the distance between particles is few times its diameter, provided the medium is wet and the electric field is not switched off. The directional nature of DEP In this wet phase, is shown to chain nanoparticles aligned with the main electric field direction. Although there is a repulsive force between chains in the orthogonal direction to the field, it is minimum when the beads align with the voids in the nearby chains. DEP is a dominant force in the close distances of nanoparticles compared to double layer, van der Waals, electrophoretic retardation, weight and buoyancy.Preprin

Steady-state and transient conductivity of collodial solutions of gold nanobeads

Steady-state and transient conductance measurements of gold nanobeads solutions deposited on top of interdigitated electrodes have been performed. It is shown that the application of an electric field of moderate value between electrodes during the drying process of the droplet makes the resulting steady-state conductance value to increase significantly. The dynamics of the gold nanobeads in the solution has been studied by means of transient current measurements during the drying process and the effects correlated to the changes in the morphology of the association of the gold nanobeads when they reach the substrate. It is seen that the application of the electric field foster the formation of gold beads monolayers, chains, and dendritic associations which, in combination with the humidity conditions of the sample surface, are believed to be the reasons for the conductance increase.Peer Reviewe

Radiation damage evaluation on AlGaAs/GaAs solar cells

A computer model to evaluate radiation damage on AlGaAs-based solar cells is reported. The model is based on a piecewise approach that divides the cell structure in an adaptive number of slices. Inside a particular slice the semiconductor parameters are constant; consequently, it is easy to find an analytical solution of the semiconductor transport equations with suitable boundary conditions for the interfaces with the adjacent slices. The model provides all electrical parameters of the cells in the operating temperature range. Different structures, including graded band gaps and double heterofaces can be analyzed. Proton damage coefficients as well as proton damage ratios can be calculated for energies between 30 and 10/sup 4/ keV with only two adjustable parameters. Coirradiation experiments with different energy protons were simulated by improving the conventional method of degradation computering.Peer ReviewedPostprint (published version

Multiphysics simulation of REMS hot-film anemometer under typical martian atmosphere conditions

The purpose of this paper is to describe numerical electro-thermal simulations of the REMS wind sensor unit [3] and the results obtained by using COMSOL multiphysics. This device is a hot-film anemometer for 2D wind measurements, which does not have movable parts and is based on the air stream forced heat convection to the environment. This wind sensor works as a thermo-electrical transducer where the same equilibrium temperature is reached for every value of the wind speed, by means of a power supply modulations. Therefore, thestraightforward relationship between the amount of power delivered to the unit and the wind speed can be derived as earlier presented [2]. Detailed finite element simulations enabled us to predict the temperature distribution, recognize hot and cold spots and characterize besides the thermal profile the operating sensing magnitudes.Postprint (published version

Modeling and simulation of a cost-effective microfluidic circuit for particles' manipulation

Preprin

Colloidal crystals by electrospraying polystyrene nanofluids

Postprint (published version

Impedance modeling of silica nanoparticle metal insulator metal capacitors

In this study, we have fabricated metal-insulator-metal (MIM) capacitors where the insulator layer is made of 255¿nm diameter silica nanospheres. The MIM devices have been characterized and modeled by electrochemical impedance spectroscopy (EIS) and charge-discharge transients. Fitting the results with modified Randles models agreed well with three constant phase elements, three leakage resistors, and a Warburg element. According to the results of the fitting of the charge-discharge measurements and of the modified Randles model, values of real capacitances up to thousand times larger than the theoretical capacitance of a similar capacitor with a continuous layer dielectric are found. These unexpected high capacitances seemed to be related to the ability of the nanospheres to trap electric charges due to surface hydroxyl groups that are originated by the adsorption of water molecules, thereby indicating that the environmental humidity plays a role. This has been ascertained by measurements at several temperatures above the ambient and the resulting capacitance decreases as temperatures increases. Furthermore, active and reactive parts of the complex power have been measured showing capacitive or resistive behavior depending on the frequency. These results suggest that this novel MIM device based on nanospheres may be a new baseline technology for supercapacitor technology.Peer ReviewedPostprint (author's final draft

Analysis of GaAs-Ti thin films deposited by sputtering onto c-Si and GaAs

Some sputtering processes of GaAs and Ti onto glass, c-Si and c-GaAs substrates have been carried out in order to obtain thin films as candidates to be intermediate band photovoltaic materials. This work presents first results concerning the optical and structural properties of the different deposited thin films.Postprint (published version