Arnau Coll

Colloidal crystals by electrospraying polystyrene nanofluids

This work introduces the electrospray technique as a suitable option to fabricate large-scale colloidal nanostructures, including colloidal crystals, in just a few minutes. It is shown that by changing the deposition conditions, different metamaterials can be fabricated: from scattered monolayers of polystyrene nanospheres to self-assembled three-dimensional ordered nanolayers having colloidal crystal properties. The electrospray technique overcomes the main problems encountered by top-down fabrication approaches, largely simplifying the experimental setup. Polystyrene nanospheres, with 360-nm diameter, were typically electrosprayed using off-the-shelf nanofluids. Several parameters of the setup and deposition conditions were explored, namely the distance between electrodes, nanofluid conductivity, applied voltage, and deposition rate. Layers thicker than 20 μm and area of 1 cm2 were typically produced, showing several domains of tens of microns wide with dislocations in between, but no cracks. The applied voltage was in the range of 10 kV, and the conductivity of the colloidal solution was in the range of 3 to 4 mS. Besides the morphology of the layers, the quality was also assessed by means of optical reflectance measurements showing an 80% reflectivity peak in the vicinity of 950-nm wavelength.

Metal-insulator-metal capacitor using electrosprayed nanoparticles

An electrospray technique has been used to deposit SiO2 nanoparticles as insulator layer of a metal-insulator-metal device. Impedance spectroscopy measurements show that a 4.4 factor increase in capacitance is achieved compared to a continuous dielectric layer of the same permittivity and dimensions.

Influence of Amorphous Silicon Carbide Intermediate Layer in the Back-Contact Structure of Cu 2 ZnSnSe 4 Solar Cells

Cu2 ZnSn(S1-ySey )4 (CZTS) thin-film solar cells have been qualified as potential competitors of the more established CIGS ones. One of the more important handicaps of CZTS solar cells is the open-circuit voltage deficit. The rear-contact/absorber interface is known to be very sensitive to the formation of secondary phases, which are detrimental for the electrical behavior of photovoltaic devices. The addition of intermediate layers to favor the formation of an adequate interface has been repeatedly tested. In this work, an amorphous silicon carbide (a-SiC) layer is added to explore its influence on the material properties and electrical performance of CZTSe solar cells. According to scanning electron microscopy (SEM) analysis, when the a-SiC layer thickness is increased, bigger grains along the absorber are obtained. Additionally, a lower [VCu + ZnCu ] defect cluster density is also deduced from the analysis of Raman measurements. Both results indicate a favorable impact of a-SiC films on the material quality of the absorber. Fabricated solar cells show an enhancement of 0.9% abs. of efficiency compared to identical solar cells without a-SiC layers used as a reference. This increase is mainly related to an improvement of open-circuit voltage and fill factor (FF) when the proposed intermediate layer is included.

Effect of nanofluid conductivity and humidity on the self-assembly of nanoparticles deposited by electrospray

Electrospray technique has been used in previous works as an excellent way to develop ordered nanostructures. This work focuses on the necessary conditions to achieve 3D nano-ordered layers, which are mainly determined by the conductivity of the liquid where nanoparticles are solved and the existence of an electrical field gradient. Changes in the conductivity induce a different evaporation rate during the ejection phase and control the amount of liquid that is deposited on the substrate. Controlling the conductivity, the electrical field and the quantity of liquid on the substrate different nanostructures can be fabricated, ranging from a semicovered monolayer of scattered nanoparticles up to a fully 3D colloidal crystal.

Al2O3/TiO2 inverse opals from electrosprayed self-assembled templates

The fabrication of high optical quality inverse opals is challenging, requiring large size, three-dimensional ordered layers of high dielectric constant ratio. In this article, alumina/TiO2–air inverse opals with a 98.2% reflectivity peak at 798 nm having an area of 2 cm2 and a thickness of 17 µm are achieved using a sacrificial self-assembled structure of large thickness, which was produced with minimum fabrication errors by means of an electrospray technique. Using alumina as the first supporting layer enables the deposition of TiO2 at a higher temperature, therefore providing better optical quality.

From random to order

© 2016 Elsevier B.V. All rights reserved. This paper introduces the possibility to produce 1-2 cm2 and tens of layers colloidal crystals on different non-flat surfaces by means of electrospray deposition. Two different types of crystalline silicon surfaces were tested: nanostructured

From random to order: Colloidal crystals on non-flat surfaces

© 2016 Elsevier B.V. All rights reserved. This paper introduces the possibility to produce 1-2 cm2 and tens of layers colloidal crystals on different non-flat surfaces by means of electrospray deposition. Two different types of crystalline silicon surfaces were tested: nanostructured

Nanohole particle filling by electrospray

Nanostructuring materials such as silicon provides a good technology to fabricate optical and sensing devices. The possibility to fill the pores or channels with different material opens the way to new applications. In this work, we study the electrokinetics of electrospraying technique to fill porous material with nanobeads. The simulations take into account a photonic crystal topology applying a difference potential of 14 kV. Measurements show the viability of filling alumina nanoporous with 360nm polyestyrene nanospheres.

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

In this paper we propose the modeling and simulation using Comsol 3.5a of a microfluidic chip, capable to run several tasks such as focusing, mixing, sorting and trapping nano and microbeads. The microfluidic chip, based on Polydimethyl siloxane (PDMS) and Polyethylenenaphtalate (PEN), is cost effective, flexible and totally biocompatible. The fluidic part is controlled both by pressure driven flow and electrostatics. The manipulation of the beads is purely electrostatic and it is based on a mixed approach: electrophoretic (EP) and dielectrophoretic (DEP). The simulations are run in Comsol 3.5a using basically the MEMS module. The nano and microbeads used are metallic (gold) and dielectric (polystyrene, fused silica).