Nuestros investigadores

Noemí Pérez Hernández

Publicaciones científicas más recientes (desde 2010)

Autores: Fuentes, M.D.C, (Autor de correspondencia); Pérez, N; Ayerdi, Isabel;
Revista: THIN SOLID FILMS
ISSN 0040-6090  Vol. 636  2017  págs. 438 - 445
Microfabrication technology in the biomedical field has provided microelectrode arrays for neural implants with new development opportunities. The need for more complex physiological functions and miniaturization, as well as the use of new materials for more flexible electrodes, can now be satisfied. PDMS (Polydimethylsiloxane) substrates are elastic, biocompatible and permeable to oxygen, in addition to being a highly stable material. However, the implementation of microfabrication techniques such as deposition and patterning processes on these new substrates is not straightforward. This paper will describe the development of a reliable method to metalize thin film microelectrodes on a highly flexible medical grade PDMS layer that is suitable for long-term implantation. Platinum (Pt) microelectrodes were deposited by physical vapor deposition and pattern transfer by lift-off was chosen. Standard photolithography was used to pattern a conventional positive photoresist and was optimized to improve adhesion and to avoid cracks in the resist. The electrical behavior of the metal-polymer interface was analyzed using multiplexed DC measurements. The resistance values of seven samples and a control were acquired sequentially. Special attention was paid to the connectorization from the flexible microelectrodes to a rigid substrate. Measurements were carried out in an air-protected environment as well as in a biological environment designed to mimic the environment of the human body. Long-term stability of the Pt-PDMS interface was strongly influenced by the electrode configuration and its connection. A characteristic electrical behavior was observed for a straight-electrode configuration. This configuration demonstrated significant drift of resistance values of more than 4% during the initial 56 h. By contrast, a stable behavior was observed for a loop electrode design, with only small variations of less than +/- 0.5% caused by thermal fluctuations. (C) 2017 Elsevier B.V. All rights reserved.
Autores: Malagu, C.; Morandi, S.; et al.
Revista: ACTA MATERIALIA
ISSN 1359-6454  Vol. 61  Nº 4  2013  págs. 1146 - 1153
In this work the sensing mechanism of p-type semiconducting NiO thin films under the exposure to formaldehyde is explained. The influence of the sensing layer thickness and annealing treatment on the structural, optical and electrical properties of the samples is studied. The height of the potential barrier is estimated from temperature-stimulated conductance measurements. The potential barrier height is linked to oxygen ionosorption on the semiconductor surface. Furthermore, Fourier transform-IR analysis was carried out in order to determine the chemical reactions that govern the process of gas detection and the temperature range at which they occur. As a result of the study, it is possible to explain how the thickness and annealing treatment affect the sensing mechanism of the samples.
Autores: Isasa, M.; Pérez, N; Tavera, T.; et al.
Revista: THIN SOLID FILMS
ISSN 0040-6090  Vol. 548  2013  págs. 69 - 74
Micrometric periodical gold/silver alloy linear patterns have been prepared by thermal annealing of bilayer thin films (gold/silver) by means of laser interference metallurgy. These alloyed lines alternate with non-alloyed gold/silver thin films. A chemical attack with a nitric acid solution produces the dealloying of the annealed patterns (by preferential removal of the less noble material), and thus, the linear patterns acquire a nanoporous structure. These nanostructured lines alternate with gold thin films produced after the elimination of the silver thin film in the non-alloyed areas. (C) 2013 Elsevier B.V. All rights reserved.
Autores: Yurrita, P.; Pérez, N; et al.
Revista: APPLIED SURFACE SCIENCE
ISSN 0169-4332  Vol. 276  2013  págs. 229 - 235
A study of the influence of annealing temperature on the structural, morphological and optical properties of WO3 thin films is presented. The coatings are deposited by RF reactive magnetron sputtering and characterized by XRD analysis and FESEM. The XRD diagrams of the samples show a phase transition from tetragonal to monoclinic when the annealing temperature is raised from 800 to 900 degrees C. Moreover, the increase of the annealing temperature to 800 degrees C favors the presence of a granular structure on the surface of the film. A decrease in the optical energy band gap (3.65-3.5 eV and 3.5-3.05 eV for direct and indirect transitions respectively) with annealing temperature has been measured employing Tauc's relation. Furthermore, WO3 thin films are processed by laser interference lithography (LIL) and periodic nanostructures are obtained. The processed films are characterized by a hexagonal symmetry with a period of 340 nm and the diameter of the nanostructured holes of 150 nm. These films show improved morphological properties of interest in several applications (gas sensors, photonic crystals, etc.) independent of the annealing temperature. .
Autores: Rodríguez, Ainara; Pérez, N; et al.
Revista: OPTICAL MATERIALS EXPRESS
ISSN 2159-3930  Vol. 2  Nº 11  2012  págs. 1571 - 1579
Metallic gratings were fabricated using high energy laser interference lithography with a frequency tripled Nd:YAG nanosecond laser. The grating structures were first recorded in a photosensitive layer and afterwards transferred to an Au film. High quality Au gratings with a period of 770 nm and peak-to-valley heights of 20-60 nm exhibiting plasmonic resonance response were successfully designed, fabricated and characterized. (C) 2012 Optical Society of America
Autores: Pérez, N; Tavera, T.; Ellman, M.; et al.
Revista: APPLIED SURFACE SCIENCE
ISSN 0169-4332  Vol. 258  Nº 23  2012  págs. 9370 - 9373
This work presents the fabrication of hollow-core metallic structures with a complete laser interference lithography (LIL) process. A negative photoresist is used as sacrificial layer. It is exposed to the pattern resulting from the interference of two laser beams, which produces a structure of photoresist lines with a period of 600 nm. After development of the resist, platinum is deposited on the samples by DC sputtering and the resist is removed with acetone. The resulting metallic structures consist in a continuous platinum film that replicates the photoresist relief with a hollow core. The cross section of the channels is up to 0.1 mu m(2). The fabricated samples are characterized by FESEM and FIB. This last tool helps to provide a clear picture of the shape and size of the channels. Conveniently dimensioned, this array of metallic submicrometric channels can be used in microfluidic or IC cooling applications. (c) 2012 Elsevier B.V. All rights reserved.
Autores: Rodríguez, Ainara; Tavera, T.; et al.
Revista: MICROELECTRONIC ENGINEERING
ISSN 0167-9317  Vol. 98  2012  págs. 672 - 675
Femtosecond laser micromachining has progressed considerably in the last decade due to the increasing interest in glass microsystems. In this work, we present a systematic study of the femtosecond laser ablation rate of soda-lime glass as a function of the deposited energy and pulse overlapping parameters. Experimental results demonstrate that the incubation effect reported by other authors can be neglected for particular process conditions and a constant ablation rate can be obtained, thus enhancing the depth control of the fabricated features. (C) 2012 Elsevier B.V. All rights reserved.
Autores: Tavera, T.; Pérez, N; Rodríguez, Ainara; et al.
Revista: APPLIED SURFACE SCIENCE
ISSN 0169-4332  Vol. 258  Nº 3  2011  págs. 1175 - 1180
The production of periodic structures in silicon wafers by four-beam is presented. Because laser interference ablation is a single-step and cost-effective process, there is a great technological interest in the fabrication of these structures for their use as antireflection surfaces. Three different laser fluences are used to modify the silicon surface (0.8 J cm(-2), 1.3 J cm(-2), 2.0 J cm(-2)) creating bumps in the rim of the irradiated area. Laser induced periodic surface structures (LIPSS), in particular micro and nano-ripples, are also observed. Measurements of the reflectivity show a decrease in the reflectance for the samples processed with a laser fluence of 2.0 J cm(-2), probably caused by the appearance of the nano-ripples in the structured area, while bumps start to deteriorate. (C) 2011 Elsevier B.V. All rights reserved.
Autores: Herran, J.; Pérez, N; et al.
Revista: SENSOR LETTERS
ISSN 1546-198X  Vol. 9  Nº 1  2011  págs. 64 - 68
The aim of the present work is to test the performance of thin films of NiO obtained by vacuum technology to toxic gases. The first gas considered is NO2 due to the fact that it is toxic to human body and harmful to the environment. NiO thin films were deposited by RF reactive magnetron sputtering on alumina substrates provided with Pt interdigitated microelectrodes and a Pt heater on the reverse side. The samples were annealed at 600 degrees C, 700 degrees C and 800 degrees C in order to compare their response to the selected gas. XRD and energy dispersive spectroscopy (EDS) analysis were carried out to correlate the different electrical responses to the material microstructure. Moreover, morphological characterization of the sensing films was performed by field emission gun-scanning electron microscopy. Two different thicknesses were deposited (150 nm and 300 nm) in order to study the influence of this parameter. The samples were exposed to concentrations between 5 and 100 ppm of NO2. The 150 nm-thick samples at 700 degrees C showed the best responses to low concentrations at 300 degrees C.
Autores: Pérez, N; Sanza, F.J.; Rodríguez, Ainara; et al.
Revista: CRYSTAL RESEARCH AND TECHNOLOGY
ISSN 0232-1300  Vol. 46  Nº 10  2011  págs. 1044 - 1050
We have fabricated polystyrene opals by vertical deposition with colloidal spheres of 419 nm in diameter. Different parameters such as the concentration, temperature and relative humidity have been systematically varied in order to study the dependence of the crystalline quality of the opals on these parameters. The opals have been optically and structurally characterized, paying particular attention to the size and distribution of the domains for each fabrication condition. We have noticed a dependence of the size of the domains on the thickness which corroborates a previous study. From these results we can conclude that the characterization of the homogeneity of the thickness of the opals can be done just by using microscopy. We also report a dependence of the order of the opals on relative humidity and a selective adhesion of the opals to the substrate depending on concentration and surface chemistry. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Autores: Pérez, N; Rodríguez, Ainara; Olaizola, Santiago Miguel;
Libro:  Fabrication and Characterization in the Micro-Nano Range
2011  págs. 47 - 68
Autores: Pérez, N; Olaizola, Santiago Miguel;
2010 
Periodic structures in the sub-micro and nano scales have attracted the attention of researchers lately due to the novel properties they exhibit. One of the main issues which slow down the integration of this type of structures in real devices is the lack of fabrication techniques which can scale to mass production. The present work studies the fabrication of silver sub-micrometric structures by two different techniques: self-assembly of colloidal spheres and laser interference lithography. The self-assembly technique consists of different steps which are studied and optimized, starting with the optimization of the deposition conditions of indium tin oxide thin films. The next steps are the assembly of colloidal spheres, the infiltration of the resultant opals with silver and the inversion of the infiltrate opals, giving rise to ordered silver structures. The laser interference lithography technique is also used to obtain this type of structures. The resulting silver structures are structurally and optically characterized. It is demonstrated in this work that these structures present optical properties which make them feasible for future photonic applications.

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