Revistas
Revista:
RSC ADVANCES
ISSN:
2046-2069
Año:
2021
Vol.:
11
N°:
54
Págs.:
34144 - 34151
ZnO conductometric gas sensors have been widely studied due to their good sensitivity, cost-efficiency, long stability and simple fabrication. This work is focused on NO2 sensing, which is a toxic and irritating gas. The developed sensor consists of interdigitated electrodes covered by a ZnO sensing layer. ZnO has been grown by means of the aerosol assisted chemical vapor deposition technique and then nanostructured by laser interference lithography with a UV laser. The SEM and XRD results show vertically oriented growth of ZnO grains and a 2D periodic nanopatterning of the material with a period of 800 nm. Nanostructuring lowers the base resistance of the developed sensors and modifies the sensor response to NO2. Maximum sensitivity is obtained at 175 degrees C achieving a change of 600% in sensor resistance for 4 ppm NO(2)versus a 400% change for the non-nanostructured material. However, the most relevant results have been obtained at temperatures below 125 degrees C. While the non-nanostructured material does not respond to NO2 at such low temperatures, nanostructured ZnO allows NO2 sensing even at room temperature. The room temperature sensing capability possibly derives from the increase of both the surface defects and the surface-to-volume ratio. The long stability and the gas sensing under humid conditions have also been tested, showing improvements of sensitivity for the nanostructured sensors.
Revista:
RSC ADVANCES
ISSN:
2046-2069
Año:
2021
Vol.:
11
N°:
30
Págs.:
18493 - 18499
Aerosol-assisted Chemical Vapor Deposition (AACVD) is a thermally activated CVD technique that uses micro-droplets as deposition precursors. An AACVD system with a custom-designed reaction chamber has been implemented to grow ZnO thin films using zinc chloride as a precursor. The present work aims to study the impact of the deposition parameters on the thin film, as well as the microstructure evolution and growth kinetics. Aerosol flow has an effect on the density of nucleation sites and on the grain size. The temperature affects the morphology of the grown ZnO, showing a preferential orientation along the c-axis for 350 degrees C, 375 degrees C and 400 degrees C substrate temperatures. The microstructural evolution and the growth kinetics are also presented. A different evolution behavior has been observed for 350 degrees C, where nucleation site density is the highest at the early stages and it decreases over time in contrast with the cases of 375 degrees C and 400 degrees C, where there is an initial increase and a subsequent decrease. The activation energy of the chemical reaction is 1.06 eV. The optical characterization of the material has been performed through reflection measurements showing a relationship between the spectrum and the ZnO film thickness. The electrical characterization has been done by means of an interdigital capacitor, with which it is possible to measure the grain and grain boundary resistance of the material. Both resistances are of the order of 10(5)-10(6) omega.
Revista:
THIN SOLID FILMS
ISSN:
0040-6090
Año:
2017
Vol.:
636
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.
Revista:
METTERDAAD MAGAZINE
ISSN:
2212-0114
Año:
2015
Vol.:
14
N°:
Part 3
Págs.:
475 - 485
The objective of the work described in this paper is to develop a device to monitor air quality in indoor environments integrating three conductometric gas sensors based on thin film and nanostructured metal oxide semiconductors (SnO2, NiO and ZnO). The sensors are incorporated into a single robust, reliable and cheap detection platform, which includes air pre-conditioning and electronics. The main aim of the device is to integrate with HVAC (Heat Ventilation and Air Conditioning) in an energy-efficient way whilst maintaining a high air quality standard within the building. Due to the lack of common EU legislation, the target gases and detection limits have been set after reviewing the literature and the recommendations of different agencies in Europe and the US, focusing on indoor Volatile Organic Compounds (VOCs).
Autores:
Pérez, N; Tavera, T.; Ellman, M.; et al.
Revista:
APPLIED SURFACE SCIENCE
ISSN:
0169-4332
Año:
2012
Vol.:
258
N°:
23
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.