Integrated luminescent chemical microsensors based on GaN LEDs for security applications using smartphones

Development of PCB-integrateable microsensors for monitoring chemical species is a goal in areas such as lab-on-a-chip analytical devices, diagnostics medicine and electronics for hand-held instruments where the device size is a major issue. Cellular phones have pervaded the world inhabitants and their usefulness has dramatically increased with the introduction of smartphones due to a combination of amazing processing power in a confined space, geolocalization and manifold telecommunication features. Therefore, a number of physical and chemical sensors that add value to the terminal for health monitoring, personal safety (at home, at work) and, eventually, national security have started to be developed, capitalizing also on the huge number of circulating cell phones. The chemical sensor-enabled “super” smartphone provides a unique (bio)sensing platform for monitoring airborne or waterborne hazardous chemicals or microorganisms for both single user and crowdsourcing security applications. Some of the latest ones are illustrated by a few examples. Moreover, we have recently achieved for the first time (covalent) functionalization of p- and n-GaN semiconductor surfaces with tuneable luminescent indicator dyes of the Ru-polypyridyl family, as a key step in the development of innovative microsensors for smartphone applications. Chemical “sensoring” of GaN-based blue LED chips with those indicators has also been achieved by plasma treatment of their surface, and the micrometer-sized devices have been tested to monitor O2 in the gas phase to show their full functionality. Novel strategies to enhance the sensor sensitivity such as changing the length and nature of the siloxane buffer layer are discussed in this paper

Medida de perfiles de concentración por medio de AES y bombardeo iónicosimultáneo, aplicación al estudio de la oxidación del tantalio

Tesis doctoral inédita leida en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Aplicada. Fecha de lectura: 6-07-198

Towards nanometric resolution in multilayer depth profiling: a comparative study of RBS, SIMS, XPS and GDOES

An increasing amount of effort is currently being directed towards the development of new functionalized nanostructured materials (i.e., multilayers and nanocomposites). Using an appropriate combination of composition and microstructure, it is possible to optimize and tailor the final properties of the material to its final application. The analytical characterization of these new complex nanostructures requires high-resolution analytical techniques that are able to provide information about surface and depth composition at the nanometric level. In this work, we comparatively review the state of the art in four different depth-profiling characterization techniques: Rutherford backscattering spectroscopy (RBS), secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS) and glow discharge optical emission spectroscopy (GDOES). In addition, we predict future trends in these techniques regarding improvements in their depth resolutions. Subnanometric resolution can now be achieved in RBS using magnetic spectrometry systems. In SIMS, the use of rotating sample holders and oxygen flooding during analysis as well as the optimization of floating low-energy ion guns to lower the impact energy of the primary ions improves the depth resolution of the technique. Angle-resolved XPS provides a very powerful and nondestructive technique for obtaining depth profiling and chemical information within the range of a few monolayers. Finally, the application of mathematical tools (deconvolution algorithms and a depth-profiling model), pulsed sources and surface plasma cleaning procedures is expected to greatly improve GDOES depth resolution.Ministerio de Ciencia e Innovación MAT2008-06618-C02-01Ministerio de Ciencia e Innovación CSD2008- 00023 (FUNCOAT)Ministerio de Ciencia e Innovación RyC2007-002

An XPS and ellipsometry study of Cr–O–Al mixed oxides grown by reactive magnetron sputtering

Cr–O–Al thin film mixed oxides grown on Si (100) substrates by reactive magnetron sputtering using different target compositions from 90% Cr (10% Al) to 10% Cr (90% Al) and oxygen fluxes in the range from 0 to 15 sccm have been investigated using ex situ XPS, XPS depth profiles and ARXPS. The chemical information obtained with XPS as well as the observed chemical shift of the Cr 2p, Al 2s and O 1s bands points to the formation of mixed substitutional Me2O3 oxides (Me = Al + Cr) instead of the formation of single oxide phases. Compositions and stoichiometries obtained from concentration depth profile measurements (CDP) simultaneously using XPS and Ar+ bombardment confirm the formation of such a type of substitutional mixed oxides. ARXPS allows ruling out oxygen preferential sputtering during Ar+ bombardment. Finally, it is shown that the optical properties of the films like their refractive index can be controlled through their chemical composition.Ministerio de Ciencia e Innovación CSD2008- 00023 (Consolider-Ingenio 2010)Ministerio de Ciencia e Innovación MAT2008-06618-C0

High- and low-energy x-ray photoelectron techniques for compositional depth profiles: destructive versus non-destructive methods

Hard x-ray photoelectron spectroscopy (HAXPES), angle-resolved x-ray photoelectron spectroscopy (ARXPS) and x-ray photoelectron spectroscopy (XPS) with simultaneous Ar+ bombardment are used to obtain chemical information and concentration depth profiles of thin film oxides on Cr, Al, Si substrata and to explore the capabilities of analyzing buried interfaces at depths above 10 nm in Cr–O–Al thin films mixed oxides deposited on Si substrata. ARXPS and HAXPES are non-destructive techniques and within the photon energy range (7.5–15 keV) and the emission angle range (0◦–70◦) used, both techniques provide equivalent information, ARXPS being more sensitive to the surface morphology. XPS and simultaneous sputtering with Ar+ is a destructive technique and effects such as atomic mixing are unavoidable; however, the comparative study with HAXPES allowed the measurement of key parameters for the understanding of the ion–matter interaction such as the mixing extent and the interface broadening.Ministerio de Ciencia e Innovación CSD2008-00023 (CONSOLIDER-Ingenio 2010)Ministerio de Ciencia e Innovación MAT2008-06618-C0

Control of the optical properties of silicon and chromium mixed oxides deposited by reactive magnetron sputtering

The development of mixed-oxide thin films allows obtaining materials with better properties than those of the different binary oxides, which makes them suitable for a great number of applications in different fields, such as tribology, optics or microelectronics. In this paper we investigate the deposition of mixed chromium and silicon oxides deposited by reactive magnetron sputtering with a view to use them as optical coatings with an adjustable refractive index. These films have been characterized by means of Rutherford backscattering spectrometry, Auger electron spectroscopy, X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy and spectroscopic ellipsometry so as to determine how the deposition conditions influence the characteristics of the material. We have found that the deposition parameter whose influence determines the properties of the films to a greater extent is the amount of oxygen in the reactive sputtering gas.Ministerio de Ciencia e Innovación CSD2008-00023 (CONSOLIDER-Ingenio 2010)Ministerio de Ciencia e Innovación MAT2008-06618-C02-02/MATMinisterio de Ciencia e Innovación RyC2007-002

Structure–property relations in ZrCN coatings for tribological applications

ZrCN coatings were deposited by dc reactive magnetron sputtering with N2 flows ranging from 2 to 10 sccm in order to investigate the influence of the nitrogen incorporation on structure and properties. Information about the chemical composition was obtained by glow discharge optical emission spectroscopy and Rutherford backscattering spectroscopy. The evolution of the crystal structure studied by X-ray diffraction revealed the formation of a face-centred cubic ZrCN phase for N2 flows greater than 4 sccm. Additionally, the presence of an amorphous phase in the coatings deposited with the highest N2 flows could be evidenced by Raman spectroscopy and X-ray photoelectron spectroscopy. This phase can act as a lubricant resulting in a low coefficient of friction as shown in the conducted ball-on-disc tests. Nanoindentation measurements showed that coatings deposited with a 6 sccm N2 flow had the maximum hardness which also revealed the best performance in the conducted dry cutting tests.Ministerio de Ciencia e Innovación CSD2008-00023 (FUNCOAT)Ministerio de Ciencia e Innovación HP2007-011

In-depth multi-technique characterization of chromium–silicon mixed oxides produced by reactive ion beam mixing of the Cr/Si interface

The great interest of mixed metal–silicon oxides lies in their suitability, among other applications, as optical coatings with an adjustable refractive index. In this paper we investigate a new method to obtain chromium and silicon mixed oxides. Using as starting point a metallic chromium film deposited on a silicon substrate by magnetron sputtering, we induce the formation of mixed oxides using reactive ion beam mixing by bombarding the Cr/Si interface with oxygen. We have varied the ion fluence (between 5 × 1016 and 1 × 1018 ions cm−2) at a fixed implantation energy of 80 keV in order to modify the final composition of the coating. The composition profiles have been obtained with Rutherford backscattering spectroscopy (RBS), by changing the He energy from 3.035 up to 3.105 MeV, and with elastic recoil detection analysis using a time of flight configuration (ERDA-ToF). Results have been compared with those obtained from secondary ion mass spectrometry (SIMS) depth profiles and Monte Carlo TRIDYN simulations. Concentration depth profiles (CDP) have been also measured using X-ray photoelectron spectroscopy (XPS) and simultaneous Ar+ bombardment, as well as angle-resolved X-ray photoelectron spectroscopy (ARXPS). All the obtained depth profiles agree remarkably well with cross-section transmission electron microscopy (TEM) observations made on the sample implanted at the highest fluence.Ministerio de Ciencia e Innovación MAT2008-06618-C02Ministerio de Ciencia e Innovación CSD2008-00023 (FUNCOAT