Materials Science
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Ionoluminescence of ZnO in an RBS experiment

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RBS Measurements of GaN-based devices

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Plasma inside the pulsed magnetron sputtering

Surface micro- and nano-structuring and surface modification using ion beams

MeV ions beams can modify the surface and bulk properties of materials. The modification of the surface properties is of interest in order to obtain new functions for specific applications. Surface properties and characteristics such as adsorption, adhesion, hydrophilicity, charge, reactivity, roughness, biocompatibility or even magnetic properties can, thus, be modified either in extended macroscopic surfaces or following predetermined patterns of nano- or micro-size.

At CMAM we use several ion beams especially He and Si in the energy range of MeV/amu to modify the surface properties of crystalline Si (c-Si). 20 MeV Si beams with fluencies as low as 1013 ions /cm2 suffice to increase the electrical conductivity of p type c-Si with an initial resistivity of 0.05 to 0.1, inhibiting the formation of porous silicon (PSi) in the irradiated region [1]. For such low fluencies the crystalline nature of c-Si persists at least as detected by channeling measurements, therefore this increase of resistivity can be assigned to point defects induced by the irradiation process. Irradiation through micro- and nano-sized masks allows growing PSi in predetermined patterns.

Surface modification of semiconductors like Si, and special alloys like TiNO, by ion beam processing are investigated at CMAM in collaboration with Departamento de Fisica Aplicada at Universidad Autonoma Madrid (DFA-UAM) and Centro de Biología Molecuar at Universidad Autonoma Madrid and Consejo Superior de Investigaciones Científicas (CBM-UAM-CSIC) looking for applications in the differentiation of Human Mesenchymal Stem Cells (HMSC).

Irradiation on conducting materials like Highly Oriented Pyrolitic Grafite (HOPG) can induce magnetic properties. Experiments are conducted at CMAM irradiating HOPG with H, C, or N beams in the MeV energy range. The irradiation induces magnetic effects like Curie-like paramegnetism, ferromagnetism and an anomalous paramagnetic state [2].

[1] V. Torres-Costa M. Manso-Silván, E. Punzón-Quijorna, R.J. Martín-Palma, D. Martín y Marero, A. Climent-Font, submitted to Nucl. Instr. and Meth. B
[2] M.A. Ramos, J. Barzola-Quiquia, P. Esquinazy, A. Muñoz-Martín, A. Climent-Font, and M. García-Hernández. Phys Rev B 81, 214404.

Semiconductor science at CMAM

Ion beam techniques have been long time applied in semiconductor science due to its interesting applications in the modification (doping, cleaning, patterning…) and also in the analysis (composition, structure, impurities, interfaces…) of these materials. Particularly, the non-destructive character of some IBA techniques, together with the capability of elemental depth-profiling, make these tools ideal for an advance characterization of the growth of semiconductor layers, which normally requires epitaxial thin films of high purity.

The study of semiconductor materials has been an important issue since the beginning of CMAM and a large list of IV, III-V and II-VI systems have been analyzed: Si, Ge, GaN, GaAs, InAs, ZnO, CdTe, TiO2, etc. In the last years, CMAM has been especially involved in projects for the development of wide bandgap semiconductor devices, in collaboration with ISOM institute from the Polytechnic University of Madrid.

CMAM offers many useful techniques for the characterization of semiconductor thin films, comprising RBS, ERDA, NRA and PIXE. These methods have been successfully applied for the determination of the composition with depth resolution [1], the detection of light and heavy impurities [2], and the depth-profiling of specific elements [3]. Moreover, when combined with ion channeling, these methods can provide structural information about the crystal quality [1], the strain [4], the presence of defects [3] and the lattice-site location.

The Standard beamline at CMAM is well-prepared for kind of analysis, including two particle detectors for RBS, and further gamma ray or X-ray detectors. The ERDA-TOF beamline also offers a high sensitivity for the detection of impurities or light elements, which is normally a critical issue in these materials [1]. In addition to the IBA techniques, CMAM has also a pulsed magnetron sputtering system for the growth of thin films and coatings, which have been used to study different materials, including semiconductor layers such as Si, SiGe, or TiO2.

[1] S. Fernández-Garrido, A. Redondo-Cubero, R. Gago, F. Bertram, J. Christen, E. Luna, A. Trampert, J. Pereiro, E. Muñoz and E. Calleja, J. Appl. Phys. 104, 083510 (2008).
[2] F. González-Posada Flores, A. Redondo-Cubero, R. Gago, A. Bengoechea, A. Jiménez, D. Grambole, A.F. Braña and E. Muñoz, J. Phys. D: Appl. Phys. 42, 055406 (2009).
[3] A. Redondo-Cubero, K. Lorenz, R. Gago,  N. Franco, M.-A. di Forte Poisson, E. Alves and E. Muñoz, J. Phys. D: Appl. Phys. 43, 055406 (2010).
[4] A. Redondo-Cubero, K. Lorenz, R. Gago, N. Franco, S. Fernández-Garrido, P. J. M. Smulders, E. Muñoz, E. Calleja, I. M. Watson and E. Alves, Appl. Phys. Lett. 95, 051921 (2009).