Solid State Physics
Graphite sample on a sample  holder

Graphite sample placed on a sample holder

Single crystal diamond with different micro-irradiations

of boron ions

In addition to typical IBA techniques (PIXE, RBS, ERDA, etc.) for atomic elementary analysis of materials in a spatial scale ranging from nanometers to microns, ion-beam accelerators are also powerful tools for ionic implantation and modification of materials. When an energetic ion impinges on a solid target, important changes in the structure and properties of the solid are produced that can be used for different applications within the fields of physics and engineering, such as biochips or optical and electronic devices. Typical energy ranges employed in ion implantation are very wide, from a few tens of keV, obtained by small ionic sources, up to hundreds of MeV (produced by ion-beam accelerators) which use to be more interesting, though more expensive too, for scientific research.

Our research team is currently employing these techniques to address a hot topic within Solid State Physics nowadays: the study of the reported possible existence of magnetism and/or superconductivity in carbon materials (graphite, graphene, diamond…) by ion-beam irradiation, employing the 5 MV tandem ion-beam accelerator at CMAM-UAM.

Therefore, we have undertaken a joint research line to study this subject, by making use of the 5 MV tandem ion-accelerator at CMAM. For such an aim, we are also collaborating with other research groups at the Campus of Universidad Autónoma de Madrid such as the Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), and from the University of Leipzig (Germany) and the University of Johannesburg (South Africa), among others.

We have exhaustively studied [1] the change in the magnetic properties produced on highly oriented pyrolytic graphite (HOPG) samples after irradiation of H-, C- and N- ions in the MeV energy range. The use of specially made sample holders for the magnetic measurements through a SQUID magnetometer provided high reproducibility, allowing us to obtain directly the irradiation effects without any corrections or subtractions. Our results show that three main magnetic phenomena are triggered by the defects produced by the irradiation, namely Curie-like paramagnetism, ferromagnetism and an anomalous paramagnetic state that appears as precursor of the magnetic ordered state. Direct measurements of the surface sample temperature during irradiation and the decrease in the paramagnetic as well as ferromagnetic contributions after irradiation indicate that self-heating effects are one of the causes for the small yield of ferromagnetism. Taking into account the role of hydrogen, our results [1] suggest that the induced ferromagnetism appears when the average vacancy distance is around 2nm in the near surface region.Similar studies on magnetism, though with very different conclusions, were conducted on proton-irradiated single crystals of diamond, in collaboration with the University of Johannesburg and the ICMM-CSIC [2,3].

Most recently, our research group has began to study the effects of focused high-energy boron and carbon ion implantation in single crystals of diamond under different strategies, irradiation energies and fluences, including the subsequent study of the damage caused in the crystalline lattice and later recovery after annealing,employing our Internal Microbeam line [4-7].

[1] “Magnetic properties of graphite irradiated with MeV ions”, M. A. Ramos, J. Barzola-Quiquia, P. Esquinazi, A. Muñoz-Martín, A. Climent-Font and M. García-Hernández, Phys. Rev. B 81, 214404 (2010).
[2] “Investigation of the magnetic properties of proton irradiated type Ib HPHT diamond”, N. Daya, E. Sideras-Haddad, T.N.Makgato, M. García-Hernández, A. Climent-Font, A.Zucchiatti and M.A. Ramos, Diamond & Related Materials 64, 197–201 (2016).
[3] “Magnetic properties of point defects in proton irradiated diamond”, T. N . Makgato, E. Sideras-Haddad, M. A. Ramos, M. García-Hernández, A. Climent-Font, A. Zucchiatti, A. Muñoz-Martin, S. Shrivastava and R. Erasmus, Journal of Magnetism and Magnetic Materials 413, 76–80 (2016).
[4] “Highly-focused boron implantation in diamond and imaging using the nuclear reaction 11B(p, α)8Be”, M.D. Ynsa, M.A. Ramos, N. Skukan, V. Torres-Costa, M. Jakšić, Nucl. Instr. and Meth. B 348, 174–177 (2015). 
[5] “Study of the effects of focused high-energy boron ion implantation in diamond”, M. D. Ynsa, F. Agulló-Rueda, N. Gordillo, A. Maira, D. Moreno-Cerrada, and M. A. Ramos, Nucl. Instrum. Methods. Phys. Res. B 404, 207 (2017).
[6] “Micro-Raman spectroscopy of near-surface damage in diamond irradiated with MeV boron ions”, F. Agulló-Rueda , M. D. Ynsa, N. Gordillo, A. Maira, D. Moreno-Cerrada, and M. A. Ramos,  Diamond & Related Materials 72, 94-98 (2017).
[7] “ Lattice damage in 9-MeV-carbon irradiated diamond and its recovery after annealing”,  F. Agulló-Rueda, N. Gordillo, M. D. Ynsa, A. Maira, J. Cañas, and M. A. Ramos , Carbon 123, 334-343 (2017).