Energy threshold for the creation of nanodots on SrTiO3 by swift heavy ions

We present experimental and theoretical data on the threshold behaviour of nanodot creation with swift heavy ions. A model calculation based on a two-temperature model that takes into account the spatially resolved electron density gives a threshold of 12 keV nm−1 below which the energy density at the end of the track is no longer high enough to melt the material. In the corresponding experiments, we irradiated SrTiO3 surfaces under grazing incidence with swift heavy ions. The resulting chains of nanodots were analysed by atomic force microscopy (AFM). In addition, some samples of SrTiO3 irradiated under normal incidence were analysed by transmission electron microscopy (TEM). Both experiments showed two thresholds, which were connected with the appearance of tracks and the creation of fully developed tracks. The threshold values were similar for surface and bulk tracks, suggesting that the same processes occur at both glancing and normal incidence. 5 Author to whom any correspondence should be addressed

Creation of multiple nanodots by single ions

In the challenging search for tools that are able to modify surfaces on the nanometer scale, heavy ions with energies of several 10 MeV are becoming more and more attractive. In contrast to slow ions where nuclear stopping is important and the energy is dissipated into a large volume in the crystal, in the high energy regime the stopping is due to electronic excitations only. Because of the extremely local (< 1 nm) energy deposition with densities of up to 10E19 W/cm^2, nanoscaled hillocks can be created under normal incidence. Usually, each nanodot is due to the impact of a single ion and the dots are randomly distributed. We demonstrate that multiple periodically spaced dots separated by a few 10 nanometers can be created by a single ion if the sample is irradiated under grazing angles of incidence. By varying this angle the number of dots can be controlled.Comment: 12 pages, 6 figure

Les ions émis de la surface (messagers du processus initial de la nano-structuration)

Lorsqu un ion projectile interagit avec une surface, il dépose son énergie tout au long de son trajet. L énergie déposée conduit à la création d endommagements et à l émission de particules secondaires, neutres et chargées. Dans cette thèse, nous avons étudié l endommagement de surfaces cristallines induit par irradiation aux ions lents et rapides. Nous avons également étudié la pulvérisation d ions secondaires durant l irradiation aux ions rapides. Dans le cas d irradiation aux ions lents multichargés, nous avons déterminé les sections efficaces d endommagement par ion incident sur les surfaces cristallines de TiO2 et de graphite. Nous avons mis en évidence que l énergie potentielle du projectile joue un rôle important dans l endommagement de la surface. Par contre, l étude d endommagement surfacique du silicium cristallin s est révélé insensible à l irradiation aux ions (Xe, Ec = 0,92 MeV), où la perte d énergie électronique est 12 keV/nm. L efficacité maximale pour qu un ion produise une modification à la surface est 0,3 %. Par irradiation aux ions rapides, l émission d ions de CaF+ par rapport à l émission de Ca+ est plus grande dans le cas d irradiation d un cristal massif que dans le cas de couches minces de CaF2.Ion irradiation of solids leads to a deposition of its energy along the ion path. The energy deposited creates damage in the target as well as leads to the sputtering of neutral and charged particles. In this work we studied the damage induced by slow and swift ions in matter. We studied also the sputtering of secondary ions induced by swift heavy ion irradiation. We have measured the damage cross section of the surface of the Titanium (Insulator surface) and of the graphite (Conductor surface) by slow highly charged ions. The potential energy stored in the projectile has an important role for creating damage at surfaces. We studied the damage creation at the surface of cristalline silicon by swift heavy ions. We revealed that the c-Si is not sensitive to the irradiation by Xe ion at Ec = 0,9 MeV/u, where the electronic stopping power is 12 keV/nm. The maximum efficiency to create a track is 0,3 %. Under swift heavy ion irradiation, the emission of the CaF+ compared to the Ca+ is higher for solid cristals than for thin films of Calcium Fluoride CaF2 on Si.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Energy dissipation in insulators induced by swift heavy ions: A parameter study

International audienceThe irradiation of solids with high energy laser or particle beams has led to a deeper understanding of the relaxation processes inside the target material. However, a lot of open questions remain. In the present paper, we will examine the irradiation of the model system Xe23+ @ 93 MeV → SrTiO3 within the framework of the two-temperature-model and study the electron-phonon-coupling g and the electron diffusivity De as well as the lattice diffusivity Dp. These are crucial parameters for which no experimental data is available. Experimentally, g is very difficult to measure and therefore theoretical predictions are of great importance. With the approach presented here it is possible to determine the coupling-constant by one order of magnitude

Enhanced susceptibility of CaF2(111) to adsorption due to ion irradiation

International audienceWe have investigated morphological changes of freshly cleaved CaF2(111) single crystal surfaces before and after ion irradiation. We show that with or without irradiation the surface undergoes serious changes within minutes after the cleavage if the samples are exposed to ambient conditions. This is most likely due to the adsorption of water and could be avoided only if working under clean ultra-high-vacuum conditions. Ion-induced modifications on this surface seem to act as centers for an increased rate of adsorption so that any quantitative numbers obtained by atomic force microscopy in such experiments have to be treated with caution

Conductive nanodots on the surface of irradiated CaF2

International audienceCaF2(111) single crystal surfaces have been irradiated with fast heavy ions under oblique angles resulting in chains of nanosized hillocks. In order to characterize these nanodots with respect to their conductivity we have applied non-contact atomic force microscopy using a magnetic tip. Measurements in ultra high vacuum as well as under ambient conditions reveal a clearly enhanced electromagnetic interaction between the magnetic tip and the nanodots. The dissipated energy per cycle is comparable to the value found for metals, indicating that the interaction of the ion with the target material leads to the creation of metallic Ca nanodots on the surface

Swift heavy ion irradiation of SrTiO3 under grazing incidence

International audienceThe irradiation of SrTiO3 single crystals with swift heavy ions leads to modifications of the surface. The details of the morphology of these modifications depend strongly on the angle of incidence and can be characterized by atomic force microscopy. At glancing angles, discontinuous chains of nanosized hillocks appear on the surface. From the variation of the length of the chains with the angle of incidence the latent track radius can be determined. This radius is material specific and allows the calculation of the electron– phonon coupling constant for SrTiO3. We show that a theoretical description of the nanodot creation is possible within a two-temperature model if the spatial electron density is taken into account. The appearance of discontinuous features can be explained easily within this model, but it turns out that the electronic excitation dissipates on a femtosecond timescale, too rapidly to feed sufficient energy into the phonon system in order to induce a thermal melting process. We demonstrate that this can be solved if a temperature-dependent diffusion coefficient is introduced into the model