R. Brenier

Damage induced in LiNbO3 single crystals by GeV gadolinium ions

Abstract Single crystals of LiNbO3 with two different orientations (Y-cut and Z-cut) have been irradiated at GANIL with 5.17 MeV/amu 155Gd ions at room temperature. The fluence extended from 1.5 × 1011 to 1.2 × 1012 ions cm−2. The damage resulting from the high electronic stopping power (up to 30 keV/nm) has been characterized by both Rutherford backscattering ion channeling (RBS-C) and optical absorption measurements. By using a degrader, the defect efficiency has also been investigated as a function of the electronic stopping power (18 keV/nm

Phase formation study in α-Al2O3 implanted with niobium ions

Abstract Niobium ion.s of 150 keV energy have been implanted at temperatures of 77 or 300 K in α-Al 2 O 3 with doses ranging from 5 × 10 15 to 3 × 10 17 ions/cm 2 and subsequently thermal annealed up to 1273 K in H 2 gas or in air. The structure of the implanted layer has been characterized by X-ray diffraction at glancing incidence and its physical properties have been investigated by means of optical absorption spectroscopy and electrical conductivity measurements. For implantation performed at 77 K, the sapphire reaches an amorphous state at a fluence of 5 × 10 15 ions/cm 2 whereas an implantation dose of 5 × 10 16 Nb/cm 2 is required at 300 K. For heavily implanted samples the amorphous layer has an electrical resistivity typical of poor metal. Annealing treatment performed in Hi gas leads to the formation of an Nb 2 O 5 oxide plus clusters of niobium, whereas a NbA10 4 compound is observed after annealing in air.

Surface swelling of sapphire induced by MeV and GeV heavy ions

α-Al2O3 single crystals were bombarded with MeV xenon ions from 1015 to 1017 ions cm−2 and GeV uranium ions from 1011 to 1013 ions cm−2 to study the surface swelling of sapphire at 77 and 300 K due to atomic collision processes (Xe) and electronic energy loss processes in the 20–45 keV/nm regime (U). The induced damage was studied by channeling Rutherford backscattering. Surface swelling was measured with a profilometer. The step height induced by nuclear cascades of MeV xenon increases with the ion fluence and saturates. With GeV uranium, an electronic stopping power threshold for surface swelling was observed and the step height increased with the damage for dE/dx higher than this threshold.

Ion beam mixing of metal-sapphire interfaces

Abstract Thin films of Au, Ag have been evaporated on (0001) surface of sapphire and then the interfaces were irradiated with xenon ions. Ion energy of 1.5 MeV, fluences of 3 × 1015 to 2.2 × 1016 ions cm−2 and irradiation temperatures at 77 and 300 K were used. The evolutions of the interfaces were studied by different techniques such as Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM), optical absorption. X-ray diffraction at glancing incidence and electrical resistivity measurements. Blistering is observed for all specimens bombarded with fluences as low as 3 × 1015 ions cm−2. The RBS analysis seems to show a ballistic mixing at Ag or AuAl2O3 interfaces but X-ray diffraction at glancing incidence does not reveal any new compound formation at the interfaces. Nevertheless optical absorption shows the formation of silver or gold metallic precipitates embedded into Al2O3.

Amorphous alloy formation by ion beam mixing of iron-titanium multilayers

Multilayers of iron and titanium of total thickness 2000 A have been deposited on beryllium and silicon substrates, using an electron gun under ultrahigh vacuum conditions (10 −9 Torr). The respective thicknesses of the iron and titanium films have been chosen with a view to predetermining the following global compositions: Fe 29 Ti 71 (eutectic), Fe 33 T1 66 , Fe 50 Ti 50 , Fe 58 Ti 42 , and Fe 67 Ti 33 . The as-deposited multilayers have been characterized in situ by Rutherford backscattering spectrometry of alpha particles (RBS). The ion beam mixing has been performed using Xe + ions of 800 keV energy up to a dose of 2.4 × 10 16 Xe + CM −2 . The magnetic properties of the mixed samples have been measured by conversion electrons Mbssbauer spectroscopy (CEMS). Characterization by RBS and X-ray diffraction at glancing incidence have been performed. The formation of amorphous iron-titanium alloys is shown.

Plastic flow induced by ionization processes in ion-damaged MgO

Abstract The change in mechanical properties induced by ionizing radiation in pre-implanted MgO single crystals has been investigated by surface-strain measurements and defect characterization. Optically polished, oriented MgO substrates were implanted with 500 keV Xe+ ions followed by 2 MeV He+ ion bombardment at fluences up to 1.5 × 1016 He+/cm2. In order to use RBS to study the atomic migration accompanying the strain, some MgO samples were implanted with 150 keV Ca+ “marker” ions and were then irradiated with 2 MeV He+ ions. The defects induced in the material were analyzed before and after each type of irradiation by using RBS channeling and optical absorption. It appears that the ionizing radiation induces an out-of-plane strain composed of a volume expansion and a plastic flow which relax the stress in the pre-implanted layer. No long-range atomic migration appears to be involved in this effect.

Europium diffusion enhancement in lithium niobate by GeV gadolinium ion irradiations

Single crystals of lithium niobate (LiNbO3) with y‐cut orientation were irradiated at GANIL with 5.17 MeV/amu 155Gd ions at a fluence ranging from 1.5×1011 to 6.0×1011 ions cm−2. After irradiation the samples were implanted with europium ions of 70 keV energy at a fixed fluence of 5×1016 ions cm−2. Both irradiations and implantations were performed at room temperature. Thermal treatments in air, in the range 300–1100 °C, were applied to investigate the influence of the preirradiation damage on the thermal evolution of Eu implanted LiNbO3 crystals. Transmission electron microscopy micrographs exhibit the amorphous track formed by high‐energy irradiations. Rutherford backscattering spectrometry results show that these amorphous tracks enhance the europium diffusion in depth of the LiNbO3. A diffusion coefficient and an activation energy were estimated to be about 4.2×10−15 cm2 s−1 and 0.42 eV, respectively.

Latent track formation in LiNbO3 single crystals irradiated by GeV uranium ions

Abstract Single crystals of LiNbO3 (Y-cut orientation) have been irradiated at GANIL with 238U ions using three different energies: 0.84, 2.01 and 2.73 MeV/a. All the irradiations were performed at room temperature, up to a fluence of 4 × 1011 ions.cm−2. The lattice disorder resulting from the high electronic stopping power (between 28 and 40 keV/nm) has been characterized by Rutherford backscattering spectrometry in channeling geometry (RBS-C), in conjunction with high resolution transmission electron microscopy (HRTEM). According to RBS-C analysis, the damage cross-section depends on the electronic stopping power of the incident ions and a velocity effect is observed. HRTEM observations show a damage morphology consisting mainly of cylindric amorphous zones (latent tracks) having a mean core radius of about 2 nm.

Evidence of a new phase formation (BaTi4O9) by barium implantation into TiO2

Abstract Barium ions of 140 keV energy were implanted at room temperature in TiO 2 (rutile) with a fluence of 10 17 ions cm −2 . Isochronal heat treatments were carried out in air at 1000, 1100 and 1150°C for 1 h. Rutherford backscattering spectrometry (RBS) is channeling geometry, X-ray diffraction at glancing incidence and X-ray photoemission spectroscopy (XPS) were undertaken to the physico-chemical characterization of the implanted rutile. The annealing at 1150°C leads to the formation of a new phase which hae been identified as BaTi 4 O 9 with an average grain size of about 28 nm.

Electrical conductivity in niobium implanted TiO2 rutile

Abstract Single crystals of TiO 2 rutile were implanted at 300 K with niobium ions at fluences in the range 5×10 13 to 2.5×10 17 ions cm −2 , corresponding to a mean local concentration of 6×10 18 to 3×10 22 Nbcm −3 , respectively. Rutherford backscattering spectroscopy (RBS) in channeling geometry and X-ray photoemission spectroscopy (XPS) have been performed to determine the Nb substitutional fraction and the Nb oxidation state as a function of fluence. The microstructural evolution has been followed by X-ray diffraction at glancing incidence. The dc conductivity measurements were performed using the four probes technique in the temperature range of 150 to 850 K. The conductivity as a function of the Nb fluence exhibits two different behaviours: (i) at low fluence, between 5×10 13 and 5×10 14 Nbcm −2 , the conductivity increases by four orders of magnitude, (ii) while at high fluence, between 5×10 15 and 2.5×10 17 Nbcm −2 , it varies slowly from 10 2 to 2×10 3 Ω −1 cm −1 . The conductivity is thermally activated and the activation energy deduced from Arrhenius plots ( σ α (1/ T )) depends on the local concentration of implanted niobium. It decreases from 0.12 eV (5×10 14 Nbcm −2 ) to 0.01 eV (2.5×10 17 Nbcm −2 ). A high oxidation state of niobium was observed at low fluences and the conductivity could be described by a polaron process. At high fluences the niobium oxidation state vanishes and then a hopping process between metallic clusters is superimposed on the polaron mechanism.