Damage in Refractory Oxides and ion Beam Mixing at Metal-Oxide Interfaces Induced by Gev Ions and 20 Mev Cluster Beam
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dE
Although the ('-)e are close using monoatomic GeV ions and 20 MeV C60 clusters, the dx velocities of swift heavy ions and C projectiles in C60 clusters are different and the maximum kinetic energy of S-electrons emitted during the ionization process, differs strongly in the two cases: in MgO for example, 10 keV for GeV U ions and 50 eV for 20 MeV C60 in MgO. Then, in the case of cluster bombardment, the deposited energy in much more confined around the particle
trajectory. The aim of this paper is to compare damage induced in refractory oxides of different ionicity, such as MgO, A120 3 and LiNb0 3 , by GeV heavy ions. Ion beam mixing effects in MgO containing nanoprecipitates of sodium, are compared with swift heavy ions and C60 clusters. EXPERIMENTAL PROCEDURE The details of the experimental procedure are given in references [14, 15, 16]. High purity single crystals of MgO in (100) orientation, cx-A1203 of (0001) orientation and LiNb0 3 (Y cut or Z cut) were used. Swift heavy ions (U, Pb, Sn, Kr, Gd) in the GeV range were produced at GANIL Caen and C6 0 cluster beams of 18 and 23 MeV energies at the "Institut de Physique Nucl6aire d'Orsay". The characteristics of the ions and clusters (energy, range, electronic and nuclear losses) are given in table 1 for MgO irradiations and table 2 for saphire irradiations. Gd ions of 801 MeV were used for LiNb0 3 irradiations. Table 1 : Summary of the main experimental characteristics of the incident ions and clusters in MgO Incident ion
Pb
Sn
Sn
Kr
U
C60
C60
Energy (MeV)
944
1066
315
842
45
18
23
Ion range (g~m)
31
55
19
63.5
4.4
0.40
0.46
Electronic stopping power (keV/nm)
38
19
24
11
11
40
62
Nuclear stopping power (keV/nm)
0.07
0.014
0.04
7xl0-3
1.0
1.4
0.67
Table 2: Characteristics of uranium irradiations in A120 3 E
(MeV)
•=v
c
vdE
Rp
(jtm)
dE ()e (-)n dx dx keV/nm keV/nm
809
0.085
26.2
44.2
0.012
115
0.03
7.8
24
0.057
10 to 6x10 12 ions.cm- 2 and the ion flux were about 108 The fluences ranged from 5x10 2 ions.cm- .s-1. Rutherford backscattering spectrometry in channeling geometry (RBS-C) was carried out at the "Ddpartement de Physique des Mat6riaux" using and 4 He+ beam generated by a Van de Graaff accelerator working at a maximum energy of 2 MeV.
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Optical absorption data were obtained at 300 K using a CARY 2300 spectrophotometer in the 185 - 2000 nm wavelength range. To study the in-depth repartition of defects, the irradiated surface layer was successively removed by chemical etching and the optical absorption spectra were performed at each step. For ion beam mixing experiments, MgO single crystals with (100) orientation were first implanted in the laboratory at room temperature with 150 keV Na+ ions at a fluence of 1017 Na.cm-2 . The Na mean projected range was 185 nm0and the longitudinal range straggling 50 nm. The samples were then annealed up to 800 or 1000 C in order to induce the precipitation of the metallic sodium. The MgO crystals containing Na nanoprecipitates (- 10 nm) were further irradi
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