Modification of Si nanocrystallites in SiO 2 matrix by swift heavy ion irradiation

1. Modification of Si nanocrystallites in SiO2 matrix by swift heavy ion irradiation By: V. E. Thelelo & A. Rossouw In co-operation with, University of Fort Hare & Stellenbosch University Supervised By: N.S.Kirilkin, V.A.Skuratov Joint Institute for Nuclear Research, Dubna, Russia

2. Brief project overview The irradiation testing of nuclear ceramics and oxides with heavy ions of fission fragment energy Our irradiation testing experiments will be focused on study of: – correlation between surface and material bulk radiation damage induced by heavy ions with energies above 1 MeV/atomic mass unit (amu). – temperature dependence of swift heavy ion-induced phase transformations and dense ionization effect on pre-existing defect structure in irradiating materials. The project fulfillment allows us to acquire new knowledge concerning evolution of defect structure in nuclear ceramics under dense electronic excitations simulating the fission fragment impact.

3. Irradiation with swift heavy ions (SHI) The source of structural changes in tracks of high energy (E > 1 MeV/amu) heavy ions is a huge energy deposition (Se tens keV/nm) in electron subsystem of irradiating material SHI cause exotic effects in different classes of materials which cannot be generated by any other means. G. Schiwietz et al.NIMB 226 (2004) 683

4. SiO2 layers with variable NC concentration • Deposition of SiO2 and Si on Si substrate from two sourcesseparated by distance of 100 mm • 2. dSiO2 = 400 - 1000 nm • 3. Si content in oxide: 5 - 90 vol.% • 4. Annealing: 1140оС, 40 min, N2 • NC size: 3 – 5 nm Si

5. Ordered arrays of Si nanocrystals in SiO2: structural, optical and properties The ordering of composites under high-energy ion irradiation and formation of elongated particles (up to 250 nm length with diameter 3-5 nm) is known for metal nanoparticales in SiO2 Pt in SiO2 185 MeVAu NIM B 266 (2008), 3158

6. surface Irradiated NC-SiO2 layer (37 % Si) Kr, 90 MeV, 1012 cm-2 Ion pass Formation of the ordered NC distribution 30 nm substrate 20 nm

7. HREM cross sectional images for the Si NCs in irradiated layer Kr, 90 MeV, 1012 cm-2 non-irradiated layer Atomic planes of NCs in the irradiated samples are oriented along the ion tracks

8. Photoluminescence of irradiated layer Bi, 670 MeV , ex. = 488 nm, Ar laser Initial 1x1012 cm-2 8x1012 cm-2

9. Photoluminescence of 670 MeVBi ion irradiated layer

10. Experimental Setup 1. Diod with 380nm wavelength produces excitation of Nc Si 2. Nc Si specimen emit light 3. Spectrometer register this light and cuts off signal less than 550nm wavelength Spectrometer Spectrometer ANDOR iDUS Diod 380nm Nc Si specimen

11. PL intensity of initial Si NCs as a function of Si concentration 1 2 3 4 5 6 Max effect for points 3 and 4 Extra Si concentration 5% 90%

12. Acknowledgments • Dr. N. M. Jacobs • Prof. M. L. Lekala • Dr. V. A. Skuratov • Mr. N. S. Kirilkin • JINR • UFH • US • And everyone else involved in making this practice possible.

13. Thank you for your attention!