Studies of properties and modification of multilayered nanostructures under irradiation by swift ions A.Yu.Didyk G.N.Flerov Laboratory of Nuclear Reactions, Center of Applied Physics

SHORT CONTENT of REPORT 1.Radiation resistance of multilayered structure 5×(AlN/TiN)/Si 2.Studies of HTSC-Ag/YBaCuO/Hastelloy(SS) parameter changes under irradiation by various swift heavy ions 3.Modified TSM for multilayered nanostructures 4.Conclusion

Introduction As hard coating materials they offer numerous advantages over single component coatings, such as much higher hardness and strength due to a large number of interfaces, possibilities to form super lattices, graded composition, more dense and less porous structures. High strength nanolayered structures are also interesting as radiation protective materials, because of a large number of interfaces that act as obstacles to slip and sinks for radiation induced defects. High surface of volume ratio of individual nanocrystals (of up to ~10 nm in diameter) facilitates the release of ion irradiation induced vacancies and interstitials, thus enhancing radiation tolerance of this material. The AlN/TiN system was chosen because it exhibits high temperature stability, up to C, and the constituents are immiscible. Individual thicknesses of the AlN and TiN layers were above 20 nm, 5×(AlN/TiN)/Si were grown by reactive sputtering on Si(100) wafers, to a total thickness of ~270 nm, individual layer thickness was ~22 nm for AlN and ~32 nm for TiN, both growing in a nanocrystalline form. For comparison: 5×(Al/Ti) bilayers, deposited by ion sputtering on (100) Si substrates. All together 10 layers with a total thickness of 200 nm. Individual layers have approximately the same thickness of around 20 nm. First layer deposited on Si is Ti, and the outermost layer is Al.

Implantation of 200 keV 40 Ar + ions, fluence: 5,0x10 15 ÷ 4,0x10 16 Ar/cm 2 Irradiation with 166 MeV 132 Xe 27+ ions, fluence: 5,0x10 14 Xe/cm 2 R p, 1270±40 Å Cross-section 40 Ar + damage dose, dpa Inelastic energy loss, keV/nm AlN1,04× ,20 ÷ 41,60,58 TiN 1,57× ,85 ÷ 62,80,76 R p, 19,6±0,5 μm Cross-section 132 Xe 27+ damage dose, dpa Inelastic energy loss, keV/nm AlN6,06× ,03× ,90 TiN 9,21× ,61× ,80

Experimental methods 1. Reactive sputter deposition of AlN/TiN multilayers Ar + ion implantation, using 500 kV linear ion implanter installed in LAP VINCA Institute of Nuclear Sciences 3. TEM and HRTEM analyses Xe +27 swift heavy ion irradiation, using IC-100 accelerator with ECR ion source (FLNR) 5.XPS (Photoelectron Spectroscopy) and RBS analysis 6.Roentgen X-ray analysis

RBS spectra of as-deposited 5×(AlN/TiN)/Si and implanted with 40 Ar + to 2,0x10 16 ions/cm 2 PRINCIPAL CONCLUSION 1.Individual layers are well separated 2. No interface mixing (broadening) upon ion irradiation at this dose 3. Change in local density due to 40 Ar + implantation, which causes a relative shift of Ti and Al peaks in RBS spectra 4. TiN layers are stoichio- metric and AlN layers are under- stoichiometric

XPS depth profiles of 5×(AlN/TiN)/Si implanted with 40 Ar + - individual layers remain well separated upon ion irradiation - layer stoichiometry Al:N ~45:55; Ti:N~50:50 - for the highest implanted dose there is a low level migration (up to ~4-5 at%) of Ti into 2 nd and 3 rd AlN layers and no migration of Al into TiN. This is assigned to excess N in AlN layers, which can attract the knocked-on Ti atomic species - otherways there is no interface broadening (mixing) of the depth profiles -surface becomes contaminated (covered) with oxygen

TEM analysis of 5×(AlN/TiN)/Si implanted with 40 Ar + as-deposited 2x10 16 Ar/cm 2 4x10 16 Ar/cm 2 SA diffraction CB diffraction 1)Very sharp and flat interfaces and nano- crystalline structure are preserved, 2)TiN grains are larger than AlN grains, 3)Some grains increase in width (from ~10 nm up to ~20 nm),

(Al/Ti)x5 multilayers were deposited on Si to a similar thickness, and implanted with 40 Ar + at the same conditions as (AlN/TiN)x5 multilayers as-deposited Comparative TEM analysis of mutually soluble and chemically reactive pure Al/Ti metallic and AlN/TiN systems 2x10 16 Ar/cm 2 PRINCIPAL CONCLUSION 1. High Ar + fluences of 2,0x10 16 ions/cm 2 4,0x10 16 ions/cm 2 are sufficient to induce a total intermixing in this soluble system 2. The mean grain size increases significantly 3. Chemical driving forces intensify intermixing, which is by orders of magnitude higher than purely ballistic mixing 4. Opposite to this, in the immiscible AlN/TiN system, chemical driving forces increase (enhance) demixing

XPS depth profiles of (AlN/TiN)x5/Si irradiated by swift heavy 132 Xe +27 ions with energy 166 MeV to a fluence 5,0×10 14 ion/cm 2 PRINCIPAL CONCLUSION: 1. Not any redistribution of components is registered 2. No any interface broadening that would suggest mixing of the layers is registered 3. Oxygen builds up at the surface upon ion irradiation Ion sputtering was performed at PHI-TFA XPS spectrometer by a 3 keV Ar + beam rastered over 4x4 mm 2 area. Sputtered rate of about 1,5 nm/min. During depth profiling the samples were rotated to improve the depth resolution. The analyzed area was 0,4 mm in diameter. XPS spectra were excited by X-ray radiation from an Al-standard source. The based pressure in spectrometer was 2,0x10 -8 Pa. The estimated relative error for calculated concentrations is about 10%!

Cross-sectional TEM analysis of 5×(AlN/TiN)/Si irradiated with swift heavy 132 Xe +27 ions as-deposited 5x10 14 Xe/cm 2 1.Clear separation of the AlN and TiN layers, sharp and flat interfaces and nano-crystalline structure are preserved 2. Generated thermal spikes induce an Increase of nano-crystals (up to ~20 nm) uniformly throughout the depth of the multilayered structure 3. Increase in size of both TiN and AlN nano-crystals is clearly seen, however crystal growth does not induce any interface roughening

Conclusions to Radiation resistance of multilayered structure 5×(AlN/TiN)/Si A remarkable stability of nano-scaled AlN/TiN multilayered structures, both upon high dose ion implantation and swift heavy ion irradiation, is demonstrated! Despite of the small structural changes, clear separation of the AlN and TiN layers, sharp and flat interfaces and nano-crystalline structure are preserved; although nano-crystals increase in width, planarity of the interfaces is intact, which is crucial for radiation stability of multilayered structures, as a pronounced coarsening can result in their degradation. Demonstrated stability of AlN/TiN is comparable or in some cases better than in the reports given for immiscible metallic multilayers. The presented results imply that nano-scaled multilayered metal-nitrides should attract further attention as radiation protective materials.

Studies of HTSC-Ag/YBaCuO/Hastelloy(SS) parameter changes under irradiation by various swift heavy ions Cross-section of the composite YBa 2 Cu 3 O 7-X tape Production of “Super Power” Inc.Co (USA) Critical Parameters: J c =113±1 A, T c =92±0,05K S=4 mm×1μm=4,0×10 -5 cm 2, j c =J c /S=2,8 MA/cm 2

3. Modified TSM for multilayered nanostructures. Functions of sources can be written as: N.B. It is relatively simple Model just necessary to know parameters!

Fig.1. Dependences of ion track temperatures versus radius from 132 Xe 27+ (166 MeV), 84 Kr 17+ (112 MeV) and 40 Ar 8+ (48 MeV) ion trajectories at the depth in HTSC target Z=2,5 μm (time is t = c). T~600K means the critical temperature of HTSC destroying!

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