A micro-Raman spectroscopic investigation of He-irradiation damage in LiNbO3

Imaging micro-Raman spectroscopy is used to investigate the materials physics of radiation damage in congruent LiNbO3 as a result of high-energy (~MeV) He irradiation. This study uses a scanning confocal microscope for high-resolution three-dimensional micro-Raman imaging along with reflection optical microscopy (OM), and scanning electron microscopy (SEM). The tight optical excitation beam in the Raman system allows spatial mapping of the Raman spectra both laterally and normal to the irradiation axis with ≤1 μm resolution. Point defects and compositional changes after irradiation and surface deformation including blistering and microstress are observed in the stopping region. We demonstrate that the probed area of the damaged region is effectively “expanded” by a beveled geometry, formed through off-angle polishing of a crystal facet; this technique enables higher-resolution probing of the ion-induced changes in the Raman spectra and imaging of dislocation line defects that are otherwise inaccessible by conventional probing (depth and edge scan). Twodimensional (2D) Raman imaging is also used to determine the defect uniformity across an irradiated sample and to examine the damage on a sample with patterned implantation. The effects of different He doses and energies, together with post-irradiation treatments such as annealing, are also discussed. ©2012 Optical Society of America OCIS codes: (130.3730) Lithium niobate; (160.4670) Optical materials; (300.6450) Spectroscopy, Raman; (310.3840) Materials and process characterization. References and links 1. L. Arizmendi, “Photonic applications of lithium niobate crystals,” Phys. Status Solidi A 201(2), 253–283 (2004). 2. J. Rams, J. Olivares, P. J. Chandler, and P. D. Townsend, “Mode gaps in the refractive index properties of lowdose ion-implanted LiNbO3 waveguides,” J. Appl. Phys. 87(7), 3199–3202 (2000). 3. M. Levy, R. M. Osgood, R. Liu, L. E. Cross, G. S. Cargill, A. Kumar, and H. Bakhru, “Fabrication of singlecrystal lithium niobate films by crystal ion slicing,” Appl. Phys. Lett. 73(16), 2293–2295 (1998). 4. A. Kling, M. F. da Silva, J. C. Soares, P. F. P. Fichtner, L. Amaral, and F. Zawislak, “Defect evolution and characterization in He-implanted LiNbO3,” Nucl. Instrum. Meth. B 175–177(0), 394–397 (2001). 5. R. M. Roth, D. Djukic, Y. S. Lee, R. M. Osgood, S. Bakhru, B. Laulicht, K. Dunn, H. Bakhru, L. Wu, and M. Huang, “Compositional and structural changes in LiNbO3 following deep He ion implantation for film exfoliation,” Appl. Phys. Lett. 89(11), 112906 (2006). 6. T. Volk and M. Wohlecke, Lithium Niobate: Defects, Photorefraction and Ferroelectric Switching (SpringerVerlag, Berlin, Heidelberg, 2008). 7. J. E. Spanier, M. Levy, I. P. Herman, R. M. Osgood, and A. S. Bhalla, “Single-crystal, mesoscopic films of lead zinc niobate-lead titanate: Formation and micro-Raman analysis,” Appl. Phys. Lett. 79(10), 1510–1512 (2001). 8. J. E. Spanier, R. Robinson, F. Zhang, S.-W. Chan, and I. P. Herman, “Size-dependent properties of CeO2-y nanoparticles as studied by Raman scattering,” Phys. Rev. B 64(24), 245407 (2001). 9. S. Banerjee, D.-I. Kim, R. D. Robinson, I. P. Herman, Y. Mao, and S. S. Wong, “Observation of Fano asymmetry in Raman spectra of SrTiO3 and CaxSr1-xTiO3 perovskite nanocubes,” Appl. Phys. Lett. 89(22), 223130 (2006). 10. P. S. Dobal and R. S. Katiyar, “Studies on ferroelectric perovskites and Bi-layered compounds using microRaman spectroscopy,” J. Raman Spectrosc. 33(6), 405–423 (2002). 11. D. N. Jamieson, S. Prawer, K. W. Nugent, and S. P. Dooley, “Cross-sectional Raman microscopy of MeV implanted diamond,” Nucl. Instrum. Meth. B 106(1–4), 641–645 (1995). #180352 $15.00 USD Received 26 Nov 2012; revised 14 Dec 2012; accepted 15 Dec 2012; published 21 Dec 2012 (C) 2013 OSA 1 February 2013 / Vol. 3, No. 2 / OPTICAL MATERIALS EXPRESS 126 12. A. A. Balandin, S. Ghosh, W. Z. Bao, I. Calizo, D. Teweldebrhan, F. Miao, and C. N. Lau, “Superior thermal conductivity of single-layer graphene,” Nano Lett. 8(3), 902–907 (2008). 13. I. De Wolf, “Micro-Raman spectroscopy to study local mechanical stress in silicon integrated circuits,” Semicond. Sci. Technol. 11(2), 139–154 (1996). 14. S. M. Kostritskii and P. Moretti, “Micro-Raman study of defect structure and phonon spectrum of He-implanted LiNbO3 waveguides,” Phys. Status Solidi C 1(11), 3126–3129 (2004). 15. B.-U. Chen and A. C. Pastor, “Elimination of Li2O out-diffusion waveguide in LiNbO3 and LiTaO3,” Appl. Phys. Lett. 30(11), 570–571 (1977). 16. J. G. Scott, S. Mailis, C. L. Sones, and R. W. Eason, “A Raman study of single-crystal congruent lithium niobate following electric-field repoling,” Appl. Phys., A Mater. Sci. Process. 79(3), 691–696 (2004). 17. K. K. Wong, ed., Properties of Lithium Niobate (INSPEC, The Institution of Electrical Engineers, London, UK, 2002). 18. G. R. Paz-Pujalt and D. D. Tuschel, “Depth profiling of proton exchanged LiNbO3 waveguides by micro-Raman spectroscopy,” Appl. Phys. Lett. 62(26), 3411–3413 (1993). 19. A. Ofan, O. Gaathon, L. Vanamurthy, S. Bakhru, H. Bakhru, K. Evans-Lutterodt, and R. M. Osgood, “Origin of highly spatially selective etching in deeply implanted complex oxides,” Appl. Phys. Lett. 93(18), 181906 (2008). 20. A. Ofan, O. Gaathon, L. Zhang, K. Evans-Lutterodt, S. Bakhru, H. Bakhru, Y. Zhu, D. Welch, and R. M. Osgood, “Twinning and dislocation pileups in heavily implanted LiNbO3,” Phys. Rev. B 83(6), 064104 (2011). 21. J. Ziegler, 2008, http://www.srim.org. 22. A. Ridah, P. Bourson, M. D. Fontana, and G. Malovichko, “The composition dependence of the Raman spectrum and new assignment of the phonons in LiNbO3,” J. Phys. Condens. Matter 9(44), 9687–9693 (1997). 23. U. Schlarb, S. Klauer, M. Wesselmann, K. Betzler, and M. Wöhlecke, “Determination of the Li/Nb ratio in lithium niobate by means of birefringence and Raman measurements,” Appl. Phys., A Solids Surf. 56(4), 311–