Orientation dependence of swift heavy ion track formation in potassium titanyl phosphate
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Pablo Mota Santiago, Matias D. Rodriguez, Felipe Kremer, Daniel Schauries, Boshra Afra, Thomas Bierschenk, and David J. Llewellyn Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra ACT 2601, Australia
Fei Lu School of Information Science and Engineering, Shandong University, Jinan, Shandong 250100, China
Mark C. Ridgway and Patrick Klutha) Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra ACT 2601, Australia (Received 4 January 2016; accepted 21 April 2016)
Potassium titanyl phosphate crystals in both x-cut and z-cut were irradiated with 185 MeV Au ions. The morphology of the resulting ion tracks was investigated using small angle x-ray scattering (SAXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). SAXS measurements indicate the presence of cylindrical ion tracks with abrupt boundaries and a density contrast of 1 6 0.5% compared to the surrounding matrix, consistent with amorphous tracks. The track radius depends on the crystalline orientation, with 6.0 6 0.1 nm measured for ion tracks along the x-axis and 6.3 6 0.1 nm for those along the z-axis. TEM images in both cross-section and plan-view show amorphous ion tracks with radii comparable to those determined from SAXS analysis. The protruding hillocks covering the sample surface detected by AFM are consistent with a lower density of the amorphous material within the ion tracks compared to the surrounding matrix. Simulations using an inelastic thermal-spike model indicate that differences in the thermal conductivity along the z- and x-axis can partially explain the different track radii along these directions.
I. INTRODUCTION
High-energy heavy ions passing through a material can generate narrow trails of damage along their paths, socalled ion tracks. Ion track formation results from inelastic interactions of the projectile ions with the target electrons1,2 and has been observed in many crystalline and amorphous materials such as semiconductors,3–6 insulators7–10, and various metals.11,12 Potassium titanyl phosphate (KTiOPO4 or KTP) has a variety of applications spanning from nonlinear optics to electro–optics due to its large nonlinear optical coefficients and high optical damage threshold.13,14 The characterization of the ion track morphology is essential for photonic applications15 and integrated optical devices with waveguide fabrication Contributing Editor: William J. Weber a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.184
by swift heavy ion irradiation (SHII) of KTP.16 Some studies are available concerning the waveguide properties and ion radiation damage of KTP using Rutherford backscattering spectroscopy/channeling17–20; however, a detailed investigation of the ion track morphology in SHII KTP is still lacking. Small angle x-ray scattering (SAXS) is sensitive to nano-scale density changes and it has
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