List of publications with abstracts

1. E. Zolotoyabko, Y. Avrahami, "Characterization of optical waveguide layers in LiNbO₃ by high resolution X-ray Diffraction", Materials Letters, 24 (1995) pp.215-219.


Ti-diffused and He-implanted optical waveguides in Y-cut LiNbO₃ wafers were, for the first time, studied by means of high-resolution X-ray diffraction and revealed widely differing distortions of the shapes of (030)LiNbO₃ rocking curves. The depth strain profiles obtained as well as the correlations found between rocking curve broadenings and variations in lattice constant demonstrated the high sensitivity of this technique to the structural properties of waveguides, as dependent on the processing parameters. (19 References).

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2. E. Zolotoyabko, Y. Avrahami, W. Sauer, T.H. Metzger, J. Peisl, "Strain profiles in He implanted waveguide layers of LiNbO₃ crystals", Materials Letters, 27 (1996) pp.17-20.


He-implanted optical waveguides in Y-cut LiNbO₃ wafers were studied by means of conventional high-resolution and grazing incidence X-ray diffraction. The depth-resolved strain profiles were derived from the measured rocking curves, depending on the implantation dose. The obtained results demonstrated the high sensitivity of diffraction techniques to the structural modifications in He-implanted LiNbO₃ and allowed to shed some light on the mechanism of the waveguide formation in damaged layers. (10 References).

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3. W. Sauer, T.H. Metzger, J. Peisl, Y. Avrahami, E. Zolotoyabko, "Grazing incidence diffraction on LiNbO₃ under surface acoustic wave excitation", Nouvo Cimento, 19 D, 2-4, 1997. (Proceedings of 3ed European Symposium on X-ray Topography and High Resolution Diffraction, Palermo, Italy, 1996.)


He-implanted and heat-treated optical waveguide layers in Y-cut LiNbO₃ wafers were studied by means of high-resolution X-ray diffraction. The depth-resolved profiles of the lattice parameter were derived from the measured diffraction spectra as a function of annealing temperature. Using these data, the spatial distribution of the electron density related to the post-implantation lattice swelling was determined, which shed light on the waveguide formation in damaged layers. Heat treatments at temperatures T>200ºC resulted in the deterioration of waveguide properties due to annealing of the implantation-induced damage. Lattice recovery was found to be a thermally activated process with an activation energy of E_a=0.32±0.03 eV. This is accompanied by defect clustering, giving rise to diffuse scattering components in the diffraction spectra. (13 References).

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4. Y. Avrahami, E. Zolotoyabko, "Structural modifications in He-implanted waveguide layers of LiNbO₃" . Nucl. Inst. Meth. B 120, 1996. (Proceedings of EMRS-96 spring meeting, Strasbourg, France, 1996.)


X-ray diffraction under grazing incidence and exit angles, a_iand a_f(GID) was used for the first time to study longitudinal displacements in surface acoustic waves (SAW) propagating on LiNbO ₃ single crystals. The a_f -resolved (006)-diffraction spectra have been investigated as a function of the applied voltage for SAW excitation. Substantial increase of diffraction intensity (up to 100%), accompanied by a sharpening of the diffraction profile was found in these measurements. The most pronounced influence of SAW on GID was observed for both the a _i and a_f near the critical angle a_c. The diffraction rods were successfully simulated in the framework of dynamical diffraction theory, using only one SAW-related parameter, namely an additional Debye-Waller factor responsible for reduction of the scattering amplitude. This heuristic approach allowed to explain all experimental effects and served to estimate the amplitudes of the longitudinal component of the SAW in the near-surface layer of LiNbO₃. (24 References).

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5. W. Sauer, T.H. Metzger, J. Peisl, Y. Avrahami, E. Zolotoyabko, "X-ray diffraction under surface acoustic wave excitation", Physica B, (1998).


The influence of surface acoustic waves (SAW) on grazing incidence diffraction (GID) and high resolution X-ray diffraction in Bragg-geometry (HRXD) was investigated on high-quality YZ-cut LiNbO₃ single crystals. a_f -resolved GID-profiles of the (00.6) and the (00.12) reflection as a function of the SAW excitation voltages show both substantial increase of the diffracted intensity (up to 100%) and a simultaneous sharpening of the profiles. Profiles for different incident angles were measured and simulated by model calculations in the framework of dynamical diffraction theory. The lattice displacements induced by the SAW were taken into account by varying the structure factors by an additional Debye-Waller factor. The model calculations agree well with experimental results and serve as an estimate for the amplitude of the longitudinal component of the SAW reaching 0.04 nm for the highest excitation voltage. It is shown that under SAW excitation, the a_f -profile of the weaker (00.12)-reflection can also be calculated using the distorted-wave-Born-approximation, which implies a kinematic description of the scattering process. Under SAW-excitation, the integrated intensity of HRXD profiles of the (30.0) Bragg-reflection increases up to 360% of its original value. This also shows the gain of diffracted intensity caused by reduced extinction. (22 References).

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6. E. Zolotoyabko, Y. Avrahami, W. Sauer, T.H. Metzger, J.Peisl, "The dynamics of phase formation in Ti-diffused waveguide layers of LiNbO₃", Appl. Phys. Let. 73, 10 (1998).


Phase formation processes accompanying high-temperature Ti diffusion in thin waveguide layers of LiNbO₃ were studied by grazing-incidence X-ray diffraction and complementary techniques. The development and decay of a rutilelike phase (Li_0.25Nb_0.75O₂)_1-x(TiO₂)_x was directly observed as a function of annealing time. A solid-state reaction is proposed, which clarifies the mechanism of phase transformation, relating it to cation replacements. (8 References).

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7. Y. Avrahami, E. Zolotoyabko, "Study of atomic diffusion and related structural modifications by high – resolution x-ray diffraction: Ti – diffusion in LiNbO₃", J. Appl. Phys. 85, 9 (1999) pp.6447-6452.


The ability of high-resolution X-ray diffraction, as a nondestructive method, to provide information on atomic diffusion is analyzed. The analysis focuses on studying Ti-diffused waveguide layers of LiNbO₃ crystals for optoelectronic applications. Samples were prepared by a deposition of a 35-nm-thick Ti layer on the 3-in.-Y-cut LiNbO₃ wafer and subsequent annealing at 995ºC for periods of 0.5-6 h. Depth-resolved profiles of the interplanar spacing derived from X-ray diffraction data are compared with the Ti-concentration profiles measured by secondary ion mass spectrometry. It is shown that both results can be used with confidence to determine the Ti-diffusion coefficients in LiNbO₃. Comparison of the two techniques allowed us to obtain a numerical factor, K, relating the Ti concentration and the modification of lattice parameters, i.e., to characterize quantitatively the extent of lattice contraction due to Ti incorporation in the LiNbO₃ crystal. The K factor was found to increase with annealing time, indicating a variable strain contribution to the structural parameters of the waveguide layer. These variations are attributed to high-temperature phase transformation processes, which accompany Ti diffusion. (24 References).

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8. Y. Avrahami, D. Shilo, N. Mainzer, E. Zolotoyabko, "Study of atomic diffusion in crystalline structures by high-resolution X-ray diffraction", J. Cryst. Growth, 198-199, 1, (1999) pp. 264-269.


The ability of high-resolution X-ray diffraction to provide information on atomic diffusion is analyzed, the focus being on the thin film crystalline structures important to modern microelectronics and optoelectronics. Special attention is paid to the Ti diffusion in waveguide layers of LiNbO₃ crystals and to the Hg diffusion in the CdTe/Hg_1-xCd_xTe heterostructures. The depth-resolved concentration profiles obtained are compared with those measured by secondary ion mass spectrometry. The limitations of the new method, mainly due to the variable strain influence on the lattice parameters, are discussed. (14 References).

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For more information contact Ytshak Avrahami at tsachi@mit.edu or by mail at: