Cadmium tungstate, CdWO₄, related to family of wolframite-type crystals A²⁺WO₄ is one from the best scintillating mediums. Potentials of this material for laser techniques, acoustics and photocatalytic technologies are under considerations. The parameters of monoclinic cell of CdWO₄ : a = 5.0400(8) Å, b = 5.8701(6) Å, c = 5.0841(7) Å, b = 91.476(19)° , V = 150.36(1) ų, Z = 2, space group P2/c. A chain-type structure is formed by parallel zigzag chains of distorted CdO₆ and WO₆ octahedrons, spreading along the c axis. The CdWO₄ crystals are characterized by good cleavage properties of (010) planes. Micromorphology, structural and electronic properties of CdWO₄ (010) cleaved surfaces are evaluated in present study.
High quality inclusion free CdWO₄ crystal of 80-90 mm in diameter and of 180-200 mm in length was grown by Low Thermal Gradient Czochralski Technique (LTG Cz). One of the essential features of the LTG Cz technique is the low thermoelastic stresses in the crystal. Respectively, the crystals are less susceptible to post-growth cracking and the dislocation density is much lower in the crystals grown by the LTG Cz technique. The results of CdWO₄ crystal growth along the [010] direction are considered in this report. The scintillation and optical properties of ¹¹⁶CdWO₄ crystals  grown under the conditions were early reported in Ref. [1]. In practice, the CdWO₄ crystal growth along [010] direction is very hard to be realized by conventional high-temperature methods and, as a rule, is not used.
The substrates of CdWO₄ (010) with dimensions 12*0.7*12 mm³ were fabricated by accurate cleaving of a single crystal parallelepiped. The top-surface crystallographic properties were evaluated with RHEED  using EFZ4 device at electron energy of 50 keV. The surface micromorphology was studied by AFM with Solver P-47H device. The system of Kikuchi lines are found for cleaved CdWO₄ (010) by RHEED that confirms the high crystallographic state of cleaved surface. A substrate surface is formed by a system of wide plane terraces with as low rms as ~0.2 nm and typical area of 3-10 mm². At the terrace surface the point defects of 15-30 nm in diameter are present. Thermal stability of CdWO₄ (010) surface have been traced by annealing in the air over the temperature range of 400-700°C followed by RHEED analysis. High crystallographic quality of cleaved CdWO₄ (010) surface gives an opportunity to consider CdWO₄ as promising substrate material for epitaxial technologies. There is no foreign phase detected after annealing at 400-600°C. However, the low-intensity precipitation of WO₃ and W19O55 oxides was found after annealing at 650-700°C. The epitaxial relations have been obtained for the WO₃ and W₁₉O₅₅ precipitates on CdWO₄ (010) surface.

1. A.S. Barabash, P. Belli, R. Bernabei, R.S. Boiko, F. Cappella, V. Caracciolo, D.M. Chernyak, R. Cerulli, F.A. Danevich, M.L, Di Vacri, A.E. Dossovitskiy, E.N. Galashov, A. Incicchitti, V.V. Kobychev, S.I. Konovalov, G.P. Kovtun, V.M. Kudovbenko, M. Laubenstein, A.L. Mikhlin, S. Nisi, D.V. Poda, R.B. Podviyanuk, O.G. Polischuk, A.P. Shcherban, V.N. Shlegel, D.A. Solopikhin, Yu.G. Stenin, V.I. Tretyak, V.I. Umatov, Ya.V. Vasiliev and V.D. Virich, Low background detector with enriched ¹¹⁶CdWO₄ crystal scintillators to search for double β decay of ¹¹⁶Cd, J. Instrumentation 6 (2011) P08011.

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