1. ARC Centre of Excellence for Functional Nanomaterials, School of Engineering and Australian Institute for Bioengineering and Nanotechnology,
2. Centre for Computational Molecular Science, Australian Institute for Bioengineering and Nanotechnology,
3. Centre for Microscopy and Microanalysis and School of Engineering, The University of Queensland, Queensland 4072, Australia
4. Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China
5. These authors contributed equally to this work.

Correspondence to: Shi Zhang Qiao¹Gao Qing Lu¹ Correspondence and requests for materials should be addressed to G.Q.L. (Email: maxlu@uq.edu.au) or S.Z.Q (Email: s.qiao@uq.edu.au).

Owing to their scientific and technological importance, inorganic single crystals with highly reactive surfaces have long been studied^{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13}. Unfortunately, surfaces with high reactivity usually diminish rapidly during the crystal growth process as a result of the minimization of surface energy. A typical example is titanium dioxide (TiO₂), which has promising energy and environmental applications^{14, 15, 16, 17}. Most available anatase TiO₂ crystals are dominated by the thermodynamically stable {101} facets (more than 94 per cent, according to the Wulff construction¹⁰), rather than the much more reactive {001} facets^{8, 9, 10, 11, 12, 13, 18, 19, 20}. Here we demonstrate that for fluorine-terminated surfaces this relative stability is reversed: {001} is energetically preferable to {101}. We explored this effect systematically for a range of non-metallic adsorbate atoms by first-principle quantum chemical calculations. On the basis of theoretical predictions, we have synthesized uniform anatase TiO₂ single crystals with a high percentage (47 per cent) of {001} facets using hydrofluoric acid as a morphology controlling agent. Moreover, the fluorated surface of anatase single crystals can easily be cleaned using heat treatment to render a fluorine-free surface without altering the crystal structure and morphology.

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