Unidirectional growth of molybdenum dioxide nanoflakes on C-sapphire substrate via buffer layer induction

Unidirectional growth, a novel and promising approach, is a key method for synthesizing large-scale single crystals of ultra-thin materials. In this study, we present a unique and convenient method for the growth of molybdenum dioxide (MoO 2 ) nanoflakes on a c-sapphire substrate, achieving uniform orientation. Specifically, the MoO 2 (100) and MoO 2  < 02 1 ¯ > are aligned parallel to sapphire(0001) and sapphire<1 2 ¯ 10>, respectively. A crucial observation in our study is the presence of a buffer layer between the as-grown MoO 2 and c-sapphire. This buffer layer is essential in overcoming the limitation of lattice mismatch , thereby facilitating the unidirectional growth of MoO 2 . The introduction of reductants , such as H 2 and sulfur vapor, is critical for the formation of this buffer layer. Electrical measurements indicate that the electrical conductivity of the as-grown MoO 2 nanoflake is approximately 3.91 × 10 6  S/m at 300 K, which is comparable to other metallic nanomaterials . In addition, magnetotransport measurements reveal that the as-grown MoO 2 nanoflakes exhibit a temperature-dependent linear magnetoresistance (MR) under magnetic fields . These findings not only demonstrate a method for the unidirectional growth of MoO 2 on the c-sapphire substrate but also have significant implications for the application of MoO 2 in transparent electrodes and the fabrication of integrated devices based on MoO 2 .