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

Abstract

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 (MoO2) nanoflakes on a c-sapphire substrate, achieving uniform orientation. Specifically, the MoO2(100) and MoO2 < 021¯> are aligned parallel to sapphire(0001) and sapphire<12¯10>, respectively. A crucial observation in our study is the presence of a buffer layer between the as-grown MoO2 and c-sapphire. This buffer layer is essential in overcoming the limitation of lattice mismatch, thereby facilitating the unidirectional growth of MoO2. The introduction of reductants, such as H2 and sulfur vapor, is critical for the formation of this buffer layer. Electrical measurements indicate that the electrical conductivity of the as-grown MoO2 nanoflake is approximately 3.91 × 106 S/m at 300 K, which is comparable to other metallic nanomaterials. In addition, magnetotransport measurements reveal that the as-grown MoO2 nanoflakes exhibit a temperature-dependent linear magnetoresistance (MR) under magnetic fields. These findings not only demonstrate a method for the unidirectional growth of MoO2 on the c-sapphire substrate but also have significant implications for the application of MoO2 in transparent electrodes and the fabrication of integrated devices based on MoO2.