2D AlB 2 flakes for epitaxial thin film growth
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partment of Mechanical Engineering, Texas A&M University, College Station, Texas 77843, USA
Jacob L. Meyer ATSP Innovations, Champaign, Illinois 61820, USA
Stanislav V. Verkhoturov Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA
Tanil Ozkan Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843, USA
Michael Eller and Emile A. Schweikert Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA
James Economy ATSP Innovations, Champaign, Illinois 61820, USA
Andreas A. Polycarpoua) Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843, USA (Received 16 January 2018; accepted 15 May 2018)
In this study, we report on the mechanical cleavage of conductive metal-based aluminum diboride (AlB2) flakes. The cleavage resulted in a highly single crystalline 2D material and had an atomically flat and smooth surface as shown by atomic force microscopy (AFM) and secondary ion mass spectrometry. Nanoindentation and AFM imaging of freshly cleaved specimens revealed sub-nm roughness and 30% improvement in the nanomechanical properties as compared to the as-grown AlB2 flakes. Once exposed to ambient air, the cleaved AlB2 flakes formed a superficial oxidation layer of less than 1 nm thickness within 5 min. Owing to the smooth surface, ultra-thin and stable oxide layer, and the excellent mechanical and electrical characteristics of AlB2, the cleaved flakes present an ideal 2D material for emerging applications in microfabrication such as the growth of epitaxial thin films. To prove the sub-nm surface characteristics of cleaved AlB2, a 10-nm thick TiO2 film was deposited on a freshly cleaved AlB2 using atomic layer deposition. Surface roughness and compositional consistency of this film were compared with a control sample deposited on Si. The TiO2 film on AlB2 showed a distinct thin interface layer with fewer defects than TiO2 on Si and superior flatness.
I. INTRODUCTION
Since the discovery of the first graphene flake in 2004 through the mechanical cleavage of highly ordered pyrolytic graphite, two-dimensional (2D) nanomaterials have attracted attention due to their potential use in a range of applications such as catalysis, electronic and optoelectronic devices, electrodes for energy storages, and nanocomposites.1,2 2D materials such as graphene have versatile and enhanced mechanical, chemical, and electrical properties.3,4 The success of 2D graphene has motivated scientists in the last years to pursue the search for 3D materials that can be exfoliated by separating a 3D material into single or few 2D layers.5 These efforts successfully have led to the discovery of promising new a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.173 J. Mater. Res., 2018
2D materials beyond graphene such as hexagonal boron nitride and transition metal dichalcogenides.6,7 Therefore, the space of 2D materials is expanding and getting more mature as a distinct class of materials bringing new
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