title: Heterogeneous Pyrolysis: A Route for Epitaxial Growth of hBN Atomic Layers on Copper Using Separate Boron and Nitrogen Precursors.
abstract: Growth of hBN on metal substrates is often performed via chemical vapor deposition from a single precursor (e.g., borazine) and results in hBN monolayers limited by the substrates catalyzing effect. Departing from this paradigm, we demonstrate close control over the growth of mono-, bi-, and trilayers of hBN on copper using triethylborane and ammonia as independent sources of boron and nitrogen. Using density functional theory (DFT) calculations and reactive force field molecular dynamics, we show that the key factor enabling the growth beyond the first layer is the activation of ammonia through heterogeneous pyrolysis with boron-based radicals at the surface. The hBN layers grown are in registry with each other and assume a perfect or near perfect epitaxial relation with the substrate. From atomic force microscopy (AFM) characterization, we observe a moiré superstructure in the first hBN layer with an apparent height modulation and lateral periodicity of ∼10 nm. While this is unexpected given that the moiré pattern of hBN/Cu(111) does not have a significant morphological corrugation, our DFT calculations reveal a spatially modulated interface dipole layer which determines the unusual AFM response. These findings have improved our understanding of the mechanisms involved in growth of hBN and may help generate new growth methods for applications in which control over the number of layers and their alignment is crucial (such as tunneling barriers, ultrathin capacitors, and graphene-based devices).
authors.affiliation: KBRwyle, 2601 Mission Point Blvd., Dayton, Ohio 45431, United States.|Air Force Research Laboratory , Wright-Patterson AFB, Ohio 45433, United States.
authors.forename: Gene
authors.initials: G
authors.lastname: Siegel
authors.affiliation: Department of Mechanical Engineering and Materials Science Program, Colorado School of Mines , Golden, Colorado 80401, United States.
authors.forename: Cristian V
authors.identifier: 0000-0002-8476-4467
authors.initials: CV
authors.lastname: Ciobanu
authors.affiliation: Center for Nanoscale Materials, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Badri
authors.initials: B
authors.lastname: Narayanan
authors.affiliation: Air Force Research Laboratory , Wright-Patterson AFB, Ohio 45433, United States.
authors.forename: Michael
authors.initials: M
authors.lastname: Snure
authors.affiliation: Air Force Research Laboratory , Wright-Patterson AFB, Ohio 45433, United States.
authors.forename: Stefan C
authors.initials: SC
authors.lastname: Badescu
keywords: Multilayer boron nitride; atomic force microscopy; chemical vapor deposition; heterogeneous pyrolysis; moiré patterns