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Quasi-free-standing single layer of graphene and h-BN on Pt(111) by a single molecular precursor

Research in graphene (G)-based photonics and electronics is currently facing the challenge of adapting the electronic properties of this material to a wide range of applications. Here we report a novel bottom-up approach to obtain a continuous almost free-standing hexagonal single layer with merging G and hexagonal boron-nitride (h-BN) domains using only onemolecular precursor. This straightforward growth method is easily adaptable to industrial processes aiming at engineering the band gap of G by merging in the same layer the isostructural h-BN, characterized by very different carrier mobility due to its wide bandgap. Up to now, however, G-h-BN layers have been obtained only by complex routes, starting from two or three precursors or growing h-BN on existing G patches and vice-versa.

We have demonstrated that a simple thermal decomposition of dimethylamine borane is sufficient to obtain a G-h-BN layer on Pt(111).This growth route allows an easy and controlled preparation of a continuous almost freestanding layer mostly composed by G and h-BN in the same two dimensional sheet by dehydrogenation and pyrolytic decomposition of DMAB on Pt(111). The temperature is the principal parameter to selectively grow the G-h-BN layer in competition with hybridized B-C-N layers on the clean crystal surface.

We have grown and investigated the h-BNG layer on Pt(111) at the BACH beamline by high-resolution core level X-ray photoemission (XPS) and near-edge absorption spectroscopy (NEXAFS) and at the Nanospectroscopy beamline by low energy electron microscopy (LEEM) combined with X-ray photoemission electron microscopy (XPEEM), micro-spot electron energy loss spectroscopy (µ-EELS) and low energy electron diffraction (µ-LEED) data.

We have obtained the in-plane G-h-BN layer in UHV by dosing 150 L of commercial dimethylamine borane molecules on a (111)-terminated platinum single crystal held at elevated temperatures. 1000 K was found to be the optimal substrate temperature to get the most ordered and flat surface, as shown by NEXAFS (Figure 1) and core level photoemission spectroscopy.

Figure 1: Left: Pt 4f7/2 photoemission spectra of (a) the clean Pt(111) surface, (b) Pt surface exposed to dimethylamine borane at room temperature, and (c) surface covered by the h-BNG layer.  The spectra were decomposed into components corresponding to photoemission from bulk and surface top-most platinum atoms. Right: Polarization dependent NEXAFS spectra at (a) C K, (b) B K, and (c) N K edge from the h-BNG layer (adapted from DOI:10.1002/adfm.201503591, Copyright @ 2015 Wiley–VCH).
 

Evidence of in-plane G-h-BN layer continuity has been established by Temperature Programmed Desorption Spectroscopy and weak interaction with Pt substrate has been ascertained by high-resolution Pt4f7/2 core level spectroscopy, which shows bulk and surface components identical to those of the clean Pt(111) (see Figure 1). The local atomic order of the in-plane G-h-BN layer grown on Pt(111) was investigated by LEEM and µ-LEED, complemented by XPEEM and µ-EELS. The presence of a heterostructure is revealed by LEEM micrographs in bright field (BF) (see Figure 2a and a’), where a clear image contrast between darker and brighter complementary areas is ascribable to the presence of two phases on the sample.

Our findings demonstrate that dehydrogenation and pyrolytic decomposition of DMAB is an efficient and easy method for obtaining a continuous almost freestanding layer made of G, h-BN in the same two dimensional sheet on a metal substrate, such as Pt(111), paving the way for the advancement of next-generation G-like-based electronics and novel spintronic devices.

Figure 2. :  LEEM images of h-BNG layer on Pt(111). (a) Bright Field LEEM at Vstart = 6 eV. The red square indicates the zoomed area (a’). (b) Dark Field LEEM image using the graphene first-order diffraction spot of 30° rotated domains (Vstart = 35 eV). The orange square indicates the zoomed area (b’). (c) Dark Field LEEM image using the h-BN first-order diffraction (Vstart = 35 eV). The light blue square indicates the zoomed area (c’). (d) LEEM (IV) characteristics obtained from a stack of LEEM images with electron energy from 2 to 30 eV at the locations marked in (a’) (DOI:10.1002/adfm.201503591, Copyright @ 2015 Wiley–VCH).


 

This work was supported by the Italian MIUR through the national grant Futuro in ricerca 2012 RBFR128BEC ‘‘Beyond graphene: tailored C-layers for novel catalytic materials and green chemistry’’

This research was conducted by the following research team:

S. Nappini1, I. Píš1,2, T.O. Menteş2, A. Sala2, M. Cattelan3, S. Agnoli3, F. Bondino1, and E. Magnano1,4
1IOM CNR laboratorio TASC, Basovizza (TS), 34149, Italy
2Elettra - Sincrotrone Trieste, S.C.p.A., Basovizza (TS), 34149, Italy
3Department of Chemical Sciences, University of Padua, Padova, 35131, Italy
4Department of Physics, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa

Contact persons:

Federica Bondino, email: bondino@iom.cnr.it,
E. Magnano, email: magnano@iom.cnr.it

Reference

S. Nappini, I. Píš, T. O. Menteş, A. Sala, M. Cattelan, S. Agnoli, F. Bondino, E. Magnano “Formation of a Quasi-Free-Standing Single Layer of Graphene and Hexagonal Boron Nitride on Pt(111) by a Single Molecular Precursor” Advanced Functional Materials (2015) . DOI:10.1002/adfm.201503591, Copyright @ 2015 Wiley–VCH

 

Last Updated on Friday, 08 January 2016 15:16