Towards integrated manufacturing of 2D materials

Prof. Stephan Hofmann (University of Cambridge) reviews their recent progress in scalable CVD and device integration approaches of 2D materials.

The foremost challenge for 2D materials is, like for so many other nanomaterials, to develop manufacturing and processing techniques that fulfil the industrial demands for quality, quantity, reliability, and low cost. To serve the industrial demand for “electronic-grade” 2D materials, we focus on chemical vapour deposition (CVD), and in this talk I will review our recent progress in scalable CVD [1] and device integration approaches of highly crystalline graphene and hexagonal boron nitride (h-BN) films. The systematic use of in-situ metrology, ranging from high-pressure XPS to in-situ STM and environmental electron microscopy, allows us to reveal some of the key mechanisms that dictate crystal phase, structural, defect, interfacial and heterogeneous integration control at industrially relevant conditions [2,3].

We systematically explored the parameter space of atomic layer deposition (ALD) of ultrathin oxides on graphene and can show that by extending the precursor residence time, using either a multiple-pulse sequence or a soaking period, ultrathin continuous AlOx films can be achieved directly on graphene [4]. As we show, these results have model system character for rational two-dimensional (2D)/non-2D material process integration [5]. We also highlight how the interplay between the 2D material and the catalyst is not only important for growth but also decisive for transfer processes and show how intercalation processes allow for instance local Cu oxidation at the interface followed by selective oxide dissolution, which gently releases the 2D material [6]. I will also review our extensive study on charge transfer chemical doping [7], interfacial band engineering for efficient charge injection/extraction, effective wetting, and process compatibility including masking and patterning.

References

[1] Hofmann et al. J. Phys. Chem. Lett. 6, 2714 (2015).
[2] Weatherup et al., Nano Lett. 16, 6196 (2016).
[3] Caneva et al. Nano Lett. 16, 1250 (2016).
[4] Aria et al. ACS Appl. Mater. Interfaces 8, 30564 (2016).
[5] Alexander-Webber et al., 2D Mater. 4, 011008 (2016).
[6] Wang et al. ACS Appl. Mater. Interfaces 8, 33072 (2016).
[7] Sanders et al., Nanoscale 7, 13135 (2015).

Stephan Hofmann is the Professor of Nanotechnology in the Department of Engineering, University of Cambridge. He is also the Co-Director of EPSRC Centre for Doctoral Training in Sustainable and Functional Nano.

The Hofmann group explores novel materials, metrology and device architectures. A particular focus thereby lies on nanomaterials and the use of in-situ metrology to probe the fundamental mechanisms that govern their growth and functionality. Understanding matter on the nanoscale has huge technological potential in energy conversion and storage, information/communication and environmental technologies.