Extended Data Fig. 1 | Growth of a-BN on Cu and SiO 2 substrates. a–c, Raman
(a), XPS (b) and EDS mapping (c) images of a-BN grown on copper foils (plasma
power 30 W, growth temperature 300 °C) and transferred onto SiO 2 substrates
for Raman measurements. The typical Raman spectrum of the a-BN film is similar
to that of bare amorphous SiO 2. d–f, Raman (d), XPS (e) and EDS mapping (f)
images of an a-BN film grown directly on SiO 2 (plasma power 10 W, growth
temperature 200 °C). The spectra are largely the same for all substrates. The
dielectric properties obtained from spectroscopic ellipsometry reveal no
influence of the substrate. Scale bar, 40 nm.