= Luigi Colombo
{c}
\b[Luigi Colombo] coauthored the surface-oxygen <graphene> growth study and the isotope-dependent Raman study.<The role of surface oxygen in the growth of large single-crystal graphene on copper by Yufeng Hao and others>[byline]{ref}<Probing carbon isotope effects on the Raman spectra of graphene with different ¹³C concentrations by Bruno R. Carvalho and others>[byline and 2015 Texas Instruments affiliation]{ref}
An instructive growth question is whether a continuous film is also a single crystal. Domains can meet and cover a substrate while retaining <grain boundaries>. Equal coverage therefore does not determine boundary length or crystallographic uniformity.
For an original square-tiling model, cover a $1\,\mathrm{cm}$ square with square grains of side $d$, with an integer number of grains along each edge. Ignoring junction width, the internal boundary length is
$$
L_{\mathrm{int}}=2\left(\frac Ld-1\right)L,
$$
where $L=1\,\mathrm{cm}$. If $d=1\,\mathrm{mm}$, 100 grains cover the square and the internal boundaries total $0.18\,\mathrm m$. If $d=10\,\mu\mathrm m$, one million grains cover the same area and the boundary total is $19.98\,\mathrm m$.
Real graphene domains do not form a perfect square tiling, and a boundary's effect also depends on atomic structure and orientation. The stipulated geometry simply explains why two films with complete area coverage can present very different microstructures. Combining growth observations with <Raman spectroscopy>, imaging and electrical measurements tests different parts of the material description rather than substituting one coverage fraction for all of them.
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