Strain-induced reconstruction in two-dimensional silver intercalated between graphene and SiC

The realization of air-stable two-dimensional (2D) metals confined at the interface between graphene and SiC has attracted significant attention owing to their distinct properties compared to their bulk counterparts. In this work, we identify two distinct structural phases in a monolayer silver intercalated between graphene and SiC: (i) a moiré pattern arising from the lattice mismatch between graphene and monolayer silver and (ii) a striped reconstruction formed through the interaction with the underlying SiC. Using cryogenic scanning tunneling microscopy combined with density functional theory, we elucidate the origin of the silver striped reconstruction. Driven by the competition between the silver-SiC and the silver-silver interactions within a monolayer, the silver atoms form a one-dimensional Frenkel-Kontorova domain, in which an <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mo>(</a:mo> <a:mi>n</a:mi> <a:mo>+</a:mo> <a:mn>1</a:mn> <a:mo>)</a:mo> <a:mo>×</a:mo> <a:mi>√</a:mi> <a:mn>3</a:mn> </a:mrow> </a:math> silver supercell accommodates an <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mi>n</b:mi> <b:mo>×</b:mo> <b:mi>√</b:mi> <b:mn>3</b:mn> </b:mrow> </b:math> supercell <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mo>(</c:mo> <c:mi>n</c:mi> <c:mo>=</c:mo> <c:mn>20</c:mn> <c:mo>)</c:mo> </c:mrow> </c:math> of the underlying SiC, which partially relieves tensile strain, otherwise imposed by ideal epitaxy. The strain-induced reconstruction creates a long-range modulation of 2D silver electronic density, giving rise to an electronic state at <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:mo>∼</d:mo> <d:mn>0.75</d:mn> <d:mspace width="0.28em"/> <d:mi>eV</d:mi> </d:mrow> </d:math> above the Fermi level in the transition regions between different silver-SiC registries. These findings uncover the important interplay between the structural and electronic properties of intercalated 2D metals and the underlying SiC substrate, providing new insights into substrate-mediated reconstruction and electronic modulation at confined interfaces.