STM study of a rubrene monolayer on Bi(001): Structural modulations

Abstract

We report a structural modulation occurred in the rubrene monolayer grown on Bi (001) surface. A small sinusoidal variation of surface height plus the periodic distortion of molecular orientations have been observed by low temperature scanning tunneling microscopy. Further analyses demonstrate that this modulation results from the lattice rotation of rubrene monolayer with respect to Bi(001) substrate. Depending on the rotational direction of rubrene lattices, the modulation may exhibit either stripe ripples or zigzag patterns. The experimental data are discussed in term of mass density wave.

Flexible 2D Crystals of Polycyclic Aromatics Stabilized by Static Distortion Waves

“… 30 Another study claims to have observed the Novaco–McTague mechanism in rotational modulations of rubrene on Bi(001). 31 However, while all of these studies demonstrate that the adlayer structure can in fact respond locally to the underlying substrate, none of them rule out reciprocal lattice coincidences to evidence true incommensurability. Hence, the local distortions may arise due to varying adsorption sites but are not necessarily needed to understand the adlayer orientation, in contrast to the incommensurate case of Novaco and McTague where SDWs rule the epitaxy.…”

“…Even though incommensurate epitaxial systems could be explained reasonably well with the model of local relaxations, no direct experimental confirmation of SDWs in their crucial role for the orientational epitaxy of an incommensurate adlayer exists to date. Yet, in some studies, local distortions of an adlayer have been reported − and in a few cases could be directly linked to the local interaction with the underlying substrate. , In a recently published indirect visualization of SDWs for the case of graphene on hexagonal boron nitride, a two-dimensional Young modulus was imaged and a difference of the graphene lattice constant within near-commensurate areas and soliton-like domain walls was reported . Another study claims to have observed the Novaco–McTague mechanism in rotational modulations of rubrene on Bi(001) .…”

“…Yet, in some studies, local distortions of an adlayer have been reported − and in a few cases could be directly linked to the local interaction with the underlying substrate. , In a recently published indirect visualization of SDWs for the case of graphene on hexagonal boron nitride, a two-dimensional Young modulus was imaged and a difference of the graphene lattice constant within near-commensurate areas and soliton-like domain walls was reported . Another study claims to have observed the Novaco–McTague mechanism in rotational modulations of rubrene on Bi(001) . However, while all of these studies demonstrate that the adlayer structure can in fact respond locally to the underlying substrate, none of them rule out reciprocal lattice coincidences to evidence true incommensurability.…”

Soft Crystals in Flatland: Unraveling Epitaxial Growth

“…As a result, the lowest energy state can have a definite nonsymmetry relative angle of orientation.”Novaco and McTague were referring here to configurations that stabilize the overlayer–substrate system overall, recognizing that this could occur even for incommensurate arrangements, wherein “each adatom is statically displaced from its ideal lattice site, and these displacements vary sinusoidally across the monolayer.” Fast forward to Meissner et al , who used a combination of ultraprecise low-energy electron diffraction, scanning tunneling microscopy (STM), and density functional theory to reveal the existence of static distortion waves (SDWs) for overlayers of the organic molecule hexa- peri -hexabenzocoronene (HBC), a kind of “nanographene”. Though other overlayers have been suggested to conform to the SDW model because local distortions were observed, such as rubrene on Bi(001), a sinusoidal incommensurism across the entire substrate can be difficult to ascertain. In the case of HBC on graphite, the SDW structure was deduced from a Moiré pattern of triangles in which displacements of only 0.52 Å, on average, point away from the corners of the triangles.…”

“…Fast forward to Meissner et al, who used a combination of ultraprecise low-energy electron diffraction, scanning tunneling microscopy (STM), and density functional theory to reveal the existence of static distortion waves (SDWs) for overlayers of the organic molecule hexa-perihexabenzocoronene (HBC), a kind of "nanographene". Though other overlayers have been suggested to conform to the SDW model because local distortions were observed, such as rubrene on Bi(001), 20 a sinusoidal incommensurism across the entire substrate can be difficult to ascertain. In the case of HBC on graphite, the SDW structure was deduced from a Moirépattern of triangles in which displacements of only 0.52 Å, on average, point away from the corners of the triangles.…”