Defect-Tolerant Aligned Dipoles within Two-Dimensional Plastic Lattices

Abstract

Carboranethiol molecules self-assemble into upright molecular monolayers on Au{111} with aligned dipoles in two dimensions. The positions and offsets of each molecule's geometric apex and local dipole moment are measured and correlated with sub-Ångström precision. Juxtaposing simultaneously acquired images, we observe monodirectional offsets between the molecular apexes and dipole extrema. We determine dipole orientations using efficient new image analysis techniques and find aligned dipoles to be highly defect tolerant, crossing molecular domain boundaries and substrate step edges. The alignment observed, consistent with Monte Carlo simulations, forms through favorable intermolecular dipoleÀdipole interactions.

A van der Waals density functional investigation of carboranethiol self-assembled monolayers on Au(111)

“…Hence, SAMs of CTs and their derivatives have attracted increasing interest in recent years. [47][48][49][50][51][52][53][54][55][56][57][58] Recently, Lübben and coworkers have demonstrated that by using pure and mixed SAMs of two carborane dithiol isomers [1,2-(HS 2 )-1,2-C 2 B 10 H 10 and 9,12-(HS 2 )-1,2-C 2 B 10 H 10 ] with opposite dipole moments, the surface potential of silver surfaces could be tuned. Weiss et al, on the other hand, used two CT isomers [1-HS-1,7-C 2 B 10 H 11 (M1) and 9-HS-1,7-C 2 B 10 H 11 (M9), see figure 1 for naming of CT isomers] and were able to tune the gold work function over a range of 0.8 eV by preparing mixed SAMs of these two isomers in different ratios.…”

“…Hence Weiss et al proposed that the head-to-tail orientation of the dipoles of the M1 molecules could yield a more favorable adsorption when compared with M9. In addition, very recently they showed that dipole-dipole interactions to be highly defect tolerant based on STM measurements 57…”

Two-Dimensional Compact Variational Mode Decomposition

“…Here, the goal is to isolate defects and artifacts from interfering with the regular modes. We note that these image defects and artifacts can be the result of important physical structures [8,36,67,68].…”

“…Nanoscale images such as these are a useful testbed since data are often oversampled relative to the smallest observable features, atoms and molecular parts. Also, segmentation in one imaging modality can be used to guide segmentation or data acquisition in a complementary imaging mode [3,8,36,51,67].…”

“…Recent work in crystal orientation detection includes variational methods based on tensor maps in conjunction with a regularization scheme [19] and 2D synchrosqueezed transforms [75]. In nanoscale imaging, segmentation enables analyses and comparisons of surface regions of different structures as well as directed measurements of function, spectra, and dynamics [63,67]. Ultimately, efficient segmentation will enable directed data acquisition and parsing acquisition time between different modalities to assemble and to converge complementary structural, functional, and other information.…”