Hydrogen-bonded one-dimensional molecular chains on ultrathin insulating films: Quinacridone on KCl/Cu(111)

Abstract

We report on the growth of one-dimensional (1D) chains of the prochiral quinacridone (QA) molecule on ultrathin KCl films on Cu(111) in ultrahigh vacuum. Using low-temperature scanning tunneling microscopy (STM), we observe straight homochiral 1D chains of QA molecules on one (1L), two (2L), and three (3L) atomic layer thick (100)-terminated KCl islands. The KCl films mostly consist of 2L-thick KCl islands delineated by long polar and short nonpolar edges. These 2L-thick KCl islands are topped by smaller one-atom-thick KCl islands or pits, which are delineated by nonpolar step edges. We find that QA chains can nucleate at these nonpolar step edges or on top of KCl terraces without assistance of step edges. In both cases, the longest straight QA chains observed grow along the KCl 100 directions or slightly rotated (typically less than 10 • ) from them. Intermolecular distances ranging from 6.4 Å to 6.8 Å are measured for QA chains on KCl/Cu(111), which is compatible with hydrogen bonds between neighboring flat-lying QA molecules. These intermolecular distances being larger than the measured KCl lattice parameter (i.e., 6.21 Å at 78 K), QA chain growth on KCl/Cu(111) is incommensurate. Molecular arrangement models for the QA chains on KCl are proposed, based on the analysis of the STM images.

Growth of Hydrogen-Bonded Molecular Aggregates on a Thin Alkali Halide Layer: Quinacridone on KCl/Ag(100)

“…To the best of our knowledge, on AH layers, self-assembled molecular chains consisting of flat-lying molecules that are connected by H-bonds have not been reported yet. We note, however, that during the finalization of this work, Bretel et al published data on a very similar system . Finally, we mention that recently, a slightly different topic in this context has also become of interest, namely the growth of new hybrid structures of organic molecules and AH molecules. − …”

“…We note, however, that during the finalization of this work, Bretel et al published data on a very similar system. 35 Finally, we mention that recently, a slightly different topic in this context has also become of interest, namely the growth of new hybrid structures of organic molecules and AH molecules. 36−38 In this work, we report the growth of QA chains on KCl layers on Ag(100).…”

Directed growth of quinacridone chains on the vicinal Ag(35 1 1) surface

“…The chains exhibit a small set of distinct orientations, which are determined by the underlying substrates on all these surfaces. Furthermore, chains of QA have also been observed on insulating layers of KCl grown on Ag(100) or Cu(111) [ 19 , 26 ].…”

Core-Level Binding Energy Shifts in Ultrathin Alkali-Halide Films on Metals: KCl on Ag(100)

“…Alkali halides (AH) are naturally abundant ionic crystals, which are increasingly used as ultrathin insulating layers in nanoscience and nanotechnology. This is because, on the one hand, AH films as thin as two or three atomic layers already exhibit a wide, bulk-like electronic bandgap. , On the other hand, such films can be grown through simple techniques, such as thermal evaporation from a crucible, on a variety of metal − and semiconductor − surfaces. Ultrathin AH films epitaxially grown on metals have been key in recent breakthroughs in scanning probe microscopy experiments in nanophysics and nanooptics to probe and control the states of individual atoms and molecules electronically decoupled from their substrate. − AH thin films are also increasingly used as electronic buffer layers at the electrode/semiconductor interfaces of organic-based optoelectronic devices to engineer the band-bending effects at these interfaces and thus optimize the device performance. − In such applications, understanding the effects of the atomic-scale structure, low dimensionality, and interfacial interactions of the insulating layer on its electronic properties is crucial.…”