Well-Ordered Monolayer Growth of Crown-Ether Ring Molecules on Cu(111) in Ultra-High Vacuum: An STM, UPS, and DFT Study

Abstract

Crown-ether (CR) ring molecules are known as host molecules for capturing guest species inside the ring. So far CR molecular films have only been grown by drop-casting a CR solution on an inert substrate in air which offers little control over the molecular structure. Here we report the successful growth of a well-ordered CR molecular array on an atomically flat and clean noble metal Cu(111) substrate at 300 K in ultra-high vacuum (UHV), using 4,4′,5,5′-tetrabromodibenzo[18] crown-6 ether (Br-CR). The adsorption, self-assembly, and electronic structures of Br-CR were studied by means of UHV low-temperature scanning tunneling microscopy and spectroscopy, low electron energy diffraction, and angle-resolved ultraviolet photoemission spectroscopy. We found that (1) the Br-CR ring, which is bent both in the crystal and gas phase, flattens upon adsorption on Cu(111). Density functional theory reveals that the two benzene groups of the molecule lie flat on the surface such as to maximize the substrate-molecule interaction. (2) The moderate molecule−substrate interaction allows thermal diffusion of the Br-CR molecules, resulting in the formation of self-assembled monolayer islands with 7 × 4 superstructure. (3) While the deposition of 0.05 ML Br-CR forms multidomain islands with disordered defects, a drastic improvement occurred at 0.25 ML, where only atomically flat single-domain islands were grown. This Br-CR flat ring cavity array could become a template for designing novel two-dimensional arrays of desired guest atoms, ions, or functionalized molecules.

Carbon Monoxide Stripe Motion Driven by Correlated Lateral Hopping in a 1.4 × 1.4 Monolayer Phase on Cu(111)

“…The experiment was performed with a home-built low-temperature STM instrument at 4.6 K under UHV. The setup consists of introduction, preparation, and analytical chambers with a base pressure of <10 –8 Pa (see details in refs − ). A UHV cryostat (CryoVac), including an outer liquid nitrogen tank (8 L) and an inner helium tank (4 L), is docked on the analytical chamber.…”

“…Cu­(111) Preparation . The Cu(111) single crystal was cleaned by repeated cycles of Ar + sputtering (1.0 kV, 0.80 μA) for 15–30 min with subsequent annealing (820 K) (see details in refs and ). The cleanliness of the substrate was checked using LEED.…”

Fundamental Properties of Transition-Metals-Adsorbed Germanene: A DFT Study

“…The theoretical framework built from the first-principles simulations is used to understand the significance of chemical bonds in generating rich and unique geometrical structures as well as custom-tailored electronic and magnetic properties. The theoretical predictions about the geometrical structures, band structures, van Hove singularities, and charge/spin-density distributions can be verified through high-resolution scanning tunneling microscopy/transmission electron microscopy (HRSTM/TEM) [28,29], angle-resolved photoemission spectroscopy (ARPES) [30], scanning tunneling spectroscopy (STS) [31], and STM spin excitation spectroscopy [32], respectively.…”

On-surface growth of transition-metal cobalt nanoclusters using a 2D crown-ether array

“…38,39 The numerical settings were the same as in our previous study on BrCR/Cu(111). 24 We used the PBE exchange-correlation potential and Grimme's DFT-D2 van der This journal is © The Royal Society of Chemistry 2024…”

“…However, it was recently shown that the crown ring can be unfolded when BrCR forms a self-assembled monolayer (SAM) ring array on a metal Cu(111) surface. 24 Herein, Co was selected as the ''guest'' since the growth, electronic, and magnetic structures of bilayer triangularshape Co nanoislands on Cu(111) substrate are well known. [25][26][27][28] Although there are reports on the adsorption of Co ions on crown ether molecules in bulk, 29 no studies have been conducted on crown ether and metal clathrate compounds on solid surfaces in a vacuum.…”