Preparation of monolayers of [MnIII 6CrIII]3+ single-molecule magnets on HOPG, mica and silicon surfaces and characterization by means of non-contact AFM

Abstract

We report on the characterization of various salts of [MnIII6CrIII]3+ complexes prepared on substrates such as highly oriented pyrolytic graphite (HOPG), mica, SiO2, and Si3N4. [MnIII6CrIII]3+ is a single-molecule magnet, i.e., a superparamagnetic molecule, with a blocking temperature around 2 K. The three positive charges of [MnIII6CrIII]3+ were electrically neutralized by use of various anions such as tetraphenylborate (BPh4-), lactate (C3H5O3-), or perchlorate (ClO4-). The molecule was prepared on the substrates out of solution using the droplet technique. The main subject of investigation was how the anions and substrates influence the emerging surface topology during and after the preparation. Regarding HOPG and SiO2, flat island-like and hemispheric-shaped structures were created. We observed a strong correlation between the electronic properties of the substrate and the analyzed structures, especially in the case of mica where we observed a gradient in the analyzed structures across the surface.

Crystallographic order and decomposition of [MnIII6CrIII]3+ single-molecule magnets deposited in submonolayers and monolayers on HOPG studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin probe force microscopy in UHV

“…The sample was put inside the load lock of the ultra-high vacuum (UHV) apparatus immediately following deposition of the solution with the molecules. The SMM molecules adsorbed on the HOPG surface by this procedure stay intact with respect to the composition, magnetic properties, and their oxidation state, as was confirmed earlier using XAS [ 16 , 17 ] and X-ray photoelectron spectroscopy (XPS) [ 18 ]. Experiments were performed with a modified Omicron UHV AFM/STM in non-contact mode at room temperature (approximately 22°C) and a pressure of 3 × 10 -8 Pa.…”

“…In addition, a cluster of molecules with a height of over 4 nm occurs which exhibits no internal structure. Even higher clusters have been observed on silicon substrates [ 18 ]. In the line scan of Figure 6 c, the heights of two islands are shown.…”

“…HOPG allows the SMMs to form islands of monolayers, whereas on substrates like Si, the formation of hemispheric clusters on the surface has been observed [18]. …”

“…The arrangement of the adsorbed molecules of [Mn III 6 Cr III ] 3+ depends heavily on the substrate used. HOPG allows the SMMs to form islands of monolayers, whereas on substrates like Si, the formation of hemispheric clusters on the surface has been observed [ 18 ].…”

Probing the magnetic moments of [MnIII6CrIII]3+ single-molecule magnets—A cross comparison of XMCD and spin-resolved electron spectroscopy

“…Efforts are being made to replace bulk magnetic and semiconductor devices by single molecules, which can perform as memory cells, transistors or even logical electron spectroscopy (SPES) experiments on SMM were performed [33] using the most stable [Mn III 6 Cr III ] 3+ type with perchlorate anions. With the controlled deposition of the [Mn III 6 Cr III ] 3+ SMM on surfaces being a central question for future applications, the deposition behaviour on surfaces was studied as well by AFM and STM [34,35]. Within the work presented here, SPES measurements were performed at the L 3,2 edge of the Mn ions in the [Mn III 6 Cr III ] 3+ SMM, using circularly polarized synchrotron radiation for the excitation step.…”