Self-Assembled Organic Radicals on Au(111) Surfaces: A Combined ToF-SIMS, STM, and ESR Study

Abstract

Electron spin resonance (ESR), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and scanning tunneling microscopy (STM) have been used in parallel to characterize the deposition on gold surface of a series of nitronyl nitroxide radicals. These compounds have been specifically synthesized with methyl-thio linking groups suitable to interact with the gold surface to form self-assembled monolayers (SAMs), which can be considered relevant in the research for molecular-based spintronics devices, as suggested in recent papers. The degree of the expected ordering on the surface of these SAMs has been tuned by varying the chemical structure of synthesized radicals. ToF-SIMS has been used to support the evidence of the occurrence of the deposition process. STM has shown the different qualities of the obtained SAMs, with the degree of local order increasing as the degree of freedom of the molecules on the surface is decreased. Finally, ESR has confirmed that the deposition process does not affect the paramagnetic characteristics of radicals and that it affords a complete single-layered coverage of the surface. Further, the absence of angular dependence in the spectra indicates that the small regions of local ordering do not give rise to a long-range order and suggests a quite large mobility of the radical on the surface, probably due to the weak interaction with gold provided by the methyl-thio linking group.

Formation of dense nitroxide radical layers on the Au(111) substrate for ESN-STM measurement

“…The most recent studies showed that the self-assembled monolayer of family of nitronyl nitroxide radicals (NitRs) can be obtained by immersing of the Au(1 1 1) substrate in dichloromethane solution of NitRs. In this case the paramagnetic character of NitRs molecules is retained while the local order on the surface strongly depends on the particular chemical structure of molecules [22].…”

A Toolbox for Controlling the Energetics and Localization of Electronic States in Self‐Assembled Organic Monolayers

“…This local spin‐polarization is also clearly visible in the LDOS contour maps in Figure 6c (spin up channel) and Figure 6d (spin‐down channel). Such SAMs are of potential interest for spintronic applications 52, 53, 54, 55, 56, 57, 58. Combining these spin‐selective elements with other functional, e.g., polar units could even open up the way for entirely new applications, such as, magnetic molecular quantum wells.…”

The study of paramagnetic self‐assembled monolayers formed by nitroxide radical (TEMPO)3O3P on HOPG

“…There are a number of works reporting the possibility of keeping paramagnetic properties by nitroxides after the deposition on well-defined surfaces. [24][25][26] The first part of EPR studies was devoted to investigations of powdered (TEMPO) 3 O 3 P compound. In Fig.…”