Spin‐Crossover Complex on Au(111): Structural and Electronic Differences Between Mono‐ and Multilayers

Abstract

Submono-, mono- and multilayers of the Fe(II) spin-crossover (SCO) complex [Fe(bpz)2 (phen)] (bpz=dihydrobis(pyrazolyl)borate, phen=1,10-phenanthroline) have beenprepared by vacuum deposition on Au(111) substrates and investigated with near edge X-ray absorption fine structure (NEXAFS) spectroscopy and scanning tunneling microscopy (STM). As evidenced by NEXAFS, molecules of the second layer exhibit a thermal spin crossover transition, although with a more gradual characteristics than in the bulk. For mono- and submonolayers of [Fe(bpz)2 (phen)] deposited on Au(111) substrates at room temperature both NEXAFS and STM indicate a dissociation of [Fe(bpz)2 (phen)] on Au(111) into four-coordinate complexes, [Fe(bpz)2 ], and phen molecules. Keeping the gold substrate at elevated temperatures ordered monolayers of intact molecules of [Fe(bpz)2 (phen)] are formed which can be spin-switched by electron-induced excited spin-state trapping (ELIESST).

Influence of a Metal Substrate on Small‐Molecule Activation Mediated by a Surface‐Adsorbed Complex

“…This approach potentially entails some problems. Firstly, due to the direct contact between the metal complex and the surface, some complexes may decompose . Depending on the nature of the complex, the interaction between the surface and the metal complex may be weak or sensitive to changes in its electronic and geometric structure .…”

Temperature-induced transport changes in molecular junctions based on a spin crossover complex

“…We and others elsewhere showed later on the feasibility of obtaining thin films by sublimation of 1 and reported their properties. 14,[20][21][22][23] In this paper, we study the modulation in tunnelling current densities across Au TS //1//EGaIn junctions as a function of temperature and film thickness. We show that, as expected, there is a significant change in current density with temperature due to the switching between HS and LS states.…”

“…Thanks to the relatively high geometrical contact area in the crossbar junctions (about 1000×50 µm 2 ), we were able to measure very low current densities (down to log |J|≈ -9.5) with a reasonable signal-to-noise ratio, which constitutes a significant improvement in respect to our previous study. 7 For both film thicknesses, we measured full J/V traces between -1 and +1 V at different temperatures between 300 and 100 K (corresponding to the temperatures in which the SCO complex is in either HS or LS states as determined by magnetometry and by X-Ray Absorption Spectroscopy, XAS, in previous works 14,22,30,31 ). The log|J|/V curves measured between +1 V and -1V present the usual symmetrical V-shaped characteristics of non-rectifying junctions (see Figure 2).…”

Engineering On‐Surface Spin Crossover: Spin‐State Switching in a Self‐Assembled Film of Vacuum‐Sublimable Functional Molecule

“…Among them, the [Fe(H 2 B(pz) 2 ) 2 (L)] complexes have been studied in detail on metallic Au(111), nonmetallic Bi(111), and highly oriented pyrolytic graphite (HOPG) surfaces . The switching is reported to be coverage dependent on metallic Au(111) substrate on which the first layer of the complex undergoes fragmentation and loss of SCO, whereas switching is retained on Bi(111) and HOPG surfaces even at sub‐monolayer level due to the weak molecule–surface interfacial interactions …”