Interface versus Bulk Light-Induced Switching in Spin-Crossover Molecular Ultrathin Films Adsorbed on a Metallic Surface

Abstract

Spin-crossover molecules present the unique property of having two spin states that can be controlled by light excitation at low temperature. Here, we report on the photoexcitation of [Fe II ((3, ) 2 Pz) 3 BH) 2 ] (Pz = pyrazolyl) ultrathin films, with thicknesses ranging from 0.9 to 5.3 monolayers, adsorbed on Cu(111) substrate. Using Xray absorption spectroscopy measurements, we confirm the anomalous light-induced spin-state switching observed for sub-monolayer coverage and demonstrate that it is confined to the first molecular layer in contact with the metallic substrate. For higher coverages, the well-known light-induced excited spin-state trapping effect is recovered. Combining continuous light excitation with thermal cycling, we demonstrate that at low temperature light-induced thermal hysteresis is measured for the thicker films, while for sub-monolayer coverage, the light enables extension of the thermal conversion over a large temperature range. Mechanoelastic simulations underline that, due to the intermolecular interactions, opposite behaviors are observed in the different layers composing the films.

All-atom molecular dynamics simulation of the [Fe(pyrazine)][Ni(CN)4] spin-crossover complex. II. Spatiotemporal study of a bimorph actuator

“…2). At this stage, it may be worth to note that in ultrathin SCO films one may expect a modification of SCO properties [32,[55][56][57][58], but these finite size effects will be ignored in the present calculations due to the reason that the change of sample geometry which plays an important role in the finite size effect is not considered in the present simulation.…”

Effects of the surface energy and surface stress on the phase stability of spin crossover nano-objects: a thermodynamic approach

“…† On the whole, an increase of the residual HS fraction as well as a downshift of the equilibrium temperature are clearly observed with the size reduction, which is in qualitative agreement with experimental observations on different SCO compounds. 49,[54][55][56][57][58][59] In particular, a gradual spin conversion with a transition temperature of ∼266 K as well as a residual HS fraction of x = 0.4 at 200 K was derived from the calculation for a 5-layer (∼3.5 nm) thin film (Fig. 6).…”

Bistable Spin‐Crossover Nanoparticles for Molecular Electronics

“…A remarkable example is provided by the molecule [Fe(Pyrz) 2 ] (Figure 1c) that can be deposited over different substrates (Cu, Au) leading to organized arrays at the few-layer limit, which still exhibit thermal and lightinduced SCO effects. [71][72][73] BF 4 ) placed between a nanojunction of gold electrodes with a gap of 5-10 nm. d) Electrical conductivity as a function of the temperature of microcontact printed 2D assemblies of Fe(Htrz) 2 (trz)(BF 4 ) nanorods (25 × 10 nm) interdigitated between Au electrodes with a gap of ≈50 nm.…”

“…A remarkable example is provided by the molecule [Fe(Pyrz) 2 ] (Figure 1c) that can be deposited over different substrates (Cu, Au) leading to organized arrays at the few‐layer limit, which still exhibit thermal and light‐induced SCO effects. [ 71–73 ]…”