Spin Transition in Arrays of Gold Nanoparticles and Spin Crossover Molecules

Abstract

We investigate if the functionality of spin crossover molecules is preserved when they are assembled into an interfacial device structure. Specifically, we prepare and investigate gold nanoparticle arrays, into which room-temperature spin crossover molecules are introduced, more precisely, [Fe(AcS-BPP)2](ClO4)2, where AcS-BPP = (S)-(4-{[2,6-(dipyrazol-1-yl)pyrid-4-yl]ethynyl}phenyl)ethanethioate (in short, Fe(S-BPP)2). We combine three complementary experiments to characterize the molecule-nanoparticle structure in detail. Temperature-dependent Raman measurements provide direct evidence for a (partial) spin transition in the Fe(S-BPP)2-based arrays. This transition is qualitatively confirmed by magnetization measurements. Finally, charge transport measurements on the Fe(S-BPP)2-gold nanoparticle devices reveal a minimum in device resistance versus temperature, R(T), curves around 260-290 K. This is in contrast to similar networks containing passive molecules only that show monotonically decreasing R(T) characteristics. Backed by density functional theory calculations on single molecular conductance values for both spin states, we propose to relate the resistance minimum in R(T) to a spin transition under the hypothesis that (1) the molecular resistance of the high spin state is larger than that of the low spin state and (2) transport in the array is governed by a percolation model.

Charge Transport and Electrical Properties of Spin Crossover Materials: Towards Nanoelectronic and Spintronic Devices

“…These transport measurements reveal a double-quantum-dot behavior combined with a split Kondo peak, which can be interpreted as an indication of an SCO behavior. The spin crossover phenomena and the charge transport properties at the single molecule level have been studied recently by two different approaches: by grafting SCO molecules to an array of gold nanoparticles [77] and also by means of mechanically controlled break junctions [78].…”

“…In the remaining 24 junctions a negative differential conductance (Figure 13b Left panel: SEM image and schematic drawing of the SCO molecule-gold nanoparticle 2D array used in ref. [77] for single molecule conductance studies. Right panel: Resistance as a function of temperature of a gold nanoparticle network with (A) octanethiol molecules, (B) dithiolated oligo(phenylene ethynylene) molecules, (C) SCO molecules (three layers) and (D) SCO molecules (monolayer).…”

Surface and Size Effects in Spin-Crossover Nanocrystals

“…Decreasing the size of the molecular system from macroscopic (bulk) down to nanometric scale can provide unique insight into fundamentals of spin transition properties, with applications to nanoelectronics and spintronics [7, 8]. The group of Bousseksou [9] is particularly advanced in the synthetic elaboration of nanometric thin films and nano-sized patterns that are obtained by electron beam lithography and in the application of an external perturbations in the hysteresis loop of spin-crossover materials leading to an irreversible switching of their physical properties.…”

Inelastic cotunneling with energy-dependent contact transmission

“…4 Apart from these device concepts, however, molecular charge transport is of fundamental interest due to the quantum nature of the molecules and hence of their conductance properties, even at elevated temperatures. [4][5][6] Here, we focus on a specific regime of quantum transport that directly connects to a practical molecular device structure, i.e., inelastic cotunneling through hybrid molecule-nanoparticle junctions.…”