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

Abstract

This work describes the study of molecular junctions embedding the spin crossover complex [Fe(H2B(pz)2)2(phen)] as an active switchable thin film.

Room temperature conductance switching in a molecular iron(iii) spin crossover junction

“…S4 and S5 show another 2 sets of data). Figure 4C shows the corresponding evolution of the values of J at -1.0 and +1.0 V. The observed difference in the width and the position of the hysteresis under positive and negative bias polarity is most likely due to mall conformational differences of the SCO complex similar to observations made by Miyamachi et al 15 and Poggini et al 4 Moreover, from these data we make the following 3 observations. 1) The value of J changes by one order of magnitude with T. This large switch in the observed current proves that Fe III complexes can perform Please do not adjust margins Please do not adjust margins similarly well as Fe II complexes and the transition from HSLS does not preclude efficient current switching in molecular junctions.…”

“…[1][2][3] Given that switching can be triggered by various external stimuli, such as, temperature, pressure, light, or adsorption of guest molecules, SCO molecules also find applications as smart materials that respond to several stimuli. Devices based on thin films [4][5][6][7] (with a thickness of typically 10 -100 nm) of SCO molecules exhibit spin-polarized current switching, 8 voltage-bias, 9 and stretching 10 induced resistance switching, and memristive properties, 11 but it is still challenging, however, to incorporate SCO molecules in molecular tunnel junctions as they are prone to decomposition, or conformational distortion, such that they lose their SCO properties. 4,5,8 In addition, the moleculeelectrode coupling has to be optimized because too strong molecule-electrode coupling leads to drastic alteration of their magnetic properties, even a complete loss of SCO behaviour, [12][13][14] yet too weak coupling compromises stability of the devices.…”

“…21 An inherent challenge with break junctions is the high failure rate and difficulty in achieving consistent orientation of the molecules in the junction. Recently, [Fe(HB(tz) 3 ) 2 ] molecules have been incorporated in large-area junctions [1][2][3][4]22 in the form of thin films (6-100 nm thick), but depending on the fabrication methods either conductance switching was associated with a LSHS transition, 7 or HSLS 4,5 highlighting the challenges in controlling the characteristics of the device.…”

“…11,[23][24][25] By comparison, despite their greater robustness, Fe III SCO complexes are almost entirely absent in SCO molecular junctions. The first report involved subliming [Fe(pap) 2 ]ClO 4 (pap = N-2-pyridylmethylidene-2hydroxyphenylaminato) onto Au(111), but only a small proportion of the molecules were switchable. 11 Use of Cu 2 N islands on the Au(111) surface decouples the SCO molecules from the Au and allowed for more efficient electrical switching using an STM tip at low T = 4.5 K. 24 Nevertheless, the harshness of the deposition technique risks changing the oxidation state of the iron centre and it was not confirmed that the SCO molecules remain in the Fe III state on the surface.…”

Surface effects on a photochromic spin-crossover iron(ii) molecular switch adsorbed on highly oriented pyrolytic graphite

“…In particular the possibility of obtaining bistable thin films of Fe(II) SCO complexes has been suggested in several recent reports. [19][20][21][22][23][24][25] Most of these studies highlighted that direct surface-adsorbate interactions can significantly modify the thermodynamics of SCO. While HOPG (Highly Oriented Pyrolytic Graphite) supported SCO systems were reported to preserve its switching capability similarly to bulk, 23,26 sub-monolayer deposits of several Fe(II) complexes show a selective stabilization of one of the spin states in detriment of the others and loss of their original SCO behaviour when evaporated on metallic surfaces.…”