29HIGHLIGHTS 2020

Fig. 17: a) Comparison between bulk SQUID magnetic characterisation (red dots), Mössbauer spectroscopy of [Fe(qnal)2] in bulk (green dots) and High-Spin Fe(II) thermal distribution profile obtained from X-ray absorption spectroscopy (XAS) on a thin film (blue dots) (originally

reported in [1]). b) SMS spectra of the drop cast sample of [Fe(qnal)2] at 3.0 K (blue line) and 290 K (red line). c) SMS spectra of the

100 nm-thick sublimated sample of [Fe(qnal)2] at different temperatures. Figures adapted with permission from principal publication.

Fig. 18: a) Scheme of vertical multi- layered junctions (grey and yellow represent, respectively, the silver and gold electrodes, purple, the embedded molecular thin film) and (b) dark- field scanning transmission electron microscopy (STEM) image of a thin section of it. c) J-V characteristics at different temperatures. J ~ Vl+1 indicates the presence of an SCLC mechanism with the presence of a trap distribution. d) Trend of the Tt parameter, obtained from the J-V analysis, related to trap distributions as a function of temperature. A transition between shallow traps SCLC (low T) to exponential traps distribution SCLC (high T), consistent with the LS HS crossover, is observed. Figures adapted with permission from principal publication.

inorganic complexes have been proposed as active components of functional devices presenting magnetic and/or electrical field- dependent responses. To achieve this goal, three preliminary steps are necessary: to find a SCO molecular system that is capable of producing good-quality films, to verify that the films retain the SCO properties, and to characterise the electronic properties.

This study reports the development and characterisation of a multilayer structure comprising a molecular thin film (ca. 40 nm) of the [Fe(qnal)2] SCO complex. The possibility of obtaining smooth high-quality films by thermal sublimation of this molecule was previously demonstrated (Figure 17a) [1]. To evaluate the persistence of the SCO transition in the whole depth of the [Fe(qnal)2] deposit to be embedded in a device, SMS was employed as a function of temperature and light irradiation at beamline ID18. The results revealed a complete spin conversion for the thickest drop cast film (Figure 17b), similar to the behaviour observed for bulk samples by standard transmission Mössbauer spectroscopy. Thinner (100 nm) sublimated films showed reduced SCO behaviour (Figure 17c), presenting a HS residual contribution at the lowest achievable temperature (3 K). However, a reduction of the SCO when thin films of molecules are deposited on a substrate is not unexpected. This detrimental effect can arise from the possible interaction of the deposited molecules with the substrate, as well as from possible differences in the organisation of the sublimated molecules with respect to the bulk phase.