properties of SCO compounds is fundamental, to understand how they behave under electronic stimuli, especially when prepared as thin films. [8,9] Indeed, these molecules can be switched between two electronic states-termed high-spin (HS) and low-spin (LS)-with different magnetic, optical, and structural properties by the action of external stimuli (pressure, temperature, light-irradiation) [10][11][12][13][14] making them promising systems for new functional materials. [7] This is particularly important since the use of electrical stimuli to control (read/write) the spinstate of the system would provide a great advantage toward technological applications, compared to other conventional addressing methods such as light irradiation, and changes in temperature or pressure, that are less easily implemented. In this paper, we show that it is possible to design large area switchable molecular tunnel junctions, in which the switchable tunneling barrier is made of a thin film of a SCO compound. Those thin films, made by evaporation on TS Au (template-stripped gold), were thoroughly characterized using highly-sensitive and specific surface tools. Electrical switching has been studied as a function of temperature in a tunnel junction configuration, and the experimental results have been rationalized thanks to a theoretical model based on energy levels and electronic densities obtained at density functional theory (DFT) level. The good correlation we establish between experimental measurements and modeling proves the feasibility to design, manipulate, and read such ultrathin film devices, an important prerequisite for the development of future active multistable devices. The most critical issues toward the development of large-area spin-crossover based molecular junctions are i) to obtain high quality SCO thin films over large areas and ii) to have a measurement methodology that allows to measure their properties in an efficient and reliable manner. Moreover, to facilitate further developments and applications of those systems, it is highly desirable to have a transition temperature (and thus, possibly, a switching temperature) close to room temperature. For those reasons, we have chosen the [Fe(HB(trz) 3 ) 2 ] SCO complex, hereafter called 1 (HB(trz) 3 = tris(1H-1,2,4-triazol-1-yl)borohydride), [15][16][17][18] for which it was shown recently that it can be deposited as continuous thin films on surfaces by thermal evaporation. [19,20] Some recent efforts have focused on vertical large area SCO junctions with film thicknesses in the 10-200 nm range Thin films of a molecular spin crossover (SCO) Iron(II) complex featuring a high transition temperature are grown by sublimation in high vacuum on TS Au and investigated by X-ray and UV photoelectron spectroscopies. Temperaturedependent studies demonstrate that the thermally induced spin crossover behavior is preserved in thin films. A large-area ultrathin switchable spin crossover molecular vertical tunnel junction with top electrodes of the liquid eutectic of gallium and indium...
