Surface and interfacial effects in Spin crossover molecular systems.*

Surface and interfacial effects are known to give rise to phenomenon which do not occur in the bulk. In other words, the surface is different from the bulk. In this regard, we report on the surface properties of spin crossover molecular systems namely [Fe(qsal)₂][Ni(dmit)₂] and [Fe(qsal)₂][Pd(dmit)₂], where, (qsalH = N-(8-quinolyl)salicylaldimine, dmit^2- = 1,3-dithiol-2-thione-4,5-dithiolato). We employ angle resolved X-ray photoemission spectroscopy (XPS) to study surface segregation in thin films of the said molecular complexes. Angle resolved XPS is also employed to study the spin state transition on the surface and in the bulk. It is seen that due to surface effects, the spin state on the surface is robust to temperature variations as compared to the bulk. We also report on a spin crossover/2-D semiconductor interface between [Fe(H₂B(pz)₂)₂(bipy)], where,  (pz=(pyrazol-1-yl)-borate and bipy = 2,2’-bipyridine) and WSe₂. Using angle resolved XPS, we are able to report on the core level shift for W and Se at and away from the interface. This study ties to earlier reported surface and interfacial phenomenon in Spin crossover molecular systems. However, the surface segregation in spin crossover systems has not been reported earlier.