Fig. 2: Optical and vibrational spectroscopy of V[TCNE]_x.

The sub-100 nm thickness and optical transparency of ALD alumina, spanning from DUV to mid-IR, enable detailed spectroscopic studies of V[TCNE]_x. a Photographs of bare (left) and alumina-encapsulated V[TCNE]_x samples (right) before and after 3 days of ambient exposure. The encapsulated sample retains the characteristic dark blue color of V[TCNE]_x, while the bare sample shows visible degradation. b UV-vis-NIR absorbance spectra of alumina-encapsulated V[TCNE]_x on a CaF₂ substrate as a function of exposure time to ambient conditions, demonstrating minimal changes in absorbance over time. c Schematic of the ATR-FTIR measurement for alumina-encapsulated V[TCNE]_x. The ultrathin alumina layer and IR-transparent CaF₂ substrate allow for artifact-free measurements in ATR mode. d ATR-FTIR spectra of alumina-encapsulated V[TCNE]_x on a CaF₂ substrate and a blank CaF₂/alumina substrate, highlighting the vibrational features of V[TCNE]_x.