Probing the Structure of V[TCNE]_x via Electron Energy Loss Spectroscopy

Vanadium tetracyanoethylene (V[TCNE]_x) is an organic-based ferrimagnetic semiconductor which has garnered interest due to its superb magnetic resonance properties, room temperature magnetism, and insensitivity to substrate. The magnetic properties have been well studied but the details of the mechanism are not understood due to a lack of structural information. V[TCNE]_x films are typically amorphous, and the material is extremely air-sensitive when not encapsulated, making characterization challenging. In general, the structure is believed to be V²⁺ in octahedral coordination with six TCNE molecules. We present scanning transmission electron microscopy (STEM) electron energy loss spectroscopy (EELS) of V[TCNE]_x films using a vacuum transfer holder. The high spatial resolution EELS data confirms the V²⁺ oxidation state with no variation in the V[TCNE]_x layer. Additionally, splitting observed on the L₂ peak suggests the V is in a perfect octahedral environment. Upon oxidation, the C K edge 1s-π* peak is drastically decreased while the N K edge 1s-π* peak remains consistent suggesting that the carbon-carbon double bond of the TCNE is targeted during oxidation. These results shed significant light on the elusive structure of V[TCNE]_x.