| Popis: |
Stage 1–4 compounds of HOPG intercalated with SbF 5 and AsF 5 were carefully prepared and characterized. Optical reflectance was measured from 0.07 to 2.0 eV using in situ techniques; such methods were necessary because surface decomposition always occurred when samples were transferred to an environment lacking a partial pressure of the intercalate. Although the reaction characteristics were profoundly different, the general behaviour of the SbF 5 and AsF 5 compounds was similar. Detailed measurements of AsF 5 compounds during intercalation displayed the emergence of metallic reflectance well within the dilute limit [8], consistent with a downward shift of E F in a rigid band approximation. Spectra for stage 1 and 2 compounds exhibit simple metallic behavior. However, the best fits to the overall spectra were obtained by including a small dispersionless interband contribution. For the AsF 5 compounds σ opt = ω p 2 τ 4π is in good agreement with σ dc ; for SbF 5 the comparison cannot be drawn as clearly, but σ opt and σ dc are still comparable [3]. Several observations indicated that dilute AsF 5 compounds are more stable in air than the corresponding SbF 5 compounds. For stage 1 and 2, both materials decomposed rapidly in air, accompanied by gross exfoliation and emission of fumes of white solids. Dilute compounds of both types were more stable; the IR reflectance remained high, but the plasma edge broadened drastically. After 1 000 h, stage 4 SbF 5 exhibited a 10% weight loss and complete disappearance of the c -axis superlattice diffraction, implying conversion to a residue compound. Conversely, stage 3 AsF 5 left in air for 1 000 h exhibited no weight loss, no degradation of the X-ray pattern, and no decrease in σ a ( i.e. , σ a remained comparable with that of copper). |
