Investigation of ${\text{Gd}}_3{\text{N@C}}_{2n}\left(40\le n\le 44\right)$ family by Raman and inelastic electron tunneling spectroscopy

The structure and vibrational spectrum of ${\text{Gd}}_3{\text{N@C}}_{80}$ is studied through Raman and inelastic electron tunneling spectroscopy as well as density-functional theory and universal force field calculations. Hindered rotations, shown by both theory and experiment, indicate the formation of a ${\text{Gd}}_3\text{N-}{\text{C}}_{80}$ bond which reduces the ideal icosahedral symmetry of the ${\text{C}}_{80}$ cage. The vibrational modes involving the movement of the encapsulated species are a fingerprint of the interaction between the fullerene cage and the core complex. We present Raman data for the ${\text{Gd}}_3{\text{N@C}}_{2n}\left(40\le n\le 44\right)$ family as well as ${\text{Y}}_3{\text{N@C}}_{80}$, ${\text{Lu}}_3{\text{N@C}}_{80}$, and ${\text{Y}}_3{\text{N@C}}_{88}$ for comparison. Conductance measurements have been performed on ${\text{Gd}}_3{\text{N@C}}_{80}$ and reveal a Kondo effect similar to that observed in ${\text{C}}_{60}$.

Figure 1

(Color online) Spectrophotometry data of ${\text{Gd}}_3{\text{N@C}}_{2n}\left(40\le n\le 44\right)$ in toluene. Unusually high absorption peak in ${\text{Gd}}_3{\text{N@C}}_{86}$ is observed.

Figure 2

(Color online) Analysis of low-energy Raman lines of ${\text{Gd}}_3{\text{N@C}}_{80}$ taken at 90 K indicating a hindered rotation due to the coupling of the core complex to the cage. Inset gives the ${\text{Gd}}_3{\text{N@C}}_{80}$ structure.

Figure 3

Analysis of low-energy Raman lines of ${\text{Gd}}_3{\text{N@C}}_{2n}\left(40\le n\le 44\right)$ taken at 90 K indicating a hindered rotation due to the coupling of the core complex to the cage.

Figure 4

Analysis of Gd-cage stretching mode plotted against the square root of the reciprocal reduced mass. As the carbon mass increases, there is a linear downshift in the frequency.

Figure 5

Comparison of ${\text{Y}}_3{\text{N@C}}_{80}$, ${\text{Gd}}_3{\text{N@C}}_{80}$, and ${\text{Lu}}_3{\text{N@C}}_{80}$ low-energy Raman data taken at 90 K. Analysis of the data identifies ${\text{C}}_{80}$ cage modes, hindered rotation modes, and center-of-mass modes.

Figure 6

Comparison of ${\text{Y}}_3{\text{N@C}}_{88}$ and ${\text{Gd}}_3{\text{N@C}}_{88}$ Raman data taken at 90 K. Analysis of the data identifies ${\text{C}}_{88}$ cage modes, hindered rotation modes and center-of-mass modes. Prominent peak correlations are denoted by dotted lines.

Figure 7

(Color online) Experimental conductance data of Kondo effect and zero-bias anomaly in ${\text{Gd}}_3{\text{N@C}}_{80}$ taken at 4.2 K. Right inset adapted from Ref. 42 shows the experimental setup: Au crossed-wire apparatus forms a junction with the ${\text{Gd}}_3{\text{N@C}}_{80}$ thin film. Left inset shows the calculated fit (solid line) using the Fano model.

Figure 8

Experimental IETS spectrum obtained for ${\text{Gd}}_3{\text{N@C}}_{80}$ with modulation amplitude ${\text{V}}_{\omega }=4\text{mV}$, scan $\text{rate}=1.5\text{mV}/\text{s}$, and time $\text{constant}=1\text{s}$. The antisymmetric Gd-N stretch mode is identified at 81.6 mV $\left(658{\text{cm}}^{-1}\right)$ as well as Raman ${\text{C}}_{80}$ cage modes at 155.1 (1251) and 187.5 mV $\left(1512{\text{cm}}^{-1}\right)$.