Ultrafast rattling motion of a single atom in a fullerene cage sensed by terahertz spectroscopy

Abstract

Superatoms have been regarded as new building blocks for artificially synthesized electronic and magnetic materials and have been attracting great attention in nano-assembly and cluster science. 1,2 Upon the discovery of the superatom states in fullerene 3 and its derivatives 4 , particularly, endohedral metallofullerenes 5-7 (a positively charged core metal atom is surrounded by a negatively charged carbon cage), the superatom properties have become more attractive, because ultrafast motion of the trapped atom modifies the electron density distribution in a local area of a picometer-scale 8 . So far, the encapsulated atom position was imaged by scanning tunneling microscopy 9 (STM) or transmission electron microscopy 10 (TEM). However, they can image the encapsulated metal atom only in a time-averaged manner; the observation of ultrafast atom motion is very challenging because dynamical processes take place in the terahertz (THz) frequency range 11,12 in a picometer-scale. In the present work, a C82 fullerene molecule that encapsulates a Ce atom is placed in a sub-nm gap of metal electrodes and excited by THz radiation to investigate the ultrafast dynamics of the Ce atom. We have observed two THz-induced photocurrent peaks associated with the bending and stretching motions of the encapsulated Ce atom. Furthermore, by measuring the bias voltage dependence of the THz-induced photocurrent, we have found that the THz-induced photocurrent flows not only by the photoconductive effect but also by the

Novel Terahertz Spectroscopy Technology for Crystallinity and Crystal Structure Analysis of Cellulose

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Inelastic Electron Transport and Ortho–Para Fluctuation of Water Molecule in H2O@C60 Single Molecule Transistors

“…The endohedral fullerenes, − which host various types of atoms and molecules in their cage structures, are particularly attractive, because they exhibit a variety of novel properties due to the presence of the encapsulated atom/molecule. Furthermore, the combination of the endohedral fullerene molecules and the single molecule transistor (SMT) geometry is very promising, because the source/drain electrodes of the SMTs can read out the electronic states of the encapsulated atoms/molecules. − …”

“…We deposited a 12 nm thick NiCr layer on the substrate as a backgate electrode, together with a 28 nm thick Al 2 O 3 gate-insulation film. The source and drain electrodes were designed in a shape of an 18 μm long bowtie antenna to efficiently concentrate THz radiation onto the molecule . We captured a single H 2 O@C 60 molecule by performing the EBJ process at ∼4.6 K in a cryostat with THz windows and filters (see Supporting Information).…”

“…As shown in Figure a, we illuminated the sample with a broadband blackbody radiation and measured a THz-induced photocurrent by using a standard lock-in technique. Details of the THz measurements can be found elsewhere …”

Structural Transition Dynamics in Carbon Electrode‐Based Single‐Molecule Junctions

“…To improve the detection resolution and obtain more details of the molecular structures, super‐resolved imaging and ultrafast spectroscopy techniques can be combined with single‐molecule electrical detection. [ 64‐65 ] When the time resolution is improved to the femtosecond level, it can be expected to observe the detailed processes of rearrangement and rotation of single chemical bonds, which will help to understand the processes of molecular structure transitions. These investigations will improve the understanding of molecular structures and provide more possibilities for molecular applications in biology, chemistry and materials.…”