Molecular Orientation of Individual Lu@C₈₂Molecules Demonstrated by Scanning Tunneling Microscopy

Abstract

We identified the orientation of individual Lu@C 82 molecules on alkanethiol self-assembled monolayers (SAMs) by scanning tunneling microscopy (STM) at a molecular resolution. STM images of Lu@C 82 on alkanethiol SAMs at 65 K showed a striped structure corresponding to the molecular orbitals of the Lu@C 82 molecule, suggesting that thermal rotation of Lu@C 82 on alkanethiol SAMs is prevented at 65 K. By comparing these molecular-resolution STM images with Kohn-Sham molecular orbitals of Lu@C 82 calculated by density functional theory (DFT), we identified the molecular orientation of Lu@C 82 . Spatial mapping of the differential conductance on individual Lu@C 82 molecules revealed that the local conductivity within a molecule became large around the Lu atom at a negative sample bias voltage. From spatial mapping of the differential conductance measurements, we also evaluated the HOMO-LUMO gap of Lu@C 82 to be 0.47 eV. From the results of the spatial mapping of the differential conductance and DFT calculations, the locally high conductivity around the Lu atom was attributed to the HOMO-2 level orbital concentrated on the Lu atom and its six nearest C atoms at 0.055 eV below the HOMO level. We demonstrated changes in the molecular orientation of Lu@C 82 by applying a high electric field (about 1 × 10 7 V/cm) with a large tunneling current (1.5 nA).

Nanoparticle characterization based on STM and STS

“…Dr Tada is a member of the Chemical Society of Japan, the American Chemical Society, and the Japan Society of Applied Physics. nanomaterials 8,[12][13][14][15] and organic molecules [16][17][18][19][20][21][22] has been determined by STS.…”

“…Alkanethiol SAMs self-assemble on an Au (111) surface to form a ffiffi ffi 3 p  ffiffi ffi 3 p R30 structure. 15,[88][89][90][91] Fig. 2 shows the STM image of a Lu endohedral metallofullerene (Lu@C 82 ) on an octanethiol SAM/Au(111) surface.…”

“…Because of the molecular resolution, STM can display local electrical characteristics of nanomaterials by scanning tunneling spectroscopy (STS). The conductivity of a single nanomaterial particle such as carbon 8,[12][13][14][15] and organic molecules [16][17][18][19][20][21][22] has been determined by STS.…”

Molecular Manipulation Technologies Using an Electric Field and Application to Organic Nanoelectronics

“…However, in reality, even basic physical measurements such as X-ray diffraction are impractical for several-molecule-sized crystals. Several single-molecule devices have been realized [6]- [13]; however, identification of the molecular orientation is difficult except for special cases [12]- [14]. In addition, although many macroscopic and microscopic scale orientation control methods have been proposed [15]- [25], the development of universally suitable techniques for molecular scale fabrication is required.…”

Room-temperature single molecular memory

“…1 Various molecular switching phenomena have been reported, for example, in catenane-rotaxane interlocked molecules, 2 oligo(phenylene-ethynylene) (OPE), 3,4 and fullerene. 5,6 Molecular switching behaviors by porphyrin derivatives have been especially studied toward the realization of molecular switches. 7 The origin of the switching behaviors has been attributed to, for example, adsorption geometry, 8 conformational changes of molecules, 9 and reduction-oxidation reactions.…”