Cesium-Filled Single Wall Carbon Nanotubes as Conducting Nanowires: Scanning Tunneling Spectroscopy Study

Metal-filled single wall carbon nanotubes (SWCNTs) are examined for possible application to conducting wires in nanoelectronics architecture. The local electronic structure of SWCNTs partially filled with cesium atoms is studied with scanning tunneling spectroscopy. The conduction and valence bands are shifted downward with two localized states in the gap at the location where the Cs atoms are filled. From a first-principles calculation, we confirm that these two gap states are bound states originating from the two lowest conduction bands.

Figure 1

(a) A typical STM topographic image of a Cs-SWCNT. The image is 12.8 nm long and the sample bias voltage is $-1.5\mathrm{V}$. (b)–(d) 3D plots of various SR-STS maps measured along the tube axes of 3 different Cs-SWCNTs.

Figure 2

(a) The STM topographic image of a Cs-SWCNT corresponding to Fig. 1d. The image length is 10 nm. The sample bias voltage is 1.0 V. (b) The SR-STS map of a Cs-SWCNT corresponding to Fig. 1d. (c) STS data which are the selections of vertical line profiles from (b). Blue, green, and red curves are sampled from the spatial positions indicated with the vertical arrows (1), (2), and (3) in (b), respectively. Two arrows indicate the appearance of localized states. (d) Horizontal line profiles sampled from the SR-STS map in (b). Blue, green, and red curves correspond to the energy levels indicated with the horizontal arrows (4), (5), and (6) in (b), respectively.

Figure 3

(a) Theoretical STS map of a Cs atom encapsulated (16,0) carbon nanotube. The wave functions of two gap states located at 0.28, 0.06 eV in (b), (c) and the valence band maximum at $-0.59\mathrm{eV}$ in (d), respectively. For the visual clarity, we use $\exp \{{\mathrm{DOS}}^2\}$ scale in the two-dimensional STS map.

Figure 4

The vertical and horizontal cuts of STS data shown in Fig. 3a are plotted. The horizontal cut in (a) is shown as smooth curve in (b) again. The PDOS of carbon atom which is located near the Cs atom and far from the Cs atom are shown in (c).