Potassium-intercalated single-wall carbon nanotube bundles: Archetypes for semiconductor/metal hybrid systems

The electronic properties of matter are on the nanometer scale strongly influenced by its local environment. The site-dependent electronic properties in composites of semiconducting and metallic matter are at the heart of establishing molecular electronics. Our combined theoretical and experimental investigations comprise first-principles calculations, resonant x-ray absorption as well as core-level and valence-band photoemission on pristine and potassium intercalated bundles of mixtures of semiconducting and metallic single-wall carbon nanotubes. We present a coherent picture of the archetypical changes in the site selective electronic properties of this tunable semiconductor/metal hybrid system.

Figure 1

(Color online) Photoemission spectra of the $\text{C}1s$ and the split $\text{K}2p$ core-level excitations as recorded at $\text{Al}K\alpha =1486.6\text{eV}$ and the $\text{C}1s$ line at 400 eV photon energy of pristine (bottom) and successively potassium intercalated SWNT above.

Figure 2

(Color online) Linewidth (full width half maximum) and asymmetry $\left(\alpha \right)$ of the $\text{C}1s$ core-level photoemission line at 1486.6 eV (circles) and 400 eV (squares). The asymmetries are calibrated for the Shirley background from the pristine samples. The arrow marks the onset of the intermediate doping regime.

Figure 3

(Color online) Left panel: VB photoemission spectra of intercalated SWNT as recorded at 21.22 eV photon energy of pristine (bottom) and successively potassium intercalated SWNT (above). Right panel: power-law scaling parameter of the Tomanaga-Luttinger liquid vs doping level. The figure is reproduced from Ref. 19.

Figure 4

(Color online) Left panel: x-ray response of the $\text{C}1s\to {\pi }^{\star }$ absorption edge of pristine (top) and successively potassium intercalated SWNT below. The fine structures are successively depleted with progressing doping steps. Right panel: diameter cumulative CB DOS of SWNT and Fermi-level shifts within the intermediate doping regime. Diamonds: PES experiments at $\text{Al}K\alpha$ 1486.6 eV excitation. Circles: PES at 400 eV excitation and XAS.

Figure 5

(Color online) Right column: sketch of the electronic DOS in scSWNT and mSWNT, respectively. The individual stages are from top to bottom pristine, low doping, the transition to intermediate doping, intermediate doping, and high doping. Open circles represent semiconducting, gray circles normal metallic, and black circles doped SWNT with a high metallicity. Left column: sketches of the respective intrabundle contact potentials and their Fermi-level shifts.