Multiple Ionic-Plasmon Resonances in Naturally Occurring Multiwall Nanotubes: Infrared Spectra of Chrysotile Asbestos

Chrysotile asbestos is formed by densely packed bundles of multiwall hollow nanotubes. Each wall in the nanotubes is a cylindrically wrapped layer of ${\mathrm{M}\mathrm{g}}_3{\mathrm{S}\mathrm{i}}_2{\mathrm{O}}_5(\mathrm{O}\mathrm{H}{)}_4$. We show by experiment and theory that the infrared spectra of chrysotile present multiple ionic-plasmon resonances in the Si-O stretching bands. These collective charge excitations are universal features of the nanotubes that are obtained by cylindrically wrapping an anisotropic material. The multiple plasmons can be observed if the width of the resonances is sufficiently small as in chrysotile.

Figure 1

Multiwall nanotubes of chrysotile, arranged as a hexagonal close-packed array. The cylinders are infinitely long in the $z$ direction. Inset: Structure of lizardite showing the stacking of two layers.

Figure 2

Transmission electron micrography of the investigated chrysotile sample (Salt River Canyon, Arizona), viewed along the tube axes. Inset: Selected area electron diffraction pattern showing the parallel texture of chrysotile tubes.

Figure 3

Transmission powder IR absorption spectra of chrysotile and lizardite in KBr pellets (absorbance units). Spectra are recorded at room temperature using an FT-IR spectrometer Nicolet Magna 560 with a resolution of $2\mathrm{c}{\mathrm{m}}^{\mathrm{-}\mathrm{1}}$. $z$ and $p$ denote polarizations parallel and perpendicular to the tube axis, respectively.

Figure 4

Attenuated total reflectance IR spectra of chrysotile. Spectra in absorbance units are recorded with an ATR Thunderdome device equipped with an AgBr polarizer. The orientation of the chrysotile aggregate with respect to the incident IR wave is indicated; Chr: chrysotile; Ge: germanium crystal.

Figure 5

Dissipated power density in an isolated nanotube at the resonances ${\mathrm{C}}_{\mathrm{2}}$ and ${\mathrm{C}}_{\mathrm{3}}$. The darker gray indicates larger dissipation. The arrow shows the direction of ${\mathbf{E}}_{\mathrm{e}\mathrm{x}\mathrm{t}}$.