Characterization of pressure-induced phenomena in carbon nanostructures by optical spectrosopy

• Applicant: Professorin Dr. Christine Kuntscher
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2006 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 30266112

• Final Report Year: 2017

Final Report Abstract

Within the project “Characterization of pressure-induced phenomena in carbon nanostructures by optical spectroscopy” various carbon nanostructures were synthesized, namely single-walled carbon nanotubes (SWCNTs), SWCNTs filled with C60 or C70 molecules (so-called peapods), iodine- and bromine-doped SWCNTs, double-walled carbon nanotubes (DWCNTs), enriched (6,5) SWCNTs, enriched (11,10) SWCNTs, enriched (11,10) peapods, few-layer graphene, and the Jahn-Teller active fullerides A4C60 with A=K, Rb. In these carbon nanostructures pressure-induced phenomena such as structural or electronic phase transitions were studied by pressure-dependent optical studies. SWCNTs with average tube diameter 1.4 nm undergo two pressure-induced structural phase transitions and collapse in the pressure range up to 20 GPa. Filling the SWCNT with fullerene molecules (peapods), iodine or an inner tube (DWCNTs) leads to the mechanical stabilization of the tube. The pressure-induced effects strongly depend on the hydrostaticity level of the pressure transmitting medium used. The frequency positions of the optical transitions in enriched (11,10) SWCNTs are very sensitive regarding the filling species, like C60 molecules or inner tube, since the filling influences the internal dielectric constant of the tube. Thus, our findings demonstrate that chirality-enriched SWCNTs could possibly be used as sensors regarding the dielectric environment. Few-layer graphene samples with large lateral size suitable for optical studies under pressure turned out to be difficult to prepare by mechanical exfoliation. Therefore, large-area CVD-grown graphene samples were used for our studies. The CVD-grown bilayer and trilayer graphene samples show different absorbance spectra compared to samples prepared by mechanical exfolation, which most probably is related to the different stacking of the single graphene layers. Pressure-dependent optical studies on CVD-grown monolayer graphene did not show any drastic effect on the electronic band structure up to 8 GPa. High-pressure infrared reflectivity measurements on Rb4 C60 revealed a bad metal behavior already at the lowest applied pressure (0.8 GPa). With increasing pressure the metallic character is enhanced. Our results exclude the phase separation scenario as an explanation for the metallic character of pressurized Rb4C60 and rather suggest the closing of the charge gap with increasing pressure.

Publications

• Pressure effects on unoriented and oriented single-walled carbon nanotube films studied by infrared microscopy, J. Appl. Phys. 111, 112614 (2012)
  C. A. Kuntscher, A. Abouelsayed, K. Thirunavukkuarasu, F. Hennrich, and Y. Iwasa
  
• Stabilization of carbon nanotubes by filling with inner tubes: An optical spectroscopy study on double-walled carbon nanotubes under hydrostatic pressure, Phys. Rev. B 86, 155454 (2012)
  B. Anis, K. Haubner, F. Börrnert, L. Dunsch, M. H. Rümmeli, and C. A. Kuntscher
  
• High-Pressure Optical Microspectroscopy Study on Single-Walled Carbon Nanotubes Encapsulating C60 , J. Phys. Chem. C 117, 21995 (2013)
  B. Anis, F. Börrnert, M. H. Rümmeli, and C. A. Kuntscher
  
• Role of the pressure transmitting medium on the pressure effects in DWCNTs, Phys. Status Solidi B 250, 2616 (2013)
  B. Anis, F. Börrnert, M. H. Rümmeli, and C. A. Kuntscher
  
• High-pressure optical study of bromine-doped single-walled carbon nanotube films, Phys. Status Solidi (b) 251, 2378 (2014)
  J. Strauch, B. Anis, and C. A. Kuntscher
  
• Hints for the metallic phase in Rb4 C60 under pressure, Phys. Status Solidi (b) 251, 2569 (2014)
  E. A. Francis and C. A. Kuntscher
  
• Optical Microspectroscopy Study of the Mechanical Stability of Empty and Filled Carbon Nanotubes under Hydrostatic Pressure, J. Phys. Chem. C 118, 27048 (2014)
  B. Anis, F. Börrnert, M. H. Rümmeli, and C. A. Kuntscher
  
• High-pressure optical study of small-diameter chirality-enriched single-wall carbon nanotubes, Phys. Status Solidi (b) 253, 2446 (2016)
  M. Krottenmüller, W. Gao, B. Anis, J. Kono, and C. A. Kuntscher
  
• Optical microspectroscopy study on enriched (11,10) SWCNTs encapsulating C60 fullerene molecules, Carbon 107, 593 (2016)
  B. Anis, K. Yanagi, and C. A. Kuntscher