Terahertz Dynamics of Quantum-Confined Electrons in Carbon Nanomaterials

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dc.contributor.advisorKono, Junichiroen_US
dc.creatorRen, Leien_US
dc.date.accessioned2013-03-08T00:37:58Zen_US
dc.date.available2013-03-08T00:37:58Zen_US
dc.date.issued2012en_US
dc.description.abstractThe terahertz (THz) frequency range. 0.1 - 20 THz, exists between the microwave and infrared ranges and contains abundant information on the dynamics of charge and spin carriers in condensed matter systems. Since its advent two decades ago, THz spectroscopy has been extensively used to study a wide range of solid state materials, including typical semiconductors, conducting polymers, insulators, superconductors, and artificially grown structures such as quantum wells. In these systems, electronic and photonic events tend to occur on the time scale of tens to hundreds of femtoseconds, which results in many important excitations, resonances and dynamical phenomena in the THz frequency range. In this dissertation work, we have developed a typical THz time-domain spectroscopy (TDS) system to investigate the THz dynamics of quantum-confined electrons in two important types of carbon nanomaterial: single-walled carbon nanotubes (SWNTs) and graphene. Polarization dependent THz transmission measurements were conducted on a highly-aligned SWNT film on a sapphire substrate, revealing extremely high anisotropy: virtually no attenuation was observed when the polarization of the THz beam was perpendicular to the nanotube axis, while the THz beam was strongly absorbed when its polarization was parallel to the tube axis. From the measured absorption anisotropy, we calculated the reduced linear dichrosim to be 3, corresponding to a nematic order parameter of 1. These observations are a direct result of the one-dimensional nature of conduction electrons in the nanotubes and at the same time, demonstrate that any misalignment of nanotubes in the film mast have characteristic length scales much smaller than the wavelengths used in these experiments (1.5 mm - 150 μm). Based on this work, an ideal THz linear polarizer built with parallel stacks of such aligned SWNT films was synthesized, exhibiting a degree of polarization of 99.9% throughout the frequency range 0.2 - 2.2 THz and a high extinction ratio of 10 -3 (or 30 dB). The THz complex conductivity of the thin SWNT film was extracted through a proper model directly from the TDS data without Kramers-Kronig analysis. Both real and imaginary parts of the conductivity showed a non-Drude frequency dependence, indicating the presence of plasmon-dipole resonance at higher frequencies. Finally, the optical conductivity of large-area. graphene grown from solid state carbon source was studied in a wide spectral range (7 cm -1 - 9500 cm -1 ) using THz-TDS and Fourier transform infrared spectroscopy. We observed that the Fermi level E f of graphene could be tuned by both electrical gating and thermal annealing. The optical conductivity measured at different carrier concentrations exhibited Drude-like frequency dependence, and different 2 E f onsets in the spectrum were probed as well.en_US
dc.format.extent157 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoTHESIS PHYS. 2012 RENen_US
dc.identifier.citationRen, Lei. "Terahertz Dynamics of Quantum-Confined Electrons in Carbon Nanomaterials." (2012) Diss., Rice University. <a href="https://hdl.handle.net/1911/70405">https://hdl.handle.net/1911/70405</a>.en_US
dc.identifier.digitalRenLen_US
dc.identifier.urihttps://hdl.handle.net/1911/70405en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjectApplied sciencesen_US
dc.subjectPure sciencesen_US
dc.subjectCarbon nanotubesen_US
dc.subjectGrapheneen_US
dc.subjectOptical conductivityen_US
dc.subjectNanoscienceen_US
dc.subjectCondensed matter physicsen_US
dc.subjectOpticsen_US
dc.titleTerahertz Dynamics of Quantum-Confined Electrons in Carbon Nanomaterialsen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentPhysicsen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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