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Research On Terahertz Spectroscopy Of V2O3, Pharmaceutical Cocrystal And Carbon Nanotubes

Posted on:2013-01-22Degree:MasterType:Thesis
Country:ChinaCandidate:W J TangFull Text:PDF
GTID:2231330371988372Subject:Radio Physics
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Terahertz (THz) wave is the electromagnetic waves in the frequency range of0.1to10THz (1THz=1012Hz), which belongs to the far infrared band. Terahertz spectra of various materials contain a wealth of physical and chemical information, such as the density of semiconductors materials’carrier, impurity and defects, superconducting gap as well as biological macromolecules’vibration, nanomaterials’ absorption and so on. So the THz spectrum has a lot of important applications in physics, chemistry, medicine, biology and materials science.Terahertz time-domain spectroscopy (THz-TDS) technology is a very effective coherent detection technology, which is developed in the recent20years. The THz-TDS system has the advantages of a high signal-to-noise ratio, a good stability, a large bandwidth and a good working at room temperature. It can obtain terahertz pulse amplitude and phase information with and without the sample. Then, we can easily get the complex refractive index of the sample. So this technology can be widely used for measuring the THz spectrum of a various kind of samples.In the paper, we measure and study THz spectrum of the V2O3powder, pharmaceutical cocrystal and carbon nanotubes. The main work is as follows:1. In order to observe the metal-insulator transition in V2O3powder, we measured V2O3powder sample by terahertz time-domain spectroscopy (THz-TDS) in the temperature range from8K to220K. Through the analysis of the transmission and phase information of V2O3sample in the terahertz band, we got the sample’s complex refractive index or complex dielectric constant. Maxwell-Garnett effective medium theory (EMT) together with Boltzmann function is employed to describe the dielectric properties of the sample. The calculated results agree with the measurement indicating a metal-insulator phase transition, in which the volume fraction of metallic domain gradually increases with the temperature around the transition temperature.2. The application of THz-TDS technology in the pharmacy field has attracted more and more attention. Cocrystal is a new pharmaceutical physical form, which has great application value and can greatly improve the physicochemical properties. It has becoming a new hot topic in the pharmaceutical research. Studies in the THz spectral of the pharmaceutical cocrystal have a positive scientific meaning for the detection and comprehensive understanding of samples’structure, properties and molecular interactions. In this paper, we use the solution synthesis to get the cocrystal samples by barbitalum and benzoic acid, succinic acid, malonic acid, and characterize the cocrystal by THz spectral. The results show that: barbitalum molecules with the acid molecules form hydrogen bonds, generating new lattice structure, namely the pharmaceutical cocrystal, and generate new absorption peaks in the THz absorption spectrum.3. Carbon nanotubes have special physical, chemical and mechanical properties, with a wide application prospect. In this paper, we use the THz-TDS to measure the THz response of the carbon nanotube sample, get the refractive index and absorption spectra. We also compare THz absorption spectrums of the N-doped carbon nanotube at the different doping temperature. The experimental results have a certain reference value for the further studies of doped carbon nanotubes and the applications of carbon nanotube materials.
Keywords/Search Tags:Terahertz time-domain spectroscopy, THz optical parameters, V2O3, phase transition, effective medium theory, pharmaceutical cocrystal, barbitalum, carbon nanotubes
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