I. Investigations of Valence/ Rydberg States of 2-Methylallyl Radical and Thioformaldehyde by Resonant Ionization Multiphoton Spectroscopy. II. Electrical Transport Properties of One Dimensional Nanoscale Materials: SnO2 nanowire and Hydrocarbon helix wire.
Date Issued
2007
Date
2007
Author(s)
Wu, Hsing-Chen
DOI
en-US
Abstract
The content of this thesis would be divided into two main parts. First, the molecular spectroscopy was concerned. Gas phase vibronic spectra of radical and small molecule were studied by resonant multiphoton ionization (REMPI) technique. The purpose of second part was to explore the electrical transport characters of one dimensional nanomaterials. The carrier number, mobility, and transport mechanism etc. were included.
To begin with the flash pyrolytic generated 2-methylallyl radical, one- and two-photon excitations were applied at 4.6-5.6 eV. Combining with the ab initio calculations, information of excitation energies, oscillator strengths and Franck Condon factors (FCFs) of electronic states at 4–6 eV making the spectra successfully resolved. In the 2+2 REMPI spectrum, the 3s Rydberg state along with its vibrational progressions were identified. On the other hand, seven lowest-lying electronic states below 6 eV, were assigned by MRCI calculation in the 1+1 spectrum. The other point to notice was the much broader 1+1 bands at higher energy region which were due to an intensity borrowing from the (n,pi*) transition that accidentally near-resonant in energy.
Secondly, another molecule studied was the simplest molecule in the thiocarbonyl family- thioformaldehyde (H2CS). There is fairly general agree that H2CS is unstable as a monomeric species under normal conditions. Here, we use a two-color REMPI scheme to investigate electronic states of H2CS. The vibronic excited states of H2CS were studied by 1+1'+1' double-resonance enhanced three-photon ionization (1+1'+1')REMPI) spectroscopy. The C1B2 state of H2CS was selected as an intermediate for the double resonance to high-lying excited states at 62000-72000 cm-1. According to distinct selection rules between one-photon absorption and two-photon transitions excited from X1A1 and C1B2, respectively, new electronic sates of H2CS can be assigned by 1+1'+1'DRETPI spectroscopy.
The second part of this thesis was focused on the electrical transport prooperities of nano-materials. First, an investigation of hydrocarbon helical wires (HCHWs) with wire diameters ranged from nano- to micro-meter scale was conducted. HRTEM and EELS investigations reveal that the HCHWs comprise graphite-short-range-ordering (GSRO) clusters with sp3 bonds inserted in the discontinuous graphitic layers, suggesting hydrogen termination in the broken boundaries of the GSRO domains. A crystallite size of ~5 nm for the GSRO domains has been determined by micro-Raman spectroscopy. Electric transport in single HCHWs has been measured from ambient temperature to 64 mK. The temperature-dependent resistance was analyzed with the Mott-variable range hopping model, indicating a three-dimensional electron hopping conduction among the GSRO domains inside the HCHWs. The analysis also yields a hopping length of ~5 nm, in excellent consistence with the GSRO domain size determined by micro-Raman spectroscopy.
Second, the SnO2 nanowire (NW) based filed–effect transistor (FET) was fabrecated. It was observed that the conductance could improve three orders of magnitude when the applying gate voltage up to ten volts. From this variation of conductance with gate voltage, the device parameters such as threshold voltage, carrier density and mobility etc. were found. In addition, we have successfully demonstrated that the sensitization of photocurrent by electron transfer from dye molecules to semiconductor, a prevalent mechanism in dye-sensitized solar cells, can also be studied in single-nanowire scale.
Finally, a biosensor based on carbon nanotube was studied. The target molecule was Chromogranin A (CgA), it is a neuron transmittance that released from secretory vesicles when fused with plasma membrane. We have successfully demonstrated that the detection limit of molecular recognition could down to ~100 pM. An in-situ detection of CgA by living neuron cell was also observed.
Subjects
雷得堡態
ab initio 計算
Franck-Condon Factors
VRH hopping model
二氧化錫奈米線場效電晶體
奈米碳管生物檢測器
嗜鉻粒蛋白A
Ab initio
SnO2 nanowire field effect transistor
dye-sensitized solar cell
carbon nanotube FET biosensor
Chromogranin A.
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-96-F90223007-1.pdf
Size
23.31 KB
Format
Adobe PDF
Checksum
(MD5):e7bc09625491e013e27524edfeb2d2e3