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theses

Metal-oxide semiconductor materials have found application in numerous fields such as photo-electronics, catalysis, and sensing. The interfaces between semiconductor materials and bio-, organic molecules used to functionalize the semiconductor materials have attracted considerable attention. It is necessary to better understand and improve the surface chemistry of semiconductor materials in order to develop a new generation of functional devices with excellent performance.
In the first project of this thesis, which is chapter B, we present an efficient functionalization and characterization method for MgxZn1-xO (4%<x<5%) nanorod (abbreviated MZOnano) films. FTIR microscopic imaging, was employed, for the first time, to visualize the binding distribution of organic molecules on a large area (µm scale) of semiconductor films. The influence of various parameters including solvent, concentration, binding time, and morphology of MZOnano film on the binding of 11-azidoundecanoic acid on MZOnano film were investigated. The stability of the functionalized MZOnano film to etching and solvents was also evaluated.
In chapter C, a stepwise functionalization method was developed to bind hexadecyl alkynated folic acid (HAFA), which has a high affinity to the cancer cell biomarker-folate binding protein. The binding methodology involved two steps. Step A, binding with 11-azidoundecanoic acid, which was fully studied by FTIR microscopic imaging, and Step B, immobilization of HAFA via copper-catalyzed azide-alkyne click reaction (CuAAC). The surface click reaction between functionalized MZOnano film and HAFA was monitored by FTIR microscopic imaging and fluorescence spectroscopy. The resulting MZOnano film was bound with a bio-reactive HAFA layer that could be used in biosensing. This stepwise method was successfully applied in the functionalization of MZOnano-modified quartz crystal microbalance (QCM) and MZOnano-modified thin film transistor (TFT), leading to QCM- and TFT- based biosensors with high sensitivity. The sensing of a folate-binding protein is still in progress.
In the second project of this thesis, that is chapter D, we describe an innovative design of the organic molecules that will be used to functionalize semiconductor materials for renewable energy projects. For example, in a dye-sensitized solar cell (DSSC), the electron transfer between sensitizer molecule and semiconductor surface is the key step that might be affected by the energy level alignment between sensitizer molecule and semiconductor surface. This energy level alignment is directly related to the properties of the sensitizer molecule. In this thesis, we introduce a dipole containing bridge into the sensitizer to tune the energy alignment between sensitizer and semiconductor-TiO2, using oligopeptides made of α-aminoisobutyric acid (Aib). The synthesis and optical characterization of sensitizer molecules combing such dipole bridge with di-tert-butyl-perylene (DTBPe) and zinc tetraphenylporphyrin (ZnTPP) chromophores are reported in this thesis. The element composition and occupied and unoccupied electronic structure (particularly the HOMOs and LUMOs energy) of ZnTPP-(Aib)6-COOH were probed by a combination of X-ray and Ultraviolet photoemission spectroscopies (XPS and UPS). The binding study of these sensitizers on TiO2 film and the energy level alignment study are still in progress.

ETD_9919

doi:10.7282/t3-ykbz-n670

Ph.D.

Includes bibliographical references

ETD doctoral

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