Abstract:
One of the main complications in the synthesis of Zinc oxide (ZnO) nanowires (NWs), is the ability to reproduce well aligned wires. ZnO was studied due to its optoelectronic applications. Its simple crystal growth abilities, lead to potentially lower cost for ZnO based devices. Other semiconductors such as MoS2 in bulk form contain an indirect bandgap of 1.2 eV. As layers are removed, the materials band gap undergoes a shift and switches from indirect to direct bandgap for a single monolayer. This monolayer of MoS2 contains a bandgap of 1.8 eV, therefore the goal was to synthesis single layer MoS2 on various substrates. In this doctoral research wide bandgap ZnO and emerging MoS2 were studied individually. These novel semiconductors were then fabricated together to form heterostructures to enhance the functionality of ZnO and MoS2 by covering the UV (380 nm) to the visible region (650 nm). ZnO powders were reduced by carbo-thermal reduction and grown onto sapphire substrates to act as a ZnO NW scaffold. The material properties such as the crystalline phase of the hexagonal wurtzite ZnO were examined by SEM, TEM and complemented by optical characterizations. X-ray photoelectron spectroscopy determined the chemical species and lack of impurities present in the NW. Local electrode atom probe analysis of the crystal stoichiometry and concentration gradient of oxygen content from the center of the NW to the edge wall. A single ZnO NW was removed from the surface and a Schottky diode device was fabricated to determine the effects of UV illumination. Defects at the edge of the wire can lead to external growth of MoS2 and good bonding at the interface of the heterostructure. The triangular formation, thickness and edge effects at the grain boundaries were studied by SEM and AFM. The two main phonon modes in MoS2 are used to determine the number of layers present by Raman spectroscopy. TEM led to determination of the 2H phase of MoS2. When the 1D-2D hybrid structure is fabricated regions of molybdenum and sulfur on the ZnO NW were mapped by EDS on a SEM and TEM.
