Functional behaviors of nano-materials are largely dependent on their particle size, shape and surface properties. The objectives of this thesis are (i) to develop electrochemical methods for the size- and shape-controlled fabrication of cuprous oxide (Cu₂O) nano- and micro-crystals (N/MCs) without employing any surfactants, capping agent, and dispersion agent, (ii) to employ the as-fabricated Cu₂O N/MCs as galvanic templates for the synthesis of Cu₂O@M (M = Au, Ag, Pt, Pd) nano-on-meso composites, (iii) to study their shape- and size-dependent electro-catalytic and optical properties, and (iv) to explore their applications in three different areas, including single-particle surface-enhanced micro-Raman spectroscopy (sp-SERS), the size- and shape-dependent electro-catalysis, and the ele...[ Read more ]

Functional behaviors of nano-materials are largely dependent on their particle size, shape and surface properties. The objectives of this thesis are (i) to develop electrochemical methods for the size- and shape-controlled fabrication of cuprous oxide (Cu₂O) nano- and micro-crystals (N/MCs) without employing any surfactants, capping agent, and dispersion agent, (ii) to employ the as-fabricated Cu₂O N/MCs as galvanic templates for the synthesis of Cu₂O@M (M = Au, Ag, Pt, Pd) nano-on-meso composites, (iii) to study their shape- and size-dependent electro-catalytic and optical properties, and (iv) to explore their applications in three different areas, including single-particle surface-enhanced micro-Raman spectroscopy (sp-SERS), the size- and shape-dependent electro-catalysis, and the electro-chemical switch of semiconducting type of Cu₂O films, as well as the fabrication of p-n homo-junctions potentially useful for solar energy conversion.

This thesis reports a facile electrochemical method to tune the size of cubic and octahedral Cu₂O from a couple of hundred nanometers to several microns. The as-fabricated Cu₂O cubes and octahedra were used as the sacrificial galvanic templates to synthesize Cu₂O@M (M = Ag, Au, Pt, Pd) core-shell composites and hollow structures. The effects of such parameters as the concentration of precursors, the reaction time, the ionic strength and the photo-illumination to the properties of the fabricated Cu₂O@M were studied. An enhancement factor as high as ~10⁷ was obtained from the SERS on Cu₂O@M single composite particle. The as-prepared Cu₂O@M structures can be easily tracked under common optical microscopy, and can be illuminated one particle each time, making it very convenient to conduct sp-SERS.

The electrochemical tuning of Cu₂O morphology at nano- and micro-scale, respectively, without using any surfactants and additives, is also studied. Effort was spent to establish the relationship between the electrodepositing conditions (deposition potential, time, anion type, concentration of electrolyte and pH) and the morphologies of Cu₂O (size and shape), as well as the density of particles.

The size- and shape-dependent electro-catalytic activity of Cu₂O N/MCs by using the redox of H₂O₂ as a test reaction was also studied. We showed that Cu2O particles containing more (111) surface are more electro-catalytically active.

We also showed that the conductivity type of Cu₂O semiconducting film can be electrochemically switched by adjusting the electrodepositing conditions (anion type, pH and potential). To the best of our knowledge, our work is the first time to demonstrate the switch of conductivity type by adjusting electrochemical deposition potential.

In addition to above systematic study on Cu₂O system, a couple of other relevant work have also been carried out, including: (i) a template-confined electro-corrosion method for the fabrication of highly uniform and active SERS-substrates of nano-porous Ag and Au films, (ii) a generic method for the fabrication of nano-on-meso structures highly active for SERS application. In this method, a pre-designed pattern of a given shaped silicon structure was fabricated by conventional photolithographic technique. Metal sputtering technique was then employed to decorate nano-structured metal such as Ag film on Si array. The as-fabricated nano(Ag)-on-meso(Si) structures were shown to be excellent substrates for SERS.