Synthesis And Optical Properties Of Gold-Semiconductor Hetero-structures

Over the past a few decades,nanomaterials have drawn much attention in the fields of physics,chemistry,materials,and energy because of their unique characteristics.These nanomaterials would provide new solutions to global environmental pollution problems,energy crisis issues,and biomedical problems.Among the single-component nanomaterials,the chemical and physical properties of noble metal nanostructures such as gold,silver,platinum(Au,Ag,Pt)are relatively stable.Localized surface plasmon resonance of metal can be induced under the action of the external light field,which can enhance the electromagnetic field around the metal and induce great light scattering and light absorption.These features would be used to high-sensitivity detection,degradation of organic pollutants and high performance optical devices.Plasmonic metals are widely used in combination with other nanostructured materials to form composite nanostructures.These composite nanostructures not only exhibit the characteristics of a single component,but some new synergistic properties,which can provide a good idea for photocatalytic degradation,light sensing,biomedicine and other fields.In the metal-semiconductor composites,surface plasmon properties of metals can generate strong local field enhancements which can act on adjacent semiconductors to enhance semiconductor luminescence.In addition,metal-excited hot electrons can pass through the schottky barrier to the valence band of the semiconductor to achieve photodetection;or the electrons in the semiconductor can be transferred to the metal to separate the electron and hole pairs and improve the catalytic efficiency of the semiconductor.The surface plasmon resonance can be purposely adjusted by changing the size and morphology of the noble metal and the type and morphology of the surrounding semiconductor(i.e.the dielectric constant of the environment).For example,a composite nanostructure composed of an oxide semiconductor and a plasmon metal can achieve plasmon adjustment of the metal nanostructure and result in interesting optical phenomena,In this paper,we prepared different noble metal-oxide semiconductor nanostructures,and investigated their optical properties.The contents are shown in the following aspects.First,we synthesized the Au@Cu2O core-shell nanostructure with tunable Cu2O shell thickness.The transverse surface plasmon resonance is broadened when the Au nanorods were coated with Cu2O shells in the extinction spectrum,which is caused by the multiple resonance modes.The nonlinear absorption and nonlinear refraction of bare Au nanorods and Au@Cu2O nanorods was tested by the Z-scan technology.The nonlinear absorption of Au@Cu2O nanorods were observed to enhance by 5 times compared with the bare Au nanorods and the nonlinear refraction of Au@Cu2O nanorods decreased as the Cu2O shell increased at the longitudinal surface plasmon resonance wavelength.More intriguingly,largely enhanced nonlinear refraction and sup-pressed nonlinear absorption at the transverse plasmon resonance wavelength were observed in the Au@Cu2O nanorods.Our findings indicate the existence of strong local field enhancement at the Au core and the Cu2O shell.Second,many high-sensitivity sensors and photocatalysts were made by tungsten oxide because of its gas sensitivity and catalytic properties.Therefore,we used the hydrothermal method to synthesize different morphology of tungsten oxide nanostructures by changing experimental parameters.For example,tungsten oxide nanostructures with different sizes and shapes can be obtained using different tungsten sources,surfactants and different reaction temperatures.Among those samples obtained,there are rod-like,cluster-like tungsten oxide and so on.Thirdly,as a matrix material,the performance of tungsten oxide can be greatly improved by the modification of some noble metals.Tungsten oxide-gold composite material were synthesized in our experiment,in which tungsten oxide was synthesized by a hydrothermal method,and the tungsten oxide-gold composite structure was synthesized at room temperature.Degradation of methyl blue is tested under full spectrum irradiation by pure tungsten oxide and tungsten oxide-gold particles,and the experimental results showed that the effect of photocatalytic degradation of methyl blue of tungsten oxide-gold composite structure is better than that of the pure tungsten oxide.