The Preparation And Characterization Of 11-Mercaptoundecanoic Acid-Stablized Au Nanoparticle Film

In recent decades,Au nanoparticles(NPs)have a good application prospect in catalysis,nanometer microelectronics,drug carriers,information storage,and optics.Due to nano-gold particles localized surface plasmon resonance(LSPR),they are often applied in biosensors,and also in photovoltaic devices to enhance light absorption efficiency to improve photoelectric conversion efficiency.However,the electron emission effect of nano gold particles is less studied.Although there are a lot of free electrons near the gold Fermi level,the work function of 4.5-5.2 eV is not conducive to the electron emission.By combining Au nanoparticles with other ligands,such as alkanes,the work function can be reduced,thereby promotes secondary electron emission from gold surface.Although alkane has low electron affinity(LEA)or negative electron affinity(NEA),the larger HOMO-LUMO gap(> 8 e V)makes this small molecule exhibit electrical insulating properties.Therefore,alkanes cannot be directly used as electron emitters.Alkane thiol is one of the most common ligands for gold nanoparticles modification,and it is easy to self-assemble on gold nanoparticles by Au-S bond,which reduces the HOMO-LUMO gap of the organic molecule coated nano-gold particles,and enhances electrons emiting capability from the ligandencapsulated nano-gold particles into the vacuum.Organic ligand coated gold nanoparticles have good dispersion and stability in the liquid.By depositing them on a clean Si3N4 substrate,organic ligand coated gold nanoparticles(5.5 nm)precursor solution can be self-assembled and the film formed has a long range ordered superlattice structure.Alkane-coated 3 nm gold nanoparticles has enhanced secondary electron emission in the previous work.However,there is no studies of secondary electrons emission from small-sized gold nanoparticles below 3 nm.For smaller gold nanoparticles than 3 nm,it is much difficult to get a better monodispersed precursor solution.In order to study the factors that affect the electron emission of gold nanoparticle films,in this thesis,mercaptoundecanoic acid is added to the solution of reduced chloroauric acid by liquid-liquid two-phase method.The monodispersed gold nanoparticles with 1.5 nm,1.8 nm,2.4 nm and 3.9 nm particle size are prepared by adjusting the molar ratio of Au: S,and then,the long-range ordered gold nanoparticle film is prepared.As shown by the SEM images,the obtained films of Au nanoparticle are consisted of many micron size blocks.GIXRD studies show that superlattice structure with strong preferred out-of-plane orientation is formed in the obtained Au nanoparticle film.Fourier transform infrared spectroscopy(FT-IR)and XPS indicate that Au-S bonds are successfully formed in nanoparticle film.The secondary electron peaks observed in UPS spectrum of the 1.5-nm nanoparticle film is about 10 times of that of Au(111)reference sample at room temperature.However,the Full Width Half Maximum(FWHM)of the 1.5-nm nanoparticle film is a quarter that of Au(111)sample.Therefore,MUA-coated gold(3 nm)nanofilms have promising applications in electron emission sources and photodetectors.