Spectroscopic Study On Nanosized Metal Particles

The assembly of nano-sized metal with functionalized molecules is a rapidlyemerging field of great fundamental and practical interest due to the prospectiveapplications in future nanoelectronic devices. The charge transfer properties ofindividual particles are dependent of the particle size and the distance between theparticles. Importantly, the activation energy for the electron transfer between theparticles can be varied by the structure of the interconnected molecules. In particular,tunneling charge transfer may occur for the particles covalently linked withπ-conjugated molecules. On the other hand, recent progresses in surface-enhancedRaman spectroscopy (SERS) study have made single-molecule detection possible,which is considerably interesting for the communities of nanomaterials, analyticalchemistry, and single-molecule spectroscopy. An enhancement factor of approximately1011 has been estimated at the junctions between the closely spaced nanoparticles dueto the electromagnetic (EM) enhancement mechanism. The contribution of the chargetransfer (CT) mechanism has also been suggested to play important role in thesingle-molecule SERS.[4]In most of SERS studies, the difficulty to experimentally gain deep insight into theenhancement associated with the CT mechanism is that the chemical enhancement isnormally inextricably linked with the EM enhancement. Considering that the EMenhancement is strongly related to the SPR of the metal, particles in the visible spectralregion, in the present study, we measured the SERS spectra with a 1064 nm excitation,which is far way from the SPR bands of the nanoparticles in the assemblies. Therefore,the SERS spectral features obtained under the present experimental conditions may berelatively largely associated with the CT effect.Main work and conclusions of this paper:(1) Silver nanoparticles which are of stable nature and big size were prepared by hydrogen reduction. Compounds of silver nanoparticles and functional molecules PABAwere pared under different conditions, and studied by SERS technique with a 1064nmirradiation. In this research, we found that b2 vibration was greatly enhanced as thePABA concentration was lower, this may be the result of charge transfer of functionalmolecules between silver nanoparticles. While the concentration was higher, alvibration dominated in SERS spectra, because silver particles were surrounded byfunctional molecules, by which the particles are far away from each other and thecharge transfer between the particles was blocked.(2) Ag-PATP compound was synthesized by one step in water-ethanol systemusing PATP as stabilizer. This compound was studied by absorption spectrum, TEM andRaman Spectroscopy. It is demonstrated that in acidic condition, the silver particlesobtained are not only of small in radius and irregular shape, but also unstable; while inacidic condition, the particles are very stable and in sphereical shape with largeparticlesize.(3) Gold nanoparticles with stable nature and even radius were prepared,two-dimension- sub-monolayer gold nanostructure on ITO glass was built byself-assembly. Next, semi-conductor material CdS was deposited using electrochemicalmethod. Under different conditions, CdS with different shape and optic nature wasobtained.