Localized Surface Plasmon Resonance Effect of Gold Nanoparticles Using 3-Mercaptopropionic Acid as Capping Material for Sensing Probe

Gold nanoparticles (AuNP) has been used in a wide range of applications especially in medicine and optoelectronic applications due to its localized surface plasmon resonance (LSPR) effect. LSPR observation of AuNP solution shows that the plasmonic peak in the absorbance spectra lies in the range of visible light around 520 nm with deep red-wine color. The optical characteristic is controlled by the size and shape of the nanoparticles including its surface functionalization. Our research is focused on the adsorption study of 3-mercaptopropionate (3-MP) on AuNP (AuMP) surface synthesized by ligand exchange method and also by direct reduction method. The characterizations are conducted by use of UV-vis and FTIR spectroscopies in order to investigate the effect of LSPR. The absorbance spectra show that both experimental methods of AuMP give a similar profile of red-shifted in the plasmonic peaks in comparison to that of citrate-capped AuNP as a reference from 519 nm to 520 nm. The ligand exchange method of AuMP synthesis results in an unstable colloidal solution after being stored for a week at room temperature while the reduction method results in a stable colloidal solution of AuMP even though it has been stored for 2 months. The FTIR spectra show the difference in vibrational peak intensities between the 3-MP on AuNP and the 3-MPA as reference. The peak of carboxylate (COO-) asymmetric stretching is shifted to low frequency from 1708 cm-1 to 1632 cm-1 indicate the effect of LSPR while the shift to high frequencies for some vibrational peak intensities relates to the strong effect of chemical coordination between gold and capping material. The simulation of the vibration energy by use of the Density Functional Theory (DFT) method shows a similar tendency to that of the peak intensities along the infrared spectrum from experimental results.

Spectra (UV-Visible, IR transmission) of Sc3+, Fe3+ and Cu2+ tri-doped LiNbO3 crystals with various [Li]/[Nb] ratios

The Sc:Fe:Cu:LiNbO3 crystals were grown with Fe[Formula: see text](0.3 wt.%), Cu[Formula: see text](0.1 wt.%) and Sc[Formula: see text](1 mol.%) by the Czochralski method with various [Li]/[Nb] ratios (0.946, 1.05, 1.20 and 1.38). The influence of the [Li]/[Nb] ratios on the defect structure of Sc:Fe:Cu:LiNbO3 crystals was analyzed by the UV-Visible spectra and IR transmission spectra. The spectra show that the absorption edge shift to the red with [Li]/[Nb] ratios enhancing. The Sc:Fe:Cu:LiNbO3 crystals with [Li]/[Nb] ratio of 1.05 is nearly stoichiometric. A new narrow OH[Formula: see text] associated vibrational peak at 3505 cm[Formula: see text] was revealed in Sc:Fe:Cu:LiNbO3 crystals with the ratio of [Li]/[Nb] = 1.38. It is attributed to the (Sc[Formula: see text])-(OH)[Formula: see text]. The results show that the defect structure changes with the [Li]/[Nb] ratios variation.

CHARACTERIZATION OF SURFACE DEFECTS THROUGH THE MODIFICATION OF THE INFRARED PROFILE OF ADMOLECULES: APPLICATION TO CO MOLECULES ADSORBED ON (100) MgO AND NaCl SURFACES

Real surfaces display defects originating either from thermodynamic principles or from local instabilities. In order to help and characterize these surfaces and their defects, infrared spectroscopy of physisorbed test molecules can be used. As an example, we study the behavior of the infrared response of CO molecules randomly deposited on ionic surfaces of MgO and NaCl with the concentration of dipolar defects randomly distributed on these surfaces. The vibrational peak is shifted and asymmetrically broadened when the defect concentration increases as a result of surface inhomogeneity, in semi-quantitative agreement with experimental data.