Balaguera Gelves, Marcia del R.
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Publication Low temperature aqueous synthesis of Zno nanorods and coating of Au On ZNO for enhanced Raman spectroscopy studies(2013) Balaguera Gelves, Marcia del R.; Hernández Rivera, Samuel P.; College of Arts and Sciences - Sciences; Perales Pérez, Oscar; Torres, Jessica; Briano Peralta, Julio G.; Department of Chemistry; Navarro Rodríguez, Ana J.This thesis reports results on the growth-controlled synthesis of zinc oxide nanorods (ZnO NRs) in aqueous phase has been investigated. ZnO NRs were grown on ZnO films previously deposited onto Si (100) and indium tin oxide (ITO) substrates by RF magnetron sputtering. The formation of the rods took place in the presence of hexamethylenetetramine (HMT) as habit-controller reagent. The grains in the base ZnO film acted as seeds that promoted the longitudinal growth of the oxide. As-synthesized base films and rods were characterized by X-ray diffraction, scanning electron microscopy (SEM), field emission SEM, optical absorption, and photoluminescence spectroscopy techniques. The rod thickness was controlled by adjusting in deposited using RF magnetron sputtering parameters such as temperature, and reaction time and afterwards, a wet chemistry procedure was performed for ZnO NRs growth. The precise control of the synthesis conditions was conducive to the formation of ZnO NRs of a relatively narrow distribution of diameters (60-70 nm) with lengths in the 1-3 μm range. ZnO NRs/ZnO base film/ITO exhibits a strong UV absorption around 360 nm Photoluminescence spectra presented narrow near-band-edge (NBE) dominant peak indicate with a relatively higher oxygen vacancy concentration in the ZnO- NRs grown on ZnO/ITO in comparison with those on the ZnO/Si (100). The other hands a second goal, was focused in the optimization of conditions to control of Ion beam and UV process for coating the ZnO NRs with gold (Au). Au-coated ZnO NRs were characterized using X-ray diffraction, EDS and field emission scanning electron microscopy (FE-SEM). Au coated/ZnO NRs were developed for the identification to trace levels by surface-enhanced Raman scattering SERS of adenine, 4- nitrobenzenethiol and 2, 4-aminobenznethiol (ABT) and 1, 3, 5-trinitroperhydro-1, 3, 5- triazine (RDX) with a detection limits down in orders of picograms. Zinc oxide (ZnO) was first deposited using RF magnetron sputtering, and afterwards, a wet chemistry procedure was performed for ZnO NRs growth. Ion beam and UV process were used for coating the ZnO NRs with gold (Au). Au coating on ZnO NRs were used to evaluate the detection capability by SERS with different analytes. Au- coated ZnO NRs were characterized using X-ray diffraction, EDS and field emission scanning electron microscopy (FE-SEM). Ultraviolet photo-reduction showed a higher SERS than the ion beam method. This Au coating on ZnO NRs could successfully detect analytes such as: adenine, 4-nitrobenzenethiol and 4-aminobenznethiol (4-ABT) and 1, 3, 5-trinitroperhydro-1, 3, 5-triazine (RDX) at low levels. Strong SERS spectrum of Raman was observed for 4-ABT. ZnO NRs/ZnO base film/ITO was SERS active from a laser wavelength at 785 nm. Therefore, the intensities were normalized to laser power and acquisition time with final units of counts·mW-1s-1 at 1076 cm-1. A limit of detection (LOD) of 1x10-8 M for ABT was achieved corresponding to a minimum of 5.4 X105 molecules detected under the experimental conditions at excitation wavelength of 785 nm with a sensitivity of the ZnO NRs in the range of 11 fentogram under laser spot, with a SEF of 7.54 x108. Chemical and electromagnetic effects can contribute a high SERS enhancements factor for Au coated ZnO NRs. Results shown here demonstrate a good reproducibility expressed as relative standard deviation 11.8 % for Au coated ZnO NRs/ZnO base film/ITO. Our studies have demonstrated that these Au-coated nanostructures are highly stable and reproducible and allow for the detection of explosives such as RDX. In addition, our modification of Vayssieres’ method has proven its versatility as it has been successfully applied in the preparation of a biosensor for urea.Publication Detection of nitroexplosives by surface enhanced Raman spectroscopy on colloidal metal nanoparticles(2006) Balaguera Gelves, Marcia del R.; Hernández Rivera, Samuel P.; College of Arts and Sciencies - Sciences; Morell Cruz, Luis A.; Briano Peralta, Julio G.; Department of Chemistry; Coutin, SandraGold and silver colloids have been synthesized by chemical reduction methods, and they have been used for detecting molecules in solution with high sensitivity and molecular specificity. The present study focuses on metallic nanoparticles of silver and gold colloids with ~60-80 nm particle size in surface enhanced Raman and surface enhanced resonance Raman scattering (SERS). The nanoparticles were characterized using techniques such as UV-Vis spectroscopy using a Varian Cary-100 UV-visible double beam and Scanning Electron Microscopy (JEOL JSM 6460LV). Microscopy images were taken with 1μL of colloids. The colloids were developed for the identification of trace levels of nitroexplosives with detection limits down to femtomolar concentration. Detection of TNT deposited on gold and silver colloids was achieved at a wavelength of 785 nm with a laser operating at 6W power. TNT dye was detected at a wavelength of 532 nm with laser power set at 170 mW by Resonance Raman Scattering (SERS) at concentration levels as low as 1.1 X 10⁻¹⁷ grams at pH 10. The excitation source was a diode-pumped 532 nm green laser with a variable output power of up to 0.1 W (Millennia II laser from Spectra Physics). ARenishaw Raman Microspectrometer RM2000 with Leica objectives with 10xs magnifications was used. The spectra were obtained in the 100-3500 cm⁻¹ range acquiring 10 scans with 30 seconds of integration time. The azo structures, obtained by derivatizing the TNT, are highly colored derivatives which contain a functionality that will enable a strong bond with the metal surface. Recent experimental data have demonstrated the effect of metal nanostructures coated with hydrophilic copolymers (silver on thin-polymer film coated glass slide). Results indicated a decrease in the intensity of the SERS in TNT and TNT dye which was still detectable by the enhanced presence of the NO₂ out-of-plane bending modes at 820 and 850 cm⁻¹ and the NO₂ stretching mode at 1300-1370 cm⁻¹. It was also observed that the polymer film does not interfere with the signal of SERS in the film and some stretching bands of TNT were detected. In conclusion we found that polymers with carboxylic side chains like 2-hydroxyethylmethacrylate (Methacrylic Acid) cause the silver colloid surface layer to replace citrate ions by chemical species of like charge and similarly with aril carboxyl groups in polymer addition.