| Summary: | 碩士 === 國立中興大學 === 化學系所 === 96 === Abstract
Surface-Enhanced Infrared Absorption (SEIRA) spectroscopy has received great attention since it was reported two decades ago. The phenomenon of SEIRA can be observed when a small number of molecules are deposited on an island-shape metal thin film. Enhancement factor of 100 can be easily reached. The preparation of the active substrate for SEIRA is generally based on physical vapor deposition (PVD) method, which requires expensive equipments and skillful in operation. In this work, an electroless deposition method to prepare SEIRA substrates was proposed and examined to offer the advantages of simplicity and low cost in preparations. Five metals, including Ag, Au, Pd, Pt and Cu, were prepared on the surface of Ge substrate to examine their performances in terms of SEIRA effect. Through probing the surfaces of the prepared substrates with thio compounds, the enhancement factors could be obtained. To examine the morphologies of the prepared substrates, the surface of the substrates were examined by scanning electron microscope (SEM) and used to correlate with the enhanced signals. Several factors in the preparation of the SEIRA substrates were also examined including concentrations of reagents, reaction temperatures and pH of the reaction solutions. Results indicated that the particle size of the metal thin film varies and in general, the diameters of the particle of Ag, Au, Pd, Pt and Cu are around 100, 20, 80, 400 and 5 nm, respectively. In terms of reaction rate, gold reacts faster than other metals and the order of reactivity is Au ＞ Ag ＞ Pd ＞ Pt ＞ Cu. The generated SEIRA signals of silver is the largest among the examined metals and the order of the SEIRA signal is Ag ＞ Au ＞ Pd ＞ Pt ＞ Cu.
In the results of varying the concentration of reagents and temperature of reactions, variations of the signals and morphologies were only observed for Au and Pt systems. In general, the fast of the reaction, the small in particle sizes were observed. On the other hand, the higher concentration and temperature gave smaller sizes of the formed nanoparticles. Morphologies of the nanoparticles were also influenced by the pH of the solution. Under acidic conditions, the observed SEIRA signals of Ag and Au were weaken but no obvious variations in Pd, Pt and Cu.
To further improve the performances of SEIRA substrates, nanoparticles were prepared using two metals to form alloy type of nanoparticles on the surface of Ge substrates. The use of second metal offers a better control of the morphologies of the metal nanoparticles to meet the requirements in SEIRA effect. Result indicated that the increase of surface enhancement for the produced Au@Cu, Au@Sn and Pt@Cu were 43, 64 and 173 % respectively. The particle size of the produced Au@Sn nanoparticles become increased compared to Au alone and around 20 to 50 nm in diameter. Also, the number of Pt nanoparticle in an unit area was increased when Cu was first grown on the Ge substrates. When Au was first grown on Ge substrates, nanowires of Pt could be formed and the diameter and length of the Pt nanowires can be controlled by the reaction conditions. Basically, the width of nanowire was increased as the reaction time in Au solution was increased. For instance, with 0.5 mM and 5 min of reaction time in Au solution, the formed Pt nanowires have a diameter around 200 nm. When reaction time was reduced to 2.5 min, the width of nanowire was reduced to 100 nm. The concentration of Pt would influence the compactness of nanowires and no obvious influence to the width of the nanowires.
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