紅外光表面訊號增強效應之奈米銀粒研製以及在分子化學結構對表面訊號增強效應影響之應用

Development of Chemical Methods for Production of silver nanoparticles for Infrared Surface Enhancement and Their application in Surface-Enhanced Infrared Absorption Spectroscopy

陳昇熙(Sheng-Hsi Chen)

指導教授 ： 黃悉雅 ； 楊吉斯

中原大學/理學院/化學研究所/博士(2003年)

https://doi.org/10.6840/cycu200300597

摘要

中文摘要

表面訊號增強效應現象雖然發現已近20年，然對其作用機制與應用的範圍，仍有不甚瞭解之處。有鑑於此本研究針對上述問題，提出克服的方法，並透過分析不同化學結構之表面訊號增強之大小，來瞭解此效應之應用範圍。本論文著重在兩大方向:一.改進現有之製造表面訊號增強之基材方法;二.透過歸類分析建立具有表面訊號增強效應的分子結構規則。
本論文提出新的奈米銀島之製程，並詳加探討製程各變因對奈米銀島之型態與表面訊號增強之影響。探討上以化學還原鍍法將金屬銀島覆膜在聚乙烯薄膜上。藉由改變配方和控制銀離子的還原時間，可得到最佳的適合表面增強效應的銀島大小形狀。當進一步的探討，將這些覆膜在聚乙烯薄膜上的銀島薄膜，以掃描式電子顯微鏡照相，發現其中的關聯性。銀層可分為兩部分來看，上面的大結晶銀塊大到數個μm大小，下面的銀島形狀從橢圓形的棒狀，大小大約40 nm左右，而且對應著不同增強效應的對位硝基苯甲酸振動吸收值。測量後發現，隨著銀粒子還原時間的增加，銀島會開始堆積在一起，從圓形慢慢長成棒狀，且會開始彎曲糾結在一起。慢慢增加還原劑的濃度，也發現到大銀結晶塊，越來越小，而且也得到比較強的增強效應。最後將化學鍍銀法所得到的增強效應吸收值，與一般利用真空鍍法所得到的結果互相比較之後，發現有類似的增強效應。
再利用此基材探討不同官能基的硝基苯化合物之表面增強效應係數，更由官能基與銀層的幾何吸附，來推導NO2拉伸振動的表面增強效應影響大小。從實驗中發現到主要影響NO2拉伸振動大小的要素，得知不同特性的官能基有不同的增強係數。一.官能基與銀層之間的吸附作用屬性，亦即化學吸附還是物理吸附；二.化學吸附在金屬上，表面是否為垂直；三.官能基的電子性如推電子基或是拉電子基，其對苯環的震動吸收峰影響較大及對NO2拉伸振動吸收峰只有波數的位置影響。為詳細探討這些效應，以十幾種具有NO2官能基之對位雙取代基苯環類化合物為指標分子，加以偵測其表面訊號增強效應，進行推導出最適合表面訊號增強之分子結構。
為進一步瞭解當分子具有雙化學吸附官能基時，分子其排列之狀態能否亦有表面訊號增強效應，及探討雙化學吸附官能基分子，其官能基之間的競爭性。因此選用苯環帶有COOH與OH官能基之分子進行測試，選用之指標分子為對位、間位、鄰位羥基苯甲酸(p-, m- o- hydroxyl benzoic acid, HBA)，藉表面訊號增強效應來判斷其與銀層之吸附結構。

關鍵字

紅外光 ； 表面訊號增強效應 ； 官能基 ； 化學還原 ； 銀粒 ； 奈米

並列摘要

Abstract

Surface-enhanced infrared (SEIR) absorption spectroscopy has received great attention since it was reported by Harstein et al. Enhanced infrared (IR) spectra can be observed when a small number of molecules are deposited on a very thin metal film. This thin metal film must be distributed discontinuously on an IR substrate, usually described as metal islands with prolate ellipsoid shapes. Although there is a long history in the development of techniques for SEIR measurements, the preparation of the substrate for surface enhancement has been based mainly on physical vapor deposition (PVD). This method requires expensive instrumentation and is limited to the preparation of thin metal films on flat substrates. A new method is needed to deposit metal films to extend SEIR measurements to other non-planar IR-compatible media (e.g., optical fibers). Lowering the expense of instrumentation can also increase the availability of this technique to other fields of application.
In this work, an electrode-less plating method was examined for the preparation of thin metallic films on IR-transmitting substrates for surface-enhanced measurements. Thin films of Ag were deposited on polyethylene (PE) thin film. Mid-infrared spectra were recorded in transmission after the surfaces were prepared. Reaction conditions were altered to maximize SEIR absorption by varying the deposition time, formulation of the plating solution, and method of mixing. The morphology of the Ag clusters or islands was characterized by scanning electron microscopy (SEM) and correlated with the level of SEIR absorption.
To invent a method of making this research more accessible by provide another process of producing the metal particles through chemical reduction of silver plating. Then to better understand which chemical structures will have the strongest enhancement; it required a categorization of different p-disubstituted nitrobenzene compounds. In this dissertation, two aspects were investigating : the first, it provided an alternative method of producing metal nano-particles for surface enhancement. The second, By created a configuration database of the chemicals tests to clearly understand the rules that affect the surface enhancement. Surface enhancement research can be greatly assisted by the improvement of producing the nano-particles, and further research facilitated for the analysis of probe sample by the organization of the rules of the chemical structures for surface enhancement.
A method based on the electrode-less deposition of silver islands on an infrared substrate is proposed and examined for surface-enhanced infrared (SEIR) measurements. The simplicity of this metal island- forming method can largely reduce the cost of surface preparation. Mean- while this preparation method also provides the advantage of being applicable to substrates with non-planar surface. The influence of formula and reaction time on silver ion reduction was studied to obtain optimum condition for island formation suitable for SEIR measurements. The morphologies of the forming silver islands or clusters were examined by a scanning electron microscope and correlated with the level of the enhancement effect. Small silver clusters (~40 nm) with a round to rod shape produced the greatest surface enhancements. Large silver crystals (or clusters) of around a few micrometers were formed during long reaction times. These crystals showed no effect on surface enhancement and only served to block IR energy. Precisely controlled reaction time were critical to prevent the stacking of unwanted silver clusters. Both formula and concentration of reactants influenced the reduction rates of silver ions; hence the IR enhancement. With an increase of the concentra- tion of reduction agents, the formed silver surface provided higher enhancement effect. With the use of the optimized reaction conditions, the silver films deposited by electrode-less solution provided levels of enhancement similar to those for to metallic surfaces prepared by conventional physical vapor deposition.
By using this develop of the electrode-less plating or chemical reduce- tion plating to produce silver nano-particles for surface enhancement and analyze the surface enhancement effect of the different p-disubstituted nitrobenzene compounds. Utilizing the knowledge about the geometric structure of chemical compounds on the surface of silver, to predict the magnitude of surface-enhancement. The nitrobenzene was selected to investigate because NO2 stretching vibration is a very strong absorption of infrared radiation and it wouldn’t react with silver though the chemical adsorption on the surface of silver. During the research, some affects influenced the surface enhancement of chemical compounds were found and different level of surface enhancement for different p-disubstituted nitrobenzene compounds. The first effect is the kind of adsorption between chemical compound and silver, eg. chemical or physical adsorp -tion. Chemical adsorption has the large surface enhancement, and physical adsorption has no surface enhancement. The second effect is chemical compound is perpendicular to the surface of silver or not. The third effect is the polar of substitute whether it is withdraw-electrons or release-electrons and it is a major influence for the vibrations of benzene and it caused the wavenumbers of NO2 stretching vibrations were shifted little. Further the discussion of these affects in detail, around 10 probe samples of different p-disubstituted nitrobenzene were investigated for surface enhancement find out the suitable chemical structure. From the result of analysis of almost all kinds of substitutes, the chemical compounds adsorbed on the surface of silver have larger surface enhancement. In the result, the surface enhancement effect of COOH is greater than OH and SH group, their absorptions are about 50, 18 and 8 times of the original ones.
To further understand how it works for p-disubstituted benzene compounds that both substitutes would be chemical adsorption with silver. P-, m-, o-hydroxybenzoic acid (HBA) that has COOH and OH group were investigated to determine the competition of two substitutes reacted with silver. Utilizing the magnitude of the surface enhancement effect and spectra, it can be determined the configuration of these chemical compounds on the surface of silver.

並列關鍵字

surfaced-enhanced Infrared Spectroscopy ； substitude ； silver ； elctrodeless ； SEIR

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