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. Meanwhile, this preparation method also provides the advantage of being applicable to substrates with nonplanar surfaces. The influence of formula and reaction time on silver ion reduction was studied to obtain optimum conditions 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 times 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 concentration 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.
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