Optimisation of the electroless metal deposition technique for use in photonics

Even if the first approach toward metamaterials was made more than 40 years ago [1] the topic was not considered for practical applications until 2000 due to the lack of natural materials with tuneable magnetic interaction with electromagnetic waves. In 1999 the first engineered metamaterial was suggested [2] and, one year later, it was characterised [3] thus starting the research interest in this field. Since then, the operating wavelength decreased from microwave to visible frequencies, the newest results showing negative refraction in the yellow region of the spectrum [4]. With all the progress made in the last years, there is still a long way until practical implementation into everyday devices. One of the main bottlenecks, from the fabrication point of view, is the necessity for depositing silver on complex 3D structures. To our knowledge, the best result so far, was obtained using plasma enhanced chemical vapour deposition (PECVD) technique [5]. Even if the results are promising, the parameter space of such technique is huge thus making it almost impossible to avoid the local optimum points. In this work we present an optimised technique for 3D deposition of metals. Our technique is based on the well known Tollen’s test for detecting the presence of aldehyde groups inside a solution [6]. By optimising the concentration and the ratio of the chemicals involved, one can obtain very smooth and thin Ag layers (see figure 1a). In the same time, since the reaction takes place in solution, it is by definition isotropic and thus suitable for depositing the metal on complex structures (see figure 1b).