On these basis, in the following we shall treat and describe the particular case of electroless deposition on a silicon surface.In the described case, metal deposition takes place on the patterned substrate, where silver ions and silver dangling bonds react through a direct redox reaction to form the desired nanoparticles [31,38].The scheme of the electroless chemical reaction is briefly summarized in Figure 1D. This is a particular case in which the reducing agent is the substrate itself, silicon, that through its dangling bonding, oxidizes and reduces silver ions to the metallic forms, as described by the following chemical reaction: [23,39�C41]:4Ag++Si(s)+6HF��4Ag0+H2SiF6+4H+(1)which can be separated into two half-cell reactions, that are, the Si oxidation, as the anode:Si+2H2O��SiO2+4H++4e?(2)and the Ag reduction, at the cathode:Ag++e?��Ag0(3)In a first stage, the nanoparticle formation is dominated by the direct reaction of some silver ions with the silicon substrate, forming metallic nuclei.
These Ag nuclei are strongly electronegative, and on account of this they attract other electrons from the silicon bulk becoming negatively charged; then new silver ions react with disposable electrons on silver grains, reducing to Ag0 and thus inducing the growth of the original Ag nuclei [22]. An autocatalytic mechanism is therefore induced, which continues also when all the silicon surface has been covered by silver, until electrons can be attracted from bulk silicon. In electroless deposition, the rate of the reactions is regulated by a balance between diffusion and kinetics, and these mechanisms are closely correlated [31].
Using this technique, a wide range of systems were realized, ranging from thin films, to sub-micrometric metallic structures and metal nanoparticles [38,42�C45]. In [46], this concept was utilized for the realization of silver nanolenses, GSK-3 with single molecule detection capabilities, where the shape and size of those lenses was controlled at the
With the rapid development of wireless communication technology, wireless ways to track and identify a variety of items have become reality [1]. Radio-frequency identification (RFID) technology is highly thought of as an effective tracking and recognition method by more and more people [2]. As the RFID technology makes advances, its application is no longer limited to goods in supply chain management, entrance-guard systems, highway-charge systems [3], etc.
In recent years, the RFID technology and sensor combination has extended the functionality of RFID systems. Reference [4] reports the use of passive high-frequency (HF) and ultra-high- frequency (UHF) RFID sensors to monitor the humidity and temperature of concrete buildings, to achieve the effect of long-term continuous monitoring that does not need maintenance.