Porous silicon microcavities: synthesis, characterization, and application to photonic barcode devices
© Ramiro-Manzano et al.; licensee Springer. 2012
Received: 15 May 2012
Accepted: 18 June 2012
Published: 3 September 2012
We have recently developed a new type of porous silicon we name as porous silicon colloids. They consist of almost perfect spherical silicon nanoparticles with a very smooth surface, able to scatter (and also trap) light very efficiently in a large-span frequency range. Porous silicon colloids have unique properties because of the following: (a) they behave as optical microcavities with a high refractive index, and (b) the intrinsic photoluminescence (PL) emission is coupled to the optical modes of the microcavity resulting in a unique luminescence spectrum profile. The PL spectrum constitutes an optical fingerprint identifying each particle, with application for biosensing.
In this paper, we review the synthesis of silicon colloids for developing porous nanoparticles. We also report on the optical properties with special emphasis in the PL emission of porous silicon microcavities. Finally, we present the photonic barcode concept.
KeywordsPorous silicon colloids Photoluminescence emission Optical cavity modes
Silicon is a key material in many industrial sectors as metallurgy, electronics, and photonics. Depending on the applications, different degrees of purity are used. It ranges from the metallurgical grade (MG), solar grade (SG), and electronic grade (EG) silicon. Most applications of MG silicon concerns bulk physico-chemical properties derived from its electronic structure (sp3-like bonding). Also, silicon is a semiconductor material, being nowadays the base material for electronics[1–3]. Finally, the huge refractive index (n = 3.5) value of silicon has allowed developing new optical devices as photonic crystals[4, 5], waveguides, multiplexers, and nanolasers. It is well known from the technology sector that silicon can grow spontaneously in the form of small particles as silicon powder. Several groups have reported on the formation of silicon colloids. Korgel et al.[9, 10] have developed sub-micrometric colloidal particles of amorphous silicon by the thermal decomposition of trisilane. Our research team has also developed silicon colloids through chemical vapor deposition methods. They are spherical micro- and nanoparticles of polycrystalline, amorphous or porous silicon with a diameter size between 0.5 and 5 μm. We have also shown that they work pretty well as optical microcavities in the visible and infrared regions of the optical spectrum. Porous silicon also shows photoluminescence (PL) emission, and it can be used for sensing devices[14, 15]. The PL emission of porous colloids resonates with the whispering gallery modes (WGM) of the microcavity resulting in a high PL intensity. The PL spectrum displays a unique photonic profile identifying each particle, which constitutes the basic idea of a new type of photonic bar encoding, similar to other previously reported encoding systems. As porous silicon is a biocompatible material, such photonic barcodes are envisaged for applications in the fields of biology and medicine. In this paper, we will review the synthesis procedure of porous silicon colloids. Also, we will report on the optical properties (optical transmission and PL) of both particle ensembles as well as single particles. Finally, we will report on the concept of the photonic barcode concept based on porous silicon microcavities and its potential applications to biosensing.
Synthesis of silicon colloids based on chemical vapor deposition
Results and discussion
Optical properties of silicon colloids
Porous silicon colloids for biosensing: the photonic barcode concept
We have reviewed the synthesis method we have developed for processing amorphous, polycrystalline and porous silicon colloids with diameter values between 0.5 and 5 μm. Because of both their spherical shape and micrometric size, all silicon colloid allotropes work pretty well as optical microcavities in the near-infrared region. Furthermore, the PL emission of porous silicon colloids is greatly enhanced when it resonates with the optical microcavity modes, resulting in a unique photonic fingerprint we call it as the photonic barcode.
This work has been partially supported by the Spanish CICyT projects, FIS2009-07812, Consolider CSD2007-046, and PROMETEO/2010/043.
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