Silver Coated Platinum Core–Shell Nanostructures on Etched Si Nanowires: Atomic Layer Deposition (ALD) Processing and Application in SERS

Abstract

A new method to prepare plasmonically active noble metal nanostructures on large surface area silicon nanowires (SiNWs) mediated by atomic layer deposition (ALD) technology has successfully been demonstrated for applications of surface-enhanced Raman spectroscopy (SERS)-based sensing. As host material for the plasmonically active nanostructures we use dense single-crystalline SiNWs with diameters of less than 100 nm as obtained by a wet chemical etching method based on silver nitrate and hydrofluoric acid solutions. The SERS active metal nanoparticles/islands are made from silver (Ag) shells as deposited by autometallography on the core nanoislands made from platinum (Pt) that can easily be deposited by ALD in the form of nanoislands covering the SiNW surfaces in a controlled way. The density of the plasmonically inactive Pt islands as well as the thickness of noble metal Ag shell are two key factors determining the magnitude of the SERS signal enhancement and sensitivity of detection. The optimized Ag coated Pt islands on SiNWs exhibit great potential for ultrasensitive molecular sensing in terms of high SERS signal enhancement ability, good stability and reproducibility. The plasmonic activity of the core-shell Pt//Ag system that will be experimentally realized in this paper as an example was demonstrated in numerical finite element simulations as well as experimentally in Raman measurements of SERS activity of a highly diluted model dye molecule. The morphology and structure of the core-shell Pt//Ag nanoparticles on SiNW surfaces were investigated by scanning- and transmission electron microscopy. Optimized core-shell nanoparticle geometries for maximum Raman signal enhancement is discussed essentially based on the finite element modeling.

Raman Signal Enhancement Tunable by Gold-Covered Porous Silicon Films with Different Morphology

“…The plasmonic surfaces, which include solid substrate with metallic nanostructures and chemically synthesized noble metal colloids, and their fabrication methods were reviewed in a number of papers [ 15 , 16 , 17 ]. From another side, a number of publications have shown that different porous materials can be used as a matrix for SERS-active metals, for example: alumina [ 18 ], porous Si/SiO 2 [ 19 ], porous silicon [ 20 ], silicon nanowires [ 9 , 21 , 22 ], porous titanium oxide [ 23 ] and porous silver [ 13 ]. As is well-known, the bio-friendly properties [ 24 ] of porous silicon have been proven to act as a biocompatible and biodegradable material [ 25 , 26 ], as shown in a number of papers related to its biomedical applications [ 27 , 28 ].…”

Deposition of metallic silver coatings by Aerosol Assisted MOCVD using two new silver β-diketonate adduct metalorganic precursors

“…Few examples of ALD of Ag coatings have also been reported previously. [20][21][22][23][24][25] In the cases where AA-CVD was used, nonenvironmentally friendly solvents, such as THF and toluene, were used in combination with organometallic precursors. 10,11,16 Concerning the design of Ag metalorganic precursors, previous works have introduced different systems, including β-diketonate adducts Ag(hfac))(L) 26 or Ag(fod)(L),…”

Laser Annealing as a Platform for Plasmonic Nanostructuring

“…A critical parameter in delivering practical plasmonic devices is the material preparation methods, which should allow the production of nanostructures with tunable plasmonic properties. So far, nanomaterials and nanodevice manufacturing have traditionally followed two distinct routes: (a) the top-down approach, where a process starts from a uniform material and subsequently finer and finer tools are employed to create smaller structures, like lithographic processes [35][36][37] and/or ion beam nanofabrication [38] and (b) the bottom-up approach, where smaller components of atomic or molecular dimensions self-assemble together, according to a natural physical principle or an externally applied driving force, to give rise to larger and more organized systems, like atomic layer deposition [39], cold welding [40], flash thermal annealing [41,42], pattern transfer [43] and template stripping [44][45][46]. Practically, the top-down approach offers unequalled control and reproducibility down to a few nanometres in feature size but at high cost for large area manufacturing, while the bottom-up route applies for macroscopic scale nanopatterning albeit without the fine feature and reproducibility control.…”