Silver coated platinum core-shell nanostructures on etched Si nanowires: atomic layer deposition (ALD) processing and application in SERS.

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.

[1]  D. Farmer,et al.  High density Ru nanocrystal deposition for nonvolatile memory applications , 2007 .

[2]  Mikko Ritala,et al.  Atomic layer deposition chemistry: recent developments and future challenges. , 2003, Angewandte Chemie.

[3]  U. Gösele,et al.  Selectively deposited silver coatings on gold-capped silicon nanowires for surface-enhanced Raman spectroscopy. , 2009, Chemphyschem : a European journal of chemical physics and physical chemistry.

[4]  Shuming Nie,et al.  Near-Field Surface-Enhanced Raman Spectroscopy on Single Silver Nanoparticles , 1997 .

[5]  J. H. Weaver.  Optical properties of Rh, Pd, Ir, and Pt , 1975 .

[6]  R. W. Christy,et al.  Optical Constants of the Noble Metals , 1972 .

[7]  J. Michler,et al.  Signal enhancement in nano-Raman spectroscopy by gold caps on silicon nanowires obtained by vapour–liquid–solid growth , 2007, Nanotechnology.

[8]  Ki-Bum Kim,et al.  Formation of Ru nanocrystals by plasma enhanced atomic layer deposition for nonvolatile memory applications , 2006 .

[9]  M. Dresselhaus,et al.  Nonlinear Raman Probe of Single Molecules Attached to Colloidal Silver and Gold Clusters , 2002 .

[10]  R. Gordon,et al.  Atomic Layer Deposition of Ultrathin Copper Metal Films from a Liquid Copper(I) Amidinate Precursor , 2006 .

[11]  Zhipeng Huang,et al.  Extended arrays of vertically aligned sub-10 nm diameter [100] Si nanowires by metal-assisted chemical etching. , 2008, Nano letters.

[12]  U. Gösele,et al.  Growth peculiarities during vapor–liquid–solid growth of silicon nanowhiskers by electron-beam evaporation , 2006 .

[13]  V. Sandoghdar,et al.  A single gold particle as a probe for apertureless scanning near‐field optical microscopy , 2001, Journal of microscopy.

[14]  M. Ritala,et al.  Radical-enhanced atomic layer deposition of silver thin films using phosphine-adducted silver carboxylates , 2007 .

[15]  Tae-Sik Yoon,et al.  Nucleation kinetics of Ru on silicon oxide and silicon nitride surfaces deposited by atomic layer deposition , 2008 .

[16]  M. Ritala,et al.  Reaction Mechanism Studies on Atomic Layer Deposition of Ruthenium and Platinum , 2003 .

[17]  D. L. Jeanmaire,et al.  Surface raman spectroelectrochemistry: Part I. Heterocyclic, aromatic, and aliphatic amines adsorbed on the anodized silver electrode , 1977 .

[18]  M. Moskovits.  Surface-enhanced spectroscopy , 1985 .

[19]  George C. Schatz,et al.  Gold nanoparticle dimer plasmonics: finite element method calculations of the electromagnetic enhancement to surface-enhanced Raman spectroscopy , 2009, Analytical and bioanalytical chemistry.

[20]  M. Ritala,et al.  Atomic Layer Deposition of Platinum Thin Films , 2003 .

[21]  Yin Wu,et al.  Uniform, axial-orientation alignment of one-dimensional single-crystal silicon nanostructure arrays. , 2005, Angewandte Chemie.

[22]  M. Ritala,et al.  Ruthenium/aerogel nanocomposites via atomic layer deposition , 2007 .

[23]  S. T. Lee,et al.  Fabrication of Single‐Crystalline Silicon Nanowires by Scratching a Silicon Surface with Catalytic Metal Particles , 2006 .

[24]  Steven R. Emory,et al.  Probing Single Molecules and Single Nanoparticles by Surface-Enhanced Raman Scattering , 1997, Science.

[25]  David R. Smith,et al.  Plasmon resonances of silver nanowires with a nonregular cross section , 2001 .

[26]  Markku Leskelä,et al.  Chemie der Atomlagenabscheidung (Atomic Layer Deposition): jüngste Entwicklungen , 2003 .

[27]  Yunjie Yan,et al.  Synthesis of Large‐Area Silicon Nanowire Arrays via Self‐Assembling Nanoelectrochemistry , 2002 .

[28]  Ning-Bew Wong,et al.  Ordered silicon nanowire arrays via nanosphere lithography and metal-induced etching , 2007 .

[29]  M. Albrecht,et al.  Anomalously intense Raman spectra of pyridine at a silver electrode , 1977 .

[30]  S. Bent,et al.  Ultralow loading Pt nanocatalysts prepared by atomic layer deposition on carbon aerogels. , 2008, Nano letters.

[31]  T. Russell,et al.  Using a ferrocenylsilane-based block copolymer as a template to produce nanotextured Ag surfaces: uniformly enhanced surface enhanced Raman scattering active substrates , 2006 .

[32]  P. Rice,et al.  Crystalline reconstruction in Ni–Cr–Fe/Ni–Fe films , 2004 .

[33]  R. M. Tromp,et al.  The influence of the surface migration of gold on the growth of silicon nanowires , 2006, Nature.

[34]  J. Michler,et al.  The SERS and TERS effects obtained by gold droplets on top of Si nanowires. , 2007, Nano letters.

[35]  J. Tersoff,et al.  Sawtooth faceting in silicon nanowires. , 2005, Physical review letters.

[36]  Samuel Hoffmann,et al.  Nanowires enabling signal-enhanced nanoscale Raman spectroscopy. , 2008, Small.

[37]  Ki-Bum Kim,et al.  Atomic Layer Deposition of Ru Nanocrystals with a Tunable Density and Size for Charge Storage Memory Device Application , 2008 .

[38]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[39]  Chueh-Yang Liu,et al.  Atomic layer deposition of platinum nanoparticles on carbon nanotubes for application in proton-exchange membrane fuel cells. , 2009, Small.

[40]  E. I. Givargizov.  Fundamental aspects of VLS growth , 1975 .

[41]  M. Fleischmann,et al.  Raman spectra of pyridine adsorbed at a silver electrode , 1974 .

[42]  David-Wei Zhang,et al.  Physical and electrical characterization of atomic-layer-deposited Ru nanocrystals embedded into Al2O3 for memory applications , 2008 .

[43]  M. Hersam,et al.  Controlled growth of platinum nanoparticles on strontium titanate nanocubes by atomic layer deposition. , 2009, Small.

[44]  R. S. Wagner,et al.  VAPOR‐LIQUID‐SOLID MECHANISM OF SINGLE CRYSTAL GROWTH , 1964 .