Please cite this article in press as: K. Grochowska, et al., Properties of ordered titanium templates covered with Au thin films for SERS applications, Appl. Surf. Sci. (2016), http://dx.doi.org/10.1016/j.apsusc.2016.01.186 ARTICLE IN PRESS G Model APSUSC-32418; No. of Pages 7 Applied Surface Science xxx (2016) xxx–xxx Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Properties of ordered titanium templates covered with Au thin films for SERS applications Katarzyna Grochowska a,∗ , Katarzyna Siuzdak a , Michał Sokołowski b , Jakub Karczewski b , Mariusz Szkoda a,c , Gerard ´ Sliwi ´ nski a a Centre for Plasma and Laser Engineering, Szewalski Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Fiszera 14 St., 80-231 Gda´ nsk, Poland b Faculty of Applied Physics and Mathematics, Gda´ nsk University of Technology, Narutowicza 11/12 St., 80-233 Gda´ nsk, Poland c Faculty of Chemistry, Gda´ nsk University of Technology, Narutowicza 11/12 St., 80-233 Gda´ nsk, Poland a r t i c l e i n f o Article history: Received 18 December 2015 Received in revised form 18 January 2016 Accepted 21 January 2016 Available online xxx Keywords: Anodization Dimpled Ti templates Au thin layers SERS measurements a b s t r a c t Currently, roughened metal nanostructures are widely studied as highly sensitive Raman scattering sub- strates that show application potential in biochemistry, food safety or medical diagnostic. In this work the structural properties and the enhancement effect due to surface enhanced Raman scattering (SERS) of highly ordered nano-patterned titanium templates covered with thin (5–20 nm) gold films are reported. The templates are formed by preparation of a dense structure of TiO 2 nanotubes on a flat Ti surface (2 × 2 cm 2 ) and their subsequent etching down to the substrate. SEM images reveal the formation of honeycomb nanostructures with the cavity diameter of 80 nm. Due to the strongly inhomogeneous dis- tribution of the electromagnetic field in the vicinity of the Au film discontinuities the measured average enhancement factor (10 7 –10 8 ) is markedly higher than observed for bare Ti templates. The enhancement factor and Raman signal intensity can be optimized by adjusting the process conditions and thickness of the deposited Au layer. Results confirm that the obtained structures can be used in surface enhanced sensing. © 2016 Elsevier B.V. All rights reserved. 1. Introduction During last decades the Raman spectroscopy has become a powerful and widely used technique for the non-destructive and label-free detection, identification and structure investigation of the organic and inorganic species and is broadly used in areas such as diagnostics, analytical chemistry, pharmacy, biomedical and photovoltaics technologies or in forensic and cultural heritage studies [1–8]. Bands observed in the Raman spectra correspond to energy transitions arising from specific molecular vibrations due to interaction of incident light with the studied substance [9]. As each molecule has unique set of vibrational energy levels and Raman signal is highly sensitive to the chemical structure of the molecule, this technique allows to differentiate and identify species [10]. Recently, more than 25 types of linear and nonlinear techniques based on Raman scattering are in use, such as spontaneous Stokes and anti-Stokes Raman Spectroscopy, Surface Enhanced Raman Spectroscopy (SERS), Coherent Anti-Stokes Raman Spectroscopy (CARS), Coherent Stokes Raman Spectroscopy (CSRS) or Stimulated Raman Scattering (SRS) [11–15]. However, the drawback of the vast ∗ Corresponding author. E-mail address: kgrochowska@imp.gda.pl (K. Grochowska). majority of above mentioned techniques is the weak intensity of the measured Raman signal due to low cross-section for inelastic light scattering that is on the order of 10 -28 –10 -30 cm 2 /sr [10,16,17]. This results in limited level of detection as scattering from about 10 12 –10 14 molecules/cm 2 usually present in a monolayer is hardly enough to be detected and at least milimolar concentrations are typically required in order to observe any Raman signal [18]. One of the easiest ways to enhance the scattering cross-section is the use of rough metallic structures or nanoparticles (NPs) of differ- ent size (obviously 10–100 nm in diameter) and shape [19], i.e. SERS technique. SERS is sensitive to specific environmental proper- ties such as ion concentration and pH which makes this technique most valuable for chemical and biological applications [10]. Due to collective oscillations of excited conduction electrons (plasmons) within metallic arrays the enhancement up to ca. 10 4 of the local electric field occurs. Independently, the dynamic charge transfer between studied molecules of the analyte and metal causes addi- tional enhancement of two to three orders of magnitude. Typically, estimated EF (enhancement factor) values of the electric field for very good SERS substrates lie in the range of 10 3 –10 6 [20]. Never- theless, these values strictly depend on geometry of the metallic structure that is the roughness, size of particles, spacing and their distribution (degree of order). For non-optimized geometry con- ditions the EF is quite small and takes values in the range of http://dx.doi.org/10.1016/j.apsusc.2016.01.186 0169-4332/© 2016 Elsevier B.V. All rights reserved.