Surface Enhanced Raman Scattering Substrates Made by Oblique Angle Deposition: Methods and Applications

Abstract

Surface Enhanced Raman Spectroscopy presents a rapid, non-destructive method to identify chemical and biological samples with up to single molecule sensitivity. Since its discovery in 1974, the technique has become an intense field of interdisciplinary research, typically generating >2000 publications per year since 2011. The technique relies on the localised surface plasmon resonance phenomenon, where incident light can couple with plasmons at the interface that result in the generation of an intense electric field. This field can propagate from the surface from the metal-dielectric interface, so molecules within proximity will experience more intense Raman scattering. Localised surface plasmon resonance wavelength is determined by a number of factors, such as size, geometry and material. Due to the requirements of the surface optical response, Ag and Au are typical metals used for surface enhanced Raman applications. These metals then need to have nano features that improve the localised surface plasmon resonance, several variants of these substrates exist; surfaces can range from nanoparticles in a suspension, electrochemically roughened electrodes to metal nanostructures on a substrate. The latter will be the focus of this review, particularly reviewing substrates made by oblique angle deposition. Oblique angle deposition is the technique of growing thin films so that the material flux is not normal to the surface. Films grown in this fashion will possess nanostructures, due to the atomic self-shadowing effect, that are dependent mainly on the deposition angle. Recent developments, applications and highlights of surface enhanced Raman scattering substrates made by oblique angle deposition will be reviewed.Keywords: surface enhanced Raman spectroscopy; coatings on polymer; special substrate materials; metal coatings; deposition, characterisations and applications of sculptured and textured thin films

Simulation and Optimization of Film Thickness Uniformity in Physical Vapor Deposition

“…Physical vapor deposition (PVD) is an important family of techniques for thin film processes. Applications of PVD deposited thin films include: optical band-pass filters [1], surface enhanced Raman spectroscopy [2], hydrophobic coatings, and sensors [3]. PVD involves the conversion of a source material into the gas phase, which is then deposited onto a substrate surface [4] and can be achieved through either evaporation or sputtering [5].…”

Fabrication of Au Nanorods by the Oblique Angle Deposition Process for Trace Detection of Methamphetamine with Surface-Enhanced Raman Scattering

“…Numerous other groups had optimized the performance of AgNRs substrate by adjusting the process parameters [44,45,46]. In recent years, more methods based on OAD have been investigated to fabricate novel SERS substrate for improving SERS performance, reducing costs, etc [47]. Singh et al demonstrated that if AgNRs grew at 140 K, it would get the same length of nanorods as those done at room temperature in a lower deposition time and show greater SERS performance than the substrate made at room temperature [48].…”

“…However, Oh et al got the opposite conclusion that substrates made at higher temperatures had higher SERS enhancements [49]. There is little in the literature that studies this temperature dependence with other nanostructures, such as AuNRs; perhaps this will be a new area that will be expanded on in the near future for higher SERS performance [47]. For fabrication into smaller dimensions with better control, template assisted deposition was investigated.…”

“…For fabrication into smaller dimensions with better control, template assisted deposition was investigated. Templates are surfaces with defined surface structures, so when used in OAD, there will be predefined shadowing [47]. Lithography [50], self-assembled nanoparticles [51], and nano-imprinted polymers [52] are typically used for making templates.…”

Surface-Enhanced Raman Spectroscopy (SERS) Study Using Oblique Angle Deposition of Ag Using Different Substrates

“…Lithography-based sputtering is convenient for fabricating nanostructured SERS substrate, but it requires a lot of money and time. In recent years, research has been reported on obtaining a nanorod-structured SERS substrate by simply tilting the substrate during sputtering [22,23,24]. In this way, SERS substrates can be fabricated at a lower cost in a shorter time than other methods.…”