The Use of Aligned Silver Nanorod Arrays Prepared by Oblique Angle Deposition as Surface Enhanced Raman Scattering Substrates

Abstract

Aligned Ag nanorod arrays have been fabricated on glass substrates using an oblique angle vapor deposition (OAD) method. The surface morphology and structure of the Ag rods were studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Individual nanorods were found to be primarily cylindrical, albeit with irregularly shaped surface protrusions of the rods. The surface enhanced Raman scattering (SERS) response as a function of nanorod length was investigated using trans-1,2-bis(4pyridyl)ethene as a probe molecule at an excitation wavelength of 785 nm. The enhancement factors reached a maximum of ∼5 × 10 8 as the nanorod length approached 868 nm and then decreased to ∼3 × 10 6 as the nanorod length increased further to 1900 nm. For the 868 nm nanorod array, signals collected over multiple spots within the same substrate resulted in a relative standard deviation (RSD) of 10%, while an RSD of 15% was measured in signals collected from different substrates. When stored in a food vacuum bag, the substrates are stable with respect to SERS intensity for greater than 2 months. This study demonstrates that the OAD Ag nanorod arrays are highly sensitive, uniform, and stable SERS substrates that are suitable for a variety of surface chemical analysis applications.

Light enhancement in surface-enhanced Raman scattering at oblique incidence

“…More details on sample preparation can be found elsewhere [7,8]. The morphology of the Ag nano-islands was inspected by scanning electron microscopy [SEM, Fig.…”

Rapid Detection and Recognition of Organic Pollutants at Trace Levels by Surface-Enhanced Raman Scattering

“…[24][25][26][27][28] Other researchers found that multilayer structures of Ag/Au nanostructures on the smooth metallic underlayer exhibited better SERS sensitivity compared to those without metallic underlayer (EF = 5 × 10 8 ). [29][30][31] However, the factor that governs the enhancement for multilayer structures is not very clear. Recently, Misra et al obtained remarkably high SERS sensitivity using a micro-cavity with a radius of several micrometers.…”

“…[33] All the above experiments and those conducted by Driskell et al suggested that the underlayer reflectivity could play an important role in the multilayer SERS substrates. [29] We have investigated in detail the relationship of underlayer reflectivity and the SERS enhancement of Ag nanorod substrates prepared by oblique angle deposition. We use thin films of different materials with different thicknesses as underlayers to modulate the reflectivity systematically.…”

“…The twelve deposited planar thin film samples were then loaded into another customdesigned electron-beam evaporation system for Ag nanorod deposition through the socalled oblique angle deposition (OAD). [16,29,37] In this deposition, the background pressure was 1×10 -7 Torr and the substrate holder was rotated so that the deposition flux was incident onto the thin films with an angle = 86º with respect to the surface normal of the substrate holder. The Ag nanorod arrays were formed through a self-shadowing effect.…”

“…The Ag nanorod arrays were formed through a self-shadowing effect. [16,29,37] During the deposition, the Ag deposition rate was monitored by a QCM directly facing the incident vapour. The deposition rate was fixed at 0.3 nm/s and the deposition ended when the QCM read 2000 nm (our optimized condition).…”