Design and fabrication of Cu conical (Spiral+Helical) sculptured thin films and their application in SERS

Abstract

Cu conical (spiral + helical (spiral (3 turns) + helical (2, 12 and 17 turns)) nanostructures were grown on stainless steel mesh (SSM) and glass microscope slide by glancing angle deposition (GLAD). The SSM substrates were used in surface enhanced Raman spectroscopy (SERS) for detection of 4,4′-Bipyridine (4,4′-Bipy) molecules. This design fulfilled the main electromagnetic mechanisms of enhancement of Raman signals, which are near field coupling and the lightning rod effect. The size of the sculptured nanostructures produced on the SSM substrates matched the wavelength of the laser beam of the Raman spectrometer and satisfied the requirements for the enhancement of the surface Raman spectroscopy of the 4,4′-Bipy molecules. A comparison is made on the morphology of the produced nanostructures on SSM, microscope slide and previously published works on other surfaces with the view to different surfaces with different surface roughness. Field emission scanning electron microscope (FESEM) analysis of the samples clearly revealed the morphology of the designed and fabricated nanostructure as conical (spiral + helical) features on both SSM and glass substrates. Crystal structures and optical spectra of the produced samples obtained using grazing angle incident x-ray diffraction (GIXRD) and Vis-NIR spectroscopy. The SERS results showed that although according to the GIXRD data the coated Cu films were oxidized, good enhancement is obtained. Hence, this can be considered as a favor to the applied fields of these samples. Vis-NIR results showed that as the number of turns of the helical part of the structure increased, the absorption of the spectra increased consistent with the discrete dipole approximation (DDA) results reported in the literature. Surface-enhanced Raman spectroscopy results of this work when compared with the available published data showed higher/comparable enhancement irrespective of the type of material used (e.g., Ag, Au and Mn), 4,4′-Bipy concentration, Bipy substrate shape, the method of fabrication and the excitation wavelength of the Raman spectrometer.