Nano-morphology induced additional surface plasmon resonance enhancement of SERS sensitivity in Ag/GaN nanowall network

Abstract

The GaN nanowall network, formed by opening the screw dislocations by kinetically controlled MBE growth, possesses a large surface and high conductivity. Sharp apexed nanowalls show higher surface electron concentration in the band-tail states, in comparison to blunt apexed nanowalls. Uncapped silver nanoparticles are vapor deposited on the blunt and sharp GaN nanowall networks to study the morphological dependence of band-edge plasmon-coupling. Surface enhanced Raman spectroscopy studies performed with a rhodamine 6G analyte on these two configurations clearly show that the sharp nanowall morphology with smaller Ag nanoparticles shows higher enhancement of the Raman signal. A very large enhancement factor of 2.8 × 10(7) and a very low limit of detection of 10(-10) M is observed, which is attributed to the surface plasmon resonance owing to the high surface electron concentration on the GaN nanowall in addition to that of the Ag nanoparticles. The significantly higher sensitivity with same-sized Ag nanoparticles confirms the unconventional role of morphology-dependent surface charge carrier concentration of GaN nanowalls in the enhancement of Raman signals.

Charge transfer-induced enhancement of a Raman signal in a hybrid Ag–GaN nanostructure

“…[19][20][21] Similarly, the GaN thin lms of various morphologies (planar and porous) have been used as supports for depositing silver nanoparticles, on which a signicant enhancement in the Raman signal has been reported. 22,23 This wide band-gap semiconductor is an attractive material because of its chemical resistance, high temperature/high power capability, electron saturation velocity, and internal spontaneous and piezoelectric polarization. 24,25 However, studies related to the inuence of the optoelectronic properties of the substrate on the characteristics of the metal nanoparticles/substrate hybrid material systems and on the enhancement of the Raman signal have been scarce.…”

Controlling the Electron Concentration for Surface-Enhanced Raman Spectroscopy

“…Specifically, the resonant electron oscillations on metallic surfaces and molecular orbitals are the main contributions to LSPR- and CT-induced EFs, respectively. , That is to say, if the number of electrons participating in the resonant event can be increased, either on the metal or on the molecule, the SERS intensity should go up. This notion is supported by various experimental results in the literatures. − For example, Sharvani et al found that the SERS intensity of rhodamine 6G (R6G) molecules on sharp GaN nanowalls is much higher than that on the blunt ones . By Hall and relevant measurements, the authors attributed the result to the concentrated electrons at the sharp apexes of nanowalls, which facilitate the induction of SERS.…”

“…Frankly, even with the substantially boosted electron concentration, the highest EF demonstrated in Figure is still lower than those achieved on many other SERS substrates. ,− This is an expected result considering the flat surface, on which the condition (sharp nanostructures) for hot spots is barely satisfied. To improve the EF, we adjusted MOCVD parameters to increase surface roughness on the nitride QWs.…”

“…Even in the area containing no pits, the AFM line scan still reveals a much larger roughness variation on the pitted 7QW sample (Figure S9), compared with the result on the flat 7QW. As pointed out by Sharvani et al, the roughened GaN surface with sharp curvatures can effectively confine electrons at the apexes, which contain high densities of band-tail states . This morphology-induced charge confinement is expected to be more pronounced with the presence of QWs, where additional carrier imprisonment is built by the quantum barriers.…”

A Multilayer Interlaced Ag Nanosheet Film Prepared by an Electrodeposition Method on a PPy@PEDOT:PSS Film: A Strategy to Prepare Sensitive Surface-Enhanced Raman Scattering Substrates

“… 18 In addition, owing to the high SERS performance of Ag nanostructures, many meaningful results have been reported in the field of SERS-based biosensors. 19 − 22 At present, many types of Ag nanostructures have also been synthesized, such as nanorods, 23 NPs, 24 , 25 nanonets, 26 nanowires, 27 , 28 nanosheets, 29 etc. Especially, a Ag nanosheet nanostructure has a large surface area for easily adsorbing some biomolecules, which is considered as an ideal material for the SERS detection.…”