The Raman enhancement effect on a thin GaSe flake and its thickness dependence

Abstract

Chemical enhancement is one of the important mechanisms in surface-enhanced Raman spectroscopy, however, its origin is still under debate. Recently, a two dimensional (2D) layered material has been thought to be a strong candidate to investigate the chemical mechanism of Raman enhancement because it has a flat surface, a well defined structure and is without the interference of electromagnetic enhancement. Herein we report systematic studies of the Raman enhancement effect on a gallium selenide (GaSe) flake by using a copper phthalocyanine (CuPc) molecule as a probe. It is found that the Raman signal of CuPc on the monolayer GaSe can be significantly increased by one order of magnitude compared to that on a SiO 2 /Si substrate. Moreover, the enhancement effect is found to decrease with increasing thickness of the GaSe flake. The origin of the Raman enhancement is attributed to the chemical mechanism resulting from the charge transfer between the GaSe flake and the detected molecules. The supposition is further verified by the investigation of the quenching photoluminescence of GaSe as well as the Raman enhancement effect of CuPc with different thicknesses on the GaSe flake.Our work will shed more light on the understanding of the chemical mechanism for Raman enhancement and expand more practical applications of GaSe.

Strong modulation of optical properties in rippled 2D GaSe via strain engineering

“…The total power at the sample was ~ 100 µW to prevent overheating and laser damage of the samples and the spot of the excitation laser was 1 µm in diameter. We can identify the silicon peak around 520 cm -1 and the GaSe peaks A 1g 1 , E 2g 1 and A 1g 2 around 130, 220 and 310 cm -1 [11,12,16].…”

Shear Exfoliation and Photoresponse of 2D‐Layered Gallium Selenide Nanosheets

“…The intensity of A 1 1g mode decreases dramatically as shown in Table . The ratio A 1 1g and Si diminishes from 0.169 to 0.013, and the full wave at half maximum (FWHM) also increases, this result can be explained by the interaction between neighboring layers which becomes weak for thin nanoflakes . Furthermore, A 2 1g is almost invisible; it is hard to study the remaining small peak around 300 cm −1 , because Si peak may overlaps with GaSe spectra .…”

Recent Advances in 2D Inorganic Nanomaterials for SERS Sensing

“…The atomically thin (2D layer) exhibits unique valance band dispersion which makes it an interesting material for optoelectronic applications . The investigation of SERS effect of GaSe on the CuPc probe molecule demonstrated a 14‐fold increase in the Raman signal compared to a SiO 2 substrate (Figure b) . The effect of the thickness of GaSe on the enhancement, and demonstration of influence of excitation wavelength for interference enhancement, first layer effect, and resonant Raman scattering, confirms the dominant charge transfer process for the chemical enhancement.…”

“…The 2D‐layered, p‐type semiconducting GaSe, has been widely used in nonlinear optical applications . The in‐plane geometry of GaSe has a honeycomb‐like hexagonal structure (fourfold layer with the unique Se–Ga–Ga–Se sequence) ( Figure a).…”

“…Copyright 2018, The Authors, Springer Nature. b) Reproduced with permission . Copyright 2015, Royal Society of Chemistry.…”