Surface-Enhanced Raman Spectroscopy of Carbon Nanomembranes from Aromatic Self-Assembled Monolayers

Abstract

Surface-enhanced Raman scattering spectroscopy (SERS) was employed to investigate the formation of self-assembled monolayers (SAMs) of biphenylthiol, 4'-nitro-1,1'-biphenyl-4-thiol, and p-terphenylthiol on Au surfaces and their structural transformations into carbon nanomembranes (CNMs) induced by electron irradiation. The high sensitivity of SERS allows us to identify two types of Raman scattering in electron-irradiated SAMs: (1) Raman-active sites exhibit similar bands as those of pristine SAMs in the fingerprint spectral region, but with indications of an amorphization process and (2) Raman-inactive sites show almost no Raman-scattering signals, except a very weak and broad D band, indicating a lack of structural order but for the presence of graphitic domains. Statistical analysis showed that the ratio of the number of Raman-active sites to the total number of measurement sites decreases exponentially with increasing the electron irradiation dose. The maximum degree of cross-linking ranged from 97 to 99% for the three SAMs. Proof-of-concept experiments were conducted to demonstrate potential applications of Raman-inactive CNMs as a supporting membrane for Raman analysis.

Synthesis and nanoscale characterization of hierarchically assembled molecular nanosheets

“…In addition, spurious signals occur which were not assigned due to the low signal to noise ratio. This behavior is consistent with the surface enhanced Raman spectroscopy (SERS) investigation by Zhang et al [61] who showed a gradual loss of Raman signal upon cross-linking of the NBPT SAM. We believe that this low signal is due to the nature of the CNM itself, which is formed from a laterally disordered carbon network [62] that typically shows low Raman crosssections.…”

“…We believe that this low signal is due to the nature of the CNM itself, which is formed from a laterally disordered carbon network [62] that typically shows low Raman crosssections. [61] The low Raman scattering cross section of NH2-CNM is a considerable advantage, as it allows to specifically distinguish the specific overlayers in the following experiments without interference.…”

Bottom-up fabrication of the multi-layer carbon metal nanosheets

“…7(c) and (d). Electron irradiation of the SAMs produces carbon-carbon links between neighbouring molecules, 3 which reduce the spatial separation between molecules. Fig.…”

“…It has been shown that selfassembled monolayers (SAMs) can be used to form thick, highly ordered molecular carbon systems. [1][2][3] Going beyond the self-assembled monolayers, conjugate organic molecules can lead to new hybrid materials with novel functionalities, which can open new vistas in nanoelectronics and nanotechnology. [4][5][6][7][8] A particular focus has been to create new functional materials for information processing and energy conversion using the self-assembly strategy.…”

Charge Transfer Tuned by the Surrounding Dielectrics in TiO2-Ag Composite Arrays

“…Compared to pure Ag, the TiO 2 -Ag nanocaps exhibited strong absorption in the UV and visible region, as shown in Figure 4. The absorption peaks of the Ag film at about 340 nm and 460 nm came from dipole resonance and quadrupole resonance, which broadened due to the coupling between the quadrupole resonance and the octupole resonance [22]. As the small Ag nanoparticles were almost trapped inside the TiO 2 matrix and there was no exposure to oxygen, the excited electrons transferring from the surface of the Ag nanoparticle to the TiO 2 conduction band remained in the Ag-TiO 2 complex, leading to the increased concentration of free conduction electrons, which broadened the absorption band of the Ag-TiO 2 complex.…”