Plasma semiconductors and nanomaterials can be coupled to develop photocatalytic and detection systems. Nanoscale compounds containing semiconductors and metals can enhance plasmon-assisted spectroscopy and increase catalytic performance by modulating the charge states of metals.
Study: Hybrid composite based on conductive polymers and plasmonic nanomaterials applied to catalysis and detection. Image credit: GiroScience / Shutterstock.com
An article published in Materials Research Express showed an improvement in Raman dispersion through the use of conductive polymers as semiconductor platforms.
An Introduction to Raman Spectroscopy
Vibrational spectroscopy is a method of determining the molecular framework caused by the vibrational oscillations of particles. Raman scattering is a popular technique of vibrational spectroscopy.
The Raman signal produces a different spectrum for molecules and is beneficial for analytical purposes. However, Raman scattering has weaknesses and requires considerable improvement before widespread use can be made in analytical studies.
In the spectroscopy technique, only one in 106 photons is transformed into Stokes Raman scattering, resulting in an inadequate strength of the analytical signal. The introduction of nanostructures can enhance the Raman effect by plasmon amplification, allowing Raman detection of single molecules.
Nanostructured materials can be created using advanced materials processing and characterization techniques, including metal nanostructures with various morphologies and characteristics.
Figure 1. (a) FTIR spectra of treated and untreated P3HT: PCBM also showed different temperatures of 50, 100, 150, 200 and 250 ° C in the oven for 40 min (b) P3HT fluorescence spectra: PCBM before and after thermal annealing at 250 ° C. (c) The water contact angle of the mixed P3HT: PCBM shows different temperatures from 0 to 250 ° C. (d)) SEM images of (i) Ag NPs size 40 nm (ii) P3HT. (iii) PCBM. (iv) P3HT: PCBM / Ag NPs.
Improved Raman scattering
A significantly amplified electromagnetic field (MS) is generated on the surfaces of the metal nanostructure by excitation of localized surface plasmons. A chemical process or EM technique can enhance the Raman effect.
The chemical process has received less attention due to its lower Raman amplification effects compared to those of EM origin. Load transfer activities to the molecule-platform complex, such as those caused by derived resonance coupling, improve the signals of the Raman effect.
Raman spectroscopy enhanced by photoinduced
It is possible to achieve surface-enhanced Raman dispersion (SERS) by combining photoactivated oxygen vacancy defects on the surface of semiconductor materials such as TiO2.
Oxygen vacancy states were shown to promote derived couplings between semiconductor materials, defects, metals, and analytes. These couplings, in turn, enhance the Raman effect. The mechanism was called photoinduced enhanced Raman spectroscopy, or PIERS, for short.
PIERS can be used to detect tiny amounts of different small molecule analytes for a variety of semiconductor materials. Together with PIERS methods, semiconductor materials can build bonds between metals and themselves, allowing efficient carrier segregation through a Schottky bond.
Schottky bonding is generated when semiconductor material and metal come very close, and charge carriers traverse from side to side, which helps bring their Fermi levels into equilibrium.
Figure 2. SERS spectra of 4-nitrophenol (4NP) recorded at P3HT: PCBM (a) SERS recorded in polymer mixtures that were annealed at different temperatures. (b) SERS intensity normalized before (black) after heat treatment (red). (c) Scheme of the oxidation reaction and formation of 4-aminophenol from 4-nitrophenol.
Which semiconductor was used in the study?
A combination of p-type and p-type semiconductor materials, such as P3HT: PCBM, is a commonly used conductive organic semiconductor.
The P3HT polymer exhibits a large charge motion in highly crystallized sheets and serves as an electron donor in the photoexcitation phase. The decomposition of the exciton is possible thanks to the complementary PCBM. When used with gold (Au) or silver (Ag) nanoparticles, the P3HT: PCBM polymer combination creates a Schottky bond.
Research methodology
As a framework to enhance the Raman effect, in this work P3HT nanoparticles were mixed: PCBM and Ag. The team demonstrated that heat treatment of this semiconductor-plasmonic complex significantly improved the surface-enhanced Raman spectroscopy signal that analytes can generate. In addition, the team demonstrated that the polymer complex supports plasmonic catalytic processes.
The team also examined the photoluminescence (PL) spectra of the polymer complex. They measured the contact angle of the different samples before and after the heat treatment.
Figure 3. An energy band diagram illustrating the electronic transition between P3HT: PCBM and Ag NPs and the MB analyte molecule. The red lines show the transitions of electrons excited by the Raman excitation laser.
Important results of the study
In this study, the team showed how the signal strength of PIERS was improved approximately fivefold by the use of conductive polymeric materials with plasmonic properties. Support mechanisms based on charge transfer were found to promote the oxidation of the desired molecules in active plasmonic nanostructures.
Heat treatment of the polymer mixture improved the impact of self-trapped localized excitons on photoluminescence.
Using an optimized chemical mechanism, the charge transfer-based approach improved the signals of the Raman effect. The study showed how conductive polymers could be used as semiconductor frameworks for catalysis and plasmonic detection.
Reference
Alanazi, AT and Rice, JH (2022). Hybrid compound based on conductive polymers and plasmonic nanomaterials applied to catalysis and detection. Search for Materials Express. Available at: https://iopscience.iop.org/article/10.1088/2053-1591/ac7d9a
Disclaimer: The views expressed herein are those of the author expressed in private and do not necessarily represent the views of AZoM.com Limited T / A AZoNetwork the owner and operator of this website. This disclaimer is part of the Terms and Conditions of Use of this website.