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The latest research published in Advanced Optical Materials magazine shows that adding precious metals to the nanoscale design of semiconductors affects the properties of nanoparticle gel networks.
Research: reveal the influence of nanoscale design on the separation of carriers in the semiconductor-metal nanoparticle gel network. Image Credit: George Shafeev/Shutterstock.com
Mr. Bigall and his team are committed to first-class and effective charge carrier separation methods. The research paper pointed out that the combination of precious metals and semiconductors on the nanoscale has produced advantageous properties, especially for photovoltaic industry and photocatalytic applications.
The performance of this combination is highly dependent on the separation of charge carriers. Since the valence energy gap between the conduction bands of CdSe and CdS and CdSe/CdS nanorods (NRs) is very small, they themselves provide some charge carrier separation.
The latest research proves that the integration of building blocks into nanoparticle gels can increase their applications in industry to a greater extent. The unique characteristics of the composition are retained in the nanogel. Different methods of synthesizing hybrid nanostructures have been discussed because the classical methods have their limitations in the separation of charge carriers.
Schematic diagram of the gel network from CdSe/CdS NRs to gold decoration using two different methods. Image source: Schlenkrich, J. et al., Advanced Optical Materials
The main difference between these gels is that the spatial separation between adjacent gold regions in the hybrid nanostructure is significantly different. In this study, various gold-decorated CdSe/CdS NRs were integrated to form a nanogel structure, which effectively performed the charge separation process.
Use light-induced growth process and thermal growth process to generate gold decoration/pointed NRs. A transmission electron microscope (TEM) was performed, where the excitation spectrum wavelengths of the CdSe core and CdS NR were 600nm and 450nm, respectively.
The difference in the 480-700 nm wavelength range between the pointed NR and the random NR system can be explained by the size change of the generated gold nanostructures.
However, in a mixed particle system, very basic conditions can lead to the decomposition and separation of the gold domain. Within picoseconds, the delocalized electrons along the CdS shell move to the metal domain, while the holes are located in the CdSe core.
During irradiation, electron delocalization can be detected in the entire coupled CdSe/CdS NRs, thereby increasing the electron transport to the metal domain.
An overview of the comparative morphology of different mixed aerogel networks assembled by af) H2O2 (above) and gl) Y3+ (below). SEM images (a,d,g,j) and TEM images of random NR aerogels assembled by H2O2 (b,c) and Y3+ (h,i) and by H2O2 (e,f) and Y3+ (k,l) ). The inset of the SEM image shows a photo of the macroscopic aerogel as a whole. Image source: Schlenkrich, J. et al., Advanced Optical Materials
The network of NRs is mainly synthesized due to the instability of nanoparticles. H2O2 causes oxidation of the surface attached to mercaptopropionic acid (MCA). This process produces synthetic active sites that serve as connection points for nanorods. The nanoparticle gel network is finally produced in a controlled manner.
Compared with the random NR network, the interval between the two gold domains (tip is 10 nm, random NR is 40 nm) and the size of the domain (tip is 3.2 ± 1.2 nm, random NR is 2.0 ± 0.6 nm) is larger ( The tip is 3.2 ± 1.2 nm, and the random NR is 2.0 ± 0.6 nm).
On dry gel samples, intensity modulated photocurrent spectroscopy (IMPS) is used to evaluate the influence of nanostructures on the spectroelectrochemical properties (charge carrier dynamics) of the hybrid macrostructure.
At bias potentials of 0 and +150 mV, the positive photocurrent dominates, but at 150, 300, and 450 mV, the negative photocurrent is observed to turn to the positive photocurrent direction.
The structure and optical characteristics of the gel network depend on whether the hybrid particles are assembled by the oxidation method or the ion method. In addition, the influence of various building block designs on the separation process of charge carriers was discussed from the perspective of spectroelectrochemistry.
In the latest research, a model of charge carrier dynamics is derived. When the semiconductor-metal hybrid gel network is irradiated, regardless of the position of the gold on the NRC, the excited electrons will gather in the metal region. This is facilitated by the inherent small conduction band energy difference (0.23 eV) between the CdSe core and the CdS shell, which allows electrons to delocalize on the NR.
Under longer irradiation time and subsequent changes in the direction of the photocurrent, the energy spectrum, electron accumulation, and the rise of the Fermi level in the metal domain are schematic diagrams of the different nanoparticles. The conduction band shift at the CdSe/CdS heterojunction is about 0.23 eV, which results in the formation of a quasi-type II arrangement. For the positioning of the Au Fermi energy level, the volume value (-5.1 eV) is used, which can rise after contact with the semiconductor surface, but remains within the band gap of the CdS shell. Image source: Schlenkrich, J. et al., Advanced Optical Materials
As the frequency decreases (that is, the radiation period increases), the Fermi level of the gold domain rises, making the transfer of electrons from the semiconductor conduction band to the gold domain less favorable.
The higher photoelectric flux electron efficiency of the cutting-edge NR network indicates more effective charge carrier separation and therefore electron transport to the electrolyte.
The tip structure has only one Au domain on each semiconductor NR, which results in a semiconductor-semiconductor contact, allowing electrons to delocalize and pass through a wider part of the network.
In short, a nanogel particle network composed of interconnected CdSe/CdS/Au semiconductor-metal hybrid nanoparticles was prepared. Using IMP, the effect of the atomic distance between metal domains on the separation efficiency of charge carriers was discovered. Compared with random NR networks, charge carrier separation is more successful in cutting-edge NR networks, resulting in better negative photocurrent efficiency, in which charge recombination is more prominent. Indeed, this novel method makes the charge separation process more efficient.
Schlenkrich, J., Zámbó, D., Schlosser, A., Rusch, P. and Bigall, North Carolina (2021). Reveal the influence of nanoscale design on the separation process of carriers in the semiconductor-metal nanoparticle gel network. Advanced optical materials. https://onlinelibrary.wiley.com/doi/full/10.1002/adom.202101712
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Ibtisam graduated from the Islamabad Institute of Space Technology with a bachelor's degree in aerospace engineering. During his academic career, he participated in multiple research projects and successfully managed multiple extracurricular activities such as International World Space Week and International Aerospace Engineering Conference. Ibtisam participated in an English essay competition during his undergraduate course and has always been interested in research, writing and editing. Soon after graduation, he joined AzoNetwork as a freelancer to improve his skills. Ibtisam likes to travel, especially to the countryside. He has always been a sports fan and enjoys watching tennis, football and cricket. Ibtisam was born in Pakistan and one day hopes to travel the world, build strong bonds of friendship, and spread the message of peace and love.
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