Chemical Engineering: Characterization of HgS/CdS Core-Shell Nanocomposite Using Photoacoustic (Research Proposal Sample)

Characterization of HgS/CdS Core-Shell Nanocomposite Using Photoacoustic
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Abstract
Nanocomposite materials provide a chance for better functionality as well as multifunctional properties compared to their single-component counterparts that are perceived as more limited. A good example of Nanocomposite material includes inorganic core cell structure where the core and the shell comprise of semiconductors. Besides, there is enhanced photoluminescence through the shell motif, enhanced stability against photochemical oxidation, improved processability amongst engineered band structures. Despite the current modifications and improvements made in the core shell structures, there are still gaps in the characterization of these samples. This study seeks to provide an efficient characterization technique for HdS/CdS core-shell Nanocomposite through Photoacoustic. Besides, these results will be compared with TEM, UV-vis and XRD results with an intent of shedding more light on the solar cell.
KEYWORDS:
HgS/CdS Core-Shell Nanocomposite, Photoacoustic, TEM, XRD, UV-vis, Photoluminescence
Introduction
In reference to Chaudhuri and Paria (2012), nanomaterials possess various dimensions on the nanometer scale in addition to depicting novel properties from their bulk materials. In this case, the synthesis, characterization as well as the application of nanoparticles provide the basic areas of nanotechnology. Over the past few years, nanoparticles have been in the spotlight as there is increased need to advance from microparticles to nanoparticles. This study will seek to provide a medium to characterize HgS/CdS core-shell Nanocomposite that is vital in enhancing immense changes in the chemical or physical properties of a material.
Background: Core/Multishell Semiconductor Nanoparticles
There are several benefits associated with this class of nanoparticles. Chaudhuri and Paria (2012) state that multilayer semiconductor nanoparticles give higher quantum yield, improved optical properties, photoluminescence, easier detection of the emission spectra since they are shifted toward greater wavelength in the visible range. Besides, these particles also present improved electronic properties as well as better structural properties compared to unlayered CS particles. Wu, Bittner and Kern (2005) define this lattice mismatch as a situation where two materials with varying lattice constants are brought together through depositing one material on top of the other.
Some of the advantages associated with lattice mismatch between the material making up the core and the shell are that the shell grows to significant thickness while conserving its luminescence properties. The rationale for this study follows the influx of interested parties in nanoparticles due to their enormous, exciting applications. In reference to Harrison et al. (2000) when a smaller band gap semiconductor material is embedded between the core and the outer shell of the material with a larger band, such particles are thus defined as QDQW (Quantum Dot Quantum Well).
The selection of core and shell materials is carried out mainly considering the band gap and the lattice structure of the sample used to make the CSS semiconductor particles. In this study, the author will characterize HgS/cdS core-shell Nanocomposite, which is an example of the particles mentioned above. Chaudhuri and Paria (2012) state that the optical or photostability of the multilayered particle is comparable to that of HgS/CdS as a result of the further coating on CdS, which is a high band gap compound. In this case, the quantum yield also escalates. HgS is a low band gap compound, and when sandwiched with a high band gap compound such as CdS, the electrons are consequently confined within the HgS layer as well as forming a quantum well.
Problem Statement
Normally, the TEM micrographs fail to show the core as well as shell structure as a result of the similarity in the core and shell materials as well as the nanometer size. In this case, a better characterization technique is required to facilitate proper characterization of these Nanocomposite particles. As of the moment, it is not clear on how core and shell nanoparticles can be documented clearly and characterized adequately. In general, the research on synthesis and characterization of core and shell nanoparticles is in its infancy and as a result, focused studies are called for to ensure better formation methods and better techniques for characterization.
Hypothesis
Photoacoustic offers a better channel to characterize HgS/CdS core-shell Nanocomposite amongst other Core/Multishell semiconductor nanoparticles.
Objectives
• To characterize HdS/CdS core-shell Nanocomposite
• To find out the most efficient method for HdS/CdS characterization between the four methods of sample analysis used in the study.
• To provide a vast background on Multishell semiconductor nanoparticles.
• To analyze previous research studies carried out on this topic in the literature review and point out gaps in current literature.
• To provide a glimpse of the four tools deployed in the methodology for analyzing the sample
• To examine the differences in the particle sizes as indicated by the various analytical methods used.
Literature Review
In reference to Harrison et al. (2000), the resulting hybrid nanocrystals showed a considerable increase in the QE (Quantum Efficiency) over the CdS material. Semiconductors are defined as quantum dots that belong to a state of matter between the molecular material and that of the bulk. Their large surface to volume ration and the quantum confinement effect are behind the unique physical and chemical properties. The quantum confinement effect comes about when the particle size is less than the exciton dimensions. Also, there is the widening of the bandgap as well as a blueshift of the photoluminescence (PL).
Besides, Kim et al. (2004) argue that Nanocomposite materials do provide possibilities for enhanced functionality as well as multifunctional properties. The authors claim that in cases where semiconductors are made of the core and the shell, the core-shell motif allowed enhanced photoluminescence as well as enhanced stability against photochemical oxidation. Harrison et al. (2000) state that some of the variables affecting the Photoluminescence behavior, charge carrier dynamics, non-linear optical properties and phase transitions include particle size distribution, special properties, and the nanocrystals surface.
There exist numerous recent achievements in the wet chemical synthesis of nanoparticles of higher quality as described by Harrison et al. (2000). Improved characterization of these particles has enabled their applications in optoelectronic and electrical devices. Besides, the authors note that precise monolayer control of the chemical growth process is enabled and can be exploited in the formation of core/shell structures. An example includes HgS/CdS, which is more robust physically with better surface passivation. As a result, better quantum efficiencies (QEs) are achieved in such samples compared to the other basic organic capped particles. Harrison et al. (2000) reports that quantum dot quantum Wells (QDQW) are alternating multi-layer structures such as CdS/HgS/CdS.
On the article presented by Kim et al. (2004), X-ray powder diffraction (XRD) determines the growth in Co nanocrystals (NCs) as the preparative method deployed here. The yielding XRD pattern contains extra diffraction peaks that are indexed to wurtzite CsSe. The extra broadness of the XRD reflections in the composite structure pattern is as a result of the small domain size characteristics of the polycrystalline CdSe shell. In reference to Kim et al. (2004), TEM is used in observing the core size and shape in Co in which decrease in blocking temperature is associated with the reduced interparticle magnetostatic interactions resulting from changes in encapsulation matrix. The matrix changes from strictly organic surfactants to an inorganic CdSe layer.
In reference to Chaudhuri and Paria (2012), the process of synthesizing nanoparticles is complex in that there are various techniques to produce different types of nanoparticles. Some of the techniques deployed include synthesis by chemical reaction, condensation from vapor as well as milling that is a solid-state process. Chaudhuri and Paria (2012) argue that the above techniques were used, pure nanoparticles, hybrid or coated nanoparticles with hydrophobic or hydrophilic materials were synthesized depending on the suitability of the applications. The core/shell nanoparticles are classified according to the multiple or single materials into simple and core/shell or composite nanoparticles. While simple nanoparticles are generated from a single material, composite and core/shell are made up of more than two materials. In the classification of these materials, they can be defined broadly as comprising an inner material (core) and outer layer material (shell) such as inorganic/inorganic, organic/inorganic, inorganic/organic as well as organic/organic materials.
Chaudhuri and Paria (2012) state that the choice of the shell material depends greatly on the expected use or application of the nanomaterial. The most common core/shell nanoparticles include the concentric spherical type in which the simple spherical core is coated completely with the shell of another material. Smith, Mohs and Nie (2009) argue that following their different novel properties, differently shaped core/shell nanoparticles have continues to attract immense research interest. In reference to Mbese and Ajibade (2014), CdS/HgS is an inorganic (semiconductor)/Inorganic (semiconductor) Core/Shell formed through precipitation.
As per Chaudhuri and Paria (2012), some of the characteri...