Synthesis and thermoelectric application of conductive polymer capped silicon nanoparticles and composites

A solution reduction synthesis method has been used to produce organic ligand capped silicon nanoparticles in a large scale, and with electrochemical etching method in comparison. Nanoparticles produced are explored in a variety of aspects, including particle size, elemental composition, thermal stability and optical property. These results are used to determine how different ligands could affect the silicon core and the thermoelectric performance. Polymerisation of thiophene is studied to produce two types of oligomer capped nanoparticles, with the difference that whether the polymerisation happens before or after ligand capping. The order of reactions has an effect on the nanoparticle surface coverage of ligands, which influences other properties such as solubility and thermal stability. Two types of polymer-capped SiNPs are applied in thermoelectric use via different paths. A terthiophene capped sample was prepared by cold press and work in room temperature (25 °C). The product is suitable for wearable device application due to its flexibility even after doping. The other polymer capped sample is prepared by SPS with doping of graphene, and is aiming for high temperature (500 °C) applications. Muon spin spectroscopy is involved during my research as a side project to study the microscopic conductivity between silicon nanoparticles with conductive ligand (phenylacetylene) as bridge. Both SiNPs and model molecule [tetrakis (2-phenylethynyl) silane] are studied using TF - μSR and ALC - μSR along with DFT calculation as theoretical support

Hybrid silicon nanostructures with conductive ligands and their microscopic conductivities

Silicon nanoparticles (SiNPs) functionalized with conjugated molecules promise a potential pathway to generate a new category of thermoelectric materials. While the thermoelectric performance of materials based on phenyl-acetylene capped SiNPs has been proven, their low conductivity is still a problem for their general application. A muon study of phenyl-acetylene capped SiNPs has been recently carried out using the HiFi spectrometer at the Rutherford Appleton Laboratory, measuring the ALC spectra as a function of temperature. The results show a reduction in the measured line width of the resonance above room temperature, suggesting an activated behaviour for this system. This study shows that the muon study could be a powerful method to investigate microscopic conductivity of hybrid thermoelectric materials

A Muon Spectroscopic and Computational Study of the Microscopic Electronic Structure in Thermoelectric Hybrid Silicon Nanostructures

Phenylacetylene-capped silicon nanoparticles (Phenyl-SiNPs) have attracted interest as a novel thermoelectric material. Here, we report a combined muon spectroscopic (μSR) and computational study of this material in solution to investigate the microscopic electronic structure of this system. For comparison, the model molecular compound tetrakis(2-phenylethynyl)silane has also been investigated. μSR measurements have shown that the muon isotropic hyperfine coupling constant, A μ, which depends on spin density at the muon, is greatly reduced for the Phenyl-SiNPs system when compared to the model compound. Results have also demonstrated that the temperature dependence of A μ for the Phenyl-SiNPs is of opposite sign and proportionally larger when compared to the model compound. Ab initio DFT methods have allowed us to determine the muon addition site in the model compound, while a wider computational study using both DFTB+ and CASTEP offers a qualitative explanation for the reduced coupling seen in the Phenyl-SiNPs system and also the contrasting temperature dependence of A μ for the two materials. Calculations suggest an increase in the density of electronic states at the energy level of the highest occupied molecular state for the Phenyl-SiNPs, even in the presence of an organic cap, suggesting a mechanism for enhanced electron transport in this system when compared to the tetrakis model compound

Emission and theoretical studies of Schiff-base [2+2] macrocycles derived from 2,2′-oxydianiline and zinc complexes thereof

The emission properties of a number of solvates of the [2 + 2] Schiff-base macrocycles {[2-(OH)-5-(R)–C 6H 2–1,3-(CH) 2][O(2-C 6H 4N) 2]} 2 (Me L 1H 2, tBu L 2H 2, Cl L 3H 2), formed by reacting 2,6-dicarboxy-4-R-phenol with 2,2′-oxydianiline (2-aminophenylether), (2-NH 2C 6H 4) 2O, have been investigated. Macrocycles L 1−3H 2 exhibited different maximum emission wavelengths in different solvents, from λ max at 508 nm (in acetonitrile) to 585 nm (in dichloromethane). DFT studies on systems L 1−3H 2 involving solvents of different polarity (DMF versus n-hexane) indicated that the energy level gap increases with solvent polarity in line with the observed hypochromic shifts. Reaction of macrocycle L 1H 2 with three equivalents of ZnBr 2, in the presence of Et 3N, affords the complex [(ZnBr)(ZnNCMe)L 1] 2[ZnBr 4]·2.5MeCN (1·2.5MeCN). In the case of L 2H 2, reaction with two equivalents of ZnBr 2 affords [(ZnBr)L 2H 2][ZnBr 3NCMe]·3MeCN (2·3MeCN), whilst in the presence of two equivalents of Et 3N, work-up led to the isolation of the complex [(ZnBr) 2L 2]·4.5MeCN (3·4.5MeCN). The molecular structures of 1, 2 and 3 are reported, together with their emission behaviour