ABSTRACT The production of nanostructured bulk materials from silicon powders has been well docum... more ABSTRACT The production of nanostructured bulk materials from silicon powders has been well documented as being one way of bringing down the thermal conductivity of silicon while still maintaining its high power factor. This reduction of thermal conductivity is predicted to lead to significant increases in its figure-of-merit, ZT. The size of the starting particles has a major effect on the nanostructuring and grain size of the final silicon-based materials. Using particles of differing size and distribution, pellets were produced using spark plasma sintering. The results show a significant lowering in the thermal diffusivity as the particle size in the powders is decreased. As the starting particle size deceases from 1 μm to 60 nm, we see a tenfold decrease in the thermal diffusivity at 300 K, from 20 mm2 S−1 to 2 mm2 S−1. Both these show a significant decrease from the thermal diffusivity of 88 mm2 S−1 observed from bulk silicon. A further decrease to 1 mm2 S−1 is observed when the particle size of the starting material is decreased from 60 nm to sub-10 nm. The results also highlight the potential of using particles from solution approaches as a potential starting point for the prediction of nanostructured bulk materials.
ABSTRACT Of ever growing interest in the fields of physical chemistry and materials science, sili... more ABSTRACT Of ever growing interest in the fields of physical chemistry and materials science, silicon nanoparticles show a great deal of potential. Methods for their synthesis are, however, often hazardous, expensive or otherwise impractical. In the literature, there is a safe, fast and cheap inverse micelle-based method for the production of alkyl-functionalized blue luminescent silicon nanoparticles, which nonetheless found limitations, due to undesirable Si-alkoxy and remaining Si-H functionalization. In the following work, these problems are addressed, whereby an optimisation of the reaction mechanism encourages more desirable capping, and the introduction of alcohol is replaced by the use of anhydrous copper (II) chloride. The resulting particles, when compared with their predecessors through a myriad of spectroscopic techniques, are shown to have greatly reduced levels of ‘undesirable’ capping, with a much lower surface oxide level; whilst also maintaining long-term air stability, strong photoluminescence and high yields.
Thin films made up of arrays of amine-terminated silicon nanoparticles (NH2-SiNPs) synthesized by... more Thin films made up of arrays of amine-terminated silicon nanoparticles (NH2-SiNPs) synthesized by a new evaporation technique have been formed by employing TEM grids as nanostencils. FTIR imaging illustrates the feasibility of the method in nanoscale device fabrication applications. Micro-mapping over areas of the nanoparticle material allows the surface chemistry to be examined. FTIR imaging shows trace amounts of oxide confined to the NP surfaces. Thicker films formed by dropcasting allowed the nanoparticle behaviour to be studied under conditions of extended exposure to 150 eV photons radiation by X-ray photoelectron spectroscopy (XPS). The XPS spectrum was monitored over the Si2p region and the initial peak at 100.53 eV was observed to shift to higher binding energies as irradiation progressed which is indicative of charge trapping within the film. This result has potential consequences for applications where NH2-SiNPs are used in X-ray environments such as in bioimaging where the increasing charge buildup is related to enhanced cytotoxicity.
X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy have been used to study ... more X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy have been used to study the makeup of thin films of 6.5 nm diameter dodecyl-capped silicon nanoparticles (SiNPs) formed in a one-pot synthesis method of micelle reduction. Thermostability measurements show the SiNPs undergo thermal desorption at ∼240 °C, a higher temperature than for SiNPs capped by shorter hydrocarbon layers owing to the
ABSTRACT Silicon is a highly attractive material for the fabrication of thermoelectric materials.... more ABSTRACT Silicon is a highly attractive material for the fabrication of thermoelectric materials. Nanostructured silicon materials, such as silicon nanowires (SiNWs), show great potential as they show low thermal conductivities due to efficient phonon scattering but similar electrical conductivities to bulk silicon. Silicon nanoparticles (SiNPs) are easier to synthesize and show a greater number of surface defects, which suggests that more efficient phonon scattering can be achieved, but these materials also show low electrical conductivity due to defects within the materials unless pressed at high temperatures (1100°C). Conjugated capping layers show the potential to bridge these defects, giving higher conductivity without the need for this process. Phenylacetylene-capped SiNPs are synthesized via the micelle reduction method and pressed into a pellet. Measurements of the electrical conductivity, Seebeck coefficient, and thermal conductivity were taken. The results show that the material produced from these particles shows a relatively high Seebeck coefficient (3228.84 μV K−1) which would have a positive effect on the figure of merit (ZT). A respectable electrical conductivity (18.1 S m−1) and a low thermal conductivity (0.1 W m−1 K−1) confirm the potential of using conjugated molecules as a way of cross-linking between nanoparticles in a bulk material fabricated from SiNPs. These results give a figure of merit of 0.57, which is comparable to better established thermoelectric materials.
ABSTRACT Silicon is an attractive material for the fabrication of thermoelectric materials. Previ... more ABSTRACT Silicon is an attractive material for the fabrication of thermoelectric materials. Previously, it was reported that phenylacetylene capped silicon nanoparticles (PA-SiNPs), which were synthesized from micelle reduction, displayed a ZT of up to 0.6 at ambient temperature. The major contributing factor to this result was the material’s low thermal conductivity. However, this material also displayed a low electrical conductivity compared to other thermoelectric materials. This is contributed to, in part, by low charge carrier concentration, which is difficult to control in micelle reduction-based methods. Top–down methods allow control of the carrier concentration as the material is doped prior to the breaking down of the material. PA-SiNPs were synthesized using electrochemical etching followed by functionalization. These particles were then analyzed with transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, thermo-gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The DSC and TGA trace were compared to those of PA-SiNPs synthesized by micelle reduction to show that the thermal stability range is much higher in the particles synthesized from the top–down method giving them a wider range of potential thermoelectric applications.
Two hexanuclear zinc complexes have been structurally characterized, and evaluation against sever... more Two hexanuclear zinc complexes have been structurally characterized, and evaluation against several cells showed selective toxicity. Cellular uptake revealed a non-specific process, resulting in accumulation within the cell cytoplasm.
ABSTRACT The production of nanostructured bulk materials from silicon powders has been well docum... more ABSTRACT The production of nanostructured bulk materials from silicon powders has been well documented as being one way of bringing down the thermal conductivity of silicon while still maintaining its high power factor. This reduction of thermal conductivity is predicted to lead to significant increases in its figure-of-merit, ZT. The size of the starting particles has a major effect on the nanostructuring and grain size of the final silicon-based materials. Using particles of differing size and distribution, pellets were produced using spark plasma sintering. The results show a significant lowering in the thermal diffusivity as the particle size in the powders is decreased. As the starting particle size deceases from 1 μm to 60 nm, we see a tenfold decrease in the thermal diffusivity at 300 K, from 20 mm2 S−1 to 2 mm2 S−1. Both these show a significant decrease from the thermal diffusivity of 88 mm2 S−1 observed from bulk silicon. A further decrease to 1 mm2 S−1 is observed when the particle size of the starting material is decreased from 60 nm to sub-10 nm. The results also highlight the potential of using particles from solution approaches as a potential starting point for the prediction of nanostructured bulk materials.
ABSTRACT Of ever growing interest in the fields of physical chemistry and materials science, sili... more ABSTRACT Of ever growing interest in the fields of physical chemistry and materials science, silicon nanoparticles show a great deal of potential. Methods for their synthesis are, however, often hazardous, expensive or otherwise impractical. In the literature, there is a safe, fast and cheap inverse micelle-based method for the production of alkyl-functionalized blue luminescent silicon nanoparticles, which nonetheless found limitations, due to undesirable Si-alkoxy and remaining Si-H functionalization. In the following work, these problems are addressed, whereby an optimisation of the reaction mechanism encourages more desirable capping, and the introduction of alcohol is replaced by the use of anhydrous copper (II) chloride. The resulting particles, when compared with their predecessors through a myriad of spectroscopic techniques, are shown to have greatly reduced levels of ‘undesirable’ capping, with a much lower surface oxide level; whilst also maintaining long-term air stability, strong photoluminescence and high yields.
Thin films made up of arrays of amine-terminated silicon nanoparticles (NH2-SiNPs) synthesized by... more Thin films made up of arrays of amine-terminated silicon nanoparticles (NH2-SiNPs) synthesized by a new evaporation technique have been formed by employing TEM grids as nanostencils. FTIR imaging illustrates the feasibility of the method in nanoscale device fabrication applications. Micro-mapping over areas of the nanoparticle material allows the surface chemistry to be examined. FTIR imaging shows trace amounts of oxide confined to the NP surfaces. Thicker films formed by dropcasting allowed the nanoparticle behaviour to be studied under conditions of extended exposure to 150 eV photons radiation by X-ray photoelectron spectroscopy (XPS). The XPS spectrum was monitored over the Si2p region and the initial peak at 100.53 eV was observed to shift to higher binding energies as irradiation progressed which is indicative of charge trapping within the film. This result has potential consequences for applications where NH2-SiNPs are used in X-ray environments such as in bioimaging where the increasing charge buildup is related to enhanced cytotoxicity.
X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy have been used to study ... more X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy have been used to study the makeup of thin films of 6.5 nm diameter dodecyl-capped silicon nanoparticles (SiNPs) formed in a one-pot synthesis method of micelle reduction. Thermostability measurements show the SiNPs undergo thermal desorption at ∼240 °C, a higher temperature than for SiNPs capped by shorter hydrocarbon layers owing to the
ABSTRACT Silicon is a highly attractive material for the fabrication of thermoelectric materials.... more ABSTRACT Silicon is a highly attractive material for the fabrication of thermoelectric materials. Nanostructured silicon materials, such as silicon nanowires (SiNWs), show great potential as they show low thermal conductivities due to efficient phonon scattering but similar electrical conductivities to bulk silicon. Silicon nanoparticles (SiNPs) are easier to synthesize and show a greater number of surface defects, which suggests that more efficient phonon scattering can be achieved, but these materials also show low electrical conductivity due to defects within the materials unless pressed at high temperatures (1100°C). Conjugated capping layers show the potential to bridge these defects, giving higher conductivity without the need for this process. Phenylacetylene-capped SiNPs are synthesized via the micelle reduction method and pressed into a pellet. Measurements of the electrical conductivity, Seebeck coefficient, and thermal conductivity were taken. The results show that the material produced from these particles shows a relatively high Seebeck coefficient (3228.84 μV K−1) which would have a positive effect on the figure of merit (ZT). A respectable electrical conductivity (18.1 S m−1) and a low thermal conductivity (0.1 W m−1 K−1) confirm the potential of using conjugated molecules as a way of cross-linking between nanoparticles in a bulk material fabricated from SiNPs. These results give a figure of merit of 0.57, which is comparable to better established thermoelectric materials.
ABSTRACT Silicon is an attractive material for the fabrication of thermoelectric materials. Previ... more ABSTRACT Silicon is an attractive material for the fabrication of thermoelectric materials. Previously, it was reported that phenylacetylene capped silicon nanoparticles (PA-SiNPs), which were synthesized from micelle reduction, displayed a ZT of up to 0.6 at ambient temperature. The major contributing factor to this result was the material’s low thermal conductivity. However, this material also displayed a low electrical conductivity compared to other thermoelectric materials. This is contributed to, in part, by low charge carrier concentration, which is difficult to control in micelle reduction-based methods. Top–down methods allow control of the carrier concentration as the material is doped prior to the breaking down of the material. PA-SiNPs were synthesized using electrochemical etching followed by functionalization. These particles were then analyzed with transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, thermo-gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The DSC and TGA trace were compared to those of PA-SiNPs synthesized by micelle reduction to show that the thermal stability range is much higher in the particles synthesized from the top–down method giving them a wider range of potential thermoelectric applications.
Two hexanuclear zinc complexes have been structurally characterized, and evaluation against sever... more Two hexanuclear zinc complexes have been structurally characterized, and evaluation against several cells showed selective toxicity. Cellular uptake revealed a non-specific process, resulting in accumulation within the cell cytoplasm.
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