Super Strong Wide TM Mie Bandgaps Tolerating Disorders

This study demonstrates the appearance of super intense and wide Mie bandgaps in metamaterials composed of germanium rods in air that tolerate some disordering of rod position and rod radius under transverse magnetic (TM) polarized light waves. Results for Mie bandgap modes TM01 and TM11 tolerate rod-position disordering of 50%, and rod-radius disordering of 34 and 20%, respectively. Using these characteristics of TM11 under position and radius disordering, ultra-narrow straight, L-shaped and crossing waveguides that contain 14, four, and two rows of Ge rods in air are designed. Also, it is shown that TE01 Mie bandgap appear in metamaterials contain high refractive index, and disappear in metamaterials with lower refractive index such as silicon; in contrast, a new phenomenon of intense and broadband TM01, TM11, and TM21 in metamaterials with lower refractive index such as silicon appear. Also, in Si-based metamaterials, TM01 tolerates high rod-position and rod-radius disordering of 50% and 34%, respectively, and TM11 shows robustness to rod-position and rod-radius of 20%. This strong tolerance of disordering of TM modes in silicon and germanium metamaterials opens a new way to design small, high-efficient, and easy-fabricable optical devices for optical integrated circuits.

Electrochemical Synthesis of Unique Nanomaterials in Ionic Liquids

The review considers the features of the processes of the electrochemical synthesis of nanostructures in ionic liquids (ILs), including the production of carbon nanomaterials, silicon and germanium nanoparticles, metallic nanoparticles, nanomaterials and surface nanostructures based on oxides. In addition, the analysis of works on the synthesis of nanoscale polymer films of conductive polymers prepared using ionic liquids by electrochemical methods is given. The purpose of the review is to dwell upon an aspect of the applicability of ILs that is usually not fully reflected in modern literature, the synthesis of nanostructures (including unique ones that cannot be obtained in other electrolytes). The current underestimation of ILs as an electrochemical medium for the synthesis of nanomaterials may limit our understanding and the scope of their potential application. Another purpose of our review is to expand their possible application and to show the relative simplicity of the experimental part of the work.

Synthesis, Surface Modification and Purification of Silicon and Germanium Quantum Dots for Biological Applications

<p>Quantum dots have applications in biomedical fields such as bio-imaging and drug delivery systems. This thesis describes research on silicon and germanium nanoparticles (quantum dots) synthesis and surface modification for biological applications. Purification methods of these quantum dots were also explored. In chapter 6 the application of silica nanoparticles into dry eye diagnosis was studied. The purpose of this research is to contribute the application of nanotechnology into biological fields. The crystalinity of the quantum dots was characterised by Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction analysis (SAED). The molecules on the surface of the quantum dots were characterised by Fourier Transform Infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR). Silicon quantum dots were synthesised with a microemulsion system and various types of molecules were attached on the surface of the silicon quantum dots. However, some of the capping molecules which have oxygen atoms tend to form bonds between oxygen and silicon. Therefore, in the later chapter (chapter 4) various chemical reactions were conducted on the molecules attached to the silicon quantum dots. The silicon quantum dots were capped with diene molecules and one of the double bonds was left on the terminal end. The terminal end double bonds were converted to the functional groups which contain oxygen atoms to form peptide bonds. In this way it was confirmed that it can reduce the risk of oxygen atoms to be attached on the surface of the silicon quantum dots. The molecules on the surface of the silicon quantum dots were characterised mainly by FTIR and ¹H NMR. Optical properties and cyto-toxicity of these silicon quantum dots were also measured and analysed depending on the surface molecules. Two synthetic approaches were taken to produce germanium quantum dots. The first approach was the microemulsion system at room temperature. Different combinations of the surfactant and capping molecules were tested. For the second approach, high temperature bench top system was applied. In this method the bio-friendly molecules which have high boiling points were chosen as capping agents. The surface molecules were characterised by FTIR spectroscopy. In chapter 6 the synthesis of dye molecules conjugated silica nanoparticles was described. The purpose of this research is to produce biologically safe nanoparticles which can be applied in dry eye diagnosis. Three different dyes were used to conjugate with the silica nanoparticles. Only fluorescein isothiocyanate (FITC) succeeded in conjugating with the nanoparticles. Optical properties of this sample were measured and compared with the free dye molecule. Also the sample was applied in human eyes to analyse the tear film layer. An overall conclusion and future plans for the research were given in the last chapter.In this chapter, ideas of overcoming the problems and improving the techniques conducted in the research were described.</p>

Synthesis and Characterization of Silicon and Germanium Nanocrystals and Titanium Disulphide Nanostructures

<p>This thesis is concerned with the synthesis and characterization of nanostructured materials in the solution, in particular silicon and germanium nanocrystals, their applica-tion as fluorescent whitening agents and titanium disulphide nanostructures. The aim of this research with regards to the synthesis of silicon and germanium nanocrystals was to obtain size control and provide functionality using simple room temperature solution techniques. In the case of the nanostructures of titanium disulphide, the focus was to synthesize in the colloid using simple one-pot bench top techniques. The above were realized with chemical techniques in the solution using organic solvents and surfactants to control their size. The morphology, chemical composition and crystal structure of the synthesized nanomaterials were characterized using techniques such as High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction (SAED), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectrosco-py (EDX) and Optical Spectroscopies. Whilst chapter one is a brief introduction of the thesis, chapter two talks in detail about the various characterization techniques used in this research. Chapter three of the thesis focuses on the synthesis of alkyl- and amine-functionalized silicon nanocrystals using a microemlusion technique. The effect of reducing agents, surfactants and precursors on particle size was studied. The surfactant C12E5 was found to be very effective in producing silicon nanocrystals that were freestanding and pure. Whilst the hydride reducing agents lithium aluminium hydride and lithium tri-ethyl borohydride were found to be effective in synthesizing nanocrystals of narrow size distribution, it was found that using silicon tetrachloride yielded smaller particles compared to silicon tetrabromide. The fourth chapter in the theses is concerned with the synthesis and characterization of germanium nanocrystals by both microemulsion and high temperature techniques. Using lithium aluminium hydride; a strong reducing agent, very small nanocrystals were obtained, whilst weaker reductants such as sodium borohydride produced larger nano-crystals. Another effective method to control the particle size of germanium nanocrystals was found to be by varying the concentration of precursor. The germanium nanocrystals which were amine capped were found to luminesce in the blue and were used to image HePG2 cells. Toxicity studies on these nanocrystals proved their relative non-toxicity. The high temperature experiments, though not as flexible as the room temperature syntheses were found to facilitate a certain degree of size control. Chapter five of the theses deal with the application of silicon and germanium nanocrys-tals as fluorescent whitening agents in wool fabrics. Both nanocrystals, when applied to the fabric were found to emit matching blue fluorescence that was demonstrated to be more suited to improving the brightness properties of fabric than the commercial fluo-rescing whitening agent Uvitex. In particular Silicon-amine and Silicon-hexene functionalized nanocrystal (low concentration) treated fabrics were found to have improved color stability against both UVA and UVB radiation. The treated fabrics were in addition found to maintain a stable color than untreated fabric. Silicon-amine treated fabrics were found to have a stable color even after 48h exposures to UVA radiation. It should be noted that this is the first evidence of the application of group IV semiconductor nanocrystals as fluorescing whitening agents. The sixth chapter of this thesis deals with the one-pot synthesis of titanium disulphide nanostructures using both coordinating and non-coordinating solvents and their subse-quent characterization. By varying the injection temperature of the titanium source into the 1-Octadecene sulphur solution, two different morphologies were synthesized. Two different pathways were suggested for the formation of the flower-like and flake-like morphologies; an instant nucleation to form titanium disulphide flakes whilst spherical nuclei to form flower-like nanostructures. The flower-like nanostructures were found to have higher BET surface area compared to the flake-like nanostructures and previously reported surface areas for analogous TiS₂ nanostructures. Whilst using oleylamine as solvent, the low temperature injection yielded hollow spheres of TiS₂ and the high temperature injection, fullerene-like nanoparticles of TiS₂. The property of oleylamine to selectively bind to the nanostructure surface in conjunction with the effect of injection temperature was understood to be behind the growth of these nanostructures. The synthesis of flower-like and flake-like morphologies by solution phase techniques were the first evidence of this kind for titanium disulphide and provides a new and exciting material for a variety of applications. A final chapter on conclusions and recommendations for future work is then presented.</p>

Synthesis, Surface Modification and Purification of Silicon and Germanium Quantum Dots for Biological Applications

<p>Quantum dots have applications in biomedical fields such as bio-imaging and drug delivery systems. This thesis describes research on silicon and germanium nanoparticles (quantum dots) synthesis and surface modification for biological applications. Purification methods of these quantum dots were also explored. In chapter 6 the application of silica nanoparticles into dry eye diagnosis was studied. The purpose of this research is to contribute the application of nanotechnology into biological fields. The crystalinity of the quantum dots was characterised by Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction analysis (SAED). The molecules on the surface of the quantum dots were characterised by Fourier Transform Infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR). Silicon quantum dots were synthesised with a microemulsion system and various types of molecules were attached on the surface of the silicon quantum dots. However, some of the capping molecules which have oxygen atoms tend to form bonds between oxygen and silicon. Therefore, in the later chapter (chapter 4) various chemical reactions were conducted on the molecules attached to the silicon quantum dots. The silicon quantum dots were capped with diene molecules and one of the double bonds was left on the terminal end. The terminal end double bonds were converted to the functional groups which contain oxygen atoms to form peptide bonds. In this way it was confirmed that it can reduce the risk of oxygen atoms to be attached on the surface of the silicon quantum dots. The molecules on the surface of the silicon quantum dots were characterised mainly by FTIR and ¹H NMR. Optical properties and cyto-toxicity of these silicon quantum dots were also measured and analysed depending on the surface molecules. Two synthetic approaches were taken to produce germanium quantum dots. The first approach was the microemulsion system at room temperature. Different combinations of the surfactant and capping molecules were tested. For the second approach, high temperature bench top system was applied. In this method the bio-friendly molecules which have high boiling points were chosen as capping agents. The surface molecules were characterised by FTIR spectroscopy. In chapter 6 the synthesis of dye molecules conjugated silica nanoparticles was described. The purpose of this research is to produce biologically safe nanoparticles which can be applied in dry eye diagnosis. Three different dyes were used to conjugate with the silica nanoparticles. Only fluorescein isothiocyanate (FITC) succeeded in conjugating with the nanoparticles. Optical properties of this sample were measured and compared with the free dye molecule. Also the sample was applied in human eyes to analyse the tear film layer. An overall conclusion and future plans for the research were given in the last chapter.In this chapter, ideas of overcoming the problems and improving the techniques conducted in the research were described.</p>

Synthesis and Characterization of Silicon and Germanium Nanocrystals and Titanium Disulphide Nanostructures

<p>This thesis is concerned with the synthesis and characterization of nanostructured materials in the solution, in particular silicon and germanium nanocrystals, their applica-tion as fluorescent whitening agents and titanium disulphide nanostructures. The aim of this research with regards to the synthesis of silicon and germanium nanocrystals was to obtain size control and provide functionality using simple room temperature solution techniques. In the case of the nanostructures of titanium disulphide, the focus was to synthesize in the colloid using simple one-pot bench top techniques. The above were realized with chemical techniques in the solution using organic solvents and surfactants to control their size. The morphology, chemical composition and crystal structure of the synthesized nanomaterials were characterized using techniques such as High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction (SAED), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectrosco-py (EDX) and Optical Spectroscopies. Whilst chapter one is a brief introduction of the thesis, chapter two talks in detail about the various characterization techniques used in this research. Chapter three of the thesis focuses on the synthesis of alkyl- and amine-functionalized silicon nanocrystals using a microemlusion technique. The effect of reducing agents, surfactants and precursors on particle size was studied. The surfactant C12E5 was found to be very effective in producing silicon nanocrystals that were freestanding and pure. Whilst the hydride reducing agents lithium aluminium hydride and lithium tri-ethyl borohydride were found to be effective in synthesizing nanocrystals of narrow size distribution, it was found that using silicon tetrachloride yielded smaller particles compared to silicon tetrabromide. The fourth chapter in the theses is concerned with the synthesis and characterization of germanium nanocrystals by both microemulsion and high temperature techniques. Using lithium aluminium hydride; a strong reducing agent, very small nanocrystals were obtained, whilst weaker reductants such as sodium borohydride produced larger nano-crystals. Another effective method to control the particle size of germanium nanocrystals was found to be by varying the concentration of precursor. The germanium nanocrystals which were amine capped were found to luminesce in the blue and were used to image HePG2 cells. Toxicity studies on these nanocrystals proved their relative non-toxicity. The high temperature experiments, though not as flexible as the room temperature syntheses were found to facilitate a certain degree of size control. Chapter five of the theses deal with the application of silicon and germanium nanocrys-tals as fluorescent whitening agents in wool fabrics. Both nanocrystals, when applied to the fabric were found to emit matching blue fluorescence that was demonstrated to be more suited to improving the brightness properties of fabric than the commercial fluo-rescing whitening agent Uvitex. In particular Silicon-amine and Silicon-hexene functionalized nanocrystal (low concentration) treated fabrics were found to have improved color stability against both UVA and UVB radiation. The treated fabrics were in addition found to maintain a stable color than untreated fabric. Silicon-amine treated fabrics were found to have a stable color even after 48h exposures to UVA radiation. It should be noted that this is the first evidence of the application of group IV semiconductor nanocrystals as fluorescing whitening agents. The sixth chapter of this thesis deals with the one-pot synthesis of titanium disulphide nanostructures using both coordinating and non-coordinating solvents and their subse-quent characterization. By varying the injection temperature of the titanium source into the 1-Octadecene sulphur solution, two different morphologies were synthesized. Two different pathways were suggested for the formation of the flower-like and flake-like morphologies; an instant nucleation to form titanium disulphide flakes whilst spherical nuclei to form flower-like nanostructures. The flower-like nanostructures were found to have higher BET surface area compared to the flake-like nanostructures and previously reported surface areas for analogous TiS₂ nanostructures. Whilst using oleylamine as solvent, the low temperature injection yielded hollow spheres of TiS₂ and the high temperature injection, fullerene-like nanoparticles of TiS₂. The property of oleylamine to selectively bind to the nanostructure surface in conjunction with the effect of injection temperature was understood to be behind the growth of these nanostructures. The synthesis of flower-like and flake-like morphologies by solution phase techniques were the first evidence of this kind for titanium disulphide and provides a new and exciting material for a variety of applications. A final chapter on conclusions and recommendations for future work is then presented.</p>

Non-covalent interactions of Cysteine onto C60, C59Si, and C59Ge: A DFT study

The study of intermolecular interactions is of great importance. This study attempted to quantitatively examine the interactions between Cysteine (C3H7NO2S) and fullerene nanocages, C60, in a vacuum. As the frequent introduction of elements as impurities into the structure of nanomaterials can increase the intensity of intermolecular interactions, nanocages doped with silicon and germanium have also been studied as adsorbents C59Si and C59Ge. Quantum mechanical studies of such systems are possible in the density functional theory (DFT) framework. For this purpose, various functionals, such as B3LYP-D3, ωB97XD, and M062X, have been used. One of the most suitable basis functionals for the systems studied in this research is 6-311G (d), which has been used in both optimization calculations and calculations related to wave function analyses. The main part of this work is the study of various analyses that reveal the nature of the intermolecular interactions between the two components introduced above. The results of conceptual DFT, natural bond orbital, non-covalent interactions, and quantum theory of atoms in molecules were consistent and favored physical adsorption in all systems. Germanium had more adsorption energy than other dopants. The HOMO–LUMO energy gaps were as follows: C60: 5.996, C59Si: 5.309, and C59Ge: 5.188 eV at B3LYP-D3/6-311G (d) model chemistry. The adsorption sensitivity increased when an amino acid molecule interacted with doped C60, and this capability could be used to design a nanocarrier to detect Cysteine amino acids.

Plasmon Coupling - The Root Cause of Raman Anomaly and Laser Cooling in Nanocrystal Ge

Laser cooling of matter through anti-Stokes photoluminescence, where the emitted frequency of light exceeds that of the impinging laser by virtue of absorption of thermal vibrational energy, has been successfully realized in condensed media, and in particular with rare earth doped systems achieving sub-100K solid state optical refrigeration. Studies suggest that laser cooling in semiconductors has the potential of achieving temperatures down to ~10K and that its direct integration can usher unique high-performance nanostructured semiconductor devices. While laser cooling of nanostructured II-VI semiconductors has been reported recently, laser cooling of indirect bandgap semiconductors such as group IV silicon and germanium remains a major challenge. Here we report on the anomalous observation of dominant anti-Stokes photoluminescence in germanium nanocrystals principally associated with plasmon coupling. Specifically, we attribute this Raman anomaly to the confluence of ultra-high purity nanocrystal germanium, generation of high density of electron-hole plasma, the inherent degeneracy of longitudinal and transverse optical phonons in non-polar indirect bandgap semiconductors, and commensurate spatial confinement effects. At high laser intensities, plasmon-assisted laser cooling with lattice temperature as low as ~50K is inferred.