As semiconductor device scaling is reaching the 45 nm node, the need for novel device concept, architecture and new materials has never been so pressing as today. Flash memories, the driving force of semiconductor memory market in recent years, also face the same or maybe more severe challenges to meet the demands for high-density, low-cost, low-power, high-speed, better endurance and longer retention time. As traditional continuous floating gate flash struggles to balance the trade-off between high speed and retention requirement, nanocrystal (NC) floating gate flash has attracted more and more interest recently due to its advantages over traditional flash memories in many areas such as better device scaling, lower power consumption and improved charge retention. However, there are still two major challenges remaining for embedded NC synthesis: the deposition method and the size and distribution control. Nowadays using bio-nano techniques such as DNA, virus or protein for NC synthesis and assembly has become a hot topic and feasible for actual electronic device fabrication. In this dissertation a new method for NC deposition wherein a colloidal suspension of commercially-available NCs was organized using a self-assembled chaperonin array. The chaperonin array was applied as a scaffold to mediate NCs into an assembly with uniform spatial distribution on Si wafers. By using this method, we demonstrated that colloidal PbSe and Co NCs in suspension can self-assemble into ordered arrays with a high density of up to 10¹²cm⁻². MOSCAP and MOSFET memory devices were successfully fabricated with the chaperonin protein mediated NCs, showing promising memory functions such as a large charge storage capacity, long retention time and good endurance. The charge storage capacity with respect to material work function, NC size and density was explored. In addition to NC engineering, the tunnel barrier was engineered by replacing traditional SiO₂ by high-k material HfO₂, giving a higher write/erase speed with a reduced effective oxide thickness (EOT). Suggestions for future research in this direction are presented in the last part of this work. / text

Silicon nanocrystals (NCs), especially Si NCs embedded in SiO₂, have been studied intensely for decades for their potential application in silicon photonics, especially as efficient room temperature light emitters. Despite progress in fabricating photonic devices from Si NCs, the origin of the efficient photoluminescence (PL), the electronic and microscopic structure of the nanocrystals, and the structure of the elusive NC/SiO₂ interfaces for the oxide-embedded nanocrystals, remain controversial. Optical spectroscopy provides a powerful noninvasive tool for probing the structure of the Si NCs, including the active buried NC/SiO₂ interfaces of embedded particles. In this thesis work, oxide-embedded and free-standing alkyl-passivated silicon nanocrystals, prepared by different techniques, have been studied by linear and nonlinear optical spectroscopies. Cross-polarized 2-beam second-harmonic and sum-frequency generation (XP2-SHG/SFG) has been applied spectroscopically to study oxide embedded Si NCs of different sizes (3 to 5 nm diameter) and interface chemistries. The SHG/SFG spectra of silicon nanocrystals (Si NCs) prepared by implanting Si ions uniformly into silica substrates, then annealing, are compared and contrasted to their spectroscopic ellipsometric (SE) and photoluminescence excitation (PLE) spectra. Three resonances--two close in energy to E₁ (3.4 eV) and E2 (4.27 eV) critical-point resonances of crystalline silicon (c-Si), and a broad resonance intermediate in energy between E₁ and E₂--are observed in all three types of spectra. These features are observed in conjunction with a sharp 520 cm⁻¹ Raman peak characteristic of c-Si and an a-Si tail in the Raman spectra. The appearance of bulk-like CP resonances in the parallel PLE, SE and SHG/SFG spectra from Si NCs suggests the basic electronic structure of the bulk c-Si is preserved in nano-particles as small as 3 nm in diameter, albeit with significant size-dependent modification. At the same time, the prominence of a non-bulk-like resonance intermediate in energy between E₁ and E₂ CPs in all three types of spectra demonstrates the important contribution of nano-interfaces to the electronic structure.We also applied Raman spectroscopy to study oxide-embedded and oxide-free alkyl-passivated Si NCs with diameters ranging from 3 nm to greater than 10 nm synthesized by thermal decomposition of hydrogen silsesquioxane (HSQ). While oxide matrix complicates the size-dependence of the Raman peak shift for oxide-embedded nanocrystals, the Raman peak of the free-standing alkyl-passivated Si NCs shifts monotonically with NC size. / text

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Using a novel two-beam technique developed to greatly enhance quadrupolar contributions to the second-order nonlinear polarization, we performed a nonlinear spectroscopic study of silicon nanocrystals implanted in an SiO₂ matrix.

Mainstream non-volatile memory technology dominated by the planar Flash transistor with continuous floating-gate has been historically improved in density and performance primarily by means of process scaling, but is currently faced with significant hindrances to its future scaling due to fundamental constraints of electrostatics and reliability. This dissertation is based on exploring two pathways for circumventing scaling limitations of the state-of-the-art Flash memory technology. The first part of the dissertation is based on demonstrating a vertical Flash memory transistor with nanocrystal floating-gate, while the second part is based on developing fundamental understanding of the operation of Phase Change Memory. A vertical Flash transistor can allow the theoretical minimum cell area and a nanocrystal floating-gate on the sidewalls is shown to allow a thinner gate-stack further conducive to scaling while still providing good reliability. Subsequently, the application of a technique of protein-mediated assembly of preformed nanocrystals to the sidewalls of the vertical Flash transistor is also demonstrated and characterized. This technique of ordering pre-formed nanocrystals is beneficial towards achieving reproducible nanocrystal size uniformity and ordering especially in a highly scaled vertical Flash cell, rendering it more amenable to scaling and manufacturability. In both forms, the vertical Flash memory cell is shown to have good electrical characteristics and reliability for the viability of this cell design and implementation. In the remaining part of this dissertation, studies are undertaken towards developing fundamental understanding of the operational characteristics of Phase Change Memory (PCM) technology that is expected to replace floating-gate Flash technology based on its potential for scaling. First, a phenomenon of improving figures of merit of the PCM cell with operational cycles is electrically characterized. Based on the electrical characterization and published material characterization data, a physical model of an evolving "active region" of the cell is proposed to explain the improvement of the cell parameters with operational cycles. Then, basic understanding is developed on early and erratic retention failure in a statistically significant number of cells in a large array and, electrical characterization and physical modeling is used to explain the mechanism behind the early retention failure.

Thesis (M. Tech. degree in Chemistry) Tshwane University of Technology 2013. / Discusses the nanostructured platinum group catalysts provide an efficient route for the oxidative coupling of naphthols. The potential of a new catalytic reaction described in the patent literature has not yet been fully explored, although the reaction could provide an efficient new route to chromophoric systems containing conjugated aromatic rings.

In the past decade, electrostatic layer-by-layer (LBL) assembly has gained attention because it is a facile and robust method to prepare thin polymer films. Due to the industrial importance and natural abundance of cellulose, its incorporation into LBL films is of particular interest. This thesis examines the use of nanocrystalline cellulose, prepared by sulfuric acid hydrolysis of cotton, in polyelectrolyte multilayer films. Conventional solution-dipping and a spin-coating variant of LBL assembly both resulted in chemically defined, reproducible, and smooth films with adjustable properties. Surface morphology was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and film growth was monitored by X-ray photoelectron spectroscopy (XPS) and optical techniques. Orientation of the rod-like cellulose nanocrystals imparted anisotropic film properties, and birefringence was calculated from angle dependent and wavelength dependent optical reflectometry measurements. While spin-coating resulted in radial orientation of the nanocrystals, electrostatic adsorption in a magnetic field led to linear alignment. The internal structure, surface orientation and wettability of these materials were investigated. The attractive and repulsive forces acting close to the surface of the multilayer films in aqueous media were measured by colloid-probe AFM and the interaction forces between the film surfaces and charged colloidal-probes were compared to the predictions of the DLVO theory. The applications and advantages of polyelectrolyte multilayers containing nanocrystalline cellulose and their potential as model cellulose surfaces are discussed.

We plan to study the attachment of a cationic tetranuclear palladium II-based macrocyclic square onto a planar gold surface or a gold nanoparticle. To understand the possible mechanisms of attachment of inorganic molecular square to gold we will see if certain related salts can cause an induced aggregation of nanoparticles.The replacement of the surface-passivated citrate layer on the gold nanoparticles can be characterized by infrared spectroscopy and shifts in the surface plasmon resonance band. Consequently, if it can bond gold nanoparticles via electrostatic interactions, then it may be possible that the square can attach to a planar gold surface by a similar mechanism.Infrared spectra of the aggregated nanoparticles will be compared to those obtained using the attachment of molecular square on a planar gold surface. By comparing.infrared spectra it may be possible to determine by what mechanism the square is attaching to gold. / Department of Chemistry

Nanopowders and bulk nanostructred materials have gained large interest in recent years. Bulk nanostructured materials exhibit properties that are far superior in comparison to conventional micron grained alloys. The fabrication of large scale nano-grained materials has been achieved in a two step process: (1) the production of nanostructured aluminium alloy powders and (2) the consolidation of the powder using a electromagnetic shockwave process. / The first part consists of cryo-milling; the milling of powder in an attritor filled with liquid nitrogen. This causes successive welding and fracturing events as the powder is milled, thereby creating the nano-structure. The low temperature prevents the possibility of recrystallization and grain growth. The alloy used for this work was Al 5356 (Al-5%Mg). Two different types of raw source materials were investigated: pre-alloyed powders and a mixture of aluminum with pure magnesium or an Al12Mg17 intermetallic. Experiments have been conducted in order to determine the optimum milling parameters that will simultaneously give a grain size smaller than 100 nm; equiaxed milled particles and mechanically alloyed powder (in the case of the mixture). The optimum milling parameters were established at 15 hours of milling time with a rotational speed of 300 RPM and ball to powder weight ratio of 24:1 in the case of the pre-alloyed powders. For the mixture of pure aluminum with pure magnesium the parameters were 15 hours, 300RPM and 32:1. The parameters for the mixture with the intermetallic were 18 hours, 300RPM and 32:1. / The dynamic magnetic compaction technique was done with a peak pressure of 1.1 GPa. This ultra-high strain rate process minimizes the exposure of the powders to high temperature and therefore reduces the possibility of recrystallization and grain growth. Relative densities of compacted pieces obtained ranged from 86.39% to 97.97%. However consolidation characterized by particle to particle bonding with a melted layer was not accomplished.

Sulfuric acid hydrolysis of native cellulose fibers produces stable suspensions of cellulose nanocrystals. Within a specific concentration range, the suspensions spontaneously form an anisotropic chiral nematic liquid crystal phase. This thesis examines the phase separation behaviour of these suspensions, alone and in the presence of added macromolecules. Initially, the effect of hydrolysis conditions on the nanocrystal and phase separation properties for hydrolyzed softwood pulp were investigated and compared to suspensions prepared from hardwood pulp. The macromolecules studied, blue dextrans of varying molecular weights and dye ligand densities, were synthesized and characterized with a number of techniques. The polyelectrolytic nature of these macromolecules was found to strongly influence their physico-chemical properties. Added blue dextran causes separation of an isotropic phase from highly concentrated, completely anisotropic suspensions. The observed phase separation was found to be associated with the charged dye molecules attached to the dextran. The partitioning behaviour of blue dextrans in biphasic aqueous suspensions of native cellulose nanocrystals was also studied with regard to the effect of total concentration of blue dextran, degree of dye substitution and dextran molecular weight on the blue dextran partition coefficient. Electrostatic and entropic contributions to the partition coefficient of blue dextran were discussed. Triphase isotropic-isotropic-nematic (I1--I 2--N) equilibria are observed in suspensions containing both neutral dextrans and polyelectrolytic blue dextrans of varying molecular weight. Based on these results, phase diagrams for cellulose nanocrystal suspensions with different combinations of dextran and blue dextran are presented.