J. K. Efavi

Subthreshold characteristics of p-type triple-gate MOSFETs

The fabrication and characterization of triple-gate p-type metal-oxide semiconductor field effect transistors (p-MOSFETs) on SOI material with multiple channels is described. To demonstrate the beneficial effects of the triple-gate structure on scaling, the output and transfer characteristics of 70 nm printed gate length pMOSFETs with 22 nm MESA width are presented. The geometrical influence of triple-gate MESA width on subthreshold behavior is investigated in short- and long channel devices. The temperature dependence of subthreshold characteristics is discussed.

Scalable gate first process for silicon on insulator metal oxide semiconductor field effect transistors with epitaxial high-k dielectrics

A “gate first” silicon on insulator (SOI) complementary metal oxide semiconductor process technology for direct evaluation of epitaxial gate dielectrics is described, where the gate stack is fabricated prior to any lithography or etching step. This sequence provides perfect silicon surfaces required for epitaxial growth. The inverted process flow with silicon dioxide (SiO2)/polysilicon gate stacks is demonstrated for gate lengths from 10μm down to 40nm on a fully depleted 25nm thin SOI film. The interface qualities at the front and back gates are investigated and compared to conventionally processed SOI devices. Furthermore, the subthreshold behavior is studied and the scalability of the gate first approach is proven by fully functional sub-100nm transistors. Finally, a fully functional gate first metal oxide semiconductor field effect transistor with the epitaxialhigh-k gate dielectric gadolinium oxide (Gd2O3) and titanium nitride (TiN) gate electrode is presented.

Formation of Chitosan Nanoparticles Using Deacetylated Chitin Isolated from Freshwater Algae and Locally Synthesized Zeolite A and their Influence on Cancer Cell Growth

This work reports the isolation and characterization of chitin from green algae using XRD, 13C CP/MAS NMR, FTIR and Microscopy. The XRD diffraction pattern confirmed orthorhombic structure of the crystalline polysaccharide, whereas the FTIR spectra revealed strong absorption bands at 896.9 cm-1 and 852 cm-1 typical of C–H axial and C–H equatorial vibrations within the anomeric center of the glucopyranosicyclic moiety. Another strong absorption band was observed at 1039.9 cm-1 and was assigned to C–O–C, C–O stretching bands. The purity and structure of the deacetylated chitin was confirmed using 13C NMR, showing overlapping peaks around 65 ppm assigned to both the sugar carbon at C2, as well as a methylene carbon at C6. An intense peak at 74 ppm is assigned to C3 and C5 with corresponding resonances at 81 and 104 ppm assigned to C4 and C1 respectively. Zeolite/Chitosan nanocomposites were synthesized by ionic cross-linking of chitosan with sodium tripolyphosphate. Chitosan nanoparticles and LTA of different concentrations were incubated with HeLa cancer cells to investigate their cytotoxicity effects. The exposure of the cells to chitosan nanoparticles resulted in a decreased in cell growth and this was concentration-dependent. Our results revealed the utility of locally available materials to produce new biodegradable nanoparticles to investigate their biological nanotoxicity.

Development and Comparative Analysis of Aluminosilicate Based Ceramic Filters for Ground Water Defluoridation

Low levels of fluoride in drinking water is healthy for the teeth enamel, however, higher concentrations result in dental fluorosis with prolonged exposures leading to skeletal fluorosis. Fluoride removal capacities of ceramic filters using aluminosilicates (Anfoega clay, Kibi kaolin, Laterite soil and Termitaria earth) samples from Ghana Geological Survey Department have been investigated and analysed for possible application in the Bongo District of Ghana noted forhavinghigh fluoride concentration in its ground water. Batch sorption studies conducted revealed that the amount of fluoride ions removed increased proportionally with increasing filter thickness, temperature and contact time to an optimum value. Using particle size ranges of <355μm and 1cm filter thickness at room temperature, the percentage of fluoride removed by the samples reached an optimum value after 70mins. Increases in filter thickness, contact time or temperatureincreased the amount of fluoride ions removedand the time required to reach the optimum value reduced significantly.

Modified halloysite nanoclay as a vehicle for sustained drug delivery

This paper presents the effect of modified halloysite nanotubes on the sustained drug release mechanisms of sodium salicylate. Acid treatment and composite polymer-halloysite modification techniques were adopted in this study. After each modification, sodium salicylate drug was loaded, and in vitro release properties were evaluated and compared with the raw unmodified halloysite nanotubes. The results obtained from SEM, TEM and FTIR analyses indicate that both acid treatment and composite formation have no effect on the tubular structure and morphology of halloysite. However, modification of the halloysite nanotubes did influence the drug release rate. In the acid treatment modification, there was an improved loading of sodium salicylate drug which resulted in the sustain release of large amount of the sodium salicylate. In the polymer/halloysite composite formation, a consistent layer of polymer was formed around the halloysite during the composite formation and thus delayed release providing sustained release of sodium salicylate drug over a longer period of time as compared to the acid treated and unmodified halloysite. The results from the invitro release were best fitted with the Higuchi and the Koresymer-Peppas models.

Synthesis and characterisation of zeolite-A and Zn-exchanged zeolite-A based on natural aluminosilicates and their potential applications

Abstract Zeolites have been hydrothermally synthesized using alumina and silica based deposits (kaolin, bauxite, silica and feldspar) sampled from three regions in Ghana and the chemical compositions of the zeolites varied by batch formulations. The as-synthesized zeolites were characterized using X-ray Diffraction, Fourier Transform Infra-Red and Porosimetry techniques. The morphology and elemental compositions were examined using Scanning Electron Microscopy and energy dispersive X-ray spectroscopy (EDX). The results indicate that zeolite A was formed with a cubic structure and structural variations depending on the batch formulations. By increasing the silica content (Si/Al ratio) through batch formulations, the crystallite sizes of zeolites increased forming Zeolite A with LTA structure and Zeolite A (K-exchanged dehydrated). Samples with higher alumina content produced Zeolite A (Hydrated), Zeolite-Na and Zeolite A (Na, Dehydrated) with lower crystallite sizes. The zeolite synthesized was then used in the synthesis of zinc exchanged Zeolite A (Zn-zeolite A). EDX analysis confirmed a complete exchange of Na in the Zeolite framework with Zn and the feasibility as an adsorbent for methylene blue tested. The synthesized Zn-exchanged Zeolite A showed strong adsorption for methylene blue dye. The adsorption kinetics of the MB onto Zn-exchanged Zeolite A was observed to follow pseudo-second-order model. Freundlich model better described the interaction among adsorbate molecules onto the Zn-exchanged Zeolite A adsorbent, suggesting a multilayer distribution of adsorbate molecules with some level of interaction between adsorbed molecules. The regeneration capacity of the adsorbent was low and calculated to be about 48% at pH of 12.

Synthesis and Pore Structure Characterisation of Novel Mesoporous MgO-CeO 2 /SBA-15 as a Potential Catalyst Support

The high interest in the synthesis of mesoporous catalyst demands that novel materials are developed with simple methods capable of improving process yields. In this work, a novel heterogeneous mesoporous catalyst support has been synthesized using mesoporous SBA-15 loaded with mixed bimetal oxides of CeO2 and MgO. Formation of the SBA-15 was actuated in air at room temperature (25°C) and in oven conditions at 100°C after which cerium nitrate and magnesium nitrate precursors were then impregnated into the SBA-15 framework and calcined at 550°C for each of the air and oven crystallization processes. XRD peak patterns confirmed SBA-15 formation and dispersion of nanocrystallites of CeO2 and MgO within the porous framework of SBA-15. Both the air and oven dried processes produced mesoporous MgO-CeO2/SBA-15 catalysts with isotherms that exhibit typical H1 type hysteresis confirming that they possess open-ended cylindrical mesopores. The structural data extracted gave average pore size, pore volume and surface area values in the ranges of 3-5.2 nm, 0.600-2.500 cc/g and 400-500 m2/g respectively which is ideal for several industrial applications.

A study of polybromide chain formation using carbon nanomaterials via density functional theory approach

Abstract We use a density functional theory approach under the local density approximation (DFT/LDA) to describe the formation of polybromide chain structures, their stretching frequency modes and charge transfer induced by the interaction of these molecules with a graphene sheet. In many cases, we find polybromides to be more thermodynamically stable than the equivalent Br2 molecular structures adsorbed on graphene sheet. This results in lower frequency stretch modes at around 170–190 cm−1. We propose that these are rarely observed experimentally due to the bromination techniques used, which introduces molecular Br2 into the carbon host material. Charge transfer with their host material means that these molecules and their associated hole charge in the neighbouring carbon materials, are then coulombically repelled from other bromine molecules which acts as a barrier to combination into polybromides. Our calculated barrier for polybromide formation (2Br2→Br4) on a graphene sheet was 0.35 eV which is an exothermic process with an enthalpy value of −0.28 eV. Therefore, thermodynamically, chain polybromide formation seems to be favourable but kinetically, is unlikely, since there is an activation barrier that needs to be overcome to give stable bromine chain structures.