Ultrafast switching in nanoscale phase-change random access memory with superlattice-like structures

Phase-change random access memory cells with superlattice-like (SLL) GeTe/Sb(2)Te(3) were demonstrated to have excellent scaling performance in terms of switching speed and operating voltage. In this study, the correlations between the cell size, switching speed and operating voltage of the SLL cells were identified and investigated. We found that small SLL cells can achieve faster switching speed and lower operating voltage compared to the large SLL cells. Fast amorphization and crystallization of 300 ps and 1 ns were achieved in the 40 nm SLL cells, respectively, both significantly faster than those observed in the Ge(2)Sb(2)Te(5) (GST) cells of the same cell size. 40 nm SLL cells were found to switch with low amorphization voltage of 0.9 V when pulse-widths of 5 ns were employed, which is much lower than the 1.6 V required by the GST cells of the same cell size. These effects can be attributed to the fast heterogeneous crystallization, low thermal conductivity and high resistivity of the SLL structures. Nanoscale PCRAM with SLL structure promises applications in high speed and low power memory devices.     

Kinetics of copper drift in PECVD dielectrics

We quantified the drift of Cu ions into various PECVD dielectrics by measuring shifts in capacitance-voltage behavior after subjecting Cu-gate MOS capacitors to bias-temperature stress. At a field of 1.0 MV/cm and temperature of 100°C, Cu ions drift readily into PECVD oxide with a projected accumulation of 2.7×10¹³ ions/cm ² after 10 years. However, in PECVD oxynitride, the projected accumulation under the same conditions is only 2.3×10¹⁰ ions/cm². These findings demonstrate the necessity of integrating drift barriers, such as PECVD oxynitride layers, in Cu interconnection systems to ensure threshold stability of parasitic field n-MOS devices     

Estimating computation times of data-intensive applications

We present a holistic approach to estimation that uses rough sets theory to determine a similarity template and then compute a runtime estimate using identified similar applications. We tested the technique in two real-life data-intensive applications: data mining and high-performance computing.     

Cell culture imaging using microimpedance tomography

We present a novel, inexpensive, and fast microimpedance tomography system for two-dimensional imaging of cell and tissue cultures. The system is based on four-electrode measurements using 16 planar microelectrodes (5 microm x 4 mm) integrated into a culture chamber. An Agilent 4294A impedance analyzer combined with a front-end amplifier is used for the impedance measurements. Two-dimensional images are obtained using a reconstruction algorithm. This system is capable of accurately resolving the shape and position of a human hair, yielding vertical cross sections of the object. Human epithelial stem cells (YF 29) are also grown directly on the device surface. Tissue growth can be followed over several days. A rapid resistivity decrease caused by permeabilized cell membranes is also monitored, suggesting that this technique can be used in electroporation studies.     

Sustainability of the four generations of biofuels – A review

Biofuel has emerged as an alternative source of energy to reduce the emissions of greenhouse gases in the atmosphere and combat global warming. Biofuels are classified into first, second, third and fourth generations. Each of the biofuel generations aims to meet the global energy demand while minimizing environmental impacts. Sustainability is defined as meeting the needs of the current generations without jeopardizing the needs of future generations. The aim of sustainability is to ensure continuous growth of the economy while protecting the environment and societal needs. Thus, this paper aims to evaluate the sustainability of these four generations of biofuels. The objectives are to compare the production of biofuel, the net greenhouse gases emissions, and energy efficiency. This study is important in providing information for the policymakers and researchers in the decision-making for the future development of green energy. Each of the biofuel generations shows different benefits and drawbacks. From this study, we conclude that the first generation biofuel has the highest biofuel production and energy efficiency, but is less effective in meeting the goal of reducing the greenhouse gases emission. The third generation biofuel shows the lowest net greenhouse gases emissions, allowing the reduction of greenhouse gases in the atmosphere. However, the energy required for the processing of the third generation biofuel is higher and, this makes it less environmentally friendly as fossil fuels are used to generate electricity. The third and fourth generation feedstocks are the potential sustainable source for the future production of biofuel. However, more studies need to be done to find an alternative low cost for biofuel production while increasing energy efficiency.     

A review of synthesis and morphology of SrTiO3 for energy and other applications

With the increasing demand and depleting trend of commercial energies, it has forced the researchers all over the world to accelerate research and development in the area of renewable energy. Currently, unique and interesting features of binary compounds have gained more attention by researchers, and it became a favourite research topic among various groups of researchers around this world. It was noticed that strontium titanate (SrTiO₃) consists of several extraordinary properties that can apply for miscellaneous applications especially for energy storage, fuel cells, as well as to generate hydrogen fuel via photocatalysis process. Besides that, it was noticed that SrTiO₃ can be synthesised in different pathways. The method of preparation and amount of precursors can affect the surface properties of SrTiO₃. Thus, this article presents a critical review on how SrTiO₃ synthesis methods affect its surface morphology and the applications of SrTiO₃ in various fields.     

Customizing MRI-Compatible Multifunctional Neural Interfaces through Fiber Drawing

Fiber drawing enables scalable fabrication of multifunctional flexible fibers that integrate electrical, optical, and microfluidic modalities to record and modulate neural activity. Constraints on thermomechanical properties of materials, however, have prevented integrated drawing of metal electrodes with low-loss polymer waveguides for concurrent electrical recording and optical neuromodulation. Here, two fabrication approaches are introduced: 1) an iterative thermal drawing with a soft, low melting temperature (T_m) metal indium, and 2) a metal convergence drawing with traditionally non-drawable high T_m metal tungsten. Both approaches deliver multifunctional flexible neural interfaces with low-impedance metallic electrodes and low-loss waveguides, capable of recording optically-evoked and spontaneous neural activity in mice over several weeks. These fibers are coupled with a light-weight mechanical microdrive (1 g) that enables depth-specific interrogation of neural circuits in mice following chronic implantation. Finally, the compatibility of these fibers with magnetic resonance imaging is demonstrated and they are applied to visualize the delivery of chemical payloads through the integrated channels in real time. Together, these advances expand the domains of application of the fiber-based neural probes in neuroscience and neuroengineering.     

Conceptual design of a hybrid thin layer cascade photobioreactor for microalgal biodiesel synthesis

Even though microalgae are able to produce various valuable metabolites, microalgal culture on an industrial scale still faces challenging difficulties. Open systems may be cheaper to construct, easier to operate and maintain, and possess greater surface area to volume ratio, but they are also easily contaminated, have high water loss due to evaporation, and suffer from unfavorable weather. On the other hand, closed photobioreactor systems possess higher biomass yields, better control over culture parameters, and lower contamination risks. However, photobioreactors are costlier to construct and maintain. Thus, a hybrid semi-closed thin layer cascade photobioreactor was proposed to cultivate high-density microalgal cultures for biodiesel production. Computational fluid dynamics analysis was carried out to observe fluid behavior in the hybrid photobioreactor design. The simulation results showed satisfactory performance in the improved design, making the photobioreactor a potential candidate for microalgal biodiesel production.     

Economic potential of bioremediation using immobilized microalgae-based microbial fuel cells

Clean Technologies and Environmental Policy - The cathodic microalgae-based MFC converts the nutrients within wastewater and produces oxygen as oxygen supply for cathodic reactions, leading to the...