Deterministic control of structural and optical properties of plasma-grown vertical graphene nanosheet networks via nitrogen gas variation

The effect of nitrogen on the growth of vertically oriented graphene nanosheets on catalyst-free silicon and glass substrates in a plasma-assisted process is studied. Different concentrations of nitrogen were found to act as versatile control knobs that could be used to tailor the length, number density and structural properties of the nanosheets. Nanosheets with different structural characteristics exhibit markedly different optical properties. The nanosheet samples were treated with a bovine serum albumin protein solution to investigate the effects of this variation on the optical properties for biosensing through confocal micro-Raman spectroscopy and UV-Vis spectrophotometry. © 2012 Optical Society of America.

Copper-capped carbon nanocones on silicon : plasma-enabled growth control

Controlled self-organized growth of vertically aligned carbon nanocone arrays in a radio frequency inductively coupled plasma-based process is studied. The experiments have demonstrated that the gaps between the nanocones, density of the nanocone array, and the shape of the nanocones can be effectively controlled by the process parameters such as gas composition (hydrogen content) and electrical bias applied to the substrate. Optical measurements have demonstrated lower reflectance of the nanocone array as compared with a bare Si wafer, thus evidencing their potential for the use in optical devices. The nanocone formation mechanism is explained in terms of redistribution of surface and volumetric fluxes of plasma-generated species in a developing nanocone array and passivation of carbon in narrow gaps where the access of plasma ions is hindered. Extensive numerical simulations were used to support the proposed growth mechanism.

Property-performance control of multidimensional, hierarchical, single-crystalline ZnO nanoarchitectures

Diverse morphologies of multidimensional hierarchical single-crystalline ZnO nanoarchitectures including nanoflowers, nanobelts, and nanowires are obtained by use of a simple thermal evaporation and vapour-phase transport deposition technique by placing Au-coated silicon substrates in different positions inside a furnace at process temperatures as low as 550 °C. The nucleation and growth of ZnO nanostructures are governed by the vapour–solid mechanism, as opposed to the commonly reported vapour–liquid–solid mechanism, when gold is used in the process. The morphological, structural, compositional and optical properties of the synthesized ZnO nanostructures can be effectively tailored by means of the experimental parameters, and these properties are closely related to the local growth temperature and gas-phase supersaturation at the sample position. In particular, room-temperature photoluminescence measurements reveal an intense near-band-edge ultraviolet emission at about 386 nm for nanobelts and nanoflowers, which suggests that these nanostructures are of sufficient quality for applications in, for example, optoelectronic devices.

Plasma control of morpho-dimensional selectivity of hematite nanostructures

Highly controllablefabrication of the nanowire, nanocone, and mixed nanowire/nanowall arrays of iron oxide (hematite, α-Fe2O3) nanostructures in a simple, environment-friendly process is achieved by exposing the metal foils to low-temperature oxygen plasmas. Very dense forests of thin (≈50 nm) and long (up to several μm) nanowires are grown on the electrically biased substrates, whereas the use of the electrically insulated substrate resulted in the formation of a mixed array of nanowires and nanowalls. The proposed mechanism of the nanostructure growth is supported by the numerical simulations demonstrating the key role of the plasma environment in the growth morphology selection.

Control of energy and matter at nanoscales : challenges and opportunities for plasma nanoscience in a sustainability age

Plasma nanoscience is an emerging multidisciplinary research field at the cutting edge of a large number of disciplines including but not limited to physics and chemistry of plasmas and gas discharges, materials science, surface science, nanoscience and nanotechnology, solid-state physics, space physics and astrophysics, photonics, optics, plasmonics, spintronics, quantum information, physical chemistry, biomedical sciences and related engineering subjects. This paper examines the origin, progress and future perspectives of this research field driven by the global scientific and societal challenges. The future potential of plasma nanoscience to remain a highly topical area in the global research and technological agenda in the age of fundamental-level control for a sustainable future is assessed using a framework of the five Grand Challenges for Basic Energy Sciences recently mapped by the US Department of Energy. It is concluded that the ongoing research is very relevant and is expected to substantially expand to competitively contribute to the solution of all of these Grand Challenges. The approach to controlling energy and matter at nano- and subnanoscales is based on identifying the prevailing carriers and transfer mechanisms of the energy and matter at the spatial and temporal scales that are most relevant to any particular nanofabrication process. Strong accent is made on the competitive edge of the plasma-based nanotechnology in applications related to the major socio-economic issues (energy, food, water, health and environment) that are crucial for a sustainable development of humankind. Several important emerging topics, opportunities and multidisciplinary synergies for plasma nanoscience are highlighted. The main nanosafety issues are also discussed and the environment- and human health-friendly features of plasma-based nanotech are emphasized.

3-Orders-of-magnitude density control of single-walled carbon nanotube networks by maximizing catalyst activation and dosing carbon supply

Tailoring the density of random single-walled carbon nanotube (SWCNT) networks is of paramount importance for various applications, yet it remains a major challenge due to the insufficient catalyst activation in most growth processes. Here we report on a simple and effective method to maximise the number of active catalyst nanoparticles using catalytic chemical vapor deposition (CCVD). By modulating short pulses of acetylene into a methane-based CCVD growth process, the density of SWCNTs is dramatically increased by up to three orders of magnitude without increasing the catalyst density and degrading the nanotube quality. In the framework of a vapor-liquid-solid model, we attribute the enhanced growth to the high dissociation rate of acetylene at high temperatures at the nucleation stage, which can be effective in both supersaturating the larger catalyst nanoparticles and overcoming the nanotube nucleation energy barrier of the smaller catalyst nanoparticles. These results are highly relevant to numerous applications of random SWCNT networks in next-generation energy, sensing and biomedical devices. © 2011 The Royal Society of Chemistry.

From nucleation to nanowires : a single-step process in reactive plasmas

This feature article introduces a deterministic approach for the rapid, single-step, direct synthesis of metal oxide nanowires. This approach is based on the exposure of thin metal samples to reactive oxygen plasmas and does not require any intervening processing or external substrate heating. The critical roles of the reactive oxygen plasmas, surface processes, and plasma-surface interactions that enable this growth are critically examined by using a deterministic viewpoint. The essentials of the experimental procedures and reactor design are presented and related to the key process requirements. The nucleation and growth kinetics is discussed for typical solid-liquid-solid and vapor-solid-solid mechanisms related to the synthesis of the oxide nanowires of metals with low (Ga, Cd) and high (Fe) melting points, respectively. Numerical simulations are focused on the possibility to predict the nanowire nucleation points through the interaction of the plasma radicals and ions with the nanoscale morphological features on the surface, as well as to control the localized 'hot spots' that in turn determine the nanowire size and shape. This generic approach can be applied to virtually any oxide nanoscale system and further confirms the applicability of the plasma nanoscience approaches for deterministic nanoscale synthesis and processing.

Disentangling fluxes of energy and matter in plasma-surface interactions : effect of process parameters

The possibility to discriminate between the relative importance of the fluxes of energy and matter in plasma-surface interaction is demonstrated by the energy flux measurements in low-temperature plasmas ignited by the radio frequency discharge (power and pressure ranges 50-250 W and 8-11.5 Pa) in Ar, Ar+ H2, and Ar+ H2 + CH4 gas mixtures typically used in nanoscale synthesis and processing of silicon- and carbon-based nanostructures. It is shown that by varying the gas composition and pressure, the discharge power, and the surface bias one can effectively control the surface temperature and the matter supply rates. The experimental findings are explained in terms of the plasma-specific reactions in the plasma bulk and on the surface.

Deterministic control of plasma-assembled self-organized Ge/Si quantum dot arrays

Self-assembly of size-uniform and spatially ordered quantum dot (QD) arrays is one of the major challenges in the development of the new generation of semiconducting nanoelectronic and photonic devices. Assembly of Ge QD (in the ∼5-20 nm size range) arrays from randomly generated position and size-nonuniform nanodot patterns on plasma-exposed Si (100) surfaces is studied using hybrid multiscale numerical simulations. It is shown, by properly manipulating the incoming ion/neutral flux from the plasma and the surface temperature, the uniformity of the nanodot size within the array can be improved by 34%-53%, with the best improvement achieved at low surface temperatures and high external incoming fluxes, which are intrinsic to plasma-aided processes. Using a plasma-based process also leads to an improvement (∼22% at 700 K surface temperature and 0.1 MLs incoming flux from the plasma) of the spatial order of a randomly sampled nanodot ensemble, which self-organizes to position the dots equidistantly to their neighbors within the array. Remarkable improvements in QD ordering and size uniformity can be achieved at high growth rates (a few nms) and a surface temperature as low as 600 K, which broadens the range of suitable substrates to temperature-sensitive ultrathin nanofilms and polymers. The results of this study are generic, can also be applied to nonplasma-based techniques, and as such contributes to the development of deterministic strategies of nanoassembly of self-ordered arrays of size-uniform QDs, in the size range where nanodot ordering cannot be achieved by presently available pattern delineation techniques.

Deterministic shape control in plasma-aided nanotip assembly

The possibility of deterministic plasma-assisted reshaping of capped cylindrical seed nanotips by manipulating the plasma parameter-dependent sheath width is shown. Multiscale hybrid gas phase/solid surface numerical experiments reveal that under the wide-sheath conditions the nanotips widen at the base and when the sheath is narrow, they sharpen up. By combining the wide- and narrow-sheath stages in a single process, it turns out possible to synthesize wide-base nanotips with long- and narrow-apex spikes, ideal for electron microemitter applications. This plasma-based approach is generic and can be applied to a larger number of multipurpose nanoassemblies. © 2005 American Institute of Physics.

A gray-box neural network-based model identification and fault estimation scheme for nonlinear dynamic systems

A novel gray-box neural network model (GBNNM), including multi-layer perception (MLP) neural network (NN) and integrators, is proposed for a model identification and fault estimation (MIFE) scheme. With the GBNNM, both the nonlinearity and dynamics of a class of nonlinear dynamic systems can be approximated. Unlike previous NN-based model identification methods, the GBNNM directly inherits system dynamics and separately models system nonlinearities. This model corresponds well with the object system and is easy to build. The GBNNM is embedded online as a normal model reference to obtain the quantitative residual between the object system output and the GBNNM output. This residual can accurately indicate the fault offset value, so it is suitable for differing fault severities. To further estimate the fault parameters (FPs), an improved extended state observer (ESO) using the same NNs (IESONN) from the GBNNM is proposed to avoid requiring the knowledge of ESO nonlinearity. Then, the proposed MIFE scheme is applied for reaction wheels (RW) in a satellite attitude control system (SACS). The scheme using the GBNNM is compared with other NNs in the same fault scenario, and several partial loss of effect (LOE) faults with different severities are considered to validate the effectiveness of the FP estimation and its superiority.

Control of cell cycle progression by phosphorylation of cyclin-dependent kinase (CDK) substrates

The eukaryotic cell cycle is a fundamental evolutionarily conserved process that regulates cell division from simple unicellular organisms, such as yeast, through to higher multicellular organisms, such as humans. The cell cycle comprises several phases, including the S-phase (DNA synthesis phase) and M-phase (mitotic phase). During S-phase, the genetic material is replicated, and is then segregated into two identical daughter cells following mitotic M-phase and cytokinesis. The S- and M-phases are separated by two gap phases (G1 and G2) that govern the readiness of cells to enter S- or M-phase. Genetic and biochemical studies demonstrate that cell division in eukaryotes is mediated by CDKs (cyclin-dependent kinases). Active CDKs comprise a protein kinase subunit whose catalytic activity is dependent on association with a regulatory cyclin subunit. Cell-cycle-stage-dependent accumulation and proteolytic degradation of different cyclin subunits regulates their association with CDKs to control different stages of cell division. CDKs promote cell cycle progression by phosphorylating critical downstream substrates to alter their activity. Here, we will review some of the well-characterized CDK substrates to provide mechanistic insights into how these kinases control different stages of cell division.

Reducing bubble defect on the outsole production process in the footwear manufacturing industry

The purpose of this study is to discover the significant factors causing the bubble defect on the outsoles manufactured by the Case Company. The bubble defect occurs approximately 1.5 per cent of the time or in 36 pairs per day. To understand this problem, experimental studies are undertaken to identify various factors such as injector temperature, mould temperature; that affects the production of waste. The work presented in this paper comprises a review of the relevant literature on the Six Sigma DMAIC improvement process, quality control tools, and the design of the experiments. After the experimentation following the Six Sigma process, the results showed that the defect occurred in approximately 0.5 per cent of the products or in 12 pairs per day; this decreased the production cost from 6,120 AUD per month to 2,040 AUD per month. This research aimed to reduce the amount of waste in men’s flat outsoles. Hence, the outcome of research presented in this paper should be used as a guide for applying the appropriate process for each type of outsole.

Artemisinin resistance in Plasmodium falciparum : a process linked to dormancy?

Artemisinin (ART) based combination therapy (ACT) is used as the first line treatment of uncomplicated falciparum malaria in over 100 countries and is the cornerstone of malaria control and elimination programs in these areas. However, despite the high potency and rapid parasite killing action of ART derivatives there is a high rate of recrudescence associated with ART monotherapy and recrudescence is not uncommon even when ACT is used. Compounding this problem are reports that some parasites in Cambodia, a known foci of drug resistance, have decreased in vivo sensitivity to ART. This raises serious concerns for the development of ART resistance in the field even though no major phenotypic and genotypic changes have yet been identified in these parasites. In this article we review available data on the characteristics of ART, its effects on Plasmodium falciparum parasites and present a hypothesis to explain the high rate of recrudescence associated with this potent class of drugs and the current enigma surrounding ART resistance.

Geographical distribution of human Schistosoma japonicum infection in the Philippines : tools to support disease control and further elimination

S. japonicum infection is believed to be endemic in 28 of the 80 provinces of the Philippines and the most recent data on schistosomiasis prevalence have shown considerable variability between provinces. In order to increase the efficient allocation of parasitic disease control resources in the country, we aimed to describe the small scale spatial variation in S. japonicum prevalence across the Philippines, quantify the role of the physical environment in driving the spatial variation of S. japonicum, and develop a predictive risk map of S. japonicum infection. Data on S. japonicum infection from 35,754 individuals across the country were geo-located at the barangay level and included in the analysis. The analysis was then stratified geographically for Luzon, the Visayas and Mindanao. Zero-inflated binomial Bayesian geostatistical models of S. japonicum prevalence were developed and diagnostic uncertainty was incorporated. Results of the analysis show that in the three regions, males and individuals aged ≥ 20 years had significantly higher prevalence of S. japonicum compared with females and children <5 years. The role of the environmental variables differed between regions of the Philippines. S. japonicum infection was widespread in the Visayas whereas it was much more focal in Luzon and Mindanao. This analysis revealed significant spatial variation in prevalence of S. japonicum infection in the Philippines. This suggests that a spatially targeted approach to schistosomiasis interventions, including mass drug administration, is warranted. When financially possible, additional schistosomiasis surveys should be prioritized to areas identified to be at high risk, but which were underrepresented in our dataset.