Removal of epoxy-attached thin-sections from glass slides by plasma-etching

Thin-sectioned samples mounted on glass slides with common petrographic epoxies cannot be easily removed (for subsequent ion-milling) by standard methods such as heating or dissolution in solvents. A method for the removal of such samples using a radio frequency (RF) generated oxygen plasma has been investigated for a number of typical petrographic and ceramic thin sections. Sample integrity and thickness were critical factors that determined the etching rate of adhesive and the survivability of the sample. Several tests were performed on a variety of materials in order to estimate possible heating or oxidation damage from the plasma. Temperatures in the plasma chamber remained below 138°C and weight changes in mineral powders etched for 76 hr were less than ±4%. A crystal of optical grade calcite showed no apparent surface damage after 48 hr of etching. Any damage from the oxygen plasma is apparently confined to the surface of the sample, and is removed during the ion-milling stage of transmission electron microscopy (TEM) sample preparation.

Metal ion levels post unilateral primary Exeter total hip replacement

There has been much discussion and controversy in the media recently regarding metal toxicity following large head metal on metal (MoM) total hip replacement (THR). Patients have been reported as having hugely elevated levels of metal ions with, at times, devastating systemic, neurolgical and/or orthopaedic sequelae. However, no direct correlation between metal ion level and severity of metallosis has yet been defined. Normative levels of metal ions in well functioning, non Cobalt-Chrome hips have also not been defined to date. The Exeter total hip replacement contains no Cobalt-Chrome (Co-Cr) as it is made entirely from stainless steel. However, small levels of these metals may be present in the modular head of the prosthesis, and their effect on metal ion levels in the well functioning patient has not been investigated. We proposed to define the “normal” levels of metal ions detected by blood test in 20 well functioning patients at a minimum 1 year post primary Exeter total hip replacement, where the patient had had only one joint replaced. Presently, accepted normal levels of blood Chromium are 10–100 nmol/L and plasma Cobalt are 0–20 nmol/L. The UK Modern Humanities Research Association (MHRA) has suggested that levels of either Cobalt or Chromium above 7 ppb (equivalent to 135 nmol/L for Chromium and 120 nmol/L for Cobalt) may be significant. Below this level it is indicated that significant soft tissue reaction and tissue damage is less likely and the risk of implant failure is reduced. Hips were a mixture of cemented and hybrid procedures performed by two experienced orthopaedic consultants. Seventy percent were female, with a mixture of head sizes used. In our cohort, there were no cases where the blood Chromium levels were above the normal range, and in more than 70% of cases, levels were below recordable levels. There were also no cases of elevated plasma Cobalt levels, and in 35% of cases, levels were negligible. We conclude that the implantation with an Exeter total hip replacement does not lead to elevation of blood metal ion levels.

A rapid and sensitive UPLC-ESI MS method for analysis of isofraxidin, a natural antistress compound, and its metabolites in rat plasma

Isofraxidin is one of the main bioactive constituents in the root of Acanthopanax senticosus, which has antifatigue, antistress, and immuno-accommondating effects. In this study, an ultraperformance LC (UPLC)-ESI MS method was developed for analyzing isofraxidin and its metabolites in rat plasma. The analysis was performed on a UPLC coupled with ESI MS (quadropole MS tandem TOF MS). The lower LOD (LLOD) for isofraxidin was 0.25 ng/mL, the intraday precision was less than 10%, the interday precision was less than 10%, and the extraction recovery was more than 80%. Isofraxidin and two metabolites (M1 and M2) were detected in rat plasma after oral administration of isofraxidin, and the molecular polarities of M1 and M2 were both increased compared to isofraxidin. The metabolites were identified as 5,6-dihydroxyl-7-methoxycoumarin and 5-hydroxyl-6,7-dimethoxycoumarin when subjected to parent ion spectra, product ion spectra, and extract mass and element composition analyses.

Dense plasmas in magnetic traps : generation of focused ion beams with controlled ion-to-neutral flux ratios

Customized magnetic traps were developed to produce a domain of dense plasmas with a narrow ion beam directed to a particular area of the processed substrate. A planar magnetron coupled with an arc discharge source created the magnetic traps to confine the plasma electrons and generate the ion beam with the controlled ratio of ion-to-neutral fluxes. Images of the plasma jet patterns and numerical vizualizations help explaining the observed phenomena.

Guided ionization waves : theory and experiments

This review focuses on one of the fundamental phenomena that occur upon application of sufficiently strong electric fields to gases, namely the formation and propagation of ionization waves-streamers. The dynamics of streamers is controlled by strongly nonlinear coupling, in localized streamer tip regions, between enhanced (due to charge separation) electric field and ionization and transport of charged species in the enhanced field. Streamers appear in nature (as initial stages of sparks and lightning, as huge structures-sprites above thunderclouds), and are also found in numerous technological applications of electrical discharges. Here we discuss the fundamental physics of the guided streamer-like structures-plasma bullets which are produced in cold atmospheric-pressure plasma jets. Plasma bullets are guided ionization waves moving in a thin column of a jet of plasma forming gases (e.g.,He or Ar) expanding into ambient air. In contrast to streamers in a free (unbounded) space that propagate in a stochastic manner and often branch, guided ionization waves are repetitive and highly-reproducible and propagate along the same path-the jet axis. This property of guided streamers, in comparison with streamers in a free space, enables many advanced time-resolved experimental studies of ionization waves with nanosecond precision. In particular, experimental studies on manipulation of streamers by external electric fields and streamer interactions are critically examined. This review also introduces the basic theories and recent advances on the experimental and computational studies of guided streamers, in particular related to the propagation dynamics of ionization waves and the various parameters of relevance to plasma streamers. This knowledge is very useful to optimize the efficacy of applications of plasma streamer discharges in various fields ranging from health care and medicine to materials science and nanotechnology.

The effect of microscopic texture on the direct plasma surface passivation of Si solar cells

Textured silicon surfaces are widely used in manufacturing of solar cells due to increasing the light absorption probability and also the antireflection properties. However, these Si surfaces have a high density of surface defects that need to be passivated. In this study, the effect of the microscopic surface texture on the plasma surface passivation of solar cells is investigated. The movement of 105 H+ ions in the texture-modified plasma sheath is studied by Monte Carlo numerical simulation. The hydrogen ions are driven by the combined electric field of the plasma sheath and the textured surface. The ion dynamics is simulated, and the relative ion distribution over the textured substrate is presented. This distribution can be used to interpret the quality of the Si dangling bonds saturation and consequently, the direct plasma surface passivation.

Plasma enables edge-to-center-oriented graphene nanoarrays on Si nanograss

The formation of clearly separated vertical graphenenanosheets on silicon nanograss support is demonstrated. The plasma-enabled, two-stage mask-free process produced self-organized vertical graphenes of a few carbon layers (as confirmed by advanced microanalysis), prominently oriented in the substrate center–substrate edge direction. It is shown that the width of the alignment zone depends on the substrate conductivity, and thus the electric field in the vicinity of the growth surface is responsible for the graphene alignment. This finding is confirmed by the Monte Carlo simulations of the ion flux distribution in the silicon nanograss pattern.

Thin single-walled carbon nanotubes with narrow chirality distribution : constructive interplay of plasma and Gibbs–Thomson effects

Multiscale, multiphase numerical modeling is used to explain the mechanisms of effective control of chirality distributions of single-walled carbon nanotubes in direct plasma growth and suggest effective approaches to further improvement. The model includes an unprecedented combination of the plasma sheath, ion/radical transport, species creation/loss, plasma–surface interaction, heat transfer, surface/bulk diffusion, graphene layer nucleation, and bending/lift-off modules. It is shown that the constructive interplay between the plasma and the Gibbs–Thomson effect can lead to the effective nucleation and lift-off of small graphene layers on small metal catalyst nanoparticles. As a result, much thinner nanotubes with narrower chirality distributions can nucleate at much lower process temperatures and pressures compared to thermal CVD. This approach is validated by a host of experimental results, substantially reduces the amounts of energy and atomic matter required for the nanotube growth, and can be extended to other nanoscale structures and materials systems, thereby nearing the ultimate goal of energy- and matter-efficient nanotechnology.

Energy and matter-efficient size-selective growth of thin quantum wires in a plasma

It is shown that plasmas can minimize the adverse Gibbs-Thompson effect in thin quantum wire growth. The model of Si nanowirenucleation includes the unprecedented combination of the plasma sheath, ion- and radical-induced species creation and heating effects on the surface and within an Au catalyst nanoparticle. Compared to neutral gas thermal processes, much thinner, size-selective wires can nucleate at the same temperature and pressure while much lower energy and matter budget is needed to grow same-size wires. This explains the experimental observations and may lead to energy- and matter-efficient synthesis of a broader range of one-dimensional quantum structures.

Minimizing the Gibbs–Thomson effect in the low-temperature plasma synthesis of thin Si nanowires

An advanced combination of numerical models, including plasma sheath, ion- and radical-induced species creation and plasma heating effects on the surface and within a Au catalyst nanoparticle, is used to describe the catalyzed growth of Si nanowires in the sheath of a low-temperature and low-pressure plasma. These models have been used to explain the higher nanowire growth rates, low-energy barriers, much thinner Si nanowire nucleation and the less effective Gibbs–Thomson effect in reactive plasma processes, compared with those of neutral gas thermal processes. The effects of variation in the plasma sheath parameters and substrate potential on Si nanowire nucleation and growth have also been investigated. It is shown that increasing the plasma-related effects leads to decreases in the nucleation energy barrier and the critical nanoparticle radius, with the Gibbs–Thomson effect diminished, even at low temperatures. The results obtained are consistent with available experimental results and open a path toward the energy- and matter-efficient nucleation and growth of a broad range of one-dimensional quantum structures.

Heating and plasma sheath effects in low-temperature, plasma-assisted growth of carbon nanofibers

Plasma sheath, nanostructure growth, and thermal models are used to describe carbon nanofiber (CNF) growth and heating in a low-temperature plasma. It is found that when the H2 partial pressure is increased, H atom recombination and H ion neutralization are the main mechanisms responsible for energy release on the catalyst surface. Numerical results also show that process parameters such as the substrate potential, electron temperature and number density mainly affect the CNF growth rate and plasma heating at low catalyst temperatures. In contrast, gas pressure, ion temperature, and the C2H2:H2 supply ratio affect the CNF growth at all temperatures. It is shown that plasma-related processes substantially increase the catalyst particle temperature, in comparison to the substrate and the substrate-holding platform temperatures.

Ion-assisted precursor dissociation and surface diffusion : enabling rapid, low-temperature growth of carbon nanofibers

Growth kinetics of carbon nanofibers in a hydrocarbon plasma is studied. In addition to gas-phase and surface processes common to chemical vapor deposition, the model includes (unique to plasma-exposed catalyst surfaces) ion-induced dissociation of hydrocarbons, interaction of adsorbed species with incoming hydrogen atoms, and dissociation of hydrocarbon ions. It is shown that at low, nanodevice-friendly process temperatures the nanofibers grow via surface diffusion of carbon adatoms produced on the catalyst particle via ion-induced dissociation of a hydrocarbon precursor. These results explain a lower activation energy of nanofiber growth in a plasma and can be used for the synthesis of other nanoassemblies. © 2007 American Institute of Physics.

Plasma-assisted self-sharpening of platelet-structured single-crystalline carbon nanocones

A mechanism and model for the vertical growth of platelet-structured vertically aligned single-crystalline carbon nanostructures by the formation of graphene layers on a flat top surface are proposed and verified experimentally. It is demonstrated that plasma-related effects lead to self-sharpening of tapered nanocones to form needlelike nanostructures, in a good agreement with the predicted dependence of the radius of a nanocone's flat top on the incoming ion flux and surface temperature. The growth mechanism is relevant to a broad class of nanostructures including nanotips, nanoneedles, and nanowires and can be used to improve the predictability of nanofabrication processes. © 2007 American Institute of Physics.

Uniformity of postprocessing of dense nanotube arrays by neutral and ion fluxes

The advantages of using low-temperature plasma environments for postprocessing of dense nanotube arrays are shown by means of multiscale hybrid numerical simulations. By controlling plasma-extracted ion fluxes and varying the plasma and sheath parameters, one can selectively coat, dope, or functionalize different areas on nanotube surfaces. Conditions of uniform deposition of ion fluxes over the entire nanotube surfaces are obtained for different array densities. The plasma route enables a uniform processing of lateral nanotube surfaces in very dense (with a step-to-height ratio of 1:4) arrays, impossible via the neutral gas process wherein radical penetration into the internanotube gaps is poor. © 2006 American Institute of Physics.

Structure of the magnetized sheath of a dusty plasma

A three-component fluid model for a dusty plasma-sheath in an oblique magnetic field is presented. The study is carried out for the conditions when the thermophoretic force associated with the electron temperature gradient is one of the most important forces affecting dust grains in the sheath. It is shown that the sheath properties (the sheath size, the electron, ion and dust particle densities and velocities, the electric field potential, and the forces affecting the dust particles) are functions of the neutral gas pressure and ion temperature, the dust size, the dust material density, and the electron temperature gradient. Effects of plasma-dust collisions on the sheath structure are studied. It is shown that an increase in the forces pushing dust particles to the wall is accompanied by a decrease in the sheath width. The results of this work are particularly relevant to low-temperature plasma-enabled technologies, where effective control of nano- and microsized particles near solid or liquid surfaces is required.