Table of contents

Dust particles in a plasma are charged negatively and are subject to various types of forces, including a drag force by plasma particles and a force due to the collective nature of a plasma. Dust particles are found in a sheath in laboratories balanced by the gravitational force and the electric force, while dust particles in space are ubiquitous, including planetary magnetospheres and interstellar space. Because of the novel nature of a complex system involving plasma particles and dust particles in a collective way, the dusty plasma is often called a complex plasma. The complex plasma is characterized by two distinctly different scales in time and in space. The plasma with electrons, ions and neutrals is characterized by the collective motion with a fast time scale and a short wavelength, while the dust particles move in a slow time scale and a long spatial scale. Some fundamental aspects of a complex plasma are reviewed and possible applications are discussed.

We report on the magnetic and magnetotransport properties of Fe clustered particles embedded in a ZnSe matrix. The samples are prepared by molecular beam epitaxy and consist of discontinuous Fe planes of unconnected particles covered by a 4.5 nm-thick epilayer of ZnSe, repeated in 20 cycles. Scanning tunnelling microscopy and transmission electron microscopy revealed well isolated and regularly dispersed Fe nanoparticles. This particle assembly displays a dominant superparamagnetic response with weak inter-particle magnetic interactions. The magnetotransport experiments performed in the current-in-plane geometry showed a negative magnetoresistance of 2% at low temperature, which is described by localized states through a ZnSe semiconducting barrier.

Structural, magnetic and transport properties were investigated for heterogeneous (Fe_xSn_1−x)_1−y(SiO₂)_y films deposited on oxidized silicon substrates at room temperature with RF magnetron sputtering. X-ray diffraction indicated that the films consist of a nanocrystalline phase of FeSn₂ embedded into an amorphous background. For (Fe_xSn_1−x)_92.33(SiO₂)_7.67, it was demonstrated that with the increase in the Fe component an evolution from negative isotropic magnetoresistance (MR) behaviour to one with a mixture of anisotropic magnetoresistance and isotropic negative MR occurs. On fixing the SiO₂ percentage and decreasing the Fe–Sn ratio, the negative transverse MR first increases and then decreases. For samples having a fixed Fe–Sn ratio, the negative transverse MR increases with the increase in SiO₂. Compared with the Fe–Sn system, the addition of 7.67 at.% SiO₂ enhances the saturated Hall resistivity. Further increase in SiO₂ introduces a complicated saturated Hall resistivity dependence on the concentration of SiO₂.

Interfacing of ferroelectric and semiconductor materials provides a means of coupling unique properties associated with ferroelectric materials to high performance semiconductor devices. In this work we report the electronic properties of ferroelectric/ZnO heterostructures, where (Pb,Zr)TiO₃ (PZT) is used as a prototypical ferroelectric oxide. Metal–PZT–metal structures demonstrate ferroelectric hysteresis with remanent polarization of 28 µC cm⁻² and coercive field of 75 kV cm⁻¹ for a loop of 15 V. The metal–PZT–ZnO capacitor structures demonstrate a characteristic metal–insulator–semiconductor capacitance–voltage (C–V) behaviour with a hysteretic memory window of approximately 4 V. The heterostructure C–V characteristics do not change significantly with varying frequency. Metal–PZT–ZnO capacitors are also used as part of a simple RLC circuit to demonstrate the ability to shift resonant frequency of the circuit with switching ferroelectric polarization.

High contrast ratio and high power efficiency organic light-emitting diodes (OLEDs) using a dual electron transporting layer of copper phthalocyanine (CuPc)/ titanium oxide phthalocyanine (TiOPc) as an anti-reflection layer have been investigated. The OLED configuration comprises indium tin oxide (ITO)/4,4',4''-tris{N,-(3-methylphenyl)-N-phenylamino}- triphenylamine) (m-MTDATA)/N, N'-diphenyl-N,N'-bis(l-naphthyl-phenyl)-(l,l'-biphenyl)-4, 4'-diamine (NPB)/tris(8-hydroxyquinolino)-aluminium (Alq₃)/CuPc/TiOPc/LiF/Al. The contrast ratio of the device with a CuPc/TiOPc anti-reflection layer is about double and the power efficiency higher than that of a conventional device without the anti-reflection layer. The improvement in the power efficiency and the contrast ratio of the device that is obtained using a CuPc/TiOPc anti-reflection layer is attributable to the stepwise electron transporting barrier and the reduced optical reflection from the cathode. The contrast ratio suffices for outdoor display applications.

Sb₂S₃ thin films have been obtained by physical vapour deposition on LiNbO₃ and glass substrates. Films with amorphous structure originally became polycrystalline by annealing in a sulfur atmosphere. Changes in optical and structural properties have been studied as a function of annealing temperature. A drastic variation in optical transmission, energy gaps, refractive index, crystallite size, etc is observed at a temperature near 200 °C.

Indium tin oxide (ITO) and titanium dioxide (TiO₂) films have been deposited by radio-frequency magnetron sputtering on glass substrates, both individually and in a sequence of ITO/TiO₂/ITO, etc in order to produce multi-layer structures. The aim is to arrive at an assembly with good optical transmission, but capable of completely blocking the transmission of infra-red (IR) wavelengths. Optical modelling, of the individual oxide films and of the multi-layer stack, was carried out in order to understand the nature of the experimentally measured reflection and transmission curves and to predict the number of layers required to obtain a transmission cut-off of all wavelengths above 800 nm. The study indicates that for a 7-layer assembly IR transmission cut-off is due to (a) a reflection interference maximum between wavelengths 800 and 1200 nm, (b) high absorption in the ITO layers between 1200 and 1500 nm and (c) high reflection for wavelengths >1500 nm, caused by a large increase in the refractive index of ITO. Experimentally more than 85% transmission cut-off for wavelengths >900 nm has been achieved using a 7-layer assembly. Modelling indicates an even better transmission cut-off for wavelengths >850 nm with 8 such layers.

This paper presents a theoretical investigation of the temperature distributions generated by a small heat source mounted on or embedded in semiconductor material. The dynamic thermal behaviour of the structures is studied in the frequency domain using phasor notation for the temperature and heat flux fields. Both classical and hyperbolic thermal conductions are considered. The latter accounts for the finite heat propagation speed, which is necessary for accurately describing very fast transitions. Although a uniform power density is applied, the temperature distribution inside the source is spatially non-uniform. As is already well known, this even holds for steady state conditions. For high frequencies, however, the maximum magnitude (i.e. largest oscillations) of the temperature occurs near the edges and corners of the heat source, rather than in the centre where it could intuitively be expected. This anomalous behaviour is observed for a wide variety of configurations, ranging from a simple 1D analytical slab model to numerical results for a 3D multi-layered electronic package. The classical theory clearly underestimates the edge effect, particularly for submicrometre structures. The substantial deviation from the distributions obtained by non-Fourier theory illustrates that special care should be taken when analysing fast heat transfer in small electronic devices.

This paper presents the characteristics of vacuum laser acceleration in circularly polarized (CP) fields with the capture and acceleration scenario (CAS) scheme. Compared with linearly polarized laser fields, the main advantage for using a CP field is that its acceleration channel occupies a relatively larger phase space, stemming from the distribution of the longitudinal electric component, the dependence on the laser initial phase and on the incident polarization azimuth angle, etc. These features can give rise to greater acceleration efficiency. One of the disadvantages is the 'energy saturation' phenomenon if the laser intensity is sufficiently high, which comes from the additional Lorentz force component in the CP field. The output properties of the accelerated CAS electron bunch, such as the energy spectra, the angular distributions, the energy-angle correlations, the acceleration efficiency, the rms emittance and the energy divergence, are also examined. Physical explanations concerning these characteristics are presented.

Broadband infrared luminescence centred at around 1300 nm with full-width at half maximum of about 342 nm was observed from transparent Ni²⁺-doped lithium-alumino-silicate glass-ceramics embedded with β-eucryptite crystallines. The room temperature fluorescent lifetime was 98 µs. The transparent glass-ceramics may have potential applications in a widely tunable laser and a super-broadband optical amplifier for optical communications.

Due to the difficulty of H₂ storage, development of real time H₂ generators would be advantageous for portable fuel cells. In this paper, the real time production of H₂ using microdischarge devices is discussed with results from a computational investigation. Ar/NH₃ mixtures were studied using plug flow and two-dimensional models. Dissociation of NH₃ by electron impact and thermal processes produces H atoms which recombine to form H₂. We found that for sandwich type microdischarges with a diameter of 300 µm, dissociation of NH₃ is approximately 95% by electron impact and 5% by thermal processes for a NH₃ mole fraction of 5%. Efficiency of conversion of NH₃ to H₂ is dependent on residence time in the discharge, mole fraction and geometry, as these properties determine the eV/molecule deposited into NH₃. Conversion efficiencies (fraction of H in NH₃ converted to H₂) in excess of 83% are predicted for optimum conditions.

An electric thruster is presented that makes use of the properties of an asymmetric hollow cathode glow discharge that ejects a collimated plume of high velocity neutral atoms. Ions are accelerated electrostatically outwards from within the asymmetric hollow cathode and undergo charge exchange with the background gas resulting in energetic neutrals being ejected, thus producing thrust. This thruster is entirely self-contained allowing thrust generation and beam neutralization within the discharge. Doppler spectroscopy was used to determine the speed of atomic hydrogen in the plume and was found to produce a specific impulse greater than 3 × 10⁴ s for applied voltages and powers of the order of 5 kV and 100 W, respectively. An estimate of the thrust of 1 mN for a power input in the order of 1 kW was obtained from previously measured ion densities in similar discharges. This work builds on recent work associated with the ejection of high velocity neutrals from hollow cathode discharges. The simple but effective design of the thruster has the potential for large thrust densities as well as successful long term operation.

Electron swarm parameters, such as the drift velocity and the ionization coefficient, in water vapour have been measured for relatively wide ranges in reduced electric fields (E/N) at room temperature. The drift velocity (W_m) was obtained based upon the arrival-time spectra of electrons by using a double-shutter drift tube for the E/N from 60 to 1000 Td, while the first and second ionization coefficients (α and γ) were determined by the steady-state Townsend method from 50 to 3000 Td. A comparison between the results and other data in the literature shows that our results for both the drift velocity and the effective ionization coefficient are lower than those of the other data in the above ranges.

A wall-stabilized arc in a polytetrafluoroethylene nozzle was investigated. Very similar arc properties as in the ablation dominated high-current phase of SF₆ circuit breakers were expected. Spectroscopic measurements of arc temperature profiles were performed. Spectral lines of fluorine and ionized carbon were observed. The side-on intensities of optically thin spectral lines were measured. Abel inversion was applied and the emission coefficient was determined. Temperatures of 16 000 to 18 000 K in the arc centre were obtained at various times of the current pulse. The pressure values were in the range 10–30 bar and arc currents varied from 10 to 20 kA. In the framework of the model, radial temperature profiles were determined with an accuracy of ±4%.

Propagation of sound in a medium where the rate of local heat addition is a function of gas density is analysed theoretically and the results are applied for modelling the experimentally observed effect of amplification of acoustic waves by an extended glow discharge in air. The model adequately describes the experimental dependences of the gain on the wave frequency and discharge power density and predicts that the amplification of sound by an unconfined glow discharge in air increases with discharge current density but does not change noticeably with gas pressure when the current density is kept constant. Quantitative estimates indicate that a gain of as high as 1 m⁻¹ (or 9 dB for a 60 dB wave passing through 1 m of plasma) could be realized using a discharge in air with a current density of 100 mA cm⁻².

Micro-electrical discharge machining is an evolution of conventional EDM used for fabricating three-dimensional complex micro-components and microstructure with high precision capabilities. However, due to the stochastic nature of the process, it has not been fully understood. This paper proposes an analytical model based on electro-thermal theory to estimate the geometrical dimensions of micro-crater. The model incorporates voltage, current and pulse-on-time during material removal to predict the temperature distribution on the workpiece as a result of single discharges in micro-EDM. It is assumed that the entire superheated area is ejected from the workpiece surface while only a small fraction of the molten area is expelled. For verification purposes, single discharge experiments using RC pulse generator are performed with pure tungsten as the electrode and AISI 4140 alloy steel as the workpiece. For the pulse-on-time range up to 1000 ns, the experimental and theoretical results are found to be in close agreement with average volume approximation errors of 2.7% and 6.6% for the anode and cathode, respectively.

In this work a model of the breakdown that includes the photoeffect on the cathode is presented. We observed successful development of the cylindrical ionization wave sliding along the insulator in the plasma focus as it does in the real device at a pressure of 3 Torr.

The mechanisms of the volumetric erosion rate reduction of the channel wall were studied theoretically and numerically in order to explain the reasons why the volumetric erosion rate of Hall thruster channel decreases over time. The results of the theoretical analysis indicate that the variation of three sputtering conditions results from the increase in the tilt angle and the erosion depth of the channel wall erosion surface during the surface evolution process. The mass loss of the Hall thruster channel wall material is a reduction process due to which the ion flux divergent angle is smaller than the value that corresponds to the sufficient condition of the reduction process. The simulation results of the channel wall erosion process qualitatively agree well with the experimental results, and the numerical analysis of the reduction process shows that the magnitude orders of three sputtering condition variation effects on the volumetric erosion rate reduction are the same, and the reduction rate reaches its maximum value in the initial operation period when the ion radiation angle equals the optimum sputtering rate angle. This work provides theoretical fundamentals of the channel wall erosion reduction process and it can be used for the lifetime prediction and optimum design of the Hall thruster.

A simple collisional–radiative model for low-pressure argon discharges is proposed. Using this model and the measured cross section data from recent literature, the relationship between the electron density and some emission line intensities is investigated, resulting in a semi-empirical formula relating the electron density and the emission intensity ratio of argon lines (from levels 3p and 4p). The electron density determined from this model is compared with that from a Langmuir probe in an inductively coupled argon plasma. The application and validity of this model in other kinds of low-pressure argon plasmas, such as capacitively coupled and helicon plasmas, or in discharges containing both argon and other gases are discussed.

We report a systematic study to determine local elastic properties of surfaces using atomic force acoustic microscopy(AFAM). AFAM is a combination of atomic force microscopy (AFM) and acoustic waves. We describe the technique and principle of AFAM in detail and interpret the obtained images using simple arguments. We have used (1) polished commercial piezoelectric PZT, Pb(Zr,Ti)O₃ ceramic, (2) thin film of PZT deposited by the sol–gel technique and (3) thin film of Au deposited on a Si(0 0 1) substrate to elucidate the capability of the AFAM technique to image the distribution of local stiffness over the sample surface. We have also used a complementary technique such as force–distance measurements using the AFM mode to support the interpretation of the AFAM images. We have determined semi-quantitatively the change in the local stiffness over the sample surface using both the force–distance measurement and the change in the contact resonance peak frequency at various regions. We have also shown that the AFAM technique can be used to get a better surface image contrast where contact mode AFM shows poor contrast.

Iron oxide nanostructures with significantly fewer droplets were successfully synthesized by pulsed laser deposition using a special target–substrate geometry, which is coined backward plume deposition. The morphology of deposited nanostructures for backward plume deposition is found to be strongly controlled by the ambient gas pressure and changes from a thin film to an assemble of nanoclusters to nanoclusters with loosely bound floccule-like network with the increase in ambient gas pressure. The post-annealing considerably changes the structural properties of deposited materials, which were determined to be magnetite FCC-Fe₃O₄. It also causes the relaxation of long range stress in the film and hence leads to an increase in the saturation magnetization. The coercivity is found to decrease upon annealing due to the growth of randomly oriented Fe₃O₄ nanocrystallite as well as the relaxation of internal stress.

Poly(o-anisidine) (POA) films were synthesized on mild steel from an aqueous oxalic acid solution by electrochemical polymerization of o-anisidine using cyclic voltammetry. These films were characterized by cyclic voltammetry, UV–visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The enzyme glucose oxidase (GOx) was entrapped into the POA film by a physical adsorption method. The resulting POA–GOx films were characterized by UV–visible absorption spectroscopy, FTIR and SEM. The amperometric response of the POA–GOx films was measured as a function of glucose concentration in phosphate buffer solution (pH 7.3). The POA–GOx films exhibited a fast amperometric response (1–5 s) and a linear response in the range of 2–20 mM glucose. The maximum current density and Michaelis–Menten constant of POA/GOx films were found to be ∼406 µA cm⁻² and 1.03 mM, respectively. The shelf stability, operational stability and thermal stability of these films were also investigated.

Carbon nanotubes (CNTs) have substantial promise as nanocontainers filled with fluid in their hollow cavity in nanotechnology. This paper reports the result of an investigation into the influence of internal fluid on the coupling vibration of fluid-filled CNTs. The coupling vibrational behaviour of fluid-filled CNTs under different supported ends, aspect ratio, surrounding elastic medium, mass density of the fluid and layer number is investigated. The results obtained describe the effect of end condition, aspect ratio, surrounding elastic medium, mass density of the fluid and layer number on the coupling natural frequencies. The new features of the coupling vibration of fluid-filled CNTs and some meaningful and interesting results in this paper are helpful for the application and design of nanostructures conveying fluid in which CNTs act as basic elements.

Using a nm-level powder fabricated by a wet chemical method as precursor, the CeO₂-doped WO₃ ceramics were prepared by the conventional solid state reaction at sintering temperatures from 600 to 1100 °C. The x-ray diffraction analysis reveals the coexistence of different WO₃ phases in the samples sintered at temperatures below 900 °C, whereas a single phase appears in the samples sintered above 1000 °C. No new Ce–W compound appears. As the sintering temperature increases, the electrical properties of the samples display an interesting transformation from linear to nonlinear behaviour. The measurements of scanning electron microscope, complex impedance and electrical stability indicate that a lot of grain boundary regions in the samples sintered at low temperatures strongly influences the electrical transportation. Therefore, the electrical nonlinearity is due to a basic process controlled by the back-to-back Schottky barriers at grain boundaries with suitable thickness as well as the coexistence of phases.

One-dimensional photonic crystals and quasiperiodic structures composed of positive and negative index materials were physically fabricated by using conventional microstrip line units and composite right/left-handed transmission line units. It is theoretically shown that the structures possess zero- gaps which are invariant with a change in the scale length, and the edges of the zero- gap are determined by and , respectively. We experimentally demonstrate the independence of the zero- gaps on the scaling by augmenting the respective length by the same factor and confirm the crucial function of and by constructing quasiperiodic structures. The experimental measurements agree well with the simulations.

The dependence of the thermoluminescent (TL) LiF : Mg,Ti response as a function of linear energy transfer (LET) has been investigated, through a careful analysis of the induced glow curve. We have irradiated TLD-100 chips in a stack with low fluences (5 × 10⁵–5 × 10⁷ cm⁻²) of a variety of ions: 1, 3, 25 and 40 MeV µ⁻¹ hydrogen, 25 and 40 MeV µ⁻¹ helium, 15, 25 and 40 MeV µ⁻¹ carbon, 25 MeV µ⁻¹ oxygen and 40 MeV µ⁻¹ neon, spanning a LET interval from 1.55 to 517 keV μ m⁻¹. For all peaks, except peak 8, the measured TL response is a linear function of deposited energy. We have observed differences between the LET dependence of the low- (4 and 5) and the high- (6a to 9) temperature peaks: the low-temperature peaks decrease their presence in the glow curve as LET increases, while the high-temperature peaks do the opposite. The peak 8 response exhibits linear–supralinear behaviour as a function of dose, the strongest LET dependence and the highest efficiency relative to gamma rays (about 20 near 200 keV μ m⁻¹). The observed evidence of the glow curve shape evolution with LET and the response to gamma rays suggests that the entities responsible for the LiF : Mg,Ti high- and low-temperature peaks have widely different properties.

We have investigated the emission characteristics of a Co–Dy liquid alloy ion source intended for focused ion beam implantation of cobalt and dysprosium ions. An alloy composition of Co₂Dy was selected in order to have a relatively low melting temperature, sufficient cobalt concentration for ion implantation purposes and low corrosion effects of the alloy and emitter tungsten wires. We have measured the melting behaviour of the alloy, the emission current stability, the current–voltage characteristics and the mass and energy spectra as a function of source current using a time-of-flight spectrometer. The ion source exhibits a good performance even after storage for several weeks in dry air. The mass spectra show a high intensity of doubly charged dysprosium ions and singly and doubly charged cobalt ions. The Co–Dy source works in a stable way for at least several days.

A collision model, modified from the Smoluchowski model, is developed for simulating coagulation and growth of a large number of aerosol particles with significantly different sizes. In this collision model, the particle-size distribution is discretized in volume bins, and the total mass among all the bins is conserved. In situations with significantly different particle sizes, the present model reduces the number of bins compared with the previous models, thus reducing the computational cost. By comparing the results of the present model with the exact solution of Smoluchowski's original model, the accuracy of the solution is not sacrificed. Therefore, this model enables the real-time simulation of three-dimensional, two-phase flow when flow/particle interactions need to be considered. After implementation with a flow solver, the model is further validated with the data from a smoke-reduction experiment in a room-scale chamber using flow-injected nanoparticle aggregates.

An incorrect version of figure 3 was included in the published article. The detail should be rotated by 45° as in the corrected figure below. This new image also shows more detail than the previously published one, and is in colour in the online edition.

Figure 3. Scan of the reciprocal (2KL) plane of Co₂FeSi/MgO. The intensity is plotted with a logarithmic colour scale and a constant background is subtracted. The square marks the investigated area.

On page 1842, the validity condition for equation (3) is given as T > _D/4, but should read as T < _D/4.

Plasma-aided nanofabrication is a rapidly expanding area of research spanning disciplines ranging from physics and chemistry of plasmas and gas discharges to solid state physics, materials science, surface science, nanoscience and nanotechnology and related engineering subjects. The current status of the research field is discussed and examples of superior performance and competitive advantage of plasma processes and techniques are given. These examples are selected to represent a range of applications of two major types of plasmas suitable for nanoscale synthesis and processing, namely thermally non-equilibrium and thermal plasmas. Major concepts and terminology used in the field are introduced. The paper also pinpoints the major challenges facing plasma-aided nanofabrication and identifies some emerging topics for future research.

Plasma fabrication provides an approach to create nanostructured materials. We summarize recent studies on the quantum dot, nanograss, porous film and nanocone that have been developed using plasma methods to date and investigate the antireflection properties of the nanograss by spectrophotometric measurements and rigorous coupled-wave analyses. The results show that the reflection of silicon wafer etched for 40 min can be reduced below 4.5% in the range DUV to near-IR (200–900 nm), which agrees well with the simulation as the two-dimensional periodic pyramidal shapes with a period of 25 nm are used to mimic the nanograss surface. With these novel nanostructures and interesting properties, plasma processes will be increasingly significant to nanofabrication, especially when process compatibility is necessary for Si technology.

Low pressure silane plasmas are known for their ability to synthesize silicon nanoparticles via gas phase nucleation. While in the past this particle formation has often been considered from the viewpoint of a contamination problem in semiconductor processing, we here describe a silane low pressure plasma that enables the synthesis of highly oriented, cubic-shaped silicon nanocrystals with a rather monodisperse size distribution. These silicon nanocubes have successfully been used in the manufacture of single nanoparticle vertical transistors. We discuss the advantages of this new paradigm of building nanoelectronic devices. The plasma synthesis process is characterized in more detail than in prior work. The particle nucleation, growth and shape evolution are studied. Results indicate that the process provides two spatially distinct zones: a diffuse plasma for particle growth and a constricted plasma zone for particle annealing. Measurements of the plasma ion density using a capacitive probe suggest that the plasma density in the constricted region of the plasma is about an order of magnitude higher than in the diffuse region, likely aiding the formation of cubic silicon nanocrystals. The process of particle extraction from the plasma reactor is discussed based on the balance of various forces acting on the particles. It is found that the use of a critical orifice for particle extraction enables the detrapping of particles which carry as many as 35 elementary charges.

The synthesis of silicon nanocrystals in standard radio-frequency glow discharge systems is studied with respect to two main objectives: (i) the production of devices based on quantum size effects associated with the small dimensions of silicon nanocrystals and (ii) the synthesis of polymorphous and polycrystalline silicon films in which silicon nanocrystals are the elementary building blocks. In particular we discuss results on the mechanisms of nanocrystal formation and their transport towards the substrate. We found that silicon nanocrystals can contribute to a significant fraction of deposition (50–70%) and that they can be positively charged. This has a strong influence on their deposition because positively charged nanocrystals will be accelerated towards the substrate with energy of the order of the plasma potential. However, the important parameter with respect to the deposition of charged nanocrystals is not the accelerating voltage but the energy per atom and thus a doubling of the diameter will result in a decrease in the energy per atom by a factor of 8. To leverage this geometrical advantage we propose the use of more electronegative gases, which may have a strong effect on the size and charge distribution of the nanocrystals. This is illustrated in the case of deposition from silicon tetrafluoride plasmas in which we observe low-frequency plasma fluctuations, associated with successive generations of nanocrystals. The contribution of larger nanocrystals to deposition results in a lower energy per deposited atom and thus polycrystalline films.

Transport of nano-particles in rf discharges without and with an amplitude modulation (AM) of the discharge voltage has been examined using a two-dimensional laser-light-scattering method. During the discharging period, nano-particles are mainly generated in the plasma/sheath boundary region near the powered electrode. They move away from their generation region towards the upper grounded electrode after turning off discharges due to thermophoretic force. Using AM discharges, nano-particles can be transported, during the modulation period, from their generation region to the plasma/sheath boundary region near the upper grounded electrode. The transport time is at least six times shorter than that after turning off unmodulated discharges. Two key parameters for the fast transport using AM discharges are the discharge voltage and the period of the AM.

A review is provided covering metal plasma production, the energetic condensation of metal plasmas, and the formation of nanostructures using such plasmas. Plasma production techniques include various approaches to ionizing metal vapour in a high-current discharge. Of special importance are different forms of ionized physical vapour deposition, namely magnetron sputtering with ionization of sputtered atoms in radio frequency discharges, metal self-sputtering, and high power impulse magnetron sputtering, filtered cathodic arcs and pulsed laser ablation. The discussion of energetic condensation focuses on the control of the kinetic energy by biasing. It also includes considerations of the potential energy and the surface and sub-surface processes occurring during ion subplantation and implantation. In the final section on nanostructures, two different approaches are discussed. In the top-down approach, the primary nanostructures are lithographically produced and metal plasma is used to conformally coat or completely fill trenches and vias. Additionally, multilayers with nanosize periods (nanolaminates) can be produced. In the bottom-up approach, thermodynamic forces are used to fabricate self-organized nanocomposites and nanoporous materials by decomposition and dealloying.

This paper presents a number of factors which have been found to be important to the growth of carbon nanotubes and nanofibres by plasma enhanced chemical vapour deposition. The effect of the electric field in a plasma discharge on nanotube growth is investigated and shown to be important in achieving nanotube alignment. The use of a plasma discharge also enables deposition to take place at lower temperatures, facilitating the use of substrates which would otherwise be damaged. The effect of varying the ratio of carbon feedstock gas to etchant gas is investigated and the ratio is shown to be important for controlling the shape of deposited nanostructures. The effects of varying plasma power are investigated, showing that greater plasma power results in a lower growth rate. Higher levels of plasma power are also shown to cause the sidewalls of deposited carbon nanotubes to be etched. Finally, the growth rate of carbon nanotubes and nanofibres is shown to depend upon the strength of the local electric field. It is proposed that a higher field causes greater ionization within the plasma, which results in a higher growth rate. This is borne out by comparing simulation results with experimental observations.

Zirconia (ZrO₂) thin films were prepared on Si (1 0 0) substrates by plasma-assisted cathodic arc deposition under different processing conditions. The structure and phase composition of the zirconia films were investigated by x-ray diffraction, x-ray photoelectron spectroscopy, and atomic force microscopy. Their properties, including the ability to induce the formation of apatite on the surface in a simulated body fluid, and dielectric characteristics were studied. The tetragonal phase predominates in the ZrO₂ film and its surface microstructures are strongly dependent on the processing conditions such as substrate temperature and bias applied during plasma-assisted deposition. The influence of the deposition parameters on the microstructures and properties of the ZrO₂ films was systematically investigated and our results indicate that the desired attributes and performance of the ZrO₂ films can be achieved by optimization of the plasma and deposition processing parameters. Our results provide further insight into producing films of the required quality using plasma-assisted cathodic arc deposition.

Recombination of neutral oxygen atoms on oxidized niobium foil was studied. Three sets of samples have been prepared: a set of niobium foils with a film of polycrystalline niobium oxide with a thickness of 40 nm, another one with a film thickness of about 2 µm and a set of foils covered with dense bundles of single-crystal Nb₂O₃ nanowires. All the samples were prepared by oxidation of a pure niobium foil. The samples with a thin oxide film were prepared by exposure of as-received foils to a flux of O-atoms, the samples with a thick polycrystalline niobium oxide were prepared by baking the foils in air at a temperature of 800 °C, while the samples covered with nanowires were prepared by oxidation in a highly reactive oxygen plasma. The samples were exposed to neutral oxygen atoms from a remote oxygen plasma source. Depending on discharge parameters, the O-atom density in the postglow chamber, as measured with a catalytic probe, was between 5 × 10²⁰ and 8 × 10²¹ m⁻³. The O-atom density in the chamber without the samples was found rather independent of the probe position. The presence of the samples caused a decrease in the O-atom density. Depending on the distance from the samples, the O-atom density was decreased up to 5 times. The O-atom density also depended on the surface morphology of the samples. The strongest decrease in the O-atom density was observed with the samples covered with dense bundles of nanowires. The results clearly showed that niobium oxide nanowires exhibit excellent catalytic behaviour for neutral radicals and can be used as catalysts of exhaust radicals found in many applications.

Silicon carbide thin films are self-assembled onto crystalline silicon substrate from a sintered SiC target at low substrate temperature of 400 °C in Ar + H₂ discharge using inductively coupled plasma (ICP) assisted RF magnetron sputtering system. Surface morphology and structural properties of SiC films are investigated by SEM, XRD, FTIR and EDX. SEM, XRD and FTIR results show that the SiC film deposited at an ICP power of 800 W is 3C-SiC nanocrystalline film while the film deposited without ICP power exhibits an amorphous structure. At ICP power of 800 W, there exists a large amount of dissociated H in the plasma, leading to the structural relaxation of the amorphous network towards the crystalline state. The EDX result shows that elemental compositions of Si and C atoms in both the films are almost stoichiometric.

A complex multi-scale model and numerical simulations are used to demonstrate, by simulating the development of patterns of nanotips, nanowalls, nanoislands and nanovoids of a characteristic size of 5–100 nm, a greater degree of determinism in the formation of various nanostructures by using the low-density, low-temperature plasma-based processes. It is shown that in the plasma, in contrast to the neutral gas-based processes, one can synthesize nanostructures of various dimensionalities and shapes with a larger surface density, desired geometrical parameters and narrower size distribution functions. This effect is mainly attributed to strong ion focusing by irregular electric fields in the nanopatterns, which effectively redistributes the influxes of plasma-generated building units and thus provides a selective control of their delivery to the growing nanostructures.

This paper reviews the discovery and developments of a new material, sp³-bonded 5H–BN, and some other related new nanomaterials such as hollow-cored nanoforms of BN and B/BN, which have been prepared by synergetic deposition processes using a radio frequency plasma and an excimer laser at 193 nm. The sp³-bonded 5H–BN is a new member to the old sp³-bonded couple of wurtzite and cubic BN. Regarding the growth mechanisms, the roles of plasma and laser, which have been investigated by the authors in the last decade, are reviewed and integrated to emphasize the synergetic effects. Excellent electron field emission and ultraviolet light emission at 225 nm have been found in the film and powder samples of sp³-bonded 5H–BN, respectively. Deep insights into the vapour growth mechanism of cubic boron nitride (cBN) with the help of laser and/or plasma have also been obtained.

In this work a low-cost parallel technique for creating chemical nano-patterned surfaces using nano-spheres as masks is presented. This technique, called nano-sphere lithography, makes use of different steps of plasma etching and deposition processes, for the creation of polymeric nano-structures of different chemical functionalities with relevant applications to bio-interfaces. In this study, the attention is focused on the plasma processing aspects for the etching of the polymeric masks (colloidal masks) in order to control the shape and the size of the etched nano-structures. The bio-functionality of the nano-patterned surfaces has been proved with a selective immobilization of proteins on the bioactive spots.

TiO₂ nanoparticles have been synthesized in this work via Ar/O₂ RF thermal plasma oxidation of atomized liquid precursors containing titanium tetrabutoxide and diethanolamine. Quench gases (Ar or He), either injected from the shoulder of the reactor (transverse injection) or injected counter to the plasma plume from the bottom of the reactor (counter-flow injection), are used to affect the quench rate and therefore the particle size and phase constituent of the resultant powders. The experimental results show that counter-flow injection is more effective in reducing the particle size, while He is more effective than Ar. As a result, well-dispersed TiO₂ nanopowders with controllable phase structure (up to ∼90% of anatase) and average particle size (down to 20 nm) are obtained. The experimental results are well supported by numerical analysis on the effects of the quench gas on flow pattern and temperature field of the thermal plasma as well as trajectory and temperature history of the particles.

Two methods for the synthesis of nanostructured silicon carbide films are discussed and compared, thermal plasma chemical vapour deposition (TPCVD) and hypersonic plasma particle deposition (HPPD). Both methods produce β-SiC films with high growth rates on the order of 10 µm min⁻¹. In TPCVD the generation of nanoscale grain sizes is caused by the fact that the film growth rate is much higher than the rate of surface diffusion. In HPPD a nanostructured film is grown by direct nanoparticle impact. In general, the films grown by TPCVD are denser and harder than in HPPD. X-ray diffraction spectra show that β-SiC is essentially the only crystalline phase in the TPCVD films, whereas in HPPD a silicon crystalline phase is also present, even for films that are overall carbon-rich. Evidence is presented to support the hypothesis that HPPD films actually grow by a combination of nanoparticle impact and CVD. If this parallel process can be controlled, it could potentially lead to the design and high-rate synthesis of new nanostructured materials.

Carbon nanostructures have received much attention for a wide range of applications. This paper reviews the historical role of plasmas in the gas-phase synthesis of carbon nanostructures and the present plasma technologies for industrial production purposes. It enumerates the advantages and disadvantages with respect to concurrent technologies commonly employed nowadays. Finally, some carbon nanostructures produced in our laboratory will serve as examples of the plasma processes potential.

High quality single-walled carbon nanotubes (SWNT) have been synthesized at large scales by the method of direct evaporation of carbon black and metallic catalyst mixtures, using induction thermal plasma technology. The processing system consists mainly of an RF plasma torch, which generates a plasma jet of extremely high temperature (∼15 000 K), with a high energy density and abundance of reactive species (ions and neutrals). With the present reactor system, it has been demonstrated that carbon soot product which contains approximately 40 wt% of SWNT can be continuously synthesized at the high production rate of ∼100 g h⁻¹. The processing parameters involved have been examined closely in order to evaluate their individual influences on SWNT synthesis. The results have shown that the quality and purity of the SWNT produced are critically affected by the grade of carbon black, the plasma gas composition and the metallic catalyst employed. Theoretical calculations, including thermodynamic and two-dimensional thermal flow analyses, have also been performed to determine the optimal process environment most suitable for SWNT synthesis and to obtain a better understanding of the effects of process parameters. Finally, product comparisons have been made against other reference materials using Raman spectroscopy, which has shown that the quality of thermal plasma-grown SWNT is superior to that of arc discharge-grown SWNT and approaches the quality of laser-grown SWNT. This result confirms that the induction thermal plasma technology developed in this work is one of the most promising methods for the production of high quality SWNT at large scales for commercial uses.

In this paper a model of single wall carbon nanotube (SWNT) interactions with thermal plasma is developed. Several effects such as momentum, charge and energy transfer between the SWNT and plasma are considered. It is shown that the SWNT charge and potential with respect to the plasma, as well as SWNT aspect ratio, depend on plasma density and electric field in the interelectrode gap. For instance, the SWNT charge changes from negative to positive value with electron density decrease. This model suggests several ways to improve the controllability of SWNT synthesis in arc discharge, such as an increase in plasma density and the application of an electric field. It is predicted that higher plasma density in the SWNT formation region and electric field lead to the formation of SWNT with a very high aspect ratio.

Suspension direct current plasma spraying allows achieving finely structured coatings whose thickness is between few tens and few hundreds of micrometres. Drops (200–300 µm in diameter) or liquid jets are mechanically injected in the plasma jet. With radial injection they are rapidly (a few µs) fragmented into droplets (a few µm in diameter). The latter are vaporized (in a few µs) and the solid particles contained in suspension droplets are accelerated and melted by the plasma jet. As in conventional plasma spraying (CPS), much smaller splats (with diameters between 0.2 and 3 µm and thicknesses between 30 and 200 nm) are arranged in layers up to form the coating. The low inertia of particles requires spray distances between 40 and 60 mm which induces plasma heat fluxes up to 22 MW m⁻² participating in coating densification. Even more than in CPS, the plasma jet fluctuations, particularly for plasmas containing di-atomic gases, perturb drops penetration and fragmentation. It has been chosen to illustrate difficulties and possibilities of this new method, through the spraying of the three layers of an element of solid oxide fuel cells. Indeed, it requires a dense stabilized zirconia electrolyte, if possible thin (15–20 µm) with two porous electrodes: cathode made of perovskite prone to decomposing upon spraying and anode made of two materials (nickel and zirconia) with very different melting points. These components were obtained by spraying ethanol suspensions, with, first, LaMnO₃ perovskite particles doped with 10 mol% of MnO₂ and 3 µm in mean diameter sprayed with pure argon to limit their decomposition and achieve porous coatings, second, Yttria (13 wt%) stabilized zirconia (YSZ) with two different particle size distributions and morphologies for which plasma compositions were adapted, producing in both cases 15 µm thick and fully dense coatings, third, porous Raneigh nickel by co-spraying the YSZ suspension and solution of nickel nitrate.

An experimental and computational study is conducted for the Si-based functional nanoparticle fabrication in an inductively coupled thermal plasma reactor. In the computational study, the improved multi-component co-condensation model with nodal discretization is proposed to clarify the nanoparticle growth mechanism in the consideration of coagulation and thermophoresis as well as simultaneous co-condensation. The nanoparticle growth by nucleation and co-condensation completes approximately in 12.6 ms for the Mo–Si system and in 5.0 ms for the Ti–Si system. Mo nanoparticles grow in advance, and then Si vapour condenses on the Mo nanoparticles in the Mo–Si system, while vapours of Si and Ti simultaneously co-condense following Si nucleation in the Ti–Si system. A smaller number of larger nanoparticles are created with an increase in the powder feed rate. When the silicon content in the feed powders is 66.7%, nanoparticles of MSi₂ (M = Mo, Ti) are fabricated as the main product. Nanoparticles of Ti₅Si₃ are mainly synthesized in the case of the silicon content 33.0%. In the experiment, the nanoparticles are successfully fabricated and examined by x-ray diffractometry and transmission electron microscopy. The experimental and computational results show good agreement in the size distribution and the composition.