Table of contents

This review paper presents historical perspectives, recent advances and future directions in the multidisciplinary research field of plasma nanoscience. The current status and future challenges are presented using a three-dimensional framework. The first and the largest dimension covers the most important classes of nanoscale objects (nanostructures, nanofeatures and nanoassemblies/nanoarchitectures) and materials systems, namely carbon nanotubes, nanofibres, graphene, graphene nanoribbons, graphene nanoflakes, nanodiamond and related carbon-based nanostructures; metal, silicon and other inorganic nanoparticles and nanostructures; soft organic nanomaterials; nano-biomaterials; biological objects and nanoscale plasma etching. In the second dimension, we discuss the most common types of plasmas and plasma reactors used in nanoscale plasma synthesis and processing. These include low-temperature non-equilibrium plasmas at low and high pressures, thermal plasmas, high-pressure microplasmas, plasmas in liquids and plasma–liquid interactions, high-energy-density plasmas, and ionized physical vapour deposition as well as some other plasma-enhanced nanofabrication techniques. In the third dimension, we outline some of the 'Grand Science Challenges' and 'Grand Socio-economic Challenges' to which significant contributions from plasma nanoscience-related research can be expected in the near future. The urgent need for a stronger focus on practical, outcome-oriented research to tackle the grand challenges is emphasized and concisely formulated as from controlled complexity to practical simplicity in solving grand challenges.

Low-temperature plasmas find numerous applications in growth and processing of nanomaterials such as carbon nanotubes, inorganic nanowires and others. This paper provides an overview of the history, current status of the literature, challenges ahead in some of the technical areas and the potential for plasma-grown nanomaterials in various nanotechnology applications.

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.

Plasma-based nanotechnology is a rapidly developing area of research ranging from physics of gaseous and liquid plasmas to material science, surface science and nanofabrication. In our case, nanoscopic plasma processing is performed to grow single-walled carbon nanotubes (SWNTs) with controlled chirality distribution and to further develop SWNT-based materials with new functions corresponding to electronic and biomedical applications. Since SWNTs are furnished with hollow inner spaces, it is very interesting to inject various kinds of atoms and molecules into their nanospaces based on plasma nanotechnology. The encapsulation of alkali-metal atoms, halogen atoms, fullerene or azafullerene molecules inside the carbon nanotubes is realized using ionic plasmas of positive and negative ions such as alkali–fullerene, alkali–halogen, and pair or quasipair ion plasmas. Furthermore, an electrolyte solution plasma with DNA negative ions is prepared in order to encapsulate DNA molecules into the nanotubes. It is found that the electronic and optical properties of various encapsulated SWNTs are significantly changed compared with those of pristine ones. As a result, a number of interesting transport phenomena such as air-stable n- and p-type behaviour, p–n junction characteristic, and photoinduced electron transfer are observed. Finally, the creation of an emerging SWNTs-based nanobioelectronics system is challenged. Specifically, the bottom-up electric-field-assisted reactive ion etching is proposed to control the chirality of SWNTs, unexplored SWNT properties of magnetism and superconductivity are aimed at being pioneered, and innovative biomedical-nanoengineering with encapsulated SWNTs of higher-order structure are expected to be developed by applying advanced gas–liquid interfacial plasmas.

The exceptional mechanical, chemical, thermal, electrical and optical properties of single-walled carbon nanotubes (SWCNTs) have tantalized the scientific community for over two decades. However, SWCNTs must be prepared with a high degree of uniformity, which represents a significant synthetic challenge, to make the envisioned technological applications a reality. Among the various approaches that have been developed to synthesize SWCNTs, plasma-based processes are attractive because of their important role in the electronics industry. In this perspective paper, the most recent and promising applications of plasma technology for chirality-controlled SWCNT synthesis are presented including preparation of well-defined catalysts, selective nucleation etching and reacting tubes after growth. Overall, these strategies have achieved improved uniformity over the structure and properties of SWCNTs and offer great potential for the integration of these novel materials in future electronic and optical devices.

In this perspective paper, we critically analyse the state-of-the-art of arc discharge technique of carbon nanoparticle synthesis. We discuss improving controllability of the arc discharge synthesis of carbon nanotubes, synthesis of graphene as well as general understanding of the synthesis process. Fundamental issues related to relationship between plasma parameters and carbon nanostructure characteristics are considered. Effects of electrical and magnetic fields applied during single-wall carbon nanotube synthesis in arc plasma are explored. Finally our personal opinion on what future trends will be in arc discharge synthesis is offered.

An atmospheric-pressure radio-frequency discharge (APRFD) has great advantages over vacuum-oriented plasma-enhanced chemical vapour deposition (PECVD) as well as other types of atmospheric-pressure plasma sources in terms of single-walled carbon nanotube (SWCNT) growth. We first provide an overview on the recent advances in PECVD synthesis of CNTs, ranging from low pressure to atmospheric pressure, and then we present our current work focusing on the analysis of reactive species generated in the cathodic plasma sheath for further understanding of the SWCNT growth mechanism in PECVD. It was found that the plasma-generated C₂H₂ is the main CNT growth precursor in PECVD. Approximately 30% of the CH₄ (initial feedstock) was converted into C₂H₆, C₂H₄ and C₂H₂. A trace amount of C₂H₂ enabled the synthesis of SWCNTs in the thermal chemical vapour deposition (CVD) regime. H₂ is necessary to grow SWCNTs using PECVD because H₂ suppresses the formation of excess amount of C₂H₂; however, H₂ does not eliminate amorphous carbon even at H₂/C₂H₂ ratios of 300. PECVD using a binary mixture of C₂H₂ and isotope-modified ¹³CH₄ demonstrated that CH₄ does not contribute to CNT growth in C₂H₂-assisted thermal CVD. Atmospheric-pressure PECVD performed with a He/CH₄/H₂ system is equivalent to C₂H₂-assisted thermal CVD without an etching gas. APRFD appears to produce a hidden species, which influences the CNT growth process.

The ability to synthesize free-standing, individual carbon nanofibres (CNFs) aligned perpendicularly to a substrate has enabled fabrication of a large array of devices with nanoscale functional elements, including electron field emission sources, electrochemical probes, neural interface arrays, scanning probes, gene delivery arrays and many others. This was made possible by development of a catalytic plasma process, with DC bias directing the alignment of nanofibres. Successful implementation of prototypical devices has uncovered numerous challenges in the integration of this synthesis process as one of the steps in device fabrication. This paper is dedicated to these engineering and fundamental difficulties that hinder further device development. Relatively high temperature for catalytic synthesis, electrical conductivity of the substrate to maintain DC discharge and other difficulties place restrictions on substrate material. Balancing non-catalytic carbon film deposition and substrate etching, non-uniformity of plasma due to growth of the high aspect ratio structures, plasma instabilities and other factors lead to challenges in controlling the plasma. Ultimately, controlling the atomistic processes at the catalyst nanoparticle (NP) and the behaviour of the NP is the central challenge of plasma nanosynthesis of vertically aligned CNFs.

Semiconductor nanocrystals (NCs) offer new opportunities for optical and electronic devices ranging from single-electron transistors to large-area solar cells. Solution synthesis methods cannot reach the temperatures necessary to produce crystalline nanoparticles of covalently bonded materials, and most gas-phase techniques suffer from particle agglomeration and sintering. Nonthermal plasma synthesis, however, can produce high-quality NCs of key materials such as Si and Ge. In this review, we examine the current state and future challenges of the growing field of plasma-synthesized NCs from a device applications perspective. We identify NC microstructure, morphology, ensemble monodispersity, surface chemistry and doping as being vital to the success of next-generation devices, and we discuss research opportunities to understand and control these properties during plasma synthesis.

Plasma-made nanostructures show outstanding potential for applications in nanotechnology. This paper provides a concise overview on the progress of plasma-based synthesis and applications of silicon nanograss and related nanostructures. The materials described here include black silicon, Si nanotips produced using a self-masking technique as well as self-organized silicon nanocones and nanograss. The distinctive features of the Si nanograss, two-tier hierarchical and tilted nanograss structures are discussed. Specific applications based on the unique features of the silicon nanograss are also presented.

Plasmas have been widely utilized to pattern various materials, from metals to semiconductors and oxides to polymers, for a vast array of applications. The interplay between physical, chemical and material properties that comprises the backbone of plasma etching is discussed in this perspective paper, with a focus on the needed tools and approaches to address the challenges facing plasma etching and to realize the desired pattern transfer fidelity at the nanoscale.

The advances in information and communication technologies have been largely predicated around the increases in computer processor power derived from the constant miniaturization (and consequent higher density) of individual transistors. Transistor design has been largely unchanged for many years and progress has been around scaling of the basic CMOS device. Scaling has been enabled by photolithography improvements (i.e. patterning) and secondary processing such as deposition, implantation, planarization, etc. Perhaps the most important of the secondary processes is the plasma etch methodology whereby the pattern created by lithography is 'transferred' to the surface via a selective etch to remove exposed material. However, plasma etch technologies face challenges as scaling continues. Maintaining absolute fidelity in pattern transfer at sub-16 nm dimensions will require advances in plasma technology (plasma sources, chamber design, etc) and chemistry (etch gases, flows, interactions with substrates, etc). In this paper, we illustrate some of these challenges by discussing the formation of ultra-small device structures from the directed self-assembly of block copolymers (BCPs) where nanopatterns are formed from the micro-phase separation of the system. The polymer pattern is transferred by a double etch procedure where one block is selectively removed and the remaining block acts as a resist pattern for silicon pattern transfer. Data are presented which shows that highly regular nanowire patterns of feature size below 20 nm can be created using etch optimization techniques and in this paper we demonstrate generation of crystalline silicon nanowire arrays with feature sizes below 8 nm. BCP techniques are demonstrated to be applicable from these ultra-small feature sizes to 40 nm dimensions. Etch profiles show rounding effects because etch selectivity in these nanoscale resist patterns is limited and the resist thickness rather low. The nanoscale nature of the topography generated also places high demands on developing new etch processes.

Current approaches for analysis of the interrelations among plasma processing, morphological characteristics, electronic and optical properties of nano-structured materials are reviewed briefly. Practical implementation of these approaches is demonstrated for the cases of the plasma-assisted formation of silicon–germanium (Si_1−xGe_x, 0 ⩽ x ⩽ 1.0) nano-structures on Si substrates with different crystalline orientations. Both numerical simulations and experimental studies on the effects of plasma parameters, germanium concentration, boron doping, crystalline orientations of the substrate on low-temperature photoluminescence (PL) of the Si_1−xGe_x structures are considered. Different mechanisms of Si_1−xGe_x morphology formation (e.g. traditional Stranski–Krastanov route as well as new approaches like cluster fluxes created in the plasmas) are compared; the latter ones are more flexible and exhibit wider range of the potential applications. Furthermore, effects of morphological characteristics and phonon confinement as well as energetic characteristics of the optic and acoustic phonons on the PL and electronic parameters of the experimentally studied nano-structures are analysed within the generalized Skettrup model and 'displaced oscillator' approximation.

Large quantities of nanomaterials, e.g. nanowires (NWs), are needed to overcome the high market price of nanomaterials and make nanotechnology widely available for general public use and applications to numerous devices. Therefore, there is an enormous need for new methods or routes for synthesis of those nanostructures. Here plasma technologies for synthesis of NWs, nanotubes, nanoparticles or other nanostructures might play a key role in the near future. This paper presents a three-dimensional problem of large-scale synthesis connected with the time, quantity and quality of nanostructures. Herein, four different plasma methods for NW synthesis are presented in contrast to other methods, e.g. thermal processes, chemical vapour deposition or wet chemical processes. The pros and cons are discussed in detail for the case of two metal oxides: iron oxide and zinc oxide NWs, which are important for many applications.

Plasmas have been widely used for the fabrication of nanomaterials owing to their unique properties in chemical reactions. The plasma-enhanced chemical vapour deposition (PECVD) technique has been applied to produce a large variety of materials. In this perspective, we take a look at the progress made in the research of PECVD using chloride precursors in the last decade. We discuss the advantage of using a plasma compared with the thermal chemical vapour deposition technique and emphasize the special effects of plasma on nanomaterial fabrications in the PECVD technique, including kinetic and thermodynamic effects. We also outline the current challenges for this technique, and attempt to offer our personal opinion on the future applications of the PECVD technique with chloride precursors.

Plasma-related methods have been widely used in the fabrication of carbon nanotubes and nanofibres (NFs) and semiconducting inorganic nanowires (NWs). A natural progression of the research in the field of 1D nanostructures is the synthesis of multicomponent NWs and NFs. In this paper we review the state of the art of the fabrication by plasma methods of 1D heterostructures including applications and perspectives. Furthermore, recent developments on the use of metal seeds (Ag, Au, Pt) to obtain metal@oxide nanostructures are also extensively described. Results are shown for various metal substrates, either metal foils or supported nanoparticles/thin films of the metal where the effects of the size, surface coverage, percolation degree and thickness of the metal seeds have been systematically evaluated. The possibilities of the process are illustrated by the preparation of nanostructured films and supported NFs of different metal@oxides (Ag, Au and SiO₂, TiO₂, ZnO). Particularly, in the case of silver, the application of an oxygen plasma treatment prior to the deposition of the oxide was critical for efficiently controlling the growth of the 1D heterostructures. A phenomenological model is proposed to account for the thin-film nanostructuring and fibre formation by considering basic phenomena such as stress relaxation, inhomogeneities in the plasma sheath electrical field and the local disturbance of the oxide growth.

We present an overview of the possibilities offered by plasma technologies, in particular the combination plasma polymers deposition, colloidal lithography, e-beam lithography and microcontact printing, to produce micro- and nanostructured surfaces with chemical and topographical contrast for applications in nanobiotechnology. It is shown that chemical and topographical patterns can be obtained on different substrates, with dimensions down to a few tenths of 10 nm. The applications of these nanostructured surfaces in biology, biochemistry and biodetection are presented and the advantages and limitation of the plasma techniques in this context underlined.

Nanoparticles and low-temperature plasmas have been developed, independently and often along different routes, to tackle the same set of challenges in biomedicine. There are intriguing similarities and contrasts in their interactions with cells and living tissues, and these are reflected directly in the characteristics and scope of their intended therapeutic solutions, in particular their chemical reactivity, selectivity against pathogens and cancer cells, safety to healthy cells and tissues and targeted delivery to diseased tissues. Time has come to ask the inevitable question of possible plasma–nanoparticle synergy and the related benefits to the development of effective, selective and safe therapies for modern medicine. This perspective paper offers a detailed review of the strengths and weakenesses of nanomedicine and plasma medicine as a stand-alone technology, and then provides a critical analysis of some of the major opportunities enabled by synergizing nanotechnology and plasma technology. It is shown that the plasma–nanoparticle synergy is best captured through plasma nanotechnology and its benefits for medicine are highly promising.

The fast advances in nanotechnology have raised increasing concerns related to the safety of nanomaterials when exposed to humans, animals and the environment. However, despite several years of research, the nanomaterials safety field is still in its infancy owing to the complexities of structural and surface properties of these nanomaterials and organism-specific responses to them. Recently, plasma-based technology has been demonstrated as a versatile and effective way for nanofabrication, yet its health and environment-benign nature has not been widely recognized. Here we address the environmental and occupational health and safety effects of various zero- and one-dimensional nanomaterials and elaborate the advantages of using plasmas as a safe nanofabrication tool. These advantages include but are not limited to the production of substrate-bound nanomaterials, the isolation of humans from harmful nanomaterials, and the effective reforming of toxic and flammable gases. It is concluded that plasma nanofabrication can minimize the hazards in the workplace and represents a safe way for future nanofabrication technologies.

Some important issues related to the self-organization in the arrays of nanoparticles on solid surfaces exposed to the low-temperature plasma are analysed and discussed. The available tools for the characterization of the size and position uniformity in nanoarrays are examined. The technique capable of revealing the realistic adsorbed atom and adsorbed radical capture zone pattern based on the surface physics is indicated as the most promising characterization tool. The processes responsible for the self-organization are analysed, the main driving forces of the self-organization are discussed, and possible ways to control the self-organization by controlling the plasma parameters are introduced. A view on the possible ways to further improve the methods of nanoarray characterization and self-organization is presented as well.

We describe how plasma–wall interactions in etching plasmas lead to either random roughening/nanotexturing of polymeric and silicon surfaces, or formation of organized nanostructures on such surfaces. We conduct carefully designed experiments of plasma–wall interactions to understand the causes of both phenomena, and present Monte Carlo simulation results confirming the experiments. We discuss emerging applications in wetting and optical property control, protein immobilisation, microfluidics and lab-on-a-chip fabrication and modification, and cost-effective silicon mould fabrication. We conclude with an outlook on the plasma reactor future designs to take advantage of the observed phenomena for new micro- and nanomanufacturing processes, and new contributions to plasma nanoassembly.

The origin of organization of nanostructured silica coatings deposited on stainless steel substrates by remote microplasma at atmospheric pressure is investigated. We show by resorting to thermal camera measurements coupled with modelling that deposition, limited to a few seconds in time, occurs at low temperature (∼below 420 K) although the gas temperature may reach 1400 K. Raman analyses of deposited films with thicknesses below 1 µm show the presence of oxidized silicon bonded to the metallic surface. The origin of nanodots is explained as follows. Close to the microplasma nozzle, the concentration of oxidizing species and/or the temperature being high enough, a silica thin film is obtained, leading to ceramic–metallic oxide interface that leads to a Volmer–Weber growth mode and to the synthesis of 3D structures over long treatment times. Far from the nozzle, the reactivity decreasing, thin films get a plasma–polymer like behaviour which leads to a Franck–Van der Merwe growth mode and films with a higher density. Other nanostructures, made of hexagonal cells, are observed but remain unexplained.

Low-pressure, low-temperature plasmas are widely used for materials applications in industries ranging from electronics to medicine. To avoid the high costs associated with vacuum equipment, there has always been a strong motivation to operate plasmas at higher pressures, up to atmospheric. However, high-pressure operation of plasmas often leads to instabilities and gas heating, conditions that are unsuitable for materials applications. The recent development of microscale plasmas (i.e. microplasmas) has helped realize the sustainment of stable, non-thermal plasmas at atmospheric pressure and enable low-cost materials applications. There has also been an unexpected benefit of atmospheric-pressure operation: the potential to fabricate nanoscale materials which is not possible by more conventional, low-pressure plasmas. For example, in a high-pressure environment, nanoparticles can be nucleated in the gas phase from vapour (or solid metal) precursors. Alternatively, non-thermal, atmospheric-pressure plasmas can be coupled with liquids such as water or ethanol to nucleate and modify solution-phase nanoparticles. In this perspective paper, we review some of these recent efforts and provide an outlook for the rapidly emerging field of atmospheric-pressure plasmas for nanofabrication.

The application of nanosecond discharges towards nanomaterials synthesis at atmospheric pressure is explored in this perspective article. First, various plasma sources are evaluated in terms of the energy used to include one atom into the nanomaterial, which is shown to depend strongly on the electron temperature. Because of their high average electron temperature, nanosecond discharges could be used to achieve nanofabrication at a lower energy cost, and therefore with better efficiency, than with other plasma sources at atmospheric pressure. Transient spark discharges and nanosecond repetitively pulsed (NRP) discharges are suggested as particularly useful examples of nanosecond discharges generated at high repetition frequency. Nanosecond discharges also generate fast heating and cooling rates that could be exploited to produce metastable nanomaterials.

In this paper, we review the recent progress in nanofabrication by thermal plasmas, and attempt to define some of the most important issues in the field. For synthesis of nanoparticles, the experimental studies in the past five years are briefly introduced; the theoretical and numerical modelling works of the past 20 years are reviewed with some detailed explanations. Also, the use of thermal plasmas to produce nanostructured films and coatings is described. A wide range of technologies have been developed, ranging from chemical vapour deposition processes to new plasma spraying processes. We present an overview of the different techniques and the important physical phenomena, as well as the requirements for future progress.

Several advances in materials research have been made due to the wide array of tools currently available for the processing of materials: plasmas, electron beams, ion beams and lasers. The area of material science is fortunate to have seen the development of these tools over the years, be it for new bulk materials, coatings or for surface modification. Several applications have benefited and many more will in the future as the properties of the materials are altered on a micro/nanoscale. Currently, several techniques exist to modify the physical, chemical and biological properties of the material surface; however, this review limits itself to surface modification applications using the rapid thermal processing (RTP) technique. First, a brief overview of the existing surface modification methods using the principles of RTP is reviewed, and then a novel method to create micro/nanostructures on the surface using pulsed plasma exposure of materials is presented.

Nanofabrication processes employing reactive plasma, such as etching and deposition, were discussed in this paper on the basis of knowledge of reactive species in the plasma. The processing characteristics were studied based on the absolute density measurements of radicals and ions. In the case of organic low-k film etching employing N–H plasma, H and N radicals have different roles from each other; the H radicals contribute to the chemical etching, while the N radicals form the protection layer. Therefore, the ratio of H and N radical densities is an important factor for determining the etching performance. Furthermore, the radical injection technique, an active way to control the composition of radicals in the reaction field, was successfully applied to grow carbon nanowalls, self-organized, free-standing, layered graphenes. For example, with increasing density ratio of H and fluorocarbon (CF_x) radicals, the density of carbon nanowalls decreases. In addition, according to the carbon nanowalls' growth by the simultaneous irradiation of CF_x radicals, hydrogen atoms and Ar ions, the ion bombardment is crucial for the nucleation and vertical growth of carbon nanowalls. Identification and characterization of radicals and ions in the processing plasma could open the way to the precise controls of nano-scale plasma processing.

A promising method for the synthesis of metal oxide nanowires is based on the application of the extremely non-equilibrium gaseous environment found in oxygen plasma created by some types of discharges. The kinetic temperature of neutral gas is kept close to the room temperature, the electron temperature is a few eV, the ionization fraction below 10⁻⁶ and the dissociation fraction close to 100%. Plasma with such characteristics is obtained using electrodeless high frequency discharges driven by radiofrequency or microwave generators. Plasma parameters such as the electron density and energy distribution function, the Debye length, the dissociation and ionization fractions, the density of negatively charged molecules, the ratio between the positively charged molecules and atoms and the distribution of atoms and molecules over excited states depend on discharge parameters. The most important discharge parameters are the generator power, frequency and coupling, the purity and pressure of working gas and the gas flow, the dimensions of the discharge chamber, the materials facing plasma, the residual atmosphere, and, usually very importantly though often neglected, the properties of the samples mounted into a discharge chamber. Proper construction of the experimental system for the synthesis of metal oxide nanowires allows for almost 100% dissociation fraction and thus extremely rapid growing of nanowires. The particularities of oxygen plasma as well as real-time monitoring of the dissociation fraction are elaborated in this contribution. The lack of reliable experimental results on characterization of extremely non-equilibrium oxygen plasma is stressed.

Determination and understanding of energy fluxes to nano- or microparticles, which are confined in process plasmas, is highly desirable because the energy balance results in an equilibrium particle temperature which may even initiate the crystallization of nanoparticles. A simple balance model has been used to estimate the energy fluxes between plasma and immersed particles on the basis of measured plasma parameters. Addition of molecular hydrogen to the argon plasma results in additional heating of the particles due to molecule recombination. The measured particle temperature is discussed with respect to appearing plasma–particle interactions which contribute to the particle's energy balance.

In this review paper, an overview is given of different modelling efforts for plasmas used for the formation and growth of nanostructured materials. This includes both the plasma chemistry, providing information on the precursors for nanostructure formation, as well as the growth processes itself. We limit ourselves to carbon (and silicon) nanostructures. Examples of the plasma modelling comprise nanoparticle formation in silane and hydrocarbon plasmas, as well as the plasma chemistry giving rise to carbon nanostructure formation, such as (ultra)nanocrystalline diamond ((U)NCD) and carbon nanotubes (CNTs). The second part of the paper deals with the simulation of the (plasma-based) growth mechanisms of the same carbon nanostructures, i.e. (U)NCD and CNTs, both by mechanistic modelling and detailed atomistic simulations.

Results on modelling of the plasma-assisted growth of vertically aligned carbon nanostructures and of the energy exchange between the plasma and the growing nanostructures are reviewed. Growth of carbon nanofibres and single-walled carbon nanotubes is considered. Focus is made on studies that use the models based on mass balance equations for species, which are adsorbed on catalyst nanoparticles or walls of the nanostructures. It is shown that the models can be effectively used for the study and optimization of nanostructure growth in plasma-enhanced chemical vapour deposition. The results from these models are in good agreement with the available experimental data on the growth of nanostructures. It is discussed how input parameters for the models may be obtained.

There has been tremendous interest and progress with synthesis of inorganic nanowires (NWs). However, much of the progress only resulted in NWs with diameters much greater than their respective quantum confinement scales, i.e. 10–100 nm. Even at this scale, NW-based materials offer enhanced charge transport and smaller diffusion length scales for improved performance with various electrochemical and photoelectrochemical energy conversion and storage applications. In this paper, these improvements are illustrated with specific results on enhanced charge transport with tin oxide NWs in dye sensitized solar cells, higher capacity retention with molybdenum oxide (MoO₃) NW arrays and enhanced photoactivity with hematite NW arrays compared with their nanoparticle (NP) or thin film format counterparts. In addition, the NWs or one-dimensional crystalline materials with diameters less than 100 nm provide a useful platform for creating new materials either as substrates for heteroepitaxy or through the phase transformation with reaction. Specific results with single crystal phase transformation of hematite (a-Fe₂O₃) to pyrite (FeS₂) NWs and heteroepitaxy of indium-rich InGaN alloy over GaN NW substrates are presented to illustrate the viability of using NWs for creating new materials. In terms of energy applications, it is essential to have a method for continuous manufacturing of vertical NW arrays over large areas. In this regard, a simple plasma-based technique is discussed that potentially could be scaled up for roll-to-roll processing of NW arrays.

Plasma-aided fabrication has been largely employed in the photovoltaic industry and widely reported in the literature for the growth of Si-based solar cells and the dry etching of Si substrates. This paper reviews the current status of plasma technologies for the synthesis of Si-based thin films (including silicon nitride: SiN) and solar cells, removal of phosphorus silicate glass or parasitic emitters, wafer cleaning, masked or mask-free surface texturization and the direct formation of a p–n junction by means of p-to-n type conductivity conversion. The plasma physics and chemistry involved in these processes and their fundamental mechanisms are briefly discussed. Some examples of superior performance and competitive advantages of plasma processes and techniques are selected to represent a range of applications for solar cells. Finally, an outlook in the field of plasma-aided fabrication for photovoltaic applications is given.

The utilization of silicon-based materials for thermoelectrics is studied with respect to the synthesis and processing of doped silicon nanoparticles from gas phase plasma synthesis. It is found that plasma synthesis enables the formation of spherical, highly crystalline and soft-agglomerated materials. We discuss the requirements for the formation of dense sintered bodies, while keeping the crystallite size small. Small particles a few tens of nanometres and below that are easily achievable from plasma synthesis, and a weak surface oxidation, both lead to a pronounced sinter activity about 350 K below the temperature usually needed for the successful densification of silicon. The thermoelectric properties of our sintered materials are comparable to the best results found for nanocrystalline silicon prepared by methods other than plasma synthesis.

Over the years dust particles formed in plasmas and used for microelectronic technologies were considered as an important source of irremediable defects. They grow in the gas phase through homogeneous chemical reactions and remain trapped in the plasma gas phase due to the negative charge they acquire by electron attachment. The earlier formed particles are, under certain conditions, crystallites of 2 to 4 nm in diameter when operating at room temperature. These nanocrystallites can be used as quantum dots for many applications in nanoelectronics (single electron devices, etc), photoluminescent devices, optical amplification and biomedical applications. We show here that dusty plasmas can be a very efficient tool for the synthesis of these nano-objects. Using its physical properties we showed that it is possible to control the synthesis of nanocrystallites or nanoparticles with well-defined sizes. The sizes of the earlier nanocrystallites can also be tuned by varying the plasma physical parameters.

Space weather is a relatively new and important field of research. It is relevant to diverse topics such as radio communication, space travel, diagnostics of ionospheric and space plasmas, detection of pollutants and re-entry objects, prediction of terrestrial weather and global warming. Recently it has been shown that nano- and micrometre-sized electrically charged particulates from interplanetary space and from the Earth's atmosphere can affect the local properties as well as the diagnostics of the interplanetary, magnetospheric, ionospheric and terrestrial complex plasmas. In this report the sources of the charged dust particulates and the effects of the latter on the near-Earth space weather are examined.

The range of applications for plasmas in liquids, plasmas in contact with liquid surfaces and plasmas containing liquid drops is growing rapidly across a range of technologies. Here the focus is on plasmas where the electrodes are immersed in liquids and their applications in nanoscience. The physical phenomena in both high voltage (tens of kilovolts) and low voltage (a few hundred volts) plasmas in liquid are described together with a discussion of the plasma-induced chemistry. Studies show that in water the plasmas are formed in water vapour created by Joule heating as either channels in the liquid or as layers on the electrodes. The chemistry in these water vapour plasmas and at their interface with the liquid is discussed in the context of the highly reactive radicals produced, such as H and OH. The current use of a variety of plasmas-in-liquid systems in the area of nanoscience is discussed, with an emphasis on nanoparticle growth.

We propose the concept of 'nano-factory in plasma' which is a miniature version of a macroscopic conventional factory. A nano-factory in plasma produces nanoblocks and radicals (adhesives) in reactive plasmas, transports nanoblocks towards a substrate and arranges them on the substrate. We describe several key control methods for a nano-factory in plasma: size and structure control of nanoparticles, control of their agglomeration, transport and sticking, and then explain the combination of several types of control. Finally we point out remaining important issues in nano-factories in plasma.