sustainable nanoscience for a sustainable future

716 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 41, NO. 4, APRIL 2013

Sustainable Nanoscience for a Sustainable FutureKostya (Ken) Ostrikov

Abstract—The concept of sustainable nanoscience is introducedand illustrated using a focused example of plasma-based growthof carbon nanotubes. This concept relates control of energy andmatter at nanoscales (Grand Science Challenges) to practicalapplications that are relevant to a sustainable future of humankind(Grand Societal Challenges). Specific roles of plasma-related ef-fects in nanoscale synthesis and processing that lead to superiorproperties and performance of nanomaterials in relevant applica-tions are also examined. The path toward the impact in the age ofsustainable development is also discussed.

Index Terms—Control of energy and matter, Grand Science andSocietal Challenges, plasma nanoscience, sustainability, sustain-able nanoscience.

I. INTRODUCTION

SUSTAINABILITY is commonly perceived as the capacityto endure some challenges, obstacles, stress, varied condi-

tions, etc., and to continue normal or even improving operation[1]. This concept has recently become global and is currentlyapplied to economies, environment, ecosystems, industries,natural resource management, and several other fields of humanactivities [2]. To enable sustainability in any particular field, aspecific action is required to generate a positive impact, whichnot only mitigates any adverse effects of any deterioratingexternal factors or conditions but also leads to certain progressand tangible improvements. One can thus generically determinesustainability as the capacity to act to positively impact. This inturn warrants the development of this capacity and the specificcourses of actions to generate this positive impact.

One of the most widespread efforts to produce this im-pact is in the development of “green” and sustainable society,industries, technologies, etc. These efforts in particular aimat meeting the raising demands of the society at the sameor even lower level of environmental impact, balancing theindustrial production and consumption or natural resources, anddeveloping lasting renewable sources of energy and materials.Such approach has recently become critical in many diversefields, including materials science and engineering. Indeed, thenext-generation materials and processes to fabricate these ma-terials are expected to be guided by the fundamental principlesof sustainability, industrial ecology, eco-efficiency, and greenchemistry [3]. Enhancing these materials, both in terms of their

Manuscript received September 13, 2012; accepted December 2, 2012. Dateof publication January 4, 2013; date of current version April 6, 2013. This workwas supported in part by the Commonwealth Scientific and Industrial ResearchOrganisation through the Office of the Chief Executive Science LeadershipProgram and in part by the Australian Research Council.

The author is with the Commonwealth Scientific and Industrial Research Or-ganisation Materials Science and Engineering, Lindfield, NSW 2070, Australia(e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TPS.2012.2232670

Fig. 1. Challenges that are particularly relevant to sustainable future devel-opment and representative science and technology areas that contribute to thesolution of these challenges.

performance and “green” attributes, by using nanoscience andnanotechnology has recently become a highly topical field ofintense research and development.

Research in this field faces enormous challenges. From thesocietal perspective, this research is strongly shifted from moregeneric and academic to a lot more focused and practicalproblem orientation [4]. Common examples of these problemsinclude, but are not limited to, clean water and environment;plentiful, nutritious, and safe food; preventative health; energyproduction and storage; personal security; and the overarchinggoal of total human happiness. These problems are stronglyinterlinked and raise as Grand Societal Challenges. To ad-dress these challenges, scientific research faces Grand ScienceChallenges, which also currently aim at giving higher prior-ities to those fundamental scientific problems of importanceto applications that are particularly relevant to sustainablefuture development. For example, mastering effective controlof energy and matter at nanoscales has been identified asa viable enabling approach toward eco-efficient and human-health-benign nanotechnologies of the future [5]. The issues ofparticular importance to humankind and the relevant enablingscience and technology areas are sketched in Fig. 1.

This fundamental approach will ultimately lead to atom- andenergy-efficient synthesis and processing of nanomaterials withnovel properties, which will be used in applications relevantto a sustainable future. This is one of the key Grand ScienceChallenges that has been formulated recently by the U.S.Department of Energy [5]. One of the important features ofthe enabling nanoscale processes is balancing the demand andsupply of matter and energy during the nanomaterial production[6]. This is the nanoscale analog of the balanced resource pro-duction and consumption, which is one of the key attributes ofeconomic sustainability. In other words, this means that the so-lution of the above Grand Science Challenge requires enablingnanoscience to be sustainable, i.e., sustainable nanoscience

0093-3813/$31.00 © 2013 IEEE

OSTRIKOV: SUSTAINABLE NANOSCIENCE FOR A SUSTAINABLE FUTURE 717

Fig. 2. Sustainable nanoscience in plasma-based catalyzed growth of CNTs.

for nanoscale control of energy and matter, which is criticalfor the applications that are relevant for a sustainable future.By removing the few intermediate logical links between theitalicized terms in the previous sentence, one obtains the titleof this paper: sustainable nanoscience for a sustainable future.

In the following, we will clarify the meaning of sustainablenanoscience by considering a focused example of the plasma-based catalytic growth of carbon nanotubes (CNTs). We willalso introduce a range of nanomaterials produced in our re-search group, the plasmas used to fabricate them, and theapplications that are relevant to a sustainable future. This paperwill conclude with the vision on how the research efforts in theplasma nanoscience field [7]–[11] should be directed in the nearfuture to meet the challenges of the sustainability age [12] or,in other words, how should researchers working in this field actto positively impact.

II. SUSTAINABLE NANOSCIENCE: FOCUSED EXAMPLES

The commonly accepted scenario of catalyzed thermalgrowth of CNTs is sketched in Fig. 2. The process starts fromthe formation of metal catalyst nanoparticles, which to a largeextent determine the nanotube thickness. Carbon-bearing pre-cursors precipitate from the gas phase. After precursor speciesdecomposition, either in the gas phase or on the surface (in-cluding the surfaces of the catalyst nanoparticles), carbon atomssaturate the nanoparticles, as shown by a change of color frompurple to red upon transition from stages 1 to 2. The processof saturation is nonsimultaneous, i.e., some nanoparticles arefully saturated, whereas others are left unsaturated. CNT capsnucleate on the saturated catalysts during stage 3. The initialCNT growth stage is characterized by nonuniform length distri-butions: Some nanotubes are longer, whereas others are shorter,yet some catalyst nanoparticles do not produce nanotubes at all.In other words, only some fraction (which in some cases can beas small as only ∼1%) of these nanoparticles produce CNTs[13]. A huge amount of carbon material is also wasted duringthe growth process. For example, when a purified gaseousprecursor (e.g., methane) is used, only a small fraction of it isusually dissociated into carbon atoms to be used to grow theCNTs, whereas the rest flows (e.g., pumped) out of the reactorand releases more carbon emissions into the environment.

CNTs, particularly single-walled ones, require high temper-atures (typically in the 600 ◦C–1000 ◦C) to nucleate. Thesehigh temperatures are usually provided through the externalheating of the entire growth substrate and the substrate stage.

The amount of heat supplied to the substrate stage is used todecompose carbon precursors on the surface and to providethem with the energy sufficient for incorporation into the nan-otube walls. Thinner CNTs usually have higher incorporationbarriers; hence, stronger external heating is needed for nucle-ation. However, as the surface temperatures increase, the ratesof desorption and evaporation of carbon species also increase.Numerical simulations suggest that, in some cases, ∼90% (oreven more) carbon atoms produced on the surface do notcontribute to the single-walled CNT (SWCNT) nucleation andgrowth [14]. Most of these species therefore either recombine inthe gas phase (e.g., with hydrogen or oxygen to form hydrocar-bons or carbon dioxide) and then contaminate the environment,or redeposit to contaminate the substrate or the nanotubes.Deposition of large amounts of amorphous carbon may be verydetrimental for the CNT growth as these deposits may com-pletely bury the catalyst nanoparticles even before the nano-structures can nucleate [15]. If the latter process is avoided andthe nanotubes nucleate, the growth process continues (stage 4)until the catalyst is poisoned or, in other words, is no longer ableto sustain the balanced flow of carbon material through its bulkand surface to the nanotube walls. The loss of sustainabilityin the flow of carbon atoms [building units (BUs)] createsimbalance in their demand and supply, thereby leading to thepartial or even complete loss of catalytic activity of the metalnanoparticles.

Our research on the plasma-assisted growth of CNTs (as wellas a large number of other nanostructures and nanomaterials)is an example of a sustainable nanoscience approach. First ofall, to improve the productivity (which is one of the GrandSocio-Economic Challenges at multiple levels, spanning fromsmall and medium businesses to global economy) of the growthprocess, more nanotubes should be produced. In this regard,plasma-based processes offer several competitive advantagesover many other (e.g., thermal) processes in terms of muchhigher growth rates, bulk quantities of nanotubes and graphenesproduced (e.g., kilogram quantities can be produced in arcdischarges [16]), denser growth patterns, longer CNTs grown,maintaining the catalyst to be longer lasting and reusable.Quality of products is also one of the most important genericattributes of sustainability. Indeed, better quality products notonly will serve for the purpose better but will almost certainlylast longer. Plasma-grown CNTs in many cases show excellentmorphological and structural features such as a small numberof structural defects and uniform distributions of their lengthsand thicknesses across large patterns and arrays. Recently,it was demonstrated experimentally [17]–[21] and explainedtheoretically [22] that plasma-based processes lead to signif-icantly narrower chirality distributions of SWCNTs. Plasma-specific effects also lead to the pronounced vertical alignmentof the CNTs [23] and many other 1-D nanostructures (e.g.,nanowires), which is one of the most important attributes ofmorphological quality of nanopatterns. The structural quality ofSWCNTs is characterized by the G/D peak ratios in the Ramanspectra; ratios exceeding 50, which are among the highestreported, have been achieved in our laboratories [24].

The next issue in Fig. 2 is to enable a faster nanostructuregrowth, which offers significant energy savings (e.g., by short-ening the supply of heat and precursor gas to the substrate).


Very high growth rates and fast and simultaneous nucleation ofCNTs and other nanostructures have been reported in plasma-based processes. Smaller amounts of building material (lessmaterial in Fig. 2) can be achieved through better precursorutilization and minimizing BU loss in a plasma. The firsteffect becomes possible through high dissociation rates inthe gas phase and on the surfaces (e.g., through ion-assistedreactions), whereas the second effect stems from the much-reduced surface temperatures in plasma-based processes. Forexample, the growth temperatures of SWCNTs in a plasmacan be several hundred degrees lower than in thermal chemicalvapor deposition (CVD) [25]. Such significant reductions ofthe process temperatures dramatically reduce the rates of BUdetachment and evaporation from the surface. The much lowergrowth temperatures in turn make it possible to use muchless energy in the process. In plasma-based processes, thisis possible not only through the reduction of the amount ofheat supplied through external heating of the substrate but alsothrough customized smart energy input to generate the plasma.For example, it is currently possible to produce high-qualitymetal and oxide nanostructures by supplying energy to generatethe plasma discharge intermittently, e.g., using nanosecondrepetitive pulses at atmospheric pressure rather than supplyingenergy continuously and at low pressures [26].

Since it is possible to produce more nanomaterials faster andto use smaller amounts of energy and materials, the plasma-based process can also be made cheaper, as is highlightedin Fig. 2. Reducing complexity of nanoscale fabrication, i.e.,by using much simpler processes, is also a promising wayof reducing the energy/material consumption, labor intensity,environmental impact, and cost. For example, the performanceof Si wafer-based photovoltaic cells remains very competitiveafter a multistage fabrication process commonly used in solarcell manufacturing is replaced by a simple plasma-enablednanoscale texturing of a Si wafer [27].

This process is also much greener compared with severalexisting processes because it does not rely on flammable silane(SiH4) and other toxic, corrosive, explosive, etc., precursorsor processing chemicals, which also produce large amountsof waste and pose a significant environmental hazard [28].Moreover, reactive plasmas are very effective for the nearlycomplete reforming of hazardous silane into silicon atoms orless hazardous SiHx radicals [28]. The process of nanoscalesurface texturing of Si wafers in Ar + H2 plasmas (which leadsto self-organized arrays of Si nanocones or nanograss) is verysimple because it relies on self-organized etching and doesnot require any masks or pattern delineation by lithography orany other means. Moreover, the p-n junction is simultaneouslyformed under the layer of Si nanocones, which eliminates theneed to conduct a costly and environment-impacting diffusionprocess or to separately fabricate and dope p- and n-type Silayers. These plasma-guided self-organization-based processesare among the main goals of the plasma nanoscience research.

Dry-plasma-based nanoscale synthesis and processing alsooffer several indisputable advantages in terms of reducing anypotentially adverse toxicological effects of the nanomaterialsproduced. Plasma-based nanofabrication in most cases is con-ducted in confined space (e.g., of vacuum vessels) and leadsto nanoscale structures or features that are firmly bound to

Fig. 3. Research directions of our research group that are particularly relevantto sustainable future development. Acronyms NMs and PVD stand for nano-materials and physical vapor deposition, respectively.

the surface, therefore reducing the risks of their entry into thehuman body [29].

Let us now recall that sustainability is intimately related toenduring and solving the challenges. Even from the given briefdiscussion, it is clear that the challenges during the nanoscalesynthesis are numerous. These challenges include but are notlimited to structural and morphological defects, inferior qualityof the nanostructures, catalyst poisoning, amorphous carbondeposits, high process temperatures leading to melting of heat-sensitive substrates, premature loss of nanoparticle catalyticactivity, pattern uniformity, etc. Solutions of these and manyother problems benefit from the plasma-specific effects [30].

Last but not the least point highlighted in Fig. 2 is the needto align the “sustainable nanoscience” research to applicationsthat are critical for a sustainable future. This crucial require-ment should ideally be included into the structure and researchprograms of research groups, centers, and institutes that carryscientific research in relevant areas. One such example is pre-sented in the following.

III. PLASMA NANOSCIENCE FOR A SUSTAINABLE FUTURE

Fig. 3 shows an example of organization of research pro-grams within our research group. The targeted applications arechosen among those that are particularly related to a sustainablefuture development of humankind. Some of these applicationsare presented on the bottom right in Fig. 3 and are relatedto energy conversion; saving and storage; light sources; bio-compatible, bioactive, and smart responsive materials; [31],plasmonic, photonic, and optoelectronic functionalities; na-noelectronic devices and circuits; environmental monitoringand remediation; water purification; food processing; health;hygiene; toxicology; and medicine. The materials or plasmasare customized to meet the specific requirements of theseapplications. This can be achieved by, e.g., tailoring the com-position, dimensionality, morphology, and structure of the mostsuitable nanomaterials that would offer the best performancein the envisaged applications. The currently available materialssystems include carbon-, silicon-, metal-, polymer-, oxide-,


nitride-, and carbide-based nanomaterials that exhibit dielectric,semiconducting, and conducting properties.

By structure and morphology, these materials can be ar-ranged into soft and hard matter, nanostructures of all dimen-sionalities (0D, 1-D, 2-D, and 3-D nanomaterials, noted as0D, 1-D, 2-D, and 3-D NMs in Fig. 3, respectively), porousnanomaterials, and living cells and tissues. Hybrid nanomateri-als may be composed from nanostructures made of differentmaterials, leading to exotic electrical and other properties.For example, topological insulators may simultaneously fea-ture highly conducting edges and dielectric bulk [32]. Hybridnanomaterials can also be made of nanostructured elementsof different dimensionalities, e.g., 1-D nanowires decoratedby 0D quantum dots. Using this approach, one can buildmaterials virtually at will, e.g., the rapidly emerging class ofmetamaterials with the exotic properties that are not available innatural materials of the same elemental composition [33]. Thevariety of the available nanomaterials offers flexibility not onlyto pursue any targeted applications but also to quickly realignresearch programs under conditions of the rapidly changingresearch and funding priorities, and industry-funded contractswith the specific delivery targets and deadlines.

Importantly, every specific synthesis or treatment processrequires a customized plasma reactor and a plasma-based pro-cess, which are also designed by using the basic principles ofsustainable nanoscience sketched in Fig. 2 and discussed in theprevious section. The available plasmas are sustained in gas,liquid, and solid matter and find them localized to macroscopic,microscopic, or even nanometer dimensions as highlightedon the left-hand side of Fig. 3. These plasma sources rangefrom low-pressure reactors for semiconductor processing [28]to atmospheric-pressure plasmas for plasma health care andmedicine applications [34]–[36]. Nanoplasmas are sustainedin metal nanoparticles and find numerous applications in therapidly developing field of plasmonics, which emerged on thefoundations of the plasma physics [37]. Relevant studies in-volve a combination of theory, simulation, plasma diagnostics,development of plasma sources and process control instrumen-tation, etc. Numerical simulation and theoretical work is usedto carry on scientific research at the edge of plasma physics andchemistry, materials science, surface science, nanoscience, andseveral other disciplines. This point is highlighted at the bottomin Fig. 3.

In our research, we follow the principle: plasma improve-ment → better property, energy efficiencyenvironment friend-liness, etc. → useful application, which we try to apply toas many nanomaterials systems as possible. Some highlightsof this approach are presented in the following in a briefdiscussion of a few representative nanomaterials produced inour research group and their existing and potential applications.These nanomaterials are presented in Figs. 4–7, with the firsttwo representing carbon-based systems and the last two repre-senting inorganic material systems.

Fig. 4 shows the structure and morphology of CNTs thatsignificantly benefit from the plasma-specific effects and showgood performance in applications. For example, plasma pre-treatment of catalyst or substrate surface functionalization leadsto the possibility to control the nanotube density from extremelyrare and barely connecting horizontal CNTs [see Fig. 4(a)] to

Fig. 4. Representative examples of CNTs. (a) Very rare SWCNTs alignedalong the substrate. (b) Typical “tropical forest” of CNTs produced in selectedsubstrate areas. (c) TEM image of SWCNTs. (d) CNTs decorated with metalnanoparticles form hierarchical nanostructures that show excellent performancein bio- and gas-sensing applications. Courtesy of Z. J. Han and S. Yick(unpublished).

dense “tropical forests” of tangled and twisted CNTs depositedon selected areas of the substrate [see Fig. 4(b)]. The nanotubeforests can also be produced very dense and vertically aligned,which to a large extent is attributed to the effects of the electricfield in the plasma sheath. The size distribution of the CNTsproduced in the plasma is often more uniform than in theequivalent thermal CVD processes. For example, the thicknessand chirality distributions of SWCNTs [a typical transmissionelectron microscopy (TEM) image is shown in Fig. 4(c)] canbe made much more uniform even after generating a relativelyshort plasma discharge during the (time-programmed) growthprocess [20].

Therefore, by using plasmas, one can improve and effec-tively control the morphological and structural properties ofthe SWCNT patterns and arrays. This in turn improves thenanotube performance in several applications, where such prop-erties are critical. For example, growth of uniform arrays ofvery thin SWCNTs with the selected predominant conductivitytype (semiconducting or metallic) would open exciting possibil-ities in next-generation nanodevice applications. Indeed, verythin semiconducting nanotubes would have a quite significantenergy bandgap enabling their integration in photovoltaic so-lar cells or field-effect transistors in nanoelectronic devices.On the other hand, very thin metallic SWCNTs would shownear-superconducting properties, which would warrant theirapplication in current-conducting channels in nanoelectronicand sensing devices. From this perspective, CNTs may beconsidered as a viable alternative material for the integrationinto the currently Si-dominant nanodevice platform [38].

The sensing properties of the nanotubes can be further im-proved by depositing small metal nanoparticles on their surface,as shown in Fig. 4(d). Through the use of plasmas, one canachieve a better attachment of the nanoparticles to the normallynonreactive CNT walls, e.g., by activating their reactive edgesor tethering functional moieties to the nanotube surface. This


Fig. 5. Representative examples of graphenes. (a) Thickness of horizon-tal graphenes determines transparency of the graphene films in a solution.(b) Growth of horizontal graphene on metal catalyst layers often leads tononuniform numbers of atomic carbon layers and the formation of graphenegrains with different orientations in different areas. (c) Typical very thingraphene flake that is transparent to electron beam. (d) TEM image shows thata typical vertical graphene nanosheet is made of only 4–5 atomic carbon layers.(e) and (f) Two typical (random and directional, respectively) alignments ofvertical graphenes achieved in plasma-based processes. Courtesy of S. Kumarand T. van der Laan (unpublished).

leads not only to better adhesion/bonding of the nanoparticleswith the nanotubes but also significantly improves the sizeuniformity and crystallinity of the nanoparticles. Importantly,the plasma treatment can be optimized (e.g., by using plasmaswith low-energy ion fluxes such as atmospheric plasma jets) toonly affect the outer CNT wall while leaving the inner wallsintact. The improved interfacing between the metal and theCNT in turn leads to the effective electron transport throughthe interface [39], which is critical in detecting the response inenvironmental sensing. When the nanotubes are decorated witha small amount of Pd nanoparticles, they can be used for high-precision highly selective sensing of trace amounts of hydrogenin open air at room temperature.

Fig. 5 shows representative examples of horizontal (a and b)and vertically oriented (c–f) graphenes produced using plasma-based techniques. The use of plasmas helps to substantiallyreduce the growth temperatures (by at least a couple of hun-dred degrees) of metal-catalyst-supported horizontal graphenes[40]. This means better energy efficiency of the process,which in other words, will produce less carbon emissions.Likewise, highly selective etching of graphene edges makes

Fig. 6. Representative examples of inorganic nanomaterials. (a) Si nanograss.(b) Si nanotrees. (c) SiC-core/AlSiC-shell nanowires grown on top of theAAO nanoporous template. (d) atomic-resolution TEM of highly crystallinenanowires. (e) ZnO nanobelts and nanowires. (f) FeO nanowires. Courtesy ofS. Kumar, D. H. Seo, J. H. Fang, and Q. J. Cheng (unpublished).

it possible to fabricate narrow graphene nanoribbons, whichfeature a nonzero energy bandgap, contrary to the single-layer graphene. The bandgap opening, achieved using a simplehydrogen plasma etching process [41], is one of the mainscience challenges of the present-day graphene research [42].This effect makes graphene useable in nanoelectronic devices,which can benefit from the extremely high mobility of electronsin graphene. One of the most promising application of low-temperature plasmas is related to the intentional creation of de-fects in graphene layers, which are crucial for the applicationsthat rely on reactivity of the nanostructures; this reactivity isquite limited in ideal flat graphene because of the inertness ofthe main graphitic plane and poor accessibility of the edges.

Vertically oriented graphenes shown in Fig.5(c)–(f) featuremuch higher chemical reactivity compared with their horizontalcounterparts, mostly due to the availability of long reactiveedges. The length of the open reactive edges of the verticalgraphenes grown directly on an Si/SiO2 substrate of a surfacearea of ∼1 cm2 may reach kilometers. The low growth temper-atures are achieved by localized exposure of the substrate to theplasma, and any external heating in many cases is redundant[43]. These structures typically feature only 3–8 graphene lay-ers [see Fig. 5(d)] and can be grown without any metal catalystdirectly on a Si/SiO2 surface exposed to the plasma. Impor-tantly, it is not possible to produce these structures in similarthermal processes under the same precursor gas, temperature,


Fig. 7. Representative examples of inorganic nanomaterials. (a) and (b)MoO3 nanoparticles. (c) Cu2O nanowires. (d) Nanostructured SnO2 surface.(e) (top view) AAO nanoporous template. (f) Vertical graphenes grown on topof the AAO nanoporous template. Courtesy of S. Kumar, J. H. Fang, T. van derLaan, Q. J. Cheng, and D. Z. Pai (unpublished).

substrate, and pressure conditions. Therefore, these verticalgraphene nanosheets are uniquely plasma enabled. Moreover,this ability contributes to the solution of a major scientificproblem of producing vertically standing and highly reactivegraphenes. The presence of very-high-density open reactiveedges is highly promising for several applications in waterpurification, bio- and environmental sensing, cell control in re-generative medicine, energy storage (e.g., supercapacitors andLi-ion batteries), and some others. Of particular interest is thepossibility to produce vertically aligned graphenes from naturalresources such as coal, sugars, milk, honey, fats, starches, etc.This is a very new and exciting area with the many promisingoutcomes in the future [44].

Numerous inorganic nanomaterials significantly benefit oreven owe their existence to the plasma-specific effects. Sometypical examples of these materials are shown in Figs. 6 and 7.For example, Si nanocone/nanograss structures in Fig. 6(a)are etched from a piece of a crystalline Si wafer using mask-less etching in an environment-friendly simple process [27]that is already briefly discussed earlier. These and variousother configurations of nanostructured Si [see, e.g., branched“nanotrees” in Fig. 6(b)] are used in antireflection layers inphotovoltaic solar cells, biomimetic optical structures (e.g.,mimicking the moth eye effects [45]), electrodes in batteries,and other applications. A combination of nanoporous templatesupport and plasma effects produce hybrid SiC-core/AlSiC-

shell nanowires depicted in Fig. 6(c) [46]. High-resolutionTEM [see Fig. 6(d)] makes it possible to study atomic ar-rangements in the nanowires with atomic precision. The othertwo examples of inorganic nanomaterials in Fig. 6(e) and (f)show ZnO nanowires/nanobelts and FeO nanowires, respec-tively. These inorganic nanowires find numerous applications inoptoelectronics, photodetectors, energy conversion and storage,UV filters, bio- and chemical sensors, etc. [47], [48]. Moreover,many of them owe their existence to the plasma-specific effectsupon direct exposure of metal surfaces to reactive oxygenplasmas [49], [50].

Fig. 7 shows further examples of inorganic nanomaterials,which include (a and b) MoO3 nanoparticles, (c) cuprous oxidenanowires, (d) nanostructured SnO2 surface, (e) nanoporousanodized aluminum oxide (AAO) template, and (f) verticalgraphenes grown on top of the AAO template. The MoO3

nanoparticles were deposited at room temperature, on a plasticsubstrate, from a nanosecond repetitive spark discharge inopen air between Mo electrodes [26]. The special selection ofthe repetitive kilovolt pulses of tailored shapes, duration, andrepetition made it possible to dramatically reduce the amountof energy needed for the incorporation of each atom into theMoO3 crystalline structure, possibly nearing the ultimate ther-modynamic thresholds of energy efficiency. This is particularlyrelevant to the solution of the Grand Science Challenge ofultimate atom- and energy-efficient nanoscale synthesis [5]. Onthe other hand, these MoO3 nanoparticles are highly promisingas electrode materials in Li-ion batteries, which is one of theenergy storage applications of importance for a sustainablefuture [51].

The next example in Fig. 7(c) shows Cu2O nanowires syn-thesized by a direct exposure of a Cu foil to oxygen plasmas.The relatively high percentage of the nanostructured cuprousoxide phase over the depth of at least several tens of microm-eters make this nanostructured material very suitable for thedetection of very low amounts of methane at room temper-ature. The simplicity and fast rates of the production of thissensing structure and its low energy and material cost (see thebasic attributes of sustainable nanoscience in Fig. 2) makes itparticularly promising for applications in mining and livestockindustries, which are very important for the energy- and food-sufficient future of humankind.

A SnO2 surface nanostructured in a quite similar way isshown in panel (d). This material is particularly important forelectrocatalysis, thermoelectrics, sensing, and optoelectronics[52]. The nanoporous AAO template in Fig. 7(e) is an idealtemplate material for plasma-assisted deposition of plasmonicnanoarrays, e.g., made of Au or Ag nanoparticles [37]. Becauseof the simplicity to tune the diameters of the nanopores andthe spacings between them, the AAO nanoporous membraneshave become among the most effective self-organized and cost-effective nanoscale etching masks. A combination of thesemasks and highly anisotropic plasma etching makes it possibleto very effectively and precisely transfer these regular patternsonto the underlaying substrates being etched. Another appli-cation of nanoporous AAO membranes is in separation (chro-matography) of biological species according to their size andchemical reactivity. Plasma-assisted functionalization of theinner surfaces of the nanoporous channels is very promising in


this regard. The last example in Fig. 7(f) shows a hybrid nanos-tructure made of vertical graphene nanosheets grown on top ofthe nanoporous AAO membrane. This process is also plasmaenabled and fails in the equivalent thermal CVD process. Thepotential applications of this unique hybrid nanostructure maybenefit from the presence of nanochannels in the AAO and thevertical graphene walls with open reactive edges. This is also anew research direction with many highly promising results.

The examples presented in this section are just a top ofthe iceberg of the available manifestations of the usefulnessof the plasma-specific effects to produce nanomaterials thatenable applications of particular relevance to sustainable futuredevelopment. Due to the specific scope of this paper and spaceconstraints, these examples are mostly selected among theresults produced very recently by our research group. Most ofthem are still unpublished, which also prevents us from thein-depth analysis of the plasma effects, physical and chemicalproperties of these nanomaterials, etc. These results will bereported elsewhere in the near future.

This is why we apologize for not discussing other relevantresults by other authors, which are plentiful and their numberis continuously increasing. The aim of this paper is to showthe relevance of sustainability concepts to nanoscience andsome examples of possible organization of research programsin research groups that work in the plasma nanoscience field toalign their research efforts with the Grand Science and SocietalChallenges posed in the age of sustainable development. Wehave also showed some examples of nanomaterials producedor processed using low-temperature plasmas and highlightedhow any specific features of these materials or the fabricationprocesses are related to the concepts of sustainable nanosciencesummarized in Fig. 2.

IV. VISION FOR THE FUTURE: THE PATH TO IMPACT

Therefore, what is the next step? What should researchersdo to apply the concepts of sustainable nanoscience in practice,and how should this research be directed to address the chal-lenges of the sustainability age? Fig. 8 explains a possible wayof practical implementation of this idea by using an exampleof the plasma nanoscience research field. The primary motiva-tion of most of the research programs should be a significantproblem that is commonly accepted as significant from thescientific point of view or, in other words, poses a significantscience challenge that requires urgent solution. Importantly, thisproblem should advance the applications that enable sustainablefuture development. To solve this problem, competitive cutting-edge multidisciplinary scientific approaches should be used.

For the plasma nanoscience field, it is critical to offer thesolutions and improvements that are based on uniquely plasma-specific effects. The examples of these positive effects includethe improved properties of the plasma-treated nanomaterials,which in turn lead to their superior performance in applications,e.g., in devices for energy conversion and storage, environmen-tal sensing and remediation, biomedical monitoring and inter-vention, food processing, water purification, next-generationintegrated labs-on-a-chip, smart electronic gadgets, intelligentrobots, etc. From the nanomaterial fabrication point of view,the plasma-related solution should lead to more effective, faster,

Fig. 8. Path for the plasma nanoscience research to produce an impact in theage of sustainable development and the critical importance of multidisciplinarycollaborations.

and better controllable processes that are also energy and costefficient. We warmly welcome any comments or suggestionson this topic that will undoubtedly be of a stronger andstronger interest because of the rapidly increasing industrialapplications of the relevant technologies for the production ofnanotechnology-enhanced products and services.

Most importantly, given the intrinsically multidisciplnarycharacter of the challenges, collaboration between researchers,engineers, and business developers from many different fieldsis the viable way forward. Similar to microorganisms that self-organize in colonies and biofilms to withstand external stress[53], everyone involved should self-organize into cohesive,efficient, interacting, creative, productive, and sustainability-minded research, development, and commercialization teams toact to positively impact on the way toward a sustainable future!

ACKNOWLEDGMENT

The author would like to thank S. Kumar, D. H. Seo,Z. J. Han, Q. J. Cheng, J. H. Fang, T. van der Laan, S. Yick,and D. Z. Pai for the unpublished figures that are used in thispaper.

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Kostya (Ken) Ostrikov received the Ph.D. degree in1992 and the D.Sc. degree in 1996.

He is currently a Chief-Executive-Officer Sci-ence Leader, an Australian Future Fellow, and aChief Research Scientist with Commonwealth Sci-entific and Industrial Research Organisation Mate-rials Science and Engineering, Lindfield, Australia.He is also an Honorary Professor with the Univer-sity of Sydney, Sydney, Australia; the University ofWollongong, Wollongong, Australia, and the Univer-sity of Technology Sydney, having ten full-professor-

level appointments in six countries in total. He has more than 350 refereedjournal papers and three research monographs. He has held more than 90 ple-nary, keynote, and invited talks at international conferences. He has supervisedresearch training of 25 researchers with Ph.D. degree and 57 research students,has more than 120 collaborators in last six years, and has also secured morethan $10 million in competitive research funding. His main research programon nanoscale control of energy and matter in plasma–surface interactionscontributes to the solution of the grand and as-yet-unresolved challenge ofdirecting energy and matter at the nanoscale, which is a challenge that is criticalfor the development of renewable energy and energy-efficient technologies fora sustainable future.

Dr. Ostrikov was the recipient of two prestigious medals from nationalacademies of sciences, the Walter Boas Medal of the Australian Institute ofPhysics 2010, and six highly competitive international fellowships, in additionto the recent Building Future Award 2012. As a Leader of a large internationalcollaborative network, a Convenor of annual conferences, and a Lead Editorof special issues in his respective field, he leads a large international plasmananoscience community.

sustainable nanoscience for a sustainable future

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