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Friction is important in material design for robotic systems that need to perform tasks regardless of environmental changes. Generally, robotic systems lose their friction in wet environments and fail to accomplish their tasks. Despite the significance of maintaining friction in dry and wet environments, it is still challenging. Here, we report a smart switching surface, which helps to complete missions in both wet and dry environments. Inspired by the reversible wrinkling mechanism of a human finger, the surface reversibly generates and removes wrinkles to adapt to both environments using volume-changing characteristics of the Nafion film. The switchable surfaces with manipulated wrinkle morphologies via patterns of diverse densities, sizes, and shapes induce a relationship between the wrinkle morphologies and friction: wrinkles on denser and smaller hexagonal patterns generate six times more friction than non-switching flat surfaces in wet environments and a similar amount of friction to the flat surfaces in dry environments. In addition, the wrinkle morphologies according to the patterns are predicted through numerical simulation, which is in good agreement with experimental results. This work presents potential applications in robotic systems that are required to perform in and out of water and paves the way for further understanding of wrinkling dynamics, manipulation, and evolutionary function in skin.

Summary Manufacturing unconventional alloys remains challenging owing to the seamless interplay between kinetics and thermodynamics. High-entropy alloys (HEAs), for example, enable paradigm shifts in materials science but these shifts are hindered by traditional liquid-solid transformations. In contrast, vapor–crystal transformations offer the most kinetically efficient pathways to form alloys. Here, a well-mixed vapor is quenched to create 55 distinct alloys confined in nanoparticles (NPs), including unprecedented ones. This confinement is found to stabilize their alloyed states. Unlike precursor feeding, a microseconds-long oscillatory spark mixes the vapors and determines the composition of the alloy NPs. To epitomize practicalities, we apply the NPs as integral building blocks for high-performance catalysts and to nanoscale additive manufacturing. The resulting HEA nanostructures cannot be fabricated by other additive manufacturing techniques. The present work breaks the miscibility limits, thereby providing a powerful roadmap to uncharted territories in metallurgy, catalysis, and additive manufacturing.

Recently we gave arguments that only two unique topologically different configurations of 7 equal all mutually touching round cylinders (the configurations being mirror reflections of each other) are possible in 3D, although a whole world of configurations is possible already for round cylinders of arbitrary radii. It was found that as many as 9 round cylinders (all mutually touching) are possible in 3D while the upper bound for arbitrary cylinders was estimated to be not more than 14 under plausible arguments. Now by using the chirality and Ring matrices that we introduced earlier for the topological classification of line configurations, we have given arguments that the maximal number of mutually touching straight infinite cylinders of arbitrary cross-section (provided that its boundary is a smooth curve) in 3D cannot exceed 10. We generated numerically several configurations of 10 cylinders, restricting ourselves with elliptic cylinders. Configurations of 8 and 9 equal elliptic cylinders (all in mutually touching) are generated numerically as well. A possibility and restriction of continuous transformations from elliptic into round cylinder configurations are discussed. Some curious results concerning the properties of the chirality matrix (which coincides with Seidel's adjacency matrix important for the Graph theory) are presented., 27 pages, 10 figures

Despite the excellent performance of organic–inorganic hybrid perovskite materials in recent years, the mechanism of their decomposition under actual operating conditions has not yet been elucidated. Herein, we elucidated the breakdown process of CH3NH3PbI3 perovskite crystals and identified the polarity-dependent degradation pathway via localized charges by performing time-evolution measurements of the absorption spectra of perovskite films with different underlying charge transport layers and ab initio molecular dynamics calculations. It was found that the carrier polarity (hole-rich or electron-rich) inside the perovskite films played a critical role in the degradation rate, and the polarity-dependent degradation pathway strongly depended on the combination of the surrounding gaseous molecules. The hole-rich perovskite films degraded more rapidly than the electron-rich ones in the presence of H2O, while this degradation trend was reversed in oxygen-only ambient environments. Interestingly, the hole-rich film is extremely unstable in atmospheric air containing both H2O and O2, whereas the MAPbI3 film with excessive electrons was stable in air. An ab initio molecular dynamics simulation was performed to obtain the detailed degradation pathway of MAPbI3 under atmospheric conditions for different polarities of the localized charge. The simulation results are in good agreement with experimental results, and the production of Pb(OH)I predicted in our simulations is confirmed by X-ray-assisted spectroscopic measurements.

Three-dimensional (3D) nanoprinting is designed to harness properties such as size, geometry, material, and topology to obtain metamaterials for nano-photonics and nano-electronics with unique functionalities. Although previous works based on charged aerosols have printed various 3D nanostructures, understanding the additive process remains essentially unexplored. Here, we uncover the physics of 3D nanoprinting by observing anomalous nanoparticle structures originating from a floating layer of concentrated charged nanoparticles (named nano-dust cloud and being the source for additive manufacturing) over a charged surface. An analytical approach has been developed to extract essential printing parameters – the charge concentration of the floating layer and the charge density on the dielectric surface – from the experimental data of a designed virtual probe. Our work can provide new vistas for controlling and programming 3D nanoprinting via charged aerosols.

Strain gated switch systems have recently been developed for direct human–machine interfacing wearable electronics. These switch systems that use piezotronic nanowires or metal/elastomer bilayer films have limitations of low on–off ratios or large threshold strain. Herein, we present a metal–elastomer bilayer reversible switch system utilizing the superexponential behavior of crack widening. The crack width exhibits a superexponential dependence on the applied strain, instead of a linear dependence of regular widening. Such superexponential behavior of widening of a crack leads to an almost infinite resistance of the metal film when the applied strain approaches 2%. The resistance of the switch increases approximately by 5 orders of magnitude when 1.6% strain is applied, resulting in an overall gauge factor that exceeds 6 × 106, which shows that our device can perform as a switch. By combination of metal–elastomer bilayer strain-gated switches, we demonstrated logic elements such as AND, OR, NAND, and NOR gates by expressing the gestures of fingers as numbers on a seven-segment display. The newly proposed switch system also showed excellent durability, reproducibility, low energy consumption and tunable threshold strain.

Controlled synthesis of unconventional spherical/terraced MgO nanoparticles that show a unique optical property was done via the flame metal combustion method. We investigated the optimal condition for selectively producing these spherical/terraced MgO nanoparticles over conventional cubic MgO nanoparticles. Furthermore, it was possible to control the proportion of the morphology of generated MgO nanoparticles using different carrier gases. The size distribution of the MgO nanoparticles was measured to understand the surface-induced growth mechanism of the spherical/terraced MgO nanoparticles, which was different from that of cubic MgO nanoparticles grown from the normal molecule condensation. In addition, the catalytic property of the Li-doped spherical/terraced MgO particles was investigated.

Three-dimensional (3D) printing1-9 has revolutionized manufacturing processes for electronics10-12, optics13-15, energy16,17, robotics18, bioengineering19-21 and sensing22. Downscaling 3D printing23 will enable applications that take advantage of the properties of micro- and nanostructures24,25. However, existing techniques for 3D nanoprinting of metals require a polymer-metal mixture, metallic salts or rheological inks, limiting the choice of material and the purity of the resulting structures. Aerosol lithography has previously been used to assemble arrays of high-purity 3D metal nanostructures on a prepatterned substrate26,27, but in limited geometries26-30. Here we introduce a technique for direct 3D printing of arrays of metal nanostructures with flexible geometry and feature sizes down to hundreds of nanometres, using various materials. The printing process occurs in a dry atmosphere, without the need for polymers or inks. Instead, ions and charged aerosol particles are directed onto a dielectric mask containing an array of holes that floats over a biased silicon substrate. The ions accumulate around each hole, generating electrostatic lenses that focus the charged aerosol particles into nanoscale jets. These jets are guided by converged electric-field lines that form under the hole-containing mask, which acts similarly to the nozzle of a conventional 3D printer, enabling 3D printing of aerosol particles onto the silicon substrate. By moving the substrate during printing, we successfully print various 3D structures, including helices, overhanging nanopillars, rings and letters. In addition, to demonstrate the potential applications of our technique, we printed an array of vertical split-ring resonator structures. In combination with other 3D-printing methods, we expect our 3D-nanoprinting technique to enable substantial advances in nanofabrication.

We consider a dilute gas of bosons with repulsive contact interactions, described on the mean-field level by the Gross-Pitaevskii equation, and bounded by an impenetrable "hard" wall (either rigid or flexible). We solve the Bogoliubov-de Gennes equations for excitations on top of the Bose-Einstein condensate analytically, by using matrix-valued hypergeometric functions. This leads to the exact spectrum of gapless Bogoliubov excitations localized near the boundary. The dispersion relation for the surface excitations represents for small wavenumbers $k$ a ripplon mode with fractional power law dispersion for a flexible wall, and a phonon mode (linear dispersion) for a rigid wall. For both types of excitation we provide, for the first time, the exact dispersion relations of the dilute quantum liquid for all $k$ along the surface, extending to $k \rightarrow \infty$. The small wavelength excitations are shown to be bound to the surface with a maximal binding energy $\Delta= \frac18 (\sqrt{17}-3)^2 mc^2 \simeq 0.158\, mc^2$, which both types of excitation asymptotically approach, where $m$ is mass of bosons and $c$ bulk speed of sound. We demonstrate that this binding energy is close to the experimental value obtained for surface excitations of helium II confined in nanopores, reported in Phys. Rev. B 88, 014521 (2013)., Comment: 9 pages of RevTex4-1, 3 figures

Sensors to detect motion with high precision have been extensively studied in diverse engineering research fields. Among them, transparent devices, which have strong adaptability in various fields such as display panels, have not gained much academic interest. In this study, we present a highly sensitive pressure and strain sensor based on a cracked transparent epilayer, indium-tin oxide (ITO), deposited on a transparent PET substrate. This sensor system, with which we demonstrate how to detect pressure and finger motions, exhibits ultra-sensitivity to strain (gauge factor about 4000 at 2% strain), pressure (sensitivity is about 1.91 kPa−1 at pressures from 30 to 70 kPa), and transparency (up to 89% at a wavelength of 560 nm). Also, durability has been validated over 5000 cycles. The sensor thus boasts broad applications including touchscreens and motion detectors.

Magnesium oxide (MgO) is generally a wide band-gap oxide unable to conduct electric current in the bulk at room temperature. In this study, MgO nanocubes synthesized by self-burning micro-sized Mg metal powders in air showed electrical conductivity when they were sandwiched between two gold-mesh electrodes and steadily applied a voltage at room temperature (∼25 °C). In addition, a simultaneous light emission caused by the microdischarge of nitrogen molecules occurred adjacent to the cathode. The light emission was observed when traces of water vapor existed in the gas environment. In the case of a voltage pulse produced by switching off, transient emissions of Mg I and Mg II were detected on both sides of the electrodes. However, those steady and transient light emissions were not observed in the commercial MgO nanoparticles devoid of nanocubes. The light emissions shown in the cases of the steady-state might be caused by electron injection into the empty conductive states, which exist along the edges of MgO nanocubes, as a result of the spontaneous dissociation of water vapors at reactive sites of the nanocube surfaces as well as a result of the reduction of the energy barriers between the cathode and MgO nanocubes in contact. For transient emission, electrons trapped in the low coordinate sites were released with voltage pulse and neutralized the nearby Mg+ and Mg2+ ions, driving them into the excited neutral states, Mg I and Mg II.Magnesium oxide (MgO) is generally a wide band-gap oxide unable to conduct electric current in the bulk at room temperature. In this study, MgO nanocubes synthesized by self-burning micro-sized Mg metal powders in air showed electrical conductivity when they were sandwiched between two gold-mesh electrodes and steadily applied a voltage at room temperature (∼25 °C). In addition, a simultaneous light emission caused by the microdischarge of nitrogen molecules occurred adjacent to the cathode. The light emission was observed when traces of water vapor existed in the gas environment. In the case of a voltage pulse produced by switching off, transient emissions of Mg I and Mg II were detected on both sides of the electrodes. However, those steady and transient light emissions were not observed in the commercial MgO nanoparticles devoid of nanocubes. The light emissions shown in the cases of the steady-state might be caused by electron injection into the empty conductive states, which exist along the edges of ...

Recently developed flexible mechanosensors based on inorganic silicon, organic semiconductors, carbon nanotubes, graphene platelets, pressure-sensitive rubber and self-powered devices are highly sensitive and can be applied to human skin. However, the development of a multifunctional sensor satisfying the requirements of ultrahigh mechanosensitivity, flexibility and durability remains a challenge. In nature, spiders sense extremely small variations in mechanical stress using crack-shaped slit organs near their leg joints. Here we demonstrate that sensors based on nanoscale crack junctions and inspired by the geometry of a spider's slit organ can attain ultrahigh sensitivity and serve multiple purposes. The sensors are sensitive to strain (with a gauge factor of over 2,000 in the 0-2 per cent strain range) and vibration (with the ability to detect amplitudes of approximately 10 nanometres). The device is reversible, reproducible, durable and mechanically flexible, and can thus be easily mounted on human skin as an electronic multipixel array. The ultrahigh mechanosensitivity is attributed to the disconnection-reconnection process undergone by the zip-like nanoscale crack junctions under strain or vibration. The proposed theoretical model is consistent with experimental data that we report here. We also demonstrate that sensors based on nanoscale crack junctions are applicable to highly selective speech pattern recognition and the detection of physiological signals. The nanoscale crack junction-based sensory system could be useful in diverse applications requiring ultrahigh displacement sensitivity.

Mn2+ ion doping is used as an electron paramagnetic resonance (EPR) probe to investigate the influence of low-coordination structural defects such as step edges at the surface of terraced (001) MgO nanoparticles on the electronic properties. Beside the well-known hyperfine sextet of Mn2+ ions in the cubic crystal field of MgO, an additional EPR feature with a striking nonmonotonous temperature dependent shift of the g-factor is observed in terraced nanoparticles in the temperature range from 4 K to room temperature. By linking the difference in the temperature dependence of the Mn2+ sextet intensity in cubic and terraced nanoparticles with the possible s-d exchange shift and enhanced Zeeman splitting we conclude that the novel EPR feature originates from the loosely trapped charge-compensating carriers at the abundant structural defects at the surface of terraced nanoparticles due to their exchange interaction with neighboring Mn2+ ions.

Novel 3D metallic structures composed of multipetal flowers consisting of nanoparticles are presented. The control of surface plasmon hotspots is demonstrated in terms of location and intensity as a function of petal number for uniform and reproducible surfaceenhanced Raman spectroscopy (SERS) with high field enhancement.

Perovskite solar cells have shown unprecedent performance increase up to 22% efficiency. However, their photovoltaic performance has shown fast deterioration under light illumination in the presence of humid air even with encapulation. The stability of perovskite materials has been unsolved and its mechanism has been elusive. Here we uncover a mechanism for irreversible degradation of perovskite materials in which trapped charges, regardless of the polarity, play a decisive role. An experimental setup using different polarity ions revealed that the moisture-induced irreversible dissociation of perovskite materials is triggered by charges trapped along grain boundaries. We also identified the synergetic effect of oxygen on the process of moisture-induced degradation. The deprotonation of organic cations by trapped charge-induced local electric field would be attributed to the initiation of irreversible decomposition., Improving the stability of perovskite solar cells remains crucial. Here, Ahn et al. show that trapped charges at grain boundaries induce the dissociation of the perovskite compound in the presence of moisture, and explain why degradation is irreversible under illumination and reversible in the dark.

Continuous wave CO 2 laser was irradiated on SiO 2 /TiO 2 composite nanoparticles generating in a flame to in-situ control the crystalline phase. The laser irradiation was not only shown to transform originally amorphous composite nanoparticles into the crystalline ones, but also to control the crystallite size of TiO 2 embedded in SiO 2 nanoparticles by altering the irradiating laser power. X-ray diffraction analysis and transmission electron microscope analysis confirmed that the size of TiO 2 anatase crystallites in silica nanoparticle increased with increasing the irradiation laser power. It was shown that the corresponding absorption edge of SiO 2 /TiO 2 composite nanoparticles could be controlled by changing the crystallite size of TiO 2 inside SiO 2 nanoparticles.

We provide a complete classification of possible configurations of mutually pairwise-touching infinite cylinders in Euclidian three-dimensional space. It turns out that there is a maximum number of such cylinders possible in three dimensions independently of the shape of the cylinder cross-sections. We give the explanation of the uniqueness of the non-trivial configuration of seven equal mutually touching round infinite cylinders found earlier. Some results obtained for the chirality matrix, which is equivalent to the Seidel adjacency matrix, may be found useful for the theory of graphs.

Auxetics are novel counterintuitive materials that grow thicker perpendicularly to the applied force when stretched and therefore are described by a negative Poisson's ratio. We show that a regular lattice of individual multipods properly assembled in three dimensions has the ultimate negative Poisson's ratio-1: the lattice expands or contracts uniformly in all directions. Our ball-and-stick working model verifies the mathematical construction. Application of the model to real materials is discussed. Our result is important for understanding the ways to create entangled materials with interesting mechanical properties.

We developed a simple and direct thermo-compression method for integrating single-walled carbon nanotube (SWCNT) mats of adjustable thicknesses, transparency and conductivity into polymer films. Produced SWCNT/polyethylene composite films have exhibited good optical transparency and conductivity as well as high mechanical flexibility. It was found that the electrical conductivity of the SWCNT mats could be significantly improved by ethanol densification. SWCNT/polyethylene thin films demonstrated excellent cold electron field emission properties.

Shell shaped carbon nanoparticles were synthesized from acetylene flow injected inside an oxygen-hydrogen diffusion flame when it was irradiated with a focused beam of a CW CO2 laser above a certain laser power and at a certain position [1]. In the present study, the evolution of carbon nanoparticles generated under laser irradiation has been investigated together with a study on the visualization of particle generating flames. The size distributions of carbon shell nanoparticles and soots have been determined by examining the images of TEM grid on which particles were captured by local thermophoretic sampling. The variations of radii of gyration and fractal dimensions of soot and shell shaped particulate aggregates are obtained at different laser powers.

It is known that auxetic properties (for example, negative Poisson ratios, that is, when a solid experiences lateral expansion under stretching instead of lateral contraction) start showing themselves in materials where there is a certain kind of geometrical orientational correlations between "rigid" constituents. Properly arranged orientational degrees of freedom of building blocks govern the characteristic distances in auxetic materials and thus determine the way in which the materials contract or expand. Very often the building blocks are filamentous. We suggest a way to arrange filamentous objects into highly interwoven regular structures which may exhibit auxetic properties with negative Poisson ratio. Our purely geometrical consideration can be extended to an irregular positional arrangement. This implies that a solid of sufficiently dense "random" arrangements of filaments (for example, "wool" of nanowires or of carbon nanotubes) may become auxetic.

The cellular toxicity of multi-walled carbon nanotubes (MWCNTs) and onion-like shell-shaped carbon nanoparticles (SCNPs) was investigated by analyzing the comparative cell viability. For the reasonable comparison, physicochemical characteristics were controlled thoroughly such as crystallinity, carbon bonding characteristic, hydrodynamic diameter, and metal contents of the particles. To understand relation between cellular toxicity of the particles and generation of reactive oxygen species (ROS), we measured unpaired singlet electrons of the particles and intracellular ROS, and analyzed cellular toxicity with/without the antioxidant N-acetylcysteine (NAC). Regardless of the presence of NAC, the cellular toxicity of SCNPs was found to be lower than that of MWCNTs. Since both particles show similar crystallinity, hydrodynamic size, and Raman signal with negligible contribution of remnant metal particles, the difference in cell viability would be ascribed to the difference in morphology, i.e., spherical shape (aspect ratio of one) for SCNP and elongated shape (high aspect ratio) for MWCNT.

Multifurcated assemblies composed of charged nanoparticles (NPs) are fabricated by using spark discharge and manipulating the electric field. The multifurcated structure of the assembly of NPs and spontaneous interconnections between the near structures are described. The gas sensor with the tetrafurcated-NP-assembled structure demonstrates ≈200% enhanced response to 100 ppm CO at 300 °C.

We report a strong size-selective effect of the non-uniform external electric field on unitary charged nanoparticles in a residual dusty plasma generated by spark discharge. It has been found that the field influences the outcome particle size distribution function considerably by expelling smaller particles out of the residual plasma cloud so that they cannot neutralize or agglomerate. Meantime, larger particles being dragged by the plasma cloud neutralize and disappear at walls; therefore, the particle size distribution function shifts to small sizes. We give a simple theory explaining the field effect and suggest its application for a patterning technique.

The two-process model on electron field emission from nanocarbons that we recently suggested [I. S. Altman, P. V. Pikhitsa, and M. Choi, Appl. Phys. Lett. 84, 1126 (2004)] has solved the existing experimental puzzles such as an occurrence of the sharp knee in the Fowler-Nordheim (FN) plot. Our model implies two successive processes: (1) Tunneling from the metallic region into the semiconducting region under the external macroscopic electric field and (2) tunneling from the semiconducting region into vacuum under the Coulomb field of an additional electron appearing in the first process. However, this model in its original form was inapplicable at finite temperatures. We develop the model (remaining within the framework of the two-process approach, which allows the knee occurrence in the FN plot) in order to describe temperature effects in field emission from nanocarbons. Fitting of the recent experimental data on the temperature behavior of field emission from carbon nanotubes allowed us to extract parame...

We show that the conventional consideration of the electron-field emission from nanocarbons cannot explain the experimentally observed results. We suggest a mechanism of the field emission occurrence from nanocarbons that can solve the existing puzzles. This mechanism implies two successive processes: (1) Tunneling through the low-energy barrier from the metallic region into the semiconducting region under the external macroscopic electric field and (2) tunneling through the high-energy barrier from the semiconducting region into a vacuum under the Coulomb field of an additional electron appearing in the first process.

The size and crystalline phase changes of Fe2O3 nanoparticles formed in a H2/O2 flame have been investigated. At flame temperatures below 1350 °C, the mean particle size increased monotonously with the distance from the burner edge; but in high-temperature flames above 1650 °C, it suddenly decreased from 20 to ∼3 nm with the distance from the burner edge. The results of X-ray diffraction and high-resolution transmission electron microscopy showed that this sudden reduction of the size of nanoparticles was accompanied by a partial phase transformation from the metastable γ-Fe2O3 into α-Fe2O3. We suggest the structural instability due to γ- to α-phase transformation as a mechanism for a rapid fragmentation of 20 nm particles into 3 nm ones.

We report the photoluminescence (PL) observation of extremely sharp zero-phonon lines originating from transitions of Mn2+ and Cr3+ ions embedded into MgO matrix of nanoscale (nanocrystals and films). The excellent performance of PL compared to that from quantum dots makes our finding attractive for applications.

We report on a shell-shaped carbon nanoparticle (SCNP)-based gas sensor that reversibly detects reducing gas molecules such as CO and H2 at room temperature both in air and inert atmosphere. Crystalline SCNPs were synthesized by laser-assisted reactions in pure acetylene gas flow, chemically treated to obtain well-dispersed SCNPs and then patterned on a substrate by the ion-induced focusing method. Our chemically functionalized SCNP-based gas sensor works for low concentrations of CO and H2 at room temperature even without Pd or Pt catalysts commonly used for splitting H2 molecules into reactive H atoms, while metal oxide gas sensors and bare carbon-nanotube-based gas sensors for sensing CO and H2 molecules can operate only at elevated temperatures. A pristine SCNP-based gas sensor was also examined to prove the role of functional groups formed on the surface of functionalized SCNPs. A pristine SCNP gas sensor showed no response to reducing gases at room temperature but a significant response at elevated temperature, indicating a different sensing mechanism from a chemically functionalized SCNP sensor. (Some figures may appear in colour only in the online journal)

The capability of assembling nanoparticles into a desired ordered pattern is a key to realize novel devices which are based not only on the unique properties of nanoparticles but also on the arrangements of nanoparticles. While two-dimensional arrays of nanoparticles have been successfully demonstrated by various techniques, a controlled way of building ordered arrays of three-dimensional (3D) nanoparticle structures remains challenging. We report that a variety of 3D nanoparticle structures can be formed in a controlled way based on the ion-induced focusing, electrical scaffold, and antenna effects from charged aerosols. Particle trajectory calculations successfully predict the whole process of 3D assembly. New surface enhanced Raman scattering substrates based on our 3D assembly were constructed as an example showing the viability of the present approach. This report extends the current capability of positioning nanoparticles on surface to another spatial dimension, which can serve as the foundation of future optical, magnetic, and electronic devices taking the advantage of multidimensions.

The formation of a novel hybrid material, NanoBuds, single-walled carbon nanotubes (CNTs) with covalently attached fullerenes was investigated in a ferrocene–carbon monoxide system. Fullerenes and CNTs were simultaneously formed by carbon monoxide disproportionation on the surface of iron particles in the presence of etching agents such as H2O and CO2. On the basis of parametric investigations and in situ sampling of the product from different locations in the reactor the mechanisms for NanoBud formation are discussed.

Luminescent defect centers in wide bandgap materials such as MgO are of great interest for science and technology. Magnesium oxide nanocubes obtained by the self-combustion of Mg metal have long exhibited only a broad 2.9 eV cathodoluminescence band owing to oxygen vacancies (F centers). However, in this work, a room-temperature ultraviolet 4.8 eV cathodoluminescence band has been observed coincident with a 2.5 eV band of the same intensity from an unexplored intrinsic defect in MgO terraced nanocubes and nanospheres produced from Mg metal combustion in an H2/O2 flame. Synchrotron radiation excitation spectra reveal that the excitation energy at the onset of both bands is just above the bandgap energy of 7.7 eV, where electrons and holes are generated. We determine that a defect, responsible for both emission bands, creates proximal anion-cation vacancy pairs named P centers that may appear instead of F centers because of changes in the MgO nanoparticle growth conditions.

Both fullerenes and single-walled carbon nanotubes (SWNTs) exhibit many advantageous properties. Despite the similarities between these two forms of carbon, there have been very few attempts to physically merge them. We have discovered a novel hybrid material that combines fullerenes and SWNTs into a single structure in which the fullerenes are covalently bonded to the outer surface of the SWNTs. These fullerene-functionalized SWNTs, which we have termed NanoBuds, were selectively synthesized in two different one-step continuous methods, during which fullerenes were formed on iron-catalyst particles together with SWNTs during CO disproportionation. The field-emission characteristics of NanoBuds suggest that they may possess advantageous properties compared with single-walled nanotubes or fullerenes alone, or in their non-bonded configurations.

We presented detailed studies of the formation of single-walled carbon nanotubes by an aerosol method based on the introduction of pre-formed catalyst particles into conditions leading to carbon nanotube synthesis. Carbon monoxide and iron nanoparticles were used as a carbon source and a catalyst, respectively. The vital role of etching agents such as CO2 and H2O in CNT formation was demonstrated on the basis of on-line Fourier-transform infrared spectroscopy measurements. Hydrogen was shown to participate in the reaction of carbon release and to prevent the oxidation of the catalyst particles and the hot wire. The addition of H2 and small amounts of CO2 and H2O led to an increase in the carbon nanotube lengths. The catalyst particle evaporation process inside the reactor was found to become significant at temperatures higher than 1100 degrees C. The carbon nanotube growth was found to occur at a temperature of around 900 degrees C in the heating section of the reactor by in situ sampling and the growth rate was calculated to exceed 1.1 microm/s. A detailed analysis of possible processes during carbon nanotube formation revealed heptagon transformation as a limiting stage. A mechanism for carbon nanotube formation was proposed.

The development of nanodevices that exploit the unique properties of nanoparticles will require high-speed methods for patterning surfaces with nanoparticles over large areas and with high resolution. Moreover, the technique will need to work with both conducting and non-conducting surfaces. Here we report an ion-induced parallel-focusing approach that satisfies all requirements. Charged monodisperse aerosol nanoparticles are deposited onto a surface patterned with a photoresist while ions of the same polarity are introduced into the deposition chamber in the presence of an applied electric field. The ions accumulate on the photoresist, modifying the applied field to produce nanoscopic electrostatic lenses that focus the nanoparticles onto the exposed parts of the surface. We have demonstrated that the technique could produce high-resolution patterns at high speed on both conducting (p-type silicon) and non-conducting (silica) surfaces. Moreover, the feature sizes in the nanoparticle patterns were significantly smaller than those in the original photoresist pattern.

We report the observation and the explanation of the famous $220\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ spectral feature in UV absorption from continuous layer multishell carbon nanoparticles. Historically, attempts to find this feature in carbon allotropes led to the discovery of the ${\mathrm{C}}_{60}$ fullerene. We discerned the physical origin of this feature to be the well-defined pentagonal corner defects in polyhedral multilayer carbon nanoparticles. These new topological columnar defects should have large influence on the electronic properties of nanomaterials and are worthwhile further detail studying.

Single-walled carbon nanotubes (CNTs) were synthesised at different conditions by a novel aerosol method based on the introduction of pre-formed iron catalyst particles into conditions leading to CNT formation. The results of statistical measurements of individual CNT dimensions based on high-resolution TEM images showed the effects of the residence time and temperature in the reactor. The ratio between catalyst particle and CNT diameters was close to 1.6 and independent of the experimental conditions, thus revealing an astonishing “universality” in the growth process. A proposed geometric model of heptagon defect formation, which initiates and maintains the CNT growth, allowed us to theoretically explain the phenomenon.

This paper is devoted to a detailed analysis of processes accompanying nanoparticle formation in flames. These processes are treated in the contexts of both macro and micro approaches. The macro approach includes consideration of heat and mass transfer during particle growth from the gas phase. The leading role of radiation in the total heat exchange between a growing particle and its environment is a critical factor of a particle’s temperature history. It leads to the existence of a certain size of a particle growing in a flame. The micro approach shows the necessary generation of a large number of defects during the particle formation. The critical dependence of the defect concentration, and the emission characteristics for a particle growing under flame condition, are predicted. The proposed scheme for the description of the particle growth allows one to explain some experimentally observed peculiarities for particles formed in flames.