Artificial Structuring Research Articles

Improved Energy Storage Performance of PVDF Nanocapacitors by Utilizing 2D Inorganic Barrier Layers

We demonstrated a rational approach for designing high-performance polymer-based energy storage capacitors. Two-dimensional paraelectric Ca2Nb3O10 nanosheets were deposited on a ferroelectric poly(vinylidene fluoride) (PVDF) film to form paraelectric/ferroelectric hetero-assemblies. Such an artificial structuring enabled tailoring of the breakdown strength and dielectric response, realizing an enhanced energy density (~10 J cm−3) compared to pristine PVDF film (~ 1 J cm−3).

Superlattice-induced ferroelectricity in charge-ordered La1/3Sr2/3FeO3

Charge-order-driven ferroelectrics are an emerging class of functional materials, distinct from conventional ferroelectrics, where electron-dominated switching can occur at high frequency. Despite their promise, only a few systems exhibiting this behavior have been experimentally realized thus far, motivating the need for new materials. Here, we use density-functional theory to study the effect of artificial structuring on mixed-valence solid-solution La1/3Sr2/3FeO3 (LSFO), a system well studied experimentally. Our calculations show that A-site cation (111)-layered LSFO exhibits a ferroelectric charge-ordered phase in which inversion symmetry is broken by changing the registry of the charge order with respect to the superlattice layering. The phase is energetically degenerate with a ground-state centrosymmetric phase, and the computed switching polarization is 39 μC/[Formula: see text], a significant value arising from electron transfer between [Formula: see text] octahedra. Our calculations reveal that artificial structuring of LSFO and other mixed valence oxides with robust charge ordering in the solid solution phase can lead to charge-order-induced ferroelectricity.

Enhancing artificial sum frequency generation from graphene-gold metamolecules.

The enhanced artificial sum frequency generation (SFG) is realized by graphene-gold metamolecules at the mid-infrared without any natural nonlinear material. The unit cell of the proposed metamolecules combines an inner graphene cut-wire meta-atom and an outer gold split-ring resonator meta-atom. In order to achieve high efficiency of the artificial SFG, not only the novel material of graphene with high mobility is used as the constituent material, but also the double resonances at two fundamental frequencies are excited to form an intensive magnetic Lorentz force. Both time domain response and frequency domain response are analyzed numerically. Results show that the SFG efficiency is at least two orders of magnitude larger than that of second-harmonic generation, which involves only a single resonance. The tunability of graphene on the SFG is studied as well. This work will facilitate the engineering of nonlinear metamaterials, whose nonlinear properties can be customized by artificial structuring, in their practical applications.

‘Native’ Villages, ‘Coolie’ Lines, and ‘Free’ Indian Settlements: The Geography of Indenture in Fiji

Ceded to Great Britain in 1874, five years later, in 1879, Fiji became the final British colony to start using Indian indentured labour for sugar cultivation. This paper focuses on the historical geography of indentured labour in Fiji, bringing to the fore spatial representations of the indenture experience in the colony. The paper examines how colonial policy demarcating spaces and places shaped the lived experience of Indian indentured labourers during this period. Of particular interest is the administrative use of the words ‘native’ (village), ‘coolie’ (line), and ‘free’ (settlement), which attempted to create an artificial socio-racial structuring of society. In the eyes of the colonial administration, Indian indentured men, women, and children ceased being native and were cast as coolies. Once their contracts were completed, they became free. The paper argues that whilst this concealed and oversimplified socio-racial complexities and was instrumental in the manifestation of distinct spatial identities, there were many instances where these categories were subverted by Indian labourers who endeavoured to permeate spaces not designated to them in the colony. In doing so, the paper highlights the issue of agency amongst Indian indentured labourers and explores how they negotiated the colonially reconfigured landscape of the Fijian archipelago.

Coexistence of Magnetic Order and Ferroelectricity at 2D Nanosheet Interfaces.

Multiferroic materials, in which the electronic polarization can be switched by a magnetic field and vice versa, are of fundamental importance for new electronic technologies. However, there exist very few single-phase materials that exhibit such cross-coupling properties at room temperature, and heterostructures with a strong magnetoelectric coupling have only been made with complex techniques. Here, we present a rational design for multiferroic materials by use of a layer-by-layer engineering of 2D nanosheets. Our approach to new multiferroic materials is the artificial construction of high-quality superlattices by interleaving ferromagnetic Ti0.8Co0.2O2 nanosheets with dielectric perovskite-structured Ca2Nb3O10 nanosheets. Such an artificial structuring allows us to engineer the interlayer coupling, and the (Ti0.8Co0.2O2/Ca2Nb3O10/Ti0.8Co0.2O2) superlattices induce room-temperature ferroelectricity in the presence of the ferromagnetic order. Our technique provides a new route for tailoring artificial multiferroic materials in a highly controllable manner.

Artificial design for new ferroelectrics using nanosheet-architectonics concept

Control over the emergence of ferroelectric order remains a fundamental challenge for the rational design of artificial materials with novel properties. Here we report a new strategy for artificial design of layered perovskite ferroelectrics by using oxide nanosheets (high-k dielectric Ca2Nb3O10 and insulating Ti0.87O2) as a building block. We approached the preparation of superlattice films by a layer-by-layer assembly involving Langmuir–Blodgett deposition. The artificially fabricated (Ti0.87O2/Ca2Nb3O10)2(Ti0.87O2) superlattices are structurally unique, which is not feasible to create in the bulk form. By such an artificial structuring, we found that (Ti0.87O2/Ca2Nb3O10)2(Ti0.87O2) superlattices possess a new form of interface coupling, which gives rise to ferroelectricity with a good fatigue-free characteristic. Considering the flexibility of self-assembled nanosheet interfaces, this technique provides a route to synthesize a new kind of layered ferroelectric oxides.

3-D Manipulation of ZnO Nanowire Using Optically Activated Thermoplastic Tip on Silica Fiber Taper

Semiconductor nanowire offers various opportunities in novel optoelectronics yet its precise manipulation technique has not been fully developed. We proposed a new method to transport and manipulate individual single ZnO nanowire in 3-D space using an optically activated ethylene-vinyl acetate (EVA) tip on microtapered silica fiber. The microtaper fiber delivered laser light to optically activate the plasticity in the microscopic EVA spot, where the single ZnO nanowire was selectively adhered. Detailed principles and procedures are discussed along with a unique artificial structuring of nanowires.

Epitaxial strain effects on magnetic ordering and spin-phonon couplings in the (SrMnO3)1/(LaMnO3)1superlattice from first principles

We have studied the influence of epitaxial strain on magnetic orderings and the couplings between the spin and polar phonons in the 1:1 SrMnO$_3$/LaMnO$_3$ superlattice from first principles. Magnetic phase transitions of the superlattice induced by epitaxial strain are observed, consistent with previous reports. We find that oxygen octahedral rotations lower the ground state energy but do not destroy the magnetic phase transitions induced by strain. We compute zone center phonon frequencies and eigenvectors as functions of epitaxial strain and magnetic ordering. A substantial increase of the coupling strength between the spin and the lowest-frequency polar mode is observed for tensile strains. This increase can be attributed to a change of character of the lowest mode resulting from different relative couplings of the various polar modes to epitaxial strain. Finally, spin-phonon coupling strengths are computed in a Heisenberg formalism. This analysis directly reveals the changes in exchange couplings due to specific atomic displacements or phonon modes, as well as the nonequivalence of the out-of-plane exchange couplings across LaO layers and across SrO layers, the latter being the result of the artificial structuring in the superlattice.

Polarization-controlling dual-band absorption metamaterial

We investigated sandwich structure of the conventional absorber metamaterials to expand the study on dual-band absorption in our previous work (2013 Appl. Phys. Lett.102 081122). The advantages of the artificial structuring of plasmonic resonators or ‘meta-atoms’ were exploited to gradually enhance/degrade the absorption peaks by polarization angle of electromagnetic wave. By reshaping the rings at the font of slab, dual- or single-peak absorption is controlled. The absorber is demonstrated in the GHz region.

Flux Exclusion Superconducting Quantum Metamaterial: Towards Quantum-level Switching

Nonlinear and switchable metamaterials achieved by artificial structuring on the subwavelength scale have become a central topic in photonics research. Switching with only a few quanta of excitation per metamolecule, metamaterial's elementary building block, is the ultimate goal, achieving which will open new opportunities for energy efficient signal handling and quantum information processing. Recently, arrays of Josephson junction devices have been proposed as a possible solution. However, they require extremely high levels of nanofabrication. Here we introduce a new quantum superconducting metamaterial which exploits the magnetic flux quantization for switching. It does not contain Josephson junctions, making it simple to fabricate and scale into large arrays. The metamaterial was manufactured from a high-temperature superconductor and characterized in the low intensity regime, providing the first observation of the quantum phenomenon of flux exclusion affecting the far-field electromagnetic properties of the metamaterial.

Engineered Interfaces of Artificial Perovskite Oxide Superlattices via Nanosheet Deposition Process

Combining different materials into desired superlattice structures can produce new electronic states at the interface and the opportunity to create artificial materials with novel properties. Here we introduce a new, rather unexpected, and yet simple way to such a superlattice assembly of perovskite oxides: in the Dion-Jacobson phase, a model system of layered perovskites, high-quality bicolor perovskite superlattices (LaNb(2)O(7))(nL)(Ca(2)Nb(3)O(10))(nC) are successfully fabricated by a layer-by-layer assembly using two different perovskite nanosheets (LaNb(2)O(7) and Ca(2)Nb(3)O(10)) as a building block. The artificially fabricated (LaNb(2)O(7)/Ca(2)Nb(3)O(10)) superlattices are structurally unique, which is not feasible to create in the bulk form. By such an artificial structuring, we found that (LaNb(2)O(7)/Ca(2)Nb(3)O(10)) superlattices possess a new form of interface coupling, which gives rise to ferroelectricity.

Correlation of geometrical and electronic properties in metallic nanowires

AbstractThe structure on the atomic scale was found to be directly correlated with the electronic and transport properties of ultra‐thin metallic wires. We present examples of both self‐organized and artificially structured nanowires in the system Pb/Si(557). We demonstrate that artificial structuring on the nanoscale allows identification and determination of the electrical transport properties of atomic size defects, using Si(557) as a quasi‐insulating substrate and a Si double step in a monolayer high Pb nanowire as an example. One‐dimensional (1D) properties with strong electron correlation and various instabilities in metallic chains or ribbons generated by metal adsorption of sub‐monolayers on insulating substrates like Si(111) or Si(557) turn out to always be modified by the unavoidable coupling to 2D and 3D. The wealth of new and partly unexpected phenomena is exemplified here again in monolayers of Pb on Si(557), which forms wire‐like arrays. We identify structural self‐stabilization as the origin of 1D electronic transport and show that a new 1D state is generated by step decoration. Magnetoconductance measurements yield even deeper insight into mechanisms of electronic transport, as also exemplified in this specific system.

Artifical chiral materials

In 1898 Acharya J C Bose, a researcher from Calcutta, India, wrote in the Proceedings of the Royal Society of London: 'In order to imitate the rotation by liquids like sugar solutions, I made elements of molecules of twisted jute, of two varieties, one kind being twisted to the right (positive) and the other twisted to the left (negative).... The twisted structure produces an optical twist of the plane of polarization'. This paper[1], published 111 years ago and reporting experimental microwave tests on the optical activity of the artificial chiral medium, was the first publication on what has now become a flourishing and dynamic field of metamaterials - man-made media with all sorts of unusual functionalities that can be achieved by artificial structuring smaller than the wavelength scale of the external stimulus. An increasing number of researchers are currently designing, fabricating and studying artificial metamaterials composed of tailored chiral building blocks that may be viewed as 'artificial chiral molecules'. This special section is devoted to this vibrant and emerging research direction and has a special emphasis on the theory of light interactions with artificial chiral media.

Effects of artificially structured micrometer holes on the transport behavior of Al-doped ZnO layers

We study the transport properties of artificially structured n-type ZnO:Al thin films prepared by rf magnetron sputtering on glass substrates. The samples were patterned with an array of 4×4 and 8×8 μm2 holes. With decreasing hole size, the resistance of the samples increases. Filling the holes with Au or Al increases and decreases the resistance, respectively. All samples show a negative magnetoresistance, which becomes more pronounced with decreasing hole diameter. The filling of the holes with Au or Al reduces the effects of the artificial structuring on the magnetoresistance.

Ferroelectricity in Artificial Bicolor Oxide Superlattices

We report on the growth and properties of high quality bicolor oxide superlattices, composed of two perovskites out of BaTiO{sub 3}, CaTiO{sub 3}, and SrTiO{sub 3}. The artificially grown superlattices are structurally unique and have a macroscopically homogeneous phase, which is not feasible to recreate in bulk form. By artificial structuring, it is found that the polarization of such superlattices can be highly increased as compared to pseudo-binary ceramics with the same overall composition. Such strong enhancement in superlattice is attributed to newly-developed ionic motions of A-site cations at the hetero-interfaces due to the interfacial coupling of electrostatic and elastic interactions, which cannot be found in single phase materials.

Nanometric artificial structuring of semiconductor surfaces for crystalline growth

The coupling of standard self-organization methods with surface artificial nanostructuring has recently emerged as a promising technique in semiconductor materials to control simultaneously the size distribution, the density and the position of epitaxial nanostructures. Some physical aspects of the morphology and elastic strain engineering are reviewed in this article. The emphasis is on the effects of capillarity, growth rate anisotropy, strain relaxation and entropy of mixing for alloys. The interplay among these driving forces is first illustrated by III–V compound semiconductor growth on lithographically patterned surfaces, then by germanium growth on implanted substrates and nanopatterned templates obtained by chemical etching of buried strain dislocation networks. To cite this article: J. Eymery et al., C. R. Physique 6 (2005).

Effect of artificial structuring on the use of laying hen runs in a free-range system

1. This study examined whether a free range with roofed boxes with sand to structure the hen run had an effect on the numbers of hens going outside and on the distribution of the hens in the hen run. 2. On a poultry farm with 8 flocks of laying hens of roughly 500 birds per flock, each flock was observed with and without roofed boxes with sand. 3. There was no difference in the number of hens on free range with and without roofed boxes but there was an influence on the distribution. 4. In free range with structures there was a higher percentage of the hens outside in the furthest quarter where the structures were located. 5. We conclude that structures in the free range have an effect on the distribution of laying hens.

Structure and dynamics of liquid water with different long-range interaction truncation and temperature control methods in molecular dynamics simulations.

We have used molecular dynamics simulations to study the physical properties of modified TIP3P water model included in the CHARMM program, using four different methods-the Ewald summation technique, and three different spherical truncation methods-for the treatment of the long-range interactions. Both the structure and dynamics of the liquid water model were affected by the methods used to truncate the long-range interactions. For some of the methods artificial structuring of the model liquid was observed around the cutoff radius. The model liquid properties were also affected by the commonly applied temperature control methods. Four different methods for controlling the temperature of the system were studied, and the effects of these methods on the bulk properties for liquid water were analyzed. The system size was also found to change the dynamics of the model liquid water. Two control simulations with the SPC/E water model were carried out. The self-diffusion coefficient (D), the radial distribution function (g(OO)), the distance dependent Kirkwood G-factor [G(k)(r)] and the intermolecular potential energy (E(pot)) were determined from the different trajectories and compared with the experimental data.

Observations concerning the treatment of long‐range interactions in molecular dynamics simulations

AbstractMolecular dynamics simulations of pure water employing two different empirical water models have been used to study the effects of different methods for truncation of long‐range interactions in molecular mechanics calculations. As has been observed previously in integral equation studies, “shifting” these interactions on an atom‐by‐atom basis was found to produce artificial structuring in the water and affect diffusion rates. In cases where some form of short‐range truncation must be used, the ST2 switching function applied on a group‐by‐group basis was found to be the most realistic procedure. If atom‐based shifting must be employed, a cutoff distance greater than or equal to 12.0 Å was found to be required to produce realistic results. © 1993 John Wiley & Sons, Inc.

Isotopic lattice symmetry: An unexplored area of research

The existence of isotopes is a well-known and widely used fact of chemistry. Nevertheless, despite all the attention to the isotopes of individual elements, there have been very few, if any, attempts to look at the whole notion of isotopicity as a unique phenomenon in its own way. This article is an attempt to fill this gap. The general assumption of the perfect isotopic randomness in molecules and crystals might have a complimentary aspect in the possibility of positional correlations in isotope distribution. I introduce the notion of isotopic freedom to reflect positional flexibility of different isotopes within structural constraints of a given elemental sublattice. In this vein, the whole notion of isotopicity can be seen as an overlooked outfit for “Nature's quest for patterns,” complimentary to other known manifestations of spontaneous pattern formation. I also discuss the potential of artificial isotopic structuring for fundamental and applied research directions, an option that also has remained largely unused until the present time.