Lattice Nanostructures Research Articles

On novel topological characteristics of graphene

Molecular topological indices are quantitative measurements that only take into account the topology of a compound’s molecular graph, disregarding any knowledge of the atom locations or chemical connections. An allotrope of carbon called graphene is composed of a single layer of atoms set up in a hexagonal lattice nanostructure. A single layer of carbon atoms organized in a honeycomb pattern make up the two-dimensional substance known as graphene. Graphene possesses significant inherent qualities like strong strength and great thermal and electrical conductivity. It is a sustainable substance with practically countless eco-friendly applications. In this study, we calculate the R molecular topological indices, S molecular topological indices, and Van molecular topological indices of graphene structure, taking into account all conceivable combinations of the number of rows and hexagons. There are high correlations between R, S Van index values and neighbourhood-based entropy values of graphene. This shows that these new indices can be used in QSPR/QSAR studies in chemistry and physics.

Imaging of Antiferroelectric Dark Modes in an Inverted Plasmonic Lattice.

Plasmonic lattice nanostructures are of technological interest because of their capacity to manipulate light below the diffraction limit. Here, we present a detailed study of dark and bright modes in the visible and near-infrared energy regime of an inverted plasmonic honeycomb lattice by a combination of Au+ focused ion beam lithography with nanometric resolution, optical and electron spectroscopy, and finite-difference time-domain simulations. The lattice consists of slits carved in a gold thin film, exhibiting hotspots and a set of bright and dark modes. We proposed that some of the dark modes detected by electron energy-loss spectroscopy are caused by antiferroelectric arrangements of the slit polarizations with two times the size of the hexagonal unit cell. The plasmonic resonances take place within the 0.5-2 eV energy range, indicating that they could be suitable for a synergistic coupling with excitons in two-dimensional transition metal dichalcogenides materials or for designing nanoscale sensing platforms based on near-field enhancement over a metallic surface.

Концепція спряжених на критичній ізохорі циклів Стірлінга, працюючих на двоокису вуглецю

В роботі пропонується нова концепція реалізації циклу Стірлінга в області не тільки надкритичних, але й, власне, критичних температури і тиску, заснована на виявленій в наших попердніх роботах вираженій гетерогенній структурі надкритичних флюїдів. Існування такої гетерогенної стаціонарної наноструктури решіткового типу в достатньо широких діапазонах надкритичних властивостей, які були названи не-гіббсівською фазою флюїду, було запропановане (Роганковим В.Б та іншими) у рамках моделі ФТ (флуктуаційної термодинамики). Така флюїдна структура в практичному використанні може бути досить перспективною. Вона проявляється в наявності досить регулярного, решіткового типу просторового розподілу густини флюїду і його теплових властивостей в т.зв. мезоскопічних малих об’ємах всередині робочих порожнин стискання і розширення пропонованої схеми спряжених стірлінгів. Саме поняття спряження означає ідею максимально-ефективного використання теплоти, одержаної в циклі від джерела, шляхом поєднання двох підциклів високого (І) і помірного (ІІ) тиску вздовж критичної ізохори. В роботі введене нове поняття ступеня теплофізичної досконалості (доповнюючий прийняте поняття термодинамічної досконалості, для окремих стадій – ізоліній і вузлів – нод спряженого повного циклу типу Стірлінга-Рейліса, яке дозволяє кількісно оцінити позитивний ефект додаткової внутрішньої рекуперації на загальну регенерацію теплоти. Ізольована від навколишнього середовища конструкція обох підціклів (І) і (ІІ) і об`єднуючого стірлінга є його перевагою у порівнянні з циклами внутрішнього згоряння. В якості потенціально-перспективної робочої речовини пропонується двоокис вуглецю. Таким чином, наша мета полягає у використанні виявлених нанодисперсних властивостей флюїду для формулювання концепції створення спряженного, досить ефективного циклу Стірлінга з перспективним робочим тілом - надкритичним двоокисом вуглецю, замість традиційного використання водороду або гелію.

Optical, Magnetic and Photocatalytic Activity Studies of Li, Mg and Sr Doped and Undoped Zinc Oxide Nanoparticles.

Nanoparticles of Li, Mg and Sr doped and undoped zinc oxide was prepared by simple precipitation method. The structural, optical, and magnetic properties of the samples were investigated by the Powder X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Fourier Transform Infrared (FTIR) spectroscopy, Ultra-violet Visible spectroscopy (UV-vis) spectra, Photoluminescence (PL) and Vibrational Sample Magnetometer (VSM). The Powder X-ray diffraction data confirm the formation of hexagonal wurtzite structure of all doped and undoped ZnO. The SEM photograph reveals that the pores availability and particles size in the range of 10 nm-50 nm. FTIR and UV-Visible spectra results confirm the incorporation of the dopant into the ZnO lattice nanostructure. The UV-Visible spectra indicate that the shift of blue region (lower wavelength) due to bandgap widening. Photoluminescence intensity varies with doping due to the increase of oxygen vacancies in prepared ZnO. The pure ZnO exist paramagnetic while doped (Li, Mg and Sr) ZnO exist ferromagnetic property. The photocatalytic activity of the prepared sample also carried out in detail.

Near-infrared optical characteristics of composite Ag-porous Si dielectric film for solar devices

Ag-porous Si (Ag-pSi) composite as metallo-dielectric based periodical lattice nanostructure is proposed and studied to improve the light efficiency in such structure in near-infrared range of 750–3000 nm. To achieve this, Finite-Differential Time-Domain (FDTD) implements were applied in analyzing the effects of number of layers (nLs) as well as porosity on optical characteristics of reflection, transmission and absorption using “FDTD solutions”. Perfectly matched layers (PML) and periodic boundary conditions (PBC) were selected as suitable boundaries for this simulation. The results revealed that these highlighted optical properties through the composite are influenced by variation in the nLs and porosity in near-infrared wavelengths. The reflection and transmission spectra presented contrasting patterns. Optimum transmission was attained at 80% porosity with the thickness higher than 500 nm. For the composite Ag-pSi, all the peaks found in these optical properties tended towards higher wavelengths as compared to the case of the composite Ag-Air which had an empty structure. The optimum absorption was improved by 10% with the incorporation of pSi into the Ag material. Therefore, the enhancement of optical properties in this proposed design can be achieved by controlling both the nLs and porosity.

Comparative study on predicting Young's modulus of graphene sheets using nano-scale continuum mechanics approach

In this research, nano-scale continuum modeling is employed to predict Young's modulus of graphene sheet. The lattice nano-structure of a graphene sheet is replaced with a discrete space-frame structure simulating carbon-carbon bonds with either beam or spring elements. A comparative study is carried out to check the influence of employed elements on estimated Young's moduli of graphene sheets in both horizontal and vertical directions. A detailed analysis is also conducted to investigate the influence of graphene sheet sizes on its Young's modulus and corresponding aspect ratios that unwelcomed end effects disappear on the results are extracted. At the final stage, defected graphene sheets suffering from vacancy defects are investigated through a stochastic analysis taking into account both number of defects and their locations as random parameters. The reduction level in the Young's moduli of defected graphene sheets compared with non-defected ones is analyzed and reported.

Transition from disordered aggregates to ordered lattices: kinetic control of the assembly of a computationally designed peptide.

Natural biomolecular self-assembly typically occurs under a narrow range of solution conditions, and the design of sequences that can form prescribed structures under a range of such conditions would be valuable in the bottom-up assembly of predetermined nanostructures. We present a computationally designed peptide that robustly self-assembles into regular arrays under a wide range of solution pH and temperature conditions. Controling the solution conditions provides the opportunity to exploit a simple and reproducible approach for altering the pathway of peptide solution self-assembly. The computationally designed peptide forms a homotetrameric coiled-coil bundle that further self-assembles into 2-D plate structures with well-defined inter-bundle symmetry. Herein, we present how modulation of solution conditions, such as pH and temperature, can be used to control the kinetics of the inter-bundle assembly and manipulate the final morphology. Changes in solution pH primarily influence the inter-bundle assembly by affecting the charged state of ionizable residues on the bundle exterior while leaving the homotetrameric coiled-coil structure intact. At low pH, repulsive interactions prevent 2-D lattice nanostructure formation. Near the estimated isoelectric point of the peptide, bundle aggregation is rapid and yields disordered products, which subsequently transform into ordered nanostructures over days to weeks. At elevated temperatures (T = 40 °C or 50 °C), the formation of disordered, kinetically-trapped products largely can be eliminated, allowing the system to quickly assemble into plate-like nanostructured lattices. Moreover, subtle changes in pH and in the peptide charge state have a significant influence on the thickness of formed plates and on the hierarchical manner in which plates fuse into larger material structures with observable grain boundaries. These findings confirm the ability to finely tune the peptide assembly process to achieve a range of engineered structures with one simple 29-residue peptide building block.

Polymer Nanodot-Hybridized Alkyl Silicon Oxide Nanostructures for Organic Memory Transistors with Outstanding High-Temperature Operation Stability

Organic memory devices (OMDs) are becoming more important as a core component in flexible electronics era because of their huge potentials for ultrathin, lightweight and flexible plastic memory modules. In particular, transistor-type OMDs (TOMDs) have been gradually spotlighted due to their structural advantages possessing both memory and driving functions in single devices. Although a variety of TOMDs have been developed by introducing various materials, less attention has been paid to the stable operation at high temperatures. Here we demonstrate that the polymer nanodot-embedded alkyl silicon oxide (ASiO) hybrid materials, which are prepared by sol-gel and thermal cross-linking reactions between poly(4-vinylphenol) (PVP) and vinyltriethoxysilane, can deliver low-voltage (1~5 V) TOMDs with outstanding operation stability (>4700 cycles) at high temperatures (150 °C). The efficient low-voltage memory function is enabled by the embedded PVP nanodots with particular lattice nanostructures, while the high thermal stability is achieved by the cross-linked ASiO network structures.

On the derivation of the elastic properties of lattice nanostructures: The case of graphene sheets

Abstract Several nanomechanics formulations based on common two and three-body bonding potentials are compared. Numerical simulations and analytical approaches are used to investigate the not negligible differences among the predictions of the in-plane elastic constants of graphene sheets in the literature, separately exploring the role of the potentials and that of the structural descriptions (beams and trusses) of the original molecular mechanics (MM) model. The energetic differences between the structural models and the MM model are highlighted through exact discrete homogenization procedures. In so doing, some theoretical expressions of the graphene elastic constants available in the literature are recovered and supported by the numerical experimentation. The results provide also an assessment of the accuracy of some potentials largely employed in the literature with respect to several ab-initio reference solutions and the experimental measurements available. Some suggestions towards a reparametrization of the modified Morse potential are consequently formulated.

Self-consistent analysis of electron transport in GaN/AlGaN super lattice nanostructure for light emission

Schrödinger and Poisson’s equation have been solved self-consistently to investigate the electron transport in GaN/AlGaN super lattice nanostructure. Effect of applied bias along with spatial variation in effective mass of GaN and AlGaN has been taken in to account for realizing the electron confinement and recombination in one dimensional super lattice nanostructure. We have investigated in detail the influence of applied bias and Aluminum mole composition on Eigen energy, probability density and recombination rate. Here, we have determined the electron concentration through self-consistent solutions of Schrodinger and Poisson’s equations. The electron concentration deduced was 1.75×1020cm−3 under applied bias voltage of 5V with Aluminum mole fraction of 20%. The probability density along X direction clearly reveals that electrons are confined very well within the central region of superlattice nanostructure.

Mesoporous self-assembled nanoparticles of biotransesterified cyclodextrins and nonlamellar lipids as carriers of water-insoluble substances.

Soft mesoporous hierarchically structured particles were created by the self-assembly of an amphiphilic deep cavitand cyclodextrin βCD-nC10 (degree of substitution n = 7.3), with a nanocavity grafted by multiple alkyl (C10) chains on the secondary face of the βCD macrocycle through enzymatic biotransesterification, and the nonlamellar lipid monoolein (MO). The effect of the non-ionic dispersing agent polysorbate 80 (P80) on the liquid crystalline organization of the nanocarriers and their stability was studied in the context of vesicle-to-cubosome transition. The coexistence of small vesicular and nanosponge membrane objects with bigger nanoparticles with inner multicompartment cubic lattice structures was established as a typical feature of the employed dispersion process. The cryogenic transmission electron microscopy (cryo-TEM) images and small-angle X-ray scattering (SAXS) structural analyses revealed the dependence of the internal organization of the self-assembled nanoparticles on the presence of embedded βCD-nC10 deep cavitands in the lipid bilayers. The obtained results indicated that the incorporated amphiphilic βCD-nC10 building blocks stabilize the cubic lattice packing in the lipid membrane particles, which displayed structural features beyond the traditional CD nanosponges. UV-Vis spectroscopy was employed to characterize the nanoencapsulation of a model hydrophobic dimethylphenylazo-naphthol guest compound (Oil red) in the created nanocarriers. In perspective, these dual porosity carriers should be suitable for co-encapsulation and sustained delivery of peptide, protein or siRNA biopharmaceuticals together with small molecular weight drug compounds or imaging agents.

Precise Normal Mode Analysis and Frequency Prediction of DNA Nanostructure through Mass-Weighted Chemical Elastic Network Model

In our previous study on self-assembly mechanism of DNA nanostructures, using elastic network model (ENM) based normal mode analysis (NMA), we successfully explained the reason why planar DNA tiles were self-assembled as a helical nanotube, which was totally contrast to our preconception such that they could form a planar lattice nanostructure. Although this traditional ENM based NMA is very useful to catch collective motions of biomolecules in a timely fashion, it is impossible to predict vibration frequency due to its dimensionless uniform mass and spring constants.We propose a mass-weighted chemical elastic network model (MWCENM) which takes inertia effect and chemical bond information into account. For example, lumped masses are assigned to the representative atoms and different spring constants are given to bonded and non-bonded interactions including covalent bond, hydrogen bond, and van der Waals interaction.Several comparison studies convince us that MWCENM is able to catch DNA dynamics more precisely and more effectively. It is also expected that one can use MWCENM based NMA results, which include both predicted frequencies and corresponding mode shapes, as a fingerprint to characterize molecular dynamics by a comparison with vibration spectrum data.

Array formation and size effects in chemically synthesized FePt nanoparticles

Monodisperse FePt nanoparticles (NP’s) have been synthesized by reduction of platinum acetylacetonate [Pt(acac)2] followed by thermal decomposition of iron pentacarbonyl [Fe(CO)5] in the presence of oleic acid (OA) and oleyl amine (OY) as surfactants at a low reaction temperature. Particle size is controlled by the injection temperature of Fe(CO)5. The effect of particle size on the blocking temperature has been investigated for nanoparticles with sizes of 3.0 and 6.0nm. The interparticle spacing is varied by changing the addition time of the OA and OY. Well-aligned mono- and multi-layered hexagonal-closed-packed (hcp) to square lattice nanostructures are formed for 5nm FePt NP’s. Surfactant layer thickness, ⟨L⟩ to metal core radius R (⟨L⟩∕R) ratios of 0.46 and 0.60 are evaluated for the monolayer of hexagonal-closed-packed and square lattice array structures, respectively. For hcp arrays bilayer and trilayer structures are also observed. Subjecting the NP’s to thermal processing at 800°C results in a transformation of the nanoparticles from the disordered fcc phase to the ordered L10 phase.