One-dimensional Stacks Research Articles

Emittance and absorptance tailoring by negative refractive index metamaterial-based Cantor multilayers

We investigated electromagnetic wave propagation through one-dimensional stacks of alternating positive and negative refractive index layers arranged as truncated quasi-periodic (fractal) Cantor multilayers. We considered the occurrence of phase compensation in these structures. In our calculation we utilized the transfer matrix technique and applied the Kirchhoff's second law to calculate emittance and absorptance modification by negative index metamaterials. We took into account dispersion and absorptive losses and analysed both on-axis and off-axis radiation. We showed that Cantor structures formed by inserting negative refractive index layers as a substitution part in the multilayer lattices enable tailoring of both spectral and angular dependences of emittance/absorptance. We conclude that phase compensation could significantly extend the applicability of Cantor-type multilayers containing negative refractive index materials.

Experimental verification of zero order bandgap in a layered stack of left-handed and right-handed materials

A theoretically, predicted bandgap corresponding to the zero volume-averaged refractive index is verified experimentally by measuring the scattering parameters of a one-dimensional layered stack composed of left-handed and right-handed materials. The unique property of the zero-n gap, also denoted zero order bandgap, is verified by experiments, showing that unlike a conventional photonic band gap, the frequency corresponding to the zero order gap remains unchanged when the periodicity is altered.

Tunable spatial demultiplexer based on the Fabry-Perot filter

Superprism effect is exhibited in one-dimensional thin film stacks due to their abnormal dispersion and anisotropy properties near the bandgap. Thin film Fabry-Perot filter (FPF) was designed and fabricated to realize this effect. Furthermore, the polychromatic light was operated at different incident angles onto the device to get more demultiplexing channels at different wavelength range. This means FPF, which fabricated low-costly and simply can be used as a tunable demultiplexing device. Meanwhile, distinguished with other researchers' arithmetic, transfer matrix method (TMM) with the Gaussian angular spectrum method was introduced to calculate more accurate spatial shift at different wavelength as well as to analysis beam splitting phenomena in FPF.

Columnar liquid crystalline π-conjugated oligothiophenes

Polycatenar oligothiophenes possessing three alkoxy chains at each terminal self-organise into columnar liquid crystalline phases, and one-dimensional columnar stacks can be oriented uniaxially by mechanical shearing in the mesophases.

Liquid Crystalline Metal-Free Phthalocyanines Designed for Charge and Exciton Transport

A joint theoretical and experimental study of the electronic and structural properties of liquid crystalline metal-free phthalocyanines bearing a strong potential for charge and exciton transport has been performed. The synthesis of such compounds has been triggered by quantum chemical calculations showing that: (i) hole transport is favored in metal-free phthalocyanines by their extremely low reorganization energy (0.045 eV) and large electronic splittings; and (ii) the efficiency of energy transfer along the one-dimensional discotic stacks is weakly affected by rotational disorder due to the two-dimensional character of the molecules. We have synthesized two metal-free phthalocyanines with different branched aliphatic chains on the gram scale to allow for a full characterization of their solid-state properties. The two compounds self-organize in liquid crystalline mesophases, as evidenced by optical microscopy, differential scanning calorimetry, X-ray powder diffraction, and molecular dynamics simulations. They exhibit a columnar rectangular mesophase at room temperature and a columnar hexagonal mesophase at elevated temperature.

Nanobelt Self-Assembly from an Organic n-Type Semiconductor: Propoxyethyl-PTCDI

Nanobelt structures have been fabricated for an n-type semiconductor molecule, N,N'-di(propoxyethyl)perylene-3,4,9,10-tetracarboxylic diimide (PTCDI). The short alkyloxy side chain not only affords effective pi-pi stacking in polar solvents for self-assembling but also provides sufficient solubility in nonpolar solvents for solution processing. As revealed by both AFM and electron microscopies, the nanobelts have an approximately rectangular cross section, with a typical thickness of about 100 nm and a width in the range of 300-500 nm. The length of the nanobelts ranges from 10 to a few tens of micrometers. The highly organized molecular packing (uniaxial crystalline phase) has been deduced from the measurement of electron diffraction and polarized microscopy imaging. The detected optical axis is consistent with the one-dimensional stacking of the molecules.

Stacked Clusters of Polycyclic Aromatic Hydrocarbon Molecules

Clusters of polycyclic aromatic hydrocarbon (PAH) molecules are modeled using explicit all-atom potentials using a rigid-body approximation. The considered range of PAHs goes from pyrene (C10H8) to circumcoronene (C54H18) and clusters containing between 2 and 32 molecules are investigated. In addition to the usual repulsion-dispersion interactions, electrostatic point-charge interactions are incorporated, as obtained from density functional theory calculations. The general electrostatic distribution in neutral or singly charged PAHs is reproduced well using a fluctuating-charges analysis, which provides an adequate description of the multipolar distribution. Global optimization is performed using a variety of methods, including basin-hopping and parallel tempering Monte Carlo. We find evidence that stacking the PAH molecules generally yields the most stable motif. A structural transition between one-dimensional stacks and three-dimensional shapes built from multiple stacks is observed at larger sizes, and the threshold for this transition increases with the size of the monomer. Larger aggregates seem to evolve toward the packing observed for benzene in bulk. Difficulties met in optimizing these clusters are analyzed in terms of the strong anisotropy of the molecules. We also discuss segregation in heterogeneous clusters and vibrational properties in the context of astrophysical observations.

Formation of a One-Dimensional Stacking Structure of π-Conjugated Nitroxyl Radical Bearing a 1,2,5-Thiadiazole Ring and Its Magnetic Property

A novel stable organic radical, 7,7-diphenyl-6,7-dihydro[1,2,5]thiadiazolo[3,4-f]quinoline-6-oxyl (1), forms a one-dimensional columnar structure consisting of slipped π-stacks, which is in contrast to dimer formation of the isoelectronic benzologue, 3,3-diphenyl-3,4-dihydrobenzo[f]quinoline-4-oxyl (2). Magnetic susceptibility of 1 obeyed an antiferromagnetic chain model with J = −47 cm-1, while 2 behaved as an isolated doublet spin state even in the dimer.

One-dimensional fluorescent stacking structure based on zinc mixed-complex salt encapsulated within an ‘ice-like’ three-dimensional hydrogen-bonded water network

Self-assembly of the fluorescent mixed-complex salt [Zn(HL)(phen)2][Zn(L)(HL)(phen)]·13H2O (1) [HL = methyllactato(−1) and L = methyllactato(−2)] created an ‘ice-like’ three-dimensional open framework by hydrogen-bonded crystallisation water molecules that encapsulates an infinite stacking chains result of the intercalation of phenanthroline ligands of complex ions.

A pyrimidine thiolate Rh(i) complex: structure, bonding and one-dimensional interactions in solid and in solution

The reaction of [Rh(micro-Cl)(COD)]2 with 4,6-dimethyl-pyrimidinethiolate (Me2-pymt) and subsequent substitution of COD by CO yields [Rh(Me2-pymt)(CO)2]. The stacking pattern found in this compound is in contradiction with previously studied comparable square-planar complexes of type d8-[M(chelate)(monodentate)2] in which each ligand has different pi-acidic character. A theoretical study of the intermolecular interactions and conformation of the title compound has been carried out, combining semi-empirical band calculations on the real chains and ab initio(MP2 level) calculations on a model dimer. The combination of electronic and steric effects determines the rotation of the successive monomers and the deviation from linearity of the one-dimensional stacks. Its behaviour in solution is also special, developing a blue colour and forming micelles, when adding water to acetone solutions.

Magnetic characterization of the frustrated three-leg ladder compound[(CuCl2tachH)3Cl]Cl2

We report the magnetic features of a new one-dimensional stack of antiferromagnetically coupled equilateral copper(II) triangles. High-field magnetization measurements show that the interaction between the copper triangles is of the same order of magnitude as the intra-triangle exchange although only coupled via hydrogen bonds. The infinite chain turns out to be an interesting example of a frustrated cylindrical three-leg ladder with competing intra- and inter-triangle interactions. We demonstrate that the ground state is a spin singlet which is gaped from the triplet excitation.

Formation of solid-state excitons in ultrathin crystalline films of PTCDA: from single molecules to molecular stacks.

We directly follow the evolution of the absorption spectrum from a single molecule to a dimer and further to a one-dimensional molecular stack: We determine the optical absorption properties of ordered monolayer to multilayer films of PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) on muscovite mica(0001) surfaces by in situ differential reflectance spectroscopy. The data clearly show the transition from the single molecule to a dimer spectrum, followed by the exciton delocalization to a molecular crystal exciton. The accompanying spectral shifts compare favorably with recent model concepts.

Optical modulation in photonic band gap structures by surface acoustic waves

We investigate theoretically the modulation of light beams in photonic band gap (PBG) structures by surface acoustic waves (SAWs). In these structures, the propagation of light beams can be actively controlled through an external acoustic stimulus. We have extended the mathematically rigorous transfer matrix method to calculate the light flow in PBG structures subjected to the spatial- and time-dependent dielectric function modulation induced by the SAW. The calculational procedure, which applies for SAWs with a frequency much smaller than that of the light, is employed to determine the transmission spectra of a one-dimensional Bragg stack with a cavity and that of a two-dimensional GaAs PBG structure with periodic air holes. We demonstrate that these two structures can be configured as an on∕off optical switch with very high contrast ratios and, in the two-dimensional case as an efficient wavelength-tunable optical filter.

Omnidirectional reflection from a slab of uniaxially anisotropic negative refractive index materials

In this paper, we explore the reflection properties of multilayer containing a slab of uniaxially anisotropic materials with negative refractive index. The conditions are discussed under which the omnidirectional reflection can occurs in a certain frequency region. In addition, we also investigate the photonic band gaps (PBGs) of the one-dimensional layered stack that consists of uniaxially anisotropic slabs. It is found that the PBGs is invariant upon a change of scale length and is insensitive to disorder of the layer thickness.

Di-μ-2-aminopyridinato-bis[(2,2′-bipyridine)platinum(II)] dinitrate tetrahydrate as a head-to-tail isomer

In the title compound, [Pt2(C10H8N2)2(C5H5N2)2](NO3)2·4H2O, two 2-amino­pyridinate ligands bridge two Pt atoms in a head-to-tail fashion, the Pt—Pt distance being 2.8724 (6) A. The dimers form a one-dimensional stack based on π–π stacking interactions between the bpy (2,2′-bi­pyridine) units, where the interplanar separations are estimated as 3.44 (2) and 3.45 (1) A. No metal–metal interaction exists between the dimers.

Energy Spectra of One-Dimensional Stacks of Polycyclic Aromatic Hydrocarbons without Defects

The energy spectra of one-dimensional (1-D) stacks consisting of large π−π interacting polycyclic aromatic hydrocarbons (PAH) have been investigated theoretically with the Bloch band theory, taking...

Dipole interactions and electrical polarity in nanosystems: the Clausius-Mossotti and related models.

Point polarizable molecules at fixed spatial positions have solvable electrostatic properties in classical approximation, the most familiar being the Clausius-Mossotti (CM) formula. This paper generalizes the model and imagines various applications to nanosystems. The behavior is worked out for a sequence of octahedral fragments of simple cubic crystals, and the crossover to the bulk CM law is found. Some relations to fixed moment systems are discussed and exploited. The one-dimensional dipole stack is introduced as an important model system. The energy of interaction of parallel stacks is worked out, and clarifies the diverse behavior found in different crystal structures. It also suggests patterns of self-organization which polar molecules in solution might adopt. A sum rule on the stack interaction is found and tested. Stability of polarized states under thermal fluctuations is discussed, using the one-dimensional domain wall as an example. Possible structures for polar hard ellipsoids are considered. An idea is formulated for enhancing polarity of nanosystems by intentionally adding metallic coatings.

Ab initio study on geometrical structures of the TTTA molecular crystal

The crystal made of organic radical, 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA), exhibits a large first-order magnetic and structural phase transition between a paramagnetic high-temperature (HT) phase and a diamagnetic low-temperature (LT) phase, with a surprisingly wide thermal hysteresis loop over room temperature. We investigate theoretically the crystal structures for the two phases by means of the ab initio structural optimization method based on the local density approximation. We present necessary and sufficient atomic coordinates in this paper. The resulting structures are in good agreement with the recent X-ray diffraction experiment. In the HT phase, uniform one-dimensional stacking of the radical molecule appears, while, in the LT phase, strong dimerization along the stacking direction appears.

Bis(2-aminopyridine)(2,2′-bipyridine)platinum(II) tetracyanoplatinate(II) dihydrate

In the title compound, [Pt(C10H8N2)(C5H6N2)2][Pt(CN)4]·2H2O, cations and anions alternate along the a axis, giving a one-dimensional chain of the Magnus green salt type. The electrostatic interactions between the divalent cations and anions, together with the π–π stacking associations between the 2,2′-bi­pyridine moieties, contribute to the stabilization of the crystal packing. Two different Pt⋯Pt distances [5.2034 (6) and 4.5599 (6) A] alternate along the one-dimensional stack.

Bit-serial architecture for rank order and stack filters

An algorithm for one-dimensional stack filter is presented in this paper, along with its hardware structure. The proposed digital realization is simple and modular. Unlike other hardware realizations which are based on Positive Boolean Function, this new realization is based on a compare and swap circuit. Compared with other reported one-dimensional structures for stack filters, and based on VLSI implementation, the new structure has a better performance in terms of area and time delay. The new one-dimensional structure proposed in this paper has been extended to a separable two-dimensional stack filter.