Long-range Periodic Structure Research Articles

Atomic and mesoscopic structure of Dy-based surface alloys on noble metals

Surface alloys are a highly flexible class of low dimensional materials with the opportunity to tune and control the spin and charge carrier functionalities on the nanoscale. Here, we focus on the atomic and mesoscopic structural details of three distinct binary rare-earth-noble metals (NM) surface alloys by employing scanning tunneling microscopy and low energy electron diffraction. Using Dysprosium as the guest element on fcc(111) NM substrates, we identify the formation of non-commensurate surface alloy superstructures, which lead to homogeneous moiré patterns for DyCu2/Cu(111) and DyAu2/Au(111), while an inhomogeneous one is found for DyAg2/Ag(111). The local structure was analyzed for these samples and the observed differences are discussed in the light of the lattice mismatches of the alloy layer with respect to the underlying substrate. For the particularly intriguing case of a DyAg2 surface alloy, the surface alloy layer does not show a uniform long-range periodic structure, but consists of local hexagonal tiles separated by extended domain walls, which occur likely to relieve the in-plane strain within the DyAg2 surface alloy layer. Our findings clearly demonstrate that surface alloying is an intriguing tool to tailor the local atomic structure as well as the mesoscopic moiré structures of metallic heterostructures.

Radiation damage and thermal annealing in tunnel structured hollandite materials

Three tunnel structured hollandite samples (Cs1.33Ga1.33Ti6.67O16, Cs1.33Fe1.33Ti6.67O16, and Cs1.33Zn0.67Ti7.33O16) with demonstrated thermodynamic stability and chemical durability were synthesized and irradiated by a 1.1 GeV Au ion beam in order to study effects of B-site dopants on radiation stability. A crystalline-to-amorphous transformation induced by the high-energy ion irradiation was confirmed by complementary characterization techniques sensitive to different length-scales, such as powder X-ray diffraction, Raman spectroscopy and neutron total scattering. High-temperature oxide melt solution calorimetry was performed to determine the energy landscape before and after ion irradiation. Together, structural and thermodynamic analyses demonstrated distinctly different radiation responses of the hollandite with different B-site dopants; the Ga-substituted hollandite exhibited the smallest enthalpy of damage indicating the best radiation stability among the three samples. The hypothesized origin of the different radiation responses is the structural feature in the binary oxide form of the respective B-site dopants (e.g., Ga2O3versus Fe2O3/ZnO for Ga and Fe/Zn dopants, respectively). Moreover, thermal analysis (i.e., differential scanning calorimetry) was conducted to investigate structural changes from the irradiation induced damaged states after thermal annealing. Results of thermal analysis revealed that the annealing-induced structural evolution of the radiation damaged hollandite structure is complex and decoupled at different length-scales. The long-range periodic structure (nanometers) was not recovered after thermal annealing and structural changes over a shorter range (≤ ∼3 Å) occurred in multiple steps during the annealing process.

Selecting ‘convenient observers’ to probe the atomic structure of CVD graphene on Ir(111) via photoelectron diffraction

CVD graphene grown on metallic substrates presents, in several cases, a long-range periodic structure due to a lattice mismatch between the graphene and the substrate. For instance, graphene grown on Ir(111), displays a corrugated supercell with distinct adsorption sites due to a variation of its local electronic structure. This type of surface reconstruction represents a challenging problem for a detailed atomic surface structure determination for experimental and theoretical techniques. In this work, we revisited the surface structure determination of graphene on Ir(111) by using the unique advantage of surface and chemical selectivity of synchrotron-based photoelectron diffraction. We take advantage of the Ir 4f photoemission surface state and use its diffraction signal as a probe to investigate the atomic arrangement of the graphene topping layer. We determine the average height and the overall corrugation of the graphene layer, which are respectively equal to 3.40 ± 0.11 Å and 0.45 ± 0.03 Å. Furthermore, we explore the graphene topography in the vicinity of its high-symmetry adsorption sites and show that the experimental data can be described by three reduced systems simplifying the moiré supercell multiple scattering analysis.

Radiation Damage and Thermal Annealing in Tunnel Structured Hollandite Materials

Three tunnel structured hollandite samples (Cs 1.33 Ga 1.33 Ti 6.67 O 16 , Cs 1.33 Fe 1.33 Ti 6.67 O 16 , and Cs 1.33 Zn 0.67 Ti 7.33 O 16 ) with demonstrated thermodynamic stability and chemical durability were synthesized and irradiated by a 1 GeV Au ion beam in order to study effects of B-site dopants on radiation stability. The structural changes induced by radiation were analyzed by complementary characterization techniques at different length-scales, such as powder X-ray diffraction, Raman spectroscopy and neutron total scattering. High-temperature oxide melt solution calorimetry was performed to determine the energy landscape before and after radiation. Together, structural and thermodynamic analyses demonstrated distinctly different radiation responses of the hollandite with different B-site dopants. The hypothesized origin of these differences is the structural feature in the binary oxide form of the respective B-site dopants (e.g., Ga 2 O 3 versus ZnO for Ga and Zn dopants, respectively). Moreover, thermal analysis (i.e., differential scanning calorimetry) was conducted to investigate structural changes from the radiation induced damaged states after thermal annealing. Results of thermal analysis revealed that the annealing-induced structural evolution of the radiation damaged hollandite structure is complex and decoupled at different length-scales. The long-range periodic structure (nanometers) was not recovered after thermal annealing and structural changes over a shorter range (≤ ~3 A) occurred in multiple steps during the annealing process.

Chiral doping effect in the B2 phase of a bent-core liquid crystal: The observation of resonant X-ray satellite peaks assigned to the 5/10 layer periodic structure

We studied the details of a local layer structure in the B2 phase of bromo-containing bent-core liquid crystals mixed with a small amount of chiral molecules using microbeam resonant X-ray scattering. In this measurement, we detected the 1 ± 0.2 order satellite peaks, which suggest that the B2 phase of the mixture has a long-range periodic structure. Dielectric and electro-optic measurements indicate almost the same behavior as the antiferroelectric SmCAPA(B2) of pure bromo-containing bent-core liquid crystals, so that the B2 phase of the chiral mixture is also antiferroelectric, and it is concluded that the B2 phase of the chiral mixture forms a ten-layer periodic structure. Such a long-range periodic structure did not appear by mixing the racemate of the same compounds, which indicates the chiral effect on the long-range periodic structure.

Manipulation and Formation Mechanism of Silica One-Dimensional Periodic Structures by Roller Electrospinning

A roller electrospinning technique is combined with sol-gel chemistry to fabricate silica and polymeric materials on conductive and nonconductive substrates to verify its ability for controlling the long-range periodic structure of the final product. According to the experimental results, formation of the one-dimensional periodic silica structure was dependent on the electrical conductivity of the collector substrate. The periodic density seems to be related to the width of silica product. No effect from the electrical conductivity of collector substrate on the structure of polymeric system was observed. An energy transformation model was proposed to investigate the formation mechanism of this periodic structure. The theoretical simulation indicates that large width-to-thickness ratio of the product and high-energy transformation efficiency favor the formation of the long-range periodic structure.

Polymerized Ionic Liquid Block and Random Copolymers: Effect of Weak Microphase Separation on Ion Transport

A series of polymerized ionic liquid (PIL) block and random copolymers were synthesized from an ionic liquid monomer, 1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium bis(trifluoromethanesulfonyl)imide (MEBIm-TFSI), and a nonionic monomer, methyl methacrylate (MMA), at various PIL compositions with the goal of understanding the influence of morphology on ion transport. For the diblock copolymers, the partial affinity between the PIL and PMMA blocks resulted in a weakly microphase-separated morphology with no evident long-range periodic structure across the PIL composition range studied, while the random copolymers revealed no microphase separation. These morphologies were identified with a combination of techniques, including differential scanning calorimetry, small-angle X-ray scattering, and transmission electron microscopy. Surprisingly, at similar PIL compositions, the ionic conductivity of the block copolymers were ca. 2 orders of magnitude higher than the random copolymers despite the weak microphase...

2D-Ising-like critical behavior in mixtures of water and 3-methylpyridine including antagonistic salt or ionic surfactant

The effect of an antagonistic salt on the phase behavior and nanoscale structure of a mixture of D2O and 3-methylpyridine was investigated by visual inspection and small-angle neutron scattering (SANS). The addition of the antagonistic salt, namely sodium tetraphenylborate (NaBPh4), induces the shrinking of the two-phase region in contrast to the case in which a normal (hydrophilic) salt is added. Below the phase separation point, the SANS profiles cannot be described by the Ornstein–Zernike function owing to the existence of a long-range periodic structure. With increasing salt concentration, the critical exponents change from the values of 3D-Ising and approach those of 2D-Ising. These results suggest that the concentration fluctuation of the mixture of solvents is limited to a quasi two-dimensional space by the periodic structure induced by the adding the salt. The same behaviors were also observed in mixtures composed of water, 3-methylpyridine, and ionic surfactant.

Nanopyramid surface plasmon resonance sensors

We report the achievement of sensitive chemical and biological sensing using periodic gold nanopyramids with nanoscale sharp tips created by a simple and scalable colloidal templating approach. The sharp tips and the long-range periodic structure of the nanopyramid arrays enable the excitement of both localized and propagating surface plasmons. The optical reflection and the detection sensitivity of the templated nanopyramid surface plasmon resonance sensors agree reasonably well with the theoretical predictions using a finite-difference time-domain model. We have also demonstrated that specific antigen-antibody binding can be detected by using nanopyramid arrays in a real-time and label-free manner.

Surface plasmon on aluminum concentric rings arranged in a long-range periodic structure

The enhanced optical transmission through the annular aluminum metal with different number of concentric rings arranged in a long-range periodic structure on the silicon substrate is investigated. The measured transmission spectra demonstrate that the surface plasmon modes depend sensitively on the structural parameters of the metallic rings. The degenerate (1,0), (1,1), and (2,1) Al∕Si surface plasmon modes are determined by the long periodicity of the structure. The localized modes in cavities with different length can be observed in this structure as well. These phenomena suggest that both surface plasmons and localized cavity modes are excited within super unit cell.

Ｘ線分光の現在 ＩＶ．Ｘ線吸収微細構造分光法

XAFS (X-ray Absorption Fine Structure) is a powerful technique, which provides element-specific information on atomic and electronic structures even for samples without long-range periodic structure. Owing to the recent developments of synchrotron radiation facilities, it has become possible also for non-expert researchers to obtain such information using XAFS. In this lecture, the basic concept and analytic procedures are presented including the utilization of X-ray polarization and time-resolved measurements.

Observation of Fabry-Pérot-type surface plasmon on Ag film with perforated short-range 3×3 hole array arranged in long-range periodic structure

This letter elucidates enhanced optical transmission through a Ag film with perforated short-range 3×3 hole arrays arranged in a long-range periodic structure. The 3×3 squared hole array constitutes an individual microcell. The measured transmission peak wavelength reveals that the surface plasmons are generated by Fabry-Pérot-type waveguide resonances with integer order. The ratio of periodicity between the superperiodic structure p and the 3×3 microcell d determines the integer order. Namely, when p∕d>3, the order 3, 4, and 5 surface plasmon modes with average hole spacings p∕3, p∕4, and p∕5 are observed. The transmission intensities of order 3 modes are the strongest, and those of order 5 modes are barely seen. But as p∕d approaches 4, the order 3 modes gradually disappear with the emergence of order 4 and 5 modes. These phenomena suggest that the surface plasmons are Fabry-Pérot-type resonance within a super unit cell.

USANS investigations of solutions of diblock copolymers in partially miscible solvents

We report the results of ultra-small-angle neutron scattering (USANS) experiments from diblock copolymers A–B dissolved in a mixture of partially compatible solvents a and b. Solvent a is dimethylformamide, which is a good solvent for block A (polystyrene) and a bad solvent for block B poly(ethylene- co-propylene), and vice versa for solvent b, namely, cyclohexan. Such samples are microphase-segragated into a-rich and b-rich domains separated by interfaces covered with diblock copolymer. Our USANS measurements have shown that a long-range periodic structure of these segregations is limited in extend, it consists of grains with mean radius of several microns. Structural characteristics of these grains and kinetics of their formation depending on the temperature were studied by means of USANS for various chemical compositions of the samples.

Long-range periodic structure induced by coupling of the solvation effect and concentration fluctuation in water and 3-methylpyridine with salts

Small-angle neutron scattering (SANS) experiments were performed on mixtures of 3-methylpyridine, D 2O, and salts to investigate concentration fluctuations and structures in the vicinity of the critical point. The temperature-dependence of the SANS profile of a mixture without salt showed critical phenomena that were consistent with 3D-Ising behavior. On the other hand, the SANS profiles with salt added mixtures could not be explained solely in terms of critical scattering, because they include both the concentration fluctuation and a periodic structure. The periodic structure could be induced by the coupling of solvation and a critical concentration fluctuation.

High-Strengthening of Mg–5.5 mass%Y–4.3 mass%Zn Cast Alloy by Friction Stir Processing

High-strength Mg–Y–Zn alloy plate was obtained by friction stir processing (FSP) after casting. In this study, the Mg–Y–Zn alloy by FSP showed sufficiently high performance with low cost. As-cast material was held at 723 K for 95 h. It then showed a lamellar structure, which might have resulted from long-range periodic structure. However, this lamellar structure showed very low hardness, as did the as-cast material. Plates cut from heat-treated ingot were processed as single, overlapped double, and multiple pass FSP. After FSP, each processed materials was cut for microscopic measurement and hardness testing. Ultra-fine-grained microstructures are obtainable using the FSP. Micro-Vickers hardness tests for each pass result in the occurrence of strengthening for FSP of Mg–Y–Zn alloy. There was little change in grain size and hardness of prestirred zone by the next pass of stirring.

Phase diagram for ortho-para-hydrogen monolayers

The phase diagram for orientational ordering of hydrogenmonolayers on graphite and boron nitride is revised in view ofcurrent theory and experimental observations from nuclearmagnetic resonance (NMR) studiesrecently reported for ortho-H2 concentrations0.35 ⩽ c ⩽ 0.92 and temperatures 0.14 ⩽ T ⩽ 1.80 K. The characteristic interaction coupling Γ0 = 0.50 ± 0.03 K and the crystalline field amplitudeV0 = 0.70 ± 0.10 K are derived from experimental data, anddistinct types of the local orientationally ordered structuresare analysed using a proposed model for site-diluted uniaxialquadrupoles on a triangular plane lattice of hexagonal symmetry.The long-range periodic pinwheel structure and theshort-range quadrupolar glass (QG) phase are stable above the 2Dsite-percolation limit, cp = 0.72, and for 0.48 < c < cp,respectively, where quadrupolar-order effects dominate. At verylow T, the QG phase shows instability with respect tolocal dipole-like polarization effects and the ground statechanges to a hindered rotor state. Two para-rotationallocal ordered PRA and PRB structures driven, respectively, bypositive and negative crystalline fields are well distinguished,experimentally and theoretically, and are rather different from theunique PR phase suggested earlier by Harris and Berlinsky.

Scanning Tunneling Microscopy Studies of Metal on Metal Epitaxy.

Prior to the advent of the scanning tunneling microscope (STM), most experimental studies measured average properties such as overall chemical composition and long-range periodic structure using techniques such as electron- and photon-based spectroscopies and diffraction. This article reviews selected contributions that STM has made in the understanding of metal-on-metal epitaxy. This is presented not from a historical perspective but rather by highlighting key scientific issues that STM has and will continue to impact. The paper is divided into three topic areas: nucleation, structure, and composition. This is done only for organizational purposes and not to imply that they can be viewed distinctly. There exist fundamental interactions between all of these phenomena that lead to the rich behavior in metal films highlighted throughout the article. One of the great contributions of STM has been precisely to discover these links. 106 refs.

Crystal structure and effects of Fe doping of a non-superconducting phase (B-phase) in the Bi-Sr-Cu-O system

Crystal structure and effects of Fe doping of a non-superconducting phase (B-phase) in the Bi-Sr-Cu-O system are examined by electron-diffraction and high-resolution transmission electron microscope measurements. The B phase has a long-range periodic structure closely related to the modulated structure of the superconducting phase and it crystallizes in a monoclinic superlattice with a s =0.54, b s =2.0, c s =2.5 nm and α=104°. The (BiO) 2 double layer is not a complete continuous sheet but suffers from a periodic displacement along the c-direction to form a terraced (BiO) 2 layer. Each BiO terrace consists of seven Bi atoms, and at every eighth lattice plane a vertical shear plane containing few Bi atoms is inserted. Fe doping has an effect on the periodicity of the terraced structure. Intergrowth of narrow (BiO) 2 terraces is induced in crystals doped with Fe.

The structure of moving grain boundaries in aluminium as revealed by synchrotron X-ray topography

Abstract The structure of moving grain boundaries during recrystallization of refined (99·99%) and zone-refined (99·999%) aluminium has been studied. both in situ and in bulk samples, by synchrotron X-ray topography. It has been observed that moving grain boundaries can have a long-range periodic structure depending on the orientation of the moving grain boundary plane relative to that of crystallographic planes of the growing crystals. These results are discussed on the basis of equilibrium grain boundary structure and on crystal growth kinetics from vapour or liquid phases.