Kink Structure Research Articles

Structure and Interfacial Properties of Germanium Nanowires Grown on Titanium

Single-crystal germanium nanowires have been grown directly on amorphous titanium films using the vapor-liquid-solid method and studied using transmission electron microscopy. Forty nanometer wires are observed to grow only in the 〈111〉 and ( 112) directions and have a sharp (∼1 nm) metal-semiconductor interface to both the catalyst (Au) and the titanium substrate. They exhibit a defective base region comparable in size to the catalyst diameter terminated by a kink structure after which they are single crystalline. The physical characteristics of these nanowires are examined. A simple lithographic method to produce grids for rapid characterization is introduced.

Pressure-Induced Phase Transition in Zn–Fe Prussian Blue Lattice

Recently, Mastuda et al. reported negative thermal expansion in a series of Prussian blue type cyanides, (Cs,Rb)xM[Fe(CN)6]yzH2O (M is a transition metal). The compound belongs to a face-centered cubic (Fm 3m; Z 1⁄4 4), in which M and the [Fe(CN)6] unit form a rock-salt lattice bridged by the cyano groups. The alkaline metals and water molecules are accommodated in the nanopores of the lattice. The coefficient ( d ln a=dT) of the thermal expansion systematically decreases with an increase in the lattice constant a: 1⁄4 þ1:49 10 K 1 for Rb0:49Zn[Fe(CN)6]0:803.8H2O (a 1⁄4 9:943 A) and 1⁄4 0:59 10 K 1 for Rb0:64Zn[Fe(CN)6]0:882.3H2O (a 1⁄4 10:392 A). The negative thermal expansion as well as the systematic change of were ascribed to the thermally-induced rotational displacement of the [Fe(CN)6] units. Such a rotational instability of the [Fe(CN)6] units may cause a significant structural response to external stimuli, e.g., hydrostatic pressure, magnetic field, electric field, and photo-irradiation. In this Note, we report pressure effects on the Prussian blue lattice with the negative thermal expansion, Rb0:85Zn[Fe(CN)6]0:951.5H2O (abbreviated as RZF) and Cs0:64Zn[Fe(CN)6]0:883.5H2O (CZF). We observed prominent kink structures in the Raman shifts of the CN stretching modes and a at Pc 1⁄4 1:0GPa for RCF and at Pc 1⁄4 1:4GPa for CZF. These observations suggest a pressure-induced phase transition driven by the rotational instability of the [Fe(CN)6] units. Powder samples of RZF and CZF were prepared by reacting an aqueous solution of ZnCl2, RbCl, CsCl, and K3[Fe(CN)6]. Chemical compositions of the prepared samples were determined by inductively coupled plasma (ICP) and standard microanalytical methods. The high-pressure Raman spectroscopy was performed at 300K using a diamond anvil cell (DAC) and a microscopic Raman system. The sample powders were sealed in a gasket hole of the DAC, 100 mm in thickness and 300 mm in diameter. The pressure-transmitting medium was Daphne 7373 oil (made by Idemitsu), and applied pressure P was determined by the R1 luminescence line 6) of a small peace of a ruby. The excitation energy was 2.54 eV and excitation area was 30 mm in diameter. Scattering light was detected with a single monochromator equipped with a charge-coupled device (CCD). The high-pressure synchrotron-radiation x-ray powder diffraction measurements were performed at the BL10XU beamline of SPring-8. The powder samples were sealed in a gasket hole of a specially-designed DAC, 100 mm in thickness and 300 mm in diameter. The wavelength of the incident x-ray was 0.41131 A. The 2 range used in the Rietveld refinement was 2–30 degree. Figure 1 shows Raman scattering spectra of (a) RZF and (b) CZF at 300K against P. The higher-lying and lowerlying CN stretching bands are ascribed to A1g and Eg modes of the [Fe(CN)6] units with Oh symmetry. 4) In (a) RZF, both the A1g and Eg modes show a significant blue shift with an increase in P in the low-P region. The Raman frequencies, however, becomes nearly constant in the high-P region. A similar behavior is also observed in (b) CZF. In Fig. 2(a), we plotted the Raman shifts of the CN stretching modes of RZF against P. Solid and broken straight lines are the least-square-fitted results in the low-P and high-P regions, respectively. The Raman frequency linearly increases with an increase in P in the low-P region (P Pc 1⁄4 1:0GPa; upward arrows), but becomes nearly constant in the high-P region (P Pc). A kink structure is observed in (c) CZF at Pc 1⁄4 1:4GPa, even though the data points in the high-P region are rather scattered. We further investigated the x-ray powder diffraction patterns of RZF and CZF against P. With increase of P, the diffraction peaks shift to the high-2 side and their line widths become broader. All the diffraction peaks can be indexed in the cubic setting (Fm 3m) in both below and above Pc. We observed neither peak splitting nor extra peak above Pc. The magnitude of a was refined by the Rietveld method, and plotted in Figs. 2(b) and 2(d). In (b) RZF, a kink structure is observed around Pc 1⁄4 1:0GPa, as indicated 215

Superconducting electronic state in optimally dopedYBa2Cu3O7−δobserved with laser-excited angle-resolved photoemission spectroscopy

Low-energy electronic structure of optimally doped ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ is investigated using laser-excited angle-resolved photoemission spectroscopy. The surface state and the CuO chain band that usually overlap the ${\text{CuO}}_{2}$ plane derived bands are not detected, thus enabling a clear observation of the bulk superconducting state. The observed bilayer splitting of the Fermi surface is $\ensuremath{\sim}0.08\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$ along $(0,0)\ensuremath{-}(\ensuremath{\pi},\ensuremath{\pi})$ direction, significantly larger than ${\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}$. The kink structure of the band dispersion reflecting the renormalization effect at $\ensuremath{\sim}60\text{ }\text{meV}$ shows up similarly as in other hole-doped cuprates. The momentum dependence of the superconducting gap shows ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave-like amplitude but exhibits a nonzero minimum of $\ensuremath{\sim}12\text{ }\text{meV}$ along the $(0,0)\ensuremath{-}(\ensuremath{\pi},\ensuremath{\pi})$ direction. Possible origins of such an unexpected ``nodeless'' gap behavior are discussed.

Small amplitude electron-acoustic double layers and solitons in fully relativistic plasmas of two-temperature electrons

A Korteweg–de Vries (KdV) equation for fully relativistic one dimensional plasmas of arbitrarily large streaming speed and temperature is derived by using the reductive perturbation method. For plasmas with more than two species of particles, the coefficient representing quadratic nonlinearity in KdV can vanish at critical values of certain parameters. To describe the nonlinear evolution at this critical parameter, a modified KdV (mKdV) equation that contains a cubic nonlinear term is obtained. Furthermore, a mixed mKdV equation pertaining to parameters in the vicinity of the critical values is also derived, in which the quadratic and cubic nonlinearities are both present. As an illustration of the results, the mixed mKdV equation is applied to a plasma comprised of cold ions and electrons having cold (T=0) and finite temperature components. For warm temperature T⪡mec2, it is found that electron-acoustic nonlinear waves in the shape of double layer (kink) and solitary waves can exist, which have phase speed 3T/(4+α)me in the rest frame of plasma, where α is the polytropic index of the equation of state of the warm electrons. The thickness of the transitional layer of the kink structure is of the order of Debye length λD. For extremely high temperature T⪢mec2, it is also found that double layer and soliton-type solutions can exist with phase speed α−1c, which is equal to the well known relativistic sound speed c/3 for α=4/3. The thickness of the transition layer scales as δ∼T−1/4, which is different from the T⪡mec2 case.

Finding mechanism of transitions in complex systems: formation and migration ofdislocation kinks in a silicon crystal

We demonstrate how a saddle point search method can be used to study dislocationmobility in a covalent material—a non-trivial transition mechanism in a complex system.Repeated saddle point searches have been carried out by using the minimum modefollowing algorithm and dimer method in combination with several empirical potentialfunctions for silicon in order to determine the mechanisms for the creation andmigration of kinks on a non-dissociated screw dislocation in a silicon crystal. For theenvironment-dependent interatomic potential, three possible kink migration processes havebeen identified with activation energies of 0.17, 0.25, and 0.33 eV. The Lenosky potentialgives a single, low energy migration mechanism with an activation energy of 0.07 eV,in good agreement with density functional theory results. The kink formationmechanism determined using this potential has an activation barrier of 1.2 eV.Calculations were also carried out with the Tersoff potential, Stillinger–Weberpotential and Bolding–Andersen potential. The various potential functions givequite different results for the kink structure and the mechanism of transition.

Electronic structure and doping effect of kink in edge dislocation of body-centred cubic iron

The self-consistent discrete variational method and the DMol method， based on the density functional theory， are employed to study the electronic structure and the doping effect （N，O） of the kink in the 1/2［111］（110） edge dislocation of body-centred cubic Fe. Our calculations of energies （impurity segregation energy and structural energy） show that N and O each have a strong segregation tendency to enter a kink region， which is related to the lattice distortion introduced by the kink. Furthermore， we find that there exist some charge accumulations between impurity and its neighbouring Fe atoms， resulting in unhomogeneous charge distribution in the kink. N and O atoms obtain electrons while the neighbouring Fe atoms lose electrons. It is found that the interactions between impurity N atom and neighbouring Fe atoms are strengthened due to the strong hybridizations between N-p and Fe-3d4s4p states. The migrations of kink and dislocation motion are impeded by N， which may be beneficial to an increase in strength of material. While the interaction between O and its neighbouring Fe atoms is weaker. The localized effect of impurity-kink complex distinctly affects the electronic structure and properties of the system.

High-Resolution Angle-Resolved Photoemission Study of the Al(100) Single Crystal

The free-electron-like surface-derived electronic state in Al(100) has been examined in detail by high-resolution angle-resolved photoemission spectroscopy (ARPES). We observed a kink structure in the energy band-dispersion at the energy of ∼ -40 meV, which is derived from the electron-phonon interaction. Based on the quantitative analyses of the ARPES line shapes, we have obtained the imaginary and real parts of the self-energy. The electron-phonon coupling parameter has been evaluated to be λel-ph = 0.67, which is much larger than the electron-electron coupling parameter λel-el = 0.06. [DOI: 10.1380/ejssnt.2009.57]

On the structural and magnetoelectrical characterization of epitaxial SrRuO 3 thin films grown on (001) SrTiO 3 substrates

High-quality epitaxial thin films of the ferromagnetic metallic oxide SrRuO 3 (SRO) were fabricated by dc-sputtering at high oxygen pressure and their structural and magnetoelectrical properties were carefully studied. The films featured a Curie temperature T C ∼ 160 K and a magnetic moment of ∼0.7 μ B per Ru ion. The temperature dependent magnetization could be well described by the scaling relation M( T) ∝ ( T C − T) β with a critical exponent β = 0.53 over the entire ferromagnetic temperature range. A negative magnetoresistance, MR, on the order of a few percent was found up to room temperature. MR showed a maximum of ∼4% right at T C where a kink structure of the resistivity, ρ, at zero field was flattened out on magnetic field application. This ρ contribution could be related to scattering due to orientational disorder of the Ru magnetic moments which become aligned by an external magnetic field. In addition, an equally strong MR effect, related to localization phenomena, could be observed at lower temperature. Particularly, the second MR peak at ∼35 K might be related to a Fermi-liquid to non-Fermi-liquid crossover. A scaling behavior d ρ/d T ∝ | T − T C| α was observed only above T C. Here, values for the exponent α ≈ −0.4 and α ≈ −1.4 were obtained in zero field and in a field of 9 T, respectively. The commonly observed ρ minimum, appearing at low temperatures (∼3 K in the present case), is correlated with the structural disorder of the SRO films and is believed to have its origin in quantum corrections to the conductivity (QCC).

The effect of hydrogen on the electronic structure of kink in bcc iron

The electronic structures of kinks in the [100](010) and 1/2[111](−110) edge dislocations in bcc iron containing hydrogen are investigated by means of the first-principles DMol method and the discrete variational method. The effects of hydrogen on the kinks are discussed. The results show that hydrogen forms weak bonding states with its neighboring host atoms, and since hydrogen draws charge from its neighboring host atoms, the interactions between most of the host atoms are weakened compared with those of the corresponding atomic pairs in the clean kinks. This indicates that the migration of kink, i.e. the motion of dislocation, is easier in the doping hydrogen kink than in the clean kink, which may be the solid solution softening effect resulting from the impurity hydrogen.

Electron–boson coupling and oxygen-isotope effect in the optical conductivity of high- Tc superconductors

We have investigated electron–boson coupling in the optical conductivity of high- T c superconductors through the optical self-energy. The real part of the self-energy (Re Σ op( ω)) of YBa 2Cu 3O y (YBCO) shows a characteristic doping dependence. In the optimally doped YBCO, Re Σ op( ω) has a single peak around 65 meV, which corresponds to the kink structure of the band dispersion. On the other hand, in the under-doped YBCO, the peak structure of Re Σ op( ω) splits into two parts. To evaluate contribution from the phonons in electron–boson coupling, we have measured oxygen-isotope effects by substituting 16O→ 18O for the optimally doped and under-doped YBCO.

First-principles investigation of the impurity-kink interaction in bcc iron

Using the first-principles self-consistent discrete variational method based on density functional theory, we investigated the effect of light impurities C and N on the electronic structure of kink on the [100](010) edge dislocation (ED) in bcc iron. Our energetic calculations show that the light impurities have a strong segregation tendency to enter the kink. The results of the charge distribution and the local density of states indicate that the strong bonds between the impurity atoms and the neighboring Fe atoms are formed due to the hybridizations of impurity atoms 2p states and Fe 3d4s4p states. The introduction of light impurities can stabilize the kink system, and impedes the sideward motion of the kink in the [100](010) ED. This is, the light impurities induce a strong pinning effect on the [100](010) ED and may result in the solid solute hardening.

Superconducting State of Silver-Oxide Clathrate Ag6O8AgNO3

We report the normal-state and superconducting properties of the silver-oxide clathrate Ag 6 O 8 AgNO 3 . Electrical resistivity, specific heat, and DC and AC susceptibility measurements as functions of magnetic field and temperature show phase transitions near 90 and 185 K. We find that Ag 6 O 8 AgNO 3 is a bulk superconductor with the superconducting transition temperature T c =1.04 K. We observe a clear kink structure in the field dependence of the real part of AC susceptibility, suggesting a change in vortex state. Furthermore, we present the H – T phase diagram of this compound and estimate the upper critical field H c2 (0) to be about 770 Oe. We also discuss the superconducting properties in a Ginzburg–Landau framework.

Theoretical study of kinks on screw dislocation in silicon

Theoretical calculations of the structure, formation, and migration of kinks on a nondissociated screw dislocation in silicon have been carried out using density functional theory calculations as well as calculations based on interatomic potential functions. The results show that the structure of a single kink is characterized by a narrow core and highly stretched bonds between some of the atoms. The formation energy of a single kink ranges from $0.9\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1.36\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, and is of the same order as that for kinks on partial dislocations. However, the kinks migrate almost freely along the line of an undissociated dislocation unlike what is found for partial dislocations. The effect of stress has also been investigated in order to compare with previous silicon deformation experiments which have been carried out at low temperature and high stress. The energy barrier associated with the formation of a stable kink pair becomes as low as $0.65\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for an applied stress on the order of $1\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, indicating that displacements of screw dislocations likely occur via thermally activated formation of kink pairs at room temperature.

Measuring superparticle masses at hadron collider using the transverse mass kink

We present a detailed study of the collider observable mT2 applied for pair-produced superparticles decaying to visible particles and a pair of invisible lightest supersymmetric particles (LSPs). Analytic expressions of the maximum of mT2 over all events (mT2max) are derived. It is noticed that if the decay product of each superparticle involves more than one visible particle, mT2max being a function of the trial LSP mass mχ has a kink structure at mχ = true LSP mass, which can be used to determine the mother superparticle mass and the LSP mass simultaneously. To see how well mT2max can be constructed from collider data, a Monte-Carlo analysis of the gluino mT2 is performed for some superparticle spectra.

Atomistic simulation of kink structure on edge dislocation in bcc iron

Based on the general theory of dislocation and kink, we have constructed the three kink models corresponding to the 1/2 〈111〉{011} and 1/2 〈111〉{112} edge dislocations (EDs) in bcc Fe using the molecular dynamics method. We found that the geometric structure of a kink depends on the type of ED and the structural energies of the atom sites in the dislocation core region, as well as the geometric symmetry of the dislocation core and the characteristic of the stacking sequence of atomic plane along the dislocation line. The formation energies and widths of the kinks on the 1/2 〈111〉{011} and 1/2 〈111〉{112} EDs are calculated, the formation energies are 0.05eV and 0.04eV, and widths are 6.02b and 6.51b, respectively (b is the magnitude of the Burgers vector). The small formation energies indicate that the formation of kink in the edge dislocation is very easy in bcc Fe.

Effect of impurity P on electronic structure of kink in the edge dislocation of α-iron

Using the first-principles self-consistent discrete variational method based on density functional theory, we have investigated the effect of impurity P on the electronic structure of the kink on the ［100］(010) edge dislocations in bcc iron. Furthermore，we have calculated the segregation energy, the interatomic energy, the local density of states and the charge density. Our results show that the P atom proeures electrons from its neighboring Fe atoms when trace P is introduced into interstitial sites in the kink. It is found that the interactions between impurity P atom and neighboring Fe atoms are strengthened due to the strong hybridizations between P-p with Fe-3d4s4p states. The migration of kink and dislocation motion are impeded by P, which may be beneficial to increase the strength of material. Meanwhile, the bonding between the impurity P and the host Fe atoms are mainly ascribed to contribution of p and d states, which leads to the bonding between them to have strong orientation. This is not beneficial to the toughness of materials.

Observation of the fine structure in local density-of-states in La2−x−yNdySrxCuO4

Scanning tunneling spectroscopy measurements have been performed on La1.68Nd0.2Sr0.12CuO4 (LNSCO, Tc=13K) at 4.2K to reveal the low energy fine structure in the tunneling spectra. A kink structure was observed at ±6–7meV regardless of the superconducting gap value, which spatially varied from 6 to over 15meV. We found that the energy where the kink appears is close to the minimum value of the superconducting gap distribution. These features of the kink structure found in LNSCO qualitatively agree with those observed in Bi2Sr1.6La0.4CuO6+δ.

Soliton patterns and breakup thresholds in hydrogen-bonded chains

The dynamics of protons in hydrogen-bonded quasi one-dimensional networks are studied using a diatomic lattice model of protons and heavy ions including a φ4 on-site substrate potential. It is shows that the model with linear and nonlinear coupling of the quartic type between lattice sites for the protons admits a richer dynamics that cannot be produced with linear couplings alone. Depending on two types of physical boundary conditions, namely of the drop or condensate type, and on conditions requiring the presence of linear and nonlinear dispersion terms, soliton patterns of compact support, whether with a peak, drop, bell, cusp, shock, kink, bubble or loop structure, are obtained within a continuum approximation. Phase trajectories as well as analytical studies provide information on the disintegration of soliton patterns upon reaching some critical values of the lattice parameters. The total energies of soliton patterns are computed exactly in the continuum limit. We also show that when anharmonic interactions of the phonon are taken into account, the width and energy of soliton patterns are in qualitative agreement with experimental data.

Spin Wave Excitations in the Ferromagnetic Phase of Iron –Study with a Tight-Binding Model–

Spin wave excitations and the electron self-energy corrections in the ferromagnetic phase of iron are studied using the Naval Research Laboratory tight-binding model. It is found that the spin wave excitation spectrum obtained with this model is in good agreement with the experimental results. Transverse spin fluctuations contribute to the self-energy and reduce the band width uniformly, but does not cause a prominent kink structure in the quasiparticle dispersion near the fermi level. Comparison with recent angle-resolved photoemission experiments on Fe is made.

High-resolution photoemission study of electron–electron interaction in the Ni(1 1 1) surface state

High-resolution angle-resolved photoemission study of the surface state in ferromagnetic Ni(1 1 1) has been performed to evaluate the strength of many-body interactions. We could not observe a kink structure in the energy band dispersion derived from the electron–phonon interaction. The imaginary part of the self-energy was evaluated; it increases significantly with increasing energy, indicating a strong electron–electron interaction.