Effects of hydroxyls on the structural and room temperature ferromagnetic properties of Co doped SnO2 nanoparticles

Co doped SnO₂ nanoparticles have been prepared via a wet chemical method with different precipitation processes. The structure and morphology of Co doped SnO₂ nanoparticles demonstrate that the nanoparticles are in a rutile single phase and uniform, respectively. X-ray photoelectron spectroscopy shows that the Co dopants are in 2+ oxidation valence state and doped ∼2 atm% in SnO₂ nanoparticles. Moreover, Raman spectroscopy further confirms that Co doped SnO₂ nanoparticles have single phase crystallinity without forming any extra modes related to secondary phases. The magnetic measurements reveal that all nanoparticles exhibit room temperature ferromagnetism (RTFM) due to the presence of disorders and defects introduced by hydroxyls in the crystal structure. In addition, it has been clearly observed that the saturated magnetic moments are strongly affected by the precipitation processes which control the incorporation of hydroxyls into the lattice.     

High heat generation ability in AC magnetic field for nano-sized magnetic Y3Fe5O12 powder prepared by bead milling

Nano-sized magnetic Y₃Fe₅O₁₂ ferrite having a high heat generation ability in an AC magnetic field was prepared by bead milling. A commercial powder sample (non-milled sample) of ca. 2.9 μm in particle size did not show any temperature enhancement in the AC magnetic field. The heat generation ability in the AC magnetic field improved with a decrease in the average crystallite size for the bead-milled Y₃Fe₅O₁₂ ferrites. The highest heat ability in the AC magnetic field was for the fine Y₃Fe₅O₁₂ powder with a 15-nm crystallite size (the samples were milled for 4 h using 0.1 mm? beads). The heat generation ability of the excessively milled Y₃Fe₅O₁₂ samples decreased. The main reason for the high heat generation property of the milled samples was ascribed to an increase in the Néel relaxation of the superparamagnetic material. The heat generation ability was not influenced by the concentration of the ferrite powder. For the samples milled for 4 h using 0.1 mm? beads, the heat generation ability (W g⁻¹) was estimated using a 3.58×10⁻⁴ fH² frequency (f/kHz) and the magnetic field (H/kA m⁻¹), which is the highest reported value of superparamagnetic materials.     

Quantum Hall effect, screening, and layer-polarized insulating states in twisted bilayer graphene

We investigate electronic transport in dual-gated twisted-bilayer graphene. Despite the subnanometer proximity between the layers, we identify independent contributions to the magnetoresistance from the graphene Landau level spectrum of each layer. We demonstrate that the filling factor of each layer can be independently controlled via the dual gates, which we use to induce Landau level crossings between the layers. By analyzing the gate dependence of the Landau level crossings, we characterize the finite interlayer screening and extract the capacitance between the atomically spaced layers. At zero filling factor, we observe an insulating state at large displacement fields, which can be explained by the presence of counterpropagating edge states with interlayer coupling.     

Naturalness bounds on dipole moments from new physics

Assuming naturalness that the quantum corrections to the mass should not exceed the order of the observed mass, we derive and apply model-independent bounds on the anomalous magnetic moments and electric dipole moments of leptons and quarks due to new physics.     

Universal function for the brilliance of undulator radiation considering the energy spread effect

Angular and spatial profiles of undulator radiation have been investigated to derive a universal function that evaluates the brilliance of undulator radiation and takes into account the effects of electron beam emittance and energy spread. It has been found that the effects of energy spread on the angular divergence and source size can be expressed by simple analytic expressions, and a universal brilliance function has been derived by convolution with the electron beam distribution functions. Comparisons with numerical results have been carried out to show the validity and applicability of the universal function.     

Influence of Cu electroplating solutions on boron carbon nitride (BCN) film

Cu electroplating is required for the fabrication of Cu/low-k interconnections. The permeation of a plating solution into low-k films during Cu electroplating is a serious challenge for 45-nm nodes and more complex devices. We investigated the influence of Cu electroplating solutions on boron carbon nitride (BCN) as a low-k film. After dipping it into a Cu electroplating solution that contained additives, the BCN film's hydrophilic surface changed to a hydrophobic surface, and the incorporation of water into the BCN film was suppressed by surfactant adsorption. Sulfuric residue was detected on the BCN sample by thermal desorption spectroscopy after treatment in the Cu electroplating solution with additives; however, it was found through electrical measurements that this solution did not affect the leakage current or the dielectric constant of the BCN film. We successfully fabricated an electroplating Cu layer on a BCN film with good adhesion, and we believe that this BCN film is a sufficiently useful material for Cu/BCN integration in LSI.     

Patterning on single crystalline silicon by laser scanning and alkaline etching

The applicability of laser processing for small-lot micro-electromechanical system devices is discussed in this paper. This simple process could replace conventional complex processes designed with mass production in mind. Ablation, protrusions or surface modification is revealed to occur by argon ion laser scanning into silicon. Which of them occurs depends on the laser power. It is found that the protrusions are covered by a thin layer of oxide; however, oxidation of the modified surface is not established even though some results suggest it. Surface modification is more applicable to surface patterning than coarse protrusion is because the laser-modified surface can be used as a mask in KOH etching to make sharp patterns. The applicability of this method is indicated by demonstrating pattern width control, patterning over a large area and the fabrication of a 16-bit linear scale.     

Vehicular motion on a selected path in a 2d traffic network controlled by signals

We study the dynamic behavior of vehicular traffic through a series of traffic lights on selected paths in a two-dimensional (2d) traffic network. The city traffic network is made of one-way perpendicular streets arranged in a square lattice with traffic signals where vertical streets are oriented upwards and horizontal streets are oriented rightwards. A vehicle moves through the series of signals on a path selected by the driver. The selected path is one of the straight, zigzag, and random paths in a 2d traffic network. The vehicular motion on a selected path is presented by the nonlinear-map model. Vehicular traffic exhibits very complex behavior with varying selected paths, cycle times, and vehicular density. The dependence of the arrival time on cycle time, selected path, and density is clarified for 2d city traffic.     

Characterization of attosecond XUV pulses from photoelectron spectra of atoms

A method to characterize attosecond extreme ultra violet (XUV) pulses from photoelectron spectra of atoms is presented. A pump pulse prepares a coherent superposition of two atomic bound states, from which photoionization takes place after variable time delays by the attosecond XUV pulse. Information on the spectral phase of the attosecond XUV pulse is extracted from the analysis of photoelectron spectra as a function of photoelectron energy and time delay. Together with information on the spectral intensity obtained from a separate optical measurement, a temporal shape of the attosecond XUV pulse can be precisely reconstructed. After the theoretical formulation of the problem, we present numerical examples for H atom and show that, depending on the choice of energy separation of two bound states, a different accuracy is reached to characterize attosecond XUV pulses.     

Cu chemistry of YBa2Cu3O6+x investigated by nuclear quadrupole resonance

The nuclear quadrupole resonance (NQR) technique has been utilized to characterize the local oxygen coordination of inequivalent Cu sites in YBa₂Cu₃O_6+x(0 ≤ x ≤ 0.91). Essentially, four distinct NQR lines which correspond to 2, 3,4 oxygen coordinated Cu sites in the Cu-O chains and 5 oxygen coordinated Cu sites in the Cu-O planes have been observed. The zero-field NQR frequencies of these are centered at about 30.1, 24.0, 22.0 and 31.5 MHz for ⁶³Cu, respectively. For the antiferromagnetic ordered state (x ≤ 0.3), antiferromagnetic nuclear resonance (AFNR) has been observed at 90 MHz with quadrupole splittings associated with the moment-bearing Cu sites in the Cu-O planes. The relative intensities of these resonance lines depend on the oxygen content, and this gives us a microscopic understanding of the Cu chemistry of this system.