Fine-tunable plasma nano-machining for fabrication of 3D hollow nanostructures: SERS application.

Novel processing sequences for the fabrication of artificial nanostructures are in high demand for various applications. In this paper, we report on a fine-tunable nano-machining technique for the fabrication of 3D hollow nanostructures. This technique originates from redeposition effects occurring during Ar dry etching of nano-patterns. Different geometries of honeycomb, double ring, nanotube, cone and crescent arrays have been successfully fabricated from various metals such as Au, Ag, Pt and Ti. The geometrical parameters of the 3D hollow nanostructures can be straightforwardly controlled by tuning the discharge plasma pressure and power. The structure and morphology of nanostructures are probed using atomic force microscopy (AFM), scanning electron microscopy (SEM), optical emission spectroscopy (OES) and energy dispersive x-ray spectroscopy (EDS). Finally, a Ag nanotube array was assayed for application in surface enhanced Raman spectroscopy (SERS), resulting in an enhancement factor (EF) of 5.5 × 105, as an experimental validity proof consistent with the presented simulation framework. Furthermore, it was found that the theoretical EF value for the honeycomb array is in the order of 107, a hundred times greater than that found in nanotube array.

Skin-effect-mediated magnetoionic control of charge transport in thick layers.

In the rapidly developing area of magnetoionics (MI), which combines electrochemistry and magnetism, changes in the surface chemistry of magnetic materials in response to gate voltages cause dramatic modifications in the magnetic characteristics, resulting in low power-consuming charge transport tuning. Due to the surficial character, only magnetic thin films have been addressed for the MI effect's role in controlling charge transfer. Here, we show how it can be used to regulate the transit of charges in bulk magnetic materials. This is accomplished by combining high-permeability magnetic materials with a high-frequency passing current, allowing the skin effect and the MI effect to control the magnetic materials' impedance due to the impedance's high sensitivity to magnetic permeability. Our in-situ impedance measurement and magneto-optical characterization show the role of redox reactions at the surface in controlling impedance in magnetic materials. This research paves the way for using the MI effect in high-permeability bulk magnetic materials.

Spin-wave-mode coexistence on the nanoscale: a consequence of the Oersted-field-induced asymmetric energy landscape.

It has been argued that if multiple spin wave modes are competing for the same centrally located energy source, as in a nanocontact spin torque oscillator, that only one mode should survive in the steady state. Here, the experimental conditions necessary for mode coexistence are explored. Mode coexistence is facilitated by the local field asymmetries induced by the spatially inhomogeneous Oersted field, which leads to a physical separation of the modes, and is further promoted by spin wave localization at reduced applied field angles. Finally, both simulation and experiment reveal a low frequency signal consistent with the intermodulation of two coexistent modes.

Enhancement in electrical conductivity of liquid crystals by graphene metal oxide composites.

Enhancing the electrical conductivity of liquid crystal (LC) circumvents challenges for application in advanced electronic components. Toward this, using additives made of different nanostructures that could result in functional LCs is suggested. In this paper, various concentrations of graphene (Gr)/metal-oxide (Fe3O4) nanocomposite (GMN) (0.0001-1 w%) were added to E7 nematic LC. We found that the role of anisotropic Gr flakes, their edges as well as surface-decorated-metal-oxide-additives have significant impact on electrical properties of E7. A range of appropriate additives of such a nanocomposite enhances the electrical conductivity of LCs. This effect can be traced through the decrease in the formation of GMN aggregates in the E7 and increase in the electrostatic field at the edges of the Gr sheets. Moreover, the presence of metal-oxide nanoclusters due to the presence of oxygen vacancies and defects facilitates the construction of conductive network for improving the charge transfer pathways and contributes to a stronger interaction of the Gr surface with charged species. These factors can provide Gr layers as dipole moments and lead to signal propagation in the dielectric medium. Our finding conveys a pathway toward significant enhancement of electrical conductivity in the LC family which can be useful for functional applications.

Twenty years of breast cancer in Iran: downstaging without a formal screening program.

BACKGROUND: breast cancer (BC) is the most common malignancy among Iranian women. Although the relative incidence of BC is low, the cause-specific mortality is much higher than developed countries. The present study surveyed the overall trend of BC in Tehran. PATIENTS AND METHODS: all breast pathologic records were studied in five major hospitals in Tehran during three phases (1: 1985-1995; 2: 1996-2000; and 3: 2001-2005). Malignant cases were classified according to the tumor-node-metastasis classification. Data were compared across the study. RESULTS: Of 9050 medical records from male and female patients with 'breast disease', 2946 females with BC were included. A significant increase in the diagnosis of palpable early BCs (stage II increased, stage III decreased) was observed between phases 1 and 2. A relative increases in stages 0 and I were noted between phases 3 and 2. Nevertheless, 76.8% of cases were T2 or higher and 65.3% had positive lymph nodes in the last phase. The proportion of patients with stage IIIb was increased in phase 3, despite the reduction in phase 2. CONCLUSIONS: despite the relative improvement in the status of BC patients, the vast majority are diagnosed in advanced stages. Specific screening measures should be implemented in Iran.

Spin Hall effect originated from fractal surface.

The spin Hall effect (SHE) has shown promising impact in the field of spintronics and magnonics from fundamental and practical points of view. This effect originates from several mechanisms of spin scatterers based on spin-orbit coupling (SOC) and also can be manipulated through the surface roughness. Here, the effect of correlated surface roughness on the SHE in metallic thin films with small SOC is investigated theoretically. Toward this, the self-affine fractal surface in the framework of the Born approximation is exploited. The surface roughness is described by the k-correlation model and is characterized by the roughness exponent H [Formula: see text], the in-plane correlation length ξ and the rms roughness amplitude δ. It is found that the spin Hall angle in metallic thin film increases by two orders of magnitude when H decreases from H = 1 to H = 0. In addition, the source of SHE for surface roughness with Gaussian profile distribution function is found to be mainly the side jump scattering while that with a non-Gaussian profile suggests both of the side jump and skew scatterings are present. Our achievements address how details of the surface roughness profile can adjust the SHE in non-heavy metals.

Investigation of magnetic droplet solitons using x-ray holography with extended references.

A dissipative magnetic soliton, or magnetic droplet, is a structure that has been predicted to exist within a thin magnetic layer when non-linearity is balanced by dispersion, and a driving force counteracts the inherent damping of the spin precession. Such a soliton can be formed beneath a nano-contact (NC) that delivers a large spin-polarized current density into a magnetic layer with perpendicular magnetic anisotropy. Although the existence of droplets has been confirmed from electrical measurements and by micromagnetic simulations, only a few attempts have been made to directly observe the magnetic landscape that sustains these structures, and then only for a restricted set of experimental parameter values. In this work we use and x-ray holography technique HERALDO, to image the magnetic structure of the [Co/Ni]x4 multilayer within a NC orthogonal pseudo spin-valve, for different range of magnetic fields and injected electric currents. The magnetic configuration imaged at -33 mA and 0.3 T for devices with 90 nm NC diameter reveals a structure that is within the range of current where the droplet soliton exist based on our electrical measurements and have it is consistent with the expected size of the droplet (∼100 nm diameter) and its spatial position within the sample. We also report the magnetisation configurations observed at lower DC currents in the presence of fields (0-50 mT), where it is expected to observe regimes of the unstable droplet formation.

Mutually synchronized bottom-up multi-nanocontact spin-torque oscillators.

Spin-torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ultrawide band signal generation from 100 MHz to close to 100 GHz. However, their low output power and large phase noise still limit their applicability to fundamental studies of spin-transfer torque and magnetodynamic phenomena. A possible solution to both problems is the spin-wave-mediated mutual synchronization of multiple spin-torque oscillators through a shared excited ferromagnetic layer. To date, synchronization of high-frequency spin-torque oscillators has only been achieved for two nanocontacts. As fabrication using expensive top-down lithography processes is not readily available to many groups, attempts to synchronize a large number of nanocontacts have been all but abandoned. Here we present an alternative, simple and cost-effective bottom-up method to realize large ensembles of synchronized nanocontact spin-torque oscillators. We demonstrate mutual synchronization of three high-frequency nanocontact spin-torque oscillators and pairwise synchronization in devices with four and five nanocontacts.

Spin torque-generated magnetic droplet solitons.

Dissipative solitons have been reported in a wide range of nonlinear systems, but the observation of their magnetic analog has been experimentally challenging. Using spin transfer torque underneath a nanocontact on a magnetic thin film with perpendicular magnetic anisotropy (PMA), we have observed the generation of dissipative magnetic droplet solitons and report on their rich dynamical properties. Micromagnetic simulations identify a wide range of automodulation frequencies, including droplet oscillatory motion, droplet "spinning," and droplet "breather" states. The droplet can be controlled by using both current and magnetic fields and is expected to have applications in spintronics, magnonics, and PMA-based domain-wall devices.