When the constitutive materials of photonic crystals (PCs) are magnetic, or even only a defect introduced in PCs is magnetic, the resultant PCs exhibit very unique optical and magneto-optical properties. The strong photon confinement in the vicinity of magnetic defects results in large enhancement in linear and nonlinear magneto-optical responses of the media. Novel functions, such as band Faraday effect, magnetic super-prism effect and non-reciprocal or magnetically controllable photonic band structure, are predicted to occur theoretically. All the unique features of the media arise from the existence of magnetization in media, and hence they are called magnetophotonic crystals providing the spin-dependent nature in PCs.
We have studied the optical and magneto-optical properties of bismuth-substituted yttrium iron garnet (Bi:YIG) films with Au nanoparticles dispersed on their top surfaces. These structures exhibit surface plasmon resonances due to light coupling to Au nanoparticles, showing, for any direction of polarization of the incoming light beam, an absorption band in the spectral range of 500–750nm. For transmitted light beams with the plasmon-resonant wavelengths, the plane of polarization rotates slightly when the structure is not magnetized. Polarization-resolved transmission spectra show that this rotation is due to anisotropy of light propagation through the array of Au nanoparticles. For the structure comprising the 90-nm-thick Bi:YIG film and the array of Au nanoparticles of several tens of nanometers, the Faraday rotation angle enhances as compared with that for the original Bi:YIG film of the same thickness.
Using a scanning tunneling microscope, single adatoms can be extracted from a Si(l 11)7x7 surface by field evaporation, when the sample voltage is pulsed at 4 V or more in either polarity. Statistically, adatoms at the center of the 7x7 unit cell are more frequently removed than those near the corner holes, by a ratio of 1.6:1. This difference can be explained by assuming that the binding energy of center adatoms is approximately 0.1 eV less than for corner adatoms. The relationship of this result to previous observations of greater chemical reactivity at center adatom sites is discussed.PACS numbers: 68.35.Dv, 73.40.Gk Atomic-scale modification of surfaces by scanning tunneling microscopy (STM) provides a unique means to probe the local physics and chemistry of such surfaces [1], as well as a promising technology for the fabrication of novel electronic devices [2]. Modification of semiconductor surfaces is of particular interest for practical applications. In their pioneering work, Becker, Golovchenko, and Swartzentruber [3] made atomic-scale protuberances on Ge(lll) by briefly increasing the bias between tip and sample above 3 V. The proposed mechanism was field ion emission. However, Si(lll) could not be modified in the same way, even for biases up to 20 V. Lyo and Avouris [4] have succeeded in manipulating single atoms on Si(l 11) by moving the tip to within a few A units of the surface and applying a 3 V pulse. Because of the close proximity of tip and sample, this process is believed to depend on direct chemical interaction as well as electric field.Recently, grooves several nanometers wide were made on Sid 11) at bias voltages in the range 3-6 V, without first moving the tip towards the sample [5]. The process was directly dependent on electric field, rather than on current or voltage, indicating that the mechanism was field evaporation. In this Letter, we show that a similar process can be used to modify Si(lll) on the atomic scale and remove single Si adatoms from the surface. The statistics of adatom vacancy creation yield information about the differences of binding energy for different adatom sites in the Si(l 11)7x7 unit cell. The approach presented here for studying surface energetics, by directly comparing how easily different atoms are extracted from a surface, should prove widely applicable.The experiments were made with a commercial ultrahigh vacuum (UHV) STM (JEOL JSTM-4000 XV). Samples cut from wafers of p-doped Si(lll) were cleaned in UHV by repeated flash heating to 1200°C. The base pressure in the chamber was 1 x 10~^ Pa, The STM tip was a 0.1 mm W wire, sharpened by electrolytic etching using a 0.57V solution of KOH. Electron bombardment heating of the tip to above 1200°C was performed in the UHV chamber. This step has been shown to be critical for obtaining reproducible modification [5].Silicon adatoms were extracted as follows. A clean, flat area of the surface was imaged at + 2 V and -2 V at a tunneling current of 0.6 nA, revealing the regular pattern of Si adatoms of the Si(l 11)7x...
In the fifty years since the postulation of Moore’s Law, the increasing energy consumption in silicon electronics has motivated research into emerging devices. An attractive research direction is processing information via the phase of spin waves within magnonic-logic circuits, which function without charge transport and the accompanying heat generation. The functional completeness of magnonic logic circuits based on the majority function was recently proved. However, the performance of such logic circuits was rather poor due to the difficulty of controlling spin waves in the input junction of the waveguides. Here, we show how Snell’s law describes the propagation of spin waves in the junction of a Ψ-shaped magnonic majority gate composed of yttrium iron garnet with a partially metallized surface. Based on the analysis, we propose a magnonic counterpart of a core-cladding waveguide to control the wave propagation in the junction. This study has therefore experimentally demonstrated a fundamental building block of a magnonic logic circuit.
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