Search Results (3 total)

Engineering of stop gaps between higher photonic bands provides an alternative to miniaturization of photonic crystals. Femtosecond laser microfabrication of highly correlated void channel polymer microstructures results in photonic crystals with large stop gaps and a multitude of higher-order gaps in the mid- and near-infrared spectral regions. The gap wavelengths obey Bragg’s law. Consistent with theory, varying the woodpile structure unit cell allows for tuning the number of higher-order gaps, and transitions from mere resonant Bragg scattering to stop band total reflection are observed.

By magnetization induced second harmonic generation (MSHG) the surface magnetization of fcc Fe films on Cu(100) is studied. The tetragonally distorted phase below 4 monolayers (ML) and the relaxed fcc phase above 4 ML can unambigously be distinguished by different average MSHG signals. Nearly constant asymmetry of the second harmonic intensities between 1.3 and 10 ML proves, to a good approximation, thickness independence of the surface magnetization irrespective of the phase transition at 4 ML. The nonlinear Kerr angle amounts to 4°.

Ultrathin γ-Fe/Cu(001) films are unstable with respect to the fcc→bcc phase transition with the reported onset of transformation as early as at 5 ML. Here we demonstrate that with the help of a collaborative surfactant effect of carbon and oxygen, γ-Fe films up to more than 60 ML thickness can easily be produced. The interstitial incorporation of carbon atoms into the fcc lattice is the main reason for this stabilizing effect. Oxygen plays a very important role in improving the layer-by-layer growth. This strong surfactant effect of oxygen, however, reveals itself only in the presence of carbon. The interstitial carbon does not influence the magnetic properties of fcc iron significantly, except for the surface anisotropy value. © 1996 The American Physical Society.