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Different thicknesses of amorphous silicon carbide (a-SiC) and amorphous silicon nitride (a-SixNy) coatings were deposited on randomly aligned multiwall carbon nanotubes (MWNTs) by plasma enhanced chemical vapor deposition (PECVD). Their optical limiting properties were studied as a suspension in water. Optical limiting experiments show that they had slightly reduced optical limiting properties compared to pure MWNTs, the extent depending on the thickness and coating material. However, the linear transmission spectra of these coated MWNTs show a broader band transmission than pure MWNTs. This suggests that the coated MWNTs are more ideal as protective material for optical sensors as compared to pure MWNTs because they are effective over a wider optical transmission band.

O2+ ion beams are used to modify the surface of 50 nm thick Fe catalyst films deposited on Si(100) substrates to demonstrate selective area growth of aligned multiwall carbon nanotubes (MWNT). Aligned MWNTs were grown on the modified Fe/Si substrate using the hot filament plasma enhanced chemical vapor deposition (HF-PECVD) method. A higher growth rate and density of MWNTs was observed on the ion-modified areas, facilitating selective area growth of aligned MWNTs at temperatures as low as 560 °C. Deposition of graphitic sheets at the initial growth process on the unmodified areas inhibits the deposition of MWNTs.

The temperature dependence of the Hall plateaus at microwave frequencies (∼ 30 GHz) and their disappearance at 160 GHz suggest a unified phenomenological model of the integral quantum Hall effect at zero and high frequencies. In laterally structured samples depolarization effects as well as the Hall plateaus are observed in the Hall conductivity.

Microwave experiments with crossed waveguides allow measurement of the Hall conductivity Oxy of a two-dimensional electron gas. The quantized behavior of σxy is equivalent to that of πxy measured with DC. In this contribution we report on new results regarding phenomena not accessible to DC techniques.