Material parameter extraction in THz-TDS using a converging beam transfer function

We demonstrate a parameter extraction algorithm based on a theoretical transfer function, which takes into account a converging THz beam. Using this, we successfully extract material parameters from data obtained for a quartz sample with a THz time domain spectrometer. © 2010 IEEE.

Observation of the ordered growth of coronene on Ag(111): a scanning tunnelling microscopy study of vacuum deposited molecules

The molecular ordering of coronene (C24H12) obtained by vacuum-deposition onto predominantly Ag(111) on mica has been investigated using the scanning tunnelling microscope. Real-space topographic images reveal that in certain regions we obtain layer-by-layer ordered growth of the molecules on this substrate which agrees with previous indirect measurements (the growth did not display this ordering in other regions). In our experiments on the ordered regions, we observe the best imaging contrast at a voltage bias of -0.28 V which may correspond to a resonant tunnelling process through the molecules. © 1995.

Material properties and tribological performance of rf-PECVD deposited DLC coatings

Diamond-like carbon (DLC) coatings were deposited on to silicon, glass and metal substrates, using an rf-plasma enhanced chemical vapour deposition (rf-PECVD) process. The resultant film properties were evaluated in respect of material and interfacial property control, based on bias voltage variation and the introduction of inert (He and Ar) and reactive (N2) diluting gases in a CH4 plasma. The analysis techniques used to assess the material properties of the films included AFM, EELS, RBS/ERDA, spectroscopic, electrical, stress, microhardness, and adhesion. These were correlated to the tribological performance of the coatings using wear measurements. The most important observation is that He dilution (>90%) promotes enhanced adhesion with respect to all substrate material studies. Coatings typically exhibit a microhardness of the order of 10-20 GPa in films 0.1material and interfacial property control, based on bias voltage variation and the introduction of inert (He and Ar) and reactive (N2) diluting gases in a CH4 plasma. The analysis techniques used to assess the material properties of the films included AFM, EELS, RBS/ERDA, spectroscopic, electrical, stress, microhardness, and adhesion. These were correlated to the tribological performance of the coatings using wear measurements. The most important observation is that He dilution (>90%) promotes enhanced adhesion with respect to all substrate materials studied. Coatings typically exhibit a microhardness of the order of 10-20 GPa in films 0.1 < d < 2 μm thick, with associated electrical resistivity in the range 108 < ρ < 1012 Ω·cm, coefficient of friction <0.1 and surface RMS roughness as low as 2 A. The results are discussed with respect to surface pre-treatment, ion surface bombardment, interfacial reactivity and changes in plasma gas breakdown processes.

Controlling magnetic ordering in coupled nanomagnet arrays

We have fabricated using high-resolution electron beam lithography circular magnetic particles (nanomagnets) of diameter 60 nm and thickness 7 nm out of the common magnetic alloy supermalloy. The nanomagnets were arranged on rectangular lattices of different periods. A high-sensitivity magneto-optical method was used to measure the magnetic properties of each lattice. We show experimentally how the magnetic properties of a lattice of nanomagnets can be profoundly changed by the magnetostatic interactions between nanomagnets within the lattice. We find that simply reducing the lattice spacing in one direction from 180 nm down to 80 nm (leaving a gap of only 20 nm between edges) causes the lattice to change from a magnetically disordered state to an ordered state. The change in state is accompanied by a peak in the magnetic susceptibility. We show that this is analogous to the paramagnetic-ferromagnetic phase transition which occurs in conventional magnetic materials, although low-dimensionality and kinetic effects must also be considered.