Hydrogen and disorder in diamond-like carbon

Diamond-like carbon is a system of rather high disorder as it has a wide optical absorption tail and a high density of paramagnetic defects. The defect density remains high even in DLCs containing 30-60% hydrogen, so hydrogen does not appear to passivate defects well unlike in a-Si:H. To investigate the role of hydrogen on the disorder in DLCs we have investigated the effect of low concentrations of hydrogen on the disorder in ta-C, by introducing 10(-6)-10(-3) mbar hydrogen into the deposition of ta-C by filtered cathodic vacuum are (FCVA), which corresponds to 0.1-15 at.% hydrogen in the films. Higher pressures of hydrogen reduces the ionisation leading to sp(2) bonding, and ultimately the thermalisation of the plasma leads to nanotubes and fullerenes. The deposited ta-C:H films were investigated by electron energy loss spectroscopy (EELS), Raman spectroscopy, optical measurements, electronic transport and N-15 resonant nuclear reaction analysis. Plasma characterisation with a retarding field analyser showed that the ion current density remains nearly unchanged in the pressure range used to deposit the films. Raman measurements indicate the onset of clustering of sp(2) sites when the hydrogen pressure exceeds 2 x 10(-4) mbar. We find that small amounts of hydrogen increase the optical gap up to 2X10(-6) mbar hydrogen pressure, and then the band gap decreases continuously. The absorption tail sharpens by the addition of hydrogen, as measured by photothermal deflection spectroscopy (PDS) and thus confirms the Raman measurements that suggest that the order in the material increases with increasing hydrogen content

Anisotropic deformation of colloidal particles under MeV ion irradiation

Spherical silica colloids with a diameter of 1.0 um made by wet chemical synthesis, were irradiated with 2-16 MeV Au ions at fluences ranging from 2*10^(14) to 11*10^(14) cm^(-2). The irradiation induces an anisotropic plastic deformation turning the sperical colloids into ellipsional oblates. After 16 MeV Au irradiation to a fluence of 11*10^(14) cm^(-2) a size-asapect ratio of 4.7 is achieved. The size polydispersity (~3%) remains unaffected by the irradiation. The transverse diameter increases with the electronic energy loss above a threshold value of ~0.6 keV/nm. Non-ellipsoidal colloids are observed in the case that the projected ion range is smaller than the colloid diameter. The deformation effect is also observed for micro-crystalline ZnS and amorphous TiO2 colloids, as well as ZnS/SiO2 core/shell particles. No deformation is observed for crystaline Al2O3 and Ag particles. The data provide strong support for the thermalspike model of anisotropic deformation