Hydrogen-passivated detonation nanodiamond:an impedance spectroscopy study

Detonation nanodiamond (DND) is an attractive class of diamond material, which has a great potential to be used for a wide range of applications. In this paper, untreated DND was employed to perform hydrogen passivation process using microwave plasma enhanced chemical vapor deposition in order to investigate the influence of hydrogen-terminated surface on the DND's electrical properties. Impedance spectroscopy (IS) has been used to characterize the electrical properties of DND samples using a newly-developed measurement set-up. It is found that hydrogen-passivation process has increased the electrical conductivity of the DND by up to four orders of magnitude when compared with the untreated sample. An RC parallel equivalent circuit with a Warburg element has been proposed to model the DND's impedance characteristics. © 2012 Elsevier B.V. All rights reserved.

Stress-induced platelet formation in silicon:a molecular dynamics study

The effect of stress on vacancy cluster configurations in silicon is examined using molecular dynamics. At zero pressure, the shape and stability of the vacancy clusters agrees with previous atomistic results. When stress is applied the orientation of small planar clusters changes to reduce the strain energy. The preferred orientation for the vacancy clusters under stress agrees with the experimentally observed orientations of hydrogen platelets in the high stress regions of hydrogen implanted silicon. These results suggest a theory for hydrogen platelet formation. © 2005 The American Physical Society.

A study of the electrical and optical properties of unhydrogenated neon-sputtered amorphous silicon

Films of amorphous silicon (a-Si) were prepared by r.f. sputtering in a Ne plasma without the addition of hydrogen or a halogen. The d.c. dark electrical conductivity, he optical gap and the photoconductivity of the films were investigated for a range of preparation conditions, the sputtering gas pressure, P, the target-substrate spacing, d, the self-bias voltage, Vsb, on the target and the substrate temperature, Ts. The dependence of the electrical and optical properties on these conditions showed that various combinations of P, d and Vsb, at a constant Ts, giving the same product (Pd/V sb) result in films with similar properties, provided that P, d and Vsb remain vithin a certain range. Variation of Pd/Vsb between about 0.2 and 0.8 rrTorr.cm!V varied the dark conductivity over about 4 orders of magnitude, the optical gap by 0.5 eV and the photoconductivity over 4-5 orders of magnitude. This is attributed to controlling the density-of-states distribution in the mobility gap. The temperature-dependence of photoconductivity and the photoresponse of undoped films are in support of this conclusion. Films prepared at relatively high (Pd/Vsb) values and Ts=300 ºc: exhibited low dark-conductivity and high thermal activation energy, optical gap and photoresponse, characteristic properties of a 'low density-of-states material. P-type doping with group-Ill elements (Al, B and Ga) by sputtering from a composite target or from a predoped target (B-.doped) was investigated. The systematic variation of room-temperature conductivity over many orders of magnitude and a Fermi-level shift of about 0.7 eV towards the valence-band edge suggest that substitutional doping had taken place. The effects of preparation conditions on doping efficiency were also investigated. The post-deposition annealing of undoped and doped films were studied for a temperature range from 250 ºC to 470 ºC. It was shown that annealing enhanced the doping efficiency considerably, although it had little effect on the basic material (a-Si) prepared at the optimum conditions (Pd/Vsb=0.8 mTorr.cm/V and Ts=300 $ºC). Preliminary experiments on devices imply potential applications of the present material, such as p-n and MS junctions.

Effect of dopants on the fracture toughness of silicon

Fracture experiments were conducted on p-type and n-type Si in the presence and absence of hydrogen. It was found that fracture toughness is slightly less than the fracture toughness of n-type silicon. Annealing silicon in an Ar/H atmosphere gave a hydrogen concentration of less than 0.1 ppm, which did not have any measurable effect on fracture toughness. Likewise, the exposure of pre-cracked specimens to H did not cause any measurable change in fracture toughness.