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The elastic-plastic deformation mechanism of single crystal diamond under spherical nanoindentation was emphasised using molecular dynamics (MD). The benchmark tests to determine the empirical potential that accurately describe the interactions between diamond atoms were completed. Tensile strength of diamond at different temperatures was studied under the empirical potential preferentially selected by benchmark tests. The nanoindentation process of the diamond is subsequently carried out on the surface (001). Plastic deformation behaviour of brittle diamond was found, such as amorphisation, phase transformation, graphitisation and dislocation evolution were analysed and discussed using combined methods. The simulation results show that the plastic deformation behaviour of the diamond material is also evident, even though diamond is a brittle material with high strength and hardness. 'Pop-in' event of the P-h curve is the turning point from elastic to plastic deformation. The elastic stage can be divided into the pure elastic and the quasi-elastic deformation stages. The plastic deformation behaviour of diamond is dominated by a combination of phase transformation, graphitisation and dislocation nucleation. It is also found that the primary dislocation type is 1/2<110> perfect dislocation, which was distributed in the area of large stress concentration below the indenter. [ABSTRACT FROM AUTHOR]

Thin films of amorphous carbon nanowire (a-CNW) have been fabricated from crossed multi-walled carbon nanotube (MWCNT) thin film. The fabrication was done by means of ion beam irradiation on various substrates. It is found that the a-CNW thin films show electrical conduction behaviour, and electrical conductivity varies after annealing. In addition, the transmission spectra in the visible range reveal that the film has above 90% optical transmission. It can be ascribed to the fact that the decreased crystallinity of MWCNTs by ion beam irradiation has caused the incremental increase of optical transmission. We also report on a method for cutting or destroying a-CNWs using low-energy focused electron beam from a scanning electron microscope. [ABSTRACT FROM PUBLISHER]

Using experimental data for the structure factor S(q) of supercooled liquid silicon, and amorphous and supercooled liquid cobalt, we have calculated and compared the Fourier transform c(q) of the Ornstein–Zernike direct correlation function for these two systems. Differences of c(q) between Si and Co are ascribed to the different atomic coordination and packing, high in Co due to typical metallic bonding, and lower in Si due to more directional bonding. Also, in contrast to previous expectations, differences are found between the direct correlation function of amorphous and supercooled liquid cobalt. [ABSTRACT FROM PUBLISHER]

Severe plastic deformation (SPD) can be used to make bulk, nanostructured materials. Three L12 long-range ordered (LRO) intermetallic compounds were studied by TEM methods. The superlattice glide dislocations can dissociate according to two schemes: antiphase boundary (APB) coupled unit dislocations or superlattice intrinsic stacking fault (SISF) coupled super Shockley partials; both of them are analysed by weak-beam TEM methods. The nanostructures resulting from SPD carried out by high pressure torsion (HPT) are strongly affected by the different dissociation schemes of the dislocations. APB-dissociated superlattice dislocations and especially the APB tubes they form lead to the destruction of the LRO by HPT deformation as observed in Cu3Au and Ni3Al, whereas in Zr3Al heavily deformed (∼100,000% shear strain) at low temperatures the order is not destroyed since the deformation occurs by SISF-dissociated dislocations. In addition to the effects on the LRO the different dissociation schemes of the dislocations have a strong impact on the refinement and destruction of the crystalline structure by SPD. They seem to be decisive for the dynamic recovery considered as the limiting factor for the final grain sizes and the possibility of reaching amorphisation. Finally, the correlation between the reduction of the LRO and the structural refinement occurring during SPD is different in the three different alloys: In Cu3Au, the LRO is already strongly reduced before the structural refinement reaches saturation, in Ni3Al both are occurring simultaneously, whereas in Zr3Al, the formation of the nanograins does not seem to be connected with disordering. [ABSTRACT FROM AUTHOR]

Attempts at generating nanograins through uniaxial single compression were made by deforming copper samples at 298 K and 77 K. At 298 K, dynamically-deformed samples (DDS) become softer, in contrast to quasi-statically deformed samples (QDS), which show a hardness close to the saturation value. The microstructure of DDS is characterised by deformation twins and equiaxed micron-sized grains, and the observed softening is due to the occurrence of recrystallisation (RX). At a reduced temperature of 77 K, nanograins are generated in DDS, whereas QDS show forest dislocations and twins. The generation of nanograins, which evolve through rotational DRX, is associated with the formation of shear bands with an amorphous structure. Compared with twinning, it appears that amorphisation plays a more pronounced role in high strain rate deformation at reduced temperatures (77 K). The hardness of DDS, obtained from compression at 77 K, exceeds the saturation value by 16%, whereas that of QDS corresponds approximately to saturation. [ABSTRACT FROM AUTHOR]

Optical, electrical and structural properties of argon (Ar) ion-irradiated buckypapers of multi-walled carbon nanotube (MWCNT) at various doses prepared by a vacuum filtration method were investigated. It was found that the direct current (DC) conductivity and absorption spectra in the visible range were decreased with an increasing Ar ion irradiation dose. A subsequent heating of nanotube buckypapers at 800 K in a vacuum at each irradiation dose improved the conductivity of buckypapers, whereas optical absorption was unchanged. Moreover, the graphite structure of MWCNTs was transformed to amorphous structure with an increasing Ar ion irradiation dose. The decrease of optical absorption and electrical conductivity of MWCNT buckypaper at room temperature can be ascribed to the increase of defects in the irradiated MWCNTs. [ABSTRACT FROM AUTHOR]

Defect production and amorphisation due to energetic uranium recoils in zircon (ZrSiO4), which is a promising ceramic nuclear waste form, is studied using molecular dynamics (MD) simulations with a partial charge model. An algorithm that distinguishes between undamaged crystal, crystalline defects and amorphous regions is used to develop a fundamental understanding of the primary damage state. The amorphous cascade core is separated from the surrounding crystal by a defect-rich region. Small, chemically inhomogeneous amorphous clusters are also produced around the core. The amorphous regions consist of under-coordinated Zr and polymerised Si leading to amorphisation and phase separation on a nanometer scale into Zr- and Si-rich regions. This separation could play an important role in the experimentally observed formation of nanoscale ZrO2 in ZrSiO4 irradiated at elevated temperatures. [ABSTRACT FROM AUTHOR]