Flash sintering occurs when an electric field is applied to a heated ceramic powder compact. At a critical combination of field and temperature, a power surge occurs (the "flash event") and sintering takes place in a few seconds. This paper investigates the possibility that this surge occurs by runaway Joule heating. The resistivity of 3YSZ was measured under the relevant conditions. To a good approximation, resistivity was found to be history-independent and to have the same temperature dependence before and after the flash event. These data were used to model the thermal and electrical response of 3YSZ to an applied electric field. All electrical characteristics of the flash event observed experimentally were predicted with a high degree of accuracy. It is concluded that the thermal and electric characteristics of flash sintering are a classical consequence of the negative temperature coefficient of resistivity leading to runaway Joule heating at constant voltage.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.Silicon wafer solar cells continue to be the leading photovoltaic technology, and in many places are now providing a substantial portion of electricity generation. Further adoption of this technology will require processing that minimises losses in device performance. A fundamental mechanism for efficiency loss is the recombination of photo-generated charge carriers at the unavoidable cell surfaces. Dielectric coatings have been shown to largely prevent these losses through a combination of different passivation mechanisms. This review aims to provide an overview of the dielectric passivation coatings developed in the past two decades using a standardised methodology to characterise the metrics of surface recombination across all techniques and materials. The efficacy of a large set of materials and methods has been evaluated using such metrics and a discussion on the current state and prospects for further surface passivation improvements is provided.

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The growing use of secondary electron imaging in the scanning electron microscope (SEM) to map dopant distributions has stimulated an increasing interest in the mechanism that gives rise to so-called dopant contrast. In this paper a range of experimental results are used to demonstrate the wide applicability of the technique. These results are then incorporated into a model where, in particular, the effect of the surface barrier and the vacuum level are considered. It is found that the dominant contribution to the contrast mechanism is due to the three-dimensional variation of the vacuum level outside the semiconductor.

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Articles you may be interested inThe effect of impurity-induced lattice strain and Fermi level position on low temperature oxygen diffusion in silicon J. Appl. Phys. 109, 063532 (2011); 10.1063/1.3555625 Nitrogen diffusion and interaction with dislocations in single-crystal siliconThe locking of dislocations by oxygen atoms in Czochralski-silicon at temperatures between 350 and 700°C has been studied. Both experimental and theoretical investigations were carried out for different oxygen concentrations, different annealing times ͑from 10 to 3ϫ10 7 s͒, and different point defect concentrations. It was found that the unlocking stress of dislocations at low temperatures follows similar trends to those previously observed at higher temperatures and is determined by annealing temperature, time, and oxygen concentration. However, in the present temperature range, experimental results indicate an enhanced transport of oxygen to dislocations. Numerical simulations solving the diffusion equation for oxygen transport to the dislocations show that the effective diffusivity of oxygen at lower temperatures diverges from ''normal'' diffusivity of oxygen. We have shown that oxygen transport can be as much as three orders of magnitude higher than that which would be assumed by extrapolation of the ''normal'' data obtained at higher temperatures. In the low temperature regime the effective diffusivity is dependent on the oxygen concentration and has an activation energy of about 1.5 eV.

Thin, nano-porous, highly adherent layers of anodised aluminium formed on the surface of titanium alloys are being developed as coatings for metallic surgical implants. The layers are formed by anodisation of a 1-5 microm thick layer of aluminium which has been deposited on substrate material by electron beam evaporation. The surface ceramic layer so produced is alumina with 6-8 wt % phosphate ions and contains approximately 5 x 10(8) cm(-2) pores with a approximately 160 nm average diameter, running perpendicular to the surface. Mechanical testing showed the coatings' shear and tensile strength to be at least 20 and 10 MPa, respectively. Initial cell/material studies show promising cellular response to the nano-porous alumina. A normal osteoblastic growth pattern with cell number increasing from day 1 to 21 was shown, with slightly higher proliferative activity on the nano-porous alumina compared to the Thermanox control. Scanning electron microscopy (SEM) examination of the cells on the porous alumina membrane showed normal osteoblast morphology. Flattened cells with filopodia attaching to the pores and good coverage were also observed. In addition, the pore structure produced in these ceramic coatings is expected to be suitable for loading with bioactive material to enhance further their biological properties.