An updated bibliography of diffusion data in oxides is provided for the materials scientist who requires a convenient source of published results. The scope of the review has been enlarged to include data for the diffusion of the host and impurity species in both binary and multiple oxides. Brief descriptions of terminology, diffusional behaviour and new measurement techniques are followed by tables of selected results and associated experimental details.

Self-diffusion and impurity diffusion in oxides

Electrical switching of a kind can be observed in a great variety of materials in many different forms and structures. Much the most reproducible switching is observed, however, in small and geometrically well-defined devices fabricated from thin films of certain amorphous semiconductors. This paper is concerned with such devices. The general features of electrical switching are first reviewed, followed by a more detailed account of recent work in the authors' own laboratories on digital and analogue switching in hydrogenated amorphous silicon.

Switching in amorphous devices

Electrode-embedded nanopore is considered as a promising device structure for label-free single-molecule sequencing, the principle of which is based on nucleotide identification via transverse electron tunnelling current flowing through a DNA translocating through the pore. Yet, fabrication of a molecular-scale electrode-nanopore detector has been a formidable task that requires atomic-level alignment of a few nanometer sized pore and an electrode gap. Here, we report single-molecule detection using a nucleotide-sized sensing electrode embedded in-plane nanopore. We developed a self-alignment technique to form a nanopore-nanoelectrode solid-state device consisting of a sub-nanometer scale electrode gap in a 15 nm-sized SiO2 pore. We demonstrate single-molecule counting of nucleotide-sized metal-encapsulated fullerenes in a liquid using the electrode-integrated nanopore sensor. We also performed electrical identification of nucleobases in a DNA oligomer, thereby suggesting the potential use of this synthetic electrode-in-nanopore as a platform for electrical DNA sequencing.

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Single-molecule sensing electrode embedded in-plane nanopore

Calculated phase diagrams of ternary Ga-As-metal systems for the metals Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Re, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au are presented. The predictive calculations are based on the following simplifications: Ternary phases and solid solubilities are disregarded and the Gibbs energy of formation of binary compounds is estimated by the enthalpy of formation and calculated from Miedema’s model. The predicted diagrams agree surprisingly well with experimental data and they may be useful for the many cases where data are lacking or fragmentary. The phase diagrams and the thermodynamic data are shown to be a powerful tool for the understanding of interface reactions of metallic contacts to GaAs and hence for the development of improved contact materials.

Stability of metal/GaAs-interfaces: a phase diagram survey

Although gold and gold-based alloys are frequently used in making ohmic contacts to Ga x Al 1− x As, the temperature- and time-dependence of the reactions which take place during the alloying procedure have not been extensively described previously. Using an evolved gas analysis (EGA)[11] with mass spectrometer, we have directly detected As which has passed through the thin gold contact film during alloying. With this technique, we have studied the dissociation of GaAs and Ga 0.7 Al 0.3 As during alloying as a function of processing temperature, time, and gold thickness. The total quantity of As released after prolonged annealing increases linearly with gold thickness, consistent with the idea that gold becomes “saturated” with Ga with respect to solid GaAs. An attempt to correlate the As evolved with the Au-Ga phase diagram is given. The amount of arsenic evolved and the rates of evolution were the same for gold on clean GaAs and GaAlAs. Changes in the surface preparation procedure prior to gold deposition had no effect on the As evolved from the Au/GaAs contact. On the Au/GaAlAs contact, poor or no predeposition cleaning lead to reduced As evolution.

Dissociation of GaAs and Ga0.7Al0.3As during alloying of gold contact films

Experimental evidence is presented which suggests that the degradation of Au-GaAs Schottky-barriers after annealing is due to the outmigration of gallium into the gold, resulting in the formation of an n+ region beneath the contact.

Outmigration of gallium from Au-GaAs interfaces

Rapid migration of the gold electrode on C–SiOx–Au devices has been found for temperatures above the Au/Si eutectic point. Approximate concentration profiles have been determined by means of Rutherford scattering. Electrical measurements have been performed on both virgin and diffused devices. Comment is made on the relevance of electrode migration to the forming process and bistable memory switching in metal‐insulator‐metal devices.

C. J. Madams

Papers

Outmigration of gallium from Au-GaAs interfaces

Migration of gold atoms through thin silicon oxide films

Low Temperature Migration of Gold Through Thin Films of Silicon Monoxide

Low temperature migration of gold through thin films of silicon monoxide