Resistance rise in ultrathin metallic wires at low temperatures

The wires, which have cross-sectional dimensions as small as 220A x 200A, are fabricated using a versatile step-edge shadowing technique. The dimensions of the wires can be precisely determined by easily-controlled fabrication parameters such as thin film thickness and shadowing angle. In order to verify the dimensions and integrity of the wires, we have developed a convenient and reliable technique for thinning the substrate. This allows nondestructive examination of the structures by high resolution transmission electron microscopy. We have used a similar technique to investigate grain sizes of thin metal films. The theoretical models for the low temperatures resistance rise in samples of reduced dimensionality are usually classed as based on one-electron localization or many-electron interaction effects. Our experimental results for copper, AuPd alloy, and nickel wires accurately confirm the proportionality to T to the -1/2 predicted by the interaction model of Altshuler, Khmelnitzkii, Larkin, and Lee. Moreover, we find that our results and the results of a careful reanalysis of the data already in the published literature give an absolute magnitude consistent within a factor of approx. 2 with the quantitative predictions of this model, using independently determined parameters. We therefore infer that interaction effects are at least as important as, and may dominate over, localization effects in all one dimensional lithographically-produced samples reported to date.