Theoretical and Experimental Studies of Magneto-tunneling in Quantum Dots

We study the magneto-transport in vertical quantum dots boththeoretically and experimentally. We focus our attention onthe non-linear transport regime. We demonstrate that the peakamplitudes in the I–V characteristics show a dramaticallydifferent behaviour as a function of the magnetic field,depending on the value of the angular momentum of the dotstate through which tunnelling occurs. The investigationallows us to probe details of the quantum dot wavefunctionsand to distinguish tunnelling through localised states relatedto impurities or to quantum dots.     

Electrical properties of individual CoPt/Pt multilayer nanowires characterized by in situ SEM nanomanipulators

Here we report for the first time accurate and comprehensive measurements of electrical properties of individual CoPt/Pt multilayer nanowires both with periodic and non-periodic layer structures. A remarkably high failure current density of 1.69 × 10(12) A m(-2) for the periodic MNW and a similar 1.76 × 10(12) A m(-2) for the non-homogeneous MNW has been measured. The resistance of both types of multilayer nanowire structures are well fitted by a series resistance model, determining the separate resistance contribution of the component layers and magnetic/nonmagnetic interfaces for a single multilayer nanowire. The field-dependent interface resistance of both samples is calculated, 13.2 Ω for periodic layer structures and 4.84 Ω for non-periodic layer structures. The clear physical picture of the resistance distribution within individual multilayer nanowires is then determined. The accurate electrical testing of magnetic multilayer nanowires provides basic and necessary electrical parameters for their usage as building blocks or interconnects in nanoelectronics and nanosensors.     

Prediction of phosphate requirements of Swedish turnips from soil phosphate values

Yields from 199 field experiments, extending over about 15 seasons and covering six soil groups in northeast Scotland, were used to calculate correlation coefficients between the responses of Swedish turnips to 120 1b P₂O₅/acre and readily soluble phosphate values for the soils, determined by six methods. There were marked effects of soil parent material and drainage on the correlations, which ranged from ?0.05 to ?0.74. the Morgan and bicarbonate methods were inferior to the NH₄F-HCl, Truog, acetic and lactate methods; the last method was usually the best. By fitting a Mitscherlich equation to the yields the optimum economic phosphate dressings were calculated for four combinations of fertiliser and crop prices. the average profit from these was about 30 shillings/acre greater than from using the mean optimum rate for the soil group or from using a standard rate of 120 1b P₂O₅. Calculations and adjustments tested so far have shown no convincing benefit from using the soil values to recommend phosphate dressings for individual soils. Neither inclusion of other soil properties nor use of the logarithms of the soil phosphate values in multiple regressions produced any appreciable improvement in response predictions. The main reason for the generally rather poor correlations seems to be variations in site characteristics and agricultural factors, rather than soil chemical and textural properties, coupled with the fact that the optimum rates are not well defined. the present indications are that the main practical usefulness of the soil P values is in monitoring of the phosphate status to guide rotational manuring and ensure that adequate dressings can be given for sensitive crops, rather than in the precise prediction of optimum dressings for individual fields.     

Patterned ion beam implantation of Co ions into a SiO2 thin film via ordered nanoporous alumina masks

Spatially patterned ion beam implantation of 190 keV Co(+) ions into a SiO(2) thin film on a Si substrate has been achieved by using nanoporous anodic aluminum oxide with a pore diameter of 125 nm as a mask. The successful synthesis of periodic embedded Co regions using pattern transfer is demonstrated for the first time using cross-sectional (scanning) transmission electron microscopy (TEM) in combination with analytical TEM. Implanted Co regions are found at the correct relative lateral periodicity given by the mask and at a depth of about 120 nm.     

Electrical nanowelding and bottom-up nano-construction together using nanoscale solder

A new bottom-up nanowelding technique enabling the welding of complex 3D nanoarchitectures assembled from individual building blocks using nanovolumes of metal solder is reported in this work. The building blocks of gold nanowires, (Co72Pt28/Pt)n multilayer nanowires, and nanosolder Sn99Au1 alloy nanowires were successfully fabricated by a template technique. Individual metallic nanowires dispersed on Si/SiO2(100 nm) wafers were manipulated and assembled together. Conductive nanostructures were then welded together by the new electrical nanowelding technique using nanovolumes of similar or dissimilar nanosolder. At the weld sites, nanoscale volumes of a chosen metal are deposited using nanosolder of a sacrificial nanowire, which ensures that the nanoobjects to be bonded retain their structural integrity. The whole nanowelding process is clean, controllable and reliable, and ensures both mechanically strong and electrically conductive contacts. The quality check of nanoweld achieve a resistance as low as 20 omega by using Sn99Au1 alloy solder. This technique should provide a promising way to conquer the challenge of the integration obstacle for bottom-up nanotechnology.