Nanoscale Advanced Materials Engineering via Localised Ion Doping

Most advanced materials are actually composite systems where each part is specifically tailored to provide a particular functionality, often via doping. In electronic devices this may be p- or n-type behaviour (the preference to conduct positive of negative charges), in optical devices the ability to emit light at a given wavelength (such as in the infrared for optical fibre communications), or in magnetic materials the ability to store information based on the direction of a magnetic field for example. To enable the realisation of new devices it is essential to increase the density of functionality within a given device volume. Simple miniaturisation (i.e. to fit more devices of the same type but of smaller size) is limited in scope as the nanoscale regime is reached, not only by the well-known emergence of quantum effects, but by the simple capability to control the materials engineering on this scale. Self-assembly methods for example enable the creation of 0D (so called 'quantum dots' or 'artificial atoms'), 1D (wire-like) and 2D (sheet-like) materials with unique properties, but the subsequent control and modification of these is non-trivial and has yet to be demonstrated in many cases.

This research project will support the establishment of a world-leading Platform for Nanoscale Advanced Materials Engineering (P-NAME) facility that incorporates a new tool which will provide the capability required to deliver a fundamental change in our ability to design and engineer materials.

The specific objectives of the project are:
- to develop and validate the P-NAME tool capability to deliver nanoscale doping of semiconductor materials;
- to develop advanced doped materials processing methods in order to activate doped atoms and repair implantation damage;
- to develop suitable characterization protocols to study the effect of nanoscale doping;
- to demonstrate an exemplar photonic/spintronic device realized via nanoscale doping.

These objectives are to be addressed using the recently commissioned P-NAME tool that will enable high resolution imaging, doping and patterning of materials with multiple ion species at low energies and high doses to locally engineer materials, giving a unique capability for advanced materials engineering providing nanoscale functionality on demand. Ion species including B, P, As and Sb (for Si), key transition metals (e.g. Ti, V, Mn, Co, Ni) and the rare-earth ions, and other technologically important species (e.g. Pd, Pt, Bi) will be provided using liquid-metal alloy ion sources. The tool will incorporate a mass filter to enable ion species (and isotope) separation and is designed using a modular LMAIS concept to enable efficient change over between sources.

The ion dose and energy may be spatially varied to enable a wide parameter range to be accessed and studied. Ion doses will range from very low (e.g. ~10 ions) through to levels typically used to electronically dope semiconductors (1014 - 1016 ions/cm2) and higher. The ion energy range will be from 5 keV (to enable shallow doping in thin films) upwards to 40 keV. Higher energies are also available through the use of doubly charged ions etc. selected using the ExB mass filter. Dopant species may be varied and material synthesis performed in-situ on the nano-scale with an ion beam spot size of 20nm available for high-precision doping. This along with nanometer-precision sample handling and integrated ion beam control provide a IBL capability not previously available. This will enable localised ion doping of pre-deposited nanostructures and devices (e.g. nanowire pn-junctions, Si-photonics...), or of in-situ structures created using IBL.

Validation will involve the doping of test samples and study using HRTEM, THz-spectroscopy and scanning probe spectroscopy as appropriate. This will be done in collaboration with others.