Compact Ion-Sources based on Surface-Patterned Atom Chips

In this project I will use recently developed techniques in laser-cooling of atoms to improve focused ion beams (FIBs).
FIBs are used across a vast range of applications; from circuit editing and defect review in the semiconductor industry, to failure analysis, sample preparation, surface analysis and much more. FIBs can be used for imaging, milling (removing material) and deposition (adding material).
The majority of FIBs currently use a gallium liquid metal ion source (LMIS) and spot sizes of < 10 nm are routinely achieved at low currents of around 10 pA.
Although FIBs using LMIS have been spectacularly successful, there are some serious limitations. For example, the spot size is fundamentally limited by the energy spread of the ions at the source and the source species is limited to gallium because of its unique combination of properties. Gallium is destructive when used for imaging but not heavy or reactive enough for many applications. Gallium implantation can also contaminate samples, causing unwanted effects.

Recently, researchers have begun to investigate using laser-cooled atoms as a source for FIB applications. By laser cooling atoms down to microKelvin temperatures and then photoionising them, we can achieve inherently low energy spreads in the neV range. Because the ultracold temperatures of laser cooled atoms result in small transverse ion velocities, we get low beam divergence and can focus the beam more tightly.
The Range of Species that could be laser-cooled is large and includes the alkali metals, alkaline earths, metastable Nobel gases and also a range of transition and rare earth metals; Al, Cr, Ag, Cd, Hg, Dy, Ho, Er, Tm, Yb, potentially opening up brand new possibilities in nanotechnology.

Although ion sources based upon laser-cooling have proven to be useful and are a candidate for real technological implementation of cold atoms physics, the sheer scale and complexity of the experiments makes embedding them into FIB systems impractical. The vacuum systems tend to be large and heavy and several laser frequencies are required for cooling and photoionisation.

I intend to use newly-developed surface-patterned (grating) atom chip technology to form the MOT for a cold ion source, thereby considerably reducing the size and complexity of the apparatus. This grating MOT ion source (GMIS) could then realistically be implemented as the ion source for a FIB system, providing an alternative to the ubiquitous LMIS.

We believe that the research outlined in this proposal will have impact through many routes, some short term and others long term:

1. Supplying highly-trained personnel

Impact will be achieved through the training of undergraduate and postgraduates.The researchers associated with the project (both MPhys project students and the DTA PGR) will gain expertise in state-of-the-art laser techniques, vacuum techniques, computer modelling, computer interfacing, and use of analysis software, in addition to generic transferable-skills training.

2. Outreach activities

We have a strong record in our research group of presenting our research to a wider community, which we will continue with this project. This will take the form of activities at science festivals, school visits, hosting school visits to the laboratory, and public lectures. We present concept of quantum and atomic physics to a variety of audiences ranging from Key stage 1 school children to the general public.The PI is a registered STEM ambassador and has received Institute of Physics outreach training.

3. Longer-term commercial impact and knowledge generation

In the field of "Quantum Physics for New Quantum Technologies" a major issues is the size and cost; thus there is a drive for simplification and miniaturization of devices. In the context of this work this means using simple and compact cold atom sources. There already exist many devices which seek to exploit miniaturized cold atom technology, including frequency references, magnetometers, gyroscopes, frequency stabilization and atomic sensors for accelerometers and gravimeters. We add focused ion beams to this list and will be mindful of opportunities to exploit any potential industrial applications of our research using Durham Business and Innovation Service (DBIS)
By extending the possibilities of charged particle beams to include new species and energy ranges, new applications in material sciences are highly likely.