The new external microbeam facility of the Oxford nuclear microprobe and its application to problems in archaeological science

Recent developments of the extemal beam facility of the Oxford Nuclear Microprobe have led to an enhancement of the capabilities of the instrument for analysing large or sensitive objects in air with a spatial resolution of 50 to 100 (xm. Used in conjunction with the 1 pm resolution in-vacuo facility this provides a unique elemental analysis facility which is being applied to a number of archaeological problems. This paper describes briefly the capabilities of the faci lity and outlines the range of applications

A simple edge-following scanning algorithm for proton beam writing and other direct-write lithographies

The quality of the structures fabricated using proton beam writing (PBW) and other direct-write microfabrication methods is strongly influenced by the path followed by the writing beam during the exposure. In particular, it is necessary to avoid paths in which the beam makes large jumps or changes in direction close to the edges of the structure, and ideally the scan path should follow the outline of the pattern to be exposed (sometimes referred to as turtle scanning). While this is relatively easy to implement when the patterns to be created can be built up from simple geometric shapes (circles, rectangles, etc), it has not been possible to do this in the case of arbitrarily complex images, at least using software available to the PBW community. This paper describes a simple edge-following algorithm (EFA) which uses a method of spiral searching around each pixel to determine a scan path which not only optimizes the conformity of the scan path to the edges of the required pattern, but also minimizes jumps (and hence blanking time) and scan reversals which can cause artefacts due to scanning system transients. The EFA operates on a 1-bit BMP format input image file and has been implemented in the OMDAQ-3 software package (Oxford Microbeams Ltd). The paper is illustrated with examples of complex structures written using the EFA at the University of Surrey Ion Beam Centre which demonstrate enhanced edge smoothness compared with simple blanked raster scanning.</p

On the accuracy of total-IBA

"Total-IBA" implies the synergistic use of multiple IBA techniques. It has been claimed that Total–IBA inherits the accuracy of the most accurate IBA technique used. A specific example is now given of this where (in vacuo) EBS/PIXE of a glass sample uniform in depth is validated against absolutely calibrated EPMA of the same sample. The EPMA results had a mass closure gap of 2.0 ± 0.6 wt%; the full PIXE analysis determined the composition of this missing 2 wt%. The PIXE calibration was against a single certified glass sample, with uncertainties per line ~10%. Benchmarking also demonstrates ~10% underestimation of the Si scattering cross-section at proton energies ~3 MeV. But the Total-IBA determination of the silica content had a low standard uncertainty of about 2%. This is due to the strong constraints of both the chemical prior and also the mass closure properties of the EBS. Irradiation-induced sodium migration in this soda-lime glass is explored

Simultaneous molecular and elemental mapping under ambient conditions by coupling AP MeV SIMS and HIPIXE

Ion Beam Analysis (IBA) consists of a set of analytical techniques addressing elemental composition of inorganic material normally conducted using ion beams in the MeV kinetic energy range. Secondary Ion Mass Spectrometry using MeV ions (MeV SIMS) is the only IBA technique which can provide extensive molecular information about organic materials. MeV ions can be extracted into air hence offering the potential to apply MeV SIMS under atmospheric pressure. At the University of Surrey Ion Beam Centre, a fully ambient MeV SIMS setup has been developed and termed “Ambient Pressure MeV SIMS”. This AP MeV SIMS can be optimized for analysis and imaging of organic molecules. MeV SIMS relies upon electronic sputtering of the target material and this is much more efficient in insulating or organic targets, and less efficient in conducting metallic materials. PIXE, on the other hand, is efficient at providing good signals from elemental metallic systems, but does not readily provide molecular information from organics. The combination of the two techniques – preferably simultaneously with the same beam – provides useful complementary information which can readily be combined. Here we present pioneering preliminary work in simultaneous molecular and elemental imaging of a complex sample comprising of two organic species and two metallic species by combining AP MeV SIMS with Heavy Ion Particle Induced X-ray emission (HIPIXE)