Analysis of Optical Fibres Using FIB-SEM and ToF-SIMS
Optical fibres are the backbone of the National Broadband Network (NBN) and high speed network connections due to their fast data transfer rates over long distances, especially when compared to copper cables. Our society in general is becoming increasingly reliant on high speed communications for many aspects of day-to-day life that are now commonplace. They are also used in a host of other applications such as sensors and lasers, resulting in the even more widespread usage of optical fibres.
Chemistry of an Optical Fibre
While basic optical fibres are based on thin silica fibres or polymers, others are more specialised and require doping with precise amounts optically active elements. The concentration of these dopants across length and cross section of the fibre can affect their properties.
Chemical Analysis of Optical Fibres
To accurately measure the low dopant concentration, only highly sensitive techniques with high spatial resolution such as ToF-SIMS (Secondary Ion Mass Spectrometry) are suitable. The small fibre diameter (typically 5 to 10µm) and non-conductive nature of the fibres make ToF-SIMS integrated on a FIB-SEM the ideal analysis and imaging tool. In this scenario, the (Ga+) FIB is used to ionise the sample and electrons from the SEM column are used for imaging and charge compensation. The detection limit (sensitivity) of the analysis could be improved if a plasma source was used instead of Ga, however, better sensitivity will be obtained at the expense of slightly poorer spatial resolution (~100 nm)
ToF-SIMS Integration with FIB-SEMs
System like the TESCAN LYRA, S8000G or S9000G are perfect examples of Ga FIB-SEMs that cater for ToF-SIMS integration. The SEM with large field of view allows rapid location of areas of interest and imaging. The FIB also enables depth profiling to be carried out on the samples in situ providing an added analytical dimension.