Department of Physics

Time-of-Flight Elastic Recoil Detection Analysis, ToF-ERDA


Figure 1. ToF-ERD telescope with incoming beam (green), target (thin film sample), and the telescope arm with two timing detectors and energy detector.

Time-of-Flight Elastic Recoil detection analysis, Tof-ERDA is a method where normally heavy incident ion (Cl, Cu, Br, Au) is used to kick, or recoil, sample atoms off from the sample and towards the two timing gates and energy detector. If both energy and time-of-flight is measured accurately enough one can separate all masses to different 'banana' curves and form depth profile of elements (or masses) in the surface of the sample. See figure 2. for the ToF-E principle.

Figure 2. ToF-ERDA principle.

Jyväskylä's ToF-ERD telescope came online 2010 and hundreds of samples has been measured and analyzed since. Due to the relatively low incident beam energy, maximum sample depth, depending on the sample is around 100-300 nm to be depth profiled. Elemental compositionss can be however also measured from the bulk samples too, but only at the surface region. Area where ToF-ERDA excels is light element analyisis of thin films and even sub monolayer films have been analyzed with only 1,2,3 few Atomic Layer Deposition (ALD) cycles as a film. A comparison to traditional RBS measurement with 1MeV He ions can be seen at figure 3.

Figure 3. Comparison data from same sample with 3x10 nm Al2O3 layers and 2x10 nm TiO2 layer on top of Si. RBS spectra with 1MeV He on left and ToF-ERDA spectra measured with 9 MeV Cl on right.

Timing resolution measured with 5MeV He beam scattered from thin Au layer on Si is about 160ps for the current system (including beam+sample+other effects).. This is measured also for two timing gates that has been produced/sold for the University of Montreal during the 2011.


Few more examples:

Above: 8.6 nm thick Al2O3 film measured as one of the very first cases with the new ToF-ERDA system.


Above: 10 nm thick hard coating CN with different impurities.


Co-operation with different universities and research group have led many common publications, where ToF-ERD measurements have been often one of the characterization method of the thin film on question. Also small scale commercial analysis have been conducted espcially for the ALD deposited films. Contact person for ToF-ERDA is Timo Sajavaara.