Combination of ERDA, FTIR spectroscopy and NanoSIMS for the characterization of hydrogen incorporation in natural diamonds

Hydrogen is a volatile element involved in several geological processes ranging from rock weakening to the initiation of tectonic plates. Because it is present in diamond, the investigation of hydrogen content in natural diamonds could provide valuable information. Such studies are scarce despite hydrogen being among the main impurities in their structure. Using Elastic Recoil Detection Analysis, Fourier Transform Infrared spectroscopy and Nanoscale Secondary Ions Mass Spectrometry, we analyzed the incorporation of hydrogen in three diamonds growth habits: octahedral, cuboid and fibrous. Up to 25 wt. ppm of hydrogen was measured in some samples, placing hydrogen as the second most abundant impurity in natural diamonds after nitrogen and before boron. Comparison between the three methods indicates a difference in the main mode of hydrogen incorporation depending on the growth habit. Hydrogen is more readily incorporated in the fibrous and cuboid habits compared to the octahedral one. We also show that the incorporation of hydrogen is not correlated with the incorporation of nitrogen. Results suggest no chemical equilibration of hydrogen by diffusion through geological times and also confirm that not all hydrogen may be infrared active.