Abstract
Microwave dielectric loss tangent measurements are demonstrated as a method for quantifying trace sp2-hybridized carbon impurities in sub-micron diamond powders. Appropriate test samples are prepared by vacuum annealing at temperatures from 600 to 1200 °C to vary the sp2/sp3 carbon ratio through partial surface graphitization. Microwave permittivity measurements are compared with those obtained using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The average particle size remains constant (verified by scanning electron microscopy) to decouple any geometric dielectric effects from the microwave measurements. After annealing, a small increase in sp2 carbon was identified from the XPS C 1s and Auger spectra, the EELS σ* peak in the C 1s spectra, and the D and G bands in Raman spectroscopy, although a quantifiable diamond to G-band peak ratio was unobtainable. Surface hydrogenation was also evidenced in the Raman and XPS O 1s data. Microwave cavity perturbation measurements show that the dielectric loss tangent increases with increasing sp2 bonding, with the most pertinent finding being that these values correlate with other measurements and that trace concentrations of sp2 carbon as small as 5% can be detected.
Highlights
Sub-micron diamonds allow the outstanding material characteristics of diamond relating to its electrical, thermal, chemical, and mechanical properties to be applied on microscopic scales
Annular dark field STEM micrographs with corresponding energy loss spectroscopy (EELS) spectra were taken for each sample at a number of positions on the particles, with the results presented here serving as a representative measurement
The C 1s peak is normally dominated by the contribution from the C−C bonds and is conventionally used as a charge reference at 284.8 eV, as explained earlier
Summary
Sub-micron diamonds allow the outstanding material characteristics of diamond relating to its electrical, thermal, chemical, and mechanical properties to be applied on microscopic scales. One of the most popular methods to examine diamond particles is X-ray photoelectron spectroscopy (XPS)because of its sensitivity to particle surfaces, its low sample volume requirement, and its ability to identify and infer carbon- and hydrogen-related terminations.[18] Carbon-based impurities can be identified in a number of ways, one of which is to observe the C 1s spectrum. Surface charging may shift the observed peak.[20] More effective methods use different regions of the XPS spectra, including the valence band region and the derivative of the C KLL Auger spectra.[10,22−24] Speranza and Laidani[22] showed that the latter case minimizes the referencing error in determining the sp2/sp[3] carbon ratio because it is a differential technique using the eV difference in maxima and minima
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
