Microwave properties of nanodiamond particles

Abstract

International audienceThe dielectric properties of nanodiamond powders were characterised at microwave frequencies using a cavity perturbation technique, and results were compared with UV Raman spectroscopy. Surface sp2 hybridisation in the nanodiamond samples was varied by subsequent oxygenation and hydrogenation. Dielectric polarisation and loss increased as the sp2 hybridisation was increased. The sensitivity to surface bound sp2 carbon obtained by the microwave cavity technique far exceeds that of comparable techniques (such as Raman spectroscopy) and is much more convenient in practice, lending itself to studies of real-time modification of such powders by external influences (such as temperature and chemical functionalisation).VC 2013 AIP Publishing LLC

Microwave determination of sp2 carbon fraction in nanodiamond powders

“…Sample Quartz Tube Hollow Cavity Details of this system are explained elsewhere [9]. The inner radius of the cavity has been chosen (46 mm) so that the TM 010 mode resonates at 2.5 GHz (2.49 GHz in practice) and the TM 020 mode at 5.73 GHz (5.72 GHz in practice).…”

“…Carbon black (which is almost fully sp 2 hybridised) is well known to exhibit very large microwave absorption [8,9]. Conversely, the cubic covalent bond structure of fully sp 3 hybridised carbon within the nanodiamond cores give rise to a very low microwave absorption.…”

“…Uncertainties in sample volume limit MCP for intrinsic powder measurements though as long as there is a clear difference in microwave absorption, detection can be done. We anticipate measuring a lower Q when more sp 2 carbon is present due to the much larger microwave absorption of sp 2 compared with sp 3 carbon [9]. Extraction of complex relative permittivity from Eqs.…”

Radio Frequency‐Based In Situ Determination of the Mass Loss of Supported Ionic Liquids

“…2.3. a diameter of 184 mm and a height of 80 mm. The cavity aspect ratio, which is defined by the ratio of the resonator height to the resonator radius, is low enough to avoid overlaps with other modes, whereas the vertical homogeneity of the electric field is retained [19].…”

Microwave Characterization of Activated Carbons

“…For microwave dielectric property measurements using microwave cavities, cavity perturbation analysis is used to calculate the complex permittivity by measurements of the resonant frequency shift and the change of quality factor on inserting the sample in the cavity resonator, with high Q for the host cavity desirable for accurate results [5] [9] [10].…”