Nanocrystalline diamond: Effect of confinement, pressure, and heating on phonon modes

Abstract

Micro-and nanocrystalline systems exhibit properties that differ markedly from bulk systems. Diamond, a prototypical system, demonstrates a broadening, shift, and emergence of Raman phonon modes that are believed to originate from finite-size effects. Such information should be useful in constraining confinement models developed to describe the state of these mesoscopic systems. For example, previous investigations have analyzed crystallite size and stresses in scientifically and technologically relevant environments, including chemical-vapor-deposition diamond films and diamond nanocomposites. We have experimentally measured the effect on the diamond Raman phonon modes due to confinement, pressure, and heating effects. At ambient pressure, we present Raman measurements for diamond crystallites ranging from 6 nm to 10 m, which were synthesized by both static and dynamic techniques. The Raman spectra obtained from the statically synthesized samples exhibit a characteristic strong and narrow diamond band, while those dynamically synthesized exhibit both diamond and graphiticlike features. A redshift of the diamond Raman band is observed for decreasing particle size. However, the pressure dependence of the phonon is about the same as that for the bulk system up to 30 kbar for crystallite sizes between 6 and 10 nm. Our measurements also indicate that heating effects from the incident laser dramatically affect the measured Raman spectra. This result leads us to an explanation for discrepancies among previously published results. We show that crystallite size and stress information cannot be determined without compensating for heating effects. Lastly, the phonon confinement model is able to explain the shifts of the Raman modes with size.

Increase of nanodiamond crystal size by selective oxidation

“…Metal catalyst present in the sample can further lower the oxidation temperature [12]. Even if the laser heating does not lead to oxidation temperatures, changes in the position and shape of the Raman lines are expected to occur [33]. In order to minimize heating effects induced by the laser, all Raman measurements were performed in water, as suggested in Ref.…”

Three‐Dimensional MoS2 Hierarchical Nanoarchitectures Anchored into a Carbon Layer as Graphene Analogues with Improved Lithium Ion Storage Performance

“…Furthermore, Raman spectroscopy can provide more proof of the presence of few‐layered MoS 2 nanosheets. Raman spectroscopy has been extensively used for the characterization of micro‐/nanocrystallites, including diamond, silicon, and GaAs 28–30. The clear differences between the Raman spectra of bulk and micro‐/nanocrystallites are frequency shifts and broadening of the Raman bands 30.…”

Direct characterization of nanocrystal size distribution using Raman spectroscopy

“…The method we use here could be applied to other nanocrystal systems, such as Ge, 27 SnO 2 , 48 TiO 2 , 49 and diamond. 50 The task one should achieve is the re-formulation of Eq. (11) for the particular nanocrystal system to be analyzed.…”