Advanced spectroscopic analyses on a:C-H materials: Revisiting the EELS characterization and its coupling with multi-wavelength Raman spectroscopy

Abstract

Hydrogenated amorphous carbon thin films (a:C-H) are very promising materials for numerous applications. The growing of relevance of a:C-H is mainly due to the long-term stability of their outstanding properties. For improving their performances, a full understanding of their local chemistry is highly required. Fifteen years ago, electron energy-loss spectroscopy (EELS), developed in a transmission electron microscope (TEM), was the technique of choice to extract such kind of quantitative information on these materials. Other optical techniques, as Raman spectroscopy, are now clearly favored by the scientific community. However, they still lack of 2 the spatial resolution offered by TEM-EELS. In addition, nowadays, the complexity of the physics phenomena behind EELS is better known. Here, a:C-H thin films have been isothermally annealed and the evolution of their physical and chemical parameters have been monitored at the local and macroscopic scales. In particular, chemical in-depth inhomogeneities and their origins are highlighted. Furthermore, a novel procedure to extract properly and reliably quantitative chemical information from EEL spectra is presented. Finally, the pertinence of empirical models used by the Raman community is discussed. These works demonstrate the pertinence of the combination of local and macroscopic analyses for a proper study of such complex materials.

EELS Studies on Nanodiamonds and Amorphous Diamond-like Carbon Materials

“…2 (a). This method does not require specific experimental setup and can include contributions from heterospecies [9,10]. Thus, our results provide a complete combination of Chybridization and spatial elemental analyses for shedding light on hydrogenated amorphous diamond-like carbon films.…”

“…For instance, for doped carbon nanostructures (as those of diamond family), these analyses are critical because their properties strongly depend on the chemical environment/configuration of the dopants [1-3]. Electron energy-loss spectroscopy (EELS) is an essential and powerful technique to perform such local chemical analyses [1][2][3][4].In this contribution, we will present a detailed study of the structure and local composition of nitrogen-doped ultrananocrystalline diamond (UNCD) films [5][6][7][8], hydrogenated amorphous diamond-like carbons [9] and nano-/micro-crystalline diamond films [10]. These studies have been developed combining HR(S)TEM, EELS and micro-Raman multi-wavelength spectroscopy.…”

“…Thus, our results provide a complete combination of Chybridization and spatial elemental analyses for shedding light on hydrogenated amorphous diamond-like carbon films. In particular, we will show how the deposition process induces a gradient of sp 2 ratio in the thin films and how this gradient is modified as a function of the annealing time [9].Finally, we will present our recent results on nano-and micro-crystalline diamond films [10]. We have shown strong in-depth inhomogeneities of the local chemistry in these films and we have investigated the effects of methane's excess on the evolution of the morphology, nanostructure and composition of the films [10].…”

“…In this contribution, we will present a detailed study of the structure and local composition of nitrogen-doped ultrananocrystalline diamond (UNCD) films [5][6][7][8], hydrogenated amorphous diamond-like carbons [9] and nano-/micro-crystalline diamond films [10]. These studies have been developed combining HR(S)TEM, EELS and micro-Raman multi-wavelength spectroscopy.…”

“…Thus, our results provide a complete combination of Chybridization and spatial elemental analyses for shedding light on hydrogenated amorphous diamond-like carbon films. In particular, we will show how the deposition process induces a gradient of sp 2 ratio in the thin films and how this gradient is modified as a function of the annealing time [9].…”