Raman spectroscopy of hydrogenated amorphous carbons

Abstract

We present a comprehensive multiwavelength Raman investigation of a variety of hydrogenated amorphous carbons ͑a-C:H͒, ranging from polymeric a-C : H to diamond-like a-C : H and ta-C:H, which allows us to derive values for their bonding, density, band gap, hydrogen content, and mechanical properties. The Raman spectra of a-C : Hs show two different trends. In one case, the G peak width increases with G peak dispersion. In the second case, the opposite trend is found. In the first case, the Raman parameters vary with optical, structural, and mechanical properties in the same way as in hydrogen-free carbon films. In the second case, typical of polymeric a-C:H, the G peak width correlates with the density, while the G peak dispersion varies with the optical gap and hydrogen content. This allows a unified picture of bonding and disorder of all carbon films. UV Raman is particularly useful for a-C : Hs, as it gives clear measurements in the D and G peaks spectral region even for highly hydrogenated samples, for which the visible Raman spectra are overshadowed by photoluminescence. On the other hand, the slope of the photoluminescence background in visible Raman spectra can be used to estimate the H content. UV Raman measurements also allow the detection of C u H stretching vibrations.

Making Graphene Luminescent by Oxygen Plasma Treatment

“…An The ratio of the slope of the PL background (m) to I(G) is often used in disordered carbons as a measure of the PL strength when comparing different samples. 31 We thus plot m/I(G) in Figure 2d. This reaches a maximum, then decreases for the longest treatment, consistent with the lack of PL in ref 19 after oxygen treatment targeted at layer removing.…”

Study of a-C:H thin films grown by PIII in different times for Mechanical and Tribological applications

“…I(D)/I(G) assumes values between 0.52 and 0.80. Associating at the beginning of stage 3 (three model stage) (19) , such considerations with the prevision of moderate contents of H (< 45 %), and 20 % of sp3 sites films investigated here can be classified as a-C:H instead of polymer-like carbon. It is known that, if I(D)/I(G) results in low values, that is, if is negligible (next to 0) the sp 2 phase is mainly organized in chains.…”

“…Figure 1 shows the Raman spectra in the range of wavenumber: 800 cm -1 region for films grown in different times. All films presented the peak positioned next to 1540 cm -1 of wavenumber, typical of a-C:H films according Robertson (19) .…”

Quantifying clustering in disordered carbon thin films

“…A second measure of disorder, based upon bond angle distortion, is the full width half maximum of the Raman active G band,  G . This Raman signal is found at around 1580 cm -1 and originates from the E 2g vibration between sp 2 C bonds and is therefore present in all sp 2 C containing materials [5]. It should be noted that special care must be exercised when using single wavelength Raman measurements and there is now a growing realisation that multi-wavelength measurements are important as a measure of disorder and clustering in a-C thin films.…”

“…It should be noted that special care must be exercised when using single wavelength Raman measurements and there is now a growing realisation that multi-wavelength measurements are important as a measure of disorder and clustering in a-C thin films. For example, if two films have the same G peak position under a single visible wavelength Raman measurement, the sample with the lower G peak shift under UV Raman excitation will have the higher degree of clustering [5]. A third measure of disorder is the dispersion of G peak position with excitation wavelength.…”