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Inclusions of sp-hybridised, trans-polyacetylene [trans-(CH)x] and poly(p-phenylene vinylene) (PPV) chains are revealed using resonant Raman scattering (RRS) investigation of amorphous hydrogenated carbon (a-C:H) films in the near IR - UV range. The RRS spectra of trans-(CH)x core Ag modes and the PPV CC-H phenylene mode are found to transform and disperse as the laser excitation energy \hbar{\omega}L is increased from near IR through visible to UV, whereas sp-bonded inclusions only become evident in UV. This is attributed to \hbar{\omega}L probing of trans-(CH)x chain inhomogeneity and the distribution of chains with varying conjugation length; for PPV to the resonant probing of phelynene ring disorder; and for sp segments, to \hbar{\omega}L probing of a local band gap of end-terminated polyynes. The IR spectra analysis confirmed the presence of sp, trans-(CH)x and PPV inclusions. The obtained RRS results for a-C:H denote differentiation between the core Ag trans-(CH)x modes and the PPV phenylene mode. Furthermore, it was found that at various laser excitation energies the changes in Raman spectra features for trans-(CH)x segments included in an amorphous carbon matrix are the same as in bulk trans-polyacetylene. The latter finding can be used to facilitate identification of trans-(CH)x in the spectra of complex carbonaceous materials., Comment: 31 page, 9 figures

Diamondlike amorphous carbon films have been deposited on silicon and quartz substrates by laser ablation of graphite using 120 fs pulses from an amplified Ti:sapphire laser operating at 800 nm. Ultraviolet/visible (UV/VIS) and micro-Raman spectra of these materials have shown that the sp3-bonded carbon fraction in these films is ≈27%, 55%, and 20% when deposition occurs at substrate temperatures of 77, 300, and 573 K, respectively. The presence of sp1 chains in these films is indicated by the appearance of an excitation band at 2000–2100 cm−1 in UV-Raman spectra. We also find a remarkable increase in the Tauc energy gap calculated from in situ UV/VIS optical spectra immediately after exposure to air together with a 1 eV redshift of the C 1s core-level energy in x-ray photoelectron spectra of these samples. The properties of sp1-, sp2- and sp3-bonded components of these materials have also been studied using UV/VIS Raman spectroscopy. The enhanced stability of sp1 chains in tetrahedral carbon matrix is di...

Amorphous hydrogenated carbon (a-C:H) films were synthesised using an inductively coupled plasma reactor under varying DC substrate bias voltage. Films were characterised using nanoindentation measurements, UV (325 nm) and visible (633 nm) Raman spectroscopy. Film microhardness was found to vary from 15.2 to 18.6 GPa with harder films deposited at higher bias. While visible Raman spectroscopy is a routinely accepted technique used to study the sp 2 fraction in a-Cs, we found that it was ineffective in our instance to identify differences between the samples fabricated, as indicated by largely unchanged G peak position and D peak intensity for the selected films. UV Raman analysis revealed that the sp 3 fraction is essentially the same for all the films studied, while the sp 2 fraction was found to have higher degree of bond disorder in both aromatic rings and olefinic chains in films deposited at higher substrate bias. Furthermore, an additional peak at 1200 cm − 1 appeared in both visible and UV spectra of all films examined. We believe that the peak originates from the small, hydrogenated sp 2 sites with a narrow band gap and arranged in minute clusters. We hypothesize that the observed variation of the mechanical properties of a-C:H films are not controlled by the amount of the sp 3 fraction but are also determined by the nature of the disorder within the sp 2 -bonded fraction. a-C:H films displaying higher hardness and Young's modulus have sp 2 -bonded aromatic sites arranged in smaller domains with a higher degree of ring distortion and have sp 2 -bonded olefinic sites with higher degree of clustering. This phenomenon was observed as a result of a low temperature plasma deposition.

A comparative study of carbon bonding states and Raman spectra is reported for amorphous diamondlike carbon films deposited using 120 fs and 30 ns pulsed laser ablation of graphite. The presence of sp(1) chains in femtosecond carbon films is confirmed by the appearance of a broad excitation band at 2000-2200 cm(-1) in UV-Raman spectra. Analysis of Raman spectra indicates that the concentrations of sp(1)-, sp(2)-, and sp(3)-bonded carbon are approximately 6%, approximately 43%, and approximately 51%, respectively, in carbon films prepared by femtosecond laser ablation. Using surface enhanced Raman spectroscopy, specific vibrational frequencies associated with polycumulene, polyyne, and trans-polyacetylene chains have been identified. The present study provides further insight into the composition and structure of tetrahedral carbon films containing both sp(2) clusters and sp(1) chains.

Diamond-like carbon is a promising material for MEMS and opto-electronic systems applications. There is a notion that the hybridised sp 3 (diamond-like) fraction controls the mechanical properties and the sp 2 fraction (graphite-like) determines the electro-optical properties. We investigated amorphous hydrogenated diamond-like carbon (a-C:H) films synthesised using an inductively coupled hydrocarbon plasma reactor under varying bias. The films were characterised using UV Raman, X-ray C 1s photoelectron, N-IR spectroscopy, scanning probe microscopy (SPM) and nano-indentation measurements. We found that all examined samples displayed essentially the same amount of the sp 3 constituent, whereas the configuration of the sp 2 fraction was different. The sp 2 fraction of both aromatic rings and olefinic chains in examined films. We found that Tauc gap E t , was controlled by the perturbation of the n tail states of the sp 2 fraction. The Tauc gap E t , was determined by N-IR and surface conduction band E oi , measured by SPM changed inversely with an increase of bias. Results obtained using nanoindentation measurements show that mechanical properties such as hardness and Young's modulus increased with an increase of bias for all films studied. These results indicate that mechanical properties of a-C:H films (hardness and Young's modulus) not only controlled by the amount of the sp 3 bonding but also are determined by the degree of the sp 2 bonding arrangement.

The resonant Raman scattering in N-IR - UV range from amorphous hydrogenated carbon (a-C:H) reveal inclusions of trans-polyacetylene (trans-(CH)x) chains with approximate length of up to 120 C=C units and inclusions of poly(p-phenylene vinylene) (PPV) polymer chains. The PPV is evidenced by a strong dispersive mode at ca. 1175 cm-1. It was found that the Raman response from core Ag trans-(CH)x modes incorporated into a-C:H to changing excitation energy is identical to of free-standing chains thus facilitating identification of trans-(CH)x in complex carbonaceous materials spectra., 11 pages, 3 figures

The growth, surface morphology, and electronic binding states of diamondlike films deposited by femtosecond laser ablation on Si wafers at 77 K have been studied in order to elucidate the mechanical properties of this material. Nanoscale buckling has been observed and is found to have a morphology that exhibits a strong dependence on film thickness. Nanobuckling takes the form of quasiperiodic discrete pointlike excursions extending over widths of 50–100 nm. This morphology converts to a regular structure of grooves/ripples with a modulation period of 30–50 nm as the film thickness increases to 300–600 nm. We find that microhardness is not changed in regions where nanobuckling is present. Analysis of Raman and x-ray photoelectron spectra (XPS) demonstrate that nanobuckling can be attributed to the relaxation of internal stress and to the formation of strong C-Si covalent bonds at the C-Si interface. XPS spectra show that the C 1s peak is broadened compared to that found in spectra of films deposited using...

Microscopic phase transformation from graphite to sp-bonded carbon chains (carbyne) and nanodiamond has been induced by femtosecond laser pulses on graphite surface. UV/surface enhanced Raman scattering spectra and x-ray photoelectron spectra displayed the local synthesis of carbyne in the melt zone while nanocrystalline diamond and trans-polyacetylene chains form in the edge area of gentle ablation. These results evidence possible direct "writing" of variable chemical bonded carbons by femtosecond laser pulses for carbon-based applications.