G. Mariotto

Raman spectroscopy on nitrogen-incorporated amorphous hydrogenated carbon films

Abstract Nitrogenated a-C:H films, a-C:H(N), were obtained by plasma decomposition of methane-nitrogen mixtures. The samples were thermally annealed in vacuum for 30 min at fixed temperatures between 300 and 700°C. Undoped films were implanted at room temperature with 70 keV-N+ at fluences of 6, 10 and 20 × 1016 N cm−2. The induced structural modifications were studied by Raman spectroscopy throygh the evolution of the D and G bands. The spectral evolution observed on a-C:H(N) samples shows evidence that a progressive graphitization follows the nitrogen incorporation in these films. Micro-Raman depth profile analysis indicates that the structural and modifications observed on implanted samples are due to the energy deposited by the incident ions. Thermal annealing induces the formation of graphitic domains in a-C:H(N) films.

AMORPHOUS NITROGENATED CARBON FILMS : STRUCTURAL MODIFICATIONS INDUCED BY THERMAL ANNEALING

Hard amorphous nitrogenated carbon films [a‐C:H(N)] deposited by self‐bias glow discharge were annealed in vacuum in the temperature range of 300–800u2009°C. The annealing time was 30 min. The structural and compositional modifications induced by thermal annealing were followed by several analytical techniques: secondary ion mass spectrometry (SIMS), Raman spectroscopy, Rutherford backscattering spectrometry, elastic recoil detection (ERDA), and nuclear reaction analysis. The internal stress of the films was also measured. Nuclear analyses indicate that both nitrogen and hydrogen losses occur for annealing temperatures higher than 300u2009°C. ERDA and SIMS results suggest that hydrogen and nitrogen out‐diffusion occurs by molecular transport through an interconnect network of voids. In the same temperature range, Raman scattering reveals an increase of the number and/or the size of the graphite domains. Internal stress is compressive for the as‐deposited films and changes to tensile for samples annealed at 800u2009°C...

Structural characterization of amorphous hydrogenated carbon and carbon nitride films deposited by plasma-enhanced CVD

Abstract Microstructural investigations of a-C:H and a-CN x :H films obtained by plasma-enhanced CVD were performed by means of Raman spectroscopy and positron annihilation spectroscopy (Doppler-broadening technique). Thermal gas evolution analysis has been used to gain insights about the void distribution. The effects of deposition parameters (self-bias voltage and nitrogen partial pressure in the plasma) on the film microstructure were studied. The incorporation of increasing amounts of nitrogen originates an increase in void density as well as a progressive graphitization of a-C:H films. Raman scattering from a-C:H films deposited at self-bias voltages higher than −800 V reveals a more graphitic structure of these films with respect to those deposited at lower bias.

Structural modifications in a-C:H films doped and implanted with nitrogen

Abstract The results of a study on structural modifications resulting from nitrogen incorporation into hard amorphous, hydrogenated carbon (a-C:H) films are presented. Nitrogen-doped films are produced by r.f. glow discharge deposition from CH 4 -N 2 mixtures onto silicon substrates or by 70 keV nitrogen ion implantation of a-C:H films. The films were obtained at different N 2 partial pressures ( P N 2 = 0%–50%) and bias voltages ( V b = −200 to −900 V), with a total pressure of P =8 Pa. The ion-implanted films were obtained at fluences of 4−20 × 10 16 N cm −2 . The samples were characterized by nuclear techniques (Rutherford backscattering, elastic recoil detection and nuclear reaction analysis), Raman scattering, Auger electron spectroscopy and the gas effusion method. It has been observed that nitrogen incorporation during deposition does not change the atomic density or hydrogen concentration, although the internal stress is reduced by about 40%. For the implanted samples, a depletion of hydrogen can be determined. The thickness of this depletion layer is of the order of R p . The internal stress is reduced by a factor of 5 and this is associated with the formation of an interconnected void structure.

Growth kinetics and relationship between structure and mechanical properties of a-C(N):H films deposited in acetylene–nitrogen atmospheres

Amorphous hydrogenated carbon–nitrogen films, a-C(N):H, were deposited by plasma enhanced chemical vapor deposition using acetylene–nitrogen mixtures. Film composition and density were determined by means of ion beam techniques being the film microstructure studied by infrared and Raman spectroscopies. Films were obtained with nitrogen content up to 22 at.u200a%. As for films obtained using other gas mixtures, the deposition rate showed a strong decrease upon nitrogen incorporation, although with a smaller rate. The film growth kinetic is discussed and some specific features of acetylene–nitrogen precursor gas mixtures are pointed out. A remarkable decrease on the C atom sp3 fraction was inferred for nitrogen contents higher than 10 at.u200a%, and was correlated to the film density behavior. The mechanical hardness and internal stress were relatively insensitive to low nitrogen incorporation, with a systematic decreasing behavior for nitrogen contents above 10 at.u200a%.

Carbon nitride thin films prepared by reactive sputtering: Elemental composition and structural characterization

Amorphous carbon nitride thin films (a-CNx) have been deposited onto Si (100) substrates by using a rf diode sputtering system. The films were deposited in reactive nitrogen-argon atmospheres. The partial pressure of nitrogen ranged from 0% to 100% at two different deposition pressures (Pd=2u2009Pa and Pd=8u2009Pa). The film composition was determined by ion beam techniques: Rutherford backscattering spectrometry and nuclear reaction analysis. The relative amount of carbon and nitrogen in the films is nearly independent of the nitrogen partial pressure in the reactive plasma. The maximum nitrogen content is 48 at.u2009%. The structural characterization was performed by means of Raman and infrared spectroscopies. Raman spectra revealed the presence of the D and G bands, typical of disordered carbon based materials, and a third band, at about 680u2009cm−1, also attributed to film disorder. Infrared spectroscopy results showed the D and G Raman bands, IR allowed due to the nitrogen incorporation in the carbon network, the presence of a band at 2220u2009cm−1 due to C≡N bonds, and a broadband at 3300u2009cm−1 that can be attributed to the O–H stretching of water molecules absorbed in the films’ voids. A linear correlation between the density and the internal stress of the films was also determined and the maximum values of the film density and the mechanical internal stress were measured for films deposited at 50% of nitrogen partial pressure (Pd=8u2009Pa).Amorphous carbon nitride thin films (a-CNx) have been deposited onto Si (100) substrates by using a rf diode sputtering system. The films were deposited in reactive nitrogen-argon atmospheres. The partial pressure of nitrogen ranged from 0% to 100% at two different deposition pressures (Pd=2u2009Pa and Pd=8u2009Pa). The film composition was determined by ion beam techniques: Rutherford backscattering spectrometry and nuclear reaction analysis. The relative amount of carbon and nitrogen in the films is nearly independent of the nitrogen partial pressure in the reactive plasma. The maximum nitrogen content is 48 at.u2009%. The structural characterization was performed by means of Raman and infrared spectroscopies. Raman spectra revealed the presence of the D and G bands, typical of disordered carbon based materials, and a third band, at about 680u2009cm−1, also attributed to film disorder. Infrared spectroscopy results showed the D and G Raman bands, IR allowed due to the nitrogen incorporation in the carbon network, the p...

Nucleation of Ga2O3 nanocrystals in the K2O–Ga2O3–SiO2 glass system

A multitechnique approach, consisting of x-ray diffraction, differential thermal analysis, low frequency Raman scattering from the acoustic vibrations of nanoclusters, and transmission electron microscopy associated with selected area diffraction, has been used to study the nucleation and crystallization processes in SiO2–Ga2O3–K2O glasses. The specific aim was to determine the structure and the size distribution of nanoparticles embedded in the glass matrix. It has been found that nearly spherical nanocrystals of β-Ga2O3, with a size of ∼2–3 nm, nucleate during thermal treatments at 900u200a°C. Crystallization was observed after annealing at higher temperature. The amount of the crystalline phase and the mean size of the nanocrystals increased with heat treatment, time and temperature. β-Ga2O3 was the only crystalline phase to appear in all glass samples.

Investigation on the chemical, structural and mechanical properties of carbon-germanium films deposited by dc-magnetron sputtering

Abstract Amorphous carbon-germanium films were deposited by de-magnetron sputtering onto Si substrates leading to a set of films with Ge/C ratios ranging from 0 to 2. Nuclear techniques, Rutherford backscattering spectrometry and elastic recoil detection analysis, provided both the composition and the atomic density of the films. Raman results suggest that carbon and germanium atoms are segregated into distinct amorphous domains. X-ray diffraction analysis was also performed and the results confirmed the amorphous character of the films, already determined by Raman spectroscopy. The internal stress of the films was obtained by measuring the bending of the substrates and the hardness was measured by a nanoindentation technique. These mechanical properties were correlated to the Ge content of the films; an important reduction in both hardness and internal stress with the Ge incorporation was observed.

Raman spectroscopy and scanning electron microscopy investigation of annealed amorphous carbon-germanium films deposited by d.c. magnetron sputtering

Abstract The precipitation of germanium nanocrystals in amorphous carbon–germanium films allows for the development of innovative devices, but the accurate control of both size and size distribution of Ge quantum dots in these matrices still constitutes a challenging step. In this paper, both the structure and morphology of amorphous carbon–germanium films (a-Ge 1− x C x ), deposited by d.c. magnetron sputtering onto silicon substrates and annealed in vacuum at temperatures up to 550xa0°C, are investigated by Raman spectroscopy and scanning electron microscopy. The main features of Raman spectra obtained from carbon-rich films ( x >0.43) are the D and G bands, characteristic of graphitic carbon films. The ratio between the intensities of the bands, I D / I G , increases with the annealing temperature, suggesting a progressive increase of the graphitic domains within the films. Raman spectra obtained in the low frequency region from both as-deposited and annealed germanium-rich films ( x −1 in the germanium-richest sample, and underwent annealing treatment at 550xa0°C, thus indicating the precipitation of crystalline Ge. Scanning electron microscopy analysis shows an apparently uniform nucleation of Ge crystallites at the sample surface. Microprobe Raman scattering results suggest the formation of a nearly homogeneous distribution of Ge nanocrystals in germanium-rich films annealed at 550xa0°C.

Raman spectroscopy of annealed carbon nitride films deposited by RF-magnetron sputtering

Abstract Amorphous carbon-nitrogen films deposited by RF-magnetron sputtering onto Si substrates were annealed in vacuum in the temperature range of 300–800 C during 30 min. with no sequential treatment. The films were analyzed by Raman spectroscopy, used as a probe of microstructural modifications induced by thermal treatment. The main features observed in the Raman spectra are two broad bands at ∼1360 cm−1 (D-band) and ∼ 1575 cm−1 (G-band), characteristic of amorphous carbon materials. The ratio between their intensities ( I D I G ) is found to increases with the annealing temperature. Additionally, the spectra present other two weak bands, one at ∼700 cm−1 (I700) and another at 2230 cm−1 (I2230). Normalized against the G-band, their intensities present opposite temperature dependence: I700 decreases by a factor of three, while I2230 increases by the same factor in the temperature range studied here. A strong reduction of the luminescence background with the annealing temperature is observed. These results indicate a substantial reduction of the dangling bonds accompanied by an increase of the number of Cue5fcN bonds and of the size, or the number, of the graphitic domains.