V. Vorlicek

Hardness, intrinsic stress, and structure of the a-C and a-C:H films prepared by magnetron sputtering

Abstract The 1.5-μm thick carbon films prepared by magnetron sputtering of a carbon target in Ar, Ar +CH 4 and Ar+O 2 gas mixtures show that the higher their intrinsic stress, the higher their microhardness and the lower their resistivity. The a-C films obtained without ion bombardment (unbiased; the mean free path of sputtered C atoms larger or equal to the cathode–anode distance) show microhardness up to 25 GPa. The biased a-C films (i.e. with ion bombardment) achieve the highest microhardness (up to 50 GPa) and the lowest resistivity (0.01 Ω cm). An increase in Ar pressure, or the optional addition of O 2 , results in a decrease in the microhardness and intrinsic stress and an increase in the film resistivity. In comparison to a-C films, by adding CH 4 to Ar up to certain limit, the microhardness and intrinsic stress of these a-C:H films increase and subsequently decrease steeply. It was specified by analysis of the electron diffraction patterns of thin films (30–60 nm) deposited under the same conditions that the radius of the first co-ordination sphere of C atoms for all the films is in a good agreement with the value for graphite. The prime interplanar distance for biased a-C films is considerably lower than that for unbiased ones and for graphite. Our data indicate the sp 2 -bonded carbon structure of the deposited hard carbon films, in which the prime interplanar distance is reduced due to intrinsic stress. Thus, it is more suitable to explain the hardness origin as a consequence of the film nanostructure rather than the presence of sp 3 bonds .

Laser photolysis of liquid benzene and hexafluorobenzene: Graphitic and polymeric carbon formation at ambient temperature

Abstract ArF laser-induced liquid-phase photolysis of benzene and hexafluorobenzene afford similar products which are polyaromatic hydrocarbons or fluorocarbons with the preponderance of biphenyl or decafluorobiphenyl, graphite, and polymeric H-containing or F-containing carbon. The remarkable feature is that the graphite formation occurs at ambient temperature of the irradiated liquids; photolytic graphitization modes must therefore be different from those occurring in thermally-induced graphitization at temperatures above 2500 °C.

Quantitative study of Raman scattering and defect optical absorption in CVD diamond films

Abstract Raman spectra and sub-bandgap optical absorption measured by photothermal deflection spectroscopy (PDS) of CVD diamond films are compared and discussed in terms of the concentration of the non-diamond component. A reasonably good one-to-one correspondence is found, implying the plausibility of the recent estimate of the Raman cross-section for a-C as well as the capability of the absorption spectroscopy to identify the presence of non-diamond phase with a high sensitivity.

Ablation of various materials with intense XUV radiation

Ablation behavior of organic polymer (polymethylmethacrylate) and elemental solid (silicon) irradiated by single pulses of XUV radiation emitted from Z-pinch, plasma-focus, and laser-produced plasmas was investigated. The ablation characteristics measured for these plasma-based sources will be compared with those obtained for irradiation of samples with XUV radiation generated by a free-electron laser.

Thermal stability of microhardness and internal stress of hard a-C films with predominantly sp2 bonds

Abstract Annealing in vacuum at temperatures up to 820 °C was used to study the thermal stability of mechanical properties of magnetron-sputtered thick (approx. 1.5 μm) a-C films. A predominance of sp2 bonds was characteristic for all these films. The microhardness, internal stress, electron diffraction, Raman and optical spectra of three sets of films with different initial microhardness (H≈50, 20 and 10 GPa, respectively) were compared. Annealing of the hardest film up to 500 °C led to an increase in microhardness accompanied by a decrease in internal stress. Internal stress did not relax completely for hard films, even after annealing up to 820 °C, and the microhardness remained rather high (∼40 GPa). Both the high internal stress and the specific film nanostructure are responsible for the high microhardness of these sp2-bonded films.

CNx films created by combined laser deposition and r.f. discharge: XPS, FTIR and Raman analysis

Abstract Thin CNx films were deposited by combination of KrF pulse laser deposition with additional radio frequency discharge (13.56 MHz). Nitrogen pressure was changed from 1 to 40 Pa and the r.f. power was adjusted to 100 W. N/C ratio in films higher than 1.1 was measured by wavelength dispersive X-ray analysis. Films were amorphous. Microhardness from 2 to 9 GPa and adhesion to silicon substrate from 5 to 19 N were found. The X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectral studies indicate N-sp3 C, N-sp2 C and N-sp C bondings of nitrogen atoms with respect to carbon and the presence of NH groups. The presence of different amorphous, crystalline and polymer-like phases is discussed.

Interaction of oxygen with a-C:H, a-C films and other carbon materials

Magnetron sputtered films of a-C:H, a-C, as well as of a-COx, and glassy carbon and graphite were annealed in air and vacuum at different temperatures (up to 770 °C). The a-COx films (new type of amorphous graphite-like films) contain at most 18–22% of atomic oxygen depending on the way of their preparation. Annealing in air results in the removal of H from a-C:H films and in the incorporation of O in both a-C:H and a-C films as evidenced by IR spectra. Raman spectra show the up-shift of the G band (to approx. 1605 cm−1) in a-C and a-C:H films. Annealing of a-COx films at 770 °C in vacuum shifts the G band down to ∼1595 cm−1 and decreases oxygen content sharply down to 5 at.%. Annealing of graphite and glassy carbon in air at 600 °C does not change their Raman spectra. The electron diffraction patterns for the a-COx films are almost the same as for the a-C films, implying that oxygen occupies mainly the positions along the edges of graphite layers in every cluster and acts as an etchant. Its action decreases the intrinsic stress and leads to short-range order increase.

Carbon nitride layers created by laser deposition combined with RF discharge

Abstract The structure, composition and bonding of carbon nitride films created by pulsed laser deposition in combination with radio-frequency discharge for nitrogen activation were studied by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and by Raman spectroscopy for various deposition conditions. XPS measurements revealed a maximum N/C of ∼0.5 and an increased number of N-sp 3 C bonds for lower N/C values. FTIR and Raman spectra indicate the presence of a polymeric phase.

Influence of deposition parameters on laser ablation deposited amorphous carbon

Abstract Thin amorphous carbon films were deposited by KrF laser ablation from graphite and glassy carbon targets at different substrate temperatures with beam power density on the target of 3 × 108 W cm−2. The films were characterized by electrical resistivity, spectroscopic ellipsometry, ultraviolet transmission, visible and infrared spectra and Raman spectroscopy. The influence on film properties of substrate temperature during deposition varying from room temperature to 425°C was studied. The influence of the temperature and film thickness on the film buckling was also studied. A film resistivity of 108 Ω cm and an optical band gap energy of 1.9 eV was achieved. Raman spectra with low D band ( I D I G = 0.46 ) intensity were obtained.

ArF laser photolysis of gaseous CS2–(CH3)4Sn mixtures: gas-phase reaction between tin and sulfur and deposition of nanosized tin sulfides incorporated in a polymer network

ArF laser photolysis of gaseous (CH3)4Sn–CS2 mixtures results in chemical vapour deposition of tin sulfides (SnS and SnS2) incorporated in a network of a blend of polythiene and organotin polymers. The evidence for the tin sulfides was obtained by examination of the deposited coatings by infrared spectroscopy, Raman spectroscopy and electron microscopy. The formation of tin sulfides is explained by reaction of transiently generated Sn and S atoms. The reported results reveal for the first time that nanosized clusters of Sn and S produced in the gas phase react into tin sulfides at ambient temperature of the gas phase.