Characterization of temperature-induced changes in amorphous hydrogenated carbon thin films

Abstract

Hard hydrogenated amorphous carbon thin films were heated in vacuum to different temperatures and held at these for at least 30 min. Afterwards, the cooled-down samples were analyzed by various techniques. Strict and reproducible correlations were found between all the determined parameters and the annealing temperature. Single-wavelength ellipsometry shows that the real part of the refractive index of the films at 633 nm wavelength decreases with temperature while the extinction coefficient increases. It also shows swelling of the films with a thickness increase of about 50 % for films heated to ≈ 1000 K. The associated decrease of mass density is proportional to the decrease in refractive index. Ion beam analysis shows that hydrogen is released from the films during heating with only about 5 % of the initial H remaining after annealing at 1300 K while no significant loss of carbon can be detected. The losses of hydrogen during heating are monitored by temperature programmed desorption and they are in good agreement with the ion-beam-analysis results. Raman spectroscopy delivers evidence of aromatization of the films under heat treatment. Indication of first structural changes is found already at 600 K while the quickest changes of the refractive index, thickness, and hydrogen content with temperature occur around 850 K.

Long-term H-release of hard and intermediate between hard and soft amorphous carbon evidenced by in situ Raman microscopy under isothermal heating

“…[5] for details on the deposition method). The 0.29 and 0.32 films are hard films while the 0.37 film is intermediate between a hard and a soft film [9,10] . Note that the thick film has a larger C(sp 3 ) content than the three thin films: this is indicated by its G band position at 1540 cm -1 instead of 1522 cm -1 for the thin films, their G band widths being similar (see figure 9 in [2]).…”

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

“…10b and 10c, respectively. They both follow a simple linear law with the logarithm of the annealing time, as suspected in [17]. Note that the R coefficient is 0.97 for both the linear fit of |Disp| and b.…”

“…%, was deposited on a Si wafer on the driven electrode of a capacitively coupled radio frequency plasma (13.56 MHz) in pure methane at 2 Pa and a DC self-bias of -200V [17,76]. To vary the hydrogen content and structure, the layer was cut in several samples that were heated under 1.5 bar argon atmosphere at 500°C during t = 2, 15, 60, 120, 500, 1000 and 1500 minutes.…”

“…Due to the extremely good sensitivity on structural modifications involving sp 2 carbons, Raman spectroscopy analysis has been associated to most of the last studies on a:C-H materials [3,4,17,19,[23][24][25][26][27][28][29][30]. The reason behind this high sensitivity is the resonance phenomena between the laser wavelength excitation used and a local band gap of a given sp 2 cluster in the amorphous carbon.…”

“…The proper characterization of the hydrogen content together with the sp 2 fraction is thus of particular importance. These coatings need also to be thermally stable and changes in a-C:H local chemistry during thermal annealing have then regained an interest these last few years [3,4,[12][13][14][15][16][17][18][19][20][21][22].…”