**3. Mechanical and tribology properties**

As we know, thanks to the unique topological structure, fullerene, predicted by Ruoff [44], have higher hardness than diamond, and have confirmed by other groups(is C60 fullerite harder than diamond). Vadim V. Brazhkin has synthesized a new nanomaterial by hightemperature treatment of fullerite C60 at moderate (0.1–1.5 GPa) pressures attainable for large-volume pressure apparatus, which show a high (90%) elastic recovery and fairly hardness of about 10–15 GPa [45]. It is noteworthy that in our works, so-called FL-C:H films with curved graphenes show a elastic recovery (≥80) with hardness variation from 10 to 30 GPa, depending on the growth conditions. **Figure 5** shows typical load-displacement curve and friction coefficients as function of time. A superlubricity phenomenal is observed at load of 20 N with friction coefficient at 0.009. One can notice the elastic recovery value variation with the annealing temperatures and shows the highest recovery value as shown in **Figure 6**. It is easily understood if one employs pentatomic-heptatomic theory of Raman [27, 28]. At 300°C, films show the maximum of odd rings which indicates that the most value of curved graphene exiting inside the carbon amorphous matrix.

Different from the single-way variation of the influence of duty cycle, the change of mechanical properties has a yielding point. As shown in **Figure 8**, the FL-C:H film grown at H2

**Figure 6.** Mechanical properties of the FL-C:H film before and after annealing: (a) Hardness, and (b) Elastic Recovery.

(All films were annealed for 1h in Ar at temperature of 200, 300 and 400°C, respectively).

**Figure 5.** Typical load-displacement curve for the 1500 nm thick FL-C:H film annealed at 300°C, the inset is the loaddisplacement curve of 500 nm thick typical hydrogenated carbon films (a-C:H) (a) and tribological tests on the FL-C:H

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film in air with 20% relative humidity at ambient temperature (b).

rate 5 SCCM show the lowest friction coefficient. Raman spectrum is employed here to quantify the odd member rings from both films and corresponding debris. It is showing that the friction coefficient has a significantly positive relation with odd member rings. That is, odd member rings confirm more fullerene-like structures which in turn, determine the hardness and tribology. So there is no excuse that fullerene-like structures contribute to mechanical and

To reveal how such structure affects on the tribology properties, X-ray diffraction (XRD) analysis has been performed at the original surface and wear debris and tracks of the FL-C:H films. The film pattern shows three peaks at about 2*θ* = 69.1°, 33° and 22.4°. The two peaks at 2*θ* = 69.1° and 33° are from the silicon substrate ([004] and [002], respectively (**Figure 9**)). A

tribology properties.

flow

As discussed above, it is obvious that elastic recovery and friction properties are correlated with inner nanostructures of FL-C:H films. To confirm this, we also studied the elastic recovery and friction properties using the films growth under different duty cycles and H2 flow rates. As we have already confirmed that lower duty cycle means more fullerene-like structure due to the long relaxing time. So the lower duty cycle declares that lower growth rate of the films thickness (**Figure 7** inset). One can also confirm that the hardness and the elastic recovery decrease with the decay of fullerene-like structure, as the decrease of odd member rings (**Figure 6**).

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Atmosphere influence on the nanostructures of FL-C:H films have been studied widely.

[29–33]. Interestingly, the growth of FL-C:H films show a conflicting to Hellgren's work [43] that intentional hydrogen addition to the discharge will terminate potential bonding sites for CNx precursors and hinder the growth of fullerene-like structures. But it seem that during growth FL-C:H films, hydrogen atoms during the deposition process may affect the produc-

much help on growing fullerene-like structures, so the effects of hydrogen need to be studied

At low fluorine content, many C sites bond to neighboring C and the films microstructure displays lots of well organized graphite-like and fullerene-like fragments. But as the amount of F incorporated in the network increase, F-terminated large rings, Branches and chains with

sites densify and start to interact with each other and features like interlocking pore and

As we know, thanks to the unique topological structure, fullerene, predicted by Ruoff [44], have higher hardness than diamond, and have confirmed by other groups(is C60 fullerite harder than diamond). Vadim V. Brazhkin has synthesized a new nanomaterial by hightemperature treatment of fullerite C60 at moderate (0.1–1.5 GPa) pressures attainable for large-volume pressure apparatus, which show a high (90%) elastic recovery and fairly hardness of about 10–15 GPa [45]. It is noteworthy that in our works, so-called FL-C:H films with curved graphenes show a elastic recovery (≥80) with hardness variation from 10 to 30 GPa, depending on the growth conditions. **Figure 5** shows typical load-displacement curve and friction coefficients as function of time. A superlubricity phenomenal is observed at load of 20 N with friction coefficient at 0.009. One can notice the elastic recovery value variation with the annealing temperatures and shows the highest recovery value as shown in **Figure 6**. It is easily understood if one employs pentatomic-heptatomic theory of Raman [27, 28]. At 300°C, films show the maximum of odd rings which indicates that the most value of curved

As discussed above, it is obvious that elastic recovery and friction properties are correlated with inner nanostructures of FL-C:H films. To confirm this, we also studied the elastic recovery and friction properties using the films growth under different duty cycles and H2

rates. As we have already confirmed that lower duty cycle means more fullerene-like structure due to the long relaxing time. So the lower duty cycle declares that lower growth rate of the films thickness (**Figure 7** inset). One can also confirm that the hardness and the elastic recovery decrease with the decay of fullerene-like structure, as the decrease of odd member rings

, introducing in growth process have different effects

preferentially etches the plane's sp2

show different influence on the nanostructures of the FL-C:H films.

leads to the introduction

existing in growth condition has no

phase and

flow

and CF4

tion of odd rings by two competing ways: (1) stress induced by H+

destroys the bond basis if forming odd rings. But more H<sup>2</sup>

amorphousness strongly prevail in the nanostructure [30, 32].

**3. Mechanical and tribology properties**

graphene exiting inside the carbon amorphous matrix.

Heterogeneous gases, such as H<sup>2</sup>

in detail. However, CF4

sp<sup>2</sup>

(**Figure 6**).

of odd ring into flat graphene plane; (2) H<sup>+</sup>

100 Fullerenes and Relative Materials - Properties and Applications

**Figure 5.** Typical load-displacement curve for the 1500 nm thick FL-C:H film annealed at 300°C, the inset is the loaddisplacement curve of 500 nm thick typical hydrogenated carbon films (a-C:H) (a) and tribological tests on the FL-C:H film in air with 20% relative humidity at ambient temperature (b).

**Figure 6.** Mechanical properties of the FL-C:H film before and after annealing: (a) Hardness, and (b) Elastic Recovery. (All films were annealed for 1h in Ar at temperature of 200, 300 and 400°C, respectively).

Different from the single-way variation of the influence of duty cycle, the change of mechanical properties has a yielding point. As shown in **Figure 8**, the FL-C:H film grown at H2 flow rate 5 SCCM show the lowest friction coefficient. Raman spectrum is employed here to quantify the odd member rings from both films and corresponding debris. It is showing that the friction coefficient has a significantly positive relation with odd member rings. That is, odd member rings confirm more fullerene-like structures which in turn, determine the hardness and tribology. So there is no excuse that fullerene-like structures contribute to mechanical and tribology properties.

To reveal how such structure affects on the tribology properties, X-ray diffraction (XRD) analysis has been performed at the original surface and wear debris and tracks of the FL-C:H films. The film pattern shows three peaks at about 2*θ* = 69.1°, 33° and 22.4°. The two peaks at 2*θ* = 69.1° and 33° are from the silicon substrate ([004] and [002], respectively (**Figure 9**)). A

**Figure 7.** Hardness and elastic recovery of the as-prepared films with different pulse duty cycles. Inset show the growth rate of the as-prepared films with different pulse duty cycles. (Reproduced from Ref. [42] with permission from the Royal Society of Chemistry).

Besides, the affects of F incorporation, the humidity, variation of load, plasma process, etc., on the tribology properties of FL-C:H films were widely studied [21, 23–27]. Unfortunately, though the introducing of F atoms in carbon matrix is active hydrophobicity properties, and destroys the fullerene-like structures via terminating [30–32]. But humidity has a great influence on friction coefficients that, with increasing the humidity, the friction coefficient increases quickly to 0.08 at 50% for humidity. HRTEM results show that the onion-like nanoparticles in the debris are restrained: from spherical shell structure below 30% humidity to short curved

**Figure 9.** Experiment XRD patterns from the film and wear debris showing that the debris has a structure analogous to that of C60, far from that of nc-graphite. (Reproduced from Ref. [45] with permission from the Royal Society of

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Benefit from unique bulk structures of FL-C:H films, some of well shelled graphene assemble nanoparticles are discovered on the friction interface. Thus, one can speculate that the main reason to the superlubricity is based on the bulk of fullerene-like structure which provides the

graphene dispersed in amorphous matrix [26].

**4. Superlubricity mechanisms**

Chemistry).

**Figure 8.** Friction coefficient and odd ring fraction of the FL-C:H films as a function of the gas flow rate of H2 . All the central wear tracks (WK) have a higher odd (pentagonal and heptagonal) carbon ring fraction than that of the originally deposited surfaces (OS). (Reproduced from Ref. [45] with permission from the Royal Society of Chemistry).

weak peak at 2*θ* = 22.4°, according with other studies [46], can be attributed to fullerene-like or onion-like nanoparticles (considering HRTEM and Raman results). And after friction testing, the peak at 2*θ* = 22.4° become prominent, accompanying with a new band at 2*θ* = 15° which arise from fullerene-like or onion-like nanoparticles, which leads low friction and small wear in open wear.

**Figure 9.** Experiment XRD patterns from the film and wear debris showing that the debris has a structure analogous to that of C60, far from that of nc-graphite. (Reproduced from Ref. [45] with permission from the Royal Society of Chemistry).

Besides, the affects of F incorporation, the humidity, variation of load, plasma process, etc., on the tribology properties of FL-C:H films were widely studied [21, 23–27]. Unfortunately, though the introducing of F atoms in carbon matrix is active hydrophobicity properties, and destroys the fullerene-like structures via terminating [30–32]. But humidity has a great influence on friction coefficients that, with increasing the humidity, the friction coefficient increases quickly to 0.08 at 50% for humidity. HRTEM results show that the onion-like nanoparticles in the debris are restrained: from spherical shell structure below 30% humidity to short curved graphene dispersed in amorphous matrix [26].
