9 g/cm3, which is thinner than the estimated value. Figure 3 RBS spectra of Ni/SiO2/Si with incident 2.86 MeV Li 2+ . With regard to depositing Ni film onto silica but not silicon substrate, it was

reported that the silicon oxide at a thickness of 300 nm can enhance scattered signals of Raman resonance spectrum drastically because photon can evoke continuous interferences at the interface between Ni and silica [20]. All the matrixes were implanted with the same dosage at 8 × 1015 cm−2 by ion implantation consisting of different cluster sizes at 20 keV. After implantation, these samples were annealed from room temperature to 900°C and dwell time was 60 min, then cooled down to room temperature naturally at 2.0 torr. Raman spectroscopy is always employed as one of the powerful non-destructive methods to identify ZD1839 research buy graphene and determine the layer of graphene [15, 21]. In this PR-171 study, Raman scattering was excited by an Ar laser at 514 nm and the power at the sample is below 1 mW for avoiding radiation damage. Figure 4 shows Raman spectra of the samples. For 514-nm wavelength laser, D peak position at 1,350 cm−1 is relative to the disorder and defects in the structures performing sp3 hybridization of carbon atoms, while sp2 hybridization induced by the in-plan optical phonon E2g near the first Brillouin Zone center is characterized as G peak at 1,580 cm−1[22]. The 2D peak position

at 2,700 cm−1 of graphene is single and symmetrical

to characterize monolayer. These samples were implanted with the same dosage of 8 × 1015 carbon atoms/cm2 at 20 keV by the different small carbon cluster find more sizes (C1, C2, C4, C6, C8). Almost the three characteristic peak positions appear, and every peak position for different cluster sizes has also negligible shifts, as shown in Figure 4. In most literatures, 2D peak position at 2,700 cm−1 and I G/I 2D (the intensity ratio of G peak and 2D peak), which is the smaller and thinner film that can be obtained, were also evaluated to differentiate from graphite and confirm the layers of graphene sheets [20]. The range of 2D peak position is 2,704 to 2,709 cm−1 in the spectra, corresponding to three and more layers. A visualized trend is observed that I G/I 2D decreases as carbon cluster size increases, described in Figure 5. There is a drastic decline for small clusters C1 to C4, meanwhile larger clusters C4, C6, C8 are presenting a relatively gradual shrink. In the case of such low-energy ion implantation, light cluster can penetrate into deeper sites than heavy cluster in the substrate, which is dependent on the energy distribution of cascade collision between cluster and matter. Figure 4 Raman spectra of the samples implanted by the different kinds of carbon clusters C n ( n  = 1, 2, 4, 6, 8). Figure 5 The intensity ratio I G / I 2D as functions of the mass small carbon cluster.