Surface-enhanced Raman scattering (SERS) of Methyl Orange on Ag-DLC nanoparticles

Surface-enhanced Raman scattering (SERS) of Methyl Orange on Ag-DLC nanoparticles

Materials Chemistry and Physics 242 (2020) 122559 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.el...

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Materials Chemistry and Physics 242 (2020) 122559

Contents lists available at ScienceDirect

Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys

Surface-enhanced Raman scattering (SERS) of Methyl Orange on Ag-DLC nanoparticles Arezou Zarei, Azizollah Shafiekhani * Physics Department, Alzahra University, Vanak, Tehran, 1953833511, Iran

H I G H L I G H T S

� Ag nanoparticles were synthesized in DLC on glass substrates. � Sensitivity of SERS increased by Ag-DLC. � Such substrates can be used for several times. � This type of Ag-DLC could be used as biosensor. A R T I C L E I N F O

A B S T R A C T

Keywords: Surface-enhanced Raman scattering (SERS) Methyl orange (MO) Diamond-like carbon Ag nanoparticles

In the present study, Ag nanoparticles were synthesized in amorphous hydrogenated carbon films on glass substrates by RF-PECVD and RF-sputtering co-deposition method at the room temperature. Methyl orange was utilized as an analyte with different concentrations on Ag nanoparticles that were embedded in diamond-like carbon (DLC). Ultraviolet–visible (Uv–vis) spectroscopy, XRD analysis, Raman spectroscopy, Atomic Force Mi­ croscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM) were performed to characterize films. Ag-DLC with an average size of less than 14 nm was the active site for surface-enhanced Raman scattering (SERS). Sensitivity of measurements in SERS spectra was increased by these types of thin films. This method of nano-particle synthesis is cost-effective and just requires a one-step synthesis. Such substrates can be used for several times. Moreover, they are useful for biosensors because of their hardness and other properties that may be subsequently referred.

1. Introduction The efficient Raman scattering was first introduced by Fleischmann et al., in 1974 resulting in an increase in the sensitivity of Raman signals to six orders of magnitude. This phenomenon was partly explained by Jeanmaire et al. and Crieghton et al. who independently reported similar results on the roughened silver electrode in 1977. The effect was later called the Surface Enhanced Raman Scattering (SERS) [1,2]. All theories are divided into two mechanisms namely the electromagnetic enhancement and chemical enhancement. In the first explanation, an analyte is adsorbed or is held the neighbour of a metal surface leading to an interaction between the analyte and the plasmon that is called the electromagnetic enhancement. The surface plasmon excitation largely increases the experienced local field by the molecule that is absorbed on the metal surface. The molecule is then bathed in a very freely-moving electron cloud intensifying the polarization of surface electrons.

Electrons of the analyte molecule are adsorbed on the surface interact making greater polarization around the molecule by this cloud. In other words, the adsorbate chemically bonds to the surface. Excitation is then performed by transferring electrons from metal to molecule and back to the metal. This phenomenon is called the charge transfer or chemical enhancement. Consequently, new excited states appear due to the possibility of charge transfer and local changes in the electron charge density near the surface. Therefore, if vibrational states of an analyte change, the analyte polarization will be altered [3]. MO is a dipole molecule, and when it is adsorbed on the surface, its positive charges will be placed on the surface to neutralize negative ones. Number of electrons then decreases and charge transfer occurs. M.Z. Si et al., who produced Ag colloids by an electrolysis method, could achieve enhancement peaks of Raman scattering using Methyl orange (MO) (2.5 � 10 5 M) as an analyte [4]. Ya Lu et al. synthesized Flower-Like Ag nanoparticles by chemical reduction of AgNO3 as an

* Corresponding author. E-mail address: [email protected] (A. Shafiekhani). https://doi.org/10.1016/j.matchemphys.2019.122559 Received 1 December 2018; Received in revised form 17 July 2019; Accepted 13 December 2019 Available online 13 December 2019 0254-0584/Published by Elsevier B.V.

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Materials Chemistry and Physics 242 (2020) 122559

analyte using Rhodamine (R6G) at 10 7 M. They estimated enhance­ ment factor (EF) for SERS detection of R6G at 1.3 � 105 [5]. Me�skinis et al. deposited diamond-like carbon (DLC): They grew Ag films by reactive unbalanced direct current (DC) magnetron sputtering and used different concentrations of silver nanoparticles as analyte in order to compare G line intensities in 2016 [6]. Due to tribological properties of DLC, it is often resistant to adhesive and scratcher friction. DLC film properties include the high hardness, high optical band gap, high electrical resistivity and low friction. It is also chemically inert and neutral. It is the most cost-effective and readymade synthesis method. DLC is a meta-stable carbon that is produced as a thin coating with a broad range of structures (primarily amorphous with various sp2/sp3 bonding ratios) and compositions (various hydrogen concentrations). Amorphous DLC (a-c) and hydrogenated DLC (a-c: H) are two similar categories of DLC. Hydrogenated DLC is amor­ phous, but it contains a variable and appreciable amount of hydrogen (up to fifty atomic percent) [7]. RF sputtering and RF-PECVD co-deposition has been utilized to de­ posit Ag nanoparticles that are embedded in DLC on glass substrates. It is an appropriate way to produce biosensors with high hardness. The calibration of peaks proves that such devices have reliable responses.

Table 1 The values of RMS roughness, average roughness and the mean grain size of AgDLC nanoparticles which were obtained with atomic force microscopy.

AgDLC

RMS rough (Sq) (nm)

Average rough (Sa) (nm)

Mean grain size (nm)

4.725

3.676

13.2

measured area, and RMS roughness (Sq) means the square root of the surface height distribution. Sa was about 3.676 nm for Ag-DLC indi­ cating the variety of size distribution of nanoparticles. FESEM analysis (MIRA3 TESCAN system) was performed to measure sizes of nanoparticles and the cross section of an Ag-DLC sample. As shown in Fig. 2(a), two nanoparticle sizes, which were chosen by chance, confirmed results of Fig. 1. Fig. 2(a) shows the aggregation of nanoparticles and the presence of hotspots. The cross section of layer (Fig. 2(b)) was about 212.98 nm. Fig. 3 shows the Uv–vis spectroscopy of Ag nanoparticles at 21 ms. In this figure, the localized surface plasmon resonance (LSPR) of Ag nanoparticles is demonstrated at 525.76 nm. In Fig. 3, the peak intensity refers to the amount of radiation that is adsorbed by samples. This height is calculated using the Beer’s law. SPR is constituted when free electrons of Ag nanosphere pair collectively oscillate in resonance with the inci­ dent light [10]. It has significant application in molecular sensors because of its high electromagnetic enhancement field on metallic nanostructures [11]. Uv–Vis spectroscopy also shows the size variety (the effect of quan­ tum confinement) [12]. As shows in Fig. 2, the FWHM of amorphous Ag nanoparticles was much higher than an expected amount. FWHM of absorption peaks of Ag-DLC nanoparticles was about 213.744 � 2.3 nm. For substrates, with LSPR peaks in a visible region, the surface enhanced Raman scattering (SERS) should be done with an excitation wavelength near a LSPR peak in order to strongly enhance the incident and scattered photon [13,14]; hence, we chose a green laser (532 nm) [see Fig. 7]. Fig. 4 shows the grazing XRD spectra (λ ¼ 1:540598 Å) of Ag-DLC by means of X-ray apparatus (Philips PW 1730 system). XRD refers to a cubic structure related to Ag with (100) preferred orientation. Table 2 presents the crystallite size, micro-strain and dislocation density of AgDLC films which are obtained from XRD spectra (the method is explained at [15]). The reason for peak broadening might be attributed to micro strains due to the dislocation of nanoparticles leading to decreased phonon lifetime in Raman spectroscopy [16]. Size distribu­ tion of nanoparticles is the second probability of peak broadening. The low intensity is because of a low amount of Ag in DLC matrix.

2. Experimental section 2.1. Deposition of Ag nanoparticles by hydrogenated diamond-like carbon Ag-DLC films were deposited on a glass substrate (1 cm � 1 cm) through the co-deposition of RF-sputtering and RF-PECVD methods from silver (99.9% purity) target and the 18 sccm of acetylene (C2H2) gas. Nanoparticles were synthesized by a capacitive coupled RF system with the power supply of 13.56 MHZ. The chamber was evacuated to an initial pressure of nearly 10 3 mbar prior to the deposition. The pressure then increased to an arbitrary amount of acetylene gas flow. The applied RF power was 90 W for 30 min [8,9]. The present study focused on SERS experiments that were conducted with the Ag-DLC substrate and MO analyte with a green Laser (AvaRaman-532 nm, Avantes). 2.2. Characterization of Ag-DLC nanoparticles Fig. 1(a)-(b) show typical AFM (FemtoScan model) image of Ag-DLC in order to estimate sizes of nanoparticles. According to Table 1, samples containing silver nanoparticles had a mean size of about 13.2 nm. The scan size was 1 � 1 μm2 for all images. Grain size, average roughness and root mean square (RMS) roughness are important pa­ rameters in determining the surface morphology of a film. The average roughness (Sa) is the mean height, which can be calculated in the entire

Fig. 1. a) AFM image of Ag-DLC nanoparticles. The scale was 600 nm (b) Size distribution of Ag-DLC. 2

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Materials Chemistry and Physics 242 (2020) 122559

Fig. 2. a) FESEM image of Ag-DLC nanoparticles and (b) Cross section of the film which is about 212.98 nm. The scale was 200 nm.

Fig. 3. Absorption spectrum of Ag-DLC nanoparticles. Integration time was 21 (ms).

Fig. 4. Grazing XRD spectrum of Ag-DL. Table 2 The crystallite size, micro-strain and dislocation density of Ag-DLC films which are obtained from XRD spectra.

3. Discussion Various concentrations of MO aqueous solution were prepared (9.470 � 10 3, 8.248 � 10 3, 7.026 � 10 3 and 6.110 � 10 3 M). These concentrations were separately dropped on Ag nanoparticles by a pipette [see Fig. 5]. Fig. 6 shows the LSPR peak shift in terms of concentrations. The peak shift was due to structures of samples and their surrounding chemical environment. Raman spectra of Ag-DLC nanoparticles and Methyl Orange (1.43 M) were separately recorded as the references. Ag substrate was not Raman active, but Fig. 7, which is compatible with Ref [6], shows the breathing mode vibrations of sp2 bonded carbon rings (D line) 1342.10 cm 1 and the stretching vibration mode of sp2 bonded Carbon (G line) 1537.19 cm 1. Aromatic rings created modes at 870.61 and 1270.57 cm-1 1867 – O [3]. 1183.30 cm 1 and 1463.89 cm 1 are cm 1 is assigned to C– attributed to transpolyacetylene vibrations (they are obvious in

Sample

Crystallite size (D111) (nm)

Micro- strain (ϵ111) (%)

Dislocation density (δ111 ) (nm 2)

AgDLC

12.4

0.87

0.0065

nanocrystalline diamond films) and CH (CH3 or COO), respectively [17–19]. Two AgO vibrations are at 214 cm 1 and 283.99 cm-1 Ag2O peak is at 480.65 cm 1, while 810.62 cm 1 is assigned to both of them [20]. The downshift and broadening of the Raman peak (1537.19 cm 1) is mainly related to the phonon confinement effect for NPs of 16 nm diameter [21]. MO peaks of Raman spectrum at 1.43 M were as follows in the experimental method: 837.99 cm 1, 914.90 cm 1, 1001.43 cm 1, 3

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Materials Chemistry and Physics 242 (2020) 122559

1051.90 cm 1, 1119.20 cm 1, 1164.87 cm 1, 1217.74 cm 1, 1311.48 cm 1, 1371.57 cm 1, 1424.45 cm 1, 1482.13 cm 1, 1542.21 cm 1, 1599.90 cm 1, 1664.79 cm 1, 1693.64 cm 1, 1741.71 cm 1, 1845.06 cm 1, 1881.11 cm 1 and 1936.39 cm 1 (See Fig. 8). According to Ref. [4], a band at 1128.00 cm 1 due to νðPh NÞδðC HÞ is seen at 1135.15 cm 1 in Raman spectrum. νðPh NÞδðC HÞ is related to 1128.00 cm 1 at calculated results and 1119.20 cm 1 in experimental results. 1179.00 cm 1 referred to νðPh NÞδðC HÞ in experimental results, and the stretching mode was at 1164.87 cm 1. νðC CÞδðC HÞ Stretching vibration appeared at 1302.00 cm 1 in Ref. [4], but it was 1311.48 cm 1 in experiments. The band at 1362.00 cm 1 in computational results was at 1371.57 cm 1 in experiments referring to νðN ¼ NÞνðC CÞδðC HÞ. νðC CÞ at 1430.00 cm 1 was the stretching mode in computational results, but it was at 1424.45 cm 1 in experimental results. 1557.00 cm 1 in Ref. [4] was for the stretching vibration of νðC CÞδðC CÞ, but it appeared at 1542.21 cm 1 in experimental results. Peaks at 1599.90 cm 1 and 1664.79 cm 1 referred to νðC CÞδðC CÞ. The peak at 914.90 cm 1 indicated the presence of νðC CÞMe group [3]. The band at 1048.14 cm 1 attributes to aromatic rings. Raman spec­ troscopy of the various concentrations of MO aqueous solution (9.470 � 10 3, 8.248 � 10 3, 7.026 � 10 3 and 6.110 � 10 3 M) on the glass substrate were recorded (Fig. 9). As seen, the less concentration, the higher intensity. Our experimental results are clearly coincident with reported results. The SERS spectra of Ag nanoparticles were obtained by dropped different concentrations of MO on these substrates (see Fig. 10). Peak shift towards lower or higher wavenumbers in Raman spectra was related to chemical bond lengths of the analyte. The shorter bond length of MO causes the shift to higher wavenumber and vice versa. Accordingly, if the chemical bond length of MO changes, we will have a Raman shift [3]. The peak height of SERS is a function of concentration, thickness, laser power, wavelength, scan count, the orientation of samples and other analytical conditions. Moreover, any molecule in a SERS-active hot spot indicates an enormous enhancement in its Raman scattering signals [22,24]. The Raman spectra depend on clustering of a sp2 phase, bond length and bond angle disorder, the presence of sp2 rings or chains and sp2/sp3 ratio as well [23]. Table 3 shows the highest peak shift (1371.57 cm 1) of MO. We had the least shift at 8.248 � 10 3 M. The maximum area under the highest

Fig. 5. The schematic of putting MO on the Ag-DLC substrate. The structure of MO and DLC are shown in this figure.

Fig. 6. Absorbance peak shift of MO on Ag-DLC nanoparticles in terms of concentration.

Fig. 8. Methyl Orange Raman peaks at 1.43 M. (For interpretation of the ref­ erences to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 7. Raman spectroscopy of Ag-DLC nanoparticles. 4

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constantly increased. Each experiment was repeated to reduce probable errors in the concentration measurement, peak intensity verification, and environment thermal fluctuations despite considering the minimum time (1 min) for the spectroscopy. Amounts of experimental errors were �5.214, �5.135, �5.038 and � 5.131, respectively. The main reason for a Raman shift is due to the bond length and bond angle disorder of analyte. These peaks were experimentally obtained, and thermal fluctuations were scaled down. The trend of graph is all upward. The enhancement factor (EF) of SERS can be obtained by the following equation: EF ¼ ½ISERS =PSERS :tSERS �=nSERS= ½IRaman =PRaman :tRaman �=nRaman

(1)

where, I refers to a relative signal intensity; P is the laser power; t refers to the accumulation time, and n is the number of effective molecules [14, 25]. The laser power and data accumulation time were the same for both Raman and SERS in our experiments. The surface area of each MO molecule (AMO) was 0.935 nm2; the area of the laser spot (Alaser) was a circle of 20 μm in radius (rlaser), nanoparticles were spherical with a radius (rNPs) of 8.83 nm for Ag nanoparticles as shown in AFM figures (Fig. 1). For Raman experiment, the density (dMO) of Methyl Orange was 0.468 g/mol with the molecular weight (MMO) of 327.33 g/mol. IRaman was 5.42 and ISERS was different at each concentration. According to this equation, EFs were 2.23 � 108, 2.43 � 108, 2.66 � 108 and 2.91 � 108 respectively for Ag nanoparticles at these concentrations. Due to a va­ riety of LSPR wavelengths corresponding to different roughness fea­ tures, it was impossible to provide a direct comparison between the substrate LSPR and the SERS excitation profile [13].

Fig. 9. Raman spectroscopy of MO on the glass substrate at 6.11 � 10 3 (MO6), 7.026 � 10 3 M (MO-7), 8.248 � 10 3 M (MO-8), and 9.47 � 10 3 M (MO9) have been demonstrated.

4. Conclusion Ag-DLC was grown on the glass with co-depositions of PECVD and RF sputtering. In the present paper, we used MO as an analyte with different concentrations. SERS of MO was obtained on Ag nanoparticles embedded in DLC. These nanoparticles with average sizes of below 14 nm (AFM, FESEM and XRD spectra confirmed sizes of nanoparticles) were active substrates for the SERS, despite their low enough roughness. Therefore, it was evident that high intensities were due to DLC structures and hotspots. The concentration of MO reached 6.11 � 10 3 M that could be lower than this amount. The collected data indicated that experimental results were confirmed. Fig. 10 shows high intensities of D line in comparison

Fig. 10. SERS of MO on Ag-DLC at 6.11 � 10 3 (Ag6), 7.026 � 10 3 M (Ag7), 8.248 � 10 3 M (Ag8), and 9.47 � 10 3 M (Ag9) have been demonstrated.

peak occurred at 9.470 � 10 3 M. In this table, A2/A1 was about 160.78 and A2 referred to the maximum area of the highest peak at a specific concentration; and A1 (312.36) was the area of MO at 1.43 M at the same place. The sensitivity of measurements was significantly increased by this method (DLC). Fig. 11 shows that the intensity increases when concentrations are Table 3 Raman peak shift of MO on Ag-DLC nanoparticles. The reference was MO (1.43 M) and its Raman peak at 1371.57 cm 1. Concentration M ( � 10 3)

Raman peak shift (cm 1)

Area (Count)

6.110 7.026 8.248 9.470

15.68 16.80 13.42 15.67

39553.53 47152.25 48223.28 50221.38

Fig. 11. Average peak height of SERS spectra in terms of logarithmic scale of concentration. 5

Materials Chemistry and Physics 242 (2020) 122559

A. Zarei and A. Shafiekhani

with other reported studies [6]. Enhancement factor was about 2.23 � 108, 2.43 � 108, 2.66 � 108 and 2.91 � 108 respectively for different concentrations. Substrates, which were produced by this method, were cost effective and economical. There are a lot of substrate fabrication methods, but DLC method is ready-made, reproducible and robust with a good long lifespan; hence, it can be a good choice for sensor construction.

[9] Ș. Ț� alu, M. Bramowicz, S. Kulesza, A. Shafiekhani, A. Ghaderi, F. Mashayekhi, S. Solaymani, Microstructure and tribological properties of Fe NPs- a-C: H films by micromorphology analysis and fractal geometry, Ind. Eng. Chem. Res. 54 (2015) 8212–8218. [10] M.W. Chen, Y.F. Chau, D.P. Tsai, Three dimensional analysis of scattering field interactions and surface plasmon resonance in coupled silver nanospheres, Plasmonics 3 (2008) 157–164. [11] H. Zhang, Sh Yang, Q. Zhou, L. Yang, P. Wang, Y. Fang, The suitable condition of using LSPR model in SERS: LSPR effect versus chemical effect on microparticles surface-modified with nanostructures, Plasmonics 12 (2017) 77–81. [12] S. Hussain, R.K. Ray, A.K. Pal, Incorporation of silver nanoparticles in DLC matrix and surface plasmon resonance effect, Mater. Chem. Phys. 99 (2009) 375–381. [13] A.D. McFarland, M.A. Young, J.A. Dieringer, R.P. Van Duyne, Wavelength scanned surface-enhanced Raman excitation spectroscopy, J. Phys. Chem. B 109 (2005) 11279. [14] W.Ch Lin, L.Sh Liao, Y.H. Chen, H.Ch Chang, D.P. Tsai, H.P. Chiang, Size dependence of nanoparticle-SERS enhancement from silver film over nanosphere (AgFON) substrate, Plasmonics 6 (2011) 201–206. [15] O. Kamoun, A. Boukhachem, M. Amlouk, S. Ammar, Physical study of Eu doped MoO3 thin films, J. Alloy. Comp. 687 (2016) 595. [16] A.C. Ferrari, J.C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri, F. Mauri, S. Piscanec, D. Jiang, K.S. Novoselov, S. Roth, A.K. Geim, Raman spectrum of graphene and graphene layers, Phys. Rev. Lett. 97 (2006) 187401. [17] A.C. Ferrari, J. Robertson, Raman spectroscopy of amorphous, nanostructured, diamond-like Carbon, and nanodiamond, Phil. Trans. R. Soc. Lond. A 362 (2004) 2477–2512. [18] C.P. Marshall, A.O. Marshall, The potential of Raman spectroscopy for the analysis of diagentically transformed Carotenoids, Phil. Trans. R. Soc. A 368 (2010) 3137–3144. [19] A.A. van Apeldoorn, J. de Boer, H. van Steeg, J.H.J. Hoeijmakers, C. Otto, C.A. van Blitterswijk, Physicochemical composition of osteoporotic bone in the trichothiodystrophy premature aging mouse determined by confocal Raman microscopy, J. Gerontol.: Biol. Sci. 62A (2007) 34–40. [20] G.I.N. Waterhouse, G.A. Bowmaker, J.B. Metson, The thermal decomposition of silver (I, III) oxide: a combined XRD, FT-IR and Raman spectroscopic study, Phys. Chem. Chem. Phys. 3 (2001) 3838–3845. [21] D. Tan, Sh Zhou, B. Xu, P. Chen, Y. Shimotsuma, K. Miura, J. Qiu, Simple synthesis of ultra-small nanodiamonds with tunable size and photoluminescence, Carbon 62 (2013) 374–381. [22] H.O. Güvenc, Surface Enhanced Raman Scattering from Au and Ag Nanoparticle Coated Magnetic Microspheres, Department of Chemistry, a thesis, 2008. [23] A.C. Ferrari, Determination of bonding in diamond-like Carbon by Raman spectroscopy, Diam. Relat. Mater. 11 (2002) 1053–1061. [24] A.X. Wang, X. Kong, Review of recent progress of plasmonic materials and nanostructures for surface-enhanced Raman scattering, Materials 8 (2015) 3024–3052. [25] Y. Xu, M.P. Konrad, J.L. Trotter, C.P. McCoy, S.E.J. Bell, Rapid one-pot preparation of large freestanding nanoparticle-polymer films, Small 13 (2017) 2.

Acknowledgements This work supported by research and technology consul of Alzahra University. We thank Yikai Xu and Prof. Geoffrey Dent for their valuable comments on the manuscript and their keen interest in this work. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.matchemphys.2019.122559. References [1] X. Dong, H. Gu, F. Liu, Effect of halideions on the surface enhanced Raman spectroscopy of methylene blue for borohydride-reduced silver colloid, J. Phys. 277 (2011) 1742–6596. [2] T.G. Wilkinson, J. Clarkson, P.C. White, N. Meakin, K. McDonald, Development of surface enhanced Raman scattering spectroscopy monitoring of fuel markers to prevent fraud, Proc. SPIE (2016) 8710. [3] E. Smith, G. Dent, Modern Raman Spectroscopy (A Practical Approach), John Wiley & Sons, West Sussex, 2005. [4] M.Z. Si, Y.P. Kang, Z.G. Zhang, Surface-enhanced Raman scattering (SERS) spectra of Methyl Orange in Ag colloids prepared by electrolysis method, Appl. Surf. Sci. 255 (2009) 6007–6010. [5] Y. Lu, C.Y. Zhang, D.J. Zhang, R. Hao, Y.W. Hao, Fabrication of Flower-like silver nanoparticle for Surface-Enhanced Raman scattering, Chin. Chem. Lett. 27 (2016) 689–692. � Me�skinis, T. Tamulevi�cius, G. Niaura, K. Slapikas, � [6] S. A. Vasiliauuskas, O. Ul�cinas, S. Tamulevi�cius, Surface enhanced Raman scattering effect in diamond like Carbon films containing Ag nanoparticles, J. Nanosci. Nanotechnol. 16 (2016) 10143–10151. [7] H.O. Pierson, Handbook of Carbon, Graphite, Diamond and Fullerenes (Properties, Processing and Applications), Noyes Publication, New Jersey, 1993. [8] T. Ghodselahi, M.A. Vesaghi, A. Shafiekhani, A. Baradaran, A. Karimi, Z. Mobini, Co-deposition process of RF-PECVD of copper/carbon nanocomposite films, Surf. Coat. Technol. 202 (2008) 2731–2736.

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