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+MODEL ARTICLE IN PRESS SCT-13266;NoofPages4 Surface&CoatingsTechnologyxx(2007)xxx–xxx www.elsevier.com/locate/surfcoat Carbon film deposition by powerful ion beams A.I. Ryabchikova, A.V. Petrova, N.M. Polkovnikovaa, ⁎ V.K. Strutsa, , Yu.P. Usova, V.P Arfyevb a NuclearPhysicsInstitute,Leninave.,2a,Tomsk,634050,Russia bTomskPolytechnicUniversity,Leninave.,30,645050,Russia Abstract Carbonaceous thin films can be used in microelectronics, superconductors, solar batteries, logic and memory devices, and to increase processingtoolwearresistance,andasmagneticnanocompositematerialsforinformationstorage.Thispaperpresentsastudyofcarbonaceous thin films deposited on silicon substrates using ablation plasma generated by pulsed power ion beams (H+—60%, C+—40%, E=500 keV, τ=100ns,density=8J/cm2)ongraphitictargets.Theconcentrationsofsp -bondedcrystallinediamond,andamorphousandcrystallinephasesof 3 carbon were determined by X-ray diffraction analysis (XRD). It was observed that the concentration of the crystalline diamond phase in films depositedundervariousconditionsdidnotexceed5%.Asubstantialconcentration(30–95%)ofthecarboncrystallinephaseisintheformofC 60 andC fullerenes.ItisshownthattheconcentrationoffullerenesandtheratiobetweentherelativeamountsofC andC greatlydependson 70 60 70 thegraphitictargetdensity,carbonfilmdepositionconditionsandaboveallonthedistancefromthegraphitictargettothesiliconsubstrate.This distancedeterminesthefilmdepositionrateandthedegreeofcoolingoftheplasmageneratedonthesubstrate,whichcancausechangesinfilm crystallization conditions. ©2007Elsevier B.V. All rightsreserved. Keywords:Ionbeam;Carbonaceousfilm;Fullerene;Filmdeposition 1. Introduction recording and storing information, as a basis for production of power consuming storage batteries, and as porous material for Amorphous carbon films possess good tribological proper- filters, in medicine and pharmacology, etc. [4–6]. Recent ties such as high hardness and low friction coefficient, which experiments have shown that carbon nanotubes can be used in result in significant increase in wear resistance of articles with applications which demand dense and uniform diamond film such coatings [1,2]. Diamond-like carbon films with sp [7]. 3 bonding possess high mechanical strength, low friction One of the more recent methods of obtaining thin-film coefficient, high corrosion resistance, and good insulation and carboncoatingsisbasedonultrahighspeeddepositionusinga optical properties. These properties enable them to be used as high-density, high thermal energy, ablation plasma generated protective films, vibration plates for sound sources, and for usinghighpowerpulsedionbeams[8–10].Thekeyparameter domestic water pumps, etc. [3]. Carbon allotropic forms – for such a process is the deposition rate, which determines fullerenes C and C and nanotubes – possess wider growth conditions of the thin film and, subsequently, its 60 70 application possibilities, e.g., for creation of superconducting structure and properties. It was shown elsewhere [11] that a materials, or in microelectronics, in solar cells, in logic and decreaseindepositionrateintherangeof∼40nm/pulseupto memory devices, as magnetic nanocomposite materials for ∼2nm/pulse,causescontinuousimprovementofadhesionand some physico-chemical characteristics ofcoatings. Thispaperpresentsastudyofconcentrationsofsp bonded 3 crystalline diamond-like phase, and crystalline and amorphous ⁎ graphitewithrespecttotheconcentrationsoffullerenesC and Correspondingauthor.Tel.:+72822417959. 60 E-mailaddress:[email protected](V.K.Struts). C70 in thin-film coatings obtained using ablation generated by 0257-8972/$-seefrontmatter©2007ElsevierB.V.Allrightsreserved. doi:10.1016/j.surfcoat.2006.11.045 Pleasecitethisarticleas:A.I.Ryabchikovetal.,Surf.Coat.Technol.(2007),doi:10.1016/j.surfcoat.2006.11.045 ARTICLE IN PRESS 2 A.I.Ryabchikovetal./Surface&CoatingsTechnologyxx(2007)xxx–xxx Linnik interferometer, was obtained by varying the number of ion current pulses. XRD measurements were made with a “Shimadzu 6000” diffractometer, using Cu-Kα radiation in a glancing angle geometry at an angle of θ=5°. The XRD analysis results were processed according multiphase (multi- disciplinary)programPOWDERCELL2.Theweight%ofthe entire specimen that is represented, respectively, by each crystalline phase and the amorphous material is produced. Phase analysis was also carried out using ring and point microdiffractionpatternsobtainedwiththeelectronmicroscope Tesla BS-540 under the regimes of bright-field and dark-field imagesatmagnificationsofupto56,000times.Thenanohard- ness was measured using an SCEM Nano Hardness Tester. 3. Results Fig.1.Theschematicofcoatingdeposition.SubstrateA—glass,substrateB— Table 1 presents the main results on phase concentrations silicon,dτs—thedistancefromthetargettothesubstrate. obtained from XRD analysis of carbon coatings deposited at various target–substrate distances in the center and on the pulsed ion beams on graphite targets of various density, and peripheryusingthreetypesofgraphitictargets.Inaddition,the using different deposition rates. The microstructure and phase nanohardness of the coatings was measured using the Oliver– composition of carbon coatings on silicon substrates were Pharr method [12] with a loading onto the diamond indenter investigated using XRD analysis and transmission electron equal to 1mN. microscopy (TEM). Changes in the composition were also ItisevidentthattotalconcentrationoffullerenesC andC correlated with themeasurednanohardness of thecoatings. 60 70 inthesamplesstudiedchangedintherangeof∼30–95%.The concentrationofcarbondiamondphasedidnotexceed∼5%for 2. Experiment all the targets, despite the significant difference in deposition rates.Thelargestconcentrationofthediamondphasewasfound To obtain ablation carbon plasma, high power ion beams insampleswhichwerekeptatadistance(dτs)of170mmfrom (60% H+, 40% C+n, n=1, 2, 500 keV, 100 ns, ∼8 J/cm2) the target. Fig. 2 presents the XRD photograph of the carbon generated in diode with conical focusing were used. The film for sample no. 1. The coating is composed of amorphous schematic ofthe coating deposition ispresentedin Fig. 1. carbon(∼50%),orthorhombicphaseoffullereneC andcubic 70 Graphitic targets with a diameter of 50 mm and density of phaseofC intheratioofC :C =15:85.Inthecaseofmore 60 60 70 ρ =1.68g/cm3,ρ =1.77 g/cm3 andρ =2 g/cm3 were located detailed research, (Fig. 2b), one can observe a peak 1 2 3 atanangleofα=40°totheionbeamaxis.Sisubstrateswiththe corresponding to diamond-like carbon (DLC) with a trigonal dimensionsof10×10mm2wereplacedontheglassplatewhere structure in theconcentration of approximately 5%. allthedepositionwascarriedout.Coatingformationwasdone The particles with nanocrystalline structure were observed at room temperature in a vacuum of ∼5d10−6 Torr obtained for sample no. 1 in addition to coating areas with quasiamor- using a cryogenic pumping system. The change in the phous structure during electron microscope analysis. Fig. 3 deposition rate was achieved by varying the distance dτs presents images and microdiffraction patterns of the above- between the target and substrate in the range of 100–220 mm; mentioned area. and in the case of a fixed dτs — by use of peripheral plasma The microdiffraction image represents the ring reflexes flowareas.Therequiredcoatingthickness,asmeasuredbythe characteristic of nanocrystalline structure in addition to a high Table1 TheresultsofRSAofcarboncoatings Sample Graphite Depositionrate, Coating Target–substrate RatioofphasesC : Diamond-like Amorphous Vickers 60 number density,g/cm3 nm/pulse thickness,μm distance,mm C %:% carbon,% phase,% nanohardness 70, 1 1.68 7.4 0.22 170,center 15:85 5 50 900 2 1.68 5.0 0.15 170,periphery 10:90 1 40 1837 3 1.68 3.4 0.135 220,center 60:40 1 70 960 4 1.68 2.8 0.11 220,periphery 60:40 1 70 3034 5 1.77 20.7 0.207 100 22:78 – 50 154 6 1.77 17.5 0.158 140 60:40 1 30–40 556 7 1.77 13.2 0.175 170 62:38 5 30–40 898 8 2.00 1.226 0.143 170 60:40 – 65 3943 9 2.00 1.200 0.216 220,center 0:100 – 5 1296 10 2.00 0.98 0.176 220,periphery 45:55 – 60 693 Pleasecitethisarticleas:A.I.Ryabchikovetal.,Surf.Coat.Technol.(2007),doi:10.1016/j.surfcoat.2006.11.045 ARTICLE IN PRESS A.I.Ryabchikovetal./Surface&CoatingsTechnologyxx(2007)xxx–xxx 3 plasma decrease at the expense of angular divergence, which, correspondingly,decreasesthedegreeofsubstrateheating.Low substrate temperature favors the formation of a fine-grained crystalline structure up to the amorphous state (see Ref. [13]). For the first group of samples nos. 1–4 with relatively small deposition rate (~ 2.8–7.4 nm/pulse), the substrate heating is lower, and high speeds of surface layer cooling equal to 108– 109 K/s are typical [13]. As a result, with decrease in the film growthrate,thecarbonamorphousphase(upto∼70%)prevails inthe film structure. For the second group of samples nos. 5–7, the deposition rate(∼13.2–20.7nm/pulse)ismuchhigher,asisthedegreeof substrateheating,whichtogetherwiththereleaseoflatentheat of crystallization, increases the substrate temperature and prolongs the process in the case of thicker films. In that case onecanobservetheprevalenceofthecrystallinecarbonphase. Forthethirdgroupofsamplesnos.8–10,pyroliticgraphite withhighdensitywasusedasatarget.Inthiscase,thedeposition rateof∼0.98–1.23nm/pulseisslow,andsimilarforallsamples, and the amorphous carbon phase prevails for all the samples exceptno.9,whichwaspreparedatadistanceofdτs=220mm from the substrate center. The difference for this group of samplesliesinthechangeintheratioofC :C phases,which 60 70 favours C with a decrease in the deposition rate. Moreover, 70 Fig.2.X-raydiffractionphotographfromsampleno.1. XRDofsampleno.9,asshowninFig.4,showsformationofa single-phasefilmwithsmall(∼5%)concentrationsofthecarbon intensity diffused halo. The dark-field image obtained for the amorphous phase. We also observed an unexpected film firstringreflexexplicitlyrepresentsnanocrystallinestructureof compositionforsampleno.10;theXRDpatternforthesample the material. Analysis of the microdiffraction image showed isgiveninFig.5andwasobtainedforthesamedτs=220mm, thatringreflexescorrespondtocarbonwithahexagonalcrystal butatthedistanceof20mmfromthesubstratecenter.Despite latticeandlatticeparametersofa=8.948nm,c=14.07nmand thefactthattheconcentrationoffullereneC forthissampleis 70 the c/a ratio=1.5733. The bright-field image of the area (not higherthanthatforC ,thecarbonamorphousphasedominates 60 giveninthefigure)showsextinctioncontoursthatareevidence inthefilm(upto∼60%).Thismeansthatcriticalconditionsare of thepresence ofhigh tensile stress in thefilm. neededtoobtainfullerenesfromtheablationplasma. In general, changes in coating composition have the Forthefirsttwogroupsofsamples,nanohardnessincreases character of competition between amorphous and crystalline asthedepositionratedecreases.However,thisisnotnecessarily phases of carbon. For the first two groups of samples, only an correlated with changes in phase composition. The changes in increase in the relative concentration of fullerene C is nanohardnessmaybeprimarilycausedbyinnertensilestresses 60 correlated with a decrease in deposition rate, whereas changes in thin films, appearing as a result of film dimensional in the concentration of amorphous carbon in the coating shrinking, and the film cooling on the substrate. This also compositiondonotsuggestanysimpleexplanation.Itcouldbe results in a decrease in the adhesion [11]. This effect is more understoodasfollows.Withanincreaseinthetarget–substrate evidentforlargetemperaturedifferencesbetweenthesubstrate distance,thedepositionrateandthetemperatureoftheablation andhotplasmaandcorrespondsinourcasetothesamplegroup Fig.3.Microdiffractionpattern(a)andadark-fieldimageofareflexindicated withanarrowonthemicrodiffractionimage,forsampleno.1. Fig.4.XRDpatternforsampleno.9. Pleasecitethisarticleas:A.I.Ryabchikovetal.,Surf.Coat.Technol.(2007),doi:10.1016/j.surfcoat.2006.11.045 ARTICLE IN PRESS 4 A.I.Ryabchikovetal./Surface&CoatingsTechnologyxx(2007)xxx–xxx Fig.5.XRDpatternforsampleno.10. nos. 5–7, for which nanohardness absolute magnitudes are to the changes in the phase composition, but is attributed to significantly lower. emerginginternal stresses in thethin films. Forthethirdgroupofsamplesnanohardnessdecreaseswith the decrease in deposition rate, which suggests growth of References internalstressesinthefilm,andisevidentlyconnectedwithless heating of the substrate surface layer because of low relative [1] H.Tsai,P.Body,J.Vac.Sci.Technol.,A5(1987)3287. energycontentof theablationplasma flow. [2] H.Hiroyuki,Y.Takayuki,T.Takashi,IEEETrans.Magn.37(no.4)(2001) 1789. [3] M.Tamba,K.Kawamura,K.Okazaki,H.Amemiya,Jpn.J.Appl.Phys.40 4. Conclusion (2001)1064. [4] G.N.Churilov,Prib.Teh.Eáksp1 (2000)5(Russia). Deposition of thin-film carbon coatings onto silicon [5] A.V.Eletsky,UFN167(no.9)(1997). substrates made from ablation plasma generated under the [6] A.S.Fyodorov,S.G.Ovchinnikov,Fiz.Tverd.Tela46(no.2)(2004)563 (Russia). influenceofhighpowerpulsedionbeamsontovariousdensity [7] K.Wang,etal.,Sci.Bull.40(1995)1245. graphitic targets was carried out. 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For targets made from pyrolitic graphite [13] T.J.Renk,P.P.Provencio,S.V.Prasad,etal.,Proc.,92,IEEE,New-York, with high density ρ=2 g/cm3, the ratio of C :C changes in 2004,p.1057. 60 70 favourofC .Thevariationinnanohardnessdoesnotcorrelate 70 Pleasecitethisarticleas:A.I.Ryabchikovetal.,Surf.Coat.Technol.(2007),doi:10.1016/j.surfcoat.2006.11.045