FB100 Plasma Chemical Processes Mgr. Ondřej Jašek, Ph.D. jasek@physics.muni.cz PECVD at atmospheric pressure • Plasma enhanced chemical vapor deposition with various sources • Operation at 100 kPa without a vacuum system • Plasma arcs, jets and torches - mostly operated in floating catalyst regime, most often used with microwave sources • Atmospheric pressure glow discharge (APGD) diffusion form of dielectric barrier discharge (DBD) - deposition on substrates with heated electrode Atmospheric pressure glow discharge Discharge configuration when one or both electrodes are covered with dielectric barrier (used for ozone production since 19th century) Filamentary DBD can be made diffusive with addition of He or Ne,which are both expensive gases, in can be also made homogeneous in Ar with certain hydrocarbons, N2 or ammonia addition or special electrode structure. It was shown that during the current increase the discharge transits from a non-self-sustained discharge to a Townsend discharge and then to a subnormal glow discharge in He and Ar/NH3 and, therefore, can be called atmospheric pressure glow discharge (APGD). APGD has only 1 broad current pulse in each half period while DBD has many nanosecond current pulses, non-thermal plasma at atmospheric pressure T. Nozaki, Y. Kimura and K. Okazaki, J. Phys. D: Appl. Phys. 35 (2002) 2779-2784 CNTs growth in APGD First CNTs growth published by T. Nozaki, Y. Kimura and K. Okazaki, J. Phys. D: Appl. Phys. 35 (2002) 2779-2784 Quartz substrate with 20 nm metal plated Ni, pretreatment in H2 for 30 min at 600 °C Operation in kHz mode resulted in deposition of many defective structures AC 125 kHz 500 urn - Al203 0 N coated (20 nm) substrate Thermocouple Heater Figure 3. Electrode configuration. Table 1. Growth parameters. Growth temperature ("C) Growth time (min) H2/CH4 ration (-) Flow rate of gas mixture (see min"1) Pressure (Torr) Power (current peak) 400. 500. 600 5-30 0. 5. 10 APG; He:H2:CH4 = 900:100:0-20 DBD:He:H2:CHi= 150: 150:15 760 --4 W cm-2 f~ 15 inA em-2) Figu re 6. CNTs with uniform diameter of 40-50 nm and number density of 10'-1010 cm-2 obtained after 30 min deposition. CNTs growth in APGD APG was also successfully used with modified electrode (pin to plate) by Y.-H. Lee, S.-H. Kyung, C.-W. Kim, G.-Y. Yeom. Carbon 44, 799 (2006) and capillary type by S.-J. Kyung, Y.-H. Lee, C.-W. Kim, J.-H. Lee, G.-Y. Yeom. Thin Solid Films 506-507, 268 (2006). 6 Ni (5 nm)/Cr (100 nm)/Si substrates He(6 slm)/NH3(90 seem) plasma with pretreatment at 400 °C for 5 min He/C2H2(60 seem) plasma He/N2(60 sccm)/C2H2 plasma He/NH3/C2H2 plasma He/NH3/C2H2 with dc bias 1.2 kV CNTs growth in APGD In 2006 T. Nozaki et al. J. Appl.Phys. 99, 024310 used radio-frequency power source for CNTs growth APRFD creates stable continuous regime for CNTs growth, much lower operating voltage due to ion "trapping" between the electrodes, no dielectric barrier needed He/Hj/CH, Exhaust Spectrometer Cooling water b |J] ▼ (5?) Check valve Upper electrode (Shower head) MB Power Source Heating stage (bottom electrode) Vacuum gauge. Pump, valves *- osc Linear feedthrough Figure 1. APRFD reactor and image of APRFD during CNT growth. Parameters: 2 inch Si wafer <100> coated with Cr/Ni (20 nm/20 nm(sputtered)), Discharge area: 12.6 cm2 Deposition time: 5,10, 20 min, He/H2/C2H2 (1000/4-10/2 seem) CNTs growth in APGD Even with use of APRFD the growth of SWCNTs remained a challenge, key issue was the form of the catalyst In 2007 T. Nozaki, K. Ohnishi, K. Okazaki, U. Kortshagen. Carbon 45, 364 used densely mono-dispersed Fe-Co catalysts of a few nanometers size (first used by Maruyama) for aligned layers of SWCNTs Prepared nanoparticles were reduced in He/H2 1500/10 seem at APRFD at 400 °C for 5 min, then 15 min at 700°C, deposition He/H2/CH4 1000/30/16 seem for 5 min at 700 °C 201*1» 0 w 40 W SOW CNTs growth in APGD 600 UC 650 "C 700 'C Fig. K. SHM micrographs of SWCNTs al different substrain temperatures. IO0 200 300 400 500 1200 1300 1400 1500 1600 1700 Raman shift (cm3) Raman shift (cm1) Fig. 9. Raman scattering spectra of samples shown in Fig. 8. T. Nozaki, K. Okazaki, Carbon Nanotube Synthesis in Atmospheric Pressure Glow Discharge: A Review, Plasma Process. Polym. 2008, 5, 300-321 CNTs growth in APGD 0 100 200 300 400 500 600 700 800 Time (s) Figure 5. Time-dependent change-of-mass spectrum for m/e = 16 and 28. See figure 4 caption for the conditions. T. Nozaki, S. Yoshida, T. Karatsu and K. Okazaki, Atmospheric-pressure plasma synthesis of carbon nanotubes, J. Phys. D: Appl. Phys. 44 (2011) 174007 (9pp). CNTs growth in APG in Ar/H2/C2H2 FIG. I. Electrode configuration. ]—SLmax glass dielectric, 1—upper electrode, 3—distance pillar. 4—di sc harge. 5—substrate. 6—A IN dielectric. 7—thermocouple, ft—bottom e lectr ode. 9—heater. HJ—gas inlet. 3.5 r 3.0 2.5 • > 2.0« t: 1.5 " 1.0 0.5 - Ar+C2H2; 22°C Ar+C2H2+H2; 22°C Ar+CH4+H2; 22°C 0.0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 hydrocarbon concentration (%) H(i. 2. The dependence of ignition voltage '/(>onthe concentration or acetylene or niethane added to Ar or Ar/I lj. The discharge was operated at room temperature 22 T C Argon and hydrogen flow rates were 7 slm and KM) seem, respectively. > v < r t(ms) KIG. 3. Tri* time dependence of applied voltage (dotted line) and discharge current (full Line) at room temperature for (a) DBD in pure Ar, (b) DBD in AryCI |j. and (c) APGD in AryCJK The concentration of CH, or CJI. in Ar was 0.41 vol. %. Discharges were operated slightly above the ignition voltage in particular gas mixture. FIG. 5. ICCD images of discharges at room temperature with XO/is (one half-period) exposure time: (a) filamentary DBD in Ar. lb) filamentary DBD in Ar/CIt,. (c) APGD in Ar/C:H^. and (d'l APGD in Ar/C:HyM:. The concentration of CH4 or C APGD ArC-.H./ H; at 77 °C, and (c) A PUD ANC.H.jfH., at bWC. The concentration of CH, or C.I F inAr/IF was 0.4] vol.%. Discharges were operated slightly above the ignition voltage in particular gas mixture. FIG. X. ICCD images of APGD in Ar/C;H./H< with 0.41 vol. % admixture of C.H.. and bottom electrode heated to 6X0 °C: (a) 80/ts (one half-period), instantaneous cathode at upper electrode. (bl SO fu (one half-period), cathode at bottom electrode, (c) 5/iS. cathode al uppei electrode, and Id) 5 u>. catliode :il N>nom electrode. iloriAintal lni^s indicate [lie dielectric suitjccs. 1.6 1.4 1.2 1.0 Zl (J.3 0-6 0.4 Ar+C2H2+H2; 680°C Ar+CH4+Hř; 680MC 0.0 0.3 0.6 0.9 1.2 1.5 1.8 hydrocarbon concentration (%) 2.1 FIG. 7. The ignition voltage Uc independence on the concentration of acety-Isne or methane added to Ar/llj. lor the temperature of bottom electrode fiHi)°C. Argon and hydrogen Wow rates were 7 slm and 10(1 seem, respectively. If the bottom electrode was heated up to 680 °C the ignition voltage decreases due to the decrease of neutral gas concentration. Substrate temperature is 40 °C lower then heated electrode and upper electrode temperature is 250 °C lower. Due to the temperature profile the behaviour in instantaneous cathode or anode is different in each half period. In APG in Ar/H2/C2H2 FIG. 13. Cross sectional SEM micrograph* of deposited carbon na no structures for (a) 0.1%. (b)0.2% of C>H: in Ar/QH:/H: AKJ discharges, and 0.2'*. idl OA'; of Cll4 in Ar/OWIl: DBD discharges. The substrate temperature was 710 'C. The micrographs were made using TESCAN LYRA microscope. FIG. 12. TEM micrograph of the carbon uanostructures deposited from (a), (b) 0.2% of C2H2 in Ar/C2H2/il: mixture and (c>. (d) 0.2% of CH4 in Ar/ CH4/ll, mixture. The substrate temperature was 610°C for (a> and (c) and 710 °C for (b> and (d> images. The micrographs were made using Philips CM12 microscope. CNTs deposition by plasma arcs/jets/torches at atmospheric pressure ^ At + ethylene Welding art torch Isolated subslralci-^^"3 Water-con IulI base, nl&clrodc 10 nm Ferrocene riiiima luhi; Atmospheric plasma Short-circuit F urn act it 1 M\i\K Metallic plate Swirl pm: At1 mitrvwavi; 2,45 GHz \ (b) Fumes H. Takikawa et al. Physica B 323, 277 (2002)., 0. Smiljanic et al., Chem. Phys. Lett. 356, 189 (2002). CNTs deposition by plasma arcs/jets/torches at atmospheric pressure Fig. 9. SEM images of CNTs obtained from the atmospheric microwave plasma-torch, (a) at a furnace temperature of 700. (b) 800. (c) 900. and (d) 1000 °C. Y. Ch. Hong, H. S. Uhm, Physics of plasmas 12, 053504 (2005) CNTs synthesis by microwave plasma torch at atmospheric pressure Ar Hydrocarbon Hydrogen Ar Ivnčfowáve plasma torch operating at 2,45 GHz, max. 2 kW power, dual gas flow Center - Ar(500-1500 seem)/ Outer - H2(250-500 sccm)/CH4(10-50 seem) Si/Fe, Si/SiOx/Fe, Si/AlxOy/Fe substrates Fe(1-10 nm) vacuum evaporated, SiOx PECVD O. Jašek, M. Eliáš, L. Zajíčková et al., Materials Science and Eng. C, 26, 2006, 1189 CNTs synthesis by microwave plasma torch at atmospheric pressure CNTs synthesis by microwave plasma torch at atmospheric pressure Substrate type Si/SiOJFe 10 nm (QCH4=40 seem, QH2=400 seem, At=1500 seem, TS=700°C, td=15min.). CNTs synthesis by microwave plasma torch at atmospheric pressure backscattered electrons. White points correspond to catalytic particles - tip TEM micrograph growth mode. CNTs synthesis by microwave plasma torch at atmospheric pressure CNTs synthesis by microwave plasma torch at atmospheric pressure CNTs growth a) SiOx b) AlxOy and c) without barrier layer. Ar/H2/CH4 1540/430/42 seem, 60 s, 400W, 700-750 °C CNTs synthesis by microwave plasma torch at atmospheric pressure ISI SEI 5.0kV X2,UUU 10>n WD 8.1 mm CNTs growth in microwave plasma torch with floating catalyst TEM micrograph of MWCNTs/SWCNTs deposited from mixture of Ar/H2/CH4 and Fe(CO)5 Deposition of SWCNTs on the substrate using ethanol admixture -j—i—i—i—i—i—i—i—i—r-1—i—i—i—i—p-1—i—i 100 200 3001200 1400 1600 1800 2000 2200 2400 2600 2800 Raman shift (cm1) Raman spectra of deposited nanostructures 22 Various forms of carbon Methods of making graphene (a) (g) Mlcromechamcal (b) cl«avago Liquid phase oxfoliation OI»p«r»«d CJf.iphflr uitrstound Anodic Bonding Potittv* Elvctrodo Noootivo Etoctrodo * I Growth on SIC , (00*1) Chemical Vapour Deposition Hyd/ocvImmi 9*» Molecular beam epitaxy (c) Photooxfoliation nnuniHiníninai'íHnnnnnin liiilililiiiliillilitllililllllilllllilili (0 Precipitation from metal Metal 0) t<«..l' Chemical synthesis Sub«trjt» F. Bonaccorso et. al. Production and processing of graphene and 2d crystals, Materials Today 15(12), 2012, 564 Graphene identification in Raman spectra 5LG SLG 6LG 7LG BLG Optical contrast on Si02, best around 300 nm thickness. 20um (b) =3 CO CO c CD I 2D ' I SLG J 2D1 A : i BLG ) \ ,A : 1 5LG A : 6LG 1 : 7LG 1500 2000 2500 3000 Raman shift (cm1) 3500 Highly sensitive Raman signal - strong enhancement of 2D mode. No defects - no D peak around 1300 cm1 Graphene deposition using plasma sources • Synthesis in volume of the plasma discharge • Synthesis of vertical aligned graphene nanosheets on substrates • Synthesis of graphene on metalic or dielectric substrates by PECVD • Plasma pretreatment, cleaning of the substrate, functionalization of the deposition layer - graphane (H2), graphene transfer H2 = 2 seem Time (min) Graphene deposition using plasma sources Hg. 2. (irowth kinetics in (A'D-produced graphene on various catalysts: Case of OIL on Ni and (u. R. Munoz and C. Gomez-Aleixandre, Review of CVD Synthesis of Graphene, Chem. Vap. Deposition 2013, 19, 297 Graphene deposition using plasma sources Low pressure microwave plasma surface wave discharge. Cu (30 |im),AI (12 |im), Ni foils pretreated in Ar/H2 plasma at 5 Pa for 20 minutes. Deposition parameters: 3-4.5 kW MW power, deposition time 30-180 s in CH4/Ar/H2 30/20/10 seem mixture. (a) 4000 J £ 3000 Ž '-j £>2000 = S looo FWHM,D= 37 cm1 2D (2657 cm1) D (1326 cm1) FWHMG=26cm' ■■ G( 1578 cm-1) i :■ Jj^D'(1578 cm-') ^ La lil!H.) (b) 1500 2000 2500 Raman shift (cm1) 3000 1000 2" 800 c 3 o o >, 600 £ 400 200 D(1328 cm"') 0 5 10 15 20 25 Time (min) G(1588cm'> ip'(1617cm-') 2^(2654 cm') 1000 1500 2000 2500 Raman shift (cm"') 5000 FIG. 1. (Color online) Raman spectra (638 nm laser, I ,ixm spot size) o graphene-based films deposited at substrate temperatures below 400 °C b; SWP-CVD. (a) Raman spectrum of a typical graphene-based film depositee on Cu foil (CVD conditions: 5 Pa, CH4/Ar/H,=3O/20/10 SCCM, 3 kV per a MW generator, 30 s). (b) Raman spectrum of a graphene-basei film deposited on Al foil (CVD conditions: 3 Pa, CH4/Ar/H = 30/20/10 SCCM, 4 kW per a MW generator, 180 s). (c) Substrate tern perature profile during the Ar/ H ? plasma treatment and the plasma CVD fo the synthesis of the film on Al foil shown in Fig. Kb). i c 3 e (a) D G h (H2 : CH4) 80 : 1 CM '---^ D I k 40 : 1 I A 20 :1 / A 10 : 1 —.-1-,-1-,-1-,-1-,-1-,— 1200 1500 1800 2100 2400 2700 3000 Raman shift (cm1) (3) G 2D A u D A ?5Q C A_ A 700 °C A 600 °C A ^_^ 500 °C A D' 450 °C A . -,-1-,-1-.-1-.-1-,-1-,- 1200 1500 1800 2100 2400 2700 3000 Raman shift (cm1) FIG. 1. (Color online) (a) Raman spectra taken at an excitation wavelength of 514 nm for the graphene films synthesized at various gas mixing ratio (synthesis time: 1 min. temperature: 750 C). HR-TEM images of the graphene films synthesized at various gases mixing ratio: (b) 80:1 (H2:CH4), (c) 40:l.and(d) 10:1. 450 500 550 600 650 700 750 Synthesis temperature (°C) FIG. 2. (Color online) (a) Raman spectra taken at an excitation energy of 2.41 eV for the graphene synthesized at several synthesis temperatures (gas mixing ratio (H2:CH4): 80:1. synthesis time: 1 min), (b) FWHM of the 2D peak and the intensity ratio of the 2D peak compared to the G peak as a function of synthesis the temperature. Y. Kim et al, Low-temperature synthesis of graphene on nickel foil by microwave plasma chemical vapor deposition, APPLIED PHYSICS LETTERS 98, 263106 (2011). J. Kim et al., Low-temperature synthesis of large-area graphene-based transparent conductive films using surface wave plasma chemical vapor deposition, APPLIED PHYSICS LETTERS 98, 091502 2011. Graphene deposition using plasma sources Figure i. a) The remote radiofrequency (RF) PECVD system used, b) Schematic illustration of the c-PECVD procedure, c) AFM images of a peel-off graphene flake before (left) and after (right) c-PECVD. d) Plots of the experimental results as a function of the temperature (T) and H2 content at 48, 90, and 300 mTorr. The blue, green, and red areas correspond to the parameters for edge etching, critical edge growth, and cluster nucleation, respectively. The height of the green columns indicates the growth rate. e,f) AFM images of peel-off graphene flakes after activation of the edges with a H2 plasma (250 mTorr, 500Dq for 20 min (left columns), followed by CH4 + H2 plasma CVD (30% H2, 300 mTorr, 550°C) for 80min (e, right column) or CH4 — H2 plasma CVD (20% H2, 300 mTorr, 600°C) for 40 min (f, right column). The height profile across the red line in the AFM image in (f) is shown below the AFM image. Scale bars (c,e,f): 500 nm. RF PECVD remote plasma system with furnace and Si/Si02 substrate D. Wei et al., Critical Crystal Growth of Graphene on Dielectric Substrates at Low Temperature for Electronic Devices, Angew. Chem. Int. Ed. 2013, 52, 14121 -14126. Graphene deposition using plasma sources Fig. 1 Schematic diagrams of various PECVD systems for VG growth. (a)TE-MW (reprinted with permission from ref. 67. Copyright 2010 American Institute of Physics), (b) TM-MW (reprinted with permission from ref. 25. Copyright 2006 Elsevier), (c) ICP (reused with permission from ref. 68, Copyright (2004) Elsevier), (d) helicon plasma (reprinted with permission from ref. 24. Copyright 2006 Japan Sodety of Applied Physics), (e) CCP +■ ICP (reused with permission from ref. 69, Copyright 2005 Elsevier), (f) VHFCCP + MW (reprinted with permission from ref. 29, Copyright 2008 American Institute of Physics), (g) expanding CCP (reprinted with permission from ref. 70. Copyright 2010 Institute of Physics Publishing), (h) parallel-plate dc glow discharge plasma, and (i) pin-to-plate normal glow discharge plasma. Z. Bo et al., Plasma-enhanced chemical vapor deposition synthesis of vertically oriented graphene nanosheets, Nanoscale, 2013, 5, 5180. Graphene deposition using plasma sources RF Power ( I ; MAIN Matching Network RF CoL DC Bias KX AC Heater Roughing Pump Vent—M— —tx- - Quartz Window Cooling Water -Xr-C Gate Valve Turbo -ex— Pump H _ _ MIC -XH-h li- MIC CH4 MFC h-XH-F- HXr-& 1. Schematic of the inductively coupled RF* PHCVD system used lor carbon nanosheel deposilioi i-'--r (a) D i ' i G < y 100%CH4_J ■ i ■■■ i RF 900 W 3' 680°C -12 Pa 20 min Ju \ 40%CH, _j kj \ 10%CH, _ J -1-■-1-.-1_i_l__._1_ i 1000 1500 2000 2500 3000 350 Raman Shift (cm1) £M images of carbon nanosheets grown at different CH4 Fig. 3. SEM images of carbon nanosheets grown at different substrate lions on Si substrates: (a) 10% CR,; (b) 40% CHi; (c) 100% temperatures on Si substrates: (a) 630 °C; (b) 730 °C; (c) 830 °C, Other er deposition conditions are RF 900 W. 680 °C. ~I2 Pa, deposition conditions are RF 900 W, 40%. CH4. 12 Pa. 20 min. 1000 1500 2000 2500 3000 3500 Raman Shift (cm1) J. Wang et.al. Synthesis of carbon nanosheets by inductively coupled radio-frequency plasma enhanced chemical vapor deposition, Carbon 42 (2004) 2867-2872. RF ICP CVD 13,56 MHz 900 W, 12 Pa, H2/CH4 mixture . Substrate Si, Si02, Al203, Mo, Cu etc. 31 Graphene synthesis in volume at atmospheric pressure Decomposition of ethanol C2H5OH or dimethylether CH3OCH3 leads to formation of graphene sheets. A. Dato, V. Radmilovic, Z. Lee, J. Phillips, and M. Frenklach, Substrate-Free Gas-Phase Synthesis of Graphene Sheets, Nano Letters, 8 (7), 2008, 2012. A. Dato, M. Frenklach, Substrate-free microwave synthesis of graphene: experimental conditions and hydrocarbon precursors. New Journal of Physics, 2010, 12.12:125013. E. Tatarova et al. Microwave plasma based single step method for free standing graphene synthesis at atmospheric conditions. Applied Physics Letters, 2013, 103.13:134101. Graphene synthesis in volume at atmospheric pressure Raman shift [cm1] 33 Graphene nanoribbons 3.5 (am) 1.5 goo nm Sonication cut 500 tun 6 500 nm Figure 1 | Making GNRs from CNTs. a, A pristine MVVCNT was used as the starting raw material, b, The MVVCNT was deposited on a Si substrate and then coated with a PMMA film, c, The PMMA-MWCNT film was peeled from the Si substrate, turned over and then exposed to an Ar plasma, d-g, Several possible products were generated after etching for different times: GNRs with CNT cores were obtained after etching for a short time /, (d); tri-, bi- and single-layer GNRs were produced after etching for times t2> 1} and /.„ respectively (t4 > t3 > t2 > t{; e-g). h, The PMMA was removed to release the GNR. Living Jiao et al., Narrow graphene nanoribbons from carbon nanotubes, 458, Nature, 877. Dmitry V. Kosynkin et al., Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons, Nature, 458, 2009, 872. P. Ruffieux et al., On-surface synthesis of graphene nanoribbons with zigzag edge topology, Nature, 531, 2016, 489. GNR - zig-zag metallic, archmchair - metallic and semiconducting Graphene transfer to dielectric substrate • Graphene transfer scheme on Cu foil: a) PMMA mask b) etching of graphene on one side of the foil in 02 plasma, c) chemical etching of Cu (for example in FeCI3) d) transfer of PMMA+graphene to dielectric substrate e) chemical or plasma etching of PMMA. • Gao, L. et al. Nature 505,190-194 (2014). 35 Literature • M. Meyyappan, L. Delzeit, A. Cassell, D. Hash. Plasma Sources Sci. Technol. 12, 205 (2003) • M. Meyyappan, J. Phys. D: Appl. Phys. 42 (2009) 213001 • T. Nozaki, S. Yoshida, T. Karatsu and K. Okazaki, Atmospheric-pressure plasma synthesis of carbon nanotubes, J. Phys. D: Appl. Phys. 44 (2011) 174007 (9pp) • Z. Bo et al., Plasma-enhanced chemical vapor deposition synthesis of vertically oriented graphene nanosheets, Nanoscale, 2013, 5, 5180. • E. Tatarova et al. Microwave plasma based single step method for free standing graphene synthesis at atmospheric conditions. Applied Physics Letters, 2013,103.13: 134101. • X. Chen, B. Wu, Y. Liu, Direct preparation of high quality graphene on dielectric substrates, Chem. Soc. Rev., 2016, 45, 2057. • Commercial presentations: AIXTRON Black Magic, Oxford Nanofab