Oxidation behavior of Cu nanoclusters in hybrid thin films Harm Wulff,* Steffen Drache*, Vitezslav Stranak**, Angela Kruth*** *EMAU Greifswald, **South Bohemian University, Budweis, *** INP Greifswald wulff@uni-greifswald.de XXII. Erfahrungsaustausch "Oberflächentechnologien mit Plasma- und Ionenstrahlprozessen" Mühlleithen, 10.-12. März 2015
Motivation nano composites aim: transfer cluster properties into bulk material crucial parameters: cluster size distribution, crystallinity, grain size, surface roughness examples TEM micrographs of cobalt plasma polymerized HMDSN nanocomposites * very high cut-off frequency materials for application in GHz-electronics optical composites with tuned plasmon frequency for ultra thin color filters, Bragg reflectors and other devices small-sized supercapacitors: high permittivity ε r by metal clusters embedded in an isolating TiO 2 matrix * K.L. Kolipaka et al. / Surface & Coatings Technology 207 (2012) 565 570
Experimental setup cluster source orifice 4 mm ø magnetron: 3 inch ø Cu-target basic pressure: p b, cs ~ 10-4 mbar mean Cu discharge current: I avg = 500 ma at 286 V magnetron gas feed: 40 sccm Ar, p clu = 50 Pa, p clham = 0.4 Pa mean Ti discharge current: I avg = 500 ma at 311 V (376 V with O 2 ) 20 sccm O 2 for TiO x deposition basic pressure: p b, ch ~ 10-6 mbar deposition time: 30 min
Deposition of Cu clusters and TiO 2 ( hybrid thin film ) Cu nanocluster spot center (B) and off-center position (A) B 9 mm A
Basic experiments sep. Cu films sep. TiO 2 films hybrid films Film characterization XPS : element analysis (qualitative, quantitative), oxidation number XR : film thickness, roughness GIXD: phase composition (structure model) domain size (line profile analysis) SEM-EDX (ion beam): morphology, element analysis, depth profile
intensity [cps] XPS of Si wafer substrate and Cu nanocluster deposition intensity [cps] 4000 XPS survey spectra 1000 3000 Cu 2p 1/2 Cu 2p 3/2 Cu nanoclusters Si wafer substrate 800 2000 Cu Auger LMM 600 1000 0-1000 O Auger KLL O 1s C 1s 3s 3p 3d Si 2p Si 2s 400 200-2000 1000 800 600 400 200 0 binding energy [ev] 0
intensity [cps] XPS of in-situ deposited Cu-nanocluster intensity [cps] survey scan Cu 2p high resolution peak profile 4000 2p 3/2 XPS spectrum for Cu 9000 8000 Cu peak profile Cu 2p 3/2 3000 2p 1/2 7000 2000 Cu Auger LMM 6000 5000 Cu 2p 1/2 1000 4000 3s 3p 3d 3000 0 1200 1000 800 600 400 200 0 binding energy [ev] 2000 960 950 940 930 920 binding energy [ev] - only lines attributed to Cu - no impurities - substrate fully covered - Cu 2p 3/2 at 932.7 ev: Cu or Cu 2 O - no CuO discharge conditions: Ar 40 sccm, I = 500 ma, p cs = 50 Pa, 30 min deposition
intensity [cps] XPS of TiO x deposition 1400 XPS survey spectrum of TiO x deposition 1200 1000 Ti Auger LMM O Auger KLL O 1s Ti: 29 % O: 71% 800 Ti 2p 600 Ti 2s 400 200 0 O 2s Ti 3p Ti 3s 1000 800 600 400 200 0 binding energy [ev] - substrate fully covered, no impurities
intensity [cps] intensity [cps] XPS of TiO x sample 2000 high resolution Ti 2p peak profile TiO A B x deposition Ti 2p 3/2 C 2500 high resolution O 1s peak profile O 1s peak 1500 Ti 2p 3/2 peak positions: A) TiO 2 B) TiO C) Ti 2000 1500 E B = 529.9 ev 1000 Ti 2p 1/2 1000 500 500 E = 5.67 ev 0 472 470 468 466 464 462 460 458 456 454 452 binding energy [ev] 0 540 538 536 534 532 530 528 526 524 binding energy [ev] - Ti 2p 3/2 line verifies TiO 2 - small ΔE supports TiO 2 - O 1s peak at 529.9 ev typical for metal oxides (like O in TiO 2 ) - no other O 1s components deposition conditions: 40 sccm Ar, 20 sccm O 2, p ch = 0.6 Pa I = 500 ma, 30 min deposition, α = 45
intensity [cps] XPS of hybrid thin film Hybrid layer element intensities at different sample positions 3000 2500 A) off-spot B) on-spot (with +1000 cps) 2000 1500 1000 Cu features TiO 2 features B Cu: 24 % Ti: 16 % O: 60 % 500 0 1000 800 600 400 200 0 binding energy [ev] A Cu: 5 % Ti: 26 % O: 69 % problem: high oxygen amount: indication of CuO instead of Cu?
intensity [cps] XPS comparison of Cu 2p peaks 4000 Cu 2p 1/2 Cu 2p 3/2 8000 3500 CuO pure Cu or Cu 2 O CuO pure Cu or Cu 2 O 7000 6000 shake-up line shake-up lines 5000 3000 4000 2500 hybrid layer at B pure Cu clusters 3000 965 960 955 950 945 940 935 930 925 binding energy [ev] - sep. Cu clusters: only Cu or Cu 2 O, no CuO - hybrid layer: additional second peak component from CuO likely
log I / cps XR of deposited films XR measurement 6 5 4 3 2 1 0-1 TiO 2 d = 39.6 nm (sep. deposition) TiO 2 d = 34.1 nm (hybrid dep., Cu free area) Cu (sep.) TiO x (sep.) TiO x (hybrid) A -2 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 2 / - only TiO 2 layer homogeneous, no thickness info from Cu-cluster films
SEM image of hybrid layer, spot region - spot region: much Cu, a little Ti (confirmed by EDX)
SEM image of hybrid layer, edge region - edge region: no Cu, only Ti (confirmed by EDX)
SEM image of Cu nanocluster film - (1 x 7) µm trench echted with Ga ion beam gun (2 pa at 30 kv)
SEM image of Cu nanocluster film - estimation of layer thickness (spot center): ~ 250 nm
intensity / a.u. GIXD patterns of Cu-cluster (sep. deposited), TiO x (sep. deposited) and hybrid-films 70 Cu sep TiO2 sep hybrid 60 50 40 30 crystalline material?? 20 polycrystalline Cu fcc 10 0 25 30 35 40 45 50 2 / x-ray amorphous
intensity /a.u. GIXD of depositions with different O 2 flows 120 GIXD measurement 100 80 60 40 shift +60 a.u. shift +30 a.u. shift +20 a.u. Cu sep. 0 sccm O 2 Cu sep. 1 sccm O 2 Cu sep. 20 sccm O 2 Cu TiO x hybrid 20 20 25 30 35 40 45 50 55 60 2 / - decreasing Cu amount with 1 sccm O 2 flow, but no further decrease with 20 sccm O 2 - in hybrid mode (Ti magnetron on, oxygen plasma species) no fcc Cu peaks observable
0 1 1 1 1 1 25 30 35 40 45 50 55 0 0 2 0 0 2 1 1 2 GIXD pattern of Cu cluster (separate deposition) 8400 CUtci 75,5% CU 2O 24,5% N P00_SM.R AW Cu (111) Cu 2 O (111) (200) Cu (200) m Cu / m Cu2O = 80 / 20 4200 0 T = 63 Å domain size calculated from slope F(L) vs L T = 30 Å T = 43 Å marked anisotropy in the form of the coherently diffracting domains
0 1 1 1 1 1 25 30 35 40 45 50 55 0 0 2 1 1 1 0 0 2 1 1 2 9216 CUtci 30,8% CU 2O 69,2% N P08_SM.R AW SU M Cu 2 O (111) Cu 2 O (200) Cu (111) separate Cu cluster + 1 sccm O 2 4608 Cu (200) m Cu / m Cu2O = 30 / 70 0 T = 29 Å domain size calculated from slope F(L) vs L T = 41Å
0 1 1 1 1 1 25 30 35 40 45 50 55 0 1 1 0 1 1 1 1 1-1 1 1 1 1 1 0 0 2 0 0 2 1 1 1 1 1 1 2 1 1-0 0 2 2 0 2-0 0 2 2 1 1 0 2 0 1 1 2 1 1 2 1 2 0 0 1 1 2 0 0 1 1 1 0 0 2 2 1 1-2 0 2-2 1 1 0 2 0 1 2 0 GIXD pattern of hybrid films 9216 CUtci 30,8% CU 2O 69,2% N P05_SM.R AW 3846 CUO N P05_SM.R AW With model separate Cu cluster + 1 sccm O 2 Cu 2 O (blue) Cu (red) CuO SG: C 2/c (No. 15) Reference: ICSD 628616 4608 1923 0 0 10796 CUtci 0,0% CU 2O 0,0% CU O 100,0% N P05_SM.R AW 30 35 40 45 50 55 5398 CuO 100 % WH-plot: size 38 Å, strain 7.6*10-3 0 25 30 35 40 45 50 55
scaled intensity [a.u.] XPS comparison of Cu 2p peaks XPS high resolution scan of Cu 2p peak 6000 5000 Cu clusters Cu clusters in TiO 2 (hybrid layer) Cu clusters (+1 sccm O 2 ) Cu clusters (+20 sccm O 2 ) Cu 2p 1/2 Cu 2p 3/2 CuO Cu or Cu 2 O 4000 CuO Cu or Cu 2 O 3000 960 955 950 945 940 935 930 925 binding energy [ev] - Intensities of non-hybrid films normalized for easier comparison of peak profiles
XPS, XR and GIXD results, basic experiments XPS XR GIXD separate Cu clusters only TiO x Cu cluster + TiO x (hybrid film) - pure Cu and/or Cu 2 O even with 20 sccm O 2 in deposition chamber - no other impurities - too inhomogeneous for layer thickness estimation - crystalline Cu together with Cu 2 O. Cu: 80 %, Cu 2 O:20% - Cu: 30 % Cu2O:70% - TiO 2 verified - no impurities eff. 1) deposition rate: 0.94 nm/min - x-ray amorphous (no rutile/anatas ) 1) 40 nm film during 30 min deposition 2) different oxydation pathways of Cu clusters - compositions for positions A and B: most Cu on spot - Cu 2p 3/2 indicate CuO - too inhomogeneous for layer thickness estimation - TiO 2 still amorphous, - Cu completly oxygenated, - Formation of CuO 2)
conclusions model I xcu cluster + yo Cu x O y Cu Cu different reaction pathways I II Cu 2 O O 2 gaseous O plasma Cu 2 O CuO Cu-cluster reactive spezies dµ=-sdt+vdp+rtdlna+δdo plasma chemical reaction determined process model II Cu (i) ) Cu 2 O no gaseous phase reaction CuO O plasma species (ii) Cu 2 O formation diffusion limited, TiO 2 Ti plasma species no significant changes in the domain sizes during the oxidation processes
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X-ray profile analysis h ( x) f ( y) g( x y) dy F( L) H( L) G( L) STOKES method F(L), H(L) G(L) are the Fourier Transforms of f(x), h(x) and g(x) normalized to domain of definition of experimental line profile single line analysis 1 T das dl L 0 effective particle size multi line analysis Williamson-Hall plot: diagram immediatly gives information about size and shape of the crystallites and the presence or absence of lattice strain ß f integral width of the pure physical line profile
intensity [a.u.] EDX of hybrid thin film Hybrid film EDX spectra for different positions relative to cluster spot Ti Cu Si 10 5 10 4 10 3 10 2 10 1 10 0 10 5 10 4 10 3 10 2 10 1 10 0 10 5 10 4 10 3 10 2 10 1 Ti Ti spot center 0 1 2 3 4 5 6 7 8 9 10 11 12 spot edge 0 1 2 3 4 5 6 7 8 9 10 11 12 off-spot 0 1 2 3 4 5 6 7 8 9 10 11 12 SEM voltage [kv] Cu Cu
EDX results - atom% for three characteristic sampling positions: element spot center spot edge off-spot Cu 5.03 0.67 0.00 Ti 0.06 0.43 0.42 O 5.15 1.52 0.85 - highest atom% for Si from substrate (EDX sampling depth) - decreasing Cu density from cluster beam spot center outwards - Ti gets diluted by Cu clusters in spot center - stoichiometry supports Ti as TiO 2 and Cu as CuO