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species over a wide range. Films deposited at high ion energies and deposition rates form rutile with (101)h decreasing ion energy and deposition rates, rutile is formed with random crys-

2 anambic)

Surface & Coatings Technology 222 (2013) 112117

Contents lists available at SciVerse ScienceDirect

Surface & Coatin

l seactive magnetron sputtering techniques with different effects onphase formation. Research on TiO2 deposited bymagnetron sputteringpresented in numerous papers [313] shows that the transition be-tween crystallographic phases correlates with input process parame-ters (e.g. pressure, distance between a cathode and a substrate, andgas composition) and the mode of magnetron sputtering.

The rutile phase is typically deposited in discharges with high-energy ion ux and high electron ux directed toward the substrate[14]. On the other hand, the anatase phase is obtained typically atlower energy ux [15]. These results were later summarized by Mrazand Schneider [4] who proposed a pressuredistance (pd) parame-ter. This parameter is responsible for TiO2 formation and demon-

ed at a low frequency (~100 Hz) was employed. HiPIMS dischargesprovide large fractions of ionized sputtered species [18,19] of highenergy [20,21]. External assistance by superimposed (e.g. dc, rf ormw) plasma improves re-ignition of HiPIMS pulses and their time-evolution as well as allows a reduction in the working pressure [2227].Our researchwas performed in a HiPIMS system assisted by an electroncyclotron wave resonance (ECWR) discharge [28,29]. The ECWRpre-ionization [30,31] allows the reduction of the pressure limit bymore than one order of magnitude when compared with conventionalHiPIMS discharges [913]; a pressure of 0.075 Pa at reactive Ar/O2=1HiPIMS was achieved.

The rutile phasewith (101) preferred orientationwas deposited by

strates that the phase is determined bydeposition ux ratio during magnetron sputclearly shown that optimal ion bombardmenfactor in dening the structure of oxide lmgrowth of Cr2O3 lms prepared by asymmetr

Corresponding author. Tel.: +49 3834864784.E-mail address: stranv00@centrum.cz (V. Stranak).

0257-8972/$ see front matter 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.surfcoat.2013.02.012 are known and haves and promising techno-n be prepared using re-

sputtering deposition [17,18] of TiO2 and its formation with respect toion energy and ion ux. High power impulse magnetron sputtering(HiPIMS), working with short and energetic pulses (~100 s) repeat-been investigated for their unique propertielogical applications [1,2]. TiO2 thin lm(s) caTiO2RutileAnataseIDF

1. Introduction

Different crystalline phases of TiO(tetragonal) and brookite (orthorhohigh energy during the HiPIMS pulse while the ECWR discharge is mostly responsible for substrate heatingdue to dissipated power. However, the energetic contribution of the ECWR discharge is not sufcient forannealing and phase transformation.

2013 Elsevier B.V. All rights reserved.

tase (tetragonal), rutile

pulsed magnetron sputtering combined with asymmetric pulsed sub-strate bias [16].

The work presented in this paper is focused on ionized magnetronECWR tallite orientation, and nally at low ion energies the anatase phase occurs. It is supposed that particles gainKeywords:HiPIMS a preferred orientation. WitDeposition of rutile (TiO2) with preferredmagnetron sputtering

Vitezslav Stranak a,, Ann-Pierra Herrendorf a, HarmZdenek Hubicka b, Milan Tichy c, Rainer Hippler a

a University of Greifswald, Institute of Physics, Felix-Hausdorff-Str. 6, 17489 Greifswald, Geb Institute of Physics v. v. i., Academy of Science of the Czech Republic, Na Slovance 2, 182c Charles University in Prague, Faculty of Mathematics and Physics, V Holeovikch 2, 180

a b s t r a c ta r t i c l e i n f o

Article history:Received 26 November 2012Accepted in revised form 13 February 2013Available online 21 February 2013

The effect of energetic ion bdeposited using high-powewave resonance (ECWR) pl0.075 Pa during reactive HiP

j ourna l homepage: www.ethe ion energy ux totering deposition. It wast conditions are a criticals; demonstrated on theic bipolar mid-frequency

rights reserved.ientation by assisted high power impulse

ulff a, Steffen Drache a, Martin Cada b,

nyrague, Czech RepublicPrague, Czech Republic

bardment on TiO2 crystallographic phase formation was studied. Films werempulse magnetron sputtering (HiPIMS) assisted by an electron cyclotrona. The ECWR assistance allows a signicant reduction of pressure down toS deposition and subsequently enables control of the energy of the deposited

gs Technology

v ie r .com/ locate /sur fcoatlow pressure discharge. Since the path of the deposited species (ions,neutrals) is not affected by a weak magnetic eld they can travel to-ward the substrate in a nearly collision-free regime, having high ener-gy due to reduced pressure. The ion energywasmeasured bymeans ofenergy-resolved mass spectrometry and time-resolved retarding eldanalyzer to explain the growth of the rutile with preferred orientationin assisted ECWRHiPIMS discharges. The power density ux was es-timated from a calorimetric probe measurement [41].

2. Experimental part

2.1. Principle and arrangement of ECWRHiPIMS

The ECWRHiPIMS facility had already been developed and wasdescribed in our former works [28,29]. For this reason only a limitedand requisite description is provided here. The ECWR effect resultsfrom an interaction of an electromagnetic wave and plasma in thevolume with a superimposed magnetic eld. In practice an rf induc-tively coupled discharge (fRF=13.56 MHz, Pab=300 W) is generatedinside the single turn coil electrode (diameter d=125 mm). A staticdc-magnetic eld B0, preferentially produced by a pair of Helmholtzcoils, is superimposed perpendicularly to the axis of the rf-load coil.The magnetic eld causes slight plasma anisotropicity which allowsthe propagation of electron cyclotron waves through the plasma[31,32].

Amagnetron sputtering source (equippedwith Ti target, 50 mm indiameter) was mounted in the axis of the rf-coil electrode, see Fig. 1.TheHiPIMS electrical circuit consists of a commercial dc-power supplyand a home-built pulsed power switch [33]. The HiPIMS dischargewasoperated with a repetition frequency of f=100 Hz and a pulse widthof 100 s. The average discharge current was kept constant duringall experiments Iav=500 mA.

The ECWRHiPIMS facility was mounted on the bottom angeof the stainless steel UHV chamber evacuated by a turbo-molecularpump down to the ultimate pressure of 107 Pa, Fig. 1. The reactiveprocess gas consists of Ar (purity grade 99.995%) and O2 (puritygrade 99.997%) mixed in the ratio Ar/O2=1. ECWR assistance allows

113V. Stranak et al. / Surface & Coatings Technology 222 (2013) 112117a decrease in pressure down to p=0.075 Pa during the reactiveHiPIMS process. Experiments were carried out at the pressures 0.08,1.0 and 10.0 Pa.

The energy-resolved mass spectrograph and Langmuir probe sys-tems were mounted on the upper ange of the UHV chamber. Thecalorimetric probe and the substrate holder were accommodatedinto the vacuum chamber using an axially movable holder. TiO2 lmswere deposited on externally unheatedwafer Si (100)without voltagebiasing (the substrate holder was electrically grounded). Films were

8

7

6

5

4

32

9

1

Fig. 1. Experimental arrangement. 1 turbomolecular pump, 2 valve, 3 rf-matching box,4 sputtering source, 5 single turned rf-electrode, 6 Helmholtz coils housing, 7 movableholder for diagnostic tools and/or substrate holder, 8 energy-resolved mass spectro-

graph or axially movable Langmuir probe system, and 9 rotational feed-through.deposited on the substrates at distances of 30, 50, 70 and 110 mmfrom the target.

2.2. Film and plasma diagnostics

2.2.1. Thin lm analysisThe lms were characterized by grazing incidence X-ray diffrac-

tometry (GIXD asymmetric Bragg case, incidence angle =0.5,1.0) regarding crystallographic phases, and X-ray reectometry re-garding thickness and density. The methods are described, e.g. in[34]. Both GIXD and XR were performed on a Siemens D5000 diffrac-tometer equipped with a special parallel beam attachment (parallelplate collimator) for diffractometry investigations and a special reec-tometry sample stage for the reectometry measurements. Cu K ra-diation (40 kV, 40 mA) was used. The chemical composition wasinvestigated by X-ray photoelectron spectroscopy (XPS) by means ofan Mg K, VG Microtech Twin Anode X-ray source CLAM2 analyzer.

X-ray photoelectron spectroscopy (XPS) was employed to examinethe elemental depth prole and the valence states. The analysis wasperformed by the AXIS Ultra X-ray photoelectron spectrometer (KratosAnalytical, Manchester, UK) with a monochromatic Al K X-ray sourceat 150 W(15 kV, 10 mA). A survey scan from0 to 1200 eVwasmappedwith a pass energy of 80 eV. For high resolution measurements, a passenergy of 10 eV was used. The measured spectra were processed byCasaXPS software (Casa Software Ltd., Teignmouth, UK).

2.3. Langmuir probe measurements

A time-resolved Langmuir probe diagnostic was done by ALP Sys-tem Impedans (Impedans Ltd., Dublin, Ireland) with a time resolutionof 10 s. The probe, made of tungsten wire, 100 m in diameter andwith an active length of 1.0 mm, was placed in the magnetron axis.The magnetic eld was weak in the probe region (less than 1.9 mT)and the calculated mean Larmor radius for electrons was much largerthan the radius of the probe wire. Nevertheless, the probe was orient-ed perpendicular to eld lines to minimize the effect of the magneticeld. Basic plasma parameters such as electron energy probabilityfunction (EEPF), electron density (ne), effective electron temperature(Tef) and plasma potential (Vmpl) were calculated by standard meth-ods under the assumption of a collision-free regime [35]. The probewas placed at 30, 50, 70 and 110 mm from the target.

2.3.1. Measurements of ion distribution functionTheplasmaprocessmonitor PPM421 (OerlikonBalzers, Liechtenstein)

was employed for energy-resolved mass spectrometry. The plasmaprocess monitor combines a cylindrical mirror energy analyzer anda quadrupole mass spectrometer. The PPM421 orice was xed inthe magnetron axis at z=180 mm. Measurements were carried outwith a grounded extraction orice. Hence, all measured ion energiesare related to the plasma potential Vpl with respect to the ground.The measured signal represents the ion velocity distribution func-tion (IVDF) in the forward direction versus energy [36].

Spatially and time-resolved measurements of IVDF were carriedout using a retarding eld analyzer (RFA) Semion (Impedans Ltd.,Dublin, Ireland) [37,38]. The entrance orice of the RFA sensor wasplaced in the magnetron's axis z at distances of 30, 50, 70 and110 mm, i.e. in the position of the substrate during deposition. TheRFA sensor was grounded during the measurements. Time-resolvedmeasurements were done by the so-called boxcar method using a5 s period for data averaging. Ion distribution function was derivedfrom the measured data using the method proposed in [39,40].

2.3.2. Measurement of power density uxA calorimeter probe was employed to characterize the total power

inux onto the substrate. The probe, held on the oating potential,

consists of a copper disk 8 mm in diameter and 2 mm thick, soldered

to a k-type thermocouple. The method used for the determination ofthe heat transfer to the substrate is based on the measurement of thetemporal evolution of the probe temperature located at the substrateposition [41,42]. The spatially-resolved measurements were achievedby movement of the sensor/probe in the axial direction, i.e. in a coor-dinate z=30, 50, 70, and 110 mm. The coordinate z represents themagnetron's axis where z=0 mm is the target surface.

3. Results and discussion

3.1. Properties of TiO2 lms

TiO2 lms were deposited at different pressures (p=0.08, 1 and10 Pa) and distances (z=30, 50, 70 and 100 mm from the cathode)to study the effect of incoming energy on lm growth. All experi-ments were carried out in a fully poisoned state of the target [43],determined from the hysteresis curve measurement, to avoid specu-lations regarding the target state on the lm structure. StoichiometricTiO2 lms through the lm thickness were conrmed by elementaldepth prole XPS measurement. It was also proved several timesthat a highly reactive gas mixture with a larger amount of oxygen

is required, see the results of the measurement done by the calorimet-ric probe presented in Table 1. Based on this difference, we assumethat the total power density ux is not the only decisive factor respon-

Table 1TiO2 lm properties prepared by the ECWRHiPIMS system presented together withbasic plasma parameters. The following quantities are presented in each cell of thetable: crystallographic phase estimated from XRD, deposition rate athrmd calculated asthickness/time of deposition, and total power density ux t estimated from calorimet-ric probe measurement. The structure of the table corresponds with Fig. 7 where theion energies are shown.

d=30 mm d=50 mm d=70 mm d=110 mm

0.08 Pa Rutile pref. orient. Rutile Rutile Rutile2.7 nm/min 1.3 nm/min 0.5 nm/min 0.3 nm/min205 mW/cm2 116 mW/cm2 130 mW/cm2 126 mW/cm2

1.0 Pa Rutile Rutile Rutile Rutile1.6 nm/min 0.9 nm/min 0.5 nm/min 0.2 nm/min176 mW/cm2 95 mW/cm2 105 mW/cm2 100 mW/cm2

10.0 Pa Rutile Rutile Rutile+anatase Anatase0.9 nm/min 0.3 nm/min 0.2 nm/min 0.1 nm/min126 mW/cm2 76 mW/cm2 51 mW/cm2 44 mW/cm2

Fig. 3. The time-averaged mass spectrum of positive ions produced by an ECWRHiPIMS discharge of energy 18 eV. Time-averaged measurement at p=0.08 Pa, Ar/

114 V. Stranak et al. / Surface & Coatings Technology 222 (2013) 112117(Ar/O2=1) forms a titanium dioxide lm, see e.g. [7]. Because stoi-chiometric TiO2 lms were observed regularly; we are not providingany detailed analysis of the XPS results here. Our focus here is onthe phase formation of deposited lms.

The GIXD patterns of two lms deposited at different pressures areshown in Fig. 2; a complete overview of lm properties depositedunder different conditions is presented in Table 1. Our results showthat the (101) preferred orientation of titanium oxide with a rutiletype structure changes with increasing pressure and distance from thetarget respectively. An increase in the (pd) parameter results rst inrandom rutile crystallite orientationwhich is followed by the formationof the anatase phase. The integral intensity ratio I110/I101=2 character-izes randomly oriented rutile. We found I110/I101=0.3 for samples de-posited at 0.08 Pa and d=30 mm, and I110/I101=1 for lms depositedat 0.08 Pa and d=50 mm and 1 Pa and 30 mm respectively. Thesephase formations also correspond directly with the deposition rates.Films prepared at deposition rates >1.1 nm/min form rutile with(101) a preferred orientation and lms with very low deposition ratesexhibit the anatase phase.

Mraz and Schneider [4] observed similar phase formations de-pendent on pressure and distance in dc and rf discharges. However,they reported in their paper that rutile is formed at power densityuxes >20 mW/cm2, while in our case higher ux >55 mW/cm2

Fig. 2. An example of measured GIXD patterns (=0.5) of TiO2 of lms prepared at dif-ferent pressures: 0.08 Pa (upper pattern) and 10.0 Pa (lower pattern). The substrateswere located at the same distance (z=30 mm) from the target. Ar/O2=1 was used for

all experiments.sible for lm formation. In our opinion the carriers of energy ux(metal ions, gas ions, electrons) and their energetic contribution tothe total ux play a signicant role. As a consequence, we investigatedplasma properties and energies of the deposited species.

3.2. Properties of Ar/O2 discharge

The ECWRHiPIMS discharge is based on a superposition of simul-taneously driven ECWR plasma (operated in continuous mode) andHiPIMS pulses repeated at a frequency of 100 Hz. The electron densityof ECWR plasma produced in the idle time of the HiPIMS reaches theorder ne1016 m3 which results in an ionization level of 1%.The spatial distribution of the ECWR discharge is typically homoge-neous [31]. Since the ECWR does not provide any sputtering effect,the plasma consists mainly of Ar+, O+, and O2+ ions. Further, impuri-ties such as H+, H2+, NO+ and NO2+ were also found in the positiveion mass spectrum, see Fig. 3. The energy of the ECWR-producedions is usually several tens of eV, see the IVDF of Ar+ shown in Fig. 4.It is thought that positive ECWR ions gain their energy from accelera-tion in the plasma sheath region (rf-ECWR plasma potential Vpl~27 Vwas measured by Langmuir probe).

Species to be deposited are produced during HiPIMS pulses. Newpeaks of Ti+, Ar++, O++, and Ti++ appear in the mass spectrum ifHiPIMS discharge is activated, see Fig. 3 where the time average spec-trum is presented. However, the intensities of HiPIMS-produced peaksO2=1. HiPIMS-produced species are denoted with blue labels.

discharges [48]. The rise of the current density reaches its maximumquickly (ip3 A/cm2), roughly 10 s after the voltage onset, and re-mains constant during the whole HiPIMS pulse. Such a current densitycorresponds with pulse power density pp1.5 kW/cm2.

3.3. Ion energy vs. lm growth

The energy distributions of Ti+ and Ti++ ions produced at lowpressure in an ECWRHiPIMS discharge are shown in Fig. 6. Both dis-tributions exhibit a tail of high energies up to 100 and 180 eV, respec-tively. The roughly twice as high energy of double charged Ti++ iscaused by a higher q/m ratio. The high energy tails measured mostprobably originate from HiPIMS phenomena since they were not ob-served during conventional dc-magnetron sputtering operated at thesame mean discharge current together with ECWR assistance, seeFig. 6. On the contrary, the main peak of the distribution's bodies (lo-cated around 25 eV) occurs regularly in all presented measurements,including dc-magnetron sputtering. The energy of sputtered neutralatoms, gained as a result of the sputtering process, is typically approx-

Fig. 4. A comparison of positive gas ion IVDFs measured in ECWR and ECWRHiPIMSdischarges at low pressure p=0.08 Pa. The energy scale of double-charged ions wasmultiplied by a factor of two to obtain the scale in electronvolts [21,36]. The distancebetween the target and the spectrometer's orice was 180 mm.

115V. Stranak et al. / Surface & Coatings Technology 222 (2013) 112117(Ti+, Ar++ O++, Ti++) were multiplied by a factor 100 since theHiPIMS discharge is operated only for 1% of the total time. This proce-dure was done to enhance the clarity of the presented mass spectra.Another reason for the lower peak intensity of the HiPIMS mass spec-trum is a reduced number of sputtered species due to target poisoning,since the sputtering yield of titanium oxide is lower compared tothat of pure titanium (YTiOx 0:015 and YTi=0.3 for Ar ion energy of300 eV [44,45]).

It was already described in our previous work [28] that large frac-tions of species sputtered in an ECWRHiPIMS system are ionizedwithsignicant fractions of double ionized atoms Ti++. Preferential ioniza-tion of sputtered Ti atoms is caused by: (i) the lower ionization poten-tial of titanium atoms EiTi+=6.8 eV and EiTi++=13.6 eV, and (ii) asignicantly larger ionization cross section of Ti in the energy rangeof 100600 eV [46]. Intensive production of ions increases the elec-tron density during the HiPIMS pulse as presented in Fig. 5. The elec-tron density evolution reaches its maximum value ne1018 m3,i.e. nearly two orders of magnitude higher than in a pure ECWR dis-charge and the ionization coefcient increases up to 10%. The plas-ma density decreases after reaching its maxima. This effect might beconnected with the creation of negative oxygen ions by dissocia-

tive electron attachment [47]. It was reported that the density of a neg-ative ion can reach about 35% of electron density in electronegative

Fig. 5. Time evolution of the peak HiPIMS discharge current and the electron density.Pressure in the chamber p=0.08 Pa, z=3 cm, fH=100 Hz, and HiPIMS pulse widthTa=100 s.Fig. 6. IVDFs of ionized sputtered species Ti+ and Ti++. Compared are IVDFs of Ti+ ionsproduced by (i) ECWRHiPIMS discharge (solid line) and (ii) dc-magnetron sputteringrunning with ECWR assistance (dotted line). Pressure 0.08 Pa, Ar/O2=1, distanceimated by a Thompson's distribution [4952]. Thereafter, sputteredatoms are ionized by inelastic collision with electrons in the dischargevolume and reach the substrate/spectrograph orice in a nearlycollision-free regime due to reduced pressure down to p=0.08 Pa. Itis expected that the energy of sputtered Ti atoms is not inuencedby electron impact ionization. A similar high energy tail of IVDFs wasobserved for Ar++ and O+ species originating in HiPIMS, see Fig. 4.HiPIMS ion energization is probably caused by azimuthal ion acceler-ation [53] which tangentially ejects the ions sideways, and by instabil-ities associated with ionization zones of highly dense plasma [54].

Measurements using a retarding eld analyzer were done to inves-tigate time-evolution and the effect of pressure/distance on ion energydistribution; results are summarized in Fig. 7. The highest energieswere measured at the lowest pressure and close to the target as onewould naturally expect. Maximum ion energies were measured upto ~80 eV. The typically lower value of the energy obtained by RFAwas already discussed in our previous work and is caused by the dy-namic range of the sensor and by the presence of double-ionized species[29]. Because of these limiting factors we only are able to observe IVDFof ECWR plasma at larger distances from the target (d=100 mm) or athigher pressures (p=10 Pa). The typical energy of ECWR-producedions is about ~25 eV and is not strongly affected by the pressure/distance. However, the ECWR effect can be reduced or can even vanishat higher pressure and for this reason one should consider only an ordi-nary, inductively coupled discharge running at p=10 Pa. Despite thetarget orice 180 mm.

pretionrme

116 V. Stranak et al. / Surface & Coatings Technology 222 (2013) 112117facts pointed out above, the effect of pressure/distance on IVDF canbe seen in Fig. 7 and compared with the lm properties presented inTable 1.

The rutile phase with (101) preferred orientation was deposited atthe highest ion energies obtained during the HiPIMS pulse. It was al-ready reported that different orientations of rutile can be preparedby ion beam assisted deposition depending on the impact angle andarrival ratio of ions to deposited atoms [56,57]. In general, the prefer-ential growth of a TiO2 lm results from a competition betweenthe surface free energy effect and the strain energy effect. The crystalplane with the highest atomic density exhibits the lowest surfacefree energy; this favors a subsequent preferential growth. But it isthe (110) and not the (101) plane which exhibits the lowest surface

d = 30 mm d = 50 mm

Fig. 7. Time-resolved IDFs measured by means of the retarding eld analyzer. The matrixin the chamber (rows). The x-axis of each image represents the time (HiPIMS pulse durais expressed by false color. The IVDF intensity is normalized to the maximum of all perfotechnique is shown in [55].free energy [56]. Hence, the (101) orientation cannot be explainedfrom the viewpoint of surface free energy. The preferential growth ofthe (101) is most probably controlled by the strain energy. Thepreferred growth of (101) oriented rutile is enhanced by increasingdeposition rate and lm thickness, respectively. The deposition ratedecreases with increasing working gas pressure for a selected target-substrate distance, see Table 1.

The substrates were not intentionally heated but due to power dis-sipated from the plasma the substrate temperature was increased toabout ~110 C with respect of pressure and position (measured by acalorimetric probe). A similar increase of the substrate temperatureis also reported in [4,58]. The calorimetric probe measurements re-vealed that more than 80% of the total power ux originates fromthe ECWR discharge with a signicant contribution of incoming elec-trons (e75%). Hence, we assume that substrate heating is mostlycaused by bombarding electrons and ions provided by the permanent-ly running ECWR discharge. However, this increase of the substratetemperature is not high enough for conventional thermal annealing(annealing temperatures of ~300 C for anatase and ~900 C for rutileare needed [59]). From the results presentedwe conclude that it is theenergy of the deposited species that is responsible for growth andphase formation of TiO2 lm.

4. Conclusion

The effect of particle energy on TiO2 formation during high powerimpulse magnetron sputtering deposition was studied. It was foundthat the high energy of the deposited species, gained during HiPIMSpulses, is most probably responsible for the formation of the rutilephase with the (101) preferred orientation. The preferred rutile ori-entation is controlled by the strain energy and can be enhanced byincreasing the deposition rate. With decreasing ion energy and depo-sition rates, rutile is formed with random crystallite orientation, andnally at low ion energies and deposition rates the anatase phaseoccurs.

The ECWRHiPIMS system driven in a reactive Ar/O2=1 atmo-sphere was employed. The pre-ionization, provided by the ECWR ef-fect, allows signicant pressure reduction which inuences theenergy of the deposited species. The energies of deposited ions weredetected to be several times higher at lower pressure in the HiPIMS

d = 70 mm d = 110 mm

0.08 Pa

1.0 Pa

10.0 Pa

sents time-resolved IDFs for different RFA/substrate positions (columns) and pressuresis Ta=0100 s), and the y-axis represents the ion energy. The relative IVDF intensityd measurements. A 3D graph (x time, y ion energy, z IDF) of the same diagnosticpulse. Power dissipated from the ECWR discharge is largely responsi-ble for substrate heating due to bombarding electrons and ions. How-ever, an increase in the substrate temperature (about 110 C) is notsufcient for a conventional annealing process of the deposited TiO2lms. Hence, it is assumed that the energy of the deposited speciesis responsible for lm formation.

Acknowledgments

This work was supported by the Deutsche Forschungsgemeinschaft(DFG) through SFB/TR 24 Complex Plasmas and by the German Feder-al Ministry of Education and Research (BMBF) through the projectCampus PlasmaMed. Support provided through the project LD12002of MSMT CR and Czech Grant Agency (project P205/11/0386) is alsoacknowledged.

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117V. Stranak et al. / Surface & Coatings Technology 222 (2013) 112117

Deposition of rutile (TiO2) with preferred orientation by assisted high power impulse magnetron sputtering1. Introduction2. Experimental part2.1. Principle and arrangement of ECWRHiPIMS2.2. Film and plasma diagnostics2.2.1. Thin film analysis

2.3. Langmuir probe measurements2.3.1. Measurements of ion distribution function2.3.2. Measurement of power density flux

3. Results and discussion3.1. Properties of TiO2 films3.2. Properties of Ar/O2 discharge3.3. Ion energy vs. film growth

4. ConclusionAcknowledgmentsReferences