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TiAlN coatings synthesised using adense plasma focus system and variedfocus shotsTousif Hussain a , Riaz Ahmad a , Jamil Siddiqui a & Nida Khalid aa Department of Physics, Government College University, 54000,Lahore, Pakistan

Available online: 31 Oct 2011

To cite this article: Tousif Hussain, Riaz Ahmad, Jamil Siddiqui & Nida Khalid (2011): TiAlN coatingssynthesised using a dense plasma focus system and varied focus shots, Radiation Effects andDefects in Solids, 166:11, 873-883

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Radiation Effects & Defects in SolidsVol. 166, No. 11, November 2011, 873–883

TiAlN coatings synthesised using a dense plasma focus systemand varied focus shots

Tousif Hussain, Riaz Ahmad*, Jamil Siddiqui and Nida Khalid

Department of Physics, Government College University, 54000 Lahore, Pakistan

(Received 2 May 2011; final version received 15 August 2011)

TiAlN coatings were synthesised by a 2.3 kJ pulsed plasma focus system. The effect of focus shots on crys-tallography, microstructure, surface morphology, roughness and hardness was investigated. The coating’scrystallography and microstructure were investigated using X-ray diffraction (XRD) characterisation. TheXRD data showed that TiAlN coatings were crystallised in the cubic NaCl B1 structure with orientationsin the (111), (200), (220) and (311) crystallographic planes. Texture coefficients showed a competitionbetween (111) and (200) planes. The coatings surface morphology and thickness analyses were carried outusing scanning electron microscopy (SEM). SEM micrographs showed dense and uniformly spread filmwith fine-grained morphology with hardly any pit, hole and crater. The surface roughness and hardnessof TiAlN coatings were investigated by atomic force microscopy and Vickers microhardness tester. Grainsize and roughness were found to decrease, whereas thickness and hardness were found to increase, withincreasing focus shots.

Keywords: titanium aluminium nitride; plasma focus system; X-ray diffraction; SEM; AFM

1. Introduction

Titanium nitride is a member of the refractory transition metal nitrides family showing character-istics of both covalent and metallic compounds (1, 2). For a few decades, TiN coatings have beenapplied to tools, dies and many mechanical parts to increase their lifetime and performance owingto their excellent mechanical, thermal and electronic properties, such as good thermal stability,high corrosion resistance and low electrical resistivity. Therefore, they have many applicationsranging from coatings on cutting tools to diffusion barriers in microelectronic applications. How-ever, TiN coating is degraded by oxidation at high temperature during working. So, it is importantto improve its oxidation resistance for successful use. As a possible solution to this problem, alu-minium atoms have been added to the TiN material considering that both TiN and TiAlN have thesame crystallographic structure (fcc) (3). In high-temperature applications, a dense and stronglyadhesive Al2O3 film is observed because of diffusion of Al atoms to the surface, which stopsfurther oxidation. TiAlN is expected to be a promising candidate as a hard coating layer becauseit shows excellent properties, especially for high-temperature use (4, 5).

*Corresponding author. Email: ahriaz@gmail.com

ISSN 1042-0150 print/ISSN 1029-4953 online© 2011 Taylor & Francishttp://dx.doi.org/10.1080/10420150.2011.616957http://www.tandfonline.com

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Different TiAlN coatings have been reported and been synthesised by various deposition tech-niques including cathodic arc ion plating (6–8), ion beam sputter plating (9), ion mixing and vapourdeposition (10) and reactive magnetron sputtering (11–15). The dense plasma focus (DPF) (16,17) technique is one of the prospective hybrid deposition methods for the application of TiAlNcoatings. The use of plasma focus for surface modification and thin film deposition purposes hasshown that this pulsed plasma device owns interesting features of high deposition rates and ener-getic deposition process (18–27). It may be significant to mention that the plasma focus devicehas not been reported prior to this work for the synthesis of TiAlN coatings to the best of myknowledge. The synthesis of TiAlN coatings using plasma focus deposition system is not onlyeconomic, simple, efficient and time-saving, but also provides the high deposition rate havinggood adhesion between the deposited coatings and the substrate. DPF deposition can produce adenser coated layer in less deposition time. It does not need extra substrate heating during filmdeposition because the substrates are heated during ion beam treatment compared with othertreatments.

In this work, the preparation of TiAlN coatings by varying focus shots by the DPF device isdescribed. The films were deposited at 9 cm axial position with the anode axis. The effect ofvarying focus shots on microstructure, surface morphology, surface roughness and hardness ofthese coatings was studied.

2. Experimental setup and method

Synthesis of the TiAlN thin films was done using polished 10 × 10 × 5 mm3 aluminium substratesand a titanium target fitted at the top of the anode. The substrates and target were cleaned by rinsingin an ultrasonic bath of water. The deposition was performed in a Mather-type DPF device poweredby a single 32 μF, 15 kV capacitor. Details of the plasma focus device are given in earlier works(16, 17, 27). The schematic diagram of the system is shown in Figure 1. For the deposition ofTiAlN coatings, a copper anode with a titanium target fitted at top was used. Nitrogen was used asa working gas. The chamber was evacuated up to 1 × 10−2 mbar by a rotary vane pump and filledwith high-purity nitrogen gas at optimum pressure of 1.25 mbar before plasma focus operation.The substrates are mounted, at the anode axis, at a fixed distance of 9 cm from the top of theanode using a substrate holder behind a movable metallic shutter. It always takes several focusshots to get strong focusing after each fresh loading of gas for film deposition. A metallic shutterin between the anode and the substrate was used to prevent the exposure of substrate to theseearly weak focusing shots as shown in Figure 1. The shutter is removed after two or three focusshots, after getting good focusing. The focusing action was recorded using a simple resistivevoltage probe and Rogowski coil. The dip in the Rogowski coil signal and spike in the voltageprobe signal help in ascertaining good focusing action in the plasma focus (PF) discharge. Thefocus shot at which a maximum dip in the Rogowski coil signal/maximum spike in the voltageprobe signal takes place is termed as the stronger focus, and it is a very common experience thatfocusing action becomes stronger and stronger as focus gets stabilised after firing a few focusshots resulting in the generation of higher energy, higher flux ions. The focus shots are fired at afrequency of one-shot at a time long enough to ensure thermal relaxation of specimen after beingheated by the preceding ion beam. The coatings were synthesised, at room temperature substrates,with 10, 20, 40 and 50 focus shots.

The qualitative understanding of thin film deposition process, in a DPF device, is as follows:DPF transfers the electrical energy stored in the capacitor to the chamber by a spark gap switch. Thedielectric breakdown of gas occurs along the insulator surface between an anode and a cathode andan axisymmetric current sheath forms around the insulator. This current sheath moves towardsthe open end of electrode assembly under J × B force. When this current sheath reaches the

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Radiation Effects & Defects in Solids 875

Wilson seal

Vaccumchamber

Sampleholder

SampleShutter

Insert

Electrodeassembly

C

HVS

Trigger

Figure 1. Schematic diagram of the DPF system.

top of electrode assembly, it collapses radially inward during the final focus phase. This is theinstant where microinstabilities, mainly m = 0 instabilities, start to grow and in turn strengthenthe induced electric field locally. This enhanced electric field, coupled with magnetic field, breaksthe focused plasma column by accelerating ions towards the top of chamber and electrons towardsthe positively charged anode. After this, disruption of the plasma column starts, and it breaks upcompletely to form hot (≈1–2 keV) and dense (≈1025−26 m−3) plasma.

The TiAlN coatings were characterised for their structure, surface morphology, roughness andhardness by a variety of techniques. The crystalline structure of the films was characterised byX-ray diffraction (XRD) using an X’Pert PRO MPD X-ray diffractometer. A HITACHI S-3400 Nscanning electron microscope (SEM) was used to study surface morphology of the films and tofind thickness using a cross-sectional view. The surface roughness was measured using a Picoinstrument atomic force microscope (AFM) (Molecular Imaging Inc.). The hardness measurementwas taken using a Wilson Wolpert 401 MVA Vickers microhardness tester.

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3. Results and discussion

3.1. Phase identification

Figure 2 shows the XRD peak patterns, ranging from 30◦ to 85◦, of four coatings for variousfocus shots. XRD patterns showed the development of two phases: one with fcc NaCl B1 structuresimilar to TiN structure and the other with AlN (fcc phase). Differentiation of the TiN and TiAlNphases using the diffraction method is impossible because of their isomorphous nature, as TiAlNis, in fact, the secondary solid solution based on titanium nitride. The diffraction patterns exhibita pattern of crystalline TiAlN with orientations of (111), (200), (220) and (311) and AlN withorientations of (111), (200) and (220). Native oxide of aluminium, which was presented in asubstrate surface, is removed gradually with the increase in the number of focus shots (28, 29).

The observed intensity of the TiAlN planes for TiAlN coatings showed an increasing trendwhen focus shots increased (Figure 3). Taking into account that the intensity of diffraction peaksis related to the quantity of planes that generate diffraction (30), an increase in intensity showsgreater compaction in the coatings with the increase in focus shots. The possible explanationof increasing intensity for higher focus shots is that the intensity of diffraction of the peaks isdependent on the energy and flux of ions that are impinging on the film surface. As more focusshots are fired, the focus becomes more stable and has stronger focusing action, resulting in thegeneration of high-energy and high-flux ions (31).

3.2. Lattice constant

In order to further investigate the microstructural changes of plasma focus deposited TiAlNcoatings, the lattice constants were calculated.

The peak position revealed a nonlinear variation of the lattice parameter (Figure 4), whichis considered to result from the composite nature of the ternary nitrides and the substrate highheating effect during deposition. The reported lattice parameter of TiN (32) is 0.424 nm. It isclear from Figure 4 that the lattice parameter of (111) and (200) planes are less than the reportedlattice parameter of TiN. The smaller lattice parameter was related to the formation of a solid

Figure 2. XRD patterns obtained for TiAlN coatings deposited at a distance of 9 cm at zero angular positions for variousnumber of focus shots.

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Radiation Effects & Defects in Solids 877

Figure 3. Intensity as a function of the number of focus shots.

Figure 4. Lattice constant with varying number of focus shots.

solution structure where Al atoms substitute Ti atoms in the TiN cubic lattice (remaining still a fccstructure), since the aluminium’s atomic radius (0.143 nm) is smaller than that of Ti (0.146 nm).This leads to shrinkage in the lattice parameter and hence a shift in 2θ value in the XRD.

3.3. Grain size

Using the broadening of the peaks, it is possible to determine the grain size from the Scherrerformula (33). The grain size (D) of the thin films was estimated from the following equation:

D = 0.9λ

β cos θ, (1)

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Figure 5. Grain size as a function of the number of focus shots.

where β is the full width at half maximum (FWHM) of the diffraction peak, λ is the wavelengthof the incident Cu Kα X-ray (1.514Å) and θ is the diffraction angle.

The grain size curve (Figure 5) is influenced by the number of focus shots, when increasingthe focus shots, the grain size was found to decrease linearly. With the reduction in the grain size,the dislocation activity is restricted and crack propagation along grain boundaries is prevented.

3.4. Texture coefficient

The XRD spectra consist of primarily (111) and (200) reflection. The texture coefficients of theTiAlN coatings as a function of focus deposition shots were calculated from their respective XRDpeaks using the following formula:

Texture coefficient (Tc) = I(hk1)

I(111) + I(200), (2)

where hkl represents the (111) and (200) orientations.The Tc value for a particular set of (hkl) planes is proportional to the number of grains that are

oriented with the plane parallel to the surface of sample (34). The texture coefficients of the (111)and (200) orientation are high compared with other orientations in the plasma focus depositedTiAlN thin coatings (Figure 6). The presence of mixed (111) and (200) texture for deposited filmsis due to the competitive growth between the surface and strain energy. Random orientationsmight be due to higher aluminium contents in coatings.

3.5. Surface morphology

The surface morphological studies of the plasma focus deposited TiAlN coatings that exhibit goodcrystallinity were observed by SEM as shown in Figure 7.

The sample exposed to 10 focus shots showed dense and fine-grained morphology with fewpit holes and crater present throughout the TiAlN coating. It is noticeable that there is notrace of columnar growth in all synthesised TiAlN coatings. The columnar growth results from

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Radiation Effects & Defects in Solids 879

Figure 6. Texture coefficient with varying number of focus shots.

Figure 7. SEMs of the TiAlN coatings synthesised at (a) 10 focus shots; (b) 20 focus shots; (c) 40 focus shots and(d) 50 focus shots.

self-shadowing during deposition process and is the characteristic feature for evaporation andsputter deposition (35–37). For sufficiently high energies, the impacting cluster compresses andanneals the area directly, hindering the columnar growth. The energetic cluster also leads to aself-smoothing of surface (38, 39).

The average thicknesses of the samples synthesised using various focus shots can be measuredfrom the corresponding cross-sectional SEM images as shown in Figure 8. The results showedthat the deposition thickness of the TiAlN coatings in a plasma focus system is in some way

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Figure 8. Thickness as a function of the number of focus shots (inset: cross-sectional SEM of TiAlN coating synthesisedwith 40 focus shots).

linear with the typical deposition rate of about 276 ± 50 nm per shot at focus bank storage of2.3 kJ energy. It may be noted that the deposition rate achieved in plasma focus is high comparedwith the deposition rates obtained in other devices. It may also be noted that energetic ions alsosputtered the substrate.

3.6. Roughness measurement

The coating morphology was also analysed using AFM. Figure 9(a–c) and (d) presents the 3Dsurface topography and root mean square (RMS) roughness of the TiAlN coatings synthesisedwith varying number of focus shots, respectively. All theAFM images were obtained in a scanningarea of 5 μm × 5 μm. The values of RMS roughness were derived from AFM images, which wereobtained from the average of the values measured in four random areas. Roughness decreases upto 40 number of focus shots as thickness increases (Figure 8) and again increases slightly for 50number of focus shots. The film roughness is found to decrease with the increase in the focusshots except for thin films deposited for 50 focus shots which is consistent with SEM results.Bertalot et al. (40) commented that the ions emitted in plasma focus have a wide energy rangein a fountain-like geometry with anisotropy in their angular distribution. Most of the ions areemitted in a small solid angle along the anode axis and their flux decreases with the increase inthe angle. This also infers that roughness would be different at different areas of samples, whichis consistent with our results as shown in Figure 9.

3.7. Microhardness

The Vickers microhardness (HV) as a function of imposed load for plasma focus deposited TiAlNcoatings is shown in Figure 10. Four hardness measurements at 25, 50, 100 and 200 gf loads,applied for dwell time of 5 s, for each sample were used for microhardness profile. The hardnessof untreated aluminium sample is also presented for comparison. The hardness was observed toincrease with the increase in focus shots except for 50 focus shots.A steep fall of the microhardnessvalues in the near-surface region of the samples exposed to focus shots suggests a concentration

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Figure 9. Atomic force micrographs of the TiAlN coatings synthesised at (a) 10 focus shots; (b) 20 focus shots; (c) 40focus shots and (d) graph of RMS roughness with varying focus shots.

Figure 10. Microhardness as a function of the applied load and the number of focus shots.

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gradient towards the bulk. The morphology of the material, that is, microstructure-related effects,severely affects the hardness of the material (41). The increase in the microhardness values may becredited to increase in ion flux and incorporation of titanium and nitrogen ions into the depositedTiAlN coatings (42).

There are many factors that may affect the measured hardness of TiAlN coatings, including thegrain size, residual stresses and densification of coatings. A hardening (H) because of a decreasein the average grain size (d) according to the Hall–Patch relationship Hα1/d1/2 might also beincluded in the present case. This can be deduced from the observation that hardness increases asthe grain size decreases from about 49 to 29 nm (Figure 4).

4. Conclusions

TiAlN coatings were grown by the DPF system with varying focus shots. The influence of focusshots on crystallography, microstructure, surface morphology, roughness and hardness was stud-ied. According to the XRD analysis, crystallographic orientation in (111), (200), (220) and (311)planes was found, presenting a competition between (111) and (200) planes. On the other hand,a decrease in the grain size is observed with increase in focus shots. SEM micrographs showed adense and uniformly spread film with fine-grained morphology. Hardness is found to follow theHall–Patch relationship. The observed variation in XRD, SEM and hardness results is explainedbased on the ion emission characteristics of the plasma focus system. The results showed that 40focus shots are acceptable for the synthesis of dense, smoother and harder coatings of TiAlN atroom temperature using the plasma focus system.

Acknowledgements

One of the authors, Tousif Hussain, would like to thank HEC, in Pakistan, for their financial support. Dr Shahzad Naseem(Center for Solid-State Physics, University of the Punjab, Lahore, Pakistan), Dr M. Zakkaullah (Physics Department,Quaid-i-Azam University, Islamabad, Pakistan) and R. Sammynaiken (Saskatchewan Structural Sciences Centre, Univer-sity of Saskatchewan, Saskatoon, Canada) are also acknowledged for their technical support in the SEM, hardness andAFM analyses, respectively.

References

(1) Blaha, P.; Redinger, J.; Schwarz, K. Phys. Rev. B 1985, 31, 2316–2325.(2) Schwarz, K. CRC Crit. Rev. Solid State Mater. Sci. 1987, 13, 211–258.(3) Wang, D.Y.; Chang, C.L.; Wong, K.W.; Li, Y.W.; Ho, W.Y. Surf. Coat. Technol. 1999, 120–121, 388–394.(4) Munz, W.; Dieter, X. J. Vac. Sci. Technol. A: Vac. Surf. Films 1986, 4, 2717–2725.(5) Knotek, O.; Bohmer, M.; Leyendecker, T. J. Vac. Sci. Technol. A: Vac. Surf. Films 1986, 4, 2695–2700.(6) Sato, K.; Ichimiya, N.; Kondo, A.; Tanaka, Y. Surf. Coat. Technol. 2003, 163–164, 135–143.(7) Falub, C.V.; Karimi, A.; Ante, M.; Kalss, W. Surf. Coat. Technol. 2007, 201, 5891–5898.(8) Beake, B.D.; Smith, J.F.; Gray, A.; Fox-Rabinovich, G.S.; Veldhuis, S.C.; Endrino, J.L. Surf. Coat. Technol. 2007,

201, 4585–4593.(9) Lee, S.-Y.; Wang, S.-C.; Chen, J.-S.; Huang, J.-L. Surf. Coat. Technol. 2007, 202, 977–981.

(10) Uchida, H.; Yamashita, M.; Hanaki, S.; Ueta, T. Mater. Sci. Eng. A 2004, 387–389, 758–762.(11) Kim, G.; Lee, S.; Hahn, J. Surf. Coat. Technol. 2005, 193, 213–218.(12) Huang, Y.Z.; Stueber, M.; Hovsepian, P. Appl. Surf. Sci. 2006, 253, 2470–2473.(13) Kutschej, K.; Mayrhofer, P.H.; Kathrein, M.; Polcik, P.; Tessadri, R.; Mitterer, C. Surf. Coat. Technol. 2005, 200,

2358–2365.(14) Zywitzki, O.; Klostermann, H.; Fietzke, F.; Modes, T. Surf. Coat. Technol. 2006, 200, 6522–6526.(15) Shum, P.W.; Li, K.Y.; Zhou, Z.F.; Shen, Y.G. Surf. Coat. Technol. 2004, 185, 245–253.(16) Mather, J.W. Phys. Fluids 1965, 8, 366–377.(17) Lee, S.; Tou, T.Y.; Moo, S.P.; Eissa, M.A.; Gholap, A.V.; Kwek, K.H.; Mulyodrono, S.; Smith, A.J.; Suryadi;

Usada, W.; Zakaullah, M. Am. J. Phys. 1988, 56, 62–68.(18) Bogolyubov, E.P.; Bochkov, V.D.; Veretennikov, V.A.; Vekhoreva, L.T.; Gribkov, V.A.; Dubrovskii, A.V.; Ivanov,

Y.P.; Isakov, A.I.; Krokhin, O.N.; Lee, P.; Lee, S.; Nikulin, V.Y.; Serban, A.; Silin, P.V.; Feng, X.; Zhang, G.X. Phys.Scr. 1998, 57, 488–494.

Dow

nloa

ded

by [

INA

SP -

Pak

ista

n ]

at 2

2:08

31

Oct

ober

201

1

Radiation Effects & Defects in Solids 883

(19) Lepone, A.; Kelly, H.; Lamas, D.; Márquez, A. Appl. Surf. Sci. 1999, 143, 124–134.(20) Bernard, H.B.A.; Choi, P.; Chuaqui, H.; Gribkov, V.; Herrera, J.; Hirano, K.; Krejcí, A.; Lee, S.; Luo, C.; Mezzetti, F.;

Sadowski, M.; Schmidt, H.; Ware, K.; Wong, C.S.; Zoita, V. J. Moscow Phys. Soc. 1998, 8, 93–170.(21) Kato, Y.; Be, S.H. Appl. Phys. Lett. 1986, 48, 686–688.(22) Gribkov, V.A.; Pimenov, V.N.; Ivanov, L.I.; Dyomina, E.V.; Maslyaev, S.A.; Miklaszewski, R.; Scholz, M.; Ugaste,

U.E.; Dubrovsky, A.V.; Kulikauskas, V.C.; Zatekin, V.V. J. Phys. D: Appl. Phys. 2003, 36, 1817–1825.(23) Rawat, R.S.; Arun, P.; Vedeshwar, A.G.; Lee, P.; Lee, S. J. Appl. Phys. 2004, 95, 7725–7730.(24) Bhuyan, H.; Chuaqui, H.; Favre, M.; Mitchell, I.; Wyndham, E. J. Phys. D: Appl. Phys. 2005, 38, 1164–1169.(25) Nayak, B.B.; Acharya, B.S.; Mohanty, S.R.; Borthakur, T.K.; Bhuyan, H. Surf. Coat. Technol. 2001, 145, 8–15.(26) Hussain, T.; Ahmad, R.; Khan, I.A.; Siddiqui, J.; Khalid, N.; Bhatti, A.S.; Naseem, S. Nucl. Instrum. Methods B

2009, 267, 768–772.(27) Sadowski, M.J.; Gribkov, V.A.; Kubes, P.; Malinowski, K.; Sadowska, E.S.; Scholz, M.; Tsarenko, A.; Zebrowski,

J. Phys. Scr. 2006, T123, 66–78.(28) Arai, T.; Fujita, H.; Tachikawa, H. In Ion Nitriding; Spalvinas, T., Ed.; American Society for Metals: Metals Park,

OH, 1987; p 37.(29) Parascandola, S.; Kruse, O.; Möller, W. Appl. Phys. Lett. 1999, 75, 1851–1853.(30) Srivastava, S.K.; Palit, D. Solid State Ion. 2005, 176, 513–521.(31) Rawat, R.S.; Lee, P.; White, T.; Ying, L.; Lee, S. Surf. Coat. Technol. 2001, 138, 159–165.(32) Cullity, B.D.; Stock, S.R. Elements of X-Ray Diffraction; Prentice-Hall; USA, p 664.(33) Powder Diffraction File of the International Center for Diffraction (PDF-ICDD). Card No. 381420.(34) Subramanian, B.; Ashok, K.; Jayachandran, M. Appl. Surf. Sci. 2008, 255, 2133–2138.(35) Thornton, J.A. J. Vac. Sci. Technol. 1974, 11, 666–670.(36) Barabasi, A.L.; Stanley, H.E. Fractal Concepts in Surface Growth; Cambridge University Press, USA, 1995.(37) Dörfel, I.; Österle, W.; Urban, I.; Bouzy, E. Surf. Coat. Technol. 1999, 111, 199–209.(38) Moseler, M.; Rattunde, O.; Nordiek, J.; Haberland, H. Nucl. Instrum. Methods B 2000, 164–165, 522–536.(39) Rattunde, O.; Moseler, M.; Hafele, A.; Kraft, J.; Rieser, D.; Haberland, H. J. Appl. Phys. 2001, 90, 3226–3231.(40) Bertalot, L.; Herold, H.; Jäger, U.; Mozer, A.; Oppenländer, T.; Sadowski, M.; Schmidt, H. Phys. Lett. A 1980, 79,

389–392.(41) Adachi, J.; Kurosaki, K.; Uno, M.; Yamanaka, S. J. Alloys Compd. 2005, 396, 260–263.(42) Rawat, R.S.; Chew, W.M.; Lee, P.; White, T.; Lee, S. Surf. Coat. Technol. 2003, 173, 276–284.

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