research article a numerical formula for general...

Research ArticleA Numerical Formula for GeneralPrediction of Interface Bonding between Alumina andAluminum-Containing Alloys

Michiko Yoshitake1 Shinjiro Yagyu1 and Toyohiro Chikyow2

1National Institute for Materials Science 3-13 Sakura Tsukuba 305-0003 Japan2National Institute for Materials Science 1-1 Namiki Tsukuba 305-0044 Japan

Correspondence should be addressed to Michiko Yoshitake yoshitakemichikonimsgojp

Received 19 June 2014 Accepted 9 November 2014 Published 24 December 2014

Academic Editor Dina V Dudina

Copyright copy 2014 Michiko Yoshitake et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Interface termination between alumina and aluminum-containing alloys is discussed from a viewpoint of thermodynamics byextending the authorsrsquo previous discussion on the interface termination between alumina and pure metal A numerical formulato predict interface bonding at alumina-aluminum-containing alloys is proposed The effectiveness of the formula is examinedby extracting information on interface termination from experimental results and first-principle calculations in references It isrevealed that the prediction by the formula agrees quite well with the results reported in the references According to the formula aterminating species can be switched fromoxygen to aluminum which had been actually demonstrated experimentallyThe formulauses only basic quantities of pure elements and the formation enthalpy of oxidesTherefore it can be applied for most of aluminum-containing alloys in the periodic table and is useful for material screening in developing interfaces with particular functions

1 Introduction

Interface bonding between oxides and metals is one of thecrucial factors that determine properties of materials such asbonding strength Schottky barrier height sensitivity of sen-sors catalytic activity and overpotential in batteries Metaloxides which are composed of metals and oxygen can havedifferently terminated surfaces for example the topmostsurface being occupied only by oxygen atoms or by themetal atoms that compose the oxide When such differentlyterminated surfaces form the interface with metals bondingstrength and wetting properties at the interfaces dependon surface termination species [1ndash5] Electron energy levelalignment between the Fermi level and oxidesrsquo valence bands(band alignment) also varies largely with surface terminatingspecies [6ndash10] Regarding aluminametal interface which isone of the most extensively studied systems among variousoxidemetal interfaces we have studied the thermodynamics

of interface termination and proposed a numerical formula topredict a terminating species at the interface [11] A softwareprogram that gives predicted results according to the formulahas been released [12]

Under conditions where a stable interface terminationis determined by a metal in contact alloying (mixing twoor more metals) is one of the most frequently used tech-niques for modifying interfaces especially for electric deviceapplications where an electrode metal works only as an elec-tronic conductor but is not chemically functioning Becausethe choice of oxides is based on specific properties of theoxides modification should be made on electrode metalsnot on oxides In this paper therefore the discussion on thethermodynamics of interface termination in [11] is extendedto the interface between alumina and alloys that contain alu-minum and then a numerical formula for predicting a sta-ble interface terminating species at aluminaaluminum-con-taining alloy interfaces is proposed

Hindawi Publishing CorporationInternational Journal of MetalsVolume 2014 Article ID 120840 11 pageshttpdxdoiorg1011552014120840

2 International Journal of Metals

This work aims to offer a new tool for predicting whetheralloying with aluminum is effective or not for interfacemodification so that time-consuming trials and errors oneach system would not be necessary We believe that theformula proposed in this work would be of great use in mat-erial development

2 Formula for Prediction

21 Varieties in Termination The most stable phase of alu-mina is alpha which has a corundum structure withhexagonal symmetry The planes parallel to the 119888-axis (119888-plane) have differently terminated surfaces and could be O-terminated Al-terminated or Al-double-layer-terminatedBecause experiments on the 119888-plane have been mostlyconducted using metalalumina interfaces for both solid-state bonding and film growth experiments the 119888-plane isconsidered in this study Therefore the interface bondingspecies can be either Al (MndashAl-alumina including Al-doublelayer) or O (MndashO-alumina) when an interface is formed witha metal (M)

The interface between pure metal (M) and alumina willbe terminated by either (1) MndashAl-alumina (Al-termination)or (2) MndashO-alumina (O-termination) Here the influenceof the coverage is neglected as discussed in the previouspaper [11] When the discussion is extended to the interfacewith aluminum-containing alloy (MAl)MndashAl1015840-alumina (Al-termination Al1015840 denotes terminating Al) in pure M system isreplaced by (MAl)ndashAl1015840-alumina where the atom that bindsto Al1015840 can be either Mlowast or Allowast in MAl (here Mlowast and Allowastdenote atoms from alloys) Likewise MndashO1015840-alumina (O-ter-mination O1015840 denotes terminating O) is replaced by (MAl)ndashO1015840-alumina where the atom that binds to O1015840 can be eitherMlowast or Allowast in MAl Then there would be four different typesof termination at the interface

(alloy) | interface | alumina(A) (MAl)mdashMlowastndashAlmdashalumina (Al-termination)(B) (MAl)mdashAllowastndashAlmdashalumina (Al-termination)(C) (MAl)mdashMlowastndashOmdashalumina (O-termination)(D) (MAl)mdashAllowastndashOmdashaluminaAlthough (D) is initially derived from the O-terminated

interface between (MAl) alloy and alumina it can be regardedasAl-termination because this is the same as either (A) or (B)

22 Procedure for Prediction Thermodynamic equilibriumamong the four types of termination (A)ndash(D) has beenconsidered The equilibrium is determined by Gibbs energydifference among the terminations [11] In our previous paperon the interface between alumina and pure metal we use MndashAl and MndashO bonding energy to obtain Gibbs energy differ-ence among different terminations for simplicity [11] Herefor the interface between alumina and aluminum-containingalloy (MAl) we use MndashAl AlndashAl MndashO and AlndashO bond-ing energy

As in the previous paper MndashAl bonding energy is esti-mated either by the adsorption energy of Al on M (Approx-1) or by subtracting the adsorption energy of M on M from

that of Al on M (Approx-2) The subtraction is consideredbecause the values of adsorption energy include not only theinfluence of chemical interaction between Al and M but alsothat of cohesion energy MndashO bonding energy is estimatedeither by the adsorption energy of oxygen on M (Approx-1)or by subtracting the dissociation energy ofmolecular oxygenfrom the adsorption energy of oxygen on M (Approx-2) Thereason of adopting adsorption energy of metals to estimateMndashAl or AlndashAl bonding energy and that of oxygen for MndashObonding energy is as follows values of formation enthalpy ofoxides and intermetallic compounds or of mixing enthalpyinclude terms not only from chemical interaction but alsofrom structural change At the interface structural relaxationoccursmore easily than in bulk and the structural termwouldbe smaller and can be neglected for rough estimation

The adsorption energy of Al on M (=Al on Al when M =Al) and M on M were calculated using (1) which is based onMeadimarsquos formula [13]

Δ119867ad (119860 on 119861) = minus 119865 times 120574119861times 119878119860+ (1 minus 119865) times 120574

119860times 119878119860

+ 119865 times Δ119867sol (119860 in 119861) minus Δ119867vap (119860) (1)

where Δ119867ad(119860 on 119861) is the adsorption energy of 119860 on 119861 120574119860

and 119878119860 and 120574

119861and 119878

119861are surface energy and surface area

of 119860 and 119861 respectively Δ119867sol(119860 in 119861) is the heat of mixingof 119860 in 119861 Δ119867vap is vaporization enthalpy 119865 is the portionof the area of 119860 in contact with 119861 which is typically around04 Here the energy is described per mol Δ119867sol(119860 in 119861) iscalculated by the following equation

Δ119867sol (119860 in 119861) = 2119881 (119860)23 times (119899 (119860)minus13 + 119899 (119861)minus13)minus1

times 1198730

times 119875 times minus119890 (Δ120601)2

+

119876

119875 (Δ11989913)2minus

119877

119875

(2)

where 119881(119860) is the molar volume of metal 119860 119899(119860) and 119899(119861)are the electron density of 119860 and 119861 at the boundary of theWigner-Seitz cellΔ120601 is the work function difference between119860 and 119861 and119875119876 and119877 are parameters119873

0is the Avogadrorsquos

number The detail of the calculation and values for 120574119860and

120574119861 Δ119867vap 119881(119860) 119899(119860) and 119899(119861) Δ120601 and three parameters119875119876 and 119877 are described in [14] The values of the calculatedadsorption energy for eachMndashAl combinationwere obtainedusing the software [15] released by one of the authors andlisted in Table 1

The adsorption energy of oxygen on M is estimated inthe following way It has been reported [16] that the initialheat of adsorption of oxygen on some metals [17] has lineardependence on the standard enthalpy of formation [18] of thecorresponding oxides with the highest oxidation state Thevalues of the formation enthalpy and the valence of the cor-responding oxides were reexamined using other references[19 20] We decided to use the values from [20] to cor-relate the initial heat of adsorption of oxygen (Hads) withthe formation enthalpy of the corresponding oxide with thehighest oxidation state (Hform) except Cr The following

International Journal of Metals 3

Table 1 Adsorption energy of Al and other metals (M) on M andtheir subtracted values

Metal-M

Al on M M on M (Al on M) minus (M onM)

Adsorptionenergy (kJmol)


Energy difference(kJmol)

Al 270 270 0Si 277 359 minus82Ti 384 363 21V 400 401 minus1Cr 377 303 74Fe 392 316 76CO 408 335 73Ni 407 340 67Cu 332 265 67Zn 299 113 186Ga 243 227 16Ge 258 297 minus39Zr 389 490 minus101Nb 409 582 minus173Mo 410 523 minus113Ru 454 521 minus67Rh 447 435 12Pd 413 283 130Ag 280 222 58In 228 198 30Sn 230 254 minus24La 312 358 minus46Hf 399 492 minus93Ta 433 627 minus194W 434 695 minus261Re 496 612 minus116Os 487 636 minus149Ir 474 535 minus61Pt 450 448 2Au 325 293 32Hg 262 60 202Pb 215 153 62Bi 211 169 42

numerical relationship has been obtainedwith the correlationcoefficient of 0977

Hads (kJmol-O) = 0719 timesHform (kJmol-M)

+ 230 (kJmol-O) (3)

We use values of Hads calculated by (3) as the adsorptionenergy of oxygen on M

In Table 2 formation enthalpy of various oxides to beused for the calculation (after [20] except those in italicswhich are from [19]) and the calculated adsorption energyvalues are listed For readersrsquo convenience values for metals

that were not reported in references we discuss later are alsogiven

In the previous paper the following two expressions wereused in order to predict whether the interface termination iseither MndashAl-alumina or MndashO-alumina between pure metaland alumina

Approx-1 is

(AlonM) minus (OonM) (4)

Approx-2 is

(AlonM) minus (MonM) minus (OonM)

minus

1

2

(O2dissociation energy)

(5)

where O2dissociation energy = 49307 kJmol [21] Approx-

2 has been proposed because the value of (AlonM) includesboth chemical interaction between Al and M and cohesiveenergy of atomic Al and therefore in order to extract theterm caused by only chemical interaction subtraction ofcohesive energy is necessary The situation is the same for(OonM) where both chemical interaction between O andM and cohesive energy of atomic O are included and thesubtraction of cohesive energy (=the half of O

2dissociation

energy) is needed Prediction with Approx-1 is that if (4)is positive that is (AlonM) gt (OonM) MndashAl bonding ispreferred to MndashO bonding and if (AlonM) lt (OonM) MndashO bonding is preferred With Approx-2 prediction goes asfollows if (5) is positive that is (AlonM) minus (MonM) gt(OonM) minus 12(O

2dissociation energy) MndashAl bonding is

preferred and vice versaFour types of terminations (A)ndash(D) for aluminum-

containing alloy as described in Section 21 are derivedfrom either MndashAl-alumina or MndashO-alumina interface inpure metal where (A) and (B) are derived from MndashAl-alumina and (C) and (D) are derived from MndashO-aluminaTherefore in order to predict which one of terminationsis realized at the interface with aluminum-containing alloywe first predict whether MndashAl-alumina or MndashO-aluminais realized at the interface without aluminum in the alloyusing either Approx-1 or Approx-2 Once MndashAl-alumina ispredicted the second step is to predict whether the interfaceis (A) or (B) at the interface with aluminum-containingalloy When MndashO-alumina is predicted the second step isto predict whether the interface is (C) or (D) Whether (A)or (B) is realized is determined by comparing the value of(AlonAl) with that of (AlonM) If (AlonAl)gt (AlonM) AlndashAlbonding is preferred to MndashAl bonding and the terminationbecomes (B) Similarly (C) or (D) is determined by thevalue of (OonAl) with respect to (OonM) Here the valueof (OonAl) is obtained by calculating (OonM) with M = Aland is 83306 kJmol If (OonAl) gt (OonM) AlndashO bondingis preferred to MndashO bonding and the termination becomes(D) which is regarded as Al-termination Here comparisonbetween (AlonAl) and (AlonM) or between (OonAl) and(OonM) does not need subtraction like in (5) because the


Table 2 Values of oxide formation enthalpy and calculated adsorption energy of oxygen on various metals (M) and related values

kJmol kJmol-M kJmol-O kJmol-O Energy difference (kJmol)Mg MgO 6016 6016 6016 66414 41961Al Al2O3 16757 83785 5585667 83306 58853Si SiO2 9107 9107 45535 88515 64062Ti TiO2 944 944 472 90896 66443V V2O5 15506 7753 31012 78834 54381Cr Cr2O3 11397 56985 3799 64144 39691Mn MnO2 520 520 260 60580 36127Fe Fe2O3 8242 4121 2747333 52865 28412CO CO3O4 891 297 22275 44636 20183Ni Ni2O3 4895 24475 1631667 40900 16447Cu CuO 1573 1573 1573 34647 10194Zn ZnO 3505 3505 3505 48461 24008Ga Ga2O3 10891 54455 3630333 62335 37882Ge GeO2 580 580 290 64870 40417Zr ZrO2 10943 1094324 547162 101644 77191Nb Nb2O5 18995 94975 3799 91307 66854Mo MoO3 7451 7451 2483667 76675 52222Ru RuO4 2393 2393 59825 40510 16057Rh Rh2O3 3430 1715 1143333 35662 11209Pd PdO 854 854 854 29506 5053Ag Ag2O2 243 1215 1215 24269 minus184In In2O3 9258 4629 3086 56497 32044Sn SnO2 57763 57763 288815 64701 40248La La2O3 17937 89685 5979 87525 63072Hf HfO2 11447 11447 57235 105246 80793Ta Ta2O5 2046 1023 4092 96545 72092W WO3 8429 8429 2809667 83667 59214Re Re2O7 12401 62005 1771571 67734 43281Os OsO4 391248 391248 97812 51374 26921Ir IrO2 2741 2741 13705 42998 18545Pt PtO2 1333 1333 6665 32931 8478Au AuO

119909lt0 lt0 lt0 lt0 lt0

Hg HgO 9079 9079 9079 29891 5438Pb PbO 218 218 218 38987 14534Bi Bi2O3 5739 1913 28695 37078 12625

cohesive energy is canceled when (AlonAl) and (AlonM) arecompared [(AlonAl) minus (AlonM) = (AlonAl) minus (AlonAl) minus(AlonM) minus (AlonAl)] as well as for (OonAl) and (OonM)[(OonAl) minus (OonM) = (OonAl) minus 12(O

2dissociation

energy) minus (OonM) minus 12(O2dissociation energy)] There-

fore the expressions for each termination for aluminum-containing alloy (Approx-1) are as follows where the flowchart for finding an expression is shown in Figure 1(a)

(a) (OonM) lt (AlonM) gt (AlonAl)(b) (OonM) lt (AlonM) lt (AlonAl)(c) (OonAl) lt (OonM) gt (AlonM)(d) (OonAl) gt (OonM) gt (AlonM)

WhenApprox-2 is used in the first step to predict whetherMndashAl-alumina or MndashO-alumina is realized at the interface

without aluminum in the alloy the comparison between(OonM) and (AlonM) should be made by replacing (OonM)by (OonM) minus 12(O

2dissociation energy) and (AlonM) by

(AlonM) minus (MonM) Then the corresponding expressionsto (a)ndash(d) become as follows where the flow chart for findingan expression is shown in Figure 1(b)

(a1015840) (OonM) minus 12(O2dissociation energy) lt (AlonM) minus

(MonM) gt (AlonAl) minus (MonM)(b1015840) (OonM) minus 12(O

2dissociation energy) lt (AlonM) minus

(MonM) lt (AlonAl) minus (MonM)(c1015840) (OonAl) minus 12(O

2dissociation energy) lt (OonM) minus

12(O2dissociation energy) gt (AlonM) minus (MonM)

(d1015840) (OonAl) minus 12(O2dissociation energy) gt (OonM) minus



(a) (b) (c) (d)

(AlonAl) lt (AlonM) (AlonAl) gt (AlonM) (OonAl) lt (OonM) (OonAl) gt (OonM)

(AlonAl) versus (AlonM) (OonAl) versus (OonM)

(AlonM) minus (OonM) equiv (4)

(4) gt 0 (4) le 0

(a) Approx-1

(AlonAl) lt (AlonM)

2(O2 dissociation energy)

(AlonAl) gt (AlonM) (OonAl) lt (OonM) (OonAl) gt (OonM)

(a998400) (b998400) (c998400) (d998400)


equiv (5)minus1

(5) gt 0 (5) le 0


(b) Approx-2

Figure 1 Flow chart for finding an expression that predicts termination

If (d) or (d1015840) is satisfied the interface between aluminaand puremetalM isO-terminated whereas the interface withM alloyed with Al is Al-terminated This is the key to switchinterface termination species from oxygen to aluminum byadding Al to metals that satisfy (d) or (d1015840) Whether thisswitching of interface termination species occurs or not isgoverned by the adsorption energy of oxygen on M andAl As in the expressions (d) and (d1015840) when the adsorptionenergy of oxygen on Al is larger than that on M AlndashO bond-ing is preferred at the interface and type (D) termination thatis Al-termination is formed On the other hand it is clearthat switching Al-terminated interface to O-terminated one

by alloyingwithAl is impossible from the expressions (a)ndash(d)It should be noted that the systems where different termina-tion is predicted in the first step using by either Approx-1 orApprox-2 are limited only to Ru Rh Ir Pt and Hg (predic-tions for these systems are MndashAl-alumina with Approx-1 andMndashO-alumina with Approx-2) Furthermore aluminum-containing alloys of these metals are predicted to be Al-terminated whether interface termination is predicted as MndashAl-alumina or MndashO-alumina in the first step (termination(A) or (D)) Therefore we may be able to use Approx-1 in thefirst step for predicting the interface in aluminum-contain-ing alloy


Table 3 Binding energies of Al 2p in Ti-Al compounds prepared in various conditions compared to those in alumina on Cu and Ni relatedmetals as references

Preparation conditionsBinding energy (eV)

Termination ReferenceAl 2p32 or Al 2p(ox)

Al 2p32 or Al 2p(MAl)

Al 2p32 or Al 2p(ox) minus (MAl)

Cu9Al(111) 7490 7258 232 Al [24]Cu(111) 7411 153 O [10]NiAl(110) 7491 7247 244 Al [10]Ni(111) 7411 164 O [10]TiAl(111) 1 times 10minus5 Pa 923 K 755 722 33 [25]Ti45-Al55 1 times 10minus5 Pa 923K 755 723 32 [26]Ti55-Al45 lt5 times 10minus8 Pa sim873K 749 716 33 [27]Ti3Al 1 times 10minus5 Pa 923K 755 723 32 [26]TiAl 13 times 10minus5 Pa 673ndash873K 744 717 27 [28]Ti45-Al55 10 Pa 423K amp 623K 752 7257 263 [29]TiAl air 573ndash673K 749 723 26 [30]

In summary to find a type of interface bonding in alu-minum-containing alloy (MAl) interface termination at alu-mina-corresponding pure metal (without aluminum in thealloy) should be first examined Then if the interface withpuremetal is Al-terminated values of (AlonM) and (AlonAl)are to be compared For O-terminated interface with puremetal values of (OonM) and (OonAl) should be comparedThis procedure gives the type of interface bonding in alu-minum-containing alloy from expressions (A)ndash(D) Afterlooking for M that satisfies (AlonAl) gt (AlonM) (M = GaGe In Sn Hg Pb Bi in Table 1) we found that there is noM with (OonM) lt (AlonM) Therefore there is no M thatsatisfies expression (B)

It should be noted that the values of (OonM) are derivedfrom the standard formation enthalpy of correspondingoxide which is defined at 1 bar pressure Because both oxida-tion and reduction of metal can occur in the same system atdifferent oxygen pressure a terminating species would varywith oxygen pressure especially for metals with relativelysmall standard formation enthalpy values

There is one more thing to be noted In all the abovediscussion the possibility of alumina reduction is excludedHowever if the oxide formation enthalpy ofmetalMpermol-O is larger than that of alumina formation of oxide with Mand reduction of alumina should occur which is expected forM = La Hf in Table 2

3 Termination in Aluminum-ContainingAlloys in References

31 Experimental Results There are only a limited number ofreferences that handle interface termination between aluminaand aluminum-containing alloys We have investigated inter-face termination using NiAl(110) and Cu-9Al(111) [10] andshowed that Al 2p XPS peak is a goodmeasure to judge a typeof termination If Al 2p peak has a component between thatfor Al

2O3and metallic Al the component is attributed to the

interface and the interface is Al-terminated For NiAl(110)

the shoulder in Al 2p peak in oxidized substrate has beenknown [22] which were attributed to Al that binds thesubstrate and alumina film using calculation and STM [23]

Although other references did not discuss interface ter-mination by examining the reported Al 2p XPS spectra atype of interface termination can be estimated in the aboveway For FeAl a similar shoulder in Al 2p peak as in NiAl andCu-9Al was reported [31] which indicates that the interfacebetween FeAl and alumina formed by the oxidation of FeAlwas Al-terminated though the authors of the paper didnot mention it In addition to NiAl(110) when NiAl(111) adifferent orientation of the same intermetallic was oxidizeda similar shoulder in Al 2p was reported [32]

There are XPS studies on the oxidation of TiAl and Ti3Al

but well resolved Al 2p spectra were not reported Howeverwe are able to estimate the interface termination difference byexamining the reported Al 2p binding energies in the follow-ing way In Table 3 Al 2p binding energy values of aluminaand of intermetallics taken from references [10 24ndash30] arelisted In the case of Cu and Ni systems where all the datacome from our laboratory under the same energy calibrationconditions differences of Al 2p

32values in alumina (Al 2p

32

(ox)) with respect to the ones in MndashAl (Al 2p32

(MAl)) forAl-terminated samples (23-24 eV) are clearly different fromthose for O-terminated ones (15-16 eV) For Ti systems theenergy difference between Al 2p (ox) and Al 2p (MAl) fallsin two categories one 32-33 eV and the other 26-27 (inthe references Al 2p

32and Al 2p

12were not resolved) The

smaller energy difference appears to suggest O-terminationwhile the larger one is for Al-termination If we examine thepreparation conditions for all these experiments in Table 3it seems that the suggested terminating species is dependenton the oxidation potential during the interface formation Inthe case of lower oxygen pressure andor higher temperature(=lower oxidation potential) larger energy difference that isAl-termination appears to be realized The interface termi-nation deduced from reported experiments is schematicallysummarized in Table 4


Table 4 Schematic representation of interface terminating species at interfaces with alumina reported in experiments

MgCa Sc Tilowast Vlowast Crlowast Mn Felowast COlowast Nilowast Culowast Zn

TiAlDagger FeAldagger COAl NiAldagger Cu(Al)dagger

Sr Y Zr Nblowast Mo Tc Ru Rh Pd AgDagger CdBa La Hf Ta W Re Os Ir Pt Au HglowastO-termdaggerAl-termDaggerOxygen pressure dependent

32 Theoretical Results To the authorsrsquo knowledge thereis no reference that calculates the stability of interface ter-mination at aluminaaluminum-containing alloy (includingintermetallics) by first-principle calculations The referencesthat discuss the chemical potential of AlΔ120583Al as a parameterin the thermodynamic study of interface termination foralumina-Ni Cu Ag and Au [33ndash35] interfaces handle Al-containing intermetallics Their conclusion is that an inter-face terminating species changes from oxygen to aluminumaccording to the increase of the chemical potential of Alin metals as schematically shown in Figure 2 This Δ120583Al isa function of both oxygen partial pressure and aluminumactivity 119886Al inmetalsThe figure assumes that alumina ismorestable than oxide of metal M MO Here using Figure 2 wediscuss the influence of aluminum activity under constantoxygen partial pressure where alumina is stable From theright to the left in the figure metal composition changes frompure metal to Al intermetallics On the border B at the rightside in Figure 2 the interface is not Al

2O3M (pure metal)

but Al2O3MO119909(metal oxide) When 119886Al is larger than that

at the border B the interface is O-terminated If mixed oxidephase MAlO exists the border C appears in the figure andthe interface with alumina would be Al

2O3MAlO

119909instead

of Al2O3MO119909 The interface Al

2O3MAlO

119909is regarded as

O-terminated from a bonding point of view because MndashObonding notMndashAl exists at the interface On the border A atthe left side in Figure 2 Al

2O3reduces to Al metal that forms

an intermetallic compound MAl such as Cu3Al and Ni

3Al

and the interface is Al2O3MAl not Al

2O3MTherefore the

reference tells us that the interface betweenMAl (M =Ni CuAg and Au) and alumina is Al-terminated

4 Comparison between Prediction andResults in References

Here we examine the prediction derived from the proposedexpressions for each system and compare with the resultsdeduced from the reported results

In Table 5 the prediction for pure metal (M) the exam-ination of the expression described in Section 22 (bothApprox-1 andApprox-2) and the resulting prediction for alu-minum-containing alloy (MAl) are listed for various metalsThe results from the experimental references are also shownin the table For M on which experimental results both forM and MAl are available (M = Fe Ni Cu) the interface isterminated by oxygen for pure MTherefore the terminationfor MAl should be either (C) or (D) Because (OonM) is

0

1

2

3

4

MO

Al(1)-term

Al(2)-termO-term

A B

C

MAlO

Inte

rface

ener

gy (J

m2)

0 minus1 minus2 minus3 minus4 minus5 minus6 minus7 minus8 minus9

Δ120583Al (eV)

MndashAl

Figure 2 Schematic diagram of interface energy and preferredinterface termination as a function of Δ120583Al (chemical potential ofAl) for M with intermetallic compound (MAl) and oxides (MO)formation taken into account On the left side of the border A Al

2O3

reduces to Almetal On the right side of the border B the interface isnot Al

2O3M (pure metal) but Al

2O3MO119909(metal oxide) When 119886Al

is larger than that at the border B the interface is O-terminated Ifmixed oxide phase MAlO exists the border C appears in the figureand the interface with alumina would be Al

2O3MAlO

119909instead of

Al2O3MO119909

smaller than (OonAl) expression (d) or (d1015840) applies Thismeans that our formula predicts Al-termination for MAl(M = Fe Ni Cu) The experimental results agree withthis prediction In Section 22 it is noted that switchingO-terminated interface with pure M to Al-termination byadding Al in M should be possible Our experiments onaluminaNi NiAl Cu and Cu-9Al interfaces [10] actuallydemonstrated the above idea of termination switching Theexperiment clearly showed that O-terminated interface with


Table 5 The interface prediction for pure metal (M) examination of interface type and interface prediction for aluminum-containing alloyand experimental results on interface termination in references

M Predicted interface terminationfor pure metal (M)

Predicted interface type for MAl Predicted interfacetermination for alloy (MAl)

Experimental resultsfrom referencesApprox-1 Approx-2

Si O C C OTi O C C O Al OV O D D AlCr O D D AlFe O D D Al AlCO O D D AlNi O D D Al AlCu O D D Al AlZn O D D AlGa O D D AlGe O D D AlZr O C C ONb O C C OMo O D D AlRu Al O A D AlRh Al O A D AlPd Al A A AlAg Al A A AlIn O D D AlSn O D D AlLa O mdash mdash Al2O3 reductionHf O mdash mdash Al2O3 reductionTa O C C OW O C C ORe O D D AlOs O D D AlIr Al O A D AlPt Al O A D AlAu Al A A AlHg Al O A D AlPb O D D AlBi O D D Al

pureNi and pure Cu changed toAl-terminatedwithNiAl andCu-9Al

For M = Ti where the expression (c) or (c1015840) is satisfiedour formula predicts O-termination In the experimentalreports both O-termination and Al-termination appear tobe obtained depending on the conditions (oxygen potential)for the interface formation as discussed in Section 31 Al-termination which is in disagreement with the predictionwas obtained under low oxygen pressure at high temperatureUnder such condition adsorbed oxygen is known to dissolveinto bulk Ti [36] For Ti although (OonAl) lt (OonM)it appears that dissolution of oxygen at the interface intoTi occurs resulting in Al-termination The dissolution ofoxygen into metal or alloy is highly dependent on a kind

of metals or alloy and is not taken into account in theprediction formula Among Si Ti Zr Nb Ta and W whichsatisfy expression (c) or (c1015840) similar behavior as for Ti isexpected for Zr Nb and Ta because these three metals dis-solve considerable amount of oxygen according to the phasediagrams

One more thing to be noted is that all the metals thatsatisfy expression (c) or (c1015840) have a mixed oxide phase des-cribed asMAlO in Figure 2 Al

2O3sdotSiO2 Al2O3sdotTiO2 2Al2O3

sdotZrO2 12(Al

2O3sdotNb2O5) (=AlNbO

4) 12(Al

2O3sdotTa2O5)

(=AlTaO4) 2Al2O3sdot6WO

3(=Al2(WO4)3)

As mentioned in Section 32 interface for these metalscould beAl

2O3MAlO (border C in Figure 2) which contains

AlndashOndashMndashOndash bonding at the interface and hence is regarded


MndashO versus MndashAl

Al-term(O-term for pure M)

MndashO versus AlndashO

O-term Al-term

(A) or (B)

(C) (D)

gt lt

ltgt MndashAl MndashAlMndashO

MndashO

MndashO

AlndashO MndashO AlndashO

Figure 3 Flow chart for predicting a termination type among (A)sim(D) in the text

as O-termination in this paperWhen the formation enthalpyof metal oxide increases approaching that of alumina theposition of borders B and C shifts toward left side in Figure 2while the position of border A is not influenced by oxide for-mation enthalpy but mainly by the strength ofMndashAl bonding(if the M-Al bonding is stronger the position of border Amoves toward right side)

The features shown in Figure 2 in the theoretical study arebased on thermodynamics and are common among all thesystems calculated Therefore we can expect the features tobe universal for any metal Then when the interface is Al-terminated alumina is expected to be in equilibrium withaluminum-containing alloys or intermetallics under oxygenpartial pressure that metal is not oxidized This guides thepractically useful technique to switch interface bonding froman originally O-terminated interface to Al-termination byadding Al in a metal M The exception of the applicationof this technique is the case where (OonAl) lt (OonM)(expression (c) or (c1015840) is satisfied) Interface bonding formetals that satisfy expression (c) or (c1015840) would be process-dependent in practice because the thermodynamic stabilityof Al-terminated and O-terminated interface is very close formetals that satisfy both (OonAl) lt (OonM) and (formationenthalpy of oxide of metal M) lt (formation enthalpy of

Al2O3) For such case prediction is possible by observing

which one of metal elements is preferentially oxidized inAl-containing alloys or intermetallics If Al is preferentiallyoxidized the interface would be Al-terminated whereas thepreferential oxidation of M would results in O-terminated

It should be noted that if MO is more stable than Al2O3

interface AlMO instead of Al2O3M should be formed under

thermodynamic equilibrium Among metals we consider inTable 2 Mg La and Hf correspond to the case

By incorporating the discussion on Figure 2 into theexpressions presented here we can make an algorithm tofind interface termination in Al-containing alloy as in Fig-ure 3 This algorithm guides a novel method to control inter-face termination for a metal with (OonM) lt (OonAl)an interface that exhibits O-termination in pure metal canbe switched to Al-termination by alloying the metal withAl It also concludes that a stable Al-terminated interfacecannot be formed for metals with (OonM) gt (OonAl) underequilibrium conditions if oxygen partial pressure is not lowenough to reduce Al

2O3 Therefore for such metals utiliz-

ing a quenching process is necessary to obtain Al-terminatedinterfaces One example of a quenching process is deposit-ing Al on metals followed by oxidation without sufficientannealing which avoids atomic diffusion needed to reachthermodynamically stable O-termination

The influence of oxygen partial pressure is not taken intoaccount in (1) and (3) which are used to calculate the adsorp-tion energies of Al on M and oxygen on M respectively Onthe other hand the strengths ofMndashO andAlndashO bonds shoulddepend on the oxygen partial pressure Therefore predictionby this method is not accurate especially for easily reducedmetals However it provides a guide for termination whichwe believe is quite useful for material development

5 Conclusions

Interface bonding between alumina and aluminum-contain-ing alloy (MAl) has been investigated A method to predictan interface terminating species is proposed by extendingthe prediction method already proposed for the interfacebetween alumina and pure metals In the method to findthe most stable interface termination the interface bondingenergies of differently terminated interfaces which are esti-mated using the adsorption energy of Al on base-metal Mand that of M on M and the adsorption energy of oxygenon M and Al are compared In the algorithm for predictioninterface termination at alumina-pure metal interface shouldbe first examined Then if the interface with pure metal isAl-terminated values of (AlonM) and (AlonAl) are com-pared For O-terminated interface with pure metal values of(OonM) and (OonAl) should be compared This proceduregives the type of interface bonding in aluminum-containingalloy according to the expressions (a)ndash(d) or (a1015840)ndash(d1015840) in thetext Based on the algorithm it is also revealed that O-ter-minated interface can be switched to Al-terminated one byadding Al to pure metal M

The predicted results are compared with those deducedfrom experimental studies The agreement is very good Foraluminum-containing alloys where there is little difference


between (OonM) and (OonAl) termination type would bedependent on temperature and oxygen partial pressure andthese influences should be taken into account for more accu-rate and precise prediction However for most of metals theformula for prediction proposed here should be very effec-tive and useful formaterial screening in developing interfacesbecause the method is based on thermodynamics and usesonly basic parameters of metals and oxides

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Michiko Yoshitake greatly appreciates partial support byGrants-in-Aid for Scientific Research from the Japan Societyfor the Promotion of Science (no 20560027) and from TheMitsubishi Foundation

References

[1] U Alber H Mullejans andM Ruhle ldquoWetting of copper on 120572-Al2O3surfaces depending on the orientation and oxygen partial

pressurerdquoMicron vol 30 no 2 pp 101ndash108 1999[2] V Merlin and N Eustathopoulos ldquoWetting and adhesion of

Ni-Al alloys on 120572-Al2O3single crystalsrdquo Journal of Materials

Science vol 30 no 14 pp 3619ndash3624 1995[3] D Chatain F Chabert V Ghetta and J Fouletier ldquoNew exper-

imental setup for wettability characterization under monitoredoxygen activity II wettability of sapphire by silver-oxygenmeltsrdquo Journal of the American Ceramic Society vol 77 no 1pp 197ndash201 1994

[4] S Shi S Tanaka and M Kohyama ldquoFirst-principles study ofthe tensile strength and failure of 120572-Al

2O3(0001)Ni(111) inter-

facesrdquo Physical Review B vol 76 Article ID 075431 2007[5] S Shi S Tanaka and M Kohyama ldquoFirst-principles investiga-

tion of the atomic and electronic structures of 120572-Al2O3(0001)

Ni(111) Interfacesrdquo Journal of the American Ceramic Society vol90 no 8 pp 2429ndash2440 2007

[6] S Shi S Tanaka andMKohyama ldquoInfluence of interface struc-ture on Schottky barrier heights of 120572-Al

2O3(0001)Ni(111) inter-

faces a first-principles studyrdquoMaterials Transactions vol 47 no11 pp 2696ndash2700 2006

[7] K Shiraishi T Nakayama T Nakaoka A Ohta and SMiyazaki ldquoTheoretical investigation of metaldielectric inter-faces Breakdownof Schottky barrier limitsrdquoECSTransactionsvol 13 no 2 pp 21ndash27 2008

[8] T Nagata P Ahmet Y Z Yoo et al ldquoSchottky metal library forZNO-basedUVphotodiode fabricated by the combinatorial ionbeam-assisted depositionrdquo Applied Surface Science vol 252 no7 pp 2503ndash2506 2006

[9] A Asthagiri C Niederberger A J Francis L M Porter P ASalvador and D S Sholl ldquoThin Pt films on the polar SrTiO

3(1

1 1) surface an experimental and theoretical studyrdquo SurfaceScience vol 537 no 1ndash3 pp 134ndash152 2003

[10] M Yoshitake S Nemsak T Skala et al ldquoModification of ter-minating species and band alignment at the interface between

alumina films and metal single crystalsrdquo Surface Science vol604 no 23-24 pp 2150ndash2156 2010

[11] M Yoshitake S Yagyu and T Chikyow ldquoNovel method forthe prediction of an interface bonding species at aluminametalinterfacesrdquo Journal of Vacuum Science and Technology A vol 32no 2 Article ID 021102 8 pages 2014

[12] httpinterchembondnimsgojp[13] A R Miedema and J W F Dorleijn ldquoQuantitative predictions

of the heat of adsorption of metals on metallic substratesrdquoSurface Science vol 95 no 2-3 pp 447ndash464 1980

[14] M Yoshitake Y-R Aparna and K Yoshihara ldquoGeneral rulefor predicting surface segregation of substrate metal on filmsurfacerdquo Journal of Vacuum Science amp Technology A vol 19 no4 pp 1432ndash1437 2001

[15] httpsurfsegnimsgojpSurfSegmenuhtml[16] K Tanaka and K Tamaru ldquoA general rule in chemisorption of

gases on metalsrdquo Journal of Catalysis vol 2 no 5 pp 366ndash3701963

[17] D Brennan D O Hayward and B M Trapnell ldquoThe calori-metric determination of the heats of adsorption of oxygen onevaporated metal filmsrdquo Proceedings of the Royal Society ofLondon A vol 256 pp 81ndash105 1960

[18] N A Lange Handbook of Chemistry McGraw-Hill 1956[19] L Brewer ldquoThe thermodynamic properties of the oxides and

their vaporization processesrdquo Chemical Reviews vol 52 no 1pp 1ndash75 1953

[20] D R Lide Ed CRC Handbook of Chemistry and Physics CRCPress 74th edition 1993-1994

[21] P Brix and G Herzberg ldquoFine structure of the Schumann-Runge bands near the convergence limit and the dissociationenergy of the oxygen moleculerdquo Canadian Journal of Physicsvol 32 pp 110ndash135 1954

[22] R M Jaeger H Kuhlenbeck H-J Freund et al ldquoFormationof a well-ordered aluminium oxide overlayer by oxidation ofNiAl(110)rdquo Surface Science vol 259 no 3 pp 235ndash252 1991

[23] G Kresse M Schmid E Napetschnig M Shishkin L Kohlerand P Varga ldquoMaterials science structure of the ultrathinaluminum oxide film on NiAl(110)rdquo Science vol 308 no 5727pp 1440ndash1442 2005

[24] M Yoshitake W Song J Libra et al ldquoInterface terminationand band alignment of epitaxially grown alumina films on Cu-Al alloyrdquo Journal of Applied Physics vol 103 Article ID 0337072008

[25] V Maurice G Despert S Zanna P Josso M-P Bacos andP Marcus ldquoThe growth of protective ultra-thin alumina layerson 120574-TiAl(1 1 1) intermetallic single-crystal surfacesrdquo SurfaceScience vol 596 no 1ndash3 pp 61ndash73 2005

[26] V Maurice G Despert S Zanna P Josso M-P Bacos and PMarcus ldquoXPS study of the initial stages of oxidation of 120572

2-Ti3Al

and 120574-TiAl intermetallic alloysrdquo Acta Materialia vol 55 no 10pp 3315ndash3325 2007

[27] K Kovacs I V Perczel V K Josepovits G Kiss F Reti andP Deak ldquoIn situ surface analytical investigation of the thermaloxidation of Ti-Al intermetallics up to 1000∘Crdquo Applied SurfaceScience vol 200 no 1ndash4 pp 185ndash195 2002

[28] M Schmiedgen P C J Graat B Baretzky and E J MittemeijerldquoThe initial stages of oxidation of 120574-TiAl an X-ray photoelec-tron studyrdquoThin Solid Films vol 415 no 1-2 pp 114ndash122 2002

[29] J F Silvain J E Barbier Y Lepetitcorps M Alnot and J JEhrhardt ldquoChemical and structural analysis of TiAl thin films


sputter deposited on carbon substratesrdquo Surface and CoatingsTechnology vol 61 no 1ndash3 pp 245ndash250 1993

[30] J Xia H Dong and T Bell ldquoSurface properties of a 120574-basedtitanium aluminide at elevated temperaturesrdquo Intermetallicsvol 10 no 7 pp 723ndash729 2002

[31] H Graupner L Hammer K Heinz and D M Zehner ldquoOxida-tion of low-index FeAl surfacesrdquo Surface Science vol 380 no2-3 pp 335ndash351 1997

[32] E Loginova F Cosandey and T E Madey ldquoNanoscopicnickel aluminate spinel (NiAl

2O4) formation during NiAl(1 1 1)

oxidationrdquo Surface Science vol 601 no 3 pp L11ndashL14 2007[33] W Zhang J R Smith and A G Evans ldquoThe connection

between ab initio calculations and interface adhesion measure-ments on metaloxide systems NiAl

2O3and CuAl

2O3rdquo Acta

Materialia vol 50 no 15 pp 3803ndash3816 2002[34] W Zhang and J R Smith ldquoNonstoichiometric interfaces and

Al2O3adhesion with Al and Agrdquo Physical Review Letters vol

85 no 15 pp 3225ndash3228 2000[35] J Feng W Zhang and W Jiang ldquoAb initio study of AgAl

2O3

and AuAl2O3interfacesrdquo Physical Review B vol 72 no 11

Article ID 115423 11 pages 2005[36] M Yoshitake and K Yoshihara ldquoThe surface segregation of Ti-

Nb composite film and its application to a smart gettermaterialrdquoVacuum vol 51 no 3 pp 369ndash376 1998

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


This work aims to offer a new tool for predicting whetheralloying with aluminum is effective or not for interfacemodification so that time-consuming trials and errors oneach system would not be necessary We believe that theformula proposed in this work would be of great use in mat-erial development

2 Formula for Prediction

21 Varieties in Termination The most stable phase of alu-mina is alpha which has a corundum structure withhexagonal symmetry The planes parallel to the 119888-axis (119888-plane) have differently terminated surfaces and could be O-terminated Al-terminated or Al-double-layer-terminatedBecause experiments on the 119888-plane have been mostlyconducted using metalalumina interfaces for both solid-state bonding and film growth experiments the 119888-plane isconsidered in this study Therefore the interface bondingspecies can be either Al (MndashAl-alumina including Al-doublelayer) or O (MndashO-alumina) when an interface is formed witha metal (M)

The interface between pure metal (M) and alumina willbe terminated by either (1) MndashAl-alumina (Al-termination)or (2) MndashO-alumina (O-termination) Here the influenceof the coverage is neglected as discussed in the previouspaper [11] When the discussion is extended to the interfacewith aluminum-containing alloy (MAl)MndashAl1015840-alumina (Al-termination Al1015840 denotes terminating Al) in pure M system isreplaced by (MAl)ndashAl1015840-alumina where the atom that bindsto Al1015840 can be either Mlowast or Allowast in MAl (here Mlowast and Allowastdenote atoms from alloys) Likewise MndashO1015840-alumina (O-ter-mination O1015840 denotes terminating O) is replaced by (MAl)ndashO1015840-alumina where the atom that binds to O1015840 can be eitherMlowast or Allowast in MAl Then there would be four different typesof termination at the interface

(alloy) | interface | alumina(A) (MAl)mdashMlowastndashAlmdashalumina (Al-termination)(B) (MAl)mdashAllowastndashAlmdashalumina (Al-termination)(C) (MAl)mdashMlowastndashOmdashalumina (O-termination)(D) (MAl)mdashAllowastndashOmdashaluminaAlthough (D) is initially derived from the O-terminated

interface between (MAl) alloy and alumina it can be regardedasAl-termination because this is the same as either (A) or (B)

22 Procedure for Prediction Thermodynamic equilibriumamong the four types of termination (A)ndash(D) has beenconsidered The equilibrium is determined by Gibbs energydifference among the terminations [11] In our previous paperon the interface between alumina and pure metal we use MndashAl and MndashO bonding energy to obtain Gibbs energy differ-ence among different terminations for simplicity [11] Herefor the interface between alumina and aluminum-containingalloy (MAl) we use MndashAl AlndashAl MndashO and AlndashO bond-ing energy

As in the previous paper MndashAl bonding energy is esti-mated either by the adsorption energy of Al on M (Approx-1) or by subtracting the adsorption energy of M on M from

that of Al on M (Approx-2) The subtraction is consideredbecause the values of adsorption energy include not only theinfluence of chemical interaction between Al and M but alsothat of cohesion energy MndashO bonding energy is estimatedeither by the adsorption energy of oxygen on M (Approx-1)or by subtracting the dissociation energy ofmolecular oxygenfrom the adsorption energy of oxygen on M (Approx-2) Thereason of adopting adsorption energy of metals to estimateMndashAl or AlndashAl bonding energy and that of oxygen for MndashObonding energy is as follows values of formation enthalpy ofoxides and intermetallic compounds or of mixing enthalpyinclude terms not only from chemical interaction but alsofrom structural change At the interface structural relaxationoccursmore easily than in bulk and the structural termwouldbe smaller and can be neglected for rough estimation

The adsorption energy of Al on M (=Al on Al when M =Al) and M on M were calculated using (1) which is based onMeadimarsquos formula [13]

Δ119867ad (119860 on 119861) = minus 119865 times 120574119861times 119878119860+ (1 minus 119865) times 120574

119860times 119878119860

+ 119865 times Δ119867sol (119860 in 119861) minus Δ119867vap (119860) (1)

where Δ119867ad(119860 on 119861) is the adsorption energy of 119860 on 119861 120574119860

and 119878119860 and 120574

119861and 119878

119861are surface energy and surface area

of 119860 and 119861 respectively Δ119867sol(119860 in 119861) is the heat of mixingof 119860 in 119861 Δ119867vap is vaporization enthalpy 119865 is the portionof the area of 119860 in contact with 119861 which is typically around04 Here the energy is described per mol Δ119867sol(119860 in 119861) iscalculated by the following equation

Δ119867sol (119860 in 119861) = 2119881 (119860)23 times (119899 (119860)minus13 + 119899 (119861)minus13)minus1

times 1198730

times 119875 times minus119890 (Δ120601)2

+

119876

119875 (Δ11989913)2minus

119877

119875

(2)

where 119881(119860) is the molar volume of metal 119860 119899(119860) and 119899(119861)are the electron density of 119860 and 119861 at the boundary of theWigner-Seitz cellΔ120601 is the work function difference between119860 and 119861 and119875119876 and119877 are parameters119873

0is the Avogadrorsquos

number The detail of the calculation and values for 120574119860and

120574119861 Δ119867vap 119881(119860) 119899(119860) and 119899(119861) Δ120601 and three parameters119875119876 and 119877 are described in [14] The values of the calculatedadsorption energy for eachMndashAl combinationwere obtainedusing the software [15] released by one of the authors andlisted in Table 1

The adsorption energy of oxygen on M is estimated inthe following way It has been reported [16] that the initialheat of adsorption of oxygen on some metals [17] has lineardependence on the standard enthalpy of formation [18] of thecorresponding oxides with the highest oxidation state Thevalues of the formation enthalpy and the valence of the cor-responding oxides were reexamined using other references[19 20] We decided to use the values from [20] to cor-relate the initial heat of adsorption of oxygen (Hads) withthe formation enthalpy of the corresponding oxide with thehighest oxidation state (Hform) except Cr The following



Metal-M








+ 230 (kJmol-O) (3)





Approx-1 is


Approx-2 is


minus

1

2


(5)



2dissociation











2dissociation

















(a) (b) (c) (d)




(4) gt 0 (4) le 0

(a) Approx-1

(AlonAl) lt (AlonM)



(a998400) (b998400) (c998400) (d998400)


equiv (5)minus1

(5) gt 0 (5) le 0


(b) Approx-2























32



32and Al 2p









2O3M (pure metal)



2O3MAlO

119909instead


2O3MAlO





3Al


2O3MTherefore the





0

1

2

3

4

MO

Al(1)-term

Al(2)-termO-term

A B

C

MAlO

Inte

rface

ener

gy (J

m2)


Δ120583Al (eV)

MndashAl


2O3





2O3MAlO

119909instead of

Al2O3MO119909













sdotZrO2 12(Al


4) 12(Al

2O3sdotTa2O5)


3(=Al2(WO4)3)








O-term Al-term

(A) or (B)

(C) (D)

gt lt


MndashO

MndashO














5 Conclusions







Acknowledgments


References







2O3(0001)Ni(111) inter-





2O3(0001)Ni(111) inter-





3(1




















2-Ti3Al













2O3and CuAl

2O3rdquo Acta




2O3











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





Metal-M








+ 230 (kJmol-O) (3)





Approx-1 is


Approx-2 is


minus

1

2


(5)



2dissociation











2dissociation

















(a) (b) (c) (d)




(4) gt 0 (4) le 0

(a) Approx-1

(AlonAl) lt (AlonM)



(a998400) (b998400) (c998400) (d998400)


equiv (5)minus1

(5) gt 0 (5) le 0


(b) Approx-2























32



32and Al 2p









2O3M (pure metal)



2O3MAlO

119909instead


2O3MAlO





3Al


2O3MTherefore the





0

1

2

3

4

MO

Al(1)-term

Al(2)-termO-term

A B

C

MAlO

Inte

rface

ener

gy (J

m2)


Δ120583Al (eV)

MndashAl


2O3





2O3MAlO

119909instead of

Al2O3MO119909













sdotZrO2 12(Al


4) 12(Al

2O3sdotTa2O5)


3(=Al2(WO4)3)








O-term Al-term

(A) or (B)

(C) (D)

gt lt


MndashO

MndashO














5 Conclusions







Acknowledgments


References







2O3(0001)Ni(111) inter-





2O3(0001)Ni(111) inter-





3(1




















2-Ti3Al













2O3and CuAl

2O3rdquo Acta




2O3











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









2dissociation

















(a) (b) (c) (d)




(4) gt 0 (4) le 0

(a) Approx-1

(AlonAl) lt (AlonM)



(a998400) (b998400) (c998400) (d998400)


equiv (5)minus1

(5) gt 0 (5) le 0


(b) Approx-2























32



32and Al 2p









2O3M (pure metal)



2O3MAlO

119909instead


2O3MAlO





3Al


2O3MTherefore the





0

1

2

3

4

MO

Al(1)-term

Al(2)-termO-term

A B

C

MAlO

Inte

rface

ener

gy (J

m2)


Δ120583Al (eV)

MndashAl


2O3





2O3MAlO

119909instead of

Al2O3MO119909













sdotZrO2 12(Al


4) 12(Al

2O3sdotTa2O5)


3(=Al2(WO4)3)








O-term Al-term

(A) or (B)

(C) (D)

gt lt


MndashO

MndashO














5 Conclusions







Acknowledgments


References







2O3(0001)Ni(111) inter-





2O3(0001)Ni(111) inter-





3(1




















2-Ti3Al













2O3and CuAl

2O3rdquo Acta




2O3











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b) (c) (d)




(4) gt 0 (4) le 0

(a) Approx-1

(AlonAl) lt (AlonM)



(a998400) (b998400) (c998400) (d998400)


equiv (5)minus1

(5) gt 0 (5) le 0


(b) Approx-2























32



32and Al 2p









2O3M (pure metal)



2O3MAlO

119909instead


2O3MAlO





3Al


2O3MTherefore the





0

1

2

3

4

MO

Al(1)-term

Al(2)-termO-term

A B

C

MAlO

Inte

rface

ener

gy (J

m2)


Δ120583Al (eV)

MndashAl


2O3





2O3MAlO

119909instead of

Al2O3MO119909













sdotZrO2 12(Al


4) 12(Al

2O3sdotTa2O5)


3(=Al2(WO4)3)








O-term Al-term

(A) or (B)

(C) (D)

gt lt


MndashO

MndashO














5 Conclusions







Acknowledgments


References







2O3(0001)Ni(111) inter-





2O3(0001)Ni(111) inter-





3(1




















2-Ti3Al













2O3and CuAl

2O3rdquo Acta




2O3











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






















32



32and Al 2p









2O3M (pure metal)



2O3MAlO

119909instead


2O3MAlO





3Al


2O3MTherefore the





0

1

2

3

4

MO

Al(1)-term

Al(2)-termO-term

A B

C

MAlO

Inte

rface

ener

gy (J

m2)


Δ120583Al (eV)

MndashAl


2O3





2O3MAlO

119909instead of

Al2O3MO119909













sdotZrO2 12(Al


4) 12(Al

2O3sdotTa2O5)


3(=Al2(WO4)3)








O-term Al-term

(A) or (B)

(C) (D)

gt lt


MndashO

MndashO














5 Conclusions







Acknowledgments


References







2O3(0001)Ni(111) inter-





2O3(0001)Ni(111) inter-





3(1




















2-Ti3Al













2O3and CuAl

2O3rdquo Acta




2O3











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









2O3M (pure metal)



2O3MAlO

119909instead


2O3MAlO





3Al


2O3MTherefore the





0

1

2

3

4

MO

Al(1)-term

Al(2)-termO-term

A B

C

MAlO

Inte

rface

ener

gy (J

m2)


Δ120583Al (eV)

MndashAl


2O3





2O3MAlO

119909instead of

Al2O3MO119909













sdotZrO2 12(Al


4) 12(Al

2O3sdotTa2O5)


3(=Al2(WO4)3)








O-term Al-term

(A) or (B)

(C) (D)

gt lt


MndashO

MndashO














5 Conclusions







Acknowledgments


References







2O3(0001)Ni(111) inter-





2O3(0001)Ni(111) inter-





3(1




















2-Ti3Al













2O3and CuAl

2O3rdquo Acta




2O3











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials














sdotZrO2 12(Al


4) 12(Al

2O3sdotTa2O5)


3(=Al2(WO4)3)








O-term Al-term

(A) or (B)

(C) (D)

gt lt


MndashO

MndashO














5 Conclusions







Acknowledgments


References







2O3(0001)Ni(111) inter-





2O3(0001)Ni(111) inter-





3(1




















2-Ti3Al













2O3and CuAl

2O3rdquo Acta




2O3











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







O-term Al-term

(A) or (B)

(C) (D)

gt lt


MndashO

MndashO














5 Conclusions







Acknowledgments


References







2O3(0001)Ni(111) inter-





2O3(0001)Ni(111) inter-





3(1




















2-Ti3Al













2O3and CuAl

2O3rdquo Acta




2O3











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







Acknowledgments


References







2O3(0001)Ni(111) inter-





2O3(0001)Ni(111) inter-





3(1




















2-Ti3Al













2O3and CuAl

2O3rdquo Acta




2O3











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials











2O3and CuAl

2O3rdquo Acta




2O3











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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