Chemical Physics Letters 484 (2010) 368–373

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Chemical Physics Letters

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Alloying effect on K shell X-ray fluorescence parameters and radiative Augerratios of Co and Zn in ZnxCo1�x alloys

N. Kup Aylikci a,*, E. Tiras�oglu a, _I.H. Karahan b, V. Aylikci a, E. Cengiz a, G. Apaydin a

a Department of Physics, Faculty of Arts and Sciences, Karadeniz Technical University, 61080 Trabzon, Turkeyb Department of Physics, Faculty of Arts and Sciences, Mustafa Kemal University, 31169 Hatay, Turkey

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

Article history:Received 24 August 2009In final form 16 November 2009Available online 28 November 2009

0009-2614/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.cplett.2009.11.036

* Corresponding author. Fax: +90 462 3253195.E-mail address: nuraykup@ktu.edu.tr (N.K. Aylikci

In this study, rKa,b production cross-sections, xK fluorescence yields, Kb/Ka, KLM/Ka and KMM/Kb inten-sity ratios of Co and Zn in different alloy compositions were measured. The alloying effects on the fluo-rescence parameters of Co and Zn were investigated. The changes in these parameters were interpretedaccording to the rearrangement of valance state electrons and the charge transfer process between the 3delements which constitute the alloys. The samples were excited by 59.5 keV c-rays from a 241Am annularradioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolu-tion of 150 eV at 5.9 keV.

� 2009 Elsevier B.V. All rights reserved.

1. Introduction

When an electron is removed from the K shell, for instance byX-ray bombardment, the reorganization of the atom can take placeby different processes. If the K hole is filled by an outer electron,this gives rise to the emission of a fluorescence K X-ray. The reor-ganization of the atom can also occur without emission of an X-ray.In this case, the K vacancy is filled by an outer electron and the en-ergy is transferred to another bound electron, which is ejected. Thisprocess is called the Auger transition. The ejected electron is pro-moted to a higher unfilled subshell (shakeup) or the continuum(shakeoff). Shakeoff process is dominant for inner shell electronsbut the shake up process becomes important for outer-shell elec-trons [1]. However, the reorganization of an atom can not be ex-plained only by the radiative and the non-radiative deexcitationevents. Some researchers claimed that there may be an alternativedecay process for filling a vacancy instead of undergoing a forbid-den quadrupole transition [2,3]. In this decay process, when aninner shell hole of an atom is filled, released energy is shared be-tween photon and electron. It is called radiative Auger effect. Thiseffect can provide important information on the many-particleinteraction in the atom [4]. The radiative Auger process causes asatellite structure on the low energy side of the main peak. TheKMM and the KLM Auger peak are found on the low energy sideof Kb and Ka main peak, respectively.

The Auger transitions are not possible for all elements. Manytransitions such as Auger, Coster-Kronig and Super Coster-Kronigtransitions are allowed for some elements and forbidden forothers. Cooper explained that an Auger transition was possible

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).

only when the energy of the initial state was grater than that ofthe final state and was most probable when the energy of differ-ence was not too great [5]. Namely; if the ejected electron has greatenergy, the possibility of the Auger transitions reduce.

There are a large number of investigations about the radiativeAuger effect. High resolution measurements of the KMM [1] andthe KLM [6] radiative Auger effect were carried out for 42Mo,44Ru, 46Pd, 48Cd and 50Sn. The KMM/Kb1,3 and the KLM/Ka1,2 radia-tive Auger intensity ratios were calculated and compared to therelativistic Hartree–Fock theoretical predictions of Scofield. TheKLM/Ka1,2 yield ratio of Ar was determined by means of high-res-olution X-ray diffractometry with two different reflecting-typecurved crystal spectrometers. The relative uncertainties of theexperimental results were obtained at about 20%. These uncertain-ties were attributed to the unknown shape of the radiative Augertransitions [7]. The low energy satellites of Kb1,3 lines of metallicV, Cr, Mn and Fe were measured and the spectra were interpretedin terms of the KMM radiative Auger effect. The total intensitieswere compared with the theoretical radiative Auger shakeoff cal-culation [8]. Besides the metallic elements Co, Ni, Cu and Zn, thelow energy satellites of lines were evaluated and the intensitiesof the satellite peaks were compared with theoretical predictions[9]. The 50–300 keV protons were used for exciting characteristicX-rays from thick targets of the elements from Z = 21 to 32. TheK-shell X-ray production cross-sections, the Kb/Ka X-ray intensityratios, the KLM/Ka and the KMM/Kb radiative Auger intensity ratioswere measured. The results were compared with theoretical val-ues. It was concluded that photopeak tailing effects increased forlower photon energies and this situation was explained by therelative radiative Auger intensities which exceeded theoreticalexpectations for the lighter targets because of the solid state effectson the radiative Auger intensity [10]. The KMM radiative Auger

N.K. Aylikci et al. / Chemical Physics Letters 484 (2010) 368–373 369

transition probabilities were calculated for Ca, Ti and Cr using thetime dependent perturbation theory. The obtained results werecompared with the recent experimental data and the other theo-retical values [11]. Auger parameter studies of aluminum-transi-tion metal alloys were performed. It was concluded that Alcarried a positive charge consistent with the electronegativity dif-ferences between Fe and Al [12].

The X-ray emission spectra are known to be influenced by thechemical combination and physical properties of X-ray emittingatoms. The changes of the X-ray fluorescence parameters for ele-ments in chemical compounds or alloys can be explained not onlyas a result of changes in the valance electronic configurations orcharge transfer effect but also as a result of the changes in thenon-radiative transitions such as Auger, Coster-Kronig or SuperCoster-Kronig transitions since the radiative transitions are gov-erned by the non-radiative transitions.

There are many studies have been devoted to a better under-standing at the alloying effect on the K X-ray intensity ratios andthe fluorescence yields. These studies are important for under-standing of the valance electronic structure of the 3d transitionmetal alloys because of the extensive application in technology.The valance electronic structure of Fe and Ni in FexNi1�x alloysfrom relative Kb/Ka X-ray intensity ratio was studied. The changesin the 3d electron population of elements in various alloys wereexplained by assuming rearrangement of the electrons between3d and (4s, 4p) states except for Ni in Fe0.2Ni0.8 alloy. The differentchange for the valance electronic structure of in Fe0.2Ni0.8 alloy wasinterpreted as a result of special magnetic properties of it [13,14].The valance electronic structures of Ti, Cr, Fe and Co in some alloyswere performed using the Kb/Ka X-ray intensity ratio values. Thevariation of the valance electronic structure of the element relativethe pure metal configuration was related to the rearrangementprocess between valance shells but not related to the charge trans-fer of 3d electrons from one element to another [15]. Influence ofthe alloying effect on the K X-ray intensity ratio was investigatedfor V and Ni elements in VxNi1�x alloys. The relative changes ofthe number of 3d electrons, belong to the V and Ni elements in al-loys, were considered as a function of their own concentrations.The changes in the valance electronic structure and in the 3d elec-tron population of elements in those alloys were clarified by rear-rangement and charge transfer models [16]. In addition to thesestudies, the alloying effect on the K-shell fluorescence yield wasinvestigated for Ni in Ni–Si alloys [17] and for Cr, Ni, Al elementsin CrxNi1�x and CrxAl1�x alloys [18]. The results obtained from thesestudies demonstrated that the K-shell fluorescence yield whichwas different for elements in various alloys were affected by thealloying effect.

In this study, the alloying effect on the Kb/Ka X-ray intensity ra-tios, the K X-ray production cross-sections, the fluorescence yields,the KLM/Ka1,2 and the KMM/Kb1,3 radiative Auger ratios in ZnxCo1�x

alloys relative to the pure metal for different concentrations wasinvestigated using the comparison of experimental and theoretical[19] values.

2. Experimental procedure

2.1. Sample preparation

ZnxCo1�x alloys were prepared by electrodeposition underpotentiostatic conditions on aluminum substrates from a sulfateplating bath at room temperature. The electrolytes were preparedusing twice distilled water. The pH value of the bath was adjustedto about 5 with hydrochloric acid and NaOH. Before the deposition,the substrates were prepared in the standard industrial way:chemical then electrolytic degreasing in sodium hydroxide

solution (40 gL�1; 64.5 �C) for 2 min followed by water wash,mechanically grinding with silicon carbide papers from 3 to 0.5Am and velvet, chemical pickling and activation in an acid medium(Hydrochloric acid; 30% in vol.) for 10 s, rinsed with the twice dis-tilled water and then dried in air. Thus the wettability and there-fore reactivity of the substrate surface were increased. Counterelectrode was a platinum electrode. The reference electrode usedin all experiments was a saturated calomel electrode (SCE).

The quantitative composition analysis of the electrodepositswere examined by using JEOL 6400 scanning electron microscope(SEM) with energy dispersive spectrometer (EDS) working at 15–30 kV. The compositions of the films were determined using EDS.

2.2. X-ray fluorescence analysis

The geometry of the experimental set-up for 241Am annularsource used in the X-ray fluorescence analysis is shown in Fig. 1.The excitation energy of 241Am source is 59.6 keV. This radioiso-tope source was used to obtain the K X-rays from the Co and Znelements and the K X-rays from the samples were detected by acollimated Ultra-LEGe detector having a thickness of 5 mm andan energy resolution of 150 eV at 5.96 keV. In the experimentaldeterminations, spectral deconvolution is one of the main prob-lems that arise while determining these parameters due to thestrong peak overlapping in ED-XRF system. Good statistics is notenough for this purpose and a careful fitting methodology isrequired in order to obtain accurate values for the peak areas.Conventional fitting programs have not demonstrated good perfor-mance, but the method of parameter optimization was previouslydeveloped for X-ray fluorescence analysis [20,21]. In the presentwork, the spectra were analyzed by using ORIGIN software program.In the present study, Figs. 2a and 3a show the spectra of K X-rays ofZn and Co in Zn0.94Co0.06 alloy, respectively. The residue spectrawith respect to K X-ray spectra of Zn and Co in Zn0.94Co0.06 alloyare shown in Figs. 2b and 3b, respectively.

The experimental K-shell X-ray intensity ratios Kb/Ka were eval-uated using the following equation:

IKb

IKa

¼NKb

NKa

bKa

bKb

eKa

eKb

; ð1Þ

where NKbNKa represents the ratio of the counting rates under the Kb

and Ka peak, bKa=bKbis the ratio of self-absorption correction factors

of the target that accounts for the absorption of incident photonsand emitted K X-ray photons, and eKaeKb

is the ratio of the detectorefficiency values for Ka and Kb X-rays, respectively.

The experimental K-shell radiative Auger ratios KLM/Ka1,2 werecalculated using the following equation:

IKLM

IKa

¼ NKLM

NKa

eKa

eKLM

bKa

bKLM; ð2Þ

and the KMM/Kb1,3 ratios were

IKMM

IKb

¼ NKMM

NKb

eKb

eKMM

bKb

bKMM; ð3Þ

where NKLM and NKMM represent the ratio of counting rates underthe KLM and the KMM peaks, bKabKMM and bKb

bKMM are the ratioof self-absorption correction factors of the target that accounts forthe absorption of incident photons and emitted K X-ray photons,respectively. The ratio eK�a=eKLM is the detector efficiency valuesfor Ka and KLM X-rays and eK�b=eKMM is for Kb and KMM X-rays.

The Ki X-ray production cross-sections were obtained by usingthe following relation:

rKi¼ NKi

I0GeKibKi

miði ¼ a and bÞ; ð4Þ

Mylar

Sample

Pb annular collimator

Holder annular source

Ultra-LEGe Detector

X-ray fluorescence radiation

Berillium window

Annular source ( 241Am )

Fig. 1. Geometry of the experimental set-up.

500 520 540 560 580 600 620 640 660102

103

104

105

Cou

nts

Channel

Kα

Kβ

KLM

KMM

500

-2

0

2

520 540 560 580 600 620 640 660

Fig. 2. (a) Typical K X-rays spectra of Zn in Zn0.94Co0.06 alloy. (b) A residue spectrum with respect to K X-ray spectra of Zn in Zn0.94Co0.06 alloy.

420 440 460 480 500

103

104

Cou

nts

Channel

K α

K βKLM

KMM

420

-2

0

2

4

440 460 480 500

Fig. 3. (a) Typical K X-rays spectra of Co in Zn0.94Co0.06 alloy. (b) A residue spectrum with respect to K X-ray spectra of Co in Zn0.94Co0.06 alloy.

370 N.K. Aylikci et al. / Chemical Physics Letters 484 (2010) 368–373

where NKiis the measured intensity (area under the photopeak)

corresponding to the Ki X-rays, I0 is the intensity of the incidentradiation, G is the geometric factor, eKi

is the detection efficiencyfor the Ki X-rays and bKi

is the self-absorption correction factor forthe target material, which accounts for the absorption in the targetof the incident photons and the emitted characteristic X-rays. mi isthe thickness of the target in g/cm2.

The self-absorption correction was calculated using theequation

b ¼ 1� expf½�ðlinc csc h1 þ lemt csc h2Þmi�gðlinc csc h1 þ lemt csc h2Þmi

; ð5Þ

where linc is the mass attenuation coefficient (cm2/gr) of incidentphotons and lemt is of emitted characteristic X-rays [22]. The anglesof incident photons and emitted X-rays with respect to the surfaceof the samples h1 and h2, were equal to 45� and 90� in the presentexperimental set-up, respectively. To determine the bKLM and bKMM

N.K. Aylikci et al. / Chemical Physics Letters 484 (2010) 368–373 371

values in radiative Auger ratios, the Auger energies were taken fromLarkins’ studies [23].

The product I0Ge, containing the terms related to the incidentphoton flux, geometrical factor and absolute efficiency of the X-ray detector, was determined by collecting the Ka and Kb X-rayspectra of samples of Cr, Fe, Zn, As, Se, Sr, Zr, Mo, Ru and Cd for241Am using the equation

I0GeKi¼ IKi

rKibKi

mi; ð6Þ

where IKiis the measured intensity (area under the photopeak) cor-

responding to the Ki group of X-rays, I0 is the intensity of the inci-dent radiation, G is the geometric factor, eKi

is the detectionefficiency for the Ki group of X-rays and bKi

is the self-absorptioncorrection factor for the target material, which accounts for theabsorption in the target of the incident photons and the emittedcharacteristic X-rays. mi is the thickness of the target in g/cm2.The variations of the factors I0GeKi

were plotted as a function ofthe mean K X-ray energy for 241Am and also, I0GeKi

values weredetermined for present study using the following equations:

Y ¼ Aþ B1X þ B2X2 þ B3X3 ð1st partÞ; ð7Þ

Y ¼ C þ D1X þ D2X2 ð2nd partÞ; ð8Þ

where X is the Ka, Kb, KLM and KMM energy and the constants A, B1,B2, B3, C, D1 and D2 are evaluated from the fitting polynomial. I0GeKi

variations as a function of mean K X-ray energies are demonstratedin Fig. 4.

Theoretical values of rKiX-ray production cross-sections were

calculated using the following equation:

rKi¼ rKðEÞxKfKi

; ð9Þ

2 4 6 8 10 12 14 16 18 20 22 24

6.00E+007

8.00E+007

1.00E+008

1.20E+008

1.40E+008

1.60E+008

1.80E+008

2.00E+008

2.20E+008

2.40E+008

I

I 0Gε

Energy (keV)

Ge

K-e

dge

II

Fig. 4. The variation of the factor I0Ge as a function of the mean K X-ray energy.

Table 1The experimental rKa, rKb production cross-sections and xK fluorescence yields of Co an

Sample Constitution element rKa

Present work Theoretical

Co Co 0.325 ± 0.016 0.345Zn Zn 0.600 ± 0.031 0.600Zn0.962Co0.038 Co 0.314 ± 0.016 . . .

Zn 0.550 ± 0.028Zn0.957Co0.043 Co 0.317 ± 0.016 . . .

Zn 0.547 ± 0.028Zn0.954Co0.046 Co 0.328 ± 0.017 . . .

Zn 0.546 ± 0.028Zn0.94Co0.06 Co 0.318 ± 0.016 . . .

Zn 0.557 ± 0.028

where rK(E) is the K-shell photoionization cross-section of the gi-ven element for the excitation energy E [24], xK is the K-shell fluo-rescence yield [25], and fKi

is the emission rate of the fractional X-ray for Ka and Kb X-rays [26].

The semi-empirical K-shell fluorescence yields for elements inalloys were measured by the following relation

xK ¼P

rKi

rPKðEÞ

ði ¼ a and bÞ; ð10Þ

whereP

rKiis the total K X-ray fluorescence cross-section calcu-

lated experimentally with Eq. (4) and rPKðEÞ is the theoretical K-shell

photoionization cross-sections for Co and Zn elements for the exci-tation energy 59.5 keV [24].

3. Results and discussion

The experimental results of the Kb/Ka X-ray intensity ratios, therKa,b production cross-sections, the xK fluorescence yields, theKLM/ Ka and the KMM/Kb radiative Auger intensity ratio valuesof Co and Zn elements in various alloys with respect to the puremetals are given in Tables 1 and 2.

In principle, the group of Kb X-rays comes from the transitionsbetween 3d, 3p and 1s levels. Besides, Ka X-rays consist of the tran-sitions between 2p and 1s levels. The orbital energy levels are closeto each other with increasing principal quantum number andaccordingly outer energy levels are sensitive to alteration of elec-tron population. The valance state of 3d metals is 3d and 4s levels.The outer levels can feel the alien element effect more than innerlevels of the atom. Thus the group of Kb X-rays feels the alien ele-ment effect stronger than Ka X-rays and so Kb fluorescence cross-sections are strongly influenced.

There are some probable mechanisms for interpreting the vari-ation of 3d electron population. First mechanism is the rearrange-ment process between valance energy levels of the single atom inthe alloy and the latter is the charge transfer process between themetals which constitute the alloy [16]. These changes in the X-rayemitting atoms in a given alloy modify 3p orbital more than 2porbital of the atoms. Therefore, the Kb/Ka X-ray intensity ratioand the Kb X-ray production cross-sections (rKb) values changefor the investigated atom.

The electronegativity value (Table 3) difference between themetals, which constitute the alloys, particularly has a greater effecton the structure of 3d and 4s orbitals. The element, which hasgreater electronegativity value than the other element in the alloy,attracts the valance electrons of the neighboring element and sothe neighboring element is polarized owing to the electronegativ-ity difference. As seen from Table 3, Co element has greater electro-negativity value than Zn element and little changes causes greateffect on valance shell of Zn atom since the Zn atom is more polar-izable than the Co atom.

d Zn in the pure metals and in the different alloy compositions.

rKb xK

Present work Theoretical Present work Theoretical [25]

0.0400 ± 0.0020 0.0418 0366 ± 0.018 0.3880.0720 ± 0.0036 0.0740 0.485 ± 0.024 0.4860.0334 ± 0.0017 . . . 0.348 ± 0.017 . . .

0.0884 ± 0.0045 0.460 ± 0.0230.0320 ± 0,0016 . . . 0.349 ± 0.017 . . .

0.0908 ± 0.0046 0.459 ± 0.0230.0342 ± 0,0017 . . . 0.363 ± 0.018 . . .

0.0890 ± 0.0045 0.458 ± 0.0230.0313 ± 0,0016 . . . 0.350 ± 0.017 . . .

0.0919 ± 0.0046 0.467 ± 0.023

Table 2The experimental Kb/Ka, KLM/Ka and KMM/Kb intensity ratios of Co and Zn in the pure metals and in the different alloy compositions.

Sample Constitutionelement

Kb/Ka intensity ratios KLM/Ka radiative Augerratios

KMM/Kb radiative Augerratios

Present work Theoretical Theoretical[19]

Theoretical [30] Present work Theoretical[19]

Present work Theoretical[19]

Electronicconfiguration

CoulombGauge

BabushkinGauge

Co Co 0.1230 ± 0.0062 0.1218 . . . 3d74s2 0.1356 0.1370 0.423 ± 0.021 0.422 3.574 ± 0.182 3.7903d84s1 0.1326 0.13403d9 0.1304 0.1318

Zn Zn 0.1200 ± 0.0061 0.1241 0.1410 . . . . . . . . . 0.309 ± 0.015 0.330 2.803 ± 0.142 3.000Zn0.962Co0.038 Co 0.1063 ± 0.0054 . . . . . . 0.577 ± 0.029 . . . 4.562 ± 0.232 . . .

Zn 0.1607 ± 0.0081 0.274 ± 0.014 2.495 ± 0.127Zn0.957Co0.043 Co Zn 0.1011 ± 0.0051 . . .. . . . 0.477 ± 0.024 . . . 4.547 ± 0.231 . . .

0.1659 ± 0.0084 0.268 ± 0.013 2.446 ± 0.124Zn0.954Co0.046 Co Zn 0.1039 ± 0.0053 . . .. . . . 0.476 ± 0.024 . . . 4.383 ± 0.223 . . .

0.1628 ± 0.0083 0.287 ± 0.014 2.368 ± 0.120Zn0.94Co0.06 Co Zn 0.0982 ± 0.0050 . . .. . . . 0.471 ± 0.024 . . . 4.565 ± 0.232 . . .

0.1649 ± 0.0084 0.277 ± 0.014 2.403 ± 0.122

Table 3Electronegativity values of Co and Zn.

Element Z Electronegativity

Co 27 1.88Zn 30 1.65

372 N.K. Aylikci et al. / Chemical Physics Letters 484 (2010) 368–373

The K X-ray production cross-section values are presented inTable 1. As seen from Table 1, Ka X-ray production cross-sectionvalues for both elements in a certain alloy do not change relativeto experimental error limits. The value of Kb X-ray productioncross-sections is 20%, 23%, 18.2% and 25% lower than pure elementfor Co in Zn0.962Co0.038, Zn0.957Co0.043, Zn0.954Co0.046 and Zn0.94Co0.06

alloys, respectively. On the other hand, the Kb X-ray productioncross-section of Zn is 19%, 22%, 20% and 24% bigger than the valueof pure Zn. The results obtained from the K X-ray intensity ratiosfor Co and Zn elements in various alloys are presented in Table 2.It can be seen in this table that the Kb/Ka X-ray intensity ratios ofCo elements decrease 12.7%, 17%, 15% and 19.4% in Zn0.962Co0.038,Zn0.957Co0.043, Zn0.954Co0.046 and Zn0.94Co0.06 alloys relative to puremetals respectively. On the other hand, the Kb/Ka X-ray intensityratio of Zn element increases 29.4% in Zn0.962Co0.038 alloy and33.6% in both Zn0.957Co0.043 and Zn0.94Co0.06 alloys, and 31.2% inZn0.954Co0.046 alloy.

These results can be explained by the changes of the 3d electronpopulation. To explain the results as a consequence of the chargetransfer mechanism, the changes should be observed in inversedirection for both metals in the alloy. But in the rearrangementprocess, changes should be in the same direction [14,15]. It is wellknown that the Kb X-ray production cross-section and the Kb/Ka X-ray intensity ratio values were affected by the changing of the 3delectron population and this ratio decreased with the increasedvalues of the 3d electrons. In this study, it has been observed thatthe changes of the Kb X-ray production cross-section and the Kb/KaX-ray intensity ratio values are in inverse direction for both ele-ments in a certain alloy. From this observation it can be said thatthe charge transfer mechanism is responsible for the changes ofthe 3d electron population. These changes lead to alteration ofbinding energies of valance electrons. This interpretation shouldbe explained by the changing of the screening effect and the elec-tronegativity differences between the elements constituting the al-loys. The electronegativity value of Co element is bigger than theZn element and so the electron transfer from Zn 3d state to Co3d state occurs. Electrons removed from the Zn 3d state reducethe screening effect on the 3d and 4s electrons of zinc. Therefore,the valance states of zinc shift to nucleus by this effect and the

binding energies of Zn valance electrons increase. Increasing bind-ing energies of 3d and 4s electrons cause an increase in X-ray tran-sition probability of Zn atom. But for Co element, adding electronsto 3d state causes a screening effect on valance state electrons ofcobalt. This effect results in shifting valance states from the nu-cleus to the outer levels and electrons are bonded to the valanceshell loosely. Consequently the Kb X-ray production cross-sectionand the Kb/Ka X-ray intensity ratios decrease for Co element rela-tive to the pure metal value. The contribution of the Kb productioncross-section values on the total K shell production cross-sectionvalues is small than the Ka production cross-section values. There-fore, there is no significant difference between our experimental K-shell fluorescence yield values and theoretical value and thisparameter is not sufficient to explain the alloying effect.

The charge transfer effect is also observed in the KLM and theKMM radiative Auger ratios. In our study, in ZnxCo1�x alloys thechanges in the radiative Auger ratios are in opposite directionsfor both elements in a certain alloy. The reason of this effect isthe electron transfer from Zn to Co. The transfer of the 3d electronsfrom Zn to Co causes an increase in the screening effect on the va-lance electrons of Co and so the outer levels shifts outside from thenucleus. Thus, the Auger ratios increase for Co element. Since theremoving of valance electrons from Zn element reduce the screen-ing effect on valance electrons, the 3d–4s energy states shift to thenucleus and Auger ratios decrease with the increase of binding en-ergy of valance electrons. Also, it was observed that the radiativeAuger ratios decreased where the Kb/Ka X-ray intensity ratios in-creased and that the radiative Auger ratios increased where theKb/Ka X-ray intensity ratios decreased. Thus it is confirmed thatthe probability of Auger transitions decreases with increasingbinding energy of valance electrons and the probability of X-raytransitions decreases with decreasing binding energy of valanceelectrons or vice versa.

In this study, the satellite lines were observed in the low energyregion of main peak. These lines not only occur because of the radi-ative Auger effect but also some other processes can contribute tothe intensity of these lines. First process that can contribute to theintensity of the Kb low energy tail is the radiative electron rear-rangement but it was shown that radiative electron rearrangementprocess is negligibly small compared to radiative Auger effect forelements Z 6 30 [27,28]. Second possible process is the X-ray Ra-man scattering which is similar to the radiative Auger process. Itwas shown by Kawai et al. [29] that Raman scattering is alsonegligibly small relative to the radiative Auger process. Therefore,the low energy satellite lines can be considered as the result of theradiative Auger process.

Fig. 5. (A) X-ray diffractograms of ZnxCo1�x alloys electrodeposited from chloride–sulfate bath. V = �3 V, t = 600 s, pH 5, T = room temperature. Bath cobalt concentrations: (a)0.5 M; (b) 0.4 M; (c) 0.3 M; (d) 0.2 M; (e) 0.1 M; (f) 0.04 M; (g) 0.03 M; (h) 0.02 M; (i) 0.01 M; (j) 0.005 M; (Zn) 0.0 M. (B) Corrosion potentials (Ecorr) of the ZnxCo1�x alloys.

Table 4Uncertainties in the quantities used to determine the parameters.

Quality Nature of uncertainty Uncertainty(%)

N(Ki) (i = a, b, KLM, KMM) Counting statistic 6 3I0GeKi

Errors in different parametersused to evaluate factor

6 2

b Error in the absorptioncoefficients at incident andemitted photon energies

6 3

t Non-uniform thickness 6 2

N.K. Aylikci et al. / Chemical Physics Letters 484 (2010) 368–373 373

The Kb/Ka X-ray intensity ratios, KLM/Ka and KMM/Kb valuesdecrease with increasing the Co composition or with decreasingZn composition. As seen from the Table 2, this situation was notobserved for Zn0.94Co0.06 alloy. As seen from the Fig. 5a, dependingon the increasing Zn content in the deposits, the signals belongingto the N phase become more intense. The diffraction peaks of XRDpatterns of zinc–cobalt coatings become more flat with an increaseof cobalt content in the film, and this indicates that amorphouscomponents in the coatings also increase. There was also observeda slight shift of the peaks associated with the planes (1 0 1), (1 0 3)and (1 1 2) to the higher angles, indicating the deformation of theZnxCo1�x alloy crystal. The disappearance of the peak correspond-ing to the plane (0 0 2) shows preferential orientation of the crys-tals. Namely, the increasing the Co content in the film causes thedeformation of the ZnxCo1�x alloy and this situation can affectsthe all characteristics of the investigated alloys. In addition, this ef-fect can be seen from the corrosion potentials. Fig. 5b shows thecorrosion potentials of samples obtained from different baths. Itcan be seen that the free corrosion potentials of Zn–Co alloys be-come more positive as the Co content increases but a little negativethan that of AISI 4140 steel substrate, which indicates that the Zn–Co coating is an ideal anodic protective coating for cobalt or steelproducts, and can provide longer protection for iron or steel prod-ucts than pure zinc coatings due to the smaller free corrosion po-tential difference between the Zn–Co coating and that of iron-base substrate.

In this Letter, the changes of the X-ray fluorescence parametersof the Co and Zn elements were investigated in various alloys. Theresults were interpreted using the changes in the values of param-eters relative to pure element. As a result, the valance states arevery sensitive to the changes in the valance electron density andbecause of this effect alien element effect in alloys is clearer forKb X-ray production cross-sections than Ka. In conclusion it can

be said that K X-ray fluorescence parameters are sensitive toolsto investigate the alien element effect in alloys.

The uncertainties in the measurements are estimated to be lessthan 6% and are found propagating the errors in various parame-ters used for determination of X-ray parameters. The uncertaintiesin these parameters are listed in Table 4.

To acquire more absolute results about alloying effects on the KX-ray fluorescence parameters, we plan to extend these measure-ments for various alloys.

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