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Applied Surface Science 257 (2010) 1027–1033

Contents lists available at ScienceDirect

Applied Surface Science

journa l homepage: www.e lsev ier .com/ locate /apsusc

ffective electrodeposition of Co–Ni–Cu alloys nanoparticles in the presence oflkyl polyglucoside surfactant

etia Budia,b,∗, A.R. Dauda,∗, S. Radimana, Akrajas Ali Umarc

School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Selangor, MalaysiaDepartment of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Negeri Jakarta, Jl. Pemuda No. 10, Rawamangun 13220, Jakarta, IndonesiaInstitute of Microengineering and Nanoelectronics, Universiti Kebangsaan Malaysia, 43600 Selangor, Malaysia

r t i c l e i n f o

rticle history:eceived 12 April 2010eceived in revised form 30 July 2010ccepted 30 July 2010vailable online 7 August 2010

eywords:o–Ni–Cu nanoparticle

a b s t r a c t

The effect of alkyl polyglucoside (APG) surfactant on the electrodeposition Co–Ni–Cu alloys nanoparticleshas been investigated. In a typical electrodeposition experiment, it was found that as prepared Co–Ni–Cualloys nanoparticles characteristics, such as size homogeneity, density, dispersion on the electrode sub-strate and the chemicals composition, depended strongly on the concentration of APG used in the reactionas well as the applied deposition potential. For the case of chemicals composition, low APG concentration(below CMC) was found to be effective for the preparation of excellent composition of the nanoalloys.Meanwhile, for the case of size homogeneity, density, and dispersion on the surface, high APG concentra-

lectrodepositionyclic voltammetrylkyl polyglucosideritical micelle concentration

tion (above CMC) and high deposition potential were preferred. It was also found that, at concentrationabove the CMC, the APG surfactant showed a metals ions deposition inhibition characteristic that causedincreasing in the electrodeposition overpotential of the entire metals ions, namely cobalt, nickel andcopper. As the result the copper was found to place a high percentage in the nanoalloys deposits. Owingto its simple procedure in controlling the composition and the nanoalloys growth characteristic, presentapproach should find a potential application in preparing Co–Ni–Cu magnetic nanoparticles for used in

tions

currently existing applica

. Introduction

Recently, there is an increasing interest in the synthesis of theo–Ni–Cu alloys nanoparticles due to its unique magnetic and mag-etoresistive properties, which depend on the composition, forsed in magnetic device applications such as MEMS [1], magneticecording and magnetic data storage [2]. For example, by modi-ying the composition of the Co–Ni–Cu alloys nanoparticles, the

agnetic coercivity (Hc) of 42.7 to 840 Oe can be obtained [3–5].herefore, to find technique to grow the Co–Ni–Cu alloys nanopar-icles with unique growth characteristic is highly required. Therere variety of techniques for preparation of Co–Ni–Cu alloys such asechanical alloying [3], positive microemulsion [4], melt spinning

6] and electrodeposition [1,7]. Among the available techniques,

lectrodeposition, also known as electrochemical deposition, isonsidered as a practical and widely used method for nanoparticlesreparation due to its ability to directly attach the nanoparticlesn the substrate [8,9]. Owing to its simple and easy process in

∗ Corresponding author at: School of Applied Physics, Faculty of Science and Tech-ology, Universiti Kebangsaan Malaysia, 43600 Selangor, Malaysia.el.: +60 389213806.

E-mail addresses: sbcare@yahoo.com (S. Budi), ard@ukm.my (A.R. Daud).

169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.apsusc.2010.07.103

.© 2010 Elsevier B.V. All rights reserved.

term of controlling the experimental parameters [10], economi-cally cheap [11,12] and broad range industrial applicability [12]put this technique as a prospective tool for future nanoparticlesfabrication.

Currently, the controlled-size and shape of the electrodepositedgrowth Co–Ni–Cu nanoparticles have become a central issue inthe nanomaterials chemistry synthesis field due to the presenceof strong relationship between properties on shape and size. Theaddition of surfactant into the electrolyte is amongst a straight-forward technique to control over the nanoparticles growth as theresult of their unique roles in modifying the deposition preferenceand properties that in turn enable for obtaining a controlled-size[13,14], -morphology and -nanostructure [15]. Alkyl polyglucoside(APG) can be proposed as a potential surfactant for a control overthe growth of the electrodeposited Co–Ni–Cu nanoparticles due toits nonionic characteristic with excellent psychochemical proper-ties [16,17] and good electrolyte tolerance [18]. Furthermore, it alsofeatures non-toxicity, biodegradable in aqueous medium [19,20]and environmental friendly characteristic [21–23] that made it

as a promising candidate for use in electrochemical deposition ofnanoparticles.

In this paper, we report our attempts in controlling thehomogeneity, density as well as the dispersion of the Co–Ni–Cunanoparticles growth on the substrate by optimizing the concentra-

1 ce Science 257 (2010) 1027–1033

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ion of the APG surfactant and applied electrodeposition potential.y using an optimum concentration of APG that reflected by its CMCalue, homogenous and controlled-size and -density of Co–Ni–Cuanoalloys can be successfully grown on the surface of electrode.he electrodeposited Co–Ni–Cu alloys nanoparticles should findxtensive used in magnetic device applications.

. Experimental

Technical grade Glucopone 215 CSUP, commercial name ofhe alkyl polyglucoside (APG), was obtained from Fluka. Ana-ytical grade boric acid (H3BO3) and all metal salts (technicalrade CoSO4·7H2O, ACS reagent NiSO4·6H2O and ACS reagentuSO4·5H2O) were purchased from Sigma–Aldrich. Indium-tinxide (ITO) coated on glass plate with sheet resistance 10 �/� wasbtained from Praezisions Glas & Optik GmbH.

The electrolytes containing 0.018 M CoSO4, 0.18 M NiSO4,

.002 M CuSO4 and 0.4 M H3BO3 were prepared using pure waterith resistivity of 18.2 M� cm. Prior to electrochemical studies, the

ritical micelle concentration (CMC) of APG in the electrolyte wastudied and determined by the surface tension experiments thatarried out using a KSV Tensiometer model Sigma 703D.

Fig. 1. Scatter plot of surface tension at 25 ◦C from different concentration of APGin electrolyte containing 1.8 × 10−2 M CoSO4, 0.18 M NiSO4, 2 × 10−3 M CuSO4 and0.4 M H3BO3.

ig. 2. (a) Typical cyclic voltammograms of electrolyte containing 1.8 × 10−2 M CoSO4, 0.18 M NiSO4, 2 × 10−3 M CuSO4 and 0.4 M H3BO3 in the presence of various concen-ration of APG surfactant (a) 0 wt.%, (b) 2.6 × 10−3 wt.%, (c) 0.65 wt.%, (d) 1.95 wt.% and (e) 3.25 wt.% on ITO surface. (b) Cathodic scan of the cyclic voltammogram at theotential range of −700 to −1050 mV vs. SCE. The scan rate is 10 mV s−1.

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Electrodeposition of Co–Ni–Cu was carried out in a three-lectrode cell with ITO on glass plate, platinum wire and saturatedalomel electrode (SCE) as working electrode, counter electrodend reference electrode, respectively. A Solartron potentiostatodel 1286 was used to perform all the electrochemical exper-

ments. Prior to each experiment, the electrolyte solution wasurged with a flow of pure argon gas to remove any oxygen contain

n the electrolyte. The cyclic voltammetry studies were performedith a potential window of 400 to −1100 mV vs. SCE and the scan

ate of 10 mV s−1. Finally, for the Co–Ni–Cu nanoparticles electrode-osition, a potentiostatic experiment was used in the presence ofifferent concentrations of the APG surfactant. The deposition time

as 150 s.

The morphology examination was performed using a Zeisseld emission scanning electron microscopy (FESEM) SUPRA 55VP.hemical analysis was carried out by an Oxford instruments energyispersive X-ray analyzer (EDX) coupled to the FESEM.

ig. 3. FESEM images of Co–Ni–Cu nanoparticles electrodeposited on ITO glass substratewt.%; (b) 2.6 × 10−2 wt.%; (c) 0.65 wt.%; (d) 1.95 wt.%; (d) 3.25 wt.%.

nce 257 (2010) 1027–1033 1029

3. Results and discussion

Prior to the electrodeposition process, we studied the criticalmicelle concentration (CMC) characteristic of the alkyl polyglu-coside (APG) surfactant in the electrolyte by means of a surfacetension technique. A series of electrolyte containing different con-centration of the surfactant were prepared for this purpose. Asshown in Fig. 1, the surface tension was found to linearly decreasefrom the value of 71.43–45.34 mN/m with the increasing of theconcentration of APG from 0 to 2.6 × 10−2 wt.%, correspondingly.However, the surface tensions value was found to not furtherdecrease when the concentration was increased above this value,

but reached a saturated condition with the value of ca. ∼29 mN/m.This could be as the result of the surfactant micelle formation inthe electrolyte [24–26]. Thus, no significant change was found onits surface tension. The CMC value then can be determined by sim-ply extrapolating two straight lines on the linear parts of the curve

from different concentration of APG at co-deposition potential 850 mV vs. SCE (a)

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a scarce nanoparticles formation with a relatively bigger size wasobtained (Fig. 3e). This fact could be as the result of a slow growthprocess of the nanoparticles in the presence of high concentrationof the APG surfactant in the electrolyte. As have been obtained

030 S. Budi et al. / Applied Surfa

vertical and horizontal) until intersected each other. The intersec-ion between the two lines would be considered as the value of theMC. From this process, the CMC value was estimated as high as.3 × 10−2 wt.%.

Next, we examined the effect of APG surfactant concentration onhe cyclic voltammetry characteristic of the electrolyte containinghe metals ions species. Fig. 2a is a typical cyclic voltammogram ofhe sulphate electrolyte containing cobalt, nickel and copper ions1] in the absence of APG surfactant. From the figure, a small peakt around −160 to −180 mV vs. SCE was observed. This peak cane easily related to the copper reduction [27]. As also shown in thegure, there was a drastic increase in the current at the negativeotential during the cathodic scan. This is a strong indication of theccurrence of the metals ions reduction in the electrolyte, hence thenitiation of the electrodeposition. The onset potential at which theurrent began to increase was found to be −772 mV vs. SCE. Con-idering the onset potential value of individual metal ion specieshat range in this value, it was believed that the co-deposition ofhe metals ions could be occurred at this potential.

Meanwhile, for the anodic scan, two peaks were observed toppear in the curve, namely at the potential range of 0–300 mVs. SCE. This could be associated with the oxidation of the aseposited metals nanoparticles of which is formerly formed duringhe cathodic scan. The lower and higher potential of anodic peaksould be related to the oxidation of Co–Ni and Cu, respectively [1,7].

However, the cyclic voltammograms profile of the electrolytesystem was found to significantly change when the APG surfactantntroduced. Although, at a concentration below the CMC (Fig. 2b)o significant change was observed compare to that of without thePG surfactant. When the APG concentration exceeded the CMCalue (Fig. 2c–e), the cyclic voltammogram profile started to drasti-ally change in term of metals ions reduction overpotential and thexidation potential. For the case of the cathodic scan, it can be seenhat the onset potential for the metals ions reduction was found toncrease with increasing of the APG concentration. Thus, the met-ls ions reduction overpotential increased. As can be seen from thegure, the reduction peak at region −160 to −180 mV vs. SCE wasanished when APG concentration exceeded the CMC value. Thisould be related to the effective adsorption of the APG moleculesnto the working electrode surface [28,29], in this case ITO sub-trate, forming organic layer. The thickness of the organic layeras predicted to linearly depend on the concentration of the sur-

actant used [30]. At a certain concentration, the organic layer mayecome a hindrance to the electrochemical process, thus, increasehe metals electrodeposition overpotential. Such process could beasily proved by examining the cyclic voltammograms profile athe anodic part of the curve. As can be seen from the curve, thewo oxidation peaks at the region of 0–300 mV vs. SCE underwentshifting to a more positive potential as the increasing of the APG

oncentration. In addition, the second anodic peak (higher poten-ial) was observed to significantly decrease with the increasing ofhe surfactant concentration and finally vanished when the APGoncentration reached 3.25 wt.%. This further confirmed the effec-ive organic layer formation on the ITO surface of which hinder thelectrochemical process.

Fig. 3 shows typical FESEM images of the Co–Ni–Cu alloysanoparticles prepared by co-electrodeposition in the presencef several concentration of the APG surfactant at a potential of850 mV vs. SCE. For the concentration of APG below the CMC

Fig. 3b), it was found that high-density nanoparticles were suc-essfully grown up on the surface. However, it can be seen that

arge-scale nanoparticles seemed to experience agglomerationach other forming a nanoparticles network on the surface. Thisould be due to the presence of limited surfactant concentrations the agglomeration inhibitor agent during the deposition pro-ess. This condition was actually much similar with the sample

nce 257 (2010) 1027–1033

prepared in the absence of APG (Fig. 3a). Thus, no clear effect on thenanoparticles structure when APG was below CMC. The size of thenanoparticles was found to be in the range of 1–100 nm. A signif-icant change was obtained when the APG concentration increasedabove the CMC value (Fig. 3c–e). As can be seen from the figure,the nanoparticles growth density was found to decrease with theincreasing of the APG concentration. However, at a certain rangeof APG concentration, in particular 1.95 wt.%, the nanoparticlesdispersion was found to be homogeneously distributed through-out the surface with limited observable agglomeration. Besidesimproving in the nanoparticles distribution, the increase of theAPG concentration also improved the size homogeneity of thenanoparticles. At optimum concentration that produced highly dis-persion and low size variation, namely for APG concentration of0.65 and 1.95 wt.%, the nanoparticles was found to be in the range of20–50 nm. However, further increasing concentration at 3.25 wt.%,

Fig. 4. FESEM images of Co–Ni–Cu nanoparticles electrodeposited on ITO glasssubstrate from electrolyte containing 1.95 wt.% of APG prepared at different co-deposition potential (a) −875 mV vs. SCE and (b) −925 mV vs. SCE.

S. Budi et al. / Applied Surface Science 257 (2010) 1027–1033 1031

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ig. 5. FESEM images of Co–Ni–Cu nanoparticles electrodeposited at co-depositionrowth time (a) 15 s, (b) 30 s, (c) 60 s and (d) 150 s.

n the cyclic voltammetry experiments, high APG concentrationffectively decreased the current density of the electrodepositionrocess. This certainly is an indication of a slow growth rate depo-ition of the metal species onto the substrate surface. At a slowrowth regime, the bigger nanoparticles normally grow faster thanhe smaller ones. As a consequence, bigger nanoparticles becomeominant product. Based on these experiment results, we concludehat the APG concentration of 1.95 wt.% (above CMC value) wasound to produce a better nanoparticles growth characteristic suchs particle size, size distribution and dispersion. However, if high-ensity nanoparticle preferred, APG concentration below CMC cane used.

We also investigated the effect of deposition potential on therowth characteristic of Co–Ni–Cu nanoparticles. In this experi-ent, we used the APG concentration of 1.95 wt.% (the optimum

ondition for nanoparticles growth characteristic) as the basis ofhe studies. Fig. 4 shows the FESEM images of the Co–Ni–Cu alloyanoparticles electrodeposited at potentials of −875 and −925 mVs. SCE. The shape homogeneity and the size distribution as wells the density of the nanoparticles on the surface were foundo increase when the electrodeposition potential was increased.

eanwhile, to our surprise, the size of the nanoparticles was foundo relatively unchanged with the increasing of the electrodeposi-ion potential. This could be easily understood as the effect of highlyrowth kinetic process, as the result of relatively high electrodepo-ition potential, of which facilitate the formation of high density,

xcellent dispersion as well as relatively small nanoparticles size.

Up to this stage, we have found that the concentration of APGs well as the value of the reduction potential used in the reactionxhibited a dominant function for the manipulation of the alloysanoparticles growth characteristic. So far, we observed only the

tial of −925 mV vs. SCE from electrolyte containing 1.95 wt.% of APG with different

Co–Ni–Cu alloys nanoparticles growth characteristic that preparedwith growth time of 150 s. To further understand the formationprocess of the alloys nanoparticles on the substrate surface, weobserved their growth characteristic at the early growth processnamely 15, 30 and 60 s. An optimum APG concentration (1.95 wt.%)and reduction potential of −925 mV vs. SCE was used for this pur-pose. The results are shown in Fig. 5. It was found that at anearly growth process, small nanoparticles with size in the rangeof 10–50 nm were observed. At this stage, ITO surface backgroundcan be clearly seen from the FESEM image. This is certainly strongindication of the electrochemical process for the formation of alloysnanoparticles on the surface. The nanoparticles size was found tofurther increase with the increasing of the growth time. At a rela-tively longer growth time, 150 s, an effective surface coverage bythe nanoparticles was obtained as the result of optimized nanopar-ticles evolution on the surface.

Finally, we examined the composition of the electrodepositednanoparticles of Co–Ni–Cu prepared using the present approach byEDX analysis. Fig. 6 shows typical EDX spectrum of the electrode-posited nanoparticles prepared in the presence of 1.95 wt.% of theAPG surfactant with deposition time of 150 s. It can be seen that thepeaks related to the Co, Ni and Cu were already present confirmingthe nanoparticles alloys were successfully formed on the ITO sur-face. Other peaks such as In, Sn, Si, O and Ca, were also observed. Thiscan be easily related to the component of the background substrate,namely ITO on glass plate. Typical atomic composition of the alloys

prepared using this condition was 21, 25 and 54 at.% for Co, Ni andCu, respectively. At present stage, we only examined the composi-tional growth of the alloys at the growth time of 150 s. However,the composition might be varied if the growth time is different dueto the kinetic growth process of the nanoparticles (related to the

1032 S. Budi et al. / Applied Surface Science 257 (2010) 1027–1033

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Fig. 7. (a) Chemicals composition of Co–Ni–Cu nanoparticles electrodeposited at

low APG concentration, namely below CMC, can be used. High APG

ig. 6. EDX spectra of Co–Ni–Cu nanoparticles electrodeposited on ITO glass sub-trate from the electrolyte containing 1.95 wt.% of APG surfactant with depositionime of 150 s.

hemical potential of the system). To understand such evolution ofhe composition should be very interesting and we put this as our

ain future investigation.As has been observed in the cyclic voltammograms profile

hange of the system upon variation of the APG concentration, thetomic composition of the nanoalloys was strongly depend on theoncentration of the APG in the electrolyte (Fig. 7a), in particularor the concentration above the CMC value. At this condition, theu atomic portion was found to linearly increase with the increas-

ng of the APG concentration. Meanwhile, the Co and Ni drasticallyecreased with the increasing of the APG concentration. As haseen discussed earlier, this could be related to the increase in theverpotential of metals ions electrodeposition as the APG concen-ration increased. In other word, the reduction potential for all the

etal ions species shifted to more negative potential (see Fig. 2).herefore, at a selected co-electrodeposition potential, the moreositive reduction potential (in this case Cu) would be prominentlyeposited on the electrode lower reduction potential.

For the case of the APG below the CMC value, no signifi-ant change on the chemical composition of the electrodepositedanoalloys compare to that of prepared in the absence of APGamely relatively balance composition. As can be seen from Fig. 7a,

n the absence and in the presence of APG at concentration belowMC, the cobalt content was found to be relatively higher thanickel. This should be attributed to the phenomena of anoma-

ous co-deposition of cobalt and nickel [1,29,31]. However, thishenomena was not observed when the concentration of alkylolyglucoside exceeded the CMC value, where the cobalt contentecame lower than nickel. Based on this result, it can be further con-rmed that the APG do play a unique role in controlling the growthharacteristic of the electrodeposited Co–Ni–Cu alloys nanoparti-les.

We further examined the effect of electrodeposition potential onhe chemical composition of the electrodeposited Co–Ni–Cu alloysanoparticles. For this purpose, the APG concentration of 1.95 wt.%as used. As has been discussed earlier, the reduction potentialas been found to play key role in the characteristic growth of theanoalloys such as particle morphology and size distribution on

he electrode surface. However, as can be predicted, the depositionotential also absolutely determined the final chemical composi-ion of the as prepared Co–Ni–Cu alloys nanoparticles. In this work,e found that the stoichiometry balance of the nanoalloys compo-

−850 mV vs. SCE from the electrolyte containing different concentration of APG.(b) Chemicals composition of Co–Ni–Cu nanoparticles at different potential fromelectrolyte containing 1.95 wt.% of the APG surfactant. All of the deposits preparedwith deposition time of 150 s.

sition increased with the increasing of electrodeposition potential.At certain potential (−950 mV vs. SCE), an excellent compositionwas obtained, namely 23, 35, 42 at.% for Co, Ni and Cu, respectively.However, this composition was significantly unchanged when thepotential was increased to −975 mV vs. SCE. The result is shownin Fig. 7b. This process can be easily understood as the result ofeffective co-electrodeposition of Co, Ni and Cu at a relatively highpotential due to a matching deposition potential.

4. Conclusion

The effect of the APG concentration on the Co–Ni–Cu electrode-position growth characteristics such as particles size homogeneity,density, dispersion on the surface and the alloys compositionhave been investigated. By controlling the APG concentration,the Co–Ni–Cu alloys nanoparticles with excellent growth char-acteristic can be prepared. In order to produce the Co–Ni–Cualloys nanoparticles with specific characteristic, the following factsshould be noted: (i) for the preparation of the Co–Ni–Cu nanoal-loys with excellent stoichiometry chemicals composition balance,

concentration only produced Co–Ni–Cu alloys nanoparticles withexcellent growth characteristic in term of size homogeneity anddistribution of the particles on the surface instead. (ii) At a rela-tively high concentration, the APG may exhibit an ions inhibition

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haracteristic that caused the increasing in the electrodepositionverpotential of the entire metals ions species. As the result, theetal with lowest reduction potential (Cu) become the dominant

roduct. Since high APG concentration as well as high deposi-ion potential was found to be very effective for the preparationf the Co–Ni–Cu alloys nanoparticles with excellent growth char-cteristic. The present approach can be used to prepare magneticanoalloys for used in the currently existing application. The efforto produce the nanoalloys both with excellent chemicals composi-ion and the growth characteristic are in progress.

cknowledgements

The authors thank the Ministry of Science, Technology andnnovation (MOSTI), Ministry of Higher Education (MOHE) andniversiti Kebangsaan Malaysia (UKM) for supporting this projectnder research grants of UKM-ST-07 FRGS0033-2009 and UKM-UP-NBT-08-27-106. We also thank Prof. Ambar Yarmo and Prof.

brahim Abu Thalib for providing some laboratory equipments.

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