Comparative study of ZnO and CuSCN semiconducting nanowire electrodeposition on different substrates

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Journal of Solid StateElectrochemistryCurrent Research and Development inScience and Technology ISSN 1432-8488Volume 17Number 2 J Solid State Electrochem (2013)17:391-398DOI 10.1007/s10008-012-1912-3

Comparative study of ZnO and CuSCNsemiconducting nanowire electrodepositionon different substrates

Sylvia Sanchez, Cyril Chappaz-Gillot,Raul Salazar, Hervé Muguerra, EdrisseArbaoui, Solenn Berson, Claude Lévy-Clément, et al.

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ORIGINAL PAPER

Comparative study of ZnO and CuSCN semiconductingnanowire electrodeposition on different substrates

Sylvia Sanchez & Cyril Chappaz-Gillot & Raul Salazar &

Hervé Muguerra & Edrisse Arbaoui & Solenn Berson &

Claude Lévy-Clément & Valentina Ivanova

Received: 5 September 2012 /Revised: 4 October 2012 /Accepted: 9 October 2012 /Published online: 18 October 2012# Springer-Verlag Berlin Heidelberg 2012

Abstract In this study, we are reporting on the electro-chemical deposition of two kinds of semiconducting nano-wires (ZnO and CuSCN) on different substrates. ZnO andCuSCN are n- and p-type transparent semiconductors whoseelectrochemical preparation has some similarity, and it is acombination of two steps: an electrochemical reduction withconsecutive chemical precipitation. Here, we show that de-spite the different physicochemical nature of the studiedmaterials, when they are deposited electrochemically, theirdimensions depend mainly on the surface state of the usedsubstrate. Thus, depending on the substrate morphology,nanowires with diameters between 50 and 380 nm fromboth semiconductors could be grown. It is also shown that

ZnO and CuSCN nanowires could be successfully grown onglass and plastic substrates as well as on a metallic one. Thepossibility of growing these transparent semiconductors onflexible substrates opens new perspectives for their use in“invisible” electronic devices.

Keywords Electrochemical deposition . Semiconductingnanowires . ZnO . CuSCN

Introduction

In the last years, nanostructured materials became veryattractive due to their unique properties making them suit-able for the creation of new device architectures. One of themost dynamic research areas is on the synthesis of quasi-one-dimensional (1D) materials such as nanowires (NWs),nanorods, or nanotubes [1–4]. The 1D structures owe theirunique properties to the fact that they have low defectdensity compared to thin films (2D layers) and the possibil-ity of preparing them with large surface-to-volume ratio.Various processes are used for the synthesis of nanowires,but the electrochemical deposition technique appears moreadvantageous due to the low deposition temperatures, theuse of inexpensive equipment, and the easy control of dif-ferent deposition parameters to prepare nanostructures withdesired dimensions [5].

ZnO and CuSCN are transparent n- and p-type semi-conductors, respectively. ZnO possesses very interestingoptical and electrical properties such as a direct bandgaparound 3.3 eV, a large exciton binding energy (60 meV), agood electron conductivity, piezoelectricity, and biocompat-ibility. The electrochemical deposition of ZnO is widelystudied, and since the first reports [6–9] concerning itspreparation by this method, nowadays, ZnO NWs withcontrolled dimensions and desired properties could be

It is our pleasure to dedicate this manuscript to Prof. Milchev, whospent many years studying the nucleation and growth phenomena andinspired us to investigate unusual systems. One of the authors (VI)addresses her gratitude to Prof. Milchev for his indirect contribution toher professional development.

S. Sanchez : C. Chappaz-Gillot : R. Salazar : E. Arbaoui :V. Ivanova (*)CEA, Leti, MINATEC Campus,17 rue des Martyrs,38054 Grenoble, Francee-mail: [email protected]

C. Chappaz-Gillot : S. BersonCEA, INES, Savoie Technolac,BP 332, 50 avenue du Lac Léman,73377 Le Bourget-du-Lac, France

H. MuguerraCNRS-Institut Néel,25 rue des Martyrs,38042 Grenoble, France

C. Lévy-ClémentCNRS, Institut de Chimie et des Matériaux de Paris-Est,2-8 rue Henri Dunant,94320 Thiais, France

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prepared [10–12]. In our group, ZnO electrodeposition bymolecular oxygen reduction is studied with the aim tofurther integrate it in nanostructured and polymer solar cells[13–17].

CuSCN is widely used as a solid hole transporting elec-trolyte in dye-sensitized and extremely thin absorber solarcells [18, 19] because of its energy gap (3.7 eV) and valenceband edge position. The electrochemical deposition ofCuSCN is less investigated than that of ZnO due to theinstability of the precursor aqueous electrolytes. In the earlyworks, its deposition was performed in organic solvents [18,20]. Recently, the use of aqueous electrolytes containingchelating agents was proposed [21–23]. Only in two worksis the electrodeposition of CuSCN NWs into templates withcylindrical holes from ethanolic solutions [24, 25] reported.The obtained nanowires are polycrystalline after templateremoval, and a post-annealing treatment was applied toimprove the material quality. Our group very recently pro-posed a template-free electrodeposition of CuSCN NWsfrom stable aqueous electrolyte at room temperature [26].

In the present case, a comparative study on the electro-chemical deposition of ZnO and CuSCN nanowires ondifferent substrates is performed. Our aim is to get importantinformation about the substrate morphology influence onthe growth rate, the crystalline quality, and the density ofthe nanowire arrays. It is shown that despite the differentphysicochemical nature of the studied ZnO and CuSCNmaterials, their electrochemical deposition on different sub-strates is very similar. Depending on the substrate morpholo-gy, nanowires with diameters between 50 and 380 nm couldbe obtained. It is also demonstrated that ZnO and CuSCNnanowires could be successfully grown on glass and plasticsubstrates as well as on a metallic one.

Experimental

The electrochemical deposition was carried out in a standardthree-electrode electrochemical cell with a volume of 200 mL,where a helical platinum wire was used as a counter electrode,a conductive substrate with an active area of 1 cm2 was usedas the working electrode, and a saturated calomel electrode(SCE) was used as the reference electrode. Electrochemicalmeasurements were performed using the potentiostat/galvano-stat PARSTAT 2273 (Princeton Applied Research) monitoredby the Powersuite software.

Substrates

In this study, the following kinds of substrates were used:

1. Glass substrates covered with transparent conductiveoxide, indium tin oxide (ITO), or fluorine-doped tin

oxide (FTO) with a sheet resistance of 10 Ω/sq (AGCFabritech Co., Ltd., Japan)

2. Polyethylene terephthalate (PET) covered with ITOwith a sheet resistance of 10–15 Ω/sq

3. Silicon wafer covered with a thin gold film (50 nm)prepared by chemical vapor deposition from CEA-Leti

4. Electrodeposited ZnO and CuSCN 2D layers (see thepreparation conditions below)

The glass substrates were ultrasonically cleaned consec-utively in acetone, ethanol, and isopropanol for 15 min ineach solvent, rinsing with hot MilliQ water in between,whereas for the plastic substrate, the ultrasonic treatmentwas reduced to a few minutes.

Chemicals

All chemicals for ZnO electrodeposition were from Fluka(ZnCl2, 97.0 % and KCl, 99.5 %), of analytical reagent-grade, and were used without further purification. Prior tothe deposition, molecular oxygen was bubbled through thebath until saturation (30 min at 0.25 Pa), and it was main-tained at a lower pressure during the deposition process. Theelectrolyte was stirred during deposition using a magneticstirrer at 300 rpm. For CuSCN preparation, CuSO4·5H2O(purity > 99.9 %, Sigma-Aldrich), triethanolamine (purity ≥99 %, Sigma-Aldrich) ethylenediaminetetraacetic acid(EDTA, purity ≥ 99.0 %, Fluka), and KSCN (purity ≥99 %, Sigma-Aldrich) were used as received.

ZnO electrodeposition

ZnO thin films (2D layers)

The bath temperature was fixed at 50 °C, and the layerswere deposited potentiostatically at E0−1.0 V vs SCE froman aqueous electrolyte containing 5 mM ZnCl2 and 0.1 MKCl. The passed charge density (Q) was 0.4 C cm−2 for thepreparation of films with a thickness around 250 nm.

ZnO nanowires

The ZnO nanowires were deposited potentiostatically atE0−1.0 V vs SCE from an aqueous electrolyte containing0.5 mM ZnCl2 and 1.0 M KCl. The deposition temperaturewas fixed at 80 °C, and the Q was fixed at 10 C cm−2.

CuSCN electrodeposition

CuSCN thin films (2D layers)

A 6-mMCu2+ solution was prepared by mixing CuSO4·5H2O(1 M equivalent) with 10 M equivalent triethanolamine and

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5 M equivalent KSCN into deionized water, according to theprocedure described in reference [22]. A 2D layer with athickness around 200 nm was deposited potentiostatically atE0−0.4 V vs SCE and Q025 mC cm−2.

CuSCN nanowires

A 12-mM Cu2+ solution was prepared by mixingCuSO4·5H2O (1 M equivalent) with 1 M equivalent EDTA

and 0.25 M equivalent KSCN into deionized water [26]. TheCuSCN nanowires were deposited potentiostatically eitherat −0.3 V vs SCE for the ITO- and FTO-coated substrates orat −0.1 V vs SCE for the silicon substrate covered with agold film. The Q was fixed at 80 mC cm−2.

Characterization techniques

The film morphology was investigated by scanning electronmicroscopy (SEM) on a Hitachi S-4100 apparatus. Thecrystalline structure of the ZnO deposits was analyzed usingthe Bruker X-ray Diffractometer D5000 with a copper anti-cathode (Cu, Kα1, λ01.5406Ǻ), scanning from 25° to 60°(2θ) with a step of 0.02°. X-ray diffraction (XRD) spectra ofthe CuSCN films were recorded with a PANalytical X'PertMPD using a cobalt anticathode (Co, Kα1, λ01.7889 Å).Atomic force microscopy (AFM) measurements were per-formed with a Dimension V (Bruker) equipment operatingin tapping mode, permitting to get additional morphologicalinformation and to evaluate the surface roughness. Thetapping mode was used with scan frequencies of 0.75 Hz,and the resolution of image acquisition was 512 pixels perline (512×512 pixels/image).

Results and discussion

The nucleation–growth mechanism of a deposited solidaffects both the size and the structural properties of theresulting crystals. Despite the extensive research effortsdevoted to studying the deposition and growth mechanismsof metals, relatively few new insights have been gained inthe area of electrocrystallization of semiconducting nano-wires. Milchev [27] proposes that the mass crystallization inthe case of 1D or 3D deposits could be described by theKolmogorov–Avrami formalism without restrictions. How-ever, it would be difficult to apply this formalism to oursystems (ZnO and CuSCN nanowires) despite the fact thatthey grow perpendicularly to the substrate. This is probablydue to the greater complexity of the processes where depos-its are formed on the surface as a result of a combination ofelectron transfer and chemical reactions.

Fig. 1 Chronoamperograms obtained during a ZnO nanowire electro-deposition on different substrates (as indicated) from an electrolytecontaining 0.5 mM ZnCl2 and 1.0 M KCl, E0−1.0 V vs SCE, Q010 C cm−2 at 80 °C; and b CuSCN nanowire electrodeposition ondifferent substrates (as indicated) from an electrolyte containing12 mM Cu2+ (Cu2+/EDTA/SCN−01:1:0.25), E0−0.1 V for Si/Au andE0−0.3 V vs SCE for all other substrates, Q080 mC cm−2

Table 1 Summary of differentparameters determined from thechronoamperograms and theAFM and SEM images of theZnO nanowire electrodeposition

Substrate RMS Depositiontime

Nanowirelength

Nanowirediameter

Nanowiredensity

(nm) (s) (nm) (nm) (cm−2)

Glass/ITO 3.76 9,613 1,800 250 7.0×108

PET/ITO 2.39 11,950 800 240 1.5×109

Glass/FTO 31.82 2,543 730 220 6.0×108

Glass/FTO/ZnO 2D 19.27 8,383 660 175 3.0×109

Si/Au 2.53 3,805 850 50 7.0×109

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In this study, the ZnO thin films and nanowires have beenelectrodeposited from an aqueous electrolyte containingzinc chloride, potassium chloride, and dissolved molecularoxygen. This method is based on molecular oxygen reduc-tion pioneered by Peulon and Lincot [8, 9], and its principleis very simple: the reduction of molecular oxygen leads tohydroxide ion generation (see Eqs. 1 and 2), which areforming the unstable zinc hydroxide, and due to the super-saturation and the chemical precipitation at the electrodevicinity, ZnO is obtained. ZnO nanowires are formed whenthe concentration of Zn2+ ions in the electrolyte is low [8].As-prepared ZnO nanowire arrays have high crystallinequality, and each nanowire is a single crystal.

O2 þ 2H2Oþ 2e� ! H2O2 þ 2OH�;

E� ¼ �0:065 V normal hydrogen electrode NHEð Þð Þð1Þ

O2 þ 2H2Oþ 4e� ! 4OH�; E� ¼ �0:401 V NHEð Þ ð2ÞThe overall reaction for zinc oxide formation is expressed

in Eq. 3:

Zn2þ þ 1 2O2 þ 2e� ! ZnO= ; E� ¼ �0:93V NHEð Þ ð3ÞThe CuSCN layer and nanowire electrodeposition is also

a two-step reaction. The first step is electrochemical (Eq. 4),where Cu2+ is reduced to Cu+, while the second step is thechemical precipitation of Cu+ with SCN− (Eq. 5) [22, 24]:

Cu2þ þ e� ! Cuþ; E� ¼ þ0:159 V NHEð Þ ð4Þ

Cuþ þ SCN� ! CuSCN ð5Þ

ZnO and CuSCN nanowire growth

Normally, chronoamperometric data should provide infor-mation about the nucleation and growth involved in theelectrocrystallization process. Depending on the nucleationrate, two types of growth mechanism can be distinguished:

instantaneous and progressive [27]. In the case of instanta-neous nucleation, the growth rate of a new phase is high, butthe number of formed active nucleation sites is low. On theother hand, the progressive nucleation is slow, but it occurson a large number of active sites, resulting in the growth ofcompact grains favoring good connectivity.

Figure 1a depicts chronoamperograms obtained whenZnO nanowires are grown on different substrates at −1.0 V

Table 2 Summary of differentparameters determined fromthe chronoamperograms andthe AFM and SEM imagesof the CuSCN nanowireelectrodeposition

Substrate RMS Depositiontime

Nanowirelength

Nanowirediameter

Nanowiredensity

(nm) (s) (nm) (nm) (cm−2)

Glass/ITO 3.76 1,007 600 80 2.5×109

PET/ITO 2.39 1,119 900 380 7.0×108

Glass/FTO 31.82 694 800 70 4.0×109

Glass/ITO/CuSCN 2D 20.56 1,186 1,600 50 2.0×109

Si/Au 2.53 828 900 50 3.5×109

Fig. 2 a XRD pattern of ZnO nanowires electrodeposited on a glass/FTO substrate from an electrolyte containing 0.5 mM ZnCl2 and 1.0 MKCl, E0−1.0 V vs SCE, Q010 C cm−2 at 80 °C. b XRD spectrum ofCuSCN NWs deposited on a glass/FTO substrate at −0.3 V vs SCE,Q080 mC cm−2. The diffraction peaks of the FTO substrates aremarked with stars

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vs SCE and a fixed passed charge density (Q010 C cm−2).The first observation that should be pointed is that thedeposition process takes different times, depending on thesubstrate. It is interesting that the ZnO NWs are grown withalmost the same rate on a metallic (gold) substrate and on aglass/FTO substrate, even a little bit faster on the latter one.When NWs are subsequently grown on a ZnO 2D layerelectrodeposited on a glass/FTO substrate, their depositiontakes a slightly longer time. This result could be explainedon one side by the difference in the substrate conductivity andon the other side by the different densities of the nucleationsites on these substrates. The ZnO thin film is composed ofsmall grains and thus offers more nucleation sites than the baresubstrate. The fact that the ZnO nanowire growth rate isalmost not influenced in this case should be mainly explainedby the n-type semiconducting properties of ZnO. What isastonishing here is that the highest current density is achievedwhen the deposition is performed on a glass/FTO substrate.This is probably related to the higher reactivity of this

substrate, the surface roughness of which is higher than thatof other substrates (see the AFM images shown on Fig. 3 andTable 1). The lowest deposition current is obtained when ZnONWs are grown on PET/ITO and glass/ITO substrates. Itseems that the ITO substrates have higher resistivity, and thus,the electrochemical deposition is with lower rate. Moreover,these substrates are very flat (see Table 1) with a very smallsurface roughness and a lower density of nucleation sites. Forboth substrates, with the deposition time, the current tends toreach similar values, whereas the current for the plastic sub-strate slightly increases. The latter is probably due to a pro-gressive nucleation of ZnO seeds.

The current transients (Fig. 1b) obtained for CuSCN NWelectrodeposition show a current plateau (almost constantwith time), and their shape is slightly different from thoserecorded during the ZnO nanowire growth. A current peak isobserved for all studied substrates (with the exception ofPET/ITO) in the first 25 s of the deposition. One possiblereason for the appearance of this current peak could be the

Fig. 3 In the first column aredepicted the AFM images ofthe bare substrates used inthe present study. In thesecond column are shownthe SEM images (tilted view,45°) of ZnO nanowireselectrodeposited on thesubstrates from the first column.In the third column, the SEMimages (tilted view, 45°)of the CuSCN nanowireselectrodeposited on thecorresponding substrates fromthe first column are shown.The rows refer to the followingsubstrates: a PET/ITO, b glass/ITO, c glass/FTO, and d Si/Au.The inset in the SEM imageof the second column in (b)is the same SEM image in1.5-μm scale showing the ZnOnanowire density better. Thedeposition conditions are givenin the “Experimental” section

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progressive formation of nuclei during this initial period oftime. The increase of nucleus density would lead to anincrease of the active area, which is reduced after the coa-lescence. As a consequence, the peak in the current-vs-timegraph should be related to the maximum of the activesurface area before coalescence. In the case of ZnO NWelectrodeposition, only for glass/ITO and glass/FTO sub-strates, a very slight increase of the current in the initialperiod is observed. This means that for the case of ZnOgrowth, all active surface sites were occupied in the begin-ning of the deposition process. One important differenceshould be noted when CuSCN nanowires are grown on aCuSCN 2D layer: the deposition time is longer than for theother used substrates. This is not the case for the ZnOnanowire growth on a ZnO thin film. It should be explainedwith the different nature of these semiconductors; CuSCN,being a p-type, conducts the electrons with a lower rate.

We also have to note here that the CuSCN nanowiregrowth is a very fast deposition process compared with thatof ZnO (see Tables 1 and 2), and it is realized with lowercurrent densities. To obtain CuSCN NWs with the samelength as ZnO NWs, the time is six times shorter and thereached current densities are ten times lower.

Crystalline quality of ZnO and CuSCN nanowires

The electrodeposited ZnO NWs exhibit a hexagonal wurtzitestructure with preferred growth along the c-axis, the intensityof (002) peak being higher than that of (101), (100), and (102)peaks (Fig. 2a). Here, the diffraction patterns for ZnO NWs

electrodeposited on a glass/FTO substrate are shown, but thisis valid for all studied substrates. The possibility of depositingZnO NWs with good crystalline quality at low temperatures isimportant from a technological point of view because theycould be grown on flexible substrates (as PET) and used inoptoelectronic devices without further annealing step.

Figure 2b shows the XRD pattern of CuSCN NWs elec-trodeposited on a glass/FTO substrate. It is seen that theyexhibit high crystalline quality in agreement with the rhom-bohedral β-CuSCN phase. The nanowire XRD spectrumconsists of a very intense (003) peak, together with smaller(006), (009), (116), (015), and (107) peaks. The extremelyhigh intensity of the (003) peak in comparison with theothers indicates that the nanowires are preferentially orient-ed along the c-axis, in a direction orthogonal to the substrate(in accordance with the SEM images, see Fig. 3).

Influence of the substrate on the nanowire dimensions

The results presented above show that although we aredepositing two different materials, a lot of similarities areobserved. To find an explanation for this behavior, a mor-phological study is performed. In Fig. 3, in the left columnare the depicted AFM images of the bare substrates onwhich ZnO and CuSCN NWs are grown. The surface rough-ness is important in evaluating the influence of the substratemorphology on the nanowire dimensions and density. Weuse the root mean squared (RMS) roughness experimentallydetermined using AFM in tapping mode to evaluate theroughness of the used substrates. From the AFM images

Fig. 4 In the first column are depicted the AFM images of a the ZnO2D layer electrodeposited on a glass/FTO substrate and b the CuSCN2D layer electrodeposited on a glass/ITO substrate. In the secondcolumn are shown the SEM images (tilted view, 45°) of the sameZnO and CuSCN 2D layers. In the third column, the SEM images

(tilted view, 45°) of the ZnO and CuSCN nanowires electrodepositedon these substrates are shown. The two rows refer to the a electro-deposited ZnO on a glass/FTO substrate and b electrodepositedCuSCN on a glass/ITO substrate. The deposition conditions are givenin the “Experimental” section

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and the measured RMS values (given in Tables 1 and 2), wecan say that the flatter substrates are that of PET/ITO and Si/Au (RMS02.39 and 2.53 nm, respectively). In spite of thesimilar surface roughness of these substrates, the nanowiresgrown on them are with different dimensions. On the Si/Ausubstrate, both types of nanowires (ZnO and CuSCN) havethe same diameter (50 nm), and it is the smallest diameterobtained in this investigation. The highest nanowire arraydensity on this substrate is, on one side, due to the smallestdiameter of the nanowires and, on the other side, to the goodsubstrate conductivity and the high density of nucleationcenters. Being very flat and with lower conductivity, theflexible PET/ITO substrate is a condition for depositingnanowires with very large diameters, which indeed is thecase for CuSCN NWs (diameter of 380 nm). This alsoexplains the lower nanowire density obtained on the flexiblesubstrate.

Another interesting observation is that the diameter ofZnO nanowires grown on glass/ITO, glass/FTO, and PET/ITO almost does not vary, and it is between 220 and 250 nm.From the AFM image shown in Fig. 3a, it is seen that theglass/ITO substrate is composed of larger grains, and that isprobably the reason for the larger diameter of ZnO NWs(250 nm), whereas this is not the case for CuSCN NWs. Thediameter of the latter is only 80 nm, and it is almost the samefor the glass/FTO substrate. The glass/FTO substrate consistsof small pyramids which are responsible for the nanowireorientation in different directions.

When thin films of ZnO and CuSCN have been depositedon glass/FTO and glass/ITO substrates, a change of surfaceroughness is observed (see Tables 1 and 2). For the case of aZnO 2D layer electrodeposited on a glass/FTO substrate, theRMS decreased by 10 nm, whereas for the case of a CuSCNthin film electrodeposited on a glass/ITO substrate, it in-creased 5.5 times (from 3.76 to 20.56 nm). In both cases, theZnO and CuSCN NWs subsequently grown on them havesmaller diameters than those deposited on the bare sub-strates. The ZnO 2D layer is composed of small grains about150 nm in size, and the resulting nanowires are almost withthe same diameter (about 170 nm, see Fig. 4a and Table 1).Electrodeposited ZnO thin films have been used as seedlayers for ZnO nanowire deposition, and it has been shownthat the nanowire dimensions depend on the seed layermorphology and thickness [13, 17].

For the CuSCN NWs electrodeposited on a CuSCN 2Dlayer, we find the same diameter as when they are grown onSi/Au substrates. This could be explained by the goodcrystalline quality of the CuSCN thin film electrodepositedon the glass/ITO substrate, which is composed of smallcrystallites (see Fig. 4b). Taking into account that CuSCNexhibits a rhombohedral structure, we can see on the SEMimage depicted in Fig. 4b that the crystallite form resemblesthe edges of rhombohedra. The nanowires nucleate and

grow on almost all small facets seen on the SEM image ofthe CuSCN thin film. If we measure the angle between thenanowires, we can find the same angle as in the thin film.

Before concluding, we want to note again that someimportant parameters determined from the chronoampero-grams and the morphological investigation are summarizedin the Tables 1 and 2.

Conclusions

In this manuscript, the electrochemical deposition of ZnOand CuSCN nanowires on different substrates have beenstudied. Despite the different nature of the materials, somesimilarities during their growth are observed. Both types ofnanowires grow faster on glass/FTO and Si/Au substratesthan on the other used substrates. A current peak maximumin the first 25 s of the CuSCN nanowire electrodeposition isobserved due to the progressive nucleus formation in thisperiod. The addition of an electrodeposited ZnO 2D layerdoes not really change the nanowire growth, which is relatedto the n-type conductivity of ZnO. Contrary to that, when aCuSCN thin film is electrodeposited on a glass/ITO sub-strate, the CuSCN nanowires grow very long, and this isexplained by the lower electron conductivity of the p-typeCuSCN. The nanowire diameter depends on the substratemorphology and conductivity, and it has been shown that onSi/Au substrate, nanowires with very small diameter couldbe grown. Due to this fact, the densest nanowire arrays aredeposited on this substrate. The lower conductivity of thePET/ITO substrate resulted in lower density of nanowiresand the largest diameter (380 nm in the case of CuSCN). Inthis study, we show that the material’s nature plays a minorrole on the semiconducting nanowire growth mechanismwhich is mostly determined by substrate morphology.

Acknowledgments Sylvia Sanchez is grateful to CEA for the PhDfellowship. Cyril Chappaz-Gillot acknowledges the CEA program“NTE” for his post-doctoral fellowship. Raul Salazar gratefullyacknowledges the Nanosciences Foundation of Grenoble for his PhDfunding as well as the support from CONACYT Mexico. The authorsthank Sylvie Favier for some XRD analyses and Guillaume Rodriguezfrom CEA-Leti for the Si/Au wafer preparation.

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