Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008

Supporting information for:

Template Induced Directional Growth of ZnO Nanomeshes by Colloidal

Crystals

Ming Fu, Ji Zhou*, Bo Li, Xueguang Huang, Yuehui Wang and Longtu Li

State Key Lab of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University,Beijing 100084 (P. R. China) Email:zhouji@tsinghua.edu.cn I.SEM image of colloidal crystal template

Figure S1 SEM images of (a) the cross-section of colloidal crystal template arrays on ITO substrate; (b) surface of colloidal crystal template. The self-assembled colloidal crystal has single-crystal FCC structure. It has one of its 111 crystal plane parallel to the surface of the ITO substrate.

Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008 II. Supplementary SEM image of nanomeshes grown along 111, 100 and 110 planes of colloidal crystals which can be found in one image

Figure S2 typical SEM images of nanomeshes deposited along 100, 110 and 111 planes of colloidal crystals which can be found in one image. When the colloidal crystal template is pretreated by surfactant solution, the directions and patterns of deposited nanomeshes are much different. In untreated cases, nanomeshes along 111 planes of colloidal crystals are dominantly deposited on the substrate just as shown in Figure S4. Differently, nanomeshes grown along 111, 100 and 110 planes of colloidal crystals are formed miscellaneously on the substrate by the pretreated templates. Though ZnO nanomeshes grown along 100 and 110 planes are harder to obtain compared with the ones with 111 planes, nanomeshes along all the main low index planes of colloidal crystals can be formed by varying the surface energy of the template.

III. The difference between the actual pattern and the ideal one of nanomeshes grown along 110 planes of the colloidal crystals. The ideal pattern of nanomeshes along 110 planes of the colloidal crystals is shown in figure 1b. There always are small pores or vales among the four neighboring pores. The self-accomplished colloidal crystals have face-centered cubic structure. Therefore, the distance of the 110 plane family is the smallest among the main low index planes. (The distance of the 110, 100 and 111 planes is about 0.5, 0.714 and 0.808 microsphere diameter). Because the thickness of the nanomeshes can not be neglected, the nanomeshes along one of the 110 planes of the colloidal crystal would contact the neighboring 110 plane such as plane II in figure S3b. When the nanomesh grow along 110 plane I of the colloidal crystal, a smaller vale or pore would be formed by the microsphere (Microsphere T in Figure S3a) in the neighboring plane (110 Plane II in Figure S3b) among the four normal-sized pores formed by the removed microsphere U~X.

Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008 These small pores or vales seldom exist in the nanomeshes grown along 111 planes of the colloidal crystals because the plane distance of 111 planes is large enough as shown in Figure S3c.

Figure S3 (a) Surface pattern of the 110 plane of the colloidal crystal, the yellow microspheres are the ones nanomesh grown along. (b-c)Cross section illumination of the (b)110, (c)111 planes of the colloidal crystal, the yellow microspheres are the

ones nanomesh grown along.

Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008

IV. The template induced directional growth has certain universality for other nanosheet structures deposited by different method

Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008

Figure S4 all the nanomeshes are deposited along 111 planes of colloidal crystals on the substrate. The template induced directional growth has certain universality for

Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008 other nanosheet structures deposited by different method. (a)nanomeshes deposited in 0.1M Zn(NO3)2 solution at 0~15oC; (b)nanomeshes deposited in 0.05M Zn(NO3)2+0.06M KCl solution at 70 oC. As reported in reference, zinc oxide also formed nanosheets structure when electrodeposited in 0.05M Zn(NO3)2+0.06M KCl solution at 70 oC1. When the colloidal crystal-covered ITO substrates are used as the working electrode, nanosheets with ordered pores (nanomeshes) can also be formed in Zn(NO3)2 and KCl solution just like the image shown in Figure 1d. The number of nanomeshes per area formed in Zn(NO3)2 and KCl solution is more than the one formed in Zn(NO3)2 solution at low temperature. Although the number of nanomeshes is decided by the electrolyte and process parameters, the pore periodicity in each nanosheet is similar in both electrochemical methods. In most case, the nanomeshes formed in zinc nitrate solution also tend to grow along 111 planes of colloidal crystals. Therefore, parallel and three-fold symmetrical alignments are formed between each nanomesh. In conclusion, the arrange patterns of zinc oxide nanomeshes which electrodeposited by both methods is the same except the nanomesh density. The direction of nanosheets electrodeposition is always directed by 111 planes of colloidal crystals in untreated cases.

Reference [1] Xu L F, Guo Y, Liao Q, et al. Morphological control of ZnO nanostructures by electrodeposition. J Phys Chem B, 2005, 109: 13519-13522.

V. X-ray diffraction pattern of the nanomeshes on the substrate

Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008

Figure S5 X-ray diffraction pattern of the nanomeshes on the substrate. A Rigaku D/max-RB X-ray diffraction (XRD) which equipped with a Ni-filtered CuKα radiation

(λ = 0.15418 nm) was employed in our study. The colloidal crystal template was

removed by calcinations at 450oC. A wurtzite zinc oxide structure is shown. .

25 30 35 40 45 50 55 60 65 700

1000

2000

3000

4000

5000

112

103

100

110

10100

2

inte

nsity

(a.u

.)

2θ (degree)

102

Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008 VI. Electrochemical property of nanomeshes(nanosheets) deposition:

Figure S6 shows the current density curve during the nanosheet deposition process. A potentiostatic method at -1V was applied for 8h. The current density is several orders of magnitude lower than the one affected by ion diffusions. The charge transfer resistance Rct measured by AC impedance method for zinc oxide solution at -0.234V is 1.1×106Ω. Afterwards, i0 for the electrochemical reaction is 1.15×10-8A. The deposition of zinc oxide nanosheet is a completely irreversible electrochemical process. Therefore, the morphology of the deposited nanomeshes is independent with ion diffusion in the solutions.

Figure S6 current density curve during the zinc oxide nanosheet deposition process at -1V.

Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008 VII. The origin of the Gibbs free energy equations

The patterns of the formed ZnO nanomesh along 111, 110, 100 planes of

colloidal crystal template vary as discussed in the paper. Figure S7a shows a localized

section of ZnO nanomesh. The blue areas are the ZnO nanosheet. The white circles

are the air pores which are formed by occupied space of colloidal microsphere

template. For nanomesh along 111 planes with ideal straight column, the average

surface area of ZnO nanosheet around each pore is 0.094 single pore area. It is 0.215

for along 100 planes and 0.445 for along 110 planes.

Figure S7 a) Illumination of ZnO nanomesh in surface view. b) Illumination in cross-section view for ZnO nanomesh with bowling shape pores.

There are three parts for the Gibbs energy variation during the process of ZnO

nanomesh formation. The first part comes from Gibbs energy difference (ΔGzno)

between the formed free-state ZnO in solution and ZnO crystalline in nanosheets. The

mole Gibbs energy variation of this part is independent with nanosheet growth

directions along colloidal crystals.

Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008

ZnOGGiGiGi Δ−=Δ=Δ=Δ 100110111 (1)

The second part of the Gibbs energy of nanomesh formation is increased surface

energy between nanosheet surface (Area G in Figure S7b) and solution. As the surface

area is the same for the same ZnO nanosheet deposition with different pore patterns,

the mole Gibbs energy variation of this part is independent of directions along

colloidal crystals.

hGGG watersheetjjj −Ω=Δ=Δ=Δ γ2

100110111 (2)

where γsheet-water is the surface energy of ZnO nanosheet; Ω is the mole volume of

ZnO nanosheet. The third part comes from the surface energy variation of pore edges

(Area F in Figure S7b) in nanosheet. The pore edge area for one mole ZnO deposition

varies when nanosheet grow along different planes of colloidal crystals as the pattern

of the formed ZnO nanomesh along 111, 110, 100 planes of colloidal crystal

template are different. Figure S7a shows a local part of ZnO nanomesh. The pores in

the nanosheets are always bowling shape instead of straight column shape (Figure S7b)

as the thickness of nanosheet cannot be neglected.

The edge areas of each pore is

RhhRRRSSS Hhemisphereedge πππ 2)(22

4 2

=−−=−= (3)

where Shemisphere is the hemisphere surface area of templated microsphere; SH is the

surface area of Area H. The average volume of ZnO nanosheet around each pore is

DE VVV +＝ (4)

where VE is the ideal volume of ZnO nanosheet when pores are considered as straight

column shape; VD is the accessional ZnO volume when the bowling-shape of pore is

considered. The volume VE is 0.094πhR2, 0.215πhR2 and 0.445πhR2 for nanosheet

along 111, 100 and 110 planes respectively. The accessional ZnO volume VD is

232232 ))(2(31

32))]((3[

31

34

21 hRhRRhRhRhRRRhRVD −++−=−−−−×−= ππππππ

(5)

The third part of the mole Gibbs free energy variation is

Supplementary material (ESI) for Journal of Materials Chemistry This journal is © The Royal Society of Chemistry 2008

Ω

−−=Δ −−

VS

G edgespheresheetspherewaterk)( γγ

(6)

whereγwater-sphere is the surface energy of polystyrene microsphere in the solution; γ

sheet-sphere is the interface energy between deposited nanosheet and templated

microsphere. When equation (3)~(5) are applied to equation (6), The third parts of

Gibbs free energy for nanosheet along 111, 100 and 110 planes are

⎥⎦⎤

⎢⎣⎡ −++−+

×−Ω−=Δ −−

2322111

))(2(31

32

2275.19

275.19)(

hRhRRhRhR

RhG spheresheetspherewaterk γγ

(7)

⎥⎦⎤

⎢⎣⎡ −++−+

×−Ω−=Δ −−

2322100

))(2(31

32

2306.7

306.7)(

hRhRRhRhR

RhG spheresheetspherewaterk γγ

(8)

⎥⎦⎤

⎢⎣⎡ −++−+

×−Ω−=Δ −−

2322110

))(2(31

32

2494.2

494.2)(

hRhRRhRhR

RhG spheresheetspherewaterk γγ

(9)

The total Gibbs free energy with the above three parts is

kji GGGG Δ+Δ+Δ=Δ (10)

When equation (1)(2) and equation (7)~(9) are applied to equation (10), the total

Gibbs free energy for nanosheet along 111, 100 and 110 planes are

⎥⎦⎤

⎢⎣⎡ −++−+

×−Ω−

Ω+Δ−=Δ −−−

2322111

))(2(31

32

2275.19

275.19)(2

hRhRRhRhR

Rhh

GG spheresheetspherewaterwatersheetZnO

γγγ

⎥⎦⎤

⎢⎣⎡ −++−+

×−Ω−

Ω+Δ−=Δ −−−

2322100

))(2(31

32

2306.7

306.7)(2

hRhRRhRhR

Rhh

GG spheresheetspherewaterwatersheetZnO

γγγ

⎥⎦⎤

⎢⎣⎡ −++−+

×−Ω−Ω+Δ−=Δ −−−

2322110

))(2(31

32

2494.2

494.2)(2

hRhRRhRhR

Rhh

GG spheresheetspherewaterwatersheetZnO

γγγ