Chemical Deposition of Cu 2 O Nanocrystals with Precise Morphology Control

Transcription

1 Extinction (a.u.) Supporting Information Chemical Deposition of Cu 2 O Nanocrystals with Precise Morphology Control Mariano D. Susman, Yishay Feldman, Alexander Vaskevich, * and Israel Rubinstein, * Department of Materials and Interfaces, Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 761, Israel * Corresponding authors. alexander.vaskevich@weizmann.ac.il israel.rubinstein@weizmann.ac.il.4.3 a b c Wavelength (nm) Figure S1. UV-Vis spectra of solution A (Scheme 2) and variants thereof: (a) No NaOH (replaced by water); (b) solution A (.2 ml of 5 M NaOH); and (c) higher [NaOH] (1.3 ml of 5 M NaOH). 1

2 Counts 3 15 A 1 5 E 4 2 B 1 5 F D Major axis (nm) C Major axis (nm) G 1. Figure S2. Distributions of the major axis length for the nanocrystals (NCs) in Figure Figure S3. HRSEM image of Cu 2 O nanooctahedra codeposited with odd-shaped CuO/Cu(OH) 2 prticles, using [Na 3 Cit] =.24 M, [NaOH] =.5 M. Substrate: glass slide. a) b) c) Figure S4. HRSEM images of (a) octahedral Cu 2 O NCs; (b, c) after 1 min exposure to (b) a solution G in which the CuSO 4 was replaced by water, and (c) a solution G in which the HCHO fraction was replaced by water. Substrates: glass slides. Scale bars: 1 nm. 2

3 Figure S5. Tilted-angle (45º) HRSEM images of Cu 2 O NCs supported on glass substrates: (a) sample A (octahedra), (b) sample C (truncated octahedra), (c) sample E (cuboctahedra) and (d) sample G (cubes). Scale bars: ~2 nm. Images acquired at a high accelerating voltage (1 kv), after sputtering of 3 nm Cr to reduce charging. Figure S6. HRSEM images of (a-c) sample A (octahedra); (d-f) sample C (truncated octahedra); (g-i) sample E (cuboctahedra); (j-l) sample G (cubes) on glass substrates. The selected particles were observed along the [111] (a, d, g, j), [11] (b, e, h, k) and [1] (c, f, i, l) directions. Scale bars: (a-i) 1 nm, (j-l) 5 nm. Samples were prepared for imaging as described in Figure S5. 3

4 Development of equations 5 and 6 According to the Wulff theorem, the crystal growth rate perpendicular to any crytal facet is proportional to its surface energy, i.e., R = r <1> /r <111> = 1 / 111 = h 1 /h 111. (Eq. 5) Cubic to cuboctahedral particles (.577 R.866) For the frontal view of a truncated cube, the following relations apply: For the triangular pyramid of height u and base length b h 1 s a l As b Then, by the properties of the envolving cube, v u s So, b Valid from a = l, b =, to a =, b = d 4

5 (Eq. 6) Cuboctahedral to octahedral particles (.866 R 1.732) A cross-section of a truncated octahedral NC along the diagonals of cubic faces (e) and c edges, and passing through the Wulff point produces a polyhedron as shown below. The following relations apply: l c s u h 1 For the square pyramid of height u and base length d, Therefore, And, By the properties of the envolving octahedron, Valid from c =, d = b to c = l, d = 5

6 Deposition from EDTA and tartrate solutions. A strategy for controlling the Cu 2 O NC morphology similar to that used with citrate was also carried out using different Cu(II) complexing molecules, i.e., EDTA and tartrate, 1 in an attempt to evaluate the role of the complexant type in determining the morphology of the deposited NCs. The concentrations used in the citrate based depositions, i.e., [Cu(II)]=8 mm and [HCHO]=8 mm, were maintained, while various concentrations of the complexant and base were evaluated in the preparation of Cu 2 O NP films. Figure S7. (a) HRSEM Images of Cu 2 O NCs prepared by 2 min CD using EDTA as the complexant: (A) cantellated cubes; (B, C) {11}-truncated cuboctahedra; (D) {11}- truncated Wulff polyhedra; (E) truncated octahedra; and (F) tip-truncated octahedra. Substrates: glass slides. Scale bars: 1 nm. (b) Morphology diagram for CD in EDTA based solutions. Points corresponding to the SEM images are marked (A F). 6

7 HRSEM images of representative Cu 2 O NCs prepared from EDTA solutions are shown in Figure S7a. Interestingly, {11} truncations are evident, together with {111} and {1} facets, while the morphologies include cantellated cubes, {11}-truncated cuboctahedra, {11}-truncated Wulff polyhedra, truncated octahedra, and tip-truncated octahedra. The corresponding conditions for their formation are indicated in the morphology diagram (Figure S7b). While morphologies exhibiting large {111} facets are formed at high [NaOH], lowering the [NaOH] leads to distinct stabilization of both {1} and {11} planes when EDTA is employed ( 1 ~ 11 < 111 ), seen as formation of cantellated polyhedra. EDTA solutions appear to disrupt the Au seed layer to form Au surface aggregates. This process may lead to films with a lower Cu 2 O NC surface density and may affect the film stability (Figure S8a). The minimal EDTA concentration needed corresponds to the stoichiometric ratio for forming a 1:1 Cu(II)-EDTA complex. Under conditions of EDTA deficiency, i.e., [EDTA] = 5 mm, [Cu 2+ ] = 8 mm (Figure S8b-d), Cu(OH) 2 fibers form, while the Cu 2 O deposited in the presence of large amounts of NaOH are predominantly {111} faceted (Figure S8d). Lower [NaOH] produces cantellated cubes, even under extensive excess of NaOH with respect to EDTA. Studies of EDTA based Cu CD have shown that at high ph values, Cu(II)-EDTA complexes of the type[cu(edta)] 2- and [Cu(OH)(EDTA)] 3- are present. 2, 3 Our results indicate that OH - and Cu(II)-hydroxo-EDTA complexes are capable of exerting morphological control over the NCs, as in the case of the OH - /citrate based systems. When using tartate, similar trends to those described for citrate were observed; i.e., stabilization of the {1} Cu 2 O facets upon increase of the tartrate concentration (Figure S9). Use of EDTA and tartrate 1 as complexants requires careful selection of their 7

8 concentrations, as, after a certain deposition time, metallic copper shows a high tendency to form. Depositions were therefore performed for 2 min and 1 min, respectively, thus avoiding Cu formation. Still, at high tartrate concentrations Cu may prematurely form. 1 Extensive Cu formation or very slow deposition practically preclude the possibility of obtaining complete cubes using these complexants, under conditions similar to those used with citrate. Figure S8. Cu 2 O deposition from EDTA solutions. (a) Cu 2 O NCs observed by HRSEM using the EsB (energy and angle selective backscattered electron) (left) and the SE (secondary electron) (right) detectors. Aggregated Au seeds show better contrast with the EsB detector. (b-d) HRSEM images of Cu 2 O NCs prepared under EDTA deficiency (5 mm Na 4 EDTA), using (b).5 M, (c) 1.5 and (d) 2.5 M NaOH. Thin Cu(OH) 2 fibers formed in solution adhere to the sample surface. Substrates: glass slides. A B Figure S9. HRSEM Images of Cu 2 O NCs prepared by 2 min CD using NaKT as the complexant. The deposition solutions contained 8 mm CuSO 4, 8 mm HCHO and.5 M NaOH, as well as.1 M NaKT (A) or.188 M NaKT (B). Substrates: glass slides. 8

9 ( E) 2 (ev cm -1 ) 2 Extinction a) b) A (Octahedra) E (Cuboctahedra) G (Cubes) Wavelength [nm] Figure S1. (a) Photograph of Cu 2 O NCs on glass, showing samples A G. (b) UV-Vis spectra of Cu 2 O NCs on quarz slides, for samples A (octahedra), E (cuboctahedra) and G (cubes). 4x1 4 3x1 4 A E G 2x1 4 1x1 4 E g = 2.5 ev E g = 2.43 ev E g = 2.3 ev E (ev) Figure S11. Calculation of bandgap energies from the absorption spectra of Cu 2 O NCs supported on quartz slides in Figure S1b (samples A, E, G) using the Mott and Davis expression: ( ) = [B(h -Eg) n ]/h, where n = ½ for a direct bandgap semiconductor. The calculated bandgap energies are marked. 9

10 t G (min) 5 R A-G =.72 ±.2 R A-G = 1.4 ±.3 3 R A-G = 1.36 ± t A (min) Figure S12. HRSEM images of Cu 2 O NCs on glass substrates prepared by sequential deposition. Pre-grown (in solution A) Cu 2 O nanooctahedral NCs of different sizes (controlled by the deposition time t A ) are exposed to a solution promoting the cubic morphology (solution G) for a time t G. Vector lengths are proportional to the exposure time. Scale bars: 2 nm. Errors indicate standard deviations. 1

11 Development of equations 9 and 1 (Eq. 9) Calculation of r <1>,A Equation 9 (Eq. 1) Calculation of r <111>,G 11

12 References 1. Susman, M. D.; Feldman, Y.; Vaskevich, A.; Rubinstein, I., Chemical Deposition and Stabilization of Plasmonic Copper Nanoparticle Films on Transparent Substrates. Chem. Mater. 212, 24, Norkus, E.; Vaškelis, A.; Zakaité, I., Influence of Ionic Strength and OH - Ion Concentration on the Cu(II) Complex Formation with EDTA in Alkaline Solutions. Talanta 1996, 43, Vaškelis, A.; Jagminiené, A., The Surface Layer ph in the Electroless Copper Plating Process. Surf. Coat. Tech. 1987, 31,