Hybrid Nanoscale Inorganic Cages

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LETTERSPUBLISHED ONLINE:19 SEPTEMBER 2010 | DOI: 10.1038/NMAT2848

Hybrid nanoscale inorganic cages

Janet E. Macdonald1,2, Maya Bar Sadan3, Lothar Houben3, Inna Popov2 and Uri Banin1,2

*Cage structures exhibit inherent high symmetry and beauty,and both naturally occurring and synthetic molecular-scalecages have been discovered. Their characteristic high surfacearea and voids have led to their use as catalysts andcatalyst supports, filtration media and gas storage materials1,2.Nanometre-scale cage structures have also been synthesized,notably noble-metal cube-shaped cages prepared by galvanicdisplacement with promising applications in drug deliveryand catalysis36. Further functionality for nanostructures ingeneral is provided by the concept of hybrid nanoparticlescombining two disparate materials on the same system toachievesynergistic properties stemmingfrom unusual material

combinations711

. We report the integration of the two powerfulconcepts of cages and hybrid nanoparticles. A previouslyunknown edge growth mechanism has led to a new typeof cage-structured hybrid metalsemiconductor nanoparticle;a ruthenium cage was grown selectively on the edges of afaceted copper(I) sulphide nanocrystal, contrary to the morecommonly observed facet and island growth modes of otherhybrids7,1215. The cage motif was extended by exploiting theopen frame to achieve empty cages and cages containing othersemiconductors. Such previously unknown nano-inorganic cagestructures with variable cores and metal frames manifest newchemical, optical and electronic properties and demonstratepossibilities for uses in electrocatalysis.

The advantageous attributes of hybrid nanoparticles were

already demonstrated by the use of metal tips grown selectively onthe apices of semiconductor nanorods serving as anchor points forelectrical connections and self-assembly8,14,1618. Moreover, hybridmetalsemiconductor nanoparticles exhibit light-induced chargeseparation that may be exploited for solar-energy harvesting and,in particular, in photocatalysis7. Material control in these and otherhybridnanoparticles has been chiefly achieved by means of selectivegrowth of islands of the second material on a reactive facet ordefect site on the seed nanostructure7,1215. Selective edge reactivityreported here for the first time, opens a path to a new familyof hybrid nano-inorganic cages (NICs), where the combinationof a metal frame on a semiconductor core presents intriguingopportunitiesfor studying their properties and catalyticfunction.

Cu2S seed nanoparticles were prepared by a modified litera-ture procedure13,19. The resultant monodisperse faceted particles(Fig. 1a,b) were 14

.

71.

2 nm in diameter andoftenformed crystal-lographically oriented three-dimensional (3D) superlattices (Fig. 1ainset). This was also evidenced by the spots, rather than rings, inthe selected-area electron diffraction (SAED) of a superstructure13

(Fig. 1c). For ruthenium growth, a solution of ruthenium(iii)acetyl-acetonate (Ru(acac)3) was added to a suspension of thenanoparticles in octadecylamine at 210 C. Transmission electronmicroscopy (TEM) of the resultant particles (d = 14.1 1.1nm)

1Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel, 2The Center for Nanoscience and Nanotechnology, The Hebrew

University of Jerusalem, Jerusalem 91904, Israel, 3Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Research Centre Juelich, 52425

Juelich, Germany. *e-mail: [email protected].

exhibited curious patterns of dark and light regions (Fig. 1d).High-resolution TEM (HRTEM) indicated that the core of the par-ticles remained single crystalline, and the protruding features ob-servedare suggestive of a frame structurearound thecore(Fig. 1e).

The structure of the ruthenium-containing component wasrealized by leaching the copper sulphide with a solution ofneocuproine in chloroform, which is known to bind preferentiallyto copper(i) species13. Remarkably, what remained were empty andapparently highly symmetric cage structures with clear openingsand overall dimensions d = 14.4 1.3 nm similar to that of theoriginal caged particles (Fig. 1g). Furthermore, the very ability toextract the Cu2S is direct proof of a cage structure rather than a

closed shell. The remaining empty frame motif is reminiscent ofthose seen for Au nanocages36.

The chemical nature of the cage was identified by SAED of theempty cages, showing a crystalline phase of hexagonal close-packedruthenium metal20 (Fig. 1i). Broad rings were observed, consistentwith the HRTEM of the empty cages, which showed small, typically1.53.5 nm crystallites (Fig. 1h). The formation of ruthenium metalis in line with the observation of the characteristic green colour ofCu2+ species in the supernatant above the particles after rutheniumaddition to the seed particles. This indicates some of the Cu1+ inthe Cu2S seeds was oxidized while forming the Ru(0) cage from theRu3+ precursor.

The shape of the filled caged particles was investigated by TEMand high-angle annular dark-field scanning TEM (HAADF-STEM,

Fig. 2). The latter method shows much higher signal for the heavierruthenium, as the signal is roughly proportional to the square ofthe atomic number. As both methods give only 2D projections ofthe 3D particles, analysis was carried out on various particles withdifferent orientations. All patterns could be assigned to orientationsof a truncated hexagonal biprism, a shape that has been observedpreviously for microparticles of Cu2S (ref. 21). The most notableorientation was the star shape, with six lobes on each point of ahexagon (Fig. 2a). This orientation was identified as a projectionaligned with the c axis of the truncated hexagonal biprism. Otherorientations (Fig. 2bd) showed three high-contrast parallel bands,twoon theoutside anda longerone in themiddle.Theseprojectionsare obtained by rotating the truncated hexagonal biprism, asobserved in Fig. 2a, by 90. The outside lines correspond to the twohexagonal faces andthe central line indicates a central, wider area ofthe biprism with ruthenium deposited about the circumference. Inaddition, subtle differences are observed in the banding patterns ofthese orientations perpendicular to the three strong bands, notably,thecross pattern in Fig. 2b,the two weak bands in Fig. 2c and a wideband in Fig. 2d. Figure 2e,f shows two other observed orientations.This analysis providesunequivocal evidence for the selective growthof the ruthenium on the crystal edges of the Cu2S seeds, leading to ahighly symmetrical cage around the copper sulphide core.

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NATURE MATERIALS DOI: 10.1038/NMAT2848 LETTERS

Cu2S

seeds

Ru(acac)3octadecylamine

octyl ether

210 C, 1 h

Ru NlCed

Cu1.96S

Neocuproine

chloroform

RT, 4 d

EmptyRu NICs

50 nm

20 nm

5 nm

20 nm

5 nm

20 nm

5 nm

(100)

(101)

(102) (110)

(103)

(112)

(002)

a b

c

d e

f

g h

i

Figure 1 | Preparation of Ru-NICed copper sulphide particles and empty Ru NICs. a, TEM images of Cu2S seed particles. Inset: A 3D superstructure of

individual nanoparticles commonly observed. b, HRTEM image of a Cu2S seed particle. c, SAED of the seed particles with bright spots indicative of

crystallographic alignment of the particles within the superstructures. d, TEM image of Ru-NICed copper sulphide particles. e, HRTEM image of Ru-NICed

copper sulphide particles. f, SAED of Ru-NICed copper sulphide particles showing rings of a phase similar to the original seed particles. g, TEM image of

empty Ru NICs. h, HRTEM of empty Ru NICs showing very small, typically 1.53.5 nm, crystalline domains. i, SAED with broad reflections indexed to

hexagonal ruthenium of empty Ru NICs.

The empty Ru cages were further studied using aberration-corrected HAADF-STEM (Fig. 2g). The images suggest hollowcores and also that the empty cages maintain their 3D shape. Thisindicates that the Ru cage is robust enough to endure the removalof the interior material, repeated centrifugations and the surfacetension as solutions dried on the TEM grid. The bridges that werealready observed for the hybrid filled nanoparticles remain intactafter the cage is emptied.

To provide further evidence for the retention of the 3D structureof the empty cages, the Ru NICs were examined using electrontomography22 for which they were well suited because of theabsence of strong lattice diffraction23. Tomographical data werereconstructed from a series of TEM images taken at consecutivetilt angles of the sample. A tomogram may be observed at any

viewing direction and sliced in a desired plane, providing uniqueinformation about the internal structure of the particles and thearrangement of the interconnecting bridges in space. The voxelsnapshot shows clearly the cage structure of several particles(Fig. 2h). The arrow marks a particle for which tomogram slicesare provided. Figure 2i and j show slices through the median andtop hexagonal cross-section, respectively, of one of the Ru cages.On tilting the tomogram to the side the rectangular side face of thehexagonal biprism shape of theparticle becomes apparent (Fig. 2k).Further material, including animated voxel and tomogram sliceprojections, is available in SupplementaryMovies S1 and S2.

In addition to the general behaviour of edge growth leading tothecage formation, other changes were noted in thenano-inorganiccaged (NICed) particles (Fig. 3). The powder X-ray diffraction

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LETTERS NATURE MATERIALS DOI: 10.1038/NMAT2848

a b

c d

e

g h i

j

k

f

10 nm10 nm

5 nm

5 nm

5 nm

Figure 2 | Determination of the 3D shape of the cage structures. af, Different orientations of Ru-NICed copper sulphide particles. Shown are the

geometric models of the projections of the truncated hexagonal biprism shape (left frames), corresponding TEM images (centre frames) and

HAADF-STEM images (right frames). Particle sizes are 14nm. g, Aberration-corrected HAADF-STEM of empty Ru NICs. h, Tomography of empty Ru

cages in voxel view, where each pixel is attributed opaqueness with correspondence to its intensity value. Slices through the tomogram, show the internal

structure of a particle (marked by the yellow arrow). i, The median plane with its hexagonal shape. j, The top hexagonal plane. k, A rectangular facet on a

side plane of the same particle.

Low chalcocite

Cu2S

Djurleite

Cu1.96S

30 35 40 45 50 55 60

2

300 600 900 1,200 1,500

Wavelength (nm)

Wavelength (nm)

Absorbance(a.u.)

Absorbance(a.u.)

850 1,000 1,150

0

1

a b

Figure 3 | XRD and absorbance spectra of Cu2S seeds and Ru-caged Cu1.96S particles. a, Powder XRD patterns of the Cu2S seed nanoparticles (red) and

Ru-NICed Cu1.96S particles (blue). Backgrounds were subtracted from the measured patterns. Literature reflections and relative intensities of low

chalcocite and djurleite20 are shown respectively above and below the patterns for comparison. b, Normalized absorbance spectrum of seed Cu2S

nanoparticles (red line25). Inset: A zoom-in of the Cu2S nanoparticle absorbance onset at 1,000 nm. Normalized absorbance of Ru-NICed Cu1.96S

particles (blue line) showing the characteristic plasmonic absorbance in the near-infrared region24.

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0.6

0.6 0

0.5 0.4 0.3 0.2 0.1 0

Potential (V) versus Ag/AgCl

Potential (V) versus Ag/AgCl

250

150

50

50

150

250

Current(

A)

Current(A)

5

0

5

Figure 4 | H2O2 sensing with cages. Cyclic voltammetry curves in 0.2 mM H2O2 and 0.1 M KCl of indium tin oxide (ITO) electrodes modified with Cu2S

seed particles (red), empty Ru NICs (black), Ru-NICed Cu1.96S (blue) and bare ITO (green) at a scan rate of 50 mV s1. Inset: An expanded view of thelow-current curves of the Cu2S seeds, Ru NICs and bare ITO.

Ru NICed

CdS

Ru NICed

Cu1.96S

Ru NICed

PbS

neo2Cu+ Cd2+ neo2Cu

+Pb2+

50 nm

10 nm 10 nm

50 nm

(100)

(101)

(102)

(110)(103)

(112)

(111)

(311)

(200)

(220)

(222)

(002)

0

1

Absorbance

(a.u.)

300 600 900

Wavelength (nm)

1,200 1,5000

1

Absorbance

(a.u.)

300 600 900

Wavelength (nm)

1,200 1,500

a

b c

Figure 5 | Cation exchange to give Ru-NICed CdS and PbS. a, The addition of Cd2+ and neocuproine to Ru-NICed Cu1.96S particles gives Ru-NICed CdS

(pale-yellow solution), whereas the addition of Pb2+ and neocuproine gives Ru-NICed PbS (brown solution). b, Characterization of Ru-NiCed CdS: a TEM

image, SAED indexed to hexagonal CdS (ref. 20), HRTEM image and normalized absorbance are shown. A rise in the absorbance profile at 500nm is due

to the bandgap onset of CdS (ref. 15). c, Characterization of Ru-NiCed PbS: a TEM image, SAED indexed to face-centred-cubic PbS (ref. 20), HRTEM image

and normalized absorbance (red) are shown. Normalized absorbance of empty Ru NICs is shown in black. The PbS sample showed relatively increased

absorbance throughout the visible region compared with the bare cages.

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LETTERS NATURE MATERIALS DOI: 10.1038/NMAT2848

(XRD) pattern of the filled cages did not show clear peaks resultingfrom ruthenium metal because of the small size of the rutheniumcrystallites. However, a change was observed in the copper sulphidecrystal structure from low chalcocite (Cu2S, monoclinic) in theseed particles to djurleite (Cu1.96S, monoclinic

20) with strain inthe ab plane in the caged particles (Fig. 3a and SupplementaryInformation). Chalcocite and djurleite are very similar in structurebut the latter has copper vacancies24 providing further evidence forthe partial oxidation of the seed particles by the ruthenium(iii)

precursor. This change is also manifested clearly in the absorptionspectra (Fig. 3b); whereas the Cu2S seeds have an absorption onsetaround 1,000 nm (ref. 25), after cage growth a large broad peakemerged in the near-infrared centred around 1,380 nm. This isassigned as a plasmon peak, observed previously for the djurleitephase, arising from thefreeholesrelated to thecopper vacancies24.

The remarkable observation of selective edge growth leadingto the formation of the unique cage structures differs fromthe most commonly observed island growth mode of hybridnanoparticles4,7,8,1214. On bulk surfaces, as well as in hybridnanoparticles, it is well known that crystal edges26 and defectscan provide sites for nucleation of a second material. However,other factors including ripening7,27 and the tendency for phasesegregation in nanoparticles lead to the creation of an island of

the second material and not to cage growth. The unique cageformation we observe here is first related to the strong faceting ofthe Cu2S seed particles that provide sharp edges for the reaction.Moreover, we may consider that the thiol-passivating ligands onthese well-defined facets are strongly bonded to the surface of theCu2S particles, blocking growth and leaving the higher energy edgesas thepreferred reaction sites forthe redox reductionof themetal.

Ru-NICed Cu1.96S shows remarkable synergistic properties as anelectrocatalyst towards H2O2 sensing as a result of the unique cageshape and material combination. Copper(i) sulphide nanoparticleswere demonstrated as excellent electrocatalysts for peroxide sensingbut required carbon nanotubes as a supporting conducting materialfor sufficient activity28. Figure 4 shows CV curves of electrodesmodified by the nanoparticles. Compared with the blank electrode,

afilmofCu2S seeds blocked thecurrent,because theperoxideredoxcouple occurs at voltages between the valence- and conduction-band energies. A deposition of empty Ru cages amplified thecurrents by a factor of45, probably owing to their conductiveand porous nature, which increased the effective surface area ofthe electrode. However, in neither case were the oxidation andreduction peaks of H2O2 distinct. In contrast, the hybrid Ru-NICedCu1.96S provided distinct redox peaks and remarkably, currentstwo orders of magnitude larger than the bare electrode. Theelectrochemical H2O2 sensing is achieved only by the synergy ofthe two powerful concepts of hybrid nanoparticles and cages; aconductive percolating path for electrons is provided by the Rumetalcagesthat arealsoin intimate contact with theexposedCu1.96Ssurfaces, which only then canact as the redox catalyst.

The open cage structure of the filled NICed particles not onlyprovidesopportunities for reaction with the interior semiconductorbut also for material modification. Copper sulphides are knownto readily cation exchange while leaving the initial particle shapeintact12,29. Through ion exchange, these caged nanoparticles aretherefore a gateway to NICed particles with other semiconductorsas cores, and in this manner, the properties such as the opticalbandgap may be tuned.

To this end, Ru-NICed particles of Cu2S were transformedinto Ru-NICed particles of CdS and PbS through cationexchange (Fig. 5). TEM of both products shows the characteristiccontrast patterns of the cage structure. HRTEM, SAED andenergy-dispersive X-ray spectroscopy provided direct evidencefor the formation of the CdS and PbS cores, respectively.Whereas the addition of Cd2+ formed single-crystal hexagonal

CdS cores, the cubic PbS cores were multi-crystalline. Theabsorbance spectra of both products were clearly altered by themodifications; neither shows the broad near-infrared plasmonband of Cu1.96S observed for the original caged particles

24, yetthe broad absorbance of the ruthenium cages was maintainedas evidenced by the non-zero absorbance at long wavelengths.The absorbance spectra also exhibit the features of the newsemiconductor cores. This demonstrates the enrichment ofthe family of hybrid metalsemiconductor NICs through a

straightforward reaction. Moreover, copper sulphide is closelyrelated to other technologically important semiconductors suchas CuInS2 (ref. 30). This introduces further opportunities forexpanding the selection of materials in the form of hybrid NICs.We foresee interesting nanomechanical and optical propertiesof these systems as well as possible applications in catalysisand photocatalysis.

MethodsSynthesis of Cu2S seed particles. Cu2S seed particles were prepared by a modifiedliterature procedure13,19 where copper(ii) acetlyacetonate is decomposed at 200 Cin dodecanethiol,which actsas a solvent,surfactantand sulphur source.

Synthesis of Ru-NICed Cu1.96S particles. A solution of Ru(acac)3 in octyl etherwas added to a suspension of the nanoparticles in octadecylamine at 210 C with amole ratio of copper to ruthenium of6:1.

Synthesis of empty Ru cages. Neocuproine was added to a solution of Ru-NICedCu1.96S particles in chloroform. The neocuproine selectively binds Cu

+,yielding empty Ru cages.

Cation exchange. Toluene solutions of Ru-NICed Cu1.96S were added to a toluenesolution of neocuproine and a methanol solution containing either Cd2+ or Pb2+

to give Ru-NICed CdS and Ru-NICed PbS.Details of the syntheses; instrument specifications; details of the experimental

procedures in electron microscopy, tomography and cyclic voltammetry; andfurther discussion on the interpretation of the XRD patterns are provided in theSupplementary Information.

Received 7 April 2010; accepted 2 August 2010; published online

19 September 2010

References

1. Eddaoudi, M. et al. Systematic design of pore size and functionality inisoreticular MOFs and their application in methane storage. Science 295,469472 (2002).

2. Davis, M. E. Ordered porous materials for emerging applications. Nature 417,813821 (2002).

3. Skrabalak, S. E., Au, L., Li, X. D. & Xia, Y. Facile synthesis of Ag nanocubes andAu nanocages. Nature Protoc. 2, 21822190 (2007).

4. Skrabalak, S. E. et al. Gold nanocages: Synthesis, properties, and applications.Acc. Chem. Res. 41, 15871595 (2008).

5. Yavuz, M. S. et al. Gold nanocages covered by smart polymers for controlledrelease with near-infrared light. Nature Mater. 8, 935939 (2009).

6. Zeng, J., Zhang, Q., Chen, J. Y. & Xia, Y. N. A comparison study of the catalyticproperties of Au-based nanocages, nanoboxes, and nanoparticles. Nano Lett.10, 3035 (2010).

7. Costi, R., Saunders, A. E. & Banin, U. Colloidal hybrid nanostructures: A newtype of functional materials. Angew. Chem. Int. Ed. 49, 48784897 (2010).

8. Mokari, T., Rothenberg, E., Popov, I., Costi, R. & Banin, U. Selective growthof metal tips onto semiconductor quantum rods and tetrapods. Science 304,17871790 (2004).

9. Cozzoli, P. D., Pellegrino,T. & Manna,L. Synthesis, properties andperspectivesof hybrid nanocrystal structures. Chem. Soc. Rev. 35, 11951208 (2006).

10. Wetz, F. et al. Hybrid CoAu nanorods: Controlling Au nucleation andlocation. Angew. Chem. Int. Ed. 46, 70797081 (2007).

11. Habas, S. E., Yang, P. D. & Mokari, T. Selective growth of metaland binary metal tips on CdS nanorods. J. Am. Chem. Soc. 130,32943295 (2008).

12. Sadtler, B. et al. Selective facet reactivity during cation exchange in cadmiumsulfide nanorods. J. Am. Chem. Soc. 131, 52855293 (2009).

13. Han, W. et al. Synthesis and shape-tailoring of copper sulfide/indiumsulfide-based nanocrystals. J. Am. Chem. Soc. 130, 1315213161 (2008).

14. Shi, W. L. et al. A general approach to binary and ternary hybrid nanocrystals.Nano Lett. 6, 875881 (2006).

15. Menagen, G., Macdonald, J. E., Shemesh, Y., Popov, I. & Banin, U. Augrowth on semiconductor nanorods: Photoinduced versus thermal growthmechanisms. J. Am. Chem. Soc. 131, 1740617411 (2009).

http://www.nature.com/doifinder/10.1038/nmat2848http://www.nature.com/naturematerialshttp://www.nature.com/naturematerialshttp://www.nature.com/doifinder/10.1038/nmat2848


6/6


16. Figuerola, A. et al. End-to-end assembly of shape-controlled nanocrystalsvia a nanowelding approach mediated by gold domains. Adv. Mater. 21,550554 (2009).

17. Maynadi, J. et al. Cobalt growth on the tips of CdSe nanorods. Angew. Chem.Int. Ed. 48, 18141817 (2009).

18. Zhao, N., Liu, K., Greener, J., Nie, Z. H. & Kumacheva, E. Close-packedsuperlattices of side-by-side assembled AuCdSe nanorods. Nano Lett. 9,30773081 (2009).

19. Choi, S. H. et al. Simple and generalized synthesis of semiconducting metalsulfide nanocrystals. Adv. Funct. Mater. 19, 16451649 (2009).

20. Joint Committee on Powder Diffraction Standards (JSPDS) cards employedfor structural determination: hcp ruthenium: 03-065-1863, low chalcocite:03-033-0490, djurleite: 00-034-0660, hexagonal CdS: 01-077-2306, PbS:03-065-2935.

21. Zhao, F. H. et al. Controlled growth of Cu2S hexagonal microdisks and theiroptical properties. J. Phys. Chem. Solids 67, 17861791 (2006).

22. Midgley, P. A. & Dunin-Borkowski, R. E. Electron tomography and holographyin materials science. Nature Mater. 8, 271280 (2009).

23. Bar Sadan, M., Wolf, S. G. & Houben, L. Bright-field electrontomography of individual inorganic fullerene-like structures. Nanoscale2, 423428 (2010).

24. Zhao, Y. X. et al. Plasmonic Cu2xS nanocrystals: Optical and structuralproperties of copper-deficient copper(I) sulfides. J. Am. Chem. Soc. 131,42534261 (2009).

25. Wu, Y., Wadia, C., Ma, W. L., Sadtler, B. & Alivisatos, A. P. Synthesis andphotovoltaic application of copper(I) sulfide nanocrystals. Nano Lett. 8,25512555 (2008).

26. Talapin, D. V., Yu, H., Shevchenko, E. V., Lobo, A. & Murray, C. B. Synthesis

of colloidal PbSe/PbS coreshell nanowires and PbS/Au nanowire-nanocrystalheterostructures. J. Phys. Chem. C 111, 1404914054 (2007).

27. Mokari, T., Sztrum, C. G., Salant, A., Rabani, E. & Banin, U. Formation ofasymmetric one-sided metal-tipped semiconductor nanocrystal dots and rods.

Nature Mater. 4, 855863 (2005).

28. Myung, Y. et al. Nonenzymatic amperometric glucose sensing of platinum,copper sulfide, and tin oxide nanoparticle-carbon nanotube hybridnanostructures. J. Phys. Chem. C 113, 12511259 (2009).

29. Luther, J. M., Zheng, H. M., Sadtler, B. & Alivisatos, A. P. Synthesis of PbSnanorods and other ionic nanocrystals of complex morphology by sequentialcation exchange reactions. J. Am. Chem. Soc. 131, 1685116857 (2009).

30. Connor, S. T., Hsu, C. M., Weil, B. D., Aloni, S. & Cui, Y. Phase transformationof biphasic Cu2S-CuInS2 to monophasic CuInS2 nanorods. J. Am. Chem. Soc.131, 49624966 (2009).

AcknowledgementsPartial financial support by the Israel Science Foundation (grant 972/08), and theERC grant DCENSY is acknowledged. U.B. thanks the Alfred and Erica Larisch

Memorial Chair in Solar Energy. M.B.S. thanks the Minerva Fellowship program

funded by the German Federal Ministry for Education and Research and the Sara

Lee Schupf Postdoctoral Fellowship. The authors also thank D. Mandler for use of

electrochemisty instrumentation.

Author contributionsJ.E.M. and U.B. designed the experiments and wrote the manuscript. J.E.M. carried out

the experiments,materialscharacterizationand analysis. I.P.assisted with HAADF-STEM

and energy-dispersive X-ray spectroscopy measurements and provided commentary on

the manuscript and materials analysis. M.B.S. carried out the tomography experiments

andthe analysisof itsdataand wrote partsof themanuscripts. L.H. wrotethe tomographic

processing software and assisted in the reconstruction, provided the aberration-corrected

HAADF-STEM imagesand commented on the manuscript.

Additional informationThe authors declare no competing financial interests. Supplementary information

accompanies this paper on www.nature.com/naturematerials. Reprints and permissions

information is available online at http://npg.nature.com/reprintsandpermissions.

Correspondence and requests formaterials shouldbe addressed to U.B.

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Hybrid Nanoscale Inorganic Cages