492 DOI: 10.1021/la9021504 Langmuir 2010, 26(1), 492–497Published on Web 09/01/2009

pubs.acs.org/Langmuir

© 2009 American Chemical Society

Fabrication of Micro-Nano Hybrid Patterns on a Solid Surface

Peng Liu and Jiandong Ding*

Key Laboratory of Molecular Engineering of Polymers of Ministry of Education, Department ofMacromolecular Science, Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China

Received June 15, 2009. Revised Manuscript Received August 13, 2009

A hybrid pattern with micropatterned nanoarray of Au-Pt core-shell particles in the background of Au nanoarraywas fabricated via an approach combining photolithography, block copolymer micelle nanolithography, and controlledseed growth. Two pertinent patterns were also obtained: one is a hexagonal nanopattern of Au-Pt bimetallic nanodotswith controlled thickness of Pt shells, and the other is an interlaced pattern of Pt microsheets and Au nanoarrays. Wethus present a platform to generate regular micro-nano patterns of one or more than one metal on a solid surface.

Introduction

Surface patterning with regular arrays in micro- or nanoscalehas received increasing attention in the recent decade and poten-tially applied in many fields.1-16 In general, fabricationof micropatterns on a solid surface depends on conventionalphotolithography. Advanced ray lithography17 and proximal-probe lithography suchas dip-pen lithography18 have the capacityto generate nanopatterns. Soft lithography,19 nanoimprint

lithography,20molecular self-assembly,21-24 colloidal crystal tem-plate,25 and other “unconventional” approaches26 have also beendeveloped to fabricate nanostructures. Concerning preparationof a high-throughout pattern of metal nanodots less than20 nm, block copolymer micelle nanolithography has presenteda powerful route.27-30 Patterns of alloy nanoparticles have alsobeen prepared.31,32 Combinations of block copolymer micellenanolithography with electron-beam lithography,33 photolitho-graphy,34,35 and soft lithography35 have been used to fabricatemicropatterns of gold33,34 or iron oxide35 nanoparticles. To date,we have not found any publication about micro-nano hybridpatterns with both continuous and discontinuous microregionscontaining metals.

Besides block copolymer micelle nanolithography, anotherapproach we should mention in this paper is hydroxylamineseeding. In 1998, Natan’s group found that colloidal Au nano-particles could be well grown due to reduction of gold acid(HAuCl4) by NH2OH, which was catalyzed by Au nanoparti-cles.36 In 2008, Spatz’s group developed this approach in order toachieve Au or platinum (Pt) nanoarrays with a series of definedparticle sizes due to the “controlled” seed growth;37 otherwise, theAu or Pt particles could still be enlarged, but the spatial order ofthe initial pattern could not be kept. One of their controllingapproaches is the modification of a glass surface by alkyltri-methoxysilane before seed growth but after block copolymermicelle nanolithography.

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Different from the nanoarrays of enlarged particles of eitherAu or Pt37 and suspensions or nonregular arrays of core-shellmetallic nanoparticles,38-45 we herein fabricate regular nanopat-terns of Au-Pt core-shell particles (pattern 1), as seen inFigure 1. A more significant novelty in the present paper comesfrom the first report of micro-nano hybrid patterns with bothcontinuous and discontinuous microregions composed of metals.The present approach owns an advantage of fabrication ofpatterns with more than one metal, with representative bimetallicpatterns shown in patterns 2 and 3 (Figure 1). Pattern 2 iscomposed of a nanoarray of Au and another array of bimetallicnanoparticles with Au as core and Pt as shell, and the twonanoarrays spatially distribute complementarily, forming a mi-cropattern in a larger scale. The prototype of the micropattern isintroduced via photolithography, and the Au nanoarray isgenerated via block copolymer micelle nanolithography. The

nanoarray of core-shell particles is prepared via the seed-growthapproach with Au nanoparticles as nucleus and then grown in anaqueous solution of H2PtCl6 and NH2OH.

Pattern 3 (interlaced patterns of Pt microsheets and Aunanoarrays) could be simply regarded as an extreme case ofpattern 2 if the controlled seed growth proceeds for an infinitelylong time. To significantly save time, we use an “uncontrolled”seed growth in preparation of pattern 3. The uncontrolled growthcould be carried out in high-concentrated seeding solutions, withor without octadecyltrimethoxysilane (OTMS) modification.

All of three patterns schematically presented in Figure 1 arenew. Especially pattern 2 is very difficult to obtain. Fabrication ofpattern 1 could act as a pretechnique of generation of pattern 2,and pattern 3 is an extension of pattern 2.

Experimental Section

Materials Used in Experiment. Block copolymers ofpolystyrene and poly(2-vinylpyridine), PS-b-P2VP, were fromPolymer Source Inc., Canada. The molecular weights (MWs) ofPS and P2VP blocks were 52400 and 28100, and the polydisper-sity index of the polymer defined as weight-average MW overnumber-average MW (Mw/Mn) was 1.07. OTMS were obtainedfrom Aldrich. Chloroauric acid tetrahydrate (HAuCl4 3 4H2O),hydroxylamine hydrochloride (NH2OH 3HCl), hexachloroplati-nic acid hexahydrate (H2PtCl6 3 6H2O), and other reagents wereobtained from Shanghai Chemical Reagent Corp. All chemicalswere of analytical grade. All aqueous solutions were made usingultrapure water from a Milli-Q system (Millipore). Microscopiccover glass was used after extensive and fresh cleaning.

Figure 1. Schematic presentation of fabrication of three patterns composed of twometals on glass. (a) Preparation of initial Au nanoarray.Themonolayer ofmicelles loadedwith the gold precursor is dip-coatedonto glass surfaces.After oxygenplasma treatment, gold nanodots arereduced and deposited in a hexagonal array. (b) Fabrication of pattern 1 (nanopattern of Au-Pt core-shell particles). Self-assemblymonolayer (SAM) of octadecyltrimethoxysilane (OTMS) and the controlled seed growth are used to fabricate an array of Au-Ptcore-shell nanoparticles. (c) Fabrication of pattern 2 (micro-nano hybrid patterns of Au-Pt bimetallic nanoarray and Au nanoarray)via combination of photolithography and controlled seed growthbased uponan initialAunanoarray. (d) Fabrication of pattern 3 (interlacedpatterns of Pt microsheets and Au nanoarrays) via combination of photolithography and uncontrolled seed growth based upon an initialAu nanoarray.

(38) Schmid, G.; West, H.; Mehles, H.; Lehnert, A. Inorg. Chem. 1997, 36, 891–895.(39) Scott, R. W. J.; Wilson, O. M.; Oh, S. K.; Kenik, E. A.; Crooks, R. M.

J. Am. Chem. Soc. 2004, 126, 15583–15591.(40) Henglein, A. J. Phys. Chem. B 2000, 104, 2201–2203.(41) Freeman, R. G.; Hommer, M. B.; Grabar, K. C.; Jackson, M. A.; Natan,

M. J. J. Phys. Chem. 1996, 100, 718–724.(42) Lyon, J. L.; Fleming,D.A.; Stone,M. B.; Schiffer, P.;Williams,M. E.Nano

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Liz-Marzan, L. M. J. Mater. Chem. 2005, 15, 1755–1759.(44) Mallik, K.; Mandal, M.; Pradhan, N.; Pal, T. Nano Lett. 2001, 1, 319–322.(45) Cao, L. Y.; Tong, L. M.; Diao, P.; Zhu, T.; Liu, Z. F. Chem. Mater. 2004,

16, 3239–3245.

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Fabrication of Au Nanoarray on Substrate. A solution ofPS-b-P2VP (5 mg/mL) was made by dissolving the polymer in3 mL of anhydrous toluene. After stirring for 5 h, the metalprecursor (HAuCl4 3 4H2O) with a givenmolar ratio over pyridineunit in PS-b-P2VPwas added and stirred for at least 24 h until thecolloid became transparent. Substrates were fixed on a substrateholder, dip-coatedwithmicelles loadedwith gold precursors usinga self-built pulling machine. The substrates were treated byoxygen plasma for 60 min at 100 W to reduce metal precursorsto gold nanoparticles and meanwhile to remove polymers. Final-ly, a Au nanoarray was positioned on the substrate.

Self-Assembly of OTMS on Glass Decorated with Au

Nanoarray. OTMS solution (volume 0.5%) was prepared inanhydrous toluene. A Au nanoarray on glass was treated with O2

plasma for 10 min. Then the sample was placed immediately intoOTMS solution at 60 �C for at least 24 h to form the self-assemblymonolayer. The samples were rinsed with toluene, acetone, andethanol, dried with nitrogen gas, and baked at 120 �C for 1 h.

Preparation of Nanopattern of Au-Pt Core-Shell Par-

ticles (Pattern 1). A Au nanoarray on glass decorated withOTMSwas immersed into an low-concentrated aqueous solutioncontaining 0.01 wt %H2PtCl6 and 2 mMNH2OH 3HCl at 60 �CGold nanoparticles as seeds were used to deposit Pt as shell (thecontrolled seed growth). The controlled seed growth based uponthe initial Au nanoarray resulted in an array ofAu-Pt core-shellnanoparticles.

Preparation of Micro-Nano Hybrid Patterns of Au-Pt

Bimetallic Nanoarray and Au Nanoarray (Pattern 2).A photoresist was spin-coated onto glass decorated with Aunanoarray and SAMofOTMS at 4000 rpm, resulting in the filmsof about 1.5 μm in thickness. Microstructures of the photoresistwere generated by standard photolithography.

Substrates with Au nanoarray and photoresist micropatternswere immersed into a solution containing 0.01 wt%H2PtCl6 and2mMNH2OH 3HCl. Thus, the controlled seed growth proceededjust in the unshielded region. Afterward, samples were washedwith acetone ultrasonic bath for 10 min for the lift-off of photo-resist and with Milli-Q water ultrasonic bath for another 10 minand then dried at 100 �C. After removal of photoresist, a hybridpattern of Au-Pt bimetallic nanoarray and Au nanoarray indifferent micropatterns was produced.

Preparation of Interlaced Patterns of Pt Microsheet and

Au Nanoarray (Pattern 3). Microstructures of photoresist onglass with Au nanoarray and OTMS monolayer were fabricatedby standard photolithography. The Au nanoarrays in the micro-regions unshielded by photoresists undergo uncontrolled seedgrowth in conditions such as a high-concentrated aqueous solu-tion of 0.5 wt % H2PtCl6 and 0.2 M NH2OH, and eventuallycovered by Pt (the uncontrolled seed growth). Samples werewashed with acetone ultrasonic bath for 10 min for the lift-offof photoresist and Milli-Q water ultrasonic bath for another10 min and dried at 100 �C, which resulted in interlaced patternsof Pt microsheet and Au nanoarray.

Characterization of Resultant Patterns. UV-vis spectro-scopic measurements were done using a UV-vis spectrophot-ometer (TU-1901, Beijing Puxi Inc., China) at room temperaturein the range of 200-900 nm. X-ray photoelectron spectroscopy(XPS) was carried out on a RBD upgraded PHI-5000C ESCAsystem (Perkin-Elmer) using monochromatic Mg KR X-rays at1253.6 eV operated at 250 W, and spectrum calibration wasperformed by taking the C 1s electron peak (BE = 284.6 eV) asinternal reference. The data analysis was made by using the RBDAugerScan 3.21 software provided by RBD Enterprises. Atomicforce microscopy (AFM) (Dimension 3100, Digital Instruments)was used to image the samples under ambient conditions intapping mode with a silicon cantilever (40 N/m). Scanningelectron microscopy (SEM) was carried out with a HitachiS-4800 microscope at an acceleration voltage of 2 kV. Transmis-sion electron microscopy (TEM) photographs were taken by

using a JEOL JEM-2100F electron microscope at 100 kV. Aninverted optical microscope (Zeiss Axiovert 200) equipped withan integrated digital camera was also used to observe somesubstrate surfaces.

Results and Discussion

Preparation of Initial Au Nanoarrays on Glass. WhenPS-b-P2VP was dissolved in toluene, spherical reverse micelleswere formed with the lipophobic P2VP blocks forming cores andthe lipophilic PS blocks forming coronas. Next, a metal precursor(HAuCl4) was added into the suspension. The gold precursormigrated into the cores of the micelles due to their lipophobiccharacter. PS-b-P2VP micelles loaded with HAuCl4 were depos-ited on substrate by dip-coating. Oxygen plasma was used toremove the block copolymers and meanwhile reduce the goldprecursors into gold nanoparticles. This process enabled thepreparation of ordered array of gold nanoparticles on substrate(Au nanoarray), as published previously.27,30 A typical image isshown in Figure 2a.Preparation of Nanopattern of Au-Pt Core-Shell Par-

ticles (Pattern 1). Core-shell nanoparticles with differentcomponents and thicknesses exhibit various catalytic activity aswell as optical and electrical properties.39-43 In this experiment, aAu nanoarray on substrate was immersed into H2PtCl6 and

Figure 2. AFM images of (a) an initial Au nanoarray on glass and(b) a nanopattern of Au-Pt core-shell particles. The bimetallicnanopattern was prepared after immersing the Au-patterned sub-strate in a solution containing 0.01%H2PtCl6 and 2 mMNH2OHat 60 �C for 16 h. The insets in (a) and (b) are the central part of thecorresponding autocorrelation images. (c) and (d) show heightprofiles along the lines in (a) and (b), respectively. The sizes ofAu-Pt core-shell nanoparticles resulting from different growthperiods are summarized in (e). (f ) UV-vis spectra of glass sub-strates decorated with nanopattern of Au-Pt core-shell particles.The data at “0 h” in (e) and (f ) refer to the initial Au nanoarraymodified with OTMS.

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NH2OH solution to clay Au particles by Pt. The nanopattern ofAu-Pt core-shell particles was visualized by AFM, as exampledin Figure 2b. Although not perfectly ordered, the nanoparticlesexhibited a high degree of short-range hexagonal order as evidentfrom the corresponding autocorrelation function (see inset inFigure 2b), implying the preservation of a pseudohexagonal orderof the original micelles and Au nanodots. The order arrays ofnanoparticles were thus not disturbed by the controlled seedgrowth. The height in AFM measurements gave the sizes ofnanoparticles, indicating 6 nm for the initialAunanoparticles andabout 15nm forAu-Pt core-shell nanodots after 16h growth, asseen in Figure 2c,d. The size of Au-Pt nanoparticles is almostlinearly related to the growth time (Figure 2e). The growth rate isabout 0.6 nm/h under our experimental conditions unless thegrowth lasts very long.

The size enlargement indicates the successful deposition of Ptshell on the surface of Au core in a well-controlled manner.Figure 2f shows representative UV-vis spectra of Au nanoarrayand nanopattern of Au-Pt core-shell particles. The spectralpeak of Pt nanoparticles was reported at about 265 nm.46,47 Red-shifting in our experiments (about 288 nm after 16 h growth)revealed an effect ofAu cores onPt shells. The absorbance peak atabout 520 nm caused by the excitation of surface plasmonresonance of gold nanoparticles37 was not detected by us, whichmight be due to the low amount of gold on glass.

While AFM better gives the particle height in the z direction,SEM and TEM better measure the x-y dimension. Figure 3shows representative SEM images of the initial gold nanoarrayand the nanopatterns ofAu-Pt core-shell particles after 8 and 16h growth. The enlargement of nanoparticles during growth isagain confirmed.

Before our TEM observations, a metallic nanopattern wastreated first by hydrofluoric acid to free nanoparticles from glasssubstrate, and thus the order and the so-called pattern were lost.The free nanoparticles were then transferred onto a carbon filmsupported by a copper mesh. A typical TEM image of Aunanoparticles extracted from the initial Au nanoarray is shownin Figure 4a. After 8 h growth, the resulting Au-Pt nanoparticleswere significantly enlarged (Figure 4b). Because both core andshell are metallic and the Pt shell is quite thick in our experiments,it is hard to visualize Au cores. The lattice plane with interval of2.0 A (Figure 4c) corresponds to gold (200), and the lattice planewith interval of 2.2 A comes from Pt (111) (Figure 4d).

The elemental information was further afforded by XPS, asshown in Figure 5. The XPS spectrum of the initial Au nanoarray

exhibit two obvious peaks of Au (4f ) at 83.4 and 87.2 eV. Twopeaks at 72.6 and 76.0 eV occur after seed growth, which justcorrespond to Pt (4f ). These Au characteristic peaks disappearedafter a long seed growth because the thickness of Pt shell exceedsthe detectable depth of XPS. Combination of AFM (Figure 2b,d,e), SEM (Figure 3), TEM (Figure 4), XPS (Figure 5), andUV-visabsorption (Figure 2f ) convinces the formation of array ofAu(core)-Pt(shell) nanoparticles.Preparation of Micro-Nano Hybrid Pattern of Au-Pt

Bimetallic Nanoarray and Au Nanoarray (Pattern 2). Herewe take advantage of conventional photolithography to fabricate

Figure 3. Representative SEM images of an initial Au nanoarray on glass (a) and nanopatterns of Au-Pt core-shell particles prepared insolution contained 0.01% H2PtCl6 and 2 mMNH2OH at 60 �C after growing for 8 h (b) and 16 h (c).

Figure 4. TEM images of (a) initial Au nanoparticles and (b) aAu-Pt core-shell nanoparticle resulting from 8 h growth. (c) and(d) display magnified regions marked as “1” in (a) and “2” in (b),respectively, showing crystalline lattice planes of metals. Thosenanoparticleswere removed fromglass and transferred intocarbonfilms before TEM observations.

(46) Yee, C.; Scotti, M.; Ulman, A.; White, H.; Rafailovich, M.; Sokolov, J.Langmuir 1999, 15, 4314–4316.(47) Huang, J. C.; Liu, Z. L.; Liu, X. M.; He, C. B.; Chow, S. Y.; Pan, J. S.

Langmuir 2005, 21, 699–704.

496 DOI: 10.1021/la9021504 Langmuir 2010, 26(1), 492–497

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microstructure of photoresist on Au nanoarray. Some Au nano-particles were then covered by the photoresist microregion. Onlythose bare Au nanodots in the interval region among photoresistmicropatterns served as seeds and then were claded by Pt, whichresulted in formation of nanoarray of Au-Pt core-shell parti-cles. After removal of photoresist, hybrid pattern of two nanoar-rays with amicropatterned spatial arrangement were obtained, asshown in Figure 6. Nothing was observed in the initial Aunanoarray in low magnification (Figure 6a). The SEM imagesof micro-nano hybrid pattern in low magnification show micro-patterns with gradually enhanced contrast upon longer growthtime, as presented in Figure 6b,d,f. The corresponding high-magnification images (Figure 6c,e,g) clearly display two nanoar-rays: one is the initial Au nanoarray, and the other is thenanoarray of Au-Pt core-shell particles with enlarged sizesbut still a basically uniform size distribution at early growth stage.

The SEM images observed under different magnificationsconfirmed themicro-nano patterns but did not offer any elementinformation. The energy dispersive X-ray (EDX) analysis couldnot afford the desired evidence due to very weak signals (data notshown). So, we employed a more sensitive detect approach, XPS,which has a detectable depth of several nanometers. The XPSspectrum of initial Au nanoarray on silanized substrate inFigure 7a exhibits two peaks of Au (4f ) at 83.4 and 87.2 eV.After immersed into the growth solution (0.01% H2PtCl6/2 mMNH2OH solution) for 16 h, the two characteristic peaks of Aurelatively decreased, andmeanwhile two peaks at 72.6 and 76.0 eVcorresponding to Pt (4f ) emerged. The signal of Pt demonstratedthe formation of Pt shell in the microregion of At-Pt core-shellnanoparticle array, and the signal of Au came from the remainingregion of Au nanoarray. Here we note that unlike XPS measure-ments for pattern 1 (Figure 5), the Au signal in pattern 2 did not

Figure 5. XPS spectra of the initial Au nanoarray and nanopat-terns of Au-Pt core-shell particles on glass substrate aftergrowing with 0.01% H2PtCl6 and 2 mM NH2OH solution at60 �C for 4 and 12 h.

Figure 6. SEM images of glass surfaces decorated with initial Aunanoarray (a) andmicro-nano hybrid patterns ofAu-Pt nanoar-ray andAu nanoarray (pattern 2) (b-g). The inset in (a) displays amagnified region showing theAunanodots. The hybrid patterns in(b)-(g) were obtained by growing in a solution with 0.01%H2PtCl6 and 2 mM NH2OH at 60 �C after 8 (b), 16 (d), and 48 h(f ). (c), (e), and (g) show magnified regions schematically markedin (b), (d), and (f ), respectively. Image (h) displays a three-dimen-sional schematic graph of pattern 2.

Figure 7. (a) XPS curves of the initial Au nanoarray and micro-nano hybrid pattern (pattern 2) after a controlled growth for 16 h.Just local curveswith the binding energy range characteristic ofAuand Pt are displayed. (b) Calculated Pt content as a function ofgrowth time.Here 100%refers to all of element signals (not limitedto Pt and Au). The line is just for guidance of the eyes.

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disappear even after a long seed growth (Figure 7a). In thecontrolled growth process, the Pt content gradually increased,as shown in Figure 7b. Since the content here is related to volumeinstead of size, the growth trend is reasonably more significantthan linear. The positions of the characteristic peaks ofAu and Ptare consistent with the previous reports.27,37 Our XPS experi-ments provided strong evidence of metal elements in the forma-tion of micropatterned nanoaray of Au-Pt core-shell particlesand the background Au nanoarray.Preparation of Interlaced Pattern of Pt Microsheet and

Au Nanoarray (Pattern 3). In the process of preparation ofmicro-nano hybrid pattern of Au-Pt bimetallic nanoarray andAu nanoarray (pattern 2), we observed that Au-Pt core-shellnanoparticles in designed micropattern tended to coalesce withlonger growth time (Figure 6g). Therefore, as an extension, the

grown microregion could be roughly thought as a Pt micro-sheet for a very long controlled seed growth. To save time to alarge extent, we used an uncontrolled seed growth in a high-concentrated growth solution to fabricate interlaced patternof quasi-Pt microsheet and Au nanoarray. The resultant micro-nano interlaced patterns characterized by both SEM and opticalmicroscopy are shown in Figure 8. Images in low magnificationshow quasi-Pt microsheet in triangular shapes (bright microscaleislands) (Figure 8a,b). The high-magnification SEM image of theborder region (Figure 8c) confirms the coexistence of quasi-Ptmicrosheet and Au-nanodot array. The microsheet of Pt is sodense that even optical microscopy made the pattern of thosemicrosheets visualizedwell (Figure 8d), while nothingwas seen onthe glass with the initial Au nanopattern (Figure 8e).

Conclusions

In summary, we successfully fabricated a micro-nano patterncomposed of micropatterned nanoarray of Au-Pt core-shellparticles and regular Au nanoarray via the first combination ofphotolithography, block copolymer micelle nanolithography,and controlled seed growth (pattern 2). Two other relatedbimetallic patterns, namely, a nanopattern of Au-Pt core-shellparticles (pattern 1) and an interlaced pattern of Pt microsheetand Au nanoarray (pattern 3), were meanwhile generated for thefirst time. It was also easy to prepare a micro-nano patterncomposed of just one metal such as Au (data not shown). As isknown, photolithography is flexible to produce patterns withvarious shapes and microscale sizes; the sizes and intervals ofinitial nanoarrays could be adjusted via block copolymer compo-sition and loading amount of metallic precursor;6,27,30,37 blockcopolymer micelle nanolithography have been applied to fabri-cate nanoarrays of metals including Au, Ag, Pt, Pd, etc.27 Morethan two metals could also be deposited layer-by-layer via multi-ple seed-growth steps,40 and even bimetallic nanoparticles couldbe ofmultishell.43 So the combinatorial approach suggested in thepresent paper is limited neither to fabricating Au-Pt bimetallicnanoarray nor to the demonstrated patterns. The methodology isready to be extended to generate more hybrid micro-nanostructures designed toward potential applications such as studiesof catalysis, surface-enhanced Raman spectrum and other nano-particle-related optics, and even cell-biomaterial interactions onthe molecular and supermolecular levels.

Acknowledgment. The authors are grateful for the financialsupport from Chinese Ministry of Science and Technology (973program No. 2009CB930000), NSF of China (grants 50533010and 20774020), Science and Technology Developing Foundationof Shanghai (grant 07JC14005), and Shanghai Education Com-mittee (project B112). Help by Dr. Renchao CHE in TEMobservations is also appreciated.

Figure 8. SEM images (a, b, and c) and optical micrographs (d, e)of patterned surfaces. Images of (a), (b), (c), and (d) are graphs ofinterlaced pattern of Pt microsheet and Au nanoarray (pattern 3)after an initial Au nanoarray proceeded an uncontrolled growth in0.5% H2PtCl6 and 0.2 M NH2OH solution at 60 �C for 12 h. TheSEM image at low magnification in (a) visualizes micropattern ofPt microsheet. The image at immediate magnification in (b) showsa corner of a Pt microsheet as schematically presented by the leftrectangle marked in (a). The SEM in high magnification in (c)shows the border as schematically presented by the right rectanglein (a), especially displaying the remaining Au nanoarray beside Ptmicrosheet. The grown micropattern can even be observed clearlyin an optical microscope (d), while the blank optical graph of theinitial Au nanoarray (e) is as control.