Acknowledgements

Financial support was provided by the National ScienceFoundation through a Nanoscale InterdisciplinaryResearch Team (NIRT) Grant, DMI-0506661. This workwas also supported by the National Science Foundation,through award DMR-0305418 and through a NanoscaleInterdisciplinary Research Team (NIRT), awardCMS-0304246. The authors are thankful to Dr. KengqingJian at Brown University for technical support, and ChrisRulison at Augustine Scientific, Inc. for the transientcontact angle measurements on carbon nanoparticlepellets.

References

[1] Dyke CA, Tour JM. Covalent functionalization of single-walledcarbon nanotubes for materials applications. J Phys Chem A 2004;108(51):11151–9.

[2] Mattia D, Bau HH, Gogotsi Y. Wetting of CVD carbon films bypolar and nonpolar liquids and implications for carbon nanopipes.Langmuir 2006;22(4):1789–94.

[3] Majumder M, Chopra N, Andrews R, Hinds BJ. Nanoscale hydro-dynamics—enhanced flow in carbon nanotubes. Nature 2005;438(7064):44.

[4] Chen X, Farber M, Gao Y, Kulaots I, Suuberg EM, Hurt RH.Mechanisms of surfactant adsorption on non-polar, air-oxidized andozone-treated carbon surfaces. Carbon 2003;41(8):1489–500.

[5] Kwok SCH, Jin W, Chu PK. Surface energy, wettability, and bloodcompatibility phosphorus doped diamond-like carbon films. Dia-mond Relat Mater 2005;14(1):78–85.

[6] Oberdorster G, Oberdorster E, Oberdorster J. Nanotoxicology: anemerging discipline evolving from studies of ultrafine particles.Environ Health Prospect 2005;113(7):823–39.

[7] Feng L, Li SH, Li YS, Li HJ, Zhang LJ, Zhai J, et al. Super-hydrophobic surfaces: from natural to artificial. Adv Mater 2002;14(24):1857–60.

[8] Mattia D, Rossi MP, Kim BM, Korneva G, Bau HH, Gogotsi Y.Effect of graphitization on the wettability and electrical conductivityof CVD-carbon nanotubes and films. J Phys Chem B 2006;110(20):9850–5.

[9] Jian K, Xianyu H, Eakin J, Gao Y, Crawford GP, Hurt RH.Orientationally ordered and patterned discotic films and carbon filmsfrom liquid-crystal precursors. Carbon 2005;43(2):407–15.

[10] Yan A, Lau BW, Weissman BS, Kulaots I, Yang NYC, Kane AB,et al. Biocompatible, hydrophilic, supramolecular carbon nanoparti-cles for cell delivery. Adv Mater, in press.

[11] Sheldon BW, Lau HA, Rajamani A. Intrinsic stress, island coales-cence, and surface roughness during the growth of polycrystallinefilms. J Appl Phys 2001;90(10):5097–103.

[12] Jian K, Yan A, Kulaots I, Crawford GP, Hurt RH. Reconstructionand hydrophobicity of nanocarbon surfaces composed solely ofgraphene edges. Carbon 2006;44(10):2102–6.

[13] Belmont JA, Johnson JE, Adams CE. US patent 5571311, 1996.[14] Strano MS, Dyke CA, Usrey ML, Barone PW, Allen MJ, Shan HW,

et al. Electronic structure control of single-walled carbon nanotubefunctionalization. Science 2003;301(5639):1519–22.

[15] Cheng YT, Rodak DE, Wong CA, Hayden CA. Effects of micro- andnano-structures on the self-cleaning behaviour of lotus leaves.Nanotechnology 2006;17:1359–62.

[16] Cassie ABD, Baxter S. Wettability of porous surfaces. Trans FaradaySoc 1944;40:546–51.

[17] Wenzel RN. Surface roughness and contact angle. Ind Eng Chem1936;28:988–94.

Nanoscale mesoporous carbon materials with differentmorphologies from carbon-covered alumina

Li Lin, Pei Wang, Songrui Wang, Yuexiang Zhu *, Biying Zhao, Youchang Xie

State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering,

Peking University, 100871 Beijing, China

Received 7 April 2006; accepted 3 August 2006Available online 7 September 2006

Keywords: Porous carbon; Graphitization; Pyrolysis; Transmission electron microscopy; Texture

Carbon nanosheets have attracted much attention be-cause of their open geometry which may serve as the build-ing blocks for other promising carbon materials [1], such asnanotube-like carbon nanoscrolls [2], nanohorns [3], and

nanowalls [4]. Recently, a simple process has been devel-oped by our group for the preparation of uniformly car-bon-covered alumina (CCA) [5] and titania (CCT) [6] viapyrolysis of sucrose monolayer-dispersed on the surfaceof alumina and titania, respectively. It has been proved thatthe carbon obtained is uniformly distributed on the surfaceof alumina and titania as graphene flake in the as-prepared

0008-6223/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.carbon.2006.08.002

* Corresponding author. Tel.: +86 10 62751703; fax: +86 10 62751725.E-mail address: zhuyx@pku.edu.cn (Y. Zhu).

3120 Letters to the Editor / Carbon 44 (2006) 3113–3148

samples, which is different from the amorphous carbonparticles, or particles with graphitic pore walls as an inversereplica of the pore arrangement in the inorganic materialtemplate as extensively reported [7]. Furthermore, thecoverage and number of carbon layers in CCA can be eas-ily controlled by the tuning of the sucrose content and theimpregnation times [5]. Removing the alumina in CCAwith different coverage and number of carbon layers, wesucceeded in achieving carbon materials with different mor-phologies (nanopartilces, nanoscrolls or nanosheets).

CCA was prepared with sucrose as carbon source, viathe previously reported procedure [5]. Commercialc-Al2O3 (SBA150, Engelhard) was impregnated with aque-ous solutions of sucrose, followed by drying at 90 �C andthen calcined at 600 �C in N2 (flow rate: 30 mL min�1)for 0.5 h. The as-prepared black powder was denoted asCCA03 with a weight ratio of sucrose to alumina of 0.3in the precursors. The coverage of carbon monolayer wasabout 0.6. To increase the carbon coverage, CCA03 was

further impregnated with an aqueous solution of sucrose(weight ratio of sucrose to CCA03, 0.3:1), to giveCCA03-2 with about one layer of carbon uniformly distrib-uted on the surface of alumina. Similarly, CCA03-3, andCCA03-4 were obtained with the number of carbon layersof about 1.5 and 2, respectively. The CCA samples wereimmersed in 48% HF at room temperature for 24 h to re-move the alumina containing a trace amount of silica toobtain carbon materials C–CCAs.

Fig. 1 shows the morphology of the as-preparedC–CCAs. C–CCA03 obtained from CCA03 is porous withpore sizes less than 10 nm (Fig. 1a), while C–CCA03-2 from CCA03-2 consists of nearly spherical particles withsizes between 50 and 100 nm in diameter (Fig. 1b). The dif-ferent morphologies of the carbon materials are closely re-lated to the carbon coverage of their precursors. For thecarbon coverage of only about 0.6 in CCA03, carbon flak-elets separately distributed on the alumina surface aggre-gate together to form porous carbon after the alumina is

Fig. 1. TEM and HRTEM images of (a) C–CCA03, (b) C–CCA03-2, (c) C–CCA03-3, and (d) C–CCA03-4.

Letters to the Editor / Carbon 44 (2006) 3113–3148 3121

removed. In contrast, in CCA03-2, carbon covers the entiresurface of alumina; and after removal of the alumina, thecarbon flakes form much larger particles (Fig. 1b). Whenthe second graphene layer appears as in CCA03-3 (about1.5 layers of carbon) and CCA03-4 (about two layers ofcarbon), the carbon flakes grow even larger. After the re-moval of alumina, carbon nanoscrolls appear with a yieldof more than 40% for C–CCA03-3 (Fig. 1c) and petal-likenanosheets appear with a yield of about 80% for C–CCA03-4 (Fig. 1d). In addition, from the inset ofFig. 1d, lattice fringes can be distinctly observed with aninterlayer spacing of about 0.35 nm, demonstrating theperiodical structure of the carbon material.

The XRD patterns of the as-synthesized C–CCAsshowed two broad diffraction peaks at about 24–25� and43� corresponding to the (002) and (10) diffraction planesof hexagonal graphite, respectively [8]. The interlayer spac-ing can be calculated from the position of (002) reflectionpeak, and the results are listed in Table 1. It can be foundthat with increased carbon coverage in the precursor, thedegree of graphitization is increased. The d002 value of C–CCA03-4 determined by XRD is 0.353 nm, which is consis-tent with the HRTEM image shown in the inset of Fig. 1d.The Raman spectra and TPO measurement results furtherconfirmed the powder XRD results (figure not shown).

Furthermore, the texture of the as-prepared C–CCAshas been investigated by measuring nitrogen adsorption.As shown in Fig. 2, unlike type I of activated carbon, the

nitrogen sorption isotherms of C–CCAs are all of typeIV, and exhibit hysteresis loops, indicating mesoporouscharacteristics with a capillary condensation phenomenon.In addition, there is a sharp step in the sorption isothermsof C–CCA03-3 and C–CCA03-4 in the range of relativepressure of 0.7–0.9, corresponding to the existence of mes-opores with a narrow pore size distribution centered ataround 10 nm calculated by the BJH method from the iso-therm desorption branch. The pore size distributions ofactivated carbon, C–CCA03 and C–CCA03-2 were derivedfrom the isotherm adsorption branch in order to avoid thetensile strength effect. It can be found that activated carbonshowed little mesopore while C–CCA03 and C–CCA03-2presented much more mesopore with a wide pore sizedistribution.

Table 1 summarizes the structural characteristics of thecarbon materials. The BET surface area of the as-preparedC–CCAs is in the range of 1000–1350 m2 g�1, similar tothat of activated carbon. On the other hand, the total porevolume of the C–CCAs is all much larger than that of acti-vated carbon (0.60 cm3 g�1), especially the 2.81 and3.51 cm3 g�1 of C–CCA03-3 and C–CCA03-4. It is worthnoting that the total pore volume of C–CCA03-4 exceedsthe 3.2 cm3 g�1 of a recently reported mesoporous carbonwhich claimed to have extremely high pore volume [9].Interestingly, C–CCAs presented very little micropore,with surface areas and pore volumes typical for mesopor-ous carbons, making these carbon materials promising ashighly efficient adsorbents.

Acknowledgements

The authors are grateful to the National Science Foun-dation of China (20173002), and the Major State BasicResearch Development Program (Grant No. 2006C-B806100) for financial support to this work.

References

[1] Kuang Q, Xie SY, Jiang ZY, Zhang XH, Xie ZX, Huang RB, et al.Low temperature solvothermal synthesis of crumpled carbon nano-sheets. Carbon 2004;42:1737–41.

[2] Viculis LM, Mack JJ, Kaner RB. A chemical route to carbonnanoscrolls. Science 2003;299:1361-1.

[3] Iijima S, Yudasaka M, Yamada R, Bandow S, Suenaga K, Kokai F,et al. Nano-aggregates of single-walled graphitic carbon nano-horns.Chem Phys Lett 1999;309:165–70.

Table 1Texture properties of the as-prepared carbon materials

Sample SBET (m2 g�1) aD (nm) bV (cm3 g�1) d002 (nm)

Activated carbon 1005 2.40 0.60 (0.31) 0.378C–CCA03 1014 3.08 0.73 (0.07) 0.375C–CCA03-2 1220 4.66 1.29 (0) 0.370C–CCA03-3 1031 10.9 2.81 (0) 0.358C–CCA03-4 1319 10.6 3.51 (0) 0.353

a Average pore size.b Total pore volume with micropore pore volume in parentheses.

0.0 0.2 0.4 0.6 0.8 1.00

500

1000

1500

2000

10 1000

2

4

6

8

dV

/dlo

gD

/cm

3 g-1

Pore size /nm

C-CCA03 (a) C-CCA03-2 (a) C-CCA03-3 (d) C-CCA03-4 (d) Activated carbon (a)

Vo

lum

e A

dso

rbed

(cm

3 ST

P g

-1)

Fig. 2. Nitrogen sorption isotherms and pore size distributions (inset) ofC–CCAs and activated carbon ((a) and (d) derived by BJH method fromthe isotherm adsorption and desorption branch, respectively).

3122 Letters to the Editor / Carbon 44 (2006) 3113–3148

[4] Wu YH, Qiao PW, Chong TC, Shen ZX. Carbon nanowalls grown bymicrowave plasma enhanced chemical vapor deposition. Adv Mater2002;14:64–7.

[5] Lin L, Lin W, Zhu YX, Zhao BY, Xie YC, Jia GQ, et al. Uniformlycarbon-covered alumina and its surface characteristics. Langmuir2005;21:5040–6.

[6] Dandekar A, Baker RTK, Vannice MA. Characterization of activatedcarbon, graphitized carbon fibers and synthetic diamond powder usingTPD and drifts. Carbon 1998;36:1821–31.

[7] Ryoo R, Joo SH, Kruk M, Jaroniec M. Ordered mesoporous carbons.Adv Mater 2001;13:677–81.

[8] Kim TW, Park IS, Ryoo R. A synthetic route to ordered mesoporouscarbon materials with graphitic pore walls. Agew Chem Int Ed2003;42:4375–9.

[9] Lu AH, Schmidt W, Spliethoff B, Schuth F. Synthesis of orderedmesoporous carbon with bimodal pore system and high pore volume.Adv Mater 2003;15:1602–6.

Growth of aligned CNx nanocolumns on siliconby RF-magnetron sputtering

S. Scalese a,*, V. Scuderi a, F. Simone b, A. Pennisi a, G. Compagnini c, V. Privitera a

a Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, Stradale Primosole 50, I-95121 Catania, Italyb Dipartimento di Fisica e Astronomia, Universita di Catania Viale A. Doria 6, I-95125 Catania, Italy

c Dipartimento di Scienze Chimiche, Universita di Catania Viale A. Doria 6, I-95125 Catania, Italy

Received 13 April 2006; accepted 29 July 2006Available online 8 September 2006

Keywords: Carbon composites; Carbon nanoparticles; Sputtering; Electron microscopy; Raman spectroscopy

Over the past few years, the interest for the nano-sizedC-based materials has received a growing interest, due topeculiar properties that may lead to several applicationsin electronic devices and sensors. Furthermore, recently,it was shown that carbon-based hard materials, such asdiamond-like carbon and carbon nitride thin films, canbe used as protective coatings, due to high wear resistance,low friction and high elasticity combined with high hard-ness [1,2], as dielectrics, due to high resistivity and break-down fields in metal–insulator–semiconductor (MIS)devices [3] and for display applications, since the incorpo-ration of nitrogen was shown to improve the field emissionfrom amorphous carbon (a-C) [4]. The C–N thin film sys-tem, obtained by magnetron sputtering, has been observedmainly in the amorphous phase or in a fullerene-like struc-ture, depending on the growth parameters (i.e. temperatureand deposition rate).

In the present work we report the growth of a new kindof C nanostructures, by radio-frequency (RF) magnetronsputtering technique, C deposition is performed using agraphite cathode as material source, on a Si(100) substratepatterned with SiO2 stripes, 90 nm thick and about 1 lmwide. The use of such kind of substrate allows to observe

at the same time whether a different growth takes placeon silicon and on silicon dioxide. The base pressure inthe vacuum chamber was 2 · 10�3 Pa; N2 (or Ar) was thenintroduced into the chamber, reaching an operating pres-sure of 2 Pa. The plasma is generated by applying a RFpower of 100 W. During the deposition the substrates werekept at 400 �C. Samples were thermally treated, after depo-sition, at 700 �C in Ar or O2 ambient. The structural char-acterization of the samples was performed by scanningelectron microscopy (SEM) (ZEISS SUPRA35 FE-SEM)and by transmission electron microscopy (TEM) (JEM2010F JEOL), equipped with energy filtering detection sys-tem (EF-TEM) for chemical mapping and electron energyloss spectroscopy (EELS). Furthermore, Raman spectros-copy was also used in order to get information on the localvibrational properties and, consequently, on the chemicalbonds among the atoms contained in the samples. Ramanscattering has been excited by a 514.5 nm radiation comingfrom an Ar ion laser and the scattered light has been ana-lyzed by a single 460 mm monochromator (Jobin–YvonHR460).

In Fig. 1(a) we show a SEM image of nanostructures ob-tained by depositing C for 4 h on a Si wafer patterned withSiO2 stripes, using N2 as sputtering gas. The C deposit wassuitably scratched, as shown in Fig. 1(a), in order to ob-serve by SEM the shape and the height of the structures

0008-6223/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.carbon.2006.07.022

* Corresponding author. Tel.: +39 095 5968235; fax: +39 095 5968312.E-mail address: silvia.scalese@imm.cnr.it (S. Scalese).

Letters to the Editor / Carbon 44 (2006) 3113–3148 3123