Nanoscale mesoporous carbon materials with different morphologies from carbon-covered alumina

Nanoscale mesoporous carbon materials with different morphologies from carbon-covered alumina

3120 Letters to the Editor / Carbon 44 (2006) 3113–3148 Acknowledgements Financial support was provided by the National Science Foundation through a...

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3120

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

Acknowledgements Financial support was provided by the National Science Foundation through a Nanoscale Interdisciplinary Research Team (NIRT) Grant, DMI-0506661. This work was also supported by the National Science Foundation, through award DMR-0305418 and through a Nanoscale Interdisciplinary Research Team (NIRT), award CMS-0304246. The authors are thankful to Dr. Kengqing Jian at Brown University for technical support, and Chris Rulison at Augustine Scientific, Inc. for the transient contact angle measurements on carbon nanoparticle pellets. References [1] Dyke CA, Tour JM. Covalent functionalization of single-walled carbon 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 by polar and nonpolar liquids and implications for carbon nanopipes. Langmuir 2006;22(4):1789–94. [3] Majumder M, Chopra N, Andrews R, Hinds BJ. Nanoscale hydrodynamics—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 and ozone-treated carbon surfaces. Carbon 2003;41(8):1489–500. [5] Kwok SCH, Jin W, Chu PK. Surface energy, wettability, and blood compatibility phosphorus doped diamond-like carbon films. Diamond Relat Mater 2005;14(1):78–85.

[6] Oberdorster G, Oberdorster E, Oberdorster J. Nanotoxicology: an emerging 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. Superhydrophobic 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 conductivity of 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 films from liquid-crystal precursors. Carbon 2005;43(2):407–15. [10] Yan A, Lau BW, Weissman BS, Ku¨laots I, Yang NYC, Kane AB, et al. Biocompatible, hydrophilic, supramolecular carbon nanoparticles for cell delivery. Adv Mater, in press. [11] Sheldon BW, Lau HA, Rajamani A. Intrinsic stress, island coalescence, and surface roughness during the growth of polycrystalline films. J Appl Phys 2001;90(10):5097–103. [12] Jian K, Yan A, Ku¨laots I, Crawford GP, Hurt RH. Reconstruction and hydrophobicity of nanocarbon surfaces composed solely of graphene 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 nanotube functionalization. Science 2003;301(5639):1519–22. [15] Cheng YT, Rodak DE, Wong CA, Hayden CA. Effects of micro- and nano-structures on the self-cleaning behaviour of lotus leaves. Nanotechnology 2006;17:1359–62. [16] Cassie ABD, Baxter S. Wettability of porous surfaces. Trans Faraday Soc 1944;40:546–51. [17] Wenzel RN. Surface roughness and contact angle. Ind Eng Chem 1936;28:988–94.

Nanoscale mesoporous carbon materials with different morphologies 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 2006 Available online 7 September 2006

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

Carbon nanosheets have attracted much attention because of their open geometry which may serve as the building blocks for other promising carbon materials [1], such as nanotube-like carbon nanoscrolls [2], nanohorns [3], and *

Corresponding author. Tel.: +86 10 62751703; fax: +86 10 62751725. E-mail address: [email protected] (Y. Zhu).

0008-6223/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2006.08.002

nanowalls [4]. Recently, a simple process has been developed by our group for the preparation of uniformly carbon-covered alumina (CCA) [5] and titania (CCT) [6] via pyrolysis of sucrose monolayer-dispersed on the surface of alumina and titania, respectively. It has been proved that the carbon obtained is uniformly distributed on the surface of alumina and titania as graphene flake in the as-prepared

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

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

samples, which is different from the amorphous carbon particles, or particles with graphitic pore walls as an inverse replica of the pore arrangement in the inorganic material template as extensively reported [7]. Furthermore, the coverage and number of carbon layers in CCA can be easily controlled by the tuning of the sucrose content and the impregnation times [5]. Removing the alumina in CCA with different coverage and number of carbon layers, we succeeded in achieving carbon materials with different morphologies (nanopartilces, nanoscrolls or nanosheets). CCA was prepared with sucrose as carbon source, via the previously reported procedure [5]. Commercial c-Al2O3 (SBA150, Engelhard) was impregnated with aqueous solutions of sucrose, followed by drying at 90 C and then calcined at 600 C in N2 (flow rate: 30 mL min1) for 0.5 h. The as-prepared black powder was denoted as CCA03 with a weight ratio of sucrose to alumina of 0.3 in the precursors. The coverage of carbon monolayer was about 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 give CCA03-2 with about one layer of carbon uniformly distributed on the surface of alumina. Similarly, CCA03-3, and CCA03-4 were obtained with the number of carbon layers of about 1.5 and 2, respectively. The CCA samples were immersed in 48% HF at room temperature for 24 h to remove the alumina containing a trace amount of silica to obtain carbon materials C–CCAs. Fig. 1 shows the morphology of the as-prepared C–CCAs. C–CCA03 obtained from CCA03 is porous with pore sizes less than 10 nm (Fig. 1a), while C–CCA032 from CCA03-2 consists of nearly spherical particles with sizes between 50 and 100 nm in diameter (Fig. 1b). The different morphologies of the carbon materials are closely related to the carbon coverage of their precursors. For the carbon coverage of only about 0.6 in CCA03, carbon flakelets separately distributed on the alumina surface aggregate together to form porous carbon after the alumina is

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Table 1 Texture properties of the as-prepared carbon materials Sample

SBET (m2 g1)

a

Activated carbon C–CCA03 C–CCA03-2 C–CCA03-3 C–CCA03-4

1005 1014 1220 1031 1319

2.40 3.08 4.66 10.9 10.6

a

D (nm)

V (cm3 g1)

b

0.60 0.73 1.29 2.81 3.51

(0.31) (0.07) (0) (0) (0)

d002 (nm) 0.378 0.375 0.370 0.358 0.353

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

b

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

3

dV/dlogD /cm g

2000

-1

8

3

-1

Volume Adsorbed (cm STP g )

removed. In contrast, in CCA03-2, carbon covers the entire surface of alumina; and after removal of the alumina, the carbon flakes form much larger particles (Fig. 1b). When the second graphene layer appears as in CCA03-3 (about 1.5 layers of carbon) and CCA03-4 (about two layers of carbon), the carbon flakes grow even larger. After the removal of alumina, carbon nanoscrolls appear with a yield of more than 40% for C–CCA03-3 (Fig. 1c) and petal-like nanosheets appear with a yield of about 80% for C– CCA03-4 (Fig. 1d). In addition, from the inset of Fig. 1d, lattice fringes can be distinctly observed with an interlayer spacing of about 0.35 nm, demonstrating the periodical structure of the carbon material. The XRD patterns of the as-synthesized C–CCAs showed two broad diffraction peaks at about 24–25 and 43 corresponding to the (0 0 2) and (1 0) diffraction planes of hexagonal graphite, respectively [8]. The interlayer spacing can be calculated from the position of (0 0 2) reflection peak, and the results are listed in Table 1. It can be found that with increased carbon coverage in the precursor, the degree of graphitization is increased. The d002 value of C– CCA03-4 determined by XRD is 0.353 nm, which is consistent with the HRTEM image shown in the inset of Fig. 1d. The Raman spectra and TPO measurement results further confirmed the powder XRD results (figure not shown). Furthermore, the texture of the as-prepared C–CCAs has been investigated by measuring nitrogen adsorption. As shown in Fig. 2, unlike type I of activated carbon, the

1500

1000

6

Acknowledgements The authors are grateful to the National Science Foundation of China (20173002), and the Major State Basic Research Development Program (Grant No. 2006CB806100) for financial support to this work.

4

2

0 10

100

Pore size /nm

References

500

0 0.0

nitrogen sorption isotherms of C–CCAs are all of type IV, and exhibit hysteresis loops, indicating mesoporous characteristics with a capillary condensation phenomenon. In addition, there is a sharp step in the sorption isotherms of C–CCA03-3 and C–CCA03-4 in the range of relative pressure of 0.7–0.9, corresponding to the existence of mesopores with a narrow pore size distribution centered at around 10 nm calculated by the BJH method from the isotherm desorption branch. The pore size distributions of activated carbon, C–CCA03 and C–CCA03-2 were derived from the isotherm adsorption branch in order to avoid the tensile strength effect. It can be found that activated carbon showed little mesopore while C–CCA03 and C–CCA03-2 presented much more mesopore with a wide pore size distribution. Table 1 summarizes the structural characteristics of the carbon materials. The BET surface area of the as-prepared C–CCAs is in the range of 1000–1350 m2 g1, similar to that of activated carbon. On the other hand, the total pore volume of the C–CCAs is all much larger than that of activated carbon (0.60 cm3 g1), especially the 2.81 and 3.51 cm3 g1 of C–CCA03-3 and C–CCA03-4. It is worth noting that the total pore volume of C–CCA03-4 exceeds the 3.2 cm3 g1 of a recently reported mesoporous carbon which claimed to have extremely high pore volume [9]. Interestingly, C–CCAs presented very little micropore, with surface areas and pore volumes typical for mesoporous carbons, making these carbon materials promising as highly efficient adsorbents.

0.2

0.4

0.6

0.8

1.0

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

[1] Kuang Q, Xie SY, Jiang ZY, Zhang XH, Xie ZX, Huang RB, et al. Low temperature solvothermal synthesis of crumpled carbon nanosheets. Carbon 2004;42:1737–41. [2] Viculis LM, Mack JJ, Kaner RB. A chemical route to carbon nanoscrolls. 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.

Letters to the Editor / Carbon 44 (2006) 3113–3148 [4] Wu YH, Qiao PW, Chong TC, Shen ZX. Carbon nanowalls grown by microwave plasma enhanced chemical vapor deposition. Adv Mater 2002;14:64–7. [5] Lin L, Lin W, Zhu YX, Zhao BY, Xie YC, Jia GQ, et al. Uniformly carbon-covered alumina and its surface characteristics. Langmuir 2005;21:5040–6. [6] Dandekar A, Baker RTK, Vannice MA. Characterization of activated carbon, graphitized carbon fibers and synthetic diamond powder using TPD and drifts. Carbon 1998;36:1821–31.

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[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 mesoporous carbon materials with graphitic pore walls. Agew Chem Int Ed 2003;42:4375–9. [9] Lu AH, Schmidt W, Spliethoff B, Schu¨th F. Synthesis of ordered mesoporous carbon with bimodal pore system and high pore volume. Adv Mater 2003;15:1602–6.

Growth of aligned CNx nanocolumns on silicon by RF-magnetron sputtering S. Scalese a

a,*

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

a

Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, Stradale Primosole 50, I-95121 Catania, Italy b 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 2006 Available online 8 September 2006

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

Over the past few years, the interest for the nano-sized C-based materials has received a growing interest, due to peculiar properties that may lead to several applications in electronic devices and sensors. Furthermore, recently, it was shown that carbon-based hard materials, such as diamond-like carbon and carbon nitride thin films, can be used as protective coatings, due to high wear resistance, low friction and high elasticity combined with high hardness [1,2], as dielectrics, due to high resistivity and breakdown fields in metal–insulator–semiconductor (MIS) devices [3] and for display applications, since the incorporation of nitrogen was shown to improve the field emission from amorphous carbon (a-C) [4]. The C–N thin film system, obtained by magnetron sputtering, has been observed mainly in the amorphous phase or in a fullerene-like structure, depending on the growth parameters (i.e. temperature and deposition rate). In the present work we report the growth of a new kind of C nanostructures, by radio-frequency (RF) magnetron sputtering technique, C deposition is performed using a graphite cathode as material source, on a Si(1 0 0) substrate patterned with SiO2 stripes, 90 nm thick and about 1 lm wide. The use of such kind of substrate allows to observe *

Corresponding author. Tel.: +39 095 5968235; fax: +39 095 5968312. E-mail address: [email protected] (S. Scalese).

0008-6223/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2006.07.022

at the same time whether a different growth takes place on silicon and on silicon dioxide. The base pressure in the vacuum chamber was 2 · 103 Pa; N2 (or Ar) was then introduced into the chamber, reaching an operating pressure of 2 Pa. The plasma is generated by applying a RF power of 100 W. During the deposition the substrates were kept at 400 C. Samples were thermally treated, after deposition, at 700 C in Ar or O2 ambient. The structural characterization of the samples was performed by scanning electron microscopy (SEM) (ZEISS SUPRA35 FE-SEM) and by transmission electron microscopy (TEM) (JEM 2010F JEOL), equipped with energy filtering detection system (EF-TEM) for chemical mapping and electron energy loss spectroscopy (EELS). Furthermore, Raman spectroscopy was also used in order to get information on the local vibrational properties and, consequently, on the chemical bonds among the atoms contained in the samples. Raman scattering has been excited by a 514.5 nm radiation coming from an Ar ion laser and the scattered light has been analyzed by a single 460 mm monochromator (Jobin–Yvon HR460). In Fig. 1(a) we show a SEM image of nanostructures obtained by depositing C for 4 h on a Si wafer patterned with SiO2 stripes, using N2 as sputtering gas. The C deposit was suitably scratched, as shown in Fig. 1(a), in order to observe by SEM the shape and the height of the structures