Home
Search
Collections
Journals
About
Contact us
My IOPscience
Synthesis of cubic-structured monocrystalline titanium nitride nanoparticles by means of a dual plasma process
This content has been downloaded from IOPscience. Please scroll down to see the full text. 2009 J. Phys. D: Appl. Phys. 42 102001 (http://iopscience.iop.org/0022-3727/42/10/102001) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 59.172.208.186 This content was downloaded on 03/10/2013 at 18:49
Please note that terms and conditions apply.
IOP PUBLISHING
JOURNAL OF PHYSICS D: APPLIED PHYSICS
J. Phys. D: Appl. Phys. 42 (2009) 102001 (4pp)
doi:10.1088/0022-3727/42/10/102001
FAST TRACK COMMUNICATION
Synthesis of cubic-structured monocrystalline titanium nitride nanoparticles by means of a dual plasma process J Tavares1 , S Coulombe and J-L Meunier Department of Chemical Engineering, McGill University, 3610 University St., Montr´eal, Qu´ebec, H3A 2B2, Canada E-mail:
[email protected]
Received 4 March 2009 Published 24 April 2009 Online at stacks.iop.org/JPhysD/42/102001 Abstract Titanium nitride has long been used for its favourable mechanical and chemical properties and it has been demonstrated that monocrystallinity in thin films enhances these properties. While the synthesis of monocrystalline thin films is well documented, common synthesis processes for titanium nitride nanoparticles yield only polycrystalline, spherically shaped powders. The process presented here allows for the synthesis of monocrystalline, cube-shaped nanoparticles by means of a dual plasma process. Pulsed electric arc erosion of a Ti cathode in a N-rich atmosphere produced by a radio-frequency discharge is used for the synthesis of the TiN nanoparticles. Electron microscopy revealed the cubic morphology of the synthesized powders and electron diffraction patterning confirmed the crystalline structure of the TiN nanoparticles.
instances in which a cubic morphology for particles is reported are when large, micrometre powders are produced [6]. It has been shown that a monocrystalline structure improves the corrosion resistance of TiN, thus rendering it even more inert from a chemical standpoint [14]. Moreover, monocrystalline TiN exhibits more favourable optical, electrical and transport properties [15]. Current synthesis methods of crystalline TiN nanoparticles typically involve either multi-step chemical reactions [13] or time-consuming heat treatments (such as nitridation) [11, 12]. Although plasma synthesis methods have been used to generate TiN films [16, 17], they have only been used sparingly to generate TiN nanoparticles [10, 18]. As indicated previously, almost none of the methods investigated thus far have shown the ability to produce monocrystalline TiN nanoparticles [18]. The dual plasma process presented here offers a novel, but conceptually simple method of synthesizing such monocrystalline particles.
1. Introduction Titanium nitride (TiN) is commonly used as a coating because of its mechanical properties (high hardness), its gold-like appearance (for the purposes of decoration), its relatively high chemical inertness (useful for biocompatible implants) and its transport properties (it acts as a diffusion barrier in semiconductors) [1–5]. On the nano-scale, TiN can be used as an additive, particularly in titanium-containing alloys, to improve the mechanical and electrical properties of the resulting nanocomposite [6, 7]. It also finds uses in catalysis; TiN’s chemical inertness and high melting point make it suitable as a support for various heterogeneous reactions [8]. TiN exhibits a cubic crystal cell structure [9]. However, most TiN nanoparticle images reported in the literature reveal a spherical morphology, indicative of a polycrystalline structure [7, 10–13]. The only 1
Author to whom any correspondence should be addressed.
0022-3727/09/102001+04$30.00
1
© 2009 IOP Publishing Ltd
Printed in the UK
J. Phys. D: Appl. Phys. 42 (2009) 102001
Fast Track Communication
Figure 1. Low-magnification TEM micrograph showing a cube-shaped TiN nanoparticle. Scale bar: 50 nm.
Figure 2. High-magnification TEM micrograph of a TiN nanoparticle showing its crystalline nature. The dashed lines are used to outline the nanoparticle. Scale bar: 2 nm.
2. Material and method
3. Results and discussion
The dual plasma system employed in this process was previously used for the synthesis of metal nanoparticles coated with a functionalized organic layer [19–21]. The concentric geometry for this system remains largely the same: a watercooled titanium rod (Grade 2, 98.9% pure, cathode) is placed concentrically with four stainless steel bars (grounded anode), which are themselves surrounded by a circular mesh electrode that acts as the live electrode of a capacitively coupled RF discharge system. A train of pulsed arc events between the Ti cathode and anode bars is sustained, leading to the formation of repetitive metallic vapour plumes rapidly expanding in the direction normal to the cathode. The metallic vapour plume expands into a reactive N-rich environment produced by a 20 W capacitively coupled radio-frequency (RF) glow discharge in an Ar/N2 mixture (2000/10 sccm). The arcing events on the Ti cathode typically last 10 ms and occur at a frequency of 10 Hz with a 30 A peak current. The system’s background pressure is maintained at 20 Torr. We postulate that the titanium nitride nanoparticles form on the periphery of the metallic vapour plume [22]. The nanoparticles are collected on polymer-coated copper TEM grids (SPI supplies) suspended on a circular ring placed outside of the plasma zone, past the RF mesh electrode. This ring is held at a positive potential with respect to the grounded anode to increase the collection efficiency. The imaging and structural analysis of the collected nanoparticles were performed using a FEI Tecnai 12 120 kV TEM (preliminary, lower magnification imaging) and a JEOL JEM-2100F 200 kV TEM (higher magnification imaging, electron diffraction patterning).
The micrograph in figure 1 shows a sample of the nanoparticles produced by this process. The cubic geometry of these particles is a strong indication of a monocrystalline structure. Further evidence of this monocrystallinity is given by the higher magnification micrograph shown in figure 2, in which the interference pattern of the outlined particle’s crystal structure is apparent. Moreover, image analysis has shown that the spacing between the peaks of this interference pattern is 0.21 nm, a diffraction spacing characteristic of TiN [23, 24]. An agglomeration of nanoparticles is shown in figure 3(a). Inspection of this micrograph along with the ones presented in figures 1 and 2 shows that the particles produced range in size from approximately 2 to 20 nm. Some larger micrometresized particles, not shown in the images presented here, are also generated: these are well-documented by-products of the arc erosion process [20, 25]. While the novelty of the presented process lies in the formation of monocrystalline nanoparticles, it is apparent, especially from the micrograph of figure 3(a), that a mixture of monocrystalline (cubic) and polycrystalline (spherical) nanoparticles is produced. Nonetheless, the particles formed are all composed of TiN, as evidenced by the electron diffraction pattern shown in figure 3(b) and indexed in figure 3(c). The diffraction spacing peaks identified in figure 3(c) are reported in table 1 where they are compared to the values obtained from the American Mineralogist Crystal Structure Database (data obtained for the osbornite mineral, the naturally occurring form of titanium nitride) [23, 24] and the ICDD Powder Diffraction File [26]. The experimental data shown in table 1 are slightly shifted with respect to the literature values. However, given that the shifts in the data are quite small and that all data points are shifted in the same direction, 2
J. Phys. D: Appl. Phys. 42 (2009) 102001
Fast Track Communication
Figure 3. (a) TEM micrograph of a nanoparticle agglomerate containing several cube-shaped particles (scale bar: 20 nm); (b) electron diffraction pattern from that agglomerate; (c) same electron diffraction pattern indexed with the corresponding diffraction spacing.
References
Table 1. Comparison between the experimentally obtained diffraction spacing and the values reported in the literature [22, 23, 25]. Reported diffraction spacing (Å)
Experimentally obtained diffraction spacing (Å)
Difference (%)
2.4451 2.1175 1.4973
2.43 2.05 1.46
−0.62 −3.2 −2.5
[1] Oyama S T 1996 The Chemistry of Transition Metal Carbides and Nitrides 1st edn (Cornwall: Chapman and Hall) [2] Weimer A W 1997 Carbide, Nitride and Boride Materials, Synthesis and Processing 1st edn (London: Chapman and Hall) [3] Raimondi M T and Pietrabissa R 2000 The in-vivo wear performance of prosthetic femoral heads with titanium nitride coating Biomaterials 21 907–13 [4] Wittmer M 1980 High-temperature contact structures for silicon semiconductor devices Appl. Phys. Lett. 37 540–2 [5] Sinke W, Frijlink G P A and Saris F W 1985 Oxygen in titanium nitride diffusion barriers Appl. Phys. Lett. 47 471–3 [6] Liu N, Xu Y D, Li H, Li Z H, Zhao Y, Li G H and Zhang L D 2002 Effect of addition of TiN nanoparticles on microstructure and mechanical properties of TiC based cermets Mater. Sci. Technol. 18 586–90 [7] Jiang L and Gao L 2005 Carbon nanotubes–metal nitride composites: a new class of nanocomposites with enhanced electrical properties J. Mater. Chem. 15 260–66 [8] Wieckowski A, Savinova E R and Vayenas C G 2003 Catalysis and Electrocatalysis at Nanoparticle Surfaces 1st edn (New York: Marcel Dekker) [9] Lide DR 1998 CRC Handbook of Chemistry and Physics 79th edn (Boca Raton, FL: CRC Press) [10] Kakati M, Bora B, Sarma S, Saikia B J, Shripathi T, Deshpande U, Dubey A, Ghosh G and Das A K 2008 Synthesis of titanium oxide and titanium nitride nano-particles with narrow size distribution by supersonic thermal plasma expansion Vacuum 82 833–41 [11] Ma J, Wu M, Du Y, Chen S, Li G and Hu J 2009 Synthesis of nanocrystalline titanium nitride at low temperature and its thermal stability J. Alloys Compounds at press [12] Li J, Gao L, Sun J, Zhang Q, Guo J and Yan D 2001 Synthesis of nanocrystalline titanium nitride powders by direct nitridation of titanium oxide J. Am. Ceram. Soc. 84 3045–47 [13] Kashel S, Schlichte K, Chaplais G and Khanna M 2003 Synthesis and characterisation of titanium nitride based nanoparticles J. Mater. Chem. 13 1496–9 [14] Delblanc Bauer A, Herranen M, Ljungcrantz H, Carlsson J O and Sundgren J E 1997 Corrosion behaviour of monocrystalline titanium nitride Surf. Coat. Technol. 91 208–14 [15] Patsalas P and Logothetidis S 2001 Optical, electronic, and transport properties of nanocrystalline titanium nitride thin films J. Appl. Phys. 90 4725–34
it can be assumed that an instrument bias might have caused the shifts. In fact, a shift can be explained by astigmatism of the electron beam (this is supported by the fact that the diffraction pattern shown is not perfectly circular). Unfortunately, energy dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) proved inconclusive in the analysis of the nanoparticles, due to the fact that the nitrogen K-lines overlap with the stronger titanium L-lines [27].
4. Conclusion Cubic nanocrystalline TiN nanoparticles in a size range from 2 to 20 nm can be produced using a dual plasma system based on Ti ablation from a pulsed low pressure arc plasma expanding in a capacitively coupled RF glow discharge sustained in an Ar/N2 mixture. Electron diffraction patterns and the cubic morphology seen in high resolution TEM observations confirm the TiN nature of the particles. Mixtures of both monoand polycrystalline morphologies are obtained. The method presented for the synthesis of monocrystalline TiN is novel and warrants further investigation in order to optimize the various process parameters such as to increase the fraction of monocrystalline (cubic) nanoparticles.
Acknowledgments The authors acknowledge the financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC), the Fonds qu´eb´ecois de la recherche sur la nature et les technologies (FQRNT) and McGill University. 3
J. Phys. D: Appl. Phys. 42 (2009) 102001
Fast Track Communication
[16] Tanaka Y, Kim E, Forster J and Xu Z 1999 Properties of titanium nitride films deposited by ionized metal plasma source J. Vac. Sci. Technol. B 17 416–22 [17] Kelly P J and Arnell R D 2000 Magnetron sputtering: a review of recent developments and applications Vacuum 56 159–72 [18] Yoshida T, Kawasaki A, Nakagawa K and Akashi K 1979 The synthesis of ultrafine titanium nitride in an r.f. plasma J. Mater. Sci. 14 1624–30 [19] Swanson E J, Tavares J and Coulombe S 2008 Improved dual-plasma process for the synthesis of coated or functionalized metal nanoparticles IEEE Trans. Plasma Sci. 36 886–7 [20] Tavares J, Swanson E J and Coulombe S 2008 Plasma synthesis of coated metal nanoparticles with surface properties tailored for dispersion Plasma Process. Polym. 5 759–69 [21] Tavares J, Shahryari A, Harvey J, Coulombe S and Omanovic S 2009 Corrosion behaviour and fibrinogen
[22] [23] [24] [25] [26] [27]
4
adsorptive interaction of SS316L surfaces covered with ethylene glycol plasma-polymer coated Ti nanoparticles Surf. Coat. Technol. 203 2278 Meunier J L 1999 Cathodic arc carbon plasma/gas interaction in fullerenes synthesis study J. Appl. Phys. 85 1992–4 Downs R T and Hall-Wallace M 2003 The American Mineralogist crystal structure database Am. Mineral. 88 247–50 Wyckoff R W G 1963 Crystal Structure 1 2nd edn (New York: Interscience) Utsumi T and English J H 1975 Study of electrode products emitted by vacuum arcs in form of molten metal particles J. Appl. Phys. 46 126–31 ICDD Powder Diffraction File 06-0642 Goldstein J, Newbury D, Joy D, Lyman C, Echlin P, Lifshin E, Sawyer L and Michael J Scanning Electron Microscopy and X-ray Microanalysis 3rd edn (Berlin: Springer)
