Diamond Synthesized at Room Temperature by

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Diamond Synthesized at Room Temperature by Pulsed Laser Deposition in Vacuum

This content has been downloaded from IOPscience. Please scroll down to see the full text. 2003 Jpn. J. Appl. Phys. 42 L1164 (http://iopscience.iop.org/1347-4065/42/10A/L1164) View the table of contents for this issue, or go to the journal homepage for more

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Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 1164–L 1166 Part 2, No. 10A, 1 October 2003 #2003 The Japan Society of Applied Physics

Diamond Synthesized at Room Temperature by Pulsed Laser Deposition in Vacuum Dillip K. M ISHRA1;2 , Xuemin TIAN1 , Tetsuo S OGA1; , Takashi J IMBO1 and Maheshwar S HARON2 1 2

Department of Environmental Technology and Urban Planning, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India

(Received June 20, 2003; accepted August 15, 2003; published September 25, 2003)

Here we show that diamond particles were formed on (100) silicon substrates by XeCl (308 nm, 20 ns) laser ablation using a urea doped camphoric carbon target in vacuum. The substrate temperature and the pressure were kept at room temperature (25 C) and ð4{5Þ  105 Torr, respectively without feeding any gases during the deposition. Raman spectroscopy analysis confirmed the diamond cubic structure of the crystals by the presence of a sharp peak at 1337.8 cm1 . One broad peak is also observed in the spectra centered at 1550 cm1 , which is attributed to the G-peak in the film. [DOI: 10.1143/JJAP.42.L1164] KEYWORDS: diamond, pulsed laser deposition, camphor, vacuum, room temperature

Diamond, the unconquerable and invincible, has a unique position in the world of material science because of its wide variety of applications. Synthetic diamond has been produced for the past 5 decades with high-pressure high temperature (HPHT) technology and more recently by chemical vapor deposition (CVD). The CVD process of growing diamonds can be by hot filament, microwave plasma assisted, DC plasma discharge, reactive vapor deposition and various combinations of these. In most of these processes similar substrate temperatures (around 500 C to 1000 C) are used for the growth of diamond in hydrogen ambient with a pressure of 10–50 Torr. A few attempts to synthesize diamond at room temperature have been made using laser plasma deposition,1) ion-assisted deposition,2) laser driven reaction,3) electron cyclotron resonance plasma CVD,4) rfplasma CVD5) etc. In most of the reports the precursor used were methane, acetylene or graphite in hydrogen environment or argon. But the use of any natural precursor in the growth of diamond is not yet well studied. Recently, pulsed laser deposition (PLD) was used to grow diamond films by ablating graphite target in hydrogen6) or oxygen7) ambient. But the growth temperature is as high as 450 C and 550 C, respectively. The synthesis of diamond without any gases at room temperature has not been reported so far. This paper presents the synthesis of diamond at room temperature by PLD without using any gases such as hydrogen or oxygen. Urea (CO(NH2 )2 ) doped camphoric carbon8) is used as a target. Camphor (C10 H16 O) has already been used for the production of diamond like carbon,8) fullerenes,9) semi conducting carbon,10) and nano-diamonds.11) As far as this report is concerned it is the first paper on the growth of diamonds at room temperature using a natural source, camphor. The pulsed laser deposition technique is being used here, which includes an ultraviolet excimer laser for ablation of a solid target in order to provide highly excited vapor species that are transported onto a substrate. A schematic diagram of XeCl pulsed laser deposition used in the present work is shown in the Fig. 1. Here we examined the possibility of room temperature growth of diamond film on silicon substrates by pulsed laser deposition process using a urea-doped camphoric carbon target in vacuum. The depositions were conducted in a chamber, which was evacuated to a base pressure of 

Corresponding author. E-mail address: [email protected]

Fig. 1. Schematic diagram of XeCl pulsed laser deposition used in the present work.

3:8  105 Torr. A XeCl excimer laser beam (wavelength: 308 nm, pulse duration: 20 ns, pulse energy: 240 mJ, frequency: 2 Hz, laser shots: 4800, NISSIN NEX10) was focused to the target through a quartz window. The preparation of camphoric carbon targets is described elsewhere.8,12) In brief, camphor was burnt in a quartz tube, and the soot was collected from the wall: urea was mixed (5% w/ w) in the soot, followed by making into a pellet. A pure camphoric carbon target without urea was also used for comparison. The laser-target interaction was restricted by the width of the laser beam to an area of 3:5 mm  0:5 mm with light yellow plasma plume over the camphoric soot target. The substrate, single crystal silicon of (100) orientation, was ultrasonically cleaned with acetone and methanol and then etched in 1:10 HF and H2 O for 1 min before mounting inside the deposition chamber. No pre-treatment, such as scratching or diamond powder polishing was performed for the substrate. The substrate was positioned parallel to the camphoric carbon target at a distance of 4.5 cm away. The substrate temperature was kept at room temperature (25 C) during the deposition. Hydrogen, argon or oxygen gas, which is believed to be indispensable in obtaining diamond, was not used in this experiment. Therefore, the pressure was kept constant at around ð4{5Þ  105 Torr during the deposition. The films were characterized using scanning electron microscopy (SEM) and micro-Raman spectroscopy using an Ar ion laser ( ¼ 514:5 nm).

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(b) Fig. 3. First order Raman spectra of the films deposited using urea doped camphoric carbon target (a) and pure camphoric carbon target (b).

(b) Fig. 2. SEM photographs of surface of the film on silicon substrate deposited using urea doped camphoric carbon target (a) and pure camphoric carbon target (b). Laser energy: 240 mJ, target to substrate distance: 4.5 cm and laser frequency: 2 Hz.

Figures 2(a) and 2(b) show typical SEM images of the carbon particles obtained with and without urea in the target respectively. Well faceted crystals are seen as islands in the matrix of the carbon film when the target is urea doped. In Fig. 2(a) the average size is approximately 2 mm (maximum crystallite size is 6 to 8 mm and minimum is around 0.5 mm). On the other hand, in the absence of urea doping, a kind of cluster is shown (Fig. 2(b)) and crystal facets are not observed. Micro-Raman spectroscopy was used for further characterization of the films. Figure 3(a) and 3(b) show the Raman spectra taken on a particle, with and without urea, respectively. A first order diamond peak centered at 1337.8 cm1 is observed when the target is urea doped as shown in Fig. 3(a). The full-width at half maximum is estimated to be around 2.5 cm1 , which is close to the natural diamond. Again there is a broad peak centered on 1550 cm1 indicating the graphitic carbon associated with the film, named G-peak. In the matrix, no such diamond peak at around 1337 cm1 was found. The observation of the cubic diamond peak and the Gpeak is due to diamond particles embedded in amorphous carbon. But it should be noted that the content of amorphous carbon is small because the cross-section of Raman scattering for sp2 carbon is 50–60 times larger than that for sp3 carbon.13) The positive shift of the diamond Raman peak may be due to the compressive stress created by the high-velocity

particles/ions (typical initial velocity of 106 cm/s) during deposition. Figure 3(b) shows the graphitic broad peak (G-peak) as well as a disordered carbon peak (D-peak) near the 1355 cm1 of the sample deposited without urea in the target. The peak corresponding to cubic diamond is not observed. Therefore, it should be emphasized that urea plays an important role in the formation of diamond. The interaction of laser with the target produces plasma over the target and the deposition starts from the plasma. Diamond synthesized in this study is in the form of separated islands. This may be because the amount of nitrogen present in the target is not homogeneous and its droplets condensed on the substrate and changed into diamond. The formation of diamond from droplets may be a slow process, as the localized pressure build up on the droplets by expanding particles takes time. It has been reported that a mixture of CO/O2 /H2 is suitable as precursors for synthesizing diamond at low temperature.3) Therefore it is suggested that CO and H from urea will contribute to the room temperature growth of diamond, suppressing the formation of non-sp3 carbon in this study. In the case of diamond growth by PLD in oxygen ambient also, CO molecules are believed to play an important role in the growth of diamond.14) Nitrogen from urea may also help to the growth of diamond crystals, as it has often been found in natural diamonds as an impurity and believed to abstract hydrogen from the surface via HCN formation.15) The initiations of crystal formation took place because of high velocity containing nitrogen as one of the component. Once the diamond particles are formed, they will become large during the ablation process. In order to

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understand the exact growth mechanisms further experiments are going on. Another important point in our experiments is that the diamond could be synthesized in vacuum ð4{5  105 Torr) at room temperature. As far as we know, diamond has not been synthesized on Si substrates under these conditions until now. The success in this work is due to that all the elements (C, O, N, H) necessary to grow diamond, which are usually fed by gas phase, are incorporated in the target in solid phase but the diamond growth occurred in vacuum at room temperature from the vapor droplets. The quality of diamond will be improved by optimizing the growth conditions and the amount of urea in the camphoric carbon target. Because both camphor and urea are cheap natural sources, this method will open a way to synthesize diamond at low cost in the future. In summary, the successful synthesis of diamond particles from urea-doped camphoric carbon as target at room temperature and under vacuum was achieved by PLD. The above result indicates that presence of urea is playing a major role in the growth of diamond crystals from the vapor droplets. Further investigations are going on to optimize the deposition process and to improve the nucleation density of diamond crystals in the film. The authors would like to thanks Dr. Mukul Kumar of Meijo University, Nagoya for the Raman measurement. Mr. D. K. Mishra would like to thanks the AIEJ for giving a scholarship to carry out this work. He would also like to thank the Council of Scientific and Industrial Research, New

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Delhi, India, for a fellowship and a grant to carry out this research work. 1) J. Seth, R. Padiyath, D. H. Rasmussen and S. V. Babu: Appl. Phys. Lett. 63 (1993) 473. 2) M. Kitabatake and K. Wasa: J. Vac. Sci. & Technol. A 6 (1988) 1793. 3) J. H. D. Rebello, V. V. Subramaniam and T. S. Sundarshan: Appl. Phys. Lett. 62 (1993) 899. 4) M. Zarrabian, N. Fourches-Coulon, G. Turban, C. Marhic and M. Lancin: Appl. Phys. Lett. 70 (1997) 2535. 5) G. A. J. Amaratunga, A. Putnis, K. Clay and W. I. Milne: Appl. Phys. Lett. 55 (1989) 634. 6) M. C. Polo, J. Cifre, G. Sanchez, R. Aguiar, M. Varela and J. Esteve: Appl. Phys. Lett. 67 (1995) 485. 7) M. Yoshimoto, K. Yoshida, H. Maruta, Y. Hishatani, H. Koinuma, S. Nishio, M. Kakihana and T. Tachibana: Nature 399 (1999) 340. 8) S. M. Mominuzzaman, T. Soga, T. Jimbo and M. Umeno: Thin Solid Films 376 (2000) 1. 9) K. Mukhopadhyay, K. M. Krishna and M. Sharon: Phys. Rev. Lett. 72 (1994) 3182. 10) M. Sharon, N. Sundarakoteeswaran, P. D. Kichambre, M. Kumar, Y. Ando and X. Zhao: Diamond & Relat. Mater. 8 (1999) 485. 11) K. Chakrabarti, R. Chakrabarti, K. K. Chattopadhyay, S. Chaudhuri and A. K. Pal: Diamond & Relat. Mater. 7 (1998) 845. 12) S. M. Mominuzzaman, K. M. Krishna, T. Soga, T. Jimbo and M. Umeno: Jpn. J. Appl. Phys. 38 (1999) 658. 13) N. Wada and S. A. Solin: Physica B 105 (1981) 353. 14) M. Yoshimoto, M. Furusawa, K. Nakajima, M. Takakura and Y. Hishitami: Diamond & Relat. Mater. 10 (2001) 295. 15) A. Badzian, T. Badzian and S.-T. Lee: Appl. Phys. Lett. 62 (1993) 3432.