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STUDIA UBB CHEMIA, LVI, 3, 2011 (p. 257 – 265) EFFECT OF CATALYST LAYER THICKNESS ON GROWTH OF CVD DIAMOND FATEMEH SHAHSAVARI a, b , MAHMOOD GHORANNEVISS a, † , ZAHRA KHALAJ a , MIRCEA V. DIUDEA c ABSTRACT.Tungsten Nanocrystalline Diamond (NCD) films were grown on silicon substrates by Hot Filament Chemical Vapor Deposition (HFCVD) method using three different catalyst layer thicknesses. At first, the silicon substrates are ultrasonically cleaned in acetone; ethanol and demonized water for 15 minutes in each step to remove organic contaminants, then gold layers were deposited on silicon substrate by DC magnetron sputtering. Nitrogen gas 80 Sccm was introduced into HFCVD chamber for 40 minutes and the growing process were done in a mixture of CH 4 /H 2 for 75 minutes. Crystal structure investigations were carried out by X-ray diffraction (XRD) measurements for deposited films. The XRD spectra of the NCD films demonstrated different diffraction peaks for different catalyst layer thicknesses that confirmed the presence of crystalline diamond. Morphology of the diamond films were investigated by scanning electron microscopy. The thickness of the gold nanolayer of each substrate was measured by DEKTAK surface profile measuring system. Keywords: Nanocrystalline diamond films, Catalyst, Hot filament CVD, Etching. Introduction Synthesis of diamond films by chemical vapor deposition (CVD) have been extensively studied during the last decades because of their unique properties and potential applications in mechanics, optics and electronics [1-7]. Diamond films could be produced by various chemical vapor deposition (CVD) methods, including microwave plasma [8-12], hot filament [13-17], arc plasma jet system [18-20] and magnetically enhanced radio frequency assisted plasma [21-22] methods. Among these methods, hot filament chemical vapor deposition (HFCVD) has been one of the most common methods for synthesis of diamond films. a Plasma Physics Research Center, Science and Research Branch, Islamic Azad University,Tehran,Iran.P.O.Box:14665/678 b Eghbal Techno-Center, Yazd Scientific and Technology Park,Yazd, Iran c Faculty of Chemistry and Chemical Engineering, Babes-Bolyai University, Cluj, Romania † E-mail address: Ghoranneviss@gmail.com
FATEMEH SHAHSAVARI, MAHMOOD GHORANNEVISS, ZAHRA KHALAJ, MIRCEA V. DIUDEA During the HFCVD system, various gas species formed on and near the filament which their transport to substrate play an important role in growing of diamond film [17]. Therefore the parameters, such as the gas pressure [16- 17, 23], the temperature of filament and substrate [24-28], the composition of the source gas [13, 16, 29-30] play an important role in CVD diamond growth. Another important part in growing of CVD diamond deposition is nucleation. Various nucleation processes were used such as bias enhanced nucleation (BEN) [24, 31-33], seeding the substrates by scratching with diamond powder, and ultrasonic agitation of substrate with diamond powder [16, 34-36]. It can also be done by etching gas [37]. In the present work, nitrogen used as etching gas to provide suitable nucleation sites for growing nano diamonds. Using catalyst nano layer, is a useful method to reduce the time from over than four hours to about one hour in HFCVD systems [16], so we used catalyst nano layer to reduce time into around one hour. To study the effect of different catalyst layer and find the best catalyst thickness layer on the growth of NCD films, different catalyst nano layer’s thickness were deposited on the substrates. The XRD spectra of the NCD films demonstrate different diffraction peaks for different catalyst thicknesses layer which confirm the presence of crystalline diamond. Scanning electron microscopy (SEM) shows the various morphologies of the films. RESULTS AND DISCUSSION 1. Catalyst Layer Thickness Measurements The thickness of the catalyst nano layer varied within the range of 21.6-62nm. The Fig. 1 shows the thickness measurement of the catalyst nano layer for the three samples by Dektak3 profilometer. Fig.1 (a) shows the 21.6 nm thickness for the first sample. Fig. 1(b) and Fig. 1(c) corresponded to second and third sample with thickness of 49 and 62.4 nm for catalyst layer, respectively. These three samples were named A, B and C, respectively. 2. Morphology study Fig. 2 shows the SEM morphology of the NCD films deposited at different layer thicknesses of the catalyst. The morphology of the samples are similar, as shown in the Fig. 2, revealing diamond films with cauli-flower like structure. A wide dispersion of NCD structures were observed in sample A with a lowest thickness layer (Fig.2a). By increasing the catalyst thickness layer to 49nm in sample B, the film morphology became denser and smoother and the whole surface is covered by diamond film (see Fig. 2b). In the sample C with the highest catalyst thickness layer, the crystal size increased around 200nm (see Fig. 2c). In Fig. 2c there is also changes in nucleation density and the films became less dense. For comparing the 258
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CHEMIA 3/2011
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CORINA COSTESCU, LAURA CORPAŞ, NIC
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Studia Universitatis Babes-Bolyai C
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MONICA BAIA, MONICA SCARISOREANU, I
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STUDIA UBB CHEMIA, LVI, 3, 2011 (p.
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