Deposition of ni ti n coatings by a plasma assisted mocvd using an organometallic precursor

Micro and Nanosystems, 2012, 4, 199-207 199

1876-4037/12 $58.00+.00 © 2012 Bentham Science Publishers

Deposition of Ni/TiN Composite Coatings by a Plasma Assisted MOCVD Using an Organometallic Precursor

S. Arockiasamya*, T. Maiyalaganb, P. Kuppusamic, C. Mallikad and K.S. Nagarajae

aVIT University Chennai Campus, Chennai-600 048, Tamil Nadu, India bSchool of Chemical and Biomedical Engineering, Nanyang Technological University, 70 Nanyang Drive Singapore - 639798cPhysical Metallurgy Division, Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam-603 102, Tamil Nadu, India dRRDD, IGCAR, Kalpakkam-603 102, Tamil Nadu, India eLoyola College, Department of Chemistry and LIFE, Chennai-34

Abstract: Titanium nitride (TiN)/nickel (Ni) composite coatings were synthesized by plasma assisted metal-organic chemical vapour deposition (PAMOCVD) using organo-metallic and metal-organic complexes namely dichlorobis(�5-cyclopentadienyl)titanium (IV) for titanium and N,N'-ethylene-bis(2,4-pentanedion-iminoato)nickel(II) for nickel. The growth of such films was investigated in nitrogen (N2) plasma environment in the substrate temperature range of 450-550ºC at a deposition pressure of 0.5-1 mbar. Prior to the deposition of films, the Ti precursor was subjected to the equilibrium vapour pressure measurements by employing TG/DTA in transpiration mode, which led to the value of 109.2 ± 5.6 kJ mol-1 for the standard enthalpy of sublimation (�Ho

sub). The phase identification using glancing incidence x-ray diffraction showed Ni/TiN is a nanocomposite coating containing nanocrystals of Ni and TiN with face centered cubic structure. Scanning electron microscopy revealed a uniform surface morphology of the films, while chemical analysis by energy dispersive analysis confirmed the presence of titanium, nickel and nitrogen in the composite films.

Keywords: Chemical vapour deposition, nano-composite, nickel, titanium nitride, metallic Ti, thin films, vapour pressure.

1. INTRODUCTION

Research in hard coatings for components used in heavy engineering, automotive and aerospace has evolved from the single phase coatings (TiN, CrN etc.,) to multilayered to nano-composite coatings. Titanium nitride (TiN) is a refractory, gold-coloured material that has found use in decorative and mechanical wear-resistant coatings and in microelectronic circuits [1, 2]. The cubic TiN phase exhibits metallic behaviour, extreme hardness, high melting point (3000oC), remarkable chemical resistance (e.g. inert to organic solvents and inorganic acids), and low temperature superconductivity [3, 4]. But due to porosity, internal stress and poor adhesion, TiN coating alone cannot be used for corrosion protection and the corrosion resistance of hybrid coatings such as Ni-P/TiN have been found to be better than the individual counterparts [5].

Such type of nano-composite coatings or hybrid coatings have been prepared by several techniques such as, electroless plating prepared by dc magnetron sputtering [5,], ultrasonic electrodeposition [6, 7], ion beam sputtering [8], dc magnetron sputtering [9] and high speed jet electroplating [10]. Similar to Ni/TiN, nano-composite coating of ZrN/Cu is also found to exhibit superior hardness [11]. In most cases,

*Address correspondence to this author at the VIT University Chennai Campus, Chennai-600 048, Tamil Nadu, India; Tel: +91-44-3993 1233; Fax: +91-44-3993 2555; E-mails: [email protected], [email protected]

the nickel is electroless plated first on the surface of the substrate to be protected from corrosion and then TiN coating is sputter deposited. Chemical vapour deposition (CVD) is known for conformal coverage, flexibility towards the shape of the substrate, including the capability to create films on the inner surface of pipes and on flexible substrates, and high quality of the products with good adhesions. These advantages make the CVD techniques more relevant for any practical applications [12]. High quality thin films could be obtained by employing metallo-organic CVD (MOCVD) and atomic layer deposition (ALD) among other techniques [13]. MOCVD is a special case of CVD in which one or more of the gas-phase precursors are metallo-organic compounds, whose flow and mixing can be controlled to get composite coatings [14].

We have reported the synthesis and microstructural properties of Ni/TiO2 recently [12]. In the present investigation we have reported the deposition of Ni/TiN nano-composite thin-film by employing plasma assisted CVD using the combination of metallo-oranic and organo-metallic complexes as source materials for Ni and TiN respectively along with the vapour pressure study of Ti precursor. Though there are a few reports on the development and application of Ni/TiN composite thin films prepared by host of physical techniques [5-10], no report could be traced for the simultaneous vapour phase deposition of Ni/TiN by a Plasma Assisted Metallo Organic CVD (PAMOCVD) or plasma assisted organo-metallic CVD (PAOMCVD) using a metallo-organic nickel complex and

200 Micro and Nanosystems, 2012, Vol. 4, No. 3 Arockiasamy et al.

an organo-metallic titanium complex as precursors. However, for a successful deposition of thin films for industrial applications using CVD, it is necessary to have a precursor which is commercially available at a reasonable price, has sufficient thermal stability and vapour pressure and good shelf life. Therefore, the decomposition and thermal stability of the precursor of Ti complex is also investigated.

2. EXPERIMENTAL PROCEDURES

2.1. Non-Isothermal TG/DTA of Ti Complex

Thermo-gravimetry (TG) was used to study the decomposition pattern of Ti complex because it can throw light on thermal stability, melting, decomposition and more importantly volatility which is a primary condition for chemical vapour deposition. TG was recorded in an inert atmosphere like argon or nitrogen with a heating rate of 10°C min-1 to avoid oxidation of the complexes. The calcined �-alumina powder of even weight was used as the reference.

The dynamic TG runs on all the compounds were recorded at a linear heating rate of 10oC/min using a thermo-analyser (Perkin-Elmer, Pyris-Diamond). High purity nitrogen/argon (purity >99.99%) dried by passing through refrigerated molecular sieves (Linde 4A) was used as the purge gas. The complex was dried under vacuum with anhydrous calcium chloride as a desiccant prior to the TG runs. Sample weighing 1.579 mg was loaded in an �-alumina crucible (5m�5 mm x mm) and placed in the sample pan and was subsequently dried in situ at 50oC for a few minutes to remove adsorbed moisture, if any. The purpose of the runs was to observe the mass loss steps besides identifying the final temperature for attaining nil residue or constant weight or decomposition pattern.

2.2. Vapour Pressure Measurement of Ti Complex

Prior to the deposition of the thin films using OMCVD, vapour pressure measurement of dichlorobis(�5-cyclopentadienyl)titanium (IV) or titanocene dichloride (Ti(Cp)2Cl2) complex was carried out using the TG-based transpiration technique. The block diagram of the thermo-analyser, modification for its functioning in the transpiration mode, including precise flow calibration of the carrier gas, using a capillary glass flow meter and corrections for apparent weight losses in isothermal modes have been described elsewhere [15]. The configuration of the thermo-analyser with horizontal dual-arm single-furnace has eliminated/minimized the apparent weight changes caused by temperature gradients, convection currents within the furnace tube (made of alumina), buoyancy, thermo-molecular drag and electrostatic effects. The arms of the thermo-balance served as the temperature-cum-DTA sensors. The calibration of the R-type thermocouple (Pt-13%Rh/Pt) was carried out using the recommended melting point standards (such as indium and tin) in order to make the T-scale of the balance conform to the International Practical Temperature Scale 1968 (IPTS-68) amended in 1975.

Heating the furnace to 900oC at a rate of 15oC/min under nitrogen gas at the purge rate of 12 dm3h-1 and then cooling under the same conditions to near-ambient temperature (about 40oC) was done for heat cleaning the furnace before every vapour pressure measurement. Thereafter, the samples,

finely powdered using an agate mortar and pestle, weighing in the range of 40-46 mg were spread out on a shallow alumina crucible mounted for vapour pressure measurements and was carefully flushed with nitrogen at a rate of 6 dm3h-1

at ambient temperature. The initial heating to just below 10oC of the actual vapour

pressure measurement temperature for all the complexes was rather rapid (10oC/min). After the stabilization of the temperature, the complexes were heated at 2oC/min in steps of 10oC to the respective isothermal temperatures. The flow rate of 6 dm3h-1 for nitrogen gas was employed to ensure isothermal equilibrium vapourisation in all the isothermal steps. The flow rates were monitored by a mass flow controller (model-MKS, Type 1179A, USA). The accuracy of the temperature measurements was adjusted to be better than ±0.05 K, using the recommended melting point standards namely indium, tin and aluminium. The reproducibility of the T-scale was assessed to be better than ±0.2 K.

2.3. Designing of Plasma Assisted CVD System

PAOMCVD was performed in a custom built dual wall semi-cylindrical chamber made up of type 304 stainless steel with an internal diameter of 430 mm and a height of 310 mm (Fig. 1). The chamber of the PAOMCVD was evacuated using a rotary pump (model VT-4012; Vacuum Techniques, India) connected to one port and the electrical connection to substrate heater and thermocouple were connected to the other two ports. The port at the back was for the line which carried the complex vapour and the other port at left was to pass the by-pass gas. The two ports at the right hand side were used to monitor the vacuum and air leaking respectively. A pair of parallel plate circular electrodes of diameter of 270 mm, made of stainless steel was used to establish the symmetric reactor. The bottom grounded electrode worked as a substrate holder as well. The diameter of the substrate platform was large enough, so that 13 wafers of 2 inch (50 mm) can be processed at a time. The heater (halogen lamp of 800W) provided at the bottom of the lower electrode served the purpose of heating the substrate.

Pulsed plasma source (ENI, RPG 50, 5000 W, USA) connected to the upper electrode was used to sustain the plasma in the reactor at 100 kHz with pulse time of 2976 ns. The power of the plasma were varied by changing the voltage and current. Four mass flow controllers (MFCS) (MKS, type 1179A, USA) were used to control and monitor (using four channel readout, MKS, type 247, USA) the flow of various reactant gases like nitrogen, argon and hydrogen. By-pass gas flow was attached with two 100g capacity precursor tanks and a mixing chamber, which facilitated the heating of precursors separately and mixing them in the vapour phase prior to their entry into the CVD chamber. Temperature controllers (Eurotherm) were used to control/monitor the temperature of the substrate, precursor chambers and vapour line by using K-type thermocouple.

2.4. Deposition and Characterization Methods

It is deemed as essential to optimize the process parameters since they play a vital role in determining the composition and properties of the thin film grown by CVD [16]. Therefore, various process parameters such as chamber pressure, substrate temperature, precursor chamber

Deposition of Ni/TiN Composite Coatings by a Plasma Assisted Micro and Nanosystems, 2012, Vol. 4, No. 3 201

temperature (based on the temperature of melting and congruent sublimation of precursor), carrier gas flow rates, pulsed plasma power, inter-electrode distance were optimised by carrying out repeated trial and error experiments for the deposition of Ni/TiN composite films. The optimised deposition conditions for the coating of Ni/TiN thin-films are summarized in Table 1.

The solid precursor of nickel, namely N,N’-ethylene-bis(2,4-pentanedione-iminoato)nickel(II), Ni(acac)2en was synthesized at the laboratory scale and was used for the deposition of Ni/TiN thin film. The commercial grade organo-metallic, dichlorobis(�5-cyclopentadienyl)titanium

(IV), Ti(Cp)2Cl2 was used as titanium precursor. The choice of Ti(Cp)2Cl2 as vapour source of titanium stems from the fact that it does not contain any oxygen atom in its ligand moiety and could be considered as a precursor of the deposition of non-oxygen-based thin films of titanium. A solid metallo-organic precursor was chosen for its thermal stability, sufficient volatility, less toxicity and easy handling. The silicon wafers with <100> orientation and metallographically polished (with 0.2 �m roughness) stainless steel (SS) substrates were used after ultrasonic cleaning by acetone and methanol. Substrates of dimension of 10 mm�10 mmx0.5 mm were loaded in the chamber and the chamber was evacuated to a base pressure of 30�10-3 mbar. After the initial evacuation of the CVD chamber, a base pressure value of 1.2�10-1 mbar was obtained by discharging nitrogen gas through the bypass line to strike the plasma in the deposition zone. The temperature of the substrate (Ts) was then increased slowly to the desired value of 550oC at a heating rate of 12.5oCmin-1 and it was maintained constant during the course of the complete deposition process. When the temperature reached a value of 100oC, plasma was created in the chamber by applying high voltage between the two electrodes. This helped in surface etching of the substrates. After reaching the desired substrate temperature of 550oC, the temperature of the line heater was increased slowly and maintained in the range of 200-210oC for most of the depositions. This followed the heating of the precursor chambers. After reaching the vapour flow zone, the rate of increase in the temperature was kept rather low in order to ensure complete vapourisation and transportation of precursors vapour continuously to the CVD chamber. This helped in achieving uniform thin-film coating over the substrates. After all the vapour was consumed, the supply of carrier gas was stopped and the high temperature valve (Swage Lock, SS-4BW) was closed to arrest vapour flow. The flow through the by-pass was continued until the samples were cooled down to room temperature in a reactive plasma environment.

The thickness of the films was measured by Sloan-Dektok-3010 surface profilometry. The deposited films were

Fig. (1). Schematic diagram of the PA-MO(Organo Metallic)CVD system used in the present study.

Table 1. Typical Growth Parameters for the Deposition of Ni/TiN Nanocomposite Coatings using [Ti(Cp)2Cl2]for Ti and Ni(acac)2en for Ni as Vapour Sources

Precursors for Ti Cp2TiCl2

Precursors for Ni Ni(acac)2en

Substrate temperature 550oC

Colour of the coating Golden Yellow

Substrates SS 316 and Silicon (100) oriented wafer

Pulsed DC voltage 201 V

Plasma current 150 mA

Electrode distance 45 mm

Base vacuum 220 x 10-3 mbar

Deposition pressure 0.5-1 mbar

Precursor chamber temperature 150-250oC

Temperature of line heater 195-205oC

Gas flow rate Carrier gas: nitrogen, 50sccm By-pass gas: nitrogen, 200sccm

Deposition time 60 min

Growth rate 0.5�m

N2

ArH2

MFC4

MFC

1MFC2

MFC3

Mixing Chamber

Cathode

Anode

Exhaust

HT Valve

Valves RotaryPump

Gas in

View port

Butterfly Valve

PC1 PC2

PrecursorPellets

Cold Trap

By-Pass line

Vapour line

Temperature-controlled region

PC = Precursor Chamber

MFC = Mass Flow Controller

Substrates

CVD Chamber


characterized by glancing incidence x-ray diffraction (GIXRD) by employing STOE high-resolution X-ray diffractometer with CuK� (� = 1.5406 �) radiation and the scan was performed in 2 mode over a 2 range of 20-80o.For all the measurements, the angle of incidence of X-rays was kept at 0.3o. The surface morphology of the films was examined using a Philips XL-30 scanning electron microscope equipped with an energy dispersive X-ray (EDX) spectrometer.

3. RESULTS AND DISCUSSION

3.1. Thermal Analysis and Vapour Pressure Measure-ments of the Precursor

The compound bis(5-cyclopentadienyl) titanium (II) chloride, Ti(Cp2)Cl2 was found to satisfy almost all the conditions for a ideal precursors [17, 18] and hence chosen as the precursor for the deposition of Ni/TiN thin film using CVD. The thermal analysis and vapour pressure measurements of nickel complex namely, N,N’-ethylene-bis(2,4-pentanedione-iminoato)nickel(II), Ni(acac)2en used in the present investigation for the co-deposition of Ni/TiN has been reported earlier from our group [19, 20].

The crucial test for any precursor is its thermal characterization and hence Ti(Cp)2Cl2 was subjected to thermal analysis. The recorded TG/DTA graph using a horizontal dual arm single furnace thermo-analyser at a heating rate of 10oC/min using high purity (99.99%) N2 as a purge gas is produced in Fig. (2). The thermal behaviour of Ti(Cp)2Cl2 as observed from Fig. (2) shows that the compound is thermally stable up to a temperature of 191oCand looses only 3% (0.5H2O), which could be ascribed to the evaporation of adsorbed moisture and not due to the loss of any component from the compound. It undergoes vapourisation after melting at 267oC as evidenced by a small endotherm in DTA. The melting temperature, volatility and

the complete thermal history of this compound as the precursor for CVD have been corroborated by the earlier investigation [21] including its mass spectral study confirming its molecular weight of 248Da. For a solid or liquid compound to be really suitable for CVD, it should exhibit thermal stability under a variety of ambient, sufficient volatility and good gas phase transportability (vis-à-vis higher vapour pressure) [22, 23] for maintaining adequate feed stock of the precursor.

In the present work, the vapour pressure measurement of Ti(Cp)2Cl2 was carried out in the temperature range of 402-485 K (129-212oC). The equilibrium vapour pressure (pe)(Table 2) could be calculated using the following relation,

pe = WRT/MVc (1)

derived from Dalton’s law of partial pressures for a mixture of ideal gases, where W is the mass loss (mg) at temperature

Fig. (2). Non-Isothermal TG/DTA of Ti(Cp)2Cl2 compound.

Table 2. Equilibrium Vapour Pressure of Titanium CompoundAgainst the Temperature

s. no T (K) W (mg) Pe (Pa)

1234

56789

10

11

402.18 412.44 422.82 433.21

443.54 454.01 464.34 474.92 485.30 495.64

506.16

0.0048 0.0130 0.0249 0.0472

0.0983 0.2067 0.4513 0.8624 1.3444 1.8829

2.7060

0.011 0.029 0.058 0.113

0.242 0.522 1.166 2.279 3.631 5.194

7.623


T(K) due to vapourisation, Vc (dm3) is the integral volume of the carrier gas, R is the Gas constant (8.314 J mol-1 K-1)and M (g mol-1) is the molar mass.

When the Eq. 1 is used, it is implied that only a single metal precursor species is present in the vapour phase and the congruent nature of vapourisation is confirmed by TG/DTA under equilibrium condition. The monomeric nature is confirmed by their mass spectral analysis [18]. Attainment of equilibrium conditions was evident from the isothermal-time against mass loss plots (not exceeding 10% of initial mass) at all the isothermal steps as seen from the straight line plots (as shown in Fig. 3) passing through the origin showing equal masses are vapourised in equal intervals of time. The Clausius-Clapeyron plot of log (pe)against the reciprocal temperature (1/T) is shown in Fig. (4).

The temperature dependence of pe could be represented by the least squares expressions

log (pe/Pa) =(15.23±1.27)(A)–(5704.7±53.7)(B)/T(K) (402-506 K) (2)

Multiplying the slope (B) of the equation 2 by –2.303 R, a value of 109.2 ± 5.6 kJ mol-1 could be derived for the standard enthalpy of sublimation, �Ho

sub for the Ti compound. A higher entropy of vapourisation and lower enthalpy of sublimation would both contribute to higher vapour pressure (e.g., pe = 7.62 Pa at 506 K) at constant temperature as observed in the present investigation. The higher value of sublimation enthalpy is an indicative of moderate sublimation/volatilisation behaviour of any compound. The sublimation studies are restricted to a maximum temperature of 233oC (506 K). This restriction stems from the fact that the values of pe approach the upper periphery of applicability of the TG-based transpiration technique which could not be fit into the linear regression equation plot. The restriction in the temperature for both

Fig. (3). Plot of mass loss against isothermal time for each 1h holding during the vapour pressure measurement of Ti(Cp)2Cl2 compound.

Fig. (4). Clausius-Clapeyron plot for the Ti compound.

0 10 20 30 40 50 60

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

Mas

s lo

ss (m

g)

Time (min)

T (K) 402.18 412.44 422.82 433.21 443.54 454.01 464.34 474.92 485.30 485.64 506.16

1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.60.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0 R2 = 0.995

log

p e

1000 K/T


vapour pressure measurement and for the deposition of films by heating Ti(Cp)2Cl2 well below 280oC was also evident from the fact that the complex releases HCl in the vapour phase beyond 290oC [21].

3.2. Characterisation of Ni/TiN Thin Film

The conventional XRD and GIXRD patterns of Ni/TiN composite thin film deposited under nitrogen plasma at a substrate temperature of 550oC are shown in Figs. (5 and 6), respectively, which reveal the crystalline film structure indicated by the strong reflections from fcc phases TiN and Ni. Both the patterns indicated the preferred orientation for (200) reflection. Since the thickness of the films is ~500 nm, we could not see any reflection from the substrate. Since GIXRD could probe the surface of the film better, additional peaks from metallic Ti was also seen. The observation of TiN (200) textured orientation in the present investigation could be due to the deposition of thin-films with higher energy (but low temperature) produced by the electrons of the plasma. This observation was corroborated by the

predominant formation of (200) orientation than (111) for TiN, when deposited using ammonia and nitrogen plasma by Weber et al. [24]. It is reported [25] that the microstructure of Ni/TiN coatings deposited by magnetron sputtering has a strong dependency for a bias voltage. At the higher bias voltage (higher energy), there was a more rapid change of orientation from (111) to (220) for TiN [25].

The size of the crystallite of Ni and TiN in the composite Ni/TiN film was evaluated from the full width at half maxima of the TiN (200) and Ni(200) peaks of the X-ray diffraction using the Debye-Scherrer formula (D = 0.9�/�cos�B, where D is size of the crystallite, � is the wavelength of the radiation used (in the present case CuK�of � = 0.15418 nm), � is the full width at half maxima (FWHM) of the peak measured at the Bragg angle, �B). It must be noted that the calculation of crystallite size did not take instrumental broadening and strain into consideration. The Ni/TiN thin film deposited at 550 °C (Fig. 5) showed crystallite sizes of 12.1nm for TiN(200) and 15.5 for Ni(200).

Fig. (5). XRD pattern of Ni/TiN thin-film deposited on Si (100) substrate at 550oC; For TiN: JCPDS 381420 and Ni: JCPDS 040850.

Fig. (6). GIXRD of Ni/TiN thin film deposited at 550oC on Si (100) substrate.

40 60 80 1000

25

50

75

100

125

TiN (400)Ni (311)TiN (311)

Ni (200)

TiN (200)

Inte

nsity

2 theta


The surface morphology and microstructure of thin films depend closely on the deposition kinetics and substrate temperature. The composite thin films of Ni/TiN were analysed for their microstructure using SEM and EDX and are shown in Figs. (7 and 8), respectively. The microstructure analysis of the thin film confirms the densely packed particles when deposited using high energy plasma at 550oC. It also reveals the nano-crystalline Ni/TiN grains which are aggregated significantly. The EDX spectrum of the composite film confirmed the chemical composition of the thin films due to Ti, Ni and N only. Contamination of Cl in the films was not noticed since the temperature of the precursor chamber was maintained at about 290oC, a temperature at which the compound could release HCl vapour [21].

The TiN hard coating is resistant to chemicals and is used in aerospace turbine engines. Aircraft engines can be made more efficient by operating at higher temperature. Fomblin Z

(a linear perfluoropolyalkylether (PFPAE), -CF3O[CF2CF2O]n-[CF2O]m-CF3; n/m=1.5) is a candidate oil which can be operated at higher temperature, of 370oC [26], but it chemically reacts with steel surfaces causing corrosion. While surface chemistry controls the reactions between PFPAE and TiN or Ni/TiN, the coating microstructure is also extremely important for determining its protective capability. A porous coating with columnar microstructure would provide little protection [25]; fluid could penetrate the steel surface and cause corrosion. A fully dense composite coating with fine-grained microstructure would be the best to prevent fluid penetration. Hence, the deposition of composite thin-films using high energy plasma, which could enhance the corrosion resistance nature of TiN has great industrial importance.

It must also mentioned that the strength and hardness of the TiN thin-film could be increased by forming two-phase nanostructure or multilayer thin-films, which help in

Fig. (7). SEM picture of Ni/TiN thin-film deposited at 550oC on Si(100) substrate in N2 plasma.

Fig. (8). EDX spectrum of Ni/TiN thin-film deposited at 550oC on Si (100) substrate.


restricting the movement of dislocations. In multilayers, dislocations are prevented from crossing from one layer to the next by interfaces at layer thicknesses below a few nm due to Kohler effect [27-31], which states that the dislocation occurs from layers with higher elastic modulus at a layer thickness below 10 nm [29, 30] or by a field of coherent compressive/tensile stress originating from lattice mismatches at layer thickness below 5 nm [30]. These concepts were employed to increase hardness and toughness, which was achieved in so-called super modulus [32] and super lattice [33] multilayer coatings. Though no nanomechanical properties have been reported in the present work, it is proposed that the nanocomposite materials such as Ni/TiN could be designed through the plasma assisted CVD technique to create super hard coatings [34, 35]. Though such coatings have been in practice by magnetron sputtering, the present work provides a means to coat on objects with irregular geometries and holes.

4. CONCLUSIONS

1. The Ni/TiN nanocomposite thin film deposited by PAOMCVD showed the formation of fcc structured TiN and Ni with (200) as the preferred orientation.

2. In the present investigation Ni/TiN film of about ~500 nm are obtained using the oxygen free precursor, titanocene dichloride by using N2 plasma. This could be ascribed to the efficiency of the plasma, in, enhancing molecular dissociation and producing free radicals to stimulate the chemical reactions in the CVD chamber.

3. The particle sizes of the Ni and TiN in the thin film are found to be 15.5 and 12.1 nm respectively.

4. The titanium and nickel complexes exhibited good/sufficient volatility to be used as precursors for MO(OM)CVD. The titanium compound Ti(Cp)2Cl2

which was stable up to a temperature of 191oC with a weight loss of about only 3% yielded a value of 109.2 ± 5.6 kJ mol-1 for the standard enthalpy of sublimation by a TG-based transpiration method.

CONFLICT OF INTEREST

The author confirms that this article content has no conflicts of interest.

ACKNOWLEDGEMENT

Declared none.

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Received: February 07, 2012 Revised: March 09, 2012 Accepted: May 14, 2012

Education

Deposition of ni ti n coatings by a plasma assisted mocvd using an organometallic precursor