**2. Preperation of diamond films**

Diamond, Diamond-like carbon (DLC) and Diamond-like Nanocomposite (DLN) exist in different form of amorphous carbon based thin films have generated a great interest in the academia due to its fundamental and technological importance. The carbon materials which arises from the strong dependence of their physical properties of the ratio of

Fig. 1. Ternary phase diagram of amorphous carbons. The three corners correspond to diamond, graphite and hydrocarbons respectively, ([21], permission to reprint obtained from Royal Society London).

properties present in Diamond, Diamond-like Carbon (DLC) and Diamond-like Nanocimposite (DLN) based thin films [6-14]. The amorphous carbon films based MEMS are fully dominated the silicon-based MEMS technologies. The silicon-based MEMS with mechanical loading have lack of high fracture toughness facing with high reliability. Under some extreme conditions like very high temperature or very high particle radiation, silicon may fail to sustain these properties. However, silicon have very large coefficient of friction, high surface energy, high wear rate and small band gap energy, which cannot fulfill the all material properties of MEMS [15-18]. To overcome these drawbacks of silicon materials, researchers are continuously trying to look for new materials for MEMS applications. Ceramics (wide band gap), semiconductors (such as SiC), Polymers (PDMS, PMMA), can play important role for MEMS fabrications. Except these materials, diamond, diamond-like carbon (DLC) and diamond-like nanocomposite (DLN) etc are promising materials for MEMS applications. High elasticity and tensile strength of DLC and DLN films can suitable for high frequency MEMS devices. The temperature withstanding capability of both DLC and DLN films is up to 600 0C or slightly more. The biocompatibility of DLC and DLN films is strongly effective for biosensors in diagnostics and therapies, surface coatings for surgical instruments, prosthetic replacements etc. Chemically modified DLC and DLN surfaces can act as sensing trace of gases to detect biomolecules in biological research. We have presented a brief review about the latest properties of different amorphous carbon based diamond, Diamond-like Carbon (DLC) and Diamond-like Nanocomposite (DLN) thin films and their

Diamond, Diamond-like carbon (DLC) and Diamond-like Nanocomposite (DLN) exist in different form of amorphous carbon based thin films have generated a great interest in the academia due to its fundamental and technological importance. The carbon materials which arises from the strong dependence of their physical properties of the ratio of

Fig. 1. Ternary phase diagram of amorphous carbons. The three corners correspond to diamond, graphite and hydrocarbons respectively, ([21], permission to reprint obtained

application in MEMS/NEMS devices.

**2. Preperation of diamond films** 

from Royal Society London).

sp2 (graphite-like) to sp3 (diamond-like) bonds. The amorphous carbon is a mixture of sp2, sp3 and sp1 sites with the presence of nitrogen and hydrogen. The nitrogen free carbon films are shown in Fig. 1 on ternary phase diagram. In this figure, the phase diagram defines the regions of pure carbon (designated a-C), tetrahedral amorphous carbon (ta-C), and hydrogenerated amorphous carbon (a-C:H) with the corresponding extent of hydrogenation [19-21]. To increase the degree of sp3 carbon bonding, better amorphous carbon (a-C) films can be produced by any kind of deposition systems. If sp3 carbon bonding is very high, then this a-C can be denoted as a tetrahedral amorphous carbon (ta-C) [22]. Fig. 1 shows amorphous hydrocarbon (a-C:H) or diamond like films, but it is not higher order due to large hydrogen content. To achieve less hydrogen content with much more sp3 bond, plasma enhanced chemical vapour deposition (PECVD) technique is ideal to generate tetrahedral amorphous carbon films [20]. The sp3 content influence the mechanical properties of the films. The mechanical and wear resistance properties are more prominent with increase of hydrogen content into the films. On the other hand, surface energy and coefficient of friction decreases with greater hydrogen passivation into the films. Again, the sp2 content influences the electronic properties of the films.

Diamond, Diamond-Like Carbon (DLC) and Diamond-Like Nanocomposite (DLN) thin films can be deposited by different chemical vapor deposition technique like plasma enhanced CVD, plasma assisted CVD, microwave plasma CVD or a hot filament [23-27], ion beam deposition, pulsed laser ablations, filtered cathodic arc deposition, magnetron sputtering etc. The DC plasma jet chemical vapor deposition can be used for Diamond like carbon films deposition also [28]. Table 1 shows the different properties of diamond films [29-31, 6].


Table 1. Different parameters of Diamond, Diamond-Like Carbon (DLC) and Diamond–Like Nanocomposite (DLN) thin films.

In this section, we describe diamond-like carbon deposition by plasma which consists of argon (99.998%), hydrogen (99.9%) and CH4 (99.5%) is used as a carbon source and is mixed into the plasma jet. The plasma jet is sprayed onto a substrate fixed on a water-cooled substrate holder. The hydrocarbon species in the gas phase for the CH4-Ar-H2 gas system, temperatures (500 0C to 6000 0C) and a total pressure of 0.25 atm (25 KPa) has been computed using the thermodynamic computer program. The deposition was performed on Si(111) surface with the growth rate 80 μm/hr The CH4/H2 gas ratio and substrate temperature influence the properties of diamond. Fig. 2 shows the Scanning Electron Microscopy (SEM) morphology of DLC thin films [28]. Diamond-like Carbon (DLC) and Diamond-like Nanocomposite (DLN) are is basically amorphous carbon based films. In amorphous carbon structure, there is a possibility to form both threefold coordinate (sp2 site) as in graphite and fourfold coordinate (sp3 -site) as in diamond [32]. Each of the four valance electron lies in the sp3 -site forms σ-bonds with neighbors [33]. In sp2-site, only

Diamond, Diamond-Like Carbon (DLC)

Institute of Physics (AIP)).

**Transmittance (a.u)**

Fig. 4. FTIR spectra of DLN films.

mainly comprise of the a-C:H and a-Si:O networks.

and Diamond-Like Nanocomposite (DLN) Thin Films for MEMS Applications 463

films are given in Fig. 4 The main absorption band is the Si-C stretching in 750-800 cm-1 due to Si-(CH3)3 vibration. Strong Si-O (Si-O-H) stretching in the range of 850-1000 cm-1 is due to Si-(CH3)2 vibration. A very weak C=C stretching peak appears in the range of 1560 cm-1, which indicates non graphite bonding of carbon [38]. The Si-H absorbance band appears in the range 2200 cm-1 region. C-H stretching band appears in 2850 cm-1 -3100 cm-1 region. This type of stretching is very important for DLN films. In DLN films CO2 vibration appears due to atmospheric carbon present during experiment, and N-H vibration in 3450 cm-1 region is due to presence of nitrogen in the precursors. Here C-H stretching and Si-O stretching

 Fig. 3. HRTEM image of DLN films on silicon substrate (a) HMDSO precursor (Left fig.) (b) HMDSN precursor (right fig.), ([6], permission to reprint obtained from American

**800 1600 2400 3200 4000**

**W avenumber (cm -1)**

**C-H stretching Si-H stretching**

**C=C stretching**

**Si-O stretching**

**Si-C stretching**

**N-H stretching**

three electrons are used in σ-bonds and the forth electron forms a π-bond, which lies normal to the σ -bonding plane. In sp2 -site, only the π-bond is weakly bonded, and hence, it usually lies closest to the Fermi level and controls the electronic properties of the lms. On the other hand, in sp3 -site, the σ-bond controls the mechanical properties of the lms [34]. These electrical and mechanical properties are very important parameters for every DLC and DLN based materials.

Fig. 2. SEM micrographs of diamond film surfaces deposited at different CH4/H2 ratios. (a) 1% (b) 2%, (c) 5% and (d) 8%. ( ▬ Scale bar 20 µm for all figures), ([28], permission to reprint obtained from Elsevier).
