Structure of diamond and diamond like carbon thin films grown by hot-filament chemical vapour deposition technique

Micro-crystalline diamond (MCD) and diamond like carbon (DLC) thin films were deposited on silicon (100) substrates by hot-filament CVD process using a mixture of CH₄ and H₂ gases at substrate temperature between 400–800°C. The microstructure of the films were studied by X-ray diffraction and scanning electron microscopy. The low temperature deposited films were found to have a mixture of amorphous and crystalline phases. At high temperatures (> 750°C) only crystalline diamond phase was obtained. Scanning electron micrographs showed faceted microcrystals of sizes up to 2μm with fairly uniform size distribution. The structure of DLC films was studied by spectroscopic ellipsometry technique. An estimate of the amount of carbon bonds existing insp ² andsp ³ form was obtained by a specially developed modelling technique. The typical values ofsp ³/sp ² ratio in our films are between 1·88–8·02. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Optical and mechanical properties of diamond like carbon films deposited by microwave ECR plasma CVD

Diamond like carbon (DLC) films were deposited on Si (111) substrates by microwave electron cyclotron resonance (ECR) plasma chemical vapour deposition (CVD) process using plasma of argon and methane gases. During deposition, a d.c. self-bias was applied to the substrates by application of 13·56 MHz rf power. DLC films deposited at three different bias voltages (−60 V, −100 V and −150 V) were characterized by FTIR, Raman spectroscopy and spectroscopic ellipsometry to study the variation in the bonding and optical properties of the deposited coatings with process parameters. The mechanical properties such as hardness and elastic modulus were measured by load depth sensing indentation technique. The DLC film deposited at −100 V bias exhibit high hardness (∼ 19 GPa), high elastic modulus (∼ 160 GPa) and high refractive index (∼ 2·16–2·26) as compared to films deposited at −60 V and −150 V substrate bias. This study clearly shows the significance of substrate bias in controlling the optical and mechanical properties of DLC films.     

Preparation and characterization of diamond films

Diamond films were deposited by magnetron sputtering of vitreous carbon disc and also by plasma CVD technique using C₂H₂ + H₂ or CO₂ + H₂ gas mixtures. The films were characterized by measuring the electrical, optical and microstructural properties. FTIR and Raman studies were carried out to study the effect ofsp ² andsp ³ bonds present in the films. The films had a high mechanical stress which was determined from the broadening of the optical absorption tail in the films.     

Electrical characterization of CVD diamond thin films grown on silicon substrates

Diamond thin films grown on high resistivity, 100 oriented silicon substrates by the hot filament chemical vapor deposition (HFCVD) method have been characterized by four-point probe and current-voltage (through film) techniques. The resistivities of the as-grown, chemically etched and annealed samples lie in the range of 10² Ω cm to 10⁸ Ω cm. The Raman measurements on these samples indicate sp³ bonding with a sharp peak at 1332 cm⁻¹. The surface morphology as determined by scanning electron microscope shows polycrystalline films with (100) or (111) faceted structures with average grain size of ≈2.5 μm. The through film current-voltage characteristics obtained via indium contacts on these diamond films showed either rectifying or ohmic behavior. The difference in Schottky and ohmic behavior is explained on the basis of the high or low sheet resistivities measured by four-point probe technique. 5% methane to hydrogen concentration during film growth resulted in poor surface morphology, absence of sp³ bonds, and low resistivity.     

Electron emission characterization of diamond thin films grown from a solid carbon source

Diamond films of various morphologies and compositions have been deposited on silicon substrates by a plasma-enhanced chemical transport (PECT) process from a solid carbon source. Electron emission efficiency of these diamond films is related to their morphology and composition. The electric field required to excite emission in a boron-doped polycrystalline diamond film ranged between 20 to 50 MV m⁻¹. In an undoped conducting nanocrystalline diamond composite film, the field was as low as 5–11 MV m⁻¹. The cold field electron emission of these films is confirmed from the Fowler-Nordhelm plots of the data. Enhancement of electron emission by band-bending and by the nanocrystalline microstructure are discussed. New diamond emitters made of nanocrystalline boron-doped diamond composite are proposed.     

Physical and tribological properties of diamond films grown in argoncarbon plasmas

Nanocrystalline diamond films have been deposited using a microwave plasma consisting of argon, 2–10% hydrogen and a carbon precursor such as C₆₀ or CH₄. It was found that it is possible to grow the diamond phase with both carbon precursors, although the hydrogen concentration in the plasma was 1–2 orders of magnitude lower than normally required in the absence of the argon. Auger electron spectroscopy, X-ray diffraction measurements and transmission electron microscopy indicate the films are predominantly composed of diamond. Surface roughness, as determined by atomic force microscopy and scanning electron microscopy indicate the nanocrystalline films grown in low hydrogen content plasmas are exceptionally smooth (30–50 nm rms) to thicknesses of 10 m. The smooth nanocrystalline films result in low friction coefficients (μ = 0.04–0.06) and low average wear rates as determined by ball-on-disk measurements.     

Ion beam energy effects on structure and properties of diamond like carbon films deposited by closed drift ion source

In the present study DLC films deposited from acetylene gas by a closed drift ion source were investigated. Ion beam energy effects on structure as well as optical and electrical properties of the synthesized films were studied. Non-monotonic dependence of structure of the DLC films on ion beam energy was observed. The highest sp³/sp² ratio as well as highest optical transparency was observed in the case of the films synthesized by 500 eV energy ion beam. However, the bandgap of the DLC films synthesized by 500 eV energy ion beam was the lowest between all investigated samples, while resistivity non-monotonically decreased with increase of the ion beam energy. These results were explained by changes of the sp³/sp² ratio, structure of sp² bonded clusters as well as hydrogen content in the film due to the competition between the increased (decreased) ion beam energy and decreased (increased) ion/neutral ratio.     

Evaluation of microstructures and mechanical properties of diamond like carbon films deposited by filtered cathodic arc plasma

Diamond-like carbon (DLC) films were deposited by a cathodic arc plasma evaporation (CAPD) process, using a mechanical shield filter combined with a magnetic filter with enhanced arc structure at substrate-bias voltage ranging from − 50 to − 300 V. The film characteristics were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). The mechanical properties were investigated by using a nanoindentation tester, scratch test and ball on disc wear test. The Raman spectra of the films showed that the wavenumber ranging from 900 to 1800 cm^− 1 could be deconvoluted into 1140 cm^− 1, D band and G band. The bias caused a significant effect on the sp³ content which was increased with the decreasing of I_D/I_G ratio. The XPS spectra data of the films which were etched by H⁺ plasma indicated the sp³ content are higher than those of the as-deposited DLC films. This implied that there is a sp²-rich layer present on the surface of the as-deposited DLC films. The nanoindentation hardness increased as the maximum load increased. A 380 nm thick and well adhered DLC film was successfully deposited on WC-Co substrate above a Ti interlayer. The adhesion critical load of the DLC films was about 33 N. The results of the wear tests demonstrated that the friction coefficient of the DLC films was between 0.12 and 0.2.     

Deposition of diamond like carbon (DLC) and C-N films using ion beam assisted deposition (IBAD) technique and evaluation of their properties

Diamond like carbon films and C-N films were prepared using ion beam assisted deposition technique (IBAD). Tribological properties were studied by subjecting DLC coated films to the accelerated wear tests. These tests indicated a significant improvement in the mechanical surface properties of glass by DLC coating. Better wear features were obtained for thinner DLC coating as compared to the thicker ones. We also studied the optical properties and obtained a band gap of 1·4 eV for these films. An attempt was made to prepare C₃N₄ films by using IBAD. We observed variation in the nitrogen incorporation in the film with the substrate temperature.     

Advances in piezoelectric thin films for acoustic biosensors,acoustofluidics and lab-on-chip applications

Recently, piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating, sorting/patterning, pumping, mixing, nebulisation and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these piezoelectric films onto a number of substrates such as silicon, ceramics, diamond, quartz, glass, and more recently also polymer, metallic foils and bendable glass/silicon for making flexible devices. Such thin film acoustic wave devices have great potential for implementing integrated, disposable, or bendable/flexible lab-on-a-chip devices into various sensing and actuating applications. This paper discusses the recent development in engineering high performance piezoelectric thin films, and highlights the critical issues such as film deposition, MEMS processing techniques, control of deposition/processing parametres, film texture, doping, dispersion effects, film stress, multilayer design, electrode materials/designs and substrate selections. Finally, advances in using thin film devices for lab-on-chip applications are summarised and future development trends are identified.