Daniel H. C. Chua

On the nature of carbon nitride nanocrystals formed by plasma enhanced chemical vapor deposition and rapid thermal annealing

Using high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy, carbon nitride nanocrystals were observed in films deposited by RF plasma-enhanced chemical vapor deposition (RF-PECVD) followed by a rapid thermal annealing (RTA) to 1000°C. The (30±10) nm crystals are embedded in an amorphous matrix, and the interplanar lattice spacings suggest that the crystals are the hexagonal β-carbon nitride phase. Investigations using Fourier transform infra-red spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) of the films show that RTA increases the sp3 content of the films but decreases the Cue606N (nitrile), N–H and C–H content.

Mechanism behind the surface evolution and microstructure changes of laser fabricated nanostructured carbon composite

Many studies have shown that amorphous carbon films with reduced internal stress, improved adhesion strength, and diversified material properties are obtainable through doping process, but the presence of dopants was reported to promote surface evolution and alter the microstructures of carbon matrix. By combining analyses from experimental results and theoretical estimations, this work examines the mechanism behind the surface evolution and microstructural changes in laser fabricated nanostructured copper-carbon composite. We showed that the presence of metal ions during laser deposition increased the heat dissipation on carbon matrix, which enhanced the formation of nanoislands but graphitized the carbon matrix. In addition, theoretical estimations and XPS hinted that the presence of energetic species may force the carbon ions to react with the substrate interface and form silicon carbide bonds, which contributed to the improved adhesion strength observed in copper doped carbon films, along with a reduc...

Optical and electrical properties of amorphous carbon films deposited using filtered cathodic vacuum arc with pulse biasing

Passive devices using metal containing amorphous (a-C) films have been successfully fabricated. However, difficulties in the etching of these films as well as their inferior inertness compared to pure a-C films led us to study the electrical and optical properties of pure a-C films. The films were deposited using a filtered cathodic vacuum arc system (FCVA) in conjunction with high substrate pulse biasing. It is possible to control the sp2 content and hence the properties, by varying the substrate pulse bias voltage. In this study, the a-C films were prepared by varying the high substrate bias between 3 and 11 kV using a Plasma immersion ion implantation (PI3) system. Characterization of these samples gives us an indication about the suitability of the films for integrated passive devices and other applications. Four-point probe measurement has been carried out to study the resistivity of the films deposited on quartz and SiO2. The resistivity decreases with increasing pulse bias voltage, which is likely attributed to the sp2 fraction in the film as well as the substrates’ resistivity. The sp2 content in the films is estimated using XPS and Raman spectroscopy. Optical properties of the films are characterized using spectroscopic phase-modulated ellipsometry. The band gap decreases from 2.3 to 1.49 with increasing bias voltage.

Fabrication of amorphous carbon cantilever structures by isotropic and anisotropic wet etching methods

Abstract Free-standing amorphous carbon (a-C) cantilever structures were successfully fabricated by a single photolithography step. The relatively thick (∼1 μm), smooth ( R rms ∼0.75 nm), low stress ( −9 mm 3 /Nm) were deposited by filtered cathodic vacuum arc (FCVA) deposition system, in conjunction with high substrate pulse biasing (5 kV, 600 Hz and 25 μs). The undercutting of the cantilever was carried out, both by isotropic (in a solution mixture of 40% HF (1 part) and 70% HNO 3 (3 parts)) as well as anisotropic (in 40 wt.% KOH) Si wet etching methods. The study reveals that it is not viable to fabricate perfect free-standing a-C cantilever structure by isotropic wet etching. However, by controlling the etching duration/rate, it is possible to fabricate the as-designed free-standing cantilever structures by anisotropic wet etching method. The SEM images of the free-standing a-C cantilever structures do not show any bulging, and which clearly shows that the intrinsic stress in the film is low enough to be used for the fabrication of micro-electro-mechanical system (MEMS) devices, such as micro-motors and gears.

Experimental and theoretical study on the energy-dependent surface evolution and microstructure changes in copper nanostructured composites

Many studies have shown that the properties of single carbon system films are governed by the energy of the impinging carbon ions but the role of metal in addition to carbon ions as in diamond-like carbon (DLC) nanocomposites is not yet available. In this study, DLC films doped with different fractions of copper (5 and 15?at%) were fabricated using the pulsed laser deposition technique at varied laser energies, and the energy dependence of surface evolution and changes in microstructures due to the presence of metal were experimentally characterized. By considering the substitution of carbon by copper atoms in the target, the interaction between laser/target and the role of copper ions as envisaged in Sahas equation, the energy of the ions was calculated and good agreement with experimental results was reported. In the presence of copper that increased the ion energy, the excess heat released upon the impingement of ions during the formation of composite films can (1) enhance surface diffusion and promote the formation of nanoislands, and (2) graphitize the diamond bonding in the carbon matrix as seen experimentally. Simulations showed that the metal ions were implanted into the subsurface of the carbon matrix, thus reducing the surface roughness with increasing laser energy as well as increasing copper content. Although the formation of nanoclusters reduced the sp3 bonding of the films, mechanical testing showed that the adhesion strength of the films were improved with the presence of nanoclusters and SiC formed during the deposition.

Etching behaviour of pure and metal containing amorphous carbon films prepared using filtered cathodic vacuum arc technique

A preliminary study on the etching behaviour of pure and metal containing amorphous carbon (a-C) films has been studied using reactive ion etching (RIE) as well as reactive ion beam etching (RIBE). The RIE etching of a-C films, prepared from pure and 1 at.% Al containing carbon cathodes, displays a significant increase in etching rate with increase in discharge power. The inclusion of even a small percentage of metal causes a drastic reduction in the etching rate. The films that contain higher percentages of metal become more difficult to etch using RIE with oxygen plasma. Therefore, etching of the samples by RIBE technique using a plasma mixture of oxygen and argon has been carried out. A significant reduction in the etching rate with increasing metal content was observed for both Al and Ti containing a-C films. This led us to try etching of Ti containing a-C films by RIE technique using a plasma mixture of CF4 and oxygen. The result shows that the etching rate increases with increasing Ti content. n nThe analysis of the etched surfaces measured by visible Raman indicates that all the surfaces remain almost the same regardless of the processes undergone. However, the morphology measured using Atomic Force Microscopy (AFM) shows that the surface roughness increases significantly after etching, especially for the pure carbon films.

Substrate influence on the formation of FeSi and FeSi2 films from cis-Fe(SiCl3)2(CO)4 by LPCVD

Abstract In this work, Fe(SiCl 3 ) 2 (CO) 4 was employed as a single source precursor for the formation of FeSi and FeSi 2 films at 350–500°C by low-pressure chemical vapour deposition. The films were deposited in a specially constructed hot-wall reactor either on Pyrex-glass substrates or on a (100)Si surface. On Pyrex, porous polycrystalline (cubic) FeSi films were obtained. The deposition involved a kinetically controlled, selective decomposition reaction of cis -Fe(SiCl 3 ) 2 (CO) 4 . On (100)Si substrates, (001) oriented columnar films of orthorhombic β -FeSi 2 were formed. This change in film composition and texture is ascribed to an imprint effect of the (100)Si surface on the epilayer. β -FeSi 2 can grow on (100)Si with the (010) or (001) direction parallel to the (011) direction of Si with only 1.5 or 2.1% misfit, which allows minimization of interfacial stress and strain. All films were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy and atomic force microscopy. Furthermore, microhardness and specific resistivity of the films have been measured.

Characterization of a-Se p-n junction fabricated using electrolysis in NaCl aq

In this paper, we introduce an electro-chemical doping method of amorphous selenium (a-Se) using NaClaq. Recently, an a-Se photovoltaic device fabricated using this method [1], has been announced and opened up the potential of a new impurity doping method. This study will further explore its possibilities by doping chlorine (Cl) and sodium (Na) and aim to fabricate a p-n junction by reversing the applied voltage during the electrolysis. The device is characterized through photoelectric measurements. The I-V characteristics show rectification under light illumination.

EFFECT OF FOCUSSED VACUUM ARC PLASMA DEPOSITION ON THE PROPERTIES OF TETRAHEDRAL AMORPHOUS CARBON FILMS

We have investigated the effect of using a magnetic field to confine and focus the plasma in a Filtered Cathodic Vacuum Arc (FCVA) deposition system used for the preparation of tetrahedrally bonded amorphous carbon (ta-C) thin films. The design of the magnetic field is such that the plasma can be confined into a high-density focussed spot or de-focussed into a lower density wide beam. Increasing the magnetic field directly increases the plasma density and thus increases the deposition rate. The ta-C films grown in the magnetic field were subsequently characterised. EELS and Raman measurement were used to measure the sp3/sp2 ratio and UV-vis spectroscopy for optical bandgap studies. The intrinsic stress and I-V characteristics of the thin films were also studied. The results show that it is possible to deposit the films at rates as high as 2.5 nm/sec without adversely affecting the material properties.