Deposition Of Diamond Thin Films Research Articles

Formation and characterisation of cobalt depleted outermost layer of WC–Co composite materials

The cobalt depleted layer of WC–Co composite materials was investigated after selective cobalt etching in diluted Caro’s acid. The time dependence of Co etching and the thickness of the etched layer was determined by using Glow Discharge Optical Emission Spectrometer (GD-OES) depth profiling as well as by calculation method based on determination of the dissolved Co by Atomic Absorption Spectrophotometric (AAS) measurement. The integrity of the modified outermost layer of the WC–Co composite materials were qualified using Rockwell C indentation test. This test methods were found usable for optimisation of the pre-treatment applied before the diamond thin film deposition.

The effect of MoW interlayer thickness on diamond growth on steel substrates

Abstract

Electrostatic Self-Assembly of Diamond Nanoparticles onto Al- and N-Polar Sputtered Aluminum Nitride Surfaces.

Electrostatic self-assembly of diamond nanoparticles (DNPs) onto substrate surfaces (so-called nanodiamond seeding) is a notable technique, enabling chemical vapor deposition (CVD) of nanocrystalline diamond thin films on non-diamond substrates. In this study, we examine this technique onto differently polarized (either Al- or N-polar) c-axis oriented sputtered aluminum nitride (AlN) film surfaces. This investigation shows that Al-polar films, as compared to N-polar ones, obtain DNPs with higher density and more homogeneously on their surfaces. The origin of these differences in density and homogeneity is discussed based on the hydrolysis behavior of AlN surfaces in aqueous suspensions.

Microstructure evolution of thermal spray WC–Co interlayer during hot filament chemical vapor deposition of diamond thin films

In this paper, diamond film was deposited on WC–Co coated steel substrate by hot filament chemical vapor deposition (HFCVD). This method can not only prepare diamond film on the sample, but also can be used as a new way of WC–Co coating heat treatment. Brittle phases, such as η phase, which were produced during ordinary heat treatment process, will be suppressed in HFCVD at high temperature. This paper systematically studied the microstructure (defects and phase) transition of WC–Co interlayer in the process of depositing diamond film. The mechanism of phase transition was discussed. The results showed that at high deposition temperature (e.g. 800°C), the transition of binder phase was fast. After 5h of deposition, the phase composition of WC–Co coating was almost the same as sintered WC–Co block. At low deposition temperature (e.g. 700°C), the phase transition of interlayer slowed down and there was a large amount of nano-phases in the interlayer even after 12h of deposition.Another notable feature is that phase transition of the surface part of interlayer was the fastest, followed by the inner part and the middle part was the slowest. The phase transition rate of the interlayer and the binder phase is closely related to the depth of the coating. In the surface part of the coating, Co will evaporate and diffuse into diamond film. Also, activated carbon atoms will diffuse into the interlayer, but the depth of diffusion layer was limited. Fe and Co will diffuse into each other at the interface between interlayer and steel substrate. In contrast, the middle part of interlayer was not affected by diffusion of elements.In sum, the results suggest that the change in element content (i.e. concentration diffusion) is the main driving force of the phase transition, while temperature mainly affects phase transition rate (i.e. the rate of diffusion).

Structural and electrical characterization of diamond films deposited in nitrogen/oxygen containing gas mixture by linear antenna microwave CVD process

Abstract In this paper we demonstrate the large area deposition of n-type conductive nanocrystalline diamond thin films on p-type Si substrates. We show that adding N 2 into CH 4 /H 2 /CO 2 gas mixture allows a wide controlling of diamond film morphology from micro- to nanocrystalline, blockstone-like or porous-like morphology potentially suitable for various applications. Moreover, after adding we found that the diamond films revealed a deep level with activation energy of 0.44 ± 0.03 eV.

Low temperature carbon nanotube and hexagonal diamond deposition with photo-enhanced chemical vapor deposition

Deposition of carbon nanotube and hexagonal diamond thin films at low substrate temperature with photo-enhanced chemical vapor deposition is described here. Extensive experimentation is conducted to optimize the catalyst layer utilized for deposition by varying Al/Ni/Al metal layer thicknesses on SiO2 coated Si substrates. The coated substrates are annealed to transform the thin metal layers into nanoparticles. Suitable catalyst layer thicknesses obtained are 3/2/3, 5/1/5 and 5/3/5 nm for Al/Ni/Al sandwich metal layers. Suitable annealing conditions are in the range of 350---450 °C for substrate temperature and from 0.22 to 10 Torr for chamber pressure in ammonia ambient for 25 min. Carbon tetrachloride (CCl4) is used as a carbon precursor in this work. Argon to CCl4 flow ratio is varied in 1.5---19 range, chamber pressure is varied in 3---10 Torr range, and the substrate temperature is varied in 350---450 °C range. Carbon nanotubes (CNT) growth is observed at lower chamber pressure, lower partial pressure of CCl4, lower substrate temperature and for thin Ni catalyst layer. The optimal CNT deposition condition observed is 5 Torr total chamber pressure, 9:1 partial pressure ratio of Ar to CCl4, 400 °C substrate temperature and 5/1/5 nm thick Al/Ni/Al catalyst layers. The hexagonal diamond deposition is observed at a higher chamber pressure, higher partial pressure of CCl4, higher substrate temperature and for a thicker Ni catalyst layer. The optimal condition for hexagonal diamond deposition observed is 10 Torr total chamber pressure, 7:3 partial pressure ratio of Ar to CCl4, 450 °C substrate temperature and 5/3/5 nm thick Al/Ni/Al catalyst sandwich layers.

Modelling of Hydrogen Microwave Plasma in the Conditions of Diamond Deposition

A 2D-fluid plasma model has been developed for a microwave cavity plasma reactor used for diamond thin film deposition. Dependencies of discharge characteristics on the main physical parameters namely the hydrogen pressure and the microwave power density have been numerically studied. The pure hydrogen plasma characteristics, such as electron density, electron temperature and electric potential are simulated by applying a COMSOL MWP module based on finite element method to solve electron continuity and electron energy equations coupled with Poisson’s equation. This present paper provides the spatial and temporal evolutions of different discharge characteristics for various input conditions. It is shown that the electron density was in the range (5×1016-8×1017)m-3 for the pressure range of (40-60)Torr. It is also clearly shown that as the power density increases the electron density increases and that the electron temperature and electric potential vary slightly with gas pressure and microwave power density.

Influence of hydrogen and hydrogen/methane plasmas on AlN thin films

Polycrystalline aluminum nitride (AlN) thin films are exposed to hydrogen and hydrogen/methane plasmas at different conditions. The latter plays an indispensable role in the subsequent deposition of nanocrystalline diamond thin films on AlN. The changes of AlN properties are investigated by means of Fourier transform infrared (FTIR) and Raman spectroscopies as well as atomic force microscopy. The E1(TO) and E22 phonon mode frequencies blue-shift after the exposure to plasmas. The damping constant of E1(TO) phonon, calculated from FTIR transmission spectra using the factorized model of a damped oscillator, and the width of E22 peak in Raman spectra decrease with increasing substrate temperature till the decomposition of AlN thin film becomes notable. It is proven that these changes are driven by the plasmas as annealing in vacuum does not induce them.

CCl Radicals As a Carbon Source for Diamond Thin Film Deposition.

We use first-principles quantum mechanical calculations to study diamond thin film growth on the (100) surface using CCl radicals as the carbon source. Our results show that CCl inserts into the surface dimer C-C bonds with a barrier of 10.5 kcal/mol, roughly half of the energy required for traditional CH2 insertion (22.0 kcal/mol). In addition to this, CCl has improved surface mobility (∼30.0 kcal/mol barrier, versus 35 kcal/mol for CH2, along the C-C dimer chain direction), and hydrogen abstraction from the surface is also favored via atomic Cl in the vapor phase. These results explain the lower substrate temperatures achieved in crystal diamond growth from the use of chlorinated sources in CVD processes, as opposed to the more traditional CH4/H2 derived species. Our results also suggest that further reductions in substrate temperatures are possible from using CCl as the only carbon source.

COMSOL Multiphysics Simulations of the Hydrogen Microwave Plasma Characteristics

This paper presents the numerical simulation of a MPACVD (Microwave Plasma Assisted Chemical Vapor Deposition) reactor used for diamond thin film deposition. A COMSOL MWP module, based on fluid plasma model, has been used to study impact of hydrogen pressure and incident microwave power on plasma discharge characteristics such as electron density, electron temperature and electric potential, at low pressure. It is clearly shown that the plasma volume increases either by augmenting power and keeping a constant pressure or by decreasing pressure while maintaining a constant power. It is also seen that uniformity of the plasma is obtained as the gas pressure is decreased, and that electron density increases significantly as a function of pressure and power. However, electron temperature varies in the opposite direction of the electron density, in the ranges of power and gas pressure studied. Results also indicate that electric potential increases by augmenting the incident power and maintaining a constant pressure or decreasing the pressure while keeping a constant power. Comparisons between model and experimental results are mainly satisfactory and support the fact that average electron density varies in the range of (〖1×10〗^17÷〖8×10〗^17)m^(-3) for the input power range (50W-300W) at a given pressure value (1.5Torr).

Carbonization of Si Surface Using Hot-Filament CVD Equipment and Characterization of the Char Layer

ABSTRACTTo date, many studies have been carried out to investigate the use of semiconductive diamonds in industrial applications. In these studies, it has been necessary to deposit high-quality crystalline diamond thin films on large-area substrates. Hot-filament chemical vapor deposition (HFCVD) has been a useful method for generating these thin films. While large-area silicon (Si) substrates are easily obtainable and inexpensive and Si is a suitable material for the deposition of diamond thin films, because of the large mismatch of the lattice constants of Si and diamond, it is usually difficult to grow epitaxial diamond films on Si substrates. Therefore, insertion of a buffer layer comprised of a material with a lattice constant between those of Si and diamond is required. Silicon carbide (SiC), which is readily obtained by carbonization of the Si surface, is a candidate material for such a buffer layer. Therefore, in this study, a char layer was formed on a Si surface using HFCVD equipment and analyzed from various perspectives.

Microwave Plasma Source for Fabrication of Micro- and Nano-Crystalline Diamond Thin Films for Electronic Devices

The design and utilization of an affordable compact-size high-density plasma reactor for micro- and nano-crystalline diamond (MCD/NCD) thin film deposition is presented. The system is based on a 2.45 GHz domestic microwave oven magnetron. A switching power supply module, which yields a low-voltage high-current AC filament feeding and a high-voltage low-current DC cathode bias, is constructed to serve as the magnetron power source. With a high stability of the power module combined with the usage of water cooling gaskets, over 100 h of plasma processing time was achieved without overheating or causing any damage to the magnetron. Depositions of well-faceted MCD/NCD thin films, with distinct diamond Raman characteristics, were obtained using H2–CH4 discharge with 1–5% CH4. Metal–semiconductor diode structures were fabricated using gold and aluminum as ohmic and rectifying contacts, respectively, and their responses to DC signals revealed a high rectification ratio of up to 106 in the intrinsic MCD/NCD devices.

Thin film deposition of diamond using normal paraffins as source of diamond nucleation centers

We propose a process for diamond thin film (DTF) deposition using normal paraffins (nP) as source of diamond nucleation centers. We deposited micro-crystalline diamond thin films (MCDTF) on a Cu substrate using Hot Filament CVD (HFCVD) and Passive Pt/Pd Surface Catalysis (PPt/PdSC) methods. Beeswax and a 1:1 mixture of normal paraffins of the general formula CH3(CH2)nCH3 with n=22 and 26 were tested as nP starting material. The films obtained were characterized by scanning electronic microscopy (SEM), Raman scattering temperature dependent spectroscopy and X-ray diffraction (XRD) methods, all of which confirmed that the deposited material is MCDTF.

Ultrathin W−Al Dual Interlayer Approach to Depositing Smooth and Adherent Nanocrystalline Diamond Films on Stainless Steel

The adherence of diamond coated on steel is commonly low and needs to be strengthened with thick intermediate layers. In this paper, a nanoscale W-Al dual metal interlayer has been applied on SS304 substrates to facilitate deposition of continuous, adherent and smooth diamond thin films. During the microwave plasma-enhanced chemical vapor deposition process, the Al inner layer 30 nm thick diffuses into steel surface inhibiting carbon diffusion and graphitization. The W outer layer 20 nm thick is transformed into W carbides, both preventing carbon diffusion and enhancing diamond nucleation. The diamond films synthesized are of high purity and have smooth surfaces and dense structures. Indentation and shear deformation tests indicate high delaminating tolerance of the diamond films.

Influence of periodic magnetic field on the growth of CVD diamond films at lower temperature

A periodic magnetic field (PMF) of B= B 0 sin ωt, where B 0=106 Guass and ω=40,000 rpm, was designed and first applied in a special hot-filament chemical vapor deposition (HFCVD) system for diamond synthesis. Different to the conventional HFCVD, an external PMF was introduced for diamond thin film deposition on a Si (1 1 1) substrate. The morphology and cross-section of the film were analyzed by field emission scanning electron microscopy (FESEM) while the bond structure was investigated using Raman spectroscopy. Compared with the conventional HFCVD, the growth rate of diamond film defined as the ratio of film thickness vs deposition time increases by about 7 times at 520 °C with PMF. The I Dia/ I G ratio in Raman spectra indicates that the quality of the diamond film grown with PMF is much higher than that of the film grown by conventional HFCVD. The research shows that the novel technology using PMF may have great practical application potentiality in CVD diamond growth at low temperature and in some relevant fields.

Al-enhanced low temperature deposition of diamond thin films on hetero-substrates

Synthesis of diamond thin films on aluminum and aluminum-modified Si and steel substrates has been performed at 450 °C with 1%CH 4–99%H 2 gas mixture in a microwave plasma enhanced chemical vapor deposition (CVD) reactor. A diamond scratching pre-treatment of bulk Al substrate or Al-interlayered Si/steel substrates greatly enhances diamond nucleation, and the diamond films directly synthesized on Al substrate are well faceted, continuous and densely packed. The diamond films synthesized on conventional Fe–Cr and Fe–Cr–Ni type steels are generally of poor quality due to preferential formation of graphitic carbons catalyzed by the base metal iron. An Al thin film interlayer applied on those steel surfaces has markedly enhanced the nucleation and adhesion properties of diamond films, and a direct alloying addition of Al to these steel substrates also promotes the formation of continuous, dense and adherent diamond films.

The role of inert gas in MW-enhanced plasmas for the deposition of nanocrystalline diamond thin films

Nanocrystalline diamond thin films have been deposited using microwave plasma enhanced deposition with gas mixtures of composition H 2/CH 4/X, where X was one of the inert gases He, Ne, Ar and Kr and typically constituted > 90% of the total gas flow. The diamond films obtained with each gas mixture deposited at approximately the same rate (0.15–0.5 µm h − 1 ), and all showed similar morphologies and average grain sizes, despite very obvious differences in the appearance and gas temperatures of the respective plasmas. These plasmas were probed by optical emission and cavity ring-down spectroscopy, and results from companion 2D chemical kinetic modelling of the Ar/H 2/CH 4 and He/H 2/CH 4 plasma were used to guide interpretation of the experimental observations. We conclude that the inert gas, though acting primarily as a buffer, also has significant effects on the thermal conduction of the gas mixtures, the electron temperature and electron energy distribution, and thereby changes the main channels of ionization and input power absorption. As a result, inert gas dilution elevates the electron and gas temperatures, enhances the hydrogen dissociation degree and affects the H/C mixture composition and deposition mechanisms.

Electrospray Deposition of Diamond Nanoparticle Nucleation Layers for Subsequent CVD Diamond Growth

AbstractNucleation is the rate-determining step in the initial stages of most chemical vapour deposition processes. In order to achieve uniform deposition of diamond thin films it is necessary to seed non-diamond substrates. Here we discuss a simple electrospray deposition technique for application of 5 nm diamond seed particles onto substrates of various sizes. The influence of selected parameters, such as experimental spatial arrangement and colloidal properties, are analysed in optimizing the method by optical and electron microscopy, both before and after nanocrystalline diamond deposition on the seed layer. The advantages and limitations of the electrospray method are highlighted in relation to other commonly exploited nucleation techniques.

Application of CVD nanocrystalline diamond films to cemented carbide drills

Abstract Nanocrystalline diamond coated cemented carbide drills were produced by high current extended DC arc plasma CVD system using Ar/H 2 /CH 4 gas mixture. The deposited nanocrystalline diamond films were characterized with scanning electron microscopy. Raman spectroscopy was used to investigate the purity of the nanocrystalline diamond films. X-Ray diffraction was used to analyze the structure of the diamond films. The pretreatment with Murakami and acid solution could effectively remove the Co binder in the substrates and roughen the surface of the cemented carbide drills. A uniform and smooth surface morphology of nanocrystalline diamond thin film was observed. The cutting performance of the diamond coated drills was investigated by machining metal matrix composites. The deposition of nanocrystalline diamond thin films on cemented carbide drills is helpful to improve the cutting performance of the drills.

Nanocrystalline diamond/β-SiC composite interlayers for the deposition of continuous diamond films on W and Mo substrate materials

Nanocrystalline diamond/β-SiC composite film system has been realized as an interlayer for the deposition of continuous and adherent diamond thin films on W and Mo substrate materials by microwave plasma chemical vapor deposition (MWCVD) technique in a single process step using a gas mixture of H 2, CH 4, and tetramethylsilane [Si(CH 3) 4, TMS]. Continuous and high quality diamond film growth on the interlayers was clearly evident. Scanning electron microscopy, X-ray diffraction and micro Raman scattering studies have been carried out to study the surface morphology and the crystal structure of the deposited films. The composite films consist of mainly two phases that of diamond and β-SiC. Content of β-SiC in these films can be varied by varying the concentration of TMS in the gas phase reaction. Diamond top layers on different composite interlayers are found to be possessing low residual stress values and simple Brinell indentation tests showed an improved adherence of these top layers in comparison to those deposited directly on the pre-treated substrates. Even the homogeneous composite (i.e., without the diamond top layers) as well as the gradient composite interlayers when considered as separate thin film systems, showed a very good adherence.