Comparative study of diamond films grown on silicon substrate using microwave plasma chemical vapor deposition and hot-filament chemical vapor deposition technique

Diamond films on the p-type Si(111) and p-type(100) substrates were prepared by microwave plasma chemical vapor deposition (MWCVD) and hot-filament chemical vapor deposition (HFCVD) by using a mixture of methane CH₄ and hydrogen H₂ as gas feed. The structure and composition of the films have been investigated by X-ray Diffraction, Raman Spectroscopy and Scanning Electron Microscopy methods. A high quality diamond crystalline structure of the obtained films by using HFCVD method was confirmed by clear XRD-pattern. SEM images show that the prepared films are poly crystalline diamond films consisting of diamond single crystallites (111)-orientation perpendicular to the substrate. Diamond films grown on silicon substrates by using HFCVD show good quality diamond and fewer non-diamond components.     

High-quality diamond film deposition on a titanium substrate using the hot-filament chemical vapor deposition method

Diamond film on titanium substrate has become extremely attractive because of the combined properties of these two unique materials. Diamond film can effectively improve the properties of Ti for applications as aerospace and biomedical materials, as well as electrodes. This study focuses on the effects of process parameters, including gas composition, substrate temperature, gas flow rate and reactor pressure on diamond growth on Ti substrates using the hot-filament chemical vapor deposition (HFCVD) method. The nucleation density, nuclei size as well as the diamond purity and growth tendency indices were used to quantify these effects. The crystal morphology of the material was examined with scanning electron microscopy (SEM). Micro-Raman spectroscopy provided information on the quality of the diamond films. The growth tendency of TiC and diamond film was determined by X-ray diffraction analysis. The optimal conditions were found to be: CH₄:H₂ = 1%, gas flow rate = 300 sccm, substrate temperature T_sub = 750 °C, reaction pressure = 40 mbar. Under these conditions, high-quality diamond film was deposited on Ti with a growth rate of 0.4 μm/h and sp² carbon impurity content of 1.6%.     

Microwave plasma enhanced chemical vapor deposition of diamond in silicon pores

In this work, the feasibility of growing boron-doped diamond coatings, approximately 0.3 μm thick, on thin silicon substrates that have 50-μm diameter pores etched 125 μm deep has been demonstrated using deep reactive ion etching (DRIE) in combination with chemical–mechanical polishing (CMP). Using a microwave plasma enhanced chemical vapor deposition (MPECVD) cyclic growth process consisting of carburization, bias-enhanced nucleation, diamond growth and boron-doped diamond growth, uniform diamond coatings throughout the pores have been obtained. The coatings were characterized by Raman spectroscopy and scanning electron microscopy and the secondary electron emission coefficients were found to increase from 4 to 10 between 200 and 1000 V, in agreement with reported values for thicker polycrystalline diamond films grown under similar conditions.     

Heteroepitaxial diamond nucleation and growth on silicon by microwave plasma-enhanced chemical vapor deposition synthesis

Heteroepitaxial diamond films were successfully nucleated and deposited on 1-inch diameter Si(001) substrates by microwave plasma-enhanced chemical vapor deposition (MPECVD). The precursor gases for the synthesis were methane and hydrogen. Before the application of a negative d.c. bias to the substrate, an in-situ carburization pre-treatment on the silicon was found to be an indispensable step towards the heteroepitaxial diamond on the silicon. Morphologies of the films were characterized by scanning electron microscopy (SEM). Interface observations based on the cross-sectional HRTEM directly reveal the heteroepitaxial diamond nucleation phenomena in detail. No interlayers of silicon carbide and/or amorphous carbon phases were observed. Tilt and azimuthal misorientation angles between the heteroepitaxial diamond crystals and the substrate were determined by combining the Ewald sphere construction in the reciprocal lattice space and the selected area diffraction (SAD) patterns taken across the interface.     

Free-standing diamond wafers deposited by multi-cathode,direct-current,plasma-assisted chemical vapor deposition

Free-standing diamond wafers, 100 mm in diameter, have been deposited by the multi-cathode (seven-cathode) direct-current (DC) plasma-assisted chemical vapor deposition (PACVD) method. The input power was 17.5 kW and the pressure was 100 torr. The methane concentration in hydrogen was between 3.5% and 8% at a constant flow rate of 150 sccm. Intrinsic tensile stress was controlled by introducing thermal compressive stress with step-down control of the deposition temperature during diamond deposition. A higher growth rate of 10 μm h⁻¹ was obtained by raising the methane concentration to 8%, and the deposited diamond wafer showed good thermal conductivity of 12–14 W cm⁻¹ K⁻¹. Crack-free, homogeneous and flat diamond wafers with 100 mm diameter were obtainable.     

Growth of graphene on Cu by plasma enhanced chemical vapor deposition

The growth of graphene on Cu substrates by plasma enhanced chemical vapor deposition (PE-CVD) was investigated and its growth mechanism was discussed. At a substrate temperature of 500 °C, formation of graphene was found to precede the growth of carbon nanowalls (CNWs), which are often fabricated by PE-CVD. The growth of graphene was investigated in various conditions, changing the plasma power, gas pressures, and the substrate temperature. The catalytic nature of Cu also affects the growth of monolayer graphene at high substrate temperatures, while the growth at low temperatures and growth of multilayer graphene are dominated mostly by radicals generated in the plasma.     

Nucleation of diamond films by ECR-enhanced microwave plasma chemical vapor deposition

A novel nucleation technique based on electron cyclotron resonance microwave plasma was developed to enhance the nucleation of diamond. By choosing a suitable experimental condition, a nucleation density higher than 10⁸ nuclei cm⁻² was achieved on an untreated, mirror-polished silicon substrate. Uniform diamond films were obtained by combining this nucleation method with subsequent growth by the common microwave plasma chemical vapor deposition. Furthermore, the possibility of this new nucleation method to generate heteroepitaxial diamond nuclei on (001) silicon substrates was explored.     

Synthesis of diamond hexagonal nanoplatelets by microwave plasma chemical vapor deposition

Variation of diamond deposition with temperature gradient was studied using standing-up substrates embedded within the plasma ball in microwave plasma chemical vapor deposition (MPCVD). The substrate is a polycrystalline diamond coated with a 30-nm thick iron film before deposition. Surface morphologies of the deposits and their crystalline characteristics were characterized by scanning electron microscopy, transmission electron microscopy (TEM), and selected area diffraction. On the upper area of the specimen near the center of the plasma ball where the temperature is the highest (>1100 °C), formation of diamond nanoplatelets in hexagonal shape with a thickness of 20–60 nm and side length of several hundreds of nanometers is found. In the middle region, diamond nanoplatelets with some iron nanoparticles are observed. Around the bottom region with low temperature near the edge of the plasma ball, nanodiamonds, Fe nanoparticles, and carbon nanotubes coexisted. The relative temperature distributions of diamond and carbon nanotube growth are briefly discussed.     

Hydrogen-excluded graphene synthesis via atmospheric pressure chemical vapor deposition

The morphology of graphene synthesized via atmospheric pressure chemical vapor deposition (APCVD) process was investigated with respect to the hydrogen introduction in each process step. A pristine monolayer graphene was obtained in the condition where hydrogen was excluded in all the steps. The study of growth mechanism of this hydrogen-excluded APCVD process suggests that hydrogen plays a critical role in determining the rate-limiting step, which further determines whether or not a monolayer graphene can be achieved, irrespective to the roughness of the surface. Particularly, the dominant kinetic regime changed, depending on the introduction of hydrogen in the growth step. Finally, electric properties of the graphene via the hydrogen-excluded APCVD process were characterized and compared with the one via the low pressure CVD process, along with the characterization of etch pits in a graphene-passivated etch test. The resulted better performance of the former graphene in both cases suggests that this method can be considered as an alternative but easier route for the synthesis of monolayer graphene.     

Micro-Raman analysis of the cross-section of a diamond film prepared by hot-filament chemical vapor deposition

Raman micro-spectroscopy using exciting light with an approximately 2-μm diameter exciting spot was undertaken to investigate the micro-structure of cross-section of a 100-μm thick diamond film prepared by hot-filament chemical vapor deposition (HFCVD). The Raman spectra exhibited different features with changing position, suggesting that the composition of crystalline diamond, amorphous carbon and graphitic phases varied in the HFCVD process. The presence of a broad band and high background intensity in the spectra near the substrate surface was attributed to the amorphous carbon synthesized in the nucleation process of the film. A decreasing proportion of sp²-bond structure in the amorphous carbon phase with increasing film thickness was believed to account for the decline in the intensity of the 1200–1600-cm⁻¹ band. The different composition of the diamond grains and of the grain boundaries in the film was shown in the Raman spectra obtained from different positions at the same cross-sectional thickness by scanning the exciting light parallel to the surface of the film.     

Synthesis and characterization of carbon nanowalls on different substrates by radio frequency plasma enhanced chemical vapor deposition

A radio frequency plasma enhanced chemical vapor deposition system was used for the successful growth of thin vertical carbon nanowalls, also known as vertical graphene, on various substrates. Transmission electron microscopy studies confirmed the presence of vertical graphene walls, which are tapered, typically consisting of 10 layers at the base tapering off to 2 or 3 layers at the top. The sides of the walls are facetted at quantized angles of 30° and the facetted sides are usually seamless. Growth occurs at the top open edge which is not facetted. Hydrogen induced etching allows for nucleation of branch walls apparently involving a carbon onion-like structure at the root base. Characterization by a superconducting quantum interference device showed magnetic hysteresis loops and weak ferromagnetic responses from the samples at room temperature and below. Temperature dependence of the magnetization revealed a magnetic phase transition around T = 50 K highlighting the coexistence of antiferromagnetic interactions as well as ferromagnetic order.     

Carbon nanowalls deposited by inductively coupled plasma enhanced chemical vapor deposition using aluminum acetylacetonate as precursor

Well aligned carbon nanowalls, a few nanometers thick, were fabricated by continuous flow of aluminum acetylacetonate (Al(acac)₃) without a catalyst, and independent of substrate material. The nanowalls were grown on Si, and steel substrates using inductively coupled plasma-enhanced chemical vapor deposition. Deposition parameters like flow of argon gas and substrate temperature were correlated with the growth of carbon nanowalls. For a high flow of argon carrier gas, an increased amount of aluminum in the film and a reduced lateral size of the carbon walls were found. The aluminum is present inside the carbon nanowall matrix in the form of well crystallized nanosized Al₄C₃ precipitates.     

Effects of annealing on copper substrate surface morphology and graphene growth by chemical vapor deposition

Understanding the mechanism of graphene synthesis by chemical vapor deposition and the effect of process parameters is critical for production of high-quality graphene. In the present work, we investigated the effect of H₂ concentration during annealing on evolution of Cu surface morphology, and on deposited graphene characteristics. Our results revealed that H₂ had a smoothening effect on Cu surface as its surface roughness was reduced significantly at high H₂ concentration along with the formation of surface facets, dents and nanometer-sized particles. Furthermore, H₂ content influenced the graphene morphology and its quality. A low H₂ concentration (0% and 2.5%) during annealing promoted uniform and good quality bilayer graphene. In contrast, a high concentration of H₂ (20% and 50%) resulted in multilayer, non-uniform and defective graphene. Interestingly, the annealed Cu surface morphology differed considerably from that obtained after deposition of graphene, indicating that graphene deposition has its own impact on Cu surface.     

Partially stabilized zirconia substrate for chemical vapor deposition of free-standing diamond films

In this work we investigated the use of partially stabilized zirconia (PSZ) as the substrate for deposition of CVD diamond films. The polycrystalline PSZ substrates were sintered at high temperatures and the results showed that this material has unique properties which are very appropriated for the growth of free-standing diamond films. The diamond nucleation density on PSZ is high, even without seeding, and the CVD diamond film was totally released from the substrate after the deposition process, without cracking. Micro-Raman analysis revealed that the free-standing diamond film had a good crystallinity on both surfaces with practically no stress in the structure. The same PSZ substrate can be reutilized for the deposition of a large number of diamond films. The average growth rate is about 5–6 μm/h in a microwave plasma reactor at 2.5 kW. The deposition process causes the reduction of ZrO₂, producing ZrC. The high mobility of oxygen in the zirconia matrix at high temperature would probably help to etch the interface region between the substrate surface and the diamond film, decreasing the adhesion strength and eliminating some defects in the film structure related to non-diamond carbon phases.     

绝缘衬底上化学气相沉积法生长石墨烯材料

利用化学气相沉积法,在Si衬底、蓝宝石衬底和SiC衬底上生长石墨烯材料,研究石墨烯的表面形貌、缺陷、晶体质量和电学特性。原子力显微镜、光学显微镜和拉曼光谱测试表明,Si₃N₄覆盖层可以有效抑制3C-SiC缓冲层的形成;低温生长有利于保持材料表面的平整度,高温生长有利于提高材料的晶体质量。5.08 cm蓝宝石衬底上石墨烯材料,室温下非接触Hall测试迁移超过1000 cm²·V^-1·s^-1,方块电阻不均匀性为2.6%。相对于Si衬底和蓝宝石衬底,SiC衬底上生长石墨烯材料的表面形态学更好,缺陷更低,晶体质量和电学特性更好,迁移率最高为4900 cm²·V^-1·s^-1。     

Biased enhanced growth of nanocrystalline diamond films by microwave plasma chemical vapor deposition

Smooth nanocrystalline diamond thin films with rms surface roughness of ∼17 nm were grown on silicon substrates at 600°C using biased enhanced growth (BEG) in microwave plasma chemical vapor deposition (MPCVD). The evidence of nanocrystallinity, smoothness and purity was obtained by characterizing the samples with a combination of Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy and Auger electron spectroscopy. The Raman spectra of the films exhibit an intense band near 1150 cm⁻¹ along with graphitic bands. The former Raman band indicates the presence of nanocrystalline diamond. XRD patterns of the films show broad peaks corresponding to inter-planar spacing of (111) and (220) planes of cubic diamond supporting the Raman results. Auger line shapes closely match with the line shape of diamond suggesting high concentration of sp³ carbon on the surfaces of the films. The growth of dominantly sp³ carbon by BEG in the MPCVD system at the conditions used in the present work can be explained by the subsurface implantation mechanism while considering some additional effects from the high concentration of atomic hydrogen in the system.     

Synthesis of boron-doped homoepitaxial single crystal diamond by microwave plasma chemical vapor deposition

The deposition of boron-doped homoepitaxial single crystal diamond is investigated using a microwave plasma-assisted chemical vapor deposition system. The objective is to deposit high-quality boron-doped single crystal diamond and establish the relationships between the deposition conditions and the diamond growth rate and quality. Experiments are performed using type Ib HPHT diamond seeds as substrates and growing diamond with varying amounts of diborane in a methane–hydrogen gas mixture. The deposition system utilized is a 2.45 GHz microwave plasma-assisted CVD system operating at 135–160 Torr. Experiments are performed with methane concentrations of 4–6% and diborane concentrations of 5–50 ppm in the feedgas. Diamond is deposited with growth rates of 2 to 11 µm/h in this study. The deposited diamond is measured to determine its electrical conductivity and optical absorption versus wavelength in the UV, visible and IR portions of the spectrum. Data is presented that relates the growth rate and diamond properties to the deposition conditions including substrate temperature and feedgas composition.