Growth Of Ultrananocrystalline Diamond Films Research Articles

Effects of Surface Pretreatment on Nucleation and Growth of Ultra-Nanocrystalline Diamond Films**supported by National Natural Science Foundation of China (No. 11175137) and the Research Fund of Wuhan Institute of Technology, China (No. 11111051)

The effects of different surface pretreatment methods on the nucleation and growth of ultra-nanocrystalline diamond (UNCD) films grown from focused microwave Ar/CH4/H2 (argon-rich) plasma were systematically studied. The surface roughness, nucleation density, microstructure, and crystallinity of the obtained UNCD films were characterized by atomic force microscope (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The results indicate that the nucleation enhancement was found to be sensitive to the different surface pretreatment methods, and a higher initial nucleation density leads to highly smooth UNCD films. When the silicon substrate was pretreated by a two-step method, i.e., plasma treatment followed by ultrasonic vibration with diamond nanopowder, the grain size of the UNCD films was greatly decreased: about 7.5 nm can be achieved. In addition, the grain size of UNCD films depends on the substrate pretreatment methods and roughness, which indicates that the surface of substrate profile has a “genetic characteristic”.

Fast growth of ultrananocrystalline diamond films by bias-enhanced nucleation and growth process in CH4/Ar plasma

This letter describes the fast growth of ultrananocrystalline diamond (UNCD) films by bias-enhanced nucleation and growth process in CH4/Ar plasma. The UNCD grains were formed at the beginning of the film's growth without the necessity of forming the amorphous carbon interlayer, reaching a thickness of ∼380 nm in 10 min. Transmission electron microscopic investigations revealed that the application of bias voltage induced the formation of graphitic phase both in the interior and at the interface regions of UNCD films that formed interconnected paths, facilitating the transport of electrons and resulting in enhanced electron field emission properties.

Effect Of Process Parameters On The Properties Of Ultrananocrystalline Diamond Films Deposited Using Microwave Plasma Enhanced Chemical Vapor Deposition

Ultrananocrystalline diamond (UNCD) films are deposited using microwave plasma enhanced chemical vapor deposition system. Depositions of films are carried out at low pressure 25 mbar, low temperature 400 oC and at low microwave power (800 - 1000 Watt). Diamond thin films were characterized using Raman spectroscopy, AFM, field emission scanning electron microscopy and optical contact angle measurements. In-situ diagnosis of the plasma composition is carried out using optical emission spectroscopy (OES). OES spectra show intense peak at 516.5nm corresponding to C2 dimer. Peaks at 387.0nm, 405.3nm, 431.5nm, 486.1nm, and 656.1nm have also been observed. Effect of horizontal position of plasma ball with respect to substrate position has been critically analyzed. Relation between the horizontal positioning and plasma ball along with the emission spectra of different gas species are studied which are very much crucial to predict the uniformity and morphology of the films deposited. Dependence of film wetability with the plasma ball positioning and relative intensity of carbon dimer has been studied. C2 dimer plays an important role not only in the nucleation and growth of UNCD films but also on the surface modification. Copyright © 2014 VBRI press.

Growth of ultrananocrystalline diamond films in an Ar-rich CH4/H2/Ar atmosphere with varying H2 concentrations

Growth of ultrananocrystalline diamond films in an Ar-rich CH4/H2/Ar atmosphere with varying H2 concentrations

Formation of p-Type Ultrananocrystalline Diamond/Nonhydrogenated Amorphous Carbon Composite Films Prepared by Coaxial Arc Plasma Deposition with Boron-Incorporated Graphite Targets

Boron-doped ultrananocrystalline diamond (UNCD)/nonhydrogenated amorphous carbon (a-C) composite (UNCD/a-C) films were prepared by coaxial arc plasma deposition (CAPD) with boron-blended graphite target. Their growth was achieved at room temperature and a base pressure of less than 10-3 Pa (no inflow gas) owing to CAPD, whereas the growth of UNCD films by chemical vapor deposition generally requires high substrate temperatures of more than 700°C and a hydrogen ambient gas. The formation of p-type conduction was confirmed thermally, namely Seebeck effect, and heterojunction diodes formed with n-type Si exhibited a typical rectifying action. It was demonstrated that CAPD is advantageous to the practical film formation including doping.

Growth of ultrananocrystalline diamond films in an Ar-rich CH4/H2/Ar atmosphere with varying H2 concentrations

Ultrananocrystalline diamond (UNCD) films were prepared by microwave plasma chemical vapor deposition using argon-rich CH4/H2/Ar plasmas with different H2 concentrations from 5 to 20%. The influence of the H2 concentration on the microstructure, morphology and phase composition of the UNCD films was investigated by SEM, XRD, surface profilometry and Raman spectroscopy. It is found that the grain size and surface roughness increase with the H2 concentration. The grain size of the UNCD is less than 6 nm when the H2 concentration is less than 10% and it is still less than 10 nm even when the concentration is 20%. The thickness of the UNCD films is 1.75, 1.80, 1.65 and 2.9 μm using H2 concentrations of 5, 10, 15 and 20%, respectively. All the films are dense and compact in the cross section, and smooth on the top surface.

Electrophoresis of Nanodiamond on the Growth of Ultrananocrystalline Diamond Films on Silicon Nanowires and the Enhancement of the Electron Field Emission Properties

Electrophoresis deposition (EPD) of nanodiamond was found to be a very efficient process in forming the nucleation sites for the growth of ultrananocrystalline diamond (UNCD) films. Transmission el...

Systematic studies of the nucleation and growth of ultrananocrystalline diamond films on silicon substrates coated with a tungsten layer

We report on effects of a tungsten layer deposited on silicon surface on the effectiveness for diamond nanoparticles to be seeded for the deposition of ultrananocrystalline diamond (UNCD). Rough tungsten surface and electrostatic forces between nanodiamond seeds and the tungsten surface layer help to improve the adhesion of nanodiamond seeds on the tungsten surface. The seeding density on tungsten coated silicon thus increases. Tungsten carbide is formed by reactions of the tungsten layer with carbon containing plasma species. It provides favorable (001) crystal planes for the nucleation of (111) crystal planes by Microwave Plasma Enhanced Chemical Vapor Deposition (MPECVD) in argon diluted methane plasma and further improves the density of diamond seeds/nuclei. UNCD films grown at different gas pressures on tungsten coated silicon which is pre-seeded by nanodiamond along with heteroepitaxially nucleated diamond nuclei were characterized by Raman scattering, field emission-scanning electron microscopy, and high resolution-transmission electron microscopy.

Investigation of the initial growth of ultrananocrystalline diamond films by multiwavelength Raman spectroscopy

The initial growth phase of ultrananocrystalline diamond/amorphous carbon nanocomposite films (UNCD/a-C) has been investigated by scanning electron microscopy, atomic force microscopy and especially Raman spectroscopy. As due to resonance effects Raman spectra of carbon materials strongly depend on the excitation wavelength, a multiwavelength analysis has been performed with λ exc ranging from the UV region (325 nm) over the visible range (488 and 514 nm) to the IR region (785 nm). In addition, a set of measurements has been performed with a confocal Raman microscope, i.e. depth resolved, with a wavelength of 532 nm. The samples investigated were deposited with constant parameters, the deposition time being the only parameter varied, resulting in film thicknesses from 100 to 500 nm. It turned out that the diamond fraction and also the grain boundary material do not vary during that stage whereas there are slight but distinct changes of the nature of the amorphous matrix which reflect, among others, in a shift of the graphite-related G band to higher wavenumbers and in an increase of the ratio of D and G bands with increasing film thickness. These changes are discussed in terms of the above mentioned resonance effects; the major changes are a transition of hydrogen containing sp 2 chains to hydrogen-free condensed sp 2 rings when the material is no longer in the surface region of the films but becomes incorporated within the film bulk.

Low temperature growth of ultrananocrystalline diamond

Ultrananocrystalline diamond (UNCD) films were prepared by microwave plasma chemical vapor deposition using argon-rich Ar∕CH4 plasmas at substrate temperatures from ∼400 to 800°C. Different seeding processes were employed to enhance the initial nucleation density for UNCD growth to about 1011sites∕cm2. High-resolution transmission electron microscopy, near-edge x-ray absorption fine structure, visible and ultraviolet Raman spectroscopy, and scanning electron microscopy were used to study the bonding structure as a function of growth temperature. The results showed that the growth of UNCD films is much less dependent on substrate temperature than for hydrogen-based CH4∕H2 plasmas. UNCD with nearly the same nanoscale structure as those characteristic of high-temperature deposition can be grown at temperatures as low as 400°C with growth rates of about 0.2μm∕hr. The average grain size increased to about 8nm from 3 to 5nm that is characteristic of high-temperature growth, but the relative amounts of sp3 and sp2 bonding remained unchanged. These results suggest that the activation energy for UNCD growth is about 2–3Kcal∕mole compared with ∼28kcal∕mole for traditional growth chemistries, and that hydrogen plays an important role in the growth of UNCD films using hydrogen-poor plasmas.