Microscopic properties of MPCVD diamond coatings studied by micro-Raman and micro-photoluminescence spectroscopy

Abstract

Diamond coatings were deposited on silicon (100) substrate using the microwave plasma chemical vapour deposition (MPCVD) technique at different process conditions. Process parameters such as CH 4-H 2 gas mixture concentration, microwave power, chamber pressure and substrate temperature were varied. The diamond coatings were characterized by micro-Raman and micro-photoluminescence (PL) spectroscopy techniques. In this paper we report a comparison of the overall quality of MPCVD polycrystalline diamond coatings grown under different processing conditions in terms of stress distribution, thickness uniformity and surface roughness. Micro-Raman spectroscopy studies over various points on the deposited coating showed that the Raman line widths of diamond peak varied from 3.2 to 18.3 cm −1 with the variation of CH 4 and H 2 gas concentration. The micro-PL spectra suggested the presence of impurity concentration and defects within the diamond coating synthesized at different processing conditions. Transmission electron microscopy (TEM) images provide the direct evidence of the presence of crystal defects which corroborates the Raman and PL results. The coherence scanning interferometry (CSI) showed that surface roughness of diamond coating varied from 0.43 to 11 µm with thickness at different positions of the three coating samples. It has been concluded that Raman line-width broadening and Raman-shift are due to the presence of crystal defects as well as non-uniform distribution of stresses present in the diamond crystals of the coating, due to the incorporation of Si as impurity element and non-uniform temperature distribution during growth. Defect density gets reduced at higher processing temperatures. It is also being proposed that better thickness uniformity and lower surface roughness can be achieved for coatings deposited at low methane concentration under optimized process conditions.

Some Aspects of Diamonds in Scientific Research and High Technology

“…The PCD could become completely opaque or black in colour due to the presence growth defects like dislocations, twining, grain boundaries, stacking faults etc. [121]. Figure 2c and 2d shows transmission electron microscopy images of the line defects pinned at grain boundary in one such poorer variety of black diamonds grown using 3% methane in hydrogen.…”

“…Pezzagna et al [125] suggests that small PL signal for neutral nitrogen vacancy centres is present at 575.67 nm, but for the negatively charged nitrogen vacancy centre, the PL peaks are observed at 637 nm with multiple phonon replica thereafter. It is also well known that silicon vacancy centre emits strong PL signal at 738 nm and a weak replica at 758 nm [121,126]. Although nitrogen vacancy centres are best photo emitters for diamond but it has strong photon-phonon interactions which is responsible for broad emission spectrum from 600 to 850 nm.…”

Interaction of Methane Concentration and Deposition Temperature in Atmospheric Laser Based CVD Diamond Deposition on Hard Metal

“…The clear surface of the crystals in such coatings correlates with these findings. In comparison, microwave plasma CVD diamond coatings attain quality factors between 52% and 90%, depending on the process parameters [12]. Until a concentration of 3.0% is reached, the crystal size only decreases slightly to approx.…”

“…The G-band at 1560 cm −1 [11] in the Raman spectra, was utilized to detect graphite in the deposited coatings. Equation 1 [12,13] was used to calculate the diamond quality factors Q of the deposited coatings using the peak intensity of the diamond Raman line I D and the intensity of the G-band peak I G . The diamond quality factor allows for a semi-quantitative estimate of the quality of a diamond coating, i.e., the concentration of the sp 3 -bonds compared to sp 2 -bonds.…”

Deposition and Characterisation of a Diamond/Ti/Diamond Multilayer Structure

“…The Raman spectrum from a diamond film [50,51] grown on an Ar + plasma-etched Si, deposited during a 3-day long LAMWCVD run, is shown in Figure 3b. The sp3bonded carbon peak appears at 1332 cm −1 .…”