Raman Microscopic Analysis of Internal Stress in Boron-Doped Diamond

Abstract

Analysis of the induced stress on undoped and boron-doped diamond (BDD) thin films by confocal Raman microscopy is performed in this study to investigate its correlation with sample chemical composition and the substrate used during fabrication. Knowledge of this nature is very important to the issue of long-term stability of BDD coated neurosurgical electrodes that will be used in fast-scan cyclic voltammetry, as potential occurrence of film delaminations and dislocations during their surgical implantation can have unwanted consequences for the reliability of BDD-based biosensing electrodes. To achieve a more uniform deposition of the films on cylindrically-shaped tungsten rods, substrate rotation was employed in a custom-built chemical vapor deposition reactor. In addition to visibly preferential boron incorporation into the diamond lattice and columnar growth, the results also reveal a direct correlation between regions of pure diamond and enhanced stress. Definite stress release throughout entire film thicknesses was found in the current Raman mapping images for higher amounts of boron addition. There is also a possible contribution to the high values of compressive stress from sp2 type carbon impurities, besides that of the expected lattice mismatch between film and substrate.

Analysis of Carbon-Based Microelectrodes for Neurochemical Sensing

“…Complementary analysis of CFs by confocal Raman microscopy is also presented in Figure 4a–e. A well-established characterization method in studying carbon-based materials, Raman technique has traditionally played an important role in providing information on sp 2 or sp 3 hybridization in materials, existence of chemical impurities, defects, and other crystal disorders, such as induced strain [4,6,7,8,9,15,19,32,33,34,35,41,42,43]. As compared with the previous images of conventional SEM, the surface and cross-sectional confocal Raman mapping images presented in Figure 4a–d show regions that do not lie within the focal plane of the optics and that are therefore not well defined.…”

“…However, boron-doped diamond (BDD) thin film coatings on metallic rods or on silicon substrates have been used as alternatives for improving stability, limiting background noise, and reducing microelectrode fouling [9,15,32,33]. While improved physico-chemical stability has been reported for these BDD-based microelectrodes, a lower sensitivity to neurotransmitter detection was also found, through FSCV analysis, in comparison to CFMs.…”

“…While improved physico-chemical stability has been reported for these BDD-based microelectrodes, a lower sensitivity to neurotransmitter detection was also found, through FSCV analysis, in comparison to CFMs. To meet the requirements of efficient electrochemical detection, the quality of BDD microelectrodes depends not only on the boron doping level, but also on the choice of the substrate used, as the lattice mismatch between the substrate and the BDD thin film can induce an unwanted strained structure on the latter [32,33]. Thus, deposition of BDD on carbon fibers has been proposed to reduce CF surface degradation [34,35].…”