Analysis of Diamond Micropores Forming and Defects Characteristics Under Different Laser Powers

Objective Diamond has high chemical stability, mechanical properties, high carrier mobility, and thermal conductivity, which has broad application prospects in many frontier fields. Diamond with micropores has good application prospects in high-precision lead forming and high-power microwave device heat dissipation. This study established the variation law of diamond hole patterns and defect characteristics under different laser powers. The diamond hole patterns and defect characteristics are vital in implementing the heat dissipation currently used in substrates for high-frequency electronics. The basic conditions can only be provided for the subsequent microporous metallization when the pore type meets the requirements, and the surface graphite residue and the pore wall are smooth. Methods In this study, laser technology was used to process micropores on self-supporting polycrystalline diamond films. By adjusting the laser power, the influence of laser power on diamond microporous molding was studied, the reaction mechanism of laserdiamond interaction was discussed, and the removal mechanism of diamond was analyzed. Field emission environment scanning electron microscopy was used for morphology analysis. Laser confocal scanning microscopy was used to measure microwell contours. Laser Raman spectroscopy and X-ray photoelectron spectroscopy were used for surface composition characterization to analyze the influence of laser power on the outer and inner surface of micropores and the causes of defects. The material removal mechanism and microhole forming process during laser microhole processing were revealed by introducing diamond ablation threshold analysis. Results and Discussions Morphology analysis was conducted by field emission environment scanning electron microscopy, and the results showed that the microporous surface had significant sedimentary layers and spherical deposits. When the power reaches 17.6 W, the surface of the micropores is damaged and fractured, and there is an obvious stripe structure at the fracture location, which may be formed by the interconnection of crack propagation caused by thermal stress. The diamond-layered deposits begin to fall off when the microporous surface sedimentary layer is partially detached during the fracture of the diamond surface layer [ Fig. 1(d)], and the thermal stress on the microporous surface is greater than the van der Waals force between the sedimentary layer and the diamond. In contrast, as the laser power increases, the thickness of the sediment layer on the diamond surface also increases, which may also be another cause of layered sediment shedding due to the difference in thermal expansion between the layered deposit and the diamond substrate. The topography of the inner surface of the micropores (Fig. 3) shows that a fine graphite layer covers the top of the micropores, and the graphite layer reduced from top to bottom. Simultaneously, significant cracks and flaky shedding of the inner surface can be observed. The microwell profile was measured by laser confocal scanning microscopy, and further analysis of the change of micropore taper showed that the inner surface of the upper end of the micropores was rough. The microporous taper decreased with the increase of laser power. In the downward energy transfer process, it is absorbed by the diamond and generates graphite. The energy received at the lower end of the micropores is reduced, and the diamond micropores finally take on a cone shape. Moreover, because the degree of graphitization increases with the increase of laser power, the thickness of the graphite layer on the surface and inner surface of the diamond increases, which improves the absorption of laser energy; hence, at high power, the energy difference between the upper and lower ends of the micropores increases, which in turn leads to an increase in taper. Laser Raman spectroscopy and X-ray photoelectron spectroscopy were used to characterize the surface composition, and it was proved that the main components of the surface and inner surface sedimentary layers of diamond after laser processing were graphite and then proved that the diamond underwent phase transition under the action of the laser. The effect of power on stress was analyzed by Raman spectral peak shift calculation. With the increase of laser power, the compressive stress on the diamond s outer surface and inner surface increases, and the amplitude of the increase is the same. Finally, introducing diamond ablation threshold analysis reveals the material removal mechanism and micropore forming process in laser microporous processing. The ablation threshold of polycrystalline diamond is 3.16 J/ cm2, and the corresponding average power is 2.23 W. A phase change reaction begins on the diamond surface when the laser energy is above the ablation threshold. The increase in laser power provides more energy for the phase change reaction, and the amount of diamond removal increases, which produces more defects. The reaction is terminated when the energy is absorbed below the ablation threshold. Conclusions The results show that the outer surface of the micropore is damaged when the laser power is high, and the micropore s inner surface also has a striped structure. The degree of graphitization on the outer surface and inner micropore surface increased with the laser power. The taper of the microporous type decreases with the increase of laser power, and the verticality of the micropores was improved. The stress on the inner surface of the micropore during laser processing is greater than that on the edge position of the micropore.