The detection of the surface morphology of glow discharge sputtering craters is of great significance in scientific research, engineering applications, and product quality control. The depth, size, and shape of the sputtering crater reflect the conditions of the glow discharge and sputtering rate. The surface morphology of the glow discharge sputter craters is also crucial for the layer-by-layer analysis of the plated samples. High-precision instruments, such as white light interferometers, are available in the market to detect the surface morphology of glow discharge sputtering craters and reconstruct the crater profile. However, such instruments are expensive, which increases the economic burden on small- and medium-sized research institutes and enterprises. Compared with white light interferometers and other high-precision detection instruments, optical coherence chromatography (OCT) instruments are cheaper, and their detection accuracy can meet the application requirements of glow discharge sputtering crater topography measurement. Thus, the cost performance is higher. Moreover, the application of the SD-OCT technology in the field of glow discharge analysis has not yet been reported. Therefore, this study adopts OCT technology combined with glow discharge analysis technology and proposes a surface topography detection method based on spectral domain optical coherence chromatography (SD-OCT) for large sputtering craters of glow discharges.

Glow-discharge, large-sized sputtering crater surface topography is detected via SD-OCT. An SD-OCT system is used to scan the large sputtering crater produced by glow discharge to obtain complete images of sputtering craters. By extracting the original spectral signal data from the image, filtering, denoising, and peaking processing are performed to eliminate the noise interference and accurately locate the spectral peak. The original data are stitched together to recover the complete sputter crater depth information. After the peak position data are obtained, the transverse and longitudinal coordinates of the crater depth profile are determined to reconstruct and correct the glow-discharge large-size sputtering crater profile to obtain more accurate and reliable surface topography characteristics of the sputtering crater. The method is designed to accurately measure the surface topography of large-sized sputtering craters and to provide strong technical support for scientific research and industrial applications in related fields.

Figure 9 shows the comparison of 2D contour maps measured by two methods for different sputtering craters with an average depth of 10?50 μm. Figures 9(a1)?(d1) show the sputtering crater profiles reconstructed using the SD-OCT detection method, and Figs. 9 (a2)?(d2) show the sputtering crater profiles measured using the white light interferometer. Figure 9 shows that at the same sampling location, the crater depth profiles obtained using the two methods are consistent. The SD-OCT detection method proposed in this study can accurately reflect the cut surface topography of the glow-discharge sputtering crater of a sample and reconstruct the sputtering crater depth profile. As shown in Fig. 10, the crater depth and sputtering rate measured by the glow-discharge sputtering rate detection method based on SD-OCT are consistent with the measured results of the white light interferometer, and the sputtering rate curve has a good correlation. The relative errors of the two measurement methods are within 3.97%. Moreover, the depth of a large-size glow-discharge sputtering crater is usually tens of microns to hundreds of microns. Hence, this method can meet the measurement requirements of the depth of glow-discharge sputtering craters above 1.88 μm, and it can realize the reliable detection of the glow-discharge sputtering rate. The use of SD-OCT for the standard sample sputtering rate correction and quantitative conversion of the elemental mass fraction can provide accurate qualitative judgments as well as important quantitative information. Figure 12 shows that zinc is the main element on the surface of a galvanized sheet, and the mass fraction of zinc gradually decreases with sputtering time, whereas the mass fraction of iron gradually increases with time. When the sputtering time is 200?300 s, an interface layer of zinc and iron forms in the galvanized sheet.

Through the combination of glow-discharge spectroscopy and SD-OCT, the main work of this study is as follows. A detection method for glow-discharge large-size sputtering crater surface topography based on SD-OCT is studied. The contour reconstruction of a large-size glow-discharge sputtering crater (diameter of 15?40 mm) and the accurate detection of the glow-discharge sputtering rate are realized through peak searching, denoising, and stitching the original data of an SD-OCT-scanned sputtering crater image. The glow-discharge sputtering rate data obtained using this method are compared with those obtained using a white light interferometer. The maximum relative error is 3.97%, thereby verifying the reliability of this method. In addition, the SD-OCT low-discharge large-sized sputtering crater surface topography detection method is used to complete the layer-by-layer analysis of galvanized plates along the depth direction, thereby realizing the application of this method in the analysis of galvanized plates and providing a new and effective solution for the detection of glow-discharge sputtering crater topography and sputtering rates.