What if you could see the invisible cracks inside a solid piece of steel without slicing it into thin slices? This paper proves that by tilting an electron beam with extreme precision, we can map these defects just like traditional microscopy. Electron channeling contrast imaging was applied by precisely controlling the primary electron beam incident direction of the crystal plane in a scanning electron microscope.

The researchers investigated dislocation contrast in steel materials in detail via this specific SEM method. Dislocation contrast was observed near a channeling condition where the incident electron beam direction varied and backscattered electron intensity reached a local minimum.

Comparing visualized images with transmission electron microscope images showed that the positions of all dislocation lines were coincident. In this study, observation was conducted by controlling the incident electron beam direction with high precision using a piezoelectric element as a driving unit.

The team investigated dislocation contrast in steel materials and measured the depth information of the contrast experimentally. Figure 1 demonstrates the relationship between sample orientation and backscattered electron intensity in a ferrite grain. Panel (a) displays a series of images where the contrast changes as the primary electron beam direction is adjusted relative to the (200) crystal plane at 30 kilovolts.

The corresponding plot in panel (b) quantifies this effect, showing how BSE intensity varies with tilting angle for both 15 and 30 kilovolt accelerating voltages. These results highlight that optimal imaging conditions depend on precise alignment with specific crystal planes.

As the incident primary electron beam direction angle varied concerning the two-zero-zero crystal plane, the backscattered electron intensity changed significantly near the Bragg conditions. The width of the tilting angle between the channeling positions was approximately three point six degrees, which is where the intensity reached a local minimum.

Figure 2 presents a series of electron channeling contrast images captured at an accelerating voltage of thirty kilovolts, where the incident beam is aligned with the one-zero-one crystal plane. By systematically adjusting the tilting angle from zero to point-eight degrees, the authors demonstrate how dislocation contrast emerges and varies near specific channeling conditions.

This sequence visually establishes the precise angular sensitivity required to reveal these defects, which is critical for accurately measuring their intensity and width in subsequent analysis. The dislocation contrast was varied by changing the tilting angle near the channeling condition.

To quantitatively investigate this, the dislocation contrast intensity and width were evaluated from the images. Figure 4 plots three key metrics against the sample tilt angle to characterize dislocation contrast under specific channeling conditions.

The authors track the backscattered electron intensity, the dislocation contrast intensity, and the contrast width as the crystal is tilted around the one-zero-one plane at thirty kilovolts. This analysis demonstrates how these parameters fluctuate relative to the Bragg position, highlighting the sensitivity of the imaging technique to precise angular alignment.

From fifteen to twenty-five kilovolts, the dislocation contrast width decreased as the accelerating voltage increased. However, for the range of twenty-five to thirty kilovolts, the width increased again at thirty kilovolts. This figure validates the ECCI method by directly comparing its output against a standard bright-field TEM image of the same ferrite grain.

The authors show that dislocation lines labeled with Roman numerals appear in identical positions across both techniques, even though they were captured at vastly different voltages of three hundred kilovolts and thirty kilovolts. Panel D further confirms this alignment by superimposing images taken from opposite sides of the film, proving that the surface technique accurately maps the internal defect structure.

Bright-field transmission electron microscopy observations were performed on the same thin film to validate the method as a tool for observing dislocation contrast. The direct comparison showed that the positions of all dislocation contrasts were in clear agreement between the two techniques.

Figure 8 demonstrates the characteristic analysis of dislocations using the g dot b equals zero invisibility criterion. The authors present Energy-Filtered Transmission Electron Microscopy images of ferrite grains captured at thirty kilovolts, utilizing three distinct diffraction vectors to reveal different defect structures.

By comparing these contrast variations with the inverse pole figure map in panel e, the researchers correlate specific crystallographic orientations with the visibility of dislocation networks. When the diffraction condition and the dislocation Burgers vector satisfied the condition where their dot product equals zero, the screw dislocation contrast in the images disappeared.

Additionally, an edge dislocation line was found to be wider than a screw dislocation line. This figure presents a stereo pair of ECC images captured at 30 kilovolts with a 12-degree tilt, alongside a schematic illustrating the geometric arrangement of observed dislocations.

The authors utilize this specific setup to resolve the three-dimensional depth and orientation of screw dislocation lines relative to the sample surface. By analyzing the shift in features between the two views, the study demonstrates how to extract precise depth information from what would otherwise be a flat two-dimensional projection.

Accordingly, the method where the channeling condition is strictly satisfied by controlling the incident electron beam direction can suggestively obtain dislocation contrast deeper than five times the extinction distance. This challenges the typical depth limit often cited for this imaging technique.

Table 2 quantifies the dislocation density by listing the exact number of intersections between dislocations and a grid of horizontal and vertical lines. The authors recorded specific counts for ten horizontal lines, such as seven intersections at h1 and five at h2, alongside corresponding data for vertical lines like v1 through v10.

These raw intersection numbers serve as the critical input for calculating the final dislocation density using the grid intercept method described in the text. The evaluated dislocation densities were seven point one times ten to the thirteenth and one point five times ten to the fourteenth per square meter at depths of one hundred seventy and eighty nanometers respectively.

The value measured at one hundred seventy nanometers was considered reasonable compared to well-annealed ferrite standards. Thus, the method could be used to characterize dislocation and evaluate the strain field around the dislocation, similar to the transmission electron microscope method.

The depth information provided dislocation contrast deeper than five times the extinction distance, typically used as the value for this technique's depth. The authors demonstrate that strictly controlling the electron beam angle allows SEM to reveal dislocation details matching TEM results, even reaching depths deeper than previously thought possible for this technique.