Single-crystal 4H silicon carbide (4H-SiC) is a key substrate material for third-generation semiconductor devices, where surface and subsurface integrity critically affect performance and reliability. This study systematically examined the evolution of surface morphology and subsurface damage (SSD) during nanoscratching of 4H-SiC under varying normal loads (0–100 mN) using a nanoindenter equipped with a diamond Berkovich tip. Scratch characteristics were assessed using scanning electron microscopy (SEM), while cross-sectional SSD was characterised via focused ion beam (FIB) slicing and transmission electron microscopy (TEM). The results revealed three distinct material removal regimes: ductile removal below 14.5 mN, a brittle-to-ductile transition between 14.5–59.3 mN, and brittle removal above 59.3 mN. Notably, substantial subsurface damage—including median cracks exceeding 4 μm and dislocation clusters—was observed even within the transition zone where the surface appeared smooth. A thin amorphous layer at the indenter-substrate interface suppressed immediate surface defects but promoted subsurface damage nucleation. Crack propagation followed slip lines or their intersections, demonstrating sensitivity to local stress states. These findings offer important insights into nanoscale damage mechanisms, which are essential for optimizing precision machining processes to minimise SSD in SiC substrates.

This paper presents a method to improve the alignment accuracy of a mask in linear scale projection lithography, in which the adjacent pixel gray square variance method is applied to a charge-coupled device (CCD) image to obtain the best position of the focal length of the motherboard and then realize the alignment of the focal plane. Two image positions in the focal plane of the CCD are compared with the traits overlap according to the image splicing principle, and four typical errors are corrected on the basis of the total grating errors. Simultaneously, the rotation error of the mask is used to summarize the grayscale variation function of the CCD image. Threshold functions are employed to express the factors including the wave crests of the amplitude, period error, and phase error, which govern the rotation accuracy and weight alignment accuracy expression of the established four error factors. Finally, in the experiment, the slope of the mask is corrected and adjusted to the same direction as the slide plate with the assistance of a dual-frequency laser interferometer. The effect of the alignment error on the lithography accuracy is discussed and verified in the static case, and it is found that the CCD maximum resolution pixel is 0.1 μm and accuracy of the scale is 0.79 μm in only a 200-mm-measurement range.

The transition metal Cr-doped ZnSe semiconductor is a kind of material that can realize laser output in the mid-infrared band and has broad application prospects in the fields of air monitoring, surgery, optical communication, industrial production, and national defense. In this work, the electronic structure, optical properties, and stability of ZnSe and ZnSe:Cr with vacancy defects introduced at Zn and Se sites were investigated. The vacancy affects the internal structure of the ZnSe crystal, where the Se vacancy increases the bandgap, but the Ze vacancy changes the semiconductor properties of ZnSe. Affected by the vacancy of adjacent atoms, the impurity bands produced by Cr²⁺ in ZnSe:Cr crystals have undergone changes in their position and degeneracy in the bandgap. In terms of optical properties, Zn vacancy leads to a more significant red shift (5375.37–6447.55 nm) of ZnSe:Cr absorption peak position than Se vacancy (620.48 nm). Zn vacancy and Se vacancy made the absorption peak of ZnSe red shift (2250.84 nm) and blue shift (144.71 nm), respectively. Meanwhile, Zn vacancy improved the refractive index and reflectivity of the crystal significantly. Our results suggest that vacancy defects can affect the luminescence range of ZnSe and ZnSe:Cr crystals. This phenomenon can be used to judge whether the crystals are defective or not, and long-wave laser can also be obtained from defective crystals.

This paper proposes an offline measurement method for a large aspheric mirror during its grinding stage. A measurement method and mathematical model to realize a three-dimensional (3D) profile measurement for large-diameter aspheric mirrors are proposed, based on a cylindrical coordinate system. The measurement error induced by the alignment error is examined based on the error analysis of the measurement and workpiece coordinate systems. The corresponding pose error obtained through the nonlinear least squares method is eliminated to improve the measurement accuracy. To evaluate the entire surface profile error, a 3D profile model is established. The total uncertainties of the proposed measurement system are also estimated. Comparison experiments for a 300-mm-diameter K9 glass workpiece are conducted on UPFM900 and Taylor Hobson PGI 3D profile instruments, and the profile accuracy is found to be improved from 15.3 to 7.12 μm after eccentricity and tilt error elimination.

Large-diameter aspheric mirrors made of hard and brittle materials suffer from low efficiency in the grinding stage, making them difficult to process. In this study, a nonuniform rational basis spline (NURBS) interpolation method is proposed and developed based on the grinding wheel path planning. The characteristic parameters of NURBS machining program are calculated to ensure the accuracy of curve interpolation path planning, and a series of control points are selected according to the normal vector points of the grinding wheel path. The control points were determined by the distance between the aspheric tangent and the next type value point at a fixed distance d. We then established a mathematical model for the knot point and simulated the relationship between the knot point and d. This indicated that d must be optimized according to the number of points to reduce the number of control points. According to this established model, a comparison experiment was conducted using an off-axis aspheric mirror, with a 280mm diameter. Straight line and NURBS grinding were compared, and the NURBS interpolation method was shown to effectively improve grinding accuracy and efficiency by about 30.