Lateral Resolution (X,Y) Issues:
The sidewall angles of the tip determine its ability to probe high aspect ratio features. Its radius of curvature will determine the highest lateral resolution obtainable.
Pixels are the data points of an image in the X and Y direction. The Number of Samples parameter in the Real-time menu determines this number (512, 256, or 128). Features smaller than the pixel size of the image cannot be resolved (image size [μm] / parameter setting = smallest resolution). The data displayed is an average of samplings because the feedback loop is sampling the topography many times each pixel.
Vertical Resolution (Z) Issues:
Resolution is determined by the vertical scanner movement (<1Å) rather than by the tip shape.
The number of data points in the vertical direction limits the smallest resolvable height change. This number is determined by the conversion of 65,536 data points (16 bits) over the full range of the scanner (440V). For example, if the scanner has 10 μm of total possible travel and the system is 16 bit, the resolution is 10 μm/16 bit = 10000 nm/65,536 data points.
The combined effects of electrical, mechanical, and acoustic noise sources equal the overall system noise. Overall system noise is the primary limiting factor in the obtainable vertical resolution of the SPM. A number of steps can be taken to improve the system noise. Some common approaches include acoustic vibration isolation devises, clamping cables, or placing the system on a ground floor way from noise sources. Some less common approaches are using shorter cantilevers for higher signal to noise and lasers with low point noise.