Indentation Probes

An indentation probe consists of a diamond tip mounted to a metal foil cantilever, and is used to image, indent, and wear surfaces of interest. Indentation probes are thicker, wider, and longer than standard AFM cantilevers and are made of stainless steel instead of silicon or silicon nitride. The typical ranges for the spring constant of contact mode, TappingMode, and indentation probes are 0.01–1.0 N/m, 20–100 N/m, and 100–300 N/m, respectively. The resonant frequency for indentation probes is generally in the range of 35–70 kHz, depending upon the dimensions of the cantilever and the size of the diamond. For comparison, the resonant frequency for standard TESP TappingMode probes is about 300 kHz. Unlike contact mode imaging, Bruker’s patented TappingMode technique allows the use of the high spring constant cantilevers required for nanoindentation, while still imaging the surface with minimal damage. A silicon reflector is mounted on the top side of the cantilever to obtain a well focused laser spot on the photodetector.

Figure 1: Typical indentation probe

A typical indentation cantilever has a spring constant of about 150 N/m; length, width and thickness of about 350, 100 and 13 μm, respectively, and a resonant frequency of 65 kHz. Bruker measures and supplies the customer with the spring constant of each probe purchased. The typical indentation force range available with our instrument is 1–100 μN with a resolution of less than 0.5 μN. Larger forces up to about 300 μN can be accommodated, using custom cantilevers with higher spring constants, while maintaining good imaging ability.

Nanoindentation probes available from Bruker AFM Probes include:

• PDNISP
• PDNISP-HS
• DNISP—unmounted for nanoindenting applications on all AFMs
• DNISP-HS—unmounted for high-force nanoindenting applications on all AFMs

The diamond tip mounted to the end of the cantilever has a tip radius less than 25 nm to ensure good imaging resolution and nanometer-scale indents. The diamond tip apex is the corner of a cube so that the apex “A” is formed by three right angle corners. To provide more symmetric dents, the diamond is mounted with the vertical axis of the pyramid approximately normal to the sample when mounted on the microscope.

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