Hysitron Nanoindenter
Hysitron TI950 Triboindenter with Performech II Advanced Control Module
The Hysitron TI950 Triboindenter, equipped with Performech II Advanced Control Module, is the CEMMS flagship instrument for nanomechanical and nanotribological characterisation of materials. This instrument performs reliable and flexible measurement techniques including quasi-static nanoindentation, dynamic nanoindentation, XPM mechanical property mapping, nanoscratch, nanowear, and in-situ SPM imaging.
The sample stage sits on a high-precision motorised stage with a resolution of 500 nm to enable precise positioning of the nanoindentation tip. The high-resolution optical microscope, piezo scanner, and 2D capacitive transducers are connected to the Z axis stage for optical focussing and tip positioning. The whole set-up is built on a metrology-grade granite frame and an active anti-vibration isolation table inside an environmental isolation enclosure to minimise noise and vibration, block air currents, and reduce thermal drift.
Hysitron TI950 Triboindenter
Ideal for:
- Quantifying the material hardness and reduced modulus at the micron scale.
- “Mapping” hardness/mechanical properties at the micro scale across large sample surface areas.
- Performing scratch and wear tests at the micron scale.
- Performing compression testing of columnar features produced with the FIB to quantify mechanical strength at the micron scale.
The transducer containing the nanoindentation tip is attached to the TriboScanner piezoelectric ceramic tube. Piezoelectric materials can rapidly change shape while maintaining a constant volume with the application of high voltage. The top half of the tube consists of four separate quarter cylinders that each control motion in a different direction (+X,−X, +Y , and −Y ) while the bottom half is made from a single piece of piezoelectric ceramic to control vertical motion (+Z and −Z). By controlling the voltage applied to each of the five portions of the tube, precise 3-dimensional movement in a total range of approximately 60 × 60 μm in the X-Y axis and 3 μm in the Z axis of the tip can be achieved.
After a suitable test location is found from optical microscopy, the high precision motorised stage moves the sample underneath the nanoindentation tip and the Z axis motor moves the piezo tube and transducer to a height of 10 μm above the focal plane of the microscope. The TriboScanner then moves the transducer down slowly until a small amount of force (2 μN by default) is detected, indicating that contact of the surface and the tip has been made.
During nanoindentation, the piezo tube remains stationary. Force and displacement actuation and measurement are done using the 2D three-plate capacitive transducer. The upper and lower plates are connected to high frequency out-of-phase AC signals of the same voltage. Displacement measurement is done by measuring the change in capacitance of the central plate relative to the top and bottom plates.
A drive circuit board in the transducer converts the position (capacitance C0) of the floating plate into a DC signal. When the floating plate is exactly at the centre between the upper and lower plates, the DC signal is zero. The value of C0 changes slightly with minute changes in the ambient condition. It needs to be calibrated by performing an indent with the tip hanging in air every time the door to the chamber is opened. As the tip moves up and down, the floating plate moves up and down and the DC signal changes, enabling precise displacement measurement.
Force actuation and measurement is achieved by applying a large DC bias (up to 600 V) to the lower plate. The floating plate is pulled down by electrostatic attraction to the lower plate and force is applied. Conversely, the magnitude of the force can be calculated from the magnitude of voltage applied. The three-plate capacitive transducer is able to apply a maximum of 10 mN force with a 1 nN resolution and 5 μm displacement with a 0.04 nm resolution in the Z-axis. Because of this versatility, nanoindentation testing can either be done with a load-controlled or a displacement-controlled feedback loop.
Two additional transducers are also mounted on opposite sides of the first transducer at a 90° angle to enable lateral force and displacement measurement and actuation. The 2D transducer is capable of applying a maximum of 2 mN force with 3 μN resolution and 15 μm displacement with 4 nm resolution in the X-axis. These two additional transducers enable nanotribological testing procedures to be performed.
By combining the lateral movement capability of the TriboScanner piezo tube and the sensitive force and displacement measurement ability of the transducer, the nanoindenter is able to perform in-situ Scanning Probe Microscopy (SPM) analysis on the sample using the nanoindentation tip, to obtain high resolution images. This is done by raster scanning the surface of the sample with the nanoindentation tip and measuring the force and displacement experienced by the tip. Using a Proportional-Integral-Derivative (PID) control loop feedback mechanism, the DC bias applied to the lower plate is manipulated to make the tip move up and down and maintain the contact condition of 2 μN setpoint force as it is scanned across the surface.
The depth-sensing nature of nanoindentation requires a known shape and size of the indenter in order to calculate the projected area from the indentation depth. Most of the nanoindentation tips used in this laboratory are made from diamond, the hardest material known, with a very high Young’s modulus. The most common tip in nanoindentation is the Berkovich tip due to its generalised shape and size. The depth-to-area ratio of the Berkovich tip is designed to be the same as the Vickers indenter tip commonly used for microhardness testing. For nanoscratch testing, blunt tips such as the conospherical tip are more commonly used due to its revolution symmetry that enables reproducible results in any scratching direction.
