MFP-3D NanoIndenter™

For Quantitative Surface Characterization

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Nanoindentation applications in Atomic Force Microscopy have been a popular technique for characterizing a wide range of materials. Typically, most nanoindentation is done with the AFM cantilever. Unlike commercially-available cantilever-based nanoindenters, the Asylum Research NanoIndenter drives the indenting tip perpendicular to the sample. Displacement and force are measured with optimized AFM sensors that eliminate inaccuracies present in other systems. This allows for increased sensitivity and resolution. This highly quantitative tool, combined with the high end AFM capabilities of the MFP-3D, breaks new ground in the characterization of materials including thin films, coatings, polymers, etc.

How it Works
The NanoIndenter consists of a flexure with a calibrated spring constant to which diamond tips are mounted (see schematic to the right). This flexure is attached to the MFP-3D head and replaces the standard the cantilever holder. Displacement of the indenting flexure is performed with a piezo actuator (head) and measured with a patent-pending NPS™ Nanopositioning sensor.

The force is computed as the product of the spring constant and the measured indenter flexure displacement. This measurement is done by converting the vertical flexure displacement into an optical signal measured at the standard MFP-3D photodetector. Because the two quantities of indentation, depth and force, are computed based on displacements measured with AFM sensors, the indenter has unprecedented resolution.

Operation is very simple – simply replace a standard cantilever holder with the NanoIndenter module. The figure to the right shows the module attached to an MFP-3D head.

Spring Constant Calibration
The spring constant is calibrated with three independent methods to minimize error in measurements—added mass method, calibrated springs, and microbalance. Calibration is performed at the factory in the indenter flexure and the mechanical converter/mirror mount assembly, ensuring precision and accuracy.

Samples
The sample is held rigidly to the MFP-3D scanner through specialized sample mounts. Three different sample mounts small, medium and large for easy sample handling and mounting, come standard with the system.

Models
The NanoIndenter comes in two different models, Standard and Low Force, so that material characterization is possible for a great diversity of materials on the same platform (see specifications on last page).

Tip Characterization for Accurate Computations
The tip characterization is extremely important for quantitative analysis in nanonindenting applications. Among different methods, indenting on a standard sample (fused silica) has been a traditional way to evaluate this relationship. However, this method is indirect and relies on theoretical and experimental assumptions. In contrast, the NanoIndenter allows direct tip metrology using conventional AFM metrology with our NPS.

For tip characterization, the nanoindenting tip should be of known geometry to deconvolve the true indenter tip area function. A high aspect ratio AFM tip can be used for improved metrology. Broken or used tips can be identified and discarded through AFM imaging, while proper tips can be accurately characterized as shown below. This allows repeatable imaging, quantitative feature measurement, reliable and accurate imaging offsets, quantitative force curves, and quantitative positioning for manipulation and lithography. The image below shows a) a new cube corner tip, b) a damaged tip, and c) used tip.

Applications and Examples
The NanoIndenter is ideal for a variety of nanoindenting applications including:

• Elastic behavior of metals, ceramics, polymers, etc.
• Dislocation phenomena in metals.
• Fractures in ceramics.
• Mechanical behavior of thin films, bone, biomaterials.
• Residual stresses.
• Time dependent mechanical characteristics in soft metals and polymers.

True AFM Imaging of Cracks
The MFP-3D AFM platform allows accurate estimation of pile-up and sink-in material volumes. AFM imaging is key to identification of cracks, displacement, and failure zones in indented samples as well as imaging of features revealing physical phenomena. Select the image to the right to play the movie that shows an indent on silicon performed with a cube corner diamond tip.

Force Curves
These force curves obtained with a cube corner diamond on a beryllium copper sample illustrate how the indenter performs reliable measurements in three different orders of magnitude for force.

Nanoindenting Tips
Asylum Research offers a variety of nanoindenting tips with defined standards or custom requested geometries. The tips are calibrated in compliance with the requirements of the International Standard ISO/IEC 17025.1.

Dimensions and angles comply with the ISO 14577-22 standard which defines internationally accepted micro and nanoindenter tolerances. There are numerous geometries available for the indenter shape such as three sided pyramids, four sided pyramids, wedges, cones, cylinders or spheres. The tip end of the indenter can be made sharp, flat, or rounded to a cylindrical, or spherical shape. We carry Berkovich, Modified Berkovich, Cube Corner, and Vickers as standard traceable nanoindenters following the definitions of ISO 14577-22. These indenters are inspected and measured with equipment and standards traceable to the NIST or PTB. Contact Asylum Research for quotations.

Diamond and sapphire are the primary materials of nanoindenter tips but other hard materials can also be used such as quartz, silicone, tungsten, steel, tungsten carbide and almost any other hard metal or ceramic. We also offer conductive diamond.

Conclusion
The NanoIndenter for the MFP-3D AFM offers the most technologically advanced, quantitative measurements for nanoindenting applications and can be used for a wide spectrum of measurements and methods for nanoindentation. For additional information, see our MFP-3D-SA and MFP-3D Controller brochures.

Specifications

NanoIndenter Module
Includes factory-calibrated indentation module (Standard or Low Force); two diamond tips (cube corner and Berkovich) and one sapphire sphere (other geometries may be purchased separately). Also included are a spring constant check-calibration reference; sample holders for small, medium and large samples; and MFP-3D Leg Extenders. Requires Top View Head for optical side view of indenting tip.

NanoIndenter Flexure
Two models of flexure indenter available: Standard and Low Force.
All specifications are for both models except where noted.

Force Resolution
Measured in a 1kHz bandwidth.

	Standard	Low Force
Maximum load:	14mN	2mN
Load resolution:	50nN	5nN
Depth resolution:	0.3nm	0.3nm

Range
Z range: 15µm standard, 28µm (optional).
Load rate range (Vlr): 80nm/s <Vly<80µm/s.

Sample Size/Holders
Small: 12.7mm SEM diameter.
Medium: 2.0” maximum diameter.
Large: 4.0” x 2.4” maximum diameter.

Stage
Micrometer driven stage for mechanical alignment of the cantilever tip and sample.

Scan Axes
X&Y: 90µm travel in closed loop. Closed loop position control with sensor noise <0.6nm average deviation (Adev) in a 0.1Hz-1kHz bandwidth (BW) and sensor nonlinearity <0.5% (Adev/full travel) at full scan. Optional motorized X-Y.
Z: >15µm sensored travel in closed loop. Sensor noise <0.3nm Adev in a 0.1Hz-1kHz BW and sensor non-linearity less than 0.2% (Adev/full travel) at full scan. Z height: noise <0.06nm Adev, 0.1Hz-1kHz BW.

MFP Head
Top View Head: Flexure-mounted optical lever system with low-coherence SLD, liquid-compatible and AC-capable cantilever holder, dichroic mirror and window for optical access to cantilever, 80-pitch engage screws, and Invar shell. A 10x, 0.28 NA long-working distance objective with focus and beamsteering adjustments, allows high resolution optical imaging of tip and sample. Optional 28µm Extended Head available.

Software
Based in IGOR Pro by WaveMetrics, a powerful scientific data acquisition and analysis environment. The software is user-programmable.
For nanoindentation, features include but not limited to:
• Displacement controlled.
• Force driven feedback.
• Force vs. time.
• Force vs. displacement.
• Constant loading rate.
• Quasi-static test methods: indentation creep, stress relaxation.
• Dynamic techniques.
• Advanced 3D rendering with ARgyle™.

Specifications are preliminary and are subject to change without notice.