Nanoindentation Measurements and Standards

We develop measurement methods, standard reference materials and data, and traceable calibration techniques for quantitative mechanical property measurement at small scales. Accurate measurement of elastic, plastic, and fracture properties will enable development and reliability assessment of devices that comprise nano-scale features and materials.

Development and reliability assessment of integrated devices subject to mechanical forces while in service requires measurement of mechanical properties at the nanoscale. NIST participated in the development of recent ASTM and ISO standards, which indicate the need for standards-laboratory traceable direct calibrations of forces and displacements, and for reference materials with traceably-measured elastic properties.

Our approach is to develop calibration reference materials and techniques, and disseminate these so that testing laboratories may be assured of the quality of their measurements. Furthermore, we investigate the fundamentals of contact mechanics at the nanoscale, with the goal of increasing the property parameter space that may be measured with nanoindentation techniques.

Impact and Customers:

• Quantitative nanoscale mechanical property measurements are needed in economic sectors as diverse as energy, biotechnology, magnetic storage, and microelectronics. Rapid measurement of elastic, plastic, fracture, and time-dependent properties can accelerate materials discovery and product development.

• Over 1,000 nanoindentation instruments are used daily in materials research and development laboratories worldwide. NIST participated inthe creation of the ASTM Standard Practice for Instrumented Indentation, enabling results to be compared across laboratories.

• The hard disk magnetic storage industry, which is projected to grow to $4.5B in 2009, critically needs indentation and surface probing techniques to develop next generation media and read/write heads.

For over a decade, NIST has been participating in the reation of documentary standards for nanoindentation. Two new documentary standards (ISO 14577 and ASTM E2546) require direct force verification of nanoindenters at the 1% accuracy level whenever indirect verification with test blocks fails. A common field calibration method is to hang masses from indenter shafts, which is awkward because it applies forces opposite to normal indentation,and is inaccurate for small masses.

NIST is uniquely capable of providing force calibration in the millinewton (mN) and micronewton (µN) ranges that is traceable to the International System of Units (SI). The NIST Electrostatic Force Balance (EFB) provides SI-traceable electrostatic force realization at the µN level. We have developed and are characterizing compact, portable force sensors as calibration and verification devices for commercial instrumented indenters.

Prototype capactive force sensors allow compressive forces to be applied by the nanoindentation system, just as in a nanoindention experiment. We have achieved reproducibility and short-term stability in these force cells at a level of 0.2% or better, and long-term (several-year) stability of approximately 2%. We are now building on these accomplishments by continuing to improve mechanical design and electrical detection methods such that stiffer, more accurate, and user-friendly force cells may be developed and disseminated.

Nanoindentation is uniquely capable of assessing elastic, plastic, and fracture properties of very small volumes of materials, and is therefore a useful and combinatorially friendly measurement technique. As an example, we have measured the mechanical properties across the crystalline-amorphous transition region in a HfO2-TiO2-Y2O3 thin film combinatorial library. With nanoindentation techniques, we are able to rapidly characterize elastic and plastic properties for regions of particular interest.

Recent advances from our group in the science of nanoindentation-based property measurement include the measurement of fracture and viscoelastic properties in nanoscale volumes and thin films. Nanoindentation techniques are also capable of measuring the shear stresses needed to homogenously nucleate dislocations, which is crucial information for designing and testing advanced alloys. NIST is leading a multi-laboratory effort, with a combination of rigorous experiment and finite-element modeling, to improve the accuracy with which dislocation nucleation stresses are measured.

In 2007, we have reported our work through presentations at meetings of the Materials Research Society, the NIST Combinatorial Methods Center Workshop, and the Materials Science and Technology (MS&T) conference. In 2008, we will continue to develop traceable force sensors and develop nanoindentation measurement science.