Metrology for quality control of energy harvesting systems using nano-materials
Challenge
Advanced industrial manufacturing is considered by the EU to be a Key Enabling Technology as this sector is an important driver for European employment and prosperity. One factor limiting the miniaturisation of electronics is battery size. An emerging area that could address this is piezoelectric nanowires. These are sub-micron “rods” that generate electricity when exposed to a mechanical force or movement and can be incorporated into such things as semiconductors, photonics, and microelectronics. However, to ensure products containing these meet quality standards, have no defects, and avoid waste and pollution requires improved measurement tools.
Two standard instruments for nanoscale measurements are atomic force microscopy (AFM) and scanning electron microscopy (SEM). In AFM a sharp tip at the end of a cantilever moves over a sample, generating scanlines to provide a 3D reconstruction of the surface morphology. The resolution of AFM, although high, is limited by the tips used. These are generally fragile and can be problematic when using a high probing force. In addition, the tip area function of traditional AFM probes does not align with typical nanoindenter tips in nanomaterial testing. SEM is a faster process and employs an electron beam to scan a sample but lacks the 3D resolution of AFM.
Advances in these areas would improve characterisation, and thus quality control, for nanowires and a range of advanced materials and products.
Solution
During the NanoWires project, new AFM tips tailored for nanomaterial testing were designed by partner Trinity College Dublin and produced using focused ion beam milling. Based on a standard AFM conical tip, a layer of almost flat diamond was added, making their structure similar to the standard Berkovich indenter tips used for testing the hardness of materials. Their electrical properties were characterised by LNE, the National Metrology Institute of France, using conductive AFM (c-AFM) and Kelvin Probe Force Microscopy (KPFM), demonstrating reliable nanomechanical measurement and long-term stability, even for hard semiconductor materials such as gallium nitride. In addition, novel 3D nano-printed conductive AFM probes were fabricated that provide sharp high-aspect ratio conductive tips for electrical analysis.
The new diamond AFM tips allow simultaneous electric and mechanical measurements of individual nanowires, offer high force sensitivity, and are compatible to the ISO 14577 standard for hardness indenter tips.
Impact
The company QDM, as part of Quantum Design Int., have provided technology solutions to researchers in the fields of physics, chemistry, biotechnology, materials science and nanotechnology for more than 40 years. They used their FusionScope instrument during the project to analyse nanowire samples. This instrument, the first true correlative microscopy platform that combines AFM with SEM and EDS in one device, allows the SEM function to rapidly image nanowires to identify areas containing defects, allowing the AFM function to provide a more detailed characterisation of the area. AFM tips fabricated using advanced techniques including 3D nanoprinting have now been integrated with QDM’s FusionScope instrument, providing it with enhanced functionalities and greatly expanding the range of samples it can analyse, not only nanowires but graphene sheets, plasmonic structures, semiconductors and many more.
The company acknowledge the work performed has provided them with a greater knowledge of the metrology and characterisation of nanowire-based materials – information that they can now pass onto their customers.
The innovative instrumentation, components and metrology developed will contribute to quality assurance and control of newly developed devices for energy harvesting and storage, and substantially improve the competitiveness of European industry in a range of advanced materials and products.
- Category
- EMPIR,
- Energy,
- New Technologies,
- EMN Advanced Manufacturing,