Nanoscopic strain detection

A non-invasive method for detecting nanoscale strains in semiconductors has been demonstrated by a Spanish-German research collaboration; a development that could lead to more reliable electronic devices.

Scientists at the nanoscience research centre CIC nanoGUNE in San Sebastian, Spain and the Max Planck Institutes of Biochemistry and Plasma Physics in Munich, Germany, were able to map nanoscale material properties with Scanning Near-field Optical Microscopy (s-SNOM).

The technique uses extreme light concentration at the sharp tip of an Atomic Force Microscope to resolve nanoscale images at visible, infrared and terahertz frequencies.

The research team was able to demonstrate for the first time that this microscopy technique is capable of mapping local strain and cracks of nanoscale dimensions. This was demonstrated by pressing a sharp diamond tip into the surface of a silicon carbide crystal. With the near-field microscope, the researchers were able to visualise the nanoscopic strain field around the depression and the generation of nanocracks.

‘Compared to other methods, such as electron microscopy, our technique offers the advantage of non-invasive imaging without the need of special sample preparation,’ said Andreas Huber, who performed the experiments for his PhD project at the Max Planck Institute of Biochemistry.

His colleague, Alexander Ziegler, added: ‘Specific applications of technological interest could be the detection of nanocracks before they reach critical dimensions, such as in ceramics or Micro-Electro-Mechanical Systems, and the study of crack propagation.’

The researchers also demonstrated that s-SNOM can map properties such as density and mobility in strained silicon. With this information, smaller, speedier computer chips could be designed.