AUGUST 19, 2008--A new super-resolutionx-ray microscope developed by a team of researchers from the Paul Scherrer Institut (PSI, Villegen, Switzerland; www.psi.ch) and EPFL (Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; www.epfl.ch) combines the high penetration power of x-rays with high spatial resolution. The researchers involved report that these characteristics enable them to shed light on the detailed interior composition of semiconductor devices and cellular structures for the first time.
The first super-resolution images from the microscope are available in an article published online July 18 in the journalScience.
"Researchers have been working on such super-resolution microscopy concepts for electrons and x-rays for many years," says EPFL professor and team leader Franz Pfeiffer. He credits the construction of the "dedicated multi-million Swiss-franc instrument" at PSI's Swiss Light Source with providing the stability necessary to implement the method in practice.
The microscope uses a megapixel Pilatus detector, which can count millions of individual x-ray photons over a large area. This feature makes it possible to record detaileddiffraction patterns while the sample is raster-scanned through the focal spot of the beam. In contrast, conventional x-ray (or electron) scanning microscopes measure only the total transmitted intensity.
The Swiss team formulated an image reconstruction algorithm to treat the resulting diffraction data that "deals with the several tens of thousands of diffraction images and combines them into one super-resolution x-ray micrograph," explains PSI researcher Pierre Thibault, first author on the publication. "In order to achieve images of the highest precision, the algorithm not only reconstructs the sample but also the exact shape of the light probe resulting from the x-ray beam."
Conventional electron scanning microscopes can provide high-resolution images, but usually only for the surface of the specimen, and the samples must be kept in vacuum. The Swiss team says its super-resolution microscope bypasses these requirements, allowing scientists to look deeply into semiconductors or biological samples without altering them. It can be used to non-destructively characterize nanometer defects in buried semiconductor devices and to help improve the production and performance of future semiconductor devices with sub-hundred-nanometer features. A further promising application is in high-resolution life science microscopy, where the penetration power of x-rays can be used to investigate embedded cells or sub-cellular structures. The approach can also be transferred to electron or visible laser light and aid in designing new and better light and electron microscopes.