Dutch scientists have succeeded in improving the imaging resolution of an electron microscope by a factor 2.5, by using a new type of detector. Their success is going to push efficiency and sensitivity on nanoscale materials research: it will actually make it possible to design and build the thinnest materials with improved control and quality. These processes are significant for the development of micro- and nano-electronics.
The tests with the new detector were performed by scientists from the Dutch Universities of Leiden and Twente, and IBM.This research is the first phase of the Escher Project (University of Leiden) which is supported by a 2.3 million Euro government grant through the Dutch Organization for Scientific Research (NOW).
The improvement of imaging resolution allows the Low Energy Electron Microscope (LEEM) to be used for experiments on the growth and properties of the thinnest materials on the planet, which consist of only a single atomic layer of carbon, known as graphene. This material is considered very promising for novel electronic applications. LEEM was developed to observe graphene growth processes on surfaces on the nanometer scale in real-time.
“Low Energy Electron Microscopy, a relative newcomer in the field of microscopy, is steadily gaining importance in both industrial and academic research. It is the leading technique in studies of processes that are essential for the development of micro- and nano-electronics”, says Ruud Tromp of IBM´s T.J Watson Research Center and professor at Leiden University: “In a conventional electron microscope, the electrons are accelerated to high energies to irradiate the sample. What is special about LEEM is that it uses low energy electrons. Such slow electrons are very sensitive to the finest structures at the surface. Magnetic electron lenses use the reflected electrons to form a video image of the sample and even of its electronic properties. A better detector of course results in a better image.”
The improvement in imaging resolution has been made possible by a high tech CMOS detector, called Medipix2. Medipix2 was originally developed by CERN, the Dutch NIKHEF organization, and others, to detect X-rays. Instead, Leiden University researchers Sense Jan van der Molen, Irakli Sikharulidze and Ruud Tromp of IBM installed a Medipix2 detector in the LEEM instrument at the University of Twente. Given the excellent results, the researchers expect that Medipix2 will be standard in future LEEM instruments.
The advantages of the improved image quality are significant for the development of micro- and nanotechnology. For instance, it will now be possible to study the growth and properties of graphene in depth, thereby opening up new opportunities, including developing smaller and smarter storage and memory devices.
Graphene opens up new possibilities for electronics and spintronics, but the important step from laboratory to industry has not yet been made. With LEEM, the growth of graphene can be imaged live, enabling the development of large-scale manufacturing methods. It is also a big step forwards for studies of exotic combinations between metals and organic molecular materials, as explored in molecular electronics. Plans for Escher include a series of experiments with molecular layers that are exactly one molecule thick (‘self-assembled monolayers’). By careful choice of the molecules, we can give a surface new properties, for example in controlling how well water wets the surface, which may be important in biological applications.
The Escher microscope will be installed at Leiden University later this year. Originally designed by Ruud Tromp, the instrument will be further developed by Leiden University. Escher will cover a temperature range from almost absolute zero to above 1500 Celsius. Many materials are fabricated at high temperatures, but the properties of interest occur only at very low temperatures. Escher will now be able to study high temperature fabrication processes and low temperature properties in a single instrument.