Rare milling equipment that produces nanosize semiconductor structures, or micropillars, is now at the disposal of scientists and students at the University of Warsaw. These micropillars can be used as efficient light sources and will open up educational possibilities in the field of nanotechnology engineering. “Being able to generate micropillars directly in the university laboratories is of key importance to our research, especially as regards works on really efficient yellow laser light sources,” said Wojciech Pacuski. The equipment purchased by the Institute of Experimental Physics at the university is one of only a handful of such devices in Poland. Micropillars are a variety of optical microcavities, structures in which photons are confined for a relatively long time in a small volume. Micropillars are obtained by milling a surface that previously was constructed of many layers of semiconducting materials with carefully selected characteristics. The focused gallium ion beam milling equipment is being vented by Jolanta Borysiuk. (Image: Marek Pawlowski, University of Warsaw) “The surfaces out of which we are currently fabricating micropillars were made at the university in Bremen [Germany]. Soon we will be able to make them here as well with the aid of another acquisition of the faculty, currently being installed — molecular beam epitaxy equipment,” said Tomasz Jakubczyk, student in the solid-state physics division of the Institute of Experimental Physics. To build a micropillar, scientists must remove material from the surface with precision in such a way as to create a pillar of diameter and height of the order of micrometers. Helios NanoLab device, which allows milling of a surface with a beam of gallium ions, is used for that purpose. After being accelerated to high energy, ions are focused to an accuracy of several nanometers and directed toward selected points of the surface. Given their considerable size and mass, gallium ions do not penetrate the material but rather sputter atoms from its surface. The sputtered atoms disperse in the vacuum chamber. The effects can be immediately assessed by means of a scanning electron microscope, which is an integral part of the device. Apart from micropillars, it is possible to generate other dimensional semiconductor structures using this method. This electron microscope image shows the first micropillars generated at the University of Warsaw. (Image: University of Warsaw) The 5 million zlotys’ ($1.797 million) worth of focused ion beam milling equipment was purchased as part of the Center for Preclinical Research and Technology project, co-financed under the European Regional Development Fund as part of the Operational Program Innovative Economy 2007-2013. “The equipment will be available not only to scientists but also to students [at the University of Warsaw] specializing in condensed-matter physics, including those who pursue the recently introduced nanostructure engineering interdisciplinary studies,” said Pacuski. Micropillars have many modern applications, especially in constructing single-photon sources and generating entangled photon pairs. Sources of this type are used, among others, in works on optical and quantum computers and in quantum cryptography. The logo of the Faculty of Physics, University of Warsaw was milled with an ion beam on a semiconductor surface. (Image: University of Warsaw) Scientists from the University of Warsaw are particularly interested in micropillars containing quantum dots. “Quantum dots themselves are good sources of single, and even entangled, photons, but the desired characteristics are additionally enhanced when they are placed inside micropillars. A micropillar with quantum dots can, for example, emit single photons more frequently,” explains Jakubczyk. Physicists from the University of Warsaw intend to use the new equipment to construct micropillars that are sources of yellow laser radiation. “With a method devised by Pacuski in collaboration with colleagues from Bremen and patented in 2009, we can create mirrors, which are a crucial element of a laser, on both ends of micropillars. The fact that we are one of a handful of laboratories in the world specializing in materials from the II and VI group of the periodic table is an additional asset in works on a yellow laser. These compounds emit light precisely in the wavelength range corresponding to yellow light,” said Jakubczyk. Microlasers emitting yellow light will be built as part of the “Lider” project. They may be useful in those fields of telecommunication that make use of plastic optical fibers, which attenuate yellow light the least. Increasingly popular displays offering an additional range of colors (other than the standard RGB) also rely on yellow lasers. “We try to get students involved in our research into new solutions already at the early stages of their academic studies,” says Andrzej Wysmolek, vice dean. For more information, visit: www.uw.edu.pl