Manufacturing Bits: Oct. 16
Baking A (Chip) Cake
In a process that is like baking a cake, the University of Manchester has assembled individual atomic layers on top of each other.
Researchers used individual one-atom-thick crystals to construct a multilayer cake that works as a nanoscale electric transformer. The researchers devised individual atomic planes from bulk graphite and boron nitride. Then, they assembled the crystallites one by one, in a Lego style, into a crystal with the desired sequence of planes.
Source: University of Manchester.
In its nanoscale transformer, the electrons moving in one metallic layer pull electrons in the second metallic layer by using their local electric fields. On the university’s Web Site, Professor Andre Geim said: “The work proves that complex devices with various functionalities can be constructed plane by plane with atomic precision. There is a whole library of atomically-thin materials. By combining them, it is possible to create principally new materials that don’t exist in nature.”
Butterflies Are Free
The University of Pennsylvania has devised a manufacturing technology based on the structural color and superhydrophobicity found in butterfly wings.
Based on holographic lithography and directed self-assembly (DSA), the technique could enable new materials for semiconductors, coatings for solar panels and other products.
“A lot of research over the last 10 years has gone into trying to create structural colors like those found in nature, in things like butterfly wings and opals,” said Shu Yang, associate professor in the Department of Materials Science and Engineering at the university’s School of Engineering and Applied Science, on the school’s Web site. “People have also been interested in creating superhydrophobic surfaces, which are found in things like lotus leaves, and in butterfly wings, too, since they couldn’t stay in air with raindrops clinging to them.”
Source: University of Pennsylvania
In an experiment, researchers fabricated 3D diamond photonic crystals with a controllable roughness of ≤120nm on the surface of a structure. Researchers used a block co-polymer derived from an epoxy-functionalized cyclohexyl polyhedral oligomeric silsesquioxanes (POSS) material.
The crystals were generated during the phase separation and rinsing step in the holographic lithography process, according to researchers. The degree of roughness can be tuned by the crosslinking density of the polymer network, which is dependent on the loading of photoacid generators, the exposure dosage, and the choice of developer and rinsing solvent, researchers said.
“Specifically, we’re interested in putting this kind of material on the outside of buildings,” Yang said. “The structural color we can produce is bright and highly decorative, and it won’t fade away like conventional pigmentation color dies. The introduction of nano-roughness will offer additional benefits, such as energy efficiency and environmental friendliness. It could be a high-end facade for the aesthetics alone, in addition to the appeal of its self-cleaning properties. We are also developing energy-efficient building skins that will integrate such materials in optical sensors.”
Playing The HARPES
Spintronics is a promising technology in which data is processed on the basis of electron “spin” rather than charge. Dilute magnetic semiconductors are the key materials that could enable spintronics. But understanding the source of ferromagnetism in dilute magnetic semiconductors has been a major challenge.
Researchers led by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory have devised a new technique called HARPES, or Hard X-ray Angle-Resolved PhotoEmission Spectroscopy. Using this technology, researchers have investigated the bulk electronic structure of a dilute magnetic semiconductor gallium manganese arsenide.
With the HARPES technique, a beam of hard x-rays flashed on a sample causes photoelectrons from within the bulk to be emitted. Measuring the kinetic energy of these photoelectrons and the angles at which they are ejected reveals much about the sample’s electronic structure. Here the Mn atoms in GaMnAs are shown to be aligned ferromagnetically, with all their atomic magnets pointing the same way. (Source: Alex Gray/Berkeley Labs)
“This study represents the first application of HARPES to a forefront problem in materials science, uncovering the origin of the ferromagnetism in the so-called dilute magnetic semiconductors,” said Charles Fadley, a physicist, on the lab’s Web site. “Our results also suggest that the HARPES technique should be broadly applicable to many new classes of materials in the future.”
HARPES is based on the photoelectric effect described by Albert Einstein in 1905. It enables scientists to study bulk electronic effects with minimum interference from surface reactions or contamination. “We now have a better fundamental understanding of electronic interactions in dilute magnetic semiconductors that can suggest future materials with different parent semiconductors and different magnetic dopants. HARPES should provide an important tool for characterizing these future materials,” he added.
Tags: DSA, hard X-ray angle-resolved photoemission spectroscopy, HARPES, holographic lithography, Lawrence Berkeley National Laboratory, MIT, nanoscale transformer, spintronics, U.S. Department of Energy, University of Manchester, University of Pennsylvania