Transistors reach the single atom limit

February 19, 2012 by Joerg Heber 1 Comment

A scanning tunnelling microscope image of a single-atom transistor during fabrication. The pink colours represent the areas where a single phosphorus atom (centre) as well as phosphorus source and drain contacts will be placed. The gate contacts that control the transistor action from the side are not visible here. Credit: Martin Fuechsle

When Gordon Moore made his observation in 1965 that the number of transistors integrated on a single silicon chip is doubling roughly every two years, the only logical end point for such a trend would be a transistor made from a single atom. This point has now been reached. Writing in Nature Nanotechnology, Michelle Simmons from the University of New South Wales in Sydney and colleagues report a single-atom transistor, the world’s smallest, on a silicon chip. The transistor is based on current flowing through a single atom of phosphorus embedded in a silicon wafer. Read more…

Condensed Matter Physics, Nanotechnology, Quantum physics
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Why fancy illustrations are so wrong

February 13, 2012 by Joerg Heber 7 Comments

A MoS2 FET

A beautifully looking graphics, isn't it? But there is a major caveat. As its creators would agree, this image is only a very crude depiction of reality and shouldn't be used for any scientific purpose... (c) LANES, EPFL

Nanotechnology is a wonderful science that has pushed functional devices to sizes not far away from the size of atoms. So small that if you want to image such structures, even a conventional electron microscope wouldn’t get you far. There is no way to directly see what is going on. This is a common problem. Take condensed matter physics – it is impossible to directly visualize the various interactions and events taking place inside a crystal. Or photonics, where complex light fields interact with tiny nanostructures in ways that can be really difficult to visualize, especially in real-time.

So, no wonder that artificial graphics often serve to illustrate a scientific concept or a certain device. And with the prevalence of advanced computer graphics programs such illustrations are becoming more and more fancy. In my opinion, this is a dangerous trend, because such graphics can distort the underlying science they try to depict. Read more…

Condensed Matter Physics, Nanotechnology, Photonics, Science Communication
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From ‘abbreviations’ to ‘Zen and the Art of Motorcycle Maintenance’

February 12, 2012 by Joerg Heber 0 Comments

Henry Petroski is an engineer who has written extensively about his profession. So it is no surprise that over the past decades he has amassed a broad range of facts on engineering, some of which while certainly interesting may not fit into the usual books. For example, did you know that hard hats were first worn during the construction of the Hoover Dam? Or that for the construction of the latter about 2.5 million cubic metres of concrete were used?

Well, as with so many other facts, Wikipedia would also give you the answer to these questions. But that’s not the point. What Petroski has now done is to collect and curate interesting facts related engineering, and published them in alphabetical order as “An Engineer’s Alphabet“.

There are plenty of gems to discover in the book. Many of them I would never have thought to even look up on the internet without being prompted, and in that respect the book is inspiring. I certainly enjoyed browsing through the text. Written by an American professor, it is more American Dream than Steampunk in character, although to be fair Isambard Brunel does appear in eight different entries. Herbert Hoover thirteen times. Robert Noyce only once, in passing.

The best way to go about reading this book is simply do flip through it and to read here and there. Or, to use the indispensable index at the end. Indeed, if £18.99 or $21.99 should be a bit too much of an expense it might make sense to consider the various ebook options, with the highly useful possibility of searching the book. On the Kindle or the Nook prices are about half of the hardcover ones. It doesn’t seem to be available on iBooks. Either way, if you love engineering and are interested in broadening in particular your historic knowledge of the profession, this book might be for you.

Reference:

Petroski, Henry. An Engineer’s Alphabet. Cambridge University Press, 2011. 268 pages. ISBN: 9781107015067. $21.99 / £18.99

Books, Engineering

Coaxial ‘cables’ make great lasers, too

February 8, 2012 by Joerg Heber 2 Comments

A coaxial cable plug. The coaxial nanolaser is more than 15,000 times smaller. Photo by mikemol via flickr.

When Oliver Heaviside invented the coaxial cable in 1880 he could not have foreseen the implications of his idea on modern nanotechnology. His coaxial cables consist of three layers: an inner metallic core, surrounded by an insulator, surrounded by a metallic layer on the outside. The benefit of this design is that the outer metallic layer shields the electrical signal through the cable from outside interference. This makes coaxial cables very useful for information transfer, and coax cables are used for TV antenna cables or some computer network cables. Mercedeh Khajavikhan, Yeshaiahu Fainman and colleagues from the University of California, San Diego now present a completely new application: they have fabricated coaxial lasers on the nanoscale that turn on without the usual minimum threshold power of usual lasers. To do this they had to shrink the coaxial cables first. These lasers are more than 15,000 times smaller than typical coaxial cables.

The nanoscale coaxial laser. Similar to coaxial cables it consists of an inner metal pillar and an outer metal shield. The structure is also protected from interference from the top. Inside is a semiconductor light emitter (red; insulated from the top metal through a SiO2 plug). The laser light exits through the hole in the substrate. Figure by Mercedeh Khajavikhan and Aleksandar Simic.

The benefit of a coaxial cable is that between the core and the outer metal layer well-defined and controlled electromagnetic waves can propagate shielded from any outside influence. Furthermore, shrinking such a device to the nanoscale – to length scales comparable to the light used – means that only the smallest optical beam pattern for the wavelength of light, known as the fundamental mode, fits into the small space between the metal structures. The other modes would be too large. Read more…

Nanotechnology, Photonics

A perfect couple for designing chemical reactions

February 6, 2012 by Joerg Heber 3 Comments

We are all familiar with the basic ways in which light interacts with matter, when light absorption  causes atoms to move and creates heat, or when light gets absorbed by the outer electrons of atoms so that they move into energetically excited states, which is how electricity in solar cells is created. Common to both examples is that light is mainly used as an energy source, and it is easy to visualize. When scientists draw such light interactions into the energy diagram of say a molecule, they often draw little wavy arrows from one energy state to another.

But that’s the boring stuff. Far more interesting is that light can also strongly couple to matter, but without getting absorbed. The example I am discussing here is when the interaction between light and a molecule is so strong that it profoundly alters the molecule’s energy states themselves, and not merely lifts electrons from one state to another. In particular, what Thomas Ebbesen, Tal Schwartz, James Hutchison and colleagues at the University of Strasbourg have now shown is that such interactions could find exciting new applications: to control energy levels of molecules, and in this way to influence the kinetics of  chemical reactions in a new way that creates many new possibilities.

Strong coupling of light and matter. Light confined between two mirrors can strongly interact between matter that is also between the mirrors and has a matching energy level. The strong light-matter coupling then causes a splitting of the matching energy level into two separate states.

To see how this looks in practice it is necessary to understand what the strong coupling between light and molecules means. First of all, to achieve the necessary strong coupling, it is necessary to create a strong feedback mechanism between light and matter. This can be done by squeezing the light field between two closely spaced mirrors, with the desired molecules in-between. In addition, the energy levels of the light field between the mirrors and one of the energy levels of the molecule need to match up. If all these conditions are fulfilled, then the energy state in question is split into two separated states (see figure). This is called Rabi splitting. The stronger the coupling, the larger the energy separation between the two states. Because of the beauty of quantum mechanics this doesn’t even require light to be present, the mirrors are enough. Read more…

Chemistry, Condensed Matter Physics, Photonics
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Shrinking magnetic storage devices

January 15, 2012 by Joerg Heber 1 Comment

Information stored by a chain of magnetic atoms. Left: an STM tip measures the magnetic state of the iron atoms. Right: through increasing the current between tip and atoms the magnetic states can be switched. Peaks become valleys and vice versa. (c) Science Magazine

I now finally got the time to follow-up on last week’s paper in Science by Andreas Heinrich‘s group at IBM on magnetic storage elements that are only a few atoms in size. There have been a few misconceptions in some of the news reports with some being plainly wrong (‘smallest storage device ever made’), and many didn’t mention much about the scientific principles behind this study, although these are quite interesting. One of the better reports appeared in the New York Times, albeit again without going much into details. So I hope I can still add something useful with this blog post.

And actually, we’ve come across Andreas Heinrich’s previous research before, he does very innovative research with scanning tunneling microscopes (STM). In this latest Science paper he has now explored the limits of magnetic storage devices. Magnetism is of course the basis for storage such as magnetic hard drives. The problem in increasing the storage density in any magnetic storage device is that the magnetic regions begin to interfere with each other as they become smaller and are integrated closer together, because magnetic states on the order of just a couple of atoms are not very stable. Read more…

Condensed Matter Physics, Nanotechnology
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