This week, PAUL BRAUN, the Ivan Racheff Professor of Materials Science and Engineering and the Director of the Frederick Seitz Materials Research Laboratory. He studies nano- and micro-structures in that University of Illinois lab, as well as in the Beckman Institute. His team is currently working with colleagues at Stanford and Dow Chemical Company to make discoveries in micro-optics —by electrochemically etching silicon micro-structures they form structures that have many of the properties of lenses — but at half the thickness of a human hair. The new tech has possibilities in everything from communications to cancer research.
How did you get here?
I grew up in New Jersey, went to Cornell University in Ithaca for my undergraduate studies, and came here for my Ph.D. in the 1990s. Then I did my post-doc at Bell Labs, and came back here in 1999 to join the faculty.
Do you have funding for this new technology research?
We are supported by the Department of Energy and Dow.
And what has been your most recent research?
What we recently discovered is a new way to process silicon, a common material used for almost all micro-electronics. The way we process the silicon results in the optical properties being a function of the etch current. If you change the etch current, you change the refractive index (the way the silicon bends light). During the process, the silicon doesn’t etch completely; it just becomes porous.
Depending on the current that you apply, you can vary the porosity; as you vary the porosity, or the ratio of silicon to air, you vary the refractive index. Now, instead of it being like glass, which has one refractive index, the structure has a refractive index that changes with position. We can have a low refractive index on the outside and a high refractive index on the inside, or the other way around.
How does that work in a practical way?
The process allows us to bend light so that we can make lenses and other optical devices used in things like fiber optic communication; with our material we hope to make it easier to move light onto a computer chip, and by doing that enable faster and more efficient information processing. What’s traditionally been a challenge is that lenses have curved surfaces, just like eyeglasses, and it is hard to put a curved lens on a computer chip. What we figured out how to do is to create lenses that are flat, they have a flat bottom and a flat top. These lenses are small. They are about 25 microns across, and a hair is about 50 microns. If light comes in one side of this lens, it can focus over on the other side. You make what is best described as a flat lens.
Why is that important?
We’ve made an array of lenses that look a little bit like skyscrapers.
The flat surfaces should allow us to stack lenses to control reflection, to integrate lenses with other optical components and create entirely new applications.
What might those new applications be?
Applications such as a microscope on a chip or a new way to collect solar light. Or maybe move into the human body.
About five or six years ago, we started working through a DOE center on solar energy, which has as a goal to very efficiently control and manipulate photons. We were familiar with some of the steps required to make our structures; my group had worked on electrical energy storage, and learned to do electrochemistry for things like batteries. We combined that with our interest in optics and then with our colleagues at Stanford and Dow, came up with this idea how to make unique and powerful microscale optics using electrochemistry. As already mentioned, on-chip microelectronics for communications is the most obvious application. There are applications in photo-detectors such as used in cell phones and cameras, as well as some opportunities in making very tiny microscopes, including ones that could someday go inside the human body.
That sounds like "Fantastic Voyage"!
You could look at cells inside a body, without doing a biopsy. In a study with (former top UI professor) John Rogers we showed that this material could be biodegradable, to dissolve and disappear. So, perhaps using this material you could make lenses for tiny microscopes that could also disappear.
So you would be able to use a cheap material and do a biopsy without surgery?
You’d inject the microscope in a needle. There’s still a lot of science fiction there; we haven’t worked it all out. Dow is interested, and we’ve been in discussions with them.
Where do you see this heading in the future?
Our work has been in infrared light where silicon is transparent; this is ok for fiber optics since almost all fiber optics is done in the infrared, using wavelengths around and 1.5 microns. We’re working now to change the silicon into materials which are transparent to visible light, so there’s possibilities for solar energy. That would be a whole new space. You’d be collecting sunlight and focusing it to a small region — that makes solar cells more efficient. With visible light, moving into things like cameras also becomes more interesting. Dow for example is interested in this material, and we’ve been in discussions with them. We’re well on our way.
... from PAUL BRAUN
Do you have any wearable electronics? All I have is an iPhone and a plain old watch.
Are you on social networks? I’m a casual Facebook and LinkedIn user.
Instead, I love to have the time to run around with my three kids, 4, 8 and 9.
Books, or digital when ypu read? Technical articles on my laptop, phone or old-fashioned paper. When I read to my kids, paper. We just read "Twas the Night Before Christmas" and the "Little House On The Prairie" books.