Monthly Archives: November 2017

Luqiao Liu lab synthesizing and testing manganese gallium samples

Assistant professor of electrical engineering Luqiao Liu is developing new magnetic materials, known as antiferromagnets, that can be operated at room temperature by reversing their electron spin and can serve as the basis for long-lasting, spintronic computer memory. Stephanie Bauman, an intern in the Materials Processing Center and Center for Materials Science and Engineering Summer Scholars program, spent her internship making and testing these new materials, which include manganese gallium samples.

“In our project we’re working on the area of spintronics, anti-ferromagnetic devices that switch electron spin controlled by a current,” said Bauman, a University of South Florida physics major. “I’m working with a lot of new equipment like the vibrating sample magnetometer and the sputterer to lay down thin films.”

“I’ve been working on a daily basis with Joe Finley, who is a graduate student here, and he’s been a explaining a lot of things to me,” Bauman said. “It’s a very dense subject matter. And he does help me out a lot when we go to things like the X-ray diffraction room, and he shows me how the graphs can interpret how thick each layer of the thin layers of the devices are. He’s really helpful and easy to work with.”

During a visit to the lab, where she synthesizes these thin films with a special machine called a sputter deposition chamber, Bauman said she always refers to a checklist to make sure she’s doing everything in the right order. In order to take out a sample from the machine, she follows a complicated set of steps, making sure its parts are correctly lined up and unhooking the sample holder in the main chamber. Because the chamber is pressurized, she must bring it back to everyday atmospheric pressure before taking it out. “Now that I can see that it disengaged, I go ahead and move it all the way back up,” she said. With the sample holder on a moveable arm, she is able to rotate it out.

The sample moved across a gear arm out of the main chamber into transfer chamber known as a load lock. “A very, very important part of this is to make sure you close the transfer valve again, otherwise you mess up the pressure in the main chamber,” she said. After double-checking the transfer valve is closed, she brought the load lock back to sea level pressure of 760 torr. Then she took out the sample holder.

“As you can see the sample is really tiny. It’s half a centimeter by a half a centimeter, which is what we’re working with right now,” Bauman said. As she loosened the screws on the arms holding the sample in place, she noted that she had to be careful not to scratch the sample with the arms. Once safely removed, she placed the sample in a special holder, labeled based on when each sample was made, which sample of the day it is and its thickness. That way, she noted, “we can refer back to that in our data so that we know what thickness levels that we’re testing.”

“Sometimes you end up playing tiddlywinks. I know that some younger people don’t really know what that game is, but it’s what it looks like when you push down on the arm, and the sample goes flying,” she cautioned.

Bring optical communication onto silicon chips

The huge increase in computing performance in recent decades has been achieved by squeezing ever more transistors into a tighter space on microchips.

However, this downsizing has also meant packing the wiring within microprocessors ever more tightly together, leading to effects such as signal leakage between components, which can slow down communication between different parts of the chip. This delay, known as the “interconnect bottleneck,” is becoming an increasing problem in high-speed computing systems.

One way to tackle the interconnect bottleneck is to use light rather than wires to communicate between different parts of a microchip. This is no easy task, however, as silicon, the material used to build chips, does not emit light easily, according to Pablo Jarillo-Herrero, an associate professor of physics at MIT.

Now, in a paper published today in the journal Nature Nanotechnology, researchers describe a light emitter and detector that can be integrated into silicon CMOS chips. The paper’s first author is MIT postdoc Ya-Qing Bie, who is joined by Jarillo-Herrero and an interdisciplinary team including Dirk Englund, an associate professor of electrical engineering and computer science at MIT.

The device is built from a semiconductor material called molybdenum ditelluride. This ultrathin semiconductor belongs to an emerging group of materials known as two-dimensional transition-metal dichalcogenides.

Unlike conventional semiconductors, the material can be stacked on top of silicon wafers, Jarillo-Herrero says.

“Researchers have been trying to find materials that are compatible with silicon, in order to bring optoelectronics and optical communication on-chip, but so far this has proven very difficult,” Jarillo-Herrero says. “For example, gallium arsenide is very good for optics, but it cannot be grown on silicon very easily because the two semiconductors are incompatible.”

In contrast, the 2-D molybdenum ditelluride can be mechanically attached to any material, Jarillo-Herrero says.

Another difficulty with integrating other semiconductors with silicon is that the materials typically emit light in the visible range, but light at these wavelengths is simply absorbed by silicon.

Molybdenum ditelluride emits light in the infrared range, which is not absorbed by silicon, meaning it can be used for on-chip communication.

To use the material as a light emitter, the researchers first had to convert it into a P-N junction diode, a device in which one side, the P side, is positively charged, while the other, N side, is negatively charged.

Laboratory team scores big at international hacking event

They call themselves Lab RATs, in a nod to remote access trojans, which are malware that attempt to hijack a computer’s operations. Battling teams from around the world, a team of staff members from MIT Lincoln Laboratory’s Cyber Security and Information Sciences Division and Information Services Department made it all the way to the finals of this year’s DEF CON Capture the Flag (CTF) hacking competition.

The laboratory’s cyber researchers and analysts, joined by students from Rensselaer Polytechnic Institute and MIT, were pitted against other elite teams trying to breach each other’s computers and capture “flags” — which are actually code strings — embedded within the programming. Because DEF CON CTF is an attack-and-defend tournament, competitors not only had to infiltrate opponents’ systems to steal flags and earn points, they also accrued points by keeping their own services up and running against the onslaught of 14 other teams who came to DEF CON from Germany, Israel, Russia, China, Korea, and Hungary, as well as elsewhere in the U.S.

After the 52-hour contest was over, the Lab RATs had earned 10th place among the 15 teams that had qualified for the finals of DEF CON CTF, the world’s premier hacking competition. Teams chosen for the coveted finals slots emerged from more than 4,000 entrants who competed in qualifying events.

This year’s CTF was held in Las Vegas, and was part of the annual DEF CON hackers’ convention, which attracts not only amateur codebreakers but also cybersecurity professionals from academia, governments, and businesses worldwide.

This was the first year Lab RATS qualified for the finals of the competition, which they have entered for the past three years. The team meets and practices during non-work hours at the Beaver Works facility in Cambridge, Massachusetts, and membership fluctuates between 20-30 laboratory employees and six to eight MIT students.

“Participation in DEF CON CTF is realistic cybersecurity training,” says Lab RATs captain Andrew Fasano of the laboratory’s Cyber System Assessments Group. “You have to develop the tools and mindset to attack and defend computer systems in a high-pressure environment.”

This year’s DEF CON CTF competition was a humdinger, Fasano says. The Legitimate Business Syndicate, organizer of the 2017 CTF and a previous competitor at DEF CON CTF finals, was on its last year of a multiyear contract to devise the game and was determined to make their swan song an extreme challenge.