Controlling silicon evaporation allows scientists to boost graphene quality

ScienceDaily (Sep. 22, 2011) — Scientists from the Georgia Institute of Technology have for the first time provided details of their "confinement controlled sublimation" technique for growing high-quality layers of epitaxial graphene on silicon carbide wafers. The technique relies on controlling the vapor pressure of gas-phase silicon in the high-temperature furnace used for fabricating the material.

The basic principle for growing thin layers of graphene on silicon carbide requires heating the material to about 1,500 degrees Celsius under high vacuum. The heat drives off the silicon, leaving behind one or more layers of graphene. But uncontrolled evaporation of silicon can produce poor quality material useless to designers of electronic devices.

"For growing high-quality graphene on silicon carbide, controlling the evaporation of silicon at just the right temperature is essential," said Walt de Heer, a professor who pioneered the technique in the Georgia Tech School of Physics. "By precisely controlling the rate at which silicon comes off the wafer, we can control the rate at which graphene is produced. That allows us to produce very nice layers of epitaxial graphene."

De Heer and his team begin by placing a silicon carbide wafer into an enclosure made of graphite. A small hole in the container controls the escape of silicon atoms as the one-square-centimeter wafer is heated, maintaining the rate of silicon evaporation and condensation near its thermal equilibrium. The growth of epitaxial graphene can be done in a vacuum or in the presence of an inert gas such as argon, and can be used to produce both single layers and multiple layers of the material.

"This technique seems to be completely in line with what people might one day do in fabrication facilities," de Heer said. "We believe this is quite significant in allowing us to rationally and reproducibly grow graphene on silicon carbide. We feel we now understand the process, and believe it could be scaled up for electronics manufacturing."

The technique for growing large-area layers of epitaxial graphene was described this week in the Early Edition of the journal Proceedings of the National Academy of Sciences. The research has been supported by the National Science Foundation through the Georgia Tech Materials Research Science and Engineering Center (MRSEC), the Air Force Office of Scientific Research, and the W.M. Keck Foundation.

The paper also describes a technique for growing narrow graphene ribbons, a process de Heer's group has called "templated growth." That technique, which could be useful for making graphene interconnects, was first described in October 2010 in the journal Nature Nanotechnology.

The templated growth technique involves etching patterns into silicon carbide surfaces using conventional nanolithography processes. The patterns serve as templates directing the growth of graphene structures on portions of the patterned surfaces. The technique forms nanoribbons of specific widths without the use of electron beams or other destructive cutting techniques. Graphene nanoribbons produced with these templates have smooth edges that avoid problems with electron scattering.

Together, the two techniques provide researchers with the flexibility to produce graphene in forms appropriate to different needs, de Heer noted. Large-area sheets of graphene may be grown on both the carbon-terminated and silicon-terminated sides of a silicon carbide wafer, while the narrow ribbons may be grown on the silicon-terminated side. Because of different processing techniques, only one side of a particular wafer can be used.

The Georgia Tech research team -- which includes Claire Berger, Ming Ruan, Mike Sprinkle, Xuebin Li, Yike Hu, Baiqian Zhang, John Hankinson and Edward Conrad -- has so far fabricated structures as narrow as 10 nanometers using the templated growth technique. These nanowires exhibit interesting quantum transport properties.

"We can make very good quantum wires using the templated growth technique," de Heer said. "We can make large structures and devices that demonstrate the Quantum Hall Effect, which is important for many applications. We have demonstrated that templated growth can go all the way down to the nanoscale, and that the properties get even better there."

Development of the sublimation technique arose from efforts to protect the growing graphene from oxygen and other contaminants in the furnace. To address the quality concerns, the research team tried enclosing the wafer in a graphite container from which some silicon gas was permitted to leak out.

"We soon realized that graphene grown in the container was much better than what we had been producing," de Heer recalled. "Originally, we thought it was because we were protecting it from contaminants. Later, we realized it was because we were controlling the evaporation of silicon."

Epitaxial graphene may be the basis for a new generation of high-performance devices that will take advantage of the material's unique properties in applications where higher costs can be justified. Silicon, today's electronic material of choice, will continue to be used in applications where high-performance is not required, de Heer said.

Though researchers are still struggling to design nanometer-scale epitaxial graphene devices that take advantage of the material's unique properties, de Heer is confident that will ultimately be done.

"These techniques allow us to make accurate nanostructures and seem to be very promising for making the nanoscale devices that we need," he said. "While there are serious challenges ahead for using graphene in electronics, we have overcome roadblocks before."

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Georgia Institute of Technology Research News. The original article was written by John Toon.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Controlling silicon evaporation allows scientists to boost graphene quality

ScienceDaily (Sep. 22, 2011) — Scientists from the Georgia Institute of Technology have for the first time provided details of their "confinement controlled sublimation" technique for growing high-quality layers of epitaxial graphene on silicon carbide wafers. The technique relies on controlling the vapor pressure of gas-phase silicon in the high-temperature furnace used for fabricating the material.

The basic principle for growing thin layers of graphene on silicon carbide requires heating the material to about 1,500 degrees Celsius under high vacuum. The heat drives off the silicon, leaving behind one or more layers of graphene. But uncontrolled evaporation of silicon can produce poor quality material useless to designers of electronic devices.

"For growing high-quality graphene on silicon carbide, controlling the evaporation of silicon at just the right temperature is essential," said Walt de Heer, a professor who pioneered the technique in the Georgia Tech School of Physics. "By precisely controlling the rate at which silicon comes off the wafer, we can control the rate at which graphene is produced. That allows us to produce very nice layers of epitaxial graphene."

De Heer and his team begin by placing a silicon carbide wafer into an enclosure made of graphite. A small hole in the container controls the escape of silicon atoms as the one-square-centimeter wafer is heated, maintaining the rate of silicon evaporation and condensation near its thermal equilibrium. The growth of epitaxial graphene can be done in a vacuum or in the presence of an inert gas such as argon, and can be used to produce both single layers and multiple layers of the material.

"This technique seems to be completely in line with what people might one day do in fabrication facilities," de Heer said. "We believe this is quite significant in allowing us to rationally and reproducibly grow graphene on silicon carbide. We feel we now understand the process, and believe it could be scaled up for electronics manufacturing."

The technique for growing large-area layers of epitaxial graphene was described this week in the Early Edition of the journal Proceedings of the National Academy of Sciences. The research has been supported by the National Science Foundation through the Georgia Tech Materials Research Science and Engineering Center (MRSEC), the Air Force Office of Scientific Research, and the W.M. Keck Foundation.

The paper also describes a technique for growing narrow graphene ribbons, a process de Heer's group has called "templated growth." That technique, which could be useful for making graphene interconnects, was first described in October 2010 in the journal Nature Nanotechnology.

The templated growth technique involves etching patterns into silicon carbide surfaces using conventional nanolithography processes. The patterns serve as templates directing the growth of graphene structures on portions of the patterned surfaces. The technique forms nanoribbons of specific widths without the use of electron beams or other destructive cutting techniques. Graphene nanoribbons produced with these templates have smooth edges that avoid problems with electron scattering.

Together, the two techniques provide researchers with the flexibility to produce graphene in forms appropriate to different needs, de Heer noted. Large-area sheets of graphene may be grown on both the carbon-terminated and silicon-terminated sides of a silicon carbide wafer, while the narrow ribbons may be grown on the silicon-terminated side. Because of different processing techniques, only one side of a particular wafer can be used.

The Georgia Tech research team -- which includes Claire Berger, Ming Ruan, Mike Sprinkle, Xuebin Li, Yike Hu, Baiqian Zhang, John Hankinson and Edward Conrad -- has so far fabricated structures as narrow as 10 nanometers using the templated growth technique. These nanowires exhibit interesting quantum transport properties.

"We can make very good quantum wires using the templated growth technique," de Heer said. "We can make large structures and devices that demonstrate the Quantum Hall Effect, which is important for many applications. We have demonstrated that templated growth can go all the way down to the nanoscale, and that the properties get even better there."

Development of the sublimation technique arose from efforts to protect the growing graphene from oxygen and other contaminants in the furnace. To address the quality concerns, the research team tried enclosing the wafer in a graphite container from which some silicon gas was permitted to leak out.

"We soon realized that graphene grown in the container was much better than what we had been producing," de Heer recalled. "Originally, we thought it was because we were protecting it from contaminants. Later, we realized it was because we were controlling the evaporation of silicon."

Epitaxial graphene may be the basis for a new generation of high-performance devices that will take advantage of the material's unique properties in applications where higher costs can be justified. Silicon, today's electronic material of choice, will continue to be used in applications where high-performance is not required, de Heer said.

Though researchers are still struggling to design nanometer-scale epitaxial graphene devices that take advantage of the material's unique properties, de Heer is confident that will ultimately be done.

"These techniques allow us to make accurate nanostructures and seem to be very promising for making the nanoscale devices that we need," he said. "While there are serious challenges ahead for using graphene in electronics, we have overcome roadblocks before."

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Georgia Institute of Technology Research News. The original article was written by John Toon.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

EEG headset with flying harness lets users 'fly' by controlling their thoughts

ScienceDaily (May 6, 2011) — A team of Rensselaer Polytechnic Institute students has created a system that pairs an EEG headset with a 3-D theatrical flying harness, allowing users to "fly" by controlling their thoughts. The "Infinity Simulator" will make its debut with an art installation in which participants rise into the air -- and trigger light, sound, and video effects -- by calming their thoughts.

Creative director and Rensselaer MFA candidate Yehuda Duenyas describes the "Infinity Simulator" as a platform similar to a gaming console -- like the Wii or the Kinect -- writ large.

"Instead of you sitting and controlling gaming content, it's a whole system that can control live elements -- so you can control 3-D rigging, sound, lights, and video," said Duenyas, who works under the moniker "xxxy." "It's a system for creating hybrids of theater, installation, game, and ride."

Duenyas created the "Infinity Simulator" with a team of collaborators, including Michael Todd, a Rensselaer 2010 graduate in computer science. Duenyas will exhibit the new system in the art installation "The Ascent" on May 12 at Curtis R. Priem Experimental Media and Performing Arts Center (EMPAC).

Ten computer programs running simultaneously link the commercially available EEG headset to the computer-controlled 3-D flying harness and various theater systems, said Todd.

Within the theater, the rigging -- including the harness -- is controlled by a Stage Tech NOMAD console; lights are controlled by an ION console running MIDI show control; sound through MAX/MSP; and video through Isadora and Jitter. The "Infinity Simulator," a series of three C programs written by Todd, acts as intermediary between the headset and the theater systems, connecting and conveying all input and output.

"We've built a software system on top of the rigging control board and now have control of it through an iPad, and since we have the iPad control, we can have anything control it," said Duenyas. "The 'Infinity Simulator' is the center; everything talks to the 'Infinity Simulator.'"

The May 12 "The Ascent" installation is only one experience made possible by the new platform, Duenyas said.

"'The Ascent' embodies the maiden experience that we'll be presenting," Duenyas said. "But we've found that it's a versatile platform to create almost any type of experience that involves rigging, video, sound, and light. The idea is that it's reactive to the users' body; there's a physical interaction."

Duenyas, a Brooklyn-based artist and theater director, specializes in experiential theater performances.

"The thing that I focus on the most is user experience," Duenyas said. "All the shows I do with my theater company and on my own involve a lot of set and set design -- you're entering into a whole world. You're having an experience that is more than going to a show, although a show is part of it."

The "Infinity Simulator" stemmed from an idea Duenyas had for such a theatrical experience.

"It started with an idea that I wanted to create a simulator that would give people a feeling of infinity," Duenyas said. His initial vision was that of a room similar to a Cave Automated Virtual Environment -- a room paneled with projection screens -- in which participants would be able to float effortlessly in an environment intended to evoke a glimpse into infinity.

At Rensselaer, Duenyas took advantage of the technology at hand to explore his idea, first with a video game he developed in 2010, then -- working through the Department of the Arts -- with EMPAC's computer-controlled 3-D theatrical flying harness.

"The charge of the arts department is to allow the artists that they bring into the department to use technology to enhance what they've been doing already," Duenyas said. "In coming here (EMPAC), and starting to translate our ideas into a physical space, so many different things started opening themselves up to us."

The 2010 video game, also developed with Todd, tracked the movements -- pitch and yaw -- of players suspended in a custom-rigged harness, allowing players to soar through simulated landscapes. Duenyas said that that game (also called the "Infinity Simulator") and the new platform are part of the same vision.

EMPAC Director Johannes Goebel saw the game on display at the 2010 GameFest and discussed the custom-designed 3-D theatrical flying rig in EMPAC with Duenyas. Working through the Arts Department, Duenyas submitted a proposal to work with the rig, and his proposal was accepted.

Duenyas and his team experimented -- first gaining peripheral control over the system, and then linking it to the EEG headset -- and created the Ascent installation as an initial project. In the installation, the Infinity Simulator is programmed to respond to relaxation.

"We're measuring two brain states -- alpha and theta -- waking consciousness and everyday brain computational processing," said Duenyas. "If you close your eyes and take a deep breath, that processing power decreases. When it decreases below a certain threshold, that is the trigger for you to elevate."

As a user rises, their ascent triggers a changing display of lights, sound, and video. Duenyas said he wants to hint at transcendental experience, while keeping the door open for a more circumspect interpretation.

"The point is that the user is trying to transcend the everyday and get into this meditative state so they can have this experience. I see it as some sort of iconic spiritual simulator. That's the serious side," he said. "There's also a real tongue-in-cheek side of my work: I want clouds, I want Terry Gilliam's animated fist to pop out of a cloud and hit you in the face. It's mixing serious religious symbology, but not taking it seriously."

The humor is prompted, in part, by the limitations of this earliest iteration of Duenyas' vision.

"It started with, 'I want to have a glimpse of infinity,' 'I want to float in space.' Then you get in the harness and you're like 'man, this harness is uncomfortable,'" he said. "In order to achieve the original vision, we had to build an infrastructure, and I still see development of the infinity experience is a ways off; but what we can do with the infrastructure in a realistic time frame is create 'The Ascent,' which is going to be really fun, and totally other."

Creating the "Infinity Simulator" has prompted new possibilities.

"The vision now is to play with this fun system that we can use to build any experience," he said. "It's sort of overwhelming because you could do so many things -- you could create a flight through cumulus clouds, you could create an augmented physicality parkour course where you set up different features in the room and guide yourself to different heights. It's limitless."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Rensselaer Polytechnic Institute (RPI).

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

EEG headset with flying harness lets users 'fly' by controlling their thoughts

ScienceDaily (May 6, 2011) — A team of Rensselaer Polytechnic Institute students has created a system that pairs an EEG headset with a 3-D theatrical flying harness, allowing users to "fly" by controlling their thoughts. The "Infinity Simulator" will make its debut with an art installation in which participants rise into the air -- and trigger light, sound, and video effects -- by calming their thoughts.

Creative director and Rensselaer MFA candidate Yehuda Duenyas describes the "Infinity Simulator" as a platform similar to a gaming console -- like the Wii or the Kinect -- writ large.

"Instead of you sitting and controlling gaming content, it's a whole system that can control live elements -- so you can control 3-D rigging, sound, lights, and video," said Duenyas, who works under the moniker "xxxy." "It's a system for creating hybrids of theater, installation, game, and ride."

Duenyas created the "Infinity Simulator" with a team of collaborators, including Michael Todd, a Rensselaer 2010 graduate in computer science. Duenyas will exhibit the new system in the art installation "The Ascent" on May 12 at Curtis R. Priem Experimental Media and Performing Arts Center (EMPAC).

Ten computer programs running simultaneously link the commercially available EEG headset to the computer-controlled 3-D flying harness and various theater systems, said Todd.

Within the theater, the rigging -- including the harness -- is controlled by a Stage Tech NOMAD console; lights are controlled by an ION console running MIDI show control; sound through MAX/MSP; and video through Isadora and Jitter. The "Infinity Simulator," a series of three C programs written by Todd, acts as intermediary between the headset and the theater systems, connecting and conveying all input and output.

"We've built a software system on top of the rigging control board and now have control of it through an iPad, and since we have the iPad control, we can have anything control it," said Duenyas. "The 'Infinity Simulator' is the center; everything talks to the 'Infinity Simulator.'"

The May 12 "The Ascent" installation is only one experience made possible by the new platform, Duenyas said.

"'The Ascent' embodies the maiden experience that we'll be presenting," Duenyas said. "But we've found that it's a versatile platform to create almost any type of experience that involves rigging, video, sound, and light. The idea is that it's reactive to the users' body; there's a physical interaction."

Duenyas, a Brooklyn-based artist and theater director, specializes in experiential theater performances.

"The thing that I focus on the most is user experience," Duenyas said. "All the shows I do with my theater company and on my own involve a lot of set and set design -- you're entering into a whole world. You're having an experience that is more than going to a show, although a show is part of it."

The "Infinity Simulator" stemmed from an idea Duenyas had for such a theatrical experience.

"It started with an idea that I wanted to create a simulator that would give people a feeling of infinity," Duenyas said. His initial vision was that of a room similar to a Cave Automated Virtual Environment -- a room paneled with projection screens -- in which participants would be able to float effortlessly in an environment intended to evoke a glimpse into infinity.

At Rensselaer, Duenyas took advantage of the technology at hand to explore his idea, first with a video game he developed in 2010, then -- working through the Department of the Arts -- with EMPAC's computer-controlled 3-D theatrical flying harness.

"The charge of the arts department is to allow the artists that they bring into the department to use technology to enhance what they've been doing already," Duenyas said. "In coming here (EMPAC), and starting to translate our ideas into a physical space, so many different things started opening themselves up to us."

The 2010 video game, also developed with Todd, tracked the movements -- pitch and yaw -- of players suspended in a custom-rigged harness, allowing players to soar through simulated landscapes. Duenyas said that that game (also called the "Infinity Simulator") and the new platform are part of the same vision.

EMPAC Director Johannes Goebel saw the game on display at the 2010 GameFest and discussed the custom-designed 3-D theatrical flying rig in EMPAC with Duenyas. Working through the Arts Department, Duenyas submitted a proposal to work with the rig, and his proposal was accepted.

Duenyas and his team experimented -- first gaining peripheral control over the system, and then linking it to the EEG headset -- and created the Ascent installation as an initial project. In the installation, the Infinity Simulator is programmed to respond to relaxation.

"We're measuring two brain states -- alpha and theta -- waking consciousness and everyday brain computational processing," said Duenyas. "If you close your eyes and take a deep breath, that processing power decreases. When it decreases below a certain threshold, that is the trigger for you to elevate."

As a user rises, their ascent triggers a changing display of lights, sound, and video. Duenyas said he wants to hint at transcendental experience, while keeping the door open for a more circumspect interpretation.

"The point is that the user is trying to transcend the everyday and get into this meditative state so they can have this experience. I see it as some sort of iconic spiritual simulator. That's the serious side," he said. "There's also a real tongue-in-cheek side of my work: I want clouds, I want Terry Gilliam's animated fist to pop out of a cloud and hit you in the face. It's mixing serious religious symbology, but not taking it seriously."

The humor is prompted, in part, by the limitations of this earliest iteration of Duenyas' vision.

"It started with, 'I want to have a glimpse of infinity,' 'I want to float in space.' Then you get in the harness and you're like 'man, this harness is uncomfortable,'" he said. "In order to achieve the original vision, we had to build an infrastructure, and I still see development of the infinity experience is a ways off; but what we can do with the infrastructure in a realistic time frame is create 'The Ascent,' which is going to be really fun, and totally other."

Creating the "Infinity Simulator" has prompted new possibilities.

"The vision now is to play with this fun system that we can use to build any experience," he said. "It's sort of overwhelming because you could do so many things -- you could create a flight through cumulus clouds, you could create an augmented physicality parkour course where you set up different features in the room and guide yourself to different heights. It's limitless."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Rensselaer Polytechnic Institute (RPI).

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here