David Kirkpatrick

June 15, 2010

The thick or thin solar question …

… has been solved by nanotech based on coaxial cable.

From the link:

“Many groups around the world are working on nanowire-type solar cells, most using crystalline semiconductors,” said co-author Michael Naughton, a professor of physics at Boston College. “This nanocoax cell architecture, on the other hand, does not require crystalline materials, and therefore offers promise for lower-cost solar power with ultrathin absorbers. With continued optimization, efficiencies beyond anything achieved in conventional planar architectures may be possible, while using smaller quantities of less costly material.”

Optically, the so-called nanocoax stands thick enough to capture light, yet its architecture makes it thin enough to allow a more efficient extraction of current, the researchers report in PSS’s Rapid Research Letters. This makes the nanocoax, invented at Boston College in 2005 and patented last year, a new platform for low cost, high efficiency solar power.

Boston College researchers report developing a “nanocoax” technology that can support a highly efficient thin film solar cell. This image shows a cross section of an array of nanocoax structures, which prove to be thick enough to absorb a sufficient amount of light, yet thin enough to extract current with increased efficiency, the researchers report in the journal Physica Status Solidi. Credit: Boston College

April 9, 2010

Graphene plus substrate still great thermal conductor

A graphene two-fer this evening. This news is another important finding toward commercializing graphene.

The release:

With support, graphene still a superior thermal conductor

Super-thin material advances toward next generation applications

IMAGE: A one-atom thick sheet of graphene (highlighted in the circular window) on top of a silicon dioxide support proves to be an excellent thermal conductor, according to new research published…

Click here for more information.

CHESTNUT HILL, MA (4/8/2010) – The single-atom thick material graphene maintains its high thermal conductivity when supported by a substrate, a critical step to advancing the material from a laboratory phenomenon to a useful component in a range of nano-electronic devices, researchers report in the April 9 issue of the journal Science.

The team of engineers and theoretical physicists from the University of Texas at Austin, Boston College, and France’s Commission for Atomic Energy report the super-thin sheet of carbon atoms – taken from the three-dimensional material graphite – can transfer heat more than twice as efficiently as copper thin films and more than 50 times better than thin films of silicon.

Since its discovery in 2004, graphene has been viewed as a promising new electronic material because it offers superior electron mobility, mechanical strength and thermal conductivity. These characteristics are crucial as electronic devices become smaller and smaller, presenting engineers with a fundamental problem of keeping the devices cool enough to operate efficiently.

The research advances the understanding of graphene as a promising candidate to draw heat away from “hot spots” that form in the tight knit spaces of devices built at the micro and nano scales. From a theoretical standpoint, the team also developed a new view of how heat flows in graphene.

When suspended, graphene has extremely high thermal conductivity of 3,000 to 5,000 watts per meter per Kelvin. But for practical applications, the chicken-wire like graphene lattice would be attached to a substrate. The team found supported graphene still has thermal conductivity as high as 600 watts per meter per Kelvin near room temperature. That far exceeds the thermal conductivities of copper, approximately 250 watts, and silicon, only 10 watts, thin films currently used in electronic devices.

IMAGE: Boston College physicist David Broido worked with colleagues from the University of Texas at Austin and France’s Commission for Atomic Energy to determine why graphene maintains its superior thermal conductivity…

Click here for more information.

The loss in heat transfer is the result of graphene’s interaction with the substrate, which interferes with the vibrational waves of graphene atoms as they bump against the adjacent substrate, according to co-author David Broido, a Boston College Professor of Physics.

The conclusion was drawn with the help of earlier theoretical models about heat transfer within suspended graphene, Broido said. Working with former BC graduate student Lucas Lindsay, now an instructor at Christopher Newport University, and Natalio Mingo of France’s Commission for Atomic Energy, Broido re-examined the theoretical model devised to explain the performance of suspended graphene.

“As theorists, we’re much more detached from the device or the engineering side. We’re more focused on the fundamentals that explain how energy flows through a sheet graphene. We took our existing model for suspended graphene and expanded the theoretical model to describe this interaction that takes place between graphene and the substrate and the influence on the movement of heat through the material and, ultimately, it’s thermal conductivity.”

In addition to its superior strength, electron mobility and thermal conductivity, graphene is compatible with thin film silicon transistor devices, a crucial characteristic if the material is to be used in low-cost, mass production. Graphene nano-electronic devices have the potential to consume less energy, run cooler and more reliably, and operate faster than the current generation of silicon and copper devices.

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Broido, Lindsay and Mingo were part of a research team led by Li Shi, a mechanical engineering professor at the University of Texas at Austin, which also included his UT colleagues Jae Hun Seol, Insun Jo, Arden Moore, Zachary Aitken, Michael Petttes, Xueson Li, Zhen Yao, Rui Huang, and Rodney Ruoff.

The research was supported by the Thermal Transport Processes Program and the Mechanics of Materials Program of the National Science Foundation, the U.S. Office of Naval Research, and the U.S. Department of Energy Office of Science.

December 12, 2009

“Hot electrons” and solar cells

Filed under: Science — Tags: , , , , — David Kirkpatrick @ 4:29 pm

The latest solar breakthrough news.

The release:

Elusive ‘hot’ electrons captured in ultra-thin solar cells

Shrinking cells snares charges in less than one-trillionth of a second

CHESTNUT HILL, MA (12/11/2009) – Boston College researchers have observed the “hot electron” effect in a solar cell for the first time and successfully harvested the elusive charges using ultra-thin solar cells, opening a potential avenue to improved solar power efficiency, the authors report in the current online edition of Applied Physics Letters.

When light is captured in solar cells, it generates free electrons in a range of energy states. But in order to snare these charges, the electrons must reach the bottom of the conduction band. The problem has been that these highly energized “hot” electrons lose much of their energy to heat along the way.

Hot electrons have been observed in other devices, such as semiconductors. But their high kinetic energy can cause these electrons, also known as “hot carriers,” to degrade a device. Researchers have long theorized about the benefits of harnessing hot electrons for solar power through so-called “3rd generation” devices.

By using ultrathin solar cells – a film fewer than 30 nanometers thick – the team developed a mechanism able to extract hot electrons in the moments before they cool – effectively opening a new “escape hatch” through which they typically don’t travel, said co-author Michael J. Naughton, the Evelyn J. and Robert A. Ferris Professor of Physics at Boston College.

The team’s success centered on minimizing the environment within which the electrons are able to escape, said Professor of Physics Krzysztof Kempa, lead author of the paper.

Kempa compared the challenge to trying to heat a swimming pool with a pot of boiling water. Drop the pot into the center of the pool and there would be no change in temperature at the edge because the heat would dissipate en route. But drop the pot into a sink filled with cold water and the heat would likely raise the temperature in the smaller area.

“We have shrunk the size of the solar cell by making it thin,” Kempa said. “In doing so, we are bringing these hot electrons closer to the surface, so they can be collected more readily. These electrons have to be captured in less than a picosecond, which is less than one trillionth of a second.”

The ultrathin cells demonstrated overall power conversion efficiency of approximately 3 percent using absorbers one fiftieth as thick as conventional cells. The team attributed the gains to the capture of hot electrons and an accompanying reduction in voltage-sapping heat. The researchers acknowledged the film’s efficiency is limited by the negligible light collection of ultra-thin junctions. However, combining the film with better light-trapping technology – such as nanowire structures – could significantly increase efficiency in an ultra-thin hot electron solar cell technology.

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In addition to Naughton and Kempa, the research team included Professor of Physics Zhifeng Ren, Research Associate Professor and Laboratory Director Andrzej A. Herczynski, Research Scientist Yantao Gao, doctoral student Timothy Kirkpatrick, and Jakub Rybczynski of Solasta Corp., of Newton MA, which supported the research. Naughton, Kempa and Ren are principals in the clean energy firm as well.

October 31, 2009

Public relations and web 2.0

The rules have forever changed.

The release:

Social media require ‘Community Relations 2.0’

Boston College researchers find real-time advocacy challenges long-standing corporate practices

Chestnut Hill, Mass. (October 30, 2009) — The rise of social media and real-time advocacy have re-written the community outreach rules companies followed for decades. But many American firms are dragging their feet as they approach “Community Relations 2.0,” Boston College researchers report in the November issue of Harvard Business Review.

Gone are the days when controversial projects were rolled out strictly along the corporate timeline. A worker’s blog rant unveiled major problems with a multi-billion dollar Kaiser Permanente IT initiative, putting the company in the spotlight and on the defensive.

Today, a disgruntled customer can take the world stage, as did a frustrated cable subscriber who videotaped a Comcast repairman snoozing on the couch and broadcast the now infamous nap across the world via the Internet.

Social media such as Facebook, MySpace, Twitter and YouTube, as well as tens of thousands of blogs and wikis have exponentially increased the speed of formation of these communities and magnified their impact and reach, report Carroll School of Management professors Gerald C. Kane, Robert G. Fichman and John Gallaugher and co-author John Glaser, the CIO of Partners HealthCare.

“These new social media tools let people organize extremely quickly around any issue or event that inspires them,” said co-author Kane, an assistant professor of information systems at BC. “Within hours, these virtual communities can grow to hundreds of thousands, potentially reaching millions more in short order. Companies and organizations caught unprepared can find themselves in a media firestorm, just ask companies like Domino’s Pizza, Amazon.com, Comcast, and many others have.”

These online communities form quickly, according to the researchers, and can disperse just as fast. They’re leadership can change often. Yet mobile platforms – from cell phones to PDAs to laptops – keep members on the alert, ready to push the agenda or spring into action. These communities vary widely in purpose, membership and tone – from friendly and collaborative to openly hostile. The same tools have also played central roles in recent international events, such as the 2008 Mumbai Terror Attacks and the 2009 Iranian election protests.

But for companies in this brave new Community Relations 2.0 world, executives must know that these real-time communities differ from their online predecessors – such as listservs and message boards – in critical ways, namely:

  • Deep relationships form quickly online and information can be dispersed without delay.
  • Rapid organization allows these communities to mobilize hundreds of thousands of people in a few hours.
  • Knowledge creation and synthesis take place in a far more deliberate fashion.
  • Information filtering tools like search, ratings and keywords allow people to identify information that is important to them and then act accordingly.

     

Companies need to understand these new social media – their benefits as well as their risks – and devote strategic resources to engage these communities in genuine discussions. For example, many physicians from Partners HealthCare are active on Sermo, an independently operated network for physicians, and more than 3,500 employees have joined an informal and unofficial Partners community on Facebook. Many patients belong to the social network PatientsLikeMe. For Partners, these online communities represent strategic opportunities to interact with stakeholders on issues of common interest.

“Whether or not managers, leaders, or politicians even know the difference between Wikipedia, Facebook, or Twitter, they need to begin learning how to monitor and respond quickly to trends in these social media communities,” Kane said. “Doing so, they may not only prevent the spread of damaging information, but they may also find valuable partners in their organization’s mission. Companies like Dell, Starbucks and Kaiser-Permanente have moved beyond purely reactive strategies to proactively reach out to customers as an important resource for customer service, marketing, and new product development.”

September 10, 2008

Nanonets improve solar, too

Filed under: Science, Technology — Tags: , , , , , — David Kirkpatrick @ 8:20 am

I’ve blogged on nanonets and how they improve electronics and energy applications. Here’s a Technology Review story with more detail on how nanonets improve solar energy.

And as a bonus, with picutures!

From the second link:

One problem with solar cells is that they only produce electricity during the day. A promising way to use the sun’s energy more efficiently is to enlist it to split water into hydrogen gas that can be stored and then employed at any time, day or night. A cheap new nanostructured material could prove an efficient catalyst for performing this reaction. Called a nanonet because of its two-dimensional branching structure, the material is made up of a compound that has been demonstrated to enable the water-splitting reaction. Because of its high surface area, the nanonet enhances this reaction.

Researchers led by Dunwei Wang, a chemist at Boston College, grew the nanonets, creating structures made up of branching wires of titanium and silicon. Last year, researchers at the Max Planck Institute, in Germany, showed that titanium disilicide, which absorbs a broad spectrum of visible light, splits water into hydrogen and oxygen–and can store the hydrogen, which it absorbs or releases depending on the temperature. Other semiconducting materials have been tested as water-splitting catalysts but have proved unstable.

Nanonets, structures made up of branching titanium and silicon wires, are flat yet have a high surface area, making them more efficient at using solar energy to split water into oxygen and hydrogen fuel. The top image shows a nanonet magnified 50,000 times. At bottom, a flexible nanonet rolls up when poked by the tip of a scanning tunneling microscope. Both images were taken with a tunneling electron microscope.

Net reaction: Nanonets, structures made up of branching titanium and silicon wires, are flat yet have a high surface area, making them more efficient at using solar energy to split water into oxygen and hydrogen fuel. The top image shows a nanonet magnified 50,000 times. At bottom, a flexible nanonet rolls up when poked by the tip of a scanning tunneling microscope. Both images were taken with a tunneling electron microscope.