Tag Archives: electricity

Converting light to electricity at femto speeds

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This is a pretty remarkable (to me anyway) piece of research on speeding up the process of converting light to electricity. From an April 14, 2015 Institute of Photonic Science press release (also on EurekAlert but dated April 15, 2015),

The efficient conversion of light into electricity plays a crucial role in many technologies, ranging from cameras to solar cells. It also forms an essential step in data communication applications, since it allows for information carried by light to be converted into electrical information that can be processed in electrical circuits. Graphene is an excellent material for ultrafast conversion of light to electrical signals, but so far it was not known how fast graphene responds to ultrashort flashes of light.

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The new device that the researchers developed is capable of converting light into electricity in less than 50 femtoseconds (a twentieth of a millionth of a millionth of a second). To do this, the researchers used a combination of ultrafast pulse-shaped laser excitation and highly sensitive electrical readout. As Klaas-Jan Tielrooij comments, “the experiment uniquely combined the ultrafast pulse shaping expertise obtained from single molecule ultrafast photonics with the expertise in graphene electronics. Facilitated by graphene’s nonlinear photo-thermoelectric response, these elements enabled the observation of femtosecond photodetection response times.”

The ultrafast creation of a photovoltage in graphene is possible due to the extremely fast and efficient interaction between all conduction band carriers in graphene. This interaction leads to a rapid creation of an electron distribution with an elevated electron temperature. Thus, the energy absorbed from light is efficiently and rapidly converted into electron heat. Next, the electron heat is converted into a voltage at the interface of two graphene regions with different doping. This photo-thermoelectric effect turns out to occur almost instantaneously, thus enabling the ultrafast conversion of absorbed light into electrical signals. As Prof. van Hulst states, “it is amazing how graphene allows direct non-linear detecting of ultrafast femtosecond (fs) pulses”.

The results obtained from the findings of this work, which has been partially funded by the EC Graphene Flagship, open a new pathway towards ultra-fast optoelectronic conversion. As Prof. Koppens comments, “Graphene photodetectors keep showing fascinating performances addressing a wide range of applications”.

Here’s a link to and a citation for the paper,

Generation of photovoltage in graphene on a femtosecond timescale through efficient carrier heating by K. J. Tielrooij, L. Piatkowski, M. Massicotte, A. Woessner, Q. Ma, Y. Lee,  K. S. Myhro, C. N. Lau, P. Jarillo-Herrero, N. F. van Hulst & F. H. L. Koppens. Nature Nanotechnology (2015) doi:10.1038/nnano.2015.54 Published online 13 April 2015

This paper is behind a paywall but there is a free preview via ReadCube Access.

Printing jello and conducting electricity

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The July 4, 2012 news item on ScienceDaily about a gel that behaves like biological tissue but conducts electricity is another one of those pieces of research which illustrate the idea that the boundary between the behaviour of biological and nonbiological materials is wavering,

The material, created by Stanford chemical engineering Associate Professor Zhenan Bao, materials science and engineering Associate Professor Yi Cui and members of their labs, is a kind of conducting hydrogel — a jelly that feels and behaves like biological tissues, but conducts electricity like a metal or semiconductor.

That combination of characteristics holds enormous promise for biological sensors and futuristic energy storage devices, but has proven difficult to manufacture until now.

The ScienceDaily news item originated in a June 27, 2012 article written by Max McClure for the (University of) Stanford Report,

Bao and Cui made the gel by binding long chains of the organic compound aniline together with phytic acid, found naturally in plant tissues. The acid is able to grab up to six polymer chains at once, making for an extensively cross-linked network.

“There are already commercially available conducting polymers,” said Bao, “but they all form a uniform film without any nanostructures.”

In contrast, the new gel’s cross-linking makes for a complex, sponge-like structure.  The hydrogel is marked with innumerable tiny pores that expand the gel’s surface area, increasing the amount of charge it can hold, its ability to sense chemicals, and the rapidity of its electrical response.

Still, the gel can be easily manipulated. Because the material doesn’t solidify until the last step of its synthesis, it can be printed or sprayed as a liquid and turned into a gel after it’s already in place – meaning that manufacturers should be able to construct intricately patterned electrodes at low cost.

Here’s more about the electrical conductance properties from the McClure article,

The material’s unusual structure also gives the gel what Cui referred to as “remarkable electronic properties.”

Most hydrogels are tied together by a large number of insulating molecules, reducing the material’s overall ability to pass electrical current. But phytic acid is a “small-molecule dopant” – meaning that when it links polymer chains, it also lends them charge. This effect makes the hydrogel highly conductive.

The gel’s conductance is “among the best you can get through this kind of process,” said Cui. Its capacity to hold charge is very high, and its response to applied charge is unusually fast.

The substance’s similarity to biological tissues, its large surface area and its electrical capabilities make it well suited for allowing biological systems to communicate with technological hardware.

The researchers envision it being used in everything from medical probes and laboratory biological sensors to biofuel cells and high-energy density capacitors.

“And all it’s made of are commercially available ingredients thrown into a water solution,” said Bao.

The July 4, 2012 ScienceDaily news item provided this citation for the paper,

L. Pan, G. Yu, D. Zhai, H. R. Lee, W. Zhao, N. Liu, H. Wang, B. C.- K. Tee, Y. Shi, Y. Cui, Z. Bao. Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity. Proceedings of the National Academy of Sciences, 2012; 109 (24): 9287 DOI: 10.1073/pnas.1202636109

Nanotechnology, risk, science literacy and feelings; Canada’s Science and Technology Week 2009

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The Swiss-based Innovation Society has waded into the discussion about nanoparticles and sunscreens  in the wake of the Friends of the Earth (FOE) report (mentioned here yesterday August 20, 2009).

They point out something I forgot. Despite disagreeing on the “risk  profile,” both the Environmental Working Group (EWG) and FOE advise that nanomaterials should be labelled so that consumers can make informed choices,  (I’m not sure if I’ve seen the phrase risk profile or if I just coined it but I hope it makes sense in this context.) You can read about the Innovation Society’s perspective in their media release on Nanowerk News where they also offer links to the society’s August 2009 newsletter. You have to register to receive it and the form is in German as is the page which houses the public portion of the August 2009 newsletter. So, I’m not sure what language the newsletter is written in although most of what I saw on their site is in English.

As this last week has featured a published study about two women workers who died due to nanoparticle exposure and the FOE report, I’ve been reminded of the Cultural Cognition Project at Yale Law School (mentioned here on this blog last week). One of the conclusions in the paper I read about nanotechnology and risk is that people will make judgments about emerging technologies quickly, with little information, and in line with their feelings (affect), and cultural values. In the experimental investigation they found that increasing scientific literacy (i.e. giving the respondents more factual information about nanotechnology) did nothing or very little to alter someone’s opinion once it was formed.

I can agree with this conclusion as far as it goes. I’ve observed the same process of adhering to an opinion despite any evidence to the contrary in myself and others. I noted yesterday that the FOE report did not mention the EWG findings which, in my opinion, damages their credibility and bears out the conclusions made by the team at the Cultural Cognition Project.

There is one thing which niggles at me. Technologies have emerged before, e.g. electricity. At the time, during the 19th century, it was highly contested (do take a look at Carolyn Marvin’s book, When Old Technologies were New) . Very inflammatory language was used; all kinds of “experts” emerged; scientists engaged in lots of public outreach; there were deaths and injuries; and there were predictions that life on earth would end.  Seems familiar, doesn’t it? Still, electricity has become ubiquitous for much of the world. If cultural values and feelings trump science literacy, how did electricity become ubiquitous?

The Cultural Cognition Project team seemed to suggest in their paper that once opinions have been formed they are largely intractable. If that’s so, regardless of which group’s narrative gains dominance wouldn’t the other group continue to resist? (Note: the Amish opted out from using electricity.) History tells us otherwise.

I am getting ready for my presentation at the International Symposium on Electronic Arts (ISEA) so y9u may find that my posting schedule is interrupted. Happy weekend and here are a few final nuggets,

The Government of Canada, in the person of Rona Ambrose, Minister of Labour, has recognized Quantium Technologies (Edmonton, Alberta) for its innovation in the areas of “linking scientific research to commercialization, jobs and economic growth.” More can be found  in the media release on Nanowerk News.

Nanowerk News has also published a guide to the materials on their site, 10 things you should know about nanotechology. I highly recommend checking this out. Go here.

Canada’s 2009 Science and Technology Week will take place Oct. 16 – 25, 2009 (seems more like 10 days to me). You can check out the currently scheduled events (I’m sure this will be updated) for your province here,

There’s an interesting  story about the first copyright trial in 6th Century Ireland here on Techdirt.