Saturday, March 29, 2008


Anyone out there using Twitter? I've just started playing with it. Few-to-few twittering is clearly useful, for instance as a way to help a small group converge on a meeting place, receive travel updates, and so forth. I can't decide whether many-to-many broadcast twittering serves any purpose at all, though.

For those interested in helping me investigate the question, my Twitter name is kewms. You'll need to ask to follow me.

(Political) life is a fantasy

Having been at MRS all week, I mostly missed the latest campaign brouhaha. I do think, though, that the suggestion that it's possible to "forget" or "misspeak" about something like dodging sniper fire (with your daughter!) is ridiculous. Repeating such a provably fictitious story, with increasing amounts of detail, even in the face of ridicule by people who were there, suggests a disdain for one's audience that's extreme even by political standards.

Thursday, March 27, 2008

And now the news

(Once again, all references are to MRS paper numbers, abstracts for which can be found at the conference site.)

Today at the MRS Spring Meeting, John Robertson reported (paper A13.1) that his group at Cambridge University has achieved n-channel mobility of 450 cm2/V-sec in microcrystalline silicon TFTs, and 100 cm2/V-sec p-channel mobility. Both those values are very good, and that's a problem. Plenty of models exist to explain why the material's mobility might be bad, and those models break when the mobility is good. More research needed.

(Special thanks to Dr. Robertson for walking me through yesterday morning's session on graphene, too.)

Meanwhile, Yifei Huang and a Princeton University group demonstrated (paper A13.2) a self-aligned process for low temperature polysilicon TFTs. It uses nickel silicide source and drain regions, aligned using the gate structure. At low annealing temperatures, the nickel doesn't react with the gate and can simply be etched away. Results were among the best ever recorded for top gate TFTs.

In the solar cell sessions, Makoto Shimosawa described (paper A14.1) Fuji Electric's FWave flexible solar material. It laminates roll-to-roll amorphous silicon/amorphous SiGe tandem cells (deposited by PECVD on plastic) onto steel foil. Each 2 square meter sheet generates 92 watts at peak output and weighs just 16 kg (including the steel foil). The company is now ramping production to wider rolls, targeting production of 40 MW per year.

The a-Si/a-SiGe tandem cell may be on its way out, though, as Xixiang Xu's group at United Solar Ovonic reported (paper A14.2) better results with small area triple junction a-Si/nanocrystalline-Si/nc-SI cells. Scale-up to large areas and optimization of the nc-Si component cell are the next steps.

The conference's own coverage is definitely worth a look as well.

Tuesday, March 25, 2008

Moses lists FTW!

*snort* What if the Bible were (a) a blog and (b) open for comments? What might the blogosphere have to say about Genesis or Exodus?

Guide to the perplexed

For those who don't know what the last two posts were talking about, MRS stands for Materials Research Society, the professional society for materials scientists. I'm in San Francisco for the MRS Spring Meeting this week.

Among other things, MRS gives people in the field a handy crib sheet to use when people ask, "so what's materials research?"

Briefly, materials science is the glue that pulls together subjects as diverse as Mayan bronzes, high temperature superconductors, organic and inorganic semiconductors, and ink rheology. All of these areas involve manipulating the structure and processing of materials in order to achieve the desired properties.

A whirlwind tour of this evening's MRS poster session

References are to MRS paper numbers. All abstracts can be found at the meeting site.

Two papers from Kyoto University, by Hideo Ohkita et. al. (AA5.32) and Jiamo Guo et. al. (AA5.33), presented good fundamental studies of charge generation and transport in fullerene-polymer bulk heterojunction solar cells. Extra points for providing copies of their posters as takeaways.

In paper KK5.14, Hagay Shpaisman, et. al., take a skeptical look at multiexciton solar cells, questioning whether they offer much improvement over the more conventional, and more tunable, tandem cell.

Yong Soo Kang, et. al. (KK5.1) presents a novel electrolyte for dye-sensitized solar cells, in which hydrogen bonds pull oligomers together in situ to form a self-solidified polymer that can still penetrate the cell's titanium dioxide nanostructure. Someone who saw me taking notes added the caveat that one of the components of the electrolyte is still a liquid; the author wasn't around to answer questions.

I'm not sure I quite understand this one, but in paper AA5.86 Janelle Leger and Glenn Bartholomew propose a single-layer polymer-based p-i-n transistor. The semiconducting polymer incorporates ion transport agents and ion-paired monomers, apparently creating an all-in-one electrochemical cell.

Everyone talks about how nice roll-to-roll fabrication would be, but Daniel Tobjork and coworkers (AA5.45) have actually done it. They used reverse gravure coating to put P3HT:PCBM / PEDOT:PSS organic semiconductor structures on plastic. Results were comparable to those achieved with spin-coating; roll speed controlled the coating thickness.

MRS breaks down the energy puzzle

Recommended reading for anyone interested in renewable energy and related issues: the MRS Bulletin's April issue. It's a comprehensive look at everything from controlling fossil fuel emissions, to hydrogen storage and transportation, to energy conservation. There's a lot of material here, but it's well worth the time. Reasonably accessible to nonspecialists and nontechnical people.

Thursday, March 20, 2008

Scraping the bottom

How bad is the silicon shortage? People are sending email asking to buy Thin Film Manufacturing's inventory of silicon scrap.

No, I don't have any.

Wednesday, March 12, 2008

Old-style organizing, online

A couple of weeks ago, I suggested that Barack Obama may be the first Internet president (if he wins). Apparently Rolling Stone thinks so too, and they have much better access to his operations than I do. A very interesting look at mixing newfangled tools with old-fashioned activism.

Saturday, March 8, 2008

Paying for teacher performance

Most studies show that teacher quality directly correlates to the quality of a school. And so you see all kinds of proposals for beefed up licensing requirements, more stringent evaluation of teachers, easier removal of underperforming teachers, and on and on.

Now a charter school in Manhattan is testing a much simpler approach: if you want better teachers, pay them more. A lot more.

Makes sense to me. Better pay is presumed to attract better performers in every other profession, from computer programming and graphic arts to finance and athletics. Better pay makes it easier to give a job your full attention, which can only improve results. Perhaps even more important, people who make more money generally get more respect from both society and their employers. Friends of mine who've left teaching cite lack of respect as a very serious problem: it's hard to earn the respect of students if you don't get it from administrators or parents. It's hard to maintain educational or disciplinary standards when parents and administrators won't back you up.

Thursday, March 6, 2008

How Apple Did It

Nikkei Electronics bought one of the first MacBook Air computers, and tore it apart. Fascinating reading, with lots of insight into the differences in design philosophy between Apple and companies like Sony. Six parts so far, looking at customer experience, battery design, workmanship, and thermal design, with videos of chassis opening and battery removal (video narration in Japanese).

Saturday, March 1, 2008

Circuses don't bring bread

While the Wall Street Journal's news coverage is excellent, its opinion pages tilt far to the right. I disagree with the Journal on almost everything. Still, this article on the New York Philharmonic's recent visit to Pyongyang hits the nail squarely on the head. The notion that one concert will have any impact whatsoever on the world's most closed society is beyond naive.