Updated look.

I finally bit the bullet and updated the look of the blog.  I'm still keeping it ad-free, though.

google+

I have a nagging feeling that google+ could somehow be used to significantly increase readership of my blog, if only I was appropriately savvy.  Anyone have any suggestions or thoughts on this?  I don't crave the attention per se, but I'd be fibbing if I said I wasn't jealous of the readership numbers of the folks that blog at, e.g., scienceblogs, discovermagazine.com, or scientificamerican.com.  Larger readership would undoubtedly motivate more writing, too, though that's not necessarily great for my time management....

It's all at the interface. Again.

Over the last decade, there has been a great deal of exciting work in making electronically interesting systems at atomically sharp interfaces between different oxide materials (oxide heterostructures). Analogous efforts at semiconductor-dielectric interfaces have given us the conventional field-effect transistor, something like 10⁹ of which are being used to render this page for you. Likewise, heterointerfaces in compound semiconductor systems (especially the technologically relevant III-V materials like GaAs) have given us two Nobel Prizes and a great deal of quantum electronic fun. Oxides are much trickier beasts from the materials science side, making growth and interfacial control a major challenge. Moreover, with respect to basic science, transition metal oxides can be incredibly rich systems, because in many of them electron-electron interactions lead to competing electronic and magnetic phases, with consequences like the emergence of high temperature superconductivity.

A few years ago, this paper demonstrated that it was possible to get superconductivity at the interface between SrTiO₃ and LaAlO₃, two oxides that are both insulating if perfectly stoichiometric. Still, SrTiO₃ is known to superconduct if highly doped, and therefore this observation, while a great experiment, wasn't hugely shocking, given the existence of a high density electron gas at the STO/LAO interface. More recently, this paper showed that high temperature superconductivity could happen at the interface between a nominally insulating oxide and a metallic (but not superconducting) cuprate related to the high-Tc materials. This past week on the arxiv, a logical successor to these works appeared here. The authors use two nominally insulating oxides (STO again, and CaCuO₂. Because of imperfect stoichiometry at the interface (excess oxygen, apparently), there is a conducting layer at the interface, with a superconducting transition around 50 K (in one sample, though others all show transitions exceeding 25 K). Bearing in mind that this is a preprint (and therefore has not been refereed), it is still very exciting. We are finally approaching the ability to engineer complex materials (not just semiconductors) on the atomic layer level, and this should be an incredible playground for basic science and materials engineering. It'd be great to get plugged into a collaboration working in this area.

Science and the public

I couldn't help but notice that one of my favorite producers of animated films, Aardman Animation, is coming out with a new movie (trailer here). I find it very interesting that the UK version of the movie is "The Pirates! In an Adventure with Scientists!", while the US version is "The Pirates! Band of Misfits!". The film is based on a book with the former title, by the way. I don't want to overanalyze this, but it's hard to escape the conclusion that some marketing drone decided, "scientist" is box-office poison, and that "misfit" was an acceptable and more marketable substitute in the US. Great. Wonderful. In case you're wondering, Charles Darwin shows up as a character in the book/movie. I imagine that the US ads won't be playing that up very much, or there will be protests. Sigh.

(I do have a science post I'll make shortly. I just couldn't let this pass w/o comment. And it's taking enormous self-restraint not to launch into extended political invective about the US, but there are many places where people can read that if they want to.)

Follow-up, and blogger drop-off

Regarding the story mentioned here, Nature has published both a provocative and interesting article by Eugenie Reich about the larger issues raised, and an editorial. Sorry that these are behind a pay-wall. To summarize in a few sentences: Eugenie Reich points out that the misconduct investigation relevant to this discussion highlights important problems with the US Department of Energy's handling of such cases. To wit: There are issues of independence and chain of authority of the investigators, and lack of proper record keeping, documentation, etc. of investigation reports. The conclusion is that this is a powerful argument for the DOE to establish an Office of Research Integrity, like those in some other agencies. The editorial from Nature chastises the DOE along these lines. Interesting that the Nature editorial makes no mention at all of their own role in not publishing technical comments relevant to this particular matter.

In blogging news, there has been a drop-off in the number of active physical science bloggers. David Bacon's Quantum Pontiff has decohered. The Incoherent Ponderer has gone so far as to apparently delete his entire blog and blogger profile. Other blogs have not been updated in many months. It's likely that this is all part of a natural stabilization of blogging - people run out of things to say, and the novelty of blogging has trailed off. It will be interesting to see where this trend resolves. It'll be a shame to have fewer interesting voices to follow, though. (Clearly we should all switch to Twitter, since 140 characters should be more than sufficient to carry out detailed science discussions or popularizations for the lay audience. Ahem.)

Crowd-sourcing, video games, and the world's problems

This past weekend, I caught a snippet of a rebroadcast of this NPR story about Jane McGonigal and the thesis of her recent book. In short, she points out that as a species we have spent literally millions of person-years playing World of Warcraft, an online game that involves teamwork and puzzle-solving (as well as all the usual fun silliness of videogames). Her point is that in the game environment, people have demonstrated great creativity as well as a willingness to keep coming back, over and over, to tackle challenging problems (in part because there is recognition by the players that problems are pitched at a level that is tricky but not insurmountable). She wants to harness this kind of intellectual output for good, rather than just have it as a social (or antisocial) outlet. She's not the first person to have this sort of idea, of course (see, e.g., Ender's Game, or the Timothy Zahn short story "The Challenge"), but the WoW numbers are truly eye-popping.

It would be great if there were certain scientific problems to which this could be applied. The overall concept seems easiest to adapt to logistics (e.g., coming up with clever ways of routing shipping containers or disaster relief supplies), since that's a puzzle-solving subdiscipline where the basic problems are at least accessible to lay-people. Trying this with meaty scientific challenges would be much more difficult, unless those challenges could be translated effectively into problems that don't require years and years of foreknowledge. Hmm. Still very thought-provoking.

The tyranny of the buried interface

Time and again, a major impediment to research progress in condensed matter physics, electrical engineering, materials science, and physical chemistry is the need to understand what is happening in some system at a buried interface. For example, in organic photovoltaic devices, it is of great importance to learn more about what is happening at metal/organic semiconductor interfaces (charge transfer, interfacial dipole formation, Fermi level pinning) and organic/organic interfaces (exciton splitting at the interface between electron- and hole-transporting materials). Another example: in lithium ion batteries, at the interface between either the cathode or the anode and the electrolyte, after the first couple of charge and discharge cycles, there forms the "solid electrolyte interface" (SEI) layer. The SEI is nanoscale in thickness, stabilizes the electrode surface, establishes the energetic lineup between the electrolyte redox chemistry and the actual electrode surface, strongly affects the kinetics of the lithium ion transport, etc.

Unfortunately, probing buried interfaces in situ in functioning systems is extremely hard. There generally is no Star Trek scanner device that can nondestructively reveal atomic-scale details of buried 3d structures. Many of our best characterization approaches are surface-based, or require thinned down samples, and there are always difficult questions about how information gained in such investigations translates to the real situation of interest. This is not a new problem. From the early days of surface science and before, people have been worrying about, e.g., how to connect studies performed in UHV on single crystal surfaces with "real world" situations on polycrystalline surfaces with ambient contaminants. There are some macro-scale interface sensitive approaches (exploiting x-ray standing waves, or interfacial optical effects). Still, the more people working on developing better characterization tools toward this end, the better, even if it doesn't sound terribly exciting to the masses.

a recurring story

Five years ago, there was a controversy in the pages of Nature regarding this paper from 1993, the first to claim atomic-resolution chemical analysis via scanning transmission electron microscopy.  At issue was whether or not the data in the paper had been reprocessed (in response to referee concerns) in a legitimate or misrepresentative way, and whether the authors had been honest and forthcoming with the journal and the reviewers about the procedures they'd followed.  The reason that matters came to a head more than 12 years after the original paper was the appearance of a preprint in the arxiv and subsequently submitted to Nature Physics, sharing two of the authors of the original paper, with further questions raised about the handling and analysis of data and images.  This was all discussed clearly and succinctly by ZZ at the time.  Nature allowed the authors to publish a corrigendum, a correction rather than a retraction, regarding the original '93 paper.  This was sufficiently controversial that Nature felt the need to write an editorial explaining their decision.  Oak Ridge did an investigation of the matter, and concluded that there was no fabrication or falsification of data; that report and a response by the authors are linked here.  Judging from the appearance of this on the arxiv last night, it would appear that this isn't quite the end of things.

Pitch for a tv show

Summer blogging has been and will continue to be light, as I try to get some professional writing done. In the meantime, though, I have to give my elevator pitch for the awesome new TV show that would be great fun. It's "Chopped" meets "Mythbusters" meets "Scrap Heap Challenge"/"Junkyard Wars". Start off with three teams. Give them a physics- or engineering-related task that they have to accomplish (e.g., write the opening crawl from Star Wars in one mm^2; weigh a single grain of salt), some number of tools that they have to use (e.g., a green laser pointer and an infrared corrected microscope objective), and access to a stocked "pantry" (including a PC, electronics components, etc.). Give them a time limit (4 hours, cleverly edited down to half an hour in broadcast). Points awarded for success at the task, time used, and elegance. I think it could be a hit, particularly if there are explanations (narrated by cool resident experts) delivered in a fun, accessible tone. It'd be fun, even if it did conjure up images of Guy Fleegman in Galaxy Quest.

Soliciting book or review article recommendations

I am interested in reading good books or review articles on two particular topics, and I'm hoping that by "crowd-sourcing" to my readership, I might do better than wandering through the literature.  First, I want to find an authoritative discussion of the physics behind the electrochemical potentials of battery materials - not the lore of decades of electrochemistry, but a real hashing out of the physics.  Second, I would like to find a thorough, authoritative discussion of the physics behind catalysis.  Again, I'm not interested in handwaves and parametrized empirical knowledge, but would prefer a physics-based discussion that explains, e.g., why Pd is good at splitting H₂, while Ti is not.  Any help would be greatly appreciated.

Several items

I returned late last week from Germany, where I spoke at a summer school. One fun part of the trip was a tour of the main experimental facility at the neighboring Max Planck Institute for the Chemical Physics of Solids. The facility was a large high-bay lab space, with 9 (!) dilution refrigerator apparatuses, as well as a 0.3K scanning tunneling microscope with 12 Tesla magnet. Very impressive infrastructure, and the place was neat as a pin - the very model of a lab. Note to self: figure out how to instill Germanic ultraprecise lab notebook habits in all incoming grad students...,

Other news this week that is interesting: the US National Academies have decided to make many of their books available for pdf download free of charge. I'm a particular fan of one or two of these. For example, with reference to recent discussions about helium as a resource, check this out.

There is also a great deal of attention being paid to a paper from this week's Science by the group of Aephriam Steinberg. The experiment sends single photons one at a time through a two-slit type apparatus. This is one of those experiments meant to blow the minds of undergrad physics majors taking quantum for the first time: you still build up an interference pattern from the slits, even though there's only one photon in there at a time. That means the photon must be interfering with itself(!). In the new work, the group uses optics techniques (that I freely admit I do not fully understand) to correlate, after the fact, the ("weakly" measured) momentum of the photon while in the apparatus with the (strongly measured) final position of the photon on a CCD. This does not violate the uncertainty relation, since it basically finds a quantum mechanical ensemble average of the momentum as a function of final position. Still, very neat, and discussed in some detail here and here.

I've liked Steinberg's work for years. This business about quantum measurement and post-selection is very fun to think about. For example, this comes up when considering the question, "how long does it take a quantum particle to tunnel through a classically forbidden region?". What you're basically asking is, given the successful measurement of a quantum particle at some position beyond the classically forbidden region, when did the particle, in the past, impinge upon that region in the first place? This is a very hard question to answer experimentally.

Recently in the arxiv

As I get ready to head to Germany for my first ever experience lecturing at a Max Planck summer school, I wanted to point out very briefly three of a number of interesting papers that came through the arxiv this week.

arxiv:1105.4055 - Janssen et al., Graphene, universality of the quantum Hall effect and re-definition of the SI

This paper compares the quantization of the Hall resistance in two different two-dimensional electronic systems: a conventional 2d electron gas in a GaAs/AlGaAs structure, and graphene. The authors find that the Hall resistance is quantized in units of h/e² identically in the two systems to parts in 10¹¹. On the one hand, this is really amazing, since you're seeing essentially exact quantization in two different systems, and the whole basis for the quantum Hall effect relies in part on dirt - without disorder, you wouldn't see the quantum Hall physics. And yet, even though the materials differ and dirt plays an important role, you get precise quantization in terms of fundamental constants. This is the kind of emergent, exact phenomenon that shows the profound character of condensed matter physics.

arxiv:1105.4642 - Barends et al., Loss and decoherence due to stray infrared light in superconducting quantum circuits

As someone who struggled mightily in grad school to avoid the effects of infinitesimal amounts of rf noise leaking into his ultracold sample, this impressed me. The authors demonstrate that infrared radiation from the surroundings, even when those surroundings are at 4.2 K, can have marked, detectable impact on the coherence properties of superconducting quantum bits. They compare results with and without an absorbing radiation shield in the way, and the effects aren't small. Wild. Time to break out those 50 mK shields from our old nuclear demag cryostat....

arxiv:1105.4652 - Paik et al., How coherent are Josephson junctions?

Along these same lines, these authors have been able to demonstrate coherence times in superconducting qubits that stretching into the tens of microseconds scale. They do this via a new kind of cavity, essentially controlling the environmental dissipation. This isn't really my area, but I know enough to be impressed, and also to be surprised at the apparent lack of the usually ubiquitous 1/f noise problems (in the critical current) that often limit coherence in these kinds of devices. As they point out, these numbers are encouragingly close to the thresholds needed for quantum error correction to be realistic.

Nano for batteries

Improved batteries would be of enormous benefit and utility in many sectors of technology.  A factor of 10 improvement in battery capacity (with good charging rate, safety, etc.) would mean electric cars that get 1000 miles per charge, laptops that run for days w/o charging, electrical storage to help with the use of renewable energy, and a host of other changes.  This rate of performance enhancement is completely commonplace in semiconductor electronics and magnetic data storage, yet batteries have lagged far, far behind.

There is real hope that nanostructured materials can help in this area.  Three examples illustrate this well.  Conventional lithium ion batteries have an anode (usually graphitic carbon, into which lithium ions may be intercalated) and a cathode (such as cobalt oxide), with an intervening electrolyte, and a separator barrier to prevent the two sides from shorting together.  A reasonable figure of merit is the capacity of the electrodes, in units of mA-h/g.  The materials described above, anode and cathode, have capacities on the order of 200-300 mA-h/g.  It is known that silicon can take up even more lithium than carbon, with a possible capacity of more than 3000 mA-h/g (!).  Complicating matters, Si swells dramatically when taking in Li, meaning that bulk single-crystal Si cracks and self-pulverizes when taken through a few charge/discharge cycles.  However, Si nanowires have been observed to be much better behaved - they have large surface specific surface area, and have enough free surface to swell and shrink without destroying themselves - see here.  Very recently, this paper has spectacular electron micrographs of the swelling of such nanowires.

A second example:  nanostructured cobalt oxide particles, self-assembled using selectively modified virus proteins, have been put forward as high capacity Li ion battery cathodes.  This approach has also been extended to iron phosphate cathode material.

A third example:  dramatically improved charging rates may be possible using nanostructured electrode geometries, such as these inverse-opal shapes.

There is real hope that nanostructured materials may enable true breakthroughs in battery technology, even though batteries have been studied exhaustively for many decades.  The ability to engineer materials at previously inaccessible scales may bear fruit soon.

Rice University clean room manager needed.

Just in case anyone out there has or is a promising candidate, I wanted to point out that Rice University is looking for a new clean room facilities manager.  (This is not a soft money position.)  Here is the text of the advertisement:

Rice University is seeking a technical manager to oversee the operations of its clean room user facility and associated characterization equipment.  This Class 100/1000 facility contains a suite of instruments, including a photolithography mask maker, a contact mask aligner, an e-beam evaporator, an RIE/PECVD system, and a collection of characterization tools.  The manager’s responsibilities include oversight of this facility, training of undergraduate and graduate students and other users, and maintenance and upkeep of the equipment.  Applicants must have a BS degree in a science or engineering discipline (PhD preferred but not required), and extensive experience with several of the relevant instruments or a related technical degree or diploma with an additional 2 years of the related experience (for a total of 7 years of related experience working with clean room instruments).  Salary will commensurate with experience.  The need to fill this position is immediate, and resumes will be examined as they arrive.  Please visit http://cohesion.rice.edu/campusservices/humanresources/riceworks.cfm to apply for this listing.  Rice University is an equal opportunity, affirmative action employer.

A university selling its soul

I'll get back to physics shortly.  These two articles (here and here) explain how, in exchange for $1.5M in donations, the Florida State economics department agreed to give the donors veto power over faculty hiring for the donor-supported positions.  Moreover, the donors can withdraw the positions if they aren't happy with annual performance reviews of the professors.  Wow.  I know times are tight, but FSU has clearly decided that they're up for bid.  I don't care whether the donors are right-wing or left-wing (hint:  they're right wing) or centerist - a university that allows donors direct control over faculty hiring and evaluation is out of its mind.  Gee, you think those professors are going to be free to do whatever research they want?  Do you think there's going to be pressure on all of the faculty within the department to toe the line rather than risk angering the donors?  What a mess.  Well, at least it confirms that Texas doesn't have a monopoly on idiocy.

Update:  blogger ate this post, and I had to reconstitute it from the cached version on bing (google blew this one all the way around).  Clearly the Koch brothers are responsible :-)

Gravity Probe B

Finally, after only 45 years from conception to publication of results, Gravity Probe B has announced (dramatic pause) that Einstein's General Theory of Relativity is consistent with their data.  I had mentioned GPB ("The Project that Ate Stanford") once before.  It was a fascinating, complex, multidisciplinary project that, thanks to its experimental design and extraordinarily long duration, had great impact on a large number of physics, materials science, and engineering careers.  Still, I think they were in a bit of a no-win scenario, particularly once it became clear that there were problems with interpreting the data.  Either they support general relativity, or people just wouldn't trust the results, given how much other evidence there is out there that GR is right, at least in the relatively weak field limit.

Nano for solar

Sorry about the delay in this posting.  Real life has been busy.

Solar energy is an obvious candidate for a long-term solution to many of our energy problems.  The amount of power reaching the surface of the earth is on the order of 350 W/m².  We could meet the world's projected energy needs in 2030 by covering around 250 km by 250 km with 10% efficient solar cells.  Unfortunately, the total surface area of all photovoltaics ever manufactured is less than 0.1% of that.  (This is why being able to produce photovoltaic cells by printing processes would be great.  Hint:  estimate the total area printed by the New York Times in a month.)  There are a number of challenges involved in solar.  Why might "nano" broadly defined be a big help?  Let me give three examples from the large wealth of ideas out there.

1) Semiconductor nanocrystals as absorbers.  Because of the beauty of quantum confinement, it is possible to make semiconductor nanocrystals out of a single material, and use different sizes to capture different parts of the solar spectrum.  Moreover, there is evidence (after some controversy) that nanocrystals may enhance "multiexciton generation" (e.g., here and here).  In a traditional solar cell, a photon with energy twice as large as the semiconductor band gap will generate an electron-hole pair (which must be ripped apart somehow), and inelastic processes will lead to the excess (above the band gap) energy being lost as heat.  However, at some rate, instead you can generate two band-gap-energy pairs.  The idea is that the rate of that process can be enhanced in nanocrystals, since conservation of "crystal momentum" can be relaxed in materials that are so surface-dominated.

2) Nanostructured materials for photoelectrochemical cells.  There are a number of proposals for using electrolytes in solar applications, including dye-sensitized solar cells.  In this case, one would like to use a high surface area anode, such as nanostructured TiO2 or some similar nanostructured material.  Moreover, instead of using organic dyes as the absorbers and sources of photoexcited electrons, one could imagine again using semiconductor nanocrystals.

3) Plasmon-enhanced photovoltaics.  One way to try to boost the efficiency of solar cells is to get the light to hang around the absorber material for longer.  One compact way to do so is to use plasmonically active metal nanoparticles or nanostructures as optical antennas.  The local fields near these structures can enhance scattering and local intensity in ways that tend to boost performance, though resistive losses in the metal may limit their effectiveness.  It's worth pointing out that one can also use plasmonic antennas as sources of hot electrons, also interesting from the photovoltaic angle.

There are many more ideas out there - I haven't even mentioned anything about nanotubes or graphene.  While the odds of any individual idea being a truly transformative breakthrough are small, there are probably more clever things being proposed in this area now that at any time ever before, thanks to our ability to manipulate matter on very small scales.   

Nano and energy

It might be fun to do a few posts on how nanoscale science can be used to the benefit of our energy concerns.  First, let me specify what I mean when I say that there's an "energy problem".  The fact is, average people enjoying first-world standards of living (e.g., US/Canada/Western Europe/Japan) have an enormous per capita energy consumption compared to, e.g., tribesmen in sub-Saharan Africa, or rural farmers in the hinterland of China.  If the goal is to raise the standard of living of the 5-ish billion people not enjoying the high life, and to get everyone up to a high standard of living, then we've got a problem:  there's no nice way to do so without incurring other enormous costs (e.g., burning enormous quantities of fossil fuels; building GW-scale power plants at very high rates, like several per day for the next 30 years).  Either we're not going to raise that standard of living for those billions of people, or the energy costs for the top economic tier are going to have to fall, or we're headed for major upheaval (or possibly some of all of the above).

When I teach my second-semester nano class, I point this out, and if you want interesting quantitative references, check here.  Broadly construed, nanotechnology and nanoscale science (and more broadly, condensed matter physics and materials science) can try to address several aspects of this challenge, though there are certainly no silver bullets.  The areas that come to mind are:  energy generation; energy storage; energy distribution; conservation or improved efficiency; and environmental remediation.  In future posts, I'll try to summarize very briefly a few thoughts on this.   

Public funding of science, and access to information

On multiple blogs over the last few months, I've read comments from lay-persons (that is, nonscientists) that say, in essence, "As a citizen, I paid for this research, and therefore I should have access to all the data and all the software necessary to analyze that data."  The implications are (1) research funded by the public should be publicly accessible; and (2) the researchers themselves sometimes/often? hold back information or misinterpret the results, perhaps because they are biased and have an agenda to further.  

Now, as a pragmatist, there are a number of issues here.  For example, making available raw columns of tab-delimited numerical data and, e.g., matlab code, won't give a nonscientist the technical know-how to do analysis properly, or to know what models to apply, etc.  Things really get tricky if the "data" consists of physical samples (e.g., soil, or ice cores, or zebrafish)....  Yes, scientists that are publicly funded have the responsibility to make their research results available to the public, and to explain those results and their analysis.  As a practical matter, scientists are not obligated to make any interested citizen into an expert on their research.

While this is an interesting topic, I'd rather discuss a related issue:  How much public funding triggers the need to make something publicly available?  For example, suppose I used NSF funding to buy a coaxial cable for $5 as part of project A.  Then, later on, I use that coax in project B, which is funded at the $100K level by a non-public source.  I don't think any reasonable person would then argue that all of project B's results should become public domain because of 0.005% public support.  When does the obligation kick in?  Just an idle thought on a Saturday morning.

Friction, commensurability, and superlubricity

In the limit of clean surfaces, friction has its origins in the microscopic, chemical interactions at the interface between the two objects in question.  One of the more amazing (to me, anyway) consequences of this is the extremely important role played by commensurability between the surfaces.  Let me explain with an example.  Consider a gold crystal terminated at the (111) surface, and another gold crystal also terminated at the (111) surface.  Now, if those two surfaces are brought into contact, with the right orientation so that they match up as if they were two adjacent layers of atoms inside a larger gold crystal, what will happen?  The answer is, in the absence of adsorbed contaminants, the surfaces will stick.  This is called "cold welding".  In contrast, if you bring together two ultraclean surfaces that are incommensurate, they can slide past each other with essentially no friction.  This is called "superlubricity".  Here are two great examples (pdf of first one; pdf of second one) of this.

In this new paper, Liu et al. are able to do some very cute experiments in this regard, looking at the motion of thin graphite flakes (exfoliated from and) sliding on graphite pedestals.  It's clear from the observations that graphite flakes shifted relative to the underlying graphite substrate can slide essentially frictionlessly over micron scales.  Very neat and elegant, and surprising since there is not any rotation at work here to break commensurability.  This is a very firm reminder that our macroscale physical intuition about materials and their interactions can fail badly at the nanoscale.