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Ideas for a new era

Three major reports have already been published – on atomic, molecular and optical science; plasma science; and elementary-particle physics – and reports on nuclear physics and gravitational physics are being completed. A separate NRC panel is preparing a report on astronomy and astrophysics.

The latest Physics in a New Era report to emerge, Condensed-Matter and Materials Physics: Basic Research for Tomorrow’s Technology, covers what is probably the biggest and most diverse area within physics. Prepared by a committee chaired by Venkatesh Narayanamurti of Harvard University, the report presents accessible summaries of the state-of-the-art in the field, along with recommendations for future directions and priorities.

There has certainly been plenty of progress over the past decade. The ink had barely dried on the 1986 report when high-temperature superconductivity was discovered. Other advances have included giant and colossal magnetoresistance, buckyballs and nanotubes, Bose-Einstein condensation, and the manipulation and visualization of single atoms and molecules with various atomic force microscopes. One major theme to emerge from the discussions of future directions and priorities is the broad scope for work on problems in biological physics. Some of the examples given include molecular motors, gene therapy, photosynthesis and energy transfer, protein folding and dynamics, and various non-equilibrium phenomena in biology.

Many of the recommendations are specific to the US. The report calls for increased investment in infrastructure, state-of-the-art instrumentation and fabrication capabilities, with an emphasis on partnerships between universities, national laboratories and industry to make the most of this investment. And not surprisingly it also expresses support for various advisory panels that have recommended the prompt construction of a new pulsed neutron source in the US, upgrades to other neutron sources, increased funding for existing synchrotron radiation sources, and R&D for a next-generation light source.

The report also notes that the time it takes to obtain a physics PhD in a US university is approaching seven years, and although it stops short of making specific recommendations, it does float the idea of redefining the physics PhD or developing a professional degree for the industrial physicist. This is a particular concern in condensed-matter and materials physics as many PhDs go on to work in industry.

Back at the research frontier, the report also identifies what it calls “strategic scientific themes” that will unite the various areas of condensed-matter and materials physics, and catalyse scientific and technical progress. This impressive list reads as follows: the quantum mechanics of large, interacting systems; materials with reduced dimensions; complex materials; non-equilibrium processes; soft condensed matter; the control of electrons and photons on the atomic scale; understanding magnetism and superconductivity; properties under extreme conditions; synthesis, processing and nanofabrication; and simulation.

This latest Physics in a New Era report has presented a clear agenda for taking condensed-matter physics forward, and much of it is as relevant to physicists outside the US as it is to those inside. The survey team is also to be commended for undertaking to produce an ambitious overview report, due for publication next year. This will cover the unity of physics, connections with other subjects, the contributions of physics to society and many other topics. With physics at a crossroads in so many parts of the world – and with about one third of the world’s physicists in the US – it is to be hoped that the overview committee produces an equally thorough and globally relevant report.

Learning lessons about ethics

To what extent should a formal education in ethics be part of the university physics curriculum? When this question is raised in the physics community, the response is often that there is no significant problem with fraud in physics, and hence that including ethics in the curriculum is unnecessary. Even raising the question is viewed by some as a waste of time at best and insulting at worst. I would argue, however, that such a response takes an overly narrow view of the role of ethics in physics.

“Ethics” refers to the standards of conduct associated with our actions as professional physicists. Our professional activities extend beyond traditional research to include a wide range of other activities that we do in support of research, teaching and our interaction with the rest of society. That we consider ethics to apply to the full range of these activities is important to the health of the physics community.

The “cold fusion” affair provides an interesting example. When Stanley Pons and Martin Fleischmann announced ten years ago this month that they had achieved fusion at room temperature in a table-top experiment, their declaration was, by all accounts, premature. Although a full examination of all the intricacies of the story would require a book (see, for example, Frank Close’s Too Hot to Handle: The Race for Cold Fusion), several simple observations can be made.

The fact that many others tried – and failed – to replicate the experiments of Pons and Fleischmann can be viewed as evidence that the scientific community can effectively weed out erroneous results, and hence that “the system” works. However, an enormous price was paid (in both time and money) to investigate these results. Had Pons and Fleischmann delayed in going public, these resources could have been used in a more productive manner. At the same time, it is important to recognize that they did not have the luxury of making their decisions in a vacuum. They had potentially made a discovery that could have been incredibly rich in patent rights, and their university was anxious to share the wealth.

There are many lessons that can be drawn from the cold-fusion affair. One is that real-world decisions are made in a complex environment that makes ethical decisions more challenging to implement. Another is that society can pay a steep price for ethical lapses of this sort.

Ethics for physicists

Ethics does not just apply to high-profile cases such as cold fusion. Many of us, in much less dramatic settings, have had to face the fact that some research results we have disseminated are in some way inaccurate. A calculation may have been performed incorrectly, an instrument may have been wrongly calibrated, an important factor may not have been accounted for, or a simple typographical error may have crept into a paper.

In many cases, these errors could reasonably be classified as acceptable (and, to some extent, expected) mistakes that are made in the course of scientific exploration. However, it is important for us to always question whether we have rushed our results into print prematurely. I expect all of us have read a paper where this seems to have been the case.

But there are many other situations in physics where we confront decisions that have an ethical component. For example, can we be sure that our data have been analysed and reported fairly? Does a particular individual deserve co-authorship on a paper? Are the projections we made in our grant proposal realistic? When we are asked by someone outside the scientific community for our expert opinion on a particular topic, do we have enough expertise to provide it? Are we taking our share of the responsibility for ensuring that society is getting adequate technical advice from the physics community? Are we providing guidance and training to our students that is appropriate for the current job market?

Teaching students ethics

One way of helping physicists to appreciate the role that ethics plays in their lives is to include it in the undergraduate curriculum. At Eastern Michigan University in the US, we offer a seminar course in ethics for our physics majors, who meet for one hour each week to discuss readings from a wide range of resources. We begin by discussing the five basic principles of ethics that were described in 1993 by the philosopher and ethicist David Resnik. According to him, one should

  • not harm others needlessly (the non-malificence principle);
  • promote the welfare of others (the beneficence principle);
  • allow rational people the right to self-determination (the principle of autonomy);
  • treat equals as equal (the formal principle of justice);
  • distribute goods on the basis of need or merit (the material principle of justice).

These principles can be viewed as the foundation of scientific ethics. For instance, the principles of non-malificence and beneficence presumably help guide our choice of research topics.

We then spend some time in the course discussing specific codes of ethics developed by various professional organizations. Even the most basic and apparently obvious principles can open the door to complex questions, particularly those involving conflicting standards. The rest of our course is devoted to studying specific issues, historical incidents, or particular individuals, with an eye to understanding how physicists have handled difficult decisions in the past.

For example, we look at Richard Feynman’s presence on the committee that investigated why the space-shuttle Challenger blew up in 1986, and examine his brief service on a textbook review committee for the state of California (see Ethical examples). The ethical questions of these case-studies are then used as a spring board for discussing the rights and responsibilities of physicists who are asked to provide the public with technical advice.

Another topic for discussion is the role physicists have played in weapons-related research. Fortunately, a huge amount of information is available on how physicists approached issues surrounding the development of the first atomic bomb, the fusion bomb and anti-missile or “Star Wars” technology. We also explore a wide range of ethical issues associated with the publishing process by examining the “instructions to authors” found in journals, reading editorials on the information explosion, and studying publications that contain glaring errors. Budgetary issues are another topic. These range from the very local, such as the appropriate use of grant money, to the much bigger picture of how physicists attempt to influence elected politicians to allocate more money to physics research. Projects such as the International Space Station (now under construction) and the defunct Superconducting Super Collider provide well documented case-studies.

One aspect of a student’s scientific training can be addressed particularly effectively in an ethics course. Most lab work that students do at high school and in their early college years consists of experiments in which they are guided step-by-step to verify laws that they have already seen presented elsewhere. This type of work fosters a skewed view of research as nothing more than an attempt to verify the known. As a result, data that are inconsistent with “the known” are often tossed out by the student without explanation.

While we try to teach students to report all of their data – unless they can be eliminated due to clear equipment or human error – this requirement is often dismissed by the students as unnecessarily time-consuming and too likely to distract from the “correct” results. But by examining case-studies, a course in ethics gives us the chance to convince students that there is a reason why we should not summarily discard data, namely that to do so is misleading and may actually result in treasure being pitched with the trash.

In my experience, many students who have completed the course maintain an ongoing interest in ethical issues. For example, one former student went so far as to write a Masters thesis on how ethical issues could be incorporated into the high-school physics curriculum. And with the drive in the US to incorporate written assignments in all facets of the high-school curriculum, ethical issues in science are a natural topic for this written component.

Barriers to overcome

The longer-term impact of our course on ethical issues in physics is more difficult to assess. Since it was instigated in 1988 about 60 students have taken the course. I recently collaborated in a survey of over 100 physicists in the US (not an entirely random selection), which showed that while there is a significant core of interest in ethics courses, there are at the same time significant barriers that must be overcome before ethics can be fully integrated into the physics curriculum (see Science and Engineering Ethics 1998 4 473). Chief among these are the discomfort with offering physics credit for a non-technical course and the difficulty of finding someone with the time and interest to develop and teach ethics. Despite the presence of such barriers, I believe it is worthwhile to continue to press for the development of ethics courses. While the physics community has survived up to now without most of its members receiving any formal education in ethics, it is nevertheless useful to reconsider whether the status quo is in our long-term interests. After all, as the issues we face become more complex, it becomes increasingly useful for us to consider some of these complexities before we encounter them – and having a clear picture of some of the basic ethical tenets will undoubtedly help.

The current situation is rather like being asked to analyse the motion of a block on an inclined plane before being taught about Newton’s second law of motion or the properties of friction. The analysis of the problem is possible without the background information and practice, but this is surely not the most effective approach in problem solving. One of the basic principles in academia is that we pass our knowledge on to the next generation of learners. This allows them to expand the knowledge base, rather than having to learn all of what we know by trial and error. Why not take the same approach with ethics?

Molecular materials make their mark

When physics students are taught about condensed matter and materials they mostly learn about metals, alloys, semiconductors and other inorganic materials. Organic and molecular materials are confined to chemistry and biology. But that may change in the future with the development of polymers and other molecular materials that can emit light and conduct electricity.

These organic materials offer many advantages over their inorganic counterparts: they are durable, flexible and cheap to mass-produce. It is little wonder that many of the leading electronics companies are embracing this expanding field of research. Product designers are dreaming up giant video screens that can be rolled up and carried from room to room, mobile phones with all-plastic circuitry that will not break when dropped and lightweight luminous panels that could replace the bulky light fittings in aeroplanes and cars.

The advantages of plastic

So how can plastics conduct when most commercial polymers are insulators? A special class of materials known as conjugated polymers – such as polyaniline and polyacetelyne – have the right physical and chemical properties to conduct electricity. In these so-called ¼-conjugated polymers, the electrons are delocalized along the backbone of the polymer molecule. By injecting charge carriers into the material and applying a high enough voltage, the charge carriers are able to jump from molecule to molecule. Electrons and holes can also “recombine” to generate light over a range of wavelengths. The beauty of these polymer materials is that their properties can be adjusted to suit specific requirements. For example, depending on the level of doping, the material can be a semiconductor or a conductor.

In Organic displays Junji Kido describes how the light-emitting properties of organic materials can be exploited in industry. While it has been known since the early 1960s that single organic crystals can emit light, the electric fields needed were prohibitively high. But the development of thin-film devices in the last decade has meant that organic materials are now emerging as realistic candidates for display applications. With the global market for electronic displays estimated at $50bn per year and rising, the giants of the display industry are eagerly investigating the new materials.

The colour of the output can be tuned by adding fluorescent laser dyes, and white light can be produced by having several layers, each doped with a different dye. Multilayer devices are already being used in real applications. The big advantage that polymers offer is that they are easy to fabricate. Indeed, standard inkjet printing technology is being adapted to make the different coloured pixels needed for full-colour displays.

Polymers have already been used as the active material in transistors, and are now being used for the conducting parts of devices as well. Philips Research in the Netherlands has gone a stage further and combined many components to make all-polymer integrated circuits, as Dago de Leeuw reports on plastic electronics. These devices are likely to replace silicon chips in mass-produced applications that use simple circuits, such as bar codes that can be read remotely, and other applications that demand lightweight and flexible devices.

While prototype devices have been demonstrated, the technology needs to be improved in several respects before plastic electronics can make an impact on the market. The switching speed of the plastic transistors is rather slow compared with silicon due to the relatively poor mobility of the charge carriers in the polymer material. In terms of mobility, the state-of-the-art polymers are 300 times better but are not easy to process using the current technology, although it is likely that these problems will be resolved in the future. But as improvements are made, it is important to maintain the flexibility of the circuits and their cost advantage over inorganic circuits.

Back to basics

Organic molecules are not confined to technological applications. Bernard Barbara and Leon Gunther describe in another article how certain magnetic nanomolecules are being used to investigate the boundary between quantum and classical mechanics. These molecules consist of a cluster of metal ions – manganese or iron – surrounded by water and acetate molecules. Applications are still a long way off and the unusual magnetic properties of nanomolecules look set to keep physicists busy for years to come.

Whatever happened to cold fusion?

Most physicists can probably remember where they were when they first heard of Stanley Pons and Martin Fleischmann. On 23 March 1989 the two electrochemists grabbed the world’s attention by announcing at a press conference in Salt Lake City, Utah, that they had observed controlled nuclear fusion in a glass jar. The excess heat measured in the experiment offered the promise of a new power source for the planet, as well as huge financial rewards.

However, it is clear that world energy production has not been affected in any way by cold fusion. No experiment has so far convinced the sceptics that cold fusion is real, and most of the big funding sources, which threw money at quick experiments in the early days of cold fusion, have pulled out. Retired particle physicist Douglas Morrison, one of the more persistent critics of cold fusion, says that after ten years there is “less science, fewer scientists, fewer funds, [although there are] more potential investors”.

But cold fusion is not dead and buried. A dedicated circle of enthusiasts has kept the flame alive to varying degrees, carrying out jury-rigged experiments in garages and basements, and one or two more conventional institutions still have an interest. Although governments such as those of the US and Japan have officially pulled out, the cold-fusion faithful say that several government agencies are still giving money to the field, including the US Department of Defense. And the Italian and French governments are still supporting research in a small number of labs, according to one cold-fusion insider.

Fusion on a lab bench

A couple of palladium electrodes in heavy water and any high-school kid could do it, it was said. Pons, in the chemistry department at the University of Utah, and his mentor Martin Fleischmann, of Southampton University in the UK, claimed at the press conference in 1989 that they had fused deuterium nuclei using routine electrochemical techniques on their lab bench. This was a huge claim to make – nuclear fusion had been thought possible only at temperatures in excess of a million degrees, when nuclei could overcome Coulomb repulsion. The only cold fusion that had been detected until then was the kind mediated by muons, seen in accelerator experiments in the 1950s, and then only at minuscule rates.

Indeed, questions were soon raised about the reliability of Pons and Fleischmann’s nuclear measurements, given their lack of experience in quantitative isotope analysis. Soon after they announced their findings, laboratories around the world tried but failed to replicate their results. In the rush to duplicate the cold-fusion results, chemists began attempting nuclear physics, and physicists tried to be electrochemists. In the months that followed many labs rushed into experiments, and hastily announced confirmation of cold fusion before they had carried out adequate controls. They then had to make equally speedy retractions when the experiments did not succeed.

Eventually, a group at the Massachusetts Institute of Technology (MIT) found serious flaws in the gamma-ray spectra that Pons and Fleischmann offered as proof. This was to be the death knell, and the final nails in the coffin of cold fusion were hammered in by a US Department of Energy panel that concluded in October 1989 that there was nothing to cold fusion. This in turn spawned bitter accusations that hot-fusion physicists and particle physicists were out to get the cold-fusion community.

The University of Utah continued to press forward with a cold-fusion research institute, but that lab was eventually disbanded in 1991 when it failed to replicate the earlier results. Pons and Fleischmann departed in 1992 for the south of France, where the Technova company, a subsidiary of the Toyota car company, funded a new laboratory called IMRA. As time went on, all but the diehards gave up, and the major reputable labs lost interest and dropped out of the experimental game.

Work on cold fusion continued in several countries, notably Japan, and this was often cited by cold-fusion believers as evidence that that US would be left in the dust when the new world energy order finally dawned. But in 1997 Japan’s government finally gave up. And in 1998 IMRA was closed, having spent something like £12m on cold-fusion work. Then in March 1998 something of a milestone may have been reached. The University of Utah finally gave up its struggle to obtain worldwide patents on Pons and Fleischmann’s work, having been legally bound to pursue patents until last year. The rights now revert to Pons and Fleischmann themselves, should they choose to continue the pursuit of patents.

Sporadic reports have continued to trickle in from various small research efforts, but in each case the results have proved erratic or impossible for other groups to replicate. It appeared to be a classic case of what the Nobel chemist Irving Langmuir called “pathological science”, in which the results are always near the limit of detectability and the proponents always have an ad hoc answer as to why. Yet the defenders of cold fusion have soldiered on, a number of them merging with a network of conspiracy theorists, psychic spoon-benders, UFO enthusiasts and believers in other exotic physical phenomena outside the ken of science.

Cold fusion: the culture

Cold fusion may have been written off by the scientific community at large, but it has entered cultural consciousness in interesting ways. Hollywood embraced the subject in 1997 in the action movie The Saint. Just before the female physicist and the leading man fall into bed for the happy ending, a mythical post-Yeltsin Russia is saved from demented Moscow mafia types by limitless energy generated by electrodes in a bottle. Pons and Fleischmann, though only invoked in the early scenes of the film, stand vindicated. Another film called Breaking Symmetry has just been produced by former MIT materials science professor Keith Johnson. Here, the evil hot-fusion scientists, attempting to protect their millions of tokamak research dollars, engage in various dirty tricks to squelch the discovery of real cold fusion at a fictional lab.

Cold fusion has even been turned into a game. Trevor Pinch of the Science and Technology Studies Department at Cornell University created a hypertext game in which you pretend to be an experimenter trying to replicate the Pons and Fleischmann experiment. Depending on what choices you make, you end up either with your reputation intact or a career in tatters. Cold fusion lives on in other ways too: there is a software product called Cold Fusion for hooking databases to Web sites, a rock band with that name in the US, and a sports equipment company that makes snowboards.

Cold fusion ten years on

What has become of the original protagonists? Martin Fleischmann apparently had a nasty falling out with Stanley Pons over the direction of research at IMRA and returned to Southampton in1995, where he is still working on theoretical models of cold fusion. In a recent phone interview, Fleischmann told Physics World that he just got fed up with his ideas being ignored. He is apparently still collaborating with scientists in the UK and working with Italian scientists to set up a cold-fusion programme. Looking back, he insists that he was thoroughly opposed to any public announcement of the cold-fusion results from the very beginning, but that the University of Utah insisted on a press conference.

Less is known about the activities of Stanley Pons. He has reportedly become a French citizen and now lives on a farm somewhere in the south of France. Owing to bitterness at his treatment by the press and the scientific establishment, he will not speak with anyone outside a small circle of friends and sympathetic cold-fusion researchers. But sources close to Pons say that he is attempting to re-establish himself in electrochemistry research by collaborating with scientists in France, although not in cold fusion.

There are, however, people still active in cold-fusion research. A company in Sarasota, Florida, called Clean Energy Technology (CETI) has reported a process that, they say, produces excess heat and converts radioactive isotopes into non-radioactive material, all in an electrochemical cell containing common-or-garden water. Because cold fusion is the phenomenon that dare not speak its name, CETI is careful to distance itself from the original Pons and Fleischmann work. The principals of CETI are James Patterson, a retired chemist, and his grandson James Reding, a former investment banker. In contrast to Pons and Fleischmann, who were not able to gain patents in the US, CETI has been granted a number of patents for its devices.

The CETI cell contains palladium-coated plastic beads in a glass flow chamber through which an electric current is passed. Reding says that the company has raised several million dollars to develop the device. On its Web site, CETI says that the US Department of Energy visited them and wrote an encouraging letter, but a spokesman at the DOE says that this was just a standard letter thanking CETI for their invitation to tour the company. One independent researcher who tried to reproduce the work, Barry Merriman of the University of California at San Diego, reports that no excess heat was seen in his experiment. At one time, CETI sold kits to interested researchers, but that has apparently ceased.

One of the early collaborators with CETI, George Miley, a professor of nuclear engineering at the University of Illinois, claims that he has been able to obtain results with the CETI cell in his own laboratory and, moreover, says that he has observed transmutation of elements. Using beads coated with layers of nickel and palladium, Miley says he has observed a range of elements being created electrochemically. Even so, the results have not convinced other researchers, who raise questions about contamination and misinterpretation of the data. For instance, Richard Blue, formerly of Michigan State University, believes the processes going on inside the CETI cell are purely chemical, rather than nuclear. “There are several different elements in the secondary ion mass spectrum, all with the correct natural abundance ratios, ” he says. “The source is an assorted mess of chemical contaminants deposited on the beads through long hours of electrolysis. This is not evidence for any nuclear reaction process.”

Another claim that has attracted attention comes from Les Case, a retired chemical engineer in New Hampshire. Case claims that he has constructed a closed system consisting of palladium-coated carbon pellets and deuterium gas that creates helium-4, one of the possible products of deuterium fusion, when heated. However, Case’s cells were examined at Lockheed Martin Energy Systems, in Oak Ridge, by Lynn Marshall, who says that the amount of helium he measured was the same as background levels. “There was a substantial amount of air in the sample, ” says Marshall, “so there must have been leakage at some point.” Moreover, he explained, the metal bottles that Case sent had fairly low-tech valves that could have easily passed helium either in or out.

The Case cell is now being studied by veteran cold-fusion researcher Michael McKubre at the Stanford Research Institute, using mass spectroscopy to evaluate the helium production. He says that the results are so far inconclusive, but he is planning to discuss his findings at the meeting of the American Physical Society in Atlanta this month. “I’m not going to report anything that I’m not 100% sure of, ” he says. “The field has been embarrassed by premature announcements too many times in the past.”

Overall, the experimental situation remains murky. In spite of the claims by cold-fusion proponents that “hundreds of successful experiments” have provided evidence of tabletop nuclear reactions, the results are not clear cut and are beset by complexity. Hundreds of erratic findings do not necessarily add up to solid proof.

One excuse given for the lack of clear results is low funding. Estimates of cold-fusion funding are difficult at best, but when all the salaries and lab equipment are added up, the cost may total hundreds of millions of dollars – a large number for a phenomenon supposedly achievable on a tabletop. The retort is often given that hot-fusion research has run into the billions, but no one doubts the existence of deuterium-tritium fusion in a hot plasma. No such statement is possible about cold fusion.

Proponents also bemoan lack of access to scientific journals to communicate their work, yet we now have the Internet. Could they not distribute all of the experimental results on-line for critical comment, perhaps on one of the many pre-print servers now available? Part of the problem is that, from the start, many cold-fusion researchers have wanted it both ways – scientific acceptance as well as untold riches via proprietary patent rights. Whatever the next ten years will hold for cold fusion, the field will continue to be a feast for the sociologists of science studying the many ways that research findings become reality, or not.

DESY director, Bjorn Wiik, dies

Wiik was born in Norway in 1937. He moved to Germany in 1956 and after spending several years in the United States, joined the Hamburg laboratory in 1972. At DESY he was a member of the TASSO collaboration, one of four groups studying electron-positron collisions at the PETRA collider. In 1979 the TASSO collaboration won the race to observe the first experimental evidence for the gluon, the particle responsible for the strong force. Wiik was also given special responsibility for the superconducting proton ring at HERA, the first accelerator to collide electrons (or positrons) and protons.

HERA was successfully commissioned in 1991 and Wiik became director of DESY in 1993. He maintained his interest in superconducting accelerator technology and in 1997 DESY produced a 1100-page conceptual-design report for a superconducting 500 GeV electron-positron linear collider called TESLA.

A press release from DESY said that the laboratory learnt of Wiik’s death with disbelief. “Words cannot express the shock and sadness that is felt by everyone. Our heartfelt sympathies and condolences go from each one of us to his wife and three children.”

Brian Foster, spokesman for the ZEUS collaboration at HERA, said: “Bjorn was a great scientist, a great leader and a good friend to many of us. He will be sorely missed.”

Hubble upsets star-formation theories

The stellar history of local galaxies is calculated by plotting the different size and brightness of stars in the target galaxy. However, when viewed from Earth, star systems and star clusters can sometimes appear as a single bright star.

The photographs taken with the Wide-Field Planetary Camera indicate that this mistake has happened with at least half of the stars previously identified in galaxy NGC 205. This led Cappellari and colleagues to calculate that in the last 100 million years, 1000 solar masses of gas has been turned into stars in this galaxy. They also suggest that this leads to one final puzzle – where did the gas come from? They speculate that high velocity hydrogen clouds may be orbiting NGC 205.

Laser accelerators receive a boost

Physicists hope to develop new ways of accelerating particles because of the high cost and large size of traditional accelerators. Electrons in standard accelerators gain energy by surfing large electromagnetic (EM) waves contained by powerful magnetic fields. However it may be possible to adapt the intense EM waves generated when a laser pulse interacts with a plasma to create a ‘table-top’ accelerator.

The problem to date has been how to inject the electrons into the laser-based accelerator. Moore and colleagues have shown that lasers can be used for this process as well. The terawatt laser was tightly focussed onto a small volume of krypton in a vacuum chamber. The laser pulse rips up to 18 electrons off each atom in the gas. The amount of energy absorbed by the electrons is so large that some of them are ejected at 80% of the speed of light. Surprisingly, instead of scattering in all directions, the electrons shoot off in two tightly focussed beams.

However, laser-based accelerators are extremely demanding in terms of alignment and synchronization, and engineers are unlikely to be able to take advantage of these new techniques in the short term.

Optical computing moves forward

The pairs are created by illuminating a semiconductor quantum well with a pulsed laser diode. A slight voltage difference on the semiconductor keeps the electron and the hole in separate levels inside the quantum well. When the voltage is switched off, the electron-hole pair move together under Coulomb attraction and radiatively recombine – producing a photon. So far the researchers have been able to ‘store’ a photon for 35 microseconds – five times longer than its natural lifetime and long enough for such a memory chip to work in an optical computer.

Bucky ball memories

Buckyballs, nanotubes and related structures have great potential for storage applications because their small size offers the possibility of high switching speeds and low power consumption. However, the unusual conducting properties of nanotubes have made it extremely difficult to construct devices. The Michigan-NEC team realised that inserting a positive ion into the buckyball made it easier to locate its position inside the nanocapsule. Moreover, the bucky shuttle remains fixed at one end of the nanocapsule because of weak van der Walls and covalent forces. However, a electric field is strong enough to break these bonds and push it to the other end. The whole process takes less than 10 picoseconds – which is four orders of magnitude faster than current magnetic storage devices.

ESF announce new physics programmes

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