All That Matters

How do you approach the life of James Martin, a man who has given $150 million to Oxford University in what is the largest donation by a single donor for any British universities. Who has written 103 best-selling textbooks mainly in the computer sciences, who for decades has advised business and political leaders first on information technology and now on the broader challenges for humanity. The $150 million he donated to Oxford University (and $50 million more in matching funds from others) are used to support the Oxford Martin School, whose research aims to tackle these challenges of the 21st century though interdisciplinary collaboration.

In his book, ‘The Change Agent‘, Andrew Crofts, a prolific ghostwriter and author, uses two narrative streams to approach his subject from different angles. The first section of each chapter describes Crofts’ visit to Martin’s own island in the Bahamas. The second part provides biographic sketches of Martin’s life.

Chapter by chapter, both narrative streams merge into a unified description of how Martin became such a successful entrepreneur and influential thinker. We gradually understand Martin’s concerns for the challenges that await humanity, and the steps he considers necessary to the survival of our society.

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Domains in a ferroelectric material, where electric charges have a different orientation. Here, there are two separate sets of domains. The cross-hatched patterns indicate domains in the plane, the rounder shapes are domains where the polarization points out of the plane. Reprinted by permission from Macmillan Publishers Ltd. Nature Materials 7, 209-215 (2008).

Insulators might seem pretty boring materials for an electronic device such as a computer memory, because by the very nature of their definition, they don’t conduct any electrical current. But some insulators show some pretty intriguing properties. Amongst them are the so-called ferroelectrics.

Dipoles in a ferroelectric. During switching, positive and negative charges interchange.

A ferroelectric is a material where positive and negative electrical charges, are permanently separated along a common direction. These are the positive and negative ions that make up the crystal. Their order leads to an overall electrical polarization of the material. This can only happen in an insulator, because if the crystal would enable electrical charges to move around the separated plus and minus charges could be compensated easily by such movements of electrons.

In some special materials, ferroelectricity and magnetism occur simultaneously. These are known as multiferroics, and I blogged about their potential applications before. In particular, the dipoles in a ferroelectric can be switched by an electric field, which makes them attractive for electronic applications as ferroelectrics can be used to permanently store information as a new form of computer memory.

But how can the electric polarization in a ferroelectric be switched? There are two options. One mechanism is similar to what happens in a magnet. If an electric field is applied, new domains with a polarization aligned in direction of the external field form (see figure below). These domains gradually replace the old ones. This process is abrupt, because as the new domains expand, the ions in the crystal swap places in a single process.

The second possibility of switching electric polarization is a continuous mechanism. There, the positive and negative ions move slowly in opposite direction. First, the electric polarization weakens, vanishes, and then builds up again in opposite direction. This process occurs without the involvement of any domains. Of these two processes, the domain-based switching is far more favourable, which is why the switching process without domains hasn’t been observed before. Two independent papers now both claim to have seen switching without domains. […]

Stretchable electronic arrays. The LED sheets can be twisted by 720 degrees and considerably stretched. The wavy metal wires are visible in the image on the on the right. Reprinted by permission from Macmillan Publishers Ltd. Nature Materials (2010). doi:10.1038/nmat2879

Take a piece of silicon, try to bend it and it will break. Stretch a thin film of gold and it will rupture. Conventional metals and semiconductors are brittle and not elastic at all. But these are properties that you need when you want to use electronic devices in unusual places and for unusual applications. In biomedicine for example, if you want to put a diagnostic sensor on top of a muscle. In electronics, when you want to put a large-scale solar cell on the curved top surface of a car.

Sure, you can make a thin film and warp it around a cylinder, and if you do this with electronic circuits it is called flexible electronics. Organic electronics and very thin metal films on plastic can do this. But you cannot fit a two-dimensional sheet on a sphere without stretching it. For such applications you need what is called stretchable electronics, which is different to the flexible electronics that has been around for a while.

The latest milestone has been achieved by John Rogers and colleagues from the University of Illinois in Urbana-Champaign. They demonstrate (disclaimer: in my journal, Nature Materials) a fully biocompatible and implantable stretchable structure containing large arrays of light-emitting diodes and photodetectors. The sheets are stretchable and can be twisted by more than 720 degrees without damage, and can be brought into almost any desirable shape or configuration, says Rogers. “This advance suggests a technology that can complement features available with organic light emitting diodes, where peak brightness and lifetime are limited, and conventional inorganic LEDs, where relatively thick, brittle supports restrict the way that they can be integrated together and the substrates that can be used.”

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