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Posts Tagged Radio NZ

The southern lights Shaun Hendy Aug 26

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Tonight I will be talking about the aurora on Bryan Crump’s radio show (Nights, Radio New Zealand National, 8.42pm, Thursday August 26th).  I won’t spend much time here explaining the underlying physics of the effect, but take a look at the beautiful infographic posted by Peter Griffin.

Now although I didn’t see any sign of the predicted aurora a few weeks ago (did anyone with clear skies that night see anything?), I did regularly encounter aurora during the early years of my PhD studies at the University of Alberta in Edmonton, Canada. In fact, I managed to take a girl out to see an absolutely spectacular display on our first date.

“Ah, physics …” I said, as we stared up at the blue, red and green streaks shimmering in the sky. Not the greatest line ever used but good enough that the girl in question married me a few years later.

Now  you might guess that my apparent good planning was down to some quick back of the envelope calculation. Not so – although theoretical physicists have many powers (and lets face it, they have special need of them when romance is called for), predicting the time and place for watching aurora is not yet one of them.    

When to see an aurora

Both the northern and the southern aurora are caused by electrons and protons (known as a plasma) from the sun colliding with nitrogen and oxygen in the Earth’s upper atmosphere.  This flow of plasma from the sun, known as “space weather”, is concentrated by the Earth’s magnetic field at the poles so that you are more likely to see an aurora in Edmonton or Dunedin than Wellington.

Like terrestrial weather, space weather can be quite irregular, which is why aurora can be relatively special events.  As the plasma coming from the sun consists of charged protons and electrons, its flow from is strongly affected by the magnetic activity of the sun.  At periods of high solar magnetic activity, it turns out that the sun is more likely to be eject plasma. 

Solar magnetic activity cycles over a period of just under 11 years for reasons that are not yet well understood.  We are entering a period of maximum solar activity now, so the flow of plasma from the sun should be relatively strong.  Yet if I look at when I took my date out to see the aurora (May 1994), the sun was actually in a period of minimum activity.  And since 2009, the sun has been in an active period, yet we are only just starting to see aurora at our latitudes now. 

Picking a good night for an aurora is obviously not so straightforward. 

The trouble with space weather

So what’s the problem? Well, the flow of a plasma is a complicated thing:  a flowing plasma generates a magnetic field, but the flow itself depends on the magnetic field.  So to understand a plasma you need to work out both the magnetic field and the flow at the same time: it’s the physicists’ version of the chicken and the egg problem.      

In fact, doing this is so difficult that it gets its own sub-field of physics known as magnetohydrodynamics, or MHD for short.  The equations that are used to model MHD are nonlinear and difficult to solve, requiring large supercomputers for even simple flows.  In the case of the aurora, part of the difficulty seems to lie in the way in which the magnetic field of the sun, the Earth and the plasma itself interact to direct the plasma towards the atmosphere. 

Now knowing when plasma from the solar wind is going to hit the atmosphere is not just important for the love lives of physicists.  Intense flows of plasma can cause geomagnetic storms, which can knock out power grids and satellites. 

For this reason NASA launched the THEMIS space mission a few years ago to put in place a collection of satellites that can monitor the space weather.  Data from this mission will be used to help improve the models we use for the flow of plasma from the sun and may even allow scientists to forecast the solar weather in the way terrestrial weather is forecast today. 

And if the space and terrestrial weather were to cooperate to put on a show in Wellington then I will get a chance to come up with a better line than the one I used in 1994. Suggestions in the comments section please …

How the transistor took over our lives Shaun Hendy Jul 12

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On Thursday, I will be back on Bryan Crump’s radio show (Nights, Radio New Zealand National, 8.42pm, Thursday July 15th).  This week, we will continue our discussion of transistors, several billion of which are currently helping you read this article.  Last time, we talked about how quantum mechanics allows transistors to work as electronic switches.  This week, Bryan wants to discuss how transistors became so embedded in so many of the technologies we rely on in the modern world, and what exactly they are doing there!

A valley of silicon?

Although the idea had been around since the 1920s, the first transistor was made by John Bardeen and Walter Brattain at Bell Labs in New Jersey in 1947.  It was made out of germanium, a semiconducting material similar to silicon, and was about the size of something you might put on your mantelpiece.

However, it was their boss, William Shockley, who tried to commercialise the transistor.

Bell Labs has been credited with pretty much inventing the modern world (just take a look at this list of its inventions).  It has been criticised, however, for stifling the commercialisation of its inventions.  Indeed, Shockley didn’t get an opportunity to try to turn a buck from the transistor at Bell Labs.  Rather, he founded Shockley Semiconductor Laboratory on the opposite coast of the US:  in Mountain View, California.

Why there?  Well, the San Francisco Bay area already had a healthy electronics industry, which supplied components to the US military.  This meant that there was a supply of skilled electronics workers.  Nearby Palo Alto was home to Stanford University, which had set up the Stanford Industrial Park to encourage the development of high-tech industries such as Hewlett-Packard in the region.  And importantly, Palo Alto was also home to William Shockley’s aging mother.

Silicon Valley was born.

Creative destruction

Putting together a team of talented physicists and engineers, Shockley immediately set to work on developing silicon transistors.  But Shockley was a terrible manager.  Within a few years, Shockley Semiconductor was haemorrhaging its best young staff, including Gordon Moore (of ‘Moore’s Law’), who would later go on to co-found Intel.  The firm was not well placed to react to the invention of the integrated circuit by Texas Instruments in Dallas in 1958.

The integrated circuit revolutionised the manufacture of electronics.  Instead of making individual components, like transistors, separately, and then assembling them one by one on a circuit board, Jack Kilby developed a multi-step technique to fabricate the components and the circuit on a sheet of germanium all in one go.  This tremendously sped up mass production, and led to cheap, light-weight electronic devices.

However, a Bay Area company that had been founded by disgruntled Shockley employees was not far behind Texas Instruments in making integrated circuits.  In fact, Robert Noyce at Fairchild Semiconductor produced the first silicon integrated circuit six months after Kilby.  And in the end, it was Noyce’s design that prevailed.

The military-industrial complex

From its invention until the mid-1960s, the Apollo program and the US military bought almost every integrated circuit built. Costs fell dramatically as production volumes increased and companies like Fairchild began to outsource to Asia.

By the end of the decade, however, pressures on the US military budget meant that the gravy train began to dry up, and the semiconductor industry had to develop new consumer markets.  Today, you’ll find integrated circuits in cell phones, computers, and many other digital appliances.

Fabrication

So how are integrated circuits made?  The process, known as photolithography, is actually a bit like taking a photograph using film.

The layout of the circuit is defined by a light shining it through a cut-out template, known as a mask, onto a wafer of silicon.  The wafer will be covered in film of light sensitive chemicals called photo resist, which ‘cure’ when exposed to light.  Regions that are shaded by the template don’t undergo this curing process, and chemical treatments can then be used to etch these regions away, engraving a pattern defined by the template into the silicon wafer underneath the resist.

I like traffic lights

So what can be done with a circuit full of transistors?

In my previous article on transistors, I explained that a transistor is an electronic switch:  the current that flows through a transistor is turned on and off by applying a voltage at what is called its ‘gate’.

Transistors can be assembled into logic devices.  A traffic light is a type of logic device, for instance:  if the light is green light is on, the red light should be off.  We could ensure this always happened using just a single transistor.

Imagine we set up the circuit that supplies electricity to the red light so that it can be short-circuited by a transistor. The transistor will now act as an inverter: the red light will switch on when the transistor is off but will switch off when the transistor is on.

Now by allowing the transistor to be switched on and off by the circuit that supplies current to the green light, then we ensure the red light will never be on when the green light is on.

More complicated logic operations can be performed if we assemble more transistors.  If we have traffic lights running north-south and east-west, we could use the transistor that shorts the north-south red light to switch a transistor that short-circuits the green east-west light.  Thus, when the north-south green light is on, it switches off the east-west green light and so on …

Unless your cell phone is modelled on something out of the original Star Trek, it probably doesn’t work by switching red and green lights off and on.  Rather, it is adding and multiplying many, many ones and zeroes (“ons” and “offs”) using arrays of transistors assembled for the purpose.

Silicon Valley

Today, of course, Silicon Valley is a hub not only for electronics, but also for software and biotechnology.  This is partly due to the fact that those early semiconductor companies not only invented the integrated circuit, but being far from the traditional sources of finance on the east coast, also had to pioneer the modern venture capital industry.  William Shockley’s decision to set up in Mountain View and his subsequent mismanagement had far reaching implications indeed.

The quantum mechanics of gadgets Shaun Hendy May 31

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I will be on Bryan Crump’s show again this week (Radio New Zealand Nights, 8.42pm Thursday June 3rd).  Bryan wants to talk about how quantum mechanics underpins modern technology.

If quantum mechanics exists in the public consciousness at all, it is through some of its spookier concepts like Schrödinger’s cat, wave-particle duality or Heisenberg’s uncertainty principle.  While these ideas are important in quantum mechanics, at least in the present day, few technologies directly exploit these more exotic phenomena. Today, rather, it is the “quantum” that we make most use of in modern electronics through a device called a transistor.

File:P45N02LD.jpgYou probably own billions of transistors … but do you know what they do or how they do it?  Transistors are basically an electrically operated switch that can be used either to perform logical operations or to amplify signals.  Logic is very important for any sort of computing, whereas amplification is a vital part of any communications technology.

Who put the quantum in quantum mechanics?

In fact, it was German physicist Max Planck’s suggestion that light came in discrete chunks, known as quanta, that set physicists on the path to quantum mechanics and transistors.  Planck himself was deeply sceptical about his idea (scientists are a cautious bunch), and at least initially, seems to have regarded it as a mathematical “trick” to model the data on the frequencies of light produced by electric light bulbs.

A few years later however, Albert Einstein used Planck’s idea to explain something called the photoelectric effect.  This effect occurs when light of high enough frequency (i.e. blue rather than red) is shone on a metal, causing electrons to be spat out.  What is puzzling is why it is the frequency of light that controls this process, rather than its intensity:  a dim blue light will do it, but not a bright red light.

Einstein was able to neatly explain this, using Planck’s “trick” of modelling light as quanta that have energies that are multiples of its frequency.  Blue light has a higher frequency than red light, so according to Planck, blue light should consist of quanta with higher energy than the quanta in red light.

Einstein realised that if a minimum amount of energy is needed to knock an electron out of a metal, then a red light, which consists of light quanta each having an energy that is too low to eject an electron, will have no effect.  Increasing the intensity of the red light, which just means increasing the number of quanta, will still have no effect, even though there is apparently more energy being shone on the metal.  In contrast, a dim blue light will trigger the effect, because although there are fewer quanta, each individual blue light quanta still has the energy to eject an electron.

Electrons get together to form bands

Now that Planck’s idea of quanta had been shown to explain two independent phenomena, it had to be more than just a mathematical “trick”.  Quantum mechanics was born.

In quantum mechanics, all things come in quanta, e.g. photons.  This applies to particles as well as light.  Atoms consist of a positively charged nucleus and negatively charged electrons.  The reason that electrons orbit the nucleus is that the laws of quantum mechanics allow them only to have certain energies, i.e.  electrons can only occupy certain discrete energy levels in atoms.

However, one of the things that makes electrons different to photons is that an electron “fills up” its energy level:  once an electron occupies an energy level, no other electron can join it (there is a subtlety here that I won’t go into, as electrons also have a property called “spin”, and electrons of different spins can occupy the same energy level).  As electrons are added to an atom, they sit in higher and higher energy levels as they pile up on top of one another.

This is the picture in single atoms, but in solid materials, which consist of atoms that are bound together by chemical bonds, things are more complicated.  In compounds, electrons are allowed to occupy distinct ranges of energy, i.e. there are ranges of energies that electrons can have (called energy bands), and ranges of energies electrons can’t have (called energy gaps).  These energy bands will still fill up, and once full, additional electrons have to move to a higher band.

Vegetable, mineral, metal, insulator

Now we are in a position to understand the difference between a metal and an insulator.  In a material, the highest energy band that contains electrons is called the valence band.  Whether the valence band is full or not determines whether a material is a metal or an insulator.  In a metal, the valence band is only partially full – when you apply a voltage across a metal, electrons can flow in the direction of the voltage because they have space in their valence band.  Hence metals are said to conduct electricity.

In an insulator, however, the valence band is full.  For an insulator to conduct electricity, you need to apply a voltage of sufficient strength to lift an electron up out of its valence band, across the energy gap, and into the next available energy band.  If the energy gap is large, you will need a very large voltage to do this.  Because such materials do not conduct electricity unless very large voltages are applied, they are called insulators.

Almost there:  semiconductors

Materials that have full valence bands, but which have relatively small energy gaps, are called semiconductors.  Silicon is a semiconductor, for instance.

Semiconductors can be turned into conductors by a process called doping.  Doping a semiconductor is like adding a car pooling lane to an otherwise gridlocked motorway.  Electrons from dopant atoms can move freely up and down the almost empty extra lane while the other electrons sit glumly in the traffic jam.

Silicon has four electrons per atom in its valence band, but if you add a small amount of an impurity atom that contributes only three electrons to the valence band (e.g. boron), then you create “holes” in the valence band that allow silicon to conduct.  Silicon that has been doped so that it has holes in its valence band is called a p-type semiconductor (it is called p-type because, with a bit of mental gymnastics, you can think of these “holes” in the valence band as positive charges that carry electricity).

On the other hand, n-type semiconductors (n for negative) have been doped with atoms that have extra electrons (e.g. phosphorus will contribute 5 valence electrons to silicon).  These extra electrons can’t sit in the full valence band, so they sit in the next highest energy band.  As this new band is only partially occupied, the electrons that sit in it can conduct.

And finally:  the transistor

npnForty years after Planck introduced his idea of quanta, three researchers at Bell Labs in the USA built the first transistor.  The first step in making a transistor is to construct what’s called an n-p-n junction.  That is, take a wire of n-type semiconductor, chop out a piece and replace it with a chunk of p-type semiconductor.

Can this new wire conduct?  No, not very well.  If a voltage is applied, the electrons in the n-type part of the wire will drop into the holes in the p-type part of the wire, filling the valence band once more.  Then, if they can make it once more to the n-type part of the wire, they have to have enough energy to jump back up over the energy gap.   transistor-on

Once you have a n-p-n junction, you need to add what is called a gate.  The gate is the “switch” which sits over the p-type part of the junction.  However, it is insulated from the  junction so that current can’t flow from the gate into the wire.  Nonetheless, if you apply a voltage to the gate, electrons in the p-type part of the junction become polarised and build up near the gate.  This fills the valence band with electrons near the gate, and suddenly current can flow through the energy band above the valence band.

When the gate is off, the junction reverts to its original state and current is not able to flow. transistor-off

Thus the transistor acts as an electrically activated switch.  When a gate voltage is applied, current can flow; when no gate voltage is applied, current can’t flow.  The transistor can be used to amplify signals:  a weak signal, if applied to the gate, can modulate a stronger current passing through the transistor by switching it on and off .

Logic operations can also be performed:  if you allow transistor A to provide the gate signal for transistor B, then you can make a circuit that allows a current to flow if transistor A or transistor B is on, for instance.

Today, while it is impossible to imagine a modern world without transistors, it’s worth remembering that Planck just set out to build a better light bulb!

A few noteworthy happenings Shaun Hendy Mar 04

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The Crown Research Institute (CRI) Taskforce report was released this morning – it is available here.  Reading the recommendations, I think that the Taskforce has nailed it.  If its recommendations are implemented, I think CRIs will finally gain the ability to work strategically for the interests of New Zealand.  Not everyone will be pleased; I have no doubt that fully contestable funding has been good for the universities, but I would argue that it has forced the CRIs to become more like universities, while neglecting their role as agents of technology transfer.

Tonight I am back on Bryan Crump’s show (‘Nights’) on Radio New Zealand at 8.40pm.  I am planning that this will be the first in a series of chats about nanotechnology.

And get in quick to get your tickets to see talks by Martin Lord Rees this month.  Tickets are free (but disappearing fast) from the Royal Society’s website.  He is giving a talk in Wellington and a talk in Christchurch:

Martin Lord Rees is a successor of Sir Isaac Newton and Ernest Lord Rutherford as President of the Royal Society of London, the world’s oldest and most prestigious scientific institution.  He is also UK’s Astronomer Royal and Master of Trinity College, Cambridge.  He comes to New Zealand as the Rutherford Memorial Lecturer in the 350th year since the founding the Royal Society of London.

The World in 2050

7.00pm, Tuesday, 23 March 2010
Wellington Town Hall, Wakefield Street, Wellington

As a cosmologist, Lord Rees studies the universe and tries to understand its evolution on grand timescales of billions of years.  But he is also concerned with the much smaller time scale of a human life.  In his book Our Final Century, he gave our civilization a 50/50 chance of surviving the 21st century.  He is not a prophet or a doomsayer, but a scientist and ‘a worried member of the human race’.  What does he think now, five years on from the publishing of his book and what is his view of how things will stand in 2050?

The next 20 years in astronomy:  Probing the Big Bang, Galaxies and Planets

7.30pm, Monday, 22 March
Limes Room, Christchurch Town Hall, Christchurch

We can trace cosmic history from the mysterious ‘beginning’  of the universe nearly 14 billion years ago to our current home and the complex biosphere of which we are part.  But with advancing technology  in the coming decades, we can expect further breakthroughs in our knowledge of the spread of life in our cosmos.  Is physical reality even more extensive than the domain that our telescopes can probe?  What can we expect in the next 20 years in astronomy?

I will certainly be going to his Wellington talk.

Finally, congratulations to one of my PhD students, Dmitri Schebarchov, who submitted his thesis today.  He has done some fantastic work on the growth of carbon nanotubes, something that is still poorly understood, despite almost two decades of intense research.

Who hid the Higgs? Shaun Hendy Jan 29

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I had a lot of fun being interviewed by Bryan Crump on Radio NZ on Monday evening about why particle physicists have had such trouble finding the Higgs boson.  If you missed it and are interested, you can listen to the audio here.

It was a good opportunity to highlight some of the wonderful stuff going on at CERN, even if the catalyst for the interview verged on the frivolous.  As you’ll hear if you listen to the interview, Holger Nielsen and Masao Ninomiya proposed in a recent paper that production of the Higgs might be suppressed by some exotic non-local physics.  This was colourfully described in the New York Times as sabotage from the future. 

In the interview, I characterised their speculations as mathematical philosophy, although perhaps it is a bit more subtle than that:  their prediction that production of the Higgs specifically might be suppressed is actually falsifiable.  We’ve built the Large Hadron Collider (LHC), and in three to four years, most particle physicists believe that we’ll either have found it, or else have sufficient data to conclude that it doesn’t exist.  Either outcome will falsify their prediction.

As pointed out by Sean Carroll though, there doesn’t seem to be any reason why it should be the Higgs in particular that is suppressed in this way, even if it is a mathematical possibility.  If we find the Higgs, then perhaps it’s the neutralino (the hypothetical supersymmetric partner of the neutrino) that’s being suppressed, and so on.  In this way, the theory underlying Nielsen and Ninomiya’s prediction is not itself falsifiable. 

If physics had a propensity for this type of non-locality though, I think we’d have a lot more missing pieces in our description of the Universe.  I’m also not impressed by the card game suggested to test this (pick a card from a million card deck, where just one says “Don’t build the LHC”).  There are plenty of ways to not find the Higgs other than falling victim to a spot of bad luck in a card game.  Perhaps the Universe should have avoided evolving physicists in the first place? 

Anyway, I’ve been invited to appear every 5-6 weeks on Nights on Radio NZ in the Thursday science slot at 8.45pm.  I will be trying my best to mix fun and fact, and I am happy to consider any suggestions readers might have for topics to discuss with Bryan. 

I will leave the last word to a Radio NZ listener who sent in a text during the interview: “If the Swiss can build a 27km long tunnel for $8bn, how come we can’t build a tunnel under the harbour for $3bn?”.