Photon (Nano Story - 1)

'Don't tell me sky's the limit when there are footprints on the moon'

I've come across this from the TV show 'The Apprentice' on BBC.  The one who came up with this for the first time might have thought this is brilliant, but it feels like it rather tends to clarify the limit which is Neil Armstrong's footprints on the moon. For this reason, I prefer 'Sky is the limit' as sky also means Universe in a larger context.

In the last year, I've experienced multidisciplinary nature of nanotechnology in the lecture theatres and laboratories at Cambridge. Nanotechnology incorporates physics, chemistry, mechanical engineering, material science and bioscience. My background is mechanical engineering and there was another student who had the same background with me in the master's programme. She and I both had to admit that nanotechnology is way more interesting than mechanical engineering. There is nothing wrong with mechanical engineering, but simply nanotechnology was amazing and mind-blowing.

A number of scientists across the world are carrying on diverse projects associated with nanotechnology, and the outcome is normally published in journal articles. However, the public (here, I define the public as non-scientiests) cannot readily access those scientific papers, so this is where the scientific news articles come in. Yet I still occasionally find that scientific news articles often fail to deliver scientific information to the public because they are always missing the introduction part of the story. Among method is to use analogy to introduce the concept and the impact of technology, but it tends to rather exeggerate the original story. This motivates me to introduce novel technologies focusing on the fundamental nanotechnologies where the new devices and techniques are based on. Any one who happens to read my scientific blog, and find any part incorrect or controversial, please do not hesitate to make comments. Criticism is always welcome!

"Tripping the light fantastic"  (Original Article)

I am going to begin this story with throwing one of the most significant questions to physicians, 'What is light?' Light is definitely sort of a wave. But could you believe that light also consists of particles called 'photons'? Fundamentally speaking, Li-fi is based on photons. In fact, light emitting diode and laser diode also exploit manipulating photons.

As most would know, 'photo' has a meaning 'photograph' as well as 'light'. Then how about 'photon'? In quantum mechanics, all the particles are treated as waves as well as particles, and this is called 'Wave-particle duality'. To help your understanding, we better get started with 'Double-slit experiment with electron'.

Double-slit experiment (from Wikipedia)

The above figure shows the principle of double slit experiment. A plane wave of light illuminates the screen with two slits, and the waves interfere each other after passing through the slits. In terms of interference, the light can be regarded as a wave, but the illuminated light on the screen is also observed groups of particles.



Inteference pattern on the screen (from Wikipedia)

This figure illustrates that the intensity of absorbed particles on the screen increases over time. From this aspect, the light behaves as particles do. However, the figure also shows the similar pattern which is normally observed from wave interference. As I remember from the lecture 'Physics at the nanometre-scale' at Cambridge, we still get this interference pattern even if you shoot a single electron to the screen including two slits. Therefore, the fact of the matter is that, nobody knows whether electron is particle or wave. With said that, a number of physical experiments are well explained when we regard them as waves.

The wave-particle duality of electron is a good example to introduce photon since it corresponds to the particle of light wave. Thus, the light generated from LED is a series of photons. Whe it comes to the technology of those devices, the key issue is how to manipulate every single photon. To improve the efficiency of light generation, a specific semiconductor is chosen and engineered for the specific purpose. And in semiconductor industry, one of the key technologies is confining electron and hole in a extremely small area, and hence doping in nanometre scale is required. Accordingly, several fabrication techniques to deposit dopants in such small area have been developed. Equally importantly, characterization techniques also became extremely important, and hence gradually have been developed. To observe and evaluate the heterostructure in nanoscale, electron and atomic force microscopy are preferentially used in industry and research institutes. I believe there willl be more chances in the future to talk about characterization techniques and why those structures cannot be observed through optical microscope.