Nanotechnology for engineering applications

If you wish to deign alienware, you would be better off asking a science fiction author to suggest an approach for science. Which is why, yesterday's science fiction is today's technology.

A number of reasons have contributed to the fact that we are now looking towards the applications of smaller and smaller equipment. Nanotechnology can be used to compliment almost any other technology as it allows for 'more' literally. In some cases, nanotechnology is needed simply because only a component that small could fit in there without much disturbance or due to physical dimensions. Nanometer scale sensors make the possibilities of even the craziest ideas look real.

The idea of nano robots is one of the factors that drives nano scientists' motivation. It might be extremely useful to create a nano robot that is equipped with a nano scale sensor to measure localized real time stresses in structures. Structural integrity of a engineering equipment, constructions and large sized installations is vital in most cases. Materials engineers usually have to perform non destructive and destructive tests time and again to make sure that the structure will hold. This results in a lot of man hours and expenses. Furthermore, it is mostly mixed qualitative and quantitative decision by the engineer about when the structure needs to be reinforced, totally replaced or retested for cracks or failures again. An engineer might be wrong (human error) and might delay the test above a duration before which the structure might fail or the engineer might wrongly predict the duration period itself. This can result in catastrophic structural failures and result in either the equipment being shut down / totally replaced or even accidents.

To avoid such errors and to further add continuous monitoring, nano sensors can be placed within the structure itself which can then monitor the structure for local stresses. The combination of local stresses at different point can then give the overall view of stresses in the structure. When nano sensors are placed within the structure itself and are able to send the data to a monitoring computer, it would be able to not only monitor the real time stresses of the structure, but it would also give statistics for how the structure is used, what tasks put the most amount of stresses (and hence fatigue) on the structure. A higher fatigue would mean a higher degradation and early failure of the structure. Such statistics from actual real time monitoring rather than by timed testing can be of more use. As compared to the timed and scheduled testing, real time monitoring will give usage data of each second, enabling the computer to plot a graph of the statistics. This data will help engineers decide how to best use their equipment so that its structure gets minimum fatigue. In short, this will result in optimization and minimum wastage.

This can be easily done by using nano sensors that detect stresses. Piezoelectric materials would be a good category to start looking for the possible implementation materials and designs as they convert compression and tension into electricity (that can be used as the signal for computer to interpret).

R&D around the world

How R&D scores up for different countries.

Smell of new electronic equipment

A question I was asked a few years ago; what is the familiar smell in all electronic stores and in new electronic equipment. I asked some electronic engineers, they didn't know anything specific and had different theories about it. Then I came across a few concepts of electronic materials which I compiled to suggest the most precise reasons possible.

Smell of new electronic equipment (almost similar or atleast recognizable) depends on these major factors:

• Capacitor compounds.
• Lead vapors in small amounts from soldered points.
• Silicone (which is used in coating silicon wafers or protecting/damping circuits) "Cures" itself by reacting with moisture in the air to for acetic acid (smells a bit pungent like car hydraulics).
• Ozone in small amounts (in case they are ON).

(In old and running equipment it might be burning dust.)

...a mixture of above smells in variable quantities attributes to the smell of new electronic equipment. Smell might vary to some extent as the quantity of each factor changes.

Different compounds used in the manufacturing contribute in both old and new equipment. Adding ozone if its on and dust in old or stored new one. It's ozone that makes the rodents afraid to dwell behind the 'ON' electronic equipment. Ozone is toxic for humans too so sleeping while there's something sparking in a circuit board is dangerous.

I think present analyzers have the capacity to check which type of vapours are present in any air sample and this could further be verified.

Why do tubelights make noise?

If you ever wondered why does your tube light or other fluorescent lights make noise (often noticeable in a quiet room and sometimes even in normal background noise in case of old lights). The reason magnetostriction. When current moves through coils or wires, magnetic field is produced with it. This magnetic field causes the material to magnetic and demagnetize (and in case of alternating current (AC) at the frequency of ~50Hz). During the process of magnetization and its reversal, the magnetic domains change their orientation and hence the material changes dimensions to some extent.

This change due to rotation of magnetic domains to align with the magnetic field causes the material to vibrate at hence causing the noise. This is generally the noise that we hear from the tube lights, but one man's limitation is another man's sensor. This effect can be used to create magnetostrictive materials that act as sensors or actuators.

Note (from Wikipedia under creative commons share alike license): Most magnetic materials are polycrystalline, composed of microscopic crystalline grains. These grains are not the same as domains. Each grain is a little crystal, with the crystal lattices of separate grains oriented in random directions. In most materials, each grain is big enough to contain several domains. Each crystal has an "easy" axis of magnetization, and is divided into domains with the axis of magnetization parallel to this axis, in alternate directions.

Why do two parts of a broken magnet repel each other?

When you break a magnet, it often seems that the polarities have flipped.

This doesn't actually happen.

No polarity reversal occurs when you think the poles have flipped

- you are dealing with a magnet that has an axial field 

(pointing out through the flat face.) When you break 
it, each half has similar field, pointing in the same direction, which 
is unstable. One piece will want to flip so that the fields line up 
anti-parallel (lower energy situation).  

Whether the broken magnet attracts or repels each other depends

on how the poles were previously present.

If the original magnet looked like
  +-----------------------------+
N |                             | S
  +-----------------------------+ 

After it's broken, it becomes
  +-----------+     +---------------+
N |           |S   N|               | S
  +-----------+     +---------------+ 

The two broken parts will attract each other.

However, if the original magnet looked like:

(poles on the flat faces of the magnet)

                N
  +--------------------------------+
  |                                |
  +--------------------------------+
                S

After it is broken, it becomes


         N                    N
  +---------------+   +-----------------+
  |               |   |                 |
  +---------------+   +-----------------+
         S                    S

Therefore the two parts will repel each other and will try to invert.

These are only two simple cases. In reality, the poles
of a magnet can be more complicated. This just illustrates how the poles
affect behavior of magnets.

Tensile testing a single molecule

Nanotechnology has enabled things like Atomic Forced Microscopy (AFM) to benefit materials scientists and engineers but there's a use of the same equipment a materials engineer would find extremely amazing and would probably not have thought of using AFM for; tensile testing a single molecule.

This can be done by combining AFM with a piezoelectric positioner. under the cantilever probe of the microscope. The molecule once attached / bound (chemically or otherwise), at one side to the probe and the other side to the positioner, can be stressed by the piezoelectric material which will change height with application of electricity and the tensile testing data will be recorded by AFM's sensors. Now how much information can be acquired by tensile testing a single molecule alone puts materials engineering to a nano scale perspective against the bulk and the macro properties which are often completely different.

Basic operation of the AFM. As the AFM cantilever probes the surface by moving its tip along its contours, or when it pulls on a protein, the movement of the cantilever is detected with a laser beam that is focused to beam to the head of the cantilever and refracts into a photodetecter. The movement, or deflection, of the cantilever deflects the laser correspondingly, and this creates an image or produces other data about the surface or the sample (which may be a molecule). In single molecule force spectroscopy, the cantilever is pressed against a layer of proteins attached to a substrate, and the tip adsorbs a single protein molecule, which is then extended. Extension of the molecule by retraction of the piezoelectric positioner results in deflection of the cantilever. [Oberhauser et al. PNAS (January 2001), Vol. 98 (2): 468-472]

 

Quantum confinement

Quantum confinement is to limit the size of the waves like you do in a guitar string by shortening the size of the string with your finger. Only in this case you are doing the same to the wave of light by limiting the wave by decreasing the size of the material to nano scale. That effect results in a change in the colour being emitted given that the colour differences are there due to the change in wavelengths. Hence you are getting a variety of different colours from the same material just like you can get a variety of tunes from the same string by shortening its length by holding it. This can have a wide range of applications (including sensors).

But why does nano gold look red when red has a longer wavelength than yellow? Shouldn't it shift to a colour with smaller wavelength due to quantum confinement? Here's a little Q/A session I had with Professor Daniel Mittleman of RICE University that clears things up a bit further with regard to gold being red in colour as nano particles and metals behaving in similar scenario:

Professor Mittleman: The reason that a chunk of gold is gold-colored has to do with the electronic level structure of the metal. In other words, it is a quantum effect, not easily explained by ordinary classical physics. 

When you make gold small, there are additional effects, completely unrelated to the electronic level structure, which dictate the color.  In other words, the reason that macroscopic gold is gold-colored has essentially nothing to do with the reason that nano-gold is red.  It is not as if this is a shift from yellow to red - instead, it is a completely different mechanism.  In the case of a metal like gold, the mechanism is the excitation of a plasmon, which is a collective oscillation of all the electrons in the nanoparticle.

The brief description of quantum confinement is applicable to semiconductors, where the number of free electrons is small (e.g., one per nanoparticle). When you have just one electron per nanoparticle, the dominant issue is the energy for that electron to be excited or de-excited - that is, the quantum confinement effect.  On the other hand, in a metal the number of electrons is large, even in a nanoparticle (e.g., one per atom), so the description is understandably quite different.  In that case, the electrons do not need to be excited out of chemical bonds in order to be free, so the energy of excitation is no longer an issue.  Instead, you have the possibility of having all the electrons oscillating together, like water sloshing back and forth in a jar.  That's a plasmon.  And that's why nano-gold is red.

Me: So does this mean that metals in general are exceptions to quantum confinement at nano scale given that metals will generally have much more than 1 free electron per nano particle or does this stand for gold only (why not other metals if in this case)? In short, the plasmon concept supersedes in case of all metals?

Secondly, does quantum confinement still have a partial effect on the net result when talking of gold? As in, a participation to a minor extent as the size of the particles still has been reduced? Or does quantum confinement has no effect at all in case of gold for the reasons you gave (having more free electrons) and the change in colour is fully credited to plasmon?

Professor Mittleman: To answer your specific questions:

1. I would not say that metals are an exception.  I would say it a slightly different way.  In semiconductors, the natural size of an electronic excitation (which is really both an electron and a hole, not just an electron) is in the range of 10 nanometers or larger, so quantum confinement is a big deal when your particle size is in that range.  In contrast, in metals, the effective size of a free electron is much smaller, so that they still behave the same even if the metal particle is only 2 nanometers across - they don't feel 'squeezed' at all by the small size of the particle, since they're smaller. Pretty much any metal will exhibit plasmon effects, similar to gold.  Gold is the one we talk about most often because it is one of the easiest nanoparticles to make.  But color changes due to plasmons can be seen in any nano-metal.
2. The change in color of metal nanoparticles is entirely due to plasmonic effects.  (Well, I guess I should say "almost entirely" just to hedge my bets, but I think it is really entirely.)  In other words, you can describe the change in color using purely classical physics, with no quantum mechanics at all (since plasmons are essentially a classical phenomenon).  Quantum confinement (in semiconductor particles) cannot be described using classical physics, so it is really a different thing entirely.

Now the question is how does quantum confinement affect the colour when the the applications of such do not actually go below the size of the atoms (which is ~ 0.1 nm) and actually don't directly squeeze the emission at atomic level? The relation is similar to a skier sking on a mountain and the height of the mountain. In this analogy, electron is the skier ofcourse. This can also be defined in semi conductors in relation to the exciton created by the absorption of light when electrons jump from their valance state to conducting state by absorbing energy. The electron leaves behind a hole and either drifts apart from it due to voltage or the hole and the electron start to orbit each other, hence creating an exciton. These excitons are much larger than a hydrogen atom and are the physical entity being directly affected by the quantum confinement in such cases as they may range from 2.3 nm (in ZnO) to 46 nm (in PbSe). Quantum confinement here directly affects their size and hence the levels at which they can exist due to the size of the material and this changes the colour the emit from red to green and to blue as the size gets smaller. This is also used to create 'quantum wells' by trapping excitons of different energy levels (say red trapped in green) in each other so that they can only travel in their plane and not in 3D. What use is a quantum well to us? They have a wide range of applications starting from DVD and CD lasers as well as the coloured (eg. red) lasers in laser pointers. Mass manufacturing the quantum well lasers are set of parallel processes which makes them inexpensive; a few rupees a piece.

Multiple uses and effects:

• Quantum confinement in 3D; quantum dots, can be used to form optical fibres with near zero energy loss (hence data loss) over long distances making a possibility for extremely reliable and high data transfer rates.
  
• Quantum confinement in 2D; quantum wires, to solve the 'wiring problem' in nanotechnology where we have the nano components but are limited to wire them using larger sized wiring, to create P-N junctions and hence transistors in a whole new paradigm or even to be used as sensors.
  
• Quantum confinement in 1D; quantum wells, can be used to create lasers and other light emitters as explained above.

Quantum confinement as a nano-physics concept can be applied to engineering applications that make life easier and technology the high end either in designing sensors or otherwise. Pakistan should soon take up its role on the high end of technology as these are concepts not far from the grasps of Pakistani engineers.