Introduction to ALD and MLD

ALD and MLD refer to "Atomic Layer Deposition" and "molecular layer Deposition". They are used to produce both organic and inorganic polymers. Miniaturization to the nanometer scale has been one of the most important trends in science and technology over the last several years. The chemistry to fabricate nanolayers, the engineering for nanocomposite design and the physics of nanostructure properties have created many exciting opportunities for research. These new interdisciplinary areas in nanoscience and nanotechnology supersede the more traditional disciplines and demand new paradigms for collaboration.





Many of our surface chemistry and thin film growth investigations utilize atomic layer deposition (ALD) techniques. ALD is based on sequential, self-limiting surface reactions as illustrated in the accompanying figure. This unique growth technique can provide atomic layer control and allow conformal films to be deposited on very high aspect ratio structures. ALD methods and applications have developed rapidly over the last few years. In particular, ALD is on the semiconductor road map for high-k gate oxides and diffusion barriers for backend interconnects.


ALD is based on sequential, self-limiting surface chemical reactions. For example, for Al2O3 deposition, the binary reaction: 2Al(CH3)3 + 3H2O -> Al2O3 + 6CH4 can be split into the following two surface half-reactions


A) AlOH* + Al(CH3)3 -> AlOAl(CH3)2* + CH4
B) AlCH3* + H2O -> AlOH* + CH4


where the asterisks denote the surface species. In the (A) reaction, Al(CH3)3 reacts with the hydroxyl (OH*) species and deposits aluminum and methylates the surface. The (A) reactions stops after all the hydroxyl species have reacted with Al(CH3)3. In the (B) reaction, H2O reacts with the AlCH3* species and deposits oxygen and rehydroxlates the surface. The (B) reactions stops after all the methyl species have reacted with H2O. Because each reaction is self-limiting, the Al2O3 deposition occurs with atomic layer control. By applying these surface reactions repetitively in an ABAB... sequence, Al2O3 ALD is achieved with a growth rate of 1.1 Å per AB cycle. We have also extended the ALD method to deposit single-element metal films.





Similar self-limiting surface reactions can be employed for the growth of organic polymer films. This film growth is described as molecular layer deposition (MLD) because a molecular fragment is deposited during each reaction cycle.The precursors for MLD have typically been homobifunctional reactants. A cartoon illustrating the MLD process is shown in the nearby figure. MLD methods have been developed for the growth of organic polymers such as polyamides.The polyamides have been deposited using dicarboxylic acid and diamines as the reactants. New approaches to MLD involve heterobifunctional and ringopening precursors. In addition to organic polymers, the precursors for ALD and MLD can be combined to grow hybrid organic-inorganic polymers.


Source:
One of the research groups that pioneers in this study can be visited from here.

Fluidics

Fluidics (also known as Fluidic logic) is the use of a fluid or compressible medium to perform analog or digital operations similar to those performed with electronics. 

The physical basis of fluidics is pneumatics and hydraulics, based on the theoretical foundation of fluid dynamics. The term Fluidics is normally used when the devices have no moving parts, so ordinary hydraulic components such as hydraulic cylinders and spool valves are not referred to as fluidic devices. The 1960s saw the application of fluidics to sophisticated control systems, with the introduction of the fluidic amplifier. 

A jet of fluid can be deflected by a weaker jet striking it at the side. This provides non-linear amplification, similar to the transistor used in electronic digital logic. It is used mostly in environments where electronic digital logic would be unreliable (e.g., systems exposed to high levels of electromagnetic interference or ionizing radiation).

Nanotechnology considers fluidics as one of its instruments. In this domain, effects such as fluid-solid and fluid-fluid interface forces are often highly significant. Fluidics have also been used for military applications.

Amplifiers :

The basic concept of the fluidic amplifier is shown here. A fluid supply, which may be air, water, or hydraulic fluid, enters at the bottom. Pressure applied to the control ports C₁ or C₂ deflects the stream, so that it exits via either port O₁ or O₂. The stream entering the control ports may be much weaker than the stream being deflected, so the device has gain.

Given this basic device, flip flops and other fluidic logic elements can be constructed. Simple systems of digital logic can thus be built.

Fluidic amplifiers typically have bandwidths in the low kilohertz range, so systems built from them are quite slow compared to electronic devices.

Systems :

Fluidic components appear in some hydraulic and pneumatic systems, including some automotive automatic transmissions. As digital logic has become more accepted in industrial control, the role of fluidics in industrial control has declined.Fluidic injection is being researched for thrust vectoring in aircraft jet engine nozzles, and for ships. Such systems divert thrust via fluid effects . Tests show that air forced into a jet engine exhaust stream can deflect thrust up to 15 degrees. Such nozzles are desirable for their lower: mass, cost (up to 50% less), inertia (for faster, stronger control response), complexity (mechanically simpler, no moving parts or surfaces), and radar cross section for Stealth. This will likely be used in many unmanned aircraft and 6th generation fighter aircraft.

Professor Nikolai Priezjev of the Department of Mechanical Engineering writes about fluidics and micro - fluidics  here .The transport and manipulation of small amounts of fluids are crucial for emerging technologies. A brisk demand for micro-devices, which are  used for the transportation of nanovolume  liquid samples, gave rise to a new exciting field called microfluidics. This field combines various  disciplines including engineering, chemistry, physics, and biology. The long range goal in modern technology is a reduction in size and the further development of microfluidic devices, which could be used for diagnoses of diseases, for the autonomous or remote detecting of biological and chemical  agents, and for gene and drug delivery.  

A very good introduction to microfluidics can be found at the wiki page. Microfluidics news is another kind of a aggregator for papers published on this subject . 

Food for thought :

  Is it possible to use constructal theory as a basis to design applications using microfluidics  ?? What would be the implications of doing so ?

Sources of information :

Wikipedia and Google .

A not-so-ordinary insight into everything around us ... Constructal theory .

This is one of the most fascinating theories developed in recent times which actually gives a very different insight into nature and its structure . For example in the field in thermodynamics it replaces the black boxes , we as mechanical engineers assume while designing any system by actually delving into the flow configuration.

The core of the theory is the constructal law :

“For a finite-size flow system to persist in time (to survive) its configuration must evolve in such a way that it provides an easier access to the currents that flow through it”

This principle predicts natural configuration across the board: river basins, turbulence, animal design (allometry, vascularization, locomotion), cracks in solids, dendritic solidification, Earth climate, droplet impact configuration, etc. The same principle yields new designs for electronics, fuel cells, and tree networks for transport of people, goods, and information.

An amazing way to describe phenomena around us . To what extent is it adopted by the industry is something we have to wait n watch ....

Cya ... Have a gr8 day ahead ....

Sources :

Constructal theory of generation of configuration in nature and engineering - Adrian Bejan¹ and Sylvie Lorente²

Constructal.org - A site dedicated to it .

The Art of Approximation in Engineering and Science

Approximation. Aren't we supposed to be exact ? This counter intuitive statement raises a lot of doubts and questions . Like , how can approximate models be at all useful? or what makes some models more useful than others?
For the first one , an approximate model is only something our systems , intellect can decipher . So when we represent or model any process in the world , we need to throw away things that dont matter . Say for example , if you want to analyse the trajectory of a piece of stone thrown at an angle of 45 degrees , including air viscosity , wind speed , coriolis force , etc. all are fine but simply way to difficult to comprehend and also a waste of time distracting the observer from the main problem .
In this post lets explore this art and apply it to a certain physical phenomenon .
One of my favourites : Drag.
a sphere of radius $R$ falling through a fluid of viscosity $\nu$ .
Lets start out by describing the physics exactly. The terminal velocity of the sphere can be calculated by solving the partial differential equations for fluid flow - namely the navier stokes equations . For incompressible flow ,
\[ \frac{\partial v}{\partial t} + (\nabla . v) = - \frac{1}{\rho} \nabla p + \nu \nabla^{2} v\]
\[\nabla . v = 0\]
Here $v$ is the fluid velocity , $p$ is the pressure , $\rho$ is the density and $\nu$ is the kinematic viscosity . All the equations are coupled partial differential equations and three of them are non - linear . Closure to these equations can be described if the boundary conditions are accurately known , which can also be written in terms of primitive variables . Further more someone did require a decent program to discretize the equations and solve it , here in this case the famous SIMPLE(Semi-Implicit Method for Pressure Linked Equations) algorithm .All this for a simple analysis of a sphere through a fluid !!!!!!
Relax there is a naive but practical way out .

Dimensional Analysis : To use dimensional analysis follow the usual steps of the buckingham-pi theorem which can be found in any standard fluid dynamics textbook . Make the appropriate groups and finally you will get a dimensionally balanced equation of the form :
speed = some function of groups formed during the Buckingham - Pi analysis . Performing a couple of experiments one can determine the conversion factors at a reasonably accurate value .

A Simpler Approach : (Dont confuse this with the previous SIMPLE algo ..)
We have to calculate the terminal velocity or speed . The 'terminal' word suggest at a final instant i.e. after long long time . It indicates that the speed has become constant , i.e. no net force acts on it . That is weight balances the drag and buoyancy forces at this time . So ,
\[ F_{gr} = \frac{4\pi}{3}r^{3}g \rho_{sphere} \]
In accordance with Archimedes principle ,the buoyant force is ,
\[ F_{bu} = \frac{4\pi}{3}r^{3}g \rho_{fluid} \]
The drag calculation can be easily done with another dimensional analysis with the Buckingham - Pi theorem the force can be estimated to be a function of viscosity , speed , density of fluid and radius of sphere . Fortunately , the British Mathematician Stokes , the first to derive its value , found that ,
\[ F_{dr}=6\pi\eta r v\]

Now lets do the approximation part .. ;) .
To balance out the forces its clear that ,
\[ F_{gr}=F_{dr}+F_{bu}\]
Lets ignore their constant terms , namely $6 \pi$ etc. To specify how accurate we are , we can assume to be first order accurate .
Hence ,
\[ F_{gr} \approx F_{dr}+F_{bu} \]
Rearranging the terminal speed is then ,
\[ v \approx \frac{gr^{2}}{\nu} ( \frac{\rho_{sp}}{\rho_{fl}} - 1 )\]

This is a very decent approximation to our system . A factor of 2/9 is achieved if the constants from Stokes equation , etc. are not neglected . However this gives a fairly reasonable value to the terminal speed .

The above is just an example of how approximation , dimensional analysis can solve certain problems in engineering and science . However this method is used just for a preliminary design of a system to get a feel of the behaviour of the system . Empirical data and equations should not be neglected at any cost .

Source of Information : MIT OCW .
Image Sources : Here , here and here .

Wireless and Beyond

My first post is about something very simple, in the news today, and extremely compelling. Wireless Electricity. It had a typical story-book conception, an MIT professor who was irritated by his wife's cellphone beeping on low battery, and a group of brilliant MIT students helping him realize his dream. Although the MIT experimental prototype was relatively bulky, its tremendous potential was immediately realized and, in the great American fashion, a big company called WiTricity Corp. was set up.


The concept is pretty simple- Resonant Energy Transfer. The key was the working of a transformer, in which energy is transferred from the primary coil to the secondary coil without actual contact, ie. magnetic coupling. But the primary and secondary coils are wound extremely close to each other, their insulation touching, so as to avoid losses. In resonant energy transfer, the primary coil, which we will call the transmitter, and the secondary coil, the receiver, are tuned to a mutual resonant frequency. Thus when the transmitter transmits magnetic waves at this frequency, the receiver picks it up. But even the resonance effect cannot help transfer energy over larger distances, so you'd be mistaken if you're imagining charging your cellphone with the transmitter in the next room, or across the same room. It can transmit energy to a distance a few times the size of the transmitter. So all it does, basically, is eliminate the need for cables. They also talk about the environment, and how the need for batteries is eliminated.


What we have in the end, is an extremely commercial product that will, probably, hit households at large within the next couple of decades. The following video shows a demonstration:





But what really caught my eye when I was reading about wireless electricity was, initially, the work of Nikola Tesla and later on, in fact currently, the work of Prof. Konstantin Meyl. Tesla had the vision of a global power grid based on the facts that:
1. The Earth is a conductor.
2. Higher atmosphere is a conductor.
Hence, there is a small insulating patch of atmosphere between the earth and the conducting atmosphere. Tesla proposed long distance transmission of Electricity through a spherical transmitter that transmitted Electric potential waves from transmitter to receiver, which are longitudinal, or scalar, as opposed to conventional electromagnetic waves, which are transverse. Thus, in Tesla's vision, energy was transferred from transmitter to receiver much like the vibration of a guitar string. The following figure shows Tesla's transmitter.
The existence of such transverse electromagnetic waves, or more popularly known as scalar waves, was disputed by classical physicists as not adherent to Maxwell's equations. But Prof. Meyl successfully constructed a working prototype of a scalar wave transmitter and receiver, and showed that electricity can, thus, be transmitted over longer distances, irrespective of the size of the transmitter. Meyl also propounded a theory based on Faraday's laws, as opposed to Maxwell's equations, to prove the existence of a potential vortex, which is a longitudinal potential wave, while still adhering to the laws of classical physics (for info about Prof. Meyl's work, click here). He demostrates his prototype in the following video:



(for more videos, click here.)


The idea of a worldwide wireless power grid is breathtaking, to say the least. Thinking this, I continued reading about scalar waves, and I chanced upon a most curious page about Keylontic Science, which was defined as "the Point of Union between Scientific and Spiritual perspective, through which we can begin to understand the reality of our connection to the Divine and to comprehend the purposes for and the processes of our Personal Evolution." Scalar waves are, apparently, very important in Keylontic Science, as they are essentially standing energy waves, ie. each point in a scalar wave only stands and oscillates. Keylontic science calls these points 'static points of light', and hence 'flashing points of consciousness'. It was a fascinating read, although thankfully, I'm cynical enough to dismiss it as merely interesting and hence did not go through a spiritual-scientific awakening. If you want in on the mysteries of the universe, click here.


May the force be with you.