Project Updates / Status

I had not gave an update about the project for some time, because of lots of HRM meetings and presentations.

Finally, I met advisor on Monday and he went through some of the portions that were wrong and the areas that needed revisions. Some of the portions were not clear and needed to change.

Made the required revisions quickly and later part of the week focused on simulations results and discussions. This is a big chapter that had the most changes to do. According to adviser, part of the algorithm to compute the required values in the model were wrong and therefore unable to obtain the required simulation results.

Quickly schedule a time to meet him again to clear my remaining doubts. He took time to explain. The later part of the week spent most of the time thinking it through and checking and modifying the code and verifying the results.

Hope the computed results are correct!

Some information about Field Emission

I was searching through the net for some information and I came across this article.

Field Enhanced Emission

The current density in Thermionic-Schottky emission is weakly dependent on the magnitude of the applied electric field. Experimentally it is known that if the field is increased then a point is reached when the emission current starts to exceed the predictions of this theory. There are two models which may be used to explain this behaviour. First though we should discuss the Enhanced Electron Emission concept. If the field is increased above some finite level, then the width of the surface potential barrier becomes small enough that a considerable fraction of the electrons in the bulk material can 'quantum tunnel' through it. The number of electrons at or close to the Fermi energy (for cool metals (T less than T(Fermi)) in particular the bulk of the electrons exist just below the Fermi energy) is very much larger than at the high energies corresponding to the height of the surface potential. Therefore when the width of the barrier becomes such that these electrons can tunnel out, the emission current becomes very sensitive to the electric field. This field emission current quickly becomes much larger than the thermionic current. However the experiments indicate that this happens when the electric field strength is a few orders of magnitude less than theoretical considerations would indicate.

At this point we meet the two competing models: both are based on the concept of surface discontinuities

i) The difference between experiment and theory can be explained if one assumes that on the surface of a cathode, micron sized discontinuities having the form of an outward spike exist. If the length of the spike is>10 times its base dimension then it is relatively easy to expect the local electric field to be enhanced by a considerable amount (> x1000). Then the theoretical model discussed above applies to the surface of the discontinuity. It is interesting that the enhanced emission current from a handful of such micron sized sites can exceed (by many orders of magnitude) the total thermionic current from the bulk cathode at sufficiently high electric fields. Such discontinuities have been observed on real cathode surfaces, and in some experiments at the University of Strathclyde specially manufactured Field Emission Arrays consisting of millions of such individual tips machined in a semiconductor surface have been used as a source of a high quality, highly controllable, electron beam.

ii) The other model is based on the assumption that the onset of Field Enhanced Emission at such a low electric field can be attributed to insulating inclusions (micron sized) in the cathode surface. Electrons emitted from the bulk cathode into the conduction band of the insulator are accelerated towards the vacuum, collisions with electrons in the valance band of the insulator cause an 'avalanche' of electrons. In this model it is assumed that electrons are emitted from the insulator by the thermionic process and the temperature is described in terms of the electric field that has accelerated them through the insulator. This yields a close match to many experimental measurements of Field Enhanced Emission.**

**R.V. Latham, 1983, "Prebreakdown Electron Emission", IEEE Trans. on electrical Insulation, EI-18, pp194-203

- wong chee tat :)

Project Updates / Status

I'm supposed to provide an update last week but I'm busy testing out different sets of simulations, so hence the delay in providing the updates. Anyway, here is a quick update regarding the project.

Previously, testing out different , but related components gave me new insights to the problem.

Currently, I'm working on the problem on particle trajectories due to the field emission caused by different current regime. The first set of "correct" simulation data is just out. I will analyze and see if it make sense or not. If not, I'll have to modify it. I guess this will take a while and hopefully, I can finish the simulation as quickly as possible.

- wong chee tat :)

Project Updates / Status

Nothing much progress for these few days except for tuning up the codes and reading and re-reading the papers. Totally unexpected and unacceptable.

- wong chee tat :)

Project Updates / Status

I ought to give an update on Friday or so, but I'm busy. Well, never mind, a quick update is posted here:

One of the selected 2D models were refined and used. The latter model was not used because the model would be too long and too complicated for a typical reader and can be hard to debug too.

The 2D model quite agreed with the literature.

The main specs as discussed last week were analyzed, tested and completed.

The next steps to consider:

1) Applying classical mechanics to study the ejected particles. Had long forgotten my classical mechanics, and I need to read up a bit and clear my cobwebs. Oops,.... Now you know..... =D

2) Validity of the model in generalized Nth-D and extension of CL Law in Nth-D. Possible? or too hard? =) I have no ideas but it will be fun to explore into the unknown.

3) etc....



- wong chee tat :)

Project Updates / Status

This little blog post is to provide a quick update about the project that I am currently working on.

After meeting with Prof on Friday, he gave me new tasks to do.For my part, I gave him updates about my progress and he explained that the methods that I used in the 5 different models (Yes, I programmed 5 different models) are correct for planar models only, and the equations, unfortunately, do not apply to what we are doing or researching on. :(

He explained that in order to do that, the methods or rather the equations have to be changed , of course.

So for the weekends, I came up with some simple methods in order to solve the new tasks. I will provide more updates later on.

- wong chee tat :)

Project Updates / Status

Code Fixing:

- A more efficient method to compute current of a specific field emitter model

A more efficient method is needed to compute surface current of a specific field emitter model without going through the hassle of using complicated integration.

Currently, the simplified version used to solve the above mentioned problem proved to be slow and at times error prone. (See C4)

- wong chee tat :)

Project Updates / Status

Code Fixed:

- Area determined for one of the field emitter models found to be computed incorrectly

Applied a too low minimum voltage to one of the field emitter models (V approx. 2V therein ) can sometimes caused area computed incorrectly and the current obtained was inconsistent with other models even though it was thought to be in agreement with the theory.

- wong chee tat :)

Project Updates / Status

Code fixed:

- Added newer field emitter models to study emission details

This is needed to understand different models and how each geometry affect emission

- Improved area calculation and current calculation.

Previous methods were slow and unreliable.

- Pre-allocation added for vectorization.

Optimization for fast computation.

- Fast transition voltage calculation.

Just added this code today. Determination of transition voltage was through graphical plots which are more error prone. A simpler and faster approach is used to compute transition voltage.

- Code cleanup

As above.


Wish List =)

Faster automated code testing



- wong chee tat :)

Project Updates / Status

Currently, I am reading and understanding this paper: Electric field distribution on knife-edge field emitters.

- wong chee tat :)

Project Updates / Status

Exams are over!

And now I continue to do the assigned project. I am quite busy these few days because I have been reading one of the PhD's thesis (Thanks Dr K! =) )and digging through the local campus database for more information and more reading, and programming too.

- wong chee tat :)

Project Updates... Stuck!

Currently, I am reading up one of the research papers that were given by Prof. While reading and coding in high level langauge, I came across this interestingly strange mathematical stuff named as: Incomplete elliptical integral of the second kind.

Like this:

My first reaction: Oh God! What is that???? Not taught in my engine courses..... How?

Lets' turn to Google and see what does it showed up in the searches:

Elliptic integral

Elliptic Integral of the Second Kind (Complete)

Elliptic integrals of the first and second kind and Elliptic Integral Overview and a quick calculator is here (link).

Great! But how to code it?

- wong chee tat :)

Project Status / Updates

For the project that I am currently working on, I had compiled the data and simulations results and sent.

I intended to do more as the scope of the project is interesting but that required a lot of reading and reading of materials and I don't have the time. Instead, I will focus on the coming exams. Oh, I only have less than a month o prep for exam.

Here are the things I did not include in the current results due to lack of time:

Obtain the smallest possible D_bar and from there find the extracted area.

Obtain the data from the previous simulation and perform a complete simulation.

Comparing the current simulation model from Feng and Verboncoeur's model.

And maybe somemore....

Maybe I will try to implement and / or improve on the models and the codes after the exams if possible.

- wong chee tat :)

Project Updates & Status

Happy New Year !

Welcome to Year 2009!

Okay, I'm back and in this blog post, I decided to blog about my project and update it.Well, it could be quite bored to read unless you are really interested in my project & care about my project progress that I am currently working on it. :)

I saw this comic strip released some days ago,and some random thoughts regarding my project came to my mind on and off. This comic strip seemed somehow linked to my project and I should quick wrote it down but I didn't because I was quite busy some days ago.

(Note: Nothing against my advisor/ Prof or anyone by showing this comic strip.)

What's new since dec vacations are just over?

Here are some of the progress about the project that I have been working on during the December vacations: (I decided to be very brief here)

a basic model created from the specs given.

simulation results are checked against hand calculations. They are compared and analyzed.

I'm not sure whether the results are correct or not.

- wong chee tat :)

Project Status & Updates

Here are some updates regarding the project that I am currently doing.

As mentioned in my previous post, there were some errors that puzzled me.

I rechecked and recoded that portion and thus it matched the value that Prof had calculated.

Different configurations are tried out and the results are as expected. Yes!

The next step is to check for J and from there, A can be obtained. Next, different profiles will be simulated soon.

- wong chee tat :)