Atomic Force Microscopy

Day 9

AFM - Atomic Force Microscope

Today, I have been show the functions of an AFM, which basically scans the surface of the sample at a nanometre scale, so that any roughness can be seen. A smooth sample is considered to only change its contours by a maximum of 5nm.

First, Dr Ong explained to me the functions of the AFM, how it functions and what it does.
As mentioned above, the AFM is meant to scan the surface of the sample to determine its countours on a nanoscale.

There are 3 ways a AFM can employ the scan the sample:

First, it could be a certain distance away from the sample, and measures the coulomb forces between the sample and the tip of which the AFM uses to scan the sample. The distance from the sample would determine how much force can be measured by the machine, and hence could be used to determine the distance from the tip, allowing the contours to be plotted.

The second method would be to ensure that the tip is always in contact with the sample, such that any contours would change the shape of the tip, and as a laser is shone on the tip, the deflection of the laser by the tip of the sample would be collected by a detector, allowing the machine to know how much the contours have changed, allowing the contours to be plotted as well. This method may not be very good on a soft sample, as it could potentially scratch the sample.

The third method would be to vibrate the tip, and every time the tip contacts the sample the height of the sample could be taken using the same mechanism as the second method. This method would be better used on a soft sample, as it would reduce the damage done to the sample, allowing the true surface to be taken more accurately.

My sample, after the polishing done yesterday, ..., remains a very bad failure in terms of smoothness.



A topography showing an area of my sample

My sample has contours which would measure up to 200nm change, as well as traces of the polishing agent used yesterday, although it look very smooth with the naked eyes. This portion of the sample is part of the same portion shown in yesterday's post (the smoother part).

That concludes the day, and in fact, it concludes the entire research programme for me. If there are any questions or comments, do leave them at the chat box beside and I will respond to them as soon as possible.

Treatment of sample for analysis

Day 8

Sample cleaning

The day started off with the cleaning of the sample prepared yesterday.

This process uses acetone to "wash" away the organic portions of the die left, and by putting the die into a beaker filled with acetone, and putting the beaker into an ultrasonic cleaner, so that the dirts could be "shaked" away from the die.

After washing with acetone, the die is rinsed with alcohol, then blown dry, so that it can be clean for sample analysis. This process was fustrating, as the sample is rather small and light, and the blow gun have blown away my sample multiple times - once it even took some time for us to find it. Once the sample is blown away, it has to be washed again (which I did multiple times). Until finally, I successfully got the sample dry without dirtying it (much)



Under the microscope (before polishing)



Fig 7.1 Higher magnification (before polish)



Sample polishing

After cleaning the sample, it is time to polish it. Polishing the sample is meant to scrap away the top few layers so that the layers below could be seen for analysis.

First, a very rough polish is done. The sample is dragged across a sandpaper (grit 800) lightly 5 times.

The damage done:



After rough polishing



After rough polishing









 Only 5 times across the , see how badly it is damaged!

Next, a smoother pad is used, so that it can be more finely polished, such that the surface can be smoothed out again. particles of size 50microns were used for this part.

It was a long and extremely boring process.. I spent more than half an hour, doing exactly the same motion, trying to keep the path of motion consistant. Non-stop for more than half an hour. After putting it under the microscope, it is not much better than after the rough polishing. I do not have time to complete the polishing, as it was time to move on the the FIB (again)

after smooth polishing

after smooth polishing

FIB

Refer to day 4, Milling for previous experience with the FIB.
Today, Dr Ong showed me another usage of the FIB. After some brief introducion to the FIB, he showed me a different usage of the FIB - To cut the sample so that the cross section could be examined.

A layer of Platinum is deposited first to protect the area of interest



Cutting of the sample with an ion beam is done to create a hole



The cutting have to be done again to smooth out the edge

 

After smoothing of sample, and measurements made

 Notice the different layers of the sample? They are the metal paths, (top 2) and the transistor layer (bottom layer). All this are contained in 1 small die! (as shown in previous day's photo) Even then, we have only seem the top 3 layers, there are more below. This small chip contains all the information in our phones, computers, and many other electronic products!

That concludes day 8, do leave any comments on the chat box beside!

Introduction to Microelectronics

Day 7

Introduction to Microelectronics

It is the seventh day of this attachment, and my first day following Dr Ong to learn more about microelectronics and failure analysis.For today, Dr Ong gave me a brief introduction to the things I will learn about (transistors, and other electronics stuff), as well as common failure in electronics and what causes them.

Next, he showed me some machines commonly used for failure analysis, such as the SHIMADZU Micro Focus X-ray TV system 2000 (SMX) to see on a larger scale if any defects are present, and the Sesame 1000 (a laser) to cut open the package to reveal the main component inside a chip, so that further analysis can be done.

Fire Drill

At 2pm, the Fire alarm went off!  Fire safety is of utmost importance in NTU, as incidents of fire has really happened in NTU before, so NTU will conduct a fire drill at least once a year to ensure that all students and staff knows what to do and where to gather in events of emergencies.

When we have all gathered at the assembly point, the fire manager gave a few reminders of safety and reinforced the procedures to take in case of a real fire. The entire event lasted around half an hour, where at the end we went back to the lab.

Acid Treatment

Next, Dr Ong showed me how to do an acid treatment of a package.

First, fuming nitric acid would be poured into a beaker, and the package dropped into it. After swirling the content in the beaker for awhile, it is left to stand for the reaction to take place.

When the colour of the nitric acid changes too much (due to reaction with the package), it is poured away and replaced. This process is repeated until only the die (a component inside the package) is left.



The original package



For today, every time the nitric acid was replaced, we would place the package under an optical microscope to see certain features of it before the acid completely dissolves them.

   



Dissolving the package using nitric acid



First (few) treatments



During treatment (notice the fumes - very faint on camera)

A closer look (under the microscope)

Few more treatments later (notice the black areas reduced?)

showing connection between die and metal legs

connecting pad (after gold wire is removed)

After package is mostly dissolved (green deposites are copper being desolved)

One sample which is dissolving copper, the other still at the package

The final product - the die

   SAFETY!
Wait! Before the above procedure could even be started,  some safety precautions have to be in place. First, a lab coat must be worn - To prevent chemical spillage from directly coming into contact with skin or clothes.

Then nitrile gloves (2/3 layers) must be worn - To prevent direct contact of chemicals with hands

.
A mask must be worn - To prevent breathing in fumes from chemicals (like the fuming nitric acid).

A safety goggle must be worn (supposedly? ><) - To prevent chemicals from coming into contact with eyes.

That concludes day 7, do leave your comments at the chat box beside!

Insights to other areas

Day 6

It has already been the sixth day into the programme, and is my last day following Dr Du. The aim of today was to get to know more about other aspects of MSE, rather than just solely focused on armor research. She has brought me around other labs, such as the biomaterial lab, where a few commercial products (such as Biodegradable Drug Eluting Stent) were developed from, as well as showed me other researches going on, such as graphene and capacitors.

Graphene has only been discovered not too long ago, and its potential for application is extremely wide. Researchers in NTU have been trying to grow graphene on different metals, such as copper, steel and nickel, as they require different conditions to grow in different metals.

Capacitors are being developed such that a very small capacitor can be light and reliable enough to be used in military purposes, such as for soilders to carry them out-field to power certain military equipments.

I apologise for the short post today, but I am not feeling well, so the update today is rather brief. Tomorrow will be longer and more interesting! Do watch out the for the next post!

Firing in 3, 2, 1

Day 5

Today, I followed Dr Yuan and a DHS student Li Ting to the High Speed Dynamics Lab where they investigate the properties and reactions of some materials under collision with a high velocity projectile. Today they were testing the effects of some ceramics under collision with high velocity projectiles.

No pictures will be included in today's post as certain information might be sensitive.

Setting Up

For the first time, I witness a firing (the process not the actual firing. A distance have to be kept during the actual firing so I could not actually see it fire).

First, the air gun has to be cleaned and set up, so that the velocity of the projectile obtained can be optimal, as well as to prevent accidents such as blockages that could potentially be dangerous. Dr Yuan allowed me to help out with the setting up of the air gun (rather minimally, but still a previllage). In the mean time, Li Ting was setting up her equipment (high-speed camera, lights) for her experiments (explained later).

There were many steps to the setting up (cleaning, assembling, ensuring vacuum, etc, etc.), so as to ensure the safety of everyone inside the lab, as well as to make sure that the experiment will go accordingly to plan.

Next, we went back to a room where it is safe to do firing, and where the launch button is located, as Li Ting explained to me what her experiment is all about.

Li Ting's Experiment

In order to accurately capture the motions of the projectile just before the impact and during impact, high speed photography have to be utilised. Dr Yuan have found that in some instances, the impact cannot be seen clearly due to the quality of the images. Hence, Li Ting is tasked to experiment with various lighting conditions to find the best lighting condition for which the photographs will turn out sharp and clear.

In the experiments conducted today, she used a lighting lamp and the high-speed lens. She angled the lamp at roughly 15 degrees on the left of the camera, and in the second experiment, roughly 35 degrees. The angle on the left is smaller to avoid the large shadows formed due to the target holder's position in the light, and with the shadows, the projectile may not be clearly seen.

In both experiments, there is a few steps to the recording. First, the trigger have to be set, and with Dr Yuan and another researcher, they counted down and fired the projectile. Afterwards, a programme will record and play back the impact for the researchers to analyse and evaluate. Since the images are not always clear, Li Ting will edit the photographs using the same software used to record the impact to attempt to make the quality of the images better.

She has found out that the images will differ from different position the lamps are placed, due to the shadows formed, and is still trying to determine the best position that it could be placed to obtain better results.

Problem: Fireball

One major problem that Li Ting has faced in the capturing of a good image is the formation of a "fireball" during impact. This "fireball" could cause the image to be totally obscured by a blinding white light, making sure that no image could be seen during that period of time.

The formation of the fireball seemed to be curious to me, as the target chamber would be vacuumed out before the experiment, and only inert gas would be used to pump the projectile forward - meaning that there is no oxygen available for combustion. So why could there be a fireball?

We have theoricised that it could be the heated fragments of the target and projectile.

As the projectile collides with the target, deformation of both will take place, a process which would produce heat. Since the time taken for the collision is very short, and the velocity very high, the compression takes place very quickly and by very much, possibly producing enough heat for the metal fragments to glow.

For the second experiment (the first experiment was only a target metal), where a ceramic plate is placed in front of a metal, the fireball is much smaller and it dissipates faster, it indicates that our hypothesis might be correct.

Li Ting has kindly allowed me to take some of her photographs of what she is analysing


Experiment 1 - Fireball effect

 Experiment 2 - Fireball effect

Only one way to prove it - experiments. Sadly I could not do it during this period of attachment.

It was really an interesting day, thinking of possible explainations for different phenomenons that occured. An insight to what research is about? Thinking of possible explainations for certain phenomenons then proving (or disproving) them?

Do leave your comments or questions on the chat box beside!

Characterising!

Introduction to Equipments (Day 4)

F.A.C.T.S

Morning today, I was brought into F.A.C.T.S (Facility for Analysis, Characterisation, Testing, Stimulation), and introduced to many cutting-edge equipments used for characterisation of different materials.



FE SEM - Field Emission Scanning Electron Microscope

 The FESEM have various functions, such as to obtain a SEI image of the object at very very very small scale, e.g. a few nm (an helium atom is about 0.1nm).

This is done by passing a beam of electrons (with adjustable acceleration of 2kV to 15kV) through a field, and obtaining an image from the emerging electrons.

This machine is also attached with an EDX - Electron Dispersing X-ray spectometer, its function is to determine the elements found in a specimen through the X-ray emission when the electrons hit the sample (A level physics knowledge put into use - never thought it ever would, have you?). I guess that the compositions are found through the K-alpha and K-beta characteristics of the X-ray emitted.

(small )screen showing the physical position of the lens and sample in the FE SEM

There is also a camera inside the FESEM champer which allows the user to see where the beam apertures is relative to the sample stage, so that they will not come into contact and potentially spoil the aperture.

An experience I can relate to the optical microscope - usually too focused on the image I obtain in the optical microscope, I forgot to check if I was adjusting the knob too much and if it would cause the lens to touch the specimen. Many times a session, I would. Luckily for me, it was only a light tap and I would immediately reverse the direction of the knob as soon as it happens. Hence, no damage is done. (or my wallet would lost weight very fast T.T)


Ion milling

This machine is used to produce very thin layer of materials for TEM abservance and analysis in day 3!



X-ray diffraction (XRD, Bruker D8)

 

Close up (X-ray deflector)



Very simply put, this machine uses X-ray, and the rorating of the sample, to determine the crystalline structures of materials. 

Another good thing about it is that it can be fully automated (look at the close up photo), where 15 samples can be loaded into the two sample tower each, and tested automatically. Hence, there is no need to spend an eternity waiting for the samples to be scanned (unlike the Tribolndenter - look at day 3 part 2), freeing up the researcher to do other things to improve the speed the research can proceed.

 

A poster beside the XRD

XRF - X-ray fluorescence spectroscopy

This equipment is used to test the average composition of a large area of sample. (similar to EDX, but on a larger scale, a few centimeters)

 

Some other equipments were introduced, but photos could not be taken as they were in use.

TEM - Transmiting Electron Microscope. Basically used to magnify the sample to up to 1nm, but it can also be used to see into the sample without damaging it.

A mini photography contest (literally) - mostly from images taken using TEM

Other works of photography that involves images from the TEM or SEM

Milling

Next, Dr Du showed me the procress of creating the pillars (Post: Research Techno Plaza). It is done using the FIB - Focused Ion Beam. An extremely expensive equipment, it can serve many purpose, such as being an electron microscope and as an ion mill.

An electron microscope operates by expose a beam of electron onto the target, and then the secondary electron ( electrons emitted by the sample) will be collected to form a visual image of the sample.

The ion mill functions the same way, but instead of producing a beam of electrons, it generate a beam of gallium ions, although it still collects the secondary electrons for imaging. The main use of the ion mill is not for visual imaging though, as it will damage the sample if is exposed for prolonged period of time. Its main purpose is to mill off a layer of the sample to produce the pillars with the pre-setted dimentions.



Preparation of the sample




Stub (left) and copper tape (right)

Prepared sample

The copper strips have to be attached to the sample so that it can conduct the charges away. This will help obtain a better image for the sample. Notice the black parts on the sample? They are a conductive coating so that the image can be produced better. Usually the coat is Carbon, Platinum, as their particle size is very small.

The sample goes in here

FIB - focused ion beam



some images of the pillar



A broken pillar. image from the electron microscope (left) and from the ion mill (right)

Doesn't the image on the right look like an upside down bear?

The controls of the FIB

It was a tedious process, which requires careful and precise handling, where the voltage of the electron beam, current, and many other stuff have to be taken note of such that it will not spoil the sample by over milling. Even observing the sample for too long will adversely affect the sample.

Much patience have to be put into the milling on manometre scale, as well as effort and skills.

That concludes the fourth day of the attachment, please leave your comments on the chatbox beside!