Scanning Electron Microscope

I have always wanted to use a Scanning Electron Microscope (SEM) and my chance came last week at Cambridge University.  What a thrill.  I received an optical microscope for Christmas one year as a child and had endless fun and excitement with it, but the SEM is a whole new ball game and has a resolution down to 1.4 nm.   That’s a thousandth of a micron or a millionth of a millimeter. Hard to imagine.  To add to my excitement, it also had a focused ion beam (FIB) microscope adjacent to it that we used.  I didn’t even know what they were until a few days before we used it.  Its similar to the SEM microscope but fires ion instead of electrons which are much bigger and heavier so can inflict more damage.  When the current is turned up, you can machine or mill the sample in a very controlled and accurate way.  We also injected gas molecules (organic platinum) between the sample and the FIB.  If the current is just right, it won’t machine the surface but rather split the platinum from the organic part of the molecules and deposit them on the surface of the sample.  Because you have the SEM pointing at the same place you can look at what you have done.  I want one!

SEM with FIB at 54 degrees

You don’t think of a microscope firing a current, but that’s exactly what a current is, a flow of electrons.  To get an idea of how many electrons are being fired at the sample; A Coulomb = 1 Amp per second.  The charge of a single electron is around 1.6 x 10-19 coulombs so there are 1 / 1.6 x 10-19 = 6.25 x 1018 electrons per second for 1 Amp.  We have a typical probe current of 200 pA so there will be 6.25 x 1018 x 200 x 10-12 = 1250 million electrons per second or 1250 electrons every μs bombarding the sample.  Just shows how unimaginably small they are and how many of everything must move before we can even notice it.  Of course, the FIB also fires a current, just not the negative electrons rather the positive part of the atoms that are left once some electrons have been stripped.  They usually use Gallium ions because it melts below 30°C.  Its solid at room temperature but melts in your hand, unlike treats (now called M&M’s).  A proton weighs 1.6727 x 10-24, a neutron about the same at 1.6750 x 10-24 and an electron 9.110 x 10-28 so a proton is 1837 times heavier than an electron.  Gallium normally has 31 protons and normally 39 neutrons in its nucleus.  It therefore normally has 31 electrons in orbitals around the nucleus but if the electrons are stripped from the outermost shell (valance) it will become a little smaller and be positively charged.  Because only one electron is in the outermost shell of gallium it will have exactly the same charge as an electron but be positive rather than negative (1.6 x 10-19 coulombs).  So, each ion in the FIB will carry the same charge as each electron in the SEM but weigh about 1837 x 70 = 128,590 times as much.  So, you can imagine how much more momentum and damage a beam of ions can do to the sample surface compared to electrons.  That’s the same difference as an average man (70 kg) compared to a freight train with an engine and 63 loaded rail cars.

We started by measuring the features on a DMD (Digital Micromirror Device) using the SEM.

Image of DMD mirrors

The mirrors are about 13 μm square with a Ø1.5 μm hole and the gaps between the mirrors are about 1.1 μm.  So surprisingly we could get an array of 100 x 100 or 10,000 mirrors in a square of 1.3 mm on the side.

Well a DMD chip has several hundred thousand microscopic mirrors arranged in a rectangular array on its surface; each of which correspond to a pixel in the image displayed.  Each mirror can be individually rotated by around ±10° which represents an on or off state.  When on, light from the projector is reflected off the mirror, through a lens onto the screen as a bright pixel.  When off, the light is directed to a heatsink, so the same pixel appears dark.  To produce grey, the mirror is toggled on and off very quickly by pulse width modulation, so the shade of grey corresponds to the ratio of time on to time off.  To produce colour, three coloured projectors and three mirrors are required for each pixel and the ratio of on to off for each colour determines the pixel colour brightness.  The mirrors are made from aluminium and are mounted on a yoke which is connected to support posts by torsion hinges.  Because of the small scale, hinge fatigue does not usually cause a problem.

We did a few more experiments, carrying the acceleration voltage and the probe current etc, and then changed the sample for an EPROM and set up the FIB.  If you set the distance an M stage tilt correctly, its possible to be able to view the same part of the sample with the SEM and the FIB without changing the focus or moving the sample.  This is called the Eucentric point.  Below is the same image using both devices.Compare

TrapYou can see that the SEM is viewing the sample at an angle but there is a tilt correction mode if you like.  The resolution and contrast of the SEM is so much better than with the FIB.  Next we drew a trapezium on the sample that we were to mill out by setting the accelerating voltage and current just right we got a really nice cut of 3 microns deep.D200pSEM

We found the optimum current to be around 200 pA.  Its amazing how accurate and easy it is to machine the sample; this image is taken at 4000 times magnification.  The maximum optical lens you can use is about 1000 times.  This is just run of the mill, its capable of far greater magnification if you like.  When looking at biological samples, they have to be stained with a rigorous process prior to viewing so that the different tissue types stand out and can be seen.  When looking at anything else, you just put it in and focus; and the images are so much better than the ones I could get on my optical microscope as well.

GISOur next step was to inject a gas between the FIB and sample when it was scanning.  The gas we used was made from platinum organic molecules.  If everything is set correctly it will split the gas and deposit the platinum part on the sample while the organic part is vented away.  This time we drew a small rectangle on the sample as it takes a while.

Platinum deposit on EEPROM

We then decided to do the same cut, half on the deposit and half off.108

We noticed some funny furry deposit at the front of the cut so zoomed in for a closer look.Fur

This view was taken at 8200 time magnification and we could have gone in much further.  We then moved onto our last part where we analysed the surface at different places to do a spectral analysis and find out which elements were present.

Map Sum Spectrum
Spectrum of area around the cut out and deposit
Summary of elements at various places

The redeposit column was taken on the furry deposit which was found to be made up of platinum, silicon and carbon.  Basically, everything that was blasted away when the cut was made.  Its interesting that there is so much carbon around; I think the only place that could come from is the organic part of the gas which should have been vented away.  Not quite sure how it gets vented away anyway as everything happens in a vacuum and to vent away you need a lower pressure than where it is.  Well, you don’t get much lower pressure than in a vacuum.

Image inside vacuum chamber

Sorry its been so long since my last post but I have been so busy I cant tell you.  We have lectures all next week at Cranfield then the following week at Cambridge and then no more!  So once I have written up the reports for those I will only be doing my thesis so should have more time to catch up with everything else that has happened.  I will get there in the end.


NPL Realisation of SI Unit Definitions

I though that I should make it clearer exactly which of the SI units will be changed.  There are 7 fundamental SI units that all others are derived from.  This will probably be the biggest ever single change to our fundamental units since they started.  Great effort has been made to remove historical artifacts from our definitions because any variation in these artifacts change our standard to which everything else is measured against.  Its also very difficult to scale up or down from an artifact without further uncertainties creeping in.  It also means that as we get better and more accurate at measuring everything, the fundamental constants keep changing as they get more and more decimal places at the end.  If we fix the fundamental constants they will e forever constant and the unit definition can change getting more accurate with our increasing technology.  However, there are growing suspicions that our fundamental constants may not be absolutely constant after all, but this is not the place to be distracted.


The kg will change, and the Plank constant will be fixed forever at h = 6.62607015 x 10-34 Js exactly.


No change to the SI unit of length (m)

When this was previously changed, the speed of light was fixed forever at 299,792,458 m/s exactly.


No Change to the SI unit of time (s).

MOLE (mol)

The amount of substance (mol) will change by making Avogadro constant NA is 6.02214076 x 1023 mol-1 exactly.  The previously defined mass of carbon 12 will no longer be exactly 0.012 kg/mol.


The SI definition of current (A) will change, the elementary charge of an electron will be fixed forever at e = 1.602176634 x 10-19 C exactly.


The SI unit of temperature (K) will change, the Boltzmann constant will be fixed forever at k = 1.380649 x 10-23 J/K exactly.


No Change to the SI unit of light (cd).

Of course, many derived units will be affected by the redefinition’s, but great care has been taken so that all changes will lie within the area of uncertainty of the previously defined units, so it shouldn’t make any difference to any previous work.  All these changes will be approved during November 2018 and implemented on world metrology day on 20th May 2019.  No further changes are anticipated in the near or medium future after this date as all artifacts will have been removed and all fundamental units will rely on fundamental constants or atomic data.

Nanotechnology is too big for NPL

Had a slow start with taxi arriving 15 minutes after I had booked it the day before to get to MK station to start our week in Teddington at the National Physical Laboratories NPL.  The others travelling from MK station had already texted to ask where I was.  No problem as we caught the 9.49 express; next stop Euston.  The underground doesn’t go to Teddington, the home of The National Physical Laboratory so we had to get the tub e to the closest station then transfer to the national rail line.  We met up with two others at Vauxhall.  That only left XY who had driven and Mohammad who had worked at Ted Bakers the weekend so traveled straight there.  We bumped into Mohammad at Teddington when we were there so almost full house.

They had put on sandwiches, fresh fruit, cakes, coffee etc.  Nice spread while we waited for the Cambridge crew who arrived before the food had all gone.

DSCF3303We were led into a lecture room with beautiful ceiling roses and old paintings around the walls.  This building used to belong to King William IV back in the day but now its part ofDSCF3311 NPL.  Our first days lectures were held in the Bushy road entrance but all other days at the main entrance where the iconic glass entrance is.  They started off slowly with introductions to what was to follow the rest of the week.

The lecturers for the day were, Robert Gunn, Stephanie Bell and Ian Robertson.  Our host and Course Director was Andrew Lewis.  I must say that I find it hard to get excited

Andrew Lewis

about the history of the SI units, organisations, tractability and uncertainty but they had regular breaks with coffee, tea, juice, biscuits, fruit and other snacks.  They also showed us down in the cellar where plenty of artifacts were held.  This was very interesting, I wish I had more space for pictures as I took so manyDSCF3305 every day.  I seem to have become the official photographer of our group as everyone wants me to put the pictures on our shared Google Drive.  They had lots of old light bulbs from the 1900’s which were huge and over DSCF3313complicated.  They had the standard yard that we had in England and preceded the Meter which was held in France.  But one of my highlights was the lecture notes that were sectioned in a folder.  The best that I have ever seen and so accurate; we only had one page change the entire week.

DSCF3324Tuesdays lectures focused on mass.  Its a huge time for metrology at the moment, next year, three of the seven SI units will be redefined in a modern way using fundamental constants rather than artifacts.  The kilogram (kg) is one of them.  At the moment, we have a physical weight made from platinum-iridium alloy since 1883 that everything else has to be ultimately measured against.  This is a single artifact that is very vulnerable.  It also looses weight constantly when it is cleaned.  It gains weight from buildup of hydrocarbons in the air and water vapor in the air until itDSCF3327 is cleaned.  Prior to this the kg was defined as the mass of one cubic decimeter of pure water held at 4 degrees Celsius.  But water evaporates, it has surface tension so its difficult to measure, how pure, 4 degrees Celsius exactly etc.  So this definition was immediately replaced by a pure platinum weight in 1799 held inside 3 glass jars.  In 1889 another 40 copies were produced and spread around the world to be used as a local standard.  Every now and then (four times), they all have to be compared with the ultimate standard held in Paris.  DSCF3329The picture above is kg number 18 held at NPL.  At the moment, the kg is only 3 micro-grams accurate because of its variations.  Clearly, we desperately need a better way to define it.  Of course, its not just mass that is affected, the derived units, including pressure and density rely on the kg and if we measure something really light or really heavy like a plane, it has to be in multiples of this standard kg where more accuracy is lost.  It was decided that an accuracy of less than 2 parts in 100,000,000 is required.  There have been two contenders, the Avogadro based kg or the electrical Watt based kg that uses the Plank constant.  The first is a perfectly roundDSCF3326 sphere made of silicon so that the total number of atoms can be measured and calculated.  This would also redefine the mole at the same time, fixing Avogadro’s constant.  The Watt balance, or Kibble balance after Dr Bryan Kibble from NPL who invented it in 1975, uses electrical energy to balance physical objects and rely s on fixing the Plank constant.  The Kibble balance is the one that will be approved next year and the Plank constant will be fixed forever more.  Although the silicon sphere worked we would still end up with an artifact, which by the way, is the most spherical object ever made.  The beauty of the electrical balance is that one could be made anywhere.  This second one, is the new version that will actually be used in the kg’s redefinition.  Planks constant will be fixed at exactly 6.62606 x 10 -34 expressed in Js on 20th May 2019 which is world metrology day.  Our lecturers for the day were, Stuart Davidson, Ian Robinson, Andy Knott and Kevin Douglas.  Ian Robinson was great friends with Bryan Kibble and worked with him for years before he passed.  It is Ian that continues this work today.  We also managed to hold a conference meeting at lunchtime.

ULTIMUMWednesday’s lectures were all about the redefinition of the meter.  Again, the international prototype meter was an artifact that was redefined in 1960 and again in 1983 by fixing the speed of light to the distance traveled by light in 1/299792458 of a second (in a vacuum), thus fixing the speed of light to exactly 299792458 m/s forever.  Of course, light is electromagnetic radiation which has a frequency.  The frequency of light ranges greatly, of which visible light (that we can see) is only 1 ten trillionth of the total spectrum.  Light of all frequencies travel at the same speed in a vacuum, but vary through any other medium according to the wavelength.  Today, the workhorse of distance measurement is the interferometer that creates interference patterns by splitting light and changing the path distances slightly.  Arthur Schawlow at Stanford University said, “Never measure anything but frequency!” in his Nobel prize speech.DSCF3350  When measuring distances, the greatest enemy is temperature because when temperature changes, size changes.  Also different materials vary by differing amounts with temperature which doesn’t help either.  Its expensive to make a room that doesn’t vary with temperature from 20 plus or minus 0.1 degrees Celsius.  That’s why the eccentric Tim Coveney of NPL has designed the NPL ULTIMATUM.  Just pop in what you want DSCF3353measuring and it will measure it to an accuracy of 1µ / m while holing the temperature constant to 1/10 degree Celsius.  Other lecturers included, Geoffrey Barwood, Andrew Lewis, Ben Hughes and Andrew Yacoot.  In the evening we were all treated to a 3 course meal with drinks at the Kings Head.  What a great day, it just keeps on getting better.


ResonateOn Thursday we switched our attention to temperature.  Currently, temperature rely s on the triple point of pure water which is 273.16 K (0.01 ·C).  There is only one temperature where water can exist as a gas, liquid and solid at the same time.  This can currently be measured to 50 µK.  As I have mentioned in a previous post, temperature will be redefined as well and the instrument that will be used was madespike by Paul Morantz that finished working for Cranfield today (end November 2017).  He built this for NPL who are again instrumental in the redefinition of the Kelvin.  The spherical resonator is filled with Argon and the frequency of sound is varied until the fundamental frequency is found inside the resonator.  Because the sphere is made so accurately and the frequency is well known, this DSCF3378frequency will vary with temperature according to the Bolzmann constant so its possible to accurately measure the temperature from the frequency.  To make it even more accurate, the sphere has three slightly different diameters which creates three resonant frequencies.  Our lecturers included, Andrew Yacoot, Robin Underwood, Jonathon Pearce, Radka Veltcheva and Gavin Sutton.  In the evening, I took the train to Waterloo to meet Georgina.  Had a bit of a hitch as my phone has almost expired and refused to work at the critical time when we were trying to make contact.  Just managed to get it going in time otherwise we would never have found each other in the busiest station in Europe.  We had a meal at Wagamama’s but it was freezing.  I really must get myself a jumper or warm coat.

pmFriday, our final morning looked at the units that are derived from temperature.  Our lecturers were Jonathon Pearce, Helen McEvoy and Stephanie Bell.  They fed us lunch and we were on our way.  Mohammad bought chocolates (we all contributed) for Andrew, our host and Emma and Ronnie who had organised our week.  Andrew was very touched and said that we were the first group ever to buy a gift for them.  We were given our assignment and away we went.  What a week, I wont forget that in a hurry.  We asked Andrew Yacoot who took us for lectures on Wednesday and Thursday to speak at our Conference next

Andrew Yacoot

year as he has managed to make an Xray interferometer that can measure distances to a resolution of 24 pm.  To do this he has to hold the temperature stable to less than 1 mK.  Considering that the Silicon atom that he measured is only 192 pm it seems impossible to measure smaller but because its possible it will be done.  It will be used initially for the calibration of optical interferometer’s but I am certain that we will find further uses for it in time.  Its rarely that you ever have the opportunity to meet such an intelligent group of people as this bunch of wonderful mad scientists!

National Physical Laboratory Class of 2017

Social Life

Somehow, I have managed to retain most of my social life as much as possible.  I don’t like to work evenings if I don’t have to anyway, but I have retained my three evenings out.  I meet Jim, my best friend, at the pub I can walk to on a Tuesday, where we normally eat and talk about all things science.  I am out with the old boys on a Wednesday night where we also eat.  Dr George, who was my course tutor at the OU is one and Jim comes along occasionally.  There are usually 4 or 5 of us, including, Steve, Prof Alfi and Georges son Chris.  Alfi isn’t really a prof, he just likes to think he is.  He has never owned a tv or been married so he has the knowledge of a professor anyway.  The feature picture is a sign outside the Red House where we eat on a Wednesday.  I thought of another one, “When its foggy, look for the VW”.

I have recently resurrected a Friday, early doors night out with Dr George and his rugby crowd.  I used to stop off for a drink with them years ago but only started again since I have been single.  Claire, my ex-wife comes around, on her way home from work on a Sunday for dinner and takeaways for the week.  The only social things that have suffered so far is, seeing my Mum and Harriet.  Quite often Harriet and Billy would come around on a Thursday after work for a pancake supper.  I did get back to see my Mum again last Sunday but that’s the first time since I started this course.  Claire has been a couple of times, which has helped.

DSCF3297I haven’t seen much of Georgina either lately, but that’s because she has been working in sub-Saharan Africa for over 12 months.  This Friday, Georgina texted me to say that she had to come home early because some troubles had flared up in South Sudan and it wasn’t safe.  Normally, this would be good news, but she had a few interviews set up which are crucial for her thesis for her MSc that must be in by January 5th, 2018.  She won’t be going back again until December, so it doesn’t leave much time to rearrange and write up.  On the plus side, she couldIMG_6876 come back to Melton Mowbray with me to see her Grandma last Sunday.  Grandma was pleased to see us both and had prepared a nice soya cottage pie with vegetables because Georgina is still a vegetarian.  If it’s got lamb in, it’s called shepherd’s pie, if it’s got beef, it’s a cottage pie, maybe a vegetable one should be called a ploughman’s pie?

This is Georgina’s “field kit” for when she travels in the wilds of South Sudan without an armored car.  A stab vest, hard hat, satellite phone and what looks like a puncture repair kit.  She had to use this 2 weeks ago when she visited some of SS’s top officials.  They are rolling in it while their people are literally starving but are looking for aid to sort all their problems out.

DSCF3239We had another trip to Cambridge a couple of weeks ago for a “Kick Off Meeting” to start organizing our student led Conference.  We started by electing a Project Manager for both Universities and then I was elected Secretary and I don’t even have a short skirt.  Sorry to put that image in your mind.  Anyway, we have already set our event date for DSCF3242Thursday 24th May 2018.  I was also assigned to create a poster for the event.


I just noticed when I selected the poster to put here, that I had the date wrong.  That’s so me, the only mistake on the drawing is the title or the date.  Don’t tell anyone, I will replace it with the one on our shared Google drive and they may never know.  I’m surprised that nobody else had noticed it either as this is the third version I have done.

It was an early start in the morning and Bilal was very tired.  Dillep was tired when we got back as well but that was probably more to do with his 40 hour a week job that he has because he has no funding.DSCF3269DSCF3245






DSCF3246Another event that I managed to attend, was (Wednesday night) Steve’s wife Jan’s joint 60th Birthday.  Jim and Shirley went as well so I managed to get a lift so I could get a few downDSCF3247 me.  It was nice to find that the bar was free for most the night but when you had to pay, they hit you hard at £10 for two draft beers.  It was a great night as Jan has also just passed her business degree with The OU.  Quite an achievement, especially for a girl that has been doing it part time whilst handling a full time job at the same time.  It was also nice to see their kids, Dan and Charlotte, but I only managed to get pictures of Steve and Charlotte.

IMG_6863I even managed to catch up with Harriet and Billy, when we went to the Cosgrove Park firework display where Claire works.  It was cold but we had a lovely time eating hot dogs while drinking beer and watching the display.  They had spent over £7000 on fireworks and it was really spectacular.  I intended to put a great firework video at the end of this entry but I have to upgrade before I can.  Never mind, I will get photo’s next year.  I was also going to put some pictures of some of the sights around Cranfield University, but will have to save those for next time now.


Last Man Standing

The Bang continues; our deadline for our second assignment was today at 2pm (Friday 17th Nov 2017).  According to our WhatsApp chatter, it seems like everyone was working until the last minute again.  We have another assignment to hand in next week (Management and Innovation) and out Metrology assignment should have been in next week, but they have now given us a two-week extension.  Trouble is, we have wall to wall lectures, Monday to Friday for the next 4 weeks.


In my post before my last entry (Precision Engineering), I mentioned that our most experienced lecturer, Dr Paul Morantz had been made redundant and will be leaving us at the end of November.  Well, now


our Course Director, Dr Renaud Jourdain has been cut loose and finishes next March.  Poor Renaud, he was only promoted to Course Director this year, they wouldn’t even let him finish one year.  It’s not as if we don’t need lecturers and thesis supervisors, three were cut loose last year, now these two which I think only leaves us two left, the youngest ones.  Even though they are young, they are very bright and enthusiastic, but they do not have the experience to offer as many supervisory options as we have now.  I’m not even sure what will happen to me as I was hoping to work on the R2R machine.  Who can supervise me?

KernAnyway, it’s been so hectic that I have had no time to write a post for ages.  Our Precision Engineering assignment was to describe and criticize a KERN Evo automatic milling machine.  I had never even heard of one before I read the assignment at the end of the weeks lectures.  I don’t believe that it was even mentioned, so that’s what Research Students must put up with.  No starting information at all, all research.  It’s a wonderful machine, it’s amazing how much Engineering has changed since I started my apprenticeship.   I spent 3 months in machine shop shortly after our first your in the training school; I was placed with the operator of an automatic turret lathe.  It was state of the art at the time as it used a roll of punched tape that provided the control.  The operator put the casting in, clamped it and pressed the green button.  We then waited for 15 minutes while all the machining operations were done and he changed the casting and pressed the green button again.  It’s very difficult to keep up with it, especially as a contractor where you are moving onto different projects all the time.

The second part of the assignment described a cylindrical part that was to have 25, 80-micron diameter x 20 mm pins machined at one end.  Well, the first thing that struck me was that it was impossible!  Why would you want to?  Why not fit the pins to the cylinder rather than machine them from solid?  I couldn’t believe that it was possible anyway, so I created a solid model to see.

80 micron diameter pins                                      800 micron diameter pins

Surely, its not possible to machine this from solid?  Even if it is, it would be so delicate, what the hell could you use it for.  Trouble is, things have changed so much that I am starting to doubt myself.  Have to wait until we get our results now anyway.  We had to talk about how they would be made from Aluminium and Tungsten Carbide.  Again, tungsten Carbide is so strong and hard that it is glass brittle.  I cant see, even the 800 micron pins being able to be used for anything.  I’m hoping that they have put trick questions in, otherwise, the most experienced chap in the group is going to look pretty stupid.  Mohammad found a relevant 2017 paper written by the two lecturers that will be marking this assignment.  I cited it and wrote that it was written by “very distinguished Dr’s”.  The second time, I also mentioned that they were also handsome.  You have to hedge your bets and there is always room for a little humor.


We also had a week of lectures for Management and Innovation.


Although its not really my cup of tea, our two lecturers couldn’t have done more to make it interesting.  I don’t remember falling asleep once.  However, from day one, they split us into groups and we seemed to have to do a presentation at least once a day.  I have never known a course like it, but at least its helping to diminish my phobia about public speaking.  Our main lecturer was Dr Clive Savory who was at DeMontfort University and the Open University before he came to Cranfield.  The other one was Professor Marek Szwejczewski who has published more than 50 papers.  I couldn’t help thinking that Prof Marek looked just like a young Jasper Carrot.  His mannerisms were the same as well.  He didn’t tell any jokes, but I still called him Jasper once, but I think I got away with it.

DSCF3255.JPGAnyway, by Friday, we had to do a group project where we were to design a “City Car”.  We were to create a business model and build a prototype out of Lego.  It had to park autonomously in a multi-story car park.  It also had to park itself in one of three spaces and if they were full, parallel park.  It had to have lights, carry luggage and make a noise when it reversed.  Ours, even had a soft top that tilted up.   We only had about 3.5 hours so we had to split into different jobs and work concurrently to save time.  We didn’t stop for lunch or even a cup of DSCF3257bloody tea.  Luckily we had a “coder” to write the software, so I worked with him as the hardware engineer.  I used to love Lego.  Anyway, we were the only team that managed to complete every task and it ran autonomously almost perfectly.  We had the most luggage, it was a sports car and top end but we only came second because of the others in our team that created the business model I guess.  Anyway it was great fun; except for the damn presentations.  The base was a controller with three sensors that we had to build Lego parts onto, program, download the program and run it autonomously.  Have to go now as I’m out on the lash with Dr George and its an hour walk so more next time.

Under Pressure

We certainly started with a Bang!  The deadline for our Laser reports was yesterday (Tuesday 24th Oct) at 4 pm.  To achieve this date, we all seemed to have to work silly hours at the end.  Working long hours all weekend wasn’t enough, and I started at 4.15am on Monday before lectures.  Continuing again in the evening, following our lectures until 11pm.  I had set my alarm for 5am on Tuesday but got up earlier and started again at 3.45am.  I picked Mohammad up earlier at 7am so he could help me sort out my references and submit the reports.  I say 7am, but he didn’t wake up until 7.04 when I texted him to see if he was awake.  He had worked until 3am.  We were all wiped out for our Matlab lectures on Tuesday, as GC Ren didn’t finish his off until 4am.  He said that his submitted report contained 9000 words and that his thesis for his previous MSc only contained 8000.  Mohamad had done 8900 and I had about 9050.  Although mine had the most words, it also has the most waffle and bullshit so I expect the worst marks.  I don’t care if I manage 50% to pass.

Although it’s been long and hard, we have learnt so much in such a short space of time.  We used an ultrafast laser to machine our snake paths.  Ultrafast has a wavelength of femto seconds (10 -15s or a millionth of a billionth of a second).  Below is a micrograph of the corner of the silicon sample where we machined our snakes.


We started on around 32% power with our first cut, bottom right where it blasted the hell out of the silicon.  We reduced the power with 2 attenuators progressively towards the left. Stepping over before each cut.  The 3rd to last cut was our best but we did two more with increased mode power in case it was too feint to see well enough to measure the trench widths and depths.  We started by measuring the track widths with a microscope and got what seemed like a consistent set of results.  To get a better result we took 3 track widths for each leg of the snake and averaged them.

central 0 offset 1

When we measured again using the interferometer microscope to find the depths we discovered that you should use an interferometer every time.  You can place the cursor in an appropriate position on the sample and see cross sections of the sample surface.  As the track width reading were much wider using the interferometer, we had to repeat our results again as they are obviously more accurate.  We think that the dark lines that we measured on the microscope must be the shadowed part of the illumination which is part way down the sloping trench.


Ultra-fastAn ultrafast laser is so fast it doesn’t really have time to melt the target.  It works by concentrated hi-power photons knocking valence electrons out of the target solid structure lattice.  As these valance electrons are forming the covalent bonds within the crystal lattice, when they are removed these atoms become vaporised changing from solid to gas.  The vaporised ions and free electrons are ejected as plasma.  When there is a great enough concentration of photons to knock out electrons, the free electrons knock out other electrons in the structure and cause an avalanche of ionisation.  This is called the ablation threshold.  Oh shit, I wish I had written this in my report!

It’s quite interesting to look at the profile of the trenches, with the build-up of material either side of the trenches.  It reminds me a bit of a meteorite crater.  The shape of the trench is completely different but the sides are similar.  I guess that some the free electrons hit ions to reform a solid again locally before they have chance to get too far apart.  The extreme slopes and sharp base of the laser trench is interesting as well.  I guess that the middle is where the highest concentration of photons is and so ionises the most matter on average.  I suppose if it wasn’t such a quick pulse or stayed in the same place for more pulses, it would drill a parallel walled hole through the target.  It’s amazing how much more you learn when writing up reports than you do in the lecture or laboratory work.  The lab work and lectures are enjoyable but also necessary so you have something to research about.  You can’t do this sort of research without the facilities in the first place.

Our laser setup the beam is expanded as it can be focused smaller with the objective lens

Back to work today for the first time since I started the course.  Three new faces there, it doesn’t take long for changes to be made.  My computer still doesn’t work and nobody has done a thing about it so not everything changes fast.   It’s still nice to come back for a rest and free lunch.  Shame I can’t get on the internet though as I could have saved plenty of time for me in my own time.  My accountant told me not to pay myself anything for coming to work occasionally as it will complicate the funding with the tax man but someone told me that if you earn with a part time job when you are funded its tax free.  Sounds like I need to find out PDQ either way.  Anyway, I will now be behind with my assignment for last week’s lectures, and we have another week of lectures next week with an assignment.  We also have the same again the following week so I will probably have stacked up 3 unfinished assignments by then.  Added to the problem is that we have the odd week free to do assignments but they keep slotting in additional stuff then.  Like this Friday we all have to go over to Cambridge University again.  We are not sure what for but someone thinks it is a kick off meeting with their students to organise a student lead Conference next April.  Anyway, I guess that we will find out when we are there but maybe we could have done a little research before we went if we knew.

Still having trouble with administration, having to jump through hoops several times to get things sorted, but finally got my funding so it should be automatic each month now.  They are still inventing unimaginable and exciting ways to challenge us.  I had an email saying that my registration time had been extended by a month.  I emailed back to say that I had registered, I had a student card that lets me in everywhere, I have been paid registration fees and now funding, what did the mean and what do I need to do?  I had an email back saying that I “had only been registered for 11 months and this is a year’s course so I need to go to security to have my student card extended”.  Wow, that one must have taken some imagination.

Although we were exhausted, we quite enjoyed our Matlab for beginners 2 day course.  In fact I wish I had done it at the beginning of my last MSc as it would be so useful with all the matrix manipulation we were doing on that course.  Matlab can handle matrices with dimensions of millions by millions if necessary.  It was developed by an analyst called Cleve Moler using Fortran who found it was inadequate to manipulate matrices in the 1960’s.  The main competitors are “Python” that came from an object orientation background and “R” which came from a statistical background.

Venkat Sastry

Before joining Cranfield University in 1989, Venkat was a Lecturer at Plymouth Polytechnic having been appointed in 1987 following his work there as a Post Doctoral Research Fellow.


I was very pleased when the lecturer asked us for a group photo to put on his website, saved me taking an unofficial one.



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Matlab students 2017

Precision Engineering

B40A very full week this week with very little time to work on our previous assignments from Cambridge University.  All week is 9am until 5.30pm but most lecturers ran over eating into our breaks and lunch time.  We are only scheduled 45 minutes for lunch anyway which is not normal for Universities.  Two days we couldn’t even buy sandwiches so survived on cakes and tea.  Its even difficult to buy tea as Building 40, where all the lectures are this week, is only close to the Stafford Cripps Building that has Costa Coffee which is not only expensive but, more importantly, takes forever if you have a couple of people in front of you.

Dr Paul Morantz

Paul Morantz, the top man in Ultra-precision Engineering at Cranfield University took us for the majority of our lectures this week. Cranfield University which is the only University in England that only has only post graduate students and therefore is comparatively quite small. As a result, they have as many staff as they have students.  This ratio is as good as any top cruise line and it surprises me why we don’t have a similar service.

boltzmann-acoustic-resonatorPaul started by talking about some of the prestigious projects that Cranfield have been involved with, that I wasn’t aware about.  They have made so many mirrors for the best telescopes in the world, I could hardly believe it.  When Paul took us around the ultra-precision engineering laboratories, it was a feast for the eyes, but you are not allowed to take pictures.  There is one part that Paul designed and made for the project with NPL to modernise temperature using the Bolzman acoustic resonator method,  that was beyond belief.  It is around 100 mm diameter sphere with holes, that sensors are inserted into that will change one of the 7 fundamental SI units next year.  To do this, the sphere had to be made to an accuracy of 1 nm on its internal diameter.  How is this possible?  That’s about 10 atoms accuracy over 100 mm.  Paul has held dozens of world records for accuracy over about 3 decades.  He has unbelievable knowledge and experience which became more and more evident with every lecture he gave.  We found out that Paul will be leaving Cranfield in November so won’t be able to mark our assignments for this week.  I caught him outside to ask him where he was going but was amazed to find out that he was being made redundant.  Since our interviews, he was as shocked as me, to find this out.  Whet a massive loss for the University and for us for the next 4 years. “WTF”.


We had our first lecture from Claudiu Giusca, Tuesday lunchtime about Calibration.  He was so enthusiastic about his subject as he had been working for NPL but I found it hard to hold concentration for more than 10 minutes.  We had Saurav Goal again first thing Wednesday morning talking about single point diamond turning which I found much more interesting.


Because diamonds are anisotropic, they can only be polished in a certain direction.  Also, water is a better coolant than oil based coolants with diamonds.  When diamond turning, its possible to take 1 nm cut off with each turn.  Obviously, this makes the progression time very slow.  Who would have thought that turning would beat lasers and ion beams hands down?

The Chinese guy in our group that I call Hugh because I cant pronounce his name, or even remember it.


Other than Paul Morantz, we only had Xavier Tonnellier talking about abrasive processes  and Renaud, talking about non-conventional machining processes on Thursday. I was surprised to hear that Kodak were first to produce and develop a plasma ion beam.  This is Renaud’s specialty.


The final thing on Thursday was the group presentations that we only had a few hours to prepare.  Also, they split groups up randomly, with 3 or 4 to a group.  Our presentation was about the current state of ultra-precision engineering.


They seem to be so keen on embarrassing us this year, as we had another impromptu presentation on Friday where we only had about an hour to prepare. To make things worse, we were allocated what we would be talking about when the presentations were made.  We hadn’t time to research our subject, so it was done while we watched other groups presenting.

Our group

The big German refused to help and the Chinese guy did his usual shrinking so poor Marta got up on her own.  I couldn’t leave her to do it on her own so I got up with her, even though I hate this sort of thing.  I know that they hit you hard at the front end of MSc type courses, but I’m not sure that I am really enjoying this as it much too frantic.


I spent very long hours working on the Cambridge assignments at the weekend but I am nowhere near finishing while writing this on Sunday evening, while watching the USA GP with a drink.  They must be in by Tuesday evening, and we have lectures Monday and Tuesday so I have set my alarm for 4am in the morning.  The only other time I have is after lectures Monday evening or at 4am Tuesday morning.  Happy days!  Maybe I’m getting too old for these silly games.