Author: Arturo Rodríguez

Posted on by Arturo Rodríguez

How does a Scanning Tunnelling Microscope (STM) work?

How do microscopes work?

Each type of microscope uses different ways of obtaining information from the sample they are studying. Classical optical microscopes use light to probe the samples, this of course has its limitations, as light is just visible between certain wavelengths. This means that just objects slightly smaller than those wavelengths can be observed with them, setting the minimum observable distance with them at around 200 nm. Therefore, with this kind of microscopes we can study cells or other biological systems which are bigger than this distance, but we cannot obtain information of  smaller things such as atoms.

But what if we want to observe these smaller things? One possible solution for that is using particles with smaller wavelengths as probes. This typically means using more massive particles, as the wavelength decreases when the mass increases. One of the easiest ways to do that is using electrons as waves, the microscopes that do that are called electron microscopes, and the most used ones are transmission electron microscopes (TEM) and scanning electron microscopes (SEM). With this kind of microscopy, it is possible to resolve objects down to around 15nm (High resolution TEMs (HRTEM) can reach 0.05 nm under very special conditions).

But there is another big family of microscopes. This is the scanning probe microscopy (SPM) family, to which STM belongs. All the techniques inside the SPM family are characterized for approaching the tip of the microscope to the sample to obtain information from it in different ways and then scan with it to form a complete image. Every technique inside this family uses different physical properties to work, and the property that STM uses is the quantum tunnelling effect (hence the name). With STM, features smaller than 0.1nm can be resolved horizontally, and 0.01nm features regarding depth. These values are especially useful as atoms have a typical size of around 0.3 nm, which means that STMs can achieve atomic resolution.

Figure 1.- Worm studied with SEM

The quantum tunnelling effect

STMs use the quantum tunnelling effect as their principle of operation. This is a purely quantum mechanical effect that allows a particle to go through a potential energy barrier. If we make a comparison with the classical day by day world, it would be as if someone would go through a wall as a ghost, without interacting with it. This effect is related with the wave properties of the particles in the nanoscale, and the probability of it happening decreases the thicker the barrier is (the thicker the wall is for the ghost) and the bigger the particle is. What kind of particles are we talking about then? Well, some of the smallest particles that we humans know how to work with are electrons, so those will be the particles used in our STMs. And, what is a barrier for these electrons? A barrier is anything the electrons can’t go through. That can be an isolator such as plastic or wood, or in this case, the absence of anything, the vacuum.

If we apply a difference of potential in a wire, the electrons should be able to travel through it. But if we then cut the wire in the middle, the electrons will stop flowing from one side to the other. We will no longer have a current. The quantum tunnelling effect tell us that if we now put the two extremes of the wire really close (less than one atom of distance from one another), the quantum properties of the electrons will allow them to “jump” from one wire to the other quite often. The electrons will “tunnel” through the empty space and will reach the other cable, and the movement of electrons is a current, so then we will observe a current in our basic circuit even though it is not closed. As we know that the probability of tunnelling decreases when the barrier increases, if we separate our wires a little, the current will decrease, and if we put them closer it will increase. It will reach the maximum current when the wires touch, when we will observe the normal current that we had when the wire was not cut.

Figure 2.- Classical particles need enough energy to go over the barriers, quantum particles can go through the barriers instead.

So how does a STM work then?

Let’s imagine our theoretical circuit already cut in the middle. The only important things here are the wires and the gap in between them. The wires are made out of metal and the gap is made out of nothingness. Perfect. Now we want to see tiny things with this setup, so the first thing is choosing what we want to see; that’s the sample. The sample is going to be attached to one of the cut sides of the wire, which makes of it just the new end of the wire as it is also metallic. Then we take the other cut side and we sharpen it. We sharpen it the best we can until the very tip is just one atom thick; this is our tip. If we now approach the tip and the sample we will get the same thing that we got before with the two cut wires: some current going through due to the tunnelling effect when really close, but there is a difference, our tip is now one atom thick. This means that if we now move to the side we can observe the current in a different atom. We can keep moving the tip sideways keeping it at the same distance of the sample all the time (this means making sure we let the same current go through the vacuum), but sometimes the sample will have holes (so we will have to approach the tip) or mountains (so we will have to retract the tip). If we keep track of how do we have to move the tip to keep the current constant, we will get lines of the topography of the sample! If we stack several lines of the topography, this is, if we scan the surface of the sample, we will get complete three-dimensional images of the sample!

Of course, all the details about how to keep the wires so close without touching, how to move the tip sideways, how to read the currents, etc. are complex issues that require high level engineering to be solved, but those are not the things that explain how a STM works. Many other things have to be done to properly obtain images out of these microscopes, for example, due to the close distance between tip and sample, it is necessary to have damping systems in order to decouple the microscope from any kind of vibration that could crash the tip into the sample.

Figure 3.- Monoatomic Iridium step edges and terraces observed via STM. Size of the image is 300x300nm.
Figure 4.- Closer look to the Iridium surface showing individual Iridium atoms arranged in a hexagonal structure. Some defects can be seen in the sample.

References:

Figure 1: Philippe Crassous / FEI Company (www.fei.com)

Figure 2: https://cosmosmagazine.com/science/physics/quantum-tunnelling-is-instantaneous-researchers-find/

Posted on by Arturo Rodríguez

How to be a NERD as a self-preservation technique in your PhD (or other stressful situations)

Sometimes being in a continuously intense environment such as doing your PhD in a country you are not familiar with, where they speak a language you don’t understand, with no friends in the beginning and while learning a new complex job, can be too much to bear with. Sometimes you just need to do something new, something manageable, something in which you can choose how much do you want to invest yourself. But, what can that thing be? That thing can be anything, but it is supposed to help you escape the dark days, and if possible, maybe help you make some friends. Some examples can be learning to do pottery, hypnotism, programming in Arduino, learning about history or a new language. Maybe you are more into crafting, then crocheting or cosplay building could be your thing. Perhaps you have always wanted to learn about the role-playing games that you have seen in movies such as Dungeons & Dragons (DnD). Well, whatever rings your bell, this is your call to do it.

Ok, this is a tutorial to become a nerd. But, what is a nerd? Well, the official definition of nerd is: A person who is extremely enthusiastic and knowledgeable about a particular subject, especially one of specialist or niche interest. That means something that most of the people forget; everyone is a nerd. Your aunt, the one who is a football enthusiast, is a nerd (of football), whether she likes it or not. Your cool cousin, the one who is into cars and rap, that guy is a clear nerd of (surprise surprise) cars and rap. Does your mother know everything about the Kardashians? Nerd. Is your father obsessed with knitting? Nerd. Can your brother in law talk for hours about politics? Neeeeeeeeerd.

And why would you want to be a nerd? Easy, being a nerd grants you the opportunity to have something you like always present in your mind. As it is something you really like, it will help you with the bad times while making you better at it. It will be like a safe place that you are always carrying around.

Now that we have stabilised the basics, let’s see how to become a nice, beautiful and healthy nerd.

Me, a nerd. This is what the media wants you to believe a nerd looks like, and eventhough I do look like that in this picture, I swear it is just for educational porpouses only.

Step 1, Choosing. – What topic do you want to learn? As said before, it can be anything, but if you are in a new environment, I recommend something that can help you to make friends. It is important that you feel really some kind of interest about it. It can be that you find it cool, that you always wanted to know more about it, or that you want to check why people talk so good about it.

As an example, let’s say you have heard about DnD. Maybe you have a friend who plays it. Maybe this post encourages you to do it. Why don’t you give it a try?

Step 2, Resetting. – Forget about any preconceived ideas you have about a topic. Just focus in how awesome something would be if it just worked, if you just would enjoy it with your friends. It is cool because you chose to do it! Who is going to come and tell you that this new hobby of yours is not good enough? Good enough for whom? It just needs to ring a bell for you. We are here to be nerds, because nerding rocks!

We will focus in the playing DnD example. You may start asking yourself what exactly DnD is. Well, maybe you are not sure, but you see that the people that play it are usually committed to it. They seem to have a lot of fun that comes from nowhere for an external observer. And they usually play with their friends, or make life lasting friends while playing! So instead of judging that from the outside, know that you can be one of them easily, you just need a little of context to start.

Step 3, Researching. – How do you do whatever you have chosen? Well, this part is when the fun begins. You are going to learn. But you are going to learn at your own pace, do not stress. Internet has introductions, tutorials, and everything step by step just in the most common pages. Do you want more? Search for forums for already nerds in your topic or get a book about it. You can do many things about it today, but none in 3 days. Maybe you can read a chapter of a book about your hobby per day, or maybe you just can watch a youtube video in the train while going to work. No problems, this is for fun, you choose how you do it. In this step you should find out what kind of equipment you will need in your new hobby in case you need any, and maybe get ready to buy it or borrow it.

In the DnD example you could have a few talks with that friend that already plays the game. You can also check the DnD webpage or any kind of introductory video online. You could even start thinking about potential people that you think would be interested in playing with you, or whether or not are you going to buy the books. Do you want to see how the community is? r/DnD or r/dndmemes are great forums in reddit where you can find newcomers like you along experienced players.

Step 4, Action. – Time to start doing your hobby. You have the objects you need, you have gathered the people you are going to do it with… now, enjoy! It may be even cooler than you expected. Well, that’s because you are enthusiastic about it. Make sure you do it again tomorrow, or next week, that depends on the type of hobby. Now that you are doing it, you are allowed (and encouraged) to dream and daydream about it. Remember, we are here to get nerdy, not just to enjoy a hobby. We are here to enjoy the hobby even when we are not doing it. And what if you change a tiny aspect of the hobby? Maybe it gets better, maybe it is so different while still awesome that you now have two hobbies! That way you can become a nerd of 2 things! Great!

You just played DnD for the first time. It is great! You played with people from your work, and that way it seems that maybe you may end up being friends, not just co-workers. You did a nice character, it can do really impressive magic. “How will my character face certain difficulties that will arise in futures adventures?” you wonder the next day while eating. “Maybe I could fight the enemies, or charm them with my magnetic personality… or a spell…” you find yourself thinking while taking a walk in the park.

Step 5, Nerd. –  You are almost there, almost a nerd. Congratulations. You have already freed yourself from the chains of what is acceptable to be a nerd of. Now it is time to be proud of it. Don’t just think about what you love, show it too, share it, say it. If your aunt can watch her football match during the family meeting, why wouldn’t you talk meanwhile to your little cousin about your DnD session? Maybe he likes the idea of trying it too. You can buy t-shirts to show what you like to the people around you. Imagine if they would also like the same thing you do! You could share your hobby with even more people! Maybe doing it together, or just discussing about it afterwards.

After this step, you are finally a nerd, congratulations, you did great : )

Posted on by Arturo Rodríguez

Annweiler am Trifels- Part 1

Last week I had the chance to join the Skyrmionics Retreat in Annweiler am Trifels. Not long after arriving at my remote destination, I found myself in this peculiar scenery straight out of a novel by Agatha Christie: a group of elite scientists secluded in a forgotten mansion in the forests of the german frontier with France. The place took just one day to become completely isolated from civilization due to the strong winds and rains that seemed to be waiting for all of us to arrive at our final destination. And I say final because something was forever lost in the dark forests that now populate my scariest nightmares.

It all started as a normal workshop about skyrmions: we talked about skyrmions, we showed simulations of skyrmions, we said “Dzyaloshinskii–Moriya” several times, and different people showed micromagnetic simulations of skyrmions dancing, playing basketball and even one paying its taxes. Everything was going fine, but at that moment I got distracted and I didn’t see the evident danger. For several days we mixed all these talks and discussions with billiard games and more relaxed topics in the evenings. The isolated mansion had a full pantry, so we managed to eat plenty and we didn’t bother about the dark forest that surrounded us every night, every minute of our sleep, always wet, always rainy, always expectant…

[Part 2 will come soon]

The Path leading to the mansion before the rain started
Posted on by Arturo Rodríguez

The Fellowship of the Spins

Recommended music to listen while reading: https://www.youtube.com/watch?v=oWFEVbfCcOY&ab_channel=DurealFirali

It is known by all that at the beginning of the world it was Thales of Miletus the one and First Lord of the Magnet. Over the thousands of years that followed him, many others searched for similar powers and honours trying to understand the Great Power of the Magnet, and from time to time, succeeding. Some of these heroes and their circumstances have been long ago forgotten, others persist in the millenary legends, such as Shen Kuo, Leonardo Garzoni, Hans Christian Orsted or Gauss among many others.

The title of Lord of the Magnet travelled through borders and was inherited for honours and achievements for tens of centuries, until the Shattering of the Unshattered occurred near a hundred years ago.  The destruction of the Unshattered, the most basic piece of reality, plunged the world into chaos and instability. The pillars of reality crumbled under the heavy weight of a new, hostile and terrifying way of understanding nature. It was at that time when, for the first time in millennia, the title of the Lord of the Magnet was lost.

Not too long after the Shattering, remains of the Unshattered were found. Here we will not talk about these remains such as the Heart of Addition, or his sister, the Star of Subtraction. Not even about their guardian; the Neutral Peacekeeper, or other smaller pieces. Here we will talk about their essences. We will talk about their hearts, and about a part of them that defines what they are: here, we will talk about the Spin.

After the Shattering, with the disappearance of the Lord of the Magnet, thousands of false idols and corrupted prophets arose. Among them, some good men and women carried the remains of reality over their shoulders, and, with time and effort, unified the Spin as much as they could, for a future when a new Lord of the Magnet arrives. But times have changed, and maybe no more Lords of the Magnet will come, and maybe, no single person should ever bear this title again as there is no longer Magnet, but Spins.

And the remaining Spins have now been gathered, and they have been entrusted to us. And the ones who remember or dream about the great good times before the Shattering hope to see among us a new Lord of the Magnet. And we will not be that Lord, but we will wield its spirit together, like brothers and sisters, like a united hand where every finger plays its role for a greater good.

We will unshatter the Shattered. We will bring back the peace.  We are the Fellowship of the Spins.

Posted on by Arturo Rodríguez

Hamburg

Hamburg exudes moisture and breathes fog. It flows, as a slippery snake sweating in silence among its canals. Hamburg embraces you with its omipresent humidity in an eternal, soft and vaporous hug. From time to time, Hamburg smiles shyly through a distant sun, and reminds you that it loves you (what Hamburg really does).

At weekends, at night, a new river, smaller and warmer than the Elbe, appears. A human surge coming from everywhere leads to its burning heart which is Reeperbahn. The wetness is forgotten, and the fog becomes steam born from the skin of an incommensurable inexhaustible crowd. The next morning, as if it were a beach full of stranded mermaids, the Fischmarkt gathers the ones who have survived the night.

Hamburg walks slowly side by side with you, but it walks ruthless. It never stops, and it encourages you to do the same, as if this millenary city believed in you even more than yourself.

Hamburg is my new home. I didn’t understand the city when I arrived in August, and I have not understood it yet, but I want to, and I will do it. Every day that I live in this great city I learn something new, I grow as a person, and I become more aware of the city, the culture, the world and myself. I love Hamburg, I love where I am and what I am. And this is just the beginning.

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