Nano in your Daily Life

Nano became a major trending label in the beginning of the 21st century. Nowadays, you see socks, packages, food, cars, mp3 players, etc. labeled with nano. Nano sells! I want to show you what’s the science behind some of the major nano labels. For this, let me first describe to you very quickly what nanoparticles are and why they are so beneficial.

What are Nanoparticles?
Nanoparticles are small structures with a diameter of 1-100nm. At this length scale, some materials have different properties than in their bigger bulk material. Because these particles are so small, the surface area per volume is much higher. Most reactions usually happen at the surface of a material, therefore, a higher surface area means more reaction happening. Nanoparticles are actually not an invention of the modern world. These particles were around since a long time. However, nowadays these particles are trending and a good selling label.

What are Socks with Silver Nanoparticles?
There are many brands who offer socks enhanced with silver particles. But what exactly do these silver particles do? These silver nanoparticles can kill many different types of bacteria and therefore the smell from your socks. Silver nanoparticles are not only added to the fabric of socks or underwear, but also to food packaging, cosmetics, tooth brushes and even bandages.

Why add Titanium Dioxide to Sunscreen?
Most of the available sunscreens contain titanium dioxide nanoparticles (TiO2) or zinc oxide (ZnO). These specific nanoparticles are added to sunscreens as they block ultraviolet (UV) light very efficiently. Usually, the higher the blocking factor of your sunscreen, the whiter the sunscreen appears. However, if you shrink the size of titanium dioxide to the nano size, these particles are transparent and can therefore be added to light sunscreens without the thickening white effect.

Are Nanoparticles dangerous?

There is a strong debate whether particles are harmfull to your body or not. Many believe, that due to their small size they can enter into parts of your body, where you do not want to have any other materials. One can not say that nanoparticles in general are dangerous, as these properties differ very strongly among different types. There is a lot of research going on to measure the effect of nanosized particles to our bodies and environment. But don't worry, most countries have very strict regulations about putting nanoparticles into the market. 

Writing with Atoms

How can you see single atoms?
Atoms are the building blocks of every cell and every material. An atom is only about 0.3 nm in diameter. To “see” these atoms, you have to use special microscopes. The most famous one, is the AFM (Atomic Force Microscope), which I briefly described in my first post. This technique basically feels the atoms underneath it with a very very sharp tip, ideally so sharp that there is only one atom at the tip. The tip (called cantilever) is scanning slowly over the whole surface and creates a topographical image. Below you can see salt at atomic resolution. Each "dot" is one single atom, isn't that just amazing?

Salt (NaCl) atoms under an AFM.
The frame size is 5nm.
(Image taken from: Jessica Topple)

Who wrote with atoms first?
The first amazing demonstration and milestone of modern nanotechnology, was the fact that one can write and manipulate single atoms. This was first archived by Don Eigler from IBM in 1989. He successfully managed to arrange 35 Xenon atoms to write the famous letters "IBM" (see image below). This was realized with an STM (Scanning Tunneling Microscope) tip. An STM works very similar to an AFM, the main difference is, that the tunneling current between the tip and the sample is controlled and kept constant. With an AFM, the force between the atoms are measured therefore it works on non-conducting materials as well. 

IBM logo with 35 Xenon atoms. (Image taken from IBM) 

How do you write?

Don Eigler, who was the first to ever write with atoms, used an low-temperature ulta-high vacuum (UHV) system (check out my other post on Extreme Science). This system is required in order to have a super clean environment with no other disturbing atoms and to reduce the vibration of the atoms by lowering the temperature. The trick now to move an atom across the surface is to get very close to the atom with the STM tip. At some point, a positive van der Waals attraction between the atom on the tip of the STM and the atom to be moved is created, the atom is attached to the tip. Now by keeping this distance short, the atom can be moved to a different location. Once at the correct position, the STM tip just needs to be moved away from the atom and it stays put. In only 22 hours, the first IBM logo written with single atoms was created.

Why is it important?

First of all, it's fun and amazing! Second, it was the first ever approach for nanometer scale manipulation. Third, you can now move atoms to where you want them to be to create new structures.

Since then, many more universities, institutes and companies all over the world created atomic sized versions of their logo. Here are some cool examples:

Image by: NIST, USA

Image by: Technische Universität München, Germany

Image by: University of British Columbia, Canada

The Wonderful Adventure of a Small Little Tiny Drop

What is microfluidics?
As explained in my first post, nanotechnology is all about reducing size and discovering new phenomena. Scaling down the volume inside a channel filled with water is no exception to this rule. Microfluidics is all about fluidic structures with a volume of about 1 microliter (as a comparison: one drop of water has a volume of approximately 60 µl). One main characteristics of microfluidics is that inside the channels, there is a so called laminar flow. This means the flow is not turbulent like we usually see a water stream. If you turn on your faucet and water flows out, you’ll see a lot of turbulences, this doesn’t happen with microfluidics. It’s incredible hart to mix two fluids in a microfluidic channel, as can be seen in the image below. Although different colored food-dye runs from separate channels into one big channel, it does not mix, it rather flows side by side. Mixing only occurs after a while due to diffusion. This main phenomenon of microfluidics can be tricky to handle, but also super useful.

Turbulent (left) vs. laminar flow (right)
(Image by: J. Schulze and D.B. Weibel)

How do you design a microfluidics device?
The most common material used for microfluidics is a polymer called polydimethylsiloxane (short PDMS). It is a viscous solution and will harden upon placing into an oven. Lets discover how you can create a simple channel (0.05 mm wide, that's 50 µm) with an in- and outlet. First, prepare a master mold of your structure to pour the PDMS into. This is done by spin coating a thin layer of a photoresist (which is a lightactive solution which will harden upon illumination) onto a wafer. Next, a photolithographic mask of your desired channel structure is illuminated onto the photoresist. This will harden the desired structure. The rest is washed away and one is left with a negative of your channel. Finally, PDMS is poured onto the master, cured in the oven and simply peeled of your master. Punch two holes into, one for your in- and one for your outlet. Because the channel is open on one side, the PDMS is bond to e.g. a glass substrate and you're done It's that simple!

Taking it to the next level
Because it can be that simple to fabricate a microfluidics structure, several people are using microfluidics to handle small sample volumes, reduce costs and be able to fast fabricate these devices. Several applications do exist on the market or are promising candidates for market ready device. Most of them are in the field of biosensing. As explained before one can detect a disease in a smaller volume more easily and most importantly less costly. However, microfluidics devices do not only have one straight channel and that's it. Rather it can get really complex. You can integrate all sorts of features like pumps and mixers. Hundreds of in-/outlets, valves and channels can be integrated into one microfluidic chip.

Valve in action, closed position (left) and
open position (right)

What is paper microfluidics?
One really awesome application platform is the so-called paper microfluidics. These devices are simply made from paper, no PDMS, no glass etc. On a paper the outer lines of your channels are printed with a hydrophobic solution, i.e. liquids will avoid these areas and therefore stay within your desired channel configuration. One of the first of these structures is shown in the image below and used for glucose testing for people having diabetes. These devices are easy to use, disposable and very cheap. More and more applications are coming out of these paper based microfluidics, like body-on-a-chip, lab-on-a-chip and organ-on-a-chip devices (which I will cover in more detail in one of my next posts).

Paper microfluidics to test the glucose level in urine
(Image by: Whitesides, Harvard)

Microfluidics meets art!

Now sit back and enjoy these beautiful microfluidic art pieces. Doesn't they look just amazing? Science can be so great.

Images taken from (in order top to bottom): 

Albert Folch, Michael Roukes, Stephen Quake, Albert Folch, Ann-Lauriene Haag

Extreme Science

Why do we care about ultra, micro, high and fast?
Science is trying to push human knowledge a bit further every day. In science you can find people working with extreme conditions to push these limits and gain an even deeper knowledge about fundamental science. To be able to know what happens in fundamental processes, you have to push these limits. Here, I want to walk you through some of the main extreme sides of research in physics and try to explain why we care about them.

Nano 
As this blog focuses mostly on nanotechnology, let’s start with that extreme. Trying to work on smaller and smaller length scales opens up a whole new dimension and possible discoveries. Why? If you want to study or manipulate single atoms or molecules, you have to work in the nano scale, which is a hundred thousand times smaller than the width of a hair.

One of the four huge detectors at CERN. In the centre
is the actual beamline (image: CERN). 

High-energy
One of the most famous example of high-energy physics is the large hadron collider (LHC) established in 2008 at Cern in Geneva, Switzerland. This massive huge ring underneath the surface is accelerating protons, the positive charged particles in an atom, to energies up to 7 Teraelectronvolt. The energy is so high that two protons are accelerated in the ring to almost near the speed of light, to be precise it's 99.9999991% of the speed of light. The protons travel in opposite directions in this ring and at some point they collide. Detectors like the one in the left image are recording these collisions. Why? The purpose of the LHC is to discover new particles. Once the two protons collide, they will break into smaller particles  One specific particle, the Higgs-Boson is of special interest, as this is supposed to be the particle giving mass to all other particles.

Low-Temperature

Many experiments on single atoms are performed at low temperatures. Temperature is a measure of how fast atoms move. If the temperature of e.g. water is above 100°C it will boil, the movement of water molecules is so strong that it will become a gas. If the temperature is below 0°C, the atoms do not move that much anymore and ice is formed. The absolute zero for the temperature is -273.15°C (or 0 Kelvin, the temperature unit system used most commonly in science). At this temperature, atoms do not move any more. However, it is really difficult to reach this zero value. Most low-temperature experiments usually run at the milli Kelvin scale, which is 1000 times colder than 1 Kelvin (-272.15°C), so already pretty cold. Why? Because the atoms almost do not move anymore, you can measure them very precisely. It's like taking a picture of moving object, it's so much easier to take a sharp image of still objects. You can study quantum mechanical effects e.g. to better understand how to improve quantum computers. 

Typical UHV set-up

Ultra High Vacuum (UHV)

In my last blog, I talked about cleanrooms. An UHV system is like an even better cleanroom on smaller scale. However, you can not enter a UHV system, as there is almost no air in there, only the samples are inside. For a vacuum in the range of 10^-11 mBar, one atom has to travel for about 7000 km to collide with another particle. In practice, one atom is hitting the wall of the chamber much earlier than any other particle. It’s amazing how few atoms are in the whole system. It is also amazing to see how these UHV systems look like. Usually, you'll find a UHV system covered with a huge amount of aluminium foil and cables hanging everywhere. ;-) Why? In a UHV system, one can study atomic structures without ANY other unwanted particles. As explained before, it's like the ultimate cleanroom. 

If you want to know more about these individual techniques, subscribe to my blog. See you soon. 

Quantum Computing 101 - Part 1

“I think I can safely say that nobody understands quantum mechanics.” - R. Feynman (1965)

The strange and wonderful world of quantum mechanics will be the main topic of my first series of blogs. First, I’ll start off with quantum computing, followed by more general topics in quantum mechanics like Schrödinger’s cat. But first, let me start with some basics.

What is the difference between a “normal” computer and a quantum computer? Computers nowadays are based on transistors and handle information using binary bits. These bits can have values of either 0 or 1. Every text or image file is encoded using only 0 or 1. In contradiction, a quantum computer operates using so called qubits (quantum bits). A qubit must have two states, 0 or 1 as well. However, in addition they can also be in a superposition of both, that means in both of them at the same time. You could think of a qubit as an electron. An electron is rotating along it’s axis, which is called spin. The electron’s spin is either directed upwards (spin up) or downwards (spin down). The up or down state is now acting as your 1 or 0. As previously explained, this qubit can also be in a superposition of both.

Why are quantum computers so powerful? The principle of superposition can be scaled with the number of qubits. A computer with two qubits can be in a superposition of 4 states, whereas a classical computer can only be in one of it’s 4 possible states. Because qubits can be in a superposition of both states, the state is rather presented by a probability. There is a certain probability you can find the electron in either of these states. With that you can enhance current processing speeds enormously.

Are their any commercial applications of quantum computing yet? In 2011, a canadian based company, called D-Wave started selling the first commercially available quantum computer. It features a 128 qubit processor which is housed in a cryogenic system. Earlier in 2009, Google demonstrated the use of D-Wave’s technology for image recognition. This brings us a big step forward, however, with a cost of $10,000,000 it’s still a bit pricy for the everyday use.

What is a cleanroom and why do you wear these funny white overalls?

Ever wondered how your cell phone camera sensor is build or the processor in your computer? These tiny but incredibly powerful sensors are fabricated in clean rooms, or so called fabs (short for microfabrication, the process done in cleanrooms). What is a fab? Its not just a room which is being cleaned often. You can not just enter this kind of room without preparing yourself for it. In principle it is a room which has way less dust particles in the air than every other room. In the average environment there are about 35,000,000 dust particles flying in 1 cubic meter. However, if you enter an average fab, there are only 3,500 particles in the same area! In high class fabs you will even only have about 35 particles in 1 cubic meter. Some of the questions that I'm trying to answer in this post are, how do you get rid of all the dust, how do you keep it clean and most importantly why do we need fabs in the first place?

Why? Clean rooms in general are used to manufacture small, complicated and delicate sensors, e.g, CMOS chips (the camera sensor in your cell phone), gyroscopes (the thing that makes your screen turn on your cell phone) or computer processors. All of these sensors feature very small parts and electronic circuits. These tiny structures are usually only a few micrometer or even smaller in size, some features are in the nanometer scale, current processors have 22 nm features. The sensors are fabricated on single crystal silicon wafers, which are round thin plates with a size of 4 to 12 inch. Multilayer coating, etching and developing steps are done to fabricate these sensors. Several dozens or hundreds of sensors are fabricated at once on one of these wafers and are cut afterwards. Due to the fact, that these chips have small features one dust particle alone can block a channel, gap or pixel in the case of the CMOS. The whole chip can be ruined afterwards. Therefore, the fewer particles in the air, the better the yield from one wafer and the lower the cost.

How to achieve a clean environment? Clean rooms are expensive facilities used in industry, research facilities or universities. The basic idea of a clean room is to have a constant air flow coming from the ceiling going straight down to the ground. In high end fabs, the floor is made from tiles with tiny holes, so air can flow through. This way any dust particles which happen to flow in the air are forced downwards and will be sucked by the ground. Another method is to suck the air from the sides in the floor. Of course, the air which is blown from the ceiling needs to be filtered first, so no particles are blown in the room at the first place. Once you have a clean environment, several procedures need to be taken to maintain the cleanliness. The air flow in the fab is crucial, therefore you shouldn’t move too fast in a fab, as dust particles on the floor might be whirled up. 

What are the precautions to take before entering a clean room? Humans bring in most of the contamination into a fab, all the dust from your clothes will ruin the clean room. Therefore, you need to wear a hairnet, a mouth protection, a hood, gloves, shoes and a protective overall. Depending on how 'clean' the clean room is, you’re now ready to enter the clean room. However, if you’re about to enter a class 100 fab (cleanroom category indicating less than 3,500 particles per 1 cubic meter), you need to do much more than that. Intel e.g. has a 42 step protocol on how to enter a clean room. One of these steps is to drink a glass of water before entering the fab to clean the throat from any dust, incredible right? Additionally, regular paper, make-up and mechanical pens are not allowed. Some fabs also have a small room which you have to enter first in which all excess dust particles on your body will be blown away by strong air nozzles, it’s like taking an air shower to clean yourself. This is how you might look like before entering a cleanroom. The picture on top shows my brother and me inside the clean room facilities at the Kavli Nanoscience Institute at Caltech, USA. 

Why do most clean rooms look yellow? One main procedure done in fabs is to perform photolithographic steps. It’s similar to taking pictures and developing them in a dark room. However, the wafers will be coated with a photoresist first, which is a light sensitive liquid. Subsequently, a transparency mask with your desired features is laid on top of the wafer and the wafer is exposed to light. Depending on the type of photomask the photoresist will be hardened. Afterwards, you can develop the wafer and the uncrosslinked photoresist will be removed. As the photoresist is light sensitive, yellow light is installed in some parts of the fab, because the photoresist is only sensitive to white light and will not develop under yellow light. 

Overall, clean rooms are awesome and very useful. Without them, we wouldn’t be able to fabricate better, smaller and faster processors. 

What is ‘Power of Minus 9’?

Power of Minus 9 is a nanotechnology blog which explains the beautiful, mysterious and inspiring world of life in the nano-scale and beyond. This blog intends to explain current nano-related topics to the curious, anxious, attentive future nerds and all others. I want to show you how awesome science can be. 

So, what exactly is the name ‘Power of Minus 9’ referring to? It is an allusion to the scale of a nanometer (nm), which is a billionth of a meter and in scientific terms written as 1*10^-9 m, which is 0.000000001 m, a loooot of zeros. This scale is really small, e.g. an atom has a size of 0.1 nm, only a tenth of a nanometer. Amazing, isn’t it? To show you how small a nanometer is, imagine a hair, which is roughly 0.1 mm thick, now cut it into 100’000 pieces then you end up with hair pieces that have a thickness of 1 nm. It’s like looking at stars, but the other way around. Instead of looking extremely far away, you’re looking to the other side of the scale, extremely zoomed in. 

What is all the hype about nano then, except that it’s incredibly small and hard to see, feel or imagine? Well, if you are dealing at this scale, you are trying to understand what single molecules, atoms and cells are doing. Quantum effects play an important role as well, particles do not behave like we used to know anymore. They start to exist at two different places at the same time, a lot of weird stuff is going on down there. Useful applications result out of nanoscience as well, like designing new electronic memories built out of single atoms to enhance performance and decrease size. A more futuristic idea is to fabricate a nano-sized small robot which navigates through your blood system and repairs the human body from the inside.

Principle of Atomic Force Microscopy (AFM). The cantilever scans over the surface. Due to forces between the atoms the cantilever will bend and a topography map is created.

What’s different about this scale is how to ‘see’ what you’re dealing with. With a microscope you can’t visualize single atoms; the resolution is by far not high enough. However, there exist several techniques, which allow you to see what atoms look like and are what they are doing. One of them is Atomic Force Microscopy (AFM). It’s a very powerful tool and actually a quite simple technique. You take a cantilever made of silicon, which looks like a long arm attached to a base. At the far end of the cantilever is a tip shaped like a pyramid. Ideally, this tip is very sharp with only one single atom at the end. The tip scans over the surface and senses individual atoms underneath. If there is a valley or a hill, the cantilever will bend towards or away from it. With a laser, which emits light onto the cantilever, the movement can be detected and a topographic map is created (see image). The AFM was invented in the 80s and opened the door to the nanoworld, as this was the first tool to imagine non-conducting surfaces at the nanoscale.

This blog will explain and discuss the latest development in the broader field of nanotechnology, trying to answer questions like, what does a quantum computer do? How does your cell phone camera works? What is a brain chip? What’s up with nanofluidics? and many more. Getting curious? All of these questions will be clarified in a simple but challenging way, so that everyone can have a piece of the awesome nano-cake. If you’re interested in a topic, leave me a comment and I will try my best to cover this in one of my next posts.