How to Win a Car Race at a Nanoscale
Scientists from the University of Basel won the first nano car race in the world using a small molecule propelled by a scanning microscope tip.
The term ‘car race’ usually induces images of long race tracks, incredibly fast cars and racers risking their lives. However, there are other, way cooler, ways of racing cars.
A few weeks ago, a fascinating race took place in French Toulouse (CNRS’s Centre d’élaboration de matériaux et d’études structurales, CEMES). To spot the race cars was kind of hard though since they were only about 100 atoms in size. And instead of racing on kilometers of asphalt, the so-called nano cars competed on a golden race track that was 100 nanometers long and included turns and obstacles.
In total, six teams from three continents entered the race. The drivers were supposed to move their tiny car along the race track, using the electrons flow from the tip of a scanning tunneling microscope (STM). Each interval took about one minute and moved the vehicle forward for approximately 0.3 nanometers. The race, therefore, took a staggering 36 hours to complete.
What about the winner, you ask? First place was awarded to a Swiss team from the University of Basel with the two drivers Dr. Remy Pawlak and PhD candidate Tobias Maier. Their nano car, dubbed the Swiss Nano Dragster, finished 133 nanometers in 6-and-a-half hours.
Putting the knowledge to work
“We already had experience in manipulating molecules on surfaces. When we heard about the competition, we thought we had a good chance to win it,” says Tobias Maier. “The racing as such is not an entire research project, but I will dedicate a chapter in my PhD thesis on it.”
The competing scientists had to prove their ability to move molecules on a gold surface. One of the biggest challenges was to move their systems to another location. What worked fine in one’s home lab now had do be replicated in a different setting. Molecules had to be moved to France, and a different STM had to be used. In the course of their preparation, the Basel team went to France twice before the actual competition. They also spent an entire week in France before the race getting used to the new conditions, finding the right parameters and making all the necessary preparations.
“Had we been able to run the race on our own system, the outcome would have been even better. Although the physics and chemistry are the same here and in France, many variables are affecting such a delicate system,” explains driver Remy.
The race consisted of two 45 degree turns separated by straight sections aligned with obstacles. To win the race, good teamwork is necessary. The pilot steers the car by operating the tip of the STM and thus manipulating the molecule on the surface. The second team member is the navigator and tries to calm down the driver. “You need to be in tune with each other; otherwise you end up yelling a lot,” adds Remy.
Several car crashes
“We had several car accidents, four times actually,” laughs Tobias. “Twice the molecule jumped to the tip and disappeared. Twice we crashed the tip of the microscope into the surface.” Luckily, every team was allowed to change their car in case of an accident.
“Two days before the race, we cleaned our portion the course and placed our extra cars along the track so that we would have spare ones in case of crashes. If we lost a molecule, we could simply take up another one and continue the race,” explains Remy.
The official rules of the competitions were the following:
- The racecourse: 20 nm + one 45° turn + 30 nm + one 45° turn + 35 nm, for a total of 100 nm
- 36h maximum duration
- Authorization to change one’s nano car in case of an accident
- Pushing one’s nano car is forbidden
- One sector of the gold surface per team
- Maximum 6 hours to clean one’s portion of the course before starting
- No tip changes allowed during the 36 hours
Beauty isn´t everything
The winning Uni Basel team raced with the smallest molecule of the competition. The molecule was designed by the chemistry research group of Prof. Catherine Housecroft at the University of Basel.
“The molecule was chosen because of its interactions with the surface. Other teams, mostly chemists, were thinking more about the design and the looks of the molecule, not necessarily thinking about its properties to move it using the STM,” adds Remy.
The competition rules originally stated that the molecule had to be larger than 100 atoms. The rules were later changed, and smaller nano cars were allowed to participate. The winning team used a nano car made of only 43 atoms.
The bigger molecules might have been prettier and evoked the picture of a real car, showing wheels or even a chassis. In the end, looks didn’t count, and the car-like larger molecules ended up not moving on the surface at all.
“There were only two molecules larger than 100 atoms. The problem with a large molecule is that you also need a big engine. You need to find a way to have proper propulsion for your molecule,” says Tobias.
“It is a lot about the molecule; our idea was to have one point that is fixed to the surface and that we can manipulate. While the rest of the molecule is not connected to the surface to reduce friction,” adds Remy.
Trophy is just the beginning
The long preparations and good teamwork brought a beautiful trophy to the lab at the Department of Physics in Basel. The award will be placed next to the STM that was used during training. But a cool trophy is not the only outcome of this “nano-journey”:
“Manipulation of molecules is significant, as it could allow us to build structures. For instance, in Toulouse the plan is to manipulate single molecules and use them to create nanotransistors consisting of only one molecule,” explains Remy.
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