The Nanocar Race Is

PRESS KIT I PARIS I APRIL 4, 2017

NanoCar Race, the first international molecule-car race

A CNRS event

Contact CNRS Press Officer l Alexiane Agullo l T + 33 (0)1 44 96 43 90 l [email protected] 1

Contents

The Nanocar Race is:

A catalyst for research ………………………………………………………………………………………………... 3 Experts in molecular engineering …………………………………………………………………………………... 4 The first steps of "atom technology" ………………………………………………………………………………… 4

Join the race!

A one-of-a-kind microscope ……………………………………………………………………………………...... 5 Why a racetrack made of gold? ……………………………………………………………………………………... 6 The process ……………………………………………………………………………………………………………. 6 The rules ……………………………………………………………………………………………………………….. 8

The organizers ………………………………………………………………………………………………… 10

The teams ………………………………………………………………………………………………………... 11

Resources ……………………………………………………………………………………………………….. 22

The Nanocar Race is:

A catalyst for research

The Nanocar Race—and associated development of nanocars—promotes research in synthetic chemistry, as well as the construction of increasingly high-performance microscopes and the control of molecule- machines.

Beyond the competition itself, every stage of the organization of the race, along with every nanocar synthesis and strategy for evaporation and propulsion, has already been or will be the subject of scientific publications, providing the physics and chemistry community with answers to unresolved questions in the field.

Researchers have thus had to contend with many unknowns; for instance, why do scanning tunneling microscopy images ensure the reconstruction of molecular orbitals1, thereby enabling the drivers to identify their nanocar instead of an unrecognizable jumble of electronic states? These questions are at the heart of the event, as nanocars cannot take part in the race without being properly imaged by the CEMES-CNRS scanning tunneling microscope.

Other questions arise: why does a quantum object such as a molecule-motor measuring 1.5 nm in diameter, behave in an almost classical2 fashion when it is placed on a surface? Can this motor run in only one direction? How can the engine power of the molecule-motors that equip each nanocar be measured and calculated?

Inelastic phenomena, in which a very small proportion of the total electrons transferred relinquish a few quanta of energy to the nanocar (thus enabling it to move forward or turn), are very little known. This is one of the challenges of the Nanocar Race, as each participating vehicle must be propelled using such phenomena, which supply the molecule with small amounts of energy.

The challenges addressed by researchers in preparing for this race will be so many steps forward in new fields of chemistry and physics. Each team will leave with new skills, data, and know-how that will one day contribute to the development of surface chemistry (which enables chemical synthesis directly on a particular surface), for example, as well as to the establishment of new rules for designing molecule- machines, and to a new science of surfaces known as membrane science, which could make it possible to deposit a molecule-machine on the surface of a cell or to control the movement of a single molecule in a liquid.

1 In chemistry, a molecular orbital is a mathematical function describing a molecule's electronic states. This function can be used to calculate physical or chemical properties, such as the probability of finding an electron in a specific area. 2 A motor is either classical—which is to say that the movement is created by the rotation or the flip of a chemical group—or quantum, which is when the movement is created by the passage of electrons through the molecule's different electronic states with a certain probability. 3

Experts in molecular engineering

A central issue in molecular engineering is to ensure the proper functioning of the desired molecular mechanism, and to succeed in controlling a change in the molecule's structure.

A series of movements are being sought, such as the flip of a chemical group in the manner of a switch, the spinning of a molecular rotor, the closing of molecular pliers to grasp an atom, the stretching of a molecular arm to reach for an atom or small molecule far away on the surface—all without touching the neighboring molecule, which may be only a few nanometers away.

For the Nanocar Race, this entails moving and steering a nanocar for 36 hours. Each team used complex chemical syntheses to develop each vehicle. Months of synthesis, modeling and tests were needed to design and drive a high-performance nanometric racing car. High command of molecular engineering is therefore essential to create the best possible machine.

The years to come will probably see the use of such molecular machinery—activated individually or in synchronized fashion—to manufacture common devices. It could also be of great use in the atom-by-atom deconstruction of industrial and urban waste, or the capture of energy, for example.

The first steps of "atom technology"

Beyond hosting the Nanocar Race, the CEMES-CNRS four-tip microscope will eventually enable the atom- by-atom construction of the electronic circuits of the future, whether classical or quantum, as well as their characterization. It will also make it possible to measure the engine power of a single molecule-motor with the goal of driving silicon nanogears. This is one of the first steps toward a genuine "atom technology," in which electronic chips will be built atom-by-atom, with a precision on the order of a picometer.3

The development of multi-tip instruments like the one at the CEMES-CNRS, motivated by the organization of the race, will in the long run enable the synchronization of a large number of molecule-motors, which should also increase their engine power, for example to store or capture energy on a hot metallic surface.

3 1 pm = 10-12 m (or a billionth of a millimeter). 4

Join the race!

A one-of-a-kind microscope

The nanocar race will take place in a unique instrument, the LT-Nanoprobe, built by Scienta Omicron for the CEMES-CNRS. The instrument consists of four scanning tunneling microscopes that can simultaneously and independently scan the same surface at low temperature and in an ultrahigh vacuum, providing atomic- scale images with a resolution of 2 picometers.

This type of microscope (called STM) uses the quantum mechanics phenomenon known as the "tunnel effect." It can very precisely measure the distance between an ultra-fine metallic tip and a conductive or semi-conductive surface, through an electric current established between the tip and the surface for distances inferior to a nanometer. The tunnel effect that occurs at the atomic and subatomic scale indicates a quantum object's capacity to cross an energy barrier, even if its own energy is lower than the minimum threshold needed to cross this barrier.

The CEMES's microscope is the only one in the world with four tips that can be independently controlled by four users on the same surface. The necessary adjustments to make it operational for the Nanocar Race posed a series of challenges to the researchers.

First, they had to modify the microscope to simultaneously place four nanocars in the same spot, so that four drivers could move their vehicle at the same time on the same surface. It took three months for a specialized company to build the evaporator enabling this operation. However, only a single rotating shutter will be available in the ultrahigh vacuum: it will uncover the containers housing the nanocars one by one, and evaporate them on the gold surface. The researchers therefore invented a system of caches to divide the racetrack into four sections—one for each competitor. Finally, as all of this takes place in an ultrahigh vacuum, the researchers designed a mini lift with an exit carousel to position these caches.

They also extended the tip mounts by 1 mm on each STM to allow for four simultaneous scans without the mounts touching one another. Modifications were also made to the steering system: the control software was divided into four distinct software programs, one for each tip, so that each team has its own driving seat.

A great deal of preparation was necessary before the microscope's tungsten tips could be used. The procedure for preparing tips of this type has been standardized over the past few decades. After an electrochemical attack in a basic environment on a tungsten wire measuring 250 microns in diameter, the researchers obtain tips of approximately 100 nm in radius curvature, albeit oxidized. They must then mount the tips on a small stainless steel tube with a 250-micron internal diameter, called a "tip holder", which attaches the tip to the STM. Once attached, and before being placed in a vacuum, the tip is heated to between 200 °C and 400 °C to remove the oxide. These steps will be carried out at the CEMES in a specific preparation chamber installed in the laboratory before the start of the race.

Why a racetrack made of gold?

The gold surface was selected for the race because most nanocars form few chemical bonds with this surface, regardless of their chemical composition. The race's four tracks must simultaneously be cleared of all molecules other than those competing. The researchers will do this by using the experimental atom manipulation technique discovered in 1989 by the pioneering research of D. Eigler at IBM, and which later featured in the work of J.K. Gimzewski and C. Joachim in 1996 with respect to the manipulation of large molecules.

The gold surface will be prepared a first time across its 8mm diameter, and simultaneously tested by each team. The molecules will then be evaporated section-by-section on this surface. However, even with great care, molecules will be dispersed across the entire racetrack, and it is likely that some of them will end up in another competitor's section. Before the start of the race, each pilot will have to clean their dedicated zone by pushing "opposing" molecules one-by-one, and by clearing their own in order obtain a 70 to 100 nm molecule-free track.

The gold surface naturally shows highly regular folds in the shape of chevrons, with a gap of approximately 6 nm between them. Each competitor's track will thus be defined between 2 chevrons, consisting of 3 straight lines of 20 nm, 30 nm, and 20 nm, respectively, separated by a 45° right turn and a 45° left turn, for a total length of about 100 nm, based on the structure of the turns.

A race referee will be in charge of verifying that all tracks have the same atomic structure, as well as the same length between the starting and finishing lines. These two lines will be marked by the positioning of two molecule-cars that will not be used for the race.

The process

The enclosure in which the race will take place will be cooled to -269 °C, so that the molecules do not make any spontaneous movements and are easy to manipulate. Liquid helium will be used for this cooling, and the amount of the CEMES reserves limit the competition's duration to 36 hours.

5 steps must be completed before the cars can start racing.

Step 1: Preparation of the tips

The final preparatory stage for the tips consists in bringing them close to the surface to create a small contact, in order to "wet" the end of the microscope's tip (the apex) with gold atoms, and thereby perfect its atomic structure. This will be performed by each of the teams.

Duration: One night at 200 °C in an ultrahigh vacuum (UHV) chamber, and then a full afternoon per tip at the field emission array that CEMES researchers have installed in the preparation chamber of the four-tip microscope.

Protocol: Most teams will keep their preparatory procedures a secret, except for the final part involving the tip's small indentation in the gold surface, that is to say how they will finalize the atomic structure with the end of their tip.

Difficulties: The four tips must all be ready at approximately the same time (at the start of the race), and be of the same quality, for once the race starts it will be impossible to open the cryostat to change tips for 36 hours. However, if a tip becomes damaged, researchers can easily reform it without disturbing the other teams.

Step 2: Initial preparation of the gold surface

Duration: Approximately 90 minutes.

Protocol: The gold sample is a very pure commercial monocrystal called Au (111), with only one side polished for superior optical quality. After it is placed in the STM's ultrahigh vacuum preparation chamber, the sample's surface is cleaned by argon ion bombardment for 10 minutes. The gold sample is then reheated to 450 °C for 20 minutes. After three cycles of argon bombardment and reheating, a clean surface with practically no structural defects is obtained.

Stage 3: Evaporation of molecules

Duration: On average, it takes a week to fifteen days to achieve the conditions of sublimation (in other words, of evaporation) for a new small molecule of less than 100 atoms. The protocol can then be reproduced. For the race, the duration of sublimation is on the order of a minute. However, the following processing times must also be taken into account: - Placing the crucibles in the evaporator: 45 mn. - Pumping and heating the evaporator: 8 h. - Positioning of caches for molecule-by-molecule evaporation: 1 h of UHV handling per cache.

This step should therefore last a little more than a night and half a day, and over a week if counting the time needed to image each section of the track before the race.

Protocol: The exact protocol of each team will remain a well-kept secret, and includes the exact temperature of sublimation, the weight in milligrams of the molecular powder placed in each crucible, the duration of evaporation, and even the cleaning procedure for the crucibles.

Difficulties: Should the molecules be evaporated team by team on the gold surface, and the proper depositing of molecules be verified after each sublimation? Or on the contrary, should all of the evaporations be performed at the same time (in one night and a half-day) before imaging everything in STM, at the risk of having to re-clean the entire surface and start all over again? This is one of the race's unknowns, and it is of interest to all of the teams working on a potential multi-step chemical synthesis of molecules on a surface. This is a new field in synthetic chemistry that several researchers, particularly those at the CEMES, discovered in the mid-2000s.

In ultrahigh vacuum: start of the 36-hour countdown

Stage 4: Pilots prepare the tracks

Duration: An average of 6 hours are needed to clear the track of all the molecule-cars that will not be used during the race. This will be followed by another 2 hours imaging the position of gold atoms along the way, especially in the two turns, in order to develop strategies and complete the turns without exiting the racetrack.

The drivers will be able to prepare their tip again by making it touch the gold surface.

Stage 5: Track mapping

Duration: Each team must use the tip of their microscope to map the track at the atomic scale. This takes approximately 30 mn for a good image of approximately 200 nm x 200 nm. The track must then be mapped by sections of 5 nm on each side, especially the turns, which can take three minutes to an hour depending on the desired image quality.

Once their track is fully mapped, the pilots can start racing!

The rules

For this first edition, all types of nanocars were accepted, even though it was advisable to use molecules with four wheels, a chassis, and an engine. The nanocars selected for the race have a chemical structure of at least one hundred atoms.

Since the mid-1990s, researchers have known how to manipulate a molecule at will, by "pushing" it through repulsive interactions with the tip of the microscope. Today, the objective is to synthesize and control a particular form of propulsion, called inelastic, without the tip touching the molecule.

Generally, the electronic tunnel effect is called elastic: electrons passing through the molecule via this effect do not lose energy, and therefore do not excite it. For a standard current used in tunnel imaging, one billion electrons pass through a molecule per second. However, a very small percentage of these electrons lose a bit of energy: this is the inelastic effect. The race is a way of shedding light on this little-known phenomenon by testing it on different types of molecules, using four electron sources (one per tip) of equal quality.

Researchers estimate that less than 0.01% of electrons leave some energy behind while passing through. In order to obtain a well-conceived molecule, this effect is reinforced by choosing a voltage that can electronically reach unoccupied states. A little energy is deposited in these excited states4, thereby moving

4Electronic configuration is the distribution of electrons (of an atom, a molecule, or any other body) according to their energy and spin. There are a number of possible electronic configurations for the same atom or molecule: if the state corresponding to the electronic configuration is the one with the lower energy, it is called a fundamental state, and if the opposite is true, it is called an excited state. 8

the molecule forward. The nanocars must be propelled using this inelastic effect in order to participate in the race.

The electric voltage passing through the molecule will be generated using small pulses of approximately two volts, which will propel it by only 0.3 nanometers per pulse on average. The drivers must be particularly careful not to break the molecule's chemical bonds through too many pulses, or a succession of pulses too close together in time.

Each team will choose their own strategy for generating images. This takes approximately 3 minutes for tunneling currents of a few picoamperes; they will therefore have to decide whether to wait for several movements, or whether to record an image for each movement of the molecule.

Certain gold atoms could also move down the length of the scanning tunneling microscope's tip during these small electrical pulses. The resulting change in the lines of the electrostatic field would attract the nanocars onto the tip, and cause them to disappear from the scientists' control screen. The teams will be allowed to continue the competition by retrieving one of the cars evaporated on the surface at the beginning of the race, and set aside for this purpose (or to replace a broken nanocar).

However, if a team breaks its tungsten tip, it will be considered as disqualified, as it is impossible to open the microscope to change tips.

The winning team will be the one whose molecule-car crosses its finish line first, or is the furthest along its track at the end of the 36 hours.

The organizers

Jean-Pierre Launey Christian Joachim Race referee Director of the race Professor at the Université Toulouse III – CNRS senior researcher Paul Sabatier [email protected] [email protected]

The CNRS's Centre d’élaboration de matériaux et d’études structurales (CEMES)

This laboratory, which was created in 1988, conducts basic research in materials science, solid-state physics, and molecular chemistry. It is associated with the Université Toulouse III - Paul Sabatier and the Institut national des sciences appliquées de Toulouse (INSA). Its activities primarily involve the production, study, and manipulation of nanomaterials. It also aims to develop cutting-edge microscopes and spectroscopes. The equipment and skills needed for picotechnology, i.e. technologies applied at a scale as small as a billionth of a millimeter, are housed within the PicoLab at the CEMES.

To find out more: PICOLAB, interacting with the nanoworld

The teams

US-Austrian NanoPrix Team

Name of the car: Dipolar Racer Country: United States / Austria Laboratories: Smalley Institute for Nanoscale Science and Technology (Rice University) / Institute für Chemie (University of Graz) Team

Leonhard Grill Victor Garcia-Lopez Grant Simpson Team leader Designer Pilot

Austria United States Austria Professor at the University of Associate Professor at Rice Associate Professor at the Graz University University of Graz [email protected] [email protected] [email protected]

James Tour Team leader and designer

United States Professor at Rice University [email protected] 11

Propulsion method: The team has not yet chosen its final molecule for the race. A few are still undergoing optimization. Nevertheless, they adopted the same strategy as the other teams: the Dipolar Racer is propelled by the interaction of its dipole with the electric current supplied by the microscope.

Composition: The Dipolar Racer is an assembly of different components: wheels, axles, chassis, and a motor that changes shape when exposed to a current.

Nano-windmill Company

Name of the car: Windmill Country: Germany Laboratory: Institute for Materials Science and Max Bergmann Center of Biomaterials - TU Dresden Team:

Frank Eisenhut Francesca Moresco Pilot Team leader and co-pilot

Germany Germany Senior researcher and lecturer at PhD student at Dresden University [email protected] Dresden University [email protected] dresden.de dresden.de

Propulsion method: The electrical energy applied to the car is converted into motion. By using voltage electric pulses with the tip of the microscope, Windmill is able to move in a precise and controlled manner. The four molecules can be steered in one of the four possible directions.

Composition : Windmill consists of four ABP (acetylbiphenyl) molecules connected by hydrogen bonds (the circle in the image). Electric pulses will be applied to precise steering points of the molecule .

ABP is commercially available, although the molecules must be assembled to form a nanocar. The conditions of evaporation of the molecule must be adjusted in order to maximize the formation of structures.

NIMS-MANA team

Car name: NIMS-MANA car Country: Japan Laboratory: International Center for Materials Nanoarchitectonics Team:

Marek Kolmer Kosuke Minami Katsuhiko Ariga Pilot Chemist Japan Senior researcher at NIMS-MANA Poland Japan [email protected] Researcher at Jagiellonian Postdoctoral fellow at NIMS-MANA University [email protected] [email protected]

Waka Nakanishi Yasuhiro Shirai We-Hyo Soe Team leader and designer Designer Pilot

Japan Japan Japan Senior researcher at NIMS-MANA Senior researcher at NIMS-GREEN Researcher at NIMS-MANA [email protected] [email protected] Toulouse Satellite [email protected]

Propulsion method: The molecules that make up the car can rotate around their bonds, moving in the manner of a caterpillar.

Composition :

The NIMS-MANA car is composed of two naphthalenes known for their odor. Each naphthalene acts as a kind of "paddle" for the NIMS-MANA car.

Ohio Bobcat Nano-wagon Team

Car name: Ohio Bobcat Nano-wagon Country: United States Laboratory: Laboratory for single atom and molecule manipulation (Athens, United States) Team:

Saw-Wai Hla Eric Masson Pilot Designer

United States United States Professor at Ohio University Professor at Ohio University [email protected] [email protected]

To date, the team has preferred not to communicate on their car.

Swiss Team

Car name: Swiss Nano Dragster Country: Switzerland Laboratory: Nanolino Lab, University of Basel Team:

Catherine Housecroft Tobias Meier Designer Ernst Meyer Co-pilot Team leader

Switzerland Switzerland Professor at the University of Switzerland PhD student at the Basel Professor at the University of University of Basel [email protected] Basel [email protected] [email protected]

Rémy Pawlak Pilot

Switzerland Postdoctoral fellow at the University of Basel [email protected] 18

Propulsion method: The Swiss Nano Dragster is propelled by applying the microscope's electric pulses to its motor, which is located at the tail of the molecule (blue section in the image). The motor consists of three steering units. The Swiss Nano Dragster moves in different directions depending on the unit that is activated.

Composition :

The Swiss Nano Dragster does not have wheels, it is more like a hovercraft: the motion of the car is almost frictionless due to weak interactions between the molecule's (carbon-based) structure and the racetrack.

Toulouse Nanomobile club

Car name: The Green Buggy Country: France Laboratory: CEMES-CNRS/Université Toulouse III - Paul Sabatier (Toulouse, France) Team:

Corentin Durand Sébastien Gauthier Claire Kammerer Pilot Co-pilot Technical director

France France Associate Professor at the Associate Professor at the Université CNRS Senior researcher Université de Toulouse III – Paul de Toulouse III – Paul Sabatier [email protected] Sabatier [email protected] [email protected]

Gwénaël Rapenne Team leader and designer

Professor at the Université de Toulouse III – Paul Sabatier [email protected]

Propulsion method: Each of the Green Buggy's wheels is equipped with a chemical group that can easily rotate around an axis, supplemented with a molecular ratchet. The tunneling current passing through this molecular group should trigger the rotation of a wheel and thereby propel the Green Buggy by 0.3 nanometers per electric pulse.

Composition :

As the construction of the nanocar proceeds, the size of the molecule increases (see image). The last step is the simultaneous connection of the four wheels using a coupling reaction.

Resources

These and other visuals will be available at the CNRS photo library : http://phototheque.cnrs.fr/p/389-1-1-0/ For rush videos, please contact Alexiane Agullo: [email protected]

Designing the cars:

The racetrack:

The microscope: