Ricerca IBM: catturata l'immagine dell'“anatomia” di una molecola

Milano, 31 agosto 2009 - Gli scienziati IBM del centro di Zurigo sono riusciti ad acquisire l'immagine dell'“anatomia” - o struttura chimica - all'interno di una molecola con una risoluzione senza precedenti, utilizzando una tecnica complessa, nota come microscopia a forza atomica senza contatto. I risultati stimolano l'esplorazione dell'uso di molecole e atomi sulla più piccola scala e potrebbero avere un enorme impatto nel campo della nanotecnologia, che cerca di comprendere e controllare alcuni degli oggetti più minuscoli noti all'umanità.

"Sebbene non sia un confronto esatto, se pensiamo al modo in cui un medico utilizza una radiografia per visualizzare le ossa e gli organi nel corpo umano, noi utilizziamo il microscopio a forza atomica per acquisire l'immagine delle strutture atomiche che costituiscono l'ossatura delle singole molecole”, spiega Gerhard Meyer, ricercatore IBM. “Le tecniche a scansione di sonda offrono un potenziale sbalorditivo per creare prototipi di strutture funzionali complesse e per adattarne e studiarne le proprietà elettroniche e chimiche su scala atomica.

Per guardare il video: http://www.youtube.com/watch?v=jnLRl_74BZs

La recente pubblicazione dello studio è successiva a un altro esperimento, pubblicato solo due mesi fa sul numero del 12 giugno di Science (Volume 324, Numero 5933, pagg. 1428-1431), in cui gli scienziati IBM hanno misurato gli stati di carica degli atomi utilizzando un microscopio a forza atomica (AFM). Questi risultati rivoluzionari apriranno nuove possibilità per studiare la modalità di trasmissione della carica attraverso le molecole o le reti molecolari. Comprendere la distribuzione della carica su scala atomica è essenziale per costruire componenti di calcolo più piccoli, più veloci e più efficienti dal punto di vista energetico rispetto ai processori e ai dispositivi di memoria di oggi. Questi componenti potrebbero un giorno contribuire a realizzare la visione di IBM di un pianeta più intelligente, aiutando a dotare di strumenti ed a interconnettere il mondo fisico.

Come riportato nel numero del 28 agosto della rivista Science, gli scienziati del centro IBM di Zurigo Leo Gross, Fabian Mohn, Nikolaj Moll e Gerhard Meyer, in collaborazione con Peter Liljeroth dell'Università di Utrecht, hanno utilizzato un microscopio a forza atomica in ultravuoto e bassissime temperature (-268 °C, o -451 °F) per acquisire le immagini della struttura chimica di singole molecole di pentacene. Con il microscopio AFM, gli scienziati IBM, per la prima volta nella storia, sono riusciti a guardare attraverso la nuvola di elettroni e vedere l'ossatura atomica di una singola molecola. Anche se non si tratta di un confronto tecnologico diretto, ciò ricorda le radiografie che passano attraverso il tessuto molle per consentire di acquisire immagini chiare delle ossa.

La punta decisiva

Il microscopio AFM utilizza una punta di metallo affilata per misurare le minuscole forze tra la punta e il campione, come ad esempio una molecola, per creare un'immagine. Negli esperimenti in questione, la molecola studiata è stata il pentacene. Il pentacene è una molecola organica oblunga, composta da 22 atomi di carbonio e 14 atomi di idrogeno e lunga 1,4 nanometri. Lo spazio tra gli atomi di carbonio adiacenti è di appena 0,14 nanometri - circa 1 milione di volte più piccolo del diametro di un granello di sabbia. Nell'immagine sperimentale, le forme esagonali dei cinque anelli di carbonio, nonché gli atomi di carbonio, nella molecola sono chiaramente definiti. Dall'immagine possono essere dedotte perfino le posizioni degli atomi di idrogeno della molecola.

“Per ottenere la risoluzione atomica è stato utilizzato l'apice della punta atomicamente affilato e definito, oltre all'elevatissima stabilità del sistema”, ricorda Leo Gross, scienziato IBM. “Per acquisire l'immagine della struttura chimica di una molecola con un AFM, è necessario intervenire in strettissima prossimità alla molecola. L'intervallo in cui le interazioni chimiche danno un contributo significativo alle forze è inferiore a un nanometro. Per raggiungere questo obiettivo, gli scienziati IBM hanno dovuto aumentare la sensibilità della punta e superare un'importante limitazione: così come due magneti si attraggono o si respingono quando si avvicinano, le molecole possono essere facilmente spostate dalla punta o aderire ad essa quando la punta si avvicina troppo, rendendo impossibile qualsiasi ulteriore misurazione.

Aggiunge Leo Gross: “Abbiamo preparato la punta scegliendo deliberatamente singoli atomi e molecole e abbiamo dimostrato che è il primo atomo o molecola della punta a governare il contrasto e la risoluzione delle nostre misurazioni con l'AFM”. Una punta terminata da una molecola di monossido di carbonio (CO) ha prodotto il contrasto ottimale, a un'altezza della punta di circa 0,5 nanometri sopra la molecola oggetto di indagine e - agendo come una potente lente di ingrandimento - ha definito i singoli atomi all'interno della molecola di pentacene, rivelandone l'esatta struttura chimica su scala atomica.

Inoltre, gli scienziati sono stati in grado di evidenziare una mappa completa tridimensionale della forza della molecola esaminata. “Per ottenere una mappa completa della forza, era necessario che il microscopio fosse altamente stabile, sia meccanicamente che termicamente, per assicurare che sia la punta dell'AFM che la molecola rimanessero inalterati durante le oltre 20 ore di acquisizione dei dati”, spiega Fabian Mohn, che sta svolgendo la sua tesi di dottorato presso IBM Research - Zurigo.

Per avvalorare i risultati sperimentali e ottenere ulteriori elementi di conoscenza sull'esatta natura del meccanismo di acquisizione delle immagini, lo scienziato IBM Nikolaj Moll ha eseguito i calcoli della teoria del funzionale della densità da principi primi del sistema oggetto d'indagine. Spiega: “I calcoli ci hanno aiutato a capire che cosa ha causato il contrasto atomico. In effetti, abbiamo riscontrato che la sua origine è stata la repulsione di Pauli tra la molecola di CO e di pentacene". Questa forza repulsiva deriva da un effetto meccanico quantico, denominato principio di esclusione di Pauli. Tale principio afferma che due elettroni identici non possono avvicinarsi troppo l'uno all'altro.

IBM e la nanotecnologia

IBM è stata pioniera nelle nanoscienze e nella nanotecnologia sin dallo sviluppo del microscopio a effetto tunnel nel 1981 da parte di Gerd Binnig e Heinrich Rohrer, IBM Fellows, presso IBM Research, Zurigo. Per questa invenzione, che ha reso possibile acquisire l'immagine di singoli atomi e in seguito manipolarli, Binnig e Rohrer sono stati insigniti del premio Nobel per la Fisica nel 1986. L'AFM, un discendente del microscopio a effetto tunnel (STM), è stato inventato da Binnig nel 1986. L'STM è considerato lo strumento che ha aperto le porte al mondo delle nanoscienze. Una nuova struttura per la ricerca collaborativa su nanoscala di altissimo livello, il Nanoscale Exploratory Technology Laboratory, sarà inaugurata nel 2011 nel campus del centro di Ricerca di Zurigo. Il centro nanotech s'inserisce in una partnership strategica nella nanotecnologia on l'ETH di Zurigo, una dei più prestigiosi politecnici europei.

Lo studio scientifico intitolato “The Chemical Structure of a Molecule Resolved by Atomic Force Microscopy”, di L. Gross, F. Mohn, N. Moll, P. Liljeroth e G. Meyer, è pubblicato su Science, Volume 325, Numero 5944, pagg. 1110 - 1114 (28 agosto 2009).

Naked molecule exposed

Posted: Thursday, August 27, 2009 8:10 PM by Alan Boyle
http://cosmiclog.msnbc.msn.com/archive/2009/08/27/2046556.aspx

IBM Research - Zurich
This graphic shows how scientists used a metal tip terminated with a carbon monoxide molecule to obtain an image of a pentacene molecule's structure. The colored surface represents experimental data, and the black-and-white version shows the theoretical position of atoms in the pentacene molecule.

Scientists have traced the structure of a complete molecule in all its glory, using the sharpest pen ever devised: an atomic force microscope tipped with a single molecule of carbon monoxide.

The experiment, detailed in Friday's issue of the journal Science, could help open up a new frontier for molecular-scale circuitry and construction.

Researchers have been imaging molecules and their constituent atoms in crystals for decades, but the trick is to get a fine-resolution fix on the structure and behavior of an entire, self-contained molecule as it sits on a surface.

If you have the wrong stuff at the very tip of your probe, the very act of mapping the molecule can spoil the picture.

Leo Gross and his colleagues at IBM's Zurich Research Laboratory found that a carbon monoxide molecule (with its oxygen atom sticking straight out from the tip) produced "spectacular" images of the pentacene molecule. That's a well-studied type of hydrocarbon composed of five benzene rings interlocked in a row (C22H14).

Science / IBM
Several pentacene molecules are imaged using non-contact atomic force microscopy.

The benzene rings showed up brightly in the atomic-scale images, just as predicted by theory. One of the images published in Science even showed several of the five-ring molecules scattered around a surface like nano-caterpillars.

The researchers said their results were so good because the carbon monoxide molecule could get incredibly close to the pentacene molecule without picking it up or moving it around. When they tried probes that were tipped in metals, such as gold or silver or copper, the pentacene molecule would move around before the tip came close enough to map the chemical forces holding the molecule together.

The IBM team concluded that non-contact atomic force microscopy can be a great way to see how molecules are put together, but only if the microscope's probe is tipped with the right stuff.

The next step is to probe differently constructed molecules to see how they react with various types of tips - and see which kinds of surfaces work best as a molecular-scale lab bench. The goal of all this is to devise a molecular construction toolkit, as well as methods for watching how the tools in the kit work together.

"Eventually we want to investigate using molecules for molecular electronics," Gross told Chemistry World. "We want to use molecules as wires or logic switches or elements."

Experts in nanotechnology have long dreamed of creating molecular-scale circuitry that could revolutionize the computer world. But Gross told EETimes that the revolution is still far off. "It will take at least 15 years to see molecular electronic applications," he said, "and it is by no means certain that we will succeed."

That sounds like a refreshingly realistic assessment to me - but what do you think? Feel free to add your comments below.

Join the Cosmic Log team by signing up as my Facebook friend or hooking up on Twitter. And reserve your copy of my upcoming book, "The Case for Pluto." You can pre-order it from Amazon, Barnes & Noble or Borders.

August 28, 2009

Single molecule's stunning image
By Jason Palmer
Science and technology reporter, BBC News
http://news.bbc.co.uk/1/hi/sci/tech/8225491.stm

The detailed chemical structure of a single molecule has been imaged for the first time, say researchers. The physical shape of single carbon nanotubes has been outlined before, using similar techniques - but the new method even shows up chemical bonds. Understanding molecular structure on this scale could help in the design of many things on the molecular scale, particularly electronics or even drugs. The IBM researchers report their findings in the journal Science. It is the same group that in July reported the feat of measuring the charge on a single atom.

Fine tuning
In both cases, a team from IBM Research Zurich used what is known as an atomic force microscope or AFM. Their version of the device acts like a tiny tuning fork, with one of the prongs of the fork passing incredibly close to the sample and the other farther away. When the fork is set vibrating, the prong nearest the sample will experience a minuscule shift in the frequency of its vibration, simply because it is getting close to the molecule. Comparing the frequencies of the two prongs gives a measure of just how close the nearer prong is, effectively mapping out the molecule's structure. The measurement requires extremes of precision. In order to avoid the effects of stray gas molecules bounding around, or the general atomic-scale jiggling that room-temperature objects experience, the whole setup has to be kept under high vacuum and at blisteringly cold temperatures. However, the tip of the AFM's prong is not well-defined and isn't necessarily sharp on the scale of single atoms. The effect of this bluntness is to blur the instrument's images. The researchers have now hit on the idea of deliberately picking up just one small molecule - made of one atom of carbon and one of oxygen - with the AFM tip, forming the sharpest, most well-defined tip possible. Their measurement of a pentacene molecule using this carbon monoxide tip shows the bonds between the carbon atoms in five linked rings, and even suggests the bonds to the hydrogen atoms at the molecule's periphery.

Tip of the iceberg
Lead author of the research Leo Gross told BBC News that the group is aiming to combine their ability to measure individual charges with the new technique, characterising molecules at a truly unprecedented level of detail. That will help in particular in the field of "molecular electronics", a potential future for electronics in which individual molecules serve as switches and transistors. Although the approach can trace out the ethereal bonds that connect atoms, it cannot distinguish between atoms of different types. The team aims to use the new technique in tandem with a similar one known as scanning tunnelling microscopy - in which a tiny voltage is passed through the sample - to determine if the two methods in combination can deduce the nature of each atom in the AFM images. That would help the entire field of chemistry, in particular the synthetic chemistry used for drug design. The results are of wide interest to others who study the nano-world with similar instruments. For them, implementing the same approach is as simple as picking up one of these carbon monoxide molecules with their AFM before taking a measurement.

August 27, 2009 11:00 AM PDT

IBM eyes molecule 'anatomy' for future computers

By Brooke Crothers
http://news.bbc.co.uk/1/hi/sci/tech/8225491.stm

IBM scientists have imaged the chemical structure of an individual molecule, increasing the possibility for creating electronic building blocks on the atomic and molecular scale. By using an atomically sharp metal tip terminated with a carbon monoxide molecule, IBM scientists were able to obtain an image of the inner structure of the molecule. The colored surface represents experimental data. The model below shows the position of the atoms within the molecule.Scientists In Zurich, Switzerland, have, for the first time, imaged the "anatomy," or chemical structure, of an individual molecule with "unprecedented" resolution, using noncontact atomic force microscopy (AFM), IBM said Thursday. Resolving individual atoms within a molecule has been a long-standing goal of surface microscopy, according to the computer company, which has a research and development program dating back to 1945.

This research will be essential for building computing elements at the atomic scale that are vastly smaller, faster and more energy-efficient than today's processors and memory devices, IBM said.

The research is reported in the August 28 issue of Science magazine.

Though in recent years progress has been made in research of nanostructures on the atomic scale with AFM, imaging the chemical structure of an entire molecule has never been achieved with atomic resolution, according to IBM.

The atomic force microscopy was done in an ultrahigh vacuum and at very low temperatures (5 Kelvin equals minus 268 degrees Centigrade or minus 451 Fahrenheit) to image the chemical structure of individual pentacene molecules. Pentacene has a crystal structure that gives it properties as an organic semiconductor.

Scientists were able "to look through the electron cloud and see the atomic backbone of an individual molecule for the first time." This is roughly analogous to X-rays that pass through soft tissue to enable clear images of bones, IBM said.

The Science magazine article follows another piece published two months ago in the June 12 issue of the magazine covering the "determination of atomic charge states." The results discussed in both of these articles will "open new possibilities for investigating how charge propagates through molecules or molecular networks," IBM said.

Understanding the charge distribution may lead to building computing elements at the atomic scale. This is the Holy Grail of semiconductor research and development. As circuit geometries get infinitesimally smaller, it becomes prohibitively challenging to make circuits with geometries below 10 nanometers, or even 20 nanometers."

"It is accepted that in the future this work can contribute to assemble prototypical structures of molecular systems and the idea is these circuits could have much lower power consumption and reduce fabrication costs," said Gerhard Meyer, scientist, IBM Research, Zurich, in response to an e-mail query. "This is an important step, but one of many that will need to be achieved to build computing elements at the atomic scale. Techniques like self assembly might be used for manufacturing," he said.

How it's done
As described by IBM, the microscope uses a sharp metal tip to measure the tiny forces between the tip and the sample, such as a molecule, to create an image. Pentacene is an oblong organic molecule consisting of 22 carbon atoms and 14 hydrogen atoms measuring 1.4 nanometers in length. The spacing between neighboring carbon atoms is only 0.14 nanometers--roughly half a million times smaller than the diameter of a human hair, according to IBM.

In the experimental image, the hexagonal shapes of the five carbon rings as well as the carbon atoms in the molecule are clearly resolved. Even the positions of the hydrogen atoms of the molecule can be deduced from the image, IBM said.

To image the chemical structure of a molecule with an AFM, it is necessary to operate in very close proximity to the molecule. IBM scientists were required to keep the molecules from attaching to the tip when the tip was approached too closely.

Brooke Crothers is a former editor at large at CNET News.com, and has been an editor for the Asian weekly version of the Wall Street Journal. He writes for the CNET Blog Network, and is not a current employee of CNET. Contact him at mbcrothers@gmail.com. Disclosure.

Researchers at IBM have used an atomic-force microscope to resolve the chemical structure of pentacene.
By Katherine Bourzac

This image of pentacene, a molecule made up of five carbon rings, was made using an atomic-force microscope. Credit: Science/AAAS

Using an atomic-force microscope, scientists at IBM Research in Zurich have for the first time made an atomic-scale resolution image of a single molecule, the hydrocarbon pentacene.

Atomic-force microscopy works by scanning a surface with a tiny cantilever whose tip comes to a sharp nanoscale point. As it scans, the cantilever bounces up and down, and data from these movements is compiled to generate a picture of that surface. These microscopes can be used to "see" features much smaller than those visible under light microscopes, whose resolution is limited by the properties of light itself. Atomic-force microscopy literally has atom-scale resolution.

Still, until now, it hasn't been possible to use it to look with atomic resolution at single molecules. On such a scale, the electrical properties of the molecule under investigation normally interfere with the activity of the scanning tip. Researchers at IBM Research in Zurich overcame this problem by first using the microscope tip to pick up a single molecule of carbon monoxide. This drastically improved the resolution of the microscope, which the IBM scientists used to make an image of pentacene. They arrived at carbon monoxide as a contrast-enhancing addition after trying many chemicals. The researchers hope that looking this closely at single molecules will give them a better understanding of chemical reactions and catalysis at an unprecedented level of detail.

The imaging work is described today in the journal Science.

IBM Scientists Take First Close-Up Image of a Single Molecule
By Clay Dillow
Posted 08.27.2009 at 4:55 pm

As part of a greater effort to someday build computing elements at an atomic scale, IBM scientists in Zurich have taken the highest-resolution image ever of an individual molecule using non-contact atomic force microscopy. Performed in an ultrahigh vacuum at 5 degrees Kelvin, scientists were able to "to look through the electron cloud and see the atomic backbone of an individual molecule for the first time," a feat necessary for the further development of atomic scale electronic building blocks.

Atomic force microscopy employs a cantilever so small that its tip tapers to a nanoscale point. As the microscope scans, the cantilever bounces up and down in response to the miniscule forces between the tip and the sample, generating a picture of the sample’s surface. The pentacene molecule sampled consists of 22 carbon atoms and 14 hydrogen atoms and measures 1.4 nanometers in length, with the space between carbon atoms registering at 0.14 nanometers, or half a million times smaller than the diameter of a human hair.

Imaging Atoms: IBM researchers used atomic force microscopy to take the best image yet of a single molecule. IBM
The image should help researchers determine how charge moves through molecules and networks of molecules, which in turn could lead to breakthroughs in building computing elements at the atomic scale. As circuits grow smaller, it becomes harder and harder to break the sub-10-nanometer scale, a benchmark that several research groups are trying to reach. Breakthroughs in circuit board and semiconductor technology involving self-assembling DNA promise to deliver infinitesimally smaller circuits, but reaching atomic-scale computing has thus far eluded researchers.

Understanding the charge distribution of molecules could bring scientists a large step closer to cracking atomic scale computing, which could vastly reduce power consumption and fabrication costs.

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