Estrutura interna de uma molécula de pentaceno, de 1,4 nanômetro de comprimento.
Abaixo, modelo da mesma molécula (os átomos cinzas são de carbono, e os brancos, de hidrogênio).
Foi a primeira vez que se conseguiu ver os átomos que formam uma molécula, através de um microscópio de forças atômicas sem contato (AFM).
Este feito dos cientistas do laboratório da IBM em Zurique (Suíça) representa um avanço na nanotecnologia e na eletrônica molecular, além de melhorar o funcionamento de dispositivos eletrônicos, diz a empresa. A molécula fotografada é o pentaceno (C22H14), consistente em cinco anéis de benzeno entrelaçados formando uma cadeia aromática, que poderá vir a ser utilizada em novos semicondutores orgânicos. Os pesquisadores da IBM Research – Zurich - Leo Gross, Fabian Mohn, Nikolaj Moll e Gerhard Meyer, em cooperação com Peter Liljeroth, da Universidade de Utrecht, usaram um AFM operado sob vácuo ultra alto, e a baixíssimas temperaturas (–268°C ou – 451°F) para fotografar a estrutura química de moléculas avulsas de pentaceno.
A novidade, publicada na revista Science, sucede a outro experimento publicado na mesma revista, há dois meses, no qual equipamento mediu os estados de carga dos átomos, com o mesmo tipo de microscópio. Assim será possível investigar como se transmite a carga através das moléculas ou de redes moleculares. Ademais, os pesquisadores conseguiram descobrir que a força repulsiva que lhes permitiu obter o contraste suficiente para ver a imagem deve-se ao efeito quântico denominado Princípio de Exclusão de Pauli.
Nos últimos anos, se havia conseguido definir nanoestruturas a escala atômica, e agora foi possivel mostrar a estrutura química de uma molécula com uma resolução atômica, vendo-se os átomos individualmente, disse o pesquisador Gerhard Meyer, segundo quem se pode considerar este feito similar à capacidade de trespassar um tecido opaco com raios-X para obter uma imagem nítida dos ossos.
Pressupõe um progresso significativo no desenvolvimento da eletrônica molecular, já que para aumentar a velocidade e funcionalidade de dispositivos eletrônicos, computadores, telefones celulares, e reduzir seu tamanho, é preciso trabalhar sobre estruturas atômicas, utilizando ferramentas que permitam ver e manipular a matéria àquela escala. Mais em : http://www.zurich.ibm.com/
Estructura interna de una molécula de pentaceno, de 1,4 nanómetros de longitud. Abajo, modelo de la misma (los átomos grises son de carbono y los blancos de hidrógeno). Los átomos que forman una molécula se han logrado visualizar bien por primera vez, a través de un Microscopio de Fuerzas Atómicas sín Contacto (AFM). Este logro de los científicos del laboratorio de IBM en Zúrich (Suiza) representa un hito en el ámbito de la nanotecnología y la electrónica molecular y un avance en el desarrollo y mejora de las prestaciones de los dispositivos electrónicos, explica la empresa. La molécula es el pentaceno (C22H14), consistente en cinco anillos de benceno enlazados formando una cadena aromática, que es candidato a ser utilizada en nuevos semiconductores orgánicos.
Este logro, que se ha publicado en la revista Science, sigue a otro experimento publicado en la misma revista hace dos meses en el que el equipo midió los estados de carga de los átomos con el mismo tipo de microscopio. Los investigadores de IBM Research – Zurich - Leo Gross, Fabian Mohn, Nikolaj Moll y Gerhard Meyer, en cooperación con Peter Liljeroth, de la Universidad de Utrecht, utilizaran un AFM operado bajo vácuo ultra alzo, y muy bajas temperaturas (–268°C o – 451°F) para fotografar la estructura química de moléculas sueltas de pentaceno.
Así se podrá investigar cómo se trasmite la carga a través de las moléculas o de redes moleculares. Además, los investigadores han conseguido descubrir que la fuerza repulsiva que les ha permitido obtener el contraste suficiente para la imagen procede del efecto cuántico denominado principio de exclusion de Pauli.
En los últimos años, se había conseguido definir nanoestructuras a escala atómica y ahora ha sido posible mostrar la estructura química de una molécula con una resolución atómica, viendo los átomos individuales, ha comentado el investigador Gerhard Meyer, según el cual se puede considerar este hecho similar a la capacidad de traspasar un tejido blando con rayos X para obtener una imagen nítida de los huesos.
Supone un avance significativo en el desarrollo de la electrónica molecular, ya que para aumentar las prestaciones de los dispositivos electrónicos, ordenadores o teléfonos móviles, y reducir su tamaño, es preciso trabajar sobre estructuras atómicas, utilizando herramientas que permitan ver y manipular la materia a dicha escala.Más en: http://www.zurich.ibm.com/
IBM Scientists First to Image the “Anatomy” of a Molecule
Opens new possibilities for exploring the building blocks of future microprocessors and other nanodevices.
IBM scientists have been able to image the “anatomy”—or chemical structure—inside a molecule with unprecedented resolution, using a complex technique known as noncontact atomic force microscopy.
The results push the exploration of using molecules and atoms at the smallest scale and could greatly impact the field of nanotechnology, which seeks to understand and control some of the smallest objects know to mankind.
“Though not an exact comparison, if you think about how a doctor uses an X-ray to image bones and organs inside the human body, we are using the atomic force microscope to image the atomic structures that are the backbones of individual molecules,” said IBM Researcher Gerhard Meyer.
“Scanning probe techniques offer amazing potential for prototyping complex functional structures and for tailoring and studying their electronic and chemical properties on the atomic scale.”
The team’s current publication follows on the heels of another experiment published just two months ago in the June 12 issue of Science (Volume 324, Issue 5933, pp. 1428 – 1431) where IBM scientists measured the charge states of atoms using an AFM.
These breakthroughs will open new possibilities for investigating how charge transmits through molecules or molecular networks.
Understanding the charge distribution at the atomic scale is essential for building smaller, faster and more energy-efficient computing components than today’s processors and memory devices.
These components could one day contribute to IBM's vision of a smarter planet by helping instrument and interconnect the physical world.
As reported in the August 28 issue of Science magazine, IBM Research – Zurich scientists Leo Gross, Fabian Mohn, Nikolaj Moll and Gerhard Meyer, in collaboration with Peter Liljeroth of Utrecht University, used an AFM operated in an ultrahigh vacuum and at very low temperatures (–268°C or – 451°F) to image the chemical structure of individual pentacene molecules.
With their AFM, the IBM scientists, for the first time ever, were able to look through the electron cloud and see the atomic backbone of an individual molecule. While not a direct technological comparison, this is reminiscent of X-rays that pass through soft tissue to enable clear images of bones.
The tip that tipped the scale
The AFM uses a sharp metal tip to measure the tiny forces between the tip and the sample, such as a molecule, to create an image. In the present experiments, the molecule investigated was pentacene. 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 1 million times smaller than the diameter of a grain of sand. 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.
“The key to achieving atomic resolution was an atomically sharp and defined tip apex as well as the very high stability of the system,” recalls IBM scientist Leo Gross. To image the chemical structure of a molecule with an AFM, it is necessary to operate in very close proximity to the molecule.
The range, where chemical interactions give significant contributions to the forces, is less than a nanometer.
To achieve this, the IBM scientists were required to increase the sensitivity of the tip and overcome a major limitation: Similar to the way two magnets would attract or repel each other when getting close, the molecules would easily be displaced by or attach to the tip when the tip was approached too closely—rendering further measurements impossible.
Leo Gross adds, “We prepared our tip by deliberately picking up single atoms and molecules and showed that it is the foremost tip atom or molecule that governs the contrast and resolution of our AFM measurements.”
A tip terminated with a carbon monoxide (CO) molecule yielded the optimum contrast at a tip height of approximately 0.5 nanometers above the molecule being imaged and—acting like a powerful magnifying glass—resolved the individual atoms within the pentacene molecule, revealing its exact atomic-scale chemical structure.
Furthermore, the scientists were able to derive a complete three-dimensional force map of the molecule investigated. “To obtain a complete force map the microscope needed to be highly stable, both mechanically and thermally, to ensure that both the tip of the AFM and the molecule remained unaltered during the more than 20 hours of data acquisition,” says Fabian Mohn, who is working on his PhD thesis at IBM Research – Zurich.
To corroborate the experimental findings and gain further insight into the exact nature of the imaging mechanism, IBM scientist Nikolaj Moll performed first-principles density functional theory calculations of the system investigated.
He explains, “The calculations helped us understand what caused the atomic contrast. In fact, we found that its source was Pauli repulsion between the CO and the pentacene molecule.” This repulsive force stems from a quantum mechanical effect called the Pauli exclusion principle. It states that two identical electrons can not approach each other too closely. More at:
Watch the video
Veja o vídeo
Nenhum comentário:
Postar um comentário