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La plataforma permanente Atomium Culture reúne a las universidades, periódicos y empresas más prestigiosos de Europa para promover el flujo del conocimiento más allá de fronteras, entre sectores y hacia el público en general.

It’s a Small World After All: Manipulations at the Nanoscale

Por: | 20 de marzo de 2014

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By Sergei Vlassov, University of Tartu

Alchemy aims to transform base metals into gold; nanotechnology, on the other hand, can transform gold into something else — or at least make it behave differently. For example, the melting point of gold changes greatly when it comes to melting nanoparticles of gold, and the temperature at which the particles melt changes, sometimes by as much as several hundred degrees, depending on the size of the nanoparticles.

Nanotechnologies have long become part of our day-to-day life. From mobile phones and computers to cosmetics and foods, we are surrounded by objects that benefit from or are based on ‘nano’ effects, and many more are round the corner.

However, few people know the magic behind nanotechnology, which goes far beyond merely making things smaller. The miracle of nanotechnology, and the reason why it is of enormous scientific and technological interest, can be explained by the fact that the properties and behaviour of materials at the nanoscale are very different from those at the micro- and macro-scale. These differences are exploited in many unique applications of nanotechnology. The properties include melting point (explained earlier), electrical and thermal conductivity, mechanical strength and many other essential characteristics of materials. In addition to size, the shape of the structures also contributes to the changed properties, which can be fine-tuned to satisfy precise requirements of some applications — the colour of LEDs (light emitting diodes), for example. Thus, nanotechnology is totally novel; nanotechnology creates something that never existed before.

In recent years many scientists have focused their attention on the mechanical and frictional properties of nanowires (wires smaller than 100 nm in diameter: the diameter of a human hair is about 80 000 to 100 000 nm). Nanowires, because they are ultra-thin, possess exceptional mechanical and electrical properties and are used in many electromechanical systems and sensors.

The changed properties of nanowires are mainly the result of a large surface-to-volume ratio. Such vastly larger surfaces of nanowires relative to their bulk make them far more sensitive to the chemicals that the wires can adsorb, making them far superior in sensing the presence of chemicals. Nanowires are also extremely elastic and do not crack or break despite enormous stress. At the same time, even minimal force is enough to make nanowires vibrate, making them particularly useful in ultrasensitive devices.

Studying and manipulating such small materials, however, pose serious challenges. To get the most out of nanomaterials, it is essential to study individual nanostructures and measure their properties and behaviour. However, measuring on such a small scale is tricky and requires extremely fine and sensitive tools. Computer simulations would be a good way to study the nanoworld; unfortunately, the properties as measured by physical experiments turn out to be quite different from those predicted by such simulations — nanomaterials, it seems, are beyond the pale of the laws of classical physics. Nor can the novel computational methods widely used in studying atoms and molecules be easily applied to nanoscale objects, because when viewed from that end of the spectrum (that is, relative to molecules), nanostructures are seen to be huge, consisting of thousands of atoms; precise calculations would require enormous computing power and time even by today’s standards. Actual physical experiments are therefore unavoidable, and many such experiments are required to generate the masses of data we need for a better understanding of the nanoworld.

Our team at the University of Tartu, Estonia, is engaged in manipulating (dragging, pushing, bending, breaking, etc.) nanostructures using nanopositioners inside a scanning electron microscope (SEM). We use a device that has an ultrafine tip and extremely precise controls. The device is installed and works inside a chamber of the SEM. Work can be quite entertaining and is in some ways similar to playing billiards or hockey — the set-up is even equipped with a game console controller. However, fun is incidental to what we do.

The sharp tip that we use for manipulating nano-objects is attached to a force sensor, of our own making, which is based on a tiny tuning fork made of quartz. The fork oscillates thousands of times in a second, and its oscillation parameters depend on the force (load) acting on it. We can measure many relevant properties of nanomaterials. For example, we can measure the friction between different nanostructures and various substrates when our test objects are pushed or dragged. The laws of friction at nanoscale are dramatically different from those we have known for centuries. It is absolutely necessary to understand the fundamentals of nanofriction for building any nanomachine. In addition to friction measurements, we conduct a number of mechanical tests by deforming nanostructures to the limits of their elasticity or plasticity — or even past their breaking point, in a controlled fashion — as we simultaneously record the forces acting on the structures and those generated by the structures. In this way, we obtain information about strength, rigidity and other mechanical properties. We also supplement these measurements by applying suitable algorithms to the experimental results. For example, the profile of a nanowire deformed but within its elastic limits provides essential information on its mechanical and frictional properties.

Manipulations at the nanoscale provide the most natural and straightforward method of studying the peculiarities of nanoworld as well as of developing, assembling and testing the prototypes of innovative devices. The study involves habitual actions that often give totally new and unexpected results: ‘the next big thing is small’.


Sergei Vlassov
University of Tartu

Hay 1 Comentarios

Me encanta conocer el mundo desde la escala atomica, la naturaleza trabaja a escala molecular y dai su gran eficiencia

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