Where less is more
Tiny dimensions, great expectations. That’s nanoscience in a nutshell. Its underlying principle is a revolution in the way we view matter itself. Rather than working with existing materials, nanoscientists aim to create novel materials and structures from the bottom up, out of the tiniest building blocks available - atom by atom, molecule by molecule. Hence the prefix “nano,” (from the Greek for dwarf), which means one millionth of a millimeter or roughly one hundred-thousandth the width of a human hair.
Envsioned application lists, whether offered by starry-eyed futurists or old-school conservatives, sketch a remarkably altered world. Nanoscience, they predict, might touch nearly every area of human existence. Given the ability to control matter at the atomic and molecular scales, we might create nanoscopic drug delivery systems or achieve a far greener environment born of solar energy triumphs and streamlined production lines. Our workplaces might be revolutionized by superfast computers operating on the extraordinary principles of quantum physics, while feather-light yet highly durable materials transform our material landscape - ushering in unsurpassed bridges, skyscrapers and jetliners.
The challenge, however, is significant, and nanoscience has a long way to go before it will shape daily life. To build nanoscopic structures one must be able not only to see but also to manipulate atoms individually, developing minuscule roboarms able to pick up and deposit these tiny building blocks according to design.
Nevertheless, confidence in nanoscale science runs high, with many regarding it as the most important scientific frontier of the twenty-first century. Worldwide investment in this field has increased roughly fivefold in as many years and experts predict that annual nanotech production will exceed $1 trillion by 2015.
Researchers at the Weizmann Institute of Science are carving important advances in this field, working on novel tools or strategies with which to manipulate matter on the nano scale, designing new materials, and probing new ideas for tomorrow’s electronics, medicine and more.
The Institute is optimally poised to make important contributions at this frontier, bringing together top-ranking researchers in an interdisciplinary setting that is highly conducive to the pursuit of nanoscience - where the study of structures far smaller than the human cell demands the expertise and resources of different fields, from materials and computer science, to chemistry and physics and bioengineering.
Here’s a look into a tiny world with huge potential...
A NANO TOOLBOX
Tools for building a small world
How many times when working on something frustratingly tiny like your wife's wrist watch, have you said to yourself, “If I could only train an ant to do this!” - Richard Feynman lectures on miniaturization, 1959
Tools wheel civilization forward. As early humans experimented with the raw materials of their environment, they discovered fire and the miracles it could perform - reorganizing materials to convert clay into pottery, sand into glass, and ores into bronze, iron and other metals.
By the early 17th-century Galileo’s telescope had rocked the very foundations of theology, providing the first concrete observations in support of the Copernican model, which placed the sun, rather than Earth, at the center of the universe. And within decades, Robert Boyle had formulated the idea of chemical elements, paving the way for a conceptual tool - the periodic table - that would later prove an irresistible playground for chemists. These set about heating, cooling, distilling and mixing different combinations of matter in a wave of experimentation that would soon bring about the industrial revolution and, later, the wonders of 20th-century materials science: plastics, computers, lasers, aircraft and even the first space probe, Sputnik 1, launched by the USSR on October 4, 1957.
Unappeased however, by the challenge of exploring the vastness of space, the winds of science were soon blowing in the opposite direction, with researchers seeking the ability to study matter on the tiniest of scales. In 1959 physics Nobel laureate Richard Feynman, speaking at the California Institute of Technology, gave his classic talk “There’s Plenty of Room at the Bottom,” firing the imagination of scientists with the vision of a new discipline devoted to manipulating matter down to the level of a single atom.
But it would take years for researchers to come up with the critical ingredients. They first had to develop the techniques and tools needed to view individual atoms and fleeting, nanosecond-scale events, such as those occurring in the human cell.
Today’s nano toolbox features instruments that perform a range of imagination-stretching functions, including microscopes that can view and even pick up and move individual atoms according to design. These technological advances have been coupled with ever more powerful computers, facilitating the calculation of the properties of nanoparticles.
Weizmann Institute researchers are applying the tools of nanoscience to advance microelectronics. Others are working to develop sensors capable of identifying minute traces of various compounds - a quest with medical and industrial applications; while yet others have pioneered the use of X-rays to analyze the structure of nanosized crystals. Their studies are yielding insights into long-explored riddles, including the origin of life on Earth.
I have discovered something interesting, but I do not know whether or not my observations are correct. - Wilhelm Conrad Roentgen, discoverer of X-rays
In November 1895, German physics professor Wilhelm Conrad Roentgen was in his laboratory studying light phenomena generated by dis-charging an electrical current in a vacuum glass tube when, to his utter disbelief, he suddenly saw the bones of his hand outlined through his flesh.
Roentgen had discovered X-rays. Within weeks, physicians were using these magical rays to see inside the human body and less than three months later, 14-year-old Eddie McCarthy of Massachusetts became the first person to have a broken bone set with their help. The new technology quickly found its way into scientific research, exploding into experimental significance following the 1912 development of X-ray crystallography, which offered a first-time look into the atomic-scale arrangement of crystals. Having exposed crystals to X-ray beams, the father-son team of Henry and Lawrence Bragg, found that the beams diffracted off the crystal’s atoms, and could be captured on film to disclose the crystal structure.
X-ray crystallography has since contributed to the discovery of DNA’s double-helix structure, drug development and far more. Today, sophisticated computational methods are applied to analyzing crystal diffraction patterns.
Studies of how crystals form may weave together a web of unrelated fields, from those targeting semiconductor technologies, to studies of the origin of life, to the design of polymorphs - crystal formations of key importance in pharmacology.
The common denominator is size. To study these research challenges, Institute scientists apply X-rays to view as well as control the growth of crystals at the atomic level.
Profs. Meir Lahav and Leslie Leiserowitz of the Institute’s Materials and Interfaces Department pioneered the use of grazing incidence X-ray diffraction (GIXD) to analyze the structure of nanosized crystallites formed at the interface between air and water. The investigators are able to work out the exact structure of the crystals formed, according to the way the beam diffracts.
In their analyses, the team has yielded insights into a list of riddles, including how cholesterol crystals form in the body, causing heart disease and gallstones when in excess; the fundamental mechanisms of how water freezes; and the possible routes by which biological molecules such as proteins were first formed. The approach was developed in collaboration with a team of Danish physicists.
The team is currently studying how to control the design and growth of polymorphs - crystals that have different shapes despite being made from the same compound. Polymorphs are of keen interest to the pharmaceutical industry due to their potential influence on drug efficacy. For instance, penicillin crystallized into a form that easily dissolves in the body may be more potent than a penicillin drug packaged in a less soluble crystal. Polymorphs also feature prominently in the production of nanoscopic films used in semiconductors.
Delving into the nanoscopic
Ever tried to find out what’s inside a layered chocolate cake without slicing it? How about tackling a similar task, but at the nanoscale? Take ultra-thin films for instance. Used in diverse applications, from opto-electronics to biological sensors, these films are frequently less than 10-15 nanometers thick. Looking inside these tiny, often multilayered films, calls for highly sensitive probes.
Most existing technologies do not provide information about depth, which is essential for evaluating layered structures. Techniques devised to solve this problem tend to be complicated and frequently damage the sample, distorting the results.
Dr. Hagai Cohen of the Weizmann Institute Chemical Services and Prof. Israel Rubinstein of the Materials and Interfaces Department developed a novel method for evaluating certain ultra-thin films that builds upon a common technique for analyzing material surfaces, known as X-ray photoelectron spectroscopy (XPS).
In XPS, the sample is irradiated with X-rays, causing photoelectrons to be ejected. By measuring the energy level of these photoelectrons, it is possible to determine the atoms from which they originated.
Once the photoelectrons have exited, the remaining sample has a positive surface charge, an outcome researchers traditionally sought to eliminate, since the charging distorts the measurements. However, proving that one person’s stumbling block may be another’s stepping stone, Cohen and Rubinstein realized that the charging effect actually provides structural information - the magnitude of change in charge correlates directly with the atoms’ depth within the film, such that the deeper the atom, the smaller the change. They decided to magnify this effect, causing controlled, easily detectable changes that enabled them to determine both the atom type and its depth within the film.
This Weizmann innovation should yield insights into chemical and biological systems as well as advancing a range of microelectronic applications.
Picture a millimeter, then try divide this into a thousand parts. If you've got a good imagination, you might have just managed to visualize a micrometer. To get to a nanometer divide by a thousand again. If you've managed to visualize that, apply for a job with Steven Spielberg. - A nanometer, as described by NanoInvestorsNews.
New sensors capable of identifying minute traces of various compounds are among the hottest items in nanotechnology. Their applications are in areas ranging from industry and medicine to safety and security. For instance, future “cell-on-a-chip” biosensors might be used to diagnose and monitor diabetes and other diseases, food quality and environmental toxins. Biosensors currently represent a rapidly expanding field with an estimated 60 percent annual growth rate.
Doing what comes naturally
Institute scientists have applied the idea of integrating organic molecules into electronics to create a highly sensitive generic sensor that is based on the unique ability of molecules in nature to “recognize” each other in a key-fits-lock manner.
The sensor, called a molecular-controlled semi-conductor resistor (MOCSER), was developed by Profs. David Cahen of the Material and Interfaces Department, Abraham Shanzer of the Organic Chemistry Department and Ron Naaman of the Chemical Physics Department. Its sensing capacity is determined by the type of molecules glued onto the semiconductor surface.
The molecules are synthesized in such a way that one end binds to the semiconductor surface, while the other end is free to bind to molecules in the target sample. When the molecule bound to the semiconductor “senses” the presence of a specific molecule, it undergoes a change that can be translated by the solid-state device into an electronic signal, providing a clear diagnosis of the sample.
Using a MOCSER, the scientists were able to identify the presence of nitric oxide - a molecule crucial to a variety of biological processes, including brain stimulation. The molecule could be detected down to a minute concentration of a few parts per billion in solutions and in air. Tests with brain tissue were also performed in collaboration with Prof. Menahem Segal of the Neurobiology Department. The device could potentially offer an important early warning system for asthma sufferers.
Tomorrow’s reporters - cells on a chip
Institute scientists are collaborating in a multinational project aimed at using living cells as “reporters” or biosensors. The idea is to fit the silicon chips used in today’s computers with cells that will turn on and off (through fluorescence) to indicate the presence of specific molecules.
Systems of this sort could potentially be used to sense hundreds of substances - from environmental toxins to viruses and food contaminants. At the Institute, Prof. Benjamin Geiger and Dr. Uri Alon of the Molecular Cell Biology Department are addressing some of the obstacles to creating these sensors. Geiger - whose research focuses on the way cells move around the body, adhering to anchorage points along the way - is searching for the best strategy with which to physio-logically connect the cells to the chip. Alon hopes to determine how best to “rig up” the cellular elements destined to serve as fluorescent reporters, on the basis of his experience in tracing the networks of genes and proteins that govern the cell’s response to its environment.
On the road to computer miniaturization a team of Institute scientists has come up with a bonus byproduct - an ultrasensitive tool for detecting foreign material on surfaces, even when present in minuscule amounts.
Conducting the project were Prof. Yehiam Prior, Dr. Gad Haase and Prof. Ilya Averbukh of the Chemical Physics Department and Prof. Abraham Shanzer of the Organic Chemistry Department.
The team had set out to explore a growing idea in materials science: the use of light instead of electrical current to store and transmit information in electronic devices, thus increasing storage capacity and speed. Their idea was to use light to “read” and “write” information on a nano scale, using a modified form of microscopy.
Current atomic force microscopy (AFM) methods use a sharp-tipped instrument to observe atom-sized features on a surface (see box). But while such methods can see (“read”) the surface topography very well, they cannot alter the surface (“write”) reliably. To address this difficulty, the team set out to study whether the AFM tip could be used to read information by scanning incoming light pulses or similarly, to write information through a series of outgoing light pulses.
The first step, reading information as a sequence of light pulses, proved successful. “We were able to identify molecules on the target surface, even when present in minute amounts,” says Prior. This new diagnostic tool, described in Physical Review, should prove valuable in identifying submicron or nanosized defects in microelectronic devices. Next, the team plans to target the other, more challenging step of writing nanoscale information using light pulses. An achievement of this sort would open a world of possibilities for electronic devices.
Edging in on the atomic scale
In the early 1980s, IBM researchers in Switzerland startled the scientific community with the development of two novel technologies that offered a spectacular view into atomic-scale landscapes: atomic force microscopy (AFM) and scanning tunneling microscopy (STM).
AFM works like an old-fashioned record player, reading surfaces with a needle-fine probe. As the probe moves up and down over this surface it causes a cantilever arm to which it is attached to bend in response. These tiny movements are detected by a laser beam and decoded via a computer, which translates the incoming tactile information into an atom-by-atom image.
STM, which earned its developers the 1986 Nobel prize in physics, works by measuring a quantum effect called tunneling. As it sweeps across the target surface, nanometers away, an ultrasharp probe carrying a small electrical charge causes electrons to “tunnel” across an existing gap. This tiny electrical current is then decoded via a computer to create an atomic-scale image.
Of sieves and sensors
Zeolite minerals have researchers around the world scurrying to uncover their structural secrets. Organized in the form of a porous sieve into which other molecules can fit, zeolites are used in a variety of industrial applications, including petroleum refinement. Nevertheless, researchers believe that these materials might have far more to offer in areas ranging from microelectronics to medical diagnosis - if only it were possible to change a tiny structural detail: the size of their holes.
The potential of these materials stems primarily from their porous and electrically charged nature, which allows them to interact with atoms, ions and molecules throughout their material body rather than at their surface alone. However, the range of chemical interactions that zeolites can promote is limited by the size of their pores. “Zeolite pores are generally 0.5-1.2 nanometers in size, making them inaccessible to many materials, which explains why widespread efforts target the production of larger-pored zeolites,” explains Prof. Daniella Goldfarb of the Institute’s Chemical Physics Department.
Efforts to synthesize large-pore zeolites recently led to the synthesis of a new family of materials (referred to as mesoporous materials) by scientists at Mobil Oil. Goldfarb is currently collaborating with Prof. Shimon Vega of the same department to better understand the surface properties and formation process of these materials. A better understanding of how mesoporous materials are formed might enhance the ability to control their resulting structure and pore size, advancing the production of new catalysts and molecular machines. These would contain porous materials that could function as scaffolds for synthetic and biological materials, serving for instance, as support material for protein-based sensors in medical diagnosis as well as for future nano-wires in microelectronics and optical communications.
Islands of gold
Chemical sensors generally consist of two primary units: a “recognition unit” that detects and identifies substances, and a “reporting unit,” that receives information from the recognition unit and passes it on to a human operator.
A new sensor developed by researchers at the Institute’s Department of Materials and Interfaces allows the construction of flexible reporting units that can successfully communicate with a variety of sensor recognition units. The study was performed by Prof. Israel Rubinstein, Dr. Alexander Vaskevich, then doctoral student Gregory Kalyuzhny and post-doc Dr. Marie Anne Schneeweiss.
The method is based on depositing vaporized gold on a transparent surface (such as glass or plastic), in layers so thin (less than a millionth of a centimeter) they create “gold islands” that are practically see-through. Because of their transparency scientists can beam a ray of light through an island to its other side, where the ray’s intensity and the spectrum of its wavelengths can be measured.
The researchers then bind a recognition unit (such as antibodies that bind to a toxic molecule) to the gold island. Upon recognizing a substance, the recognition units change the way in which the island absorbs the incoming ray of light. This change indicates to the human operator that a substance has been identified, and its specific nature.
The method, described in the Journal of the American Chemical Society, might allow the construction of new recognition units for use in chemical and biological sensors. Yeda, the Institute’s technology transfer arm, has filed a patent application for this approach.
Sensing material defects
Material failure is a grave concern in man-made structures. Wind, friction, extreme temperatures and a range of other mechanical and environmental stresses are all in a day’s work for planes, bridges, skyscrapers, satellites and other fixtures of modern civilization. Engineers have devised a battery of tests to prevent sudden material failure by prior detection of material fatigue.
Nanotubes may soon join these preventive efforts. Prof. Daniel Wagner of the Institute’s Materials and Interfaces Department has found that the nanotubes (tiny, extremely tough tubes made of a web of carbon atoms) can be used to monitor mechanical stress in materials. His study, published in Applied Physics Letters, revealed that nanotubes offer a highly sensitive means of detecting material defects induced by stress, such as microscopic breaks or holes. Future applications based on this finding may use nanotubes as an early warning system of material fatigue in airplanes and other structures.