Chemical thermometers – a breakthrough that cater the need in microelectronics industry

With the massive miniaturisation of electronic components, density of the electronic components has been enhanced significantly along with the flowing of heat which results in overheating of the components. But conventional methods are unable to estimate the temperature in the electronic components due to limitation imposed by size of it.

Researchers have recently devised a solution of the above issue by fabricating a molecular film and using it in an electronic component of a nanometric scale. The film is made by spin crossover molecules, a temperature sensitive molecule, which is extremely stable even after several uses. Due to the bi-stability property of these molecules, these molecules exist into two electronic states with difference physical property and interchange the states by absorbing and loosing energy.

Once deposited in the form of a film on an electronic component, the optical properties of SCO molecules change depending on the temperature, enabling this chemical thermometer to establish a nanometric-scale thermal map of the surface of microelectronic circuits. The devise will soon be sued at industrial scale with improved design.

Storage solution using silicon in battery with the aid of nanotechnology

Silicon along with carbon nanotubes has been used to develop a nanostructure to make an effective design for battery anodes. CNT is used to strengthen the material and modify the way the silicon interacts with lithium, which has been extensively used in electrical cars and other devices.

Scientists at the U.S. Department of Energy's Pacific Northwest National Laboratory have used a novel way to use silicon. Silicon, used in computer chips is attractive as it can hold 10 times the electrical charge per gram compared to graphite. The trouble is, silicon expands greatly when it encounters lithium, and it is too weak to withstand the pressure of electrode manufacturing.

To tackle these issues, a unique nanostructure that prevents silicon's expansion when it is mixed with carbon. Scientist work, which was recently published in the journal Nature Communications, could inform new electrode material designs for other types of batteries and eventually help increase the energy capacity of the lithium-ion batteries in electric cars, electronic devices, and other equipment.

How they do it!!

A conductive and stable form of carbon, graphite is well suited to packing lithium ions into a battery's anode as it charges. Silicon can take on more lithium than graphite, but it tends to expand about 300 percent in volume, causing the anode to break apart. The researchers created a porous form of silicon by aggregating small silicon particles into microspheres about 8 micrometers in diameter.

The electrode with porous silicon structure exhibits a change in thickness of less than 20 percent while accommodating twice the charge of a typical graphite anode. However, unlike previous versions of porous silicon, the microspheres also exhibited extraordinary mechanical strength, thanks to carbon nanotubes that make the spheres resemble balls of yarn.

The researchers created the structure sequentially, starting by coating the carbon nanotubes with silicon oxide. Next, the nanotubes were put into an emulsion of oil and water. Then they were heated to boiling. The coated carbon nanotubes condense into spheres when the water evaporates. Then aluminum and higher heat is used to convert the silicon oxide into silicon, followed by immersion in water and acid to remove by-products. What emerges from the process is a powder composed of the tiny silicon particles on the surface of carbon nanotubes.

Electrostatic Force Microscopy (EFM): Imaging electric charge using microbial nanowires: Breakthrough in protein based nanoelectronics

Recent study carried out by UMass Amherst researchers has showed that electric charges propagate along microbial nanowires of the microbe Geobacter just as they do in carbon nanotubes.

Physicists affirmed that injection of electrons at one end in the microbial nanowires lit up the whole filament as the electrons propagated through the nanowire, similar to the other highly conductive materials. The technique applied here is known as electrostatic force microscopy (EFM). This technique has immense environment implications as conversion of waste to biogas is possible by conducting electricity through these wires. The nanowires permit Geobacter to live on iron and other metals in the soil, significantly changing soil chemistry and playing an important role in environmental cleanup. Microbial nanowires are also key components in the ability of Geobacter to produce electricity, a novel capability that is being adapted to engineer microbial sensors and biological computing devices.

In biological materials, electrons typically move by hopping along discrete biochemical stepping-stones that can hold the individual electrons. By contrast, electrons in microbial nanowires are delocalized, not associated with just one molecule, leading to metallic-like conductivity phenomena.

This investigation not only brings up an important new principle in biology but also in materials science. Natural amino acids, when arranged correctly, can propagate charges similar to molecular conductors. It opens exciting opportunities for protein-based nanoelectronics due to the fact that manipulating microbes for electrical application seems feasible. Efforts are also directed towards building electronic sensors to detect environmental contaminants and microbiological computers using Geobacter.

Mechanosensation device by molybdenum disulfide (MoS2)

In a breakthrough invention, scientists have successfully executed an experiment of piezoelectricity and the piezotronic effect in an atomically thin material, molybdenum disulfide (MoS₂), resulting in a unique electric generator and mechanosensation devices; although the piezoelectric effect in this material had already been predicted theoretically.

Piezoelectricity is defined as a phenomenon in which pressure generates an electrical voltage in a material or vice-versa. But no experimental observation of piezoelectricity has been made yet for few atom thickness material. The observation of molybdenum disulfide material has unfolded the potential for new types of mechanically controlled electronic devices.

In an interesting application of this phenomenon, this material could be made as a wearable device, integrated into clothing, to convert energy from your body movement to electricity and power wearable sensors or medical devices, or perhaps supply enough energy to charge cell phone.

There are two keys to using molybdenum disulfide for generating current: using an odd number of layers and flexing it in the proper direction. The material is highly polar, but an even number of layers cancels out the piezoelectric effect. The material's crystalline structure also is piezoelectric in only certain crystalline orientations.

Group of researchers placed thin flakes of MoS₂ on flexible plastic substrates and determined how their crystal lattices were oriented using optical techniques. They then patterned metal electrodes onto the flakes and measure current flow as the samples were mechanically deformed. They monitored the conversion of mechanical to electrical energy, and observed voltage and current outputs.

The researchers also noted that the output voltage reversed sign when they changed the direction of applied strain, and that it disappeared in samples with an even number of atomic layers, confirming theoretical predictions published last year. The presence of piezotronic effect in odd layered MoS₂ was also observed for the first time.

To be piezoelectric, a material must break central symmetry. A single atomic layer of MoS₂ has such a structure, and should be piezoelectric. However, in bulk MoS₂, successive layers are oriented in opposite directions, and generate positive and negative voltages that cancel each other out and give zero net piezoelectric effect.

In fact, MoS₂ is just one of a group of 2D semiconducting materials known as transition metal dichalcogenides, all of which are predicted to have similar piezoelectric properties. These are part of an even larger family of 2D materials whose piezoelectric materials remain unexplored. The research could lead to complete atomic-thick nanosystems that are self-powered by harvesting mechanical energy from the environment. This study also reveals the piezotronic effect in two-dimensional materials for the first time, which greatly expands the application of layered materials for human-machine interfacing, robotics, MEMS, and active flexible electronics.

Modulated Nanostructure: Nanowire bridging transistors: The new Buzz word for next-generation electronics

Silicon has been established as one of the widely used material in the integrated circuit since approximately 60 years. It is used to fabricate transistors using conventional method, where etching of the layers was done to formulate some structures. However, circuit based on silicon reach its operational speed limit and does not work above certain temperature. In addition to that, ever increasing demand of miniaturization has led to the development of advanced manufacturing technique where nanostructure material plays significant roles along with the addition of other semiconducting material such as gallium nitride. It does not only show promise for a new generation of fast, robust electronic and photonic devices, but also opens up the scope of innovation for the researchers. Such is the case of three dimensional nanowire transistors, developed by scientists of University of California.

 

 One of the technical problem silicon substrate is facing over the years is the lattice parameter mismatch with other materials. Match is necessary due to the growth technique associated with integrated circuit, which in turn faces major limitation as far as the growth material is concerned. To overcome these challenges, nanowire made of semiconductor materials was made on top of silicon surfaces. Due to the lower surface area of nanowire which acquires the place of silicon, problem of lattice mismatch does not arise. The new technology could be used, for example, to build sensors that can operate under high temperatures, for example inside aircraft engines. In the near future, machine will be dependent on a variety of sensors and control systems that operate in extreme environments, such as motor vehicles, boats, airplanes, terrestrial oil and ore extraction, rockets, spacecraft, and bodily implants.

 

The researchers have been able to make these nanowires operate as transistors, and combine them into more complex circuits as well as devices that are responsive to light. They have developed techniques to control the number of nanowires, their physical characteristics and consistency. The technology also leverages the well-established technology for manufacturing silicon integrated circuits.

Self assembled nanostructure through field assisted phase transition

In the year of 2012, scientist developed the idea of using nanoparticles as building block of functional material which can be engineered to make a computer chip that can assemble itself.

The research carried out by researchers of NASA and University of Delware reported an article about the self assembled with specific structures, built by nanomaterials.

They have observed transition of paramagnetic colloids from random structures to organised crystalline structures when an external magnetic field with desired frequency and field strength was applied into it. This kind of phase separation/transition provides the opportunity to build crystals using magnetic field. It is also useful in understanding the phenomena/mechanisms through which the materials are turned into crystalline.

This new phenomenon could prove worthy for manufacturing new nanoscale self assembled components due to a definite relationship between applied electric field and the conversion of disorder to order structure.

For further reading regarding field assisted phase transition:

http://www.pnas.org/content/109/40/16023.full.pdf+html?sid=d4c55815-5d87-4419-b4da-dd7cc0eaeb9c

Nanotechnology Breakthroughs by International Business Machines Corporation (IBM)

Source : http://www-03.ibm.com/press/attachments/28488.pdf

 

In chronological order:

 

1981 - IBM scientists invent the  Scanning Tunneling Microscope, giving ready access for the first time to the nanoscale world of individual atoms and molecules on electrically conducting substrates.

1986 -The  Atomic Force Microscope is invented by IBM and Stanford University scientists, quickly becoming the workhorse of nanoscience, providing general purpose imaging and manipulation in the nanometer realm.

1986 - IBM scientists Gerd Binnig and Heinrich Rohrer win the  Nobel Prize in Physics for the Scanning Tunneling Microscope.

1988 - IBM scientists observe  photon emission from local nanometer-sizes areas stimulated by a scanning tunneling microscope, allowing phenomena such as luminescence and fluorescence to be studied on the nanometer scale.

1989 - IBM Fellow Don Eigler is the  first to controllably manipulate individual atoms on  a surface, using the STM to spell out "I-B-M" by positioning 35 xenon atoms, and in the process, perhaps creating the world’s smallest corporate logo.

1991 -IBM scientists demonstrate an  atomic switch, a significant milestone on the road to the eventual design of electronic devices of atomic dimensions.

1993 – Scientists at IBM and NEC  independently discover single-wall carbon nanotubes and the methods to produce them using metal catalysts.

1996 - IBM scientists extend STM manipulation techniques to  position individual  molecules at room temperature for the first time.

1996 - The  world's smallest abacus is created out of 10 atoms by scientists at IBM, another major milestone in engineering at the nanoscale.

1998 -  IBM scientists and partners discover a molecular wheel, which shows promise for making nanoscale mechanical gears and motors.

 2000 - IBM and university researchers develop nanomechanical sensors using  tiny silicon  fingers to detect minute quantities of biochemical substances and to recognize specific patterns of DNA.

2001 - IBM's "constructive destruction" method overcomes major hurdle for building computer chips beyond silicon with a  method to separate semiconducting and metallic  nanotubes to form a working transistor on the nanoscale

2001 - IBM scientists unveil the  world's first single-molecule computer circuit, carbon nanotube transistors transformed into logic-performing integrated circuits, a major step toward molecular computers.

 

2002 - IBM researchers build world's smallest operating computing circuits using a  molecule cascade, wherein molecules move in a manner analogous to falling dominos.

2003 -- Scientists from IBM, Columbia University and the University of New Orleans demonstrate the first  three-dimensional self assembly of magnetic and semiconducting nanoparticles, a modular assembly method that enables scientists to bring almost any materials together.

2003 - IBM scientists demonstrate the  world's smallest solid-state light emitter, suggesting that carbon nanotubes may be suitable for optoelectroinics.

2004 -- IBM scientists develop a new technique called “spin-flip spectroscopy” to study the properties of atomic-scale magnetic structures. They use this technique to measure  a  fundamental magnetic property of a single atom -- the energy required to flip its magnetic  orientation.

2004 – IBM scientists measure the tiny  magnetic force from a single electron spin using an ultra sensitive magnetic resonance force microscope, showing the potential of vastly extending the sensitivity of magnetic resonance imaging (MRI).

2004 -- IBM scientists  manipulate and control the charge state of individual atoms. This ability to add or remove an electron charge to or from an individual atom can help expand the scope of atom-scale research. Switching between different charge states of an individual atom could enable unprecedented control in the study of chemical reactivity, optical properties, or magnetic moment.

2004 -- IBM scientists make breakthrough in  nanoscale imaging -- the ability to detect the faint magnetic signal from a single electron buried inside a solid sample is a major milestone toward creating a microscope that can make three-dimensional images of molecules with atomic resolution.

2005 -- Using nanoelectronic fabrication technologies, IBM researchers create a tiny device that  slows the speed of light, representing a big advance toward the eventual use of light in place of electricity in the connection of electronic components, potentially leading to vast improvements in the performance of computers and other electronic systems.

2006 -- IBM researchers build the  first complete electronic integrated circuit around a  single “carbon nanotube” molecule, a new material that shows promise for providing enhanced performance over today’s standard silicon semiconductors. The achievement is significant because the circuit was built using standard semiconductor processes and used a single molecule as the base for all components in the circuit, rather than linking together individually-constructed components. This can simplify manufacturing and provide the consistency needed to more thoroughly test and adjust the material for use in these applications.

2006 -- IBM scientists develop a powerful new technique for  exploring and controlling  atomic magnetism, an important tool in the quest not only to understand the operation of future computer circuit and data-storage elements as they shrink toward atomic dimensions, but also to lay the foundation for new materials and computing devices that leverage atom-scale magnetic phenomena.

2006 – In a study investigating the fundamentals of molecular electronics, the  quantum  mechanical effects of attaching gold atoms to a molecule were elucidated. The work demonstrated that it is not only possible to control the atomic-scale geometry of a metal-molecule contact, but also its coupling strength and the phase of the orbital wave function at the contact point.

2007 -- IBM demonstrates the first-ever manufacturing application of "self assembly" used to create a vacuum -- the ultimate insulator -- around nanowires for next-generation microprocessors for its  airgap chip technique.

2007 - IBM researchers in collaboration with scientists from the ETH Zurich demonstrate a new, efficient and precise technique to  “print” at the nanoscale.

2007 - IBM unveils two  nanotechnology breakthroughs as building blocks for atomic structures and devices: Magnetic atom milestone brings single-atom data storage closer to reality; single-molecule switching could lead to molecular computers.

2007 - IBM researchers develop magnetic resonance imaging (MRI) techniques to visualize nanoscale objects. This technique brings  MRI capability to the nanoscale level  for the first time.

2008 - IBM scientists, in collaboration with the University of Regensburg in Germany, are the first ever to measure  the force it takes to move individual atoms on a surface.

2009 – IBM Research builds  microscope with 100 million times finer resolution than current MRI, extending three-dimensional MRI to the nanoscale.

 2009 - IBM scientists reach a landmark in the field of nanoelectronics: the development and demonstration of novel techniques to  measure the distribution of energy and heat in  powered carbon nanotube devices. By employing these techniques, IBM researchers have determined how the energy of electrical currents running through nanotubes is converted into heat and dissipated into collective vibrations of the nanotube's atoms, as well as surface vibrations of the substrate beneath it.

2009 - IBM scientists in collaboration with the University of Regensburg, Germany, and Utrecht University, Netherlands, for the first time demonstrate the ability  to measure the  charge state of individual atoms using non contact atomic force microscopy.

2009 - In an effort to achieve energy-aware computing, the Swiss Federal Institute of Technology Zurich (ETH) and IBM plan to build a  first-of-a-kind water-cooled  supercomputer that will directly repurpose excess heat for the university buildings. The system is expected to save up to 30 tons of CO2 per year, compared to a similar system using today's cooling technologies.

 

2009 – IBM launches new research effort for  next generation electric energy storage, exploring battery technologies to drive electric vehicle adoption and make energy grids more efficient.

 

Breakthrough in transistor fabrication without semiconductors

Michigan Technological University scientists led by professor of physics Yoke Khin Yap have created a quantum tunneling device that acts like like an FET transistor and works at room temperature without using semiconducting materials.

The trick was to use boron nitride nanotubes (BNNTs) with quantum dots made from gold. When sufficient voltage is applied to the device, it switches from insulator to a conducting state. When the voltage is low or turned off, it reverts to its natural state as an insulator. There is no leakage current of electrons escaping from the gold dots into the insulating BNNTs, thus keeping the tunneling channel cool. In contrast, silicon is subject to leakage, which wastes energy in electronic devices and generates a lot of heat, limiting miniaturization of transistors.

Carpets of boron nitride nanotubes, which are insulators and highly resistant to electrical charge were grown on a substrate. Using lasers, quantum dots (QDs) of gold  are deposited as small as three nanometers across on the tops of the BNNTs, forming QDs-BNNTs. BNNTs are the perfect substrates for these quantum dots due to their small, controllable, and uniform diameters, as well as their insulating nature. BNNTs confine the size of the dots that can be deposited. Now if we applied biasing, electrons jumped very precisely from gold dot to gold dot, which is known as quantum tunneling.

Other people have made transistors that exploit quantum tunneling. However, those tunneling field effect transistors have only worked in low temperature. The gold islands have to be on the order of nanometers across to control the electrons at room temperature. If they are too big, too many electrons can flow.

For further reading
http://www.readcube.com/articles/10.1002/adma.201301339?

Thermocrystal: an excellent idea to control the direction of heat by nanoparticle alloy

An MIT scientist has developed a technique that provides a new way of manipulating heat, allowing it to be controlled much as light waves can be manipulated by lenses and mirrors.

The approach relies on engineered materials consisting of nanostructured semiconductor alloy crystals. Heat is a vibration of matter, a vibration of the atomic lattice of a material like sound. Such vibrations can also be thought of as a stream of phonons, which is equivalent to the photons that carry light. The new approach is similar to recently developed photonic crystals that can control the passage of light.

The spacing of tiny gaps in these materials is tuned to match the wavelength of the heat phonons. It’s a completely new way to manipulate heat. Heat differs from sound in the frequency of its vibrations: Sound waves consist of lower frequencies (up to the kilohertz range, or thousands of vibrations per second), while heat arises from higher frequencies (in the terahertz range, or trillions of vibrations per second).

In order to apply the techniques already developed to manipulate sound, first step was to reduce the frequency of the heat phonons, bringing it closer to the sound range. Phonons for sound can travel for kilometres, but phonons of heat only travel for nanometers. That’s why we couldn’t hear heat even with ears.
Heat also spans a wide range of frequencies, while sound spans a single frequency. To get rid of the problem, the first thing to do is to reduce the number of frequencies of hea, bringing these frequencies down into the boundary zone between heat and sound. Making alloys of silicon that incorporate nanoparticles of germanium in a particular size range accomplished this lowering of frequency, scientist found.

Reducing the range of frequencies was also accomplished by making a series of thin films of the material, so that scattering of phonons would take place at the boundaries. This ends up concentrating most of the heat phonons within a relatively narrow window of frequencies.

Following the application of these techniques, more than 40 percent of the total heat flow is concentrated within a hypersonic range and most of the phonons align in a narrow beam, instead of moving in every direction.
As a result, this beam of narrow-frequency phonons can be manipulated using phononic crystals similar to those developed to control sound phonons. Because these crystals are now being used to control heat instead, these are referred to as thermocrystals, a new category of materials.

These thermocrystals might have a wide range of applications, including in improved thermoelectric devices, which convert differences of temperature into electricity. Such devices transmit electricity freely while strictly controlling the flow of heat.

Most conventional materials allow heat to travel in all directions, like ripples expanding outward from a pebble dropped in a pond; thermocrystals could instead produce the equivalent of those ripples only moving out in a single direction. The crystals could also be used to create thermal diodes; materials in which heat can pass in one direction, but not in the reverse direction. Such a one-way heat flow could be useful in energy-efficient buildings in hot and cold climates.

Other variations of the material could be used to focus heat to concentrate it in a small area. Another intriguing possibility is thermal cloaking, materials that prevent detection of heatto shield objects from detection by visible light or microwaves.

For further reading: http://prl.aps.org/pdf/PRL/v110/i2/e025902

New Graphene Sensor for more sensitive camera

Recently scientists at Nanyang Technological University invented a new camera sensor which could revolutionize current camera market by its ability to take clear photos in dim conditions.

The new sensor made from graphene, is believed to be the first to be able to detect broad spectrum light, from the visible to mid-infrared, with high photoresponse or sensitivity. This means it is suitable for use in all types of cameras, including infrared cameras, traffic speed cameras, satellite imaging and more.

Not only is the graphene sensor 1,000 times more sensitive to light than current imaging sensors found in today's cameras, it also uses 10 times less energy as it operates at lower voltages. When mass produced, graphene sensors are estimated to cost at least five times cheaper due to its high electrical conductivity among other properties such as durability and flexibility.

This sensor could have great impact not only on the consumer imaging industry, but also in satellite imaging and communication industries, as well as the mid-infrared applications, While designing this sensor, current manufacturing practices have been kept in mind. This means the industry can in principle continue producing camera sensors using the CMOS (complementary metal-oxide-semiconductor) process, which is the prevailing technology used by the majority of factories in the electronics industry. Therefore manufacturers can easily replace the current base material of photo sensors with our new nano-structured graphene material. Cost of manufacturing imaging sensors will fall, which eventually leads to cheaper cameras with longer battery life, if this is adopted by industry.

Researcher came up with an innovative idea to create nanostructures on graphene which will trap light-generated electron particles for a much longer time, resulting in a much stronger electric signal. Such electric signals can then be processed into an image, such as a photograph captured by a digital camera. The trapped electrons is the key to achieving high photoresponse in graphene, which makes it far more effective than the normal CMOS or CCD (charge-coupled device) image sensors. Essentially, the stronger the electric signals generated, the clearer and sharper the photos. The performance of graphene sensor can be further improved through nanostructure engineering of graphene.

Material That Slows Light Opens New Possibilities in Solar Energy

University at Buffalo engineers have created a more efficient way to catch rainbows, an advancement in photonics that could lead to technological breakthroughs in solar energy, stealth technology and other areas of research.

They developed a hyperbolic metamaterial waveguide, which is an advanced microchip made of alternate ultra-thin films of metal and semiconductors and insulators. The waveguide halts and ultimately absorbs each frequency of light, at slightly different places in a vertical direction, to catch series of wavelengths.

Electromagnetic absorbers have been studied for many years, especially for military radar systems. Right now, researchers are developing compact light absorbers based on optically thick semiconductors or carbon nanotubes. However, it is still challenging to realize the perfect absorber in ultra-thin films with tunable absorption band.

 Ultra-thin films are developed that will slow the light and therefore allow much more efficient absorption. Light is made of photons; because they move extremely fast are difficult to control. In their initial attempts to slow light, researchers relied upon cryogenic gases. But because cryogenic gases are very cold, this process is not industrially feasible.

Earlier researchers made nano-scale-sized grooves in metallic surfaces at different depths, which altered the optical properties of the metal. While the grooves worked, they had limitations; the energy of the incident light cannot be transferred onto the metal surface efficiently, which hindered its use for practical applications. The hyperbolic metamaterial waveguide solves that problem because it is a large area of patterned film that can collect the incident light efficiently. It is referred to as an artificial medium with subwavelength features whose frequency surface is hyperboloid, which allows it to capture a wide range of wavelengths in different frequencies including visible, near-infrared, mid-infrared, terahertz and microwaves.

It could lead to advancements in an array of fields. For example, in electronics there is a phenomenon known as crosstalk, in which a signal transmitted on one circuit or channel creates an undesired effect in another circuit or channel. The on-chip absorber could potentially prevent this.

The on-chip absorber may also be applied to solar panels and other energy-harvesting devices. It could be especially useful in mid-infrared spectral regions as thermal absorber for devices that recycle heat after sundown.

Technology such as the Stealth bomber involves materials that make planes, ships and other devices invisible to radar, infrared, sonar and other detection methods. Because the on-chip absorber has the potential to absorb different wavelengths at a multitude of frequencies, it could be useful as a stealth coating material.

 

 

For further reading: http://www.nature.com/srep/2013/130213/srep01249/full/srep01249.html

Carbon Atom for Ultra-Small Energy-Efficient Electronic Devices

A team of scientists from Tyndall National Institute at University College Cork and the National University of Singapore have designed and fabricated ultra-small devices for energy-efficient electronics. By finding out how molecules behave in these devices, a ten-fold increase in switching efficiency was obtained by changing just one carbon atom. These devices could provide new ways to combat overheating in mobile phones and laptops, and could also aid in electrical stimulation of tissue repair for wound healing.

 Scientists opined that these molecules are very useful because they allow current to flow through them when switched ON and block current flow when switched OFF. The results of the study show that simply adding one extra carbon is sufficient to improve the device performance by more than a factor of ten. Atom-level computer simulations showed how molecules with an odd number of carbon atoms stand straighter than molecules with an even number of carbon atoms. This allows them to pack together more closely. Tightly-packed assemblies of these molecules were formed on metal electrode surfaces and were found to be remarkably free of defects. These high quality devices can suppress leakage currents and so operate efficiently and reliably. The device can be cleanly switched on and off purely on the basis of the charge and shape of the molecules, just like in the biological nanomachines that regulate photosynthesis, cell division and tissue growth.

Modern electronic devices such as telephones and tablets in manufacture today rely on tiny switches approaching molecular sizes. This provides new challenges for electronics but opens up exciting opportunities for blending molecular properties to be used to advantage. This study is an exciting new avenue to exploit molecular design to achieve new ways to perform information processing. A key enabling feature for nanoscale electronics will be the ability to use molecules as rectifiers and switches. By demonstrating the rational design of molecules that rectify current with a large and highly-reproducible ON/OFF ratio, the study provides a key advance towards the creation of technologically viable ultra-small device components. Fifty thousand of the rectifier molecules strung end to end would fit across the diameter of a human hair. Advances in computing, synthesis and characterisation means scientists can now understand and control material at the scale of atoms and molecules.

The combined experiments and simulations show for the first time that minute improvements in molecule orientation and packing trigger changes in Van-der Waals forces that are sufficiently large to dramatically improve the performance of electronic devices. These van der Waals forces are the weakest of all intermolecular forces and only become significant when summed over large areas. Hence, up until now, the majority of research into ultra-small devices has used stronger pi-pi interactions to stick molecules together, and has ignored the much weaker Van-der Waals interactions. The present study shows, how Van-der Waals effects, which are present in every conceivable molecular scale device, can be tuned to optimise the performance of the device.
The devices are based on molecules that act as diodes by allowing current to pass through them when operated at forward bias and blocking current when the bias is reversed. Molecular rectifiers were first proposed back in 1974, and advances in scientific computing have allowed molecular‐level design to be used over the past decade to develop new organic materials that provide better electrical responses. However, the relative importance of the interactions between the molecules, the nature of the molecule-metal contact and the influence of environmental effects have been questioned. This new research demonstrates that dramatic improvements in device performance may be achieved by controlling the van der Waals forces that pack the molecules together. Simply changing the number of carbon atoms by one provides significantly more stable and more reproducible devices that exhibit an order of magnitude improvement in ON/OFF ratio. The research findings demonstrate the feasibility of boosting device performances by creating tighter seals between molecules.

Light replaces electricity through metatronics

The technological world of the 21^st century owes a tremendous amount to advances in electrical engineering, specifically, the ability to finely control the flow of electrical charges using increasingly small and complicated circuits. And while those electrical advances continue to race ahead, researchers at the University of Pennsylvania are pushing circuitry forward in a different way, by replacing electricity with light.

Different arrangements and combinations of electronic circuits have different functions, ranging from simple light switches to complex supercomputers. These circuits are built of different arrangements of circuit elements, for example resistors, inductors and capacitors, which manipulate the flow of electrons in a circuit in mathematically precise ways.

Now, researchers at Penn have created the first physical demonstration of lumped optical circuit elements. This represents a milestone in a nascent field of science and engineering. In electronics, the lumped designation refers to elements that can be treated as a black box, something that turns a given input to a perfectly predictable output without an engineer having to worry about what exactly is going on inside the element. Optics has always had its own set of elements, things like lenses, waveguides and gratings, but they were never lumped. Those elements are all much larger than the wavelength of light because that's all that could be easily built in the old days. For electronics, the lumped circuit elements were always much smaller than the wavelength of operation, which is in the radio or microwave frequency range.

 Nanotechnology has now opened that possibility for lumped optical circuit elements, allowing construction of structures that have dimensions measured in nanometers. In this experiment's case, the structure was comb-like arrays of rectangular nanorods made of silicon nitrite.

 The "meta" in "metatronics" refers to metamaterials, the relatively new field of research where nanoscale patterns and structures embedded in materials allow them to manipulate waves in ways that were previously impossible. Here, the cross-sections of the nanorods and the gaps between them form a pattern that replicates the function of resistors, inductors and capacitors, three of the most basic circuit elements, but in optical wavelengths.

 In their experiment, the researchers illuminated the nanorods with an optical signal, a wave of light in the mid-infrared range. They then used spectroscopy to measure the wave as it passed through the comb. Repeating the experiment using nanorods with nine different combinations of widths and heights, the researchers showed that the optical current and optical voltage were altered by the optical resistors, inductors and capacitors with parameters corresponding to those differences in size.

A section of the nanorod acts as both an inductor and resistor, and the air gap acts as a capacitor.

 Beyond changing the dimensions and the material the nanorods are made of, the function of these optical circuits can be altered by changing the orientation of the light, giving metatronic circuits access to configurations that would be impossible in traditional electronics. This is because a light wave has polarizations; the electric field that oscillates in the wave has a definable orientation in space. In metatronics, it is that electric field that interacts and is changed by elements, so changing the field's orientation can be like rewiring an electric circuit.

 When the plane of the field is in line with the nanorods, the circuit is wired in parallel and the current passes through the elements simultaneously. When the plane of the electric field crosses both the nanorods and the gaps, the circuit is wired in series and the current passes through the elements sequentially.

This principle could be taken to an even higher level of complexity by building nanorod arrays in three dimensions. An optical signal hitting such a structure's top would encounter a different circuit than a signal hitting its side. Another reason for success in electronics has to do with its modularity.