New generation of superlattice cameras add more 'color' to night vision

ScienceDaily (Oct. 20, 2011) — Recent breakthroughs have enabled scientists from the Northwestern University's Center for Quantum Devices to build cameras that can see more than one optical waveband or "color" in the dark. The semiconducting material used in the cameras -- called type-II superlattices -- can be tuned to absorb a wide range of infrared wavelengths, and now, a number of distinct infrared bands at the same time.

The idea of capturing light simultaneously at different wavelengths isn't new. Digital cameras in the visible spectrum are commonly equipped with detectors that sense red, green, and blue light to replicate a vast majority of colors perceived by the human eye. Multi-color detection in the infrared spectrum, however, offers unique functionalities beyond color representation. The resonant frequencies of compounds can often be found in this spectral range, which means that chemical spectroscopy can be relayed in images real-time.

"When coupled with image-processing algorithms performed on multiple wavebands, the amount of information rendered in a particular scene is tremendous," said Manijeh Razeghi, Walter P. Murphy Professor in Electrical Engineering and Computer Science at the McCormick School of Engineering and director of the Center for Quantum Devices.

Razeghi's group engineered the detection energies on the cameras to be extremely narrow, close to one-tenth of an electron volt, in what is known as the long-wave infrared window. Creating the cameras was difficult, however, because the light-absorbing layers are prone to parasitic effects. Furthermore, the detectors were designed to be stacked one on top of another, which provided spatially coincident pixel registration but added significantly to the growth and fabrication challenges. Nevertheless, a dual-band long-wave infrared 320-by-256 sized type-II superlattice camera was demonstrated for the first time in the world, the results of which were published in the July 2011 issue of Optics Letters.

Such infrared photon cameras based on another material called HgCdTe were used in disaster relief in March 2011 when a catastrophic tsunami damaged Japans' nuclear reactors. These cameras provided accurate temperature information about the reactors from unmanned aerial vehicles, providing officials the information they needed to orchestrate cooling efforts and prevent nuclear meltdown.

HgCdTe, however, is considered to be an expensive technology in the long-wave infrared due to its poor spectral uniformity and therefore yield -- areas in which type-II superlattices may prove more efficient.

"Type-II superlattices can be grown uniformly even at very long-wavelengths because its energy gap is determined by the alternating InAs and GaSb quantum well thicknesses, rather than its composition as is the case with HgCdTe," Razeghi said. The high-resolution multi-band type-II superlattice camera also offered very impressive performances, requiring only 0.5 milliseconds to capture a frame with temperature sensitivities as good as 0.015°C. "The high-performance, multi-functionality, and low cost offered by type-II superlattices truly make it an attractive infrared technology," she added.

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The above story is reprinted from materials provided by Northwestern University.

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Journal Reference:

Edward Kwei-wei Huang, Abbas Haddadi, Guanxi Chen, Binh-Minh Nguyen, Minh-Anh Hoang, Ryan McClintock, Mark Stegall, Manijeh Razeghi. Type-II superlattice dual-band LWIR imager with M-barrier and Fabry–Perot resonance. Optics Letters, 2011; 36 (13): 2560 DOI: 10.1364/OL.36.002560

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Laser ion source will produce a new generation of semiconductors

ScienceDaily (Oct. 20, 2011) — For ion implantation, that is 'hammering' ions into the surface layer of the material, conventional ion accelerators are commonly used. Laser ion sources are much simpler, cheaper and more universal. However, they emit wide energy ions usually accompanied by some admixtures. In the Institute of Plasma Physics and Laser Microfusion in Warsaw a unique laser ion source has been built which is equipped with a special system for accelerating ions to a chosen energy and for eliminating admixtures. This device has already been used to produce samples of a new generation of semiconductors: a layer of silica (SiO2) in which germanium nanocrystals have been formed.

Laser Ion Sources (LIS) are simple devices that produce ions in interaction of a focused laser beam with the target placed in a vacuum vessel. Admixtures that happen to be in the target often cause problems -- together with the proper ions, they can modify the sample. Moreover, the laser pulse also pulls out atoms and debris from the target which are deposited on the irradiated sample and modify its surface. "To prevent such effects, we have designed and built a device for ion implantation with a unique electric system for ion acceleration," says Marcin Rosinski, a PhD student from the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw.

Ion implementation is the process of embedding ions into the surface layer of the sample in order to change some properties of the material, mechanical or electrical. Currently, ion accelerators are routinely used for this purpose. Laser ion sources have a chance to excel those devices: they are smaller, simpler and can produce ions from high-melting materials such as tantalum or tungsten. What is more, the ion beam can easily be modified by the change of parameters and the geometry of the laser-target-sample system. The released ions can well be accelerated in the external electric field.

However, to be able to use the LIS type sources in industry, some requirements must be fulfilled: the beam of ions cannot possess impurities and the ions should have almost the same specific energy. To meet both requirements the laser ion source with special electrostatic system must be applied.

In the device built at the IPPLM the low-energy laser pulse lasts 3.5 nanoseconds. The laser pulse energy, in the first phase of laser-matter interaction, is transferred to free electrons which subsequently ionise atoms of target material and admixtures. The main part of the laser pulse energy directly heats ionised matter (plasma) causing its quick expansion. A broad energy distribution of the ions expanding from plasma results from the nature of the process of plasma generation.

Some particles and debris extracted from the target by the laser pulse are electrically neutral, which is why they expand without deflection in the electric field and go straight onto the screen that is placed exactly on the axis of the system, to shield the sample. At the same time, laser-produced ions which avoid the screen are accelerated and focused by the electric field on the sample located on the axis behind the screen. "We have selected the parameters of the field in such a way that only the chosen ions of the target reach the sample. The spot of the focused beam is 1 mm in diameter," explains Rosinski.

The low-energy laser used in the experiment does not heat itself and is capable of generating 10 thousand or more laser pulses within some ten minutes. Those advantages make it possible for scientists to control precisely the number of ions that reach the sample.

The solution proposed by the scientists from the IPPLM has successfully been used to explore the process of germanium ion implantation in silica (SiO2) layer with a view to fabricate germanium nanocrystals within it. Thus, a modified semiconductor has been created whose prospective implementation in electronics is widely anticipated, for example in miniaturisation of some memory chips or in elements for light emission.

To obtain germanium nanocrystals from the laser-produced ions, the implanted sample should be heated in the temperature of 600 to 1200 Celsius degrees. In this process some germanium crystals, ranging in size from a few to 20 nanometres (billionth of a metre) are created. "Our implanted samples, after heating, are examined with the use of various sophisticated, currently available measuring methods in the specialised laboratories, mainly at the Universities in Messina and Catania in Sicily. We have analysed both the results of ion implantation and the formation of nanocrystal structures in the samples," says Rosinski.

Laser ion source built and tested at the IPPLM is a prototype device expected to find applications in industry. "In two years, we will have finished the work connected with optimization of our device regarding industrial usage but we have already started looking for enterprises that are interested in implementing this technology," summarises Prof. Jerzy Wolowski, the Head of Laser Plasma Division at the IPPLM.

The construction of the device for laser induced implantation was started at the IPPLM a few years ago within the framework of European SEMINANO project.

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The above story is reprinted from materials provided by Institute of Plasma Physics and Laser Microfusion, via AlphaGalileo.

Note: ScienceDaily reserves the right to edit materials for content and length. For further information, please contact the source cited above.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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New generation of superlattice cameras add more 'color' to night vision

ScienceDaily (Oct. 20, 2011) — Recent breakthroughs have enabled scientists from the Northwestern University's Center for Quantum Devices to build cameras that can see more than one optical waveband or "color" in the dark. The semiconducting material used in the cameras -- called type-II superlattices -- can be tuned to absorb a wide range of infrared wavelengths, and now, a number of distinct infrared bands at the same time.

The idea of capturing light simultaneously at different wavelengths isn't new. Digital cameras in the visible spectrum are commonly equipped with detectors that sense red, green, and blue light to replicate a vast majority of colors perceived by the human eye. Multi-color detection in the infrared spectrum, however, offers unique functionalities beyond color representation. The resonant frequencies of compounds can often be found in this spectral range, which means that chemical spectroscopy can be relayed in images real-time.

"When coupled with image-processing algorithms performed on multiple wavebands, the amount of information rendered in a particular scene is tremendous," said Manijeh Razeghi, Walter P. Murphy Professor in Electrical Engineering and Computer Science at the McCormick School of Engineering and director of the Center for Quantum Devices.

Razeghi's group engineered the detection energies on the cameras to be extremely narrow, close to one-tenth of an electron volt, in what is known as the long-wave infrared window. Creating the cameras was difficult, however, because the light-absorbing layers are prone to parasitic effects. Furthermore, the detectors were designed to be stacked one on top of another, which provided spatially coincident pixel registration but added significantly to the growth and fabrication challenges. Nevertheless, a dual-band long-wave infrared 320-by-256 sized type-II superlattice camera was demonstrated for the first time in the world, the results of which were published in the July 2011 issue of Optics Letters.

Such infrared photon cameras based on another material called HgCdTe were used in disaster relief in March 2011 when a catastrophic tsunami damaged Japans' nuclear reactors. These cameras provided accurate temperature information about the reactors from unmanned aerial vehicles, providing officials the information they needed to orchestrate cooling efforts and prevent nuclear meltdown.

HgCdTe, however, is considered to be an expensive technology in the long-wave infrared due to its poor spectral uniformity and therefore yield -- areas in which type-II superlattices may prove more efficient.

"Type-II superlattices can be grown uniformly even at very long-wavelengths because its energy gap is determined by the alternating InAs and GaSb quantum well thicknesses, rather than its composition as is the case with HgCdTe," Razeghi said. The high-resolution multi-band type-II superlattice camera also offered very impressive performances, requiring only 0.5 milliseconds to capture a frame with temperature sensitivities as good as 0.015°C. "The high-performance, multi-functionality, and low cost offered by type-II superlattices truly make it an attractive infrared technology," she added.

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The above story is reprinted from materials provided by Northwestern University.

Note: ScienceDaily reserves the right to edit materials for content and length. For further information, please contact the source cited above.

Journal Reference:

Edward Kwei-wei Huang, Abbas Haddadi, Guanxi Chen, Binh-Minh Nguyen, Minh-Anh Hoang, Ryan McClintock, Mark Stegall, Manijeh Razeghi. Type-II superlattice dual-band LWIR imager with M-barrier and Fabry–Perot resonance. Optics Letters, 2011; 36 (13): 2560 DOI: 10.1364/OL.36.002560

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Laser ion source will produce a new generation of semiconductors

ScienceDaily (Oct. 20, 2011) — For ion implantation, that is 'hammering' ions into the surface layer of the material, conventional ion accelerators are commonly used. Laser ion sources are much simpler, cheaper and more universal. However, they emit wide energy ions usually accompanied by some admixtures. In the Institute of Plasma Physics and Laser Microfusion in Warsaw a unique laser ion source has been built which is equipped with a special system for accelerating ions to a chosen energy and for eliminating admixtures. This device has already been used to produce samples of a new generation of semiconductors: a layer of silica (SiO2) in which germanium nanocrystals have been formed.

Laser Ion Sources (LIS) are simple devices that produce ions in interaction of a focused laser beam with the target placed in a vacuum vessel. Admixtures that happen to be in the target often cause problems -- together with the proper ions, they can modify the sample. Moreover, the laser pulse also pulls out atoms and debris from the target which are deposited on the irradiated sample and modify its surface. "To prevent such effects, we have designed and built a device for ion implantation with a unique electric system for ion acceleration," says Marcin Rosinski, a PhD student from the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw.

Ion implementation is the process of embedding ions into the surface layer of the sample in order to change some properties of the material, mechanical or electrical. Currently, ion accelerators are routinely used for this purpose. Laser ion sources have a chance to excel those devices: they are smaller, simpler and can produce ions from high-melting materials such as tantalum or tungsten. What is more, the ion beam can easily be modified by the change of parameters and the geometry of the laser-target-sample system. The released ions can well be accelerated in the external electric field.

However, to be able to use the LIS type sources in industry, some requirements must be fulfilled: the beam of ions cannot possess impurities and the ions should have almost the same specific energy. To meet both requirements the laser ion source with special electrostatic system must be applied.

In the device built at the IPPLM the low-energy laser pulse lasts 3.5 nanoseconds. The laser pulse energy, in the first phase of laser-matter interaction, is transferred to free electrons which subsequently ionise atoms of target material and admixtures. The main part of the laser pulse energy directly heats ionised matter (plasma) causing its quick expansion. A broad energy distribution of the ions expanding from plasma results from the nature of the process of plasma generation.

Some particles and debris extracted from the target by the laser pulse are electrically neutral, which is why they expand without deflection in the electric field and go straight onto the screen that is placed exactly on the axis of the system, to shield the sample. At the same time, laser-produced ions which avoid the screen are accelerated and focused by the electric field on the sample located on the axis behind the screen. "We have selected the parameters of the field in such a way that only the chosen ions of the target reach the sample. The spot of the focused beam is 1 mm in diameter," explains Rosinski.

The low-energy laser used in the experiment does not heat itself and is capable of generating 10 thousand or more laser pulses within some ten minutes. Those advantages make it possible for scientists to control precisely the number of ions that reach the sample.

The solution proposed by the scientists from the IPPLM has successfully been used to explore the process of germanium ion implantation in silica (SiO2) layer with a view to fabricate germanium nanocrystals within it. Thus, a modified semiconductor has been created whose prospective implementation in electronics is widely anticipated, for example in miniaturisation of some memory chips or in elements for light emission.

To obtain germanium nanocrystals from the laser-produced ions, the implanted sample should be heated in the temperature of 600 to 1200 Celsius degrees. In this process some germanium crystals, ranging in size from a few to 20 nanometres (billionth of a metre) are created. "Our implanted samples, after heating, are examined with the use of various sophisticated, currently available measuring methods in the specialised laboratories, mainly at the Universities in Messina and Catania in Sicily. We have analysed both the results of ion implantation and the formation of nanocrystal structures in the samples," says Rosinski.

Laser ion source built and tested at the IPPLM is a prototype device expected to find applications in industry. "In two years, we will have finished the work connected with optimization of our device regarding industrial usage but we have already started looking for enterprises that are interested in implementing this technology," summarises Prof. Jerzy Wolowski, the Head of Laser Plasma Division at the IPPLM.

The construction of the device for laser induced implantation was started at the IPPLM a few years ago within the framework of European SEMINANO project.

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Story Source:

The above story is reprinted from materials provided by Institute of Plasma Physics and Laser Microfusion, via AlphaGalileo.

Note: ScienceDaily reserves the right to edit materials for content and length. For further information, please contact the source cited above.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Graphene's 'Big Mac' creates next generation of chips

ScienceDaily (Oct. 10, 2011) — The world's thinnest, strongest and most conductive material, discovered in 2004 at the University of Manchester by Professor Andre Geim and Professor Kostya Novoselov, has the potential to revolutionize material science.

Demonstrating the remarkable properties of graphene won the two scientists the Nobel Prize for Physics last year and Chancellor of the Exchequer George Osborne has just announced plans for a £50m graphene research hub to be set up.

Now, writing in the journal Nature Physics, the University of Manchester team have for the first time demonstrated how graphene inside electronic circuits will probably look like in the future.

By sandwiching two sheets of graphene with another two-dimensional material, boron nitrate, the team created the graphene 'Big Mac' -- a four-layered structure which could be the key to replacing the silicon chip in computers.

Because there are two layers of graphene completed surrounded by the boron nitrate, this has allowed the researchers for the first time to observe how graphene behaves when unaffected by the environment.

Dr Leonid Ponomarenko, the leading author on the paper, said: "Creating the multilayer structure has allowed us to isolate graphene from negative influence of the environment and control graphene's electronic properties in a way it was impossible before.

"So far people have never seen graphene as an insulator unless it has been purposefully damaged, but here high-quality graphene becomes an insulator for the first time."

The two layers of boron nitrate are used not only to separate two graphene layers but also to see how graphene reacts when it is completely encapsulated by another material.

Professor Geim said: "We are constantly looking at new ways of demonstrating and improving the remarkable properties of graphene."

"Leaving the new physics we report aside, technologically important is our demonstration that graphene encapsulated within boron nitride offers the best and most advanced platform for future graphene electronics. It solves several nasty issues about graphene's stability and quality that were hanging for long time as dark clouds over the future road for graphene electronics.

We did this on a small scale but the experience shows that everything with graphene can be scaled up."

"It could be only a matter of several months before we have encapsulated graphene transistors with characteristics better than previously demonstrated."

Graphene is a novel two-dimensional material which can be seen as a monolayer of carbon atoms arranged in a hexagonal lattice.

Its remarkable properties could lead to bendy, touch screen phones and computers, lighter aircraft, wallpaper-thin HD TV sets and superfast internet connections, to name but a few.

The £50m Graphene Global Research and Technology Hub will be set up by the Government to commercialise graphene. Institutions will be able to bid for the money via the Engineering and Physical Sciences Research Council (EPSRC) -- who funded work leading to the award of the Nobel prize long before the applications were realised.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Manchester, via EurekAlert!, a service of AAAS.

Journal Reference:

L. A. Ponomarenko, A. K. Geim, A. A. Zhukov, R. Jalil, S. V. Morozov, K. S. Novoselov, I. V. Grigorieva, E. H. Hill, V. V. Cheianov, V. I. Fal’ko, K. Watanabe, T. Taniguchi, R. V. Gorbachev. Tunable metal–insulator transition in double-layer graphene heterostructures. Nature Physics, 2011; DOI: 10.1038/nphys2114

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Graphene's 'Big Mac' creates next generation of chips

ScienceDaily (Oct. 10, 2011) — The world's thinnest, strongest and most conductive material, discovered in 2004 at the University of Manchester by Professor Andre Geim and Professor Kostya Novoselov, has the potential to revolutionize material science.

Demonstrating the remarkable properties of graphene won the two scientists the Nobel Prize for Physics last year and Chancellor of the Exchequer George Osborne has just announced plans for a £50m graphene research hub to be set up.

Now, writing in the journal Nature Physics, the University of Manchester team have for the first time demonstrated how graphene inside electronic circuits will probably look like in the future.

By sandwiching two sheets of graphene with another two-dimensional material, boron nitrate, the team created the graphene 'Big Mac' -- a four-layered structure which could be the key to replacing the silicon chip in computers.

Because there are two layers of graphene completed surrounded by the boron nitrate, this has allowed the researchers for the first time to observe how graphene behaves when unaffected by the environment.

Dr Leonid Ponomarenko, the leading author on the paper, said: "Creating the multilayer structure has allowed us to isolate graphene from negative influence of the environment and control graphene's electronic properties in a way it was impossible before.

"So far people have never seen graphene as an insulator unless it has been purposefully damaged, but here high-quality graphene becomes an insulator for the first time."

The two layers of boron nitrate are used not only to separate two graphene layers but also to see how graphene reacts when it is completely encapsulated by another material.

Professor Geim said: "We are constantly looking at new ways of demonstrating and improving the remarkable properties of graphene."

"Leaving the new physics we report aside, technologically important is our demonstration that graphene encapsulated within boron nitride offers the best and most advanced platform for future graphene electronics. It solves several nasty issues about graphene's stability and quality that were hanging for long time as dark clouds over the future road for graphene electronics.

We did this on a small scale but the experience shows that everything with graphene can be scaled up."

"It could be only a matter of several months before we have encapsulated graphene transistors with characteristics better than previously demonstrated."

Graphene is a novel two-dimensional material which can be seen as a monolayer of carbon atoms arranged in a hexagonal lattice.

Its remarkable properties could lead to bendy, touch screen phones and computers, lighter aircraft, wallpaper-thin HD TV sets and superfast internet connections, to name but a few.

The £50m Graphene Global Research and Technology Hub will be set up by the Government to commercialise graphene. Institutions will be able to bid for the money via the Engineering and Physical Sciences Research Council (EPSRC) -- who funded work leading to the award of the Nobel prize long before the applications were realised.

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and Google +1:

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Manchester, via EurekAlert!, a service of AAAS.

Journal Reference:

L. A. Ponomarenko, A. K. Geim, A. A. Zhukov, R. Jalil, S. V. Morozov, K. S. Novoselov, I. V. Grigorieva, E. H. Hill, V. V. Cheianov, V. I. Fal’ko, K. Watanabe, T. Taniguchi, R. V. Gorbachev. Tunable metal–insulator transition in double-layer graphene heterostructures. Nature Physics, 2011; DOI: 10.1038/nphys2114

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here