Autor: Liliana Decu

Cercetătorii evaluează centralele electrice care convertesc toate emisiile de CO2 în nanotuburi de carbon(Researchers assess power plants that convert all of their CO2 emissions into carbon nanotubes)

CO2 capturat fie direct din atmosferă, fie dintr-o centrală de gaze naturale cu ciclu combinat, poate fi electrolizat pentru a produce gaz de oxigen și nanofibre de carbon, care pot fi apoi folosite pentru a produce o varietate de produse valoroase

Researchers

Un nou mod de a degrada materialele plastice care le transformă în combustibil(A new way to degrade plastics that turns them into fuel)

O echipă de cercetători de la Academia Chineză de Științe și Universitatea din California a găsit o modalitate de a degrada plasticul obișnuit într-un mod care să permită crearea unui combustibil din gunoi de plastic.În plus, catalizatorii sunt compatibili cu diferiți aditivi de poliolefine

A new

De ce Spiderman nu poate exista: geckos sunt limita de dimensiune pentru lipirea pe pereti(Why Spiderman can’t exist:Geckos are size linit for sticking to walls)

cele mai recente cercetări relevă de ce geckos sunt cele mai mari animale capabile să scadă zidurile verticale netede – chiar și alpiniștii mai mari ar necesita picioarele lipsite de manevră mari;iar scalarea este esențială pentru îmbunătățirea performanțelor adezivilor pe suprafețe mult mai mari

107 sept

Rusă Yu-71 Avionul Hipersonic Atac (HAA) / „Nuke Glider” și Yu-74 Ultra-Maneuverable Hipersonic Glide Vehicule (HGV) Amenințări atac nuclear: Putem apăra împotriva lor?(Russian Yu-71 Hypersonic Attack Aircraft(HAA)/’Nuke Glider’ and Yu-74 Ultra-Maneuverable Hypersonic Glide Vehicle (HGV) Nuclear Attack Threats :Can We Defend Against Them?)

Avionul Hipersonic Atac (HAA) / „Nuke Glider” și Yu-74 Ultra-Maneuverable Hipersonic Glide Vehicule (HGV)

Stimpex 12

O nouă formă de fotodetectoare hibride cu puncte cuantice și grafen(A new form of hybrid photodetectors with quantum dots and graphene)

Dezvoltarea fotodetectoarelor a fost o chestiune de interes considerabil în ultimele decenii, deoarece aplicațiile lor sunt esențiale pentru multe domenii diferite, cum ar fi camerele, dispozitivele medicale, echipamentele de siguranță, dispozitivele de comunicații optice sau chiar instrumentele de măsurare, printre altele.

Posted: Jun 17, 2016

A new form of hybrid photodetectors with quantum dots and graphene

(Nanowerk News) The development of photodetectors has been a matter of considerable interest in the past decades since their applications are essential to many different fields including cameras, medical devices, safety equipment, optical communication devices or even surveying instruments, among others.
Many efforts have been focused towards optoelectronic research in trying to create low cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse. This is of paramount importance especially in the short wave infrared which currently is addressed by very expensive III-V InGaAs photodetectors. The development of two main classes of photodetectors, photodiodes and phototransistors, have partially been able to accomplish these goals because even though they both have many outstanding properties, none seem to fulfill all of these requirements. While photodiodes are much faster than phototransistors, phototransistors have a higher gain and do not require low noise preamplifiers for their use.
To overcome these limitations, ICFO researchers Ivan Nikitskiy, Stijn Goossens, Dominik Kufer, Tania Lasanta, Gabriele Navickaite, led by ICREA professors at ICFO Frank Koppens and Gerasimos Konstantatos, have been able to develop a hybrid photodetector capable of attaining concomitantly better performance features in terms of speed, quantum efficiency and linear dynamic range, operating not only in the visible but also in the near infrared (NIR: 700-1400nm) and SWIR range (1400-3000nm).
At the same time this technology is based upon materials that can be monolithically integrated with Si CMOS electronics as well as flexible electronic platforms. The results of this work have been recently published in Nature Communications („Integrating an electrically active colloidal quantum dot photodiode with a graphene phototransistor”).
hybrid photodetector with quantum dots and graphene
This is a schematic of the device structure. (Image: ICFO)
To be able to achieve this, the team of researchers developed a hybrid device by integrating an active colloidal quantum dot photodiode with a graphene phototransistor. By including an „active” quantum dot photodiode, they were able to increase charge collection in a highly absorbing thick QD film, which in turn increased the quantum efficiency as well as the photoresponse. The active quantum dot layer enabled a more effective charge collection by exploiting carrier drift towards the graphene layer instead of relying only on diffusion. The researchers then combined this scheme with a graphene transistor to register ultra-high-gains and record gain-bandwidth products, thanks to Graphene’s 2D character and remarkably high carrier mobility.
The results obtained in this study have shown that this hybrid architecture does clearly demonstrate the potential of graphene and active quantum dot materials, opening new pathways for their integration in other optoelectronic materials in search for much higher performance and a broader spectrum of functionalities.
Source: ICFO

Laser manipulează proprietățile electronice(Laser manipulates electronic properties)

Un material semiconductor nou, care are doar trei straturi atomice groase, a apărut cu proprietăți electronice mai exotice, maleabile decât cele ale semiconductorilor tradiționali.Un nou material semiconductor ultra-subțire (disulfură de wolfram sau WS 2 ) constă din trei straturi atomice într-o configurație „sandwich atomică”, cu un strat de atomi de tungsten de metal greu între straturile de atomi de sulf mai ușori. Materialul este cvasi-dimensional, are doar trei atomi grosime și prezintă o structură electronică unică, cu diferențe subtile, în funcție de direcția în raport cu legăturile atomice repetate în planul stratului.

Posted: Jun 17, 2016

Laser manipulates electronic properties

(Nanowerk News) A new semiconducting material that is only three atomic-layers thick has emerged with more exotic, malleable electronic properties than those of traditional semiconductors. These properties come from electrons, like a ball rolling down a hill to a valley, that prefer the lower energy levels at the bottom of electronic energy “valleys”. Now, the valley depth can be shifted optically and with extreme speed with sculpted laser pulses (Nature Materials, „Valley-selective optical Stark effect in monolayer WS2„).
Electrons have distinct energy levels where the energy is minimized, similar to a ball rolling down a mountain to a valley
Electrons have distinct energy levels where the energy is minimized, similar to a ball rolling down a mountain to a valley. In the artistically enhanced depiction, a valley in the electronic structure interacts with and is controllably manipulated by circularly polarized laser light. The laser causes valleys with initially equal energies to have slightly different energies. This is the first time a laser has separated energy valleys in an atomically thin semiconductor (tungsten disulfide), which could lead to advanced electronics based on energy valley states instead of conventional electronics based on charge flows and accumulation. (Image: Massachusetts Institute of Technology. Illustration by Ella Marushchenko and Alex Tokarev)
Layered materials where electrons are constrained to two dimensions can be engineered into novel electronic structures with unique electronic and optical properties. Optical manipulation of electrons can lead to new modes of energy conversion and computational devices such as electronics based on energy valleys states instead of conventional electronics based on charge flows and accumulation.
A new ultra-thin semiconducting material (tungsten disulfide or WS2) consists of three atomic layers in an “atomic sandwich” configuration with a heavy metal tungsten atom layer between lighter element sulfur atom layers. The material is quasi-two dimensional, just three atoms thick, and exhibits a unique electronic structure with subtle differences depending on the direction relative to the repeating atomic bonds in the layer plane.
The differences create two distinct but similar valleys in the electronic structure, where electrons can accumulate with different directions, but with associated energy levels and gaps that are equal. Adding a specific type of laser beam, where the polarization direction (the direction of interacting electric forces) rotates as the light propagates, creates a new type of electron energy structure that can be probed and manipulated.
The electron structural landscape, which began with two similar valleys, can also be made to have different distinct valleys with different energy depths. The valley depth can now be manipulated with light to encode information like zeroes and ones for conventional data.
Additionally, changing the energy of the valleys with light allows for fast manipulation without the need for contact with complex electrodes as in conventional electronics.
Source: Department of Energy, Office of Science

Graphene nu este singurul Lego din caseta de jucării pentru materiale științifice din domeniul nanoelectronicii(Graphene isn’t the only Lego in the nanoelectronics materials-science toy box

disulfidul de molibden (MoS 2 ), este un material cu un singur strat, cu proprietăți interesante dincolo de cele ale grafenului. MoS 2 poate absorbi de cinci ori mai multă lumină vizibilă ca grafenul, făcându-l util în detectoarele de lumină și celulele solare. În plus, se propun și se sintetizează zilnic și materiale mai noi, cum ar fi borofenul (un material cu un singur strat format din atomi de bor proiectat a fi mecanic mai puternic decât grafenul).

Posted: Jun 15, 2016

Graphene isn’t the only Lego in the nanoelectronics materials-science toy box

(Nanowerk News) You may have heard of graphene, a sheet of pure carbon, one atom thick, that’s all the rage in materials-science circles, and getting plenty of media hype as well. Reports have trumpeted graphene as an ultra-thin, super-strong, super-conductive, super-flexible material. You could be excused for thinking it might even save all of humanity from certain doom.
Not exactly. In the current world of nano-electronics, there is a lot more going on than just graphene. One of the materials I work with, molybdenum disulphide (MoS2), is a one-layer material with interesting properties beyond those of graphene. MoS2 can absorb five times as much visible light as graphene, making it useful in light detectors and solar cells. In addition, even newer materials like borophene (a one-layer material made of boron atoms projected to be mechanically stronger than graphene) are being proposed and synthesized every day.
Layering two-dimensional materials
Layering two-dimensional materials. (Image: Peter Byrley)
These and other materials yet to be discovered will be used like Lego pieces to build the electronics of the future (the paper is titled van der Waals heterostructures). By stacking multiple materials in different ways, we can take advantage of different properties in each of them. The new electronics built with these combined structures will be faster, smaller, more environmentally resistant and cheaper than what we have now.
Looking for an energy gap
There is a key reason that graphene will not be the versatile cure-all material that the hype might suggest. You can’t just stack graphene repeatedly to get what you want. The electronic property preventing this is the lack of what is called an “energy gap.” (The more technical term is “band gap.”)
Metals will conduct electricity through them regardless of the environment. However, any other material that is not a metal needs a little boost of energy from the outside to get electrons to move through the band gap and into the conducting state. How much of a boost the material needs is called the energy gap. The energy gap is one of the factors that determines how much total energy needs to be put into your entire electrical device, from either heat or applied electrical voltage, to get it to conduct electricity („Physics of Semiconductor Devices”). You essentially have to put in enough starting energy if you want your device to work.
Some materials have a gap so large that almost no amount of energy can get electrons flowing through them. These materials are called insulators (think glass). Other materials have either an extremely small gap or no gap at all. These materials are called metals (think copper). This is why we use copper (a metal with instant conductivity) for wiring, while we use plastics (an insulator that blocks electricity) as the protective outer coating.
Everything else, with gaps in between these two extremes, is called a semiconductor (think silicon). Semiconductors, at the theoretical temperature of absolute zero, behave as insulators because they have no heat energy to get their electrons into the conducting state. At room temperature, however, heat from the surrounding environment provides just enough energy to get some electrons (hence the term, “semi”-conducting) over the small band gap and into the conducting state ready to conduct electricity.
Comparing the band gap in metals (left), semiconductors (center) and insulators (right)
Comparing the band gap in metals (left), semiconductors (center) and insulators (right). (Image: Peter Byrley)
Graphene’s energy gap
Graphene is in fact a semi-metal. It has no energy gap, which means it will always conduct electricity – you can’t turn off its conductivity.
This is a problem because electronic devices use electrical current to communicate. At their most fundamental level, computers communicate by sending 1’s and 0’s – on and off signals. If a computer’s components were made from graphene, the system would always be on, everywhere. It would be unable to perform tasks because its lack of energy gap prevents graphene from ever becoming a zero; the computer would keep reading 1’s all the time. Semiconductors, by contrast, have an energy gap that is small enough to let some electrons conduct electricity but is large enough to have a clear distinction between on and off states.
Finding the right materials
Not all hope is lost, however. Researchers are looking at three main ways to tackle this:
  • Using new materials similar to graphene that actually have a sufficient energy gap and finding ways to further improve their conductivity.
  • Altering graphene itself to create this energy gap.
  • Combining graphene with other materials to optimize their combined properties.
There are many one-layer materials currently being looked at that actually have a sufficient energy gap. One such material, MoS2, has been studied in recent years as a potential replacement for traditional silicon and also as a light detector and gas sensor.
The only drawback with these other materials is that so far, we have not found one that matches the excellent though always-on conductivity of graphene. The other materials can be turned off, but when on, they are not as good as graphene. MoS2 itself is estimated to have 1/15th to 1/10th the conductivity of graphene in small devices. Researchers, including me, are now looking at ways to alter these materials to increase their conductivity.
Using graphene as an ingredient
Strangely, an energy gap in graphene can actually be induced through modifications like bending it, turning it into a nanoribbon, inserting foreign chemicals into it or using two layers of graphene. But each of these modifications can reduce the graphene’s conductivity or limit how it can be used.
To avoid specialized setups, we could just combine graphene with other materials. By doing this, we are also combining the properties of the materials in order to reap the best benefits. We could, for example, invent new electronic components that have a material allowing them to be shut off or on (like MoS2) but have graphene’s great conductivity when turned on. New solar cells will work on this concept.
A combined structure could, for example, be a solar panel made for harsh environments: We could layer a thin, transparent protective material over the top of a very efficient solar-collecting material, which in turn could be on top of a material that is excellent at conducting electricity to a nearby battery („Extraordinary Sunlight Absorption and One Nanometer Thick Photovoltaics Using Two-Dimensional Monolayer Materials”). Other middle layers could include materials that are good at selectively detecting gases such as methane or carbon dioxide.
Researchers are now racing to figure out what the best combination is for different applications. Whoever finds the best combination will eventually win numerous rights to patents for improved electronic products.
The truth is, though, we don’t know what our future electronics will look like. New Lego pieces are being invented all the time; the ways we stack or rearrange them are changing constantly, too. All that’s certain is that the insides of electronic devices will look drastically different in the future than they do today.
Source: By Peter Byrley, Ph.D. Candidate in Chemical Engineering, University of California, Riverside