Etichetă: grafen

Un nou material 2-D ar putea ridica grafenul

Au demonstrat că prin combinarea celor trei elemente este posibil să se obțină un material de 2 atomi gros, cu adevărat 2D, cu proprietăți care pot fi reglate pentru a se potrivi diferitelor aplicații dincolo de ceea ce este posibil cu grafenul

Posted: Feb 29, 2016

New 2-D material could upstage graphene

(Nanowerk News) A new one atom-thick flat material that could upstage the wonder material graphene and advance digital technology has been discovered by a physicist at the University of Kentucky working in collaboration with scientists from Daimler in Germany and the Institute for Electronic Structure and Laser (IESL) in Greece.
Reported in Physical Review B, Rapid Communication („Prediction of a new graphenelike Si2BN solid”), the new material is made up of silicon, boron and nitrogen – all light, inexpensive and earth abundant elements – and is extremely stable, a property many other graphene alternatives lack.
New Material Made of Silicon, Boron and Nitrogen
The atoms in the new structure are arranged in a hexagonal pattern as in graphene, but that is where the similarity ends. The three elements forming the new material all have different sizes; the bonds connecting the atoms are also different. As a result, the sides of the hexagons formed by these atoms are unequal, unlike in graphene. (Image: Madhu Menon)
„We used simulations to see if the bonds would break or disintegrate – it didn’t happen,” said Madhu Menon, a physicist in the UK Center for Computational Sciences. „We heated the material up to 1,000 degree Celsius and it still didn’t break.”
Using state-of-the-art theoretical computations, Menon and his collaborators Ernst Richter from Daimler and a former UK Department of Physics and Astronomy post-doctoral research associate, and Antonis Andriotis from IESL, have demonstrated that by combining the three elements, it is possible to obtain a one atom-thick, truly 2D material with properties that can be fine-tuned to suit various applications beyond what is possible with graphene.
While graphene is touted as being the world’s strongest material with many unique properties, it has one downside: it isn’t a semiconductor and therefore disappoints in the digital technology industry. Subsequent search for new 2D semiconducting materials led researchers to a new class of three-layer materials called transition-metal dichalcogenides (TMDCs). TMDCs are mostly semiconductors and can be made into digital processors with greater efficiency than anything possible with silicon. However, these are much bulkier than graphene and made of materials that are not necessarily earth abundant and inexpensive.
Searching for a better option that is light, earth abundant, inexpensive and a semiconductor, the team led by Menon studied different combinations of elements from the first and second row of the Periodic Table.
Although there are many ways to combine silicon, boron and nitrogen to form planar structures, only one specific arrangement of these elements resulted in a stable structure. The atoms in the new structure are arranged in a hexagonal pattern as in graphene, but that is where the similarity ends.
The three elements forming the new material all have different sizes; the bonds connecting the atoms are also different. As a result, the sides of the hexagons formed by these atoms are unequal, unlike in graphene. The new material is metallic, but can be made semiconducting easily by attaching other elements on top of the silicon atoms.
The presence of silicon also offers the exciting possibility of seamless integration with the current silicon-based technology, allowing the industry to slowly move away from silicon instead of eliminating it completely, all at once.
„We know that silicon-based technology is reaching its limit because we are putting more and more components together and making electronic processors more and more compact,” Menon said. „But we know that this cannot go on indefinitely; we need smarter materials.”
Furthermore, in addition to creating an electronic band gap, attachment of other elements can also be used to selectively change the band gap values – a key advantage over graphene for solar energy conversion and electronics applications.
Other graphene-like materials have been proposed but lack the strengths of the material discovered by Menon and his team. Silicene, for example, does not have a flat surface and eventually forms a 3D surface. Other materials are highly unstable, some only for a few hours at most.
The bulk of the theoretical calculations required were performed on the computers at the UK Center for Computational Sciences with collaborators Richter and Andriotis directly accessing them through fast networks. Now the team is working in close collaboration with a team led by Mahendra Sunkara of the Conn Center for Renewable Energy Research at University of Louisville to create the material in the lab. The Conn Center team has had close collaborations with Menon on a number of new materials systems where they were able to test his theory with experiments for a number of several new solar materials.
„We are very anxious for this to be made in the lab,” Menon said. „The ultimate test of any theory is experimental verification, so the sooner the better!”
Some of the properties, such as the ability to form various types of nanotubes, are discussed in the paper but Menon expects more to emerge with further study.
„This discovery opens a new chapter in material science by offering new opportunities for researchers to explore functional flexibility and new properties for new applications,” he said. „We can expect some surprises.”
Source: University of Kentucky

Read more: New 2-D material could upstage graphene

Grafen se sprijină pe sticlă pentru a avansa electronica (Graphene leans on glass to advance electronics )

a crea grafenă flexibilă, personalizată și cu performanțe ridicate: stratificându-l pe partea de sus a sticlei comune. Acest proces scalabil și ieftin facilitează deschiderea unei noi clase de dispozitive microelectronice și optoelectronice – totul de la celule solare eficiente la ecrane tactile.De exemplu, conductivitatea ridicată și transparența graphenei o fac un candidat foarte promițător ca un electrod transparent și conducător pentru a înlocui oxidul de staniu indiu relativ fragil și scump (ITO) în aplicații cum ar fi celule solare, diode emițătoare de lumină organică (OLED) afișaje și ecrane tactile. Pentru a înlocui ITO, trebuie dezvoltate metode scalabile și cu costuri scăzute pentru a controla rezistența grafenului la fluxul de curent electric prin controlarea puterii de dopaj. Acest nou sistem de sticla-grafen se poate ridica la aceasta provocare, spun cercetatorii.

Posted: Feb 12, 2016

Graphene leans on glass to advance electronics

(Nanowerk News) Graphene, the two-dimensional powerhouse, packs extreme durability, electrical conductivity, and transparency into a one-atom-thick sheet of carbon. Despite being heralded as a breakthrough „wonder material,” graphene has been slow to leap into commercial and industrial products and processes.
Now, scientists have developed a simple and powerful method for creating resilient, customized, and high-performing graphene: layering it on top of common glass. This scalable and inexpensive process helps pave the way for a new class of microelectronic and optoelectronic devices—everything from efficient solar cells to touch screens.
The collaboration—led by scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, Stony Brook University (SBU), and the Colleges of Nanoscale Science and Engineering at SUNY Polytechnic Institute—published their results February 12, 2016, in the journal Scientific Reports („Spontaneous and strong multi-layer graphene n-doping on soda-lime glass and its application in graphene-semiconductor junctions”).
Schematic of a graphene field-effect-transistor
Left: Schematic of a graphene field-effect-transistor used in this study. The device consists of a solar cell containing graphene stacked on top of a high-performance copper indium gallium diselenide (CIGS) semiconductor, which in turn is stacked on an industrial substrate (either soda-lime glass, SLG, or sodium-free borosilicate glass, BSG). The research revealed that the SLG substrate serves as a source of sodium doping, and improved device performance in a way not seen in the sodium-free substrate. Right: A scanning electron micrograph of the device as seen from above, with the white scale bar measuring 10 microns, and a transmission electron micrograph inset of the CIGS/graphene interface where the white scale bar measures 100 nanometers. (click on image to enlarge)
„We believe that this work could significantly advance the development of truly scalable graphene technologies,” said study coauthor Matthew Eisaman, a physicist at Brookhaven Lab and professor at SBU.
The scientists built the proof-of-concept graphene devices on substrates made of soda-lime glass—the most common glass found in windows, bottles, and many other products. In an unexpected twist, the sodium atoms in the glass had a powerful effect on the electronic properties of the graphene.
„The sodium inside the soda-lime glass creates high electron density in the graphene, which is essential to many processes and has been challenging to achieve,” said coauthor Nanditha Dissanayake of Voxtel, Inc., but formerly of Brookhaven Lab. „We actually discovered this efficient and robust solution during the pursuit of something a bit more complex. Such surprises are part of the beauty of science.”
Crucially, the effect remained strong even when the devices were exposed to air for several weeks—a clear improvement over competing techniques.
The experimental work was done primarily at Brookhaven’s Sustainable Energy Technologies Department and the Center for Functional Nanomaterials (CFN), which is a DOE Office of Science User Facility.
The graphene tweaks in question revolve around a process called doping, where the electronic properties are optimized for use in devices. This adjustment involves increasing either the number of electrons or the electron-free „holes” in a material to strike the perfect balance for different applications. For successful real-world devices, it is also very important that the local number of electrons transferred to the graphene does not degrade over time.
„The graphene doping process typically involves the introduction of external chemicals, which not only increases complexity, but it can also make the material more vulnerable to degradation,” Eisaman said. „Fortunately, we found a shortcut that overcame those obstacles.”
The team initially set out to optimize a solar cell containing graphene stacked on a high-performance copper indium gallium diselenide (CIGS) semiconductor, which in turn was stacked on an industrial soda-lime glass substrate.
The scientists then conducted preliminary tests of the novel system to provide a baseline for testing the effects of subsequent doping. But these tests exposed something strange: the graphene was already optimally doped without the introduction of any additional chemicals.
„To our surprise, the graphene and CIGS layers already formed a good solar cell junction!” Dissanayake said. „After much investigation, and the later isolation of graphene on the glass, we discovered that the sodium in the substrate automatically created high electron density within our multi-layered graphene.”
Pinpointing the mechanism by which sodium acts as a dopant involved a painstaking exploration of the system and its performance under different conditions, including making devices and measuring the doping strength on a wide range of substrates, both with and without sodium.
„Developing and characterizing the devices required complex nanofabrication, delicate transfer of the atomically thin graphene onto rough substrates, detailed structural and electro-optical characterization, and also the ability to grow the CIGS semiconductor,” Dissanayake said. „Fortunately, we had both the expertise and state-of-the-art instrumentation on hand to meet all those challenges, as well as generous funding.”
The bulk of the experimental work was conducted at Brookhaven Lab using techniques developed in-house, including advanced lithography. For the high-resolution electron microscopy measurements, CFN staff scientists and study coauthors Kim Kisslinger and Lihua Zhang lent their expertise. Coauthors Harry Efstathiadis and Daniel Dwyer—both at the College of Nanoscale Science and Engineering at SUNY Polytechnic Institute—led the effort to grow and characterize the high-quality CIGS films.
„Now that we have demonstrated the basic concept, we want to focus next on demonstrating fine control over the doping strength and spatial patterning,” Eisaman said.
The scientists now need to probe more deeply into the fundamentals of the doping mechanism and more carefully study material’s resilience during exposure to real-world operating conditions. The initial results, however, suggest that the glass-graphene method is much more resistant to degradation than many other doping techniques.
„The potential applications for graphene touch many parts of everyone’s daily life, from consumer electronics to energy technologies,” Eisaman said. „It’s too early to tell exactly what impact our results will have, but this is an important step toward possibly making some of these applications truly affordable and scalable.”
For example, graphene’s high conductivity and transparency make it a very promising candidate as a transparent, conductive electrode to replace the relatively brittle and expensive indium tin oxide (ITO) in applications such as solar cells, organic light emitting diodes (OLEDs), flat panel displays, and touch screens. In order to replace ITO, scalable and low-cost methods must be developed to control graphene’s resistance to the flow of electrical current by controlling the doping strength. This new glass-graphene system could rise to that challenge, the researchers say.
Source: Brookhaven National Laboratory

Read more: Graphene leans on glass to advance electronics

Descoperirea proprietăților specifice ale materialelor carbonice pe bază de grafit

echipă de cercetare a susținut-o în trecut și dezvăluie recent proprietățile unice ale materialelor carbonice pe bază de grafit cum ar fi grafenul , Care ar putea fi folosite ca materiale noi în dispozitive electronice sau pentru cataliză.

Posted: Feb 04, 2016

Discovery of the specific properties of graphite-based carbon materials

(Nanowerk News) University of Tsukuba Faculty of Pure and Applied Sciences Associate Professor Takahiro Kondo and Professor Junji Nakamura, in cooperation with Researcher Donghui Guo and Professor Susumu Okada of the same faculty, have shown from detailed measurements that in atomically flat areas of a nitrogen-doped graphite surface in the absence of external magnetic fields, Landau levels manifest corresponding to super strong magnetic fields of approximately 100 tesla across bilayer graphene (Scientific Reports, „Observation of Landau levels on nitrogen-doped flat graphite surfaces without external magnetic fields”).
Prof. Junji Nakamura (front), Dr. Donghui Guo (left), Assoc. Prof. Takehiro Kondo (right)
Prof. Junji Nakamura (front), Dr. Donghui Guo (left), Assoc. Prof. Takehiro Kondo (right).
There has been some debate thus far that the source of Landau levels generated under non-magnetic fields has been pseudo-magnetic fields induced by asymmetries, but in this study the researchers observed Landau levels on atomically flat surfaces without asymmetries, showing for the first time the existence of Landau levels generated by sources other than asymmetries.
These results further endorse the “domain model” (the mechanism for Landau level generation under a non-magnetic field) that this same research team has advocated for in the past, and newly reveals the unique properties of graphite-based carbon materials such as graphene, which could be used as new materials in electronic devices or for catalysis.
Graphite-based carbon materials such as graphene exhibit powerful electrical conductivity and excellent strength in small quantities, so there is hope that they may contribute to next-generation materials in a variety of fields. The discovery of new physical properties of carbon materials in this study could lead to new applications in environmental materials like electronic materials that make use of electronic state controls such as band gap controls, catalysts, or batteries.
Source: University of Tsukuba

Read more: Discovery of the specific properties of graphite-based carbon materials

Oamenii de știință cresc grafenul de înaltă calitate din extractul de ceai(Scientists grow high-quality graphene from tea tree estract)

Graphene a fost cultivat din materiale, cum ar fi plasticul, gândacul, gulile Scout și fecalele câinilor și pot fi cultivate teoretic din orice sursă de carbon;Cu toate acestea, oamenii de știință încă caută un precursor de grafen și o metodă de creștere care este durabilă, scalabilă și fezabilă din punct de vedere economic, deoarece toate acestea sunt cerințe pentru realizarea comercializării pe scară largă a dispozitivelor pe bază de grafen;Ei au demonstrat această posibilitate prin sandwiching un semiconductor între grafen și aluminiu, creând un dispozitiv care prezintă proprietăți memoriative

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