Showing Spotlights 257 - 264 of 268 in category All (newest first):
The most promising applications of graphene are in electronics, detectors, and thermal management. The first graphene field-effect transistors have already been demonstrated. At the same time, for any transistor to be useful for analog communication or digital applications, the level of the electronic low-frequency noise has to be decreased to an acceptable level. Low frequency electronic noise dominates the noise spectrum to a frequency of about 100 kHz. Despite the fact that modern electronic devices such as cell phones and radars operate at a much higher carrier frequency, the low frequency noise is extremely important. Due to unavoidable non-linearities in devices and systems, the low frequency noise gets up-converted, and contributes to the phase noise of the system, thus limiting its performance. It is not possible to build a communication system or detector based on graphene devices until the noise spectral density is decreased to the level comparable with the conventional state-of-the-art transistors. Researchers at the University of California - Riverside have now reported the results of experimental investigation of the low-frequency noise in a double-gate graphene transistors.
Jul 14th, 2009
Graphene has two distinct types of edges produced when it is cut - armchair type or zigzag type - which correspond to the two crystal axis of graphene. These edge types are predicted theoretically to have distinct electronic, magnetic, and chemical properties, but current fabrication methods have no way of controlling which type of edge is produced and are dominated by disorder. For example, a common method is to use plasma etching which is an isotropic etching process and is not selective in which crystallographic direction it etches. This is a problem in especially nanoelectronics applications and devices where the potential performance of the device depends strongly on the edge structure as well. A solution to this problem has now been found. Researchers have demonstrated anisotropic etching in single-layer graphene which produces connected graphene nanostructures with crystallographically oriented edges. This opens many future avenues to study graphene nanostructures such as nanoribbons, nanoconstrictions, and quantum dots with crystallographic edges.
Jun 30th, 2009
Graphene is a recently discovered allotrope of carbon, which consists of a planar single sheet of carbon atoms arranged in honeycomb lattice. It has attracted tremendous attention of the nanotechnology research community owing to a number of unique physical properties. From a practical point of view, some of the most interesting characteristics of graphene are its extraordinarily high room temperature carrier mobility and recently measured extremely high thermal conductivity. The outstanding current and heat conduction properties of graphene are beneficial for the proposed electronic, interconnect, and thermal management applications. There is a realistic possibility that soon the fastest transistors and most sensitive detectors will be made out of graphene. For instance, we have just reported that next generation computer memory could be made of graphene. In order to build useful devices from materials which have only atomic thickness, one has to use extensively scanning electron microscopy, transmission electron microscopy, and focused ion beam processing. Unfortunately, all material characterization techniques which involve electron beam irradiation of the samples may result in damage to the material and disordering of the crystalline lattice. So far, despite the practical importance of the issue, the scale of this potential damage to single-layer of bi-layer graphene has not been investigated. What happens with the crystalline lattice has also been unclear.
Dec 30th, 2008
Experiments with graphene have revealed some fascinating phenomena that excite researchers who are working towards molecular electronics. It was found that graphene remains capable of conducting electricity even at the limit of nominally zero carrier concentration because the electrons don't seem to slow down or localize. This means that graphene never stops conducting. Taking advantage of the conducting properties of graphene, researchers now have described how graphene memory could potentially be used as a new type of memory that could significantly exceed the performance of current state-of-the-art flash memory technology. Their results show the possibility to build next-generation memory devices with vast amounts of memory using nanocables with a silicon dioxide core and a shell of stacked sheets of graphene.
Nov 25th, 2008
Ink-jet printing of metal nanoparticles for conductive metal patterns has attracted great interest as an alternative to expensive fabrication techniques like vapor deposition. The bulk of the research in this area focuses on printing metal nanoparticle suspensions for metallization. For example, silver and gold nanoparticle suspensions have been inkjet printed to build active microelectromechanical systems (MEMS), flexible conductors and radio frequency identification (RFID) tags. Nobel metals like silver and gold are preferred nanoparticles for ink-jet formulations because they are good electrical conductors and they do not cause oxidation problems. However, gold and silver still are too expensive for most high volume, ultra low-cost applications such as RFID tags with required unit costs below one cent. A new technique developed in Switzerland uses flame spray synthesis in combination with a simple in-situ functionalization step to synthesize graphene coated copper nanoparticles which are air-stable and can be easily handled at ambient conditions. This work illustrates graphene's potential as a protective shell material for nanoparticles, enabling control and design of the chemical reactivity of non-noble metals.
Oct 14th, 2008
Carbon nanomaterials have been extensively used in electroanalysis, and the most common forms are spherical fullerenes, cylindrical nanotubes, and carbon fibers and blacks. Since the discovery that individual carbon nanotubes (CNTs) can be used as nanoscale transistors, researchers have recognized their outstanding potential for electronic detection of biomolecules in solution, possibly down to single-molecule sensitivity. To detect biologically derived electronic signals, CNTs are often functionalized with linkers such as proteins and peptides to interface with soluble biologically relevant targets. Now, for the first time, scientists have tested nanometal decorated graphene (actually graphite nanoplatelets, a thickness of 10 nm would contain approximately 30 graphene sheets, considering an interlayer spacing of 0.335 nm) in biosensor application. As it turned out, this novel biosensor is among the best reported to date in both sensing performance and production cost.
Sep 8th, 2008
The electrical properties of graphene have been the topic of recent interest from various disciplines because this novel carbon material offers exciting opportunities to develop nanocomposites with unusual electronic catalytic properties. Most of these studies involve mechanical peeling of individual graphene sheets - one at a time - from a block of graphite. The requirement to obtain graphene as individual sheets and to maintain it in the reduced form introduces a certain level of complexity into the process of designing composite systems where, for instance, semiconductor or metal nanoparticle are anchored on graphene sheets. Without some form of intervention, the strong van der Waals interactions between reduced graphene sheets would cause them to collapse and aggregate. Researchers have now developed a simple photocatalytic method to anchor semiconductor nanoparticles on a single sheet of graphene using a solution-based process.
Jul 15th, 2008
Since its discovery in 2004, graphene has created quite a buzz among scientists. The reason they are so excited is that two-dimensional crystals (it's called 2D because it extends in only two dimensions - length and width; as the material is only one atom thick, the third dimension, height, is considered to be zero) open up a whole new class of materials with novel electronic, optical and mechanical properties. For instance, the ultimate size limit for a nano-electromechanical system would be a nanoscale resonator that is only one atom thick, but this puts severe constraints on the material; as a single layer of atoms, it should be robust, stiff, and stable. Graphene, the simplest of the 2D conjugated carbon nanomaterials, could fit that bill. One hurdle for researchers is that current methods for the synthesis of two-dimensional, carbon-rich networks have many limitations including lack of molecular-level control and poor diversity. In a step to overcome these obstacles, researchers have now developed new synthetic strategies for forming monolayer films of conjugated carbon, in various configurations ranging from flat 2D sheets, to balloons, tubes and pleated sheets.
Jun 3rd, 2008