Defects - Page 4

Researchers at Japan's RIKEN have discovered that wrinkles in graphene can restrict the motion of electrons to one dimension, forming a junction-like structure that changes from zero-gap conductor to semiconductor back to zero-gap conductor. Moreover, they have used the tip of a scanning tunneling microscope to manipulate the formation of wrinkles, opening the way to the construction of graphene semiconductors by manipulating the carbon structure itself in a form of "graphene engineering."

The scientists were able to image the tiny wrinkles using scanning tunneling microscopy, and discovered that there were band gap openings within them, indicating that the wrinkles could act as semiconductors. Two possibilities were Initially considered for the emergence of this band gap. One is that the mechanical strain could cause a magnetic phenomenon, but the scientists ruled this out, and concluded that the phenomenon was caused by the confinement of electrons in a single dimension due to "quantum confinement."

Researchers at Pennsylvania’s Lehigh University have reported a breakthrough in efforts to non-invasively characterize the properties of graphene. This work could potentially enable scientists to rapidly monitor levels of strain as graphene is being fabricated, thereby helping to prevent the formation of defects. 

By using Raman spectroscopy, a technique that collects light scattered off a material’s surface, and statistical analysis, the scientists were able to take nanoscale measurements of the strain present at each pixel on the material’s surface and obtain a high-resolution view of the chemical properties of the graphene surface.

Scientists at Northwestern University have found how graphene oxide's inherent defects may present an interesting mechanical property. It seems that graphene oxide exhibits remarkable plastic deformation before breaking; While graphene is very strong, it can still break suddenly. It was found that graphene oxide, however, will deform first before eventually breaking.

The researchers used an experimentation and modeling approach to examine the mechanics of GO at the atomic level. Their discovery could potentially unlock the secret to successfully scaling up graphene oxide, an area that has been limited because its building blocks have not been well understood.

Researchers from the National Cheng Kung University in Taiwan designed a new method for tweaking the properties of graphene by introducing defects into it. Precise control over the amount and nature of defects could bring about new applications of graphene in everything from drug delivery or electronics.

The scientists used a technique called electrochemical exfoliation to strip graphene layers from graphite flakes. By varying the voltage they discovered they could change the resulting graphene’s thickness, flake area, and number of defects all of which alter its electrical and mechanical properties.

Researchers at MIT, Oak Ridge National Laboratory, and King Fahd University of Petroleum and Minerals (KFUPM) have devised a process to repair leaks, cracks and holes that are formed in graphene in the process of creating membranes for water filtration and desalination.

The process relies on a combination of chemical deposition and polymerization techniques. The team also used a process it developed previously to create tiny, uniform pores in the material, small enough to allow only water to pass through. These two techniques combined yielded a relatively large defect-free graphene membrane, about the size of a penny.

Researchers at the Russian Zelinsky Institute of Organic Chemistry of Russian Academy of Sciences developed a tomography imaging procedure that facilitates the visualization of defects on graphene layers by mapping the surface. This is a unique use of a traditionally medical imaging method to materials at the atomic scale, that may help improve existing characterization and defect-location methods. 

The scientists concentrated on a specific contrast agent - soluble palladium complex - that can selectively attach to defect areas on the surface of carbon materials. his attachment results in the formation of nanoparticles that can be detected using an electron microscope. The binding of the agent is stronger in areas where the carbon center is more reactive, and the reactivity centers and defect sites can be mapped in high resolution and excellent contrast. Also, this procedure distinguished defects not only by the differences in their morphology, but also by their varying chemical reactivity. Therefore, this imaging approach enables the chemical reactivity to be visualized with spatial resolution. 

Scientists at the University of California, San Diego discovered a method to increase the amount of electric charge that can be stored in graphene, in a research that may provide a better understanding of how to improve the energy storage ability of capacitors for potential applications in cars, wind turbines, and solar power.

The team attempted to introduce more charge into a capacitor electrode using graphene as a model material for their tests. The idea is that increased charge leads to increased capacitance, which translates to increased energy storage.

A collaboration of scientists from several institutions, including Northwestern, EFRC and more, discovered that graphene that is slightly imperfect can shuttle protons from one side of a graphene membrane to the other in seconds. The selectivity and speed of the imperfect version are compared to conventional membranes, opening the door to new and simpler model of fuel cell designs.

This, of course, goes against conventional efforts to create perfect graphene as it turns out that protons move better through imperfect graphene. The defects in the graphene trigger a chemical "conveyor belt" that shuttles protons from one side of the membrane to the other in a few seconds. In conventional membranes, which can be hundreds of nanometers thick, the desired proton selection takes minutes, compared to the quick transfer in a one-atom-thick layer of graphene.

Researchers at Rice University reached the conclusion that grain boundaries (the nanoscale places where individual grains of graphene stitch the sheet together), which are at times considered defects, may in some cases toughen polycrystalline sheets and may also create a band gap.

The scientists explain that at certain angles, these meandering boundaries relieve stress that would otherwise weaken the sheet. Alleviating this stress can enhance graphene's strength, compared to straight boundaries. 

Researchers at the Rice University have devised a process in which a computer-controlled laser burns through a polymer to create flexible, patterned sheets of multilayer graphene that may be suitable for electronics or energy storage. The process works in air at room temperature, cancelling the need for hot furnaces and controlled environments.

The product of this process is not a 2D piece of graphene but a porous foam of interconnected flakes about 20 microns thick. The laser doesn't cut all the way through the base material, so the foam remains attached to a flexible plastic base.