Graphene Nanoribbons Grown Bottom-Up for First Time
In general there are two ways to build structures; adding together smaller pieces from the bottom up, or removing pieces from a large structure. The two distinct methods also have distinct advantages, with additive techniques often being less wasteful, and subtractive methods sometimes being easier to accomplish. For the first time ever, researchers at Rice University have created graphene nanoribbons using an additive method.
Typically producing nanoribbons requires growing nanotubes that were then split open and flattened. While this approach works, it is hard to control the edge properties of the ribbons, which determine their electrical properties. The Rice researchers however have discovered a way to grow graphene sheets that also cause ribbons to form. Growing graphene usually requires depositing atoms of carbon on a flaw in a substrate, but by adding hydrogen to the environment, carbon atoms will collect along the entire edge of a graphene sheet. This causes the atoms to collect in two layers, one above the other, but the top layer grows more quickly and eventually prevents the bottom layer from growing further. Before long though, a new bottom layer will form, creating concentric rings of graphene nanoribbons.
Currently the rings vary in width from 10 to 450 nanometers, which can affect their electronic properties. The researchers are hoping they can find a way to control that though, as they should be able to create logic gates with 10 nm ribbons, and ultimately low-voltage transistors.
Source: Rice University