Electronics researchers love graphene. A two-dimensional sheet of carbon one atom thick, graphene is like a superhighway for electrons, which rocket through the material with 100 times the mobility they have in silicon. But creating graphene-based devices will be challenging, say researchers at the National Institute of Standards and Technology (NIST), because new measurements show that layering graphene on a substrate transforms its bustling speedway into steep hills and valleys that make it harder for electrons to get around.
In a new article in Nature Physics,* NIST scientists also say that graphene may be an ideal medium for probing interactions between electric conductors and insulators using a scanning tunneling microscope (STM).
According to NIST Fellow Joseph Stroscio, graphene's ideal properties are only available when it is isolated from the environment.
"To get the most benefit from graphene, we have to understand fully how graphene's properties change when put in real-world conditions, such as part of a device where it is in contact with other kinds of materials," Stroscio says.
Typical semiconductor chips are a complicated "sandwich" of alternating conducting, semiconducting and insulating layers and structures. To perform their experiment, the NIST group made their own sandwich with a single atomic sheet of graphene and another conductor separated by an insulating layer. When the bottom conductor is charged, it induces an equal and opposite charge in the graphene.
Examined under an STM, which is sensitive to the charged state of the graphene, the high electron mobility should make the graphene look like a featureless plane. But, says NIST researcher Nikolai Zhitenev, "What we found is that variations in the electrical potential of the insulating substrate are interrupting the orbits of the electrons in the graphene, creating wells where the electrons pool and reducing their mobility."<
|Contact: Mark Esser|
National Institute of Standards and Technology (NIST)