Monday, June 22, 2015

Penn State - Diode a few atoms thick shows surprising quantum effect

As publish by Penn State : A quantum mechanical transport phenomenon demonstrated for the first time in synthetic, atomically-thin layered material at room temperature could lead to novel nanoelectronic circuits and devices, according to researchers at Penn State and three other U.S. and international universities.

Atomic multilayer structure of van der Waals solids representing layering with a graphene substrate.

Current-voltage curves of single junction (green) van der Waals solid (no NDR) and multijunction (red, orange) van der Waals solids (NDR). Stacking and choice of materials determines the location and width of peak.

The quantum transport effect, called negative differential resistance (NDR), was observed when a voltage was applied to structures made of one-atom-thick layers of several layered materials known as van der Waals materials. The three-part structures consist of a base of graphene followed by atomic layers of either molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), or tungsten diselenide (WSe2).

NDR is a phenomenon in which the wave nature of electrons allows them to tunnel through any material with varying resistance. The potential of NDR lies in low voltage electronic circuits that could be operated at high frequency.

“Theory suggests that stacking two-dimensional layers of different materials one atop the other can lead to new materials with new phenomena,” said Joshua Robinson, a Penn State assistant professor of materials science and engineering whose student, Yu-Chuan Lin, is first author on a paper appearing online today, June 19, in the journal Nature Communications. The paper is titled “Atomically Thin Resonant Tunnel Diodes Built from Synthetic van der Waals Heterostructures.”

Achieving NDR in a resonant tunneling diode at room temperature requires nearly perfect interfaces, which are possible using direct growth techniques, in this case oxide vaporization of molybdenum oxide in the presence of sulfur vapor to make the MoS2 layer, and metal organic chemical vapor deposition to make the WSe2 and MoSe2.

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