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John O | June 2019

Laser technique stresses graphene and unlocks electrical conductivity in material


By Josh Perry, Editor
jperry@coolingzone.com

 

A new laser technique developed by researchers at the University of Purdue, University of Michigan, and the Huazhong University of Science and Technology (Wuhan, China) puts permanent stress on graphene, changing its structure to create a band gap and allow the flow of electric current.

 


Researchers used a laser technique to permanently stress graphene into a structure that allows the flow of electric current. (Purdue University image/Gary Cheng)

 

According to a report from Purdue, the researchers created and widened a band gap in graphene to a record 2.1 electronvolts, which is four times the previous record and allows the material to function as a semiconductor, similar to silicon. The band gap allows the material to have electrical conductivity switched on or off and enables it to be used in electronics applications.

 

This is the first time that a band gap was created in graphene without the use of chemical doping or stretching, both of which alter other properties in the material.

 

To create the band gap, scientists used laser shock imprinting, which was developed five years ago, to create shockwave impulses that penetrated a sheet of graphene. “The laser shock strains graphene onto a trench-like mold – permanently shaping it. Adjusting the laser power adjusts the band gap,” the article explained.

 

The research was recently published in Advanced Materials. The abstract stated:

 

“Graphene has a great potential to replace silicon in prospective semiconductor industries due to its outstanding electronic and transport properties; nonetheless, its lack of energy bandgap is a substantial limitation for practical applications. To date, straining graphene to break its lattice symmetry is perhaps the most efficient approach toward realizing bandgap tunability in graphene. However, due to the weak lattice deformation induced by uniaxial or in?plane shear strain, most strained graphene studies have yielded bandgaps <1 eV.

 

“In this work, a modulated inhomogeneous local asymmetric elastic–plastic straining is reported that utilizes GPa?level laser shocking at a high strain rate (dε/dt) ≈ 106–107 s−1, with excellent formability, inducing tunable bandgaps in graphene of up to 2.1 eV, as determined by scanning tunneling spectroscopy.

 

“High?resolution imaging and Raman spectroscopy reveal strain?induced modifications to the atomic and electronic structure in graphene and first?principles simulations predict the measured bandgap openings. Laser shock modulation of semimetallic graphene to a semiconducting material with controllable bandgap has the potential to benefit the electronic and optoelectronic industries.”

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