Nav: Home

Exfoliating thinner flakes of phosphorene at higher yield

April 18, 2016

In the past two years, phosphorene has attracted increased attention due to its potential in thin, flexible electronics. And because it is naturally a semi-conductor, phosphorene holds promise where miracle material graphene falls short.

"There has been a decade-long attempt to make graphene semi-conducting," said Northwestern University's Mark Hersam. "Our group and others have tried to do it with limited success. So why not just use a material that is already a semi-conductor?"

In order for phosphorene to reach its full potential, it needs to be incredibly thin -- preferably at the atomic scale. Until now, researchers have experienced difficulties in exfoliating atomically thin flakes from the bulk material, called black phosphorous, in a quick and efficient manner. Hersam, however, may have solved this problem. His group recently developed a method that results in substantially higher exfoliation yield and much thinner flakes than previous efforts.

Supported by the National Science Foundation and Office of Naval Research, the research is described online in the April 18 issue of Proceedings of the National Academy of Sciences. Joohoon Kang, a graduate student in Hersam's laboratory, is first author of the study.

After being exfoliated from black phosphorous, phosphorene has dramatically different electronic and mechanical properties from its parent material. Not only are the atomically thin, two-dimensional layers powerful semiconductors, but they also efficiently emit light, suggesting opportunities for optoelectronics.

"Graphene taught us that the most scalable method was to exfoliate in a solution," said Hersam, Walter P. Murphy Professor of Materials Science and Engineering at Northwestern's McCormick School of Engineering. "You begin with a solvent and then add graphite and a surfactant. After introducing energy via sonication, you can exfoliate the graphite down to graphene. It would seem obvious that the same approach would work with phosphorene. The difference, however, is that phosphorene is very reactive chemically, which requires important changes in protocol to achieve exfoliation without degradation."

When exposed to open air, the chemical reactivity of phosphorene leads to rapid deterioration. The result suggests that components of air, such as water and oxygen, are driving degradation and need to be avoided. Consequently, Hersam initially bypassed this issue by exfoliating with organic solvents in a closed, air-free and water-free environment.

"The problem with the organic solvent approach is that it is very inefficient," he said. "It results in low exfoliation yield and flakes that are relatively thick."

The breakthrough came when Hersam and his team realized -- after a year of studying the degradation process -- that phosphorene degrades in the presence of both water and oxygen together. By bubbling an inert gas through water, Hersam deoxygenated it to create an aqueous solvent for exfoliating black phosphorous that avoids degradation. After sonicating black phosphorous in a mixture of deoxygenated water and surfactants, he found substantially higher exfoliation yield and much thinner flakes that reached the atomically thin limit.

In addition to providing superior phosphorene materials, the method uses commonly available, environmentally benign water as opposed to organic solvents.

"We took the resulting exfoliated flakes and fabricated transistors out of them," Hersam said. "The device metrics were among the best reported for any exfoliated phosphorene, thereby confirming that we had isolated high quality material in a scalable manner without degradation."
-end-


Northwestern University

Related Graphene Articles:

New chemical method could revolutionize graphene
University of Illinois at Chicago scientists have discovered a new chemical method that enables graphene to be incorporated into a wide range of applications while maintaining its ultra-fast electronics.
Searching beyond graphene for new wonder materials
Graphene, the two-dimensional, ultra lightweight and super-strong carbon film, has been hailed as a wonder material since its discovery in 2004.
New method of characterizing graphene
Scientists have developed a new method of characterizing graphene's properties without applying disruptive electrical contacts, allowing them to investigate both the resistance and quantum capacitance of graphene and other two-dimensional materials.
Chemically tailored graphene
Graphene is considered as one of the most promising new materials.
Beyond graphene: Advances make reduced graphene oxide electronics feasible
Researchers have developed a technique for converting positively charged (p-type) reduced graphene oxide (rGO) into negatively charged (n-type) rGO, creating a layered material that can be used to develop rGO-based transistors for use in electronic devices.
The Graphene 2017 Conference connects Barcelona with the international graphene-based industry
This prestigious Conference to be held at the Barcelona International Convention Centre (March 28-31) aims to bring together academia and industry to integrate new graphene technologies into practical applications.
Graphene from soybeans
A breakthrough by CSIRO-led scientists has made the world's strongest material more commercially viable, thanks to the humble soybean.
First use of graphene to detect cancer cells
By interfacing brain cells onto graphene, researchers at the University of Illinois at Chicago have shown they can differentiate a single hyperactive cancerous cell from a normal cell, pointing the way to developing a simple, noninvasive tool for early cancer diagnosis.
Development of graphene microwave photodetector
DGIST developed cryogenic microwave photodetector which is able to detect 100,000 times smaller light energy compared to the existing photedetectors.
Adding hydrogen to graphene
IBS researchers report a fundamental study of how graphene is hydrogenated.

Related Graphene Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...