Nav: Home

Insulator-metal transition at the nanoscale

May 27, 2018

Controlling the flow of electrons within circuits is how electronic devices work. This is achieved through the appropriate choice of materials. Metals allow electrons to flow freely and insulators prevent conduction. In general, the electrical properties of a material are determined when the material is fabricated and cannot be changed afterwards without changing the material. However, there are materials that can exhibit metal or insulator behaviour depending on their temperature. Being able switch their properties, these materials could lead to a new generation of electronic devices.

Vanadium Dioxide (VO2) is one such material. It can switch from an insulating phase to a metallic phase just above room temperature, a feature exploited already for sensors. However, the reason why the properties of this material change so dramatically has been a matter of scientific debate for over 50 years.

One of the challenges in understanding why and how this switch occurs is due to a process called phase separation. The insulator-metal phase transition is similar to the ice to liquid transition in water. When ice melts, both liquid and solid water can coexist in separate regions. Similarly, in VO2, insulating and metallic regions of the material can be coexisting at the same time during the transition. But unlike water, where the different regions are often large enough to see with the naked eye, in VO2 this separation occurs on the nanoscale and it is thus challenging to observe. As a result, it has been hard to know if the true properties of each phase, or the mixture of both phases, are being measured.

X-rays are a key tool for understanding the properties of materials, but it has been hard to use them to probe materials on the nanoscale because it is hard to build lenses for microscopes that can detect them. However, in a recent study published in Nano Letters, a team of researchers from ICFO and ALBA in Barcelona, the Technisch Universitat and Max-Born Institute in Berlin, and Vanderbilt University in Tennessee, has finally been able to probe the phase transitions that occur in thin films of Vanadium Dioxide (VO2) using resonant soft X-ray holography. This technique is capable of imaging the electronic and structural changes in this material with an unprecedented resolution at the nanoscale without the need of a lens.

By looking at the material with 50 nm resolution, the scientists were able to observe that defects in the material played an important role in initiating the phase transition from the insulator to the metal. However, more importantly, the authors also observed a third intermediate state formed during the phase transformation. Whilst some regions transformed directly from the insulating to metallic phase, others transformed into a second different insulating state before becoming metallic at higher temperatures with the exact pathway taken depending on the defects present in the material. The coexistences of three phases has radically changed the views of previous studies that assumed the presence of only two states during the transition. Even more, the study presents new ways in which the transition could be controlled.

In addition to the results obtained on the phase transition in VO2, the work also highlights the possibilities that X-ray holography can bring for studying materials on the nanoscale. The technique is the only method that can image real-time nanoscale dynamics and is now being used to study the properties of other intriguing materials such as high temperature superconductors.

ICFO-The Institute of Photonic Sciences

Related Nanoscale Articles:

House cleaning on the nanoscale
A team of scientists at Friedrich-Alexander Universität Erlangen-Nürnberg (FAU) has developed a novel mechanical cleaning method for surfaces on the nanoscale.
As electronics shrink to nanoscale, will they still be good as gold?
As circuit interconnects shrink to nanoscale, will the pressure caused by thermal expansion when current flows through wires cause gold to behave more like a liquid than a solid -- making nanoelectronics unreliable?
A joint venture at the nanoscale
Scientists at Argonne National Laboratory report fabricating and testing a superconducting nanowire device applicable to high-speed photon counting.
Bending diamond at the nanoscale
A team of Australian scientists has discovered diamond can be bent and deformed, at the nanoscale at least.
Creating a nanoscale on-off switch for heat
Researchers create a polymer thermal regulator that can quickly transform from a conductor to an insulator, and back again.
Magnetic tuning at the nanoscale
Physicists from the German research center Helmholtz-Zentrum Dresden-Rossendorf (HZDR) are working to produce engineered magnetic nanostructures and to tailor material properties at the nanoscale.
Scientists can now control thermal profiles at the nanoscale
Scientists have designed and tested an experimental system that uses a near-infrared laser to actively heat two gold nanorod antennae to different temperatures.
New study shows nanoscale pendulum coupling
In 1665, Lord Christiaan Huygens found that two pendulum clocks, hung in the same wooden structure, oscillated spontaneously and perfectly in line but in opposite directions: the clocks oscillated in anti-phase.
Research reveals liquid gold on the nanoscale
Swansea University researchers have discovered what liquid gold looks like on the nanoscale - and in doing so have mapped the way in which nanoparticles melt, which is relevant to the manufacturing and performance of nanotech devices such as bio-sensors, nanochips , gas sensors, and catalysts.
Nanoscale thermometers from diamond sparkles
The development of a novel, non-invasive technique that uses quantum light to measure temperature at the nanoscale will have immediate applications for both industry and fundamental scientific research, scientists say.
More Nanoscale News and Nanoscale Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.