A strain tunable single-layer MoS2 photodetector

Lets take a single layer of MoS2. Lets attach it to a surface in such a way that it can be stretched (or compressed) and there you have it: A strain tunable single-layer MoS2 photodetector. A device which uses strain to change the electrical and optical properties of 2D materials. In particular they’ve proven that with this method, they can reversibly change the photoresponsivity, the response time and the spectral bandwidth of single layered MoS2.

At Dr. Castellanos Lab, they are excelling at beautiful and elegant research. “… we demonstrated that applying tensile biaxial strain to the MoS2 device can be an effective strategy to increase both the responsivity and the wavelength bandwidth of the photodetector (at the expense of a slower response time), while compressive strain can be exploited to yield faster photodetectors (although with a lower photoresponse and with a narrower wavelength bandwidth). This adaptable optoelectronic performance of this device can be very useful to adjust the photodetector operation to different lighting conditions, similarly to human eye adaptability (scotopic vision during the night vs. photopic vision during the daylight).

Their research is a collaboration between ICMM-CSIC, Imdea Nanociencia and the State Key Laboratory of Tribology, Tsinghua University, Beijing and has been recognized with the inner cover of Materials Today.

Waves and Stress

Measuring the mechanical strength of a material at the nanoscale is challenging . If the object we are measuring happens to be a two-dimensional material, the task amazingly difficult. But people at Castellanos-Gómez Lab are really smart. They’ve adapted a method (already used with organic thin films) to determine these materials Young Modulus that, apart from other advantages, does not require the material to be freely suspended.

To make a long story short, they compress the material. Not been freely suspended, ripples appear all over the material. The wavelength of this ripples depends only in the elastic properties of the film and the substrate, so voilá! Frankly, much easier to explain than to perform.

These results were published in Advanced Materials.

To illustrate it, and requested by Dr. Andrés Castellanos-Gómez, we did this image that made it to the back cover of Advanced Materials.

NanoCosmos: the beginning

About 4 years ago Prof. Jose Ángel Martín Gago approached me to talk me about the NANOCOSMOS project. As they explain in their website, “NANOCOSMOS will take advantage of the new observational capabilities (increased angular resolution) of the Atacama Large Millimeter/submillimeter Array (ALMA) to unveil the physical and chemical conditions in the dust formation zone of evolved stars”.  Simply put, they are studying the debris stars create and the role this dust plays in the life/death recycling story of the universe.

This is a huge ERC funded project directed by Prof. José Cernicharo which has put together research groups from Spain and France.

And this is where Natalia Ruiz Zelmanovitch (Public Information Officer of the project) appears. She happens to be the most-committed-with-outreach-and-dissemination-of-science I’ve ever met. And she wants to tell the story of the NANOCOSMOS project. And she wants to tell it right.

She is behind the production of “NANOCOSMOS: un viaje a lo pequeño.” Here you can watch the trailer:

Scixel has been in charge of the 3D visualizations of the space: stars, nebulae, galaxies and planetary systems. We have been working with the Nanocosmos people for a few years now and I can tell you, if I know Natalia enough, this is just the beginning. So, stay tunned!

Mapping stress at the nanoscale

Stress is the main cause of failure in mechanical and electronic devices incorporating thin films. At the same time, our knowledge of stress at the nanoscale, happens to be very limited and one of the reasons is that we have no access to the measurement of stress at this tiny scale.

And this is what Celia Polop, Enrique Vasco, Alma P. Perrino and Ricardo García (Universidad Autónoma de Madrid and Material Science Institute of Madrid-CSIC) have solved. They’ve just presented a novel method to map stress on surfaces with a sub 10nm resolution. This method, supported by finite element simulations, has allowed them to map stress on polycrystalline gold films.

We made this image (featured in Nanoscale) illustrating their work, strongly supported by Enrique Vasco and Celia Polop.