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vdW Heterostructures for Optical Detection II HEROD II

Carlsbergfondets internationaliseringsstipendier

What

The goal of this project is to study how ultra-broadband photosensors could be made using the 2D materials graphene and hexagonal boron nitride (hBN). The sensors would consist of two layers of graphene separated by a thin layer of hBN, which would allow energetic electrons generated in the graphene layers from absorption of light to move from one graphene layer to the other, by the quantum mechanical process of ‘tunneling’.

This exchange of electrons between the graphene layers would be measurable as a current if electrodes are attached to the device, with the current being proportional to the amount of incident light. Graphene's intrinsic flatness (one atom thick) should make it ideal for such an application, as the efficiency of the tunnelling process should be very high.

Why

It is impossible with conventional techniques to make ultra-broadband photosensors, and currently available technologies for broadband sensors have very low efficiencies. This makes them unsuitable for many applications like imaging, as the time to acquire an image would be prohibitively long.

Making efficient ultra-broadband optical sensors would enable a variety of new applications and technologies in areas like the medical and chemical sciences, security, low-light/low-visibility imaging, etc. Secondly, such detectors are expected to be extremely thin and light, and could be integrated in several new devices and technologies where conventional detectors are less than ideal.

How

We will utilise a dry visco-elastic polymer transfer technique. By using the correct polymers and heating, it is possible to mechanically pick up exfoliated flakes of graphene or hBN, and then drop the flakes off in a specific position. Like this, it is possible to stack the different materials together vertically to create van der Waals bonded heterostructures. From this, we can make a stack of 2 graphene flakes separated by a thin (few atoms thick) hBN flake.

After assembling the material stack, electrodes will be attached using the university's nanofabrication facilities, and the finished device can be characterised for its optical responsivity using laser sources and electrical source-meters.

SSR

Graphene is promising to become an incredibly important material in the future. It has already been demonstrated to have many extraordinary material properties that could be exploited within a plethora of applications and technologies, ranging from ultra-fast and compact electronics, chemical sensing, optical modulators, catalysis, flexible touch screens, etc.

Fundamental studies in how to best use graphene and how to enhance its properties as much as possible, are thus an important stepping-stone toward practical implementations of graphene into future technologies, and for its potential use in future wide-scale industry. The international aspects of this project serve an important role in further strengthening the broad European expertise in graphene and 2D materials.