Technology


Graphene valleytrionics could lead to personal quantum computers


A team of scientists at the Indian Institute of Technology (IIT) Bombay and Max Born Institut in Germany have achieved a breakthrough in valleytronics that could lead to quantum computers accessible to all. To date, quantum computers have been


large, complex and expensive, requiring temperatures of -200°C to operate. However, researchers from IIT Bombay use graphene for encoding, processing and storing quantum information at room temperature. T ey’ve used a novel approach for encoding quantum information called “valleytronics”, which harnesses the electrons’ local minima, or “valleys” in the energy bands – known as “valley pseudospin”. By manipulating how many electrons occupy each of the valleys, quantum information can be encoded,


processed and stored at less restrictive temperatures. T e scientists performed valley operations in


one-atom-thick pristine graphene to manipulate the electron valleys with light. “By tailoring the polarisation of two beams


of light according to graphene’s triangular lattice, we found it possible to break the symmetry between two neighbouring carbon atoms and exploit the electrons’ band structure in the regions close to the valleys, inducing valley polarisation, thus enabling graphene’s valleys to eff ectively ‘write’ information,” said Gopal Dixit, IIT Bombay Associate Professor, who led this project’s team. “T is could open the door to small, general-purpose quantum computers that can be used by regular people, much like laptops.”


Electron energy valley polarisation


Enriching hydrogen isotopes in silicon could lead to more durable electronics


A team of scientists from Nagoya City University (NCU) in Japan has developed an energy-effi cient strategy to enrich silicon surfaces using dilute deuterium. Deuterium is a heavier but less abundant


version of the hydrogen atom, and off ers many practical benefi ts, including in semiconductors. T e surface of silicon-based


semiconductors must be ‘passivated’ with hydrogen to ensure silicon atoms don’t detach easily (desorption), thereby increasing the durability of microchips, batteries and solar cells. It has been established that passivation with deuterium results in about one hundred times lower desorption than with hydrogen, making deuterium a potentially indispensable ingredient in electronic devices. Unfortunately, both the procurement


of deuterium and available techniques to enrich silicon surfaces with it are very energy ineffi cient and require very expensive deuterium gas. T is will change now, since the NCU researchers have found that an exchange reaction from hydrogen to deuterium can occur on the surface of nanocrystalline silicon (n-Si).


Hydrogen-to- deuterium exchange reactions at a hydrogen-terminated n-Si surface in the presence of HDO molecules (deuterium: red spheres, hydrogen: pink spheres, oxygen: green spheres, silicon: blue spheres)


[Image courtesy: Takahiro Matsumoto, NCU, Japan]


T e exchange process is closely related


to diff erences in the surface vibrational modes between hydrogen- and deuterium- terminated n-Si. Exploiting the quantum eff ects on the surface of n-Si could pave the way to new methods to produce and use deuterium. “T e effi cient hydrogen-to-deuterium exchange reaction we reported may lead


to sustainable, economically-feasible and environment-friendly deuterium enrichment protocols, leading to more durable semiconductor technology,” said Professor Takahiro Matsumoto of NCU, who led the project’s team. “Let’s hope our fi ndings allow us to benefi t more from the heavier isotopes of hydrogen without taking a toll on our planet.”


www.electronicsworld.co.uk December 2021/January/2022 05


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