Tag Archives: Discovery

New Ultrathin Semiconductors Can Make More Efficient and Ten Times Smaller Transistors Than Silicon

The researchers at Stanford University have discovered two ultrathin semiconductors – hafnium diselenide and zirconium diselenide. They share or even exceed some of the very important characteristics of silicon. Silicon has a great property of forming “rust” or silicon dioxide (SiO2) by reacting with oxygen. As the SiO2 acts as an insulator, chip manufacturers implement this property to isolate their circuits on a die. The most interesting fact about these newly discovered semiconductors is, they also form “rust” just like silicon.

enlarged cross-section of an experimental chip made of ultrathin semiconductors
An enlarged cross-section of an experimental chip made of ultrathin semiconductors

The new materials can also be contracted to functional circuits just three atoms thick and they require much less energy than silicon circuits. Hafnium diselenide and zirconium diselenide “rust” even better than silicon and form so-called high-K insulator. The researchers hope to use these materials to design thinner and more energy-efficient chips for satisfying the needs of future devices.

Apart from having the ability to “rust”, the newly discovered ultrathin semiconductors also have the perfect range of energy band gap – a secret feature of silicon. The band gap is the energy needed to switch transistors on and it is a critical factor in computing. Too low band gap causes the circuits to leak and make unreliable. Too high and the chip takes excessive energy to operate and becomes inefficient. Surprisingly, Hafnium diselenide and zirconium diselenide are in the same optimal range of band gap as silicon.

All this and the diselenides can also be used to make circuits which are just three atoms thick, or about two-thirds of a nanometer, something silicon can never do. Eric Pop, an associate professor of electrical engineering, who co-authored with post-doctoral scholar Michal Mleczko in a study paper, said,

Engineers have been unable to make silicon transistors thinner than about five nanometers, before the material properties begin to change in undesirable ways.

If these semiconductors can be integrated with silicon, much longer battery life and much more complex functionality can be achieved in consumer electronics. The combination of thinner circuits and desirable high-K insulation means that these ultrathin semiconductors could be made into transistors 10 times tinier than anything possible with silicon today. As Eric Pop said,

There’s more research to do, but a new path to thinner, smaller circuits – and more energy-efficient electronics – is within reach.

Carrageenan, a seaweed derivative, can stabilize lithium-sulfur batteries surprisingly

Lithium-sulfur batteries are suitable for both vehicle and grid applications as they are ultra-cheap, high-energy devices. Sulfur is a very low-cost material and the energy capacity is much higher than that of lithium-ion. So, lithium-sulfur is one chemistry that can possibly meet the demand for energy storage at a cheap price. However, the serious problem is, lithium-sulfur batteries suffer from significant capacity fading that makes them almost practically unusable. But, Lawrence Berkeley National Laboratory researchers’ recent surprising discovery could fix this problem.

Carrageenan is extracted from this red seaweeds
Carrageenan is extracted from this red seaweeds

The research team at Berkley Laboratory surprisingly found that carrageenan, a substance extracted from red seaweeds, acts as a good stabilizer in lithium-sulfur batteries. Better stability in a battery means more charge-discharge cycle and an extended lifetime. Gao Liu, the leader of the research team, said,

It (Carrageenan) actually worked just as well as the synthetic polymer—it worked as a glue and it immobilized the polysulfide, making a really stable electrode.

Lithium-sulfur batteries are already been used commercially in limited applications but the “critical killer” in the chemistry is that the sulfur starts to dissolve and creates polysulfide shuttling effect. Polysulfide shuttling is the primary cause of failure in lithium-sulfur (Li-S) battery cycling. To solve the problem, the research team was experimenting with a synthetic binder that holds all the active materials in a battery cell together.

A binder is like a glue and battery makers want this glue to be inert. The synthetic polymer Liu experimented with, worked remarkably well. The reason is, by chemically reacting with the sulfur, the binder formed a covalent bonding structure and was able to stop it from dissolving. This finding motivated the researchers to find a natural material that would do the same thing. Finally, they discovered that carrageenan has similar chemical properties as the synthetic polymer they used in their initial experiments.

Bekley Lab's researcher is working with advanced light source
Berkley Lab’s researcher is working with advanced light source

With this discovery to stabilize lithium-sulfur batteries­ Liu now wants to improve the lifetime of lithium-sulfur batteries even further. The target of the researchers is to get thousands of cycles from lithium-sulfur chemistry. They are striving to find answers to questions like after this polymer binds with sulfur, what happens next? How does it react with sulfur, and is it reversible? Liu said,

Understanding that will allow us to be able to develop better ways to further improve the life of lithium-sulfur batteries.

As lithium-sulfur batteries are much more lightweight, cheaper, and have higher energy density compared to lithium-ion batteries, they are ideal for airplanes and drones. Hence, Berkeley Lab researchers’ surprising discovery may be a game changer in the world of batteries.