London Calling

What Do Super-Chips, Cake Decoration, And Wine Have In Common?

The answer is 3D graphene structures. Graphene has been hailed as a game changing technology that could generate the super-chips of the future. It’s strong, light, and an excellent conductor of electricity. Its interaction with other materials and its inherently two-dimensional nature produces unique properties, such as the bipolar transistor effect, ballistic transport of charges, and large quantum oscillations.

Download this article in .PDF format
This file type includes high resolution graphics and schematics when applicable.

But when it comes to manufacturing 3D graphene, results have demonstrated weak conductivity due to poor contact between graphene sheets and impuissant structures. So what’s all this got to do with cake decoration?

Tasty Innovation

Researchers at Japan’s World Premier International Center for Materials Nanoarchitectonics (WPI-MANA) have created strong, highly conductive 3D graphene structures for use in supercapacitors using a technique that mimics blown sugar as used in food decoration.

Blowing sugar is very similar to blowing glass. A small ball of pulled sugar is attached to a tube and air is forced through it to inflate the sugar. The sugar is held under a lamp to keep it in a warm, ductile condition. When the desired shape is created, it is placed under a cooling fan and set (Fig. 1).

Xuebin Wang and Yoshio Bando at WPI-MANA surmised that structures consisting of conjoined bubbles are strong and have a propensity toward good conductivity. The question was if graphene could be fabricated in the same way.

The researchers created a syrup of ordinary sugar and ammonium chloride. Heating the syrup generated a glucose-based polymer called melanoidin, which was then blown into bubbles using gases released by the ammonium. As the bubbles grew, the remaining syrup drained out of the bubble walls.

After additional heating, deoxidization, and dehydrogenation, the melanoidin progressively graphitised to form strutted graphene, a 3D structure comprising graphene membranes linked by graphene strut frameworks.

The bubble structure facilitates movement of electrons throughout the graphene network, so the graphene retains full conductivity. Additionally, the mechanical strength and elasticity of the 3D graphene proved to be tough enough to withstand compression down to 80% of its original size with insignificant loss of conductive properties or stability.

Cork Structure Breakthrough

But what does 3D graphene have in common with a bottle of wine? The answer lies in the cork. Material engineering researchers at Australia’s Monash University have discovered what they call an effective way of forming graphene into three-dimensional forms by imitating the structure of cork (Fig. 2).

One of the problems that challenged the researchers is the known characteristic that when graphene sheets are assembled to form 3D structures, they frequently create porous monoliths that are delicate and, consequently, weak performers. This is the view of professor Dan Li of the department of materials engineering at Monash.

“It was generally thought to be highly unlikely that graphene could be engineered into a form that was elastic, which means it recovers well from stress or pressure,” explained Li.

To overcome these inherent design obstacles, the researchers used a method called freeze casting to form chemically modified graphene into a 3D structure that mimics cork. The graphene blocks it produced were lighter than air and able to support more than 50,000 times their own weight. They also were good conductors of electricity and able to recover from more than 80% deformation.

Chip Of The Future

In the United Kingdom, the University of Manchester has created a field effect transistor (FET) that may make graphene the next silicon when it comes to chip manufacture.

Professors Andre Geim and Konstantin Novoselov and their team examined numerous potential applications of graphene instead of silicon as a foundation for chip manufacture. This potential for graphene to supersede silicon has already caught the attention of major chip manufacturers, including IBM, Samsung, Texas Instruments, and Intel.

Several groups worldwide already have demonstrated individual transistors with very high frequencies (up to 300 GHz). However, those transistors cannot be packed densely to form a sufficiently powerful chip because of excessive current leakage that would cause those chips to break down and melt.

Instead, the University of Manchester scientists opted to use graphene not laterally but vertically, configuring graphene as a tunneling diode (an electrode from which electrons tunneled through a dielectric into another metal).

Then, they exploited a unique technical feature of graphene—how an external voltage can significantly change the energy gap of tunneling electrons. As a result, they generated a new type of a device, a vertical field-effect tunneling transistor in which graphene is a critical ingredient (Fig. 3).

The Manchester team made the transistors by combining graphene together with atomic planes of boron nitride and molybdenum disulfide. The transistors were assembled layer by layer in a desired sequence, like a layer cake but on an atomic scale.

Captions

1. Researchers at the World Premier International Center for Materials Nanoarchitectonics (WPI-MANA) have created 3D graphene structures for use in supercapacitors using a technique that mimics blown sugar as used in food decoration.

2. Researchers at Monash University have discovered what they say is an effective way of forming graphene into three-dimensional forms by imitating the structure of cork.

3. Researchers at the University of Manchester have developed a vertical field-effect tunneling transistor that uses graphene as a critical ingredient.

Hide comments

Comments

  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.
Publish