(University of Chicago) Microscopic spheres form strings in surprising alignments when suspended in a viscous fluid and sheared between two plates, a finding that will affect the way scientists think about the properties of such wide-ranging substances as shampoo and futuristic computer chips.

Smaller and more energy-efficient electronic chips could be made using molybdenite. In an article appearing online January 30 in the journal Nature Nanotechnology, EPFL’s Laboratory of Nanoscale Electronics and Structures (LANES) publishes a study showing that this material has distinct advantages over traditional silicon or graphene for use in electronics applications.

A discovery made at EPFL could play an important role in electronics, allowing us to make transistors that are smaller and more energy efficient. Research carried out in the Laboratory of Nanoscale Electronics and Structures (LANES) has revealed that molybdenite, or MoS2, is a very effective semiconductor. This mineral, which is abundant in nature, is often used as an element in steel alloys or as an additive in lubricants. But it had not yet been extensively studied for use in electronics.

100,000 times less energy

“It’s a two-dimensional material, very thin and easy to use in nanotechnology. It has real potential in the fabrication of very small transistors, light-emitting diodes (LEDs) and solar cells,” says EPFL Professor Andras Kis, whose LANES colleagues M. Radisavljevic, Prof. Radenovic et M. Brivio worked with him on the study. He compares its advantages with two other materials: silicon, currently the primary component used in electronic and computer chips, and graphene, whose discovery in 2004 earned University of Manchester physicists André Geim and Konstantin Novoselov the 2010 Nobel Prize in Physics.

One of molybdenite’s advantages is that it is less voluminous that silicon, which is a three-dimensional material. “In a 0.65-nanometer-thick sheet of MoS2, the electrons can move around as easily as in a 2-nanometer-thick sheet of silicon,” explains Kis. “But it’s not currently possible to fabricate a sheet of silicon as thin as a monolayer sheet of MoS2.” Another advantage of molybdenite is that it can be used to make transistors that consume 100,000 times less energy in standby state than traditional silicon transistors. A semi-conductor with a “gap” must be used to turn a transistor on and off, and molybdenite’s 1.8 electron-volt gap is ideal for this purpose.

Better than graphene

In solid-state physics, band theory is a way of representing the energy of electrons in a given material. In semi-conductors, electron-free spaces exist between these bands, the so-called “band gaps.” If the gap is not too small or too large, certain electrons can hop across the gap. It thus offers a greater level of control over the electrical behavior of the material, which can be turned on and off easily.

The existence of this gap in molybdenite also gives it an advantage over graphene. Considered today by many scientists as the electronics material of the future, the “semi-metal” graphene doesn’t have a gap, and it is very difficult to artificially reproduce one in the material.

Source: EPFL’s Laboratory of Nanoscale Electronics and Structures (LANES)

Researchers cross organic and non-organic nano wires like Mikado sticks and thereby make nanoscale prototype computer electronics. Image by Asmus Dohn.

New data from Chinese-Danish collaboration shows that organic nanoscale wires could be an alternative to silicon in computer chips. The discovery has just been published in the respected scientific journal, Advanced Materials.

Nanochemists from the Chinese Academy of Sciences and the Nano-Science Center, Department of Chemistry have developed nanoscale electric contacts out of organic and inorganic nanowires. In the contact they have crossed the wires like Mikado sticks and coupled several contacts together in an electric circuit. In this way they have produced prototype computer electronics on the nanoscale.

Alternative to silicon computers

Today the foundation of our computers, mobile phones and other electronic apparatus is silicon transistors. A transistor is in principal an on- and off- contact and there are millions of tiny transistors on every computer chip. However, we are reaching the limit for how small we can make transistors out of silicon.

We already use various organic materials in, for example, flat screens, such as OLED (Organic Light Emitting Diode). The new results show how small and advanced devices made of organic materials can become. Thomas Bjørnholm, Director of the Nano-Science Center, Department of Chemistry at University of Copenhagen explains:

- “We have succeeded in placing several transistors consisting of nanowires together on a nano device. It is a first step towards realisation of future electronic circuitry based on organic materials – a possible substitute for today’s silicon-based technologies. This offers the possibility of making computers in different ways in the future.”

Danish-Chinese nanoelectronics

The researchers have used organic nanowires combined with the tin oxide nanowires in a so-called hybrid circuit. As in a Mikado game, the nanowires cross in a device consisting of 4-6 active transistor moieties. The devices have a low operational current, high mobility and good stability and that is essential in order for the material to be able to compete with silicon.

Professor Wenping Hu, Chinese Academy of Sciences is excited over the results:

- “This work is the first significant result of our collaboration with the researchers from the Nano-Science Center. It is a good starting point for our new Danish-Chinese research centre for molecular nano-electronics and it underlines the fact that we can complement each other and that together we can achieve exciting and important results.”

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