Credit: Bent Weber
Bent Weber's work focuses on electronic silicon devices, using atomic accuracy to make electronic devices that are on the atomic scale - as small as you can make them. And we're talking small - a wire four atoms wide and one atom tall, 10,000 times thinner than a human hair.
"We test how small we can make electrical components and we have shown we can essentially make them as small as a couple of atoms without a loss of functionality - they behave the same way as if they were a much larger structure," says Weber.
Computers, mobile phones and digital devices all feature integrated circuits (miniaturised electronic circuits) usually with some type of silicon chip with interconnecting wires that transmit the electronic signals responsible for arithmetic, logic and memory functions.
The computer that you are using to read this right now uses the convention of a 'classical' bit - the basic unit of computer information, encoding data into either 0 or 1. A qubit (or quantum bit) is different, in that it can be 0, 1 or a combination of the two, leading to exponential speed-up of computations. Quantum computers, the next step in computer technology, are thus expected to be able to solve much larger and complicated problems, faster than the fastest computers today. But they require nanoscale wires, and that's where Weber comes in.
The team at the Centre for Quantum Computation and Communication Technology at the University of New South Wales in Sydney are trying to use single phosphorus atoms as the qubits themselves, from which they will use the atomic-scale wires to control and interconnect them. "To build a scalable quantum computer with multiple individual phosphorus atoms - acting as qubits - we realised that we need to shrink the size of the interconnecting wiring to the same scale as the atoms themselves," says Weber.
By doping a silicon crystal with phosphorus atoms, the crystal becomes locally conducting, as if it were a metal like copper which is commonly used in wires.
But how does he get it so small you might ask? They used a Scanning Tunnelling Microscope (STM), which Weber calls, "A very fascinating type of microscope from which you can not only resolve matter at the atomic scale but you can also manipulate matter."
The researchers initially deposit a monolayer of hydrogen atoms on the silicon surface so that every hydrogen atom is bonded to a silicon atom - making the silicon non-reactive. They then used the 'atomically sharp wire' tip of the STM to essentially scratch off a very thin line of the hydrogen atoms, exposing the reactive silicon. Phosphorus atoms were then introduced 'sticking' to the exposed silicon line and acting as if they were silicon atoms but with its additional electron donated to the silicon crystal - allowing silicon to conduct electricity.
Weber says these wires are the "building blocks of more complicated devices" and is currently moving forward with the research towards quantum computing architecture. He says it is fundamentally interesting to put together electronic devices atom by atom, "It was very fascinating to find out that if you put devices together atom by atom they behave essentially the same as they would being much, much larger."
