The hidden dragon that spews X-rays
Using huge, monstrous machines to make tiny and intricate things sounds counterintuitive or even counterproductive. But at the Singapore Synchrotron Light Source (SSLS) of NUS, this represents the cutting edge of technology. It enables the SSLS to not only produce the latest scientific discoveries, but also turn them into commercial applications.
Located at a remote corner of the NUS Kent Ridge campus, the SSLS is a particle accelerator that converts electrons into powerful beams of light, including infrared and X-rays. Working there is a specialised group of beamline scientists. One of them, Research Fellow Dr S. M. P. Kalaiselvi, uses the X-rays to make the chip for a handy-sized spectrometer that is commercially available.
Dr Kalaiselvi does this by directing the X-ray beam into a room cloaked in an eerie yellow light, as there are chemicals that become unstable when exposed to other wavelengths. Inside the room, she has to manoeuvre a heavy metal plate into a machine that looks like the huge jaws of a monster. But looks are deceptive. This gentle giant can do 3D printing at nanometer scale, precisely rotating the material in any direction.
Under Dr Kalaiselvi’s command, the machine creates a three-dimensional pattern of 1,800 tiny interference structures, crammed into an area of a few square millimeters. This so-called phase-shifting array is a patented design for splitting light into its component wavelengths, and eventually goes into the commercial hand-held spectrometer that fits in a trouser pocket. This is being done in partnership with Attonics Systems, an international spinoff from NUS.
The array is made using a centuries-old printing technique called lithography. Originally, a pattern was painted on a rock using oil, and acid was used to etch away the parts of the rock not covered by the oil. In X-ray lithography, X-rays are used to etch X-ray-sensitive material instead.
X-rays with a wavelength of 0.8 nanometers can be used, which is very short even by X-ray standards. This can produce tiny and accurate shapes with a height of up to 100 times the width.
The hand-held spectrometer is useful for purposes from counterfeit detection to food safety to skincare and many more. It is also cost-effective, as almost 150 arrays can be produced simultaneously on a single silicon wafer in about 45 minutes. This potentially translates to about a thousand pieces a day. Dr Kalaiselvi says the spectrometer is remarkably accurate and high-resolution for an asking price of less than S$2,000 a unit. They are also trying to put it in a smartphone. Other spectrometers of comparable accuracy could take up 10 times the space and cost 10 times more.
On commercial partnerships, Professor Mark Breese, Director of SSLS, said, “It is very important for the SSLS to address some very current and real-world problems which are typically outside the domain of fundamental science. The industry also benefits from having access to the latest science and technology.”
Delving into the SSLS
A synchrotron is a ring-shaped particle accelerator. The largest synchrotron in the world is the well-known Large Hadron Collider in Europe, whose circumference measures 27 kilometres.
Although the SSLS is much smaller, it turns electrons into light using powerful magnetic fields, and this light can be used in endless ways in almost every imaginable discipline – to fabricate nanostructures for smart devices like what Dr Kalaiselvi does, or to study materials from biological molecules to forensic substances using spectroscopy.
Indeed, the capabilities of the SSLS ticks off several of the key areas of focus at NUS, for example Materials Science, Biomedical Science and Translational Medicine, and Smart Nation. It is also classified as a National Research Infrastructure under the Singapore’s National Research Foundation.
The SSLS has a slogan “Makes light work for you”. The light from the synchrotron is of very high intensity and is tunable to precise wavelengths, so it can give scientists highly accurate and sensitive measurements on very small or dilute samples. For example, compared with the X-ray lamps used in conventional X-ray facilities, it is unbeatable as a source of high-quality X-rays, whether for molecular analysis or ultra-delicate work like Dr Kalaiselvi’s tiny structures.
Behind the scenes
At dawn, Research Engineer Mr Zaw Win Maung scans his ID card and enters the circular, Brutalist building nestled on a forested slope in a secluded part of the NUS campus.
Inside the building is another building – an irregular-shaped concrete sarcophagus with walls more than a metre thick. Mr Zaw enters it to check on the “hidden dragon”, Helios 2. All is quiet except for the soft hum of the air-con.
A convoluted network of tubes and cables and valves and connections makes up the “blood vessels” and “nervous system” of Helios 2. In the dragon’s gut are 1,000 litres of liquid helium at –269 °C, insulated by liquid nitrogen at –196 °C. The entire system of conduits for the accelerating electrons and the resulting light beams are under an ultra-high vacuum similar to conditions in outer space. Mr Zaw makes sure there are no broken cables or leaks, otherwise the whole setup could blow up.
Upstairs in the main building, the main control room resembles what one would find in a nuclear submarine. There is even a panel for inserting “missile keys”. Everything was made in the 1990s.
A siren wails through the entire facility as electric current starts flowing through the sleeping dragon. Laboratory Manager Dr Li Zhiwang, who oversees the operation of the particle accelerator, watches the monitors as the current steps up progressively to full power, awakening the superconducting electromagnets that are almost 500 times stronger than a fridge magnet. The particle accelerator starts radiating powerful gamma rays, X-rays, ultraviolet, infrared, light rays.
Stainless steel pipes radiate out from the sarcophagus in all directions, each carrying a light beam of a particular wavelength, called a beamline. The beam is collimated - all the photons are traveling in one direction, like a laser, rather than in all directions like a light bulb. Each beamline comprises numerous sections separated by a series of safety valves. Airtight windows of specific materials let desired wavelengths through (for example, beryllium windows for X-rays) while maintaining the high vacuum at the heart of the system, and a maze of cables and sensors constantly monitors every vital sign throughout the whole pathway.
By about 8.00am each day, the SSLS is running at full power as researchers start streaming in for another day of scientific exploration and discovery.
Prof Breese, who has helmed the SSLS for 10 years, said, “We are lucky to have an excellent team of accelerator scientists and engineers who can fix just about anything that goes wrong - we have been in business for 20 years which says a lot in itself.”
He hopes to deepen ties with other synchrotrons in the region. “We have had our ups and downs with the synchrotron, but we always manage to get back on top with all challenges.”