Lasers Rewired

A nanowire, composed of cesium, lead and bromide (CsPbBr3), emits bright laser light after hit by a pulse from another laser source. The nanowire laser proved to be very stable, emitting laser light for over an hour. It also was demonstrated to be broadly tunable across green and blue wavelengths. The white line is a scale bar that measures 2 µm. (Source: S. Eaton, UC Berkeley)

A nanowire, composed of cesium, lead and bromide (CsPbBr3), emits bright laser light after hit by a pulse from another laser source. The nanowire laser proved to be very stable, emitting laser light for over an hour. It also was demonstrated to be broadly tunable across green and blue wavelengths. The white line is a scale bar that measures 2 µm. (Source: S. Eaton, UC Berkeley)

Light can carry far more data, far more rapidly than standard electronics. And miniaturizing lasers to the nanoscale could further revolutionize computing by bringing light-speed data transmission to desktop and ultimately handheld computing devices.

“What’s amazing is the simplicity of the chemistry here,” said Peidong Yang, a chemist in Berkeley Lab’s Materials Sciences Division who led the research. More standard techniques that produce nanowires can require expensive equipment and exotic conditions, such as high temperatures, and can suffer from other shortcomings.

The research team developed a simple chemical-dipping solution process to produce a self-assembled blend of nanoscale crystals, plates and wires composed of cesium, lead and bromine (CsPbBr3). “Most of the earlier work with these types of materials is focused on these solar energy applications,” said Yang. “There has been so much progress with these materials in just the past several years – I have a feeling these materials will open a new research frontier for optoelectronics as well,” he said, and in the broader field of photonics, which is focused on using light for a range of applications.

“The whole purpose of developing nano-sized lasers is to interface photonic devices with electronic devices seamlessly,” Yang said, “at scales relevant to today’s computer chips. Today, these photonic devices can be bulky.”

Yang’s research team pioneered the development of nanowire lasers almost 15 years ago using a different blend of materials, including zinc oxide (ZnO) and gallium nitride (GaN). But these and other, more conventional combinations of materials used to make nanolasers have shortcomings that can include limited tunability, low brightness or costly manufacturing processes.

This scanning electron microscope image shows a collection of CsPgBr3 nanowires and nanoplates grown from a chemical-dipping process. To produce these structures, researchers dipped a thin lead-containing film into a methanol solution containing cesium, bromine and chlorine heated to about 50 °C. The white scale bar at the lower right represents 10 µm. The image at the bottom left shows the well-formed rectangular end of a nanowire – the white scale bar represents 500 nm in length. (Source: S. Eaton, UC Berkeley)

This scanning electron microscope image shows a collection of CsPgBr3 nanowires and nanoplates grown from a chemical-dipping process. To produce these structures, researchers dipped a thin lead-containing film into a methanol solution containing cesium, bromine and chlorine heated to about 50 °C. The white scale bar at the lower right represents 10 µm. The image at the bottom left shows the well-formed rectangular end of a nanowire – the white scale bar represents 500 nm in length. (Source: S. Eaton, UC Berkeley)

In this latest work, the research team discovered how to produce nanowires by dipping a thin lead-containing film into a methanol solution containing cesium, bromine and chlorine heated to about 50 °C. A mix of cesium lead bromide crystalline structures formed, including nanowires with a diameter from 200 to 2,300 nm and a length ranging from 2 to 40 µm. Select nanowires used in the experiment were placed on a quartz base and excited by another laser source. Researchers found that the nanowire lasers emitted light for over 1 billion cycles after being hit by an ultrafast pulse of visible, violet light that lasted just hundredths of femtoseconds, which Yang said demonstrated remarkable stability.

Yang said to his knowledge these nanowires may be the first to emit laser light using a totally inorganic blend of materials. Researchers demonstrated that the nanowire lasers could be tuned to a range of light including visible green and blue wavelengths.

“The nanowires’ crystalline structure is a lot like salt, which does make them susceptible to damage from moisture in the air”, Yang said. “That is one weakness –something we have to study and understand how to improve,” he said. It may be possible to coat the nanowires with polymers or other material to make them more damage-resistant, he said. There are also opportunities to test out other materials and learn whether they improve performance, he said, such as substituting tin for lead. (Source: UC Berkeley)

Links: College of Chemistry, University of California, Berkeley, USA • Peidong Yang Group, U.S. Department of Energy’s Lawrence Berkeley National Laboratory, California, USA

Reference: W. Eaton et al.: Lasing in robust cesium lead halide perovskite nanowires, PNAS 2016 vol. 113 no. 8; doi: 10.1073/pnas.1600789113

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