By controlling the environment around the sample, the electron microscope becomes a powerful tool for examining processes such as materials growth, catalysis, oxidation, phase transformations and defect formation. This movie shows an example of crystal growth using a nanoscale catalyst. It was recorded in the Environmental TEM at Brookhaven National Laboratory. The hemispherical droplet is a liquid catalyst, AuSi. We see it at work as it converts a reactive gas, disilane, into a solid nanowire made of silicon. Disilane molecules arrive at the droplet surface, stick there and break up. The silicon atoms are released, diffuse through the liquid and end up at the top of the existing Si crystal. Every few seconds a complete layer of Si atoms is added to the nanowire. Measuring the details of this self-assembly process allows us to visualize the pathways by which the atoms add to the nanostructure, develop models for growth, identify new growth modes, and generate strategies for precise control of the growth process.
Video 1: A Si nanowire grows when a gas (disilane, 2×10-5 torr) reacts at the surface of a liquid catalyst (AuSi) at 550 oC. Every few seconds a complete layer of atoms is added
By redesigning the microscope hardware it is possible not just to grow but to measure the properties of individual nanostructures. In this example, nanowires grow between two cantilevers to form a tiny bridge. Both the structure and the electrical transport properties of a single nanowire can be correlated. This detailed view of structure-property relationships helps to design nanostructures with specific electronic or mechanical characteristics
Image 1: In situ UHV experiments on nanowire growth provide guidance for the formation of complex structures through catalyst design (left), information on phase transformations in small volumes (center) and methods for the control of growth using parameters such as electric field (right)
Image 2: Catalytic growth of germanium from gold at 200oC. Both crystal lattices are aligned with the substrate, hexagonal boron nitride