Scanning Electron Microscope (SEM) of Ga203 Nanowire

Scanning Electron Microscope image of Ga2O3 nanowires.

Like the Au nanoparticle before, this Ga2O3 nanowire is also a single crystal implying that the periodic arrangement of atoms within the wire all have a single orientation. Nanowires (1-D nanostructures), implying wires with diameters less than 100 nm, are a very active area of pure and applied research within the nanomaterials domain. From a scientific viewpoint they are of interest for studying quantum confinement effects. In individual atoms the energy levels are discrete whereas in large aggregates of atoms such as bulk single and polycrystals the discrete energy levels are replaced by energy bands separated by forbidden gaps. As the external dimensions of bulk materials are reduced to thin films (2D), nanowires (1D) or quantum dots (0D), electrons and holes are “confined” in 1, 2 and 3 dimensions respectively. The band structure starts getting more discrete, like that of an atom and the effect is referred to as quantum confinement. From an applied view point, nanowires are interesting because of their very high surface area to volume ratio and therefore the potential to be used in sensors of various kinds.

While the Transmission electron microscope image (TEM) might be considered the mother of all characterization tools, the scanning electron microscope or SEM used to image the nanowires is a workhorse. Both belong to a family of characterization tools called electron microscopes that use a focused beam of electrons to understand the microstructure of materials. A good SEM can be used to image surface features below 100 nm and it is one of the most common tool used to study nanomaterials and enable manipulation of features at the sub-micron level.

Going Deeper:
The nanowires observed were fabricated in Dr. Nanda’s lab by oxidizing a Ga droplet in air. Monoclinic Ga2O3 exhibits a wide bandgap of 4.9 eV and can be an insulator or an n-type semiconductor depending on the concentration of oxygen vacancies. It is useful as an insulating oxide layer for all gallium-based semiconductors. It has potential applications in optoelectronic devices and oxygen gas sensors.

For more information on Dr. Nanda’s lab visit his faculty page.