Image courtesy of Oak Ridge National Laboratory
The crystallized oxide (lighter regions) spelling the word “small” was “printed” on a non-crystallized layer (darker gray) by a well-controlled beam in an electron microscope. The area shown is only 160 by 80 nanometers (about a thousandth of the diameter of a human hair). The green background is an enlarged high resolution image of the letter “s”, showing its crystalline, ordered atomic structure.
A new tool now rests in the 3D printing toolbox. The electron beam in a scanning transmission electron microscope has been exquisitely controlled with specially programmed electronics to tunnel into non-crystalline material and construct 3D features that are in perfect alignment with the underlying substrate (i.e., epitaxial). The result is designer materials with desirable structures, such as microchips, or materials with unique properties. Essentially, any shape can be created by exposing patterned areas to higher numbers of electrons than non-patterned areas, resulting in epitaxial 3D features down to 1-2 nanometers —less that the width of a strand of DNA.
Electron microscopes with atomically focused beams, even from older instruments, can easily be transformed from characterization tools to nanoscale fabrication platforms, complementing macroscopic 3D printing. This nanoscale fabrication tool could be used to make integrated circuits and non-equilibrium systems such as strategically concentrated impurities in crystals that lead to unique properties.
3D printing has revolutionized the way we can make and design materials. Now a team led by scientists at Oak Ridge National Laboratory has added another tool to the 3D printing toolbox. Combining the focused electron beam in a scanning transmission electron microscope with new electronic controls allowed the atomic sculpting of crystalline material from non-crystalline material and the construction of 3D feature sizes down to 1-2 nanometers. The crystalline features have a particular alignment with the underlying atoms, allowing mechanical and electrical properties to extend throughout the material. The electron beam from the scanning transmission electron microscope sculpted with atomic precision a crystalline oxide feature from a non-crystalline oxide layer on a crystalline substrate. Interestingly, this non-crystalline oxide layer was made by a usually undesirable process: While preparing a sample for the electron microscope, significant redeposition of the initially crystalline substrate occurs. This redeposited material is non-crystalline and is on top of the initial crystalline film. The electron beam can then sculpt and crystallize this non-crystalline material. Also, in order to achieve this atomic manipulation, scientists had to custom program external electronics to control the trajectory of the electron beam. Electrons hitting the non-crystalline material induce growth of crystalline nanostructures. The number of electrons hitting the sample controlled the growth rate of the 3D feature from the non-crystalline material. At lower electron beam intensities, the material can be imaged without inducing growth. Nanofabrication with atomic-level sculpting can lead to new 3D materials for integrated circuits as well as new fundamental experimental studies ranging from crystallization to diffusion that can complement modeling and simulation.
Albina Y. Borisevich
Oak Ridge National Laboratory
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences; the Center for Nanophase Materials Sciences and the Oak Ridge Leadership Computing Facility, DOE Office of Science User Facilities; and Laboratory Directed Research and Development Program at Oak Ridge National Laboratory.
S. Jesse, Q. He, A. R. Lupini, D. N. Leonard, M. P. Oxley, O. Ovchinnikov, R. R. Unocic, A. Tselev, M. Fuentes-Cabrera, B. G. Sumpter, S. J. Pennycook, S. V. Kalinin, and A. Y. Borisevich, "Atomic-level sculpting of crystalline oxides: Toward bulk nanofabrication with single atomic plane precision." Small 11, 5895–5900 (2015). [DOI: 10.1002/smll.201502048]
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