The Synthescope—An Approach for Synthesis at the Atomic Scale

The scanning transmission electron microscope (STEM) is evolving from a workhorse instrument for materials characterization to an atomic-scale material manipulation platform. With its capability to image and characterize atomic-scale structural formation as it occurs, the STEM is being reconceptualized as a powerful instrument for fabrication and synthesis. By incorporating synthesis processes into the STEM, new transformations can be discovered and the atomic scale evolution of material growth can be better understood.<br/> <br/>Within the STEM, there is a controlled environment with a focused beam of electrons that creates a highly localized perturbation of the sample. This perturbation can be considered a chamberless synthesis environment (CSE). Within this perturbed region of space, the sample environment is drastically different from regions outside the perturbation. The CSE can be moved around with great spatial precision and encounter a variety of different physical systems in a non-uniform sample. A reaction process can be prepared by adjusting global parameters without the intended process occurring until the CSE is created through e-beam exposure. When described in these terms, it can be seen that electron beam induced deposition (EBID) functions on the same principle. The e-beam dissociates molecular precursor gas molecules which become chemically reactive and bond with the substrate. This dissociative environment is created by e-beam exposure and can be considered to form a CSE within which the dissociation and growth of a new material occurs. The CSE concept, however, does not specify what reaction should occur, merely that the beam-sample interaction volume is a significantly different environment from that of the surrounding material.<br/> <br/>With this idea in hand, we can begin to ask what environmental parameters could be varied such that <i>some</i> material transformation occurs within the CSE. A number of experimental results have shown that the positioning of single atoms in graphene is possible and that this could be extended to atomic scale patterning and writing if the sample environment could be better controlled, specifically the supply of various materials as is done in a synthesis chamber. To enable this capability, a prototype <i>in situ</i> evaporative delivery platform has been built. The basic functionality is demonstrated and test runs confirm the delivery of material down to the level of single atoms. With separate control over evaporation and substrate temperature, conditions were found where Sn atoms could be directly ‘written’ atom-by-atom into graphene.<br/> <br/>The incorporation of synthesis processes in the STEM is opening up new possibilities for atomic-scale material manipulation and the discovery of new transformations. The concept of a chamberless synthesis environment (CSE) can lead to precise and controlled atomic-scale patterning and writing. With a prototype in situ evaporative delivery platform that can deliver material down to the level of single atoms, the future realization of the synthescope—a platform for synthesis and fabrication at the scale of an atom—shows great promise.¹<br/> <br/>(1) This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division (O.D. A.R.L., S.J.), and was performed at the Center for Nanophase Materials Sciences (CNMS), a U.S. Department of Energy, Office of Science User Facility.