CAREER: Controlling surface and interface relaxation mechanisms through the chemical environment: A route to 2D conductors between dissimilar materials

North Carolina State University, Raleigh NC

Investigators

Abstract

TECHNICAL SUMMARY: This CAREER award, funded by the Condensed Matter and Materials Theory Program in the Division of Materials Research, supports an integrated theoretical research, education, and outreach effort seeking to develop a fundamental understanding of how and to what degree atomistic and electronic compensation mechanisms compete to overcome diverging electrostatic energies in polar-oriented oxide thin films and whether this competition can be tuned to enable their low defect growth. It is proposed that overcoming the barrier to low defect growth can be accomplished through the active control of the chemical environment during epitaxy. First principles based methods will be used to evaluate surface free energies, and to what degree they reorder, as a function of chemical species, partial pressure, and temperature of the growth environment. This provides critical information that can be used by experiment to determine growth conditions that yield low defect thin films. Identification of growth conditions that produce these low defect thin films is a first step towards the ultimate goal of this proposal, which is to discover new material combinations that support a two dimensional electron gas between materials of different structure or symmetry. To this end, first principles methods will also be used to predict functionality of the heterogeneous interface. The goals of the theoretical research in this proposal, which center on controlling the relative free energy of different surface terminations, feed very well into the integrated educational outreach component. Two modules will be developed that use intuitive hands on active demonstrations to excite students and illustrate the subtle physical arguments of the effects of re-ordering surface free energies. One module is experimental and the other is computational in nature. For the experimental module, students will burn Mg ribbons, harvest the MgO smoke crystals, submerge them in water, and image them with a tabletop SEM. For the computational module students will interact in real time with an atomic simulation via 3-D visualization and a force feedback haptic device. NON-TECHNICAL SUMMARY: This CAREER award, funded by the Condensed Matter and Materials Theory Program in the Division of Materials Research, supports an integrated theoretical research, education, and outreach effort with the ultimate goal of accelerating the creation of next generation interfacial electronics by use of predictive theoretical methods. Interfacial electronics are unique in that their functionality is compressed down to layers of atoms. Their creation, however, has been limited to materials that have similar atomic structure, which, in part, has limited widespread use and integration. New functionality could be expected as this type of active interface is created between interfaces of dissimilar materials. For the most part, this has not been achievable due to the inability to fabricate atomically perfect materials or materials with low defect concentrations. It is proposed that these barriers can be overcome by changing the gas phase chemistry used to deposit one material on another and that predictive simulations can be used to determine what conditions should be explored experimentally. This approach allows for the ability to focus on materials and conditions that would be expected to be fruitful, saving both time and money and, thus, accelerating the development of these new materials. Ultimately, enabling low defect interfaces between structurally dissimilar materials not only expands the catalogue of materials that can be used to create novel devices but also endows new functionality that will impact the creation of ultra-fast transistors, very high-density memory, and magnetic sensors. An educational outreach program is strongly coupled to and feeds into the proposed research. This program will have significant impact on education through the development of the visual and active demonstration modules that will be targeted to students in local high school, in local colleges, and to the general public. These modules will not only excite participants about careers in STEM related fields but will also pass along technological vocabulary, define the role of engineers in solving real world problems, and help define Materials Science and Engineering to the participants. Two experienced educators will aid in assessing the outcomes and ensure meaningful impact of the modules to a wide range of participants.