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

技术简介:该奖项由材料研究部凝聚态物质和材料理论项目资助，支持综合理论研究、教育和推广工作，旨在发展对原子和电子补偿机制如何以及在多大程度上竞争以克服极性氧化薄膜中分散的静电能的基本理解，以及这种竞争是否可以调整以使其低缺陷生长。提出克服低缺陷生长的障碍可以通过在外延过程中主动控制化学环境来实现。基于第一性原理的方法将用于评估表面自由能，以及它们重新排序的程度，作为化学物质、分压和生长环境温度的函数。这提供了关键的信息，可用于实验，以确定生长条件，产生低缺陷的薄膜。确定产生这些低缺陷薄膜的生长条件是实现本提案最终目标的第一步，该目标是发现支持不同结构或对称材料之间二维电子气的新材料组合。为此，第一性原理方法也将用于预测异构接口的功能。本提案中理论研究的目标是控制不同表面末端的相对自由能，这很好地融入了综合教育推广部分。我们将开发两个模块，用直观的双手进行积极的演示，以激发学生的兴趣，并说明表面自由能重排序效应的微妙物理论据。一个模块是实验性的，另一个模块是计算性的。在实验模块中，学生将燃烧镁带，收集镁烟晶体，将其浸入水中，并用桌面扫描电镜对其成像。对于计算模块，学生将通过三维可视化和力反馈触觉设备与原子模拟实时交互。非技术总结：该职业奖由材料研究部凝聚态物质和材料理论计划资助，支持综合理论研究，教育和推广工作，最终目标是通过使用预测理论方法加速创建下一代界面电子学。界面电子学的独特之处在于它们的功能被压缩到原子层。然而，它们的创造仅限于具有相似原子结构的材料，这在一定程度上限制了广泛使用和集成。由于这种类型的活动界面是在不同材料的界面之间创建的，因此可以期待新的功能。在大多数情况下，由于无法制造原子完美的材料或低缺陷浓度的材料，这是无法实现的。有人提出，这些障碍可以通过改变用于将一种材料沉积在另一种材料上的气相化学来克服，并且可以使用预测模拟来确定应该在实验中探索的条件。这种方法允许专注于材料和条件，预计将是富有成效的，节省时间和金钱，从而加速这些新材料的发展。最终，在结构不同的材料之间实现低缺陷接口不仅扩展了可用于制造新型器件的材料目录，而且还赋予了新的功能，这将影响超高速晶体管，非常高密度存储器和磁传感器的创建。教育推广计划与拟议的研究密切相关，并为其提供支持。该计划将通过开发针对当地高中、当地大学和普通公众的视觉和积极示范模块，对教育产生重大影响。这些模块不仅会激发参与者对STEM相关领域的职业生涯的兴趣，还会传递技术词汇，定义工程师在解决现实世界问题中的作用，并帮助参与者定义材料科学与工程。两位经验丰富的教育工作者将协助评估结果，并确保这些模块对广泛的参与者产生有意义的影响。

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.