Elucidating Structural Transformations in MoTe2 for Efficient Optoelectronic Memory

非技术摘要：在信息时代，负担得起的和有效的光和电存储器是保存和传播知识和思想的基础。经历相变的材料，例如通常用于DVD中的硫属化物，对于新兴的应用特别有希望，所述新兴的应用将联合收割机存储器与高速计算相结合，但是需要与所切换的材料的体积成比例的相对大的编程能量。在二维（2D）材料（如碲化钼（MoTe 2））中编码数据提供了克服这一基本限制的直接途径。在可以经历相变的可用2D材料中，MoTe 2被预测为最节能的，但是明显缺乏实验证据来支持管理MoTe 2中光致相变的机制、动力学和限制的相互冲突的理论模型。该团队建议使用动态光学测量技术结合超高分辨率透射电子显微镜来解决这一知识差距。该项目克服了先前工作的实验局限性，为需要高速，可靠和高效光电存储器的应用提供了相关2D材料的新见解。该团队旨在教育初中和高中学生在日常生活中与纳米材料相关的主题，这些主题来自历史上在STEM领域代表性不足的少数民族地区，使用互动研讨会和虚拟现实工具相结合。该项目还为两名研究生提供纳米纤维和表征技术方面的培训，并在夏季接待来自代表性不足的群体的本科生，以扩大对STEM相关领域的参与。技术摘要：相变材料使光电存储器具有通过以光速处理存储器中的信息来改造低能量、非冯·诺依曼计算架构的潜力。原子级平坦的相变材料（例如MoTe 2及其合金Mo 1-xWxTe 2）将通过大幅减少经历相变的有效体积来进一步减少配置其状态所需的能量。虽然已经在MoTe 2和相关材料中观察到光学诱导的相变，但是这些相变是不可逆的，不像采用电化学掺杂和机械应变的类似观察。有限的经验证据和理论模型表明，Te空位在相变过程中起着核心作用，但迄今为止，对MoTe 2中2 H和1 T '相之间光开关的动力学和物理机制的理解仍然很模糊。该团队提出，可以通过材料合成，封装和W合金化来控制MoTe 2中的光致结构转变，从而提高运行速度，提高可靠性和降低开关能量。为了验证这一假设，本项目包括以下三个目标：（1）通过控制MoTe_2生长过程中Te空位的浓度来确定Te空位对光开关功率的影响;（2）封装MoTe_2以减少光激发过程中的Te损耗--预期的阻止可逆光开关的机制;以及（3）将MoTe 2与W合金化以设计用于高效且可重写的光电相变存储器的最佳2D材料。该方法克服了现有实验技术的时间限制，通过探测光域中的相变过程。这项研究有望通过利用MoTe 2中的结构转换来编码信息，从而实现高速，非易失性和高效的数据存储。这项研究是第一个使用光学和电光技术相结合，以解决相互矛盾的理论模型的相变机制，动力学，和最佳化学计量的MoTe 2及其合金Mo 1-xWxTe 2。对MoTe 2相变过程的新见解有望在数据存储以外的领域有广泛的应用，如神经形态计算、电光转换、柔性电子、可重构拓扑和量子器件。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstract:In the information age, affordable and efficient optical and electrical memory is foundational to the preservation and dissemination of knowledge and ideas. Materials which undergo a phase transition, such as chalcogenides that are commonly used in DVDs, are especially promising for emerging applications which combine memory with high-speed computing but require relatively large programming energies which is proportional to the volume of material switched. Encoding data in two-dimensional (2D) materials such as molybdenum tellurides (MoTe2) provides a direct route to overcome this fundamental limitation. Among available 2D materials which can undergo a phase transition, MoTe2 is predicted to be the most energy efficient, but there is a distinct lack of experimental evidence to support conflicting theoretical models governing the mechanisms, dynamics, and limitations of optically-induced phase transformations in MoTe2. The team proposes to address this knowledge gap using dynamic optical measurement techniques in combination with ultrahigh-resolution transmission electron microscopy. The project overcomes the experimental limitations of prior works to shed new light on related 2D materials for applications requiring high-speed, reliable, and efficient optoelectronic memory. The team seeks to educate middle- and high-school students on topics related to nanomaterials in daily life from districts with historically under-represented minorities in STEM fields using a combination of interactive workshops and virtual reality tools. This project also provides training for two graduate students in nanofabrication and characterization techniques and hosts undergraduates from underrepresented groups during the summer months to broaden participation in STEM-related fields.Technical abstract:Phase-change materials that enable optoelectronic memory have the potential to transform low-energy, non-von Neumann computing architectures by processing information in memory at the speed of light. A phase-change material that is atomically flat (e.g. MoTe2 and its alloy Mo1-xWxTe2) would further reduce the energy required to configure its state by drastically reducing the active volume undergoing a phase transition. While optically induced phase transformations have been observed in MoTe¬2 and related materials, these transformations have been irreversible unlike similar observations employing electrochemical doping and mechanical strain. Limited empirical evidence and theoretical modeling indicates Te vacancies play a central role in the phase transition process, but a clear understanding of the dynamics and physical mechanism of optical switching between the 2H and 1T’ phases in MoTe2 remains elusive to date. The team proposes that optically induced structural transformations can be controlled in MoTe2 through material synthesis, encapsulation, and W-alloying, resulting in higher operating speeds, improved reliability, and lower switching energies. To test this hypothesis, the project contains the following three aims: (1) determine the influence of Te vacancies on the optical switching power by engineering the concentration of Te vacancies during the MoTe2 growth process; (2) encapsulate MoTe2 to reduce Te loss during optical excitation—the expected mechanism preventing reversible optical switching; and (3) alloy MoTe2 with W to engineer an optimal 2D material for efficient and rewriteable optoelectronic phase-change memory. The proposed approach overcomes the temporal limitations of prior experimental techniques by probing the phase-transition process in the optical domain. The proposed research is expected to enable the development of high-speed, non-volatile, and efficient data storage by exploiting structural transformations in MoTe2 to encode information. This study is the first to use a combination of optical and electro-optical techniques to resolve conflicting theoretical models regarding the phase transformation mechanisms, dynamics, and optimal stoichiometry of MoTe2 and its alloy Mo1-xWxTe2. New insights into phase-transformation process of MoTe2 are expected to have broad application to fields beyond data storage, such as neuromorphic computing, electro-optic conversion, flexible electronics, and reconfigurable topological and quantum devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.