GOALI: Phase Stabilities of Rare Earth Metal Silicides and the Growth of Silicide Nanowires

这个GOALI项目是研究稀土金属硅化物的相稳定性和纳米线沿硅衬底在优选方向上的生长。许多稀土金属与硅反应形成二硅酸盐，具有与二硅酸铒相同的晶体结构。硅化物的0211方向往往与硅的110方向之一存在负晶格失配。二硅化物Er， Ho和Dy有这样的晶格错配。其他稀有金属二硅化物，如Sm、Gd和Tb的二硅化物，表现出正晶格失配。这些二硅化物沿c轴与Si垂直方向的失配总是正的。本项目通过确定三元相关系，考察了稀土金属硅化物在650℃固态下的组成稳定性。利用稀土金属的化学相似性，概述了一种确定三元相平衡的有效方法，包括二硅化物的组成稳定性。由于纳米线生长发生在高温下，这些硅化物的热膨胀系数预计与硅的不同，因此通过高温x射线衍射测量了这些二硅化物的热膨胀系数作为温度和合金成分的函数。这些调查是在威斯康星大学麦迪逊分校进行的。每年，在威斯康星大学麦迪逊分校工作的两名或两名以上的研究人员将花时间在惠普实验室进行纳米线的生长和表征，并使用惠普的专业知识和设备。在此综合研究的基础上，确定最佳晶格失配的三元硅化物纳米线的生长条件。该项目涉及具有高潜在技术相关性的材料科学主题领域的基础研究问题。该研究将为电子/光子器件的重要制造方面提供基础材料科学知识。该计划的一个重要特点是通过在一个基础和技术重要领域的研究生和博士后培训，将研究和教育结合起来。一名博士后研究员和一名研究生每年将花时间在惠普实验室现场工作，从惠普的工业协作人员的专业知识、设备和仪器中受益。独特的仪器和设施的可用性，以及与惠普员工的直接智力互动提供了宝贵的教育机会和观点，并促进了研究和教育的整合。该项目由DMR/金属和电子材料项目和MPS OMA（多学科活动办公室）共同支持。＊＊＊

This GOALI project is a study of the phase stabilities of rare earth metal silicides and the growth of nanowires on preferred directions along a silicon substrate. Many rare earth metals react with silicon to form disilicides exhibiting the same crystal structure as that of erbium disilicide. The 0211 direction of the silicides often has a negative lattice mismatch with one of the 110 directions of the Si. Disilicides of Er, Ho and Dy have such a lattice mismatch. Other rare metal disilicides, such as disilicides of Sm, Gd, and Tb, exhibit a positive lattice mismatch. The mismatch along the c-axis of these disilicides with the perpendicular 110 direction of Si is always positive. This project examines the compositional stabilities of ternary rare earth metal silicides in the solid state at 650C by determining ternary phase relationships. Taking advantage of the chemical similarity of the rare earth metals, an efficient approach is outlined for determining the ternary phase equilibria, including the compositional stability of the disilicides. Since nanowire growth takes place at high temperatures and the coefficients of thermal expansion of these silicides are expected to be different from that of Si, the coefficients of thermal expansion of these disilicides are measured as a function of temperature and alloy composition by high-temperature x-ray diffraction. These investigations are carried out at UW-Madison. Each year of the grant, two or more of the researchers working at UW-Madison will spend time at Hewlett-Packard Laboratory to carry out nanowire growth and characterization with access to HP's expertise and facilities. On the basis of this combined study, appropriate conditions for growing ternary silicide nanowires with optimal lattice mismatch will be determined. %%%The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The research will contribute basic materials science knowledge at a fundamental level to important fabrication aspects of electronic/photonic devices. An important feature of the program is the integration of research and education through graduate student and post doctoral training in a fundamentally and technologically significant area. A post doctoral research associate and a graduate student will spend time each year of the project working on site at Hewlett-Packard Laboratory benefitting from the Industrial collaboration staff expertise and facilities and instrumentation available at HP. The availability of unique instrumentation and facilities, and direct intellectual interaction with HP staff provides invaluable educational opportunities and perspectives, and fosters the integration of research and education. The project is co-supported by the DMR/Metals and Electronic Materials programs and the MPS OMA(Office of Multidisciplinary Activities). ***