Surface Diffusion and Ordering Processes Exploited for Directed Self-Assembly Using Amorphous Semiconductors

利用非晶半导体进行定向自组装的表面扩散和有序过程

• 批准号: 0203237
• 负责人: Edmund Seebauer
• 金额: $ 25.8万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-07-01 至 2005-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0203237&HistoricalAwards=false
• 关键词: Surface; Diffusion; Ordering; Processes; Exploited

This Nanotechnology research project seeks to develop a science base connected with surface diffusion and surface ordering of amorphous materials, with the ultimate goal of developing a new method for directed surface self-assembly on the nanoscale using amorphous semiconducting materials. Diffusion over amorphous and other energetically heterogeneous surfaces plays a role in sintering of ceramics and in reflow processes and memory device fabrication in microelectronics. There presently exists virtually no literature for diffusion on amorphous surfaces, and very little that specifically addresses continuously distributed energetic heterogeneity on highly defected crystalline surfaces. Such heterogeneity should lead to values of the diffusivity D that differ significantly from those measured for well-defined crystalline surfaces, however. For amorphous materials, fabrication processes can be devised based upon promoting or inhibiting surface ordering driven by surface diffusion. Example applications include fabrication of memory device electrodes, efficient solar cells, and amorphous ceramics. The rates of ordering cannot be followed experimentally by conventional techniques, rendering creation of process models difficult.The first goal of this project is to develop a science base for surface diffusion and ordering on amorphous and other energetically heterogeneous surfaces, using the combined expertise of the two laboratories. An experimental method will be developed to quantify the distribution function describing surface diffusion on energetically heterogeneous surfaces, using amorphous silicon and the ceramic titanium dioxide as paradigm cases. Experiments will also confirm that optical illumination can be used to drive surface diffusion non-thermally. With respect to surface ordering, fluctuation microscopy will be adapted to the study of near-surface regions by implementation on a scanning transmission electron microscope, with spatial resolution as small as 0.8 nm. Furthermore, the method will be extended to the study of binary compounds like titanium dioxide; up to now application has been restricted to single-element systems.The second goal of this project is to develop a new surface self-assembly method at the 10-200 nm length scale using amorphous semiconducting materials containing controlled amounts and size distributions of subcritical nuclei. Patterned optical or electron beam exposure should yield a spatially varying surface mass flux that, when performed at an annealing temperature just at the cusp of crystallization, provides the extra nudge to crystallize subcritical nuclei in regions dictated by the light flux. The full-fledged crystallites should then grow by surface diffusion and Ostwald ripening until the desired fraction of the film has accreted onto the original nuclei. Demonstrations will focus on amorphous silicon and titanium dioxide. Some computational aspects of the proposed work will be incorporated into a new interdisciplinary laboratory course for undergraduates focusing on nano-materials synthesis.The core goals of elucidating diffusion phenomena on amorphous surfaces, extending the capabilities of fluctuation microscopy, and demonstrating a version of the self-assembly method will remain in place.The downward revision in budget will impact the proposed work in several ways involving the scope of the individual tasks outlined.1. Reduce the accuracy with which we can determine the locus of conditions giving optimal medium range order in amorphous silicon.2. Limit the scope of studies for controlling medium range order via variations in hydrogen addition, ion energy and flux, and related parameters.3. Limit the implementation of the directed self-assembly method to optical means, rather than including an electron-beam.4. Limit the accuracy with which distribution functions describing surface diffusion can be obtained. (The distribution functions are more accurate with more data.)

该纳米技术研究项目旨在发展与非晶态材料的表面扩散和表面有序化相关的科学基础，最终目标是开发一种利用非晶态半导体材料在纳米尺度上进行定向表面自组装的新方法。扩散在非晶态和其他含能非均质表面上的扩散在陶瓷的烧结以及微电子中的回流工艺和存储器件制造中起着重要的作用。目前几乎没有关于在非晶态表面上扩散的文献，也很少有专门研究在高度缺陷的晶体表面上连续分布的能量不均匀的文献。然而，这种非均质性应该导致扩散系数D的值与对于明确定义的晶体表面测量的值显著不同。对于非晶态材料，可以基于促进或抑制表面扩散驱动的表面有序化来设计制造工艺。应用实例包括制造存储器件电极、高效太阳能电池和非晶态陶瓷。这个项目的第一个目标是利用两个实验室的联合专业知识，开发一个在非晶态和其他含能非均质表面上进行表面扩散和有序化的科学基础。以非晶硅和二氧化钛陶瓷为范例，发展了一种描述表面扩散分布函数的实验方法。实验还将证实，光学照明可以用来非热地驱动表面扩散。关于表面有序化，波动显微镜将适用于近表面区域的研究，方法是在空间分辨率为0.8 nm的扫描透射式电子显微镜上实现。此外，该方法还将扩展到二氧化钛等二元化合物的研究，到目前为止，该方法的应用仅限于单元素体系。本项目的第二个目标是开发一种新的表面自组装方法，该方法使用非晶态半导体材料，包含可控制的亚临界核的数量和尺寸分布，长度为10-200 nm。图案化的光学或电子束曝光应该产生空间变化的表面质量通量，当在结晶尖端的温度下进行时，该表面质量通量提供额外的推动，以在由光通量决定的区域中结晶亚临界核。然后，成熟的微晶应该通过表面扩散和奥斯瓦尔德成熟生长，直到所需的薄膜部分附着在原始原子核上。演示将集中在非晶硅和二氧化钛上。这项拟议工作的一些计算方面将被纳入一门面向本科生的新的跨学科实验室课程，重点是纳米材料合成。阐明无定形表面上的扩散现象、扩展波动显微镜的能力以及演示一种版本的自组装方法的核心目标将保持不变。预算的下调将在几个方面影响拟议的工作，涉及所概述的个别任务的范围1。降低我们确定给出非晶硅中最佳中程有序的条件轨迹的精度。通过氢添加、离子能量和通量以及相关参数的变化来限制控制中程有序的研究范围。将定向自组装方法的实现限制在光学手段上，而不是包括电子束。限制了可以获得描述表面扩散的分布函数的精度。(数据越多，分布函数越准确。)