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

这个纳米技术研究项目旨在发展与非晶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使用非晶半导体材料在纳米尺度上进行定向表面自组装的新方法。在非晶和其他能量异质表面上的扩散在陶瓷的烧结和微电子中的回流工艺和存储器器件制造中起作用。目前几乎没有关于非晶表面扩散的文献，并且很少有专门针对高度缺陷的晶体表面上连续分布的能量异质性的文献。然而，这种不均匀性应导致扩散率D的值与对于明确定义的结晶表面测量的扩散率D的值显著不同。对于无定形材料，可以基于促进或抑制由表面扩散驱动的表面有序化来设计制造工艺。示例应用包括制造存储器器件电极、高效太阳能电池和非晶陶瓷。有序的速率不能通过常规技术进行实验，使得创建过程models.The第一个目标的模型困难。该项目的第一个目标是开发一个科学基础的表面扩散和有序的无定形和其他积极异质表面，使用两个实验室的专业知识相结合。将开发一种实验方法来量化的分布函数描述表面扩散的能量异质表面，使用非晶硅和陶瓷二氧化钛作为范例的情况下。实验还将证实，光学照明可以用于驱动表面扩散非热。相对于表面排序，波动显微镜将适应于近表面区域的研究，通过实施扫描透射电子显微镜，空间分辨率小至0.8 nm。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系统。该项目的第二个目标是开发一种新的表面自组装方法，使用含有受控数量和尺寸分布的亚临界核的非晶半导体材料，在10-200 nm长度范围内进行。图案化的光学或电子束曝光应产生空间变化的表面质量通量，当在退火温度下恰好在结晶的尖端处进行时，其提供额外的轻推以使由光通量决定的区域中的亚临界核结晶。然后，成熟的微晶应该通过表面扩散和奥斯特瓦尔德熟化生长，直到所需部分的膜生长到原始核上。演示将集中在非晶硅和二氧化钛。 拟议工作的一些计算方面将纳入针对本科生的新的跨学科实验室课程，重点关注纳米材料合成。核心目标是阐明非晶表面上的扩散现象，扩展波动显微镜的能力，展示了一种自我预算的向下修订将在几个方面影响拟议的工作，涉及所概述的各项任务的范围。 降低了我们确定非晶硅中最佳中程有序的条件轨迹的精度。 限制通过氢添加、离子能量和通量以及相关参数的变化来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，而不是包括电子束。 限制描述表面扩散的分布函数的精度。(The数据越多，分布函数越准确。）

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.)