Sensors: Hierarchical Metal Oxides for Next Generation Devices

摘要：James J. Watkins Institution：马萨诸塞州/阿默斯特大学提案编号：0529034题目：传感器：用于下一代器件的分级金属氧化物在几纳米到几厘米的长度尺度上控制分级金属氧化物的结构和表面性质的能力为下一代传感器提供了极大改善灵敏度、选择性和响应时间的希望。 然而，这种潜力的实现需要开发有效的制造策略，使得能够对纳米级孔的尺寸、结构和取向进行规定性控制，并提供控制表面化学和功能元件在这些结构内的放置的能力。目标结构包括无缺陷的二氧化硅、氧化铝和二氧化钛膜，这些膜含有有序的球形孔和在这些材料中垂直于基底取向的规定直径的均匀的、功能化的圆柱形孔的紧密堆积阵列。 后一种元素不仅提供大的表面积与体积比，而且还提供用于分析物的短且无阻碍的扩散路径和薄的孔壁，使得它们的电子性质受到表面过程的强烈影响，这是高灵敏度的关键。最后，对于大批量生产，需要可以直接集成到现有器件制造线中的制造方案。PI已经开发出一种新的方法来制备介孔氧化物，可以实现这些目标。他的方法涉及金属醇盐在用超临界二氧化碳扩张的预组织嵌段共聚物模板膜的特定子域内的相选择性缩合。随后去除模板产生良好有序的中孔固体，其保留了微相分离嵌段共聚物的所有结构细节。最近，他验证了这种方法用于在全工艺硅晶片上制备器件质量的硅酸盐薄膜，以用作超低介电常数薄膜。 在这里，他利用三维复制过程的有利方面来生产分层二氧化硅，二氧化钛和氧化铝薄膜作为传感器应用的结构。这些包括（1）模板组织与金属氧化物网络形成的分离，其通过模板和前体的独立选择提供灵活的工艺化学，并去除与协同自组装相关的限制，（2）使用与二氧化钛、氧化铝和其它金属氧化物的水解敏感前体相容的非水性反应介质，和（3）在前体注入之前通过域取向和排列来操纵嵌段共聚物结构，这使得能够产生垂直于基底表面取向的圆柱形孔的纳米通道阵列，其具有可调的孔径。一旦金属氧化物框架就位，控制表面化学对于最大化传感器性能至关重要。超临界CO2的传输特性为在纳米结构氧化物中使用有机硅烷和二氢硅烷化学进行表面改性提供了明显的优势。除了控制基底表面的亲水/疏水特性之外，这些修饰可以提供用于将酶和金属簇固定在孔壁上的反应性手柄。最后，在前体注入之前用活性物质掺杂模板提供了通过包封使金属氧化物官能化的替代途径。技术优点：科学核心是开发了一种快速高效的制备官能化分级金属氧化物的路线，作为纳米传感器器件应用的平台。成功复制嵌段共聚物形态以产生有序的介孔二氧化钛和氧化铝膜，包括控制孔取向和孔尺寸，将代表材料科学的重大进步。在硅酸盐、氧化铝和二氧化钛中制造具有限定尺寸的孔（范围在10和45 nm之间）的纳米通道阵列提供了用于增强广泛类别的传感器的性能的最佳基底。更广泛的影响：具有纳米尺度周期性的定义明确的金属氧化物膜的开发对于许多应用（包括微电子中的催化、分离、微流体、能量转换和低介电常数膜）是令人感兴趣的。一种有效和普遍的生产手段将产生广泛的影响。例如，在二氧化钛中的纳米通道阵列类似于这里生产的传感器，对于共轭聚合物光伏电池的高表面积异质结的制造是理想的，而含有固定化酶或高度分散的金属簇的有序硅酸盐将在催化中具有一定的应用。该项目将使研究生接触跨学科研究，并涉及本科生的参与。 项目结果将以模块化的形式用于现有课程，包括纳米技术调查课程和本科实验室课程，并在MassNanoTech在马萨诸塞大学阿默斯特校区举办的中学访问期间用作纳米技术应用的例子。

ABSTRACTPI: James J. Watkins Institution: University of Massachusetts/AmherstProposal Number: 0529034Title: Sensors: Hierarchical Metal Oxides for Next Generation DevicesThe ability to control the structure and surface properties of hierarchical metal oxides across length scales ranging from a few nanometers to several centimeters offers the promise of next generation sensors with dramatically improved sensitivity, selectivity and response time. Realization of that potential, however, requires the development of efficient fabrication strategies that enable prescriptive control over the size, structure, and orientation of nanometer scale pores and provide the ability to control surface chemistry and placement of functional elements within these structures. Target structures include defect free silica, alumina and titania films containing well-ordered spherical pores and close-packed arrays of uniform, functionalized cylindrical pores of prescribed diameter oriented normal to substrate in these materials. The latter elements offer not only large surface to volume ratios, but also short and unencumbered diffusion paths for analytes and thin pore walls such that their electronic properties are strongly influenced by surface processes, a key to high sensitivity. Finally, a fabrication scheme that can be integrated directly into existing device fabrication lines is required for high volume production. The PI has developed a new approach for mesoporous oxides that can achieve these objectives.His approach involves the phase-selective condensation of metal alkoxides within specific sub-domains of pre-organized block copolymer template films dilated with supercritical carbon dioxide. Subsequent removal of the template yields a well-ordered mesoporous solid that retains all of the structural detail of microphase separated block copolymers. Recently he validated this approach for the preparation of device-quality silicate films on full process Si wafers for application as ultra low dielectric constant films. Here he exploits enabling aspects of the 3-D replication process to produce hierarchical silica, titania and alumina films as constructs for sensor applications. These include (1) the separation of template organization from metal oxide network formation, which provides flexible process chemistry through independent selection of template and precursor and removes constraints associated with cooperative selfassembly, (2) the use of a non-aqueous reaction media that is compatible with hydrolytically sensitive precursors for titania, alumina and other metal oxides, and (3) manipulation of block copolymer architecture by domain orientation and alignment prior to precursor infusion, which enables the production of nanochannel arrays of cylindrical pores oriented normal to the substrate surface with tunable pore diameters. Once the metal oxide framework is in place, control of surface chemistry is essential for maximizing sensor performance. The transport properties of supercritical CO2 offer distinct advantages for surface modifications using organosilanes and hydridosilane chemistry within nanostructured oxides. In addition to controlling the hydrophilic/hydrophobic character of the substrate surface, these modifications can provide reactive handles for immobilization of enzymes and metal clusters on the pore walls. Finally, doping the templates with active species prior to precursor infusion provides an alternative route to functionalizing the metal oxides by encapsulation.Technical Merit: The scientific core is the development of a rapid and efficient route for the preparation of functionalized hierarchical metal oxides as a platform for nanosensor device applications. Successful replication of block copolymer morphologies to yield well-ordered mesoporous titania and alumina films, including control of pore orientation and pore dimensions would represent a significant advance in materials science. The fabrication of nanochannel arrays in silicates, alumina and titania with pores of defined size, ranging between 10 and 45 nm, presents an optimal substrate for enhancing the performance of broad classes of sensors. Broader Impacts: The development of well-defined metal oxide films with nanometer-scale periodicity is of interest for numerous applications including catalysis, separations, microfluidics, energy conversion and low dielectric constant films in microelectronics. An efficient and general means for their production would have broad impact. For example, nanochannel arrays in titania similar to those produced here for sensors would be ideal for the fabrication of high surface area heterojunctions for conjugated polymer photovoltaic cells, while well-ordered silicates containing immobilized enzymes or highly-dispersed metal clusters would have certain application in catalysis. The project will expose graduate students to interdisciplinary research and involve the participation of undergraduate students. Project results will be put in modular form for use in existing curriculum including a survey course in nanotechnology and an undergraduate laboratory course and used as an example of applications of nanotechnology during secondary school visits hosted by MassNanoTech on the UMass Amherst campus.