Sensors: Hierarchical Metal Oxides for Next Generation Devices

摘要：James J.Watkins Institution：马萨诸塞州大学/阿默斯特学院提案编号：0529034标题：Sensors：用于下一代设备的分层金属氧化物能够在从几纳米到几厘米的长度范围内控制分层金属氧化物的结构和表面属性，这为下一代传感器提供了极大改善的灵敏度、选择性和响应时间的前景。然而，要实现这一潜力，需要开发有效的制造策略，使之能够规范地控制纳米级孔的大小、结构和取向，并提供控制表面化学和功能元素在这些结构中放置的能力。目标结构包括无缺陷的二氧化硅、氧化铝和二氧化钛薄膜，这些薄膜包含有序的球形孔和紧密排列的均匀的、指定直径的功能化圆柱孔阵列，这些材料垂直于衬底。后一种元素不仅提供了大的表面与体积比，而且还为分析物和薄的孔壁提供了短而无阻碍的扩散路径，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，需要一种可以直接集成到现有器件制造线中的制造方案，以实现大批量生产。PI开发了一种能够实现这些目标的介孔氧化物的新方法。他的方法包括金属醇盐在超临界二氧化碳膨胀的预组织嵌段共聚模板膜的特定子域内的相选择性缩合。随后去除模板可得到有序的介孔固体，其保留了微相分离的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片上制备器件级质量的硅酸盐薄膜，用于超低介电常数薄膜。在这里，他利用3D复制过程的使能方面来生产层次化的二氧化硅、二氧化钛和氧化铝薄膜，作为传感器应用的构造。这包括(1)模板组织与金属氧化物网络形成的分离，这通过独立选择模板和前体提供灵活的工艺化学，并消除与合作自组装相关的限制；(2)使用与二氧化钛、氧化铝和其他金属氧化物的水解性敏感前体兼容的非水反应介质；以及(3)通过在前体注入之前通过区域取向和排列来操纵嵌段共聚聚合物的结构，这使得能够产生垂直于衬底表面定向的具有可调节孔径的圆柱孔的纳米通道阵列。一旦金属氧化物框架就位，表面化学控制对于最大限度地提高传感器性能至关重要。超临界CO2的传输特性为利用有机硅烷和氢化硅烷在纳米结构氧化物中的表面修饰提供了明显的优势。除了控制底物表面的亲水/疏水特性外，这些修饰还可以提供活性手柄，用于固定酶和孔壁上的金属簇。最后，在前体注入之前在模板中掺杂活性物种提供了一种通过包覆使金属氧化物功能化的替代途径。技术优点：科学核心是开发一种快速有效的方法来制备功能化的分级金属氧化物，作为纳米传感器器件应用的平台。成功复制嵌段共聚物的形态以制备有序的介孔二氧化钛和氧化铝薄膜，包括控制孔取向和孔尺寸，将代表着材料科学的重大进步。在硅酸盐、氧化铝和二氧化钛中制备的纳米通道阵列具有定义的大小，范围在10到45 nm之间，为提高广泛类型的传感器的性能提供了最佳的衬底。更广泛的影响：开发具有纳米级周期性的定义良好的金属氧化物薄膜具有广泛的应用价值，包括催化、分离、微流体、能量转换和微电子中的低介电常数薄膜。一种有效和通用的生产手段将产生广泛的影响。例如，二氧化钛中的纳米通道阵列与这里为传感器生产的纳米通道阵列类似，将是制造共轭聚合物光伏电池高表面积异质结的理想选择，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有一定的应用。该项目将让研究生接触跨学科研究，并让本科生参与进来。项目成果将以单元形式在现有课程中使用，包括纳米技术调查课程和本科实验室课程，并在麻省理工学院主持的麻省理工学院阿默斯特分校的中学访问中用作纳米技术应用的范例。

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.