Fundamental Studies of Photo-Assisted Chemical Vapor Deposition on Aerosol Nanoparticles

美国国家科学基金会-化学运输系统司？&颗粒多相工艺计划（1415）提案编号：0730184主要研究者：Steven L.& Girshick Affiliation： 明尼苏达大学提案标题：气溶胶纳米颗粒上光辅助化学气相沉积的基础研究对于在各种应用中有用的纳米颗粒，必须开发控制其表面性质的方法。这可以通过用薄膜涂覆纳米颗粒，产生“核-壳”结构，或者通过将化学官能团附着到纳米颗粒表面来实现。在某些情况下，目标是稳定或钝化纳米颗粒表面，在其他情况下，赋予一些所需的功能。最近PI展示了一种新方法，其中气溶胶纳米颗粒通过光辅助化学气相沉积（photo-CVD）涂覆，由准分子灯的真空紫外辐射驱动。作为涂覆纳米颗粒的方法，光化学气相沉积具有几个潜在的优势。它可以在低温、大气压气体中实现，这些特征可能比其他方法具有重要优势。准分子灯是相对经济和易于使用，并越来越多地被用于工业上的各种应用，包括薄膜沉积在大面积基板？但到目前为止，还没有在纳米粒子上。虽然这项新技术的可行性已经得到证明，但基本的科学问题还有待解决。气相中的光解离与入射到粒子表面的紫外辐射驱动的化学反应的相对作用是什么？涂层生长速率与颗粒尺寸之间的关系是什么？温度对涂层生长有什么影响？在什么条件下纳米粒子可以被包覆，同时避免反应气体中粒子的光致均匀成核？紫外线引起的粒子带电影响涂层生长吗？紫外线诱导的粒子带电可以用来抑制凝聚吗？ 提出了具体的实验，旨在测试与这些问题中的每一个相关的假设。这些假设将在三个模型的化学系统，涉及金属，半导体和氧化物纳米粒子的背景下进行测试：铝纳米粒子上的无定形有机膜，硅纳米粒子上的致密有机单层，和磁性氧化铁纳米粒子上的SiO2膜。核-壳纳米粒子的潜在应用范围从固体燃料推进到光子学和光子学，以及从生物成像到肿瘤破坏。对于这些系统中的每一个，将使用在线诊断（包括串联微分迁移率分析和傅里叶变换红外光谱）和离线诊断（通过高分辨率透射电子显微镜和相关诊断（如能量色散X射线光谱））来研究涂层形成。在技术方面，它将导致开发一种新的和广泛适用的涂覆纳米颗粒的方法。存在相对较少的用于产生这样的涂层的方法，特别是在室温、大气压气相环境中。光CVD具有可扩展的并且能够高通量处理纳米颗粒的额外优点。因此，预计这一进程将吸引学术界和工业科学和工程界的注意，拟议的研究还将成为一系列教育和外联活动的跳板。这些措施包括K-12通过当地公立学区的推广，本科生参与研究，在高度跨学科的研究环境中至少有两名研究生研究助理的培训，跨学科研究生课程的教学，并促进妇女和代表性不足的群体更多地参与我们的研究生研究计划。

National Science Foundation - Division of Chemical &Transport Systems ? Particulate & Multiphase Processes Program (1415)Proposal Number: 0730184 Principal Investigators: Steven L. Girshick Affiliation: University of Minnesota Proposal Title: Fundamental Studies of Photo-Assisted Chemical Vapor Deposition on Aerosol Nanoparticles For nanoparticles to be useful in a wide variety of applications, methods must be developed to control their surface properties. This can be accomplished either by coating the nanoparticle with a thin film, producing a 'core-shell' structure, or by attaching chemical functional groups to the nanoparticle surface. In some cases the goal is to stabilize or passivate the nanoparticle surface, in other cases to impart some desired functionality.A new method was recently demonstrated by the PIs, in which aerosol nanoparticles are coated by photo-assisted chemical vapor deposition (photo-CVD), driven by vacuum ultraviolet radiation from excimer lamps. Photo-CVD has several potential advantages as a method for coating nanoparticles. It can be achieved in a low-temperature, atmospheric-pressure gas, features that may have important advantages over alternative methods. Excimer lamps are relatively economical and easy to use, and are increasingly being used in industry for a variety of applications, including thin film deposition on large-area substrates?but not, to this point, on nanoparticles.While the feasibility of this new technology has been demonstrated, fundamental scientific questions have yet to be addressed. What are the relative roles of photodissociation in the gas phase versus chemistry driven by UV radiation incident on the particle surface? What is the relationship between coating growth rate and particle size? What is the effect of temperature on coating growth? Under what conditions can nanoparticles be coated while avoiding photoinduced homogeneous nucleation of particles from the reactant gas? Does UV-induced particle charging affect coating growth? Can UV-induced particle charging be used to suppress coagulation? Specific experiments are proposed that are designed to test hypotheses associated with each of these questions. These hypotheses will be tested in the context of three model chemical systems, involving metallic, semiconductor, and oxide nanoparticles: amorphous organic films on aluminum nanoparticles, dense organic monolayers on silicon nanoparticles, and SiO2 films on magnetic iron oxide nanoparticles. Potential applications of the resulting core-shell nanoparticles range from solid fuel propulsion to photovoltaics and photonics, and from biological imaging to tumor destruction. For each of these systems, coating formation will be studied using online diagnostics including tandem differential mobility analysis and Fourier transform infrared spectroscopy, and off-line, by high-resolution transmission electron microscopy and related diagnostics such as energy dispersive X-ray spectroscopy.The proposed research has a wide range of broader impacts. On the technical side, it will lead to the development of a new and widely applicable method for coating nanoparticles. Relatively few methods exist for creating such coatings, especially in a room-temperature, atmospheric-pressure gas-phase environment. Photo-CVD has the additional advantages of being scalable and capable of high throughput processing of nanoparticles. It is therefore expected that this process will attract the attention of both the academic and industrial science and engineering communities.The proposed research will also serve as a springboard for a number of education and outreach activities. These include K-12 outreach through local public school districts, involvement of undergraduates in research, training of at least two graduate research assistants in a highly interdisciplinary research environment, teaching of interdisciplinary graduate courses, and fostering greater involvement of women and underrepresented groups in our graduate research programs.