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

美国国家科学基金会化学与运输系统分部？微粒和多相过程计划（1415）提案编号：0730184主要研究者：Steven L. Girshick合作单位：明尼苏达大学提案题目：气溶胶纳米粒子光辅助化学气相沉积的基础研究为了使纳米粒子在各种各样的应用中有用，必须开发方法来控制它们的表面特性。这可以通过在纳米颗粒表面涂上一层薄膜来实现，从而产生一个“核壳”结构，或者通过在纳米颗粒表面附着化学官能团来实现。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，赋予一些期望的功能。pi最近展示了一种新的方法，在准分子灯的真空紫外线辐射驱动下，通过光辅助化学气相沉积（photocvd）包裹气溶胶纳米颗粒。光- cvd作为纳米颗粒的涂层方法有几个潜在的优点。它可以在低温、常压的气体中实现，与其他方法相比，这可能具有重要的优势。准分子灯相对经济且易于使用，并且越来越多地用于工业中的各种应用，包括在大面积基板上沉积薄膜。但到目前为止，纳米粒子还没有。虽然这项新技术的可行性已经得到证明，但一些基本的科学问题还有待解决。什么是相对的作用光解在气相与化学驱动的紫外线辐射入射到粒子表面？涂层生长速率与颗粒大小的关系是什么？温度对涂层生长有什么影响？在什么条件下可以包覆纳米粒子，同时避免反应物气体引起的光致均匀成核？紫外线诱导的粒子充电会影响涂层的生长吗？紫外线诱导的微粒充电能抑制凝血吗？具体的实验被提出，旨在测试与这些问题相关的假设。这些假设将在三种模型化学系统的背景下进行测试，包括金属、半导体和氧化物纳米粒子：铝纳米粒子上的无定形有机薄膜，硅纳米粒子上的致密有机单层，磁性氧化铁纳米粒子上的SiO2薄膜。由此产生的核壳纳米颗粒的潜在应用范围从固体燃料推进到光伏和光子学，从生物成像到肿瘤破坏。对于每个系统，涂层形成将使用在线诊断（包括串联差分迁移率分析和傅里叶变换红外光谱）和离线(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）进行研究。拟议的研究具有广泛的影响。在技术方面，它将导致一种新的和广泛适用的纳米颗粒涂层方法的发展。目前制造这种涂层的方法相对较少，特别是在室温、常压气相环境中。光- cvd具有可扩展和能够高通量处理纳米颗粒的附加优点。因此，预计这一过程将引起学术界和工业科学和工程界的关注。拟议的研究也将作为若干教育和外联活动的跳板。这些措施包括通过当地公立学区进行K-12扩展，让本科生参与研究，在高度跨学科的研究环境中培训至少两名研究生研究助理，教授跨学科研究生课程，以及在我们的研究生研究项目中促进女性和代表性不足的群体的更多参与。

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.