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

国家科学基金会--化学与运输系统部门？粒子和安培多相过程计划(1415年)建议编号：0730184主要研究人员：史蒂文·L·格希克从属：明尼苏达大学建议标题：光助化学气相沉积在气溶胶纳米颗粒上的基础研究纳米颗粒要在广泛的应用中有用，必须开发控制其表面性质的方法。这可以通过在纳米颗粒上涂覆一层薄膜来实现，产生一种‘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粒子表面，在其他情况下，目的是赋予某些所需的功能。最近，PI展示了一种新的方法，在准分子灯的真空紫外线辐射的驱动下，通过光辅助化学气相沉积(Photo-Assisted CVD)来包裹纳米粒子。光化学气相沉积作为一种包覆纳米颗粒的方法有几个潜在的优点。它可以在低温、大气压的气体中实现，这一特点可能比替代方法具有重要的优势。准分子灯相对经济易用，在工业上的应用越来越广泛，包括在大面积衬底上沉积薄膜，但到目前为止，还不是在纳米颗粒上。虽然这项新技术的可行性已经得到证明，但基本的科学问题尚未得到解决。气相中的光解离与粒子表面的紫外光辐射所驱动的化学作用有什么关系？涂层的生长速度与颗粒大小之间有什么关系？温度对涂层生长有什么影响？在什么条件下可以包覆纳米颗粒，同时避免反应气体中的颗粒光致均匀成核？紫外线引起的颗粒荷电是否影响涂层的生长？紫外线诱导的颗粒荷电能用来抑制凝血吗？具体的实验是为了检验与这些问题相关的假设而设计的。这些假设将在涉及金属、半导体和氧化物纳米颗粒的三个模型化学体系的背景下进行检验：铝纳米颗粒上的非晶态有机薄膜，硅纳米颗粒上的致密有机单分子膜，以及磁性氧化铁纳米颗粒上的二氧化硅薄膜。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。对于这些系统中的每一个，都将使用在线诊断技术(包括串联差分迁移率分析和傅立叶变换红外光谱)和离线高分辨率电子显微镜以及相关诊断技术(如能量色散X射线光谱仪)来研究涂层的形成。在技术方面，这将导致一种新的、广泛适用的纳米粒子包覆方法的发展。制造这种涂层的方法相对较少，特别是在室温、大气压的气相环境中。光化学气相沉积还具有可伸缩和能够高通量处理纳米颗粒的额外优势。因此，预计这一过程将引起学术界、工业科学和工程界的关注。拟议的研究也将成为开展多项教育和外展活动的跳板。这些措施包括通过当地公立学区的K-12外展，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，以及促进女性和代表性不足群体更多地参与我们的研究生研究项目。

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.