Atomic Force Microscopy Studies of Tribochemical Phenomena

我们请求支持一项为期三年的项目，以研究在固体表面同时施加化学剂和机械应力的后果。我们探索了由于应用高度局部机械应力（由于与原子力显微镜尖端接触）和暴露于适当的溶液和溶剂中所产生的纳米级表面形貌变化。这些基础研究影响了许多技术，因为它们为化学机械平面化（CMP）、摩擦化学磨损、摩擦诱导再沉积、生物系统中的摩擦学（生物流体作为活性介质）和纳米技术等领域提供了基础理解。任何表面的相对运动，无论多么小，都会涉及耗散力，需要在纳米级设备中理解和控制。随着设备尺寸的缩小，对清洁、原子平面的需求将变得越来越迫切。我们的总体目标是开发描述和预测模型，以描述由于化学，热和机械过程引起的粗糙度和基材改性。智力优势——摩擦化学现象是复杂的，而且很难理解。我们的方法是将系统简化为一个单一的粗糙度（AFM尖端），我们可以用地形学和某些情况下的化学方法来表征，并使用简单的化学系统（例如水）。我们在压力增强过程科学中的作用是确定潜在的机制。虽然我们在纳米尺度上工作，但我们不是在做纳米技术——我们支持其他做纳米技术的人。通过仔细的定量测量，我们澄清了粗糙度和基材磨损的细节，以及粗糙度磨损与给定基材摩擦变化之间的联系。更微妙的是我们发现的一个新领域，即饱和溶液中材料的尖端控制沉积。在低接触力下在过饱和溶液中扫描可用于局部沉积结晶材料。对于偶尔有凹坑的相对平坦的表面，填充凹坑可能是一种比去除整个表面层更有效的产生原子平面的方法。在扫描相对不溶性离子材料时，我们观察到横向力的波动与过饱和程度密切相关。我们建议将该工具作为过饱和溶液中瞬态表面沉积的可能探针，并进一步了解在过饱和溶液中发生的尖端诱导沉积和结构的基本机制。我们提出了一个创新的、未经检验的想法，即将压力+化学刺激与暴露于辐射相结合。提出的辐射源是电子束、紫外和飞秒激光束。激光照射可就地应用。在辐射暴露后，我们寻求与摩擦化学刺激的协同作用。我们预计会有积极的结果，并将根据我们所知道的关于键断裂、缺陷形成和辐射暴露产生的其他化学修饰的情况，探索潜在的机制。我们希望找到一种促进表面改性的新方法。更广泛的影响。除了一名研究生外，这项工作每年将涉及4-6名本科生和至少一名高中生。我们希望我们的大多数学生，像过去一样，在同行评议的期刊上发表他们的研究结果。这些努力也满足了本科院系和荣誉学院的论文要求。作为物理学本科指导老师和荣誉物理讲师，PI经常影响女性和少数民族成为科学/技术专业，双学位专业和/或早期参与我们的研究项目。这项研究本身，通过基本的理解，为社会提供了减少磨损、延长寿命和环保的过程和系统。纳米技术涉及移动界面和/或需要原子平面、清洁表面或尖端/溶液生成结构的努力也受益于我们的研究。

We request support for a three-year project to examine the consequences of simultaneous application of chemical agents and mechanical stress to a solid surface. We explore the resulting nanometer-scale changes in surface topography due to application of combined highly localized mechanical stress (due to contact with the tip of an atomic force microscope) and exposure to appropriate solutions and solvents. These basic studies impact several technologies in that they provide underlying understanding for areas such as chemical mechanical planarization (CMP), tribochemical wear, tribo-induced redeposition, tribology in biological systems (where biological fluids serve as the active media), and nanotechnology. Any relative motion of surfaces, no matter how small, will involve dissipative forces that need to be understood and controlled in nanometer-scale devices. As device sizes shrink, the need for clean, atomically flat surfaces will become more and more pressing. Our overall goal is to develop descriptive and predictive models for asperity and substrate modification due to combined chemical, thermal, and mechanical processes.Intellectual Merit - Tribochemical phenomena are complex and poorly understood. Our approach is to simplify the system to a single asperity (the AFM tip), which we can characterize topographically and in some cases chemically, and use simple chemical systems (e.g., water). Our role in the science of stress enhanced processes is to identify the underlying mechanisms. Although we work on a nanometer scale, we are not doing nanotechnology - we support others who are doing nanotechnology. Through careful, quantitative measurements, we clarify the details of both asperity and substrate wear, and the connection between asperity wear and changes in friction with a given substrate. More subtle is a new area we have discovered, namely tip-controlled deposition of materials from saturated solution. Scanning at low contact forces in supersaturated solutions can be exploited to locally deposit crystalline material. For relatively flat surfaces with occasional pits, filling in the pits can be a much more efficient method of producing atomically flat surfaces than removing whole surface layers. We have observed fluctuations in the lateral force during scanning of relatively insoluble, ionic materials that correlate strongly with the degree of supersaturation. We propose to explore this tool as a possible probe of transient surface deposits that are expected in supersaturated solutions and to further our understanding of the fundamental mechanisms for the tip induced deposition and structuring that occurs in supersaturated solutions. An innovative, untested idea, we propose is to combine stress+chemical stimulation with exposure to radiation. The proposed radiation sources are electron beams and UV and femtosecond laser beams. Laser irradiation can be applied in situ. Following radiation exposure we seek synergisms with tribochemical stimulation. We anticipate positive results and will explore the underlying mechanisms in light of what we know about bond breaking, defect formation, and other chemical modifications generated by radiation exposure. We hope to find a new way to promote surface modification.Broader impacts. In addition to a graduate student, this work will involve 4-6 undergraduates a year, and at least one high school student. We expect most of our students, as in the past, to publish their results in peer-reviewed journals. These efforts also fulfill undergraduate department and honors college theses requirements. As undergraduate advisor for physics and honors physics instructor, the PI often influences women and minorities to become science/technology majors, double majors, and/or become involved early in our research projects. The research itself, through fundamental understanding, provides benefits to society in need of reduced wear, longer life, and environmentally friendly processes and systems. Efforts in nanotechnology involving moving interfaces and/or needs for atomically flat, clean surfaces or tip/solution generated structures also benefit from our studies.