Study of Binary Physisorbed Films by Combined IRRAS and Ellipsometry

IRRAS 和椭圆光度法相结合的二元物理吸附膜研究

• 批准号: 0305194
• 负责人: George Hess
• 金额: --
• 依托单位: University of Virginia Main Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-07-01 至 2008-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0305194&HistoricalAwards=false
• 关键词: Study; Binary; Physisorbed; Films; Combined

This surface physics project will study physical adsorption of small molecules on graphite in the monolayer to few layer regime, with emphasis on binary mixtures. Substrate interactions and dimensionality effects, especially near critical points, make the films different from 3-D fluids. In addition there is the possibility of displacement of one component from the surface or segregation between layers. Extensive computer simulations have been done for simple model systems but experimental results for real binary systems are so far limited, particularly for cases of solution, due primarily to the difficulty of measuring the coverage and state of each component separately. Here, the total coverage is determined by ellipsometry, while the vibrational spectra of suitable molecules is simultaneously determined by infrared reflection absorption spectroscopy. For model solute molecules with strong IR absorption bands, such as CF4, CCl4, or SF6, together with a solvent that may be IR-active or not, this combination of techniques allows determination of the concentration of each component on the surface. In addition, IR line shifts distinguish whether the solute is phase-separated or dispersed. For less symmetric molecules the IR technique also provides information on molecular orientation. Graphite serves as an ideal uniform substrate from atomic to micrometer scale. Molecular level understanding of the behavior of binary films on a uniform substrate should provide a basis for fundamental understanding of such films on less ideal substrates. This is likely to be relevant to problems in lubrication and adhesion, and less directly to lithography, corrosion-protection, and flow in porous media. Graduate, undergraduate, and post-doctoral students working in this program gain experience in application of a variety of physical principles and techniques, which provides good preparation for careers in industry, government labs, and teaching.%%%This research project will investigate adsorption of binary mixtures of small molecules on graphite, at coverages of one to a few molecular layers. The result may be that one component displaces the other from the surface; or one component adsorbs on top of a layer of the other component; or they form a solution within each layer. Extensive computer simulations have been done for simple model systems but experimental results for real binary systems are so far limited, especial for cases other than displacement. This is due primarily to the difficulty of measuring the coverage and state of each component separately. Our apparatus allows measurement of total film thickness by an optical technique and simultaneously the vibrational spectra of suitable adsorbed molecules by infrared absorption spectroscopy. This gives sufficient information to determine the concentration of each component on the surface. In addition IR absorption line shifts distinguish whether the solute is dissolved or phase-separated. For asymmetric molecules the IR technique also provides information on molecular orientation. Graphite serves as an ideal uniform substrate from atomic to micrometer scale. Molecular level understanding of the behavior of binary films on a uniform substrate should provide a basis for fundamental understanding of such films on less ideal substrates. This is likely to be relevant to problems in lubrication and adhesion, and less directly to lithography, corrosion-protection, and flow in porous media. Students working in this program gain experience in physical principles involved in adsorption, as well as infrared spectroscopy, vacuum, low temperature, and optical techniques, and computer interfacing, which provides good preparation for careers in industry, government labs, or teaching.

这个表面物理项目将研究小分子在单层到多层石墨上的物理吸附，重点是二元混合物。衬底相互作用和维度效应，特别是在临界点附近，使薄膜不同于三维流体。此外，还有一种可能是某一组分从表面位移或层间分离。对于简单的模型系统已经进行了大量的计算机模拟，但是对于实际的二元系统的实验结果迄今为止是有限的，特别是对于解的情况，主要是由于难以分别测量每个组成部分的覆盖范围和状态。在这里，总覆盖范围由椭偏仪确定，而合适分子的振动光谱同时由红外反射吸收光谱确定。对于具有强红外吸收带的模型溶质分子，如CF4、CCl4或SF6，以及可能具有红外活性或不具有红外活性的溶剂，这种技术组合可以确定表面上每种组分的浓度。此外，红外谱线位移可以区分溶质是相分离的还是分散的。对于不太对称的分子，红外技术也提供了分子取向的信息。从原子到微米尺度，石墨是一种理想的均匀衬底。在分子水平上理解均匀衬底上二元薄膜的行为，应该为在不太理想的衬底上理解二元薄膜提供基础。这可能与润滑和粘附问题有关，而与光刻、防腐和多孔介质中的流动问题不太直接。研究生、本科生和博士后在这个项目中工作，获得各种物理原理和技术的应用经验，为工业、政府实验室和教学的职业生涯提供良好的准备。这个研究项目将研究小分子二元混合物在石墨上的吸附，覆盖一到几个分子层。结果可能是一个分量从表面取代了另一个分量；或者一种组分吸附在另一种组分的一层上；或者它们在每一层中形成一个溶液。对简单的模型系统进行了大量的计算机模拟，但对实际的二元系统的实验结果迄今为止是有限的，特别是对位移以外的情况。这主要是由于单独测量每个组件的覆盖率和状态的困难。我们的仪器可以通过光学技术测量总膜厚度，同时通过红外吸收光谱测量合适吸附分子的振动光谱。这提供了足够的信息来确定表面上每种成分的浓度。此外，红外吸收线的位移可以区分溶质是溶解的还是相分离的。对于不对称分子，红外技术还提供了分子取向的信息。从原子到微米尺度，石墨是一种理想的均匀衬底。在分子水平上理解均匀衬底上二元薄膜的行为，应该为在不太理想的衬底上理解二元薄膜提供基础。这可能与润滑和粘附问题有关，而与光刻、防腐和多孔介质中的流动问题不太直接。在这个项目中工作的学生将获得吸附、红外光谱、真空、低温和光学技术以及计算机接口等物理原理方面的经验，为将来从事工业、政府实验室或教学工作提供良好的准备。