In Situ Characterization of Electrical and Optical Properties of Air-Sensitive Ultra-Thin Films and Thin-Film Interfaces

本计画的重点是空气敏感超薄膜与薄膜界面的制作与原位特性分析。进行这些调查的能力依赖于最近建造的样品处理真空（SHIVA）室，其中薄膜样品可以可靠地连接/断开在沉积站（在那里可以进行光学和运输测量），然后转移，而不暴露于空气中，到一个真空兼容的低温恒温器的底部低温（1.3K）和高场（7 T）磁输运测量。这种方法的基本原理集中在观察，空气敏感性可以是一个主要的障碍，解开内在的行为在各种系统。工作范围将集中在四个重叠的领域：渗流和金属绝缘过渡，金属/C60双层和复合材料，磁性在减少的尺寸，并确定在金属介电界面的屏蔽长度。 待研究的具体系统包括接近逾渗阈值的Ag膜（表现出纯几何行为和负的经典磁阻）、磁性（Ni、Fe、Co、Gd）金属/C-60双层和复合物（表现出电荷转移和异常正磁阻）、薄无序磁性和磁性半导体（例如，Fe，GdxSi 1-x）膜和具有磁性电极的隧道结电容器结构（由于屏蔽长度对磁场的依赖性而表现出磁电容）。我们期望SHIVA系统将极大地促进对空气敏感系统中发生的新物理现象的全面理解。这项研究是与学生谁将获得培训技能，这将使他们为未来在我国经济的科学/技术部门就业做好准备。随着金属膜的厚度减小，其电性能对其与下面的衬底的界面以及其与周围环境的界面变得越来越敏感。例如，许多新沉积的薄膜（例如，Al、Fe）在暴露于空气时将迅速氧化，并且如果足够薄，则将在短时间内完全氧化。 为了测量这种空气敏感薄膜的固有电特性，因此有必要利用专门的技术，其中防止空气在其制造和电特性之间的时间段到达样品。执行这些调查的能力依赖于最近建造的样品处理真空（SHIVA）室，其中薄膜样品可以在沉积站（可以进行光学和运输测量）可靠地连接/断开，然后在不暴露于空气的情况下转移到一个单独的真空兼容室的底部，用于在低温和高磁场下进行电测量。要研究的具体系统包括导电阈值附近的金属膜，磁性金属/碳-60双层和复合材料，薄无序的磁性和磁性半导体膜，以及具有磁性电极的隧道结电容器结构。我们期望SHIVA真空沉积和表征系统将大大促进对空气敏感系统中发生的新物理现象的全面理解。学生将参与这项研究。 因此，他们将获得技能和培训，为在工业、企业和政府的科学/技术部门就业做好准备。

The focus of this project is on the fabrication and in situ characterization of air sensitive ultra-thin films and thin-film interfaces. The capability to perform these investigations relies on a recently constructed Sample-Handling-In-VAcuum (SHIVA) chamber in which thin-film samples can be reliably connected/disconnected at the deposition station (where optical and transport measurements can be made) and then transferred, without exposure to air, to the bottom of a vacuum-compatible cryostat for low temperature (1.3K) and high field (7T) magnetotransport measurements. The rationale for this approach centers on observations that air sensitivity can be a primary impediment to unraveling intrinsic behavior in a variety of systems. The scope of work will be concentrated in four overlapping areas: percolation and the metal-insulating transition, metal/C60 bilayers and composites, magnetism in reduced dimensions, and the determination of screening lengths at metal-dielectric interfaces. Specific systems to be studied include Ag films near the percolation threshold (exhibits pure geometric behavior and a negative classical magnetoresistance), magnetic (Ni, Fe, Co, Gd) metal/C-60 bilayers and composites (exhibits charge transfer and anomalous positive magnetoresistance), thin disordered magnetic and magnetic semiconductor (e.g., Fe, GdxSi1-x) films, and tunnel junction capacitor structures with magnetic electrodes (exhibits magnetocapacitance due to dependence of screening length on magnetic field). We expect that the SHIVA system will greatly facilitate a comprehensive understanding of novel physical phenomena occurring in air sensitive systems. This research is carried out with students who will acquire training skills that will prepare them for future employment in the scientific/technological sector of our economy. As the thickness of a metallic film decreases, its electrical properties become increasingly sensitive to its interface with the underlying substrate and its interface with the ambient environment. For example, many freshly deposited thin films (e.g., Al, Fe) will rapidly oxidize when exposed to air and, if sufficiently thin, will in a short time become totally oxidized. To measure the intrinsic electrical properties of such air-sensitive thin films, it therefore becomes necessary to utilize specialized techniques in which air is prevented from reaching the sample in the period between its fabrication and electrical characterization. The capability to perform these investigations relies on a recently constructed Sample-Handling-In-VAcuum (SHIVA) chamber in which thin-film samples can be reliably connected/disconnected at the deposition station (where optical and transport measurements can be made) and then transferred, without exposure to air, to the bottom of a separate vacuum-compatible chamber for electrical measurements at low temperatures and high magnetic fields. Specific systems to be studied include metal films near the conduction threshold, magnetic metal/Carbon-60 bilayers and composites, thin disordered magnetic and magnetic semiconductor films, and tunnel junction capacitor structures with magnetic electrodes. We expect that the SHIVA vacuum deposition and characterization system will greatly facilitate a comprehensive understanding of novel physical phenomena occurring in air sensitive systems. Students will participate in this research. They will thereby acquire skills and training in preparation for employment in scientific/technological sectors of industry, academe, and government.