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

本项目的重点是气敏超薄膜和薄膜界面的制备和原位表征。进行这些研究的能力依赖于最近建造的真空样品处理（SHIVA）室，在该室中，薄膜样品可以在沉积站（可以进行光学和输运测量）可靠地连接/断开，然后在不暴露于空气的情况下转移到真空兼容低温恒温器的底部，进行低温（1.3K）和高场（7T）磁输运测量。这种方法的基本原理集中在观察到空气敏感性可能是揭示各种系统内在行为的主要障碍。工作范围将集中在四个重叠的领域：渗透和金属-绝缘过渡，金属/C60双层和复合材料，缩小尺寸的磁性，以及确定金属-介电界面的屏蔽长度。要研究的特定系统包括靠近渗透阈值的Ag薄膜（表现出纯粹的几何行为和负的经典磁阻），磁性（Ni, Fe, Co, Gd）金属/C-60双层和复合材料（表现出电荷转移和异常的正磁阻），薄的无序磁性和磁性半导体（例如Fe， GdxSi1-x）薄膜，带磁电极的隧道结电容器结构（由于筛分长度与磁场的关系而表现为磁电容）。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型物理现象的全面理解。这项研究是与学生一起进行的，他们将获得培训技能，为将来在我国经济的科学/技术部门就业做好准备。随着金属薄膜厚度的减小，其电性能对其与衬底的界面以及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（如Al， Fe）暴露在空气中会迅速氧化，如果足够薄，会在短时间内完全氧化。因此，为了测量这种空气敏感薄膜的固有电学特性，有必要利用专门的技术，在其制造和电学表征之间的一段时间内阻止空气到达样品。进行这些研究的能力依赖于最近建造的真空样品处理（SHIVA）室，在该室中，薄膜样品可以在沉积站（可以进行光学和输运测量）可靠地连接/断开，然后在不暴露于空气的情况下转移到单独的真空兼容室的底部，以便在低温和高磁场下进行电气测量。要研究的具体系统包括接近导通阈值的金属薄膜、磁性金属/碳-60双层和复合材料、薄的无序磁性和磁性半导体薄膜，以及带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极大地促进对空气敏感系统中发生的新型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、学术界和政府的科学/技术部门就业做准备。

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.