The understanding and utilization of electronic transport phenomena in low-dimensional, quantum-confined structures is of enormous scientific and technological interest. We have studied the electrical transport properties of systems that are quantum confined in one dimension but periodic in the other two dimensions, namely surfaces and ultrathin film materials. The electrical conductance of atomically clean, reconstructed silicon surfaces and interfaces was measured as a function of temperature in ultrahigh vacuum using the classical four-point probe technique. We employed Silicon on Insulator (SOI) technology to enhance the surface sensitivity of the four-point probe measurements. High-quality ohmic contacts were fabricated using ion-implantation.; The Si(100)2 x 1 surface reconstruction consists of a two-dimensional, anti-ferromagnetic c(4 x 2) array of buckled silicon dimers. The surface undergoes a c(4 x 2) → 2 x 1 order-disorder transition near T = 200 K. Above 200 K, dimers fluctuate rapidly and the long-range c(4 x 2) ordering is destroyed. The conductance of this two-dimensional system has a temperature-dependence that is characteristic of a metal. The surface conductance appears closely correlated with the order parameter of the low-temperature c(4 x 2) structure. Thermally activated flip-flop motion of the Si dimers thus appears to be the dominant scattering mechanism.; Recent high-resolution photoemission experiments indicate that the Si(111)7 x 7 surface reconstruction is a two-dimensional, correlated metal. The surface electrical conductivity decreases with increasing temperature, thus confirming metallic transport. However, conductivity measurements on ultrathin SOI indicate insulating behavior. The origin of this discrepancy is not understood and requires further investigation of the sheet conductance as a function of the SOI layer thickness.; The Ga/Si(112) interface consists of a self-assembled, mesoscopic array of atomic Ga wires on a high-index Si(112) surface. The structural uniformity of this atomic-wire-or quantum-wire array is far superior to those created by nano-lithography or STM atom manipulation. Transport measurements reveal a strong conductance anisotropy as expected. However, the conduction channels are orthogonal to the crystallographic chains. This counterintuitive result is in excellent agreement with electronic structure calculations by Ortega and Flores. The theoretical band structure was confirmed independently with photoemission spectroscopy.
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机译：对低维量子受限结构中电子传输现象的理解和利用具有巨大的科学技术意义。我们已经研究了一个系统的电传输特性，该系统在一维量子范围内，而在另外两个维周期内是周期性的，即表面和超薄膜材料。使用经典的四点探针技术，在超高真空下测量原子清洁，重建的硅表面和界面的电导率随温度的变化。我们采用绝缘体上硅（SOI）技术来增强四点探针测量的表面灵敏度。使用离子注入制造了高质量的欧姆接触。 Si（100）2 x 1表面重建由屈曲的硅二聚体的二维反铁磁c（4 x 2）阵列组成。表面在T = 200 K附近经历c（4 x 2）→2 x 1有序无序过渡。在200 K以上，二聚体迅速波动，长距离c（4 x 2）有序被破坏。该二维系统的电导具有金属所特有的温度依赖性。表面电导似乎与低温c（4 x 2）结构的有序参数密切相关。 Si二聚体的热激活的触发器运动因此似乎是主要的散射机制。最近的高分辨率光电发射实验表明，Si（111）7 x 7表面重建是二维的相关金属。表面电导率随温度升高而降低，从而确认了金属的迁移。然而，超薄SOI的电导率测量表明绝缘性能。这种差异的原因尚不清楚，需要进一步研究薄板电导率与SOI层厚度的关系。 Ga / Si（112）界面由高折射率Si（112）表面上原子Ga线的自组装介观阵列组成。这种原子线或量子线阵列的结构均匀性远远优于纳米光刻或STM原子操纵所产生的均匀性。传输测量显示出预期的强电导各向异性。但是，传导通道与晶体链正交。这个违反直觉的结果与Ortega和Flores的电子结构计算非常吻合。用光发射光谱法独立地确认了理论带结构。
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