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This chapter presents basic experimental methods and the basic theory of tunneling. The classical metal-insulator-metal tunneling junction experiment of Giaever, designed to verify the Bardeen-Cooper-Schrieffer theory of superconductivity, is the motivation for Bardeen to invent his perturbation theory of tunneling. That Bardeen theory then became the starting point of the most useful models of STM. Section 2.2 presents the Bardeen tunneling theory from time-dependent perturbation theory of quantum mechanics, starting from a one-dimensional case, then proceeds to three-dimensional version with wave-function corrections. The Bardeen theory in second-quantization format, the transfer-Hamiltonian formalism, is also presented. As extensions of the original Bardeen theory, the theories and experiments of inelastic tunneling and spin-polarized tunneling are discussed in depth.

This chapter focuses on coherence and decoherence, starting from the basis of quantum mechanics and including the classical paradox of Schrödinger’s cat and entanglement. Decoherence and relaxation are simultaneously accounted for by an evolution equation for the density matrix, which is analysed in the case of spin tunnelling and simplifies when decoherence is complete. The final section discusses the possible exploitation of coherence in quantum computing.

This chapter presents basic experimental methods and the basic theory of tunneling. The classical metal-insulator-metal tunneling junction experiment of Giaever, designed to verify the Bardeen-Cooper-Schrieffer theory of superconductivity, is the motivation for Bardeen to invent his perturbation theory of tunneling. That Bardeen theory then became the starting point of the most useful models of STM. Section 2.2 presents the Bardeen tunneling theory from time-dependent perturbation theory of quantum mechanics, starting from a one-dimensional case, then proceeds to three-dimensional version with wave-function corrections. The Bardeen theory in second-quantization format, the transfer-Hamiltonian formalism, is also presented. As extensions of the original Bardeen theory, the theories and experiments of inelastic tunneling and spin-polarized tunneling are discussed in depth.

Techniques have been developed for growing materials under controlled but non-equilibrium conditions. One category is the artificially layered materials which can be formed by exposing some substrate to alternating incoming mass fluxes from two (or more) sources, which sequentially deposit on that substrate. Such structures may be prepared as an individual layer buried in an otherwise uniform second constituent, or as systems consisting of multiple layers both periodic and non-periodic. Furthermore, the constituents may be chosen from the same or different materials categories including: metals, superconductors, semiconductors, insulators, ferromagnets and antiferromagnets, and ferroelectrics and piezoelectrics. This chapter discusses the following: artificial superlattices, multi-layer semiconductors, quantum wells and minibands, multiple wells and superlattices, metallic multilayers, spin tunneling, spin torque oscillators, surface states, atoms at a free surface, calculating surface and interface electronic properties, the chemical potential, the work function, and electron affinity. Sample problems are also provided at the end of the chapter.