Monolithic and Hybrid Spintronics

Abstract

“Spintronics” is the science and technology of using the spin degree of freedom of a charge carrier, either singly or in conjunction with the charge, to store, process and/or communicate information. Both, classical and quantum mechanical information can be encoded by spin. In this chapter, “hybrid” and “monolithic” spintronics are discussed; the distinction between the two is that, in the former case, spin is not used directly to store or process information; rather, that role is still delegated to charge. But spin influences how charge stores or manipulates information. The role of spin is secondary and may, at best, augment the role of charge. Examples of hybrid spintronic devices are spin field effect transistors (SPINFETs) and spin bipolar junction transistors (SBJTs). It is also noted that hybrid devices are not likely to yield major advances in device engineering in the short term. On the other hand, monolithic spintronics, which deals with devices in which spin single‐handedly stores and processes information, is much better poised to make major advances. An example of this is “single spin logic” (SSL), where a single electron acts as a binary element (two‐state switch), its two orthogonal spin polarizations being used to encode binary bits 0 and 1. Switching between bits is accomplished simply by flipping the spin of the electron, without physically moving charges in space and causing a current flow. In this way energy is saved, leading to a much‐reduced power dissipation. The switching time is also not limited by the speed of charge carriers as there is no charge motion. The maximum energy dissipated in SSL gate operation is the Landauer–Shannon limit of kT ln( p ) per operation (where 1/ p is the error probability). The chapter concludes with a brief discussion of spin‐based quantum computing, where the spin of an electron in a quantum dot is used to implement a qubit. Of note, this last section is necessarily brief and will most likely be outdated by the time this book is printed, as rapid strides are being made in that area.

Tailoring the Ti surface via electropolishing nanopatterning as a route to obtain highly ordered TiO2nanotubes

“…By increasing V EP , the Ti foil surface became slightly rougher: Rq = 3.4, 4.7, and 3.1 nm measured for samples 15, 18, and 20 V, respectively. Additionally, the Ti surface after EP revealed a periodic dimple-pattern structure whenever V EP was no smaller than 10 V. This shallow ripple-like structure is an EP characteristic of metals [34,42] and can be used as a pre-pattern prior to anodization to obtain highly ordered oxide nanostructures, as profusely shown in the case of Al [28,[34][35][36][37]41]. In fact, studies in Al foils demonstrated that, by combining adequate EP voltage and time, dimplepatterns from striped to hexagonal arrangements can be obtained [28,[34][35][36][37]41].…”

“…Additionally, the Ti surface after EP revealed a periodic dimple-pattern structure whenever V EP was no smaller than 10 V. This shallow ripple-like structure is an EP characteristic of metals [34,42] and can be used as a pre-pattern prior to anodization to obtain highly ordered oxide nanostructures, as profusely shown in the case of Al [28,[34][35][36][37]41]. In fact, studies in Al foils demonstrated that, by combining adequate EP voltage and time, dimplepatterns from striped to hexagonal arrangements can be obtained [28,[34][35][36][37]41]. However, EP of Ti is usually performed in sulphuric acid-based electrolytes that lead to smooth and plane surfaces [31].…”

“…Electropolishing is a well-known technique [30] for metal removal at the micrometer level [31][32][33][34][35] and to obtain smooth and highly reflective surfaces. While (mostly) at the industrial level the process is best known for the surface bright polish, at the research level other important benefits, often overlooked, arise.…”

“…A new overriding application of EP arises to create nanopatterns in the surface of aluminum, titanium, zirconium, tantalum, and tungsten [33,34], working as a pre-pattern prior to the anodization and ultimately leading to highly ordered oxide nanostructures. In fact, the EP of Al foils was shown to be a simple and efficient method to induce a high degree of organization in AAO templates, since the shallow ripple-like structures it produced favor a preferential ordered pore nucleation [28,34,35,[37][38][39][40][41]. In Al, the EP process has been widely studied and optimized, where EP parameters, such as temperature, time, stirring, distance to the electrode, and electrolyte type were found to play an important role in the process [36,37].…”

“…In Al, the EP process has been widely studied and optimized, where EP parameters, such as temperature, time, stirring, distance to the electrode, and electrolyte type were found to play an important role in the process [36,37]. Nevertheless, a parameter of crucial importance is the EP applied voltage, since its variation can result in features like stripes or hexagonally ordered dimples (from 50-150 nm) [34][35][36][37]41]. However, the nanopatterning of a Ti foil by varying the EP potential has been overlooked so far.…”