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|Solid state nanoelectronics|
Nanoionics is the study and application of phenomena, properties, effects and mechanisms of processes connected with fast ion transport (FIT) in all-solid-state nanoscale systems. The topics of interest include fundamental properties of oxide ceramics at nanometer length scales, and fast ion conductor (advanced superionic conductor)/electronic conductor heterostructures. Potential applications are in electrochemical devices (electrical double layer devices) for conversion and storage of energy, charge and information. The term and conception of nanoionics (as a new branch of science) were first introduced by A.L. Despotuli and V.I. Nikolaichik (Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Sciences, Chernogolovka) in January 1992.
There are two classes of solid state ionic nanosystems and two fundamentally different nanoionics: (I) nanosystems based on solids with low ionic conductivity, and (II) nanosystems based on advanced superionic conductors (e.g. alpha–AgI, rubidium silver iodide–family). Nanoionics-I and nanoionics-II differ from each other in the design of interfaces. The role of boundaries in nanoionics-I is the creation of conditions for high concentrations of charged defects (vacancies and interstitials) in a disordered space-charge layer. But in nanoionics-II, it is necessary to conserve the original highly ionic conductive crystal structures of advanced superionic conductors at ordered (lattice-matched) heteroboundaries. Nanoionic-I can significantly enhance (up to ~108 times) the 2D-like ion conductivity in nanostructured materials with structural coherence, but it is remaining ~103 times smaller relatively to 3D ionic conductivity of advanced superionic conductors.
Being a branch of science and nanotechnology, nanoionics is unambiguously defined by its own objects (nanostructures with FIT), subject matter (properties, phenomena, effects, mechanisms of processes, and applications connected with FIT at nano-scale), method (interface design in nanosystems of superionic conductors), and criterion (R/L ~1, where R is the length scale of device structures, and L is the characteristic length on which the properties, characteristics, and other parameters connected with FIT change drastically).
The International Technology Roadmap for Semiconductors (ITRS) relates nanoionics-based resistive switching memories to the category of "emerging research devices" ("ionic memory"). The area of close intersection of nanoelectronics and nanoionics can be called nanoelionics. Now, the vision of future nanoelectronics constrained solely by fundamental ultimate limits is being formed in advanced researches. The ultimate physical limits to computation are very far beyond the currently attained (1010 cm-2, 1010 Hz) region. What kind of logic switches might be used at the near nm- and sub-nm peta-scale integration? The question was the subject matter already in, where the term “nanoelectronics”  was not used yet. Quantum mechanics constrains electronic distinguishable configurations by the tunneling effect at tera-scale. To overcome 1012 cm−2 bit density limit, atomic and ion configurations with acharacteristic dimension of L <2 nm should be used in the information domain and materials with an effective mass of information carriers m* considerably larger than electronic ones are required: m* =13 me at L =1 nm, m* =53 me (L =0,5 nm) and m* =336 me (L =0,2 nm). Future short-sized devices may be nanoionic, i.e. based on the fast ion transport at the nanoscale, as it was first stated in.
The examples of nanoionic devices are all-solid-state supercapacitors with fast ion transport at the functional heterojunctions (nanoionic supercapacitors), lithium batteries and fuel cells with nanostructured electrodes, nano-switches with quantized conductivity on the basis of fast ion conductors (see also programmable metallization cell). These are well compatible with sub-voltage and deep-sub-voltage nanoelectronics (see http://www.nanometer.ru/2008/02/08/nanoelektronika_5900.html) and could find wide applications, for example in autonomous micro power sources, RFID, MEMS, smartdust, nanomorphic cell, other micro- and nanosystems, or reconfigurable memory cell arrays.
An important case of fast ionic conduction in solid states is that in surface space-charge layer of ionic crystals. Such conduction was first predicted by Kurt Lehovec. A significant role of boundary conditions with respect to ionic conductivity was first experimentally discovered by C.C. Liang who found an anomalously high conduction in the LiI-Al2O3 two-phase system. Because a space-charge layer with specific properties has nanometer thickness, the effect is directly related to nanoionics (nanoionics-I). The Lehovec effect has become the basis for the creation of a multitude of nanostructured fast ion conductors which are used in modern portable lithium batteries and fuel cells. Recently, a 1D structure-dynamic approach was developed in nanoionics for detailed description of the space charge relaxation processes in irregular potential relief (direct problem) and interpretation of characteristics of nanosystems with fast ion transport (inverse problem).
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