Superlattices: problems and new opportunities, nanosolids.
Bottom Line:
Superlattice is simply a way of forming a uniform continuum for whatever purpose at hand.However, new opportunities in component-based nanostructures may lead the field of endeavor to new heights.The all important translational symmetry of solids is relaxed and local symmetry is needed in nanosolids.
Affiliation: University of North Carolina at Charlotte, Charlotte, NC 28223 USA. Tsu@uncc.edu.
ABSTRACT
Superlattices were introduced 40 years ago as man-made solids to enrich the class of materials for electronic and optoelectronic applications. The field metamorphosed to quantum wells and quantum dots, with ever decreasing dimensions dictated by the technological advancements in nanometer regime. In recent years, the field has gone beyond semiconductors to metals and organic solids. Superlattice is simply a way of forming a uniform continuum for whatever purpose at hand. There are problems with doping, defect-induced random switching, and I/O involving quantum dots. However, new opportunities in component-based nanostructures may lead the field of endeavor to new heights. The all important translational symmetry of solids is relaxed and local symmetry is needed in nanosolids. No MeSH data available. |
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Mentions: Capacitance classically defined as charge per volt is no longer correct in QDs, not only quantum mechanically, but also classically, mainly due to Coulomb repulsion among the electrons in a typical QD. When the number of electron becomes so large that they are pushed to the boundary, we reach the classical results that capacitance depends on geometry. We found that capacitance very much depends on number of electrons. We show results of N-electrons confined inside a dielectric sphere. A single electron is of course located at the center. With two, one pushed the other to the extremity of the boundary. For dielectric confinement, εin> εout, so that the induced charges at the boundary is of the same sign resulting in pushing the electron back from the boundary by its image, thereby achieving equilibrium. We calculated up to N = 108. Why? We basically obtained the periodic table of the chemical elements where all the elements are neutral. To compute the energy difference with N requires same number of charge as in atoms. Our computation of energy of interaction of N-electrons with that of N + 1 electrons is based on minimization of the total interaction energy of the electrons without changing the charge state by adding an electron in the center without changing the overall symmetry. Then the difference between N + 1 and N with one in the center is solely due to the change of symmetry. Our results show that we have basically generated the periodic table. Figure 5 shows the actual positions up to 12 electrons. And Figure 6 shows the ionization energy quite comparable to the measured ionization energy. The point is about demonstrating the role of symmetry. The trend is as follows: adding an addition electron costs energy particularly adding an odd number, or worse yet, adding a prime number. In fact, I want to convince you that the most unique features of nanoscale physics are affected by the change of symmetry. Therefore, conventional capacitance is only definable within a single phase, dictated by the unique symmetry. Measurements of capacitance are therefore related to exploring the symmetry. |
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Affiliation: University of North Carolina at Charlotte, Charlotte, NC 28223 USA. Tsu@uncc.edu.
No MeSH data available.