Artificial atom

SET events at elevated temperature. Together with the limited number of free electrons, this may lead us to regard them as artificial atoms. This raises fundamental questions about the design of artificial molecules or artificial solids built up from these nanoscale sub-units [37-39]. Remade and Levine reviewed the ideas associated with the use of chemically fabricated quantum dots as building blocks for a new state of matter [40]. 

Quantum dots are the engineered counterparts to inorganic materials such as groups IV, III-V and II-VI semiconductors. These structures are prepared by complex techniques such as molecular beam epitaxy (MBE), lithography or self-assembly, much more complex than the conventional chemical synthesis. Quantum dots are usually termed artificial atoms (OD) with dimensions larger than 20-30 nm, limited by the preparation techniques. Quantum confinement, single electron transport. Coulomb blockade and related quantum effects are revealed with these OD structures (Smith, 1996). 2D arrays of such OD artificial atoms can be achieved leading to artificial periodic structures. 

Fig. 1. (a) The first successful work of artificial atomic structures created by manipu-... 

Over the last decade, we have shown that DNA can be used to construct a wide range of such nanocrystal molecules. The first such example of using DNA to organize nanocrystal molecules was shown in 1996 by Alivisatos and Schultz [12] (Fig. 9.4). This work appeared simultaneously with the work by Mirkin and Letsinger, who used DNA to assemble arrays of nanoparticles [13]. Indeed, if the nanocrystal is thought of as an artificial atom, then the construction of artificial solids is a complementary activity to the construction of artificial molecules, and this has been investigated extensively as well [14]. 

Yttrium(III) lies on the same straight line if assigned an artificial atomic number of 67.5. i.e. between those of holmium and erbium. 

T. Chakraborty, Quantum Dots A Survey of the Properties of Artificial Atoms, Elsevier, New York, 1999. 

With an STM tip as engineering tool for surface modification, artificial atomic-scale architectures can be fabricated [70-72], chemical reactions on surfaces can be induced [63-65] and properties of single molecules can be studied at an atomic level [20, 21]. Manipulations with an STM tip can be performed by precisely controlling tip-sample interactions using tunneling electrons or the inhomogeneous electric field between the tip and sample. 

In a quantum dot, which is also often called an artificial atom, the excitons are confined in all three spatial dimensions. In a bulk semiconductor, an electron-hole pair is bound within the Bohr exciton radius, which is characteristic for each type of semiconductor. A quantum dot is smaller than the Bohr exciton radius, which causes the appearance of discrete energy levels. The bandgap, AE, between the valance and conduction band of the semiconductor is a function of the nanocrystaTs size and shape. Q-dots feature slightly lower luminescence quantum yields than traditional organic fluorophors but... 

Ashoori, R. C., Electrons in artificial atoms, Nature, 379, 413M19 (1996). 

McEuen, P. L., Artificial atoms new boxes for electrons. Science, 278,1729-1730 (1997). 

Gustafsson MV, Aref T, Kockum AF, Ekstrom MK, Johansson G, Delsing P (2014) Propagating phonons coupled to an artificial atom. Science 346 207-211... 

Perhaps one of the most demanding challenges in current preparational research is the directed coupling of semiconductor nanoparticles. If the QDs were called artificial atoms, this endeavor would yield artificial molecules, and the challenge would be to create such QD molecules in a desired maimer to form, for example, dimers ( two-atomic QD molecules ) of various compositions, AB4 molecules, and so on. As the field is about to emerge from its infant status, the very first attempts in this direction are reported in the following sections. 

This size-quantization effect may be regarded as the onset of the metal-nonmetal transition such that, in another terminology, these quantum-size nanopartides may also labeled as artificial atoms [20-22]. 

Students in their first chemistry course learn that the simplest molecule, H2, is formed by the overlap of the electron wavefunctions centered on the individual hydrogen atoms. Correspondingly, the wavefunctions of artificial atoms can also... 

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