Tunnel-junction electronic

The Coulomb blockade effect was originally observed in experiments on small metallic or superconducting particles [138-141], in which nanometer-sized metallic grains were embedded within a metal oxide-metal tunnel junction. Electronic measurements performed on these systems at low temperatures (T 1 K) revealed an anomalous behavior of the resistance (or differential capacitance) at zero bias. It was realized that this behavior was caused by the extremely small capacitance of the metallic particles. In a simple model, a spherical particle of diameter d embedded in a... 

The greatest potential appHcation for single-electron devices Hes in digital circuits. However, a number of other appHcations exist, including current standards and ultrasensitive electrometers (70,71). SETs are not unique to compound semiconductors, and in fact a great deal of work has been carried out in other material systems, including Al—AlO —A1 tunnel junctions. A review of single-electron phenomena is available (72). 

Another technique that has proved useful in establishing chemical bonding of coupling agents at interfaces is inelastic electron tunneling spectroscopy (ITES). For example. Van Velzen [16] examined 3-(trimethoxysilyl)propanethiol by this technique. Approximately monolayer quantities of this silane were adsorbed on the barrier oxide of an aluminum-aluminum oxide-metal tunneling junction two metals were investigated, lead and silver. It was concluded that the silane is... 

D. V. Averim and K. K. Likharev developed a theory for describing the behavior of small tunneling junctions based on electron interactions. They had started from previous work on Josephson junctions (Likharev and Zorin 1985, Ben-Jacob 1985, Averin and Likharev 1986b) and established the fundamental features of the single-charging phenomena. Their work is based on a quantization theory and handles the tunneling phenomenon as a perturbation, described by annihilation and creation operators of a Hamiltonian. 

Among these one of the most promising concepts is the development of single electron (SE) devices, which retain their scalability down to the molecular level. At present, due to exploitation of charging (Coulomb) effects in metallic SE devices comprising tunnel junctions with submicrometer size, individual charge carriers can be handled... 

Figure 1. The tunneling of a single electron (SE) between two metal electrodes through an intermediate island (quantum dot) can be blocked of the electrostatic energy of a single excess electron trapped on the central island. In case of non-symmetric tunneling barriers (e.g. tunneling junction on the left, and ideal (infinite-resistance) capacitor on the right), this device model describes a SE box .

The control parameter in an STM, the current in the tunneling junction, is always due to the same physical process. An electron in one lead of the junction has a nonvanishing probability to pass the potential barrier between the two sides and to tunnel into the other lead. However, this process is highly influenced by (i) the distance between the leads, (ii) the chemical composition of the surface and tip, (iii) the electronic structure of both the systems, (iv) the chemical interactions between the surface and the tip atoms, (v) the electrostatic interactions of the sample and tip. The main problem, from a theoretical point of view, is that the order of importance of all these effects depends generally on the distance and therefore on the tunneling conditions [5-8]. 

Keywords Charge transport Electrochemical molecular junctions Electron tunnelling Electron hopping Molecular electronics Photoactive molecular junctions... 

Slowinski K, Fong HKY, Majda M (1999) Mercury-mercury tunneling junctions. 1. Electron tunneling across symmetric and asymmetric alkanethiolate bilayers. J Am Chem Soc 103 7257-7261... 

Young RL, Nguyen PT, Slowinski K (2003) Long-range electron transfer through monolayers and bilayers of alkanethiols in electrochemically controlled Hg-Hg tunneling junctions. J Am Chem Soc 125 5948-5953... 

Equation (1) suggests that tunnel junctions should be ohmic. This is true only for very small bias. A much better description of the tunneling current results when the effects of barrier shape, changes in barrier with applied potential, and effective mass of the electron are all included. An example of such an improved relationship is given by (2), where / is the current density, a is a unitless parameter used to account empirically for non-rectangular barrier shape and deviations in the effective electron mass, and barrier height given by B = (L + work function of the left-hand metal ... 

Li B, Zeng C, Zhao J, Yang J, Hou JD, Zhu Q (2006) Single-electron tunneling spectroscopy of single C60 in double-barrier tunnel junction. J Chem Phys 124 064709-064720... 

The principle of the light-emitting tunnel junction warrants particular mention because of the similarities which exist between the CTRIPS process for electron injection and the emission process which occurs in tunnel junctions /11,12/. In the first case electrons... 

Figure 1. Schematic representation of an inelastic electron tunnel junction.

The details of the transport process occurring in atomically resolved STM are significantly different from the tunneling process associated with classical metal-insulator-metal (M-I-M) tunnel junctions. In the latter case the thickness of the insulator between the conducting electrodes is typically 20-30 A, whereas the ability to resolve the electronic density of individual atoms using STM requires a lateral resolution of 2 A. To obtain such... 

FIG. 12. A schematic representation of the possible role of water on the potential profile within the tunnel junction. Fast electronic polarization of the solvent diminishes the barrier, while the possibility of forming an intermediate hydrated electron resonant state has also been suggested. (From Ref. 96.)... 

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