Tunneling junctions

Ainong the first TFIz mixers to be constructed were those based on room-temperature Schottky diodes [11]. Over the past decade, new mixers based on superconducting tunnel junctions have been developed that have effective noise levels only a few tunes the quantum limit of [12]. Flowever, certain conditions... 

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... 

The promise of 3-D detectors The ideal detector would be able to measure the wavelength dimension of each photon in addition to the two spatial dimensions - a 3-D detector . There is progress being made on 3-D detectors - for example, the superconducting tunneling junction (STJ). However, at present, 3-D detectors are experimental and have only achieved limited wavelength resolution ( /5 < 25) with relatively slow count rates (few kHz per pixel) on a small number of pixels 100 j. Since these devices are experimental and are not being used... 

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. 

The tip-particle distance, using (Vbias = 1 V, /tmmei = 1 nA) as tunnel parameters does not correspond to that needed to observe the Coulomb staircase. The particle-substrate distance is fixed by the coating with dodecanethiol. Hence the two tunnel junctions are characterized by fixed parameters. Similar Coulomb blockade behavior has been observed [58,59]. 

Rendell, R., Scalapino, D. and Miihlschlegel, B. (1978) Role of local plasmon modes in light emission from small-particle tunnel junctions. Rhys. Rev. Lett., 41, 1746-1750. 

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 .

Figure 11. Experimental and predicted differential conductance plots of the double-island device of Figure 10(b). (a) Differential conductance measured at 4.2 K four peaks are found per gate period. Above the threshold for the Coulomb blockade, the current can be described as linear with small oscillations superposed, which give the peaks in dljdVj s- The linear component corresponds to a resistance of 20 GQ. (b) Electrical modeling of the device. The silicon substrate acts as a common gate electrode for both islands, (c) Monte Carlo simulation of a stability plot for the double-island device at 4.2 K with capacitance values obtained from finite-element modeling Cq = 0.84aF (island-gate capacitance). Cm = 3.7aF (inter-island capacitance). Cl = 4.9 aF (lead-island capacitance) the left, middle and right tunnel junction resistances were, respectively, set to 0.1, 10 and 10 GQ to reproduce the experimental data. (Reprinted with permission from Ref [28], 2006, American Institute of Physics.)...

Figure 2.5 Schematic representation of the gap of a metal-oxide-vacuum-metal tunneling junction in the case of a low (a) and a high (b) sample bias voltage.

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]. 

Coulomb blockade thermometry (CBT) is based on the electric conductance characteristics of tunnel junctions. This type of thermometer has been developed at Jyvaskyla University. The basic results are reported in ref. [112],... 

The useful temperature range of CBT is defined by the number and size of the tunnel junctions. These are realized by vacuum evaporation of 100nm A1 layers (which are... 

Wold DJ, Frisbie CD (2000) Formation of metal-molecule-metal tunnel junctions microcontacts to alkanethiol monolayers with a conducting AFM tip. J Am Chem Soc 122 (12) 2970-2971... 

Muller CJ, van Ruitenbeek JM, de Jongh LJ (1992) Experimental observation of the transition from weak link to tunnel junction. Physica C191 485-504... 

Averin DV, Likharev KK (1986) Coulomb blockade of tunneling, and coherent oscillations in small tunnel junctions. J Low Temp Phys 62 345-372... 

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... 

Pobelov I, Li Z, Wandlowski T (2008) Electrolyte gating in redox-active tunneling junctions -an electrochemical STM approach. J Am Chem Soc 130 16045-16054... 

Delonno E, Tseng HR, Harvey DD, Stoddard JF, Heat JR (2006) Infrared spectroscopic characterization of [2]rotaxane molecular switch tunnel junction devices. J Phys Chem B 110 7609-7612... 

Nijhuis CA, Reus WF, Barber JR, Dickey MD, Whitesides GM (2010) Charge transport and rectification in arrays of SAM-based tunneling junctions. Nano Lett 10 3611-3619... 

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... 

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