A 3-terminal single molecule transducer is presented which is able to measure tunnel current intensities. The conformation of a pyrene–phenyl molecule is changed under an intramolecular inelastic current effect. This conformation change is detected by a third lateral electrode interacting also with the molecule. The full multi-channel electronic scattering matrix of the device is calculated taking into account the chemisorption of the molecule at one end and the details mechanics of the conformation change of this molecule. A semi-classical model is used to describe the intramolecular transduction effect between the electrons transferred through the molecule and its conformation change. It results a linear transduction curve between the input and the detection currents of the device for a range of tunnel current of interest for mono-molecular electronics.

A Morse manipulator like molecule able to modulate the electronic standing wave pattern of metallic Shockley surface states is presented. Its design is based on a molecular arm holding a phenyl whose distance to the metal surface is controlled by the tip apex of an STM. The standing wave patterns are calculated using an extension of the N-ESQC technique. The corrugation of the surface state modulation is proposed to be detected by a small 127 k Omega atomic scale tunnel junction supposed positioned very close to the surface and a few nanometers away from the molecule. A variation of 150 Omega of this junction resistance is detected for a phenyl surface distance variation from 0.4 to 0.24 nm. (c) 2006 Elsevier B.V. All rights reserved.

In Stadler et al (2003 Nanotechnology 14 138), a scheme for a molecular memory was presented. It was based on the influence of the positions of chemical side-groups attached to aromatic molecules on the paths for electrons propagating through these molecules in the ballistic and tunnelling transport regimes. Here we extend this concept in the following ways. (i) A graphical method is derived from an electron scattering formalism based on a topological Huckel description, which allows us to estimate whether the electron transport between two electrodes attached to specific atomic sites in an arbitrary molecule is finite or zero at the Fermi level. (ii) The same scheme that was used for the implementation of the molecular memory is extended to logic functions, in particular a half-adder. (iii) A more realistic description of the chemical nature of the proposed intra-molecular circuits is achieved by using the elastic scattering quantum chemistry (ESQC) technique in an extended Huckel implementation and by specifying the side-groups as nitro-groups, which are rotated in order to feed the signal inputs into the computational circuit.(Some figures in this article are in colour only in the electronic version).

The design of a 1-bit half-adder diode logic circuit inside a single molecule is investigated, with the chemical groups for diodes and wires bonded together to form the molecular circuit. With a circuit working in the ballistic transport regime, interference effects between the different electron paths in the circuit make the optimization of the circuit's logic function very delicate. In the tunnelling regime, these effects are partly suppressed. But the exponential decay of the current with the wire length imposes additional constraints for circuit design. A programmable gate logic array-like architecture would be expected be more useful for the design of a 1-bit adder in the ballistic regime due to the regularity of the circuit lattice, which might reduce interferences. On the other hand, a dedicated design which minimizes the amount of wiring might be the better choice for the tunnelling regime. However, we find that the logic output of classical diode logic circuits cannot be reproduced in either regime because Kirchhoff-like circuit rules do not apply. Furthermore, the geometry dependence of electron transmission in both regimes would make it impractical to build up logical functions like the SUM of an adder from simple OR- and AND-gates, even if the output pattern of these gates could be perfectly reproduced.

Using the extended Hückel molecular orbital–N elastic scattering quantum chemistry technique, the scattering electronic properties of four-and two-electrode monomolecular Wheatstone bridges are discussed. Simple intramolecular circuit rules are given for the design of an intramolecular electronic circuit integrated in a single molecule. The balancing condition of the four-electrode monomolecular Wheatstone bridge is provided. The value of the tuning resistance of the bridge is the same applying the new tunnel circuit rules and the standard Kirchhoff node and mesh laws. Only the way of reaching the equilibrium of the bridge is different.

The possibilities for the design of larger diode logic circuits such as a one-bit half-adder inside a molecule are investigated, based on a recent extension of the elastic scattering quantum chemistry technique. Since any diode logic circuit for an adder needs OR-gates and AND-gates as basic components and the properties of OR-gates have already been discussed in the ballistic and tunnelling electron transport regime, we focus on the more complicated AND-gates in the present work. For this case the output current, calculated from the transmission coefficients by using the Landauer-Büttiker formula, shows four different logical levels instead of two. The origin of this level variety is analysed in detail. The concept of programmable gate logic arrays is also addressed, where for intra-molecular circuits distinct deviations from earlier macroscopic or mesoscopic implementations of this scheme are found.

Based on the N electrodes elastic scattering quantum chemistry (NESQC) technique, an intramolecular circuit simulator is presented for the design of electronic logic functions integrated inside a single molecule interconnected to the N electrodes. Using molecular rectifier groups, a molecule-OR and a molecule-AND are designed, their current-voltage characteristics calculated and their logic response presented. Both the OR and AND molecules have approximatively the targeted function. The running current of the OR gate, 10 fA, is quite low and the AND gate works only in an output voltage mode. This forbids the design of larger logic functions inside a single molecule with molecular rectifiers.

The scattering matrix technique is extended to describe the electronic transport characteristics of intramolecular circuits driven in a ballistic or a tunnel transport regime. The circuit is assumed to be connected by N electrodes. As a working example, the electronic properties of a T-node circuit are presented leading to the design of an OR logic gate working in a ballistic regime. In the tunnel regime, only the ``node'' Kirchhoff law of circuit remains valid at the nodes of an intramolecular tunnel circuit and the electronic characteristics of the branches composing the circuit are mutually independent. It results in a difficult design of a logic OR intramolecular gate of high performance and stability, pointing out the urge for new architectures to implement complex logic functions inside a single molecule.

A recent proposal, in which 1-bit memory cells and simple logic gates such as NOT and NOR gates were based on C60 molecules in an electromechanical grid acting as transistors, is extended to larger architectures. In order to meet the requirements of standard digital circuit architectures, some modifications have to be made compared to the original model. For example, the number of transistors has to be increased from two to thirteen for a single NOR gate to guarantee balanced logical levels. In the scheme employed to achieve this in the current work, all two-input gates, namely OR, AND and XOR gates, can be easily constructed using the same concept. These gates are then used to design a 1-bit full-adder and a clocked D-latch, which are then combined with the earlier proposed 1-bit memory cell as the basic constituents of a memory/adder model. Clocked signal transmissions, corresponding to the read process of two 2-bit words from memory cells, their movement through registers and finally their addition and passing the output through another register, are simulated using the electrical circuit software SPICE. For the design of this memory/adder circuit, 464 single C60 transistors are used.

We study the fluctuations of membranes with area and curvature elasticity and calculate the renormalization of the curvature elastic constants due to thermal fluctuations. For the mean curvature elastic constant the result is the same as obtained previously for “ideal membranes” which resist only to curvature deformations. The renormalization of the gaussian curvature, on the other hand, depends on the elastic contants. In an incompressible membrane, it is five times weaker than in an ideal membrane.

We study the properties of topological excitations in the two-dimensional XY model by performing a loop expansion on the duality-transformed version of the model. The results for internal energy and heat capacity are in good agreement with recent Monte Carlo data.

We investigate the melting transition of an ensemble of two-dimensional crystal defects in a recently developed local lattice model, which describes these defects via a duality transformation. We calculate the mean field approximation, the one-loop correction to it, and give the high temperature series up to β 11 . The result is in excellent agreement with recent Monte Carlo simulations Etude de la fusion d'un ensemble 2D de defauts cristallins, a l'aide d'un modele reticulaire local qui represente ces defauts d'une maniere duale. Calcul a l'approximation du champ moyen suivi des corrections a une boucle. Developpement a haute temperature jusqu'a l'ordre β 11 . Accord avec des simulations numeriques recentes par la methode de Monte Carlo

We calculate the two-loop effective action of O(N) spin models on the lattice in a 1D expansion to order 1D2. The resulting free energy depends on β = 1T and the order parameter Φ. It matches the high and low temperature regimes and is quite reliable close to the phase transition where it has a simple Landau expansion.

A 740 L1Hz SAV oscillator is developed for application as a fixed local oscillator in the transmitter of a satellite system. The SAN oscillator, in a 2.4 cubic inch package contains a heater, second stage amplif ier/buff er , power leveling and harmonic suppression filtering. The advantages of this system are the reduced size and complexity due to the elimination of the multiplier chains required in bulkwave oscillators, a short term stability of 2 X 10-10 for 100 second averaging times, low single side band noise floor and 1.1:l VSWR. Theoretical and practical consideration in the optimization of SAW resonator design parameters for short term stability and phase noise are discussed. A fabrication process resulting in improved long term stability and turning point control is presented. Fabrication tolerance variations in resonance frequency are dealt with by a plasma process trim and by design optimization of static to notional capacity ratio or pulling range of the resonator. The introduction of seniconductor doping techniques reduces metal migration and attendent instabilities due to drive level.

We reexamine theoretically the fluctuation-induced conductivity of dirty type-II superconductors in bulk above the superconducting transition [i. e., $H>{H}_{c2}(T)$ or $T>{T}_{c}(H)$]. In our calculations, we have included the contribution from dynamic fluctuations. The resulting conductivity decreases much faster than predicted by earlier theories, as the field (or the temperature) increases, which satisfactorily accounts for the experimental data obtained by Hake et al., and by Johnson et al.

By the use of Ginzburg-Landau equations, which include the effect arising from the sinusoidal variation of the impurity concentration in one direction, the stability of variety of the vortex lattice configuration in the type II superconductors is studied.