[show abstract][hide abstract] ABSTRACT: The primary metric for gauging progress in the various semiconductor integrated circuit technologies is the spacing, or pitch, between the most closely spaced wires within a dynamic random access memory (DRAM) circuit. Modern DRAM circuits have 140 nm pitch wires and a memory cell size of 0.0408 mum(2). Improving integrated circuit technology will require that these dimensions decrease over time. However, at present a large fraction of the patterning and materials requirements that we expect to need for the construction of new integrated circuit technologies in 2013 have 'no known solution'. Promising ingredients for advances in integrated circuit technology are nanowires, molecular electronics and defect-tolerant architectures, as demonstrated by reports of single devices and small circuits. Methods of extending these approaches to large-scale, high-density circuitry are largely undeveloped. Here we describe a 160,000-bit molecular electronic memory circuit, fabricated at a density of 10(11) bits cm(-2) (pitch 33 nm; memory cell size 0.0011 microm2), that is, roughly analogous to the dimensions of a DRAM circuit projected to be available by 2020. A monolayer of bistable, rotaxane molecules served as the data storage elements. Although the circuit has large numbers of defects, those defects could be readily identified through electronic testing and isolated using software coding. The working bits were then configured to form a fully functional random access memory circuit for storing and retrieving information.
[show abstract][hide abstract] ABSTRACT: Standard apparent rate constants for the reduction of bis(biphenyl)chromium(I) tetraphenylborate on hanging mercury electrodes in N,N-dimethylformamide were determined from cyclic voltammetry in a two-electrode system. The kinetic data were extracted from multicyclic voltammograms with the help of digital simulation. The numerical simulation procedure accounts for the uncompensated potential drops due to the faradaic and double layer charging currents, allows the incorporation of constant or potential-dependent (experimental) double layer capacitance data and permits the selection of linear or spherical diffusion geometry. Simulations show the importance of the rigorous calculation of capacitive current for the precise determination of rate constants of fast electrode processes. Error limits in the ksapp-values due to uncertainties in measured resistances and double layer capacitances can be assessed. The apparent standard rate constants for bis(biphenyl)chromium(I) couple obtained from this procedure proved that the increase in the reaction rate constants with the concentration of the supproting electrolyte is an electrochemical characteristic of this system and not due to an uncompensated resistance.
[show abstract][hide abstract] ABSTRACT: Photochromic compounds change their color under illumination. In most instances, a colorless state switches to a colored one upon ultraviolet irradiation. The photogenerated species reverts to the original one either by thermal means or upon visible irradiation. These reversible transformations are accompanied by pronounced structural and electronic modifications, which often alter the ability of the photochromic compound to emit light. Under these conditions, the photoinduced and reversible interconversion of the colorless and colored states results in the modulation of the fluorescence intensity. Alternatively, fluorescence modulation can be implemented by attaching covalently a fluorescent group to a photochromic compound. Photoinduced changes in the dipole moment or conjugation of the photochromic component can then be designed to alter the emissive behavior of the fluorescent appendage. Similarly, photoinduced shifts in the redox potential or absorption wavelength of the photochromic fragment can be engineered to activate electron or energy, respectively, transfer pathways. Both processes can efficiently quench the fluorescence of the emissive component. Furthermore, the reversible absorption changes of a photochromic compound can effectively filter the emission of a compatible, but separate, fluorophore as long as the emission bands of the latter overlap the absorption bands of one of the two states of the former. When this design requirement is satisfied, fluorescence modulation can be achieved even if the two functional components are operated in distinct environments. Thus, either one of these ingenious mechanisms can be exploited to regulate the emissive behavior of collections of molecules in solution or even in rigid matrixes. In fact, the investigation of these fascinating systems can eventually lead to novel photoresponsive materials for photonic applications, while contributing to advance our basic understanding of the photochemical and photophysical properties of organic compounds.
The Journal of Physical Chemistry A 09/2005; 109(33):7343-52. · 2.77 Impact Factor
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