The problem of mass manufacturing electrode structures suitable for contacting nanoscale elements lies primarily in the difficulty of fabricating a nanometre-scale gap between two electrodes in a well controlled, highly parallel manner. In ULSI circuit production, the gate and substrate in MOSFETs are routinely fabricated with a precise vertical spacing of 3 nm between them. In this work, we have investigated a number of highly parallel methods for the generation of nanogaps, including reconfiguration of the ubiquitous MOS device structure. The silicon dioxide layer that provides vertical separation and electrical insulation between two regions of silicon (the crystalline substrate and the poly-crystalline gate) gives a leakage current of 1 nA μm−2 at 1 V for an oxide thickness of 2 nm [1]. This will enable objects the size of single molecules that are held across this layer to be detected electrically if they provide currents on the nanoampere scale, assuming a parasitic area for leakage between gate and substrate of order 1 µm2. In the future this kind of device has the potential to provide a bolt-on technology for the fabrication of ULSI circuits in which conventional CMOS devices are directly hybridised with functional nanoscale elements.

Simulations have been made to analyze the use of molecular resonant tunneling diodes for local refresh of DRAM (Dynamic Random Access Memory) cells. Local refresh can be provided by a latch consisting of a pair of resonant tunneling diodes connected to the storage capacitor of the cell. Such a solution would significantly reduce the standby power consumption of the DRAM cell. We have compared the requirements on the resonant tunneling diodes for proper refresh operation with the electrical properties of published molecules with resonant IV-curves. The simulations show that no molecules with resonant electrical properties published so far in the literature have properties making them useful for this particular application. This is true also for low temperature operation. The issues of maximum tolerable series resistance and of maximum tolerable fluctuations in the number of attached molecules have also been addressed. Our results show that the focus for development of molecules with resonant electrical properties should be to find molecules with resonance for lower applied voltages and lower current levels than the molecules published so far. If the synthesis of new molecules with attractive properties is successful the merging of silicon technology and molecular electronics, for instance for new generations of DRAM cells, is a realistic future path of microelectronics.

Rod-shaped dinuclear Ru/Os complexes, [Os(bimpy-X)(BL)M(bimpyH2)]n+( M = Os or Ru; bimpyH2 = 2,6-bis(benzimidazol-2-yl)pyridine, X = anchoring group such as disulfide and phosphonic acid, BL =bis tridentate ligand), as a potential candidate for molecular devices have been successfully self-assembled on gold or indium-tin oxide (ITO) electrode by using anchoring ligands. The Ru/Os assembled complexes on the solid surface were well characterized by means of MALDI-TOF mass spectrometry, XPS, and electrochemical measurements. Novel proton-coupled electron transfer reaction of the self-assembled dinuclear complex on M(bimpyH2) moiety (M = Ru or Os) was confirmed by analyzing the plots of oxidation potential, E1/2, vs pH. In the case of M = Os and BL = 1,4-bis(terpyridyl)benzene (btpb), two stepwise one-electron oxidation waves were observed at 0.67 V for the Os(III/II) process and 0.88 V vs Ag/AgCl for the Ru(III/II) process in CH3CN/H2O at pH 1.0. The E1/2-pH diagram reveals the intercrossing of Ru(II/III) and Os(II/III) processes at around pH 5.5. Therefore, the intramolecular electron transfer can be controlled by pH. Proton-gated electron rectifying effect was observed in this Ru-Os dinuclear complex.

A micro-fabricated pore is constructed and tested so that it can be used to characterize biological entities. The pore is prepared by bulk micro-machining of a silicon wafer. An oxide coated silicon diaphragm with the pore is placed between two chambers containing ionic buffer solutions to mimic a bilayer system. If a voltage is applied across the pore, electrophoretic passage of charged entities can be electrically detected through changes in the ionic current flow. When the entities traverse the pore, the ionic current is blocked and a decrease in the current can be observed. As an initial test case, negatively charged polystyrene beads which were 2.38μm in diameter, were electrophoretically driven across the pore. Then the bacterium Listeria innocua, suspended in Tris-glycine buffer, was also electrophoretically driven through the pore and its effective mobility was extracted. The device can also be used to study the interactions between organisms and the micro-fabricated surfaces. Work is continuing to scale the pore to the sub-100A range to be used for characterization and possible sequencing of single molecules such as DNA.

The pressure filling of anodic alumina templates with molten bismuth has been used to synthesize single crystalline bismuth nanowires with diameters ranging from 7 to 200nm and lengths of 50μm. The nanowires are separated by dissolving the template, and electrodes are affixed to single Bi nanowires on Si substrates. A focused ion beam (FIB) technique is used first to sputter off the oxide from the nanowires with a Ga ion beam and then to deposit Pt without breaking vacuum. The resistivity of a 200nm diameter Bi nanowire is found to be only slightly greater than the bulk value, while preliminary measurements indicate that the resistivity of a 100nm diameter nanowire is significantly larger than bulk. The temperature dependence of the resistivity of a 100nm nanowire is modeled by considering the temperature dependent band parameters and the quantized band structure of the nanowires. This theoretical model is consistent with the experimental results.

We describe our strategies and results in the preparation of supramolecularly ordered ultrathin films of DNA assemblies using the layer-by-layer (LbL) alternate polyelectrolyte adsorption technique. The properties of DNA are intimately associated with their polyelectrolyte behavior in solution. Deposition at interfaces is governed by conformation, orientation, and charge density of these biomolecules in relation to the physisorption phenomena in oppositely charged surfaces. Thus, controlling the nature of surfaces (polymer charge density, ionic strength, other non-covalent interactions, etc.) is important in modifying the adsorption phenomena. In this work, differences in adsorption and incorporation of DNA with dyes, linear polymers and dendrimers are highlighted. A number of surface sensitive spectroscopic and microscopic techniques were used to probe the adsorption and multilayer assembly phenomena, e.g. surface plasmon resonance spectroscopy (SPS), AFM, quartz crystal microbalance (QCM) and ellipsometry. These studies are important for future applications such as the use of polycations as non-viral gene transfection vectors for drug-delivery and DNA adsorption on microarray surfaces. By combining with the alternate assembly of azobenzene and phthalocyanine dyes, we have been able to prepare optobiolelectronic substrates where the phenomena of irradiation and electrochemistry can be used to probe the ordering and response of these films.

In an effort to better understand the plasticity of the tempered martensitic steels, the strain-hardening of two 7-9Cr steels is examined in terms of dislocation mechanics. It is shown that, over the temperature range investigated (173K-523K), the strain-hardening as a function of stress can be described by an equation taking account the dislocation storage and annihilation. The model of strain-hardening used in this study is based on the original Kocks description of the dislocation density evolution with plastic strain but the heterogeneous distribution of dislocations resulting from the lath boundaries and prior austenite grain boundaries is taking into account. The effect of stress and temperature on the storage and annihilation is discussed. The relation between the determined mean dislocation path associated to the heterogeneous lath dislocation structure and the transmission electron microscope observations performed on the two different steels is outlined.

The n-InP | poly(pyrrole) interface is used as a case study to discuss the calculation of the transmission coefficient, describing the probability of majority carrier transfer, at a non-ideal semiconductor interface exhibiting anomalous behavior assumed to be due to a spatial distribution of barrier heights. The most notable anomaly is a weaker dependence of current on voltage than predicted by thermionic emission (i.e. quality or ideality factor greater than unity). Central to this discussion is the calculation of the equilibrium exchange current density Jo and barrier height Φb in light of a heterogeneous and potentially voltage-dependent barrier distribution. Various approaches to the measurement of Φb and Jovalid for semiconductor interfaces characterized by a uniform, voltage- and temperature-independent barrier are discussed when applied to a heterogeneous interface. In particular, the use of a capacitance-voltage measured barrier is demonstrated to result in an overestimation of κ whereas the use of a Richardson plot barrier is demonstrated to result in an underestimation. Depending on method, errors in excess of five orders-of-magnitude are observed for the n-InP | poly(pyrrole) interface under conditions where it exhibits only mildly anomalous behavior (ideality factor ≍ 1.2). The greatest confidence in the transmission coefficients occurs when the ideality factor is unity and the capacitance-voltage barrier agrees with the Richardson Plot barrier.

In this work, a protocol for investigating Bacteriorhodopsin (BR) biomimetic systems as ultrathin films is presented. BR is one of the most well studied proteins important for investigating the primary photo-event in vision processes. The use of macromolecular assembly approaches for deposition onto solid support substrates, e.g. SiOx, gold- or ITO-coated glass (electrode) provide advantages in that surface sensitive measurements can be used to correlate photocurrent generation, photoelectric response, pH change, chromophore behavior, etc. with protein orientation at interfaces. Membrane and protein morphology were correlated to measurements using surface sensitive techniques, such as atomic force microscopy (AFM), ellipsometry, quartz crystal microbalance (QCM), etc. on solid-substrate systems. These studies can lead to applications in optobioelectronic devices (biosensors) including patterning in transducer array configurations, where the film structure is important. Hybrid films are possible with supramolecular assembly approaches, e.g. adsorption of membrane with lipidbilayers. We report our initial results on highly ordered and oriented BR protein arrays of controlled thickness, layer order, and orientation. This was done primarily using the alternate polyelectrolyte deposition (APD) or layer-by-layer (LbL) approach to functionalize substrate surfaces.

The use of the DNA duplex as a molecular wire is discussed with particular attention to recent experimental findings. Experimental studies of photo-excited hole dynamics in DNA can be understood within the phenomenological hopping model. However a microscopic first principles approach requires taking into account the interaction between charge and duplex degrees of freedom. The nature of possible metallic native DNA behavior is discussed.