摘要:

In a mechanic molecular switch, electron transfer processes are controlled by a conformation change of the molecule induced by the move of one of its part. The change in through ligand electronic coupling induced by the displacement or the rotation of benzene ring(s) included in a non saturated ligand are discussed. This change is used to build a flip‐flop switch constituted of an isomerizable handle connected to a bis 1,4(4 pyridyl ethynyl) benzene ligand. Isomerization of the handle produces a rotation of the central benzene. Calculated energetic and electron transfer properties of this switch are presented.

ISSN:0094-243X    

DOI:10.1063/1.42677

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The association of pentammine ruthenium(II) with the reducible ligand 44’azopyridine leads to a pH induced redox reaction in which ruthenium is oxidized to the III state, while 44’azopyridine is reduced to hydrazopyridine. In this process, the conjugated ligand is transformed in a nonconjugated one, with loss of its intramolecular electron transfer properties. In order to exploit thiscontrol of an intramolecularelectron transfer by a protonation process, we have prepared ‘‘shish‐kebab’’ polymers by first inserting ruthenium in tetrakis (3,5‐diterbutyl 4‐hydroxyphenyl) porphyrin under a CO atmosphere. The resulting Ru(CO)porphyrin complex is photochemically decarbonylated in the presence of bridging ligands (44×azopyridine or pyrazine). Polymers are thus obtained, which can be oxidized by iodine, giving rise to intervalence transitions between ruthenium(II) and (III) in the near‐infrared. This provides a convenient way to monitor electron transfer along the polymer chain. In the case of 44’azopyridine, the pH induced redox reaction is again observed. Starting from a homovalent ruthenium(II) chain, this gives the possibility to switch ‘‘ON’’ or ‘‘OFF’’ the intervalence transition by a protonation/deprotonation reaction.

ISSN:0094-243X    

DOI:10.1063/1.42663

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper describes fabrication methods of functional molecule materials and molecular and/or mesoscopic level conducting polymer multilayers toward molecular device, by examples: Functional molecule incorporating conducting polymer (Functional molecule materials), ultrahigh anisotropic conducting polymere LB multilayers, 50A level conducting polymer heteromultilayers (control of quantum well), and conducting polymer network.

ISSN:0094-243X    

DOI:10.1063/1.42671

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Protein molecules have successfully been incorporated in bioelectronic molecular devices through the molecular wire or interface of conducting polymer. Such enzymes as glucose oxidase and fructose dehydrogenase were adsorbed on the platinum electrode surface, which was followed by the electropolymerization of pyrrole to deposit an ultimately thin layer of polypyrrole on the electrode surface. Alcohol dehydrogenase was immobilized in a polypyrrole membrane with NAD and Meldora’s blue in the similar manner on the electrode surface. The electron transfer from the electron transfer sites of these enzymes to the corresponding electrode has been promoted through the molecular wire. It has been demonstrated that the enzyme activity is modulated by changing the potential of the electrode with which the enzyme is connected through the molecular wire. On the basis of the electronic characteristics of these enzyme proteins the design principles of biomolecular electron devices have been proposed.

ISSN:0094-243X    

DOI:10.1063/1.42672

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The ultimate resolution of electron optical systems far exceeds that of conventional electron resists. Electron beams less than 0.5 nm in diameter can be produced but the smallest features that can be written with these beams in standard resists are about 10 nm–20 nm in size and the minimum spacing for closely spaced lines is about 40 nm. The reason for this loss of resolution is not clear. It may be due to the range of the Coulomb interaction between the beam electrons and the resist molecules, due to the straggling of secondary electrons away from the primary beam, due to the high molecular weight of the resist or due to the mechanism of the development process. In the first two cases resolution would improve if the photon energy required to effect exposure was increased. With PMMA, the most studied resist, the energy required for exposure is about 5 eV. We have been working with an alternative nanolithography process using SiO2layers that has about three times better resolution than PMMA. We assume that the resolution is better because the photon energy required to effect exposure is higher than it is with PMMA. THe process relies on the electron beam induced enhancement of the etch rate of SiO2in buffered hydrofluoric acid and requires a much heavier exposure dose than PMMA. The process was discovered in the 1960s but its ultra‐high resolution was only identified last year in our Cambridge laboratory. SiO2is used in mamy semiconductor devices so the method should be readily applicable to device fabrication. This paper reviews the resolution limits of the various nanolithography techniques including ‘hole‐drilling’ and contamination resist and compares them with the SiO2process.

ISSN:0094-243X    

DOI:10.1063/1.42673

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The capability of lithium fluoride based films as a self‐developing resist for ultra‐high resolution electron beam lithography is demonstrated. The advantage of lithium fluoride is the relatively low critical exposure dose, compared to other metal halides. Homogeneous and fine‐crystalline films have been deposited using a special evaporation technique. We studied the exposure characteristics of this resist and achieved patterns with lateral dimensions below 10 nm. The properties of these films in RIE‐processes were investigated and pattern transfer into SiO2was performed.

ISSN:0094-243X    

DOI:10.1063/1.42674

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Two‐dimensional crystalline bacterial cell surface layers (S‐layers) are unique self assembly systems. They are composed of single (glyco)protein species with the inherent ability to recrystallise in suspension and on solid supports such as silica, mica, metals or synthetic polymers. Since S‐layers are composed of identical subunits functional groups are located on the lattice in an identical position and orientation. S‐layers are anisotropic structures with regard to their surface topography and distribution of charged groups. Pores in the lattice have identical size, morphology and physicochemical properties. In contrast to conventional solid supports where the functional groups are randomly distributed and oriented, crystalline bacterial surface layers allow for the first time the controlled immobilisation of (macro)molecules, leading to the formation of a monomolecular lattice. This potential is the basis for a broad spectrum of applications of S‐layers as patterning elements and immobilisation matrices in molecular nanotechnology.

ISSN:0094-243X    

DOI:10.1063/1.42675

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

By genetechnological modification of the biological photochrome bacteriorhodopsin a variety of new materials has been generated with photophysical properties adapted to the particular needs of various optical applications, like optically addressed spatial light modulators, real‐time interferometry, holographic pattern recognition and optical data storage. These materials were obtained by slight modifications of the amino acid sequence of wildtype bacteriorhodopsin. This new approach in material science illustrates the potential of gentechnological modifications of natural macromolecules in order to derive from them technically usable materials which advantageously employ their evolutionarily optimized properties.

ISSN:0094-243X    

DOI:10.1063/1.42651

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The static field third order polarizability, &ggr;xxxx(0;0,0,0), is calculated for an oligomeric series of disubstituted diphenyl polyenes and their bipolarons by using INDO‐PSDCI finite perturbation procedures. Our procedures have the advantage of maintaining a degree of size consistency that is difficult to achieve by using the sum‐over‐states approach. The chain length dependance of &ggr;xxxx(0;0,0,0) is calculated to be 21.6N1.9×10−36esu and 20.1N2.3×10−36esu for the neutral and bipolaronic species, respectively, where N is the number of carbon atoms in the polyene chain. Although our calculations agree with previous studies that predict that a bipolaron will have an enhanced third order polarizability relative to the corresponding neutral polyene, the length dependance that we observe for both the neutral and bipolaronic species is much smaller than that predicted by previous literature investigations.

ISSN:0094-243X    

DOI:10.1063/1.42652

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Bacteriorhodopsins (bR’s) modified by substitution of the chromophore with synthetic vitamin A analogues or by spontaneous mutation have been reported as successful examples of using biomaterials to construct molecular optoelectronic devices. The operation of these devices depends on desirable optical properties derived from molecular engineering. This report examines the effect of site‐directed mutagenesis on the photoelectric behavior of bR thin films with an emphasis on their application to the construction of molecular devices based on their unique photoelectric behavior. We examine the photoelectric signals induced by a microsecond light pulse in thin films which contain reconstituted oriented purple membrane sheets isolated from several mutant strains ofHalobacterium halobium. A recently developed expression system is used to synthesize mutant bR’s in their natural host,H. halobium. We then use a unique analytical method (tunable voltage clamp method) to investigate the effect of pH on the relaxation of two components of the photoelectric signals, B1 and B2. We found that for the four mutant bR’s examined, the pH dependence of the B2 component varies significantly. Our results suggest that genetic engineering approaches can produce mutant bR’s with altered photoelectric characteristics that can be exploited in the construction of devices.

ISSN:0094-243X    

DOI:10.1063/1.42653

出版商:AIP    

年代:1992

数据来源: AIP