Nanoscale electrical properties

In addition to the described above methods, there are computational QM-MM (quantum mechanics-classic mechanics) methods in progress of development. They allow prediction and understanding of solvatochromism and fluorescence characteristics of dyes that are situated in various molecular structures changing electrical properties on nanoscale. Their electronic transitions and according microscopic structures are calculated using QM coupled to the point charges with Coulombic potentials. It is very important that in typical QM-MM simulations, no dielectric constant is involved Orientational dielectric effects come naturally from reorientation and translation of the elements of the system on the pathway of attaining the equilibrium. Dynamics of such complex systems as proteins embedded in natural environment may be revealed with femtosecond time resolution. In more detail, this topic is analyzed in this volume [76]. 

Similar educational opportunities abound for carbon. The diamond and graphite allotropes of carbon have been mainstays of chemistry classes for generations of students and provide a contrast between a three-dimensional structure of great hardness and a two-dimensional structure with lubricant properties, respectively. We now have what can be regarded as zero- and onedimensional counterparts - buckyballs and carbon nanotubes, respectively - with their rich diversity of structural relatives and physicochemical properties (4). These materials are being employed in a variety of nanoscale devices because of their unusual chemical, mechanical and electrical properties. 

The first and best known near-field technique to measure electrical properties in the nanoscale is of course Scanning Tunnelling Microscopy (STM). Since its invention by Binnig et al., STM has been used to explore the mechanisms of lots of phenomena on surfaces [289-294], ranging from experiments concerning the local work function to the use of an STM-tip to induce electropolymerisation [295]. Most of all, STM provides us with atomically resolved images of the surface structure. 

The magnetic, chemical, mechanical, optical, and electrical properties of materials change as their size approaches nanoscale and as the percentage of atoms at the... 

These characteristics make CP-AFM ideal for studying electrical transport of nanotubes, nanoparticle assemblies, micro- or nanofabricated semiconductor devices, and individual molecules. Detailed appraisal of these characterizations can be obtained by comparing CP-AFM and STM. Although CP-AFM and STM share high spatial resolution imaging capability (STM 0.1 mn CP-AFM -10 nm, due to larger tip apex) that is critical in linking nanoscale structure to transport properties, an important distinction is the position of the tip with respect to the sample. In the case of CP-AFM, a metal-coated tip is directly contacted to the sample under a controlled load. This means that the measured I V relationship is mainly affected by the electrical properties of the tip-sample contact. 

Figure 5.5.23 illustrates the electrical properties of a representative nanoscale laminated transistor (channel width of 20 [tm and channel length of 150 mn). The transistor exhibits a lower charge-carrier mobility and on/off current ratio compared to laminated micron-size transistors (channel width of 20 pm and channel lengths of 2.5 and 100 pm). Zaumseil and coworkers attributed the differences to contact resistances and short-channel effects [88]. Methods to lower contact resistance, which may include the clever use of monolayer chemistty and conductive polymers as electrodes, are being explored [87,88]. 

The dimensions of the added nanoelements also contribute to the characteristic properties of PNCs. Thus, when the dimensions of the particles approach the fundamental length scale of a physical property, they exhibit unique mechanical, optical and electrical properties, not observed for the macroscopic counterpart. Bulk materials comprising dispersions of these nanoelements thus display properties related to solid-state physics of the nanoscale. A list of potential nanoparticulate components includes metal, layered graphite, layered chalcogenides, metal oxide, nitride, carbide, carbon nanotubes and nanofibers. The performance of PNCs thus depends on three major attributes nanoscopically confined matrix polymer, nanosize inorganic constituents, and nanoscale arrangement of these constituents. The current research is focused on developing tools that would enable optimum combination of these unique characteristics for best performance of PNCs. 

H.J. Lee and S.M. Park, Electrochemistry of conductive polymers 37. Nanoscale monitoring of electrical properties during electrochemical growth of polypyrrole and its aging. J. Phys. Chem. B, 109, 13247 (2005). 

C. lonescu-Zanetti, A. Mechler, S.A. Carter, and R. Lai, Semiconductive polymer blends Correlating structure with transport properties at the nanoscale. Adv. Mater., 16, 385 (2004). A. Alexeev, J. Loos, and M.M. Koetse, Nanoscale electrical characterization of semiconducting polymer blends by conductive atomic force microscopy. Ultramicroscopy, 106, 191 (2006). 

Self-Assembly Process. The ability to readily manipulate a wide variety of electroactive polymers at the nanoscale level makes it possible to create thin film heterostructures with optical and electrical properties that can be fine-tuned at the molecular level. As indicated earlier, we have demonstrated that this process can be utilized with many different conjugated, nonconjugated and electrically conductive polymers. Any variety of complex multilayer heterostructures can be fabricated with... 

The unexpected transition in the electrical conductivity was attributed to the interactions between the MWCNTs and the CPs inside the fiber due to an annealing effect of the PANl/PEO matrix from the thermal dissipation of the carbon nanotubes (CNTs). It was also related to the self-heating effect of the MWCNTs incorporated into the CPs, which will be very helpful in enhancing the electrical properties of nanoscale conducting composite fibers. 

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