Electrical transport measurements

In the previous chapters, examples of ID arrays of nanoclusters have been given, where self-assembly or ET were used to address the arrays for electrical transport measurements. So far it is evident that these methods did not lead to strictly ID defect-free arrangements. Furthermore, inherent disorder cannot be avoided. This means that the electrical transport properties through a perfect array could only be studies theoretically up to now. 

J. A. Talla, D. Zhang, S. A. Curran, Electrical transport measurements of highly conductive nitrogen-doped multiwalled carbon nanotubes/poly(bisphenol A carbonate) composites, Journal of Materials Research, vol. 22, pp. 2854-2859, 2011. 

The experiments in the solid state are based on several techniques, including imaging, spectroscopy, and electrical transport measurements that reveal the electric current flux through the molecule under an external field. The results pertain to single molecules (or bundles) and can be remeasured many times. The roles of the donor and of the acceptor are in this case played either by the metal leads, or by the substrate and a metal tip. The interpretation is generally given in terms of conductivity, determined by the electronic energy levels (if the molecular structure supports the existence of localized... 

CeRii4P]2 is a narrow gap semiconductor with a gap of 0.075 eV estimated from electrical transport measurements on polycrystalline samples (Shirotani et al., 1996). XANES measurements indicate trivalent Ce with strong hybridization with ligand orbitals. The gap is presumably formed from the hybridization of the Ce 4f states with the Ru d and P-p orbitals... 

The specimens with dimensions of 3.0 X 4.0 X10 mm for the electrical transport measurements were cut out from the sintered bodies. Samples were cleaned in ultrasonically agitated baths of acetone and ethanol. 

The ehapter is organised as follows. After the introduction, a brief overview of the fundamentals of CNTs and CNT-based FETs will be given. The next section describes a range of chemical functionalisation schemes that have been devised for the performance enhancement of CNT-FETs. The subsequent section is devoted to the characterisation of as-prepared and functionalised CNT-FETs through electrical transport measurements and scanning photocurrent microscopy. In this context, the relevant device parameters of the FETs such as saturation behaviour, field-effeet mobility, transconductance and sub-threshold slope will be analysed and compared. The chapter concludes with future perspectives for the fabrication of CNT-based FETs. 

Figure 26.10 Oxidative electrochemical modification (oECM) of individual contacted m-SWCNTs using a substituted aromatic amine, (a) Electrical transport measurements and (b) Raman spectra before and after oECM on the same contacted tube. The oECM was performed at +0.75 V versus Pt for 120 s in a solution of 10 mM 4-aminobenzylamine in ethanol. 0.1 M lithium perchlorate was used as a background electrol54e. (Reprinted with permission from [48].)...

An electron in a solid behaves as if its mass [CGS units are used in this review the exception is for the tabulation of effective masses, which are scaled by the mass of an electron (m0), and lattice constants and radii associated with trapped charges, which are expressed in angstroms (1A = 10 8 cm)] were different from that of an electron in free space (m0). This effective mass is determined by the band structure. The concept of an effective mass comes from electrical transport measurements in solids. If an electron s motion is fast compared to the lattice vibrations or relaxation, then the important quantity is the band effective mass (mb[eff]). If the electron moves more slowly (most cases of interest) and carries with it lattice distortions, then the (Frohlich) polaron effective mass (tnp[eff]) is appropriate [11]. The known band effective and polaron effective masses for electrons in the silver halides are listed in Table 1. The polaron and band effective masses are related to a... 

For the purpose of this paper global grain boundary structure refers to the interface between two grains over a finite boundary area, typically of a dimension commensurate with the size of sample used for electric transport measurements. The local grain boundary structure refers to the positions of atoms within the grain boundary as well as their chemical identity. Thus grain... 

CP-AFM conductivity measurements can be carried out independently of force feedback, which can be varied in investigation of material conductance under a controlled stress [130-137]. As a result, electrical transport measurement can be facilitated over longer distances on samples with widely varying resistances, hi addition, a repulsive force in CP-AFM during the tip approach makes it easier to detect the precise location of the tip relative to the sample. For electrical characterization, the relative merit of CP-AFM and STM certainly depends on specific goals and experimental constraints. 

The fact that the physical properties of nanocrystal organizations could be different from that of the isolated particles is being realized. Pellets of monodis-perse nanocrystals, obtained by the use of bifunctional ligand that binds to more than one nanocrystal or by applying pressure on dried nanocrystalline matter, have been used for electrical transport measurements [130-133]. Pellets made of small Au and Pd nanocrystals exhibit nonmetallic behavior with specific conductivities in the range of 10 Q cm [130-132]. The conductivity, however, increases dramatically with an increase in the diameter of the nanocrystals. An insulator metal transition has indeed been reported from pellets made of -12.5-... 

Kurucsev, T., Steel, B.J. The use of electrical transport measurements for the determination of counterion association in salt-free polyelectrolyte solutions. Rev. Pure Appl. Chem. 1961,17, 149-157. 

The structures mentioned up to this point have represented examples of quasizero-dimensional (0-D) systems, in which self-assembly or electrostatic trapping are used to place the individual (or at least a few) partides into a nanogap for electrical transport measurements. However, the processes are not necessarily suited to electrically address a well-defined number in a desired arrangement in a reliable maimer, which in turn means that neither method can lead to strict and defect-free 1-D arrangements. In addition, inherent disorder cannot be avoided. Thus, until now, the electrical transport properties through a perfect 1-D array have been studied on a theoretical basis. 

Beverly et al. [93] studied the temperature-dependent DC transport measurements on monolayers of self-assembled dodecanethiol-coated 7 nm silver nanoparticles as a function of particle size distribution-induced disorder. The superlattices disorder was adjusted by a stepwise variation of the particle size distribution. In the electrical transport measurements, six different monolayers of 7 nm silver nanoparticles, in which the size distribution was varied from 6.6% to 13.8%, were investigated at 300-10 K. Above 200 K, all films exhibited metallic conductivity, and below 200 K activated transport. However, between 30 and 100 K a second transition (Tcross) was observed that was based on the crossover from the simply activated transport to a... 

Electronic Transport, General Description. Magnesium Oxide (MgO). Electrical transport measurements on alkaline earth oxides encounter several difficulties, such as high resistance at low temperatures, a strong influence of surface layers, and high-temperature thermionic emission. The partly contradictory results depend considerably on the purity and nature of the samples (pressed porous powders, sintered samples, polycrystals, and single crystals) and on the experimental conditions. 

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