Metal size-induced

Composites containing nanometer-sized metal particles of a controllable and uniform size in an insulating ceramic matrix are very interesting materials for use as heterogeneous catalysts and for magnetic and electronic applications. They show quantum size effects, particularly the size-induced metal-insulator transition (SIMIT) [1],... 

The data in Table 9.3 were taken as an indication that the ligand which best fits the metal ion demand, in terms of the hole size, induces the highest ligand field splitting,... 

Size- Induced Metal-Insulator Transition Insulator... 

The simplest type of template directed cyclization is metal cation induced macrocycliza-tion, as discussed in Section 1.1. Mandolin and co-workers [37] have made a detailed study of the influence of alkali and alkaline earth metal cations on the cyclization of 2-hydroxyphenyl-3,6,9,12-tetraoxa-14-bromotetradecyl ether 28 in methanol and in dimethyl sulfoxide (Scheme 1-8). They studied different sizes of macrocycle and metal cation to determine the most effective combination for cyclization the results from this study will be summarized in Section 1.4.2.3. 

On the Size-Induced Metal-Insulator Transition in Clusters and Small Particles... 

Figure 1. A representation of the successive fragmentation, or division, of a single grain of metal. The inevitable size-induced metal-insulator transition now effectively links the macroscopic (metal) and the microscopic (insulator) regimes. In all cases we identify the approximate particle diameter and nuclearity, and the accompanying (Kubo) average electronic energy gap separating occupied and unoccupied energy levels. This figure is modified from Edwards. ...

Gor kov and Eliashberg investigated the problem of a size-induced metal-insulator transition in terms of the location of the gas of conduction electrons in a metal through the (finite) size-induced confinement of the electron wave packet. The de Broglie wavelength X of electrons is given by ... 

Within the context of the metal-insulator transition in metal particles and clusters, two closely interwoven problems can be identified. The first is the inevitable transition to insulating (non-metallic) behavior within an individual grain or partiele of metal as its geometric dimensions are continuously reduced. Throughout this process, the electron wavefunction is assumed to be completely confined within the single particle this is the size-induced metal-insulator transition (Fig. 1). 

Figure 6. The variation in the measured ionization potential of mercury clusters as a function of cluster size. The work function for bulk Hg (4.49 eV) is indicated. The dashed line is a plot of the ionization potential calculated for the classical (liquid drop) electrostatic model for a metalUc sphere of diameter d. Region III contains clusters which are classified as insulating. Region II denotes the size-induced metal-insulator transition, in which overlap of the 6s and 6p states sets in at around Hgn. The larger clusters, located in Region I, have valence electronic structures that closely resemble the band structures of liquid and crystalline mercury. Adapted from Rademann. i...

Measuring the d.c. conductivity of isolated metal particles, of course, is arguably the most direct method of investigating the size-induced metal-insulator transition within a single particle. Marquardt, Nimtz and coworkers believe they have succeeded in measuring the quasi-A.c. conductivity of individual indium nanoparticles... 

Figure 10. The size-induced metal-insulator transition in mesoscopic crystals of indium. The size-dependent [quasi) d.c. conductivity versus particle diameter. For comparison the bulk conductivity and the classical (surface) size-effect are also displayed. Modified from Nimtz et alP° ...

Figure 11. (a) The conduction gap observed in small clusters of gold, palladium, cadmium, and silver as a function of cluster volume, (b) Normalized slope of the /-K curves (the conductance) as a fraction of cluster volume for the four metals studied. Above a critical volume of ca 4nm the slope becomes size-independent. This is possibly a direct indication of a size-induced-metal-insulator transition, as indicated. Taken from Vinod et a/. ... 

If an individual grain of a metallic element or compound is sufficiently reduced in physical size, we expect a size-induced-metal-insulator transition (SIMIT). We have attempted here to highlight certain key features of the problem in terms of the... 

On the Size-Induced Metal—Insulator Transition in Clusters 1479... 

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