P. Marquardt

Size-induced metal-insulator transition in metals and semiconductors

Abstract We report on the size-induced metal-insulator transition discovered in tiny metal crystals. Here the electric conductivity drastically decreases with particle diameter below a few μm. On the other hand, in semiconductor crystallites a size-correlated inter-band absorption blue shift was observed. The effects are a consequence of the quantum confinement in all three dimensions (“quantum dots”) and hence are of universal character. In addition to their fundamental importance, the observations now allow the design of the ultimate microelectronic device and permit the engineering of novel devices as well.

On the quasi-static conductivity of sub-micrometer crystals

We report that both size (d) and dimensionality of the confinement imposed on an electron gas govern its conductivity. A dramatic decay of the quasi-static conductivity by more than 8 orders of magnitude has been discovered in the sub-micrometer (so-called mesoscopic) size range of metal particles when their sizes are reduced down to the nm regime. This size-induced metal-insulator transition is of universal character and can only be understood as a quantum-size effect.

Microwave absorption by small metal particles

Abstract The dielectric response of small indium and iron crystals in complementary particle topologies is characterized by microwave absorption. A transition from non-absorptive to conducting behaviour was discovered in condensed indium-oil dispersions during thermal particle coarsening. Microwave losses in low-density networks of iron “nanocrystals” (sizes ≲ 10 nm) are attributed to percolation.

Quantum-size affected conductivity of mesoscopic metal particles

Abstract The distinctively low microwave conductivity of metal colloids discovered recently during thermal particle coarsening is re-analysed with an effective medium treatment tailored for dense particle systems. The microwave data now favour the quantum-size before the classical model of the dielectric function even for mesoscopic metal particles.

Size-limited conductivity in submicrometre metal particles. Similarities with conducting polymers?☆

Abstract We report on the conductivity of submicrometre metal particles, which experience a size-induced metal-insulator transition (SIMIT). Also, their frequency behaviour and their dependence on temperature are quite different from bulk metal properties. Investigations of the conductivity of thin polyaniline layers have revealed that the two systems have some prominent properties in common; for instance both systems exhibit a pronounced relaxation process. A comparison and discussion of the similarities are presented.

The electron cut-off wavelength transistor

We propose a transistor based on the transverse quantization of electron waves. The spread of non-degenerate electrons is some 20 nm at room temperature. In a wire-like structure having a diameter of this or smaller size, the electron transport will be cut-off like that of electromagnetic modes in a wave guide. Accelerated in electric fields, hot electrons have smaller spread and may now propagate through the narrow electron waveguide. This principle presents the basis for novel minuscule and versatile simple devices.

Raoult's Law and the Melting Point Depression in Mesoscopic Systems

Data on the melting point depression in small indium or gold particles and in liquid water held between lipid bilayers indicate that these systems obey Raoults law, with the surface atoms or molecules acting like solute particles in a dilute solution.

On electron confinement effects and the ultimate size reduction in semiconductor devices

Three-dimensional electron confinements cause a blue shift of the fundamental band gap and a size-induced metal-insulator transition. These quantum-size effects are expected in confinements with diameters up to the order of 10 and 100 nm at room temperature, in metals and semiconductors, respectively. The size effect can markedly be enhanced by an additional phonon confinement which is omnipresent in isolated sub-micrometre crystals. Confinement effects represent the limitation for the ultra-large-scale integration.

Is the positive dielectric response of small metals related to heterogeneous catalysis

Abstract The dielectric response of metals is negative in consequence of the dominating inductive free carrier contribution. Recent experiments have shown that this electron contribution is strongly positive in small metal particles. The positive dielectric response may be involved in heterogeneous catalysis. Both catalytic activity and positive dielectric function indeed depend on particle size in the submicrometre range.

Dielectric and Structural Properties of a Water-Oil Emulsion at the Gel-Microemulsion Transition

The dielectric response (1 MHz ÷ 10 GHz) and the structure of a water-oil emulsion were studied as a function of temperature. It was observed that the water component causes the dielectric loss of the emulsion in the crystalline gel phase at low temperatures. However, the dielectric loss decreases discontinuously at the gel-microemulsion transition near 60 °C. At higher temperatures, i.e. in the microemulsion phase of the systems, the dipole relaxation becomes very slow, similar to that of ice. This behaviour is explained by an enhanced connectivity of the hydrogen bonds of water in the micelles of the microemulsion. We conclude that the water in the micelles behaves like frozen water, even at temperatures above 60 °C.