James A. Misewich

Carbon nanotube–nanocrystal heterostructures

The importance of generating carbon nanotube-nanoparticle heterostructures is that these composites ought to take advantage of and combine the unique physical and chemical properties of both carbon nanotubes and nanoparticles in one discrete structure. These materials have potential applicability in a range of diverse fields spanning heterogeneous catalysis to optoelectronic device development, of importance to chemists, physicists, materials scientists, and engineers. In this critical review, we present a host of diverse, complementary strategies for the reliable synthesis of carbon nanotube-nanoparticle heterostructures using both covalent as well as non-covalent protocols, incorporating not only single-walled and multi-walled carbon nanotubes but also diverse classes of metallic and semiconducting nanoparticles (221 references).

Superconductor-insulator Transition in La2-xSrxCuO4 at the Pair Quantum Resistance

High-temperature superconductivity in copper oxides arises when a parent insulator compound is doped beyond some critical concentration; what exactly happens at this superconductor–insulator transition is a key open question. The cleanest approach is to tune the carrier density using the electric field effect; for example, it was learned in this way that weak electron localization transforms superconducting SrTiO3 into a Fermi-glass insulator. But in the copper oxides this has been a long-standing technical challenge, because perfect ultrathin films and huge local fields (>109 V m−1) are needed. Recently, such fields have been obtained using electrolytes or ionic liquids in the electric double-layer transistor configuration. Here we report synthesis of epitaxial films of La2− xSrxCuO4 that are one unit cell thick, and fabrication of double-layer transistors. Very large fields and induced changes in surface carrier density enable shifts in the critical temperature by up to 30 K. Hundreds of resistance versus temperature and carrier density curves were recorded and shown to collapse onto a single function, as predicted for a two-dimensional superconductor–insulator transition. The observed critical resistance is precisely the quantum resistance for pairs, RQ = h/(2e) = 6.45 kΩ, suggestive of a phase transition driven by quantum phase fluctuations, and Cooper pair (de)localization.

MOTT TRANSITION FIELD EFFECT TRANSISTOR

A field effect transistor fabricated with an oxide channel has been shown to demonstrate switching characteristics similar to conventional siliconmetal oxide field effect transistors. This device is believed to operate via a Mott metal-insulator transition induced by the gate field, and offers a potential technology alternative for the regime beyond silicon scaling limitations.

The evolution of electronic structure in few-layer graphene revealed by optical spectroscopy

The massless Dirac spectrum of electrons in single-layer graphene has been thoroughly studied both theoretically and experimentally. Although a subject of considerable theoretical interest, experimental investigations of the richer electronic structure of few-layer graphene (FLG) have been limited. Here we examine FLG graphene crystals with Bernal stacking of layer thicknesses N = 1,2,3,…8 prepared using the mechanical exfoliation technique. For each layer thickness N, infrared conductivity measurements over the spectral range of 0.2–1.0 eV have been performed and reveal a distinctive band structure, with different conductivity peaks present below 0.5 eV and a relatively flat spectrum at higher photon energies. The principal transitions exhibit a systematic energy-scaling behavior with N. These observations are explained within a unified zone-folding scheme that generates the electronic states for all FLG materials from that of the bulk 3D graphite crystal through imposition of appropriate boundary conditions. Using the Kubo formula, we find that the complete infrared conductivity spectra for the different FLG crystals can be reproduced reasonably well within the framework a tight-binding model.

A field effect transistor based on the Mott transition in a molecular layer

Here we propose and analyze the behavior of a field effect transistor (FET)-like switching device, the Mott transition field effect transistor, operating on a novel principle, the Mott metal-insulator transition. The device has FET-like characteristics with a low “ON” impedance and high “OFF” impedance. Function of the device is feasible down to nanoscale dimensions. Implementation with a class of organic charge transfer complexes is proposed.

Colossal magnetoresistive manganite-based ferroelectric field-effect transistor on Si

An all-perovskite ferroelectric field-effect transistor with a ferroelectric Pb(Zr0.2Ti0.8)O3 (PZT) gate and a colossal magnetoresistive La0.8Ca0.2MnO3 (LCMO) channel has been successfully fabricated by pulsed-laser deposition on Si. A clear and square channel resistivity hysteresis loop, commensurate with the ferroelectric hysteresis loop of PZT, is observed. A maximum modulation of 20% after an electric field poling of 1.5×105 V/cm, and 50% under a magnetic field of 1 T, are achieved near the metal-insulator transition temperature of the LCMO channel. A data retention time of at least one day is measured. The effects of electric and magnetic fields on the LCMO channel resistance are discussed within the framework of phase separation scenario.

Carbon nanotube-based heterostructures for solar energy applications

One means of combining the unique physical and chemical properties of both carbon nanotubes and complementary material motifs (such as metal sulfide quantum dots (QDs), metal oxide nanostructures, and polymers) can be achieved by generating carbon nanotube (CNT)-based heterostructures. These materials can be subsequently utilized as novel and interesting constituent building blocks for the assembly of functional light energy harvesting devices and because of their architectural and functional flexibility, can potentially open up novel means of using and taking advantage of existing renewable energy sources. In this review, we present the reliable and reproducible synthesis of several unique model CNT-based heterostructured systems as well as include an accompanying discussion about the charge transfer and energy flow properties of these materials for their potential incorporation into a range of practical solar energy conversion devices.

Desorption by Femtosecond Laser Pulses: An Electron-Hole Effect?

Desorption of molecules from metal surfaces induced by femtosecond visible laser pulses has been reported. Since the lattice temperature rise is insufficient to explain desorption, an electronic mechanism is clearly responsible. It is shown that a theory based on direct coupling between the center-of-mass degree of freedom of the adsorbate and the electron-hole excitations of the substrate provides a satisfactory explanation of the various experimental findings

160-fsec XeCl excimer amplifier system

An amplifier system based on XeCl gain modules, which, generates bandwidth-limited, 160-fsec, 308-nm, 12-mJ pulses, is described. The UV seed pulses are derived from a colliding-pulse mode-locked laser system.

Femtosecond transition‐state absorption spectroscopy of Bi atoms produced by photodissociation of gaseous Bi2 molecules

Femtosecond transition‐state absorption spectroscopy has been performed on Bi atoms produced by the 308 nm photodissociation of Bi2 molecules contained in bismuth vapor. The transient spectra obtained are all clearly identifiable as atomic, yet they display striking asymmetries in line shapes and enhancements in intensity that clearly demonstrate that they are spectral signatures of atoms still in the force fields of their receding partners.