The fractional changes, due to a magnetic field, in the electrical conductivity, in the thermal conductivity, and in the thermoelectric power of a single bismuth crystal are measured in these experiments. These changes are determined as a function of the field strength, of the direction of the field, of the direction of the crystal axis, and of the direction of the heat and electric currents through the crystal. An electric current sent through the crystal cools one junction and heats the other by the Peltier effect. The temperature difference thus produced gives rise to a thermal e.m.f. in the crystal circuit. Observations of this e.m.f. allow the calculation of the fractional changes produced in the thermal conductivity and in the thermoelectric power. The change of electrical conductivity is influenced much more strongly by the crystal structure than is the change of thermal conductivity. Crystal structure and orientation of the magnetic field both affect strongly the change in the thermoelectric power. The theory of electrons in metals in its present form does not give an adequate explanation of the results. If the magnetic field changes the free electron density in bismuth some of the results may be explained in a general way.

The dielectric properties of perovskite type crystals are of interest because some of the compounds having this crystal structure are ferroelectric. The word ferroelectric is derived by analogy with the word ferromagnetic; it means that the material has a spontaneous electric polarization just as a magnet has a spontaneous magnetic polarization. While in this country the term ferroelectric is universally used, in Europe the term seignettoelectric is often used instead. This usage stems from the fact that the first ferroelectric discovered was Seignette salt or Rochelle salt. Ferroelectric materials are of interest because they are piezoelectric, they have high dielectric constants, and their dielectric constants are strongly temperature dependent. These properties lead to many applications. A study of the theory of ferroelectrics should be useful in utilizing their properties and in discovering new ferroelectrics.

Abstract Not Available.

Abstract Not Available.

Molecular machines, typically thought to be only the fanciful imaginings of speculative fiction, have taken great strides in recent years towards real-world viability and usefulness. Under variable temperature scanning tunneling microscopy, (STM) one family of these nascent devices is characterized with atomic resolution, and probed and manipulated with sub-angstrom precision, adding to the growing body of knowledge of how molecular devices behave and react at nanometer scales. Evidence of temperature-dependent rolling of wheel-like fullerene constituents on the Nanocar is discussed in light of newly developed image analysis techniques. Additionally, charge-transfer mediated behavior at step edges, both static and dynamic, is investigated on a Au(111) surface for a more complete understanding of translation and surface diffusion. Molecular flexibility is thought to aid in this three-dimensional atomic-step-crossing diffusion, and is explored and discussed across many species in the Nanocar family of molecules. In all, many similar molecules have been characterized and explored via STM with an eye towards their dynamic capabilities and surface behaviors, in the hopes that future, more complex versions can build on the nascent knowledge base beginning to be established here.

A method is described for the growth of high purity crystalline thin film C$\sb{60}$. Films grown by this method are analyzed by means of x-ray diffraction, low energy electron diffraction, and photoluminescence. An excimeric model of the processes leading to the observed photoluminescence spectrum is proposed. This model is supported by the locations of spectral features in the photoluminescence spectrum as well as by agreement with the cooling dependence, temperature dependence, and the lack of film thickness dependence of the photoluminescence spectrum. The model is used to explain the observed photoluminescence spectrum of polycrystalline C$\sb{60}$.

A flowing helium afterglow apparatus has been used to study thermal-energy electron exchange collisions between spin-polarized electrons and O$\sb2$ or NO molecules. Penning ionization of CO$\sb2$ by spin-polarized He(2$\sp3$S) metastable atoms is used to produce electrons which retain the spin orientation of the metastables, and which rapidly thermalize in the CO$\sb2$. The reactant gas (O$\sb2$ or NO), when introduced into the flowstream, causes a decrease in the electron spin-polarization. The electrons are then extracted from the flowtube for measurement of the polarization they retain. The rate constant for the reaction e$\sp{-}(\uparrow$) + X $\to$ e$\sp {-}(\downarrow$) + X can then be determined, given the amount of polarization decrease, reactant-gas density, and reaction time. The rates are found to be k(O$\sb2$) = (8 $\pm$ 3.5) x 10$\sp{-11}$ cm$\sp3$/sec and k(NO) = (9 $\pm$ 4) x 10$\sp{-11}$ cm$\sp3$/sec. An upper limit to the electron attachment rate for formation of an excited negative ion is derived from these measurements, and the contribution of exchange to the total scattering is discussed. In addition, a new, non-invasive technique for measuring electron-drift velocity in the flowtube is describe. Modifications of the afterglow apparatus and use of laser radiation for He(2$\sp3$S) spin-orientation enable it to produce an electron beam having moderate to high current and high spin polarization. Polarizations of 80% are achieved for currents up to 1$\mu$A, with 60% polarization retained at 25$\mu$A. This compares favorably with other polarized electron sources, making the afterglow apparatus a candidate for use as a beam source in high-energy electron accelerators.

Single-walled carbon nanotubes have been produced in a continuous flow gasphase catalytic growth process, in a heated flow of carbon monoxide at pressures of 1--10 atmospheres and temperatures of 800--1200°C. Catalytic cluster nuclei for the nanotubes are generated in situ by thermal decomposition of iron pentacarbonyl. The yield of nanotubes and their diameter distribution can be varied by varying process parameters: nanotubes as small as 0.6 nm in diameter, corresponding to the size of a C60 molecule, have been generated. This process shows great promise for scaling up for bulk production of carbon nanotubes.

The properties of associating fluids in contact with adsorbing surfaces are essential for the control of many processes of current industrial and scientific interest. Potential applications are diverse. Despite the need for a molecular understanding of interfacial properties, only in the past a few years have simple, accurate theories been developed for even simple fluids. Our group has developed a new density functional theory which applies the weighting from Tarazona's hard sphere density functional theory to Whertheim's bulk first-order perturbation theory to investigate inhomogeneous pure associating fluids confined between hard walls. This theory has been shown to be in good agreement with computer simulation results. In this work, we extend this promising theory to binary mixtures of hard spheres and associating fluids, and apply the mixture theory to non-additive hard spheres. We have accurately predicted phase separation, critical temperature and structural properties for this model. We then extend this theory to describe the properties of associating fluids near active surfaces. Metropolis Monte Carlo computer simulations are performed for one-sited (dimerizing), two-sited (linear chain forming) and four-sited (cluster forming) molecules near active surfaces. Our theory compares favorably with simulation results for a wide range of fluid density and bonding energy for surface coverage, density profiles and faction of monomers.

This work describes the development of a unique capability for electron beam excitation of hot vapors combined with VUV spectroscopy. The first result obtained with this new facility was the observation of emission from the triatomic rare gas halide Ne$\sb 2$F* at 132 nm. An investigation of the kinetic processes for both Ne$\sb 2$F* and its precursor NeF*, which emits at 108.5 nm, was performed. Several relevant rate coefficients were determined. It was concluded that this system is analogous to the Ar-Cl system, in that it predissociates due to excited halogen dimer formation. Therefore the realization of NeF* or Ne$\sb 2$F* laser action would be difficult due to F$\sb 2$* production. NeF* fluorescence, however would be more likely to achieve gain due to its higher stimulated emission cross-section.