Roy G. Gordon

Theory for the Forces between Closed‐Shell Atoms and Molecules

A simple model is presented for calculating the forces between closed‐shell atoms and molecules in the regions both of the attractive well and of the repulsive wall at shorter distances. Account is taken of both the overlap of the separate atomic densities and of electron correlation. Applications to pairs of rare gas atoms and to alkali halide molecules demonstrate quantitative agreement with empirically determined intermolecular potentials for these systems over the whole range of separations inside and including the potential minimum.

On the Rotational Diffusion of Molecules

The Debye model of rotational diffusion by small angular steps is generalized to allow molecular reorientation through angular steps of arbitrarily large size. The generalized diffusion models are found to give a rather accurate representation of molecular reorientation in liquids and gases, as observed in the infrared and Raman spectra of simple molecules. One interesting feature of both the theoretical and experimental correlation functions is that the approach to rotational equilibrium often takes the form of a damped oscillation, rather than the monotonic decay which is usually assumed.

Textured aluminum‐doped zinc oxide thin films from atmospheric pressure chemical‐vapor deposition

Aluminum‐doped zinc oxide films have been deposited on soda lime glass substrates from diethyl zinc, triethyl aluminum, and ethanol by atmospheric pressure chemical‐vapor deposition in the temperature range 367–444 °C. Film roughness was controlled by the deposition temperature and the dopant concentration. The films have resistivities as low as 3.0 × 10−4 Ω cm, infrared reflectances close to 90%, visible transmissions of 85%, and visible absorptions of 5.0% for a sheet resistance of 4.0 Ω/⧠. The aluminum concentration within doped films measured by electron microprobe is between 0.3 and 1.2 at. %. The electron concentration determined from Hall coefficient measurements is between 2.0 × 1020 and 8.0 × 1020 cm−3, which is in agreement with the estimates from the plasma wavelength. The Hall mobility, obtained from the measured Hall coefficient and dc resistivity, is between 10.0 and 35.0 cm2/V s. Over 90% of the aluminum atoms in the film are electrically active as electron donors. Scanning electron microsc...

New Method for Constructing Wavefunctions for Bound States and Scattering

A new method is developed for integrating coupled differential equations arising in bound state and scattering problems in quantum mechanics. The wavefunctions are easily constructed in piecewise analytic form, to any prescribed accuracy.

A metal-free organic–inorganic aqueous flow battery

As the fraction of electricity generation from intermittent renewable sources—such as solar or wind—grows, the ability to store large amounts of electrical energy is of increasing importance. Solid-electrode batteries maintain discharge at peak power for far too short a time to fully regulate wind or solar power output. In contrast, flow batteries can independently scale the power (electrode area) and energy (arbitrarily large storage volume) components of the system by maintaining all of the electro-active species in fluid form. Wide-scale utilization of flow batteries is, however, limited by the abundance and cost of these materials, particularly those using redox-active metals and precious-metal electrocatalysts. Here we describe a class of energy storage materials that exploits the favourable chemical and electrochemical properties of a family of molecules known as quinones. The example we demonstrate is a metal-free flow battery based on the redox chemistry of 9,10-anthraquinone-2,7-disulphonic acid (AQDS). AQDS undergoes extremely rapid and reversible two-electron two-proton reduction on a glassy carbon electrode in sulphuric acid. An aqueous flow battery with inexpensive carbon electrodes, combining the quinone/hydroquinone couple with the Br2/Br− redox couple, yields a peak galvanic power density exceeding 0.6 W cm−2 at 1.3 A cm−2. Cycling of this quinone–bromide flow battery showed >99 per cent storage capacity retention per cycle. The organic anthraquinone species can be synthesized from inexpensive commodity chemicals. This organic approach permits tuning of important properties such as the reduction potential and solubility by adding functional groups: for example, we demonstrate that the addition of two hydroxy groups to AQDS increases the open circuit potential of the cell by 11% and we describe a pathway for further increases in cell voltage. The use of π-aromatic redox-active organic molecules instead of redox-active metals represents a new and promising direction for realizing massive electrical energy storage at greatly reduced cost.

Molecular Motion in Infrared and Raman Spectra

It is suggested that Fourier transformation of infrared and Raman band shapes reveals the meaning of the spectrum in terms of molecular rotation much more clearly than does the usual frequency shape. By looking at the time dependence directly, one may separately examine the molecular motion at short and long times The motion at short times may be analyzed directly in terms of the molecular dynamics, by the use of a power series in the time, whereas the behavior at long times is best examined by statistical arguments. This kind of analysis is illustrated by several examples, including the spectra of liquid CO and CH4.

Self-Aligned Ballistic Molecular Transistors and Electrically Parallel Nanotube Arrays

Carbon nanotube field-effect transistors with structures and properties near the scaling limit with short (down to 50 nm) channels, self-aligned geometries, palladium electrodes with low contact resistance, and high-K dielectric gate insulators are realized. Electrical transport in these miniature transistors is nearly ballistic up to high biases at both room and low temperatures. Atomic-layer-deposited (ALD) high-K films interact with nanotube sidewalls via van der Waals interactions without causing weak localization at 4 K. New fundamental understanding of ballistic transport, optical phonon scattering, and potential interfacial scattering mechanisms in nanotubes is obtained. Also, parallel arrays of such molecular transistors are enabled to deliver macroscopic currents-an important milestone for future circuit applications.

High Performance n-Type Carbon Nanotube Field-Effect Transistors with Chemically Doped Contacts

Short channel ( approximately 80 nm) n-type single-walled carbon nanotube (SWNT) field-effect transistors (FETs) with potassium (K) doped source and drain regions and high-kappa gate dielectrics (ALD HfO(2)) are obtained. For nanotubes with diameter approximately 1.6 nm and band gap approximately 0.55 eV, we obtain n-MOSFET-like devices exhibiting high on-currents due to chemically suppressed Schottky barriers at the contacts, subthreshold swing of 70 mV/decade, negligible ambipolar conduction, and high on/off ratios up to 10(6) at a bias voltage of 0.5 V. The results compare favorably with the state-of-the-art silicon n-MOSFETs and demonstrate the potential of SWNTs for future complementary electronics. The effects of doping level on the electrical characteristics of the nanotube devices are discussed.

Error Bounds in Equilibrium Statistical Mechanics

A new method is presented for the calculation of thermodynamic properties from equilibrium statistical mechanics. Starting from the high‐temperature expansion coefficients for the canonical partition function, error bounds are obtained, which are both rigorous and optimal.

Quantum scattering theory of rotational relaxation and spectral line shapes in H2–He gas mixtures

A systematic study is presented of the rotational relaxation and spectral line shape properties of dilute gas mixtures of H2 in He, in an effort to determine the radial and angular dependence of the H2–He intermolecular potential. The quantum mechanical theory of relaxation in gases is reviewed, and we express the results in terms of a matrix of cross sections that determines each correlation function, and thus the relaxation properties of the system. The cross section is calculated from binary collision transition amplitudes, or S matrix elements, for H2–He scattering. A Morse‐spline‐fitted‐van der Waals potential of the form V0(R)+V2(R)P2(cosθ) is assumed and we treat the hydrogen molecule as a rigid rotor. The Schrodinger equation is solved in the close‐coupling approximation using the method of Gordon. We apply the theory to sound absorption measurements of rotational relaxation, NMR spin‐lattice relaxation times, and the S and Q branches of the pure rotational Raman spectrum of H2–He mixtures. Elasti...