Numerical simulations are presented of the potential distribution and current transport associated with metal-semiconductor (MS) contacts in which the Schottky barrier height (SBH) varies spatially. It is shown that the current across the MS contact may be greatly influenced by the existence of SBH inhomogeneity. Numerical simulations indicate that regions of low SBH are often pinched-off when the size of these regions is less than the average depletion width. Saddle points in the potential contours in close proximity to the low-SBH regions, which are shown to vary with the dimension and magnitude of the inhomogeneity as well as with bias, essentially determine the electron transport across the low-SBH regions. It is these dependences of the saddle point which give rise to various abnormal behaviors frequently observed from SBH experiments, such as ideality factors greater than unity, various temperature dependences of the ideality factor, including the T0 anomaly, and reverse characteristics which are strongly bias-dependent. The results of these numerical simulations are shown to support the predictions of a recently developed analytic theory of SBH inhomogeneity.

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The negative external impacts of aviation are currently under unprecedented scrutiny. In response, a number of studies into future prospects for improvement have recently been carried out. This paper reviews these studies and discusses their combined implications for emissions of carbon dioxide, oxides of nitrogen, and noise. The results are also compared with targets for emissions reduction proposed by ACARE and NASA. It is concluded that significant future gains are achievable, but not to the extent implied by the ACARE and NASA targets, which represent an unrealistically optimistic view of technological potential over the next 20-40 years. The focus on technological advance also deflects attention from the substantial benefits available from combining present-day technology with behavioural change. Finally, difficult policy decisions will be necessary; the greatest benefits are associated with technological developments that will require major, and long-term, investment for their realisation, and there will be increasing conflict between environmental and noise goals.

The molecules MnO, MnO2, MnO3, and MnO4 have been prepared by the vaporization and reaction of manganese atoms with O2, N2O, or O3 and isolated in various inert-gas matrices at 4 °K. ESR has been used to determine magnetic parameters which are interpreted in terms of molecular geometry and electronic structure. MnO is confirmed to have a σπ2δ2, 6Σ+ ground state with g⊥=1.990(7) (assuming g∥=ge) and a zero-field splitting in accord with the gas phase value ‖D‖=1.32 cm−1. Hyperfine splittings due to the 55Mn (I=5/2) nucleus are ‖A∥‖=176(8) and ‖A⊥‖=440(11) MHz. MnO2 is a linear 4Σ− molecule with probable configuration σδ2, ‖D‖=1.13 cm−1 (assuming g∥=g⊥=2.0023), ‖A∥‖=353(11), ‖A⊥‖=731(11) MHz. MnO3 exhibits very large hf splittings ‖A∥‖=1772(3) and ‖A⊥‖=1532(3) MHz indicative of a sdz2 hybrid 2A1 ground state of D3h symmetry. The spectrum of MnO4 is consistent with a C3v molecule distorted from a 2T1 electronic state in tetrahedral symmetry by a static Jahn–Teller effect. g and A tensors are slightly anisotropic: g∥=2.0108(8), g⊥=2.0097(8), ‖A∥‖=252(3), ‖A⊥‖=196(3) MHz. The electron hole is almost entirely in an oxygen π-bonded orbital with one oxygen atom displaced along its Mn–O bond axis.

Fourier transform infrared measurements on the spectra of the products of the vaporization of silicon/carbon mixtures trapped in solid argon in concert with ab initio calculations using second order many body perturbation theory have resulted in the identification for the first time of two vibrational fundamentals, 3 (b 1u )ϭ982.9 and 4 (b 2u )ϭ382.2 cm Ϫ1 , of the rhombic ground state structure of Si 2 C 2 . The observed frequencies, intensities, and isotopic shifts are in good agreement with the ab initio predictions. Tentative assignments are also made for fundamentals of the linear ͑SiCCSi͒ and distorted trapezoidal isomers. The relative energies of the three isomers have been estimated at various ab initio levels.

The cyclic C6 cluster has been identified for the first time in Fourier transform infrared spectra of the products from the laser evaporation of graphite rods trapped in Ar at ∼10 K. Measurements on spectra produced using both 12C- and 13C-enriched rods combined with the results of new density functional theory calculations performed in the present work as well as previous calculations by Martin and Taylor, have resulted in the assignment of the most intense infrared active mode, ν4(e′)=1694.9 cm−1 of the cyclic C6 isomer with D3h symmetry. This assignment is based on excellent agreement of the frequency, 13C isotopic shifts, and relative intensities with the theoretical predictions.