A method to calculate the optical functions n(lambda) and k(lambda) by use of the transmission spectrum of a dielectric or semiconducting thin film measured at normal incidence is described. The spectrum should include the low-absorption region and the absorption edge to yield the relevant optical characteristics of the material. The formulas are derived from electromagnetic theory with no simplifying assumptions. Transparent films are considered as a particular case for which a simple method of calculation is proposed. In the general case of absorbing films the method takes advantage of some properties of the transmittance T(lambda) to permit the parameters in the two regions mentioned above to be calculated separately. The interference fringes and the optical path at the extrema of T(lambda) are exploited for determining with precision the refractive index and the film thickness. The absorption coefficient is computed at the absorption edge by an efficient iterative method. At the transition zone between the interference region and the absorption edge artifacts in the absorption curve are avoided. A small amount of absorption of the substrate is allowed for in the theory by means of a factor determined from an independent measurement, thus improving the quality of the results. Application of the method to a transmission spectrum of an a:Si(x)N(1-x):H film is illustrated in detail. Refractive index, dispersion parameters, film thickness, absorption coefficient, and optical gap are given with the help of tables and graphs.

We present a study of amorphous hydrogenated silicon-nitrogen alloys (a-SiN":H, O~x &1.5) prepared by the rf reactive sputtering method. By combining results of x-ray photoemission spectroscopy, electron-energy-loss spectroscopy, and optical absorption, all the atom and bond densities and the kind and mean number of nearest neighbors of Si and N atoms are determined. For x & 1, SiN bonds increase at the expense of Si-Si bonds; N atoms are almost fully coordinated by three Si atoms, whereas Si atoms have N, H, and other Si atoms as nearest neighbors. For x) 1, SiN bonds increase at the expense of both Si-Si and Si-H bonds; however, this is not enough to saturate the three N valencies with Si and some N-H and possibly N-N bonds begin to appear. The opening of the optical gap occurs at x =-1.1 when the ratio of the densities of Si-Si bonds to SiN bonds has fallen below 0.10. Near stoichiometry, substantial amounts of Si-Si and N-H bonds are observed. The possibility of segregation into pure silicon and stoichiometric silicon nitride is discussed by analyzing the Si 2p line shape. A linear relationship between the Si 2p chemical shift and the mean number of N-atom nearest neighbors of Si is observed; a charge transfer of 0.35e per SiN bond is determined. I. INTRODUCTION Silicon nitride is a material widely used in the ceramic and microelectronic industries. This has prompted a number of studies conducted to obtain silicon nitride by different methods and to determine its structural and electrical properties. It is mostly prepared as thin amorphous films which, in general, are nonstoichiometric and contain H in concentrations between 10 at. % and 40 at. %. Aiyama et al. ' and Misawa et al. have studied the amorphous structure of near-stoichiometric compounds by x-ray and neutron diffraction, finding that the shortrange order strongly resembles that of the crystalline forms. The electronic structure of a-SiN, in the range 0~x (2, has been the subject of a very complete investigation performed by Karcher et al. using x-ray photoelectron spectroscopy (XPS). They thoroughly analyzed the valence bands and obtained some information about the SiN bonding by deconvoluting the Si 2p peak. Densities of electron states of the crystalline and amorphous forms have been calculated by Ren and Ching,

No abstract

This study was designed to identify the phase of rapid aimed movements responsible for hand differences in motor skill, and to evaluate potential differences between the hands in accommodating to greater accuracy demands. In both experiments, an accelerometer mounted on a stylus allowed key changes in acceleration to be used to partition the movement into phases. In Experiment 1, slower left hand movement times were attributable primarily to a terminal homing-in phase, especially as target size decreased. Since error rates varied as a function of hand and target size, speed-accuracy trade-offs may have occurred. Experiment 2 rigidly controlled error rate and confirmed the major hand difference to occur in the latter phase of the movement where error correction is presumed. Although less pronounced, adjustments were made in the earlier movement phases as well. Accommodation to greater accuracy demands involved moving the stylus closer to the target before decelerating to engage in error correction. This adjustment to gain enhanced precision was more pronounced in the left hand.

Films were deposited from glow discharge plasmas of acetylene-oxygen-argon mixtures in a deposition system fed with radio frequency power. The principal variable was the proportion of oxygen in the gas feed, X ox. The chemical structure and elemental composition of the films were investigated by transmission infrared spectrophotometry and x-ray photoelectron spectroscopy. Optical properties-refractive index, absorption coefficient, and optical gap-were determined from transmission ultraviolet-visible spectroscopy data. The latter also allowed the determination of film thicknesses and hence deposition rates. It was found that the oxygen content of the films and, within limits, the refractive index are controllable by the selection of X ox .