Excimer laser deposition of thin amorphous carbon films

A new carbon film deposition technique, based upon excimer laser vaporization of graphite in a flowing gas system has been developed. The low temperature vapor (LTV) technique alleviates high temperatures occurring in most other deposition methods. In this technique the UV laser ablation occurs in an inert flowing gas atmosphere. Atoms and molecules evaporated from graphite are cooled by gas entrainment before condensing on a substrate. The resulting films of amorphous carbon or hydrogenated amorphous carbon are free from strain. Measurement of the optical band gap of these films shows that E_g can be controlled by the hydrogen content of the carrier gas.     

CO2 laser cutting of thin metal sheets with gas jet assist

A quantitative analysis of cutting thin stainless steel sheets with cw CO₂ lasers using an oxygen gas jet assist is reported. Results are interpreted theoretically using a point source model.     

Ab initio calculation of the electronic and vibrational properties of metal‐organic molecules based on cyclic C6 intercalated with some group VIII transition metals

The vibrational and electronic properties of a new class of organometallic sandwich molecules, (C₆)_nMe_n‐1, based on stacks of cyclic C₆ intercalated with Fe and Ru have been studied using first principles density functional techniques (DFT). Spectral properties as well as the HOMO‐LUMO gap energy in molecules containing up to eight C₆ layers have been calculated. The HOMO‐LUMO energy gap in these molecules is < 1 eV and decreases significantly in longer molecules. It is shown that infinite chains should have excellent metallic properties. These molecules are promising for nanoelectronic applications, due to their predicted high stability, conductivity, and magnetic properties.     

The orange luminescence band in MgO crystals

Nominally pure MgO crystals exhibit a bright orange luminescence when excited with u v or visible laser light This luminescence has been characterized using a variety of measurements with pulsed and cw laser sources Its amplitude increases with temperature to about 400 K. while the lifetime of emission decreases from 270 μs at 290 K to 9 μs at 433 K This emission appears to originate in hole recombination with Fe²⁺ ions Hole trapping at V^?_OH and V^?_Al centers may occur as an intermediate step Bleaching with 514 5-nm Ar⁺ laser light is reversible upon exposure to u v radiation Present data are compared with those obtained previously on the thermoluminescence of irradiated MgO crystals.     

Coupling coefficient for cw CO2 laser radiation on stainless steel

Coupling coefficients for 10.6μm laser radiation on stainless steel have been measured experimentally under oxidizing and vacuum conditions. A theoretical model has been developed that relates the growth of an oxide layer to changes in coupling coefficients.     

Multiphoton excitation of visible and VUV luminescence in MgO crystals

Irradiation of pure MgO crystals with intense XeCl laser radiation yields VUV emission associated with the decay of bi-excitons. This emission exhibits a 4-photon dependence on incident laser intensity. Collisional excitation of luminescence from Cr³⁺ and Ni²⁺ impurities has been detected in doped samples. This emission also shows a multiphoton dependence on incident laser intensity.     

Photoluminescence from surface states in MgO and CaO powders

Photoexcitation spectra of luminescence from activated MgO and CaO powders have been obtained over the wavelength range 120–300 nm at sample temperatures down to 10 K. These spectra show broad features attributable to electronic transitions of O^2? ions in coordination states varying from 6-fold (bulk ions) to 3-fold. O^2? ions in 4 and 5-fold coordination contribute a broad inhomogeneously broadened spectral feature centered at 225 and $\text{\$}\text{?}$250 nm in MgO and CaO powders, respectively. This feature is interpreted as a surface exciton band well separated in energy from the bulk exciton band at 160 and 180 nm, respectively. An interaction between discrete bulk exciton levels and these surface bands yields dispersion-like structure superimposed on the broad surface photoexcitation bands.