Richard L. C. Wu

Negative ion–molecule reactions of ozone and their implications on the thermochemistry of O3−

An in‐line double mass spectrometer has been employed to determine reaction rate coefficients and excitation functions for several types of negative ion reactions involving ozone. The interactions studied include electron transfer reactions, such as, M−+O3→M+O3− (where M−=O−, OH−, F−, Cl−, Br−, I−, S−, SH−, Cl−2, C2H−, NO2−, and CO3−) and particle transfer reactions, such as MO−+O2→M+O3− (where MO−=O2−, NO2−, NO3−, CO3−). Translational energy thresholds have been determined for those reactions which are endothermic by applying exact Doppler corrections for the thermal motion of the neutral as well as corrections for the translational energy distribution of the projecticle ions. These experiments place a lower limit of 2.26+0.04−0.06 eV on the electron affinity of ozone. This value is in excellent agreement with the value computed from the bond dissociation energy of O3− in its most stable configuration, D00(O−–O2) =1.80 eV, as deduced from measurements of the translational energy thresholds for the collis...

Friction and wear of plasma-deposited diamond films

Reciprocating sliding friction experiments in humid air and in dry nitrogen and unidirectional sliding friction experiments in ultrahigh vacuum were conducted with a natural diamond pin in contact with microwave‐plasma‐deposited diamond films. Diamond films with a surface roughness (R rms) ranging from 15 to 160 nm were produced by microwave‐plasma‐assisted chemical vapor deposition. In humid air and in dry nitrogen, abrasion occurred when the diamond pin made grooves in the surfaces of diamond films, and thus, the initial coefficients of friction increased with increasing initial surface roughness. The equilibrium coefficients of friction were independent of the initial surface roughness of the diamond films. In vacuum the friction for diamond films contacting a diamond pin arose primarily from adhesion between the sliding surfaces. In these cases, the initial and equilibrium coefficients of friction were independent of the initial surface roughness of the diamond films. The equilibrium coefficients of f...

Synthesis and characterization of fine grain diamond films

A fine grain diamond film has been developed by microwave plasma assisted chemical vapor deposition. Various analytical techniques, including Rutherford backscattering, proton recoil analysis, Raman spectroscopy, and X‐ray diffraction, were utilized to characterize the diamond films. The grain size of the film was determined from bright and dark field electron micrographs, and found to be 200–1000 A. The films exhibited good optical transmission between 2.5 and 10 μm, with a calculated absorption coefficient of 490 cm−1. The friction coefficients of this film were found to be 0.035 and 0.030 at dry nitrogen and humid air environments, respectively, and the films had low wear rates.

α-Tocopherol in the developing rat retina: a high pressure liquid chromatographic analysis

High pressure liquid chromatography was used to measure a-tocopherol in the retinas of rats reared in a cyclic light or dark environment. These measurements were performed on extracts of whole retinas during the developmental period, 18–60 days, and on isolated ROS from adult animals. Similar α-tocopherol determinations were performed on retinas and isolated ROS following exposure of rats to intense visible light for 24 hr periods.The results show that a-tocopherol is chromatographically separated from the vitamin A derivatives found in the retina and is pure, as judged by mass spectrometry. In the retinas of cyclic light and dark reared rats, a-tocopherol accumulates in an age dependent fashion, so that at 60 days the level is nearly double that of animals at 18–20 days of age (P<0.001). Because the age dependent accumulation of rhodopsin is greater in dark reared rats, the average molar ratio of rhodopsin to α- tocopherol in the retina of dark reared animals is 25% higher than in cyclic light rats. Foll...

Physical and tribological properties of rapid thermal annealed diamond-like carbon films

Abstract This paper reports the physical characterization and tribological properties of diamond-like carbon (DLC) and rapid thermal annealed (RTA) DLC films. Amorphous DLC films were deposited by the direct ion beam deposition technique using methane ions. Rapid thermal annealing (RTA) of the films was performed at several fixed temperatures (350, 400, 500, 600, 700, 800, 900 and 1000°C) in a nitrogen atmosphere for 2 min. The films were then characterized by proton recoil detection analysis for hydrogen content, Rutherford backscattering for carbon content and Raman spectroscopy for structural change. The hydrogen content of the DLC films remains constant at 30 at.% in the RTA temperature range 25–500°C, decreases rapidly from 25% to 9% in the range 600–800°C and finally remains at 5% in the range 900–1000°C. The Raman spectra of the DLC films do not change in the RTA temperature range 25–400°C and begin to show the appearance of crystalline graphitic carbon above 500°C. The coefficients of friction of the DLC films do not change significantly with the RTA process; however, the wear factors are strongly dependent on the annealing temperature and the moisture in the environment.

Collisional studies of the excited state potential energy surfaces of HeH+2: Energy thresholds and cross sections for reactions of helium ions with hydrogen yielding H+, H+2, H+3, HeH+, and H*(nl)

Beam collision cell apparatuses have been employed to determine the energy dependences of the cross sections for the reactions of He+ with H2 to yield the ionic or luminescent product species H+, H+2, H+3, HeH+, H*(2l), H*(3l), and H*(4l). Distinct thresholds were observed for the formation of H+ at 7.1±0.2 eV, for HeH+ and H*(2l) at 9.0±0.1 eV, for H*(3l) at 12.7±1.0 eV, and for H*(4l) at 14.4±1.5 eV. The analogous reactions of He+ with D2 have also been studied to confirm these results. Secondary thresholds were also detected, and some of the reactions exhibit apparent isotope effects. Polarization is shown not to appreciably affect the cross sections for H* formation. Both H+2 and H+3, but not HeH+ or H*, are observed as products at near thermal collision energies. The experiments which resulted in the detection of the products H2+, H3+, and especially HeH+, as well as the more precise studies of H+ formation, which are reported herein, were suggested by the theoretical analysis. These results demonstr...

Raman scattering from hydrogenated amorphous carbon films

Amorphous hydrogenated carbon films (a‐C:H), as‐deposited and modified by rapid thermal annealing, by implantation, and by laser irradiation were studied by Raman scattering. The ratio of carbon to hydrogen in each of the samples was determined by Rutherford backscattering (RBS) and proton recoil spectra. The hydrogen content was found to decrease with increasing annealing temperatures, with ion implantation, and with laser irradiation. The Raman spectra were analyzed to obtain peak position and linewidth of the D and G lines of the disordered graphite and the intensity ratio (ID/IG) of these lines correlated with the C/H ratio obtained from RBS and proton recoil spectra. These measurements indicate that with increasing annealing temperature, with ion implantation, and with the laser radiation, the a‐C:H films are modified from less tetrahedrally bonded to more trigonally bonded; the a‐C:H films become more graphitic.

Theoretical and experimental characterization of positive‐column plasmas in oxygen glow discharge

Combined theoretical and experimental studies have been accomplished in order to elucidate the features of positive columns in oxygen glow discharges. The Langmuir probe technique was utilized to measure the plasma parameters such as electron temperature and electric field. A tandem mass spectrometer was used to measure relative concentrations of charged particles. These experimental results were found to be in good agreement with the present theoretical calculations based on a slightly ionized stationary plasma model.

CVD diamond, DLC, and c‐BN coatings for solid film lubrication

The main criteria for judging coating performance were coefficient of friction and wear rate, which had to be less than 0.1 and 10-6 mm3/(N.m), respectively. Carbon‐ and nitrogen‐ion‐implanted, fine‐grain, chemical‐vapor‐deposited (CVD) diamond and diamondlike carbon (DLC) ion beam deposited on fine‐grain CVD diamond met the criteria regardless of environment (vacuum, nitrogen, and air).

Large-area surface treatment by ion beam technique

Abstract A large-area ion beam deposition system has been used extensively for depositing diamond-like carbon films by a direct ion-beam process. An ultra high vacuum ion beam system, consisting of a 20-cm diameter RF excited (13.56 MHz) ion gun and a four-axis substrate scanner, has been used to modify large surfaces (up to 1000 cm 2 ) of various materials, including 304 and 316 stainless steel, 440C and M50 steels, aluminum, aluminum alloys, Ti-6Al-4V, silicon carbide, silicon nitride, polycarbonates, infrared windows and polycrystalline diamond, by depositing varying chemical compositions of diamond-like carbon films. The influence of ion energy, RF power, and gas composition (H 2 /CH 4 , Ar/CH 4 , O 2 /H 2 /CH 4 and N 2 /H 2 /CH 4 ), on the diamond-like carbon characteristics has been investigated. Particular attention was focused on the adhesion, environmental effects, coefficient of friction and wear factors of the diamond-like carbon films on the various substrates under space-like environments. A quadrupole mass spectrometer and a total ion-current measuring device have been utilized to monitor the ion compositions of the gas mixtures of CH 4 /H 2 , CH 4 /Ar, CH 4 /H 2 /O 2 and CH 4 /H 2 /N 2 during the deposition process for quality control and process optimization.