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  • 1
    Electronic Resource
    Electronic Resource
    Crossed molecular beam study of the reaction O(3P)+C2H2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5365-5373 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction between ground state atomic oxygen and acetylene was studied using the crossed molecular beam method with an average collision energy of 6 kcal/mol. The two major primary reaction channels are (a) formation of CH2 and CO and (b) formation of HCCO and H. Product angular distributions and time-of-flight spectra were measured and the translational energy release was determined for each channel. The reaction proceeds primarily on the triplet surface through a long-lived intermediate. For both channels the translational energy distributions were found to peak at about 30% of the total available energy, indicating the existence of an exit channel barrier in each case. The branching ratio between channel (a) and (b) was found to be 1.4±0.5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457585
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  • 2
    Electronic Resource
    Electronic Resource
    Crossed molecular beam study of the reaction O(3P)+C2H4 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6926-6936 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction between ground state atomic oxygen and ethylene was studied under single collision conditions using the crossed molecular beam method. At an average collision energy of about 6 kcal/mol, the two major primary reaction channels are (a) the formation of CH3 and CHO and (b) the formation of C2H3O and H. Product angular distributions and time-of-flight spectra were measured and the translational energy release was determined for each channel. The observed results and calculated potential energy surfaces suggest that after the addition of O(3P) to ethylene forming a triplet diradical, channel (a) occurs by way of intersystem crossing to the singlet state, 1,2-H migration and subsequent C–C bond rupture, whereas channel (b) proceeds mostly through the direct dissociation of the intermediate triplet diradical, except for a small contribution from H atom elimination of the singlet acetaldehyde intermediate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457309
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  • 3
    Electronic Resource
    Electronic Resource
    Exchange dynamics of 23Na and structural incommensuration in NaMo4O6: Dynamic line shape for the second order central transition of quadrupolar nuclei (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3713-3727 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Sodium nuclei in NaMo4O exhibit motion as evidenced by the change in asymmetry parameter describing the central transition of 23Na with variable temperature. The nonaxially symmetric electric field gradient observed in the slow motion limit implies that the preferred occupation of the sodium nucleus is not at the center of the tetragonal oxygen cage. At room temperature the sodium jumps randomly within the cage in such a manner as to experience an axially symmetric electric field gradient on average. Dynamic NMR line shape simulations invoking second order broadening of the central transition were performed based on models of four site exchange, and all-site random exchange. Both models yield results indistinguishable from experiment, with an activation energy Ea of 1.95 k cal mol−1. An anomolous upfield shoulder in the central transition is related to the existence of a structural incommensuration. A lower transition temperature Tc=140 K is evidenced by jump discontinuities in both the temperature dependence of T1 and of the quadrupolar coupling constant e2qQ. Using a plane wave approximation to describe the structural incommensuration, the appearance of, and the gradual downfield shift of the upfield shoulder can be satisfactorily fit to the data. From the temperature dependence of the quasicontinuous frequency distribution associated with the incommensurate structure, the upper transition temperature Ti is estimated to be 520 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455829
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  • 4
    Electronic Resource
    Electronic Resource
    Field dependence of the nuclear magnetic resonance static powder line shape: Studies of the mutual orientation of interaction tensors from the field dependence of the critical frequencies (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2081-2101 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A procedure for determining the interaction tensor orientations and the interaction parameters for mutually oriented electric field gradient (efg) or dipolar and shielding tensors has been developed based upon the magnetic field dependence of the critical frequencies from the polycrystalline nuclear magnetic response (NMR) spectrum. The central transition line shape of half-integer quadrupolar nuclei in the presence of mutually oriented shift anisotropy and second order quadrupolar interaction is discussed for the first time. Analytical expressions for the field dependent critical frequencies have been determined for special orientations when the shift principal Z axis lies on the XZ, YZ, or XY plane of the efg (or dipolar) tensor for the first order as well as the second order interactions. The plots resulting from the analytical expressions provide a convenient graphical approach in determining approximate tensorial orientations and interaction parameters through pattern recognition. For general orientations, a numerical procedure has been developed to determine these parameters by iteratively minimizing the squares of the differences of the calculated and the experimental critical frequencies. Higher order perturbation terms can be incorporated in the present treatment. The method is demonstrated by variable field static proton spectra of trichloro–acetic acid at three different fields (1.3, 2.3, 5.2 T). The near-orthogonal orientation between the dipolar and shielding tensors and the interaction parameters obtained from this approach are consistent with those obtained previously from single crystal studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457069
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  • 5
    Electronic Resource
    Electronic Resource
    Crossed molecular beam study of the reaction O(3P)+allene (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1644-1653 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction between ground state (3P) oxygen atoms and allene was studied under single collision conditions using the crossed molecular beams method. Product angular distributions and the translational energy distribution were determined for each channel. Two major reaction channels could be identified unambiguously: the formation of carbon monoxide and ethylene following oxygen atom attack on the central carbon atom, and the formation of allenyloxy (formyl–vinyl) radical and hydrogen atom following oxygen atom attack on the terminal carbon atom. In addition, at least one other reaction channel, which could be identified as the production of vinyl and formyl radicals, occurs. This channel involves the decomposition of acrolein which is formed by the addition of oxygen to the terminal carbon atom, followed by 1,2-hydrogen migration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465334
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  • 6
    Electronic Resource
    Electronic Resource
    Pulsed sheath dynamics in a small cylindrical bore with an auxiliary electrode for plasma immersion ion implantation (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4431-4434 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temporal evolution of the plasma sheath in a small cylindrical bore with an auxiliary electrode is calculated for zero-rise-time voltage pulses. The ion density, flux, dose, ion energy distribu-tion, and electric field are determined by solving Poisson's equation and the equations of ion motion and continuity using finite difference methods. Our results indicate that the implantation time is about halved and slightly more than 50% of the ions possess impact energy higher than the maximum achieved when an auxiliary electrode is absent. The resulting ion flux, ion current, as well as ion energy distribution, are also determined. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872607
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  • 7
    Electronic Resource
    Electronic Resource
    Computed electron oscillation inside the duct of a vacuum arc source (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6381-6384 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-dimensional numerical model has been developed to simulate the motion of electrons inside the duct of a vacuum arc metal source. It is found that electrons will travel back and forth along the center axis inside the duct tube. This phenomenon of electron oscillation can be explained by the combined effects of the electric and magnetic fields. The electron oscillation will increase the charge state of the positive ions and the ions will gain more energy. Due to the influence of electron oscillation, the plasma throughput of the duct will be different from that of a duct under the influence of only the magnetic field. This finding should be taken into account when designing metal arc sources and optimizing their performance. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370103
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  • 8
    Electronic Resource
    Electronic Resource
    Vacuum arc plasma transport through a magnetic duct with a biased electrode at the outer wall (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3329-3331 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Metal plasma formed by a vacuum arc plasma source can be passed through a toroidal-section magnetic duct for the filtering of macroparticles from the plasma stream. In order to maximize the plasma transport efficiency of the filter the duct wall should be biased, typically to a positive voltage of about 10–20 V. In some cases it is not convenient to bias the duct, for example if the duct wall is part of the grounded vacuum system. However, a positively biased electrode inserted into the duct along its outer major circumference can serve a similar purpose. In this article, we describe our results confirming and quantifying this effect. We also show the parametric dependence of the duct transport on the experimental variables. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149913
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  • 9
    Electronic Resource
    Electronic Resource
    A novel distributed system for plasma immersion ion implanter control and automation (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1495-1498 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The high voltage and electromagnetic field environment poses a big challenge to a control system for plasma immersion ion implantation (PIII). The automation process must be immune to electric field interference produced by the high voltage power supply, modulator, radio-frequency or microwave plasma generator, MEVVA plasma sources, and so on. We have recently designed and installed a distributed control system, PIIIDCS, to automate the operation of our PIII facility. Programmable logic controllers are used as the field control stations because of their good anti-interference ability and good real time response. A DH-485 network is used as the communication link between the field controllers and the management station in order to improve the robustness and reliability of the system. The newly developed interface is designed to work in a graphic mode in Microsoft Windows 95. Test runs have shown that the system is reliable, flexible, and easy to operate. The development of this novel control system will expedite the development of commercial PIII instrumentation. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148785
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  • 10
    Electronic Resource
    Electronic Resource
    Pure high dose metal ion implantation using the plasma immersion technique (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4359-4361 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: High energy implantation of metal ions can be carried out using conventional ion implantation with a mass-selected ion beam in scanned-spot mode by employing a broad-beam approach such as with a vacuum arc ion source, or by utilizing plasma immersion ion implantation with a metal plasma. For many high dose applications, the use of plasma immersion techniques offers a high-rate process, but the formation of a surface film along with the subsurface implanted layer is sometimes a severe or even fatal detriment. We describe here an operating mode of the metal plasma immersion approach by which pure implantation can be obtained. We have demonstrated the technique by carrying out Ti and Ta implantations at energies of about 80 and 120 keV for Ti and Ta, respectively, and doses on the order of 1×1017 ions/cm2. Our experiments show that virtually pure implantation without simultaneous surface deposition can be accomplished. Using proper synchronization of the metal arc and sample voltage pulse, the applied dose that deposits as a film versus the part that is energetically implanted (the deposition-to-implantation ratio) can be precisely controlled.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150094
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