Recombination of 5-eV O<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mo>(</mml:mo></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math><i>P</i>) atoms with surface-adsorbed NO: Spectra and their dependence on surface material and temperature

Orient, O. J.; Martus, K. E.; Chutjian, A.; Murad, Edmond

doi:10.1103/physreva.45.2998

Cited by 23 publications

(7 citation statements)

References 29 publications

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“…In contrast, few data are available on sputtering yields at energies below 1 keV (the low-energy regime). Furthermore, the literature that is available deals almost exclusively with atomic projectiles [6][7][8][9][10][11][12][13]. This work represents the first measurements of lowenergy sputtering yields by molecules near threshold, and shows an unexpected enhancement in sputtering yields for molecules as compared to atoms.…”

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confidence: 89%

New Molecular Collisional Interaction Effect in Low-Energy Sputtering

et al. 1998

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An unexpected pronounced enhancement is observed in sputtering yields per atom for N 1 2 compared to N 1 from a polycrystalline gold target. This effect is seen when the kinetic energy per projectile atom is below 500 eV and increases as projectile energy decreases to near-threshold energies. We report on the first observations of a pronounced enhancement in sputtering yields for molecular ions as compared to atomic ions at low projectile energies near sputtering thresholds (30 -500 eV) [1]. At high energies (* 50 keV) sputtering yield enhancement with molecules has been observed and attributed to nonlinear effects in the collision cascade [2][3][4]5]. In the medium energy (linear cascade) regime (approximately 1-50 keV) it is known that the sputtering yield per atom of a molecular ion equals that of an atomic ion at the same impact velocity. In contrast, few data are available on sputtering yields at energies below 1 keV (the low-energy regime). Furthermore, the literature that is available deals almost exclusively with atomic projectiles [6][7][8][9][10][11][12][13]. This work represents the first measurements of lowenergy sputtering yields by molecules near threshold, and shows an unexpected enhancement in sputtering yields for molecules as compared to atoms. This new effect can be attributed to the fact that the kinetic energy of a molecular projectile is most efficiently transferred when the time of collision is comparable to or larger than the vibrational period which is dependent on the detailed nature of the molecular potential. These experiments provide new and significant insight into fundamental projectile-surface interactions relevant to growth and etching.The experiments were conducted in an ultrahigh vacuum chamber with a base pressure of 3 3 10 29 Torr. Low-energy atomic and molecular ions were delivered by a unique accelerator that produces high fluxes of ions with energies tunable between 1 eV and 2 keV. A schematic of the experiment is shown in the inset of Fig. 1. Ions were produced by a discharge source and focused by an Einzel lens. Mass separation was carried out by use of a Wien filter and neutral particles are eliminated by turning the beam by 1.3 ± and passing it through a small aperture (4.8 mm diameter). The beam was then steered back onto the beam axis and refocused by a second Einzel lens. The beam was well defined spatially (FWHM 0.5 mm at 1 keV) and in energy (FWHM 1 eV at 1 keV). The beam was scanned in a raster pattern over a mask with a 2 mm diameter aperture in order to have a homogeneous current density on the target. The current density was determined via an 80% transmission nickel mesh. The kinetic energy of the primary ions ranged from 10 eV to 2 keV with a current density $100 nA͞cm 2 . Sputtering yields were acquired by monitoring the mass change of a goldcoated quartz-crystal microbalance (QCM). By using an FIG.

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confidence: 89%

New Molecular Collisional Interaction Effect in Low-Energy Sputtering

et al. 1998

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“…The fast-atom apparatus is described in detail in (Madzunkov et al 2006) [see also (Orient et al 1992;Orient et al 1993)]. The surface target consists of CO frozen on a gold surface mounted to a linear translation stage.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Neutral-neutral reactions almost certainly play a major role within cold dark clouds where UV penetration is blocked by dust, and in hot molecular cores where shock heating of neutral atomic species can occur (Ehrenfreund and Charnley 2000). The clearest example of the importance of neutral-neutral reactions is the astrophysical observation that abundant CO 2 is detected in a quiescent dark cloud (Elias 16), where no sources of UV radiation are present, and hence where photochemistry cannot have a role (Whittet et al 1998).…”

Section: Introductionmentioning

confidence: 99%

Measurements of polyatomic molecule formation on an icy grain analog using fast atoms

et al. 2006

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Carbon dioxide has been produced from the impact of a monoenergetic O( 3 P) beam upon a surface cooled to 4.8 K and covered with a CO ice. Using temperature-programmed desorption and mass spectrometer detection, we have detected increasing amounts of CO 2 formation with O( 3 P) energies of 2, 5, 10, and 14 eV. This is the first measurement of polyatomic molecule formation on a surface with superthermal atoms. The goal of this work is to detect other polyatomic species, such as CH 3 OH, which can be formed under conditions that simulate the grain temperature, surface coverage, and superthermal atoms present in shock-heated circumstellar and interstellar regions.

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“…Electron attachment or the charge transfer technique are used to neutralize the positive ion beam, 8 ' 9 whereas the photodetachment technique is applied to a negative beam. 10 " 12 The other approach works from the opposite standpoint of the ion beam method, i.e., quantitative degradation of materials is examined by accelerated testing without sufficient kinetic energy of AO. The data base constructed by this approach must be equipped with sufficient safety factors when selecting materials for space application.…”

Section: Introductionmentioning

confidence: 99%

Atomic oxygen generators for surface studies in low Earth orbit

1994

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Two facilities for the generation of energetic atomic oxygen beams have been developed to investigate the degradation of materials in low Earth orbit. An atomic oxygen generator using an ion beam method was used mainly for studying the effect of kinetic energies on surface reactions. Another generator combined pulsed supersonic valve and pulsed YAG laser systems for long-duration exposure experiments without maintenance. The velocity of atomic oxygen was measured by a retarding energy analyzer and a plasma time-of-flight analyzer. Increments of mass in silver films due to the formation of oxides show that the fluxes of atomic oxygen exceed 10 12 ~ 10 13 atoms/cm 2 s. X-ray photoelectron spectroscopy spectra of Ols on a single MoSi crystal exposed to energetic atomic oxygen showed the existence of energy dependence of the surface reaction.

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Recombination of 5-eV O(3P) atoms with surface-adsorbed NO: Spectra and their dependence on surface material and temperature

Cited by 23 publications

References 29 publications

New Molecular Collisional Interaction Effect in Low-Energy Sputtering

New Molecular Collisional Interaction Effect in Low-Energy Sputtering

Measurements of polyatomic molecule formation on an icy grain analog using fast atoms

Atomic oxygen generators for surface studies in low Earth orbit

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