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  • 1995-1999  (9)
  • 1
    Electronic Resource
    Electronic Resource
    The deposition of a GaS epitaxial film on GaAs using an exchange reaction (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1244-1246 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A GaS thin film has been formed epitaxially on GaAs(100) using a photoassisted growth-etching reaction between H2S and the GaAs substrate. In the reaction, the growth of GaS is accomplished via the replacement of As in the GaAs lattice by the photochemically generated S atom, while As is etched from the substrate as arsenic sulfide. The surface of the resulting GaS thin film is characterized by a sharp (2×1) low energy electron diffraction pattern, indicating excellent crystalline quality. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117425
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  • 2
    Electronic Resource
    Electronic Resource
    Photochemistry of phosgene in the solid phase: Dissociation, ejection, and thermal desorption (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 7895-7903 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Understanding photochemistry and energy transfer mechanisms in molecular solid films is of interest to many scientific issues, ranging from matrix-assisted laser desorption ionization mass spectrometry to photochemical processes on polar stratospheric cloud particles. We present a study of a model system: the photochemistry (hν=1.2–6.4 eV) of a molecular Cl2CO solid film at low laser power density, 10 μJ–1 mJ/cm2 for ∼10 ns pulses. At hν≥3.5 eV, photon absorption by Cl2CO leads to a major photodissociation channel resulting in CO (g) and Cl (g) and a minor molecular Cl2CO ejection channel. Both photodissociation and molecular ejection are observed at the lowest laser power density and their yields depend linearly on pulse energy. This result establishes a single photon photoexcitation mechanism. The electronically excited Cl2CO in the surface region of the solid film can either dissociate or convert its electronic energy to translational motion in Cl2CO. The translational energy distribution of CO (g) from the photodissociation channel is bimodal: the flux-weighted mean translational energy of the fast channel is photon energy dependent (〈Etrans〉=210, 135, and ∼90 meV at hν=6.4, 5.0, and 3.5 eV, respectively), while the slow channel is independent of photon energy and corresponds to completely thermalized CO molecules (〈Etrans/2k〉=84±3 K). The mean translational energy of photoejected Cl2CO is 〈Etrans〉=220±20 meV. In addition to photoejection, there is also a distinctively different thermal desorption channel due to transient laser heating. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471505
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  • 3
    Electronic Resource
    Electronic Resource
    Photochemistry of phosgene in the solid phase: State-resolved dissociation dynamics (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 7904-7913 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The translational, rotational, and vibrational state distributions of CO (g) resulting from the single photon photodissociation of Cl2CO in the condensed phase at ∼90 K have been determined by time-of-flight (TOF) distribution measurement and resonance-enhanced multiphoton ionization (REMPI) spectroscopy. The TOF distribution of CO (g) is bimodal. Internal state characterization of the slow channel reveals a completely thermalized origin, with a rotational temperature of Trot=88±5 K, which is equal to the translational temperature as well as the substrate temperature. We believe these slow CO molecules originate from photodissociation below the topmost surface of the molecular film and achieve thermal equilibrium with the substrate before escaping into the gas phase. Internal state characterization of the fast channel shows, on the other hand, an energetic origin: at hν=5.0 eV, the rotational distribution, with an overall flux-weighted mean rotational energy of 〈Erot〉=0.12±0.01 eV, is non-Boltzmann and can be approximated by a bimodal distribution with rotational temperatures of 210±40 K at low J″(s) and 2200±300 K at high J″(s); the relative vibrational population is Nν=1/Nν=0=0.33±0.05. Both rotational and translational distributions of fast CO show positive correlation with photon energy. These CO molecules must be promptly ejected into the gas phase, carrying nascent energetic information from the photodissociation reaction on the surface of the molecular film. For electronic excitation events that result in photodissociation, 74% of the excess excitation energy is distributed in the translational and internal motions of products (CO and Cl); only 26% of the available energy is converted to motions of surrounding molecules. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471506
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  • 4
    Electronic Resource
    Electronic Resource
    Superthermal vibrational state distribution of CD3 thermally desorbed from GaAs(100) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8829-8832 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational population up to v″=3 in the umbrella mode of CD3 thermally desorbed from GaAs(100) has been determined by resonance enhanced multiphoton ionization (REMPI) spectroscopy. The population ratios are superthermal. The methyl radical must desorb promptly with a transition state geometry significantly different from the planar gas phase geometry. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471607
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  • 5
    Electronic Resource
    Electronic Resource
    State resolved probe of an energetic surface reaction: Phosgene on silver (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4274-4282 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: State resolved characterization of nascent gas phase products is used as probe for the dynamics of an energetic surface reaction. This is achieved in the photodissociation of monolayer phosgene adsorbed on Ag(110). Irradiation of adsorbed Cl2CO in a broad photon energy range (hν=1.9–6.4 eV) leads to dissociation, with Cl retained on the surface and CO desorbing into the gas phase. The translational energy of product CO (g), 〈Etrans〉=0.26 eV, is independent of hν, even at the threshold photon energy (1.9 eV). This result establishes a dissociative electron attachment mechanism involving a reactive intermediate, ClCO, whose prompt dissociation serves as a probe to surface dissociation dynamics. Consistent with translation, internal state distribution of product CO (g) also shows an energetic origin: The rotational distribution, with an overall flux-weighted mean rotational energy of 〈Erot〉=0.17 eV, can be approximated by a bimodal Boltzmann distribution with rotational temperatures of 700 K at low J(s) and 7000 K at high J(s); the relative vibrational population is Nν=1/Nν=0=0.30. Contrary to common expectation based on quenching rates, both translational and rotational energies of CO (g) from monolayer photodissociation are much higher than those from the direct photodissociation in multilayers. This is taken as evidence for concerted reaction dynamics on the surface: The high exothermicity in the Cl–Ag bond formation on the surface exerts part of the energy to the Cl–CO coordinate, leading to higher energies in CO (g). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471237
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  • 6
    Electronic Resource
    Electronic Resource
    Photodissociation Dynamics of Trimethylgallium on GaAs (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 11515-11522 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100029a033
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  • 7
    Electronic Resource
    Electronic Resource
    CORRELATION OF FATIGUE CRACK GROWTH BEHAVIOUR WITH CRACK CLOSURE IN PEENED SPECIMENS (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 18 (1995), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Various residual stress conditions were introduced into the surface of a 7075-T6 aluminium alloy by shot peening. This resulted in a considerable alteration in subsequent fatigue crack growth behaviour. A systematic investigation into the effects of a variety of conditions on fatigue crack propagation behavior was conducted. The degree of shot peening was established using the Almen scale and calibration strips. Changes occurred in crack re-initiation lives, crack growth rate and hardness across the thickness profile. Residual stresses were introduced by various peening operations (such as different peening positions and loading specimens prior to and during peening). By measuring the crack opening level of peened specimens, changes in fatigue crack closure effect with respect to the crack extension in CT specimens are reported. The relations of re-initiation life versus crack opening level and Almen levels, and of the crack closure effect versus Almen scales, were addressed experimentally. It was found that the improvement in re-initiation life and the retarding effect of crack growth, both influenced by the Almen scales, are associated directly with the elevation of crack opening level, particularly at the stage of crack re-initiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.1995.tb00906.x
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  • 8
    Electronic Resource
    Electronic Resource
    Adhesion, deformation and friction for self‐assembled monolayers on Au and Si surfaces (1999)
    Springer
    Tribology letters 7 (1999), S. 103-107 
    Details
    ISSN: 1573-2711
    Keywords: friction ; self‐assembled monolayers ; hysteresis ; alkanethiols ; alkylsilanes ; nanoindentation ; IFM ; aging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Using interfacial force microscopy (IFM), we investigated the tribological behavior of hexadecanethiol monolayers on Au and films of octadecyltrichlorosilane (ODTS), perfluorodecyltrichlorosilane (PFTS) and dodecane on Si. We observe a strong correlation between hysteresis in a compression cycle (measured via nanoindentation) and friction. Additionally, we suggest that the amount of hysteresis and friction in each film is related to its detailed molecular structure, especially the degree of molecular packing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019109117742
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  • 9
    Electronic Resource
    Electronic Resource
    Molecular lubricants for silicon‐based microelectromechanical systems (MEMS): a novel assembly strategy (1999)
    Springer
    Tribology letters 7 (1999), S. 87-90 
    Details
    ISSN: 1573-2711
    Keywords: self‐assembled monolayers ; SAM ; silicon ; surface ; MEMS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Microelectromechanical systems (MEMS) are poised to bring the next technology revolution. At present, many of these are fabricated from silicon using lithographic techniques developed in the microelectronics industry. Due to the large surface area to volume ratio on the micrometer scale, surface forces, such as adhesion and friction, are often detrimental to the fabrication and operation of MEMS devices. Thus, one of the key issues in MEMS is surface engineering to reduce adhesion and friction. Here, we present a general strategy for the efficient assembly of organic layers directly onto the silicon surface in both vacuum environment and solution phases via the robust Si–N or Si–O linkage. This is achieved by the reaction between an amine or alcohol functional group and a chlorinated Si surface. The resulting surface assemblies are thermally stable. Characterization by interfacial force microscope (IFM) reveals that these assemblies have very low surface energy and are mechanically stable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019169303629
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