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  • 1
    Electronic Resource
    Electronic Resource
    Cross sections for He scattering from surface imperfections: Vacancies and CO adsorbates on Pt(111) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3722-3731 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Total cross sections for He scattering from isolated imperfections on surfaces are calculated using the Sudden approximation, and in some cases also by a numerically exact, time-dependent quantum-mechanical wave packet method. Systems studied include: CO adsorbates on Pt(111); mono-, di-, and trivacancies on Pt(111). The main results are: (1) the incidence angle and energy dependence of the cross section for He/[Pt(111)+CO] are very sensitive to the CO distance from the Pt plane. Interactions with the adsorbate image have little effect on the cross section. (2) The cross sections for clusters of vacancies are given within 10% or better, by the geometric sum of the monovacancy cross sections, the latter being treated as circles centered at each monovacancy. (3) The dependence of the cross section on the energy is sufficiently sensitive to distinguish between the "electron density hole'' and "electron density hump'' models for vacancies and vacancy clusters. (4) The Sudden approximation compares well with the exact quantum-mechanical results at typical experimental energies, when the incidence angle is not too far from the normal. These results indicate that experimental measurements of He scattering cross sections as a function of energy and incidence angle, combined with Sudden or wave packet scattering calculations, can provide detailed information on surface defects and their interactions with gas-phase atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454712
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  • 2
    Electronic Resource
    Electronic Resource
    Low-energy helium nozzle beam (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 369-372 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-intensity supersonic nozzle beam source is described, whose beam energy can be varied between 2 and 170 meV (helium). Experimental performance and time-of-flight measurements on cold helium beams are reported. Condensation in the free jet expansions of helium has been studied by mass spectrometric detection of He+2. A correlation between the maximum speed ratio and the onset of clustering is observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138305
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  • 3
    Electronic Resource
    Electronic Resource
    Low temperature measurements of the rotational relaxation in D2 free jets (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5673-5676 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational relaxation of molecular deuterium in a free jet expansion has been studied between 78 and 473 K by pseudorandom time-of-flight technique. In the temperature range 78–308 K a decrease of the rotational collision number Zrot with increasing temperature is observed as predicted theoretically by Raff and by Rabitz and Lam. Also reported are room temperature data of Zrot for H2 and HD expansions. The number of collisions required to relax H2, D2, and HD at room temperature is in the ratio 10:5:1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448554
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  • 4
    Electronic Resource
    Electronic Resource
    Resonant states of helium atoms scattered from the Pt(110)-(1×2) surface (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 8705-8712 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The specular intensity of helium atoms scattered from the missing-row reconstructed clean Pt(110)-(1×2) surface is measured as a function of the helium beam energy. Sharp resonance features were observed from which four eigenvalues of the He–Pt interaction potential could be determined; ε 0=−6.05±0.05 meV, ε1=−2.93±0.05 meV, ε2=−1.05±0.05 meV, and ε3=−0.32±0.05 meV. Several model potentials were examined and the potential parameters were fitted to these bound states. Excellent agreement with the experimental results is obtained with the shifted-Morse-hybrid (SMH)-potential with a well depth D=−8.17 meV. The shape of the so determined potential is discussed and compared to results from previous studies of the same system. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470127
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  • 5
    Electronic Resource
    Electronic Resource
    Determination of iodine adlayer structures on Au(111) by scanning tunneling microscopy (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 585-591 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Chemisorbed iodine adlayers on Au(111) films on quartz were studied using scanning tunneling microscopy (STM) at room temperature in air. The iodine was adsorbed by successive deposition of droplets of a dilute solution of iodine in methanol. As a function of coverage, various adlayer structures were obtained. By changing the tunneling parameters, either the iodine adlayer or the Au(111) substrate can be imaged with atomic resolution. In this way, the adlattice properties such as periodicity, orientation and the local absolute coverage have been characterized with high accuracy. In the low coverage range (θ〈0.33), due to the high mobility of iodine atoms, only the unreconstructed Au(111) substrate lattice could be imaged. At θ∼0.33, a (3×3)R30° structure is evident. With increasing coverage, a (p×3) structure of higher iodine packing density is observed, which can be described as a uniaxially compressed (striped) phase. Finally, near monolayer saturation coverage the iodine atoms form a hexagonal moiré-like pattern with long-range height modulation. The results are compared with previous measurements on this system under UHV and electrolyte conditions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474419
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  • 6
    Electronic Resource
    Electronic Resource
    High-resolution He-scattering apparatus for gas–surface interaction studies (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2771-2779 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-resolution apparatus designed for the study of elastic and inelastic scattering of thermal helium atoms from crystal surfaces is presented. The highly expanded He nozzle beam has an energy spread ΔE/E of about 1.4% and is collimated to 0.2°. The angle subtended by the detector opening as seen from the sample is also 0.2°. Beam intensities as low as 10−6 of the specular beam intensity from a low-temperature clean Pt(111) surface are detectable. Pseudorandom chopping with a resolution of 2.5 μs (flight path 790 mm) is used for time-of-flight (TOF) analysis of the scattered helium. The base pressure in the sample chamber is in the low 10−11 mbar. The capabilities of the apparatus are demonstrated for physisorbed Xe adlayers on Pt(111). The results presented are obtained by using He scattering in various modes: coherent inelastic, coherent elastic, and incoherent (diffuse) elastic. This technique allows for a nondestructive nearly exhaustive characterization of the thermodynamics, structure, and dynamics of physisorbed adlayers on arbitrary substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139041
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  • 7
    Electronic Resource
    Electronic Resource
    Erratum: "An ultrahigh vacuum scanning tunneling microscope for use at variable temperature from 10 to 400 K'' [Rev. Sci. Instrum. 65, 3204 (1994)] (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3717-3717 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146430
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  • 8
    Electronic Resource
    Electronic Resource
    An ultrahigh vacuum scanning tunneling microscope for use at variable temperature from 10 to 400 K (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3204-3210 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report on the construction of an ultrahigh vacuum (UHV) scanning tunneling microscope (STM) specially designed for operation in the entire range of sample temperatures between 10 and 400 K. The sample is cooled by means of a liquid helium continuous-flow cryostat, while the supporting manipulator and the surrounding devices remain at room temperature. This allows rapid variation of the sample temperature. The standard instruments for surface preparation and analysis and the STM are contained in a single UHV chamber. By rotation of the manipulator the sample can be positioned in front of any of these instruments without changing the sample temperature. The performance of the microscope is demonstrated by two examples of images of xenon adsorbed on platinum(111) showing: (a) the evolution of the morphology of a submonolayer of xenon from adsorption at 17K up to desorption at about 90 K and (b) atomically resolved images of the hexagonal incommensurate rotated phase for xenon at monolayer completion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145219
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  • 9
    Electronic Resource
    Electronic Resource
    180° low-energy impact collision ion scattering spectroscopy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 760-764 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A low-energy impact collision ion (neutral) scattering spectrometer [(N)ICISS] for exact 180° backscattering has been developed. The energy distribution of the backscattered particles is measured with the time-of-flight method (TOF). 180° backscattering spectra are compared with 145°/140° ones. The nearly identical trajectories for incoming and backscattered particles result in the main advantage of 180° NICISS, namely, a quasi-double focusing effect leads to extremely well behaved peaks in the measured angular patterns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141491
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  • 10
    Electronic Resource
    Electronic Resource
    Design principles of a variable temperature scanning tunneling microscope (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 4135-4139 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report on the construction of a variable temperature scanning tunneling microscope (STM) operating from 20 to 700 K in UHV, which routinely allows one to image dense packed metal surfaces in atomic resolution down to the lowest temperature. Central problems in designing a variable temperature STM are discussed in some detail. Methods to achieve efficient vibration isolation between the cryostat and the STM are presented. Furthermore, a sample and sample holder assembly is described, which ensures long-term mechanical stability and STM imaging, while subject to extreme temperature variations. The temperature response of the STM while cooling and heating the sample is measured and will be discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145360
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