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  • 1
    Electronic Resource
    Electronic Resource
    Time-Resolved REMPI Detection of Methyl Radicals Generated in Laser-Induced Unimolecular Reactions (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 16290-16295 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100044a014
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  • 2
    Electronic Resource
    Electronic Resource
    The ammonia dimer spectrum in cold helium clusters (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 7179-7186 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared molecular beam depletion spectroscopy has been used to measure the spectrum of ammonia dimers embedded in large helium clusters after the excitation of the umbrella mode. The spectral region from 940 to 1010 cm−1 was covered by a line-tunable CO2-laser. By measuring the dependence of the depletion signal on the pressure of the pick-up cell, we confirmed that all lines are caused by the dimer. The spectrum exhibits two groups of two lines at 978/983 and 992/997 cm−1 separated by 14 cm−1 with a line splitting of 5 cm−1 each. The infrared transitions are only marginally shifted compared to the free ammonia dimer. Also the inversion tunneling splittings are equal to those of the free dimer. Differences in the amplitudes are attributed to relaxation effects of the different inversion components of the same symmetry at the low temperature of 0.4 K. The interchange tunneling splitting, however, which dominates the line splittings in the free dimer is considerably quenched in the helium environment. In addition, the difference in the excitation of the two non-equivalent monomers is remarkably reduced in support of a more cyclic structure in the helium environment. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474957
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  • 3
    Electronic Resource
    Electronic Resource
    High resolution infrared spectroscopy of single SF6 molecules in helium droplets. I. Size effects in 4He droplets (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 5109-5123 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Single SF6 molecules have been embedded in large 4He droplets (N¯4(approximate)103–104 atoms) in a molecular beam and studied via infrared laser depletion spectroscopy. The rotational fine structure of the ν3 transition is analyzed with an effective third order gas phase Hamiltonian of SF6 yielding seven spectroscopic parameters as a function of the measured mean droplet size. From the intensities of the rotational lines the rotational temperature in droplets with N¯4〉103 atoms is determined to be Trot=0.38(1) K consistent with theoretical estimates. Quantitative information on the efficiency of evaporative cooling of the droplets could be obtained by increasing the droplet temperature up to Trot=0.55 K by many successive inelastic collisions with 4He atoms from the background gas. For small droplets the absorption maximum shows an increasing redshift with respect to the gas phase and only small downward shift with droplet sizes N¯4〉2×103. This could not be explained quantitatively with the excluded volume model assuming a liquid drop nor by the expected decrease in the internal pressure with increasing droplet radius. The much smaller decrease in the redshift observed is shown to provide evidence that the nearest neighbor shell of 4He next to the molecule is almost incompressible providing direct experimental evidence for the existence of a dense snowball-like shell structure of 4He atoms around the molecule as predicted theoretically. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479111
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  • 4
    Electronic Resource
    Electronic Resource
    High resolution infrared spectroscopy of single SF6 molecules in helium droplets. II. The effect of small amounts of 4He in large 3He droplets (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 5124-5136 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotationally resolved infrared spectra of single SF6 molecules embedded in large 3He droplets have been studied as a function of mean sizes between N¯3=2×103 and 105 atoms by the cluster beam depletion technique. The observed frequency shifts and line broadening of the dopant spectra are interpreted in terms of the small impurity of about 30–50 4He atoms, which because of their lower zero point energy completely surround the SF6 molecule. For the largest droplets, the observed rotational structure is similar to that observed in pure 4He droplets but the rotational temperature as determined from the relative line intensities is Trot=0.15(1) K, which is about a factor 2.5 lower than in pure 4He droplets. The lower temperature is expected on the basis of the lower heat of evaporation of the 3He atoms on the outside of the droplet. Mixed 3He/4He droplets produced by increasing the 4He concentration in the source gas to 1.2 and 4% of the 3He were found to have temperatures between that for the almost pure 3He droplets and that for pure 4He droplets. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479110
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  • 5
    Electronic Resource
    Electronic Resource
    Rotationally resolved IR spectroscopy of ammonia trapped in cold helium clusters (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5914-5920 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared molecular beam depletion spectroscopy of ammonia molecules embedded in large He clusters has been studied in the spectral region of the ammonia umbrella mode from 940 to 1060 cm−1. The transitions between the lowest rotational energy levels could be resolved. By fitting the spectrum with the Hamiltonian of a free rotor, we observe a large shift of the vibrational frequency of 17.4 cm−1 to the blue, an effective decrease of the rotational constant B by 24%, and a reduction of the tunneling splitting by 31% in the excited and 75% in the ground state. This implies an unusually large interaction between the host cluster and the umbrella motion of the ammonia molecule, an intermediate influence on the rotation and also a large perturbation of the inversion by the helium environment. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477214
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  • 6
    Electronic Resource
    Electronic Resource
    The rotational spectrum of single OCS molecules in liquid 4He droplets (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 4485-4495 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Single OCS molecules have been embedded in large 4He droplets (N¯=1×103–8×103 atoms) and their infrared spectra in the vicinity of the ν3-fundamental at 2062 cm−1 have been studied using coaxial laser depletion spectroscopy. Sharp lines corresponding to the P- and R-branches with a linewidth of 160 MHz or greater are observed. From the line intensities a droplet temperature of 0.37±0.02 K is obtained and from the line positions the rotational constants B for the ground and excited states and an average centrifugal distortion constant D are determined. The former are about a factor of 2.8 smaller and the latter four orders-of-magnitude larger than for the free molecule. The decrease in B is attributed to an attached nonsuperfluid component which has the same effect as a ring of about six 4He atoms in an equatorial plane around the waist of the OCS molecule, which is carried along in the end-over-end rotation. The widths of the individual lines show an interesting asymmetry which is oppositely sloped for the P- and R-branches and increases with the rotational quantum number. Several possible explanations for the line shapes and widths are presented. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481011
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  • 7
    Electronic Resource
    Electronic Resource
    Vibrational spectroscopy of methanol and acetonitrile clusters in cold helium droplets (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2436-2443 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared molecular beam depletion spectroscopy of small methanol and acetonitrile clusters embedded in large helium clusters has been studied in the spectral region of the CO stretch and the CH3 rock mode from 1023 to 1059 cm−1. The results are compared with the experimental spectra of the corresponding free clusters generated in adiabatic expansions and calculations based on density functional theory or empirical potential models. For methanol clusters, the two types of experimental results are the same for the dimer and trimer structure. Different isomers are found in cold helium for the tetramer and pentamer, namely a monomer and dimer attached to a cyclic trimer. For acetonitrile clusters in helium, aside from the dimer, different structures are observed. The spectra from the trimer to the hexamer are dominated by structures which contain the antiparallel dimer as building block with D2d symmetry for the tetramer. They do not correspond to the minimum configurations observed for the free clusters. The fragmentation of the two cluster groups in helium droplets by electron impact ionization is discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479521
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  • 8
    Electronic Resource
    Electronic Resource
    Interferon-β induction by Chlamydia pneumoniae in human smooth muscle cells (2001)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 32 (2001), S. 0 
    Details
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Clinical studies have suggested a causal or contributory role of Chlamydia pneumoniae infection in asthma and atherosclerosis. The activation of synthetic functions of smooth muscle cells (SMC) including the production of cytokines and growth factors plays a major role in the formation of fibrous atherosclerotic plaques as well as in structural remodelling of the airway wall in chronic asthma. In this study we demonstrated that C. pneumoniae induced the production of low levels of interferon (IFN)-β in bronchial and vascular SMC when infected cells were treated with tumour necrosis factor-α (TNF-α). IFN-β production was analysed by reverse transcription-PCR and enzyme-linked immunosorbent assay. The upregulation of IFN-β was paralleled by an increase in mRNA levels of interferon regulatory factor-1 and interferon-stimulated gene factor 3γ, two transcription factors activating the expression of the IFN-β gene. In addition, C. pneumoniae infection enhanced the mRNA level of indoleamine 2,3-dioxygenase, an IFN-inducible factor mediating the restriction of intracellular chlamydial growth, in TNF-α-stimulated SMC. C. pneumoniae-induced IFN-β production by SMC may modulate inflammation and tissue remodelling during respiratory and vascular infection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-695X.2001.tb00527.x
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  • 9
    Electronic Resource
    Electronic Resource
    Increased production of matrix metalloproteinases 1 and 3 by smooth muscle cells upon infection with Chlamydia pneumoniae (2003)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 38 (2003), S. 0 
    Details
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Atherosclerosis has been linked to Chlamydia pneumoniae infection. In atherosclerotic arteries chlamydiae infect macrophages, endothelial cells, and smooth muscle cells (SMC). It has been suggested that the proteolysis of the extracellular matrix by matrix metalloproteinases (MMPs) is involved in the destabilisation and rupture of atherosclerotic plaques. In this study we investigated the expression of several MMPs and tissue inhibitors of MMP (TIMPs) in C. pneumoniae-infected SMC using reverse transcription-polymerase chain reaction analysis. Chlamydial infection of SMC up-regulated the mRNA levels of MMP-1 (interstitial collagenase) and MMP-3 (stromelysin) but did not affect the expression of MMP-2 and -9 (gelatinases). Additionally, the levels of TIMP-1 and -2 mRNA remained unchanged upon infection. Cells infected with C. pneumoniae secreted increased quantities of MMP-1 and -3 proteins as demonstrated by enzyme-linked immunosorbent assays. The ability of C. pneumoniae to stimulate the production of MMP-1 and -3 by SMC may be important for its pathogenic role in the progression of atherosclerotic disease.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0928-8244(03)00126-3
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  • 10
    Electronic Resource
    Electronic Resource
    Polishing of semiconductor materials (1997)
    Springer
    Forschung im Ingenieurwesen 63 (1997), S. 7-12 
    Details
    ISSN: 1434-0860
    Source: Springer Online Journal Archives 1860-2000
    Topics: Technology
    Description / Table of Contents: Zusammenfassung Zur Produktion von mikroelektronischen Bauelementen werden Halbleitersubstratscheiben höchster Perfektion benötigt. Beim Abtrennen der Scheiben vom stabförmigen Halbzeug und der anschließenden Planbearbeitung der Scheiben durch Schleifen oder Läppen wird jedoch die monokristalline Ausgangsstruktur nachhaltig geschädigt. Die geschädigte Randschicht muß daher durch einen Polierprozeß entfernt werden. Neben der Forderung, eine ungestörte und spiegelnde Oberfläche zu erzeugen, muß der Polierprozeß auch eine gute Ebenheit der Scheibe garantieren und zudem wirtschaftlich sein. Der vorliegende Beitrag beschäftigt sich mit verschiedenen Modellen zum Abtragsverhalten beim Polieren von Halbleitersubstratscheiben. Dabei wird sowohl auf den weit verbreiteten Werkstoff Silizium als auch auf die Eigenschaften von Verbindungshalbleitern wie z.B. Gallium-Arsenid eingegangen.
    Notes: Abstract Different abrasive processes such as grinding and lapping are necessary to produce semiconductor wafers. However grinding and lapping leads to deterioration of the surface integrity of monocrystalline wafers. Therefore polishing and planarization is of utmost importance to produce microelectronic components. In this lecture the basics of polishing technology as well as different process models are presented. Additionally the properties of different semiconductor substrate materials Si, GaAs are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00010752
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