| 1. |
- Gratz, M, et al.
(author)
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X-ray generation for medical applications from a laser-produced plasma
- 1996
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In: Applied Surface Science. - : Elsevier BV. - 1873-5584 .- 0169-4332. ; 96-8, s. 443-447
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Journal article (peer-reviewed)abstract
- We present investigations on the generation of X-ray radiation suitable for different types of medical imaging. Pulses from a 10 Hz terawatt laser system with a duration of 150 fs are focused onto a solid high-Z material target, with focal spot intensities reaching 10(18) W/cm(2). The produced plasma emits broadband X-ray radiation with photon energies up to the MeV region. The application of this X-ray radiation offers new features for medical radiography. Our source allows magnification imaging as well as ultrashort single-shot exposures. New contrast imaging techniques making use of an enhanced characteristic line emission are investigated. The experimental set-up also allows the study of ablation phenomena from sub-picosecond laser pulses by means of particle deposition on thin glass plates. Deposition patterns were studied dependent on different plasma-generation parameters.
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| 2. |
- Aberg, D., et al.
(author)
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Nitrogen passivation by implantation-induced point defects in 4H-SiC epitaxial layers
- 2001
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In: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 184:04-jan, s. 263-267
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Journal article (peer-reviewed)abstract
- Ion implantation causes damage to the crystal lattice resulting in the loss of free charge carriers. In this study, low dose implantations using different ions and implantation doses are made to resolve the initial carrier loss in nitrogen-doped epitaxial layers. A strong dependence of compensation on nitrogen concentration is seen, showing that nitrogen is passivated by implantation-induced point defects. An activation energy of 3.2 eV for the dissociation of the passivated nitrogen center is obtained.
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| 3. |
- Agui, A., et al.
(author)
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Direct observation of interface effects of thin AlAs(100) layers buried in GaAs
- 2000
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In: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 166:1-4, s. 309-312
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Journal article (peer-reviewed)abstract
- A study of the electronic structure of ultrathin AlAs layers buried in GaAs(100) and their interfaces is presented. Al L2,3 soft-X-ray-emission (SXE) spectra from the AlAs layers were measured. The spectra show distinct thickness-dependent features, which are reproduced using ab initio calculations.
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| 4. |
- Amandusson, H., et al.
(author)
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Effect of CO and O2 on hydrogen permeation through a palladium membrane
- 2000
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In: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 153:4, s. 259-267
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Journal article (peer-reviewed)abstract
- Hydrogen permeation through a 25-µm thick palladium membrane during continuous exposures of hydrogen together with different combinations of oxygen and carbon monoxide has been studied at membrane temperatures of 100 °C-250 °C (total pressures of 40-150 Torr). Both CO and O2, individually, inhibit hydrogen permeation through the membrane. The cause of the inhibition is, however, somewhat different. CO blocks available hydrogen dissociation sites, while oxygen both blocks dissociation sites and also consumes adsorbed hydrogen through the production of water. When a combination of CO and O2 is supplied together with hydrogen, new reaction pathways will emerge. The carbon dioxide formation will dominate the water forming reaction, and consequently, the blocking effect caused by the formation of water will be suppressed. In a mixture of CO+O2+H2, the hydrogen permeation can become either larger or smaller than that due to only O2+H2 or CO+H2 depending on the CO/O2 ratio. It is thus possible to find a situation where carbon monoxide and oxygen react to form CO2 leaving adsorbed hydrogen free to permeate the membrane.
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| 5. |
- Bocelli, S, et al.
(author)
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Experimental identification of the optical phonon of CoSi2 in the infrared
- 1995
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 91:1-4, s. 30-33
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Journal article (peer-reviewed)abstract
- A weak but clear optical structure was detected at 329 cm−1 by both reflectance and transmittance measurements in the far infrared on a 430 Å film of CoSi2 grown on Si(100). This is the first observation of the IR vibrational mode of the cubic structure of CoSi2 and the result is in very good agreement with theoretical calculations. In order to characterize the sample, the reflectance was extended up to 5.2 × 104 cm−1 and the refractive index was also directly obtained in a more limited spectral range by spectroscopic ellipsometry. The IR structure was then quantitatively analyzed by means of a fit procedure, obtaining the values of ω0 = 327 cm−1 for the phonon energy, of γ = 10.5 cm−1 for the damping parameter and of 0.006 electronic charges for the screened effective ionic charge.
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| 6. |
- Bratus, V. Y., et al.
(author)
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Vacancy-related defects in ion-beam and electron irradiated 6H-SiC
- 2001
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In: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 184:04-jan, s. 229-236
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Journal article (peer-reviewed)abstract
- A brief review is given on EPR study of irradiation-induced defects in SiC. The results of low-temperature study of Ky1 and Ky2 centers reveal for both of them the C-S symmetry, spin S = 1/2 and close coincidence of the g-tensor components. For Ky2 defect the principal values of g-tensor have been determined as g(z) = 2.0048, g(x) = 2.0022 and g(y) = 2.0037, where z and x directions reside in the (11 (2) over bar0) plane and the z-axis makes up an angle 65 degrees with the c-axis. The same residence of z- and x-axis and an angle 59 degrees are found for Ky1 center, g(z) = 2.0058, g(x) = 2.0025 and g(y) = 2.0023. A comparison of experimental and calculated hyperfine (HF) parameters is presented which suggests that Ky2 and Ky1 defects can be assigned to the positively charged carbon vacancy in 6H-SiC. The EPR study of defects created along the Al+ ion track in n-type 6H-SiC shows that lineshape, linewidth and integral intensity of the EPR signal reflect the state of damaged layer generated by ion implantation. A variation of defect density with annealing is reported and defect origin is discussed.
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| 7. |
- Bukaluk, A., et al.
(author)
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Auger electron spectroscopy, ellipsometry and photoluminescence investigations of Zn1-XBeXSe alloys
- 2001
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In: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 175-176, s. 531-537
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Journal article (peer-reviewed)abstract
- In this paper, properties of the Zn1-XBeXSe crystals grown from the melt by the high-pressure Bridgman method are reported. Spectroscopic ellipsometry has been used for determination of the complex dielectric function of Zn1-XBeXSe. On the basis of the photon energy dependence of the dielectric function, the energy gaps of alloys containing different beryllium concentrations have been evaluated. Measurements of the photoluminescence (PL) spectra allowed to find the excitonic gap in the investigated alloys. Auger electron spectroscopy (AES) with simultaneous argon ion sputtering has been used for determination of surface composition. AES investigations allowed to make predictions concerning distribution of particular elements in the samples. © 2001 Elsevier Science B.V.
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| 8. |
- Chakarov, D V, et al.
(author)
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Photos induced desorption and intercalation of potassium atoms deposited on graphite(0001)
- 1996
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In: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 106, s. 186-192
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Journal article (peer-reviewed)abstract
- In addition to the photodesorption phenomenon previously observed for single K atoms from a graphite surface covered with a monolayer of potassium we present new results related to the photon stimulated interaction of potassium with graphite, which concerns alternative routes for energy relaxation of the photo excited K adatoms: photoinduced intercalation. The desorption yield has a threshold at h omega approximate to 3 eV and a maximum at h omega(max) approximate to 4.9 eV, Polarization measurements indicate a substrate-mediated mechanism. The coverage dependence suggests that only the ionic 2D, K-phase is photo active. The proposed mechanism includes attachment of photo-generated hot electrons to the K 4s adsorbate resonance of energy E(res). Assuming an analogous excitation process we discuss different mechanisms for the K photo intercalation and possible applications of the photon stimulated doping of carboneous materials at low temperature.
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| 9. |
- Coullerez, G., et al.
(author)
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Insights into ToF-SIMS analysis of dendritic macromolecules : cationization and PCA to probe their molecular weight on surfaces
- 2003
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In: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 203, s. 620-624
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Journal article (peer-reviewed)abstract
- Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is utilized to study dendrons, dendrimers and hyperbranched derivatives prepared from the 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) or the 3-ethyl-3-(hydroxymethyl)oxetane (TMPO). We show that the cationization experiments of the intact molecules with alkali or metal ions such as Na+, Cu+ or Ag+ allow to detect whole molecular species up to 3000 Da (low generation). It allows to probe directly their molecular TM weight and end-functionality. However, when the molecule lift-off fails for series of hyperbranched polyesters Boltorn(TM), the fingerprint part of the SIMS spectra (m/z < 300 Da) is instead used. The low-mass fragments are mainly assigned to the bis-MP repeating unit. Ions due to the core molecule are also distinguished. Data treatment is combined with the principal component analysis (PCA) multivariate statistical method to highlight the main differences between the spectra. Only one principal component (PC1) is needed to describe most of the variance between the samples taking into account the generation effect. PC1 plotted as a function of the molecular weight gives a calibration curve. Normalization of the data set by ion intensities from the core molecule allows the linearization of the SIMS intensities vs. the molecular weight.
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| 10. |
- Dannetun, Helen, 1957-, et al.
(author)
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The relative ionization gauge sensitivity of some unsaturated hydrocarbons
- 1987
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 29, s. 331-
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Journal article (peer-reviewed)abstract
- By studying the water desorption rate from an oxygen covered Pd surface which is exposed to some unsaturated hydrocarbons (and hydrogen) the relative ionization gauge sensitivity of the hydrocarbons: acetylene, ethylene, propene, 1- and 2-butene, propadiene, 1,3-butadiene, propyne and butyne has been determined.
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