| 1. |
- Muehlbacher, Marlene, et al.
(author)
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Copper diffusion into single-crystalline TiN studied by transmission electron microscopy and atom probe tomography
- 2015
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In: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 574, s. 103-109
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Journal article (peer-reviewed)abstract
- TiN/Cu bilayers were grown by unbalanced DC magnetron sputter deposition on (001)-oriented MgO substrates. Pole figures and electron back-scatter diffraction orientation maps indicate that both layers in the as-deposited state are single-crystalline with a cube-on-cube epitaxial relationship with the substrate. This is confirmed by selected area electron diffraction patterns. To study the efficiency of the TiN barrier layer against in-diffusion of Cu, we annealed samples at 900 degrees C for 1 h in vacuum and at 1000 degrees C for 12 h in Ar atmosphere. The single-crystalline structure of the TiN layer is stable up to annealing temperatures of 1000 degrees C as shown by high resolution transmission electron microscopy. While no Cu diffusion was evident after annealing at 900 degrees C, scanning transmission electron microscopy images and energy-dispersive X-ray spectrometry maps show a uniform diffusion layer of about 12 nm after annealing at 1000 degrees C for 12 h. Concentration depth profiles obtained from 3D atom probe tomography reconstructions confirm these findings and reveal that the TiN film is slightly substoichiometric with a N/Ti ratio of 0.92. Considering this composition, we propose a lattice diffusion mechanism of Cu in TiN via the formation of Cu-N vacancy complexes. The excellent diffusion barrier properties of single-crystalline TiN are further attributed to the lack of fast diffusion paths such as grain boundaries.
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| 2. |
- Mühlbacher, Marlene, 1987-, et al.
(author)
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Cu diffusion in single-crystal and polycrystalline TiN barrier layers : A high-resolution experimental study supported by first-principles calculations
- 2015
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In: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 118:8
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Journal article (peer-reviewed)abstract
- Dense single-crystal and polycrystalline TiN/Cu stacks were prepared by unbalanced DC magnetron sputter deposition at a substrate temperature of 700 °C and a pulsed bias potential of -100 V. The microstructural variation was achieved by using two different substrate materials, MgO(001) and thermally oxidized Si(001), respectively. Subsequently, the stacks were subjected to isothermal annealing treatments at 900 °C for 1 h in high vacuum to induce the diffusion of Cu into the TiN. The performance of the TiN diffusion barrier layers was evaluated by cross-sectional transmission electron microscopy in combination with energy-dispersive X-ray spectrometry mapping and atom probe tomography. No Cu penetration was evident in the single-crystal stack up to annealing temperatures of 900 °C, due to the low density of line and planar defects in single-crystal TiN. However, at higher annealing temperatures when diffusion becomes more prominent, density-functional theory calculations predict a stoichiometry-dependent atomic diffusion mechanism of Cu in bulk TiN, with Cu diffusing on the N sublattice for the experimental N/Ti ratio. In comparison, localized diffusion of Cu along grain boundaries in the columnar polycrystalline TiN barriers was detected after the annealing treatment. The maximum observed diffusion length was approximately 30 nm, yielding a grain boundary diffusion coefficient of the order of 10‑16 cm2s-1 at 900 °C. This is 10 to 100 times less than for comparable underdense polycrystalline TiN coatings deposited without external substrate heating or bias potential. The combined numerical and experimental approach presented in this paper enables the contrasting juxtaposition of diffusion phenomena and mechanisms in two TiN coatings, which differ from each other only in the presence of grain boundaries.
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| 3. |
- Ponsioen, Cyriel Y, et al.
(author)
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No Superiority of Stents vs Balloon Dilatation for Dominant Strictures in Patients With Primary Sclerosing Cholangitis.
- 2018
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In: Gastroenterology. - : Elsevier BV. - 1528-0012 .- 0016-5085. ; 155:3
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Journal article (peer-reviewed)abstract
- Dominant strictures occur in approximately 50% of patients with primary sclerosing cholangitis (PSC). Short-term stents have been reported to produce longer resolution of dominant strictures than single-balloon dilatation. We performed a prospective study to compare the efficacy and safety of balloon dilatation vs short-term stents in patients with non-end-stage PSC.We performed an open-label trial of patients with PSC undergoing therapeutic endoscopic retrograde cholangiopancreatography (ERCP) at 9 tertiary-care centers in Europe, from July 2011 through April 2016. Patients found to have a dominant stricture during ERCP were randomly assigned to groups that underwent balloon dilatation (n= 31) or stent placement for a maximum of 2 weeks (n= 34); patients were followed for 24 months. The primary outcome was the cumulative recurrence-free patency of the primary dominant strictures.Study recruitment was terminated after a planned interim analysis because of futility and differences in treatment-related serious adverse events (SAEs) between groups. The cumulative recurrence-free rate did not differ significantly between groups (0.34 for the stent group and 0.30 for the balloon dilatation group at 24 months; P = 1.0). Most patients in both groups had reductions in symptoms at 3 months after the procedure. There were 17 treatment-related SAEs: post-ERCP pancreatitis in 9 patients and bacterial cholangitis in 4 patients. SAEs occurred in 15 patients in the stent group (45%) and in only 2 patients in the balloon dilatation group (6.7%) (odds ratio, 11.7; 95% confidence interval, 2.4-57.2; P= .001).In a multicenter randomized trial of patients with PSC and a dominant stricture, short-term stents were not superior to balloon dilatation and were associated with a significantly higher occurrence of treatment-related SAEs. Balloon dilatation should be the initial treatment of choice for dominant strictures in patients with PSC. This may be particularly relevant to patients with an intact papilla. ClinicalTrials.gov no. NCT01398917.
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| 4. |
- Wu, Guorong, et al.
(author)
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Excited state non-adiabatic dynamics of N-methylpyrrole : A time-resolved photoelectron spectroscopy and quantum dynamics study
- 2016
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 144:1
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Journal article (peer-reviewed)abstract
- The dynamics of N-methylpyrrole following excitation at wavelengths in the range 241.5-217.0 nm were studied using a combination of time-resolved photoelectron spectroscopy (TRPES), ab initio quantum dynamics calculations using the multi-layer multi-configurational time-dependent Hartree method, as well as high-level photoionization cross section calculations. Excitation at 241.5 and 236.2 nm results in population of the A(2)(pi sigma*) state, in agreement with previous studies. Excitation at 217.0 nm prepares the previously neglected B-1(pi 3p(y)) Rydberg state, followed by prompt internal conversion to the A(2)(pi sigma*) state. In contrast with the photoinduced dynamics of pyrrole, the lifetime of the wavepacket in the A(2)(pi sigma*) state was found to vary with excitation wavelength, decreasing by one order of magnitude upon tuning from 241.5 nm to 236.2 nm and by more than three orders of magnitude when excited at 217.0 nm. The order of magnitude difference in lifetimes measured at the longer excitation wavelengths is attributed to vibrational excitation in the A(2)(pi sigma*) state, facilitating wavepacket motion around the potential barrier in the N-CH3 dissociation coordinate.
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| 5. |
- Wu, Guorong, et al.
(author)
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Excited state non-adiabatic dynamics of pyrrole : A time-resolved photoelectron spectroscopy and quantum dynamics study
- 2015
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 142:7
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Journal article (peer-reviewed)abstract
- The dynamics of pyrrole excited at wavelengths in the range 242-217 nm are studied using a combination of time-resolved photoelectron spectroscopy and wavepacket propagations performed using the multi-configurational time-dependent Hartree method. Excitation close to the origin of pyrrole's electronic spectrum, at 242 and 236 nm, is found to result in an ultrafast decay of the system from the ionization window on a single timescale of less than 20 fs. This behaviour is explained fully by assuming the system to be excited to the A(2)(pi sigma*) state, in accord with previous experimental and theoretical studies. Excitation at shorter wavelengths has previously been assumed to result predominantly in population of the bright A(1)(pi pi*) and B-2(pi pi*) states. We here present time-resolved photoelectron spectra at a pump wavelength of 217 nm alongside detailed quantum dynamics calculations that, together with a recent reinterpretation of pyrrole's electronic spectrum [S. P. Neville and G. A. Worth, J. Chem. Phys. 140, 034317 (2014)], suggest that population of the B-1(pi sigma*) state (hitherto assumed to be optically dark) may occur directly when pyrrole is excited at energies in the near UV part of its electronic spectrum. The B-1(pi sigma*) state is found to decay on a timescale of less than 20 fs by both N-H dissociation and internal conversion to the A(2)(pi sigma*) state.
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