| 61. |
- Coullerez, G., et al.
(författare)
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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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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 203, s. 620-624
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Tidskriftsartikel (refereegranskat)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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| 62. |
- Cuevas, Ignacio, et al.
(författare)
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Li7La3Zr2O12 interface functionalization via boric acid treatment : A step to contact improvement
- 2024
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 656
-
Tidskriftsartikel (refereegranskat)abstract
- Realization of a functional surface layer of lithium metaborate at the interface of garnet-type lithium lanthanum zirconium oxide (LLZO) electrolyte pellets is achieved via a mild, scalable solution-based route employing boric acid to transform and remove detrimental Li2CO3 typically formed on LLZO during exposure to humid air. The effects of this boric acid treatment are evaluated by systematic morphological and structural characterization of LLZO pellets that were subjected to different conditions. Surface-sensitive analyses via X-ray photoelectron spectroscopy, combined with in situ Ar-ion etching and reflection electron energy loss spectroscopy (REELS) measurements, are purposely employed to probe the extent and efficacy of resulting LiBO2 in removing Li2CO3 and protecting the modified LLZO surface from unwanted carbonation that disrupts its interfacial Li-ion conductivity. This key aspect has been corroborated by an aimed comparison of the different LLZO surface energy bandgap values extracted from the REELS measurements, which provides further insight into the actual impact of Li2CO3 and its replacement with a beneficial, ionically conducting LiBO2 layer. The latter substantially improves the surface adhesion of the modified LLZO pellets to molten lithium without introducing metallic-like species and provides an overall reduced impedance by unlocking the interfacial Li-ion conduction otherwise severely hampered by Li2CO3.
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| 63. |
- Cupak, C., et al.
(författare)
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Sputter yields of rough surfaces : Importance of the mean surface inclination angle from nano- to microscopic rough regimes
- 2021
-
Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 570
-
Tidskriftsartikel (refereegranskat)abstract
- The roughness of a surface is known to have a strong influence on the sputtering process. Commonly used 1D Monte Carlo codes for calculating sputter yields show good agreement with experimental data only for comparably flat surfaces, whereas local ion incidence angles, shadowing and redeposition influence the sputter yields in both magnitude and angular dependence on rough surfaces. In the present work, we therefore investigated tungsten samples of largely different roughness, characterised by atomic force and confocal microscopy. A highly sensitive quartz crystal microbalance was used to determine sputter yields during ion irradiation. Low ion fluences were applied to ensure that the surface morphology did not change during irradiation. The results were used to benchmark our new ray-tracing simulation code SPRAY, which can take microscopy images without limitations in size as input. SPRAY was furthermore applied to perform systematic simulations for artificially roughened and computer-generated surfaces. A clear result was that the governing parameter for description of the sputtering behaviour is the mean value of the surface inclination angle distribution, rather than the commonly used root mean square roughness. Our simulations show that this parameter is universally applicable for a wide range of different surface structures.
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| 64. |
- da Silva, A. F., et al.
(författare)
-
Optical properties of in situ doped and undoped titania nanocatalysts and doped titania sol-gel nanofilms
- 2006
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 252:15, s. 5365-5367
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO2) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO2 thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO2 absorption, which subsequently yields a strong en-fission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO2 are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO2 films prepared for undoped sol-gels and by sputtering is performed.
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| 65. |
- Damas, Giane, et al.
(författare)
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Understanding indium nitride thin film growth under ALD conditions by atomic scale modelling : From the bulk to the In-rich layer
- 2022
-
Ingår i: Applied Surface Science. - Amsterdam, Netherlands : Elsevier. - 0169-4332 .- 1873-5584. ; 592
-
Tidskriftsartikel (refereegranskat)abstract
- In recent decades, indium nitride (InN) has been attracting a great deal of attention for its potential applicability in the field of light-emitting diodes (LEDs) and high-frequency electronics. However, the contribution from adsorption- and reaction- related processes at the atomic scale level to the InN growth has not yet been unveiled, limiting the process optimization that is essential to achieve highly crystalline and pure thin films. In this report, we investigate the reaction pathways that are involved in the crystal growth of InN thin film in atomic layer deposition (ALD) techniques from trimethylindium (TMI) and ammonia (NH3) precursors. To accomplish this task, we use a solid-state approach to perform the ab-initio calculations within the Perdew–Burke–Ernzerhof functional (PBE) level of theory. The results clarify the activation role from the N-rich layer to decrease the barrier for the first TMI precursor dissociation from Δ‡H= +227 kJ/mol, in gas phase, to solely +16 kJ/mol, in the surface environment. In either case, the subsequent CH3 release is found to be thermo- and kinetically favored with methylindium (MI) formed at the hcp site and ethane (C2H6) as the byproduct. In the following step, the TMI physisorption at a nearby occupied hcp site promotes the sequential hydrogen removal from the N-rich layer at the minimum energy cost of Δ‡H < +105 kJ/mol with methane (CH4) release. An alternative mechanism involving the production of CH4 is also feasible upon dissociation in gas phase. Furthermore, the high concentration of CH3 radicals, from precursor dissociation, might be the origin of the carbon impurities in this material under the experimental conditions of interest. Finally, the passivation methodology is not found to affect the evaluation of the surface-related processes, whereas the inclusion of spin-polarization is demonstrated to be essential to the proper understanding of the reaction mechanism.
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| 66. |
- Dannetun, Helen, 1957-, et al.
(författare)
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A hydrogen-sensitive Pd-MOS structure working over a wide pressure range
- 1984
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 17, s. 259-
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Tidskriftsartikel (refereegranskat)abstract
- A Pd-MOS structure has been developed which has proven to be sensitive to hydrogen both in air at atmospheric pressures and in UHV. The ability to work over a wide pressure range makes it an interesting component in, e.g., the study of catalytic reactions involving hydrogen on metal surfaces. Here we demonstrate the hydrogen sensitivity of such a structure over a pressure range of 5x10-11 to 2 Torr.
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| 67. |
- Dannetun, Helen, 1957-, et al.
(författare)
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The relative ionization gauge sensitivity of some unsaturated hydrocarbons
- 1987
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 29, s. 331-
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Tidskriftsartikel (refereegranskat)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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| 68. |
- Das, Sourav, et al.
(författare)
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Hydrothermally grown SnS2/Si nanowire core-shell heterostructure photodetector with excellent optoelectronic performances
- 2023
-
Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 624
-
Tidskriftsartikel (refereegranskat)abstract
- Core-shell nanowire heterostructure is a new architecture for photodetector application with enlarged active surface area enhancing light absorption and photodetector performance. As an emanating coating material, SnS2 has a growing interest in next-generation optoelectronic materials. Here, we reported the enhanced optoelectronic performance of the hydrothermally grown SnS2 and Si nanowire (SiNWs) core-shell heterostructure. Hydrothermally grown SnS2 on Si nanowire creates a uniform coating over the entire surface of nanowires which enhances the heterostructure's effective junction area and improves optoelectronic performance over the broad spectral range (300 - 1100 nm). Specially, under 340 nm illumination, the core-shell photodetector exhibits large responsivity (-383 A/W) and extremely high external quantum efficiency (-2 x 105 %) at very low optical power (-20 nW/mm2). This SnS2/SiNWs core-shell heterostructure with significantly improved optoelectronic performance will be favourable for the development of photodetector with an ability to work with extremely high efficiency.
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| 69. |
- David, Denis G.F., et al.
(författare)
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Quantitative analysis of plasmon excitations in hard x-ray photoelectron spectra of bulk black phosphorus
- 2020
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 505
-
Tidskriftsartikel (refereegranskat)abstract
- Black phosphorus (BPh) is a layered material with strong in-plane anisotropy of its structural and electronic properties; in spite of the great potential of BPh for conceptually new devices in optoelectronics and plasmonics, its fundamental electronic excitations have not yet been fully elucidated. In order to discriminate collective (plasmons) and single-particle (inter band transitions) excitations, we investigate the energy-loss distribution of P 1s photoelectrons in hard X-ray photoelectron spectra of BPh over a wide energy range. The energy-loss function (ELF), averaged over the principal directions of the BPh crystal, has been retrieved by using a Fourier Transform analysis to eliminate multiple inelastic scattering events. At low loss energies (1-8 eV), weak unresolved energy loss peaks are well described by DFT calculated inter band transitions, showing some anisotropy in the dielectric function epsilon(omega, q) tensor of BPh. At high loss energies, the ELF is dominated by the collective excitation of valence electrons with a peak energy at 20.1 +/- 0.2 eV, and weak anisotropy is found in the DFT calculated Im(- 1/epsilon) tensor. The anomalously small peak energy (9.0 +/- 0.5 eV) of a weak surface plasmon resonance is attributed either to low surface electron density in the terminal phosphorene layer or to some anisotropic surface plasmon propagation.
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| 70. |
- Davila, M. E., et al.
(författare)
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Surface phase transitions at metal-semiconductor interfaces : a revisit is needed
- 2004
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 234:04-jan, s. 274-285
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we review some of the most recent progress and understanding in the low temperature surface phase transitions at prototypical metal-semiconductor interfaces. We essentially focus on quantitative surface structural information obtained by using a significant variety of specialised techniques for the individual phases of a model system, namely, tin on Ge(1 1 1) substrates. The strengths and limitations of the structural results obtained by using scanning tunnelling microscopy, photoelectron diffraction and surface X-ray diffraction are discussed in relation to their support with respect to possible mechanisms recently invoked in the literature as being at the origin of the phase transition. These investigations show that a large progress has been made in this field, taking into account the very valuable experimental and theoretical contributions provided by different groups. There remain, however, essential unresolved problems, which will be analysed in the light of the limitations of these structural methods and the difficulty presented by the complex adsorbate systems studied.
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