| 1. |
- Al-Soubaihi, Rola, et al.
(författare)
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Comparative investigation of structure and operating parameters on the performance and reaction dynamic of CO conversion on silica aerogel and fumed-silica-supported Pd catalysts
- 2022
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Ingår i: SURFACES AND INTERFACES. - : Elsevier BV. - 2468-0230. ; 29, s. 101776-
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Tidskriftsartikel (refereegranskat)abstract
- The catalyst morphology, metal-support interaction, and reaction conditions greatly influence the catalytic performance and reaction dynamics. Similarly, the dispersion of the metal within the support plays a crucial in the thermal stability and sintering of the catalyst. Furthermore, temperature-dependent conversion hysteresis is well-known to occur during ignition and extinction of exothermic CO oxidation over supported Pd catalysts due to the variation of CO adsorption on the surface or bulk oxidation of Pd and the ability of the catalyst regenerate the active sites. Herein, the catalytic performance and the hysteresis behavior of mesoporous silica aerogel supported Pd (Pd/a-SiO2), and commercial fumed silica-supported Pd (Pd/f-SiO2) were investigated compared using CO oxidation as a probe reaction under different reaction conditions and operating parameters (i.e., catalyst weight, ramp rate, and flow rate). Surface and morphologic examination using XPS, FTIR, and of Pd/a-SiO2 and Pd/f-SiO2 reveal a strong correlation between the catalyst surface and structure and its catalytic performance and stability under different reaction parameters. Moreover, this study presents the effect of surface area, particle size, and size distribution on diffusion and mass transport of reactants (CO, O-2) and products (CO2) and active sites accessibility. This study showed that Pd/f-SiO2 had better efficiency under high (turbulence) flow. Moreover, intrinsic apparent activation energy (E-a) and the number of active sites were calculated from the Kinetics of CO oxidation fitted using Arrhenius plots indicate that the ramp rate has less effect on Pd/f-SiO2 catalytic behavior. though, Pd/f-SiO2 had higher relative active sites than Pd/a-SiO2, (E-a) was lower. Cyclic stability and long-term stabilities showed that both catalysts are stable and can regenerate the active sites. The current study contributes to understanding the catalysts' surface, structural and morphological properties on the catalysts' performance toward CO oxidation and other reactions under dynamic conditions.
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| 2. |
- Baulin, R. A., et al.
(författare)
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Unique surface sensitivity to ferro- and antiferromagnetic phases by polarization analysis in synchrotron Mossbauer reflectivity
- 2021
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Ingår i: SURFACES AND INTERFACES. - : Elsevier. - 2468-0230. ; 27
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Tidskriftsartikel (refereegranskat)abstract
- Polarization analysis of the reflected radiation has been performed in Mossbauer reflectivity measurements with a Synchrotron Mossbauer Source (SMS). Effective pi ->sigma' polarization selection is attained with LiF crystal ((6 2 2) 90 degrees-reflection for 14.4 keV radiation, angular acceptance similar to 100 '') capable of high pi ->pi' suppression. Basic features of the reflectivity with the rotated pi ->sigma' polarization are revealed in the experiment with the [Fe-57(10 ML)/V(20 ML)](20) multilayer. Selection of pi ->sigma' polarization component in Mossbauer reflectivity allows to exclude nonresonant electronic scattering, besides Mossbauer pi ->sigma' reflectivity spectra (R-spectra) contain only contributions from magnetized along the beam ferromagnetic phases. The antiferromagnetic iron oxides do not contribute to pi ->sigma' R-spectra (dichroic component is compensated). Therefore, in the Mossbauer reflectivity experiment supplemented by polarization analysis the data interpretation becomes more certain and gives information about depth position for ferromagnetic layers selectively. With this new technique we locate antiferromagnetic iron phases in the very top layer of [Fe-57(10 ML)/V(20 ML)](20) multilayer and ascertain the ferromagnetic ordered iron layers in the remaining part of the structure. This new approach in Mossbauer reflectivity has interesting perspectives for investigations of hyperfine interactions for iron complexes on the surface, ultrathin layers and multilayers with complicated magnetic structures.
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| 3. |
- D'Acunto, Giulio, et al.
(författare)
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Time evolution of surface species during the ALD of high-k oxide on InAs
- 2023
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Ingår i: Surfaces and Interfaces. - 2468-0230. ; 39:102927
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the reaction mechanisms involved during the early stage of atomic layer deposition (ALD) of HfO2 on InAs is a key requirement for improving interfaces in III-V semiconductor-based devices. InAs is an excellent candidate to outperform silicon regarding speed and power consumption, and combined with HfO2, it gives promise for a new generation of ultra-fast MOSFETs. However, an improved interface quality and in-depth understanding of the involved surface species are needed. Here, we use in situ and operando ambient pressure XPS to follow in real-time the reaction mechanisms which control the ALD chemistry. Besides the removal of all unwanted oxide from the III-V, the same oxygen atoms are found to form HfOx already from the first half-cycle. In contrast to the standard ALD model, no hydroxyl groups are needed on the InAs surface. Furthermore, we observe an insertion reaction forming unexpected surface species. The second ALD half-cycle allows the immediate removal of all organic species leaving behind a uniform HfO2 layer partially terminated by hydroxyl groups. We find that prolonged exposure times upon both half-cycles guarantee a sharp InAs/HfO2 interface. Such an improved interface is an important step towards fast and sustainable III-V semiconductor-based electronics.
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| 4. |
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| 5. |
- Fabbri, Filippo, et al.
(författare)
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Silicene nanosheets intercalated in slightly defective epitaxial graphene on a 4H-SiC(0001) substrate
- 2022
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Ingår i: Surfaces and Interfaces. - : Elsevier BV. - 2468-0230. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- In the last years, epitaxial graphene (epi-Gr) demonstrated to be an excellent substrate for the synthesis of epitaxial or intercalated two dimensional (2D) materials. Among 2D materials, silicene has been for a long time a dream for the scientific community, for its importance both from the fundamental and the application point of view. Despite the theoretical prediction of silicene energetic viability, experimentally the substrate proved to play a fundamental role in the Si atom adsorption process leading, in case of metal substrates, to a mixed phase formation and, for van der Waals chemical inert substrates, to Si atom intercalation even at room temperature. Such an intercalation has been associated to the presence of surface defects. Very recently it has been shown that hundreds of nanometer area quasi-free standing silicene can be grown on top of an almost ideal epi-Gr layer synthesized on 6H-SiC substrate. In the present paper, using scanning tunneling microscopy and Raman analysis, we demonstrate that a non-ideal (slightly defective) epi-Gr network obtained by thermal decomposition of Si-terminated 4H-SiC(0001) enables the Si atom penetration forming intercalated silicene nanosheets at room temperature, thus opening a path towards controlled intercalation of silicon atoms through epi-Gr and formation of silicene nanosheets for future applications in nanotechnology.
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| 6. |
- Hosseinpour, Elnaz, et al.
(författare)
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Evaluation of alkaline and acidic modification of NaY zeolite for enhancing adsorptive removal of diclofenac sodium from aqueous solution
- 2023
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Ingår i: Surfaces and Interfaces. - : Elsevier B.V.. - 2468-0230. ; 39
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, facile and cost-effective modification methods, including alkali treatment and acid treatment, were evaluated to improve the adsorption capacity of NaY zeolite for diclofenac sodium (DFS) elimination from the aqueous solution. The performance of unmodified NaY, sodium hydroxide treated NaY (SHT-Y), hydrochloric acid treated NaY (HAT-Y), and sulfuric acid treated NaY (SAT-Y) was compared, followed by optimization of sulfuric acid concentration since sulfuric acid was recognized as the preferred modifying agent. The modified NaY with a concentration of 0.1 M of sulfuric acid exhibited the highest adsorption capacity. Analyses of FE-SEM, EDS, FTIR, BET, and XRD were used to determine the characteristics of NaY and treated zeolites. All treatments changed the Si/Al ratio of NaY. Silanol and bridging hydroxyl functional groups were detected in all zeolitic samples. Acidic modifications enhanced the specific surface area of NaY more than the alkali treatment. The influence of the major factors on the DFS adsorption, including adsorbent dosage, contact time, pH of the solution, and initial concentration of DFS was investigated and optimized in detail. The maximum adsorption capacity was obtained at pH 11 at the equilibrium time of 180 min. The hydrogen bond formation and cation-π interaction were recognized as DFS adsorption mechanisms. From the results of kinetic studies, the Elovich model has better agreement with experimental data, suggesting that the adsorbent surface is energetically heterogeneous and chemisorption leads the DFS uptake onto the adsorbent, indicative of hydrogen bond formation. In accordance with the equilibrium modeling results, the Sips isotherm better expresses the DFS adsorption mechanism onto the surface of the modified zeolite. According to the Langmuir isotherm model, the maximum adsorption capacity obtained for 0.2 g/L of treated zeolite was 117.77 mg/g. Eventually, sulfuric acid treatment was found as an effective and facile method for enhancing zeolite performance in DFS removal from aqueous solution.
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| 7. |
- Kateb, Movaffaq, 1985, et al.
(författare)
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Epitaxial growth and characterization of (001) [NiFe/M]20 (M = Cu, CuPt and Pt) superlattices
- 2023
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Ingår i: Surfaces and Interfaces. - : Elsevier BV. - 2468-0230. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- We present optimization of [(15 Å) Ni80Fe20/(5 Å) M]20 single crystal multilayers on (001) MgO substrates, with M being Cu, Cu50Pt50 and Pt. These superlattices were characterized by high resolution X-ray reflectivity (XRR) and diffraction (XRD) as well as polar mapping of important crystal planes. It is shown that cube on cube epitaxial relationship can be obtained when depositing at substrate temperature of 100 °C regardless of the lattice mismatch (5% and 14% for Cu and Pt, respectively). At lower substrate temperatures poly-crystalline multilayers were obtained while at higher substrate temperatures {111} planes appear at ∼10° off normal to the film plane. It is also shown that as the epitaxial strain increases, the easy magnetization axis rotates towards the direction that previously was assumed to be harder, i.e. from [110] to [100], and eventually further increase in the strain makes the magnetic hysteresis loops isotropic in the film plane. Higher epitaxial strain is also accompanied with increased coercivity values. Thus, the effect of epitaxial strain on the magnetocrystalline anisotropy is much larger than what was observed previously in similar, but polycrystalline samples with uniaxial anisotropy (Kateb et al. 2021).
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| 8. |
- Kazemi, Amin, et al.
(författare)
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The effect of Cl- and N-doped MoS2 and WS2 coated on epitaxial graphene in gas-sensing applications
- 2021
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Ingår i: SURFACES AND INTERFACES. - : ELSEVIER. - 2468-0230. ; 25
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Tidskriftsartikel (refereegranskat)abstract
- In this study, epitaxial graphene (EG) was grown on a 6H-SiC (0001) substrate via the thermal decomposition of SiC. Undoped and Cl- or N-doped molybdenum disulfide (MoS2) and tungsten disulfide (WS2) ultrathin films were spin-coated on the graphene surface. The scanning electron microscopy (SEM) images and topological atomic force microscopy (AFM) analysis showed good distribution of thin MoS2 and WS2 flakes on the EG surface. The X-ray photoelectron spectroscopy (XPS) confirmed the presence of Mo-related peaks of 3d(5/2) and 3d(3/2) at similar to 232.2 eV and 235.1 eV, respectively. It also represented peaks of W 4f(7/2) and 5p(5/2) at around 36.1 eV and 37.9 eV, respectively. Moreover, XPS results showed peaks at around 167.4 eV and 168.4 eV corresponding to S 2p for MoS2 and WS2, respectively. The XPS results also confirmed the presence of dopant elements in MoS2 and WS2 flakes. We fabricated sensors using undoped and chlorine- or nitrogen-doped MoS2 and WS2 ultrathin films for gas-sensing applications. These sensors were surveyed for ammonia (NH3) and nitrogen dioxide (NO2) gas sensing. As in NO2, both undoped sensors react with a decrease in relative sensor responses to NH3, hence showing n-type behavior. Doping MoS2 and WS2 with chlorine led to a higher response vis-a-vis the nitrogendoped sensors. The absolute relative response of Cl-doped WS2 and MoS2 was about 3.5 and 1.8 times more than that of their undoped counterparts toward NH3. A change of direction with a slightly smaller response (approximately x 0.8), however, could also be observed in the doping of MoS2 and WS2 with nitrogen. When exposed to NO2, the Cl-doped WS2 sensor response was 1.2 more than the N-doped one, while for MoS2 these values changed in the range of 1.2 - 1.6 for different flows of gas.
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| 9. |
- Maistro, Giulio, 1987, et al.
(författare)
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Low-temperature carburized high-alloyed austenitic stainless steels in PEMFC cathodic environment
- 2021
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Ingår i: Surfaces and Interfaces. - : Elsevier BV. - 2468-0230. ; 24
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Tidskriftsartikel (refereegranskat)abstract
- Austenitic stainless steels are promising materials for bipolar plates in polymer electrolyte membrane fuel cells (PEMFC). In this study, we explore the possibility to apply low-temperature carburized high-alloyed (high Cr, Ni, Mo) steels as bipolar plate materials. The electrochemical properties and the microstructural characteristics of the modified surfaces were analyzed by optical microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy. The carburizing treatment (Kolsterising®, Bodycote) induced the formation of a carbon-stabilized expanded austenite layer. The amount of carbon dissolved in the metal matrix was dependent on the alloy composition, in particular on the amount of Mo. Additionally, surface carbides were found at the surface of low-Ni containing steels. The interfacial contact resistance (ICR) measured in a simulated PEMFC was reduced after carburizing as a consequence of thinner oxide layer and change in oxide composition. Potentiodynamic tests revealed nobilitation of all the steels when carbon was present in solid solution. The occurrence of surface carbides, however, was highly detrimental to the corrosion properties. The ICR of carburized materials in aged condition was higher than the corresponding untreated alloys. The presence of localized corrosion in carburized materials could be responsible for this effect.
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| 10. |
- Mendoza, Ana, et al.
(författare)
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Image analysis of PDMS/ZnO nanocomposite surfaces for optimized superhydrophobic and self-cleaning surface design
- 2023
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Ingår i: Surfaces and Interfaces. - : Elsevier B.V.. - 2468-0230. ; 37
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Tidskriftsartikel (refereegranskat)abstract
- Optimized superhydrophobic and self-cleaning nanocomposite surfaces were obtained by spraying surface modified ZnO nanoparticles (NPs) onto PDMS, using octadecylphosphonic acid and octadecanethiol as hydrophobic modifiers. In this study, it is the first time to our knowledge that surface parameters such as topography, morphology, superhydrophobicity, and self-cleaning are correlated to particle surface distribution and agglomeration parameters obtained by image analysis. The topography, morphology, and wettability of the surfaces were analyzed using atomic force microscopy, scanning electron microscopy, static contact angle (SCA), and contact angle hysteresis measurements. Image analysis was performed using the new enhanced graphical user interface of a previously self-developed Matlab® algorithm. Both hydrophobization methodologies increased the NPs’ surface coverage and the hierarchical rough structure formation on the substrates, resulting in more homogenous superhydrophobic self-cleaning surfaces. A higher coated fraction and lower degree of interconnected uncoated PDMS paths are correlated to an increase in SCA. The combination of a higher agglomerates fraction, lower agglomerate radius, and lower distance between agglomerates obtained for the surfaces with hydrophobized ZnO-NPs rendered self-cleaning surfaces. The observed correlations increase the understanding of the design and modelling of superhydrophobic self-cleaning PDMS/ZnO nanocomposite surfaces for use in high voltage outdoor insulators.
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