| 1. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
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Strain-related structural and vibrational properties of thin epitaxial AIN layers
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:4, s. 045411-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of film thickness on the strain and structural properties of thin epitaxial AIN films has been investigated by high resolution x-ray diffraction techniques and transmission electron microscopy. As a result a sublayer model of the degree of strain and related defects for all films is proposed. A sublayer with low defect density and a strain gradient is found to be present in all films and it reaches a maximum thickness of 65 nm. The films are compressively strained and the strain relaxation after a thickness of 65 nm is shown to be accompanied by misfit dislocation generation and increase of the mosaic tilt. The vibrational properties of the films have been studied by generalized infrared spectroscopic ellipsometry. The proposed sublayer model has been successfully applied to the analysis of the ellipsometry data through model calculations of the infrared dielectric function which confirm the sublayer model. It is found that the strain gradient results in a gradient of the phonon mode frequencies and broadening parameter. The initial strain relaxation in the films leads to narrowing of the observable infrared modes, while further strain relaxation broadens the modes when substantial defect generation occurs.
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| 2. |
- Davisayahvorakul, Ratikorn, et al.
(författare)
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Glycerol Ketal Biobased Product Preparation from Biomass-Derived Reactants Using an H-ZSM-5 Catalyst for Oil Color Painting Application
- 2024
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Ingår i: ACS Sustainable Chemistry and Engineering. - 2168-0485. ; 12:11, s. 4598-4604
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Tidskriftsartikel (refereegranskat)abstract
- Condensation of glycerol with bioderived carbonyls yields cyclic ketals with unique properties. In this study, efficient solvent-free heterogeneously catalyzed ketalization has been achieved to give the corresponding products in good to excellent yields. Substrate-to-glycerol ratios of 1:1 have been used; the reactions were performed at 120 °C for 30 min. By using an acid-treated H-ZSM-5 catalyst, high selectivity to a five-membered ring was achieved. Furthermore, the catalyst could be recycled up to 4 times without losing activity. The ketal from glycerol and levulinic acid (GLK) was isolated and applied as a solvent in oil color paint and showed advantageous properties over commercial paint solvents in terms of aging.
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| 3. |
- Jiraroj, Duangkamon, et al.
(författare)
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Selective decarboxylation of biobased fatty acids using a Ni-FSM-16 catalyst
- 2021
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 291
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Tidskriftsartikel (refereegranskat)abstract
- A novel catalyst based on nickel supported on a folded sheet material (FSM) was synthesized and fully characterized. The resulting Ni-FSM-16 catalyst showed a high reactivity and selectivity in decarboxylation of plant-based carboxylic acids to yield the corresponding linear alkenes and alkanes in up to 75 % yield and less than 5 % of undesired cracking products. In addition, lignin-derived vanillic acid was smoothly converted to guaiacol. A comparative investigation showed that both the support and the metal of the Ni-FSM-16 catalyst proved to be pivotal for the reactivity. Particularly, substituting Ni with Fe, Pd or Al or replacing the FSM-16 support with MCM-41 or SBA-15 led to lower reactivity and selectivity towards linear decarboxylated products. The superior catalytic performance of Ni-FSM-16 was driven by a higher and more even metal distribution, more acidic silanol-group and an electron-rich, thus softer Ni, that promote coordination by the carbon-carbon double-bond of the fatty acid.
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| 4. |
- Mongkolpichayarak, Isara, et al.
(författare)
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Cr/MCM-22 catalyst for the synthesis of levulinic acid from green hydrothermolysis of renewable biomass resources
- 2022
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 405, s. 373-384
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Tidskriftsartikel (refereegranskat)abstract
- The novel Cr-loaded MCM-22 zeolite (Cr/MCM-22) was successfully synthesized, fully characterized, and applied as a heterogeneous catalyst for the transformation of biomass-derived materials (glucose, sucrose, cellulose, starch, agricultural residues, and other municipal wastes) into levulinic acid via hydrothermolysis. The novel Cr/MCM-22 gives higher yields of levulinic acid compared to other reported catalysts. Specifically, Cr/MCM-22 produced 73.2% levulinic acid yield from glucose at relatively high concentrations (solvent:biomass 20:1). For starting materials with higher structural complexity, pretreatment was required to maintain a high yield of levulinic acid. The novel catalyst was studied and compared to other related catalysts. The high efficiency is attributed to the synergistic effect induced by confinement control of the microporous material as well as Lewis and Brønsted acid sites of Cr/MCM-22. A reaction mechanism including all reaction steps has been proposed. The Cr/MCM-22 was successfully recycled three times.
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| 5. |
- Paskova, Tanja, et al.
(författare)
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Defect and stress relaxation in HVPE-GaN films using high temperature reactively sputtered AlN buffer
- 2001
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 230:3-4, s. 381-386
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Tidskriftsartikel (refereegranskat)abstract
- The influence of high temperature buffer layers on the structural characteristics of GaN grown by hydride vapour phase epitaxy on sapphire was investigated. Strain relaxation as well as mismatch-induced defect reduction in thick GaN layers grown on AlN buffer was microscopically identified using cathodoluminescence and micro-Raman spectroscopy in cross-section of the films. The results were correlated with photoluminescence and Hall-effect data of layers with different thicknesses. These relaxation processes were suggested to account for the specific defect distribution in the buffers revealed by high-resolution X-ray diffraction and transmission electron microscopy. © 2001 Elsevier Science B.V. All rights reserved.
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| 6. |
- Paskova, Tanja, et al.
(författare)
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Hydride vapour phase homoepitaxial growth of GaN on MOCVD-grown 'templates'
- 2000
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Konferensbidrag (refereegranskat)abstract
- We report on an improved quality of thick HVPE-GaN grown on MOCVD-GaN 'template' layers compared to the material grown directly on sapphire. The film-substrate interface revealed by cathodoluminescence measurements shows an absence of highly doped columnar structures which are typically present in thick HVPE-GaN films grown directly on sapphire. This improved structure results in a reduction of two orders of magnitude of the free carrier concentration from Hall measurements. It was found that the structure, morphology, electrical and optical properties of homoepitaxial thick GaN layers grown by HVPE were strongly influenced by the properties of the MOCVD-GaN 'template'. Additionally the effect of Si doping of the GaN buffer layers on the HVPE-GaN properties was analysed.
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| 7. |
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| 8. |
- Rautiainen, Sari, et al.
(författare)
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Lignin Valorization by Cobalt-Catalyzed Fractionation of Lignocellulose to Yield Monophenolic Compounds
- 2019
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 12:2, s. 404-408
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Tidskriftsartikel (refereegranskat)abstract
- Herein, a catalytic reductive fractionation of lignocellulose is presented using a heterogeneous cobalt catalyst and formic acid or formate as a hydrogen donor. The catalytic reductive fractionation of untreated birch wood yields monophenolic compounds in up to 34 wt % yield of total lignin, which corresponds to 76% of the theoretical maximum yield. Model compound studies revealed that the main role of the cobalt catalyst is to stabilize the reactive intermediates formed during the organosolv pulping by transfer hydrogenation and hydrogenolysis reactions. Additionally, the cobalt catalyst is responsible for depolymerization reactions of lignin fragments through transfer hydrogenolysis reactions, which target the beta-O-4' bond. The catalyst could be recycled three times with only negligible decrease in efficiency, showing the robustness of the system.
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| 9. |
- Valcheva, E, et al.
(författare)
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Epitaxial growth and orientation of AlN thin films on Si(001) substrates deposited by reactive magnetron sputtering
- 2006
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 100:12
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial domain formation and textured growth in AlN thin films deposited on Si(001) substrates by reactive magnetron sputtering was studied by transmission electron microscopy and x-ray diffraction. The films have a wurtzite type structure with a crystallographic orientation relationship to the silicon substrate of AlN (0001) ∥Si (001). The AlN film is observed to nucleate randomly on the Si surface and grows three dimensionally, forming columnar domains. The in-plane orientation reveals four domains with their a axes rotated by 15° with respect to each other: AlN 〈11 2- 0〉 ∥Si [110], AlN 〈01 1- 0〉 ∥Si [110], AlN 〈11 2- 0〉 ∥Si [100], and AlN 〈01 1- 0〉 ∥Si [100] An explanation of the growth mode based on the large lattice mismatch and the topology of the substrate surface is proposed. © 2006 American Institute of Physics.
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| 10. |
- Wongpanit, N., et al.
(författare)
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Etching behaviors of tunneling magnetoresistive (TMR) materials by ion beam etching system
- 2018
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Ingår i: MATERIALS TODAY-PROCEEDINGS. - : ELSEVIER SCIENCE BV. ; , s. 15186-15191
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Konferensbidrag (refereegranskat)abstract
- In data storage manufacturing, ion etching process is commonly chosen for the preparation of surface patterns, for example, under the read-write head of the hard disk drive (HDD) to form an air bearing surface (ABS). This read-write head consists of a multilayer thin film of different materials to form a tunneling magnetoresistive (TMR) device. In this work, we applied the Monte Carlo-based simulation package to calculate the etching yield of major materials in the HDD heads structure. The plasma characteristic in the industrial-size ion beam etching (IBE) system has been studied by the special plasma diagnostic probes. Effects of input parameters in IBE system such as incident beam angle, ion beam current and gas flow in the system were considered. Plasma characteristic can be obtained from plasma I-V curve characterization. The sputtering yields of materials were found maximum when an incident angle is about 70 degrees to the normal surface. The floating potential of plasma in the system with the ion/electron compensation from PBN is calculated. (C) 2018 Elsevier Ltd. All rights reserved.
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