ORCID Profile
0000-0002-9292-2357
Current Organisation
KU Leuven
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Publisher: Elsevier BV
Date: 02-2009
Publisher: The Electrochemical Society
Date: 2008
DOI: 10.1149/1.2885041
Publisher: Wiley
Date: 14-08-2008
Publisher: The Electrochemical Society
Date: 2008
DOI: 10.1149/1.2971025
Publisher: American Chemical Society (ACS)
Date: 22-11-2007
DOI: 10.1021/LA7028388
Abstract: Ellipsometric porosimetry was used to determine the adsorption isotherms of toluene, methanol, and water on b-oriented Silicalite-1 coatings with a thickness of less than ca. 250 nm and to obtain adsorption kinetics. The adsorption isotherms are of sufficient quality to reveal several aspects of the pore structure such as the adsorbate capacity and the adsorbate/framework affinity. The use of a combination of different molecular probes in ellipsometric porosimetry to elucidate the molecular accessibility of Silicalite-1 pores is demonstrated. It is shown that ellipsometric porosimetry is an appropriate technique for probing the influence of aging of the Silicalite-1 coating and of planarization polishing on the porosity, pore accessibility, and adsorbate/framework affinity.
Publisher: American Chemical Society (ACS)
Date: 11-07-2007
DOI: 10.1021/JA0723737
Publisher: Elsevier BV
Date: 02-2021
Publisher: American Chemical Society (ACS)
Date: 05-04-2008
DOI: 10.1021/LA800086Y
Abstract: We present a study on the hydrophobization of spin-on Silicalite-1 zeolite films through silylation with trimethylchlorosilane. Microporous and micro-mesoporous Silicalite-1 films were synthesized by spin coating of suspensions of Silicalite-1 nanozeolite crystallized for different times. Ellipsometric porosimetry with toluene and water adsorbates reveals that silylation decreases the porosity and makes the films hydrophobic. The decrease in porosity depends on the exposed surface area in the pores. Water contact angle measurements confirm the hydrophobicity. Fourier transform infrared spectroscopy reveals that the trimethylsilyl groups are chemisorbed selectively on isolated silanols and less on geminal and vicinal silanols due to steric limitations. Time-of-flight secondary-ion mass spectroscopy and in situ ellipsometry analysis of the reaction kinetics show that the silylation is a bulk process occurring in the absence of diffusion limitation. Electrical current leakage on films decreases upon silylation. Silylation with trimethylchlorosilane is shown to be an effective hydrophobization method for spin-on Silicalite-1 zeolite films.
Publisher: Elsevier
Date: 2007
Publisher: American Chemical Society (ACS)
Date: 24-12-2008
DOI: 10.1021/JA8066572
Abstract: Spin-on zeolite films deposited from Silicalite-1 nanocrystal suspensions prepared by hydrothermal treatment of clear solutions have the required properties for insulating media in microelectronics. However, on the scale of the feature sizes in on-chip interconnects of a few tens of nanometers, their homogeneity is still insufficient. We discovered a way to overcome this problem by combining the advantages of the clear solution approach of Silicalite-1 synthesis with a sol-gel approach. A combination of tetraethyl orthosilicate and methyltrimethoxysilane silica sources was hydrolyzed and cocondensed in the presence of an aqueous tetraalkylammonium hydroxide template. The resulting suspension of nanoparticles of a few nanometers in size together with residual oligomeric silica species were spun onto support. The final zeolite-inspired low-k films (ZLK) with respect to pore size and homogeneity satisfied all requirements and presented excellent hydrophobicity, stiffness, and dielectric constant. The size and content of initially formed nanoparticles and the spatial hindrance promoted by occluded tetraalkylammonium molecules were found to be crucial elements in the definition of the final pore network.
Publisher: American Chemical Society (ACS)
Date: 27-09-2008
DOI: 10.1021/JP804349V
Publisher: American Chemical Society (ACS)
Date: 13-11-2020
DOI: 10.1021/JACS.0C09684
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9NA00188C
Abstract: Carbon black is chemically activated by selective TiO 2 photocatalytic oxidation functionalizing the graphitic carbon fraction, while mineralizing amorphous carbon.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4RA12460J
Abstract: Kinetic separation of CO 2 from CH 4 over rubidium or cesium-exchanged ZK-5 (KFI) zeolites for upgrade of biogas to renewable fuels.
Publisher: American Chemical Society (ACS)
Date: 30-01-2007
DOI: 10.1021/CM0527219
Publisher: American Chemical Society (ACS)
Date: 15-04-2014
DOI: 10.1021/LA500121F
Abstract: Important cellular events such as ision require drastic changes in the shape of the membrane. These remodeling processes can be triggered by the binding of specific proteins or by changes in membrane composition and are linked to phospholipid metabolism for which dedicated enzymes, named phospholipases, are responsible. Here wide-field fluorescence microscopy is used to visualize shape changes induced by the action of phospholipase A1 on dye-labeled supported membranes of POPC (1-palmitoyl-2-oleoly-sn-glycero-3-phosphocholine). Time-lapse imaging demonstrates that layers either shrink and disappear or fold and collapse into vesicles. These vesicles can undergo further transformations such as budding, tubulation, and pearling within 5 min of formation. Using dye-labeled phospholipases, we can monitor the presence of the enzyme at specific positions on the membrane as the shape transformations occur. Furthermore, incorporating the products of hydrolysis into POPC membranes is shown to induce transformations similar to those observed for enzyme action. The results suggest that phospholipase-mediated hydrolysis plays an important role in membrane transformations by altering the membrane composition, and a model is proposed for membrane curvature based on the presence and shape of hydrolysis products.
Publisher: American Chemical Society (ACS)
Date: 11-07-2017
Publisher: Wiley
Date: 29-04-2019
Abstract: The extraordinary properties of lead‐halide perovskite materials have spurred intense research, as they have a realistic perspective to play an important role in future photovoltaic devices. It is known that these materials undergo a number of structural phase transitions as a function of temperature that markedly alter their optical and electronic properties. The precise phase transition temperature and exact crystal structure in each phase, however, are controversially discussed in the literature. The linear thermal expansion of single crystals of APbX 3 (A = methylammonium (MA), formamidinium (FA) X = I, Br) below room temperature is measured using a high‐resolution capacitive dilatometer to determine the phase transition temperatures. For δ‐FAPbI 3 , two wide regions of negative thermal expansion below 173 and 54 K, and a cascade of sharp transitions for FAPbBr 3 that have not previously been reported are uncovered. Their respective crystal phases are identified via powder X‐ray diffraction. Moreover, it is demonstrated that transport under steady‐state illumination is considerably altered at the structural phase transition in the MA compounds. The results provide advanced insights into the evolution of the crystal structure with decreasing temperature that are essential to interpret the growing interest in investigating the electronic, optical, and photonic properties of lead‐halide perovskite materials.
No related grants have been discovered for Johan Martens.