| 1. |
- Liu, Zheng, et al.
(författare)
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A review of fine structures of nanoporous materials as evidenced by microscopic methods
- 2013
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Ingår i: Microscopy. - : Oxford University Press (OUP). - 2050-5698 .- 2050-5701. ; 62:1, s. 109-146
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Forskningsöversikt (refereegranskat)abstract
- This paper reviews diverse capabilities offered by modern electron microscopy techniques in studying fine structures of nanoporous crystals such as zeolites, silica mesoporous crystals, metal organic frameworks and yolk-shell materials. For the case of silica mesoporous crystals, new approaches that have been developed recently to determine the three-dimensionally periodic average structure, e. g., through self-consistent analysis of electron microscope images or through consideration of accidental extinctions, are presented. Various structural deviations in nanoporous materials from their average structures including intergrowth, surface termination, incommensurate modulation, quasicrystal and defects are demonstrated. Ibidem observations of the scanning electron microscope and atomic force microscope give information about the zeolite-crystal-growth mechanism, and an energy for unstitching a building-unit from a crystal surface is directly observed by an anatomic force microscope. It is argued how these observations lead to a deeper understanding of the materials.
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| 2. |
- Tatsumi, Kazuyoshi, et al.
(författare)
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Signal enhancement of electron magnetic circular dichroism by ultra-high-voltage TEM, toward quantitative nano-magnetism measurements
- 2014
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Ingår i: Journal of Electron Microscopy. - : Oxford University Press (OUP). - 0022-0744 .- 1477-9986. ; 63:3, s. 243-247
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Tidskriftsartikel (refereegranskat)abstract
- Electron magnetic circular dichroism (EMCD) has been known as the transmission electron microscopy (TEM) counterpart of X-ray magnetic circular dichroism (XMCD). XMCD is already widely used for the characterization of magnetic materials with synchrotron radiation. There have been common difficulties encountered in quantitative analysis of the EMCD signal measured by medium-voltage TEMs, such as a small signal fraction and the low signal-to-noise ratio of the EMCD signal. Theoretical calculations of EMCD considering many-beam dynamical diffraction effects showed improved net magnetic signal fractions at an accelerating voltage of 1 MV compared with 200 kV, which is in agreement with the present experiment.
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| 3. |
- Das, Prabir Kumar, et al.
(författare)
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Microscale investigation of thin film surface ageing of bitumen
- 2014
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Ingår i: Journal of Microscopy. - : Wiley. - 2050-5698 .- 0022-2720 .- 1365-2818. ; 254:2, s. 95-107
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the mechanism of bitumen surface ageing, which was validated utilizing the atomic force microscopy and the differential scanning calorimetry. To validate the surface ageing, three different types of bitumen with different natural wax content were conditioned in four different modes: both ultraviolet and air, only ultraviolet, only air and without any exposure, for 15 and 30 days. From the atomic force microscopy investigation after 15 and 30 days of conditioning period, it was found that regardless the bitumen type, the percentage of microstructure on the surface reduced with the degree of exposure and time. Comparing all the four different exposures, it was observed that ultraviolet radiation caused more surface ageing than the oxidation. It was also found that the combined effect was not simply a summation or multiplication of the individual effects. The differential scanning calorimetry investigation showed that the amount of crystalline fractions in bitumen remain constant even after the systematic conditioning. Interestingly, during the cooling cycle, crystallization of wax molecules started earlier for the exposed specimens than the without exposed one. The analysis of the obtained results indicated that the ageing created a thin film upon the exposed surface, which acts as a barrier and creates difficulty for the wax induced microstructures to float up at the surface. From the differential scanning calorimetry analysis, it can be concluded that the ageing product induced impurities in the bitumen matrix, which acts as a promoter in the crystallization process.
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