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- Akhtar, Sultan
(författare)
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Transmission Electron Microscopy of Graphene and Hydrated Biomaterial Nanostructures : Novel Techniques and Analysis
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transmission Electron Microscopy (TEM) on light element materials and soft matters is problematic due to electron irradiation damage and low contrast. In this doctoral thesis techniques were developed to address some of those issues and successfully characterize these materials at high resolution. These techniques were demonstrated on graphene flakes, DNA/magnetic beads and a number of water containing biomaterials. The details of these studies are given below.A TEM based method was presented for thickness characterization of graphene flakes. For the thickness characterization, the dynamical theory of electron diffraction is used to obtain an analytical expression for the intensity of the transmitted electron beam as a function of thickness. From JEMS simulations (experiments) the absorption constant λ in a low symmetry orientation was found to be ~ 208 nm (225 ± 9 nm). When compared to standard techniques for thickness determination of graphene/graphite, the method has the advantage of being relatively simple, fast and requiring only the acquisition of bright-field (BF) images. Using the proposed method, it is possible to measure the thickness change due to one monolayer of graphene if the flake has uniform thickness over a larger area.A real-space TEM study on magnetic bead-DNA coil interaction was conducted and a statistical analysis of the number of beads attached to the DNA-coils was performed. The average number of beads per DNA coil was calculated around 6 and slightly above 2 for samples with 40 nm and 130 nm beads, respectively. These results are in good agreement with magnetic measurements. In addition, the TEM analysis supported an earlier hypothesis that 40 nm beads are preferably attached interior of the DNA-coils while 130 nm beads closer to the exterior of the coils.A focused ion-beam in-situ lift-out technique for hydrated biological specimens was developed for cryo-TEM. The technique was demonstrated on frozen Aspergillus niger spores which were frozen with liquid nitrogen to preserve their cellular structures. A thin lamella was prepared, lifted out and welded to a TEM grid. Once the lamella was thinned to electron transparency, the grid was cryogenically transferred to the TEM using a cryo-transfer bath. The structure of the cells was revealed by BF imaging. Also, a series of energy filtered images was acquired and C, N and Mn elemental maps were produced. Furthermore, 3 Å lattice fringes of the underlying Al support were successfully resolved by high resolution imaging, confirming that the technique has the potential to extract structural information down to the atomic scale. The experimental protocol is ready now to be employed on a large variety of samples e.g. soft/hard matter interfaces.
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| 2. |
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| 3. |
- Rubino, Stefano, et al.
(författare)
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A site-specific focused-ion-beam lift-out method for cryo Transmission Electron Microscopy
- 2012
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Ingår i: Journal of Structural Biology. - : Elsevier BV. - 1047-8477 .- 1095-8657. ; 180:3, s. 572-576
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Tidskriftsartikel (refereegranskat)abstract
- The focused-ion-beam (FIB) is the method of choice for site-specific sample preparation for Transmission Electron Microscopy (TEM) in material sciences. A lamella can be physically lifted out from a specific region of a bulk specimen with submicrometer precision and thinned to electron transparency for high-resolution imaging in the TEM. The possibility to use this tool in life sciences applications has been limited by the lack of lift-out capabilities at the cryogenic temperatures often needed for biological samples. Conventional cryo-TEM sample preparation is mostly based on ultramicrotomy, a procedure that is not site-specific and known to produce artifacts. Here we demonstrate how a cooled nanomanipulator and a custom-built transfer station can be used to achieve cryo-preparation of TEM samples with the FIB, enabling high-resolution investigation of frozen-hydrated specimens in the TEM.
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| 5. |
- Xie, Ling, 1982-, et al.
(författare)
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The visualization of Silicon nanoparticles by 3D electron tomography
- 2012
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Ingår i: European Microscopy Congress, Manchester, 2012.
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Konferensbidrag (refereegranskat)abstract
- Silicon nanoparticles (NP) size and spatial distribution in three-dimension (3D) are two critical parameters for the operation of “all-Si” tandem solar cells. The 3D distribution of Silicon NPs embedded in insulating or semiconducting matrices has attracted much interest for this third generation of photovoltaics. In this work, silicon NPs have been deposited by low pressure chemical vapour deposition (LPCVD) on a silicon carbide alloy thin-film at low temperature (700ºC) [1]. The aim of this study is to show how silicon nanoparticles are distributed in 3D on a silicon carbide thin film.
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| 8. |
- Yang, Xia, et al.
(författare)
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Direct ”Click” Synthesis of Hybrid Bisphosphonate-Hyaluronic Acid Hydrogel in Aqueous Solution for Biomineralization
- 2012
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 24:9, s. 1690-1697
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Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis of injectable in situ forming hybrid hydrogel material and investigate its ability to support the mineralization process under mild conditions. To achieve this, we have prepared a hyaluronic acid (HA) derivative that is dually functionalized with cross-linkable hydrazide groups and bisphosphonate ligands (HA-hy-BP). The hybrid hydrogel can be formed by simple mixing of two solutions: the solution of HA-hy-BP and the Ca2+ ions containing solution of aldehyde-derivatized HA (HA-al). We found that the conjugation of BP, a P-C-P analogue of pyrophosphate, to the hydrogel matrix promotes an efficient and fast mineralization of the matrix. The mineralization is facilitated by the strong interaction between BP residues and Ca2+ ions that serve as nanometer-sized nucleation points for further calcium phosphate deposition within the HA hydrogel. Compared with previously reported hydrogel template-driven mineralization techniques, the present approach is maximally adapted for clinical settings since the formation of the hybrid takes place during quick mixing of the sterilized solutions. Moreover, the hybrid hydrogel is formed from in vivo degradable components of the extracellular matrix and therefore can be remodeled in vivo through concerted HA degradation and calcium phosphate mineralization.
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