SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Scanning tunneling microscope

171

Porous silicon microcavity (PSiMc) structures were used to immobilize the photosynthetic reaction center (RC) purified from the purple bacterium Rhodobacter sphaeroides R-26. Two different binding methods were compared by specular reflectance measurements. Structural characterization of PSiMc was performed by scanning electron microscopy and atomic force microscopy. The activity of the immobilized RC was checked by measuring the visible absorption spectra of the externally added electron donor, mammalian cytochrome c. PSi/RC complex was found to oxidize the cytochrome c after every saturating Xe flash, indicating the accessibility of specific surface binding sites on the immobilized RC, for the external electron donor. This new type of bio-nanomaterial is considered as an excellent model for new generation applications of silicon-based electronics and biological redox systems.

Concepts: Photosynthetic reaction centre, Scanning tunneling microscope, Electron acceptor, Cellular respiration, Scanning electron microscope, Bacteria, Electron, Photosynthesis

168

The nanoscale electrical properties of individual self-assembled GeSi quantum rings (QRs) were studied by scanning probe microscopy-based techniques. The surface potential distributions of individual GeSi QRs are obtained by scanning Kelvin microscopy (SKM). Ring-shaped work function distributions are observed, presenting that the QRs' rim has a larger work function than the QRs' central hole. By combining the SKM results with those obtained by conductive atomic force microscopy and scanning capacitance microscopy, the correlations between the surface potential, conductance, and carrier density distributions are revealed, and a possible interpretation for the QRs' conductance distributions is suggested.

Concepts: Electricity, Scanning tunneling microscope, Energy, Kelvin probe force microscope, Scanning capacitance microscopy, Scanning probe microscopy

149

Coordinatively unsaturated (CUS) iron sites are highly active in catalytic oxidation reactions; however, maintaining the CUS structure of iron during heterogeneous catalytic reactions is a great challenge. Here, we report a strategy to stabilize single-atom CUS iron sites by embedding highly dispersed FeN4 centers in the graphene matrix. The atomic structure of FeN4 centers in graphene was revealed for the first time by combining high-resolution transmission electron microscopy/high-angle annular dark-field scanning transmission electron microscopy with low-temperature scanning tunneling microscopy. These confined single-atom iron sites exhibit high performance in the direct catalytic oxidation of benzene to phenol at room temperature, with a conversion of 23.4% and a yield of 18.7%, and can even proceed efficiently at 0°C with a phenol yield of 8.3% after 24 hours. Both experimental measurements and density functional theory calculations indicate that the formation of the Fe═O intermediate structure is a key step to promoting the conversion of benzene to phenol. These findings could pave the way toward highly efficient nonprecious catalysts for low-temperature oxidation reactions in heterogeneous catalysis and electrocatalysis.

Concepts: Density functional theory, Hydrogenation, Chemical reaction, Electron microscope, Scanning tunneling microscope, Catalysis, Hydrogen, Electron

32

Interactions between catalytically active metal particles and reactant gases depend strongly on the particle size, particularly in the subnanometer regime where the addition of just one atom can induce substantial changes in stability, morphology, and reactivity. Here, time-lapse scanning tunneling microscopy (STM) and density functional theory (DFT)-based calculations are used to study how CO exposure affects the stability of Pt adatoms and subnano clusters at the Fe3O4(001) surface, a model CO oxidation catalyst. The results reveal that CO plays a dual role: first, it induces mobility among otherwise stable Pt adatoms through the formation of Pt carbonyls (Pt1-CO), leading to agglomeration into subnano clusters. Second, the presence of the CO stabilizes the smallest clusters against decay at room temperature, significantly modifying the growth kinetics. At elevated temperatures, CO desorption results in a partial redispersion and recovery of the Pt adatom phase.

Concepts: Model theory, Ideal gas, Microscopy, Density functional theory, Fundamental physics concepts, Temperature, Scanning tunneling microscope, Electron

32

The development of methods for imaging large contiguous volumes with the electron microscope could allow the complete mapping of a whole mouse brain at the single-axon level. We developed a method based on prolonged immersion that enables staining and embedding of the entire mouse brain with uniform myelin staining and a moderate preservation of the tissue’s ultrastructure. We tested the ability to follow myelinated axons using serial block-face electron microscopy.

Concepts: Axon, Myelin, Electron, Neuron, Scanning tunneling microscope, Electron microscope, Nervous system, Microscope

31

The bacterium Geobacter sulfurreducens requires the expression of conductive protein filaments or pili to respire extracellular electron acceptors such as iron oxides and uranium and to wire electroactive biofilms, but the contribution of the protein fiber to charge transport has remained elusive. Here we demonstrate efficient long-range charge transport along individual pili purified free of metal and redox organic cofactors at rates high enough to satisfy the respiratory rates of the cell. Carrier characteristics were within the orders reported for organic semiconductors (mobility) and inorganic nanowires (concentration), and resistivity was within the lower ranges reported for moderately doped silicon nanowires. However, the pilus conductance and the carrier mobility decreased when one of the tyrosines of the predicted axial multistep hopping path was replaced with an alanine. Furthermore, low temperature scanning tunneling microscopy demonstrated the thermal dependence of the differential conductance at the low voltages that operate in biological systems. The results thus provide evidence for thermally activated multistep hopping as the mechanism that allows Geobacter pili to function as protein nanowires between the cell and extracellular electron acceptors.

Concepts: Scanning tunneling microscope, Cell, Pilus, Semiconductor, Microscopy, Electron, Bacteria, Oxygen

28

We report the growth of vertically aligned high crystalinity silicon nanotube (SiNT) arrays on silicon substrate by means of a Ni-Au bilayer catalyst engineering technique. Nanotubes were synthesized through solid-liquid-solid (SLS) method as well as vapor-liquid-solid (VLS). A precise evaluation utilizing atomic force microscopy (AFM) and lateral force microscopy (LFM) describes that the gold profile in Ni regions leads to the construction of multiwall SiNTs (MW-SiNT). The agreement of the structural geometry and stiffness of the obtained SiNTs with previous theoretical predictions suggest sp3 hybridization as the mechanism of tube formation. Apart from scanning electron and transmission electron microscopy (SEM, TEM) techniques, photoluminescence spectroscopy (PL) has been conducted to investigate the formation of nanostructures. PL spectroscopy confirms the evolution of ultra-fine walls of the silicon nanotubes, responsible for the observed photoemission properties.

Concepts: Gold, Nanomaterials, Spectroscopy, Electron, Scientific method, Scanning tunneling microscope, Transmission electron microscopy, Scanning electron microscope

28

The copolymers of N-isopropylacrylamide and sodium vinylsulphonate were synthesised by free radical polymerisation. The layer-by-layer self-assembly of the copolymers with poly(allylamine) hydrochloride was performed through assembling onto silicon wafer to form multilayer films and onto CaCO(3) microparticles doped with poly(styrene sulphonate) as well as deltamethrin microcrystals to form microcapsules. The multilayer films and microcapsules were characterised by atomic force microscopy, transmission electron microscopy and scanning electron microscopy. The release behaviour of deltamethrin in the microcapsules under different conditions was also investigated by high performance liquid chromatography. Results show that these deltamethrin microcapsules have good thermo-sensitive properties and deltamethrin release can be controlled via changing temperature or self-assembly layers.

Concepts: Radical, Scanning tunneling microscope, Semiconductor, Transmission electron microscopy, Electron, High performance liquid chromatography, Radical polymerization, Scanning electron microscope

28

To dissect the astonishing complexity of the biomolecular machinery functioning within a cell, imaging has been an integral tool in biology, allowing researches to “view” the detailed molecular biology responsible for coordinating cellular life. To visualize the molecular components of cellular structures requires, in particular, imaging techniques capable of reaching nanoscale spatial resolutions. Such nanoimaging techniques are the focus of this volume. Chapters in the current volume are divided into four parts and include specialized techniques in the areas of light, electron, and scanning probe microscopy, as well as methodologies employing combinatorial and complementary imaging approaches.

Concepts: Biomolecule, Cell biology, DNA, Scanning tunneling microscope, Microscopy, Molecular biology, Scanning probe microscopy, Biology

28

Atomic force microscopy (AFM) was used in concert with transmission electron microscopy (TEM) to image magnetotactic bacteria (Magnetospirillum gryphiswaldense MSR-1 and Magnetospirillum magneticum AMB-1), magnetosomes, and purified Mms6 proteins. Mms6 is a protein that is associated with magnetosomes in M. magneticum AMB-1 and is believed to control the synthesis of magnetite (Fe(3)O(4)) within the magnetosome. We demonstrated how AFM can be used to capture high-resolution images of live bacteria and achieved nanometer resolution when imaging Mms6 protein molecules on magnetite. We used AFM to acquire simultaneous topography and amplitude images of cells that were combined to provide a three-dimensional reconstructed image of M. gryphiswaldense MSR-1. TEM was used in combination with AFM to image M. gryphiswaldense MSR-1 and magnetite-containing magnetosomes that were isolated from the bacteria. AFM provided information, such as size, location and morphology, which was complementary to the TEM images.

Concepts: Scanning tunneling microscope, Electron, Atom, Bacteria, Transmission electron microscopy, Magnetotaxis, Magnetotactic bacteria, Protein