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Results for “Microscopy, Scanning Tunneling”

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PubMed2002

Atomic-scale spin-polarized scanning tunneling microscopy applied to Mn3N2(010).

Atomic-scale spin-polarized scanning tunneling microscopy is demonstrated in the case of the unique surface spin structure of Mn3N2(010) at 300 K. We find that the surface spin structure is manifested as a modulation of the normal atomic row height profile. The atomic-scale spin-polarized image is thus shown to contain two components, one the normal, nonpolarized part, and the other the magnetic, spin-polarized part. A method is presented for separating these two spatially correlated components, and the results are compared with simulations based on integrated local spin density of states calculated from first principles.

Journal Article↗

PubMed1990

Viewing molecules with scanning tunneling microscopy and atomic force microscopy.

Two new microscopic techniques make it possible to obtain images of biologically interesting molecules directly in air, vacuum, or under water. Scanning tunneling microscopy and atomic force microscopy both have the capacity to visualize atoms on the surface of rigid structures and provide details of molecular structure for lipids, proteins, carbohydrates, and nucleic acids. In addition to providing visualizations of individual molecules, these scanning probe techniques allow direct imaging of complexes between molecules or between molecules and higher-order subcellular structures such as membranes and cytoskeletal components. Both microscopes can be operated under a variety of ambient conditions ranging from high vacuum to above atmospheric pressure. Specimens need not be dry; both techniques have been used to image molecules in aqueous media under nearly physiological conditions. It is proposed that as these techniques mature they will allow direct observation of many molecular interactions under physiological conditions or even in vivo while they are occurring within the cell.

Brain↗

PubMed1995

Lateral electrical conductivity of mica-supported lipid bilayer membranes measured by scanning tunneling microscopy.

Lateral electric conductivity of mica-supported lipid monolayers and of the corresponding lipid bilayers has been studied by means of scanning tunneling microscopy (STM). The surface of freshly cleaved mica itself was found to be conductive when exposed to humid air. Lipid monolayers were transferred onto such a surface by means of the Langmuir-Blodgett technique, which makes the mica surface hydrophobic and suppresses the electric current along the surface in the experimentally accessible humidity (5-80%) and applied voltage (0-10 V) range. This is true for dipalmitoylphosphatidylethanolamine (DPPE) as well as dipalmitoylphosphatidylcholine (DPPC) monolayers. Repeated deposition of DPPC layers by means of the Langmuir-Blodgett LB technique does not lead to the formation of a stable surface-supported bilayer because of the high hydrophilicity of the phosphatidylcholine headgroups that causes DPPC/DPPC bilayers to peel off the supporting surface during the sample preparation. In contrast to this, a DPPE or a DPPC monolayer on top of a DPPE monolayer gives rise to a rather stable mica-supported bilayer that can be studied by STM. Electric currents between 10 and 100 fA, depending on the ambient humidity, flow along the DPPE bilayer surface, in the humidity range between 35 and 60%. The DPPC surface, which is more hydrophilic, is up to 100 times more conductive under comparable conditions. Anomalous high lateral conductivity thus depends on, and probably proceeds via, the surface-adsorbed water layers. The prominence of ambient humidity and surface hydrophilicity on the measured lateral currents suggests this. The combination of our STM data and previously published water adsorption isotherms as a function of the relative humidity indicate that one layer or less of adsorbed water suffices for mediating the measurable lateral currents. The fact that similar observations are also made for other hydrophilic substrates supports the conclusion that lateral conductivity via surface-adsorbed water is a rather general phenomenon.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1998

Interactions of DNA with fluorescent dyes: by scanning tunneling microscopy.

Genomic DNA was obtained from peripheral blood samples of healthy volunteers and interacted with two fluorescent dyes (i.e. Hoechst 33,258 and ethidium bromide) in aqueous media. These media containing DNA-dye complexes deposited on the gold coated mica surfaces. Then, STM images were obtained in which the STM was operated in air at atmospheric pressure with a tip-to-substrate bias voltage of 250-1000 mV (sample positive) and the tunneling currents in the range of 10-20 pA by using etched tips of Pt/Ir, in constant current mode. Both dyes from molecular clusters on DNA. While, the Hoechst molecules were observed on the DNA chains at regular distances, the ethidium bromide molecular clusters did not.

Bisbenzimidazole↗

PubMed1993

Surface atomic and domain structures of biomedical carbons observed by scanning tunneling microscopy (STM).

STM has been used to study the surface domain and atomic structures of three biomedical carbons: glassy carbon (GC), low-temperature isotropic carbon (LTI), and ultra-low-temperature isotropic carbon (ULTI). The images show atomic lattices on both GC and LTI, but not on ULTI. The lattices contain many defects; lattices in GC are more ordered than those in LTI. The images also show patchlike carbon crystallites with sizes of 3-15 nm for GC, 2-8 nm for LTI, and 1-3 nm for ULTI. The crystallites from surface domains that may differ in surface properties due to different orientations of the crystallites. Mechanical polishing makes the LTI surface more amorphous and more homogeneous. Based on the STM observations, we evaluate several hypotheses on the blood compatibility of biomedical carbons.

Biocompatible Materials↗

PubMed1991

Two-dimensional ordering of the DNA base guanine observed by scanning tunneling microscopy.

Guanine, one of the four DNA bases, has been observed by tunneling microscopy to form a two-dimensional ordered structure on two crystalline substrates, graphite and MoS2. The two-dimensional lattice formed by guanine is nearly identical on the two surfaces, and heteroepitaxy appears to be the growth mechanism in both cases. Although the resolution of molecular details is superior for the graphite substrate, the simpler results on MoS2 are not only easier to interpret but also facilitate the understanding of the more complex images on graphite. We propose that the interfacial structure is composed of linear chains of hydrogen-bonded molecules aligned into a closely packed two-dimensional array.

DNA↗

PubMed1990

Scanning tunneling microscopy of a liquid crystalline phase of poly((dA-dT).(dA-dT)) induced by a histone H1 peptide.

In this report, we present the first observations of uncoated poly((dA-dT).(dA-dT)) molecules organized in a liquid crystalline phase induced by the binding of a histone H1 peptide. The effect of the peptide on the polymer condensation is clearly illustrated on the large-scale STM images which reveal a well defined spacing between parallel DNA helices. High resolution images of rare isolated molecules of poly((dA-dT).(dA-dT)) exhibit two sets of helical pitch values, 6 and 7.5 nm. While the lower value can be correlated with the pitch of poly((dA-dT).(dA-dT)), the larger one may arise from peptide binding in the polymer minor groove.

Crystallization↗

PubMed1990

Scanning tunneling microscopy and spectroscopy of plasmid DNA.

We present scanning tunneling microscope (STM) images of uncoated deoxyribonucleic acid (DNA) electrochemically mounted on highly-oriented pyrolytic graphite (HOPG) and imaged in air. Images of linear abnormalities inherent to HOPG surfaces that can be confused with DNA are also presented. Scanning tunneling spectroscopic (STS) images generated by superimposing a small, high frequency ac bias onto the dc tunnel bias and recording the ac current signal were taken simultaneously with the topographic images. These spectroscopic images reveal contrast due to local conductivity variations and can be used to differentiate DNA molecules from graphite artifacts.

Carbon↗

PubMed2003

Unveiling metal-cage hybrid states in a single endohedral metallofullerene.

The local structural and electronic properties of individual metallofullerenes are studied using scanning tunneling microscopy, scanning tunneling spectroscopy, and theoretical simulations. The energy-resolved metal-cage hybrid states of a single endohedral metallofullerene Dy@C82 isomer I have been spatially mapped, supporting a complex picture consisting of the orbital hybridization and charge transfer for the interaction between the cage and the metal atom. The relative position of the encapsulated Dy atom inside the cage and the molecular orientation on the surface have been inferred by comparing the experimental results with theoretical simulations. The combined technique provides promising applications in the fields of in situ characterization and diagnostics of metallofullerene-based nanodevices.

Journal Article↗

PubMed1991

Scanning tunnelling microscopy of 16S ribosomal RNA in water.

The scanning tunnelling microscope has been used to image 16S ribosomal RNA molecules in water electrophoretically deposited on graphite surface. Two kinds of images have been obtained: images showing aggregates of 16S ribosomal RNA molecules similar to those obtained from DNA solutions and others showing individual 16S ribosomal RNA molecules. An interesting characteristic of these images, recorded in constant current mode, is that the 16S ribosomal RNA molecules appear to be located below the graphite surface. The morphology and several structural parameters of the molecules were consistent with the data obtained from electron microscopy.

Centrifugation, Zonal↗

PubMed1991

Scanning tunneling microscopy of human erythrocyte membranes.

Images of surfaces of human erythrocyte ghosts, lecithin liposomes, spectrin, erythrocyte membrane skeleton, concanavalin A and concanavalin A--decorated erythrocyte ghosts were obtained by scanning tunneling microscopy. The dimensions and surface topography of some membrane structures are described and discussed.

Concanavalin A↗

PubMed2006

Voltammetry and in situ scanning tunnelling microscopy of de novo designed heme protein monolayers on Au(111)-electrode surfaces.

In the present work, we report the electrochemical characterization and in situ scanning tunnelling microscopy (STM) studies of monolayers of an artificial de novo designed heme protein MOP-C, covalently immobilized on modified Au(111) surfaces. The protein forms closely packed monolayers, which remain electroactive upon immobilization. In situ STM images show circular structures indicating that MOP-C stands upright on the surface in accordance with the molecular design. Despite the large spatial extension of MOP-C, about 5 nm in height, conditions could be found where tip/sample interaction is minimal and proteins could be imaged without detectable tip interference. The results indicate further that the structural sensitivity of (in situ) STM depends to a significant extent on associated electron transfer kinetics. In the present case, the heme group does not contribute significantly to the tunnelling current, apparently due to slow electron transfer kinetics. As a consequence, STM images of heme-containing and heme-free MOP-C did not reveal any notable differences in apparent height or physical extension. The apparent height of heme-containing MOP-C did not show any dependence on the substrate potential being varied around the redox potential of the protein. The mere presence of an accessible molecular energy level is not sufficient to result in detectable tunnelling current modulation.

Adsorption↗

PubMed2005

In-situ scanning tunneling microscopy of carbon monoxide adsorbed on Au(111) electrode.

In-situ scanning tunneling microscopy (STM) coupled with cyclic voltammetry was used to examine the adsorption of carbon monoxide (CO) molecules on an ordered Au(111) electrode in 0.1 M HClO4. Molecular resolution STM revealed the formation of several commensurate CO adlattices, but the (9 x radical 3) structure eventually prevailed with time. The CO adlayer was completely electrooxidized to CO2 at 0.9 V versus RHE in CO-free 0.1 M HClO(4), as indicated by a broad and irreversible anodic peak which appeared at this potential in a positive potential sweep from 0.05 to 1.6 V. A maximal coverage of 0.3 was estimated for CO admolecules from the amount of charge involved in this feature. Real-time in-situ STM imaging allowed direct visualization of the adsorption process of CO on Au(111) at 0.1 V, showing the lifting of (radical 3 x 22) reconstruction of Au(111) and the formation of ordered CO adlattices. The (9 x radical 3) structure observed in CO-saturated perchloric acid has a coverage of 0.28, which is approximately equal to that determined from coulometry. Switching the potential from 0.1 to -0.1 V restored the reconstructed Au(111) with no change in the (9 x radical 3)-CO adlattice. However, the reconstructed Au(111) featured a pairwise corrugation pattern with two nearest pairs separated by 74 +/- 1 A, corresponding to a 14% increase from the ideal value of 65.6 A known for the ( radical 3 x 22) reconstruction. Molecular resolution STM further revealed that protrusions resulting from CO admolecules in the (9 x radical 3) structure exhibited distinctly different corrugation heights, suggesting that the CO molecules resided at different sites on Au(111). This ordered structure predominated in the potential range between 0.1 and 0.7 V; however, it was converted into new structures of (7 x radical 7) and ( radical 43 x 2 radical 13) on the unreconstructed Au(111) when the potential was held at 0.8 V for ca. 60 min. The coverage of CO adlayer decreased accordingly from 0.28 to 0.13 before it was completely removed from the Au(111) surface at more positive potentials.

Journal Article↗

PubMed2000

Observation of charge-density wave domains on the Cr(110) surface by low-temperature scanning tunneling microscopy

We have studied the Cr(110) surface with low-temperature scanning tunneling microscopy at 6 to 145 K. For tunneling voltages below +/-150 mV we observe a surface charge-density wave (CDW) with a wavelength of 42 A and wave fronts aligned with the [001] in-plane direction. The observed wave pattern is identified as the surface projection of the bulk CDW's arising from the spin-density wave ground state of Cr with the Q vector parallel to [100] and [010], respectively. The bulk CDW with Q parallel to the [001] in-plane direction appears, however, to be strongly suppressed at the Cr(110) surface.

Journal Article↗

PubMed2006

Anisotropic water chain growth on Cu(110) observed with scanning tunneling microscopy.

We report a novel structure of water aggregate by means of scanning tunneling microscopy. Water molecules are self-assembled into one-dimensional chains on Cu(110) at 78 K. The chain exhibits a zigzag structure with a period of 7.2 A and grows to a length of approximately 1000 A. We propose that water hexamers are arranged alternately along the chain. Interchain repulsion due to dipole interaction facilitates the 1D chain growth. A two-dimensional overlayer develops only at high coverage.

Journal Article↗

PubMed2005

The reorganization energy of azurin in bulk solution and in the electrochemical scanning tunneling microscopy setup.

The total reorganization energy lambda of azurin is theoretically studied both for the electron self-exchange reaction and for the protein in the electrochemical scanning tunneling microscopy (ECSTM) setup. The results demonstrate the importance of the proximity between the active sites in the encounter complex to reduce lambda for the electron self-exchange reaction and quantifies the effects of the presence of an STM environment (tip and substrate) on lambda. A comparison of the calculated results with experimental data is performed, and the relative magnitudes of the inner and outer contributions to lambda are discussed.

Azurin↗

PubMed1991

Conformation of DNA-DNA polymerase I complex observed by scanning tunneling microscopy.

The conformation of a complex of a 41 mer/31 mer DNA fragment and the Klenow fragment of DNA polymerase I of Escherichia coli was studied by scanning tunnelling microscopy (STM). The results shows that near two turns of double helix of this DNA fragment was outside of enzyme while another part containing more than one turn of helix and 10 nucleotides single strand was combined with enzyme. The dimension and shape of DNA polymerase I (KF) in complex were different from that of free enzyme. The conformation of DNA-DNA polymerase I (KF) complex and the application of STM in studying structure of complex of DNA polymerase with DNA were discussed.

Base Sequence↗

PubMed1992

Scanning tunneling microscopy of DNA: a novel technique using radiolabeled DNA to evaluate chemically mediated attachment of DNA to surfaces.

pBS+ plasmid deoxyribonucleic acid (DNA) was imaged by scanning tunneling microscopy (STM) after mounting microdroplets by aerosol deposition onto heated epitaxial gold surfaces. However, the instability of the adsorbate to forces exerted by the tunneling tip points out the need for more aggressive bonding of molecules to surfaces. We describe a sensitive assay for the qualitative and quantitative evaluation of chemical agents to influence binding of DNA to surfaces using 32P-labeled pBS+ plasmid DNA. We propose that such an assay can make an important contribution to immobilization techniques prior to STM imaging.

DNA↗