摘要:

Images of acetylcholine receptor rich membrane fragments from the electric organ ofTorpedomarmorataobtained with STM and EM are compared as well as different methods of their preparation for the STM. The problem of identification of the observed structures is discussed, that means whether identification of observed structures could be accomplished by finding characteristic structures, selective adsorption and chemical markers such as toxins. Finally, we propose to use the tip not only for detection but also for preparation.

ISSN:0094-243X    

DOI:10.1063/1.41414

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) have been successfully used to observe four systems of organic macromolecules; spin‐coated polystyrene; polyethylene oxide; polythiophene and polypyrrole; and phosphorylase kinase and phosphorylaseb. Images shown demonstrate the ability of AFM and STM to resolve the structure of these systems with subnanometer resolution. Further discussion supports these two techniques as valuable research tools in this area.

ISSN:0094-243X    

DOI:10.1063/1.41415

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In this paper we present scanning tunneling microscopy images of cytokeratin proteins and a monoclonal anti‐cytokeratin IgG antibody bound to their carboxyl terminal end. The images are consistent with current models of cytokeratin assembly inferred from biochemical analysis, electron microscopy evaluation of disintegrating cytokeratin filaments, and chemical cross‐linking of coiled‐coils.

ISSN:0094-243X    

DOI:10.1063/1.41436

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The principles and applications of the scanning electrochemical microscope are described. Examples are presented of images of both insulating and conductive materials, including metals, polymers, and biological specimens. The theory of SECM and applications to determinations of the rates of processes on various substrates is also discussed.

ISSN:0094-243X    

DOI:10.1063/1.41416

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effects of tip‐sample bias pulses while within tunneling distances have been investigated for graphite surfaces in contact with dry fluids, fluids containing water, and liquid water. In dry ambients, no surface modifications were observed at pulse voltages in excess of ±10 V. In fluids containing water, bias pulses exceeding a threshold voltage produced pits in the graphite surface, but the threshold voltage exhibited daily fluctuations of as much as 5 V. At the threshold for surface modification, a typical pit was found to have a diameter of approximately 30 A˚ and was 3 A˚ in depth. The diameter and depth of the pits increased with pulse amplitude above the observed threshold. In pure water, a reproducible bias pulse threshold of 4.0±0.2 V was observed, and such pulses yielded dome‐like features on the surface. The domed features were found to have a diameter of ∼7 A˚ and were ∼1.5 A˚ high. Bias pulses greater than 4.0 V were found to produce pits of approximately the same diameter as those produced in humid gases. Although little is known at present about the chemical structure of the domed features, their conversion into pits with subsequent bias pulses of only 0.2 V suggests that they are structural intermediates in the pit formation process. This hypothesis implies that the domed features may be vulnerable to chemical attack; consequently, the domes may present a viable route to the localized, designed, chemical functionalization of a graphite surface.

ISSN:0094-243X    

DOI:10.1063/1.41418

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Atomic resolution Atomic Force Microscope (AFM)1,2images of the first underpotentially deposited monolayer in the Cu on Au(111) and Ag on Au(111) are presented. These images demonstrate that the structure of this monolayer is very dependent on the nature of the electrolyte in which the upd process occurs. Specifically, Cu exhibits a (&sqrt;3 ×&sqrt;3)‐R30 °C overlayer on Au in sulfuric acid electrolyte, but is incommensurate close‐packed in perchloric acid. Ag shows a 3×3 overlayer in sulfuric acid and a 4×4 overlayer in carbonate and nitrate containing electrolytes. These different structures most likely originate in differing degrees of electrolyte participation in the monolayer.

ISSN:0094-243X    

DOI:10.1063/1.41419

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thin poly(1‐butene) (PB‐1) films drawn from the melt were deposited onto substrates of highly oriented pyrolytic graphite (HOPG) for an investigation with scanning force (SFM) and scanning tunneling microscopy (STM). The aim of this investigation was to study the surface electronic and topographic structure of these ultradrawn polymer films, which strongly influence the interfacial properties in contact with other materials, as for example in composite materials. Our SFM measurements excellently complement previous transmission electron microscopic (TEM) investigations showing the filamentary structure of the uniaxially stretched polymer as well as details within PB‐1 film defect structures (i.e., cracks). Close to monomolecular areas of the PB‐1 film, high resolution STM imaging simultaneously reveals the atomically resolved HOPG substrate surface as well as a helical structure originating from the polymer film.

ISSN:0094-243X    

DOI:10.1063/1.41420

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Scanning tunneling microscopy (STM) is used to study the kinetics of graphite gasification by oxidation and the morphology of platinum catalyzed hydrogen reaction. The graphite sample is heated conventionally for long‐term measurement at low to moderate temperatures, or by laser with millisecond exposure times at high temperatures. The oxidation of graphite takes place on step edges, domain boundaries and on individual dislocation or impurity sites on terraces. The reaction at individual reaction sites on the terraces leads either to removal of ‘‘disks’’ of graphite two monolayers deep, or to removal of cones of graphite. The reactivity of a particular site is determined (over twelve orders of magnitude) by measuring the edge’s recession velocity at the site. The rate of gasification of graphite by ozone is orders of magnitude higher than gasification by oxygen in air at a given temperature. Clusters of platinum deposited on graphite act as catalysts to dissociate molecular hydrogen and thus enhance the gasification. Discrete clusters stay with the receding carbon site, resulting in channels on the graphite surface.

ISSN:0094-243X    

DOI:10.1063/1.41421

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In this paper we discuss the application of scanning tunneling microscopy (STM) to probe the spatial distribution of surface reactions with atomic resolution. Scanning tunneling spectroscopy (STS) allows us to probe the valence electronic structure of an individual surface site and relate it to its reactivity. As an example we discuss a study of the initial stages of Si(111)‐7×7. We show that the mechanism of the reaction can be determined on the basis of STM and STS measurements. We then show that the STM can also be used to induce chemistry on the atomic scale. As examples we use desorption processes involving individual adsorbates on Si or involving substrate atoms.

ISSN:0094-243X    

DOI:10.1063/1.41422

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report on STM imaging of a polydiacetylene (the monomer is CH3(CH2)11‐C≡C‐C≡C‐(CH2)8‐COOH) on graphite. The monomer is topochemically polymerized on the graphite surface by exposure to ultraviolet light. These images represent, for different concentrations of material on the surface, individual molecules of the polymer, an ordered layer of polymer molecules and crystalline aggregates of the polymer.

ISSN:0094-243X    

DOI:10.1063/1.41423

出版商:AIP    

年代:1991

数据来源: AIP