摘要:

Scanning tunneling microscope (STM) has been used to characterize the rectifying properties of metal nanojunctions. Advances in nanofabrication have made it possible to fabricate solid state nanotunnel junctions similar to point contact and STM junctions. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.41429

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We show how, via resonant tunneling, a tight binding model of a molecular adsorbate might be used to account for the anomalous conductance observed in STM images of many molecular adsorbates. New calculations show that even strong binding to the substrate does not necessarily destroy a resonance. Electrochemistry can be used to make biomolecular adsorbates that can be imaged by STM reliably. Current‐distance and current‐voltage data obtained over DNA‐salt complexesinsuitshow that the charge transport is most likely by tunneling and that the electronic properties of the tunnel gap are very different over a molecular adsorbate when compared with a gap that contains just small inorganic contaminants. In particular, conductance over the organic adsorbate is greatly enhanced. The electronic properties of the adsorbate are strongly affected by the position of the STM tip, demonstrating that electronic states might be altered by the stress applied by the STM tip under the control of the STM servo. This provides a mechanism to bring about a resonance or to bring a state close enough to resonance so that the set‐point tunnel conductance is achieved.

ISSN:0094-243X    

DOI:10.1063/1.41430

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

New images of DNA in the atomic force microscope (AFM) show: 1) DNA on a polymerized layer of the positively‐charged lipid, dimethyl‐bis‐(2‐(pentacosan‐2,4‐diinoyl)oxaethyl) ammonium bromide and 2) DNA in Mg‐acetate solution on ruby mica. The images of DNA on mica are the first such images to show isolated molecules of DNA that were not pushed by the tip out of the scan area.

ISSN:0094-243X    

DOI:10.1063/1.41431

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The morphology of lipid membranes on solid supports was studied by micro fluorescence filmbalance technique and Atomic Force Microscopy. The potential of AFM to visualize defects in lipid bilayers was demonstrated. The structure of polymerized membranes of the two lipids 10,12‐pentacosa‐diynoic acid (PC) and Dimethyl bis(pentacosadiynoyloxyethyl) ammonium bromide (BRONCO) was investigated with AFM. In both cases molecular resolution was achieved using amorphous silicon oxide as substrate. PC showed a highly regular packing of the hydrocarbon chains whereas in the case of the BRONCO film, which was polymerized in the high temperature phase, the positional correlation was only local.

ISSN:0094-243X    

DOI:10.1063/1.41432

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Images of DNA obtained in a scanning tunneling microscope operating under ultra‐high vacuum are described, and a contrast mechanism for STM imaging of weakly‐bound adsorbates is proposed. The capability of the STM for atom‐scale imaging of DNA is demonstrated through comparison of STM data with the accepted structure of A‐DNA derived from x‐ray crystallography; seven different structural elements of the molecule are identified and used to support the data interpretation. The contrast mechanism proposed invokes the Pauli‐principle based interference of the adsorbate with the substrate wavefunction vacuum tail. The adsorbate wavefunctions themselves lie far from the Fermi level and are unlikely to support electron conduction; their interaction with substrate wavefunction tail, however, enhances the tip‐substrate electron tunneling probability at the adsorption site. The suggested mechanism is supported withabinitiocalculations. The paper summarizes a talk presented at the Engineering Foundation conference ‘‘Scanned Probe Microscopies: STM and Beyond.’’

ISSN:0094-243X    

DOI:10.1063/1.41433

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Uncoated single‐strands DNA mixed with BAC (benzyldimethylalkylammonium chloride) were deposited on gold substrates and imaged in air with Scanning Tunneling Microscopy (STM). Constant‐current and gap‐modulated STM images showed that most of the DNA filaments tend to form aggregates where it is difficult to distinguish among the different nucleotides. Along isolated filaments small structures that we have, tentatively, assigned to phosphate and sugar groups, are present; bumps in a hexagonal configuration, that correspond presumably, to the nucleotides of DNA, have sometimes been observed.

ISSN:0094-243X    

DOI:10.1063/1.41434

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

An electrodeposition method to bindE.coliRNA polymerase onto a monoatomically flat gold surface is described. The enzyme is imaged by the STM in a high humidity or water/glycerol environment which allows direct observation without a metal coating. The enzyme molecules appear as ordered arrays or disordered arrays depending on the deposition conditions used. Cyclic voltammetry reveals the blocking of the Au electrode as the electrodeposition proceeds and suggests that the attachment of the polymerase takes place by a physisorption mechanism and not by chemical bonding to the surface.

ISSN:0094-243X    

DOI:10.1063/1.41409

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Scanned probe techniques, such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM) should facilitate sequencing of the humane genome if they could reliably image DNA‐ strands and identify DNA’s bases. We show that we can reliably deposit and analyze by STM doublestranded multimers of DNA on graphite. To progress beyond imaging, one of the first tasks in sequencing is to identify what STM images of individual bases should look like. We report here STM images of adenine with near‐atomic resolution. Adenine was adsorbed from a liquid solution onto the basal plane of graphite, where it forms monolayer‐patches stable under proper STM imaging conditions. These adsorbed monolayers have definite order with respect to the underlying graphite plane. The STM images are consistent with molecular modeling of the adsorption of adenine onto the basal plane of graphite.

ISSN:0094-243X    

DOI:10.1063/1.41410

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have directly imagedn‐alkane andn‐alkanol layers at the liquid/graphite interface using a scanning tunneling microscope. The layers possessed a high degree of two‐dimensional ordering and the adsorbate was observed to enhance the tunneling current. Both commensurate and incommensurate adsorption was observed. Tip‐molecule forces and thermal motion of the adsorbed molecules are also discussed.

ISSN:0094-243X    

DOI:10.1063/1.41411

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report results on Scanning Force Microscopy of the cell sheath of an archae bacterium. Uncoated complete sheath as well as sheath fragments were imaged. The smallest structural features observed were 18 nm apart and between 0.5 and 1 nm in height. A number of problems that affect imaging and resolution on biological material are discussed.

ISSN:0094-243X    

DOI:10.1063/1.41413

出版商:AIP    

年代:1991

数据来源: AIP