摘要:

Real space studies of the interaction of the two‐dimensional electron gas provided by metal surface states with localized scatterers are presented. The results involve electron scattering by steps and point defects (adsorbates) at Au(111) and Ag(111) surfaces. These scattering events lead, through interference, to an oscillatory local density of states (LDOS), which is imaged in maps of (dI/dV)/(I/V). Analysis of the LDOS oscillations provides insights into the scattering phenomena involved. We show that the decay of the amplitude of the oscillations as a function of distance from the scatterer can be accounted for by a model that describes the loss of coherence as a result of the wave number (k∥) spread of the states probed by the STM. This model also explains the energy dependence of the amplitude of the oscillations and provides a basis for comparing results from different metal surfaces. Analysis of the properties of the oscillations shows that at lowk∥, steps act very much like hard walls isolating the surface states of different terraces. At highk∥, however, the barriers become permeable. The circular LDOS waves that surround individual adsorbates on the terraces can be used to obtain information on their nature and charge state. Finally, we show that when the size of a terrace is decreased to a few coherence lengths, as in the case of small metal islands, quantum size effects appear. State densities of confined (‘‘particle in a box’’) states are revealed in the spectroscopic images.  

ISSN:0734-211X    

DOI:10.1116/1.587314

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The success of scanning probe microscopy in the imaging of biomolecules has led to the need for specially tailored image processing and data analysis routines. To permit the correlation of topographs with x‐ray crystallographic and electron microscopy data, automated feature discrimination and measurement algorithms have been developed. Incorporation of statistical techniques, such as cluster analysis, have allowed surface features to be characterized into single molecules and aggregates where the number of molecules forming the clusters can be calculated. The application of these routines to topographic data of proteins collected in our laboratory has permitted accurate comparisons with information from complementary biophysical techniques to be made. We believe that such developments are critical for the continued success of probe techniques in the imaging of biomolecules.

ISSN:0734-211X    

DOI:10.1116/1.587315

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Plasmid pBR322 DNA (0.5 mg/ml) isolated fromEscherichacoliHB101 was suspended in Tris‐HC1/EDTA (1/0.1 mol/L,pH 8.5), deposited on a highly oriented pyrolytic graphite surface, then imaged with scanning tunneling microscope (STM) in air and under paraffin liquid in constant current mode. The methods for preparing DNA samples used in the STM study are discussed. Dynamic changes of apparent width of supercoiled pBR322 DNA were captured during an STM imaging course. The pBR322 DNA is also visualized with an atomic force microscope (AFM) built by this laboratory after the sample was absorbed on the freshly cleaved mica surface. Characteristically relaxed circular structures of pBR322 DNA have been observed in the AFM experiment.  

ISSN:0734-211X    

DOI:10.1116/1.587316

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

An improved sample preparation procedure and optimized atomic force microscope (AFM) imaging conditions that makes it possible to obtain reproducible nanometer resolution AFM images of plasmid DNA with nanograms of the sample is presented. The Bst DNA polymerase I is a special kind of DNA polymerase that can keep its function even at high temperature (∼65 °C), but little is known about its surface structure. The AFM images of the Bst DNA polymerase I show its special surface structure.  

ISSN:0734-211X    

DOI:10.1116/1.587317

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

We imaged neurons which were prepared by different methods using the contact mode and the tapping mode atomic force microscope (AFM) in air. The contact mode AFM resolved cells with very thin dendrites from the substrate, and sharpened pyramidal tips gave sharper images of the cells than pyramidal tips. Over the cell surface, the tapping mode AFM gave a higher resolution than the contact AFM. We could resolve particles several nanometers in width using the tapping mode AFM. Our results suggest that the resolution on the cell surface depended not only on the tip shape but also on the physical properties of the cell surface.  

ISSN:0734-211X    

DOI:10.1116/1.587318

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

We have compared the structures of the filamentous assembly products of different recombinant NF–L polypeptides as seen by the scanning force microscope (SFM) in buffer solution with those obtained by transmission electron microscopy (TEM) of dehydrated specimens. For SFM the filaments were immobilized on a glass surface by photocrosslinking, whereas for TEM the filaments were negatively stained and air‐dried. Regarding their length and overall shapes, there is an excellent agreement between the SFM and the TEM data. However, the significant discrepancy of the filament width measured by these two microscopies illustrates the effect of the tip shape with the SFM on width measurements.

ISSN:0734-211X    

DOI:10.1116/1.587319

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Atomic force microscopy and scanning tunneling microscopy were used to obtain molecular resolution images of biological structures such as proteins and viruses. Proteins of 10 to 20 nm scale could be reliably resolved with faintly recognizable subunit arrangements. Bacteriophage T4 was imaged with well‐resolved head, tail, and tail fibers. When the tails were prepared from the headless mutants, the sheath proteins were stripped away from the tail, revealing the tube and the base plate in a T‐shaped complex. Scanning tunneling microscopy was used on metal coated samples and provided a reliable height measurement for bacteriophage T4. Constant improvement in the instrumentation and sample preparation promises a bright future for the biomedical application of scanning probe microscopy.

ISSN:0734-211X    

DOI:10.1116/1.587320

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

We have used the scanning force microscope to image the cytoplasmic and nuclear faces of the nuclear pore complex (NPC) in physiological buffer environment. In agreement with previous electron micrographs recorded from dehydrated specimens, we have been able to reproducibly distinguish a high degree of asymmetry between the nuclear and cytoplasmic surfaces of the nuclear pore complex. Very much like seen in the electron microscope, the cytoplasmic face of the nuclear pore complex appears ‘‘donutlike’’ with a massive, ∼18 nm high annulus surrounding the membrane pore. In contrast, the nuclear face of the pore complex looks like a ∼36 nm high ‘‘dome’’ in the scanning force microscope, which in the electron microscope is resolved into a tenuous ring from which eight thin filaments emanate that are joined distally by a terminal ring, thus forming a ‘‘basket’’ or ‘‘fishtrap.’’ In addition, we were able to visualize distinct structural changes occurring upon mechanical manipulation of the nuclear pore complex periphery with the scanning tip. These preliminary data provide us with the intriguing future possibility to directly correlate NPC structure with function.

ISSN:0734-211X    

DOI:10.1116/1.587321

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

We report here on some scanning tunneling microscopy (STM) observations on iron‐loaded (1200 atoms/molecule) human liver ferritin (HLF) chemically bound to gold surfaces activated with 4,4’‐dipyridil disulfide. The samples were prepared by immersing the activated gold foils in 10–500 μg/mL ferritin solutions in 0.3 mmol/L tris(hydroxymethyl)‐aminomethan (TRIS),pH 7.4. After a 30 min incubation period the foils were washed first in water, then in ethanol, air dried, and analyzed with a STM microscope. Individual ferritin molecules were resolved under the STM as spheroidal objects of approximately 10 nm diameter. The HLF molecules appeared as positive bumps above the bare substrates both in constant current and gap‐modulated images, with a nonrandom internal structure possibly related to their quaternary structure. After the observation the HLF was extracted and quantified by an immunoenzymatic test. In conclusion, the results obtained by the STM analysis were found to concur with the information provided by x‐ray crystallography.

ISSN:0734-211X    

DOI:10.1116/1.587268

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Three different members of the immunoglobulin super‐family have been studied. An antibody molecule, prototype of the family, directed against Thy‐1, another member of the family, was seen as a V shaped structure, as expected. The corresponding antigen, Thy‐1, was imaged at different resolutions. Then, the complex of the two molecules was analyzed and distinctive structures corresponding to each of the two partners were observed. The third member of the family, CD4, was seen as a string of four beads, linearly disposed. Further work needed to draw more detailed conclusions on this family is in progress.

ISSN:0734-211X    

DOI:10.1116/1.587269

出版商:American Vacuum Society    

年代:1994

数据来源: AIP