摘要:

Uncoated single‐strand DNA mixed with BAC (benzyldimethylalkylammonium chloride) were deposited on gold substrates and imaged in air with the use of a high‐resolution scanning tunneling microscope (STM). Constant‐current and gap‐modulated STM images showed both double‐ and single‐stranded DNA. Along the single DNA backbone we have, tentatively, assigned small structures to phosphate and sugar group components; bumps aside single filaments, that correspond, presumably, to the bases of DNA, have sometimes been observed.

ISSN:0734-211X    

DOI:10.1116/1.585222

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A procedure has been developed in which mercurated DNA is covalently bonded to a modified graphite surface. This technique allows for stable adhesion of the DNA which enables one to image it with the scanning tunneling microscope. The method is outlined in this paper and images are presented of a partially modified graphite surface and one completely modified with DNA attached. The DNA images demonstrate B‐helix periodicity.

ISSN:0734-211X    

DOI:10.1116/1.585223

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

An electodeposition method has been developed for depositingE.coli. RNA polymerase onto a monoatomically flat gold surface. The scanning tunneling microscope has been used to image this enzyme in a high‐humidity or water/glycerol environment, which allows direct observation without metal coating. The deposition technique is reproducible enough to allow optimization of the deposition parameters for controlled electrodeposition. Time‐dependence studies were conducted to help determine the binding mechanism of the protein. The enzyme molecules appear as ordered arrays, amorphous features, or ‘‘jaw‐shaped’’ molecules depending on the deposition conditions used. The ‘‘jaw‐shaped’’ molecules closely resemble those observed by electron microscopy. In some of these a groove 22 Å wide can be seen.

ISSN:0734-211X    

DOI:10.1116/1.585224

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Using a scanning tunneling microscope (STM) of atomic resolution, we have directly observed variant comformations of DNA, including normal B‐form and Z‐form DNA, with a modified working condition. STM images of natural fish sperm and calf thymus B‐form DNA and poly (dG‐me5dC) and bromized poly dCG Z‐form DNA have been obtained at a subnatural environment. These results have provided some new evidence that images characteristic of DNA molecules can be obtained with STM.

ISSN:0734-211X    

DOI:10.1116/1.585225

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have shown that it is possible to image DNA with atomic resolution using scanning tunneling microscopy (STM), [R. J. Driscoll, M. G. Youngquist, and J. D. Baldeschwieler, Nature346, 294 (1990)]. Here we describe that data together with our general observations on STM of DNA in ultrahigh vacuum. We also suggest a possible contrast mechanism for DNA imaging by STM based on wave function orthogonality requirements between a molecule and its substrate. Topographic images are presented which resolve atomic features in addition to the double helical structure and nucleotide pairs of the DNA molecule. Comparisons of experimental STM profiles and modeled contours of the van der Waals surface ofA‐DNA show excellent correlation. Successive scans show that the imaging is nondestructive and reproducible. For this study, double‐stranded DNA was deposited on highly oriented pyrolitic graphite without coating, shadowing, or chemical modification.

ISSN:0734-211X    

DOI:10.1116/1.585226

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

An attempt has been made to image prospective tips by atomic force microscopy. The apex of mounted diamond fragments and of traditional metallic tips was investigated by the same diamond probe. The peculiar tip–tip configuration allowed to search for the effect of sample rotation on the images. Identical images were obtained when the diamond stylus scanned different etched tungsten tips, illustrating an interchange in the roles of tip and sample.

ISSN:0734-211X    

DOI:10.1116/1.585185

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The behavior of the magnetic moment at the tip end of the magnetic force microscope (MFM) was investigated by using two types of tip: iron wire and iron coated. MFM images of a magnetic head obtained by these two tips show quite different features. These differences were explained by assuming that the magnetic moment of the iron wire tip is almost fixed along the tip axis, while that of the iron coated tip follows the external field. In addition, it was found that the moment of the iron coated tip can respond to an ac excited head field of up to 50 MHz.

ISSN:0734-211X    

DOI:10.1116/1.585186

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

An attractive force microscope using photothermal vibration is presented. A cantilever is vibrated by the optical absorption of a laser beam whose intensity modulation frequency is at resonance frequency, and the vibration is detected by an optical deflection method. The characteristics of the photothermal vibration and the attractive force gradient versus tip‐sample distance have been measured with a Ni foil cantilever. Topographic images of digital memory disks made from a polycarbonate and Mg–Al alloy were recorded.

ISSN:0734-211X    

DOI:10.1116/1.585187

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have been measuring the electrostatic and contact forces between a tip and a graphite surface in a force microscope, which uses a polarizing optical interferometer. For large distances where the electrostatic force predominates, the data are analyzed in terms of a model which introduces the elongated shape of an actual tip. We find that the macroscopic tip has to be taken into account when analyzing the experimental data. The model allows us to deduce the effective radius of the tip which is operative in the electrostatic interaction. We also analyze the contact problem. The attractive part is consistent with van der Waals (vdW) forces. The repulsive regime shows an anomalously small level deflection which is attributed to the deformation of the sample surface. The adhesion of the tip sample is also measured.

ISSN:0734-211X    

DOI:10.1116/1.585188

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Atomic force microscopy (AFM) has already demonstrated its usefulness on a nanometer scale surpassing the resolution of conventional profilometers and probing different interactions such as repulsive contact, electrostatic, and magnetic forces. On an atomic scale the fundamental contrast mechanisms are still under investigation. The atomic resolution on layered materials such as graphite, boron nitride, transition metal dichalcogenides, and MnPS3shows the great potential of this technique. Several experimental and theoretical investigations on these layered materials have shown that the presence of the AFM tip can lead to a significant distortion of the electronic and atomic structure. For small loadings (≤10−8N) the tip causes long‐range elastic deformations while for higher loadings a sharp tip can puncture the sample. To explain the atomic scale features being measured with higher loadings, different mechanisms such as the dragging of flakes or shearing of layers have been suggested. The application of AFM to nonlayered structures gives the opportunity to exclude several of these influences. Here we present atomically resolved images of LiF(100). The measurements are compared to results from different surface sensitive techniques such as helium scattering and low energy electron diffraction (LEED). The contrast mechanisms of AFM are discussed in relation to these experiments.

ISSN:0734-211X    

DOI:10.1116/1.585189

出版商:American Vacuum Society    

年代:1991

数据来源: AIP