Gap-modulated versus constant current mode as a tool to discriminate between DNA and substrate structure in scanning tunneling microscopy

1993 ◽  
Author(s):  
Antonio Cricenti ◽  
S. Selci ◽  
M. Scarselli ◽  
Renato Generosi ◽  
F. Amaldi ◽  
...  
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Current Mode ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Substrate Structure ◽  
Constant Current Mode

Scanning tunneling microscopy of polymers: A status report

1989 ◽  
Vol 47 ◽  
pp. 330-331
Author(s):  
P.E. Russell ◽  
I.H. Musselman
Keyword(s):  
High Resolution ◽  
Scanning Tunneling Microscopy ◽  
Sample Surface ◽  
Atomic Scale ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Status Report ◽  
Tunneling Microscopy ◽  
Research Issues ◽  
Wide Range

Scanning tunneling microscopy (STM) has evolved rapidly in the past few years. Major developments have occurred in instrumentation, theory, and in a wide range of applications. In this paper, an overview of the application of STM and related techniques to polymers will be given, followed by a discussion of current research issues and prospects for future developments. The application of STM to polymers can be conveniently divided into the following subject areas: atomic scale imaging of uncoated polymer structures; topographic imaging and metrology of man-made polymer structures; and modification of polymer structures. Since many polymers are poor electrical conductors and hence unsuitable for use as a tunneling electrode, the related atomic force microscopy (AFM) technique which is capable of imaging both conductors and insulators has also been applied to polymers.The STM is well known for its high resolution capabilities in the x, y and z axes (Å in x andy and sub-Å in z). In addition to high resolution capabilities, the STM technique provides true three dimensional information in the constant current mode. In this mode, the STM tip is held at a fixed tunneling current (and a fixed bias voltage) and hence a fixed height above the sample surface while scanning across the sample surface.

scholarly journals The butterfly – a well-defined constant-current topography pattern on Si(001):H and Ge(001):H resulting from current-induced defect fluctuations

2016 ◽  
Vol 18 (28) ◽  
pp. 19309-19317 ◽  
Author(s):  
Mads Engelund ◽  
Szymon Godlewski ◽  
Marek Kolmer ◽  
Rafał Zuzak ◽  
Bartosz Such ◽  
...  
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Dangling Bond ◽  
Tunneling Microscopy ◽  
Imaging Model ◽  
Rapid Switching

Scanning tunneling microscopy of dangling bond dimers on Si(001):H and Ge(001):H involves rapid switching between equivalent geometries and we present a simple yet versatile imaging model to address this.

Scanning Tunneling Microscopy Imaging and Spectroscopy of a Single Viologen Molecule

2008 ◽  
Vol 8 (9) ◽  
pp. 4621-4625
Author(s):  
Nam-Suk Lee ◽  
Chang-Heon Yang ◽  
Won-Suk Choi ◽  
Young-Soo Kwon
Keyword(s):  
Self Assembly ◽  
Current Mode ◽  
Scanning Tunneling Spectroscopy ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Microscopy Imaging ◽  
Current Voltage ◽  
Imaging And Spectroscopy ◽  
Stm Images

A low-temperature ultrahigh-vacuum scanning tunneling microscope (UHV-STM) was used to image viologen (N-methyl-N′-di (8-mercaptooctyl)-4,4′-bipyridinium; HSC8VC8SH) molecules and to perform local spectroscopic measurements on these molecules. Self-assembly of viologen molecules was conducted on Au (111), which had been thermally deposited onto freshly cleaved, heated mica. Here, we demonstrate a novel SAM matrix appropriate for the isolation of viologen molecules composed of octanethiol (C8) in which HSC8VC8SH was inserted at defects in the molecular lattice. The isolated single molecules of viologen inserted in the SAM matrix were observed as protrusions in STM topography using a constant current mode. STM images at 298 K showed protrusions with a topographic height of about 2.71 nm (HSC8VC8SH) with viologen molecules that self-assembled on the substrate. The current–voltage (I–V) characteristics were measured while the electrical properties of the formed monolayer were scanned using scanning tunneling spectroscopy (STS). We found the high peak current-like rectification at +1.14 V (HSC8VC8SH). The rectification ratios, RR = J (at +2.5 V)/J (at −2.5 V), are in the range of 4.47.

Fast scanning tunneling microscope in constant current mode

1989 ◽  
Vol 333 (4-5) ◽  
pp. 340-342 ◽  
Author(s):  
S. Bräuer ◽  
B. Krämer ◽  
H. Pagnia ◽  
N. Sotnik ◽  
K. -H. Vetter ◽  
...  
Keyword(s):  
Scanning Tunneling Microscope ◽  
Current Mode ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Tunneling Microscope ◽  
Constant Current Mode

scholarly journals Terthiophene on Au(111): A scanning tunneling microscopy and spectroscopy study

2011 ◽  
Vol 2 ◽  
pp. 561-568 ◽  
Author(s):  
Berndt Koslowski ◽  
Anna Tschetschetkin ◽  
Norbert Maurer ◽  
Elena Mena-Osteritz ◽  
Peter Bäuerle ◽  
...  
Keyword(s):  
Scanning Tunneling Microscopy ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Constant Current ◽  
Linear Molecule ◽  
Scanning Tunneling ◽  
Striking Difference ◽  
Repulsive Interaction ◽  
Tunneling Microscopy ◽  
Homo Lumo

Terthiophene (3T) molecules adsorbed on herringbone (HB) reconstructed Au(111) surfaces in the low coverage regime were investigated by means of low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) under ultra-high vacuum conditions. The 3T molecules adsorb preferentially in fcc regions of the HB reconstruction with their longer axis oriented perpendicular to the soliton walls of the HB and at maximum mutual separation. The latter observation points to a repulsive interaction between molecules probably due to parallel electrical dipoles formed during adsorption. Constant-separation (I-V) and constant-current (z-V) STS clearly reveal the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals, which are found at −1.2 eV and +2.3 eV, respectively. The HOMO–LUMO gap corresponds to that of a free molecule, indicating a rather weak interaction between 3T and Au(111). According to conductivity maps, the HOMO and LUMO are inhomogeneously distributed over the adsorbed 3T, with the HOMO being located at the ends of the linear molecule, and the LUMO symmetrically with respect to the longer axis of the molecule at the center of its flanks. Analysis of spectroscopic data reveals details of the contrast mechanism of 3T/Au(111) in STM. For that, the Shockley-like surface state of Au(111) plays an essential role and appears shifted outwards from the surface in the presence of the molecule. As a consequence, the molecule can be imaged even at a tunneling bias within its HOMO–LUMO gap. A more quantitative analysis of this detail resolves a previous discrepancy between the fairly small apparent STM height of 3T molecules (1.4–2.0 nm, depending on tunneling bias) and a corresponding larger value of 3.5 nm based on X-ray standing wave analysis. An additionally observed linear decrease of the differential tunneling barrier at positive bias when determined on top of a 3T molecule is compared to the bias independent barrier obtained on bare Au(111) surfaces. This striking difference of the barrier behavior with and without adsorbed molecules is interpreted as indicating an adsorption-induced dimensionality transition of the involved tunneling processes.

Scanning tunneling microscopy of planar biomembranes

1989 ◽  
Vol 47 ◽  
pp. 14-15
Author(s):  
K. A. Fisher ◽  
S. Whitfield ◽  
R. E. Thomson ◽  
K. Yanagimoto ◽  
M. Gustafsson ◽  
...  
Keyword(s):  
Scanning Tunneling Microscope ◽  
Surface Deformation ◽  
Pyrolytic Graphite ◽  
Current Mode ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Biological Macromolecules ◽  
Tunneling Microscopy ◽  
Aspect Ratios ◽  
Planar Membranes

The scanning tunneling microscope (STM) is capable of imaging conductive surfaces at atomic resolution. When STMs are used to image biological samples, however, STM resolution is limited to nanometer levels whether samples are hydrated, air-dried, or metal-coated. Lateral resolution is poor due to the nature of biological macromolecules (large Image aspect ratios) as well as to STM tip effects (shape, multiple tips, and tip/sample Interactions). If samples are adsorbed to highly-oriented pyrolytic graphite (HOPG) surfaces and scanned in the topographic (constant current) mode, vertical resolution is also uncertain due to contamination-mediated surface deformation artifacts. Nevertheless, because the STM is capable of detecting sub-Ångstrom displacements in z (e.g. to 0.02 Å in UHV), we have examined the feasibility of using the STM to determine the thickness of planar membranes attached to glass and mica surfaces. Planar membrane monolayers also uniquely provide the opportunity to correlate biochemical and TEM information with STM topographic images.

Scanning Tunneling Microscopy and low-temperature force microscopy of freeze-fractured samples

1993 ◽  
Vol 51 ◽  
pp. 58-59
Author(s):  
K. A. Fisher ◽  
M. B. Shattuck ◽  
M. G. L. Gustafsson ◽  
J. Clarke
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Electron Tunneling ◽  
Freeze Fracture ◽  
Tunneling Current ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Feedback Signal ◽  
Tunneling Microscopy ◽  
Surface Features ◽  
Force Microscopy

Monolayer freeze-fracture combined with scanned probe microscopy (SPM) offers unique advantages for studies of biological structure. The freeze-fracture methodology incorporates rapid freezing approaches for sample preservation and stabilization, and the scanned probe microscopies, especially scanning tunneling microscopy (STM) and atomic force microscopy (AFM), allow high resolution examination of surface features including digital mapping, quantification, and display. In routine biological STM a sharp conductive probe is positioned with piezoelectric transducers close to a conductive surface. When electron tunneling begins, the probe is scanned while electronic feedback maintains constant current. Because the tunneling current is logarithmically sensitive to separation between the tip and the sample, the feedback signal can be calibrated to indicate height with sub-Angstrom sensitivity and precision. In routine biological AFM, the sample is scanned while the force between the tip and the sample is kept constant.There are two fundamental problems in STM examinations of biological systems. First, biological samples are soft and are often perturbed by the scanning probe; and second, they are not electrically conductive. Coating samples with metal replicas simultaneously circumvents both these difficulties, conferring sample stability and electrical conductivity. The STM can be used to measure sample heights quite accurately, and has been used to measure the thickness and changes in thickness of metal-coated purple membrane and the depth of surface features of freeze-fracture replicas of synthetic phospholipids.

Cross-Sectional Scanning Tunneling Microscopy of III-V Heterostructures Grown by Molecular-Beam Epitaxy

1994 ◽  
Vol 340 ◽  
Author(s):  
A.Y. Lew ◽  
E.T. Yu ◽  
D.H. Chow ◽  
R.H. Miles
Keyword(s):  
Molecular Beam Epitaxy ◽  
Scanning Tunneling Microscopy ◽  
Molecular Beam ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Close Inspection ◽  
Cross Sectional ◽  
Current Voltage ◽  
Strained Layer Superlattices

ABSTRACTCross-sectional scanning tunneling microscopy and spectroscopy have been used to characterize InAs/Ga1-x InxSb strained-layer superlattices grown by molecular-beam epitaxy. Atomic-resolution constant-current images of the epitaxial layers reveal monolayer roughness at the superlattice interfaces. An asymmetry in electronic structure between interfaces in which InAs has been grown on Ga1-x InxSb and those in which Ga1-x InxSb has been grown on InAs has also been observed in these images. Close inspection of the images reveals increased growthdirection lattice spacings in the Ga1-x InxSb layers compared to the InAs layers, as well as even larger lattice spacings at the InAs/Ga1-x InxSb interfaces. The latter is consistent with the formation of primarily InSb-like interfaces. Current-voltage spectra obtained while tunneling into the superlattice layers are found to be strongly influenced by extended superlattice electronic states.

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