The Atomic-Scale Characterization of Defects on Cleaved Vanadium and Molybdenum Oxide Surfaces Using Stm

1994 ◽  
Vol 357 ◽  
Author(s):  
Gregory S. Rohrer ◽  
Richard L. Smith
Keyword(s):  
Atomic Scale ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Coordination Polyhedra ◽  
Single Crystal Surfaces ◽  
Surface Plane ◽  
Crystallographic Shear ◽  
Scale Characterization ◽  
Reliable Interpretation

AbstractScanning tunneling microscopy (STM) was used to determine the structure of cleaved, single crystal surfaces of V205, V6013, Mo18052, and Mo8023. Constant current images were recorded in ultrahigh vacuum and in air. By imaging well-defined surfaces that exhibit structural and chemical similarities, and comparing the observations to the known bulk structures, it is possible to establish a reliable interpretation for the contrast in the STM images. A comparison of images from the V6013(001) and the V205(001) surfaces clearly shows that the surface V coordination polyhedra that are capped by vanadyl 0 can be distinguished from those that are not. This allows vacancies in the vanadyl 0 position to be identified on cleaved V205(001) surfaces. Mo18052(100) and Mo8023(010) provide models for two different characteristic types of surface/crystallographic shear (CS) plane intersections. The shear in Mo8023 lies in the (010) surface plane and creates dark contrast along the [001]. The CS planes in Mo18052, on the other hand, have components of shear both in and normal to the (100) surface plane and create white contrast parallel to [010]. These standards for contrast identification can be used to identify defects on inhomogeneous surfaces.

Imaging The Atomic-Scale Structure of Molybdenum and Vanadium Oxides by Scanning Tunneling Microscopy

1994 ◽  
Vol 332 ◽  
Author(s):  
Gregory S. Rohrer ◽  
Weier Lu ◽  
Richard L. Smith
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Chemical Vapor ◽  
Shear Plane ◽  
Structural Features ◽  
Atomic Scale ◽  
Constant Current ◽  
Chemical Vapor Transport ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Coordination Polyhedra

ABSTRACTSingle crystals of Na0.003V2O5 and Mo18O52 were grown by chemical vapor transport and cleaved surfaces were imaged in ultrahigh vacuum using scanning tunneling microscopy (STM). Because the Mo18O52 (100) and Na0.003V2O5 (010) surfaces of these layered materials have a bulk terminated structure, the atomic-scale contrast in constant current images can be directly compared to components of the bulk structure. Among the structural features identified in the STM images are the surface/crystallographic shear plane intersections, the different MoOx coordination polyhedra on the Mo18O52 (100) surface, and the VO5 square pyramids that make up the Na0.003V2O5 (010) surface. In each of these cases, it was found that the atoms closest to the tip dominate the image contrast.

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.

Anisotropy in Atomic-Scale Interface Structure and Mobility in Inas/Ga1_Xinxsb Superlattices

1996 ◽  
Vol 448 ◽  
Author(s):  
A. Y. Lew ◽  
S. L. Zuo ◽  
E. T. Yu ◽  
R. H. Miles
Keyword(s):  
Quantitative Analysis ◽  
Molecular Beam ◽  
Interface Structure ◽  
Interface Roughness ◽  
Atomic Scale ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Interfacial Bond ◽  
Tunneling Microscopy ◽  
Cross Sectional

AbstractWe have used cross-sectional scanning tunneling microscopy to study the atomic-scale interface structure of InAs/Ga, _In.xSb superlattices grown by molecular-beam epitaxy. Detailed, quantitative analysis of interface profiles obtained from constant-current images of both (110) and (1ī0) cross-sectional planes of the superlattice indicates that interfaces in the (1ī0) plane exhibit a higher degree of interface roughness than those in the (110) plane, and that the Ga1-xln xAs interfaces are rougher than the InAs-on-Gal1-xInxSb interfaces. The roughness data are consistent with anisotropy in interface structure arising from anisotropic island formation during growth, and in addition with a growth-sequence-dependent interface asymmetry resulting from differences in interfacial bond structure between the superlattice layers. Roughness data are compared with measurements of anisotropy in low-temperature Hall mobilities of the samples.

Atomic-scale Characterization of HF-treated 4H-SiC(0001)1×1 Surfaces by Scanning Tunneling Microscopy

2007 ◽  
Vol 996 ◽  
Author(s):  
Kenta Arima ◽  
Hideyuki Hara ◽  
Yasuhisa Sano ◽  
Keita Yagi ◽  
Ryota Okamoto ◽  
...  
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Chemical Preparation ◽  
Local Structures ◽  
Wet Chemical ◽  
Low Energy Electron ◽  
Scale Characterization

AbstractScanning tunneling microscopy (STM) observations are performed on 4H-SiC(0001) surfaces after wet-chemical preparation steps including HF treatments.1×1 structures are formed on a terrace together with other local structures. Their atomic images are investigated in conjunction with low-energy electron diffraction and electron spectroscopy for chemical analysis. It is suggested that each bright dot forming the 1×1 phase corresponds to an OH-terminated Si atom.

Atomic Scale Characterization of (NH4)2Sx-Treated GaAs (100) Surface

1994 ◽  
Vol 332 ◽  
Author(s):  
Naoki Yokoi ◽  
Hiroya Andoh ◽  
Mikio Takai
Keyword(s):  
Surface Region ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Ion Scattering ◽  
Tunneling Microscopy ◽  
Xps Spectra ◽  
Sulfur Layer ◽  
Scale Characterization ◽  
Medium Energy Ion Scattering

ABSTRACTThe geometric structure of GaAs (100) surfaces, treated in a (NH4)2Sx solution and annealed in N2 environment, has been studied in an atomic scale using high-resolution Rutherford backscattering (RBS), X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). RBS analysis using medium energy ion scattering (MEIS) could provide the thickness of the sulfur layer on the GaAs surface of about 1.5 monolayers. RBS channeling spectra indicated that the disorder of atoms in the surface region of S-terminated samples was smaller than that of untreated one. XPS spectra showed that S atoms on the surface bonded only As atoms. STM observation revealed that S atoms had a periodicity of 4 Å corresponding to that of Ga or As atoms in the (100) plane.

Experimental and Simulated Scanning Tunneling Microscopy of the Cleaved Rb1/3WO3 (0001) Surface

1994 ◽  
Vol 332 ◽  
Author(s):  
Weier Lu ◽  
Gregory S. Rohrer
Keyword(s):  
Rotational Symmetry ◽  
Tungsten Bronze ◽  
Atomic Scale ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Vertical Position ◽  
Fold Axis ◽  
Tunneling Microscopy ◽  
Tunnel Current ◽  
Advantages And Disadvantages

ABSTRACTAtomic-scale resolution scanning tunneling microscope (STM) images of cleaved (0001) surfaces of the hexagonal tungsten bronze, Rbl/3WO3, show two distinct contrast patterns. We have interpreted these images using simulated constant current STM topographs. These simulations are constructed based on calculations of the tunnel current as a function of the lateral and vertical position above the surface. By calculating simulated images for the limiting cases of different termination layers, different tip sizes, and different electronic structures, it is possible to systematically explore the important parameters and choose a model that most closely matches the experimental observations. In this case, we conclude that two distinct termination layers have been imaged, a W-O terminated surface and a Rb-O terminated surface. Also, we have found that the O atoms on the W-O surface relax to new positions nearer the 6-fold axis of rotational symmetry. Some of the advantages and disadvantages of this model are discussed.

scholarly journals Atomic-Scale Characterization of Droplet Epitaxy Quantum Dots

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 85
Author(s):  
Raja S. R. Gajjela ◽  
Paul M. Koenraad
Keyword(s):  
Quantum Dots ◽  
Optoelectronic Devices ◽  
Atomic Scale ◽  
Droplet Epitaxy ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Etch Pits ◽  
Cross Sectional ◽  
Scale Characterization

The fundamental understanding of quantum dot (QD) growth mechanism is essential to improve QD based optoelectronic devices. The size, shape, composition, and density of the QDs strongly influence the optoelectronic properties of the QDs. In this article, we present a detailed review on atomic-scale characterization of droplet epitaxy quantum dots by cross-sectional scanning tunneling microscopy (X-STM) and atom probe tomography (APT). We will discuss both strain-free GaAs/AlGaAs QDs and strained InAs/InP QDs grown by droplet epitaxy. The effects of various growth conditions on morphology and composition are presented. The efficiency of methods such as flushing technique is shown by comparing with conventional droplet epitaxy QDs to further gain control over QD height. A detailed characterization of etch pits in both QD systems is provided by X-STM and APT. This review presents an overview of detailed structural and compositional analysis that have assisted in improving the fabrication of QD based optoelectronic devices grown by droplet epitaxy.

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