Scaling of Island Size Distributions in the Growth of Ni on GaAs(110)

1995 ◽  
Vol 399 ◽  
Author(s):  
P. E. Quesenberry ◽  
P. N. First
Keyword(s):  
Atomic Scale ◽  
Scanning Tunneling ◽  
Size Distributions ◽  
Island Size ◽  
3 Dimensional ◽  
First Order ◽  
Degree Of Reaction ◽  
High Temperature Data ◽  
Average Size ◽  
Stm Images

ABSTRACTIsland size distributions have been derived from scanning tunneling microscope (STM) images of Ni deposited on cleaved GaAs(110) at room temperature and above. For submonolayer coverages, this system forms 3-dimensional (3-D) reacted islands with the degree of reaction dependent upon the growth temperature. As has been found for other systems, the average island size (sαυ) increases with temperature. The high temperature data (∼ 150° C) shows two distinct island types, each with substantially different average size. The island size distributions have maxima at the smallest island sizes. For different coverages, plots of the area-normalized island size distributions versus the scaled variable s/sαυ show significant differences. However, above a cutoff value for s/sαυ the distributions can be renormalized to fall on a common curve. These characteristics and direct atomic-scale evidence are consistent with nucleation of islands via adatom-substrate exchange, but the temperature dependence of the total island density appears to be inconsistent with this being the only first-order rate process taking place.

Scanning Tunneling Microscopy of Amorphous Carbon Films

1990 ◽  
Vol 48 (1) ◽  
pp. 318-319
Author(s):  
Mircea Fotino ◽  
D.C. Parks
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Amorphous Carbon ◽  
Carbon Films ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Amorphous Carbon Films ◽  
Image Optimization ◽  
Step Procedure ◽  
Stm Images

In the last few years scanning tunneling microscopy (STM) has made it possible and easily accessible to visualize surfaces of conducting specimens at the atomic scale. Such performance allows the detailed characterization of surface morphology in an increasing spectrum of applications in a wide variety of fields. Because the basic imaging process in STM differs fundamentally from its equivalent in other well-established microscopies, good understanding of the imaging mechanism in STM enables one to grasp the correct information content in STM images. It thus appears appropriate to explore by STM the structure of amorphous carbon films because they are used in many applications, in particular in the investigation of delicate biological specimens that may be altered through the preparation procedures.All STM images in the present study were obtained with the commercial instrument Nanoscope II (Digital Instruments, Inc., Santa Barbara, California). Since the importance of the scanning tip for image optimization and artifact reduction cannot be sufficiently emphasized, as stressed by early analyses of STM image formation, great attention has been directed toward adopting the most satisfactory tip geometry. The tips used here consisted either of mechanically sheared Pt/Ir wire (90:10, 0.010" diameter) or of etched W wire (0.030" diameter). The latter were eventually preferred after a two-step procedure for etching in NaOH was found to produce routinely tips with one or more short whiskers that are essentially rigid, uniform and sharp (Fig. 1) . Under these circumstances, atomic-resolution images of cleaved highly-ordered pyro-lytic graphite (HOPG) were reproducibly and readily attained as a standard criterion for easily recognizable and satisfactory performance (Fig. 2).

Island-Size Distributions for Submonolayer Epitaxy: Rate Equations and Beyond

1998 ◽  
Vol 528 ◽  
Author(s):  
D.D. Vvedensky ◽  
R.E. Caflisch ◽  
M.F. Gyure ◽  
B. Merriman ◽  
S. Osher ◽  
...  
Keyword(s):  
Level Set Method ◽  
Level Set ◽  
Atomic Scale ◽  
Rate Equations ◽  
Size Distributions ◽  
Scanning Tunnelling Microscope ◽  
Dynamics Model ◽  
Island Size ◽  
Boundary Velocity ◽  
Island Dynamics

AbstractThe scanning tunnelling microscope has revolutionized the quantitative analysis of epitaxial phenomena. This, in turn, has spawned a huge theoretical effort aimed at analyzing various aspects of the morphology of growing surfaces. One of the most important general approaches to have emerged from this effort is based on the application of scaling concepts to epitaxial island-size distributions in the regime of submonolayer coverage prior to coalescence. We first discuss the analytical basis for scaling solutions to rate equations. In the limit of irreversible aggregation, a solution is obtained in terms of the capture numbers which agrees with previous work. For reversible aggregation, we identify a new quantity that may be regarded as a continuous analogue of a critical island size. We then examine the influence of spatial correlations by introducing a method for modeling epitaxial phenomena in terms of the motion of island boundaries, which is implemented numerically using the level set method. This island dynamics model is continuous in the lateral directions, but retains atomic scale discreteness in the growth direction. Several choices for the island boundary velocity are discussed and computations of the island dynamics model using the level set method are presented.

scholarly journals Study on the Microstructure and Electrical Properties of Boron and Sulfur Codoped Diamond Films Deposited Using Chemical Vapor Deposition

2014 ◽  
Vol 2014 ◽  
pp. 1-7
Author(s):  
Zhang Jing ◽  
Li Rongbin ◽  
Wang Xianghu ◽  
Wei Xicheng
Keyword(s):  
Grain Boundaries ◽  
Measurement Techniques ◽  
Diamond Films ◽  
Chemical Vapor ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Force Microscopy ◽  
Si Substrates ◽  
Average Size

The atomic-scale microstructure and electron emission properties of boron and sulfur (denoted as B-S) codoped diamond films grown on high-temperature and high-pressure (HTHP) diamond and Si substrates were investigated using atom force microscopy (AFM), scanning tunneling microscopy (STM), secondary ion mass spectroscopy (SIMS), and current imaging tunneling spectroscopy (CITS) measurement techniques. The films grown on Si consisted of large grains with secondary nucleation, whereas those on HTHP diamond are composed of well-developed polycrystalline facets with an average size of 10–50 nm. SIMS analyses confirmed that sulfur was successfully introduced into diamond films, and a small amount of boron facilitated sulfur incorporation into diamond. Large tunneling currents were observed at some grain boundaries, and the emission character was better at the grain boundaries than that at the center of the crystal. The films grown on HTHP diamond substrates were much more perfect with higher quality than the films deposited on Si substrates. The localI-Vcharacteristics for films deposited on Si or HTHP diamond substrates indicate n-type conduction.

scholarly journals Crystallographic Aspects of the CDW Instabilities in NbSe3

2014 ◽  
Vol 70 (a1) ◽  
pp. C1608-C1608
Author(s):  
Albert Prodan ◽  
Herman Van Midden ◽  
Erik Zupanič ◽  
Rok Žitko ◽  
Joachim Kusz ◽  
...  
Keyword(s):  
Alternative Model ◽  
Charge Density Waves ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
One Dimensional ◽  
Domain Structures ◽  
Modulated Structures ◽  
Stm Images ◽  
Trigonal Prismatic

Charge-density waves (CDW) in some quasi one-dimensional compounds can be depinned from the lattice by an external electric field. In the case of NbSe3, two CDW transitions have been reported with onset temperatures of 144 K and 59 K. From an analysis of the published low-temperature (LT) scanning tunneling microscopy (STM) images, which inherently allow the resolution of domain structures on the atomic scale, an alternative model of the CDW modulated structures in NbSe3 is proposed. In contrast to the existing model, where two incommensurate (IC) modes, q1 = (0,0.241,0) and q2 = (0.5,0.260,0.5) are selectively confined to two of three available structurally distinguished types of bi-capped trigonal prismatic columns, the alternative model [1,2] proceeds from the assumption that both columns of the same pair are alternatively modulated by the two modes, whose IC components add within experimental error into a commensurate value. The observed domains are formed as a result of the different bonding within and between the structural layers, separated by Van der Waals gaps, and of the ability of the two modes to be easily interchanged between two symmetry-related columns of the same type. This assumption is in accord with the published LT STM results, which confirm i.a. the presence of both IC modes above 59 K, where according to the previous model only the q1 contribution should be expected. A pair of two alternatively modulated columns of the same type represents the basic structural unit of the CDW ground state. The two modes can formally be replaced by a single inharmonic modulation, obtained by "beating" between the two IC modes.

Imaging molecules and metals on metal surfaces by scanning tunneling microscopy

1991 ◽  
Vol 49 ◽  
pp. 370-371
Author(s):  
S. Chiang ◽  
D. D. Chambliss ◽  
V. M. Hallmark ◽  
R. J. Wilson ◽  
J. K. Brown ◽  
...  
Keyword(s):  
High Resolution ◽  
Scanning Tunneling Microscope ◽  
Binding Sites ◽  
Near Neighbor ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Tunneling Microscope ◽  
Lattice Constants ◽  
Stm Images

Using an ultrahigh vacuum scanning tunneling microscope (STM), we have imaged naphthalene molecules adsorbed on Pt(111) and submonolayer metal coverages of Ni, Fe, Ag, and Au on Au(111). The STM is able to observe atomic scale features on both types of systems, giving information on the ordering and binding sites of atoms and molecules on the surface.High resolution STM images of naphthalene on Pt(111) show the molecules as bi-lobed features with three discrete molecular orientations on the surface, 120° apart, as shown for the ordered layer in Fig. 1. The absolute orientation of the long axis of the molecules is observed to be parallel to the near-neighbor directions of the Pt(111) lattice. The sketch of the observed features, shown in Fig. 2, with the molecules overlayed arbitrarily onto on-top sites of a Pt(111) lattice, demonstrates that the molecules are located on 3x3 lattice sites, with separation of 4 lattice constants between domains. Although the (6x3) LEED pattern reported previously was reproduced, the proposed unit cell is seldom observed in the STM images.

Scanning Tunneling Microscopy of Carbon Blacks

1993 ◽  
Vol 66 (4) ◽  
pp. 559-566 ◽  
Author(s):  
Seog-Jun Kim ◽  
Darrell H. Reneker
Keyword(s):  
Electron Microscope ◽  
Carbon Black ◽  
Transmission Electron Microscope ◽  
Pyrolytic Graphite ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Carbon Blacks ◽  
Transmission Electron ◽  
Stm Images

Abstract Three kinds of carbon black, HAF (high abrasion furnace, N330), MT (medium thermal, N990), and graphitized MT were observed with the scanning tunneling microscope (STM), the transmission electron microscope (TEM), and the scanning electron microscope (SEM) All the STM images are formed from measurements of the x, t, and z position of points on the surface of the particle. The STM images of carbon blacks were compared to transmission electron microscope (TEM) photographs. Pitted and stepped bumps were observed on the surface of HAF carbon black. The surface of MT carbon black was more rough and disorganized At the atomic scale, ordered structure was found on the surface of HAF carbon-black particles Graphitized MT carbon-black particles were faceted polyhedra. Some facets were smooth while others had multiple terraces. The surface of graphitized MT carbon black was so well ordered that a lattice of carbon atoms similar to HOPG (highly ordered pyrolytic graphite) was observed on the smooth facets.

Scanning Tunneling Microscopy of HF-Controlled Si(111) Surfaces

1992 ◽  
Vol 259 ◽  
Author(s):  
Hiroshi Tokumoto ◽  
Yukinori Morita ◽  
Kazushi Miki
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Surface Structure ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Smooth Surfaces ◽  
Tunneling Microscopy ◽  
Dry Air ◽  
Stm Images ◽  
Made In

ABSTRACTScanning tunneling microscopy (STM) was made in order to examine the surface structure and roughness in an atomic scale. The surfaces were prepared by several ways: NH4F (pH = 8) dipping just after RCA cleaning or after keeping in dry air for a few weeks; dipping into NH4F (pH = 8) solution or dipping into solutions with pH=10 just after boiling in HNO3. The STM images clearly showed that the surface structure and roughness are dependent on the sample treatments. The smooth surfaces with less defects were obtained for surfaces prepared by removing the HNO3-oxidized layer by NH4F (pH = 8) dipping.

The Study on the Microstructure and Electrical Property of Boron and Sulfur Co-Doped Diamond Films by Chemical Vapor Deposition

2012 ◽  
Vol 184-185 ◽  
pp. 1343-1347
Author(s):  
Rong Bin Li ◽  
Xiang Hu Wang ◽  
Jing Zhang
Keyword(s):  
Grain Boundaries ◽  
Electron Emission ◽  
Measurement Techniques ◽  
Diamond Films ◽  
Chemical Vapor ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Si Substrates ◽  
Average Size

The atomic-scale microstructure and electron emission properties of boron and sulfur (denoted as B-S) codoped diamond films grown on high-temperature and high-pressure (HTHP) diamond and Si substrates were investigated using atom force microscopy (AFM), scanning tunneling microscopy (STM) and current imaging tunneling spectroscopy (CITS) measurement techniques. The films grown on Si consisted of large grains with secondary nucleation, whereas those on HTHP diamond are composed of well-developed polycrystalline facets with an average size of 10–50 nm. Large tunneling currents were observed at some grain boundaries, and the emission character is better at the grain boundaries than at the center of the crystal. The codoped films grown on HTHP diamond have an almost uniform electron emission efficiency at grain boundaries or crystalline facets, which indicates that the doped atoms are uniformly distributed in the films. The local I-V characteristics for films deposited on Si or HTHP diamond substrates indicate n-type conduction.

Resolution in the scanning tunneling microscope

1991 ◽  
Vol 49 ◽  
pp. 488-489
Author(s):  
R. J. Wilson ◽  
D. D. Chambliss ◽  
S. Chiang ◽  
V. M. Hallmark
Keyword(s):  
Scanning Tunneling Microscope ◽  
Fundamental Principle ◽  
Atomic Scale ◽  
Lateral Resolution ◽  
Scanning Tunneling ◽  
Electronic Noise ◽  
Vertical Resolution ◽  
Tunneling Microscopy ◽  
Spatial Profile ◽  
Theoretical Analyses

Scanning tunneling microscopy (STM) has been used for many atomic scale observations of metal and semiconductor surfaces. The fundamental principle of the microscope involves the tunneling of evanescent electrons through a 10Å gap between a sharp tip and a reasonably conductive sample at energies in the eV range. Lateral and vertical resolution are used to define the minimum detectable width and height of observed features. Theoretical analyses first discussed lateral resolution in idealized cases, and recent work includes more general considerations. In all cases it is concluded that lateral resolution in STM depends upon the spatial profile of electronic states of both the sample and tip at energies near the Fermi level. Vertical resolution is typically limited by mechanical and electronic noise.

A TEM study of electron tunneling in biological macromolecules

1987 ◽  
Vol 45 ◽  
pp. 140-141
Author(s):  
J. A. Panitz
Keyword(s):  
Stark Effect ◽  
Electron Tunneling ◽  
Imaging Modality ◽  
Tunneling Current ◽  
Biological Species ◽  
Scanning Tunneling ◽  
Biological Macromolecules ◽  
Flat Surfaces ◽  
Virus Particles ◽  
Stm Images

Tunneling is a ubiquitous phenomenon. Alpha particle disintegration, the Stark effect, superconductivity in thin films, field-emission, and field-ionization are examples of electron tunneling phenomena. In the scanning tunneling microscope (STM) electron tunneling is used as an imaging modality. STM images of flat surfaces show structure at the atomic level. However, STM images of large biological species deposited onto flat surfaces are disappointing. For example, unstained virus particles imaged in the STM do not resemble their TEM counterparts.It is not clear how an STM image of a biological species is formed. Most biological species are large compared to the nominal electrode separation of ∼ 1nm that is required for electron tunneling. To form an image of a biological species, the tunneling electrodes must be separated by a distance that would normally be too large for a tunneling current to be observed.

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