Initial Stages of Interface Formation: The Influence of Surface Reconstruction

1987 ◽  
Vol 94 ◽  
Author(s):  
H.-J. Gossmann
Keyword(s):  
Surface Reconstruction ◽  
Growth Parameters ◽  
Substrate Surface ◽  
Necessary Condition ◽  
Molecular Beam Epitaxy Growth ◽  
Interface Formation ◽  
Lattice Match ◽  
The Difference ◽  
Reconstructed Surface ◽  
Substrate Temperatures

ABSTRACTThe initial stages of interface formation are crucial for the growth of an overlayer, particularly for ultra-thin films. While growth rate, growth temperature and lattice match are important parameters in molecular beam epitaxy, growth of semiconductor heterostructures always begins on a reconstructed surface. The effect of this reconstruction has to be known before a complete understanding of the growth process is possible. Two examples will be discussed: (1) A necessary condition for perfect growth is the reordering of the substrate surface, i.e. those atoms at the interface which are originally displaced due to the reconstruction have to be brought back to bulk positions. Si(111)7×7 and Si(100)2×1 surfaces behave differently in this respect. The 2×1 orders upon deposition of Si, Ge or Sn at room-temperature whereas the 7×7 does not. This result will be correlated with the different classes of reconstruction to which these surfaces belong. The possible rela-tionship with the difference in substrate temperatures required to achieve homo-epitaxial growth on Si(100) and Si(111) surfaces will be discussed. (2) Perfect growth also relies on proper control of the growth-mode. As an example, the island-ing behavior found for deposition of Sn on Si will be discussed. While surface diffusion over macroscopic distances is observed, dramatic changes in the affinity for clustering occur depending on surface reconstruction and preparation, suggesting that clustering in this system may be controlled by appropriate choices of growth parameters.

Growth of Group IV-IV Heterostructures: Initial Stages of Interface Formation

1986 ◽  
Vol 67 ◽  
Author(s):  
H.-J. Gossmann ◽  
L. C. Feldman
Keyword(s):  
Surface Segregation ◽  
Substrate Surface ◽  
Group Iv ◽  
Necessary Condition ◽  
Ion Scattering ◽  
Interface Formation ◽  
General Role ◽  
Low Energy Electron ◽  
Critical Coverage

ABSTRACTThe two major issues in the growth of a heterostructure are (1) the degree of perfection of the overlayer and (2) the sharpness of the interface. The initial stages of interface formation play a crucial role in this respect. Relevant questions are addressed under atomically clean conditions in the Si/Ge Si/Si and Ge/Sn systems, using ion scattering surface analysis, low energy electron diffraction and Auger electron spectroscopy. Of particular interest with respect to (1) is the general role of reconstruction in epitaxial growth: A necessary condition for perfect growth is the reordering of the substrate surface reconstruction. We show that the deposition temperature necessary to achieve this reordering depends strongly on the topography of the substrate reconstruction. For example, Ge deposition at room-temperature reorders the Si(100)2×1 reconstruction but not the Si(111)7×7, implying different epitaxial temperatures for these two substrates. To illustrate (2) we discuss the complex growth and anomalous diffusion found in the Ge/Sn system. Below a certain critical coverage Θc (1.15·1015 cm−2) no indiffusion of the Sn overlayer takes place, even at 700 K, although above Θc severe indiffusion does occur at this temperature. This result is discussed in terms of theories of surface segregation.

scholarly journals Meditation and perception: some notes on the psychology of religious mysticism

1970 ◽  
Vol 5 ◽  
pp. 34-46
Author(s):  
Hjalmar Sundén
Keyword(s):  
Necessary Condition ◽  
Physiological Conditions ◽  
Saint John ◽  
The Subject ◽  
Mystical Experiences ◽  
The Cross ◽  
The Difference ◽  
John Of The Cross

The study of mysticism must be carried on with more attention paid to the meditative techniques used by mystics and to the problems of perception. In this paper the author presents some remarks on the difference between Saint Teresa and Saint John of the Cross, and then mentions some recent studies of meditation and some problems of perception. If meditative techniques have become of great importance in psychotheraphy, the organismic approach of the "mindcurers" and their results will permit us to complete phenomenological descriptions of mystic conscious states with more exact information of their physiological conditions. In this way "mystical experiences" in general can be seen as results of meditative techniques and we need not regard "an hysterical predisposition" of the subject as their necessary condition.

Effect of Substrate-Surface Orientation on the N Incorporation in GaAsN Films on GaAs Grown by MOVPE

2008 ◽  
Vol 55-57 ◽  
pp. 825-828 ◽  
Author(s):  
P. Klangtakai ◽  
S. Sanorpim ◽  
S. Kuboya ◽  
R. Katayama ◽  
Kentaro Onabe
Keyword(s):  
Growth Rate ◽  
High Performance ◽  
Substrate Surface ◽  
Surface Orientation ◽  
X Ray Diffraction ◽  
N Content ◽  
Long Wavelength ◽  
The Difference ◽  
N Incorporation ◽  
Novel Structures

The GaAs1-xNx alloy semiconductor has been grown on GaAs (001), (111)A and (011) substrates by metalorganic vapor-phase epitaxy. High resolution X-ray diffraction and Raman scattering were employed to examine the effective N content and the growth rate, as a function of the substrate-surface orientation. The growth rate, which was assessed though the clear Pendellösung fringes, and the N content were found to change dramatically with the substrate-surface orientations. The N content was determined in the order (111)A > (001) > (011). While, the growth rate is in the order, (001) > (011) > (111)A. The effect of substrate-surface orientation on the N incorporation found in the present study is interpreted in terms of the difference in the growth rate on each surface orientation and the number of dangling bonds with which the N atoms can be trapped on the growing surface. Our results show that controlled nitrogen incorporating for GaAsN is successfully achieved and can be applied to the fabrication of some novel structures such as a spontaneous N content modulated structure, which is applicable to high performance long wavelength laser diodes.

Diamond Deposition by a Nonequilibrium Plasma Jet

1991 ◽  
Vol 250 ◽  
Author(s):  
D. G. Keil ◽  
H. F. Calcote ◽  
W. Felder
Keyword(s):  
Substrate Surface ◽  
Supersonic Nozzle ◽  
Supersonic Jet ◽  
Plasma Jet ◽  
Nonequilibrium Plasma ◽  
Hydrogen Atoms ◽  
Raman Spectrometry ◽  
Diamond Deposition ◽  
Laser Raman ◽  
Substrate Temperatures

AbstractA nonequilibrium plasma jet has been used to deposit diamond films on a number of substrates, including silicon, silicon nitride, alumina, and molybdenum. Hydrogen is passed through a glow discharge and expanded through a supersonic nozzle to produce a highly nonequilibrium jet. Methane is added downstream of the nozzle, where it mixes and reacts with the nonequilibrium concentration of hydrogen atoms. The resulting supersonic jet strikes the substrate surface producing a high quality (determined by laser Raman spectrometry) adherent diamond film. Because of the low jet temperature, substrate cooling is unnecessary. Diamond deposition rates have exceeded 2 mg/kWh and I μm/h averaged over 16 cm2 area; good quality films prepared at substrate temperatures below 600 K. have been

scholarly journals Relationship between newborn leptin levels and selected growth parameters

2019 ◽  
Vol 47 (6) ◽  
pp. 2591-2597 ◽  
Author(s):  
Amer Mahmoud Sindiani ◽  
Rawan Obeidat ◽  
Omar Jbarah ◽  
Ethar Hazaimeh
Keyword(s):  
Gestational Age ◽  
Head Circumference ◽  
Growth Parameters ◽  
Cross Sectional ◽  
Intrauterine Growth ◽  
The North ◽  
Term Newborns ◽  
The Mean ◽  
The Difference ◽  
Umbilical Cord Vein

Objectives This study aimed to determine leptin levels in term newborns who were born in the north of Jordan. We also aimed to investigate the relationships of leptin levels with fetal growth parameters, and to assess the difference in leptin levels according to sex and gestational age. Methods A cross-sectional descriptive study that involved 170 term newborns was conducted. A working sheet for data collection was created for each newborn and included sex, weight, length, head circumference, gestational age, and Apgar score. Blood samples were obtained from the umbilical cord vein of newborns after delivery to measure serum leptin levels. Data are shown as frequency, percentages, means, and standard deviations. Results We found that the mean leptin level was 1.17 ± 0.48 ng/mL. The independent t-test showed that the mean leptin level in boys (0.93 ± 0. 34 ng/mL) was significantly lower than that in girls (1.38 ± 0.47 ng/mL). Pearson’s correlations showed that leptin levels of newborns were positively and significantly correlated with weight, length, and head circumference. Conclusion In Jordanian healthy term newborns, leptin levels correlate with sex and intrauterine growth parameters.

Growth of Co Nanoclusters on SiC Honeycomb Templates

2004 ◽  
Vol 818 ◽  
Author(s):  
Wei Chen ◽  
Kian Ping Loh ◽  
Hai Xu ◽  
A.T.S. Wee
Keyword(s):  
Substrate Temperature ◽  
Room Temperature ◽  
Scanning Tunneling ◽  
Nucleation Process ◽  
Desorption Rate ◽  
Tunneling Microscopy ◽  
Scale Range ◽  
Reconstructed Surface ◽  
Substrate Temperatures

AbstractA honeycomb-like SiC reconstructed surface with regular, periodic porosity in the nano-scale range has been used as an effective template for the formation of monodispersed Co nanoclusters. In-situ scanning tunneling microscopy (STM) was used to study the nucleation process of the Co nanoclusters on this template. The deposition of Co at different substrate temperature was investigated by STM. It is found that the failure in the deposition of Co nanoclusters on the SiC honeycomb template with substrate temperatures higher than room temperature (RT) might be due to the high desorption rate of the adsorbed Co atoms.

Epitaxial Iridium Growth on Strontium Titanate

2000 ◽  
Vol 648 ◽  
Author(s):  
Z. Dai ◽  
A.P. Li ◽  
C. Bednarski ◽  
L. I. McCann ◽  
B. Golding
Keyword(s):  
Surface Roughness ◽  
Substrate Surface ◽  
Surface Preparation ◽  
Electron Beam Evaporation ◽  
Layer By Layer ◽  
Epitaxial Relationship ◽  
Ion Channeling ◽  
Substrate Temperatures ◽  
Subsequent Layer

AbstractEpitaxial (100) iridium films have been grown on (100) SrTiO3 (STO) substrates by electron beam evaporation. The epitaxial relationship between the iridium film and STO substrate was determined to be Ir(001)[100]//STO(001)[100]. A systematic study of the role of STO substrate surface preparation, Ir thickness, and substrate temperature on Ir film crystallinity and morpholo- gy has been performed. The best Ir films typically have small Ir(200) XRD linewidths < 0.3 °, surface roughness of 0.2 nm, and low ion channeling yields, χmin≤ 4%, when deposited at 800 °C. Films generally become smoother with better crystallinity when the film thickness approaches 300 nm. A growth mode with initial island formation and subsequent layer-by-layer appears to take place at higher substrate temperatures, whereas at lower temperatures the film grows in a 3D mode.

Growth of High Quality Poly-SiGe on Glass Substrates

1996 ◽  
Vol 452 ◽  
Author(s):  
Kunihiro Shiota ◽  
Daisuke Inoue ◽  
Kouichirou Minami ◽  
Masaji Yamamoto ◽  
Jun-ichi Hanna
Keyword(s):  
Electron Microscopy ◽  
Gas Flow ◽  
Growth Parameters ◽  
Substrate Surface ◽  
Silicon Substrates ◽  
X Ray Diffraction ◽  
Glass Substrates ◽  
Transmission Electron ◽  
Composition Variation ◽  
Gas Flow Ratio

AbstractThe composition variation and strutural properties of poly-SiGe thin films were investigated by Reactive Thermal CVD with Si2H6 and GeF4. Deposition of the films was carried out at a low temperature of 450°C on oxidized silicon substrates using different growth parameters, i.e., the source gas flow ratio (Si2H6/ GeF4) and thegas flow rate. The structural profiles of as-deposited films were characterized by X-ray diffraction (XRD) and Raman scattering spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).All these films show (220) preferential orientation. The mole fractions of Si in poly-SixGe1−x films were estimated to be from 0.95 to 0.05 for x by using Vegard's law for the XRD peaks. TEM observation revealed that high crystallinity was well established even in poly-Si0.95Ge0.05 films owing to the direct nucleation on the substrate surface.

scholarly journals Application of a Theorem in Stochastic Models of Elections

2010 ◽  
Vol 2010 ◽  
pp. 1-30 ◽  
Author(s):  
Norman Schofield ◽  
Christopher Claassen ◽  
Ugur Ozdemir ◽  
Alexei Zakharov
Keyword(s):  
Formal Model ◽  
Sufficient Conditions ◽  
The United States ◽  
Character Trait ◽  
Necessary Condition ◽  
Presidential Candidates ◽  
Sufficient Conditions For Convergence ◽  
The Difference ◽  
Centripetal Effect ◽  
Necessary And Sufficient

Previous empirical research has developed stochastic electoral models for Israel, Turkey, and other polities. The work suggests thatconvergence to an electoral center(often predicted by electoral models) is a nongeneric phenomenon. In an attempt to explain nonconvergence, a formal model based onintrinsic valenceis presented. This theory showed that there are necessary and sufficient conditions for convergence. The necessary condition is that a convergence coefficientcis bounded above by the dimensionwof the policy space, while a sufficient condition is that the coefficient is bounded above by 1. This coefficient is defined in terms of the difference in exogenous valences, the “spatial coefficient”, and the electoral variance. The theoretical model is then applied to empirical analyses of elections in the United States and Britain. These empirical models include sociodemographic valence and electoral perceptions of character trait. It is shown that the model implies convergence to positions close to the electoral origin. To explain party divergence, the model is then extended to incorporate activist valences. This extension gives a first-orderbalance conditionthat allows the party to calculate the optimal marginal condition to maximize vote share. We argue that the equilibrium positions of presidential candidates in US elections and by party leaders in British elections are principally due to the influence of activists, rather than the centripetal effect of the electorate.

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