Epitaxial YBa2Cu3O7−x Thin Films: Scanning Tunneling Microscope Study of the Initial Stages of Epitaxial Growth, Growth Mechanism, and Effects of Substrate Temperature

1991 ◽  
Vol 237 ◽  
Author(s):  
Shen Zhu ◽  
Douglas H. Lowndes ◽  
X.-Y. Zheng ◽  
David P. Norton ◽  
R. J. Warmack
Keyword(s):  
Film Thickness ◽  
Growth Mechanism ◽  
Growth Temperature ◽  
Lattice Mismatch ◽  
Unit Cell ◽  
Growth Mode ◽  
Spiral Growth ◽  
Scanning Tunneling ◽  
Growth Stages ◽  
Island Growth

ABSTRACTThe surface microstructure of epitaxial YBa2Cu3O7−x films grown by pulsed laser ablation on (001) MgO and SrTiO3 substrates has been studied at various growth stages, ranging in thickness from eight c-axis perpendicular unit cells to ∼220 nm. On MgO (lattice mismatch ∼9%) even the thinnest films grow unit cell-by-unit cell by an island growth mechanism. However, on SrTi03 (mismatch ∼1%), a transition from a layer-like growth mode to island growth is observed as the film thickness increases. Islands with clear spiral growth structures are observed in even the thinnest films on MgO, but for films grown on SrTiO3 the spiral growth features are found only for film thicknesses slightly greater than the critical thickness for the switch to an island growth mode. The islands consist of stacks of atomically flat terraces whose step heights are multiples of the c-axis lattice parameter. The island density decreases significantly with increasing film thickness, while their diameters range from 50–400 nm, increasing with growth temperature. The terraced island grain morphology causes a surface roughness of from 10 to 30 nm (depending on growth temperature) in films ∼200 nm thick.

In Situ STM Observation of the Spiral Growth in the Epitaxial Fe Films on MgO(001)

1999 ◽  
Vol 580 ◽  
Author(s):  
Agus Subagyo ◽  
Kazuhisa Sueoka ◽  
Koichi Mukasa
Keyword(s):  
Film Thickness ◽  
Growth Temperature ◽  
Critical Thickness ◽  
Growth Mode ◽  
Spiral Growth ◽  
Scanning Tunneling ◽  
Mode Transition ◽  
Tunneling Microscopy ◽  
Atomically Flat

AbstractWe reported a scanning tunneling microscopy(STM) observation on the growth mode transition from 2D-nucleation to spiral growth in the epitaxial Fe films on MgO(001). As the growth temperature is increased to above 493 K, a temperature region where the Schwoebel barrier is overcome, the Fe films grow in a 2D-nucleation and growth mode formed atomically flat films. The 2D-nucleation transformed into a spiral growth as increasing film thickness. At a growth temperature of 493 K, the transition of 2D nucleation to the spiral growth was observed at a film thickness of 75 Å. The critical thickness of the emergence of growth transition decreased as the growth temperature is increased.

Scanning Tunneung Microscope Studies of Initial Epitaxial Growth of YBa2Cu3O7-δ Thin Films

1992 ◽  
Vol 263 ◽  
Author(s):  
Xiang-Yang Zheng ◽  
D. H. Lowndes ◽  
Shen Zhu ◽  
R. J. Warmack
Keyword(s):  
Thin Films ◽  
Epitaxial Growth ◽  
Growth Temperature ◽  
Lattice Mismatch ◽  
Growth Mode ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Weber Type ◽  
Film Substrate ◽  
Miscut Angle

ABSTRACTThe initial stages of epitaxial growth of laser ablated YBa2Cu3O7-δ (YBCO) thin films on (001) SrTiO3, LaAlO3, and MgO substrates, and on slightly miscut LaA1O3 and SrTiO3, have been studied with scanning tunneling microscopy (STM). Surface images show that the initial YBCO growth mode can be either of the Stranski- Krastanov or the Volmer-Weber type, depending on the film-substrate lattice mismatch and the growth temperature. A small substrate miscut angle is found to strongly influence the growth mode of YBCO films. Screw dislocation-mediated growth is suppressed, and films grown at 800°C on (001) LaAlO3 substrates with miscut angle of 2.0° along <100> or <110> directions were found to consist of tilted platelets that are epitaxially aligned with the substrate crystal lattice.

Growth mechanism of YBa2Cu3O7–δthin films and precipitates on planar and vicinal SrTiO3substrates

2000 ◽  
Vol 15 (3) ◽  
pp. 596-613 ◽  
Author(s):  
J. Kim ◽  
D. B. Chrisey ◽  
J. S. Horwitz ◽  
M. M. Miller ◽  
C. M. Gilmore
Keyword(s):  
Critical Temperature ◽  
Electrical Properties ◽  
Film Thickness ◽  
Growth Mechanism ◽  
Growth Temperature ◽  
Flow Mode ◽  
Island Growth ◽  
Step Flow ◽  
Growth Modes ◽  
Initial Nucleation

Effects of the vicinal angle, film thickness, and temperature on the growth modes, microstructures, and electrical properties of YBa2Cu3O7–δon SrTiO3were studied. Island growth transition between the initial nucleation and the later coalescence stages was observed with film thickness on a planar SrTiO3, while no islands were observed at the later stage due to the step-flow mode. As the growth temperature increased,a-axis precipitates were transformed toc-axis precipitates (islands), while no islands formed on vicinal SrTiO3. The supercurrent critical temperature was strongly related to the substrate vicinal angle due to the step-flow mode.

Growth of Laser Ablated YBa2Cu3O7−δ Films as Examined by Rheed and Scanning Tunneling Microscopy

1992 ◽  
Vol 285 ◽  
Author(s):  
Stephen E. Russek ◽  
Alexana Roshko ◽  
Steven C. Sanders ◽  
David A. Rudman ◽  
J. W. Ekin ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Scanning Tunneling Microscopy ◽  
Three Dimensional ◽  
High Energy ◽  
Spiral Growth ◽  
Scanning Tunneling ◽  
Initial Growth ◽  
Rheed Pattern ◽  
Island Growth ◽  
Tunneling Microscopy

ABSTRACTUsing scanning tunneling microscopy (STM) and reflection high energy electron diffraction (RHEED) we have examined the growth morphology, surface structure, and surface degradation of laser ablated YBa2Cu3O7−δ thin films. Films from 5 nm to ltm thick were studied. The films were deposited on MgO and LaAlO3 substrates using two different excimer laser ablation systems. Both island nucleated and spiral growth morphologies were observed depending on the substrate material and deposition rate used. The initial growth mechanism observed for a 5–10 nm thick film is replicated through different growth layers up to thicknesses of 200 run. Beyond 200 rnm, the films show some a-axis grains and other outgrowths. The thinnest films (5–10 nm) show considerable surface roughness on the order of 3–4 nm. For both growth mechanisms the ledge width remains approximately constant (∼ 30 nm) and the surface roughness increases as the film thickness increases. The films with spiral growth have streaked RHEED patterns despite having considerable surface roughness, while the films with island growth have more of a three dimensional diffraction pattern. RHEED patterns were obtained after the film surfaces were degraded by exposure to air, KOH developer, a Br-methanol etch, and a shallow ion mill. Exposure to air and KOH developer caused only moderate degradation of the RHEED pattern whereas a shallow (I nm deep) 300 V ion mill completely destroyed the RHEED pattern.

Nanopatterned Si(001) Substrates as Templates for Quantum Dot Growth

2003 ◽  
Vol 775 ◽  
Author(s):  
A. Ney ◽  
C. Pampuch ◽  
J. J. Schulz ◽  
L. Perepelittchenko ◽  
R. Koch
Keyword(s):  
Temperature Treatment ◽  
Growth Mode ◽  
Scanning Tunneling ◽  
Island Growth ◽  
Tunneling Microscopy ◽  
Preparation Conditions ◽  
Low Temperature Treatment ◽  
Reconstructed Surface ◽  
Atomically Flat ◽  
Microscopy Images

AbstractIt has been shown recently, that the formation of GeSi quantum dots on Si(001) is strongly affected by the surface properties of the substrate. With an increasing number of missing dimer vacancies the growth mode can even change from a Stranski-Krastanow to a kinetic 3D island growth mode. Here we report on atomically resolved scanning tunneling microscopy images of Si(001) after different preparation procedures, namely the conventional high temperature procedure employed for commercial wafers, and Shiraki-type samples which require only low temperature treatment. The latter method yields an atomically flat Si(001) (2 × 1) surface, however, with a defect (ad- and missing dimers) concentration depending on the respective preparation conditions. Furthermore, repeated flashing occasionally yields a (2 × n) reconstructed surface consisting of well-ordered self-assembled trenches of missing dimers, similar to the ones discussed controversially in the previous literature. From our results we can clearly exclude contaminants to be involved.

The Composition Pulling Effect in MOVPE Grown InGaN on GaN and AlGaN and its TEM Characterization

1997 ◽  
Vol 2 ◽  
Author(s):  
K. Hiramatsu ◽  
Y. Kawaguchi ◽  
M. Shimizu ◽  
N. Sawaki ◽  
T. Zheleva ◽  
...  
Keyword(s):  
Film Thickness ◽  
Lattice Mismatch ◽  
Deformation Energy ◽  
Early Growth ◽  
Crystalline Quality ◽  
Growth Stages ◽  
Pit Formation ◽  
Tem Characterization ◽  
Edge Dislocations

InGaN films have been grown on GaN and AlGaN epitaxial layers by metalorganic vapor phase epitaxy. The “composition pulling effect” during the initial InGaN growth stages has been studied as a function of the lattice mismatch between the InGaN and the underlying epitaxial layer. The crystalline quality of the InGaN is good near the InGaN/GaN interface and the composition is close to that of GaN. However, with increasing InGaN film thickness, the crystal quality deteriorates and the indium mole fraction increases. The composition pulling effect becomes stronger with increasing lattice mismatch. It is suggested that indium atoms are excluded from the InGaN lattice during the early growth stages to reduce the deformation energy from the lattice mismatch. TEM observations of the InGaN/GaN structure reveal that the degradation of the crystalline quality of InGaN films grown on GaN is caused by pit formation which arises from edge dislocations propagating through the InGaN film from the underlying GaN.

Growth Control of Twin InSb/GaAs Nano-Stripes by Molecular Beam Epitaxy

MRS Advances ◽  
2017 ◽  
Vol 2 (51) ◽  
pp. 2943-2949 ◽  
Author(s):  
Phisut Narabadeesuphakorn ◽  
Jirayu Supasil ◽  
Supachok Thainoi ◽  
Aniwat Tandaechanurat ◽  
Suwit Kiravittaya ◽  
...  
Keyword(s):  
Molecular Beam Epitaxy ◽  
Growth Mechanism ◽  
Growth Temperature ◽  
Molecular Beam ◽  
Lattice Mismatch ◽  
High Energy ◽  
Band Alignment ◽  
Type I ◽  
Growth Duration ◽  
Quantum Nanostructures

ABSTRACTInSb has been considered as a promising material for spintronic applications owing to its pronounced spin effects as a result of large intrinsic electronic g-factor. In addition, embedding InSb quantum nanostructures in a GaAs matrix could create type-II band alignment, where radiation lifetimes are longer than those of the typical type-I systems. Such characteristics are promising for memory devices and infrared photonic applications. The growth of InSb/GaAs quantum nanostructures by strain driven mechanism using molecular beam epitaxy with low growth temperature, slow growth rate, Sb soaking process prior to In deposition, and small amount of In deposition typically creates a mixture of twin and single nano-stripe structures with truncated pyramid shape. In this work, we further investigate the growth mechanism of such twin InSb/GaAs nano-stripes by controlling the growth conditions, consisting of nanostructure growth duration and growth temperature. When the growth temperature is kept to less than 300°C and In deposition is set to only a few monolayers, we found that 25-40% of formed nanostructures are twin InSb/GaAs nano-stripes. However, when the In deposition is stopped immediately after the spotty reflection high-energy electron diffraction patterns are observed, the ratio of twin nano-stripes to single ones is increased to 50-60%. We therefore describe the growth mechanism of twin nano-stripes as the early state of single nano-stripe formation, where the twin nano-stripes are initially formed during the first monolayer of InSb formation as a result of large lattice mismatch of 14.6%. When In deposition is increased to a few monolayers, the gap between twin nano-stripes is filled up and consequently forms the single nano-stripes instead. With this particular twin nano-stripe growth mechanism, the preservation of high ratio of twin nano-stripe formation can be expected by further reducing the growth temperature, i.e. less than 260°C. These twin nano-stripes may find applications in the fields of spintronics and novel interference nano-devices.

Segregation and Interdiffusion of in Atoms in GaAs/InAs/GaAs Heterostructures

1993 ◽  
Vol 312 ◽  
Author(s):  
T. Kawai ◽  
H. Yonezu ◽  
Y. Ogasawara ◽  
D. Saito ◽  
K. Pak
Keyword(s):  
Growth Temperature ◽  
Three Dimensional ◽  
Film Surface ◽  
Growth Direction ◽  
Layer Growth ◽  
Growth Mode ◽  
Layer By Layer ◽  
Island Growth ◽  
Alas Layer ◽  
Secondary Ion

AbstractThe segregation and interdiffusion of In atoms in the GaAs/InAs/GaAs heterostructures were investigated by secondary ion mass spectroscopy. When the 1 ML thick InAs layer was grown in a layer-by-layer growth mode with no dislocations, the segregation of In atoms became marked with the increase of the growth temperature. However, the segregation was observed even at relatively low growth temperature of 400°C in molecular beam epitaxy. It was found that the segregation was markedly enhanced by dislocations near the heterointerface when the thick InAs layers were grown in a three-dimensional island growth mode. The interdiffusion of In atoms toward the growth direction occurred after thermal annealing, which could be assisted by vacancies propagating from the film surface into epilayer. It became apparent that the interdiffusion was effectively suppressed by a thin AlAs layer inserted in the GaAs cap layer.

Strain Analysis in Thin La1−xCaxMnO3 Films by Grazing Incidence X-ray Scattering

1999 ◽  
Vol 602 ◽  
Author(s):  
M. Petit ◽  
L. J. Martinez-Miranda ◽  
M. Rajeswari ◽  
A. Biswas ◽  
D. J. Kang ◽  
...  
Keyword(s):  
Film Thickness ◽  
Lattice Mismatch ◽  
Compressive Strain ◽  
Strain Analysis ◽  
Grazing Incidence ◽  
Relaxation Processes ◽  
Near Surface ◽  
X Ray ◽  
X Ray Scattering ◽  
Ray Scattering

AbstractWe have performed depth profile analyses of the lattice parameters in epitaxial thin films of La1−xCaxMno3 (LCMO), where x = 0.33 or 0.3, to understand the evolution of strain relaxation processes in these materials. The analyses were done using Grazing Incidence X-ray Scattering (GIXS) on films of different thicnesses on two different substrates, (100) oriented LaAlO3 (LAO), with a lattice mismatch of ∼2% and (110) oriented NGO, with a lattice mismatch of less than 0.1%. Films grown on LAO can exhibit up to three in-plane strained lattice constants, corresponding to a slight orthorhombic distortion of the crystal, as well as near-surface and columnar lattice relaxation. As a function of film thickness, a crossover from a strained film to a mixture of strained and relaxed regions in the film occurs in the range of 700 Å. The structural evolution at this thickness coincides with a change in the resistivity curve near the metalinsulator transition. The in-plane compressive strain has a range of 0.2 – 1.5%, depending on the film thickness for filsm in the range of 400 - 1500 A.

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