The Influence of Strain-Mediated Morphological Changes on the Structural and Optical Properties of MBE-Grown GeSi/Si

1992 ◽  
Vol 281 ◽  
Author(s):  
D. D. Perovic ◽  
J. Whitehurst ◽  
J. P. Noel ◽  
N. L. Rowell ◽  
D. C. Houghton
Keyword(s):  
Elastic Strain ◽  
Morphological Changes ◽  
Broad Band ◽  
Layer Growth ◽  
Atomic Scale ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
Strained Layer ◽  
Wide Range ◽  
Half Loop

ABSTRACTRecent studies on strained layer heteroepitaxy in high misfit systems (eg. Ge on Si) have clearly indicated the importance of elastic strain on a number of surface-mediated growth effects. In this work we consider the transition from ideal, 2-D layer-by-layer growth to the initial stages of a 3-D growth morphology as a precursor to misfit dislocation injection in GexSi1−x/Si heterostructures with x as low as 0.15. Experimentally, we have studied a wide range of MBE-and CVD-grown single and multilayer GexSi1−x/Si (x<0.5) structures using transmission electron microscopy and photoluminescence spectroscopy. Firstly, we describe a new mechanism for the heterogeneous nucleation of misfit dislocations in strained epitaxial layers, the ‘double half-loop’ source, which originates from atomic-scale (<1.5 nm) interfacial perturbations. Secondly, the atomic-scale dilatational perturbations, which can exist in areal densities up to ∼109 cm−2, have been identified as the origin of intense, broad-band PL from MBE-grown GexSi1−x/Si strained layers. The change in PL behaviour with increasing strained layer thickness has been used to study the effects of elastic strain-induced surface roughening at low misfits.

Metal-organic framework (MOF) composites for photodegradation of hazardous organic materials

2021 ◽  
Vol 02 ◽  
Author(s):  
Xinxin Liu ◽  
Jiaqing Ren ◽  
Jiaqi Fang ◽  
An Pan ◽  
Nianqiao Qin ◽  
...  
Keyword(s):  
Photocatalytic Degradation ◽  
Organic Pollutants ◽  
Metal Organic Framework ◽  
Stable Process ◽  
Layer Growth ◽  
Thermal Method ◽  
Layer By Layer ◽  
Wide Range ◽  
Metal Organic ◽  
Organic Framework

: Photocatalytic degradation is an energy-efficient, cost-effective, and stable process that has a wide-range of applications. It is considered a promising method for the removal of organic pollutants. As a new type of porous materials, Metal-organic framework (MOF) composites have been proven to be an ideal catalyst for the degradation of organic pollutants due to their small size and large specific surface area. In this review, several common preparation methods of MOF composites are evaluated：microwave synthesis, solvent-thermal method, electrochemical method and layer by layer growth method. The degradation effects of MOF composites on different organic pollutants are summarized, and the excellent photocatalytic performances of some MOF composites are demonstrated. Finally, the prospect of photocatalytic degradation of organic pollutants by MOF composites is examined, and the challenges of further development of MOF composites are discussed.

Effects of Stress on Step Energies and Surface Roughness

MRS Bulletin ◽  
1996 ◽  
Vol 21 (4) ◽  
pp. 27-30 ◽  
Author(s):  
Christopher Roland
Keyword(s):  
Thin Films ◽  
Strain Relaxation ◽  
Three Dimensional ◽  
Layer Growth ◽  
Growth Mode ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
Strained Layers ◽  
The Subject ◽  
Growth Changes

Strain relaxation in lattice-mismatched, heteroepitaxial systems is one of the classic problems in materials physics, which has gained new urgency with the increased applications of strained layers in microelectronic systems. In general both the structure and the integrity of the thin films are strongly influenced by strain. For instance it has long been known that under strain, the growth changes from an initial layer-by-layer growth mode to one with three-dimensional islanding. In the seminal works of van der Merwe, and Matthews and Blakeslee, this change in growth mode is explained in terms of the introduction of strain-relieving misfit dislocations, which appear when the film has reached some critical thickness. Recently it has become clear that this change in growth mode can take place even without the introduction of misfit dislocations. Such dislocation-free coherent islanding, or “roughening,” has been observed experimentally both in Ge/Si and in InGaAs/GaAs systems. Furthermore recent experiments show that in Ge/Si(100) systems, the thin films display a curious asymmetry with respect to the sign of the strain: Films under compression roughen by forming coherent islands while those under tension remain relatively smooth. A possible mechanism behind this strain-induced type of roughening is the subject of this article.

Relationship Between Crystal Defects, Ge Outdiffusion and V/III Ratio in MOVPE Grown (001) GaAs/Ge

1993 ◽  
Vol 319 ◽  
Author(s):  
C. Frigeri ◽  
G. Atrolini ◽  
C. Pelosi ◽  
F. Longo
Keyword(s):  
Stacking Faults ◽  
Layer Growth ◽  
Crystal Defects ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
Island Growth ◽  
Planar Defects ◽  
Fault Density ◽  
Unintentional Doping ◽  
Enhanced Mobility

AbstractTwo regimes of defect generation have been found in MOVPE GaAs/Ge layers upon changing the V/III ratio between 1.3 and 11.8. For low V/III ratio the layers contained misfit dislocations along with stacking faults that had been generated by dissociation of the misfit dislocations. The stacking fault density increased with decreasing V/III ratio. This might be explained by an enhanced mobility of the dissociated partials due the reduced unintentional doping of the layer caused by reduced Ge outdiffusion from the substrate when V/III is small. The secon regime corresponds to high V/III ratios and is characterized by the absence of misfit dislocations and the presence of a high density of planar defects. This means that breakdown of the 2D layer-by-layer growth occurred and 3D island growth prevailed.

Preparation of (111)-Oriented Pt Electrode Films with Quasi-Monocrystal Properties on MgO/TiN Buffered Si(100) by PLD

2007 ◽  
Vol 280-283 ◽  
pp. 823-826 ◽  
Author(s):  
Tong Lai Chen ◽  
Xiao Min Li
Keyword(s):  
High Energy ◽  
Layer Growth ◽  
Atomic Scale ◽  
Layer By Layer ◽  
X Ray Diffraction ◽  
Pt Electrode ◽  
Force Microscopy ◽  
Atomic Force

Atomic-scale smooth Pt electrode films have been deposited on MgO/TiN buffered Si (100) by the pulsed laser deposition (PLD) technique. The whole growth process of the multilayer films was monitored by using in-situ reflection high energy electron diffraction (RHEED) apparatus. The Pt/MgO/TiN/Si(100) stacked structure was also characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The HREED observations show that the growth mode of the Pt electrode film is 2D layer-by-layer growth. It is found that the (111)-oriented Pt electrode film has a crystallinity comparable to that of monocrystals. The achievement of the quasi-single-crystal Pt electrode film with an atomic-scale smooth surface is ascribed to the improved crystalline quality of the MgO film.

Molecular Dynamics Studies of Semiconductor Thin Films and Interfaces

1987 ◽  
Vol 94 ◽  
Author(s):  
Marcia H. Grabow ◽  
George H. Gilmer
Keyword(s):  
Molecular Dynamics ◽  
Energy State ◽  
Layer Growth ◽  
Metastable Equilibrium ◽  
Free Energy Barrier ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
3 Dimensional ◽  
Smooth Film ◽  
The Stability

ABSTRACTThe structure and stability of thin epitaxial films have been investigated using molecular dynamics computer simulations. One issue of interest is the stability of a smooth film relative to 3-dimensional clusters. The simulation results show that the uniform film is never the lowest energy state for a system with finite misfit. However, the uniform film, produced in a layer-by-layer growth mode, can persist in a metastable state at substantial misfits, e.g. 10% at 1/2 the melting point. This is a result of the large nucleation barrier to the formation of clusters.The second issue is the quality of the interface between the film and the substrate. At equilibrium, the critical thickness for the introduction of misfit dislocations is larger for films on the diamond cubic (100) substrate than on the (111), and differs from predictions based on continuum mechanics. We find that coherent films remain in metastable equilibrium far beyond the critical misfit calculated for full equilibrium, because a large free energy barrier inhibits the introduction of misfit dislocations.

Laser MBE for Atomically Defined Ceramic Film Growth

1995 ◽  
Vol 397 ◽  
Author(s):  
H. Koinuma ◽  
M. Kawasaki ◽  
M. Yoshimoto
Keyword(s):  
Film Growth ◽  
Molecular Layer ◽  
High Vacuum ◽  
Layer Growth ◽  
Atomic Scale ◽  
In Situ Monitoring ◽  
Layer By Layer ◽  
Sintered Ceramic ◽  
Infinite Layer ◽  
Laser Mbe

ABSTRACTLaser MBE is a process especially useful for epitaxial layer-by-layer growth of ceramic thin films directly from sintered ceramic targets. By employing high vacuum MBE conditions, the process has a restriction in the controllability of chemical composition, e.g. nonstoi chiometry in oxides and nitrides, as compared with conventional pulsed laser deposition, but instead gains the possibility of in situ monitoring of surface reaction on an atomic scale by RHEED. Ever since our first success in observing RHEED intensity oscillation for CeO2 film growth on Si(l11), we have verified the molecular layer epitaxy by laser MBE for perovskite oxides (SrTiO3, BaTiO3, SrVO3 ,etc) and infinite-layer cuprates MCuO2 (M= Sr, Ba, Ca) on SrTiO3 substrates as well as for oxide and nitride films on Si substrates. Key factors to design the laser MBE system, operation parameters, and recent experimental results are presented and discussed.

Formation of Interfacial Dislocations in Hetero-Epitaxial Layers Grown in Two-Dimensional Mode

1995 ◽  
Vol 399 ◽  
Author(s):  
S. Oktyabrsky ◽  
J. Narayan
Keyword(s):  
Compressive Strain ◽  
Elastic Interaction ◽  
Misfit Strain ◽  
Layer Growth ◽  
Dislocation Network ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
Two Dimensional ◽  
Transmission Electron ◽  
Interfacial Dislocations

ABSTRACTHigh-resolution transmission electron microscopy has been used to study formation of interfacial defects related to misfit strain accommodation in Ge/Si heterostructures (mismatch 4%) grown in the two-dimensional mode. Special emphasis is placed on the conditions leading to a two-dimensional (layer-by-layer) growth mode. We discuss general features of a dislocation tangle resulted from glide-limited plastic relaxation, typical for highly mismatched (001)-diamond and zinc-blende heterostructures. The evolution of the dislocation network as a function of film thickness and thermal annealing is controlled by growth instabilities and dislocation interactions. The observed correlation in distribution of parallel misfit dislocations including pairing (at <2 nm) of misfit segments from intersecting glide planes and rearrangements in a nonequilibrium dislocation network driven by elastic interaction between 60° dislocation segments in the almost relaxed heterostructures are discussed in detail. Pairing of the 60° glide dislocations results either in their combination to form pure edge 90° dislocations or in the dissociation into partials. We propose and experimentally verify a model for the latter process involving the formation of extrinsic stacking faults in the heterolayers under compressive strain.

Afm Study of CeO2 Growth on Sapphire as a Buffer Layer for YBa2Cu3O7

1995 ◽  
Vol 401 ◽  
Author(s):  
M. W. Denhoff ◽  
B. F. Mason ◽  
H. T. Tran ◽  
P. D. Grant
Keyword(s):  
Ybco Film ◽  
Three Dimensional ◽  
Layer Growth ◽  
Granular Structure ◽  
Atomic Scale ◽  
Laser Deposition ◽  
Layer By Layer ◽  
Temperature Dependent ◽  
Force Microscopy ◽  
Atomic Force

AbstractThe structure of CeO2 films grown on (1102) sapphire and on YBCO thin films was investigated. The films reported on here were grown by pulsed excimer laser deposition and their surface structure was probed using atomic force microscopy. We found that CeO2 films grown on sapphire were epitaxial with a granular structure which is smooth on an atomic scale. We see evidence of a surface reconstruction on a very smooth CeO2 (100) oriented surface. At higher growth temperatures, three dimensional islands begin to form. When a CeO2 film is grown on top of a YBCO film, the growth mode is two dimensional. The steps in this layer by layer growth are a surprisingly large 2 nm. This is about equal to 4 times the CeO2 lattice constant. This step height appears to be temperature dependent.

“Barrierless” Misfit Dislocation Nucleation in SiGe/Si Strained Layer Epitaxy

1992 ◽  
Vol 263 ◽  
Author(s):  
D.D. Perovic ◽  
D.C. Houghton
Keyword(s):  
Activation Energy ◽  
Misfit Dislocation ◽  
Strain Relaxation ◽  
Dislocation Nucleation ◽  
Theoretical Treatment ◽  
Misfit Dislocations ◽  
Plan View ◽  
Strained Layer ◽  
Wide Range ◽  
Peierls Barrier

ABSTRACTThe study of the critical thickness/strain phenomenon inherent in metastable, layered heterostructures has led to the development of several models which describe elastic strain relaxation. Hitherto, the nucleation of misfit dislocations required for coherency breakdown is the least well understood aspect of strain relaxation, due to the paucity of experimental data. Moreover, existing theoretical calculations predict relatively large activation energy barriers (>10 eV) for misfit dislocation nucleation in relatively low misfit (<2%) systems. In this work it will be shown that the nucleation of misfit dislocations can occur spontaneously demonstrating a vanishingly small activation energy barrier. Specifically, experimental studies of a wide range of GexSi1−x/Si (x< 0.5) hetero-structures, grown by MBE and CVD techniques, have provided quantitative data from bulk specimens on the observed misfit dislocation nucleation rate and activation energy using large-area diagnostic techniques (eg. chemical etching/Nomarski microscopy). In parallel, the strained layer microstructure was studied in detail using crosssectional and plan-view electron microscopy in order to identify a new dislocation nucleation mechanism, the ‘double half-loop’ source. From the combined macroscopic and microscopic analyses, a theoretical treatment has been developed based on nucleation stress and energy criteria which predicts a “barrierless” nucleation process exists even at low misfits (< 1%). Accordingly, the observed misfit dislocation nucleation event has been found both experimentally and theoretically to be rate-controlled solely by Peierls barrier dependent, glide-activated processes with activation energies of ∼2 eV.

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