Dynamics of InAs Quantum Dots Formation on AlAs and GaAs

MRS Proceedings ◽

10.1557/proc-648-p2.6 ◽

2000 ◽

Vol 648 ◽

Author(s):

M. Yakimov ◽

V. Tokranov ◽

S. Oktyabrsky

Keyword(s):

Quantum Dots ◽

Self Assembly ◽

Single Layer ◽

High Energy ◽

Ex Situ ◽

Inas Quantum Dots ◽

Force Microscopy ◽

Atomic Force ◽

Kinetics Of

AbstractWe have studied the formation of InAs quantum dots (QDs) grown by molecular beam epitaxy on top of GaAs and 2 ML-thick AlAs layers in the temperature range from 350 to 500°C. In-situ reflection high energy electron diffraction (RHEED) patterns were recorded in real time during the growth and analyzed to characterize the 2D-to-3D transition on the surface, including QD formation, and ripening process. The kinetics of QD formation was studied using the InAs growth rates ranging from 0.01 to 1 ML/s and different ratios of As2/In fluxes. RHEED patterns and ex-situ atomic force microscopy images were analyzed to reveal the development of sizes and shapes of the single-layer and stacked QD ensembles. The critical InAs coverage for QD formation was shown to be consistently higher for dots grown on the AlAs overlayer than for those grown on GaAs surface. Self-assembly of multilayer QD stacks revealed the reduction of the critical thickness for dots formed in the upper layers.

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Mechanically Biased Self-Assembly of Quantum Dots by Nanoindentation

MRS Proceedings ◽

10.1557/proc-0921-t07-07 ◽

2006 ◽

Vol 921 ◽

Author(s):

Curtis R. Taylor ◽

Ajay Malshe ◽

Eric Stach ◽

Euclydes Marega ◽

Gregory Salamo

Keyword(s):

Quantum Dots ◽

Self Assembly ◽

Surface Strain ◽

Ex Situ ◽

Atomic Step ◽

Inas Quantum Dots ◽

Force Microscopy ◽

Patterned Growth ◽

Atomic Force ◽

Cube Corner

AbstractNanoindentations were created in the GaAs(100) surface to act as strain centers to bias the nucleation of self-assembled InAs quantum dots providing for patterned growth. Indents were generated using loads below 450 μN with a sharp cube corner indenter. Growth of InAs quantum dots on indent patterns is performed using molecular beam epitaxy (MBE). The effect of indent spacing and size on the patterned growth is investigated. The structural analysis of the quantum dots including spatial ordering, size, and shape are characterized by ex-situ atomic force microscopy (AFM). Results reveal that the indent patterns clearly bias nucleation with dot structures selectively growing on top of each indent. It is speculated that the biased nucleation is due to a combination of favorable surface strain and multi-atomic step formation at the indent sites, which leads to increased adatom diffusion on the patterned area.

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Initial Stages of InAs Quantum Dots Evolution in GaAs/AlAs Matrixes

MRS Proceedings ◽

10.1557/proc-749-w13.8 ◽

2002 ◽

Vol 749 ◽

Author(s):

Michael Yakimov ◽

Vadim Tokranov ◽

Alex Katnelson ◽

Serge Oktyabrsky

Keyword(s):

Quantum Dots ◽

Direct Evidence ◽

Matrix Material ◽

Single Layer ◽

High Energy ◽

Inas Quantum Dots ◽

Auger Signal ◽

The Matrix ◽

Growth Evolution

ABSTRACTWe have studied the first phases of post-growth evolution of InAs quantum dots (QDs) using in-situ Auger electron spectroscopy in conjunction with Reflection High Energy Electron Diffraction (RHEED). Direct evidence for InAs intermixing with about 6ML (monolayers) of the matrix material is found from Auger signal behavior during MBE overgrowth of InAs nanostructures. Re-establishment of 2D growth mode by overgrowth with GaAs or AlAs was monitored in single-layer and multi-layer QD structures using RHEED. Decay process of InAs QDs on the surface is found to have activation energy of about 1.1 eV that corresponds to In intermixing with the matrix rather than evaporation from the surface.

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Nanoindentation Assisted Self-Assembly of Quantum Dots

Manufacturing Science and Engineering, Parts A and B ◽

10.1115/msec2006-21139 ◽

2006 ◽

Author(s):

Curtis Taylor ◽

Eric Stach ◽

Gregory Salamo ◽

Ajay Malshe

Keyword(s):

Quantum Dots ◽

Self Assembly ◽

Surface Strain ◽

Ex Situ ◽

Atomic Step ◽

Uniform Size ◽

Force Microscopy ◽

Atomic Force ◽

And Performance ◽

Spatial Positioning

The ability to pattern quantum dots with high spatial positioning and uniform size is critical for the realization of future electronic devices with novel properties and performance that surpass present technology. This work discusses the exploration of an innovative nanopatterning technique to direct the self-assembly of nanostructures. The technique focuses on perturbing surface strain energy by nanoindentation in order to mechanically bias quantum dot nucleation. Growth of InAs quantum dots on nanoindent templates is performed using molecular beam epitaxy (MBE). The effect of indent spacing and size on the patterned growth is investigated. The structural analysis of the quantum dots including spatial ordering, size, and shape are characterized by ex-situ atomic force microscopy (AFM). Results reveal that the indent patterns clearly bias nucleation with dot structures selectively growing on top of each indent. It is speculated that the biased nucleation is due to a combination of favorable surface strain attributed to subsurface dislocation strain fields and/or multi-atomic step formation at the indent sites, which leads to increased adatom diffusion on the patterned area.

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Guided Self Assembly of InAs Quantum Dots on a Cleaved Facet

MRS Proceedings ◽

10.1557/proc-0959-m16-02 ◽

2006 ◽

Vol 959 ◽

Author(s):

Emanuele Uccelli ◽

Dieter Schuh ◽

Jochen Bauer ◽

Max Bichler ◽

Jonathan J. Finley ◽

...

Keyword(s):

Quantum Dots ◽

Atomic Force Microscopy ◽

Growth Mechanism ◽

Self Assembly ◽

Semiconductor Quantum Dots ◽

Preferential Growth ◽

Inas Quantum Dots ◽

Force Microscopy ◽

Atomic Force ◽

Long Range Ordering

ABSTRACTThe long range ordering of epitaxial semiconductor quantum dots (QDs) has been obtained by combing self assembly with the cleaved edge overgrowth technique. The introduction of nanometer thick AlAs stripes on a (110) oriented GaAs surface avoids the misfit dislocation growth mechanism of InAs on GaAs (110) and drives the formation of array of QDs. Atomic Force Microscopy (AFM) investigations highlight that InAs QDs only nucleate in chain like structure on Al-rich regions. Here, we present experimental results that demonstrate the ability to create ordered QDs lattices and discuss the conditions under which preferential growth of QDs on the AlAs stripes occurs.

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Well-Ordered Self-Assembly Growth of Strain-Modulated SrTiO3 Thin Films: Templates for Complex Oxide Quantum Wires

Materials Science Forum ◽

10.4028/www.scientific.net/msf.475-479.4255 ◽

2005 ◽

Vol 475-479 ◽

pp. 4255-4260 ◽

Cited By ~ 1

Author(s):

Yan Rong Li ◽

Jin Long Li ◽

Ying Zhang ◽

Xin Wu Deng ◽

Fan Yang ◽

...

Keyword(s):

Compressive Stress ◽

Self Assembly ◽

Quantum Wires ◽

Complex Oxide ◽

High Energy ◽

The Self ◽

Ex Situ ◽

Force Microscopy ◽

Atomic Force ◽

Self Assembled

Well-ordered self-assembled SrTiO3 thin film, as a template for complex oxide quantum wires, was fabricated on LaAlO3 (100) single crystal substrates with laser molecular beam epitaxy. The self-assembled growth was in-situ monitored by reflective high energy electron diffraction. The morphology evolutions of the films as a function of thickness were studied by ex-situ atomic force microscopy. As the thickness of the films increased from 3.875nm to 46.5nm gradually, the compressive stress-induced SrTiO3 films exhibited a periodic well-ordered ripple structure, which formed a unique nanoassembled template for the fabrication of quantum wires. Small angle X-ray scattering technique was employed to investigate the structure. Symmetric satellite peaks were discovered, indicating the well-ordered superstructure. In contrast, the similar superstructure was not observed during the growth of the tensile stress-induced LaAlO3 films on SrTiO3 substrates. The Compressive stress was considered as the main reason of the self-assembled growth, and systematical elucidation about strain mechanism was discussed. These results might provide an efficient method for the controllable formation of well-aligned template of quantum wire for complex oxide with desirable structure via proper modulation of strains.

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MBE Growth of IV-VI Nanowires on a Self-organized Template

MRS Proceedings ◽

10.1557/proc-1258-p04-56 ◽

2010 ◽

Vol 1258 ◽

Author(s):

Lee Andrew Elizondo ◽

Patrick McCann ◽

Joel Keay ◽

Matthew Johnson

Keyword(s):

Quantum Wires ◽

High Energy ◽

Ex Situ ◽

Mbe Growth ◽

One Dimensional ◽

Force Microscopy ◽

Self Organized ◽

Atomic Force ◽

Low Dimensional

AbstractWe present the experimental results for the first known molecular beam epitaxy (MBE) growth of quasi-one-dimensional PbSe wires on technologically relevant silicon.In this work, we describe the growth and characterization of low-dimensional IV-VI semiconductors as they evolve from one-dimensional dot/dot-chains to one-dimensional structures on a self-organized template epitaxially grown on Si(110). In situ and ex situ characterization were performed at various stages throughout growth by reflection high energy electron diffraction, scanning electron microscopy, and non-contact atomic force microscopy. Initial growths resulted in some preferential alignment of the PbSe dot-chains parallel to the self-organized template in the [-110] direction. By reducing the substrate temperature and increasing the supplemental Se flux, the morphology of dot-chains extend into lengthened one-dimensional structures. This is an important milestone in the fabrication of PbSe quantum wires on technologically relevant silicon.

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STRUCTURAL AND MAGNETIC PROPERTIES OF EPITAXIAL Ni80Fe20 THIN FILMS ON Cu/Si

Surface Review and Letters ◽

10.1142/s0218625x95000388 ◽

1995 ◽

Vol 02 (04) ◽

pp. 427-437 ◽

Cited By ~ 9

Author(s):

I. HASHIM ◽

H.S. JOO ◽

H.A. ATWATER

Keyword(s):

Magnetic Properties ◽

Domain Walls ◽

High Energy ◽

Ex Situ ◽

Misfit Dislocations ◽

Force Microscopy ◽

Atomic Force ◽

Transmission Electron ◽

Crystal Films

Single-crystal films of permalloy ( Ni 80 Fe 20) were grown on Cu (001) seed layers oriented epitaxially with Si (001). The microstructural properties were measured using in-situ reflection high-energy electron diffraction, and ex-situ transmission electron microscopy, x-ray diffraction, and atomic force microscopy, whereas the magnetic properties were probed using in-situ magneto-optic Kerr effect and ex-situ vibrating sample magnetometry. Anisotropic magnetoresistance and resistivity for some of the samples were also measured. The coercivity for thinner (≤5 nm) Ni 80 Fe 20 was significantly higher (10–20 Oersteds) than polycrystalline films deposited on SiO 2/ Si , and was also higher than films deposited on lattice-matched Cu x Ni 1–x alloys. These magnetic properties were explained using a theoretical model involving interaction of domain walls with defects such as misfit dislocations and coherent islands, due to the mismatch between Ni 80 Fe 20 and Cu .

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In situ X-ray Scattering Study of the Formation of Au Nano Crystals During Thermal Annealing

MRS Proceedings ◽

10.1557/proc-1027-d07-04 ◽

2007 ◽

Vol 1027 ◽

Author(s):

Do Young Noh ◽

Ki-Hyun Ryu ◽

Hyon Chol Kang

Keyword(s):

Thermal Annealing ◽

Bragg Reflection ◽

Ex Situ ◽

X Ray ◽

Force Microscopy ◽

X Ray Scattering ◽

Atomic Force ◽

Au Thin Films ◽

Ray Scattering

AbstractThe transformation of Au thin films grown on sapphire (0001) substrates into nano crystals during thermal annealing was investigated by in situ synchrotron x-ray scattering and ex situ atomic force microscopy (AFM). By monitoring the Au(111) Bragg reflection and the low Q reflectivity and comparing them with ex situ AFM images, we found that polygonal-shape holes were nucleated and grow initially. As the holes grow larger and contact each other, their boundary turns into Au nano crystals. The Au nano crystals have a well-defined (111) flat top surface and facets in the in-plane direction.

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