| 1. |
- Böttger, Michael, et al.
(författare)
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Electrospraying of colloidal nanoparticles for seeding of nanostructure growth
- 2007
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:10
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Tidskriftsartikel (refereegranskat)abstract
- Nanometre-sized particles (1-100 nm) have unique properties receiving growing attention in wide areas of research. Here, a convenient method to deposit size-selected nanoparticles on surfaces by means of electrospraying colloidal suspensions in the aerosol phase is presented. We demonstrate the deposition of individual nanoparticles and the feasibility of this method in seeding gold particles for nanostructure growth. An advantage of the present method is the easy set-up and operation, using only commercially available machinery and substances. Problems regarding low deposition rates and colloidal remnants are approached, e. g. the aerosol flow is examined in a differential mobility analyser. This method is not material dependent and could be extended to deposit any colloidal particle.
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| 2. |
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| 3. |
- Deppert, Knut, et al.
(författare)
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Epitaxielle Kristallnadeln und -bäume
- 2005
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Ingår i: Book of abstracts: DGKK-Jahrestagung, Köln, Germany (2005).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 4. |
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| 5. |
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| 6. |
- Dick Thelander, Kimberly, et al.
(författare)
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Improving InAs nanotree growth with composition-controlled Au-In nanoparticles
- 2006
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 17:5, s. 1344-1350
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Tidskriftsartikel (refereegranskat)abstract
- Au nanoparticles are commonly used as seeds for epitaxial growth of III-V semiconductor nanowires. However, the interaction between Au and In-containing III-V materials makes it difficult to control the growth of more complex nanowire structures in materials such as InAs. Here we report the growth of InAs nanowires and branched nanotrees using Au and Au-In nanoparticles. We show that the initial composition of the particle does not affect the morphology of the first-generation nanowires, nor does it affect the final composition of the particle after growth. However, when the Au-In particles were used to seed a second generation of nanowires, producing nanotrees, the branches exhibited a 2-3 times higher growth rate and more regular shape than those seeded by pure Au particles. This result is attributed to the decreased interaction between the seed particle and the trunk nanowires when Au-In particles are used. Thus the incorporation of In into the seed particle during particle production allows for modification of the particle-wire interaction.
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| 7. |
- Fröberg, Linus, et al.
(författare)
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Transients in the Formation of Nanowire Heterostructures.
- 2008
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 8:11, s. 3815-3818
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Tidskriftsartikel (refereegranskat)abstract
- We present results on the effect of seed particle reconfiguration on the growth of short InAs and InP nanowire segments. The reconfiguration originates in two different steady state alloy compositions of the Au/In seed particle during growth of InAs and InP. From compositional analysis of the seed particle, the In content in the seed particle is determined to be 34 and 44% during InAs and InP growth, respectively. When switching between growing InAs and InP, transient effects dominate during the time period of seed particle reconfiguration. We developed a model that quantitatively explains the effect and with the added understanding we are now able to grow short period (<10 nm) nanowire superlattices.
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| 8. |
- Johansson, Jonas, et al.
(författare)
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Effects of growth conditions on the crystal structure of gold-seeded GaP nanowires
- 2008
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Ingår i: Journal of Chrystal Growth. - : Elsevier BV. - 0022-0248. ; 310:23, s. 5102-5105
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Konferensbidrag (refereegranskat)abstract
- we present results that provide fundamental insights on how to experimentally tailor the planar defect density and even the crystal structure in III-V metal-particle-seeded nanowires, where zinc blende is the stable bulk crystal structure. We have grown GaP nanowires with metal-organic vapor-phase epitaxy under different conditions: pulsing of the Ga source, and Continuous growth with and without In background. The dominant crystal structure of the nanowires is zinc blende, which when grown under continuous conditions has a high density of twin planes perpendicular to the growth direction. Using pulsed growth we observed that the twin plane separations were much longer than those observed for continuous growth with an In background. On the other hand, during continuous growth, under In-free conditions, a considerable amount of the wurtzite-phase forms. Our results suggest that it might be possible to predict the conditions necessary for the growth of wires with perfect crystal structure. We interpret our results in terms of the supersaturation during growth. (C) 2008 Elsevier B.V. All rights reserved.
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| 9. |
- Johansson, Jonas, et al.
(författare)
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Effects of Supersaturation on the Crystal Structure of Gold Seeded III-V Nanowires
- 2009
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 9:2, s. 766-773
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Tidskriftsartikel (refereegranskat)abstract
- We present results that provide fundamental insights on how to experimentally tailor the planar defect density and even the crystal structure in III-V metal particle seeded nanowires, where zinc blende is the stable bulk crystal structure. We have grown GaP nanowires with metal-organic vapor phase epitaxy under different conditions: pulsing of the Ga source, and continuous growth with and without In background. The dominant crystal structure of the nanowires is zinc blende, which when grown under continuous conditions has a high density of twin planes perpendicular to the growth direction. Using pulsed growth, we observed that the twin plane separations were much longer than those observed for continuous growth with an In background. On the other hand, during continuous growth, under In-free conditions, a considerable amount of the wurtzite phase forms. We explain the importance of the In background during growth. With classical nucleation modeling we qualitatively relate the density of planar defects in a nanowire to the growth conditions. For low supersaturations, we predict a low twin plane density, consistent with our experimental observations of pulsed nanowire growth. In addition, we suggest that under certain conditions, it might be possible to grow wires with almost perfect wurtzite structure.
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| 10. |
- Johansson, Jonas, et al.
(författare)
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Growth related aspects of epitaxial nanowires
- 2006
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Ingår i: Nanotechnology. - 0957-4484. ; 17:11, s. 355-361
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Tidskriftsartikel (refereegranskat)abstract
- We use metal - organic vapour phase epitaxy for growth investigations of epitaxial nanowires in III - V materials, such as GaAs, GaP, InAs, and InP. In this paper we focus on gold assisted growth of nanowires. The nature of the metal particle - whether it is in the solid or liquid state - is discussed. For InAs and InP we have demonstrated that gold assisted wires can only grow at temperatures where the particle is solid. We continue with a discussion concerning the kinetic aspects of nanowire growth. Under common growth conditions one observes that thinner wires grow faster than thicker wires, contrary to what was described in the early days of whisker growth. We address and resolve this discrepancy by discussing a simple transport model and comparing the supersaturations of different systems. Finally, we describe the morphology of epitaxial III - V nanowires with emphasis on the crystal structure.
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| 11. |
- Johansson, Jonas, et al.
(författare)
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Structural properties of (111)B-oriented III-V nanowires
- 2006
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Ingår i: Nature Materials. - : Springer Science and Business Media LLC. - 1476-4660 .- 1476-1122. ; 5:7, s. 574-580
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Tidskriftsartikel (refereegranskat)abstract
- Controlled growth of nanowires is an important, emerging research field with many applications in, for example, electronics, photonics, and life sciences. Nanowires of zinc blende crystal structure, grown in the left fence111right fenceB direction, which is the favoured direction of growth, usually have a large number of twin-plane defects. Such defects limit the performance of optoelectronic nanowire-based devices. To investigate this defect formation, we examine GaP nanowires grown by metal-organic vapour-phase epitaxy. We show that the nanowire segments between the twin planes are of octahedral shape and are terminated by {111} facets, resulting in a microfaceting of the nanowires. We discuss these findings in a nucleation context, where we present an idea on how the twin planes form. This investigation contributes to the understanding of defect formation in nanowires. One future prospect of such knowledge is to determine strategies on how to control the crystallinity of nanowires.
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| 12. |
- Johansson, Jonas, et al.
(författare)
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The structure of <1 1 1 > B oriented GaP nanowires
- 2007
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 298, s. 635-639
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Tidskriftsartikel (refereegranskat)abstract
- Nanowires of zinc blende crystal structure, grown in the < 111 > B direction usually have a large number of twin plane defects. In order to investigate this phenomenon, we grow GaP nanowires with metal-organic vapor phase epitaxy. By rotating the nanowires in a high resolution transmission electron microscope, we show that the nanowire segments between the twin planes are of octahedral shape and are terminated by {111} facets. Due to the alternating orientations of these twin octahedra, the sidewalls of the nanowires can be described as microfaceted surfaces with an overall orientation of 11 1 2}, but composed of alternating 11 1 I}A and {1 I 1}B facets. Moreover, the segment thicknesses follow exponential distributions, which show that there is a certain probability of twin plane formation, which is independent of segment thickness. (c) 2006 Elsevier B.V. All rights reserved.
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| 13. |
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| 14. |
- Karlsson, L. S., et al.
(författare)
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Structural Characterisation of GaP <111 > B Nanowires by HRTEM
- 2008
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Ingår i: Microscopy of Semiconducting Material 2007. - 0930-8989. - 9781402086144 ; 120, s. 229-232
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Konferensbidrag (refereegranskat)abstract
- GaP < 111 > B nanowires are dominated by (111) twins orthogonal to the growth direction and show well-developed {111} side-facets. Based on this, a 3D-model has been constructed with a cross-section of an octahedron used as a building block. The twins can be of ortho- or para type i.e. by 60 degrees about the growth axis or 180 degrees in the twin plane. The segment thickness variation follows an exponential distribution with a clear dependence oil growth ternperature. Multislice simulations show different features of the twin types that are useful for further characterisation.
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| 15. |
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| 16. |
- Karlsson, Martin, et al.
(författare)
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Size-controlled nanoparticles by thermal cracking of iron pentacarbonyl
- 2005
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Ingår i: Applied Physics A: Materials Science & Processing. - : Springer Science and Business Media LLC. - 1432-0630. ; 80:7, s. 1579-1583
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Tidskriftsartikel (refereegranskat)abstract
- A gas-phase method has been developed for producing size-controlled nanoparticles by thermal cracking of iron pentacarbonyl. The method includes the formation of iron particles from vapor emanating from the cracking of the volatile compound and subsequent compacting of the selected particles. Different temperature steps were involved in the process, and their effects on the particle production were investigated. On-line differential mobility measurements and off-line transmission electron microscopy (TEM) were used to study the morphology, composition and structure of the generated particles. The aim of the study was to produce nanoparticles of pure iron. After transportation in air, the composition of the particles was analyzed by TEM and found to be magnetite, Fe3O4. The oxidation may be attributed to the exposure to air and humidity during the transport. The phase of the uncontaminated particles could not be determined. Tests for growth of silicon nanowhiskers using nanoparticles produced with this method were successful.
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| 17. |
- Molhave, Kristian, et al.
(författare)
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Epitaxial Integration of Nanowires in Microsystems by Local Micrometer-Scale Vapor-Phase Epitaxy
- 2008
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Ingår i: Small. - : Wiley. - 1613-6829 .- 1613-6810. ; 4:10, s. 1741-1746
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Tidskriftsartikel (refereegranskat)abstract
- Free-standing epitaxially grown nanowires provide a controlled growth system and an optimal interface to the underlying substrate for advanced optical, electrical, and mechanical nanowire device connections. Nanowires can be grown by vapor-phase epitaxy (VPE) methods such as chemical vapor deposition (CVD) or metal organic VPE (MOVPE). However, VPE of semiconducting nanowires is not compatible with several microfabrication processes due to the high synthesis temperatures and issues such as cross-contamination interfering with the intended microsystem or the VPE process. By selectively heating a small microfabricated heater, growth of nanowires can be achieved locally without heating the entire microsystem, thereby reducing the compatibility problems. The first demonstration of epitaxial growth of silicon nanowires by this method is presented and shows that the microsystem can be used for rapid optimization of VPE conditions. The important issue of the cross-contamination of other parts of the microsystem caused by the local growth of nanowires is also investigated by growth of GaN near previously grown silicon nanowires. The design of the cantilever heaters makes it possible to study the grown nanowires with a transmission electron microscope without sample preparation.
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| 18. |
- Mårtensson, Thomas, et al.
(författare)
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Epitaxial III-V nanowires on silicon
- 2004
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 4:10, s. 1987-1990
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Tidskriftsartikel (refereegranskat)abstract
- We present results of ideal epitaxial nucleation and growth of III-V semiconductor nanowires on silicon substrates. This addresses the long-time challenge of integrating high performance III-V semiconductors with mainstream Si technology. Efficient room-temperature generation of light on silicon is demonstrated by the incorporation of double heterostructure segments in such nanowires. We expect that advanced heterostructure devices, such as resonant tunneling diodes, superiattice device structures, and heterostructure photonic devices for on-chip communication, could now become available as complementary device technologies for integration with silicon.
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| 19. |
- Seifert, Werner, et al.
(författare)
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Growth of one-dimensional nanostructures in MOVPE
- 2004
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 272:1-4, s. 211-220
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Tidskriftsartikel (refereegranskat)abstract
- The use of metal organic vapor-phase epitaxy (MOVPE) for growth of one-dimensional nanostructures in the material systems GaAs, GaP, InAs and InP is investigated. Some kinetic effects are discussed, especially the general finding that in MOVPE thinner whiskers grow faster than thicker whiskers. Effects of growth temperature on growth rate and shape of the whiskers, the effects of different growth directions on the perfection of the materials and the possibilities to grow heterostructures in axial and lateral directions are reported. Ways to overcome the randomness in whisker growth by controlled seeding of the Au particles and by using lithography for site control are demonstrated.
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| 20. |
- Wacaser, Brent, et al.
(författare)
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Growth and characterization of defect free GaAs nanowires
- 2006
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 287:2, s. 504-508
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Tidskriftsartikel (refereegranskat)abstract
- Most III-V compound semiconductor nanowires seeded by metal particles grow preferentially in a (over bar 1 over bar 1 over bar 1)B direction (B wires) and most commonly with many stacking faults perpendicular to the growth direction. If growth proceeds in an alternate direction, defect-free growth has been observed. We present experimental results for the growth of GaAs nanowires in a previously uninvestigated growth direction, a < 111 > A direction (A wires). One novelty is that a {111} A growth plane, like a {over bar 1 over bar 1 over bar 1} B, is a close packed plane where the stacking sequence can be interrupted forming stacking faults, but unlike the B wires the A wires lack stacking faults. It is also observed that, when grown under equivalent conditions, the growth rate of the A wires is approximately twice that of the B wires. Additionally, B wires have a hexagonal cross section with three {11 over bar 2} and three {11 over bar 2} side facets. A wires, on the other hand, have only three major side facets which are of the {11 over bar 2} type, giving them a triangular cross section. (c) 2005 Elsevier B.V. All rights reserved.
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| 21. |
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| 22. |
- Wacaser, Brent
(författare)
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Nanoscale Crystal Growth: The Importance of Interfaces and Phase Boundaries Kristallväxt på Nanometer Skala: Vikten av Ytor och Gränser
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surfaces and interfaces have a special significance to nanotechnology because the surface/volume ratio of nanomaterials is larger than for bulk materials. Therefore, interfaces of nanomaterials are usually more important to the properties of nanomaterials than for larger scale materials. Furthermore, crystal growth occurs at the interfaces between the growing crystals and the supply media. An understanding of the interfaces is therefore essential to understanding growth. Nanoscale crystal growth of three, two, and to some extent one-dimensional crystals has been explained in the context of crystalline interfaces. This understanding has helped improve production of nanostructures and devices that are both scientifically and commercially beneficial. This dissertation expands on the importance of interfaces and atomistic processes occurring at these interfaces; explaining the growth and control of different nanocrystals. A brief review of crystal growth terminology and theory is given. A new technology recently developed to produce compound semiconductor quantum dots is described within the context of the interfaces involved. The majority of the dissertation will focus on explaining and understanding growth of one-dimensional nanostructures, called nanowires, grown in a three-phase system. The currently accepted growth mechanism for nanowires of this type is the vapor-liquid-solid (VLS) mechanism. The VLS and similar mechanisms lack details about the atomistic processes involved in wire growth. When these atomistic processes are examined, it is revealed that there are several different names describing what are proposed to be ?different? mechanisms that in reality rely on the same atomistic processes. The key to understanding nanowire growth lies in understanding the atomistic processes occurring at the interfaces. Due to the fundamental similarities in the mechanisms with different names, the name ?Preferential Phase-Boundary Nucleation? (PPBN) is suggested as a replacement for the many different names. Unlike previous names this name is relevant to the processes as well as emphasizing the importance of the phases and the interfaces. A better understanding of interfaces and the processes that occur at them leads to a greater understanding and control of the growth of crystalline nanostructures.
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| 23. |
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| 24. |
- Wacaser, Brent, et al.
(författare)
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Preferential Interface Nucleation: An Expansion of the VLS Growth Mechanism for Nanowires
- 2009
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Ingår i: Advanced Materials. - : Wiley. - 1521-4095 .- 0935-9648. ; 21:2, s. 153-165
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Forskningsöversikt (refereegranskat)abstract
- A review and expansion of the fundamental processes of the vapor-liquid-solid (VLS) growth mechanism for nanowires is presented. Although the focus is on nanowires, most of the concepts may be applicable to whiskers, nanotubes, and other unidirectional growth. Important concepts in the VLS mechanism such as preferred deposition, supersaturation, and nucleation are examined. Nanowire growth is feasible using a wide range of apparatuses, material systems, and growth conditions. For nanowire growth the unidirectional growth rate must be much higher than growth rates of other surfaces and interfaces. It is concluded that a general, system independent mechanism should describe why nanowires grow faster than the surrounding surfaces. This mechanism is based on preferential nucleation at the interface between a mediating material called the collector and a crystalline solid. The growth conditions used mean the probability of nucleation is low on most of the surfaces and interfaces. Nucleation at the collector-crystal interface is however different and of special significance is the edge of the collector-crystal interface where all three phases meet. Differences in nucleation due to different crystallographic interfaces can occur even in two phase systems. We briefly describe how these differences in nucleation may account for nanowire growth without a collector. Identifying the mechanism of nanowire growth by naming the three phases involved began with the naming of the VLS mechanism. Unfortunately this trend does not emphasize the important concepts of the mechanism and is only relevant to one three phase system. We therefore suggest the generally applicable term preferential interface nucleation as a replacement for these different names focusing on a unifying mechanism in nanowire growth.
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| 25. |
- Wacaser, Brent, et al.
(författare)
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Size-selected compound semiconductor quantum dots by nanoparticle conversion
- 2007
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a novel technology, called nanoparticle conversion, for producing compound semiconductor quantum dots (QDs) in which the dot size, surface density, position, and the materials system are all independently controlled. Nanoparticle conversion also lends itself to spatially controlled positioning of QDs. To demonstrate this technology we report the formation of InP QDs using nanoparticle conversion. We have produced QDs on substrates of different types by converting randomly and lithographically positioned nanoparticles into compound semiconductors in a chemical vapour deposition system. Electron microscopy and atomic force microscopy measurements reveal that the morphology of these QDs is similar to that of QDs produced by other techniques. Photo- and cathodoluminescence measurements show that the converted nanoparticles exhibit properties and behaviours typical of semiconductor QDs. These include quantum confinement, free-to-bound recombination and blinking. Production of multi-component QDs like InP, GaN, and InAsP on various substrates like Si, SiO2, and sapphire show that this technology can produce a wide variety of different types of QD on different substrates with minimal need for process optimization.
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| 26. |
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| 27. |
- Zanolli, Zeila, et al.
(författare)
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Core-shell InP-CdS nanowires: fabrication and study
- 2007
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 19:29
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Tidskriftsartikel (refereegranskat)abstract
- InP nanowires are fabricated by organo-metallic vapour phase epitaxy and studied via photoluminescence measurements performed on single nanowires, finding evidence of state filling with increasing excitation power density. To increase flexibility in fabrication technology we developed a wet chemical procedure to grow a CdS shell on these wires. In these InP-CdS wires the luminescence efficiency was decreased with respect to the bare wires. The CdS capping procedure needs further investigations to improve the emission properties of nanowires, in order to become technically useful. We suggest as possible improvements of this technique to increase the bath temperature and/or illuminate the sample with UV radiation during the capping procedure.
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