| 1. |
- Bermeo, Marie, et al.
(författare)
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Branched-gallium phosphide nanowires seeded by palladium nanoparticles
- 2023
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Ingår i: Nanotechnology. - 0957-4484. ; 34:39
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Tidskriftsartikel (refereegranskat)abstract
- Palladium nanoparticles were produced by a chemical reagent-free and versatile method called spark ablation with control over particle size and density. These nanoparticles were used as catalytic seed particles for gallium phosphide nanowire growth by metalorganic vapour-phase epitaxy. Controlled growth of GaP nanowires using significantly small Pd nanoparticles between 10 and 40 nm diameter was achieved by varying several growth parameters. Low V/III ratios below 2.0 promote higher Ga incorporation into the Pd nanoparticles. Moderate growth temperatures under 600 °C avoid kinking and undesirable GaP surface growth. In addition, a second batch of palladium nanoparticles of concentration up to 1000 particles μm−2 was deposited onto the GaP nanowires. Subsequently, three-dimensional nanostructures evolved, with branches growing along the surface of the GaP nanowires. The GaP nanowires revealed a zinc blende structure with multiple twinning and a PdGa phase at the tip of the nanowires and branches.
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| 2. |
- Caroff, Philippe, et al.
(författare)
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Controlled polytypic and twin-plane superlattices in iii-v nanowires.
- 2009
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Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3395 .- 1748-3387. ; 4:1, s. 50-55
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires show promise for use in nanoelectronics, fundamental electron transport studies, quantum optics and biological sensing. Such applications require a high degree of nanowire growth control, right down to the atomic level. However, many binary semiconductor nanowires exhibit a high density of randomly distributed twin defects and stacking faults, which results in an uncontrolled, or polytypic, crystal structure. Here, we demonstrate full control of the crystal structure of InAs nanowires by varying nanowire diameter and growth temperature. By selectively tuning the crystal structure, we fabricate highly reproducible polytypic and twin-plane superlattices within single nanowires. In addition to reducing defect densities, this level of control could lead to bandgap engineering and novel electronic behaviour.
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| 3. |
- Dick Thelander, Kimberly, et al.
(författare)
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Control of III-V nanowire crystal structure by growth parameter tuning
- 2010
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 25:2
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Tidskriftsartikel (refereegranskat)abstract
- In this work we investigate the variation of the crystal structure of gold-seeded III-V nanowires with growth parameters, in order to gain a cohesive understanding of these effects. We investigate six III-V materials: GaAs, InAs, GaP, InP, GaSb and InSb, over a variation of growth conditions. All six of these materials exhibit a cubic zinc blende structure in bulk, but twin planes and stacking faults, as well as a hexagonal wurtzite structure, are commonly observed in nanowires. Parameters which may affect the crystal structure include growth temperature and pressure, precursor molar fraction and V/III ratio, nanowire diameter and surface density, and impurity atoms. We will focus on temperature, precursor molar fraction and V/III ratio. Our observations are compared to previous reports in the literature of the III-V nanowire crystal structure, and interpreted in terms of existing models. We propose that changes in the crystal structure with growth parameters are directly related to changes in the stable side facets.
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| 4. |
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| 5. |
- Dick Thelander, Kimberly, et al.
(författare)
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Parameter space mapping of InAs nanowire crystal structure
- 2011
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Ingår i: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1520-8567. ; 29:4
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Tidskriftsartikel (refereegranskat)abstract
- Crystal structure and defects have been shown to have a strong impact on III-V nanowire properties. Recently, it was demonstrated that the issue of random stacking and polytypism in semiconductor nanowires can often be controlled using accessible growth parameters (such as temperature, diameter, and V/III ratio). In addition, it has been shown that crystal phase can be tuned selectively between cubic zinc blende and hexagonal wurtzite within individual nanowires of III-V materials such as InAs. In order for such results to be generally applied to different growth setups, it is necessary to fully explore and understand the trends governing crystal phase dependencies on all accessible growth parameters, including how they relate to each other. In this study, the authors have systematically investigated the influence of temperature, diameter, V/III ratio, and total mass flow on the crystal structure of InAs nanowires grown by metal-organic vapor phase epitaxy over a broad parameter range. The authors observed that each of these accessible parameters can affect the resulting crystal structure, and that the trends for each parameter are affected by the magnitude of the others. The authors also noted that most of the parameter dependencies are nonlinear and, in fact, exhibit threshold values at which structure changes discontinuously. By optimizing each of the growth parameters, it is shown that pure ZB or pure WZ phase can be achieved for several different sets of growth conditions. The roles of nucleation kinetics, thermodynamics, and precursor chemistry are also discussed to compare the results to current nanowire growth models. The results in this work should facilitate comparison of data and transfer of knowledge between different growth systems and techniques, which, in turn, should lead to greater understanding of polytypism in nanowires and greater control and freedom in nanowire crystal phase engineering. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3593457]
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| 6. |
- Eom, Namsoon, et al.
(författare)
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General Trends in Core-Shell Preferences for Bimetallic Nanoparticles
- 2021
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 15:5, s. 8883-8895
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Tidskriftsartikel (refereegranskat)abstract
- Surface segregation phenomena dictate core-shell preference of bimetallic nanoparticles and thus play a crucial role in the nanoparticle synthesis and applications. Although it is generally agreed that surface segregation depends on the constituent materials' physical properties, a comprehensive picture of the phenomena on the nanoscale is not yet complete. Here we use a combination of molecular dynamics (MD) and Monte Carlo (MC) simulations on 45 bimetallic combinations to determine the general trend on the core-shell preference and the effects of size and composition. From the extensive studies over sizes and compositions, we find that the surface segregation and degree of the core-shell tendency of the bimetallic combinations depend on the sufficiency or scarcity of the surface-preferring material. Principal component analysis (PCA) and linear discriminant analysis (LDA) on the molecular dynamics simulations results reveal that cohesive energy and Wigner-Seitz radius are the two primary factors that have an "additive"effect on the segregation level and core-shell preference in the bimetallic nanoparticles studied. When the element with the higher cohesive energy also has the larger Wigner-Seitz radius, its core preference decreases, and thus this combination forms less segregated structures than what one would expect from the cohesive energy difference alone. Highly segregated structures (highly segregated core-shell or Janus-like) are expected to form when both the relative cohesive energy difference is greater than ∼20%, and the relative Wigner-Seitz radius difference is greater than ∼4%. Practical guides for predicting core-shell preference and degree of segregation level are presented.
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| 7. |
- Eom, Namsoon, et al.
(författare)
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General Trends in Core-shell Preferences for Bimetallic Nanoparticles
- 2021
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Konferensbidrag (refereegranskat)abstract
- Core-shell nanoparticles have gathered much attention of the scientific community owing to their potential applications in various fields including biomedical imaging and catalysis. Predicting core-shell preference1-3 is, however, still largely based on a few experimental observations and limited theorical studies, and hence development of new core-shell nanoparticles is normally built on a trial-and-error approach. Here we present general trends of core-shell preferences for 45 bimetallic nanoparticle systems studied by molecular dynamics (MD) and Monte Carlo (MC) simulations. Simulations were performed using LAMMPS code and the embedded-atom method (EAM) potentials were employed for simulating the interactions between atoms in the bimetallic nanoparticle systems composed of 10 metals; Ag, Cu, Au, Pd, Fe, Co, Ni, Pt, Al, and Mo. In order to quantify the core-shell preference, the MD/MC results were analysed to identify surface atoms using the alpha-shapes method. The core and shell compositions of the preferred equilibrium structures of bimetallic combinations were then used to categorize each combination into one of four different types depending on the level of core- shell tendency: mixed, core-shell, highly segregated core-shell, Janus-like. The categorized MD/MC results were also analysed using principal component analysis (PCA) and linear discriminant analysis (LDA) to determine the primary factors that dictate core-shell tendency. Eight possible factors were considered, and cohesive energy and atomic radius are found to be the two primary factors that have an ‘additive’ effect on the segregation level and core-shell preference in the bimetallic nanoparticles studied. In the majority of the investigated combinations, the element with higher cohesive energy has smaller atomic radius and tend to occupy the core. Highly segregated structures (highly segregated core-shell or Janus-like) are expected to form when both the relative cohesive energy difference is greater than ~ 20 % and the relative atomic radius difference is greater than ~ 4 %. However, when the element with higher cohesive energy has larger atomic radius, the core-shell tendency decreases. The general trend observed in the current study can be used as a guide in nanoparticle synthesis methods in which heat-induced surface segregation phenomena play an essential role, and in predicting the equilibrium structures of bimetallic nanoparticles.
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| 8. |
- Eom, Namsoon, et al.
(författare)
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Sintering Mechanism of Core@Shell Metal@Metal Oxide Nanoparticles
- 2021
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:29, s. 16220-16227
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Tidskriftsartikel (refereegranskat)abstract
- Metal oxide shell layers are promising candidates to improve the performance of metal nanoparticles (NPs) in various applications. However, despite a significant amount of experimental work on metal@metal oxide (M@MO) NPs, computational modeling is scarce, particularly on the sintering mechanism, which plays a crucial role in both the synthesis and performance of NPs. Here, we present atomic diffusion and sintering dynamics of M@MO NPs investigated using molecular dynamics based on the ReaxFF potentials. The coalescence process of the metal NPs with amorphous oxide shell is mainly facilitated by the relatively mobile surface atoms and grain-boundary-like diffusion, and thus, it is similar to reported mechanisms for crystalline nanoparticles. Intriguingly, atomic trajectory tracing reveals that surface diffusion is highly localized, contrary to the common understanding of freely moving high-mobility surface atoms. These atomic descriptions provide valuable insights for designing functional NPs with oxide layers and establishing more accurate accounts of the sintering mechanism.
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| 9. |
- Eom, Namsoon, et al.
(författare)
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Sintering Mechanism of Core@Shell Metal@Metal-Oxide Nanoparticles
- 2021
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Konferensbidrag (refereegranskat)abstract
- Adding metal-oxide shell layers is a promising route for improving the performance of metal nanoparticles (NPs) in various applications. However, despite the rapidly growing interest and a significant amount of experimental work on metal@metal-oxide NPs, computational modeling is relatively scarce, particularly on the sintering mechanism, which plays a crucial role in both the synthesis and performance of NPs. It is well known that the primary sintering mechanisms are surface diffusion and grain boundary diffusion in crystalline materials (Zachariah, 1999) and viscous flow in amorphous clusters (Eggersdorfer, 2011). Therefore, the sintering mechanism of metal@metal-oxide NPs gives rise to fundamental scientific questions as they generally exhibit crystalline cores with amorphous shells. Here, we present atomic diffusion and sintering dynamics of metal@metal-oxide NPs investigated using molecular dynamics based on the ReaxFF potentials.We have investigated three metal@metal-oxide core@shell NPs as model systems: Ni@NiO, Cu@CuO, and Fe@Fe2O3, all of which are actively studied for various catalytic applications. Sintering MD simulations of two core@shell clusters are analysed using an atom- tracking approach together with crystallinity and mean square displacement (MSD) analysis. The main sintering mechanisms are found to be surface and grain-boundary- like diffusion, similar to that of crystalline NPs (Figure 1). Intriguingly, atomic trajectory tracing (Figure 2) reveals that surface diffusion is highly localized and that it is mainly the surface atoms near the contact region that actively participate in the sintering. In other words, contrary to the common understanding of freely moving high mobility surface atoms (Jose-Yacaman, 2005), atoms located away from the contact region remain distant during the early stage of the sintering process.We expect the sintering mechanism observed in metal@metal-oxide core@shell NPs here to be particularly relevant for small metal nanoclusters as they usually have a thin surface oxide layer. It can also open up promising new directions in designing aerosol NPs via sintering.
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| 10. |
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