| 1. |
- Neumüller, Daniela, et al.
(författare)
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Hydrogen Evolution Reaction on Ultra-Smooth Sputtered Nanocrystalline Ni Thin Films in Alkaline Media-From Intrinsic Activity to the Effects of Surface Oxidation
- 2023
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Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 13:14
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Tidskriftsartikel (refereegranskat)abstract
- Highly effective yet affordable non-noble metal catalysts are a key component for advances in hydrogen generation via electrolysis. The synthesis of catalytic heterostructures containing established Ni in combination with surface NiO, Ni(OH)(2), and NiOOH domains gives rise to a synergistic effect between the surface components and is highly beneficial for water splitting and the hydrogen evolution reaction (HER). Herein, the intrinsic catalytic activity of pure Ni and the effect of partial electrochemical oxidation of ultra-smooth magnetron sputter-deposited Ni surfaces are analyzed by combining electrochemical measurements with transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The experimental investigations are supplemented by Density Functional Theory and Kinetic Monte Carlo simulations. Kinetic parameters for the HER are evaluated while surface roughening is carefully monitored during different Ni film treatment and operation stages. Surface oxidation results in the dominant formation of Ni(OH)(2), practically negligible surface roughening, and 3-5 times increased HER exchange current densities. Higher levels of surface roughening are observed during prolonged cycling to deep negative potentials, while surface oxidation slows down the HER activity losses compared to as-deposited films. Thus, surface oxidation increases the intrinsic HER activity of nickel and is also a viable strategy to improve catalyst durability.
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| 2. |
- Rafailovic, Lidija D., et al.
(författare)
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High density of genuine growth twins in electrodeposited aluminum
- 2019
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Ingår i: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 5:10
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate electrodeposition as a synthesis method for fabrication of Al coatings, up to 10 mu m thick, containing a high density of genuine growth twins. This has not been expected since the twin boundary energy of pure Al is very high. TEM methods were used to analyze deposited Al and its nanoscaled twins. DFT methods confirmed that the influence of the substrate is limited to the layers close to the interface. Our findings are different from those achieved by sputtering of Al coatings restricted to a thickness less than 100 nm with twins dominated by epitaxial effects. We propose that in the case of electrodeposition, a high density of twins arises because of fast nucleation and is additionally promoted by a monolayer of adsorbed hydrogen originating from water impurities. Therefore, electrodeposition is a viable approach for tailoring the structure and properties of thicker, deposited Al coatings reinforced by twins.
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| 3. |
- Zeng, Lunjie, 1983, et al.
(författare)
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Correlation between Electrical Transport and Nanoscale Strain in InAs/In0.6Ga0.4As Core-Shell Nanowires
- 2018
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 18:8, s. 4949-4956
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Tidskriftsartikel (refereegranskat)abstract
- Free-standing semiconductor nanowires constitute an ideal material system for the direct manipulation of electrical and optical properties by strain engineering. In this study, we present a direct quantitative correlation between electrical conductivity and nanoscale lattice strain of individual InAs nanowires passivated with a thin epitaxial In0.6Ga0.4As shell. With an in situ electron microscopy electromechanical testing technique, we show that the piezoresistive response of the nanowires is greatly enhanced compared to bulk InAs, and that uniaxial elastic strain leads to increased conductivity, which can be explained by a strain-induced reduction in the band gap. In addition, we observe inhomogeneity in strain distribution, which could have a reverse effect on the conductivity by increasing the scattering of charge carriers. These results provide a direct correlation of nanoscale mechanical strain and electrical transport properties in free-standing nanostructures.
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| 4. |
- Zeng, Lunjie, 1983, et al.
(författare)
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Tuning Hole Mobility of Individual p-Doped GaAs Nanowires by Uniaxial Tensile Stress
- 2021
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 21:9, s. 3894-3900
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Tidskriftsartikel (refereegranskat)abstract
- Strain engineering provides an effective way of tailoring the electronic and optoelectronic properties of semiconductor nanomaterials and nanodevices, giving rise to novel functionalities. Here, we present direct experimental evidence of strain-induced modifications of hole mobility in individual gallium arsenide (GaAs) nanowires, using in situ transmission electron microscopy (TEM). The conductivity of the nanowires varied with applied uniaxial tensile stress, showing an initial decrease of similar to 5-20% up to a stress of 1-2 GPa, subsequently increasing up to the elastic limit of the nanowires. This is attributed to a hole mobility variation due to changes in the valence band structure caused by stress and strain. The corresponding lattice strain in the nanowires was quantified by in situ four dimensional scanning TEM and showed a complex spatial distribution at all stress levels. Meanwhile, a significant red shift of the band gap induced by the stress and strain was unveiled by monochromated electron energy loss spectroscopy.
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