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- ItemSmall-angle X-ray scattering from GaN nanowires on Si(111): facet truncation rods, facet roughness and Porod's law(Oxford [u.a.] : Blackwell, 2021) Kaganer, Vladimir M.; Konovalov, Oleg V.; Fernández-Garrido, SergioSmall-angle X-ray scattering from GaN nanowires grown on Si(111) is measured in the grazing-incidence geometry and modelled by means of a Monte Carlo simulation that takes into account the orientational distribution of the faceted nanowires and the roughness of their side facets. It is found that the scattering intensity at large wavevectors does not follow Porod's law I(q) ∝ q-4. The intensity depends on the orientation of the side facets with respect to the incident X-ray beam. It is maximum when the scattering vector is directed along a facet normal, reminiscent of surface truncation rod scattering. At large wavevectors q, the scattering intensity is reduced by surface roughness. A root-mean-square roughness of 0.9 nm, which is the height of just 3-4 atomic steps per micrometre-long facet, already gives rise to a strong intensity reduction. open access.
- ItemCore–Shell Structures Prepared by Atomic Layer Deposition on GaAs Nanowires(Basel : MDPI, 2022) Ursaki, Veaceslav V.; Lehmann, Sebastian; Zalamai, Victor V.; Morari, Vadim; Nielsch, Kornelius; Tiginyanu, Ion M.; Monaico, Eduard V.GaAs nanowire arrays have been prepared by anodization of GaAs substrates. The nanowires produced on (111)B GaAs substrates were found to be oriented predominantly perpendicular to the substrate surface. The prepared nanowire arrays have been coated with thin ZnO or TiO2 layers by means of thermal atomic layer deposition (ALD), thus coaxial core–shell hybrid structures are being fabricated. The hybrid structures have been characterized by scanning electron microscopy (SEM) for the morphology investigations, by Energy Dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis for the composition and crystal structure assessment, and by photoluminescence (PL) spectroscopy for obtaining an insight on emission polarization related to different recombination channels in the prepared core–shell structures.
- ItemPhase Diagram of a Strained Ferroelectric Nanowire(Basel : MDPI, 2022) Pavlenko, Maksim A.; Di Rino, Franco; Boron, Leo; Kondovych, Svitlana; Sené, Anaïs; Tikhonov, Yuri A.; Razumnaya, Anna G.; Vinokur, Valerii M.; Sepliarsky, Marcelo; Lukyanchuk, Igor A.Ferroelectric materials manifest unique dielectric, ferroelastic, and piezoelectric properties. A targeted design of ferroelectrics at the nanoscale is not only of fundamental appeal but holds the highest potential for applications. Compared to two-dimensional nanostructures such as thin films and superlattices, one-dimensional ferroelectric nanowires are investigated to a much lesser extent. Here, we reveal a variety of the topological polarization states, particularly the vortex and helical chiral phases, in loaded ferroelectric nanowires, which enable us to complete the strain–temperature phase diagram of the one-dimensional ferroelectrics. These phases are of prime importance for optoelectronics and quantum communication technologies
- ItemMagnetic Properties of GaAs/NiFe Coaxial Core-Shell Structures(Basel : MDPI, 2022) Monaico, Eduard V.; Morari, Vadim; Kutuzau, Maksim; Ursaki, Veaceslav V.; Nielsch, Kornelius; Tiginyanu, Ion M.Uniform nanogranular NiFe layers with Ni contents of 65%, 80%, and 100% have been electroplated in the potentiostatic deposition mode on both planar substrates and arrays of nanowires prepared by the anodization of GaAs substrates. The fabricated planar and coaxial core-shell ferromagnetic structures have been investigated by means of scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). To determine the perspectives for applications, a comparative analysis of magnetic properties, in terms of the saturation and remanence moment, the squareness ratio, and the coercivity, was performed for structures with different Ni contents.
- ItemExchange Bias Effect of Ni@(NiO,Ni(OH)2) Core/Shell Nanowires Synthesized by Electrochemical Deposition in Nanoporous Alumina Membranes(Basel : MDPI, 2023) García, Javier; Gutiérrez, Ruth; González, Ana S.; Jiménez-Ramirez, Ana I.; Álvarez, Yolanda; Vega, Víctor; Reith, Heiko; Leistner, Karin; Luna, Carlos; Nielsch, Kornelius; Prida, Víctor M.Tuning and controlling the magnetic properties of nanomaterials is crucial to implement new and reliable technologies based on magnetic hyperthermia, spintronics, or sensors, among others. Despite variations in the alloy composition as well as the realization of several post material fabrication treatments, magnetic heterostructures as ferromagnetic/antiferromagnetic coupled layers have been widely used to modify or generate unidirectional magnetic anisotropies. In this work, a pure electrochemical approach has been used to fabricate core (FM)/shell (AFM) Ni@(NiO,Ni(OH)2) nanowire arrays, avoiding thermal oxidation procedures incompatible with integrative semiconductor technologies. Besides the morphology and compositional characterization of these core/shell nanowires, their peculiar magnetic properties have been studied by temperature dependent (isothermal) hysteresis loops, thermomagnetic curves and FORC analysis, revealing the existence of two different effects derived from Ni nanowires’ surface oxidation over the magnetic performance of the array. First of all, a magnetic hardening of the nanowires along the parallel direction of the applied magnetic field with respect their long axis (easy magnetization axis) has been found. The increase in coercivity, as an effect of surface oxidation, has been observed to be around 17% (43%) at 300 K (50 K). On the other hand, an increasing exchange bias effect on decreasing temperature has been encountered when field cooling (3T) the oxidized Ni@(NiO,Ni(OH)2) nanowires below 100 K along their parallel lengths.
- ItemSelf-cross-linked arrays enabled flexible mechanical sensors for monitoring the body tremor(London : Springer Nature, 2020) Wang, Xuewen; Fu, Wei; Gao, Guanhui; Mehay, Mandeep Singh; Wang, Hong; Zhao, Wu; Loh, Kian Ping; Zhang, Ting; Huang, Wei; Liu, ZhengThin-film electronics played an important role in flexible healthcare sensor applications. The common status of their constituent blocks are solid film and network structures. However, the solid film could only sustain bend in a narrow range due to cracks, and the network structure decreased the sensitivity of flexion sensors due to the strong interactions between nanowires. New materials and technologies are urgently required for flexible sensing electronics, to produce the reliable data for assessment of the human body. Here, we report on a novel three-dimensional (3D) carbon nanorods array (CNA) that is characterized as vertically aligned nanorods and self-cross-linked junctions. We also demonstrate the CNA-based flexible healthcare sensors in monitoring the Parkinsonian tremors. Comparing with two-dimensional (2D) carbon nanotube networks and solid thin films, such self-cross-linked geometries are highly resistant to crack and fragmentation under strain. In the meantime, it shows high sensitivity and good stability (~10,000 times) to detect the flexions. These CNA-based flexible devices are capable of recording low-frequency vibrations (<6 Hz) and make it excellent to monitor the rest tremor of the human body, which is an initial symptom of Parkinson’s disease. The 3D self-cross-linked CNA film shows great potential in the fabrication of cost-effective and durable flexible sensors for early diagnosis of disease by monitoring the health-related rest tremors. © 2020, The Author(s).
- ItemCore–Shell GaAs-Fe Nanowire Arrays: Fabrication Using Electrochemical Etching and Deposition and Study of Their Magnetic Properties(Basel : MDPI, 2022) Monaico, Eduard V.; Morari, Vadim; Ursaki, Veaceslav V.; Nielsch, Kornelius; Tiginyanu, Ion M.The preparation of GaAs nanowire templates with the cost-effective electrochemical etching of (001) and (111)B GaAs substrates in a 1 M HNO3 electrolyte is reported. The electrochemical etching resulted in the obtaining of GaAs nanowires with both perpendicular and parallel orientations with respect to the wafer surface. Core–shell GaAs-Fe nanowire arrays have been prepared by galvanostatic Fe deposition into these templates. The fabricated arrays have been investigated by means of scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The magnetic properties of the polycrystalline Fe nanotubes constituting the shells of the cylindrical structures, such as the saturation and remanence moment, squareness ratio, and coercivity, were analyzed in relation to previously reported data on ferromagnetic nanowires and nanotubes.