Superior long term stability of SiC nanowires over Si nanowires under physiological conditions

International audienceSemiconducting nanowires (NWs) are raising a growing interest in nanoelectronic devices. While silicon is the most widely used material in this field, it lacks long-term stability in aqueous solution. The usage of Si must hence be reconsidered for specific applications such as devices operating in biological media with high ionic strength. Silicon carbide is a wide bandgap semiconductor that can efficiently replace Si for applications in harsh environments or high temperature thanks to its high chemical stability and thermal conductivity. Here, we compare the long term stability of Si and SiC NWs under mimicked physiological conditions. The degradation kinetics of both types of NWs was studied from accurate monitoring of their cross-sectional geometry by transmission electron microscopy (TEM) over a period of 4 weeks. Results show a linear dissolution of Si NWs whereas SiC NWs exhibit much slower degradation kinetics confirming the superior chemical stability of SiC nanostructures over Si. After 32 days, NWs with an initial diameter of 20 nm are expected to dissolve completely in the case of Si NWs while SiC NWs would shrink by only 16%

Template-Assisted Growth of Open-Ended TiO2 Nanotubes with Hexagonal Shape Using Atomic Layer Deposition

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Identifying and Mapping the Polytypes and Orientation Relationships in ZnO / CdSe Core Shell Nanowire Arrays

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Improvement of the physical properties of ZnO/CdTe core-shell nanowire arrays by CdCl2 heat treatment for solar cells

Abstract CdTe is an important compound semiconductor for solar cells, and its use in nanowire-based heterostructures may become a critical requirement, owing to the potential scarcity of tellurium. The effects of the CdCl2 heat treatment are investigated on the physical properties of vertically aligned ZnO/CdTe core-shell nanowire arrays grown by combining chemical bath deposition with close space sublimation. It is found that recrystallization phenomena are induced by the CdCl2 heat treatment in the CdTe shell composed of nanograins: its crystallinity is improved while grain growth and texture randomization occur. The presence of a tellurium crystalline phase that may decorate grain boundaries is also revealed. The CdCl2 heat treatment further favors the chlorine doping of the CdTe shell with the formation of chlorine A-centers and can result in the passivation of grain boundaries. The absorption properties of ZnO/CdTe core-shell nanowire arrays are highly efficient, and more than 80% of the incident light can be absorbed in the spectral range of the solar irradiance. The resulting photovoltaic properties of solar cells made from ZnO/CdTe core-shell nanowire arrays covered with CuSCN/Au back-side contact are also improved after the CdCl2 heat treatment. However, recombination and trap phenomena are expected to operate, and the collection of the holes that are mainly photo-generated in the CdTe shell from the CuSCN/Au back-side contact is presumably identified as the main critical point in these solar cells.This work has been supported by the Nanosciences Foundation of Grenoble through the project II-VI Photovoltaic and by Grenoble INP with a Bonus Qualité Recherche grant through the project CELESTE. This work has also been partially supported by the Spanish Ministry under contract MAT2010-16116.Peer Reviewe

Formation Mechanisms of ZnO Nanowires: The Crucial Role of Crystal Orientation and Polarity

International audienceZnO nanowires grown in liquid phase are considered as promising building blocks for a wide variety of optical and electrical devices. However, their structural morphology is still limited by the lack of understanding of their growth mechanisms. We have systematically investigated the effects of orientation and polarity of ZnO monocrystals acting as substrates on the formation mechanisms of ZnO by chemical bath deposition. Under identical growth conditions, two-dimensional layers develop on nonpolar m- and a-plane ZnO monocrystals. In contrast, nanowires form on O-polar c-plane ZnO monocrystals, while more complex nanostructures including nanowires grow on Zn-polar c-plane ZnO monocrystals. All of the structures have homoepitaxially nucleated. Very specifically to chemical bath deposition, both O- and Zn-polar c-planes are found to be active, and no polarity inversion domain boundary is observed on O-polar c-plane ZnO monocrystals, allowing the growth of O-polar ZnO nanowires. These findings reveal the crucial role of crystal orientation and polarity in the growth of ZnO nanowires in liquid phase similarly to their growth in vapor phase. They further cast a new light on the general understanding of the growth of ZnO nanowires and enable the revisiting of their formation mechanisms in liquid phase on seed layers consisting of ZnO nanoparticles

Identification of extended defect and interface related luminescence lines in polycrystalline ZnO thin films grown by sol-gel process

International audienceThe luminescence lines related to extended defects and interfaces in polycrystalline ZnO thin films grown by sol-gel process are deeply investigated by combining temperature-dependent photoluminescence and cathodoluminescence imaging with high-resolution transmission electron microscopy. A typical broad emission band is shown in the range of 3.316 to 3.333 eV and mainly consists of two distinct contributions. At high energy, a 3.333 eV line is associated with interfaces (i.e., free surfaces and grain boundaries) and predominates for small ZnO nanoparticles owing to their high density. The intensity ratio of the excitonic to interface-related transitions is low in this first configuration and the 3.333 eV line is characterized by an activation energy of 12.0 +/- 1.2 meV and a Huang-Rhys factor of 0.54 +/- 0.05 at 12 K. At low energy, a 3.316 eV line is attributed to basal plane stacking faults that are mostly of I1-type and prevail for large ZnO nanoparticles. The 3.316 eV line is characterized by an activation energy of 6.7 +/- 0.8 meV and a Huang Rhys constant of 0.87 +/- 0.03 at 12 K. Basal plane stacking faults are most likely formed as the coalescence process proceeds with the decomposition and crystallization processes during annealing. As shown by low-temperature monochromatic cathodoluminescence imaging, the luminescence corresponding to the 3.316 eV line is, in this second configuration, limited to some specific area (i.e., large nanoparticles), and the relative intensity ratio of the excitonic to interface-related transitions is increased due to the smaller free surface area and density of grain boundaries

Formation and degradation of intermetallics formed by solid-state reaction of Ni on In0:53Ga0:47As

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The Path of Gallium from Chemical Bath into ZnO Nanowires: Mechanisms of Formation and Incorporation

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