The urgent need for real-time monitoring of toxic/hazardous gases in the immediate indoor environment has attracted much attention owing to the recent advancements in the development of ...ultra-efficient gas sensors with increased accuracy and portability at around room temperature. In this work, we report on a high performance volatile organic compound (VOC) sensor using a Pd–WO3 loaded ordered mesoporous graphitic carbon nitride (g-CN)-based nanohybrid prepared via a nanocasting strategy on a hard 3D porous silica (KIT-6) template. The nanocasted Pd–WO3/g-CN sensor exhibits highly selective temperature dependent trace detection of important VOCs (formaldehyde, toluene, acetone and ethanol), which are commonly present in the indoor climate. The 3D cubic ordered mesoporous structure of the 2D layered g-CN in the hybrid nanodevice is very advantageous towards improving its sensing response with enhanced linearity, swift response/recovery time, selectivity, reversibility, stability with respect to various VOCs (at their respective optimum temperature) and reusability. The proposed functional hybrid nanomaterial-based sensing strategy offers an effective design for highly sensitive and efficient VOC detection devices, which can operate well at low temperatures also.
Chalcogenide-based thin films are employed in data storage and memory technology whereas van der Waals-bonded layered chalcogenide heterostructures are considered to be a main contender for memory ...devices with low power consumption. The reduction of switching energy is due to the lowering of entropic losses governed by the restricted motion of atoms in one dimension within the crystalline states. The investigations of switching mechanisms in such superlattices have recently attracted much attention and the proposed models are still under debate. This is partially due to the lack of direct observation of atomic scale processes, which might occur in these chalcogenide systems. This work reports direct, nanoscale observations of the order–disorder processes in van der Waals bonded Ge–Sb–Te thin films and GeTe–Sb2Te3-based superlattices using in situ experiments inside an aberration-corrected transmission electron microscope. The findings reveal a reversible self-assembled reconfiguration of the structural order in these materials. This process is associated with the ordering of randomly distributed vacancies within the studied materials into ordered vacancy layers and with readjustment of the lattice plane distances within the newly formed layered structures, indicating the high flexibility of these layered chalcogenide-based systems. Thus, the ordering process results in the formation of vacancy-bonded building blocks intercalated within van der Waals-bonded units. Moreover, vacancy-bonded building blocks can be reconfigured to the initial structure under the influence of an electron beam, while in situ exposure of the recovered layers to a targeted electron beam leads to the reverse process. Overall, the outcomes provide new insights into local structure and switching mechanism in chalcogenide superlattices.
Ultralow-fatigue shape memory alloy films Chluba, Christoph; Ge, Wenwei; de Miranda, Rodrigo Lima ...
Science (American Association for the Advancement of Science),
05/2015, Letnik:
348, Številka:
6238
Journal Article
Recenzirano
Functional shape memory alloys need to operate reversibly and repeatedly. Quantitative measures of reversibility include the relative volume change of the participating phases and compatibility ...matrices for twinning. But no similar argument is known for repeatability. This is especially crucial for many future applications, such as artificial heart valves or elastocaloric cooling, in which more than 10 million transformation cycles will be required. We report on the discovery of an ultralow-fatigue shape memory alloy film system based on TiNiCu that allows at least 10 million transformation cycles. We found that these films contain Ti₂Cu precipitates embedded in the base alloy that serve as sentinels to ensure complete and reproducible transformation in the course of each memory cycle.
Growth of freestanding nano- and microstructures with complex morphologies is a highly desired aspect for real applications of nanoscale materials in various technologies. Zinc oxide tetrapods ...(ZnO-T), which exhibit three-dimensional (3D) shapes, are of major importance from a technological applications point of view, and thus efficient techniques for growth of different varieties of tetrapod-based networks are demanded. Here, we demonstrate the versatile and single-step synthesis of ZnO-T with different arm morphologies by a simple flame transport synthesis (FTS) approach, forming a network. Morphological evolutions and structural intactness of these tetrapods have been investigated in detail by scanning electron microscopy, X-ray diffraction, and micro-Raman measurements. For a deeper understanding of the crystallinity, detailed high-resolution transmission electron microscopic studies on a typical ZnO tetrapod structure are presented. The involved growth mechanism for ZnO tetrapods with various arm morphologies is discussed with respect to variations in experimental conditions. These ZnO-T have been utilized for photocatalytic degradation and nanosensing applications. The photocatalytic activities of these ZnO-T with different arm morphologies forming networks have been investigated through the photocatalytic decolorization of a methylene blue (MB) solution under UV light illumination at ambient temperature. The results show that these ZnO-T exhibit strong photocatalytic activities against MB and its complete degradation can be achieved in very short time. In another application, a prototype of nanoelectronic sensing device has been built from these ZnO-T interconnected networks and accordingly utilized for UV detection and H2 gas sensing. The fabricated device structures showed excellent sensing behaviors for promising practical applications. The involved sensing mechanisms with respect to UV photons and H2 gas are discussed in detail. We consider that such multifunctional nanodevices based on ZnO tetrapod interconnected networks will be of interest for various advanced applications.
Laser diodes are efficient light sources. However, state-of-the-art laser diode-based lighting systems rely on light-converting inorganic phosphor materials, which strongly limit the efficiency and ...lifetime, as well as achievable light output due to energy losses, saturation, thermal degradation, and low irradiance levels. Here, we demonstrate a macroscopically expanded, three-dimensional diffuser composed of interconnected hollow hexagonal boron nitride microtubes with nanoscopic wall-thickness, acting as an artificial solid fog, capable of withstanding ~10 times the irradiance level of remote phosphors. In contrast to phosphors, no light conversion is required as the diffuser relies solely on strong broadband (full visible range) lossless multiple light scattering events, enabled by a highly porous (>99.99%) non-absorbing nanoarchitecture, resulting in efficiencies of ~98%. This can unleash the potential of lasers for high-brightness lighting applications, such as automotive headlights, projection technology or lighting for large spaces.
The single-step incorporation of multiple immiscible elements into colloidal high-entropy alloy (HEA) nanoparticles has manifold technological potential, but it continues to be a challenge for ...state-of-the-art synthesis methods. Hence, the development of a synthesis approach by which the chemical composition and phase of colloidal HEA nanoparticles can be controlled could lead to a new pool of nanoalloys with unparalleled functionalities. Herein, this study reports the single-step synthesis of colloidal CoCrFeMnNi HEA nanoparticles with targeted equimolar stoichiometry and diameters less than 5 nm by liquid-phase, ultrashort-pulsed laser ablation of the consolidated and heat-treated micropowders of the five constituent metals. Further, the scalability of the process with an unprecedented productivity of 3 grams of colloidal HEA nanoparticles per hour is demonstrated. Electrochemical analysis reveals a unique redox behavior of the particles' surfaces in an alkaline environment and a potential for future application as a heterogeneous catalyst for the oxygen evolution reaction.
The laser ablation of a bulk CoCrFeMnNi high-entropy alloy immersed in liquid yields colloidal nanoparticles with diameters below 5 nm. Both, the chemical composition and the crystal lattice of the bulk material is preserved in the nanoparticles.
Ge-Sb-Te based phase change alloys are currently used in optical data storage and are regarded as promising candidates to replace Flash memories. Detailed knowledge of structural defects in these ...materials is crucial for further understanding of the switching mechanisms, e.g., in recently proposed interfacial phase change memory. In the present work, atomic structure and dynamics of layered defects frequently reported in van der Waals bonded Ge-Sb-Te based materials and GeTeSb2Te3 based superlattices are studied using advanced transmission electron microscopy. It is shown that the defects are confined into two atomic layers of GeSb and Te and represent localized stacking faults. In situ experiments revealed that the GeSb and Te bilayers can be easily reconfigured into such bilayer stacking faults with subsequent formation of a new van der Waals gap, indicating a mechanism of structural reconfiguration of building blocks in layered Ge-Sb-Te compounds. Overall the results of the present work shed insights into the dynamics of van der Waals gaps rearrangement and mechanism of the layer exchange process in layered functional chalcogenide compounds, also relevant for an understanding of switching mechanisms in interfacial phase change alloys.
Van der Waals gaps in layered Ge-Sb-Te structures reconfigure via rearrangement of GeSb and Te atomic layers. Display omitted
Magnetoelectric composite materials are promising candidates for highly sensitive magnetic-field sensors. However, the composites showing the highest reported magnetoelectric coefficients require the ...presence of external d.c. magnetic bias fields, which is detrimental to their use as sensitive high-resolution magnetic-field sensors. Here, we report magnetoelectric composite materials that instead rely on intrinsic magnetic fields arising from exchange bias in the device. Thin-film magnetoelectric two-two composites were fabricated by magnetron sputtering on silicon-cantilever substrates. The composites consist of piezoelectric AlN and multilayers with the sequence Ta/Cu/Mn(70)Ir(30)/Fe(50)Co(50) or Ta/Cu/Mn(70)Ir(30)/Fe(70.2)Co(7.8)Si(12)B(10) serving as the magnetostrictive component. The thickness of the ferromagnetic layers and angle dependency of the exchange bias field are used to adjust the shift of the magnetostriction curve in such a way that the maximum piezomagnetic coefficient occurs at zero magnetic bias field. These self-biased composites show high sensitivity to a.c. magnetic fields with a maximum magnetoelectric coefficient of 96 V cm(-1) Oe(-1) at mechanical resonance.
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