In this work, a zT value as high as 1.2 at room temperature for n‐type Ag2Se films is reported grown by pulsed hybrid reactive magnetron sputtering (PHRMS). PHRMS is a novel technique developed in ...the lab that allows to grow film of selenides with different compositions in a few minutes with great quality. The improved zT value reported for room temperature results from the combination of the high power factors, similar to the best values reported for bulk Ag2Se (2440 ± 192 µW m−1 K−2), along with a reduced thermoelectric conductivity as low as 0.64 ± 0.1 W m−1 K−1. The maximum power factor for these films is of 4655 ± 407 µW m−1 K−2 at 103 °C. This material shows promise to work for room temperature applications. Obtaining high zT or, in other words, high power factor and low thermal conductivity values close to room temperature for thin films is of high importance to develop a new generation of wearable devices based on thermoelectric heat recovery.
A zT value as high as 1.2 at room temperature for n‐type Ag2Se films grown by pulsed hybrid reactive magnetron sputtering is reported. Obtaining such high zT for thin films with this new fabrication method that allows the use of flexible substrates is of high importance to develop a new generation of wearable devices based on thermoelectric heat recovery.
This review article gives an overview of the recent research directions in eco‐friendly, non‐toxic, and earth‐abundant thermoelectric materials. It covers materials such as sulfides, tetrahedrites, ...earth‐abundant oxides, silicides, copper iodine, Half‐Heusler intermetallic compounds, nitrides, and other environmentally friendly thermoelectrics. In all cases, their history, structure, general characteristics, thermoelectric properties, synthesis methods, and related thermoelectric applications are compiled. It is also shown that they are starting to be an excellent alternative for producing cost‐effective, sustainable, and non‐toxic thermoelectric generators. This review does not try to include all possible materials, but to show that there are high zT thermoelectric materials that are starting to be an excellent alternative for producing cost‐effective, sustainable, and non‐toxic thermoelectric generators.
This review presents the recent research directions in eco‐friendly, non‐toxic, and earth‐abundant thermoelectric materials. They can be an excellent alternative for producing cost‐effective, sustainable, and innocuous thermoelectric generators. It covers materials such as sulfides, tetrahedrites, earth‐abundant oxides, silicides, copper iodine, Half‐Heusler intermetallic compounds, nitrides, and others.
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Nanowire structures have been investigated in order to achieve improved thermoelectric performance of thermoelectric materials. This brief viewpoint article summarizes the progress ...done in the last years and our vision of which are the key points to achieve a future generation of efficient nanowire-based thermoelectric devices.
Physical properties at the nanoscale are novel and different from those in bulk materials. Over the last few decades, there has been an ever growing interest in the fabrication of nanowire structures ...for a wide variety of applications including energy generation purposes. Nevertheless, the study of their transport properties, such as thermal conductivity, electrical conductivity or Seebeck coefficient, remains an experimental challenge. For instance, in the particular case of nanostructured thermoelectrics, theoretical calculations have shown that nanowires offer a promising way of enhancing the hitherto low efficiency of these materials in the conversion of temperature differences into electricity. Therefore, within the thermoelectrical community there has been a great experimental effort in the measurement of these quantities in actual nanowires. The measurements of these properties at the nanoscale are also of interest in fields other than energy, such as electrical components for microchips, field effect transistors, sensors, and other low scale devices. For all these applications, knowing the transport properties is mandatory. This review deals with the latest techniques developed to perform the measurement of these transport properties in nanowires. A thorough overview of the most important and modern techniques used for the characterization of different kinds of nanowires will be shown.
Physical properties at the nanoscale are novel and different from those in bulk materials.
Three-dimensional (3D) nanostructures combine properties of nanoscale materials with the advantages of being macro-sized pieces when the time comes to manipulate, measure their properties or make a ...device. However, the amount of compounds with the ability to self-organize in ordered 3D nanostructures is limited. Therefore, template-based fabrication strategies become the key approach towards 3D nanostructures. Here we report the simple fabrication of a template based on anodic aluminium oxide, having a well-defined, ordered, tunable, homogeneous 3D nanotubular network in the sub 100-nm range. The 3D templates are then employed to achieve 3D, ordered nanowire networks in Bi2Te3 and polystyrene. Finally, we demonstrate the photonic crystal behaviour of both the template and the polystyrene 3D nanostructure. Our approach may establish the foundations for future high-throughput, cheap, photonic materials and devices made of simple commodity plastics, metals and semiconductors.
The synthesis of flexible photonic materials, by sustainable and scalable methods, is proved to be a difficult task for the materials science and industrial communities. Alongside, the modern society ...has also grown a strong dependence on polymeric materials, demanding superpolymers that combine functionality and cost with superior after‐use properties. The path for accomplishing this aim is made possible by mimicking nature through the merging of self‐ordered nanostructures and a commodity thermoplastic, resorting to basic fabrication infrastructure. This work presents the development of a flexible material that exhibits tunable structural color due to its 3D polyethylene based nanonetwork. These nanonetworks are hydrophobic, and change color depending on the refractive index of the material filling their voids. This developed flexible metamaterial is projected to open opportunities for the fabrication of economically affordable (around 0.008 € cm−2) and solvent‐free photonic nanostructures with multipurpose applications such as sensing, energy saving, clothing, and photovoltaics, among others.
In this work, a simple and scalable method for the fabrication of polyethylene‐based Bragg refractors is explored by a combination of pulse aluminum anodization and polymer melt infiltration. A 3D polymeric network is fabricated. This metamaterial is flexible, hydrophobic and with tunable Bragg‐reflector properties. Its cost‐effectiveness makes it suitable for large production with multipurpose applications.
Ordered anodic aluminum oxide (AAO) templates with pores <15 nm in diameter and an aspect ratio (length-to-diameter ratio) above 3 × 103 have been fabricated using a nonlithographic approach; ...specifically, by anodizing aluminum in an ethylene-glycol-containing sulfuric acid electrolyte. The pores are the smallest in diameter reported for a self-ordered AAO without pore aspect-ratio limitations and good ordering, which opens up the possibility of obtaining nanowire arrays in the quantum confinement regime that is of interest for efficient thermoelectric generators. The effect of the ethylene glycol addition on both the pore diameter and the ordering is evaluated and discussed. Moreover, 15-nm-diameter Bi2Te3 and poly(3-hexyl thiophene) (P3HT) nanowires have been prepared using these AAO templates. As known, Bi2Te3 is currently the most efficient thermoelectric bulk material for room-temperature operations and, according with theory, its Seebeck coefficient should be increased when it is confined to nanowires with diameters close to 10 nm. On the other hand, P3HT is one of the main candidates for integrating organic photovoltaic and thermoelectric devices, and its properties are also proposed to increase when it is confined to nanoscale structures, mainly due to molecular orientation effects.
Understanding the interactions among magnetic nanostructures is one of the key factors to predict and control the advanced functionalities of 3D integrated magnetic nanostructures. In this work, the ...focus is on different interconnected Ni nanowires forming an intricate, but controlled, and ordered magnetic system: Ni 3D Nanowire Networks (3DNNs). These self‐ordered systems present striking anisotropic magnetic responses, depending on the interconnections’ position between nanowires. To understand their collective magnetic behavior, the magnetization reversal processes are studied within different Ni 3D Nanowire Networks compared to the 1D nanowire 1DNW array counterparts. The systems are characterized at different angles using first magnetization curves, hysteresis loops, and First Order Reversal Curves techniques, which provided information about the key features that enable macroscopic tuning of the magnetic properties of the 3D nanostructures. In addition, micromagnetic simulations endorse the experiments, providing accurate modeling of their magnetic behavior. The results reveal a plethora of magnetic interactions, neither evident nor intuitive, which are the main role players controlling the collective response of the system. The results pave the way for the design and realization of 3D novel metamaterials and devices based on the nucleation and propagation of ferromagnetic domain walls both in 3D self‐ordered systems and future nano‐lithographed devices.
Interconnected 3D Ni Nanowire networks form intricate, controlled, and ordered magnetic systems that present striking anisotropic magnetic responses, depending on the interconnections’ position between nanowires. The results confirm that the transversal connections behave like pinning sites for the magnetic domain walls and reduce the magnetostatic interactions among nanowires. These self‐ordered systems represent a new approach that will enable the design of high‐resolution 3D‐magnetic‐metamaterials.
In this review article we present the most relevant outcomes of the joint project "Tailoring Electronic and Phononic Properties of Nanomaterials: Towards Improved Thermoelectricity (nanoTHERM)", a ...Spanish research Consolider project focused on the understanding of the thermoelectric materials and the tailoring of both their electronic and phononic properties toward the optimization of the efficiency of thermoelectric devices working at low and high temperatures.
Three-dimensional anodic alumina templates (3D-AAO) are an astonishing framework with open highly ordered three-dimensional skeleton structures. Since these templates are architecturally different ...from conventional solids or porous templates, they teem with opportunities for engineering thermal properties. By establishing the mechanisms of heat transfer in these frameworks, we aim to create materials with tailored thermal properties. The effective thermal conductivity of an empty 3D-AAO membrane was measured. As the effective medium theory was not valid to extract the skeletal thermal conductivity of 3D-AAO, a simple 3D thermal conduction model was developed, based on a mixed series and parallel thermal resistor circuit, giving a skeletal thermal conductivity value of approximately 1.25 W·m
·K
, which matches the value of the ordinary AAO membranes prepared from the same acid solution. The effect of different filler materials as well as the variation of the number of transversal nanochannels and the length of the 3D-AAO membrane in the effective thermal conductivity of the composite was studied. Finally, the thermal conductivity of two 3D-AAO membranes filled with cobalt and bismuth telluride was also measured, which was in good agreement with the thermal model predictions. Therefore, this work proved this structure as a powerful approach to tailor thermal properties.
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