In this article a microfabricated thermoelectric nanowire characterization platform to investigate the thermoelectric and structural properties of single nanowires is presented. By means of ...dielectrophoresis (DEP), a method to manipulate and orient nanowires in a controlled way to assemble them onto our measurement platform is introduced. The thermoelectric platform fabricated with optimally designed DEP electrodes results in a yield of nanowire assembly of approximately 90% under an applied peak-to-peak ac signal V sub(pp) = 10 V and frequency f = 20 MHz within a series of 200 experiments. Ohmic contacts between the aligned single nanowire and the electrodes on the platform are established by electron beam-induced deposition. The Seebeck coefficient and electrical conductivity of electrochemically synthesized Bi sub(2)Te sub(3) nanowires are measured to be -51 mu V K super(-1) and (943 + or - 160)/(Omega super(-1) cm super(-1)), respectively. Chemical composition and crystallographic structure are obtained using transmission electron microscopy. The selected nanowire is observed to be single crystalline over its entire length and no grain boundaries are detected. At the surface of the nanowire, 66.1 + or - 1.1 at.% Te and 34.9 + or - 1.1 at.% Bi are observed. In contrast, chemical composition of 64.2 at.% Te and 35.8 at.% Bi is detected in the thick center of the nanowire.
Metallic and semiconducting nanowires (NWs) are of interest in the field of thermoelectrics, because they act as model system to investigate the influence of surfaces on the thermoelectric transport ...properties. In single crystalline NWs, the grain boundary scattering is negligible and the surface‐to‐volume‐ratio is high. We present state‐of‐the‐art of the combination of the structural, chemical, and temperature‐dependent full thermoelectric characterization for individual single crystalline NWs, which is essential to conclude on surface effects. Temperature‐dependent measurements allow further conclusions on the scattering mechanisms. Simulations by the finite element method are performed on indented NWs to interpret the measurement results.
Calculated surface temperature of a single‐indented and a multi‐indented NW.
Combined thermoelectrical, structural and chemical characterisation of individual metallic and semiconducting nanowires is presented. In the temperature range between 4.2 K and room temperature the thermoelectrical properties are determined. Transmission electron microscopy yields the structural properties, the chemical composition and the morphology of the nanowires. This comprehensive study unambiguously allows identifying surface effects on the thermoelectric properties and scattering mechanisms for electrons and phonons.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We report on the functionality of our Thermoelectric Nanowire Characterization Platform (TNCP). As a proof of concept of our design, we present a set of experimental results obtained from the ...characterization of a single Bi2Te3 nanowire, allowing for the determination of the nanowire’s electrical conductivity and Seebeck coefficient.
CuI has been recently rediscovered as a p-type transparent conductor with a high figure of merit. Even though many metal iodides are hygroscopic, the effect of moisture on the electrical properties ...of CuI has not been clarified. In this work, we observe a two-fold increase in the conductivity of CuI after exposure to ambient humidity for 5 hours, followed by slight long-term degradation. Simultaneously, the work function of CuI decreases by almost 1 eV, which can explain the large spread in the previously reported work function values. The conductivity increase is partially reversible and is maximized at intermediate humidity levels. Based on the large intra-grain mobility measured by THz spectroscopy, we suggest that hydration of grain boundaries may be beneficial for the overall hole mobility.
We present a study of the control of electric field induced strain on the magnetic and electrical transport properties in a magneto-elastically coupled artificial multiferroic Fe3O4/BaTiO3 ...heterostructure. In this Fe3O4/BaTiO3 heterostructure, the Fe3O4 thin film is epitaxially grown in the form of bilateral domains, analogous to a-c stripe domains of the underlying BaTiO3(001) substrate. By in-situ electric field dependent magnetization measurements, we demonstrate the extrinsic control of the magnetic anisotropy and the characteristic Verwey metal-insulator transition of the epitaxial Fe3O4 thin film in a wide temperature range between 20-300 K, via strain mediated converse magnetoelectric coupling. In addition, we observe strain induced modulations in the magnetic and electrical transport properties of the Fe3O4 thin film across the thermally driven intrinsic ferroelectric and structural phase transitions of the BaTiO3 substrate. In-situ electric field dependent Raman measurements reveal that the electric field does not significantly modify the anti-phase boundary defects in the Fe3O4 thin film once it is thermodynamically stable after deposition and that the modification of the magnetic properties is mainly caused by strain induced lattice distortions and magnetic anisotropy. These results provide a framework to realize electrical control of the magnetization in a classical highly correlated transition metal oxide.
Individual highly pure single crystalline silver nanowires (Ag NWs) were investigated with regard to the electrical conductivity \(\sigma\), the thermal conductivity \(\lambda\) and the Seebeck ...coefficient \(S\) as function of the temperature \(T\) between \(1.4\,\mathrm{K}\) and room temperature (RT). Transmission electron microscopy was performed subsequently to the thermoelectric characterization of the Ag NWs, so that their transport properties can be correlated with the structural data. The crystal structure, surface morphology and the rare occurrence of kinks and twinning were identified. The thermoelectric properties of the Ag NWs are discussed in comparison to the bulk: \(S_{\mathrm{Ag,Pt}}(T)\) was measured with respect to platinum and is in agreement with the bulk, \(\sigma(T)\) and \(\lambda(T)\) showed reduced values with respect to the bulk. The latter are both notably dominated by surface scattering caused by an increased surface-to-volume ratio. By lowering \(T\) the electron mean free path strongly exceeds the NW's diameter of \(150\,\mathrm{nm}\) so that the transition from diffusive transport to quasi ballistic one dimensional transport is observed. An important result of this work is that the Lorenz number \(L(T)\) turns out to be independent of surface scattering. Instead the characteristic of \(L(T)\) is determined by the material's purity. Moreover, \(\sigma(T)\) and \(L(T)\) can be described by the bulk Debye temperature of silver.
Diese Arbeit demonstriert die vollständige thermoelektrische Charakterisierung einzelner einkristalliner Bismuttellurid- und Silbernanodrähte und deren anschließende lokale strukturelle und chemische ...Charakterisierung mittels analytischer Transmissionselektronenmikroskopie. Die lokale strukturelle, chemische und morphologische Charakterisierung entlang der Nanodrähte trägt essentiell zum Verständnis des thermoelektrischen Transportes bei und bestätigt die Korrelation zwischen Oberflächen- und den thermoelektrischen Eigenschaften. Für durchmesservariierte Bismuttelluridnanodrähte wird der Einfluss der Morphologie auf die Wärmeleitfähigkeit bei Raumtemperatur quantifiziert. Im Vergleich zu einem glatten Referenznanodraht zeigt der durchmesservariierte Nanodraht gleicher Zusammensetzung und Kristallorientierung eine Reduktion der Wärmeleitfähigkeit um 55 %. Diese Reduktion kann durch Phononenrückstreuung an der eingekerbten Oberfläche erklärt werden. Die elektrische Leitfähigkeit und der Seebeckkoeffizient der Bismuttelluridnanodrähte deuten auf einen topologischen Oberflächenzustand hin. Für Silbernanodrähte werden die elektrische Leitfähigkeit und die Wärmeleitfähigkeit im Temperaturbereich von 1,4 K bis 300 K gemessen. Mit fallender Temperatur steigt die relative Reduktion der Wärmeleitfähigkeit im Verhältnis zur elektrischen Leitfähigkeit stärker, sodass die Lorenzzahl die klassische Wiedemann-Franz-Relation nicht erfüllt und eine Funktion der Temperatur darstellt. Der Temperaturverlauf der Lorenzzahl der Silbernanodrähte entspricht der 1938 von Makinson aufgestellten Theorie für hochreine Metalle und ist im Tieftemperaturbereich um bis zu zwei Größenordnungen zum Sommerfeldwert reduziert.
This work demonstrates the full thermoelectric characterisation of individual single crystalline bismuth telluride and silver nanowires and their subsequent local structural and chemical characterisation via analytical transmission electron microscopy along the whole nanowires. Therefore, the correlation between the structure, in particular the surface morphology, and the thermoelectric transport properties is unambiguously shown. For diameter varied bismuth telluride nanowires the influence of the morphology on the thermal conductivity is quantified at room temperature. The diameter varied nanowire shows a reduction of 55 % with respect to the smooth nanowire of the same chemical composition and structural orientation. This reduction can be explained by phonon backscattering at the indents. The electrical conductivity and the Seebeck coefficient indicate the presence of a topological surface state. For silver nanowires the electrical and thermal conductivity are determined in the temperature range between 1.4 K and 300 K. With decreasing temperature the relative reduction of the thermal conductivity is higher than the reduction of the electrical conductivity resulting in a temperature-dependent Lorenz number, so that the classical Wiedemann-Franz relation is not fulfilled. The temperature characteristic of the silver nanowires'' Lorenz number is in agreement with the theory Makinson established for highly pure metals in 1938 and is reduced by two orders of magnitude with respect to the Sommerfeld value in the low temperature regime.
We demonstrate the design and fabrication of a novel micromachined Thermoelectric Nanowire Characterization Platform (TNCP) which is utilized to characterize the thermoelectric properties of various ...nanowires. Single nanowire is assembled onto the pre-fabricated TNCP by means of dielectrophoresis (DEP) in combination with a water droplet evaporation scheme. After assembly, a reliable ohmic contact is generated between the bismuth telluride (Bi 2 Te 3 ) nanowire and the underlying electrodes by means of scanning electron microscope (SEM) focused electron beam-induced deposition (EBID). Finally, the electrical conductivity and Seebeck coefficient of Silver (Ag) and Bi 2 Te 3 nanowires are investigated and presented in this paper.
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