Добірка наукової літератури з теми "Ag2Te Nanowire"

Silver chalcogenides have received much attention in potential thermoelectric materials research because of high carrier mobility and low effective mass. Among them, in Ag2Te, it was reported that the phase transition from monoclinic to cubic phase occurs at relatively low temperatures, so that extensive research for effective application using this material has been aroused. In this work, we investigated how 1-dimensional nanostructure affects the thermoelectric properties through as-synthesized single crystalline Ag2Te nanowires. Adopting well-defined thermoelectric MEMS device structure and transferring an individual Ag2Te nanowire, we measure electrical resistance and Seebeck coefficient as a function of temperature. When the phase changes from monoclinic to cubic, the resistance increases, while absolute Seebeck coefficient value decreases. These results are compared with previous reports for Ag2Te bulk and film, suggesting the increased density of states of the carriers due to nanowire structure.

The hydrothermal technique was used to create straight single crystal silver telluride nanowires with a diameter of around 200 nm and a length of up to micrometers of decades. There has been no template or surfactant used in the process. As-synthesized products are high purity and well-crystallized, confirmed by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectrum, transmission electron microscopy (TEM), and a high-resolution SAED pattern. Differential scanning calorimetry was used to observe the reversible structural phase shift from the low-temperature monoclinic structure to the high-temperature face-centered cubic structure. Furthermore, the dramatic drop in electrical current in a single nanowire at the phase transition temperature is revealed, paving the way for future research into the manufacturing of one-dimensional nanoscale devices. Silver telluride (Ag2Te) has large thermoelectric coefficients and it was tested by using resistor graph and calculated the values of it, thermal conductivity and Seebeck coefficient were discussed with respect to the temperature of thin films. Semiconductors were superior thermoelectric material due to higher ratio of electrical and thermal conductivities. Therefore, the AgTe thin films deposited on indium tin oxide (ITO) substrates were employed, thermoelectric power and thermal conductivity measurements, respectively.

A single step surfactant-assisted hydrothermal route has been developed for the synthesis of zigzag silver telluride nanowires with diameter of 50–60 nm and length of several tens of micrometers. Silver nitrate (AgNO3) and sodium tellurite (Na2TeO3), are the precursors and polyvinylpyrrolidone (PVP) is used as surfactant in the presence of the reducing agent, that is, hydrazine hydrate (N2H4·H2O). In addition to the zigzag nanowires a facile hydrothermal reduction-carbonization route is proposed for the preparation of uniform core-shell Ag2Te/C nanowires. In case of Ag2Te/C synthesis process the same precursors are employed for Ag and Te along with the ethylene glycol used as reducing agent and glucose as the carbonizing agent. Morphological and compositional properties of the prepared products are analyzed with the help of scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy, respectively. The detailed formation mechanism of the zigzag morphology and reduction-carbonization growth mechanism for core-shell nanowires are illustrated on the bases of experimental results.

Hybrid structures involving atomic/molecular membranes from two or more layered materials are emerging as a platform for novel class of field effect transistors (FETs), p - n junctions, photo-detectors, photo-voltaic devices and so on. The interface formed by dissimilar materials gives rise to new functionalities, which are otherwise unattainable with individual constituent species. In addition to enormous potential in device application, these hybrid devices have raised several fundamental questions, especially in the context of inter-layer transfer of charge when subjected to external electric field, optical excitation etc. It is essential to explore the microscopic nature of the interface, which plays a significant role in efficient charge transfer dynamics from one material to the other. Moreover, the accumulation of charge carriers at the interface can control the optical properties of the individual materials by modifying their band structures as well as energetics of the fundamental excitations, namely, excitons or trions, which are now generating great interest. The hybrid photo-detector is one such class of device, which is becoming popular because of its direct application to various fields as well as novel scientific research purposes. A single layer graphene has traditionally been of great interest for photo-detection due to a strong radiation coupling over a broad wavelength spectrum (_ 0:3 􀀀 6 _m). Although the sensitivity of these bare graphene devices are comparatively poor because of its low optical absorption (_ 2%) of electromagnetic radiation. In order to overcome this issue, graphene-based hybrid structures (made of graphene with an optically active material) are being investigated, which are relatively new and innovative. When the optically active material is irradiated using an optical source, electron and hole pairs are generated, out of which one species of the charge carriers gets collected in graphene. Because of high carrier lifetime in graphene, most of these graphene-based hybrid devices reach remarkably high sensitivity. In this thesis, our main objective will be to investigate the charge transfer mechanism from the optically active material to graphene via opto-electronic measurement. This work has been divided into two parts: In the first part, we look into the opto-electronic response in graphene - WSe2 (Tungsten diselenide) hybrid structure. WSe2, a member of transition metal dichalcogenides (TMDC) family, is also a two-dimensional van der Waals material. By fabricating a hybrid structure made of single layer graphene and single layer WSe2, we achieve significantly high photo-responsivity value (_ 1010 AW􀀀1). While taking the photo-current spectra by sweeping the excitation wavelength (_) from 550􀀀800 nm, we find that both the photo-response (_R) and the relaxation time (_ ) are sensitive to the signatures of both A and B excitonic peaks (at 712 and 570 nm respectively) of WSe2. By using a coherent charge transfer model, we find that graphene - WSe2 hybrid structure forms a new coherent ground state for the excitons by transferring electrons into graphene and keeping holes in WSe2. The slow relaxation in the time scale has been explained by incoherent back transfer of charge from graphene to WSe2. We have also found an alternative method to calculate the binding energy of the excitons from the photo-current spectra. In the second part, we investigate the photo-response of uniformly dropcast TeNW (Tellurium nanowire) on graphene in the near infra-red (NIR) regime (920 􀀀 1720 nm). We start with the basic opto-electronic characterization in bare TeNW, and find that TeNW because of its low band gap indeed shows infra-red detection. But the sensitivity of such devices is very poor (_ 10􀀀2􀀀10􀀀4 AW􀀀1). On the other hand, photo-responsivity in graphene - TeNW hybrid device exceeds _ 106 AW􀀀1 at 175 K. The corresponding speci_c detectivity (_ 1013 Jones) reaches the highest order of magnitude reported for infra-red detectors. The charge transfer from TeNW to graphene is dominated by photogating mechanism, which gets suppressed at high temperature because of conduction through the TeNWs. This sets the upper limit for the operating range of temperature, which can still be improved by controlling the defect density and inter-wire electronic coupling. In summary, our experimental results open up a new direction to investigate the charge transfer dynamics as well as the nature of the interface between the materials in a hybrid structure at the microscopic level. The understanding of light-matter interaction at the atomic scale will impact now opto-electronic designs as well as hybrid materials with unprecedented functionality.