Silver Selenide Films Research Articles

Stretchable and Skin-Conformal Thermoelectric Generator with Highly Flexible and Plastically Bendable Silver Selenide Films.

Among inorganic thermoelectric materials, flexible thermoelectric materials have attracted considerable attention. In this study, highly flexible and plastically bendable silver selenide films with excellent thermoelectric performance at room temperature are presented. The flexibility of the freestanding silver selenide films was significantly improved through a simple annealing treatment. The highly flexible silver selenide films with a thickness of 26.0 μm displayed outstanding n-type thermoelectric performance, achieving an in-plane zT value of 0.38 at room temperature. Because silver selenide films are plastically bendable with a bending radius of less than 1 mm, they can be shaped into various forms. To achieve stretchability and skin-conformality in the thermoelectric generator, S-shaped silver selenide strips were used as an n-type thermoelectric element. Effective harvesting of electricity from heat of the human body was successfully demonstrated.

High thermoelectric efficiency in electrodeposited silver selenide films: from Pourbaix diagram to a flexible thermoelectric module

High thermoelectric efficient is obtained in electrodeposited silver selenide films and a unileg flexible thermoelectric module is fabricated with a maximum power density of 138.6 mW m−2 at 19 K.

Enhanced thermopower in (013)-oriented silver selenide films produced by thermal annealing

Nanocrystalline thin films of thermoelectric compound Ag2Se (AS) were deposited on the glass substrate kept at room temperature by thermal evaporation technique. Deposited films were annealed in vacuum of 2 × 10–5 mbar at 90 °C, 120 °C, 150 °C, 180 °C and 210 °C for 1 h. A sudden change in crystal orientation from (121) to (013) was observed as annealing temperature was increased to 210 °C. Seebeck coefficient for (013) oriented film was also found to be − 114.6 μV/K at room temperature compared to − 62.3 μV/K for as-deposited film. Formation of silver segregates in the film was observed where variation of size of silver grains on annealing played a crucial role in optimising Seebeck coefficient. Energy filtering effect by silver grains in combination to (013) orientation of silver selenide crystals was inferred as a reason for enhancement of Seebeck coefficient. Room temperature value of power factor was optimised at annealing temperature of 120 °C (AS-120) which was calculated to be 755.0 μW/mK2 and was also found to be comparable to that of film annealed at 210 °C (AS-210) i.e., 705.6 μW/mK2. Unlike AS-120, power factor value of AS-210 was due to considerable value Seebeck coefficient.

Characterization of silver selenide thin films grown on Cr‐covered Si substrates

AbstractThermal stability of silver selenide thin films formed from the solid‐state reaction of Ag‐Se diffusion couples on Si substrates covered with a thin Cr film, is investigated. Glancing angle X‐ray diffraction (GXRD), XPS, atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) are used to characterize the as‐deposited films and those annealed at 100, 200, 300, and 400 °C. The results reveal the formation of polycrystalline orthorhombic silver selenide films that remain stable without compositional change upon thermal annealing, in marked contrast to the agglomeration exhibited by silver selenide films deposited on Si without Cr film. The improvement in the thermal stability is attributed to compressive stress relief by a grainy morphology with large surface area, the formation of which is promoted by partially oxidized Cr adhesion film. Copyright © 2008 John Wiley & Sons, Ltd.

SIMS study of effect of Cr adhesion layer on the thermal stability of silver selenide thin films on Si

Effect of heat treatment on silver selenide films grown from diffusion-reaction of Ag and Se films on Cr-buffered Si substrates was investigated up to 400°C. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the films. XRD patterns of the films showed stress assisted change in preferential orientation of the films upon annealing: the films annealed at 200°C exhibited a strong orientation along (200) plane, which changed to (013) after annealing at 300 and 400°C. Dynamic SIMS measurements showed that Cr is confined to the interface and that there is no diffusion of Cr into silver selenide.

Non-destructive analysis of silver selenide films obtained by Pulsed Laser Deposition (PLD) with Micro-XRF

Thin films of silver selenide with varying composition have been deposited on magnesium oxide substrates with pulsed laser deposition and were investigated via micro-XRF. A calibration procedure was designed to determine the absolute thicknesses of the films. The lateral homogeneity was investigated by elemental mapping, thus delivering information about the deposition process. Wet chemical analysis was performed on the dissolved layers with ICP-OES and ICP-MS to determine the stoichiometry of the Ag x Se y . The results suggest a correlation between the composition of the layers and their thicknesses by showing a silver enrichment for thinner layers.

Atomic force microscopy study of thermal stability of silver selenide thin films grown on silicon

Silver selenide thin films were grown on silicon substrates by the solid-state reaction of sequentially deposited Se and Ag films of suitable thickness. Transmission electron microscopy and particle-induced X-ray emission studies of the as-deposited films showed the formation of single phase polycrystalline silver selenide from the reaction of Ag and Se films. Atomic force microscopy images of the as-deposited and films annealed at different temperatures in argon showed the film morphology to evolve into an agglomerated state with annealing temperature. The results indicate that when annealed above 473 K, silver selenide films on silicon become unstable and agglomerate through holes generated at grain boundaries.

Influence of heating rate on the hysteresis in the phase transition in silver selenide thin films

The electrical resistance of vacuum-deposited silver selenide thin films, of thickness 70 nm was measured in the temperature range from 300 to 430 K, at different heating rates and at a pressure of 2×10 −5 mbar. The films were annealed at 430 K at a pressure of 2×10 −5 mbar for an hour. It is found that annealed silver selenide films undergo a structural phase transition exhibiting hysteresis. The structural phase transition with hysteresis in silver selenide thin films is influenced by the heating rates of the films. The effect of the heating rate on the phase transition temperature and hysteresis are discussed taking into account the presence of potential barrier and the defects. Our studies reveal that hysteresis width decreases with decreasing heating rates.

Preparation of silver thin films using liquid-phase precursors by metal organic chemical vapor deposition and their conversion to silver selenide films by selenium vapor deposition

A series of new Ag precursors containing β-diketonate and neutral phosphite ligands were synthesized and characterized by various spectroscopic methods. These volatile precursors in liquid phase were thermally stable and quite useful in the preparation of silver thin films through bubbler-type chemical vapor deposition (CVD). In a typical case of silver (I) 1,1,1-trifluoro-2,4-pentanedionate triethyl phosphite adduct ((tfac)AgP(OEt)3) precursor, very pure silver thin films were obtained under relatively mild conditions without any appreciable amount of F, O, and P impurities. These thin films were easily converted to β-orthorhombic silver selenide by simple selenium vapor deposition method. In scanning electron microscopic analyses, the average particle size of the latter was found to increase to about 1.26 μm after gas-phase selenization reaction.

Electrodeposition of silver selenide thin films from aqueous solutions

Silver selenide thin films have been electrodeposited potentiostatically from aqueous acid solutions containing silver ions complexed with SCN− and selenium dioxide at room temperature. The electrodeposition reactions were studied by cyclic voltammetry. The deposited films were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectra (XPS) and scanning electron microscopy (SEM). The influence of deposition parameters such as potential, electrolyte composition and pH-value on the chemical composition and crystallinity of the films is discussed. The compositions of silver selenide films were controlled continuously from Ag-rich to near stoichiometry by adjusting the bath concentration and deposition potential. After annealing and slowly cooling in argon atmosphere, the films are highly (002) oriented. Furthermore, the excess Ag in the films transformed into Ag2Se by annealing in Se vapor at 230 °C for 4–5 h.

Electrochemical Preparation of Silver Selenide Films and Nanowires from Aqueous Solutions

AbstractBoth thin films and nanowires of silver selenide were synthesized by electrodeposition from an aqueous acid electrolyte containing silver ion complexed with SCN- and selenium dioxide at room temperature. Orthorhombic Ag2Se films with Ag slightly in excess were obtained. After annealing in argon atmosphere, the films are highly (002) oriented. A positive transverse magnetoresistance of about 20–25% at T = 5 K, and 10–13% at T = 300 K, in fields of H=50 kOe were observed in the electrodeposited films. Furthermore, silver selenide nanowires were synthesized from the same aqueous system by electrodeposition in porous anodic alumina templates. X-ray diffraction (XRD), Transmission electron microscopy (TEM), and Energy dispersive absorption X-ray (EDAX) characterization results showed that the nanowires are highly crystalline with (002) growth direction after annealing. In addition, the atomic ratio of Ag/Se in the films and the nanowire samples can be controlled from about 3.0 to 2.1 by adjusting the concentration of AgI and SeIV source and the deposition potential.