Semiconducting behavior of Ag2Te thin films and the dependence of band gap on thickness
TL;DR: In this paper, the electrical resistance of Ag2Te films has been measured as a function of temperature during heating, which was carried out immediately after the film formation, and the observed exponential decrease of resistance with temperature up to the transition point points to the semiconducting nature of the low temperature polymorph of ag2Te.
Abstract: Thin films of Ag2Te of various thicknesses in the range 500–1500 A have been prepared by thermal evaporation of the compound under vacuum on clean glass substrates held at room temperature. The electrical resistance of the films has been measured as a function of temperature during heating, which was carried out immediately after the film formation. The observed exponential decrease of resistance with temperature up to the transition point points to the semiconducting nature of the low temperature polymorph of Ag2Te. The band gap of the low temperature phase is calculated for various thicknesses of the films and it is found that the band gap is a function of film thickness, increasing with decreasing thickness. The increase in the band gap, which was found to be inversely proportional to the square of the film thickness, is attributed to quantization of electron momentum component normal to film plane.
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TL;DR: In this article, a solution-phase synthesis of silver telluride and bismuth-telluride nanowire heterostructure using tellurium (Te) nanowires as sacrificial template and site-selective conversion strategy is reported.
Abstract: In this paper, we report a solution-phase synthesis of silver telluride and bismuth telluride nanowire heterostructure using tellurium (Te) nanowire as sacrificial template and site-selective conversion strategy. High-resolution transmission electron microscope studies confirm sharp interface with possible epitaxial growth between silver telluride and bismuth telluride regions. Through tuning the precursor amount (bismuth and silver precursors) during the reaction, the composition between silver telluride and bismuth telluride can be adjusted. Moreover, the mass produced powder of nanowire heterostructure is consolidated into nanocomposite pellets, and thermoelectric properties of the nanocomposite pellets are investigated between 300 and 400 K. Results show that our materials are p-type with reduced lattice thermal conductivity and a ZT of ∼0.41 at 400 K, which is the best reported value for p-type silver telluride.
51 citations
TL;DR: In this article, Das and Karunakaran showed that the phase transition temperature of thin films is a function of thickness increasing with a decrease in the thickness of the thin films.
Abstract: Thin films of silver selenide (Ag2Se) between thicknesses of about 700 and 2200 A have been prepared on glass substrates at room temperature in a vacuum of 5×10−5 Torr. After vacuum annealing the films (at about 373 K for 3 h) electrical resistivity measurements on these films have been carried out in vacuum. From the increase in the rate of decrease of resistance with temperature, the phase transition temperatures (orthorhombic to body‐centered cubic) of the different films have been located. It is found that the phase transition temperature of the thin films is a function of thickness increasing with a decrease in the thickness. This observation has been explained by a recently developed theory [V. Damodara Das and D. Karunakaran, J. Phys. Chem Solids 46, 551 (1985)] of phase transitions in thin films modified further. Also, an order‐of‐magnitude value of the difference in the function of specific surface and interfacial energies of the two phases has also been determined using the theory.
38 citations
TL;DR: In this article, it was observed from the studies of electrical resistivity of films of SnSe of different thicknesses and substrate temperatures that resistivity decreases with increase in thickness and substrate temperature.
Abstract: It is observed from the studies of electrical resistivity of films of SnSe of different thicknesses and substrate temperatures that resistivity decreases with increase in thickness and substrate temperature. The study of variation in band gap with thickness shows a linear relationship between band gap and 1/t2. Finally, band gap – substrate temperature studies show that the band gap increases with substrate temperature.
27 citations
TL;DR: In this article, the dependence of substrate conditions and the effective thickness of MoO3 films on the morphology of nanostructures and their structural aspects were reported, and the electron microscopy measurements show that the length and the aspect ratio of Nanobibbons increased by 260% without any significant change in the width for a change in effective thickness from 5´nm to 30´nm.
25 citations
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TL;DR: In this paper, the resistance of bismuth thin films of thickness 720 A have been vacuum deposited at various substrate temperatures on glass substrates and their resistances are recorded as a function of temperature after annealing the films at 200°C.
9 citations
TL;DR: In this paper, die Ergebnisse von Leitfahigkeits-and Halleffektmessungen sowie Untersuchungen der Magnetfeldabhangigkeit im Temperaturgebiet zwischen +20°C and -190°C mitgeteilt.
Abstract: Es werden die Ergebnisse von Leitfahigkeits- und Halleffektmessungen sowie Untersuchungen der Magnetfeldabhangigkeit im Temperaturgebiet zwischen +20°C und -190°C mitgeteilt. Der Einflus geringer Abweichungen von der stochiometrischen Zusammensetzung wurde untersucht. Schlieslich wird ein Bild des Leitungsmechanismus entworfen, das die Ergebnisse widerspruchsfrei zu erklaren vermag.
6 citations
TL;DR: In this paper, Wismuth thin films of different thicknesses between about 20 and 225 nm are vacuum deposited at room temperature in a vacuum of 3 × 10−3 Pa. The films are heat-treated "in situ" and the resistances monitored.
Abstract: Bismuth thin films of different thicknesses between about 20 and 225 nm are vacuum deposited at room temperature in a vacuum of 3 × 10−3 Pa. The films are heat-treated “in situ” and the resistances monitored. It is found that the resistivity-temperature plots of the films after heat-treatment are non-linear and exhibit a minimum whose position is a function of thickness. It is also found that the films behave as semiconductors, the band gap decreasing with increasing thickness. The observations are interpreted on the basis of quantum size effect and the limitation of the electronic mean free path by the grain size of the films.
Dunne Wismuth-Schichten verschiedener Dicken zwischen 20 und 225 nm werden bei Zimmer-temperatur im Vakuum von 3 × 10−3 Pa hergestellt. Die Schichten werden “in situ” getempert und der Widerstand verfolgt. Es wird gefunden, das die Widerstands-Temperatur-Verlaufe der Schichten nach der Warmebehandlung nichtlinear sind und ein Minimum aufweisen, dessen Lage von der Schichtdicke abhangt. Es wird ebenfalls gefunden, das sich die Schichten wie Halbleiter verhalten, wobei die Bandlucke mit zunehmender Schichtdicke abnimmt. Die Beobachtungen werden auf der Grundlage des Quantensize-Effekts und der Begrenzung der mittleren freien Weglange der Elektronen durch die Korngrose der Schichten erklart.
3 citations