Showing papers on "Antimony telluride published in 2017"

Reducing the stochasticity of crystal nucleation to enable subnanosecond memory writing

Abstract: Operation speed is a key challenge in phase-change random-access memory (PCRAM) technology, especially for achieving subnanosecond high-speed cache memory. Commercialized PCRAM products are limited by the tens of nanoseconds writing speed, originating from the stochastic crystal nucleation during the crystallization of amorphous germanium antimony telluride (Ge2Sb2Te5). Here, we demonstrate an alloying strategy to speed up the crystallization kinetics. The scandium antimony telluride (Sc0.2Sb2Te3) compound that we designed allows a writing speed of only 700 picoseconds without preprogramming in a large conventional PCRAM device. This ultrafast crystallization stems from the reduced stochasticity of nucleation through geometrically matched and robust scandium telluride (ScTe) chemical bonds that stabilize crystal precursors in the amorphous state. Controlling nucleation through alloy design paves the way for the development of cache-type PCRAM technology to boost the working efficiency of computing systems.

Resonant thermoelectric nanophotonics

Abstract: Photodetectors are typically based either on photocurrent generation from electron–hole pairs in semiconductor structures or on bolometry for wavelengths that are below bandgap absorption. In both cases, resonant plasmonic and nanophotonic structures have been successfully used to enhance performance. Here, we show subwavelength thermoelectric nanostructures designed for resonant spectrally selective absorption, which creates large localized temperature gradients even with unfocused, spatially uniform illumination to generate a thermoelectric voltage. We show that such structures are tunable and are capable of wavelength-specific detection, with an input power responsivity of up to 38 V W–1, referenced to incident illumination, and bandwidth of nearly 3 kHz. This is obtained by combining resonant absorption and thermoelectric junctions within a single suspended membrane nanostructure, yielding a bandgap-independent photodetection mechanism. We report results for both bismuth telluride/antimony telluride and chromel/alumel structures as examples of a potentially broader class of resonant nanophotonic thermoelectric materials for optoelectronic applications such as non-bandgap-limited hyperspectral and broadband photodetectors. Subwavelength nanostructures generate a localized thermoelectric voltage for non-bandgap-limited photodetection.

Synthesis and Evaluation of Thick Films of Electrochemically Deposited Bi2Te3 and Sb2Te3 Thermoelectric Materials

Abstract: This paper presents the results of the synthesis and evaluation of thick thermoelectric films that may be used for such applications as thermoelectric power generators. Two types of electrochemical deposition methods, constant and pulsed deposition with improved techniques for both N-type bismuth telluride (Bi2Te3) and P-type antimony telluride (Sb2Te3), are performed and compared. As a result, highly oriented Bi2Te3 and Sb2Te3 thick films with a bulk-like structure are successfully synthesized with high Seebeck coefficients and low electrical resistivities. Six hundred-micrometer-thick Bi2Te3 and 500-µm-thick Sb2Te3 films are obtained. The Seebeck coefficients for the Bi2Te3 and Sb2Te3 films are −150 ± 20 and 170 ± 20 µV/K, respectively. Additionally, the electrical resistivity for the Bi2Te3 is 15 ± 5 µΩm and is 25 ± 5 µΩm for the Sb2Te3. The power factors of each thermoelectric material can reach 15 × 10−4 W/mK2 for Bi2Te3 and 11.2 × 10−4 W/mK2 for Sb2Te3.

Graphene Substrate for van der Waals Epitaxy of Layer-Structured Bismuth Antimony Telluride Thermoelectric Film.

Abstract: Graphene as a substrate for the van der Waals epitaxy of 2D layered materials is utilized for the epitaxial growth of a layer-structured thermoelectric film. Van der Waals epitaxial Bi0.5 Sb1.5 Te3 film on graphene synthesized via a simple and scalable fabrication method exhibits good crystallinity and high thermoelectric transport properties comparable to single crystals.

Role of Nanostructuring and Microstructuring in Silver Antimony Telluride Compounds for Thermoelectric Applications

Abstract: Thermoelectric (TE) materials are of utmost significance for conversion of heat flux into electrical power in the low-power regime. Their conversion efficiency depends strongly on the microstructure. AgSbTe2-based compounds are high-efficiency TE materials suitable for the mid-temperature range. Herein, we explore an Ag16.7Sb30Te53.3 alloy (at %) subjected to heat treatments at 380 °C for different durations aimed at nucleation and coarsening of Sb2Te3-precipitates. To characterize the Sb2Te3-precipitation, we use a set of methods combining thermal and electrical measurements in concert with transmission electron microscopy and atom probe tomography. We find correlations between the measured TE transport coefficients and the applied heat treatments. Specifically, the lowest electrical and thermal conductivity values are obtained for the as-quenched state, whereas the highest values are observed for alloys aged for 8 h. In turn, long-term heat treatments result in intermediate values of transport coefficie...

Synthesis and Characterization of Antimony Telluride for Thermoelectric and Optoelectronic Applications

Abstract: Antimony telluride (Sb2Te3) is an intermetallic compound crystallizing in a hexagonal lattice with R-3m space group. It creates a c lose packed structure of an ABCABC type. As intrinsic semiconductor characterized by excellent electrical properties, Sb2Te3 is widely used as a low-temperature thermoelectric material. At the same time, due to unusual properties (strictly connected with the structure), antimony telluride exhibits nonlinear optical properties, including saturable absorption. Nanostructurization, elemental doping and possibilities of synthesis Sb2Te3 in various forms (polycrystalline, single crystal or thin film) are the most promising methods for improving thermoelectric properties of Sb2Te3.Applications of Sb2Te3 in optical devices (e.g. nonlinear modulator, in particular saturable absorbers for ultrafast lasers) are also interesting. The antimony telluride in form of bulk polycrystals and layers for thermoelectric and optoelectronic applications respectively were used. For optical applications thin layers of the material were formed and studied. Synthesis and structural characterization of Sb2Te3 were also presented here. The anisotropy (packed structure) and its influence on thermoelectric properties have been performed. Furthermore, preparation and characterization of Sb2Te3 thin films for optical uses have been also made.

Reduction of thermal conductivity in YxSb2–xTe3 for phase change memory

Abstract: Thermal conductivity (κ) is one of the fundamental properties of materials for phase change memory (PCM) application, as the set/reset processes strongly depend upon heat dissipation and transport. The κ of phase change materials in both amorphous and crystalline phases should be quite small, because it determines how energy-efficient the PCM device is during programming. At a high temperature, the electronic thermal conductivity (κe) is always notable for semiconductors, which is still lacking for antimony telluride under doping in the literature as far as we know. In this paper, using density functional theory and Boltzmann transport equations, we report calculations of lattice thermal conductivity κL and electronic thermal conductivity κe of the yttrium doped antimony telluride. We show that the average value of thermal conductivity decreases from ∼2.5 W m−1 K−1 for Sb2Te3 to ∼1.5 W m−1 K−1 for Y0.167Sb1.833Te3. This can be attributed to the reduced κL and κe, especially the κe at high temperature (nea...

Microstructure and Electrical Properties of Antimony Telluride Thin Films Deposited by RF Magnetron Sputtering on Flexible Substrate Using Different Sputtering Pressures

Abstract: The microstructural, electrical, and thermoelectric properties of antimony telluride (Sb2Te3) thin films have been investigated for thermoelectric applications. Sb2Te3 thin films were deposited on flexible substrate (polyimide) by radiofrequency (RF) magnetron sputtering from a Sb2Te3 target using different sputtering pressures in the range from 4 × 10−3 mbar to 1.2 × 10−2 mbar. The crystal structure, [Sb]:[Te] ratio, and electrical and thermoelectric properties of the films were analyzed by grazing-incidence x-ray diffraction (XRD) analysis, energy-dispersive x-ray spectroscopy (EDS), and Hall effect and Seebeck measurements, respectively. The XRD spectra of the films demonstrated polycrystalline structure with preferred orientation of (015), (110), and (1010). A high-intensity spectrum was found for the film deposited at lower sputtering pressure. EDS analysis of the films revealed the effects of the sputtering pressure on the [Sb]:[Te] atomic ratio, with nearly stoichiometric films being obtained at higher sputtering pressure. The stoichiometric Sb2Te3 films showed p-type characteristics with electrical conductivity, carrier concentration, and mobility of 35.7 S cm−1, 6.38 × 1019 cm−3, and 3.67 cm2 V−1 s−1, respectively. The maximum power factor of 1.07 × 10−4 W m−1 K−2 was achieved for the film deposited at sputtering pressure of 1.0 × 10−2 mbar.

Molecular Precursors for the Phase-Change Material Germanium-Antimony-Telluride, Ge2Sb2Te5 (GST)

Abstract: This review provides an overview of the precursor chemistry that has been developed around the phase-change material germanium-antimony-telluride, Ge2Sb2Te5 (GST). Thin films of GST can be deposited by employing either chemical vapor deposition (CVD) or atomic layer deposition (ALD) techniques. In both cases, the success of the layer deposition crucially depends on the proper choice of suitable molecular precursors. Previously reported processes mainly relied on simple alkoxides, alkyls, amides and halides of germanium, antimony, and tellurium. More sophisticated precursor design provided a number of promising new aziridinides and guanidinates.

Thermoelectric Micro-Refrigerator Based on Bismuth/Antimony Telluride

Abstract: Thermoelectric micro-coolers based on bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) are important in many practical applications thanks to their compactness and fluid-free circulation. In this paper, we studied thermoelectric properties of bismuth/antimony telluride (Bi/SbTe) thin films prepared by the thermal co-evaporation method, which yielded among the best thermoelectric quality. Different co-evaporation conditions such as deposition flux ratio of materials and substrate temperature during deposition were investigated to optimize the thermoelectric figure␣of merit of these materials. Micron-size refrigerators were designed and fabricated using standard lithography and etching technique. A three-layer structure was introduced, including a p-type layer, an n-type layer and an aluminum layer. Next to the main cooler, a pair of smaller Bi/SbTe junctions was used as a thermocouple to directly measure electron temperature of the main device. Etching properties of the thermoelectric materials were investigated and optimized to support the fabrication process of the micro-refrigerator. We discuss our results and address possible applications.

Features of the electron density distribution in antimony telluride Sb 2 Te 3

Abstract: Based on the results of electron density functional calculations of the electronic band structure of semiconductors Sb2Te3, Ge, Te, and semimetal Sb, the parameters of critical points in the electron density distribution (maxima, minima, and saddle points) in the lattices of the above materials are found. The data obtained are used to analyze the chemical bond nature in Sb2Te3.

Theoretical study of structural, electronic and optical properties of bismuth-selenide, bismuth-telluride and antimony-telluride/graphene heterostructure for broadband photodetector

Abstract: It remains challenging to produce high-performance broadband photodetector that can detect light from infrared to ultraviolet frequency range for biomedical imaging, gas sensing and optical communication applications. In particular, large energy band gap and low optical absorption in the material utilized as absorbing layer have prevented a report of high performance broadband photodetector in terms of quantum efficiency and photoresponsivity. However, integrating second generation topological insulators (2GTI), namely, bismuth selenide (Bi2Se3), bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) with graphene in a heterostructure appears to be the more promising approach. In this heterostructure, optical absorption takes place in 2GTI while graphene acts as charge carrier collector owing to its high carrier mobility. Therefore, detailed knowledge of the design, as well as structural, electronic and optical properties of 2GTI/graphene heterostructures, is essential to expose their hidden potentials. Structural properties of Bi2Se3, Bi2Te3, and Sb2Te3 are studied by first-principles calculations within density functional theory (DFT) framework. Many-body perturbation theory (MBPT) based one-shot GW (G0W0) and Bethe-Salpeter equation (G0W0-BSE) approaches were used to compute the quasiparticle (QP) band structure, excitonic and optical properties. The DFT calculations show that inclusion of van der Waals (vdW) correction with most recent developed Coope’s exchange (vdW-DFC09x) reproduce experimental interlayer distances, lattice parameters and atomic coordinates of Bi2Se3, Bi2Te3 and Sb2Te3 2GTI. The one-shot GW calculations confirm that Bi2Se3 and Sb2Te3 are direct band gap materials with band gap values of 0.36 eV and 0.22 eV while Bi2Te3 is indirect band gap material with 0.17 eV energy band gap. The results on the optical properties of 2GTI with inclusion of electron-hole interaction show that the exciton energy for Bi2Se3, Bi2Te3, and Sb2Te3 are 0.28, 0.14 and 0.19 eV respectively while their corresponding plasma energies are 16.4, 15.6 and 9.6 eV respectively. These values show that the investigated materials can absorb photons within broadband wavelengths. For the design, the energy analysis of Sb2Te3/graphene heterostructure reveals that the most stable configuration is the one in which the Te-1 atom of Sb2Te3 facing to graphene is above the hole centre of graphene’s hexagonal lattice. More attractively, the system of Sb2Te3/graphene heterostructure shows that strong hybridization between Sb2Te3 and graphene at smaller interlayer distance resulted in an energy gap at the Dirac states. It is, therefore, anticipated that this heterostructure will be useful for new-generation optoelectronic applications particularly in broadband photodetectors.

Rapid optical determination of topological insulator nanoplate thickness and oxidation

Abstract: The stability of 2D antimony telluride (Sb2Te3) nanoplates in ambient conditions is elucidated. These materials exhibit an anisotropic oxidation mode, and CVD synthesized samples oxidize at a much faster rate than exfoliated samples investigated in previous studies. Optical measurement techniques are introduced to rapidly measure the oxidation modes and thickness of 2D materials. Auger characterization were conducted to confirm that oxygen replaces tellurium as opposed to antimony under ambient conditions. No surface morphology evolution was detected in AFM before and after exposure to air. These techniques were employed to determine the origin of the thickness dependent color change effect in Sb2Te3. It is concluded that this effect is a combination of refractive index change due to oxidation and Fresnel effects.

Facile Control of Interfacial Energy-Barrier Scattering in Antimony Telluride Electrodeposits

Abstract: The augmented thermoelectric performance of nanocrystalline antimony telluride (Sb2Te3) films is investigated by introducing interfacial energy-barrier scattering (i.e., barrier heights), which occurs at both the grain boundaries and the interfaces with embedded second phases. It is postulated that the barriers created at both the interfaces and boundaries filter the low-energy carriers, thus favoring a high Seebeck coefficient. A facile, but high-precision composition-controlled electrodeposition technique is employed to synthesize single-phase nanocrystalline Sb2Te3 and nanocomposite Te/Sb2Te3. Both the initial composition of the Sb-Te solid solution and the post-annealing profiles are varied to control the grain size, as well as the formation of second-phase Te. The electrical and thermoelectric properties are measured and correlated with the physical properties, where an enhanced Seebeck coefficient at a fixed carrier concentration is interpreted as indicating that the energy-dependent carrier filtering effect is in force. On a promising note, modification of the Sb2Te3 film physical properties and formation of the second phase affect the interfacial energy-barrier scattering and yields an enhanced power factor. Thus, Sb2Te3 film is a promising p-type thermoelectric material for a room-temperature-operational micro-thermoelectric power generator.

Electrochemical Formation of p-Type Bi0.5Sb1.5Te3 Thick Films onto Nickel

Abstract: Bismuth-telluride-based alloys are currently the best commercially available thermoelectric materials for applications at room temperatures. Up to 150 micron thick layers of bismuth antimony telluride (Bi0.5Sb1.5Te3) were directly deposited onto nickel by either potenstiostatic or potentiodynamic electrodeposition. Cyclic voltammetry was employed to identify the optimal deposition potential. The films were characterized by scanning electron microscopy, energy dispersive X-rays and X-ray diffraction. The p-type films were found to be well adherent, uniform and stoichiometric with a high power factor of 2.3 × 10−4 W m−1 K−2 at film growth rates of up to 40 μm h−1.

Transport properties of electrically sintered bismuth antimony telluride with antimony nanoprecipitation

Abstract: Enhanced carrier mobility and reduced lattice thermal conductivity are essential for high-performance thermoelectric materials. In this letter, the influences of current-induced grain-boundary modification and nanoprecipitation on electrical and thermal transport properties of bismuth antimony telluride (BST) are investigated. With the passage of a high-density pulsed current (∼103 A/cm2), the electrically sintered BST exhibits a two-time enhancement in carrier mobility while maintaining a low lattice thermal conductivity compared to the hot-pressed BST. The modified transport properties are attributed to the reduced carrier scattering at grain boundaries and the increased phonon scattering by Sb nanoprecipitates in the electrically sintered BST. A numerical estimation based on the modified Callaway's model is provided to reveal the impact of nonoprecipitates on phonon transport in BST.

Thermoelectric film material and production process

Abstract: The present invention discloses a thermoelectric thin film material and a production process thereof The production process of the thermoelectric thin film material comprises the steps of synthesizing a thermoelectric material base material, preparing a slurry, preparing a thermoelectric thin film base body, carrying out sintering treatment and the like According to the thermoelectric thin film material and the production process thereof of the invention, a silk-screen printing technology is adopted to print the slurry on a flexible bearing base, and therefore, a process bottleneck that a thin film is deposited on a low-melting point flexible bearing base through using a high-melting point thermoelectric material can be broken through; a sectional type sintering treatment mode is adopted to sinter the dried thermoelectric thin film base body, since the sectional type sintering treatment mode has the characteristics of high heating speed, short sintering time and low sintering temperature, the low melting point requirement of the flexible bearing base can be satisfied; secondary crystallization can be realized better, and therefore, the compactness of bismuth telluride and antimony telluride after recrystalization can reach 88% to 90%; and therefore, the material obtained through synthesis is dense in surface, the specific heat capacity of the material is higher, and the material has a good heat end and cold end and can meet market demands

Fabrication and Characterization of PLD-Grown Bismuth Telluride (Bi 2 Te 3 ) and Antimony Telluride (Sb 2 Te 3 ) Thermoelectric Devices

Abstract: We report on the fabrication and characterization of multi-leg bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thermoelectric devices. The two materials were deposited, on top of SiO2/Si substrates, using Pulsed Laser Deposition (PLD). The SiO2 layer was used to provide insulation between the devices and the Si wafer. Copper was used as an electrical connector and a contact for the junctions. Four devices were built, where the Bi2Te3 and Sb2Te3 were deposited at substrate temperatures of 100°C, 200°C, 300°C and 400°C. The results show that the device has a voltage sensitivity of up to 146 μV/K and temperature sensitivity of 6.8 K/mV.

Plasmonic response of chalcogenides and switchable all-dielectric metamaterials

Abstract: Crystalline germanium antimony telluride shows a profound plasmonic response in the optical-UV spectral range that disappears in the chalcogenides’s amorphous state. We harness this effect to realize tuneable and plasmonic/all-dielectric phase-change memory metasurfaces.

Q-switched erbium doped fiber laser using antimony telluride-polyvinyl alcohol (Sb2Te3-PVA) as saturable absorber

Abstract: Q-switched erbium doped fiber laser was demonstrated using antimony telluride (Sb2 Te3 ) as saturable absorber (SA). The SA was fabricated by adding Sb3Te2 powder into PVA suspension and left dry in room temperature for two days. Then, the SA was sandwiched in between two FC/PC fiber ferrules, which can provide easy integration and flexibility into the laser cavity. Stable and self-started Q-switched laser operates at 1531 nm center wavelength. The laser repetition rate increased from 54.5 kHz to 88.4 kHz and pulse duration decreased from 6.84 μs to 4.58 μs as the pump power increased. A signal to noise ratio value of 55 dB was achieved at pump power 130 mW. At the maximum pump power, the average output power and pulse energy are 0.26 mW and 2.78 nJ.

Q-switching and mode-locking pulse generation in Ytterbium-doped fiber lasers using nanomaterial saturable absorbers / Ahmed Hasan Hamood al-Masoodi

Abstract: This research work focuses on exploring various new nanomaterials for saturable absorber (SA) application in generating Q-switched and Mode-locked pulses operating at 1 μm region These nanomaterials are Molybdenum disulfide (MoS2), Black Phosphorus (BP), Topological Insulator (TI): Bismuth (III) Selenide (Bi2Se3), Bismuth (III) Telluride (Bi2Te3), and antimony telluride (Sb2Te3), and metal oxide: Nickle Oxide (NiO) nanoparticles and cobalt oxide (Co3O4) nanocubes The fiber laser employs Ytterbiumdoped fiber (YDF) as a gain medium Firstly, molybdenum disulfide (MoS2) was proposed The Q-switched laser was obtained by using few layers MoS2, which was mechanically exfoliated by using a scotch tape The SA was sandwiched between two fiber ferrules to form a fiber compatible Q-switcher By incorporating the SA inside the YDFL cavity, a stable pulse laser operating at 10702 nm wavelength was generated with the repetition rate was tunable from 3817 to 2525 kHz A passively mode-locked YDFL was demonstrated using a few layered MoS2 film which was obtained by a liquid phase exfoliation technique The mode-locking pulses have a repetition rate of 188 MHz and pulse energy of 01 nJ Secondly, mechanically exfoliated Black phosphorus (BP) was proposed for both Q-switching and mode-locking pulses generation The Q-switched laser has a pump threshold of 551 mW, a pulse repetition rate that is tunable from 82 to 329 kHz, the narrowest pulse width of 108 μs and the highest pulse energy of 328 nJ BP based mode-locked YDFL was obtained by improving the SA preparation The laser operated at 103376 nm with a fixed repetition rate of 10 MHz Passively Q-switched YDFLs was also successfully demonstrated using a few-layers Bi2Se3, Bi2Te3 and antimony telluride (Sb2Te3) based SAs For instance, a Sb2Te3 film based Q-switched YDFL produced pulse repetition rate, which was tunable from 244 to 55 kHz with the maximum pulse energy of 2526 nJ at 823 mW pump power The mode-locked YDFL operating at 242 MHz repetition and 188 ps pulse width were also realized with Sb2Te3 based SA Finally, two transition metal oxide nanomaterials: Nickel Oxide (NiO) and cobalt oxide (Co3O4) were embedded into a polymer film, making it an SA device for both Q-switched and mode-locked YDFLs Stable Q-switched and mode-locked YDFLs were realized with both materials For instance, the mode-locked Co3O4 based YDFL was operated at 10358 nm wavelength with a fixed repetition rate of 20 MHz and picoseconds pulse width In short, an efficient and low-cost Q-switched and mode-locked YDFLs operating in 1 μm region have been successfully achieved by utilizing various new nanomaterials as SA

Chalcogenide phase change materials: An electronic perspective

Abstract: Recently, phase change materials (PCMs) have gathered attention as promising systems for a variety of emerging electronic and optoelectronic applications, including digital memory, RF switches, and switchable absorbers [1-4]. Of particular interest for electronic applications are the chalcogenide glasses, which can be repeatedly switched between two distinct, non-volatile solid phases: crystalline and amorphous, where the crystalline phase is commonly electrically conductive and the amorphous phase is generally electrically resistive. Ternary chalcogenide glasses, such as germanium antimony telluride (GeSbTe or “GST”), have been extensively examined for applications in PCM-based nonvolatile memory [5, 6]. More recently, the binary chalcogenide germanium telluride (GeTe) has gained attention for applications in RF switching due to its very low resistance in the crystalline state, relatively high amorphous-to crystalline resistance ratio (which has been found to be up to 107 in thin films), and excellent RF performance (e.g., bandwidth > 10 THz, TOI > 65 dBm) [3]. Despite significant research efforts, our understanding of electronic transport in these materials, principally in relation to RF operation and behavior, remains limited. In this presentation, we will discuss recent work at the US Naval Research Laboratory targeted at better understanding the electronic behavior of chalcogenide-based PCM devices, particularly under high-field and variable temperature conditions, with a view towards advancing the field of PCM-based reconfigurable electronics.