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Thermoelectrics are an important class of materials with great potential in alternative energy applications. In this study, two-dimensional (2D) nanoplates of the layered chalcogenides, Sb2Te3 and Bi2Te3, are synthesized and composites of the two are investigated for their thermoelectric properties. The two materials, Sb2Te3 and Bi2Te3, were synthesized as hexagonal, 2D nanoplates via a colloidal polyol route. The as-synthesized Sb2Te3 and Bi2Te3 vary drastically from one another in their lateral and vertical dimensions as revealed by scanning electron microscopy and atomic force microscopy. The single crystalline nanoplate nature is deduced by high-resolution transmission electron microscopy and selected area electron diffraction. Nanoplates have well-defined hexagonal facets as seen in the scanning and transmission electron microscopy images. The nanoplates were consolidated as an anisotropic nanostructured pellet via spark plasma sintering. Preferred orientation observed in the powder X-ray diffraction pattern and scanning electron microscopy images of the fractured pellets confirm the anisotropic structure of the nanoplates. Thermoelectric properties in the parallel and perpendicular directions were measured, revealing strong anisotropy with a significant reduction to thermal conductivity in the perpendicular direction due to increased phonon scattering at nanoplate interfaces. All compositions, except that of the 25% Bi2Te3 nanoplate composite, behave as degenerate semiconductors with increasing electrical resistivity as the temperature increases. The Seebeck coefficient is also increased dramatically in the nanocomposites, the highest reaching 210 μV/K for 15% Bi2Te3. The increase in Seebeck is attributed to energy carrier filtering at the nanoplate interfaces. Overall, these enhanced thermoelectric properties lead to a drastic increase in the thermoelectric performance in the perpendicular direction, with zT ∼ 1.26, for the 15% Bi2Te3 nanoplate composite at 450 K.

Scanning transmission electron microscopy (STEM) techniques are used to improve the understanding of out‐of‐plane oriented Sb2Te3 thin films deposited by sputtering on SiO2 and Si substrates. Nanobeam precession electron diffraction, energy‐dispersive X‐ray spectroscopy, and high‐angle‐annular dark‐field imaging show that the presence of 1–2 atomic planes of Te on top of the substrate is a crucial factor for successful growth of such films, which can be achieved by optimizing cosputtering of Te and Sb2Te3 targets. The formation of an actual van der Waals (vdW) gap between the substrate and the first Sb2Te3 quintuple layer allows for vdW epitaxy. This gap is larger than those separating Te planes in the pseudo‐2D Sb2Te3 structure. HAADF image analysis provides detailed information on the atomic arrangement such as interplanar distances, vdW gaps, and Debye–Waller coefficients, all these with a few pm precision. For the anisotropic atomic displacements, a new methodology is introduced based on the statistical analysis of atomic column positions that provides information on the low‐frequency phonon modes. Ab initio calculations are used to support our results. Overall, this study provides quantitative STEM tools particularly well suited for nonperiodic pseudo‐2D materials, such as Sb2Te3/GeTe superlattices. [ABSTRACT FROM AUTHOR]

Abstract Matching of various chalcogenide films shows the advantage of delivering multilayer heterostructures whose physical properties can be tuned with respect to the ones of the constituent single films. In this work, (Ge–Sb–Te)-based heterostructures were deposited by radio frequency sputtering on Si(100) substrates and annealed up to 400 °C. The as-deposited and annealed samples were studied by means of X-ray fluorescence, X-ray diffraction, scanning transmission electron microscopy, electron energy loss spectroscopy and Raman spectroscopy. The heterostructures, combining thermally stable thin layers (i. e. Ge-rich Ge5.5Sb2Te5, Ge) and films exhibiting fast switching dynamics (i. e. Sb2Te3), show, on the one side, higher crystallization-onset temperatures than the standard Ge2Sb2Te5 alloy and, on the other side, none to minimal Ge-segregation.

Matching of various chalcogenide films shows the advantage of delivering multilayer heterostructures whose physical properties can be tuned with respect to the ones of the constituent single films. In this work, (Ge–Sb–Te)-based heterostructures were deposited by radio frequency sputtering on Si(100) substrates and annealed up to 400 °C. The as-deposited and annealed samples were studied by means of X-ray fluorescence, X-ray diffraction, scanning transmission electron microscopy, electron energy loss spectroscopy and Raman spectroscopy. The heterostructures, combining thermally stable thin layers (i. e. Ge-rich Ge5.5Sb2Te5, Ge) and films exhibiting fast switching dynamics (i. e. Sb2Te3), show, on the one side, higher crystallization-onset temperatures than the standard Ge2Sb2Te5 alloy and, on the other side, none to minimal Ge-segregation. [ABSTRACT FROM AUTHOR]

Topological insulators have recently received attention in optoelectronic devices because of their high mobility and broadband absorption resulting from their topological surface states. In particular, theoretical and experimental studies have emerged that can improve the spin generation efficiency in a topological insulator‐based p–n junction structure called a TPNJ, drawing attention in optospintronics. Recently, research on implementing the TPNJ structure is conducted; however, studies on the device characteristics of the TPNJ structure are still insufficient. In this study, the TPNJ structure is effectively implemented without intermixing by controlling the annealing temperature, and the photocharacteristics appearing in the TPNJ structure are investigated using a cross‐pattern that can compare the characteristics in a single device. Enhanced photo characteristics are observed for the TPNJ structure. An optical pump Terahertz probe and a physical property measurement system are used to confirm the cause of improved photoresponsivity. Consequently, the photocharacteristics are improved owing to the change in the absorption mechanism and surface transport channel caused by the Fermi level shift in the TPNJ structure. [ABSTRACT FROM AUTHOR]

Sb 2-x Cr x Te 3 quantum dots (QDs) were synthesized in a host glass matrix through fusion and heat treatment methods. The results revealed the specific effects inherent to the doping of Cr3+ ions in diluted magnetic semiconductors (DMS) (Sb 2-x Cr x Te 3 QDs embedded in glass matrix). Differential Thermal Analysis shows evidence of changes in glass transition and the host glass's crystallization temperatures with the presence of Sb 2-x Cr x Te 3 QDs. Transmission electron microscopy (TEM) images and energy dispersive X-ray analysis evidenced the formation, size, and composition of these DMS QDs. The interplanar distances d hkl measured in TEM and the pattern observed in electron diffraction from the selected area reinforces the Sb 2 Te 3 crystalline nature. Structural analyses of x-ray diffraction patterns confirm that all Sb 2-x Cr x Te 3 QDs crystallize in the rhombohedral R 3 _ m − D 3 d 5 structure and that Cr3+-ions had replaced Sb3+-ions. Electronic paramagnetic resonance (EPR) spectra exhibit resonance signals confirming Cr3+ ion incorporation into the Sb 2 Te 3 crystal lattice. Moreover, EPR shows that the sp-d exchange interactions become less pronounced with the formation of Cr3+ ─ Cr3+ pairs. Raman scattering spectroscopy confirmed the formation of Sb2-xCrxTe3 QDs. The red and blue shifts of the normal Raman- and IR-active vibrational modes characteristic of Sb 2 Te 3 give strong evidence of the Cr3+ ion incorporation in QDs. Interestingly, the study results revealed better structural and magnetic properties. We believe that these Sb2-xCrxTe3 QDs in SNAB glass, with appropriate dopant concentration and chemical composition, are potentially efficient for thermoelectric, topological insulators, photovoltaic devices, solar cells, magnetic devices and spintronic applications. [ABSTRACT FROM AUTHOR]

Flexible thin‐film thermoelectric devices (TEDs) can generate electricity from the heat emitted by the human body, which holds great promise for use in energy supply and biomonitoring technologies. The p‐type Sb2Te3 hexagon nanosheets are prepared by the hydrothermal synthesis method and compounded with Ti3C2Tx to make composite films, and the results show that the Ti3C2Tx content has a significant impact on the thermoelectric properties of the composite films. When the Ti3C2Tx content is 2 wt%, the power factor of the composite film reaches ≈59 µW m−1 K−2. Due to the outstanding electrical conductivity, high specific surface area, and excellent flexibility of Ti3C2Tx, the composite films also exhibit excellent thermoelectric and mechanical properties. Moreover, the small addition of Ti3C2Tx has a negligible effect on the phase composition of Sb2Te3 films. The TED consists of seven legs with an output voltage of 45 mV at ΔT = 30 K. The potential of highly flexible thin film TEDs for wearable energy collecting and sensing is great. [ABSTRACT FROM AUTHOR]

Это исследование сосредоточено на моделировании методами DFT воздействия одноосного давления на электронные и структурные характеристики двумерных материалов, таких как MoTe2 и Sb2Te3. Особое внимание уделяется реконфигурации щели ван-дер-Ваальса (вдВ). Интуитивно, при приложении одноосного давления ожидается уменьшение расстояния между слоями и, как следствие, переход 2D–3D. Моделирование Sb2Te3 под одноосным давлением выявило металлизацию при 3 ГПа. Дополнительное увеличение давления вызывает изменение симметрии и фазовый переход при 7 ГПа, что приводит к исчезновению щели вдВ в новой фазе. Тем не менее переход к объемной фазе не всегда происходит. В случае MoTe2 под воздействием давления происходит изоструктурный переход в металлическое состояние при 10 ГПа. Дальнейшее увеличение давления при 37 ГПа вызывает фазовый переход с реконфигурацией щели вдВ. Важно отметить, что данный случай MoTe2 аналогичен ситуации с GaSe после релаксации, что также является предметом данного исследования.

Abstract Flexible thin‐film thermoelectric devices (TEDs) can generate electricity from the heat emitted by the human body, which holds great promise for use in energy supply and biomonitoring technologies. The p‐type Sb2Te3 hexagon nanosheets are prepared by the hydrothermal synthesis method and compounded with Ti3C2Tx to make composite films, and the results show that the Ti3C2Tx content has a significant impact on the thermoelectric properties of the composite films. When the Ti3C2Tx content is 2 wt%, the power factor of the composite film reaches ≈59 µW m−1 K−2. Due to the outstanding electrical conductivity, high specific surface area, and excellent flexibility of Ti3C2Tx, the composite films also exhibit excellent thermoelectric and mechanical properties. Moreover, the small addition of Ti3C2Tx has a negligible effect on the phase composition of Sb2Te3 films. The TED consists of seven legs with an output voltage of 45 mV at ΔT = 30 K. The potential of highly flexible thin film TEDs for wearable energy collecting and sensing is great.

Sb2Te3 is an important thermoelectric material. Co is a potential diffusion barrier. This study examined the electroplated Co/Sb2Te3 interfacial reactions at 300 °C, 400 °C and 500 °C. To provide fundamental information and for better understanding the reaction paths, the Co-Sb-Te phase equilibria isothermal sections at these three temperatures are proposed. No ternary compound is found. The 400 °C isothermal section contains (Co), (Sb), (Te), β-CoSb, β-Co1−xTe, CoSb3, δ-(Sb2Te), γ-(SbTe), Sb2Te3 and a continuous solid solution γ-Co(Sb,Te)2. At 500 °C, except for Te being molten, the phase relationships are similar to those at 400 °C. At 300 °C, although γ-CoSb2 and γ-CoTe2 have very significant mutual solubilities, they are two separate phases and do not form a continuous solid solution. In the Co/Sb2Te3 couple reacted at 300 °C, only one reaction phase, γ-CoTe2 with Sb solubility, is formed. Similar results are found in the Co/Sb2Te3 couple reacted 400 °C, and the reaction phase is the continuous solid solution γ-Co(Sb,Te)2. Two reaction phases, β-Co1-xTe and γ-Co(Sb,Te)2, are found in the couple reacted at 500 °C. The compositional ratio of Sb/Te in the reaction phase remained at 2/3 indicates that Co is the dominating diffusion species. The reaction phases are formed rapidly by Co penetration into the Sb2Te3 substrate. A peculiar phenomenon was found with the reaction layer that formed on the side of Co that was not in direct contact with the Sb2Te3 substrate which will be further investigated. [ABSTRACT FROM AUTHOR]

Sb2Te3 is an important thermoelectric material. The interfacial reactions in the Ni/Sb2Te3 and Co0.2Ni0.8/Sb2Te3 couples are examined to verify if Ni and Co0.2Ni0.8 are suitable barrier layer materials. The Ni-Sb-Te phase equilibria isothermal sections and Co-Ni-Sb-Te isothermal tetrahedrons are proposed to provide fundamental information and for better understanding of the interfacial reactions. Only one reaction phase, λ2-NiSb1−xTe2x, is observed in the Ni/Sb2Te3 couples reacted at 200°C, 300°C, and 400°C. When reacting at 500°C for 6 h, the reaction phase is λ1-Ni(Sb1−xTex)1+y. With a longer reaction time, the second phase, Ni5.66SbTe2, is formed. Note, the compositional ratios of Sb/Te of all the reaction phases remain as 2/3. The result indicates that Ni is the dominating diffusion species. The reaction results in the Co0.2Ni0.8/Sb2Te3 couples are similar to those in the Ni/Sb2Te3 couples. The reaction phase at 400°C is λ2-NiSb1−xTe2x , and are λ1-Ni(Sb1−xTex)1+y + Ni5.66SbTe2 phases at 500°C with a longer reaction time. The compositional ratios of Sb/Te in the reaction phases are also 2/3, and the Co contents in the reaction phases are very limited. Ni is also the dominating diffusion species in the Co0.2Ni0.8/Sb2Te3 couples. [ABSTRACT FROM AUTHOR]

The results of study of charge transfer processes in thin amorphous and crystalline Sb2Te3 films in a wide range of frequencies and temperatures are presented. The frequency spectra of conductivity were obtained by the dielectric spectroscopy method. The authors analyzed the frequency dependences of the conductivity in the electric field and the temperature dependences of the exponent s. A transition from the classical correlated barrier hopping (CBH) to quantum mechanical tunneling (QMT) was observed at a certain temperature Tt. The CBH model allowed the authors to calculate the conductivity parameters of two phases. Two areas with different types of conductivity were revealed on the conduction spectra, and the activation energies of charge transfer processes for amorphous and crystalline films were determined. The following features were discovered: the difference in the temperatures of the change of the charge transfer mechanism and the transition from the semiconductor region to the metal region on the temperature dependence of conductivity. They can help to identify the amorphous phase in the quasi-binary chalcogenide Sb2Te3-GeTe system. [ABSTRACT FROM AUTHOR]

Sb 2 Te 3 -based alloys exhibit decent thermoelectric transport properties in the mid-temperature range above 550 K. However, the study on Sb 2 Te 3 alloys has been limited in simple doping approach. Herein, evolution in the thermoelectric transport properties associated with the phase formation of solid solution alloys of Sb 2 (Te 1− x Se x) 3 (x = 0, 0.25, 0.33, 0.5, 0.75, and 1.0) compositions is investigated to widen the strategy to solid solution alloying. A single phase of the Sb 2 Te 3 rhombohedral structure formed from x = 0 to 0.5, whereas mixed phases with an orthorhombic structure of Sb 2 Se 3 was observed at x = 0.75. The electrical conductivity weighted mobility were gradually decreased as Se content increases to x = 0.75. Consequently, the power factor was decreased gradually and significantly to 0.076 mW/mK2 for x = 0.75 (Sb 2 (Te 0·25 Se 0.75) 3) compared with 2.6 mW/mK2 of the pristine sample. The total thermal conductivity of 2.0 W/mK for the Sb 2 Te 3 was significantly reduced gradually to 0.64 W/mK for x = 0.75 owing to simultaneous decrease in electrical and lattice thermal conductivities. The reduction in lattice thermal conductivity is mainly owing to the addition point defect scattering caused by the Se addition. Nevertheless, thermoelectric figure of merit zT of Sb 2 Te 3 is gradually decreased from 0.64 to 0.11 for x = 0.75 at 650 K due to the degradation in electrical transport properties. Furthermore, the theoretical zT was estimated for all samples with varying carrier concentration based on single parabolic band model. [ABSTRACT FROM AUTHOR]

Micron‐sized Sb2Te3 nanosheets are grown on p‐type Si substrate by facile vapor‐phase route. Physicochemical properties of the Sb2Te3 nanosheets are revealed using X‐ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), transmission electron microscope (TEM), Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS). Owing to their high aspect ratio, field emission (FE) characteristics of the Sb2Te3 nanosheets grown on Si substrate (termed as a "planar emitter") are investigated. Furthermore, the FE behavior of a single Sb2Te3 nanosheet attached to a blunt tungsten needle is studied. The single nanosheet emitter exhibited superior emission behavior in contrast to the planar emitter. The Fowler–Nordheim (F–N) plot for the single nanosheet emitter exhibits linear nature, whereas for the planar emitter it shows deviation from linearity. An attempt has been made to reveal the FE properties of a single Sb2Te3 nanosheet in an "in‐plane" configuration, similar to the vacuum field emission transistor (VFET). In this case, a maximum emission current of 1 μA is observed at 290 V, which is comparable to other VFETs. The observed results clearly imply the potential of the single nanosheet emitters due to topological insulators, like Sb2Te3, for the development of new generation nanoscale vacuum electronic devices. [ABSTRACT FROM AUTHOR]

The phase change material Sb 2 Te 3 (ST) exhibits a fast-switching speed and poor thermal stability because the four-fold rings are dominant and homo-polar bonds are absent in the amorphous state. Many studies have been performed on the improvement of phase change properties. Chemical doping methods have been widely used because additional chemical bonds are formed between the doped element and host atoms, leading to the modification of the local structure and electronic band structure. Previous reports have indicated the importance of the bond length and lattice mismatch in element doped ST. In this study, the electronegativity of the doped elements was investigated because it determines the strength of the bond via charge transfer between two atoms. A strong correlation between the electronegativity of the doped element and the phase change properties of the doped ST was observed. An ideal electronegativity range, which corresponds to some elements doped ST with excellent thermal stability, was found in this investigation. Nb atoms were selected as the optimal dopant to stabilize the amorphous phase of ST because Nb was in the ideal range. Additional homo-polar bonds and Nb-Te bonds can stabilize the amorphous phase because additional energy is required for ring reconstruction during crystallization. Consequently, the thermal stability and resistance difference of the Nb doped ST were significantly improved. In addition, the phase change speed of ST was not affected by Nb doping. This study highlights a new approach for pursuing better properties of phase change materials by chemical doping methods. • Electronegativity of doped element plays a crucial role in tailoring the Sb 2 Te 3 (ST) properties. • An ideal electronegativity range corresponds to the elemental doping of ST. • Nb was selected as the optimal dopant to stabilize the amorphous phase of ST. • The Nb-ST material is a potential candidate for PCM applications. • This work provides a new approach for pursuing better properties by doping methods. [ABSTRACT FROM AUTHOR]

[Display omitted] • (Bi, In) co-doped in Sb 2 Te 3 for synergistic optimization of electrical and thermal transport properties. • The high power factor is ascribed to the increase in effective mass and state density after Bi doping. • Further In co-doping can increase electrical conductivity and decrease thermal conductivity. • High power factor of 21.06 μWcm−1K−2 in (Bi, In) co-doped Sb 2 Te 3 film is obtained. • A flexible device prepared by co-doped films represents the competitive power density of ∼5.47 × 102 μWcm−2. Sb 2 Te 3 thermoelectric thin film is one of the best competitive candidates for preparing self-powered wearable micro-electronic devices. However, the interdependent relationship between Seebeck coefficient, electrical conductivity and thermal conductivity limits the improvement of thermoelectric properties. In this work, we demonstrate maximum power factor of 21.06 μWcm−1K−2 and a high average power factor of 18.77 μWcm−1K−2 in (Bi, In) co-doped Sb 2 Te 3 flexible thin film. The high power factor is ascribed to the increase in effective mass and state density after Bi doping proved by first-principles calculations and experiments, which leads to an increase in the Seebeck coefficient. Further In co-doping can increase the carrier concentration, which not only improve the electrical conductivity, but also suppress the bipolar excitation and inhibit carrier migration in the opposite direction. Moreover, the estimated thermal conductivity for the prepared thin films is low due to the enhancement of phonon scattering caused by the introduction of interfaces and defects, resulting in high ZT. A flexible device prepared by co-doped thin film represents the competitive power density of ∼ 5.47 × 102 μWcm−2 at temperature difference of 36 K. All the results confirm that hole co-doping strategy can efficiently enhance the collaborative regulations of the carrier and phonon transportation to realize high thermoelectric performance in Sb 2 Te 3 flexible thin film. [ABSTRACT FROM AUTHOR]

We successfully demonstrate Q-switched fiber laser with a 20 cm long Hafnium-Bismuth-Erbium codoped fiber (HBEDF) as an active medium in conjunction with Antimony Telluride (Sb2Te3) saturable absorber (SA). The HBEDF has an Erbium ion absorption coefficient of 100 dB/m at 980 nm; thus, the laser setup only requires a very short length of gain medium for lasing in the 1550 nm range. We realize the Sb2Te3 SA obtained by embedding the material into Polyvinyl Alcohol (PVA), and a Q-switched pulse train operating at 1560.7 nm is realized, using only a 20 cm long active fiber, when the prepared Sb2Te3 thin film is integrated into the laser ring cavity. The repetition rate of the Q-switched pulses is tunable from 47.7 to 74.8 kHz as the pump power is raised from the threshold value equal to 69.9 mW to a value of 105.0 mW. The maximum attainable pulse energy is 31.2 nJ. Our results indicate that the Sb2Te3 material is useful as an effective Q-switcher especially for the laser operation in 1.55 μm range. [ABSTRACT FROM AUTHOR]

The influence of magnetic dopants on the transport properties of topological insulators is of great interest. In this work, studies on the impact of Fe− ion implantation on the physical and electronic properties of Sb2Te3 thin films have been done. The implantation was done with low-energy Fe− ions at three different fluences (1 × 1013, 1 × 1014, and 5 × 1014 ions/cm2). The film thickness was estimated using Rutherford backscattering spectroscopy (RBS). Magnetic force microscopy (MFM) topographic image showed the Fe− ion-induced magnetization in thin films. Overall enhancement in the electrical resistivity with increasing implantation dose was observed in the temperature-dependent transport measurements. However, the mobility of the carriers was found to decrease with increasing fluence. The Hall measurements showed that the carrier concentration initially increased with the fluence up to 1 × 1014 ions/cm2, but further increase in the fluence results in a decrease in the carrier concentration. P-type nature of the dominant charge carriers was observed for all the fluences except the highest dose where a change in the type of carriers from p-type to n-type was observed. It can be explained based on Fe− ion implantation-induced donors as well as acceptors like defects. [ABSTRACT FROM AUTHOR]

Abstract One central task of developing nonvolatile phase change memory (PCM) is to improve its scalability for high‐density data integration. In this work, by first‐principles molecular dynamics, to date the thinnest PCM material possible (0.8 nm), namely, a monolayer Sb2Te3, is proposed. Importantly, its SET (crystallization) process is a fast one‐step transition from amorphous to hexagonal phase without the usual intermediate cubic phase. An increased spatial localization of electrons due to geometrical confinement is found to be beneficial for keeping the data nonvolatile in the amorphous phase at the 2D limit. The substrate and superstrate can be utilized to control the phase change behavior: e.g., with passivated SiO2 (001) surfaces or hexagonal Boron Nitride, the monolayer Sb2Te3 can reach SET recrystallization in 0.54 ns or even as fast as 0.12 ns, but with unpassivated SiO2 (001), this would not be possible. Besides, working with small volume PCM materials is also a natural way to lower power consumption. Therefore, the proposed PCM working process at the 2D limit will be an important potential strategy of scaling the current PCM materials for ultrahigh‐density data storage.

One central task of developing nonvolatile phase change memory (PCM) is to improve its scalability for high‐density data integration. In this work, by first‐principles molecular dynamics, to date the thinnest PCM material possible (0.8 nm), namely, a monolayer Sb2Te3, is proposed. Importantly, its SET (crystallization) process is a fast one‐step transition from amorphous to hexagonal phase without the usual intermediate cubic phase. An increased spatial localization of electrons due to geometrical confinement is found to be beneficial for keeping the data nonvolatile in the amorphous phase at the 2D limit. The substrate and superstrate can be utilized to control the phase change behavior: e.g., with passivated SiO2 (001) surfaces or hexagonal Boron Nitride, the monolayer Sb2Te3 can reach SET recrystallization in 0.54 ns or even as fast as 0.12 ns, but with unpassivated SiO2 (001), this would not be possible. Besides, working with small volume PCM materials is also a natural way to lower power consumption. Therefore, the proposed PCM working process at the 2D limit will be an important potential strategy of scaling the current PCM materials for ultrahigh‐density data storage. [ABSTRACT FROM AUTHOR]

One central task of developing nonvolatile phase change memory (PCM) is to improve its scalability for high‐density data integration. In this work, by first‐principles molecular dynamics, to date the thinnest PCM material possible (0.8 nm), namely, a monolayer Sb2Te3, is proposed. Importantly, its SET (crystallization) process is a fast one‐step transition from amorphous to hexagonal phase without the usual intermediate cubic phase. An increased spatial localization of electrons due to geometrical confinement is found to be beneficial for keeping the data nonvolatile in the amorphous phase at the 2D limit. The substrate and superstrate can be utilized to control the phase change behavior: e.g., with passivated SiO2 (001) surfaces or hexagonal Boron Nitride, the monolayer Sb2Te3 can reach SET recrystallization in 0.54 ns or even as fast as 0.12 ns, but with unpassivated SiO2 (001), this would not be possible. Besides, working with small volume PCM materials is also a natural way to lower power consumption. Therefore, the proposed PCM working process at the 2D limit will be an important potential strategy of scaling the current PCM materials for ultrahigh‐density data storage. [ABSTRACT FROM AUTHOR]

The properties of layered transition metal dichalcogenides intercalated with 3d metal ions are investigated. The influence of the gradient magnetic field at the intercalation front on the properties of intercalants is studied. It is shown that Co0.1Sb2Te3, Ni0.1Bi2Te3 and Ni0.2In4Se3 intercalates have ferromagnetic properties at room temperature. The dependences of the magnetic moment on the magnetic field strength along and across the layers of Co0.1Sb2Te3, Ni0.1Bi2Te3 and Ni0.2In4Se3 intercalates have the hysteresis loop. The obtained values of the coercive force of the studied samples are typical for hard ferromagnets. The properties of the obtained intercalates are determined by the crystal structure of layered crystals, localization and magnetic interaction of intercalant atoms between the layers of the crystal matrix and the influence of the magnetic field on the processes of exchange interaction between them. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Fuzhou University is the property of Journal of Fuzhou University, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

GeTe/Sb2Te3 superlattices (SLs) obtained by sputtering are integrated in phase‐change memory (PCM) devices with a "wall structure". The high structural quality of SLs deposited on TiN or SiNx layers, used as metallic bottom heater and dielectric bottom layer in PCM devices, is established by X‐ray diffraction, for as‐grown SLs and after an annealing corresponding to the maximum thermal budget during the integration process. Scanning transmission electron microscopy (STEM) images of SLs within PCM cells confirm that the SL structure is kept after integration. A robust statistical analysis on a large number of devices demonstrates unambiguously that the RESET current is lower in SL devices than in GeTe reference devices and decreases when the Sb2Te3 layer thickness in the SL increases from 2 to 8 nm. STEM imaging of a PCM cell incorporating an SL demonstrates that switching from the low‐ to the high‐resistance state occurs through a melting–quenching process and is not due to crystal–crystal transition or defect reorganization in the SL, in contrast to what is commonly stated in the literature on interfacial phase‐change memories (iPCMs). The origin of the improved switching performance of SL‐based PCM devices is discussed, linked with the impact of swapped bilayers. [ABSTRACT FROM AUTHOR]

Sb2Te3 is an end point of quasibinary GeTe–Sb2Te3 phase‐change alloys and also a prototypical topological insulator (TI). TIs are materials that behave like insulators in their interior but whose surfaces are characterized by metallic states with linear dispersion, the so‐called Dirac cones. Such surface states are symmetry protected, robust, and are maintained even in the presence of surface defects. It has been tacitly implied that any surfaces of a TI possess this property. Herein, using ab initio simulations, it is demonstrated that cleaving Sb2Te3 along certain side surfaces may lead to the disappearance of Dirac surface states. In particular, it is shown that the (110) surface of the typical TI Sb2Te3 is slightly gapped, whereas the (11¯0) surface is metallic. The significance and potential benefits of the obtained results for practical applications in planar devices and memory cells are discussed. [ABSTRACT FROM AUTHOR]

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Broadband photosensors have been widely studied in various kinds of materials. Experimental results have revealed strong wavelength-dependent photoresponses in all previous reports. This limits the potential application of broadband photosensors. Therefore, finding a wavelength-insensitive photosensor is imperative in this application. Photocurrent measurements were performed in Sb2Te3 flakes at various wavelengths ranging from visible to near IR light. The measured photocurrent change was insensitive to wavelengths from 300 to 1000 nm. The observed wavelength response deviation was lower than that in all previous reports. Our results show that the corresponding energies of these photocurrent peaks are consistent with the energy difference of the density of state peaks between conduction and valence bands. This suggests that the observed photocurrent originates from these band structure peak transitions under light illumination. Contrary to the most common explanation that observed broadband photocurrent carrier is mainly from the surface state in low-dimensional materials, our experimental result suggests that bulk state band structure is themain source of the observed photocurrent and dominates the broadband photocurrent. [ABSTRACT FROM AUTHOR]

A high-performance imipramine (IMPR) sensor has been developed based on metal chalcogenide-carbon composite materials. The antimony telluride-graphite nanofiber (Sb2Te3-GNF, hereafter SBT-GNF) composite was synthesized by the hydrothermal method and confirmed by X-ray powder diffraction (XRD) pattern. The morphology, crystalline lattice, and chemical states were characterized by HRTEM, SAED, and XPS analysis. The characterizations confirmed the formation of an effective composite, SBT-GNF. The SBT-GNF was fabricated as a disposable sensor electrode with a screen-printed carbon electrode (SPCE) and examined for the detection of IMPR by differential pulse voltammetry (DPV). The electroanalytical results of SBT-GNF are compared with the SBT and GNF, and the rational design of effective composite is discussed. SBT-GNF/SPCE showed a good linear range (0.01‑51.8 μM), sensitivity (1.35 ± 0.1 μA μM−1 cm−2), and low LOD (4 ± 2 nM). Moreover, the SBT-GNF/SPCE revealed high selectivity and high tolerance limit against potential interfering compounds in blood serum and urine samples. Therefore, this electrochemical sensor can be applicable for the detection of tricyclic antidepressant drug IMPR in clinical and pharmaceutical analysis. [ABSTRACT FROM AUTHOR]

Herein, experimental work on the ultrafast electron dynamics in the topological surface state (TSS) of three‐dimensional (3D) topological insulators (TIs) observed with time‐ and angle‐resolved two‐photon photoemission (2PPE) is reviewed. The focus is laid on the generation of ultrafast photocurrents and the time‐resolved observation of their decay. 2PPE not only allows to unambiguously relate the photocurrents to the spin‐polarized electronic surface states. Probing of the asymmetric momentum distribution of the electrons carrying the current makes it possible to study the microscopic scattering processes that govern the unusual electron transport in the time domain. Ultrashort mid‐infrared pump pulses permit not only a direct optical excitation of the TSS in Sb2Te3 but also lead to a strong asymmetry of the TSS population in momentum space. Two‐dimensional band mapping of the TSS shows that this asymmetry is in fact representative of a macroscopic photocurrent, while the helicity‐dependence of the photocurrent is found to be small. The time‐resolved observation of the photocurrent decay reveals a huge mean free path of the electrons in the TSS. [ABSTRACT FROM AUTHOR]

The electronic and transport properties of Sn-doped Sb2Te3 have been investigated by using the Heyd–Scuseria–Ernzerhof hybrid functional with spin orbit coupling. Results show that Sn preferentially substitute Sb to induce the p-type characteristics in Sb2Te3. Detailed thermodynamic examinations have been conducted to elaborate the favorability for Sn to act as a shallow acceptor in Sb2Te3. Extensive calculations of transport properties reveal that Sn doping gives rise to remarkable enhancements in hole mobility, electrical conductivity, Seebeck coefficient and power factor of Sb2Te3, thus significantly improving the thermoelectric performance. The present work offers a valuable insight on how Sn doping strongly influences the electronic and transport properties of Sb2Te3. [ABSTRACT FROM AUTHOR]

In recent years, thermoelectric materials that have the advantage of directly converting heat into electricity, have become a hot research topic. In this study, we designed a series of Sb _2 Te _3 nanofilms using molecular dynamics simulation to explore the effects of structural defects on the phonon transport properties of thermoelectric materials. We predicted that temperature variations and structural defects can greatly increase the transfer of energy invalid and decrease thermal conductivity. Designing thermoelectric materials as composite interfaces, multilayer films, and defect structures is an effective way to achieve this goal.

P-type Sb 2 Te 3 has been recognized as a potential thermoelectric material for applications in low-medium temperature ranges. However, its inherent high carrier concentration and lattice thermal conductivity led to a relatively low ZT value, particularly around room temperature. This study addresses these limitations by leveraging high-energy ball milling and rapid hot-pressing techniques to substantially enhance the Seebeck coefficient and power factor of Sb 2 Te 3 , yielding a remarkable ZT value of 0.55 at 323 K due to the donor-like effect. Furthermore, the incorporation of Nb─Ag co-doping increases hole concentration, effectively suppressing intrinsic excitations ≈548 K while maintaining the favorable power factor. Simultaneously, the lattice thermal conductivity can be significantly reduced upon doping. As a result, the ZT values of Sb 2 Te 3 -based materials attain an impressive range of 0.5-0.6 at 323 K, representing an almost 100% improvement compared to previous research endeavors. Finally, the ZT value of Sb 1.97 Nb 0.03 Ag 0.005 Te 3 escalates to 0.92 at 548 K with a record average ZT value (ZT avg ) of 0.75 within the temperature range of 323-573 K. These achievements hold promising implications for advancing the viability of V-VI commercialized materials for low-medium temperature application., (© 2023 Wiley‐VCH GmbH.)

2D van der Waals chalcogenides such as topological insulators and transition-metal dichalcogenides and their heterostructures are now at the forefront of semiconductor research. In this paper, we discuss the fundamental features and advantages of van der Waals bonded superlattices over conventional superlattices made of 3D materials and describe in more detail one practical example, namely, interfacial phase change memory based on GeTe–Sb2Te3 superlattice structures. [ABSTRACT FROM AUTHOR]

Interfacial phase-change memory (iPCM) based on layer-structured Ge-Sb-Te crystals has been recently proposed, offering an energy-efficient implementation of nonvolatile memory cells and supplementing the development of Ge-Sb-Tebased phase-change random access memories (PRAMs). Although the working principle of iPCM is still under debate, it is believed that layer-switching plays a role in the switching process between the low-resistance and high-resistance states of iPCM memory cells. However, the role of Ge in forming swapped bilayers—the key elements for layer-switching—is not yet clarified. This work manages to achieve layer-switching in Sb2Te3 thin films by manipulating the formation of bilayer defects using magnetron sputtering and post-thermal annealing. By combining scanning transmission electron microscopy (STEM) experiments with density functional theory (DFT) calculations, the essential role of Sb-Te intermixing is elucidated in stabilizing swapped bilayers at a low energy cost. In situ STEM experiments provide a real-time and real-space view of dynamical reconfiguration of van der Waals-like gaps in Sb2Te3 thin films under electron-beam irradiation. The results show that the Ge atoms are not necessary for the formation and motion of swapped bilayers, providing atomic insights on the layer-switching mechanism in layer-structured binary and ternary group V- and IV–V-tellurides for memory applications. [ABSTRACT FROM AUTHOR]

Interfacial phase-change memory (iPCM) based on layer-structured Ge-Sb-Te crystals has been recently proposed, offering an energy-efficient implementation of nonvolatile memory cells and supplementing the development of Ge-Sb-Tebased phase-change random access memories (PRAMs). Although the working principle of iPCM is still under debate, it is believed that layer-switching plays a role in the switching process between the low-resistance and high-resistance states of iPCM memory cells. However, the role of Ge in forming swapped bilayers—the key elements for layer-switching—is not yet clarified. This work manages to achieve layer-switching in Sb2Te3 thin films by manipulating the formation of bilayer defects using magnetron sputtering and post-thermal annealing. By combining scanning transmission electron microscopy (STEM) experiments with density functional theory (DFT) calculations, the essential role of Sb-Te intermixing is elucidated in stabilizing swapped bilayers at a low energy cost. In situ STEM experiments provide a real-time and real-space view of dynamical reconfiguration of van der Waals-like gaps in Sb2Te3 thin films under electron-beam irradiation. The results show that the Ge atoms are not necessary for the formation and motion of swapped bilayers, providing atomic insights on the layer-switching mechanism in layer-structured binary and ternary group V- and IV–V-tellurides for memory applications. [ABSTRACT FROM AUTHOR]

A highly textured pure Sb 2 Te 3 is fabricated via a hydrothermal method combined with high-pressure spark plasma sintering. The nanoscale texture gives rise to an extremely low thermal conductivity in the out-of-plane direction, while shows weak influence on the carrier mobility which reaches the level of single crystal. Microstructure analysis reveals large amount of low-angle boundaries, whose discriminated effect on scattering phonons and carriers should account for the observed phenomenon. Consequently, the structurally nanocrystalline electrical monocrystalline behavior leads to a high average ZT with peak value above 1 at 525 K, which is the best TE performance for undoped Sb 2 Te 3. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract In this work, a new idea of organic-inorganic hybridization was proposed to fabricate flexible p-type - Sb 2 Te 3 /CH 3 NH 3 I thin films. The CH 3 NH 3 I has a strong adsorption which can promote the growth of organic molecules, improve the crystallization, and finally increase electrical conductivity. Post-annealing of the fabricated films increased the phonon scattering, thus resulting in a reduction of thermal conductivity and an increased ZT value. The annealed hybrid-composite film showed a significant enhancement in thermoelectric performance, with a maximum ZT value of 0.94 at a temperature of 413 K, which is twice as large as that of the as-deposited film. Highlights • Flexible P-type - Sb 2 Te 3 hybrid CH 3 NH 3 I thin films was prepared. • The hybrid-composite improve the crystallization, and finally increase electrical conductivity. • Hybrid-composite film has a maximum ZT value of 0.94 which is twice as large as that of the pristine film. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanoparticles of Sb 2 Te 3 was synthesized using MW-assisted thermolysis in matter of minutes. • A special glass substrate was developed for the EPD process, to enable the transport evaluation. • Electrophoretic deposition (EPD) process was used the fabricate thick TE films of Sb 2 Te 3. • With the use of thiol molecules, a significant improvement of electronic transport achieved. • XPS analysis revealed the mechanism of thiols being through formation of slufides. With the recent advances in thermoelectric (TE) technology, there is an increasing demand to develop thick films that would enable large-scale TE devices. Assembly of TE-films from size and morphology-controlled nanoparticles has been a challenging issue that can be addressed by the use of electrophoretic deposition (EPD) technique. In this work, morphology-controlled Sb 2 Te 3 nanoparticles were synthesized through microwave-assisted thermolysis, which were subsequently used for EPD of TE films on specially developed glass-substrates. The electronic transport properties were measured in the temp-range of 22–45 °C. The as-made EPD films showed a high initial resistance, ascribed to high porosity and the presence of surface oxide/passivating layers. The impact of two types of small organic molecules -as hexanedithiol and dodecanethiol, on the electronic transport was investigated, resulting in a significant improvement in the electrical conductivity of the films. The XPS analysis suggests that the thiols bind to the surface of nanoparticles through formation of sulfides. Seebeck coefficient in the range of + 160 to + 190 µV/K was measured, revealing the p-type transport through the deposited films. Finally, a power factor of about 2.5 µW/K2.m was estimated the first time for p-type EPD films, revealing the potential of the developed nanoparticles and substrate, the small molecule additives and the EPD process presented in this work. [ABSTRACT FROM AUTHOR]

Because of the advantages of facile and fast preparation process, screen printing technology shows great potentials in the prospective large-scale production of thermoelectric materials. Herein, rGO/Sb _2 Te _3 composite powders have been prepared by a hydrothermal process, and then flexible rGO/Sb _2 Te _3 /SV4/PEDOT:PSS composite films with different weights of rGO/Sb _2 Te _3 composite powders have been prepared via a screen printing process. The effects of the contents of rGO/Sb _2 Te _3 composite powders on thermoelectric properties of the rGO/Sb _2 Te _3 /SV4/PEDOT:PSS composite films have been studied. The Seebeck coefficients of the achieved composite films was basically unchanged with the content of rGO/Sb _2 Te _3 composite powders increasing, whereas the electrical conductivities decrease, resulting in a maximal power factor of 2.96 μW/mK ^2 at 375 K for the composite film containing 85 wt.% rGO/Sb _2 Te _3 composite powders. The cold pressing combining annealing process has been employed to improve the thermoelectric properties of the composite films. After the treatment, the electrical conductivity of the composite film with 85 wt.% rGO/Sb _2 Te _3 powders has been significantly improved, while the corresponding Seebeck coefficient has slightly decreased. An optimal power factor of 14.13 μW/mK ^2 has been acquired at 375 K, which is ∼ 5 times higher when compared to the untreated composite film (2.96 μW/mK ^2 at 375 K).

Abstract Low optical absorption and large energy band gap in the material utilized as an absorbing layer prevented a report of high-performance broadband photodetector. However, integrating antimony telluride (Sb 2 Te 3) with graphene in a heterostructure appear to be the more promising approach to overcome the said issues. In this heterostructure, optical absorption takes place in Sb 2 Te 3 while graphene acts as charge carrier collector owing to its high carrier mobility. Hence, detailed knowledge of the electronic and optical properties of Sb 2 Te 3 /graphene heterostructure, is essential to expose its hidden potentials. In this study, electronic and properties of Sb 2 Te 3 surface states ad Sb 2 Te 3 /graphene heterostructure are presented using first-principles approach based on density functional theory (DFT) framework within the most recent developed Coope's exchange (vdW-DFC09x). Our surface states band structure calculations show that Sb 2 Te 3 has metallic behaviour as its valence and conduction bands are found to be overlapped when the film thickness is four quintuple layers (QLs). The energy analysis of Sb 2 Te 3 /graphene heterostructure reveals that the most stable configuration is the one in which the Te-1 atom of Sb 2 Te 3 facing to graphene is above the hole center of graphene's hexagonal lattice. More attractively, the system of Sb 2 Te 3 /graphene heterostructure shows that strong hybridization between Sb 2 Te 3 and graphene at smaller interlayer distance resulted in an energy gap at the Dirac states. The Results of optical absorption show that Sb 2 Te 3 /graphene heterostructure has strong absorption in the near infrared to ultraviolet wavelenghts, therefore, it can be used in optoelectronics devices like optical communication, biomedical imaging, remote sensing, and gas sensing. [ABSTRACT FROM AUTHOR]

Topological insulator (TI) properties of granular Sb2Te3 thin films, grown by MOCVD at room temperature on 4″ SiO2/Si substrates, are investigated. The negative magneto‐conductance (MC), analyzed in terms of the Hikami–Larkin–Nagaoka theory, reveals the presence of a clear weak antilocalization (WAL) effect, thus demonstrating the TI character of our system. The extracted WAL prefactor (α) values are explained in terms of the film conductance, in agreement with the existing models for WAL in transport disordered systems. The dephasing length ( l ϕ) dependence on temperature is affected by the grain size of the film and might in turn explain the observed temperature dependence of α and of the conductance. These results demonstrate the feasibility of technologically‐relevant processes to synthesize TIs films, at the same time providing a tool to investigate the effects of the film microstructure on the topological character of their transport properties. [ABSTRACT FROM AUTHOR]

A facile energy-saving route is developed for fabricating Sb2Te3-Te nanocomposites and nanosized Te powders. The fabrication route not only avoids using organic chemicals, but also keeps the energy consumption to a minimum. The fabrication procedure involves two steps. Energetic precursors of nanosized powders of Sb and Te are produced at room temperature followed by hot pressing at 400°C under 70 MPa for 1 h. The resulting Sb2Te3-Te nanocomposite exhibits enhanced power factor. The dimensionless figure of merit zT value of the Sb2Te3-Te nanocomposite is 0.29 at 475 K.

Sb2Te3 chalcogenide alloy has been widely investigated due to its applications in phase change random access memory (PCRAM) and thermoelectric materials. The density of Sb2Te3 alloy is a key factor for both applications. In this work, the densities of Sb2Te3 chalcogenide alloy in solid and molten states have been determined as a function of temperature by the sessile drop method. The density at room temperature was also determined by the Archimedean method to verify the reliability of data obtained by the sessile drop method. The density of solid Sb2Te3 alloy decreases linearly with increasing temperature and there is a discontinuous density decrease at the melting temperature due to the phase change. In the molten state, the density continues decreasing with increasing temperature. The molar volume of Sb2Te3 chalcogenide alloy increases by about 4% from room temperature to just below the melting temperature and by 6% at the melting temperature from the solid to molten state, which may cause large stress for PCRAM devices. [ABSTRACT FROM AUTHOR]

A comparative study of the substrate effect on the growth mechanism of chalcogenide Bi2Te3 and Sb2Te3 thin films was carried out. Obvious microstructural discrepancy in both the as-deposited Bi2Te3 and Sb2Te3 thin films was observed when grown on graphene or SiO2/Si substrate. Bi2Te3 and Sb2Te3 thin films deposited on the graphene substrate were observed to be grown epitaxially along c-axis and show very smooth surface compared to that on SiO2/Si substrate. Based on the experimental results of this study, the initial adsorption sites on graphene substrate during deposition process, which had been discussed theoretically, could be demonstrated empirically. [ABSTRACT FROM AUTHOR]