Te Films Research Articles

Control of evaporation property and film structure of Te by alloying

A new evaporation source of Te alloy is prepared with low-vapor pressure element Bi, In and Pd to replace the traditional evaporation source pure Te. The composition and structure of Te alloys are analyzed to study the effect on evaporation rate and film structure. The composition of Bi-Te alloy is Bi2Te3 phase and Te phase. In-Te alloy is composed of In2Te5 phase and Te phase. Te is provided from the Te phase of Bi-Te alloy and In-Te alloy. Pd-Te alloy consists of the PdTe phase and the PdTe2 phase. Te is evaporating from the PdTe2 phase. According to the evaporation results of different Te alloys, the evaporation rate of Te alloy is lower than pure Te and develops with the increasing saturated vapor pressure of alloying element. Te film has a needle-shaped structure. The grain size of Te film has effect on the evaporation rate.

Effect of the Buffer Layers on the Performance of Fe(Se, Te) Films Fabricated on IBAD Metal Templates by Pulsed Laser Deposition

Effect of the Buffer Layers on the Performance of Fe(Se, Te) Films Fabricated on IBAD Metal Templates by Pulsed Laser Deposition

High-performance Fe(Se,Te) films on chemical CeO2-based buffer layers

The fabrication of a Fe-based coated conductor (CC) becomes possible when Fe(Se,Te) is grown as an epitaxial film on a metallic oriented substrate. Thanks to the material’s low structural anisotropy, less strict requirements on the template microstructure allow for the design of a simplified CC architecture with respect to the REBCO multi-layered layout. This design, though, still requires a buffer layer to promote the oriented growth of the superconducting film and avoid diffusion from the metallic template. In this work, Fe(Se,Te) films are grown on chemically-deposited, CeO2-based buffer layers via pulsed laser deposition, and excellent properties are obtained when a Fe(Se,Te) seed layer is used. Among all the employed characterization techniques, transmission electron microscopy proved essential to determine the actual effect of the seed layer on the final film properties. Also, systematic investigation of the full current transport properties J(θ, H, T) is carried out: Fe(Se,Te) samples are obtained with sharp superconducting transitions around 16 K and critical current densities exceeding 1 MA cm−2 at 4.2 K in self-field. The in-field and angular behavior of the sample are in line with data from the literature. These results are the demonstration of the feasibility of a Fe-based CC, with all the relative advantages concerning process simplification and cost reduction.

Anisotropic Gap Structure and Sign Reversal Symmetry in Monolayer Fe(Se,Te).

The iron-based superconductors are an ideal platform to reveal the enigma of the unconventional superconductivity and potential topological superconductivity. Among them, the monolayer Fe(Se,Te)/SrTiO3(001), which is proposed to be topological nontrivial, shows interface-enhanced high-temperature superconductivity in the two-dimensional limit. However, the experimental studies on the superconducting pairing mechanism of monolayer Fe(Se,Te) films are still limited. Here, by measuring the quasiparticle interference in monolayer Fe(Se,Te)/SrTiO3(001), we report the observation of the anisotropic structure of the large superconducting gap and the sign change of the superconducting gap on different electron pockets. The results are well consistent with the "bonding-antibonding" s±-wave pairing symmetry driven by spin fluctuations in conjunction with spin-orbit coupling. Our work is of basic significance not only for a unified superconducting formalism in the iron-based superconductors, but also for understanding of topological superconductivity in high-temperature superconductors.

Evolution of superconductivity dependence on substrate temperature with thickness of Fe(Se,Te) coated conductors deposited on metal tapes

Fe(Se,Te) films of different thicknesses were deposited on metal tapes by pulsed laser deposition at different substrate temperatures. It is found that the substrate temperature dependence of superconductivity changes with the Fe(Se,Te) film thickness. When fabricating thin Fe(Se,Te) films with a thickness of about 150 nm, moderate substrate temperatures are conducive to balancing the influence of texture and stoichiometry on superconductivity, contributing to the obtainment of good superconductivity. When the Fe(Se,Te) films’ thickness is about 300 nm, the optimal substrate temperatures are lowered due to the determination of film superconductivity by the inhomogeneity of longitudinal chalcogen distribution via the cooperation of Te loss in the long-term-ablated target and the attraction of metal ions in the buffer layer. In addition, with a further increase in thickness from 300 to 600 nm, the self-field critical current of thick Fe(Se,Te) films continuously increases, but the critical current density increases first and then decreases, which is thought to be a result of the misoriented grains or non-superconducting phase due to the large deviation between the actual deposition temperature and the set substrate temperature, and the Se excess in the film. In addition, the 450-nm-thick Fe(Se,Te) film exhibits excellent self-field and in-field performances at 4.2 K: 1.308 MA/cm2 at self-field and over 0.5 MA/cm2 at 9 T. Point pinning, which is the local lattice disturbance randomly distributed in the film observed by transmission electron microscopy, dominates over the entire temperature range.

Smart electromagnetic interference shields based on flexible PEDOT:PSS/Bi2Te3 films

Nowadays, the electromagnetic interference (EMI) shielding materials with an excellent electrical features, favorable flexibility and low density are the admirable desires that represent great challenges. Therefore, n-type bismuth telluride nanorods with diameter of 41.3 ± 5 nm (n-Bi2Te3) were incorporated into a p-type poly(3,4-ethylene-dioxythiophene):poly (styrenesulphonate) (p-PEDOT:PSS) to fabricate a (p-PEDOT:PSS/n-Bi2Te3) films for the electromagnetic interference shielding applications for the first time. Besides, the impact of n-Bi2Te3 nanorods on the electrical conductivity and the electromagnetic interference (EMI) shielding functions of p-PEDOT:PSS/n-Bi2Te3 films has been explored. The electrical conductivity (σ) has gradually increased with the n-Bi2Te3 nanorods in the shield films to obtain the highest value of 106.73 ± 6 S/cm at 16 wt%. Moreover, the total shielding effectiveness (SET) has also dramatically increased with the n-Bi2Te3 nanorods to obtain the highest value of 42.02 dB at 12 GHz for 16 wt%. The reflection mode is the dominance contribution in the shielding effectiveness process, presenting a good reflector of EM waves. Furthermore, the shield films have displayed a high mechanical performance with young modulus of 1.9 ± 0.3 GPa and tensile strength of 42.5 ± 5 MPa at 16 wt%. It can be suggested that these p-PEDOT:PSS/n-Bi2Te3 shields can be functionalized in many fields like electromagnetic shielding interference technology, military, electronic, smart fabric, wearable and biological apparatuses.

Electrodeposited kochia scoparia-shaped Te film: Controlled synthesis and enhanced visible-light photocatalytic performance

Recently Te film is precisely designed to degrade organic pollutants under visible light irradiation owing to its suitable photoelectrochemical properties. Here, various nanostructured Te films are synthesized via a facile electrodeposition method. Different concentration of cetyltrimethylammonium bromide (CTAB) is added into electrolytic solution, and a novel kochia scoparia-shaped morphology with excellent photocatalytic activity is successfully synthesized. The as-fabricated kochia scoparia-shaped Te film is explored in detail via many analytical methods. The results show that as-synthesized kochia scoparia-shaped nanostructure has better crystallinity, enhanced light absorption ability, lower intensity in PL spectra, favorable photogenerated carrier transport and a significantly enhanced photodegradation ratio of methylene blue (MB), as compared to the feather-shaped Te film. The removal rates can reach up to 95.5 % on the degradation of MB in 60 min. In addition, the kochia scoparia-shaped Te film also shows good repeatability and stability without an apparent inactivation under visible light irradiation during four repeated photocatalytic processes. Furthermore, a possible reaction mechanism of higher MB degradation efficiency in the film is also proposed and discussed according to the ESR results. This work supplies a worthy reference for developing highly capable and reusable photocatalysts for eliminating various pollutants.

A novel Design Approach of a Micro Thermoelectric Generator for High Power Density for Ambient Heat Energy Scavenging Applications

Thermoelectric generators (TEGs) have become an excellent candidate for autonomously powering wearable and implantable microelectronics, and wireless sensor networks in the Internet of Things (IoT) systems. This paper presents a doublelayer double-circuit planar TEG with high power output. The impact of the different geometric terms on the device performance is investigated by the use of an electrical model. By studying the impact of the width of the TE films, the number of pairs is optimized to give the optimal power output. The impact of increasing the number of pairs on the output variables of the TEG is also studied. The maximum power of 0.522µW was obtained from 32 pairs at a metal width of 3.82mm with a temperature difference of 17K. Further improvement in the output power up to mW can be obtained by optimizing the temperature difference and operating in a temperature range of about 450K, such as in industrial heat recovery applications.

Laser fluence dependence of stoichiometry and superconductivity of iron chalcogenide superconducting films on metal tapes

Iron chalcogenide Fe(Se,Te) films with thicknesses of 150 nm were deposited on CeO2-buffered metal tapes via pulsed laser deposition using various laser fluences. The film crystallinity and stoichiometry improved upon increasing the laser fluence. This was explained by the ablation threshold that the superconducting performance was better at higher laser fluences and was attributed to the joint contribution of higher Te contents, better texture, and strengthened in-plane strain. In addition, the pinning mechanism was studied by analyzing the in-field performance characteristics of the Fe(Se,Te) films. The dominant pinning center remained point pinning and was independent of the magnetic field direction and temperature. A collective pinning theory-based analysis showed that the vortex pinning behavior in the Fe(Se,Te) film varied from δl pinning to δTc pinning as the temperature approached the critical temperature. This was related to film superconductivity inhomogeneity, which was driven by unreacted Se and Te atoms.

Insights in the two-step synthesis of single crystalline Ag2Te nanorods

Pure monoclinic single crystalline Ag2Te nanorods were synthesized by a two-step method. The first step concerns the electrodeposition of self-standing Te nanorods in an ionic liquid medium, taking advantage of its templating properties. These obtained nanorods are single crystalline with growth direction along the [001] axis in the hexagonal lattice. The average diameter of the as-deposited Te nanorods is 60 ± 13 nm with less than 300 nm long. Afterwards, the resulting nanostructured Te film is immerged in a dedicated silver-based bath in order to be transformed into Ag2Te binary compounds by a combined mechanism of chemical cementation and topotactic transformation. The chemical analysis reveals that the final nanostructures exhibit a slight excess of silver and TEM-SAED analysis shows that they are still single crystalline with an increase of the initial diameter, less than 30%. HR-TEM highlights the presence of an intermediate stützite phase and the hessite phase α-Ag2Te is obtained at the end of the synthesis process.

Te Film as a Saturable Absorber for the Mid-Infrared Er3+-Doped ZBLAN Fiber Laser

We demonstrate a Q-switched Er3+-doped ZBLAN fiber laser at 2.8 µm mid-infrared (mid-IR) region achieved by adopting Te as the saturable absorber mirror (SAM). The modulation depth and saturation intensity of the Te-SAM were measured to be ∼7.2% and 10.81 MW∕cm2, respectively. Stable Q-switched laser pulses with the maximum pulse energy of 3.05 µJ and the minimum pulse width of 0.457 µs at the launched pump power of 4.51 W were obtained. Maximum average output power of 357 mW with repetition rate of 116.98 kHz were achieved. The signal-to-noise ratio (SNR) is 52 dB, which is higher than that of most 2.8 µm mid-infrared Q-switched fiber lasers reported so far. To the best of our knowledge, this is the first demonstration from a Q-switched fiber laser at 2.8 µm based on a Te-SAM.

On the electrophoretic deposition of Bi2Te3 nanoparticles through electrolyte optimization and substrate design

Assembly of thermoelectric nanostructures with pre-defined morphology and surface chemistry on solid substrates has been one of the challenges for in-plane TE devices. Electrophoretic deposition (EPD) has the potential to be used for this purpose, where the use of non-conductive substrates is required to enable a reliable evaluation of the transport property of electrically active films. Bi2Te3 nanoparticles, which were synthesized using microwave-assisted hydrothermal route, were used for the EPD of thermoelectric films on glass substrates. A special substrate was fabricated using maskless photolithography, to evaluate the electronic transport properties of the TE films without the interference of the substrate. Electrolyte composition was optimized for high mobility of the suspended nanoparticles, and Bi2Te3 EPD films were fabricated with a high deposition rate, reaching 10 μm/min. Initial EPD films showed high resistivity, ascribed to the surface oxide layer and capping ligands. The resistance was significantly reduced by the addition of a dithiol molecular linker, capable of interconnecting the Bi2Te3 nanoparticles through ligand-exchange. Seebeck coefficient in the range −150 to −180 μV/K was measured, revealing the transport through the deposited films. Finally, a power factor of 169 nW/K2.m was estimated, revealing the potential for the application of this technology to large area TE films as active coatings using the developed EPD process.

Chemical CeO2-Based Buffer Layers for Fe(Se,Te) Films

Among other Fe-based superconductors, Fe(Se,Te) is particularly interesting because of the low structural anisotropy, large upper critical fields, low field dependence of the critical current density and low toxicity. It can also be grown as an epitaxial film on a metallic oriented substrate, making the fabrication of a Fe-based coated conductor (CC) possible. Less strict requirements on the template microstructure allow for the design of a simplified design compared to REBCO CCs. This design requires a buffer layer to promote the oriented growth of the superconducting film and avoid diffusion from the metallic template. In this work, CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> based buffer layers are prepared on single crystals via two chemical deposition techniques, metal organic decomposition (MOD) and polymer assisted deposition (PAD). With the design of a suitable thermal treatment, it is possible to obtain oriented buffers with large flat grains and low values of surface roughness. Fe(Se,Te) films are deposited on these templates via laser deposition, and excellent samples are obtained when a Fe(Se,Te) seed layer is used to favour chemical matching with the buffer: sharp superconducting transitions around 16 K and critical current densities exceeding 1 MA cm <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⁻</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 4.2 K in self-field are observed. These results are the demonstration of the feasibility of a Fe-based CC architecture, with all the relative advantages concerning process simplification and cost reduction.

Development of active films utilizing antioxidant compounds obtained from tomato and lemon by-products for use in food packaging

This study focused on the recovery of antioxidant compounds from lemon and tomato by-products for use as natural additives in the development of active food packaging formulated using three different polymeric matrices that included low-density polyethylene (LDPE), polylactic acid (PLA), and G-polymer (GP). The films were characterized according to chemical-physical, thermal analyses, and their barrier and mechanical properties. Migration assays were performed to evaluate the release of active compounds from polymeric matrices, which were quantified in the food simulant by high-performance liquid chromatography with a diode array detector and then confirmed via liquid chromatography coupled to mass spectrometry. The antioxidant capacities of the films were determined to evaluate their applicability for use as antioxidant-active packaging. The incorporation of extracts into polymers resulted in different structural changes and enhanced properties according to the nature of the polymeric matrix based on the interactions of the –OH groups of polyphenols and the chemical groups of the polymers. The lemon (LE) and tomato (TE) extracts lead to a substantial improvement in water barrier properties of PLA and GP-based films. The active PLA and GP films released high amounts of polyphenolic compounds (up to 65% for GP containing LE); mainly hesperidin and eriocitrin for LE films, and chrologenic acid for TE films. PLA loaded with lemon extract at 4% was selected as the most suitable for use as antioxidant packaging to extend the shelf-life of foods with high fat content.

Magnetic granularity in PLD-grown Fe(Se,Te) films on simple RABiTS templates

Iron-based superconductors are a popular candidate in the search for affordable and simple superconductors for high-field applications. In particular, the relaxed texture requirements fuel hope that films deposited on RABiTS with simple buffer layer architectures could enable cheap coated conductors. We find that a single Yttrium oxide buffer layer can act as a suitable diffusion barrier and epitaxial Fe(Se,Te) thin films were successfully grown by pulsed laser deposition. An analysis of the local current distribution by means of scanning Hall probe microscopy reveals current densities exceeding 1 MA cm−2, however, granularity still seems to be an issue. Transmission electron microscopy images and analysis by transmission Kikuchi diffraction show that the out-of-plane orientation of underlying Ni-W grains in the substrate has a severe impact on the growth of Fe(Se,Te) films.

Structural correlation of phonon dynamics in Bismuth and Tellurium for the formation of Bismuth Telluride, using ultrafast transient absorption spectroscopy

The charge carrier and phonon dynamics are highly reliant on the material structural features, and understanding their dynamics help in interpreting the underlying phenomenological qualities of any material system. The phonon and carrier dynamics of Bi, Te, and BiTe3 thin films formed on a Si (100) wafer through thermal evaporation are discussed in this article. The Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffraction (XRD) analysis are used to characterize the structural features of these films. The dynamics of charge carriers and phonons are further determined using femtosecond ultrafast transient absorption spectroscopy (UFTS). A comprehensive analysis of dynamics is carried out by performing multiple excitations probed in broad Near-Infrared (NIR) regimes. The current study would help collect the knowledge about the phonon and charge carrier dynamics of Bismuth, Tellurium, and Bismuth Telluride films for optical, spintronics, and terahertz applications.

Investigation of etching selectivity and microstructure of Ag-doped Sb2Te thin film for dry lithography

Dry lithography is a promising micro-/nanomanufacturing method owing to its advantages of being solution-free, its absence of undercut and resistance to swelling. However, heat-mode resists suitable for dry lithography are less reported. This work reports on the use of Ag-doped Sb2Te thin film as a heat-mode resist, and its etching selectivity and microstructures are investigated in detail. It is found that Ag1.44Sb2.19Te thin film possesses high etching selectivity in CHF3/O2 mixed gases and can act as a heat-mode resist. In order to elucidate the mechanism of high etching selectivity, the microstructures of the Ag-doped Sb2Te thin films are analyzed using x-ray diffraction, Raman spectra, x-ray photoelectron spectroscopy, and transmission electron microscopy methods. The results show that the etching selectivity is attributed to the phase separation of Ag1.44Sb2.19Te film and the formation of the Sb phase after laser exposure, leading to a reduction in etching resistance in CHF3/O2 mixed gases. In addition, pattern transfers from Ag1.44Sb2.19Te to SiO2 and Si substrates are achieved successfully and the etching selectivities of Si and SiO2 to Ag1.44Sb2.19Te are both higher than 2:1. This work may provide a useful guide for the research of dry lithography without wet development.

Growth of high-quality semiconducting tellurium films for high-performance p-channel field-effect transistors with wafer-scale uniformity

Achieving high-performance p-type semiconductors has been considered one of the most challenging tasks for three-dimensional vertically integrated nanoelectronics. Although many candidates have been presented to date, the facile and scalable realization of high-mobility p-channel field-effect transistors (FETs) is still elusive. Here, we report a high-performance p-channel tellurium (Te) FET fabricated through physical vapor deposition at room temperature. A growth route involving Te deposition by sputtering, oxidation and subsequent reduction to an elemental Te film through alumina encapsulation allows the resulting p-channel FET to exhibit a high field-effect mobility of 30.9 cm2 V−1 s−1 and an ION/OFF ratio of 5.8 × 105 with 4-inch wafer-scale integrity on a SiO2/Si substrate. Complementary metal-oxide semiconductor (CMOS) inverters using In-Ga-Zn-O and 4-nm-thick Te channels show a remarkably high gain of ~75.2 and great noise margins at small supply voltage of 3 V. We believe that this low-cost and high-performance Te layer can pave the way for future CMOS technology enabling monolithic three-dimensional integration.

Bi2Te3-based flexible thermoelectric generator for wearable electronics

The rapid development of the Internet of Things increases the demand for wearable devices. Compared with traditional chemical batteries, flexible thermoelectric technology contributes a solution for solving the power supply of wearable electronics. Here, we prepared n-type Bi2Te3 and p-type Bi0.5Sb1.5Te3 flexible thermoelectric films by the magnetron sputtering method, where the thermoelectric performance and their microstructures are systematically studied. The carrier concentration and mobility are optimized by adjusting the deposition temperature, eventually improving the thermoelectric performance and achieving the room-temperature power factors of 3.2 and 6.1 μW cm−1 K−2 for Bi2Te3 and Bi0.5Sb1.5Te3 films, respectively. Furthermore, after being bent 900 times with a radius of 5 mm, the resistance of these films barely increases, demonstrating the great potential for applications in wearable electronics. In order to further evaluate the practicability, these films are used to design a flexible thermoelectric generator, in which output performance improves with the increase in the temperature difference. The power density is up to ∼218.8 μW cm−2 at temperature differences of ∼41 K.

Orientated Growth of Ultrathin Tellurium by van der Waals Epitaxy

AbstractTellurium, as an elemental van der Waals semiconductor, has intriguing anisotropic physical properties owing to its inherent 1D crystal structure. To exploit the anisotropic and thickness‐dependent behavior, it is important to realize orientated growth of ultrathin tellurium. Here, van der Waals epitaxial growth of Te on the surface of 2D transition metal dichalcogenides is systematically investigated. Orientated growth of Te with a thickness down to 5 nm is realized on three‐fold symmetric substrates (WSe2, WS2, MoSe2, and MoS2), where the atomic chains of Te are aligned with the armchair directions of substrates. 1D/2D moiré superlattices are observed for the Te/WSe2 heterostructure. This method is extended to the growth of SeTe alloys, providing flexibility for band engineering. Finally, growth of textured Te film is demonstrated on the lower‐symmetry surface of WTe2.