Se Films Research Articles

Surface-enhanced Raman scattering of As2S3 and Se thin films formed on Au nano-structures

The effect of plasmonic nanostructures (NSs) on the Raman spectra and underlying structural changes in thin chalcogenide films is investigated. Several tens of nanometers thick As 2 S 3 and Se films were deposited by thermal sputtering on glass and surface-enhanced Raman spectroscopy (SERS) substrates based on gold nanostructures for comparison. The films on glass were practically not detectable by the Raman spectroscopy. Using gold NSs as the substrates enabled reliable registration of the Raman spectra of both the As 2 S 3 and Se films. The registered Raman spectra contained all the features usually present in the films with the thicknesses ~1 μm or more. Based on our analysis of the spectra obtained at different excitation wavelengths, we may conclude that the SERS chemical mechanism makes the main contribution to the enhancement of the Raman signal from chalcogenide films. Adjustment of the parameters of SERS substrates to tune their plasmon band position in resonance with the excitation laser radiation enables increasing the plasmonic enhancement contribution. Besides the effect of enhancement, localized plasmon resonance in the gold NSs causes local heating of the chalcogenide film around them leading to local structural transformations, which can be controlled using the Raman spectra.

Resonant Bonding Dependence of the Phase Change Characteristics of a VO2-Sb2Se Film for Tunable Photonic Devices in the Mid-Infrared Region

Phase change material (PCM) has gained great attraction for being widely used in tunable photonic devices due to its nonvolatility, excellent scalability, high speed, and tunable properties. However, the unclear source of the phase-change characteristics limits PCM for true device-level integrated circuits with high configuration and multifunctional attributes, especially in the mid-infrared (MIR) region. In this paper, the inherent dependences of phase-change characteristics on both the microstructure and bonding environments of the (VO2)x(Sb2Se)100–x film are disclosed for low-loss and nonvolatile tunable photonic devices. (VO2)x(Sb2Se)100–x films possess a tendency that the crystallization temperature, 10 year data-retention temperature, and optical band gap of (VO2)x(Sb2Se)100–x films increase with the increase of VO2 content. The improvement in thermal stability of (VO2)x(Sb2Se)100–x is ascribed to the complex bonding environment consisting of Se–V and Sb–V bonds with the large bonding enthalpy, which disturbs the crystallization. The symbolic value for the contribution of resonant bonding ζ is derived by the real part ε1 and imaginary part ε2 of dielectric functions with a wavelength ranging from 1.7 to 25 μm. With increasing VO2 content, a large structural distortion in the VO2-rich phase leads to a reduction in the level of resonant bonding, which accounts for a decrease in the optical refractive index contrast. These results shed light on intrinsic material science and engineering to the ongoing search for other phase-change materials for tunable photonic devices in the MIR region.

Realization of high output power density in solution-processed flexible α-Cu2Se film by compositional off-stoichiometry and optimization of length

The solution-process method can be easily realized without expensive and complicated equipment, which provides the possibility for cost-effective application of flexible thermoelectric films. Nonetheless, the reported output properties of solution-processed Cu2Se based films are not satisfactory due to the absence of effective compositional adjustment and optimal length. In this work, a series of solution-processed nylon-supported flexible Cu2+xSe films have been fabricated. The excess Cu not only fills the vacancies, but also transforms the β-Cu2Se with disordered Cu atoms into long-range ordered lamellar α-Cu2Se, thereby reducing the carrier concentration and improving the carrier mobility of the films. As a result, a high power factor of 856.59 ± 119.92 μW m−1 K−2 has been achieved in the Cu2.20Se film at 303 K. In addition, by numerical simulation, the ideal length of single Cu2.20Se film was calculated to be 2 mm. With an actual temperature difference of 6.6 K, a maximum output power density of 2.918 μW cm−2 K−2, which is superior to those of other p-type flexible thermoelectric films, is realized in the single Cu2.20Se film. This work provides a feasible idea to promote the output performance of solution-processed flexible thermoelectric films.

Linear and nonlinear optical properties of amorphous Se–Te–Sn–Cd films

This research work reports the rigorous studies of the various optical properties of Cadmium containing amorphous thin films (TFs) of multicomponent Se–Te–Sn system. The optical characteristics of prepared TFs are analyzed by using the experimental spectral data of reflection/transmission in the range 4000 Å to 25000 Å. Knowing the spectral variation of the dispersion parameters, we have determined the optical band gap Egopt and Urbach tail Ee. After the addition of Cd, The Urbach energy Ee value decreases for the parent Se–Te–Sn sample. The values of the optical bandgap for the present samples are found in the range from 1.24 eV to 1.43 eV with a reversal in trend at x = 4.The indirect optical transition is found in the current study that is confirmed by the transition power factor m. The high dielectric constant (ε∞), as well as single-oscillator dispersion parameters, are also determined. The dependence of real ε′ and imaginary ε′′ components of optical dielectric constant, relaxation time τ, dissipation factor tan δ, and the optical/electrical conductivities (σopt and σele) on photon energy hν were also studied for multi-components SeTeSnCd (STSC) system. The nonlinear optical characteristics of TFs are examined in terms of their susceptibility and nonlinear refractive index. A discussion has been also discussed about the potential values of the CB- and VB- bands, along with their location. We have observed an excellent agreement between the values of Tauc's constant B determined by Tauc's relation that is obtained by empirical fitting. The present glasses have been found useful for optoelectronic applications after their comparison with different cadmium-containing binary and ternary systems reported by other researchers.

Substrate-Free Thermoelectric 25 μm-Thick Ag2Se Films with High Flexibility and In-Plane zT of 0.5 at Room Temperature.

Thermoelectric inorganic films are flexible when sufficiently thin. By removing the substrate, that is, making them free-standing, the flexibility of thermoelectric films can be enhanced to the utmost extent. However, studies on the flexibility of free-standing thermoelectric inorganic films have not yet been reported. Herein, the high thermoelectric performance and flexibility of free-standing thermoelectric Ag2Se films are reported. Free-standing Ag2Se films with a thickness of 25.0 ± 3.9 μm exhibited an in-plane zT of 0.514 ± 0.060 at room temperature. These films exhibited superior flexibility compared to Ag2Se films constrained on a substrate. The flexibility of the Ag2Se films was systematically investigated in terms of bending strain, bending radius, thickness, and elastic modulus. Using free-standing Ag2Se films, a substrate-free, flexible thermoelectric generator was fabricated. The energy-harvesting capacity of the thermoelectric generator was also demonstrated.

Materials for Optical Sensors of X-ray Irradiation Based on (GaxIn1 – x)2Se3 Films

(GaxIn1-x)2Se3 films with 0.1 ≤ x ≤ 0.4 were deposited by the thermal evaporation technique. As-deposited (GaxIn1-x)2Se3 films were irradiated using the wideband radiation of a Cu-anode X-ray tube at different exposure times. The spectral dependences of the refractive index and extinction coefficient are measured by the spectral ellipsometry technique. The optical transmission spectra of X-ray irradiated (GaxIn1-x)2Se3 films are studied for various irradiation times. Parameters of the Urbach absorption edge for X-ray-irradiated (GaxIn1-x)2Se3 thin films are determined and compared with those of non-irradiated films. The spectral dependences of the refractive indices of non-irradiated and X-ray-irradiated (GaxIn1-x)2Se3 films are described in the framework of the model developed by Cauchy, Sellmeier, Wemple, and DiDomenico, as well as by the optical-refractometric relation. The detailed variation of the parameters of the Wemple–DiDomenico model for non-irradiated and X-ray-irradiated (GaxIn1-x)2Se3 films has been analyzed. The perspective of applications of (GaxIn1-x)2Se3 films as the materials for optical sensors of X-rays is discussed.

Fabrication of black silicon using picosecond laser irradiation assisted by Se dopant film

Black silicon with micro-nano structures were fabricated by irradiating silicon with 1064nm laser pulses of 8.7-ps duration, 4.5 μJ per single pulse, 100mm/s scanning speed in vacuum, and doping the black silicon by irradiating the silicon coated with Si-Se bilayer film. SEM images show that the surface micron-scale grooves covered with nano-scale particles pattern was produced on Si for both the sample with no film and with Se film, but the surface structure are smoother and more uniform in the presence of Se film. EDS graph demonstrated the presence of Selenium in the black silicon micro-nano structures. Furthermore, Raman spectra results indicate that the micro-nano structured black silicon is still crystal phase.

CuO:Se composite films and its photovoltaic application

Cupric oxide (CuO) and selenium (Se) are old photoelectric materials, and their photovoltaic properties have always received attention. However, CuO has a high melting point (1026℃) and will decompose near its melting point, so it is difficult to prepare high crystallinity CuO films. Selenium (Se) can not efficiently absorb sunlight because of its large optical band gap (1.9 eV). Here, a CuO:Se composite film was prepared by radio frequency magnetron co-sputtering of CuO and Se and low temperature annealing (200℃). The experimental results show that this composite material film has the advantages of CuO and Se, and overcome their disadvantages. The material has strong absorption of light in the entire solar spectral range (250-2500 nm, average absorptance ~80%). A prototype solar cell based on this composite film was fabricated and its power conversion efficiency (PCE) is up to 2.05%, which is much higher than that of the pure CuO (0.007%) or pure Se (1.05%) film solar cells. This material should be promising for photovoltaic and other photo-electrical application.

Effect of sputtering pressure on the superconducting properties of Fe(Te,Se) films

Effect of sputtering pressure on the superconducting properties of Fe(Te,Se) films

Atom-Scale Chemistry in Chalcopyrite-Based Photovoltaic Materials Visualized by Atom Probe Tomography.

Chalcopyrite-based materials for photovoltaic devices tend to exhibit complex structural imperfections originating from their polycrystalline nature; nevertheless, properly controlled devices are surprisingly irrelevant to them in terms of resulting device performances. The present work uses atom probe tomography to characterize co-evaporated high-quality Cu(In,Ga)Se2 (CIGS) films on flexible polyimide substrates either with or without doping with Na or doping with Na followed by K via a post-deposition treatment. The intent is to elucidate the unique characteristics of the grain boundaries (GBs) in CIGS, in particular the correlations/anti-correlations between matrix elements and the alkali dopants. Various compositional fluctuations are identified at GBs irrespective of the presence of alkali elements. However, [Cu-poor and Se/In,Ga-rich] GBs are significantly more common than [Cu-rich and Se/In,Ga-poor] ones. In addition, the anti-correlations between Cu and the other matrix elements are found to show not only regular trends among themselves but also the association with the degree of alkali segregation at GBs. The Na and K concentrations exhibited a correlation at the GBs but not in the intragrain regions. Density functional theory calculations are used to explain the compositional fluctuations and alkali segregation at the GBs. Our experimental and theoretical findings not only reveal the benign or beneficial characteristics of the GBs of CIGS but also provide a fundamental understanding of the GB chemistry in CIGS-based materials.

High-performance, thin-film thermoelectric generator with self-healing ability for body-heat harvesting

Flexible thermoelectric generators (TEGs) are attractive for their ability to power wearable electronics utilizing the temperature difference between the human body and the environment. Here, we present a self-healing flexible TEG assembled with high-performance Ag 2 Se films. A room temperature power factor (PF) as high as 20.8 μW cm −1 K −2 is obtained via isoelectronic copper doping. The relative resistance change of the film is less than 5% of the initial value after 1,000 bending cycles, and the resistance of the Ag 2 Se film recovers to its initial value within a few hours of the bending test. The 6-leg flexible TEG demonstrates a maximum power density of 80 W m −2 at a temperature difference of 50 K. An output voltage of 1.5–2.8 mV can be achieved on the arm in different motion states. These results demonstrate the promising application of Ag 2 Se-based flexible TEGs for wearable electronics. • RT power factor of 20.8 μW cm −1 K −2 is obtained in the Cu-doped Ag 2 Se film • The film exhibits self-healing capability • The 6-leg TEG demonstrates output power density of 80 W m −2 at Δ T of 50 K Hou et al. report a wearable thermoelectric generator (TEG) based on a copper-doped silver selenide flexible thermoelectric film. This TEG demonstrates a high output power density, excellent flexibility, and self-healing ability and is promising for wearable electronic applications.

Energy levels determination of Zn(O,Se) thin films

Ternary Zn(O,Se) films were grown onto glass and p-type Si substrates by pulsed laser deposition at substrate temperature of 500 °C, to investigate their optical properties and energy band structure using UV–Vis and UPS spectroscopic methods. It was found that the 500 nm thick Zn(O,Se) film is nearly transparent in the visible region, with an optical band gap value of 2.93 eV. The calculated valence band is positioned at −7.60 eV below the vacuum level, and it consist of O 2p and Se 4p levels or the highest bonding sp3 hybrid states with the hybridization of Zn 3d, O 2p and Se 4p orbitals, and also the coupling of 3d–3d electrons among different Zn2+ cations. The findings show that the conduction band of Zn(O,Se) layers can be tuned for alignment with the conduction band of the absorbers layer which will decrease the cliff and spike barriers in the complete solar cell structures.

Molecular Beam Epitaxy of in2Se3 Thin Films

In2Se3 is a polymorphous metal-chalcogenide system1 where each phase exhibits dramatically different functional properties. α-In2Se3 is a two-dimensional, ferroelectric semiconductor2,3 and has shown promise in low-power, neuromorphic electronic devices4,5. β-In2Se3 is a two-dimensional, centrosymmetric semiconductor and has shown promise in photodetectors6. γ-In2Se3 is a three-dimensional, defect- wurtzite wide bandgap semiconductor that has shown promise as a precursor layer for CuInSe2 solar cells7. Considered together, the bandgaps of these materials range from 1.3eV to 2.5eV8. Understanding how to synthesize phase-pure thin-films of In2Se3 is of interest to harness the properties of these materials for applications in electronic devices.α-In2Se3 is thermodynamically stable below 200 oC and transitions to the 2D, centrosymmetric β-In2Se3 phase upon heating above 200 oC1. While the β to α-In2Se3 phase transition is achievable in bulk synthesis via slow cooling2, the β to α-In2Se3 phase transition does not occur as readily in thin-films. Recent studies on thin-film synthesis of In2Se3 have demonstrated β- and/or γ-In2Se3 films at temperatures above the thermodynamic stability range of α-In2Se3 (200 oC). Two reports from the last two years demonstrate large-area synthesis of β-In2Se3 thin-films metal-organic chemical vapor deposition and molecular beam epitaxy (MBE) on sapphire at temperatures greater than 300 oC6,9. Another study reported MBE synthesis of metastable, strained, mixed phase β/γ-In2Se3 films on Si(111) substrates at 180 oC10. One study from 2018 claims deposition of large-area α-In2Se3 thin-films on graphene at a substrate temperature of 250 oC via molecular beam epitaxy; however, it is difficult to distinguish the α from β phase by the Raman spectra and TEM micrograph along the c-axis.In this study we demonstrate thin-film synthesis of In2Se3 over a wide array of synthesis conditions via molecular beam epitaxy. We systematically investigate the effects of substrate temperature, cooling rate after deposition, substrate surface, Se/In flux ratio, and precursor type on the structure and properties of In2Se3 films. We characterize the crystalline phase, stoichiometry, and crystal morphology via Raman Spectroscopy, X-ray Photoelectron Spectroscopy and Atomic Force Microscopy, respectively.(1) Okamoto, H. In-Se ( Indium-Selenium ). J. Phase Equilibria 2004, 25 (2).(2) Küpers, M.; Konze, P. M.; Meledin, A.; Mayer, J.; Englert, U.; Wuttig, M.; Dronskowski, R. Controlled Crystal Growth of Indium Selenide, In2Se3, and the Crystal Structures of α-In2Se3. Inorg. Chem. 2018, 57, 11775–11781.(3) Xiao, J.; Zhu, H.; Wang, Y.; Feng, W.; Hu, Y.; Dasgupta, A.; Han, Y.; Wang, Y.; Muller, D. A.; Martin, L. W.; et al. Intrinsic Two-Dimensional Ferroelectricity with Dipole Locking. Phys. Rev. Lett. 2018, 120 (22), 227601.(4) Tang, B.; Tang, B.; Hussain, S.; Xu, R.; Cheng, Z.; Liao, J.; Chen, Q. Novel Type of Synaptic Transistors Based on a Ferroelectric Semiconductor Channel. ACS Appl. Mater. Interfaces 2020, 12 (22), 24920–24928.(5) Wang, L.; Liao, W.; Wong, S. L.; Yu, Z. G.; Li, S.; Lim, Y. F.; Feng, X.; Tan, W. C.; Huang, X.; Chen, L.; et al. Artificial Synapses Based on Multiterminal Memtransistors for Neuromorphic Application. Adv. Funct. Mater. 2019, 29 (25), 1–10.(6) Claro, M. S.; Grzonka, J.; Nicoara, N.; Ferreira, P. J.; Sadewasser, S. Wafer-Scale Fabrication of 2D β-In2Se3 Photodetectors. Adv. Opt. Mater. 2020, 2001034, 1–9.(7) Ashok, A.; Regmi, G.; Velumani, S. Growth of In2Se3 Thin Films Prepared by the Pneumatic Spray Pyrolysis Method for Thin Film Solar Cells Applications. 2020 17th Int. Conf. Electr. Eng. Comput. Sci. Autom. Control. CCE 2020 2020, 2–7.(8) Li, J.; Li, H.; Niu, X.; Wang, Z. Low-Dimensional In2Se3 Compounds: From Material Preparations to Device Applications. ACS Nano 2021, 15 (12), 18683–18707.(9) Zhang, X.; Lee, S.; Bansal, A.; Zhang, F.; Terrones, M.; Jackson, T. N.; Redwing, J. M. Epitaxial Growth of Few-Layer β-In2Se3 Thin Films by Metalorganic Chemical Vapor Deposition. J. Cryst. Growth 2020, 533 (December 2019), 125471.(10) Shen, Y. F.; Yin, X. B.; Xu, C. F.; He, J.; Li, J. Y.; Li, H. D.; Zhu, X. H.; Niu, X. Bin. Growth and Structural Characteristics of Metastable β-In2Se3 Thin Films on H-Terminated Si(111) Substrates by Molecular Beam Epitaxy. Chinese Phys. B 2020, 29 (5).

(Invited) Selenium as a Top-Cell Absorber Candidate for Tandem Photoelectrochemical Stacks

The ideal high-bandgap partner for a tandem solar absorber using c-Si as the low-bandgap bottom cell must have a bandgap of around 1.9 eV and excellent optoelectronic properties.Selenium, perhaps the very first material to be studied for its photovoltaic properties, is emerging as an interesting candidate for this application. Indeed Se has a bandgap of around 1.95 eV [1] and a steep increase in absorption above this photon energy. Todorov et al showed [2] in 2017 that single-junction Se solar cells could reach 6.5% efficiency using a new cell architecture with a very thin absorber layer. Recently we have increased the OCV to a new record of 991 mV [2]. Simultaneously, we are also starting to identify the main shortfalls of state-of-the-art Se films which so far have prevented Se-cells from approaching their theoretical potential OCV, which is of course much higher than 991 mV. The talk will introduce Se as a solar absorber and discuss we know about its properties and use in solar devices such as PEC stacks.[1] T. K. Todorov, S. Singh, D. M. Bishop, O. Gunawan, Y. S. Lee, T. S. Gershon, K. W. Brew, P. D. Antunez and R. Haight, Nature Communications, 2017, 8, 682[2] R. Nielsen, T. Youngman, H. Moustafa, S. Levcenco, H. Hempel, A. Crovetto, T. Olsen, O. Hansen, I. Chorkendorff, T. Unold, P. C. K. Vesborg, (in preparation), 2022

A detailed investigation on the phase transformation mechanism during electroplating of Cu (In, Ga) Se2 films on FTO-glass substrates

In this study, an attempt has been made to acquire an in-depth understanding of the electroplating mechanism of Cu (In, Ga) Se2 quaternary thin films on FTO-glass substrates. A systematic approach starting with the study of unitary, binary, ternary, and finally quaternary deposition of the elements have been performed through cyclic voltammetry (CV). The salts used were CuCl2, H2SeO3, InCl3 and GaCl3 for each stage of deposition with varying combinations and proportions. CVs were first done for unitary Cu, Se, In and Ga elements, then binary combinations of Cu-In, Cu-Se, Cu-Ga, In-Se, In-Ga, and Se-Ga system, ternary baths of Cu-In-Se and Cu-In-Ga, In-Se-Ga and Cu-Se-Ga systems, and finally quaternary Cu-In-Ga-Se system. An optimum deposition potential of −0.65 V was chosen from the position of cathodic peaks for all the baths. A thorough structural and elemental analysis, defect densities, type of conductivity was carried out for the as-deposited films. Single step deposition of CIGS was found to be impossible, hence Ga was attempted to incorporate in the films through a two-stack approach. From the position and intensity of the cathodic peaks and the phase analysis, plausible mechanism has been proposed for the quaternary alloy.

Cellulose nanofiber/MXene/FeCo composites with gradient structure for highly absorbed electromagnetic interference shielding

Conductive polymer composites (CPCs) had attracted tremendous attention in the field of electromagnetic interference (EMI) shielding. However, these materials encountered an intrinsic contradiction between high EMI shielding effectiveness (EMI SE) and low electromagnetic waves reflection. Herein, an excellent EMI SE and low electromagnetic waves reflection composite film with a controllable magnetic-conductive dual gradient structure was constructed using cellulose nanofiber (CNF), MXene, and FeCo by layer-by-layer vacuum filtration method. Benefiting from the synergy of the transition layers and reflection layer with gradient structure, the composite film exhibited favorable impedance matching, abundant loss mechanism, and efficient EMI shielding ability, resulting in absorption dominated shielding characteristic. In addition, the gradient structure facilitated the “absorb-reflect-reabsorb” process when electromagnetic waves were transmitted into the composite film. The obtained CNF/MXene/FeCo-G composite film possessed a remarkable EMI SE of 58.0 dB and the reflection coefficient (R) as low as 0.61. It was proven that the electromagnetic waves absorbing ability can be enhanced by thickening the transition layers, and the EMI SE was improved with the thickening of the reflection layer. Therefore, this work provided a facile strategy to prepare high EMI SE materials with low reflection, which had a good application prospect as the new-generated smart electronic devices.

Improvement of CZTSSe film quality and superstrate solar cell performance through optimized post-deposition annealing

Improving the performance of kesterite solar cells requires high-quality, defect-free CZTS(Se) films with a reduced number of secondary phases and impurities. Post-annealing of the CZTS films at high temperatures in a sulfur or selenium atmosphere is commonly used to improve the quality of the absorbing material. However, annealing at high-temperatures can promote material decomposition, mainly due to the loss of volatile elements such as tin or sulfur. In this work, we investigate how the additional step of sulfurization at reduced temperatures affects the quality and performance of CZTSSe based solar cells. A comprehensive structural analysis using conventional and high resolution XRD as well as Raman spectroscopy revealed that the highest CZTSSe material quality with the lowest structural disorder and defect densities was obtained from the CZTS films pre-sulfurized at 420 °C. Furthermore, we demonstrate the possibility of using Sb2Se3 as a buffer layer in the superstrate configuration of CZTSSe solar cells, which is possible alternative to replace commonly employed toxic CdS as a buffer layer. We show that the additional low-temperature selenization process and the successful use of Sb2Se3 as a buffer layer could improve the performance of CZTSSe-based solar cells by up to 3.48%, with an average efficiency of 3.1%.

Step-Climbing Epitaxy of Layered Materials with Giant Out-of-Plane Lattice Mismatch.

Heteroepitaxy with large lattice mismatch remains a great challenge for high-quality epifilm growth. Although great efforts have been devoted to epifilm growth with an in-plane lattice mismatch, the epitaxy of 2D layered crystals on stepped substrates with a giant out-of-plane lattice mismatch is seldom reported. Here, taking the molecular-beam epitaxy of 2D semiconducting Bi2 O2 Se on 3D SrTiO3 substrates as an example, a step-climbing epitaxy growth strategy is proposed, in which the n-th (n= 1, 2, 3…) epilayer climbs the step with height difference from out-of-plane lattice mismatch and continues to grow the n+1-th epilayer. Step-climbing epitaxy can spontaneously relax and release the strain from the out-of-plane lattice mismatch, which ensures the high quality of large-area epitaxial films. Wafer-scale uniform 2D Bi2 O2 Se single-crystal films with controllable thickness can be obtained via step-climbing epitaxy. Most notably, one-unit-cell Bi2 O2 Se films (1.2nm thick) exhibit a high Hall mobility of 180 cm2 V-1 s-1 at room temperature, which exceeds that of silicon and other 2D semiconductors with comparable thickness. As an out-of-plane lattice mismatch is generally present in the epitaxy of layered materials, the step-climbing epitaxy strategy expands the existing epitaxial growth theory and provides guidance toward the high-quality synthesis of layered materials.

Superconducting Fourfold Fe(Te,Se) Film on Sixfold Magnetic MnTe via Hybrid Symmetry Epitaxy

Epitaxial Fe(Te,Se) thin films have been grown on various substrates but never been grown on magnetic layers. Here we report the epitaxial growth of fourfold Fe(Te,Se) film on a sixfold antiferromagnetic insulator, MnTe. The Fe(Te,Se)/MnTe heterostructure shows a clear superconducting transition at around 11 K, and the critical magnetic field measurement suggests the origin of the superconductivity to be bulk-like. Structural characterizations suggest that the uniaxial lattice match between Fe(Te,Se) and MnTe allows a hybrid symmetry epitaxy mode, which was recently discovered between Fe(Te,Se) and Bi2Te3. Furthermore, the Te/Fe flux ratio during deposition of the Fe(Te,Se) layer is found to be critical for its superconductivity. Now that superconducting Fe(Te,Se) can be grown on two related hexagonal platforms, Bi2Te3 and MnTe, this result opens a new possibility of combining topological superconductivity of Fe(Te,Se) with the rich physics in the intrinsic magnetic topological materials (MnTe)n(Bi2Te3)m family.

Influence of the substrate temperature on the formation of CuSbSe2 thin films grown by pulsed laser deposition

Cu–Sb–Se targets were obtained by solid-state reaction from Cu2Se and Sb2Se3 precursors annealed at different temperature and time conditions. The structural characterization showed that the optimum annealing conditions were at 400 °C for 3 h. Afterward, Cu–Sb–Se films onto glass/SnO2:F/ZnO/CdS substrates at 250 °C, 300 °C, 350 °C and 400 °C by pulsed laser deposition were deposited using the synthesized Cu–Sb–Se pellet as target. Cu–Sb–Se films were characterized through XRD, Raman spectroscopy, SEM, UV–Vis and XPS spectroscopy. The structural studies revealed that a substrate temperature of 350 °C promotes the CuSbSe2 phase with an orthorhombic nature and reduces the secondary phases. The best structural and optical properties are found at a substrate temperature of 350 °C, indicating that it can be used as an absorber layer in photovoltaic devices.