Sn Thin Films Research Articles

Giant room-temperature electrocaloric effect within wide temperature span in Sn-doped Ba0.85Ca0.15Zr0.1Ti0.9O3 lead-free thin films

The electrocaloric (EC) effect cooling technique of environmentally friendly lead-free thin film materials driven by electric fields has recently gained tremendous attention due to the urgent demand for microelectronic and integrated circuit refrigeration devices. However, the widespread use of lead-free materials in EC devices is seriously hindered due to the small electrocaloric temperature change (ΔT) within a narrow operation temperature span (Tspan) near room temperature. Here, lead-free Ba0.85Ca0.15Zr0.1Ti0.9-xSnxO3 (BCZT-xSn, 0 ≤ x ≤ 0.03) thin films were prepared on substrates (Pt/Ti/SiO2/Si) via a sol-gel route. The BCZT-0.02Sn thin film presents an excellent EC effect (ΔT = 32.74 K, ΔS = 37.18 J kg−1 K−1) and large EC strength (ΔT/ΔE = 0.033 K cm kV−1, ΔS/ΔE = 0.037 J cm K−1 kg−1 kV−1) over a wide Tspan (∼26 K) under 1000 kV cm−1 near room temperature. The giant ΔT is mainly attributed to the emergence of an intermediate O phase and the formation of a multiphase (R, O and T phases) coexistence structure at room temperature, while the diffuse phase transition behavior is responsible for the wide Tspan. Our study provides a new idea for developing environment-friendly EC materials with an excellent room-temperature ΔT over a broad operational temperature region.

Texture in ITO films deposited at oblique incidence by ion beam sputtering

Texture of crystalline In2O3:Sn (ITO) thin films prepared by combining ion beam sputtering (IBS) at room temperature and oblique angle deposition (OAD) has been studied depending on the vapor incidence on Si substrates (α, ranging from 50°to 85°) and the ions used to sputter the target (argon or xenon accelerated at 1.2keV). Films obtained using Xe ions show an unusual evolution depending on the deposition angle α, with the development of a dual biaxial (111) off-axis texture for α≤70°, and a switching in the preferred out-of-plane orientation from [111] to [001] for α>70°that leads to a biaxial (001) texture at highest deposition angles. These behaviors are well described by mechanisms involving a maximization of the direct capture of the adatoms on {111} planes, which can however be hindered when mobilities are exalted such as in the case of Ar deposition. The tuning of adatoms mobilities through the IBS process mixed with the control of the deposition angle offered by the OAD geometry appears as an efficient route to achieve an upgraded texture engineering in nanostructured ITO thin films.

PREPARATION OF CZTS THIN FILM EMPLOYING RAPID THERMAL PROCESSING METHOD

CZTS thin film was fabricated by sulfurization process of deposited thin films on Mo coated glass substrates. Cu, Zn, and Sn thin film layers were deposited sequentially to form Glass/Mo/CuSn/Zn/Cu. The CuSn layer in the stacked structure was formed by annealing process in the sputtering chamber after sequential deposition of Cu and Sn, respectively. The sulfurization process was performed by rapid thermal processing method (RTP) so as to obtain kesterite CZTS structure. The obtained CZTS thin film was analyzed using several characterization methods such as EDX, XRD, Raman spectroscopy, SEM and PL measurements. The EDX measurements showed that elemental loss was not observed after the annealing process in sulfur atmosphere. The fabricated CZTS thin film showed Cu stoichiometric and Zn rich composition. The XRD pattern of annealed sample revealed formation of kesterite CZTS structure. The Raman spectra of the sample proved formation of kesterite CZTS structure. In addition, some CTS phases were detected in the structure by Raman spectroscopy. Polycrystalline surface microstructure was seen in SEM surface measurement. The room temperature PL measurement exhibited a transition around at 1.39 eV that is very close to band gap of kesterite CZTS structure. Overall, with this study, it has been shown that the CZTS thin film structure can be easily produced using the RTP method with very high heating rate.

A low cost Sn doped ZnO thin film based Schottky diode for UV detection

In this paper thin films of Sn doped ZnO was prepared via low-cost chemical sol-gel spin coating process. The Ohmic electrode Aluminum (Al) and Schottky electrode Palladium (Pd) on doped ZnO thin film were deposited through a hard mask by thermal evaporation techniques to obtain a planner Metal-Semiconductor-Metal (MSM) structure; hence present device was horizontal. The electrical characterization is used to analyze the UV detection capability of the fabricated device, and various calculated parameters include saturation current = 8.31 × 10−7 A/cm−2, ideality factor = 4.02, barrier height = 0.75 eV, etc. It was observed that forward and reversed bias current increases when exposed to Ultraviolet (UV) light. In addition, responsivity and series resistance are also reported in this paper.

Annealing temperature effect on the surface properties and antimicrobial activity of SnSe thin films

In this study, tin selenide thin films with various atomic ratios were fabricated using the RF magnetron co-sputtering method and annealed at different temperatures. In order to observe the structural and chemical properties of the thin films, various characterization tools and methods such as atomic force microscope (AFM), scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy, Kelvin probe, and antimicrobial test against Escherichia coli were performed. SEM and AFM images showed that the surface morphology of the thin films changed at 573 K. Additionally, the phase changed from amorphous to orthorhombic SnO2 at high temperature, which was confirmed by XRD results. XPS results confirmed SnSe thin films was oxidized and Se evaporated as the annealing temperature increased. The work function of thin films with higher contents of Sn than Se were increased from 5.23 to 5.68 eV as the annealing temperature increased. On the other hand, the work function of thin films with higher Se content than Sn decreased from 5.86 to 5.44 eV. Antimicrobial testing revealed that the SnSe thin films exhibit a stronger effect compared to pure Sn and Se thin films.

Physicochemical Properties of SnTe Thin Films Dependent on Compositional Ratios

This study introduces physicochemical properties based on the compositional ratio of the SnTe thin films (TFs) fabricated by radio frequency (RF) magnetron cosputtering. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results show that the grain sizes decrease with increasing Te content, with pure Te TFs yielding the lowest Rq value (root mean square value of roughness) of 0.76 nm. Contact angle (CA) measurements show that pure Te TFs pertain to the highest total surface free energy. X‐Ray diffraction (XRD) patterns strongly indicate that pure Te TFs exhibit a hexagonal crystal structure and pure Sn TFs exhibit a tetragonal crystal structure. The dominant oxide species on the surface is TeO2 for Te‐rich films, which is deduced by X‐Ray photoelectron spectroscopy (XPS) results. Pure Te TFs yield a work function value of 4.88 eV when measured with ultraviolet photoelectron spectroscopy (UPS) and 5.46 eV when measured with a Kelvin probe. SnTe TFs with 70% Te content exhibit the lowest electrical conductivity among the fabricated TFs.

Electrochemical Properties of Multilayered Sn/TiNi Shape-Memory-Alloy Thin-Film Electrodes for High-Performance Anodes in Li-Ion Batteries.

Sn is a promising candidate anode material with a high theoretical capacity (994 mAh/g). However, the drastic structural changes of Sn particles caused by their pulverization and aggregation during charge–discharge cycling reduce their capacity over time. To overcome this, a TiNi shape memory alloy (SMA) was introduced as a buffer matrix. Sn/TiNi SMA multilayer thin films were deposited on Cu foil using a DC magnetron sputtering system. When the TiNi alloy was employed at the bottom of a Sn thin film, it did not adequately buffer the volume changes and internal stress of Sn, and stress absorption was not evident. However, an electrode with an additional top layer of room-temperature-deposition TiNi (TiNi(RT)) lost capacity much more slowly than the Sn or Sn/TiNi electrodes, retaining 50% capacity up to 40 cycles. Moreover, the charge-transfer resistance decreased from 318.1 Ω after one cycle to 246.1 Ω after twenty. The improved cycle performance indicates that the TiNi(RT) and TiNi-alloy thin films overall held the Sn thin film. The structure was changed so that Li and Sn reacted well; the stress-absorption effect was observed in the TiNi SMA thin films.

Acid vapor oxidation growth of SnO2 nanospheres with ultra-high sensitivity to ethanol detection at low temperature

A facile acid vapor oxidation (AVO) method has been developed to grow highly round SnO2 nanospheres from 400 nm metal Sn thin films. This synthesis approach is able to directly grow nanostructures from a substrate in a simple reaction system involving the reaction of Sn film with the vapor generated from a hydrochloric acid solution in a Teflon-lined autoclave. A possible growth mechanism for the interesting SnO2 nanospheres has been proposed based on a series of time-dependent experiments. As-prepared SnO2 nanospheres have diameters around 150 nm. The influence of reacting time on the gas sensing properties of SnO2 was investigated by the detection of ethanol gas. The as-obtained SnO2 nanospheres are ultrasensitive to ethanol with a response of 1.49–50 ppb of ethanol at the low optimal working temperature of 170 ℃, which shows the promising candidates for high performance chemical sensors. This work offers a facile, shape-controlled, and efficient route to synthesize complex SnO2 nanospheres for gas detection with high performance, including ultrahigh sensitivity, good selectivity, and reversibility.

Thickness-dependent topological phase transition and Rashba-like preformed topological surface states of α-Sn(001) thin films on InSb(001)

Topological materials, possessing spin-momentum locked topological surface states (TSS), have attracted much interest due to their potential applications in spintronics. \ensuremath{\alpha}-phase Sn (\ensuremath{\alpha}-Sn), being one of them, displays enriched topological phases via band-gap engineering through a strain or confinement effect. In this work, we investigated the band evolution of in-plane compressively strained \ensuremath{\alpha}-Sn(001) thin films on InSb(001) in a wide range of thickness from 3 bilayers (BL) to 370 BL by combining angle-resolved photoemission spectra and first-principles calculations. Gapped surface states evolved to a linearly dispersive TSS at a critical thickness of 6 BL, indicating that the system undergoes a phase transition from topologically trivial to nontrivial. For films thicker than 30 BL, additional Rashba-like surface states (RSS) were identified. These RSS served as preformed TSS in another strain-induced topological phase transition. In thick films, 370-BL \ensuremath{\alpha}-Sn(001), so as to preclude the confinement effect in thin films, our results were consistent with a Dirac semimetal phase with Dirac nodes located along $\mathrm{\ensuremath{\Gamma}}--Z$. This thickness-dependent band-structure study deepens our understanding of topological phase transitions and the evolution of Dirac states. Furthermore, the coexistence of TSS and RSS in a Dirac semimetal \ensuremath{\alpha}-Sn might significantly enhance the potential for spintronic applications.

Tin instead of aluminum as a back electrode in P3HT:PC71BM organic solar cells

In the present work, a thin film of Sn metal, instead of aluminum, was deposited as a back electrode, using thermal evaporation, for fabricating organic solar cells composed of poly(3-hexylthiophene) and [6,6]-phenyl-C71 butyric acid methyl ester. The effect of post-thermal annealing on performance parameters of the solar cell was investigated at low temperatures (suitable for organic solar cells) up to 180 °C. In addition, the effect of thermal annealing on morphological (using scanning electron microscopy) and electrical properties (using a Hall effect setup) of the Sn thin films is reported and discussed here. The obtained minor effect of thermal annealing on the morphological and electrical properties of the Sn thin films is offset by an improvement in the performance parameters of the solar cells after post-annealing at 160 °C. The present study shows good electrical properties of Sn thin films which are comparable with those of aluminum thin films.

Investigation of Sn-containing precursors for in-plane GeSn nanowire growth

The formation of Sn catalyst nanoparticles (NPs) for the growth of GeSn nanowires (NWs) requires the identification of suitable Sn-containing precursors. In this work, various Sn-containing precursors such as Sn, SnO2 and indium tin oxide (ITO) thin films as well as SnO2 nanoparticles have been investigated. Sn and SnO2 thin films did not produce NWs. This reveals that the catalyst density, as well as their wetting on the amorphous layer, play vital roles on the growth of GeSn NWs. Conversely, Ge nanocrystals (NCs) were successfully grown from ITO thin films deposited on c-Si substrates. A good crystallinity was obtained when there is no interfacial SiOx layer on the crystalline Si substrate. Finally, using SnO2 NPs allowed us to grow GeSn NWs. Their morphology is strongly impacted by the annealing environment: hydrogen atmosphere with different pressures or hydrogen plasma, the later providing the best results. The nanostructure and composition of GeSn NWs were investigated in detail. These results could pave the way to grow in-plane Ge nanostructures within several types of Sn-containing materials.

Strained α-Sn thin films on highly lattice-mismatched Ge substrates

Strained α-Sn thin films and stanene (two-dimensional counterpart of α-Sn), which have attracted significant attentions due to their electronic properties as topological insulators, were mostly deposited on nearly lattice-matched substrates through molecular beam epitaxy. In this work, contrary to prior efforts, Sn thin films are deposited on highly lattice-mismatched Ge (100) substrates through physical vapor deposition of solid Sn sources. Three different methods, 1) Acetone/Isopropyl Alcohol (IPA), 2) Acetone/IPA/H2O(80°C), and 3) Hydrogen Peroxide (H2O2)/Hydrochloric Acid (HCl), are used to clean commercially available Ge (100) substrates. X-ray diffraction (XRD) characterizations indicate that compressively strained α-Sn thin films are formed on Ge substrates cleaned by Acetone/IPA/H2O(80°C) or H2O2/HCl, but no peak associated with crystalline α-Sn appears for thin films grown on Ge substrates cleaned by Acetone/IPA. Strained α-Sn thin films deposited on Ge substrates cleaned by Acetone/IPA/H2O(80°C) are further investigated using dielectric force microscopy (DFM). Although Ge substrates where α-Sn thin films are deposited are p-type, DFM images indicate that the α-Sn thin films are n-type. The α-Sn/Ge heterostructures that we demonstrate in this work might be promising in applications in advanced electronics and photonics.

Electrochemical Properties of Sn and Cu Multilayered Thin Films for Li Ion Battery Anodes

This paper investigates the electrochemical properties of Sn and Cu multilayers as anode materials for thin film Li ion batteries. The films were sequentially deposited on Cu foils using radio frequency magnetron sputtering system. Two, three, and four alternating layers of Sn/Cu were investigated for electrochemical properties. The results indicated improved capacity retention and rate capability for multilayers as compared to single layer Sn. This is attributed to the fact that inactive Cu layers improve physical adhesion and volume change of Sn upon lithiation. Multilayer structure of electrode with active/inactive components prove to be effective solution for thin film and microbatteries.AcknowledgementsThis work was supported by the projects 091019CRP2114 “Three-dimensional all solid state rechargeable batteries” from Nazarbayev University and OPFE2021001 “New materials and devices for defense and aerospace applications” Ministry of Digital Development, Innovation and Aerospace Industry of the Republic of Kazakhstan

Electrochemical Filling of Nanoporous Gold with Silver via Surface-Limited Redox Replacement

Nanoporous (np) metals feature a unique network of interconnected pores and ligaments structured at a length scale of a few to hundreds of nanometers. As a result, np metals have an inherently higher surface area-to-volume ratio resulting in lower melting temperature compared to their bulk metal counterparts. Most applications of np metals have been associated with electrocatalysis. However, in recent years, a growing interest in the use of np metals in microelectronics have been pursued. Among these applications is the development of np-Cu-based chip-to-substrate interconnections that is achieved by Cu-on-Cu bonding. np-Cu is an ideal candidate for solder alternatives because of its relatively lower melting and sintering temperatures. Furthermore, the incorporation of a thin film of Sn in the pores and/or the surface of the np-Cu ligaments could further lower its sintering temperature while maintaining low resistivity. In order to fabricate these composites, there must be strict control over the uniform and flat deposition of the Sn thin film on np-Cu.Here we present a proof-of-concept study on the development of an all-electrochemical metal-filling of np structures. Conventional methods like electron beam induced deposition and overpotential deposition (OPD) have been developed for the filling of porous structure. However, these approaches showed only partial filling that are also accompanied by the growth of three-dimensional protrusions forming outside of the pores. In order to overcome these complications, we developed an approach based on electrochemical atomic layer deposition by surface-limited redox replacement (SLRR). This method allows for a layer-by-layer deposition of metals that has been shown to form relatively flat and uniform deposits. In this study, the model porous structure is np-Au, which is prepared by the selective de-alloying of pre-deposited Au-Cu alloys. The np-Au structure was then filled with Ag via SLRR (in a one-cell configuration) that is realized by successive cycles of the adsorption of a Pb monolayer, serving as a sacrificial metal, that is immediately replaced by Ag via electroless galvanic displacement.A comparative study suggests that the SLRR approach results in a more uniform Ag-filling compared to a stepwise potentiostatic OPD approach that was also done independently. Morphological characterization via surface and cross-sectional scanning electron microscopy (SEM) reveals progressive filling of np-Au with Ag. Additionally, electrochemical BET characterization via cyclic voltammetry of Pb-underpotential deposition (Pb-UPD) was also used to monitor the filling process by measuring the electrochemical surface area of the Ag-filled np-Au composite. The findings from this study will be discussed in detail. Reference:Castillo, Y. Xie, and N. Dimitrov “Filling in nanoporous gold with silver via bulk deposition and surface-limited redox replacement approaches” Electrochimica Acta, 2021, 380, 138196.

Comparison and influence of metal dopants on the opto-electrical, microstructure and gas sensing properties of nanostructured indium oxide films

Thin films of pure and Sn, Zn, Mn, and Ag-doped indium oxide (In2O3) with a thickness of 150 nm are grown by co-deposition using thermal evaporation technique and annealed at 500 °C. The crystal lattice strain, dislocation density, optical band gap, surface roughness, and gas sensitivity of the films are studied. Comparison of AFM results shows that the Ag-doped In2O3 has the highest roughness. The ethanol vapor sensing results demonstrate that 3% Ag-doped In2O3 films have higher sensitivity at the operating temperature of 325 °C to 1000 ppm of ethanol vapor, due to the presence of more roughness and defects than other films. The response and recovery times of this sample at 1000 ppm ethanol vapor were 32 and 51 s, respectively. Finally, it is shown how 3% of metal impurities in the In2O3 layer can affect the optical, microstructural, and gas sensing parameters of the samples, and also investigated the correlation between them.

Versatile electronic states in epitaxial thin films of (Sn-Pb-In)Te: From topological crystalline insulator and polar semimetal to superconductor

Epitaxial thin films of (Sn$_{x}$Pb$_{1-x}$)$_{1-y}$In$_{y}$Te were successfully grown by molecular-beam-epitaxy (MBE) in a broad range of compositions (0 $\leq$ x $\leq$ 1, 0 $\leq$ y $\leq$ 0.23). We investigated electronic phases of the films by the measurements of electrical transport and optical second harmonic generation. In this system, one can control the inversion of band gap, the electric polarization that breaks the inversion symmetry, and the Fermi level position by tuning the Pb/Sn ratio and In composition. A plethora of topological electronic phases are expected to emerge, such as topological crystalline insulator, topological semimetal, and superconductivity. For the samples with large Sn compositions (x > 0.5), hole density increases with In composition (y), which results in the appearance of superconductivity. On the other hand, for those with small Sn compositions (x < 0.5), increase in In composition reduces the hole density and changes the carrier type from p-type to n-type. In a narrow region centered at (x, y) = (0.16, 0.07) where the n-type carriers are slightly doped, charge transport with high mobility exceeding 5,000 cm$^{2}$V$^{-1}$s$^{-1}$ shows up, representing the possible semimetal states. In those samples, the optical second harmonic generation measurement shows the breaking of inversion symmetry along the out-of-plane [111] direction, which ensures the presence of polar semimetal state. The thin films of (Sn$_{x}$Pb$_{1-x}$)$_{1-y}$In$_{y}$Te materials systems with a variety of electronic states would become a promising materials platform for the exploration of novel quantum phenomena.

Analysis of Pressure-Induced Whisker Nucleation and Growth in Thin Sn Films

Analysis of Pressure-Induced Whisker Nucleation and Growth in Thin Sn Films

High sensitivity and low electric power consumption NO2 sensor using SnO2 thin film for smart detector design

In this research, SnO2 thin films were prepared by oxidizing the Sn thin films firstly, which was applied for NO2 sensing. The morphology, crystal structure and surface state of the film were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). By optimizing the preparation conditions of SnO2 thin films (i.e., oxidation temperature and thickness of the film), the response to 40 ppb NO2 was increased by 6 times and the response time was shortened by 1.5 times. The sensor shows low detection limit to NO2 at the concentration of 5 ppb at room temperature. It could be found that the high surface area to volume ratio and oxygen vacancy were considered to improving the sensing performance. The NO2 sensor fabricated by this method was available readily, high sensitivity and low power consumption (microwatt magnitude), which has great potential for commercial application.

Sol-gel derived ZnO:Sn thin films and fabrication of n-ZnO:Sn/p-Si heterostructure

In this work ZnO:Sn thin films were deposited onto glass and p-Si substrates by spin coating of prepared sols which contains different amounts of Zn(CH3COO)2·2H2O and SnCl2 (0, 5, 10 and 15%). Physical properties of ZnO films were examined as a function of SnCl2 in prepared sols. In addition to that, heterostructure examinations were also carried out by depositing all films on p-Si substrates as well. XRD studies revealed that all films have c-axis orientation with crystallite sizes between 38 and 47 nm. AFM and SEM images showed that morphology of the films remarkably deteriorated with the increase in amount of SnCl2 in sol. Optical transmittance and absorbance spectra showed that films have high transmittance and low absorbance in the visible region. Besides, optical band gap increased from 3.27 eV to 3.37 eV. Additional band gap energies were determined for 10% and 15% Sn doped ZnO films. Room temperature photoluminescence spectra for all films were deconvoluted for the evaluation of all emission bands and it was noted that incorporation of SnCl2 into sol led to enhancement of UV-blue emission bands and caused emission bands related to oxygen vacancies to diminish. Four-point-probe measurements revealed that electrical resistivity of ZnO:Sn films increased from 3.20 × 100 Ωcm to 2.82 × 104 Ωcm and diode ideality factor of Ag/ZnO:Sn/p-Si/Au heterostructure was calculated to be in the range of 2.14–4.59 while zero-bias barrier height is in the range of 0.63–0.78 eV.

Microstructural and Superconducting Radiofrequency Properties of Multilayer Sequentially Sputtered Nb3Sn films

Nb3Sn is considered as a potential candidate for superconducting radiofrequency cavities for particle acceleration due to its higher transition temperature of 18.3 K and higher superheating field of 400 mT. Nb3Sn films can be grown inside the surface of a Nb cavity by sequentially sputtering multiple layers of Nb and Sn thin films followed by annealing at 950 °C for 3 h. We report on the properties of Nb3Sn films grown on Nb substrates by magnetron sputtering. The films' crystal structure, surface morphology, and composition were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The films had a polycrystalline Nb3Sn structure with a fine-grain surface and an atomic Sn composition of ~23%. The RF surface resistance of the films was measured for different temperatures at 7.4 GHz to understand the feasibility of this method for the SRF application. The RF surface resistance of the films was 5 mΩ at 12 K, which is about 2 orders of magnitude higher than 60 μΩ previously measured in Nb3Sn films grown by Sn vapor diffusion. The sputtered film had a superconducting transition at 17.2 K, which is also lower than 17.9 K observed in Nb3Sn film prepared by vapor diffusion.