Showing papers on "Thin film published in 2022"

Superconductivity in infinite-layer nickelate La _1−x Ca _x NiO ₂ thin films

Abstract: We report the observation of superconductivity in infinite-layer Ca-doped LaNiO2 (La1-xCaxNiO2) thin films and construct their phase diagram. Unlike the metal-insulator transition in Nd- and Pr-based nickelates, the undoped and underdoped La1-xCaxNiO2 thin films are entirely insulating from 300 K down to 2 K. A superconducting dome is observed at 0.15 < x < 0.3 with weakly insulating behavior at the overdoped regime. Moreover, the sign of the Hall coefficient RH changes at low temperature for samples with a higher doping level. However, distinct from the Nd- and Pr-based nickelates, the RH-sign-change temperature remains at around 35 K as the doping increases, which begs further theoretical and experimental investigation to reveal the role of the 4f orbital to the (multi)band nature of the superconducting nickelates. Our results also emphasize a notable role of lattice correlation on the multiband structures of the infinite-layer nickelates.

A comprehensive review on Bi2Te3‐based thin films: Thermoelectrics and beyond

Abstract: Bi2Te3‐based materials are not only the most important and widely used room temperature thermoelectric (TE) materials but are also canonical examples of topological insulators in which the topological surface states are protected by the time‐reversal symmetry. High‐performance thin films based on Bi2Te3 have attracted worldwide attention during the past two decades due primarily to their outstanding TE performance as highly efficient TE coolers and as miniature and flexible TE power generators for a variety of electronic devices. Moreover, intriguing topological phenomena, such as the quantum anomalous Hall effect and topological superconductivity discovered in Bi2Te3‐based thin films and heterostructures, have shaped research directions in the field of condensed matter physics. In Bi2Te3‐based films and heterostructures, delicate control of the carrier transport, film composition, and microstructure are prerequisites for successful device operations as well as for experimental verification of exotic topological phenomena. This review summarizes the recent progress made in atomic defect engineering, carrier tuning, and band engineering down to a nanoscale regime and how it relates to the growth and fabrication of high‐quality Bi2Te3‐based films. The review also briefly discusses the physical insight into the exciting field of topological phenomena that were so dramatically realized in Bi2Te3‐ and Bi2Se3‐based structures. It is expected that Bi2Te3‐based thin films and heterostructures will play an ever more prominent role as flexible TE devices collecting and converting low‐level (body) heat into electricity for numerous electronic applications. It is also likely that such films will continue to be a remarkable platform for the realization of novel topological phenomena.

Efficient FeCoNiCuPd thin-film electrocatalyst for alkaline oxygen and hydrogen evolution reactions

Abstract: The creation of high-performing, robust bifunctional electrocatalysts for both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) in water-splitting is crucial for producing emerging hydrogen economy. Here we report a high entropy alloy (HEA) – FeCoNiCuPd – thin film catalyst, which demonstrated excellent alkaline HER and OER performance with ultralow overpotentials as low as 29 mV for HER and 194 mV for OER at a current density of 10 mA cm− 2. The outstanding catalytic activity for HER was found to originate from the multiple active sites present on the FeCoNiCuPd surface, while for OER it came from the highly functional (FeCoNi)-oxyhydroxide species formed on the film surface. Moreover, the two-electrode electrolyzer made of the FeCoNiCuPd film electrodes required a low cell voltage of 1.52 V to achieve 10 mA cm−2 in 1.0 M KOH, greatly outperforming commercially available Pt/C||RuO2 electrodes, while maintaining a notable durability. This work demonstrated the remarkable potential of a HEA thin film in catalyzing water-splitting process.

Solar fuel generation over nature-inspired recyclable TiO2/g-C3N4 S-scheme hierarchical thin-film photocatalyst

Abstract: Preparation of efficient photocatalysts with ease of recovery in solar fuel generation is highly desired to achieve carbon neutralization in carbon dioxide (CO2) emissions. Inspired from the forest with superior light penetration and fast gas transport, a TiO2/g-C3N4 composite nanowire arrays (NAs) film with maximized light utilization is devised. It is achieved by in-situ coating a thin layer of g-C3N4 (as the leaf) on the vertically-oriented TiO2 arrays (as tree trunks) on Ti foil (as soil). Benefiting from the effective charge separation by S-scheme charge transfer, intimate contact by the in-situ growth as well as the ingenious structure, the composite, readily recyclable, displays exciting performance in photocatalytic CO2 reduction. It is beyond doubt that the combination of heterojunction construction and “nature-inspired biomimetic photocatalyst” design promises practical applications and industrial use.

Intensive linear and nonlinear optical studies of thermally evaporated amorphous thin Cu-Ge-Se-Te films

Abstract: This article is devoted to completing the study of linear and nonlinear optical characteristics of thermally evaporated a-CuxGe20-xSe40Te40, CGST, (0 ≤ x ≤ 20 at.%) thin films. The film thickness and rate of deposition were fixed in 2000 Å and 100 Å/s, respectively. Optical constants of CGST-films have been deduced from spectrophotometric measurements in the spectral range 300nm-2500 nm. The VB and CB potentials have been determined; their values increase from 0.344 eV to 0.404 eV for the CB, while increases from (-0.864 eV) to (-0.641 eV) for VB, as Cu-percentage increases. Wemple-DiDomenico single oscillator model is applied to obtain dispersion energies and parameters. The single oscillator energy decreases from 2.411 eV to 2.232 eV, while the dispersion energy increases from 14.974 eV to 20.763 eV, as Cu-ration increases. Many other important optoelectrical and dielectric parameters have also been discussed, like static refractive index, average oscillator wavelength, oscillator-length strength parameters. The surface and volume energy loss functions, optical complex conductivity (real and imaginary parts), electronic polarizability, and some nonlinear optical parameters are also well-discussed. Total electronic polarizability values increase from 4.560 Å to 3.088 Å, while the plasma frequency increases from 4.200×1014 Hz to 3.970×1014 Hz. All mapped parameters have been discussed and linked to each other, as well as studying their dependence on Cu-ratio.

Urbach Energy and Open-Circuit Voltage Deficit for Mixed Anion-Cation Perovskite Solar Cells.

Abstract: The Urbach energy indicating the width of the exponentially decaying sub-bandgap absorption tail is commonly used as the indicator of electronic quality of thin-film materials used as absorbers in solar cells. Urbach energies of hybrid inorganic-organic metal halide perovskites with various anion-cation compositions are measured by photothermal deflection spectroscopy. The variation in anion-cation composition has a substantial effect on the measured Urbach energy and hence the electronic quality of the perovskite. Depending upon the compositions, the Urbach energy varies from 18 to 65 meV for perovskite films with similar bandgap energies. For most of the perovskite compositions studied here including methylammonium (MA) + formamidinium (FA)-based Pb iodides, mixed Sn + Pb narrow-bandgap perovskites with low or intermediate Sn contents, and wide-bandgap FA + Cs- and I + Br-based perovskites, the correlation between the Urbach energy of the perovskite thin film and open-circuit voltage (VOC) deficit for corresponding solar cells shows a direct relationship with reduction of the Urbach energy occurring with a beneficial decrease in the VOC deficit. However, due to issues related to material quality, impurity phases and stability in laboratory ambient air, and unoptimized film processing techniques, the solar cells incorporating Cs-based inorganic and mixed Sn + Pb perovskites with a higher than optimum Sn content show a higher VOC deficit even though the corresponding films show a lower Urbach energy.

Solar light induced photocatalytic activation of peroxymonosulfate by ultra-thin Ti3+ self-doped Fe2O3/TiO2 nanoflakes for the degradation of naphthalene

Abstract: Ti 3+ self-doped Fe 2 O 3 /TiO 2 ultra-thin nanoflakes have been fabricated on Ti-substrate by a facile hydrothermal route. The high solar light harvest by Ti 3+ and oxygen vacancies makes Ti 3+ self-doped Fe 2 O 3 /TiO 2 ultra-thin nanoflakes an attractive candidate for photo-activation of peroxymonosulfate (HSO 5 − ) for the degradation of naphthalene (NAP). The Fe 2 O 3 /TiO 2 ultra-thin nanoflakes synthesized with 0.053 M of FeCl 3 (TF3) exhibited high concentrations of Ti 3+ and oxygen vacancies. TF3/ HSO 5 − /solar light system showed substantial increases in the degradation of NAP with k app value of 0.1384 min –1 compared to 0.057 min –1 when no HSO 5 − was added to the system. The proposed system also showed appreciable degradation of NAP in real water samples. Based on scavenger studies, SO 4 •− , • OH, h + and O 2 •− are generated in the reaction system. Importantly, the toxicity results indicated that the proposed system (TF3/HSO 5 − /solar light) is an efficient treatment process for detoxifying water contaminated with NAP. • Ultra-thin Ti 3+ self-doped Fe 2 O 3 /TiO 2 nanoflakes were synthesized on Ti-substrate. • The ultra-thin nanoflakes exhibited high concentration of Ti 3+ and oxygen vacancies. • Synergy of HSO 5 − greatly accelerated the degradation performance of TF3 material. • ESR analysis confirmed the formation of • OH and SO 4 •− by TF3/HSO 5 − /solar light. • ECOSAR results indicated proposed system can detoxify waters contaminated with NAP.

Tunable Metasurface using thin film lithium-niobate in the telecom regime

Abstract: We demonstrate a tunable metasurface made of aluminum nanodisk array coated with ITO on a thin film of lithium niobate. A spectral resonant shift of few nanometers and modulation contrast of ~40% are observed.

Directional Thermal Diffusion Realizing Inorganic Sb2Te3/Te Hybrid Thin Films with High Thermoelectric Performance and Flexibility

Abstract: Inorganic films possess much higher thermoelectric performance than their organic counterparts, but their poor flexibilities limit their practical applications. Here, Sb2Te3/Tex hybrid thin films with high thermoelectric performance and flexibility, fabricated via a novel directional thermal diffusion reaction growth method are reported. The directional thermal diffusion enables rationally tuning the Te content in Sb2Te3, which optimizes the carrier density and leads to a significantly enhanced power factor of >20 µW cm–1 K–2, confirmed by both first‐principles calculations and experiments; while dense boundaries between Te and Sb2Te3 nanophases, contribute to the low thermal conductivity of ≈0.86 W m–1 K–1, both induce a high ZT of ≈1 in (Sb2Te3)(Te)1.5 at 453 K, ranking as the top value among the reported flexible films. Besides, thin films also exhibit extraordinary flexibility. A rationally designed flexible device composed of (Sb2Te3)(Te)1.5 thin films as p‐type legs and Bi2Te3 thin films as n‐type legs shows a high power density of >280 µW cm–2 at a temperature difference of 20 K, indicating a great potential for sustainably charging low‐power electronics.

Recent Progress in Mixed A‐Site Cation Halide Perovskite Thin‐Films and Nanocrystals for Solar Cells and Light‐Emitting Diodes

Abstract: Over the past few years, lead‐halide perovskites (LHPs), both in the form of bulk thin films and colloidal nanocrystals (NCs), have revolutionized the field of optoelectronics, emerging at the forefront of next‐generation optoelectronics. The power conversion efficiency (PCE) of halide perovskite solar cells has increased from 3.8% to over 25.7% over a short period of time and is very close to the theoretical limit (33.7%). At the same time, the external quantum efficiency (EQE) of perovskite LEDs has surpassed 23% and 20% for green and red emitters, respectively. Despite great progress in device efficiencies, the photoactive phase instability of perovskites is one of the major concerns for the long‐term stability of the devices and is limiting their transition to commercialization. In this regard, researchers have found that the phase stability of LHPs and the reproducibility of the device performance can be improved by A‐site cation alloying with two or more species, these are named mixed cation (double, triple, or quadruple) perovskites. This review provides a state‐of‐the‐art overview of different types of mixed A‐site cation bulk perovskite thin films and colloidal NCs reported in the literature, along with a discussion of their synthesis, properties, and progress in solar cells and LEDs.

Assembly‐Free Fabrication of High‐Performance Flexible Inorganic Thin‐Film Thermoelectric Device Prepared by a Thermal Diffusion

Abstract: High relative contact electrical resistance and poor flexibility in inorganic thin‐film thermoelectric devices significantly limit their practical applications. To overcome this challenge, a one‐step thermal diffusion method to fabricate assembly‐free inorganic thin‐film thermoelectric devices is developed, where the in situ grown electrode delivers an excellent leg‐electrode contact, leading to high output power and flexibility in the prepared p‐type Sb2Te3/n‐type Bi2Te3 thin‐film device, which is composed of 8 pairs of p‐n junctions. Such a device shows a very low relative contact electrical resistance of 7.5% and a high power density of 1.42 mW cm–2 under a temperature difference of 60 K. Less than 10% change of the whole electrical resistance before and after bending test indicates the robust bending resistance and stability of the device. This study indicates that the novel assembly‐free one‐step thermal diffusion method can effectively enhance the leg‐electrode contact, the device thermoelectric performance, bending resistance, and stability, which can inspire the development of thin‐film thermoelectric devices.

Layer-dependent optical and dielectric properties of centimeter-scale PdSe2 films grown by chemical vapor deposition

Abstract: Abstract Palladium diselenide (PdSe 2 ), a new type of two-dimensional noble metal dihalides (NMDCs), has received widespread attention for its excellent electrical and optoelectronic properties. Herein, high-quality continuous centimeter-scale PdSe 2 films with layers in the range of 3L–15L were grown using Chemical Vapor Deposition (CVD) method. The absorption spectra and DFT calculations revealed that the bandgap of the PdSe 2 films decreased with the increasing number of layers, which is due to the enhancement of orbital hybridization. Spectroscopic ellipsometry (SE) analysis shows that PdSe 2 has significant layer-dependent optical and dielectric properties. This is mainly due to the unique strong exciton effect of the thin PdSe 2 film in the UV band. In particular, the effect of temperature on the optical properties of PdSe 2 films was also observed, and the thermo-optical coefficients of PdSe 2 films with the different number of layers were calculated. This study provides fundamental guidance for the fabrication and optimization of PdSe 2 -based optoelectronic devices.

A New Approach to the Formation of Nanosized Gold and Beryllium Films by Ion-Beam Sputtering Deposition

Abstract: Thin films of beryllium and gold that are several tens of nanometers thick were obtained, for the first time, on silicon and quartz substrates by the ion-beam method with tenfold alternation of deposition and partial sputtering of the nanosized metal layer. Scanning electron and atomic force microscopy indicate the predominant lateral growth of nanosized metal layers along the substrate surface. Optical spectra indicate the suppression of the localized plasmon resonance. The growth of the film occurs under the influence of the high-energy component of the sputtered metal atoms’ flux. The main role in the formation of the nanosized metal film is played by the processes of the elastic collision of incident metal atoms with the atoms of a substrate and a growing metal film. Metal films that are obtained by the tenfold application of the deposition–sputtering of a nanoscale metal layer are characterized by stronger adhesion to the substrate and have better morphological, electrical, and optical characteristics than those that are obtained by means of direct single deposition.

Effect of thickness and reaction media on properties of ZnO thin films by SILAR

Abstract: Zinc oxide (ZnO) is one of the most promising metal oxide semiconductor materials, particularly for optical and gas sensing applications. The influence of thickness and solvent on various features of ZnO thin films deposited at ambient temperature and barometric pressure by the sequential ionic layer adsorption and reaction method (SILAR) was carefully studied in this work. Ethanol and distilled water (DW) were alternatively used as a solvent for preparation of ZnO precursor solution. Superficial morphology, crystallite structure, optical and electrical characteristics of the thin films of various thickness are examined applying X-ray diffraction (XRD) system, scanning electron microscopy, the atomic force microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, photoluminescence spectroscopy, Hall effect measurement analysis and UV response study. XRD analysis confirmed that thin films fabricated using ethanol or DW precursor solvents are hexagonal wurtzite ZnO with a preferred growth orientation (002). Furthermore, it was found that thin films made using ethanol are as highly crystalline as thin films made using DW. ZnO thin films prepared using aqueous solutions possess high optical band gaps. However, films prepared with ethanol solvent have low resistivity (10-2 Ω cm) and high electron mobility (750 cm2/Vs). The ethanol solvent-based SILAR method opens opportunities to synthase high quality ZnO thin films for various potential applications.

Niobium Tungsten Oxides for Electrochromic Devices with Long-Term Stability.

Abstract: There is a keen interest in the use of electrochromic materials because they can regulate light and heat, thereby reducing the cooling and heating energy. However, the long response time, short cycle life, and high power consumption of an electrochromic film hinder its development. Here, we report an electrochromic material of complex niobium tungsten oxides. The Nb18W16O93 thin films in the voltage range of 0 to -1.5 V show good redox kinetics with the coloration time of 4.7 s and bleaching time of 4.0 s, respectively. The electrochromic device based on the Nb18W16O93 thin film has an optical modulation of 53.1% at a wavelength of 633 nm, with the coloration efficiency of ∼46.57 cm2 C-1. An excellent electrochemical stability of 78.1% retention after 8000 cycles is also achieved. These good performances are due to the fast and stable Li-ion intercalation/extraction in the open framework of Nb18W16O93 with multiple ion positions. Our work provides a strategy for electrochromic materials with fast response time and good cycle stability.

Highly enhanced ferroelectricity in HfO2-based ferroelectric thin film by light ion bombardment

Abstract: Continuous advancement in nonvolatile and morphotropic beyond-Moore electronic devices requires integration of ferroelectric and semiconductor materials. The emergence of hafnium oxide (HfO2)–based ferroelectrics that are compatible with atomic-layer deposition has opened interesting and promising avenues of research. However, the origins of ferroelectricity and pathways to controlling it in HfO2 are still mysterious. We demonstrate that local helium (He) implantation can activate ferroelectricity in these materials. The possible competing mechanisms, including He ion–induced molar volume changes, vacancy redistribution, vacancy generation, and activation of vacancy mobility, are analyzed. These findings both reveal the origins of ferroelectricity in this system and open pathways for nanoengineered binary ferroelectrics. Description Ion enhanced polarization Hafnium oxide is an exciting material because it has ferroelectric behavior that makes it attractive for various device applications. Kang et al. found that the ferroelectric properties improve by bombarding films of hafnium oxide with a beam of helium ions. The ion bombardment creates oxygen vacancies and strain changes from helium implantation that push more of the polycrystalline samples into the ferroelectric orthorhombic phase. This method may become an important tool for stabilizing the ferroelectric phase for the next generation of electronic devices. —BG Helium ion bombardment of hafnium dioxide thin films improves the ferroelectric properties.

Tetrabutylammonium (TBA)-Doped Methylammonium Lead Iodide: High Quality and Stable Perovskite Thin Films

Abstract: This work reported the successive incorporation of tetrabutylammonium (TBA) into Methylammonium lead Iodide (MAPbI3) perovskite. The thin films were characterized by X-Ray diffraction (XRD), Scanning electron microscopy (SEM), Transmittance electron microscopy (TEM), Atomic force microscopy (AFM), and UV-Visible spectroscopy. It was shown that introducing TBA increases the crystallinity, grain size, surface morphology without pin-hole, and roughness of the MAPbI3 thin films. Moreover, the MA(1-X)TBAX PbI3 thin film shows better stability in a relative humidity of ∼60% after 15 days than the pure MAPbI3 thin film. The obtained results are hoped to be helpful for stability and improvement of the performance of the MAPbI3 thin films by doping TBA cations under ambient conditions.

Anisotropic super-hardness of hexagonal WB2±z thin films

Abstract: Transition metal diboride-based thin films are promising candidates to replace state-of-the-art protective and functional coating materials due to their unique properties. Here, we focus on hexagonal WB 2-z , showing that the AlB 2 structure is stabilized by B vacancies exhibiting its energetic minima at sub-stoichiometric WB 1.5 . Nanoindentation reveals super-hardness of 0001 oriented α-WB 2-z coatings, linearly decreasing by more than 15 GPa with predominant 10 1 orientation. This anisotropy is attributed to differences in the generalized stacking fault energy of basal and pyramidal slip systems, highlighting the feasibility of tuning mechanical properties by crystallographic orientation relations. GRAPHICAL ABSTRACT IMPACT STATEMENT First report of an anisotropic elastoplastic behaviour in super-hard PVD AlB 2 structured WB 2-z . Theoretical and experimental verification of thermodynamically most stable sub-stoichiometric α-WB 2-z coatings by structural and mechanical analysis.

Outstanding Charge Mobility by Band Transport in Two-Dimensional Semiconducting Covalent Organic Frameworks

Abstract: Two-dimensional covalent organic frameworks (2D COFs) represent a family of crystalline porous polymers with a long-range order and well-defined open nanochannels that hold great promise for electronics, catalysis, sensing, and energy storage. To date, the development of highly conductive 2D COFs has remained challenging due to the finite π-conjugation along the 2D lattice and charge localization at grain boundaries. Furthermore, the charge transport mechanism within the crystalline framework remains elusive. Here, time- and frequency-resolved terahertz spectroscopy reveals intrinsically Drude-type band transport of charge carriers in semiconducting 2D COF thin films condensed by 1,3,5-tris(4-aminophenyl)benzene (TPB) and 1,3,5-triformylbenzene (TFB). The TPB–TFB COF thin films demonstrate high photoconductivity with a long charge scattering time exceeding 70 fs at room temperature which resembles crystalline inorganic materials. This corresponds to a record charge carrier mobility of 165 ± 10 cm2 V–1 s–1, vastly outperforming that of the state-of-the-art conductive COFs. These results reveal TPB–TFB COF thin films as promising candidates for organic electronics and catalysis and provide insights into the rational design of highly crystalline porous materials for efficient and long-range charge transport.