Film Heterostructures Research Articles

Magnetoelectric multiferroic properties of BaTiO3-CoFe2O4-BaTiO3 tri-layer thin films fabricated by pulsed laser deposition

A magnetoelectric multiferroic bi-phase system with robust ferroelectric and ferro/ferri-magnetism response at room temperature would be ideally suitable for microelectronics, memory devices, and for spintronic applications. BaTiO3/CoFe2O4/BaTiO3(BTO/CFO/BTO) heterostructured films were pulsed laser deposition grown on Pt(111)/TiO2/SiO2/Si substrates. High quality polycrystalline films were grown by thermal annealing at 750 °C, at an oxygen partial pressure of 100 mTorr for 1 h. Crystal quality and phase formation information was monitored using X-ray diffraction (XRD). XRD confirm the growth of polycrystalline heterostructures and the coexistence of both perovskite BTO and spinel CFO phases in heterostructures. In order to obtain robust magnetoelectric coupling, we studied the tri-layer structure as a representative ferroelectric/ferrimagnetic/ferroelectric system. We report the ferroelectric, leakage current behavior, ferrimagnetic, and frequency dependent ME properties of the films. Ferroelectric BTO and ferrimagnetic inverse spinel CFO nature is also confirmed using the piezoresponse force microscopy and magnetic force microscopy measurements. These nanostructures exhibit high saturation polarization (Ps ∼ 99.86 µC/cm2), saturation magnetization (Ms ∼ 51.48 emu/cm3), and a strong ME coupling coefficient of ∼ 274 mV/cm-Oe with a bias magnetic field of + 90 Oe, anda frequency of 1 kHz revealing them as prospective candidates for multifunctional applications.

Heterostructures Based on Noble Metal Films with Ag and Au Nanoparticles: Fabrication, Study of In Vivo Biocompatibility and Antibacterial Activity

In this work, approaches to the formation of multifunctional film heterostructures based on noble metals for the modification of the surface of implant materials (titanium alloy TiAl6V4 and carbon-fiber-reinforced polyetheretherketone CFR-PEEK) are developed. Such heterostructures consist of continuous layers of platinum (Pt) or iridium (Ir) and antibacterial components on their surface, namely silver (nanoparticles or discontinuous films) and gold (nanoparticles). Chemical or physical gas-phase deposition methods were used for their preparation. The influence of the concentration and form of the antibacterial component on the antibacterial activity and in vivo biocompatibility of the film structures was evaluated for the first time. Differences in the dynamics of silver dissolution depending on Ag concentration in the sample and the type of bottom surface (the noble metal layer = Ir, Pt or TiAl6V4) surfaces allowed us to better understand the nature of the antibacterial action against Staphylococcus aureus and Pseudomonas aeruginosa (S. aureus and P. aeruginosa) of Ag/M heterostructures. From in vivo histological studies using rats, the best biocompatibility was shown by the Ag/M heterostructure with a prolonged release of the low fraction of antibacterial component (Ag).

Fabrication of ordered layered SnO2/TiO2 heterostructures and their photocatalytic performance for methyl blue degradation.

The rapid growth in population and industrialization has given rise to serious environmental issues, especially the water pollution. Photocatalysis with the assist of semiconductor photocatalysts has been considered as an advanced oxidation technique for degrading a variety of pollutants under solar irradiation. In this work, we have fabricated SnO2-TiO2 heterostructures with different ordered layers of SnO2 and TiO2 via the sol-gel dip-coating technique and utilized in photocatalysis for degradation of methyl blue dye under UV irradiation. The influence of the layer's position on SnO2 and TiO2 properties is investigated via the various techniques. The grazing incidence X-ray diffraction (GIXRD) analysis reveals that the as-prepared films exhibit pure anatase TiO2 and kesterite SnO2 phases. The 2SnO2/2TiO2 heterostructure exhibit the maximum crystallite size and smallest deviation from the ideal structure. Scanning electron microscopy cross-section images manifest good adhesion of the layers to each other and to the substrate. Fourier transform infrared spectroscopy reveals the characteristic vibration modes of SnO2 and TiO2 phases. UV-visible spectroscopy measurements indicate that all films exhibit high transparency (T = 80%) and the SnO2 film reveals a direct band gap of 3.6eV, while the TiO2 film exhibits an indirect band gap of 2.9eV. The optimal 2SnO2/2TiO2 heterostructure film revealed best photocatalytic degradation performance and the reaction rate constant for methylene blue solution under UV irradiation. This work will trigger the development of highly efficient heterostructure photocatalysts for environmental remediation.

Controlled Electronic and Magnetic Landscape in Self-Assembled Complex Oxide Heterostructures.

Complex oxide heterointerfaces contain a rich playground of novel physical properties and functionalities, which give rise to emerging technologies. Among designing and controlling the functional properties of complex oxide film heterostructures, vertically aligned nanostructure (VAN) films using a self-assembling bottom-up deposition method presents great promise in terms of structural flexibility and property tunability. Here, the bottom-up self-assembly is extended to a new approach using a mixture containing a 2Dlayer-by-layer film growth, followed by a 3D VAN film growth. In this work, the two-phase nanocomposite thin films are based on LaAlO3 :LaBO3 , grown on a lattice-mismatched SrTiO3001 (001) single crystal.The 2D-to-3D transient structural assembly is primarily controlled by the composition ratio, leading to the coexistence of multiple interfacial properties, 2D electron gas, and magnetic anisotropy. This approach provides multidimensional film heterostructures which enrich the emergent phenomena for multifunctional applications.

Scalable Solution Phase Synthesis of 2D Siloxene via a Two-Step Interlayer Expansion Process.

Two-dimensional (2D) siloxene is attracting considerable research interest recently principally owing to its inherent compatibility with silicon-based semiconductor technology. -The synthesis of siloxene has been mostly limited to multilayered structures using traditional topochemical reaction procedures. Herein, we report high-yield synthesis of single to few-layer siloxene nanosheets by developing a two-step interlayer expansion and subsequent liquid phase exfoliation procedure. Our protocol enables high-yield production of few-layer siloxene nanosheets with a lateral dimension of up to 4 μm and thickness ranging from 0.8 to 4.8 nm, corresponding to single to a few layers, well stabilized in water. The atomically flat nature of exfoliated siloxene can be exploited for the construction of 2D/2D heterostructure membranes via typical solution processing. We demonstrate highly ordered graphene/siloxene heterostructure films with synergistic mechanical and electrical properties, which deliver noticeably high device capacitance when assembled into a coin cell symmetric supercapacitor device structures. Additionally, we demonstrate that the mechanically flexible exfoliated siloxene-graphene heterostructure enables its direct use in flexible and wearable supercapacitor applications.

Schottky Barrier Control of Self-Polarization for a Colossal Ferroelectric Resistive Switching.

Controlling the domain evolution is critical both for optimizing ferroelectric properties and for designing functional electronic devices. Here we report an approach of using the Schottky barrier formed at the metal/ferroelectric interface to tailor the self-polarization states of a model ferroelectric thin film heterostructure system SrRuO3/(Bi,Sm)FeO3. Upon complementary investigations of the piezoresponse force microscopy, electric transport measurements, X-ray photoelectron/absorption spectra, and theoretical studies, we demonstrate that Sm doping changes the concentration and spatial distribution of oxygen vacancies with the tunable host Fermi level which modulates the SrRuO3/(Bi,Sm)FeO3 Schottky barrier and the depolarization field, leading to the evolution of the system from a single domain of downward polarization to polydomain states. Accompanied by such modulation on self-polarization, we further tailor the symmetry of the resistive switching behaviors and achieve a colossal on/off ratio of ∼1.1 × 106 in the corresponding SrRuO3/BiFeO3/Pt ferroelectric diodes (FDs). In addition, the present FD also exhibits a fast operation speed of ∼30 ns with a potential for sub-nanosecond and an ultralow writing current density of ∼132 A/cm2. Our studies provide a way for engineering self-polarization and reveal its strong link to the device performance, facilitating FDs as a competitive memristor candidate used for neuromorphic computing.

Dipole behavior in thin film heterostructure composed of Er-doped SnO2 and GaAs: Influence of polarization bias, temperature and stray light

The heterostructure system GaAs/SnO2 is built by resistive evaporation of Er-doped SnO2 powder on the top of GaAs semi-insulating substrate. The SnO2 powder comes from the drying of SnO2 sol-gel solution. The possible formation of dipoles in this heterostructure is investigated by the thermally stimulated depolarization current (TSDC) technique, and the possibilities for dipole formation are explored, such as the EL2 defect in the GaAs side, oxygen vacancies and Er ions in the SnO2 layer. The dipole relaxation activation energies are found in the range 0.2 eV to 0.3 eV, in good agreement with the ionization energies of these defects. The main TSDC bands: 213 meV with peak of −298 pA, for positive bias, and 218 meV with peak of 128 pA for negative bias, are modified by stray (room) light, which may correspond to the second ionization level of oxygen vacancies in SnO2, which are excited by the room lights and do not return to the original orientation.

Photocarrier transport of ferroelectric photovoltaic thin films detected by the magnetic dynamics of adjacent ferromagnetic layers

We have observed photocarrier transport behaviors in ${\mathrm{BiFeO}}_{3}/{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ (BFO/LSMO) heterostructures by using time-resolved synchrotron x-ray magnetic circular dichroism in reflectivity. The magnetization of LSMO layers was used as a probe of photo-induced carrier dynamics in the photovoltaic BFO layers. During the photo-induced demagnetization process, the decay time of LSMO ($x$=0.2) magnetization strongly depends on the ferroelectric polarization direction of the BFO layer. The variation of decay time should be attributed to the different sign of accumulated photocarriers at the BFO/LSMO interface induced by the photovoltaic effect of the BFO layer. The photocarriers can reach the BFO/LSMO interface and influence the magnetization distribution in the LSMO layers within the timescale of $\ensuremath{\sim}100$ ps. Our results provide a novel strategy to investigate carrier dynamics and mechanisms of optical control of magnetization in thin film heterostructures.

High performance ultraviolet photodetector based on CsPbCl3/ ZTO heterostructure film enabled by effective separation of photocarriers

Ultraviolet photodetectors have gained attention due to their wide range of applications. All-inorganic perovskite, especially CsPbCl3, has become a promising ultraviolet photoelectric detecting material in recent years due to its suitable band gap and excellent optical properties. However, because of the low solubility of CsCl in traditional organic solvents, the CsPbCl3 film quality is poor and its detection performance is limited to improve. During this work, we fabricated a high performance ultraviolet photodetectors based on CsPbCl3/ Zn2SnO4 heterostructure film. The introduction of Zn2SnO4 not only improves the quality of CsPbCl3 films, but also allows the interface charge of CsPbCl3 to be effectively separated. Under the dual action of heterostructure film, the on/ off switching ratio and responsivity of the device are increased by two and one orders of magnitude. In addition, we have successfully manufactured flexible ultraviolet photodetectors based on CsPbCl3/ Zn2SnO4 heterostructure film, and the devices have demonstrated excellent performance on flexible substrates. This work shows that CsPbCl3/ Zn2SnO4 heterostructure film have broad application prospects in the construction of high-performance ultraviolet photodetectors and other photovoltaic devices.

Tunable coupling in magnetic thin film heterostructures with a magnetic phase transition

The magnetic properties of permalloy-based trilayers of the form Py0.8Cu0.2/Py0.4Cu0.6/Py/IrMn were studied as the spacer layer undergoes a paramagnetic to ferromagnetic phase transition. We find the coupling between the free Py0.8Cu0.2 layer and the exchange bias pinned Py to be strongly temperature-dependent: there is negligible coupling above the Curie temperature of the Py0.4Cu0.6 spacer layer, strong ferromagnetic coupling below that temperature, and a tunable coupling between these extremes. Polarized neutron reflectometry was used to measure the depth profile of the magnetic order in the system, allowing us to correlate the order parameter with the coupling strength. The thickness dependence shows that these are interface effects with an inverse relationship to thickness, and that there is a magnetic proximity effect that enhances the Curie temperature of the spacer layer with characteristic length scale of about 7 nm. As a demonstration of potential functionality of such a system, the structure is shown to spontaneously flip from the antiparallel to parallel magnetic configuration once the spacer layer has developed long-range magnetic order.

Thermal annealing induced linear/nonlinear properties of Ag2S/As2Se3 heterojunction films for optoelectronic applications

The present study reports the annealing induced structural as well as optical properties of Ag2S/As2Se3 heterostructure film at different annealing temperatures. The trigonal AgAsSe2 phase formation was confirmed from the X-ray diffraction (XRD) and selective area electron diffraction (SAED) study. The bandgap of as-prepared Ag2S/As2Se3 film decreased on annealing. The reduction in bandgap increased the static refractive index with annealing. The Urbach energy increased from 422±3 meV to 464±2 meV whereas the optical density and extinction coefficient increased by annealing due to the formation of AgS–AsSe solid solution. The dispersion energy increased and consequently increased the oscillator wavelength and oscillator strength upon annealing. The carrier concentration and optical conductivity increased whereas the optical electronegativity decreased with annealing. The 3rd order nonlinear susceptibility (χ(3)) increased from 2.804x10−11 esu (as-prepared Ag2S/As2Se3) to 5.132 x10−11 esu upon annealing at 200 °C. The n2 value increased upon annealing which increased the nonlinear absorption coefficient but decreased the figure-of-merit. The contact angle value decreased (93°–47.6°) that shows the transformation of hydrophobicity to hydrophilic nature which is good for sensor applications like biological sensor. The surface roughness decreased upon annealing. The change in optical parameters upon annealing makes them the appropriate candidate for optoelectronics, dielectric and nonlinear optical applications such as memory devices, optical switch, etc.

Quantum-dimensional near-surface recombination of photocarriers in CdTe microcrystals

The low-temperature (T = 2 K) photoluminescence spectra of a p-CdTe/n-CdS film heterostructure containing CdTe microcrystals have been studied. In the spectral region above the intrinsic absorption edge of bulk CdTe, a dominant “superhot” radiation band was found. The band arises because of optical transitions of electrons from near-surface levels of the spatial quantization of a microcrystal to the valence band states.

Large-Area Synthesis of Ferromagnetic Fe5- x GeTe2 /Graphene van der Waals Heterostructures with Curie Temperature above Room Temperature.

Van der Waals (vdW) heterostructures combining layered ferromagnets and other 2D crystals are promising building blocks for the realization of ultracompact devices with integrated magnetic, electronic, and optical functionalities. Their implementation in various technologies depends strongly on the development of a bottom-up scalable synthesis approach allowing for realizing highly uniform heterostructures with well-defined interfaces between different 2D-layered materials. It is also required that each material component of the heterostructure remains functional, which ideally includes ferromagnetic order above room temperature for 2D ferromagnets. Here, it is demonstrated that the large-area growth of Fe5- x GeTe2 /graphene heterostructures is achieved by vdW epitaxy of Fe5- x GeTe2 on epitaxial graphene. Structural characterization confirms the realization of a continuous vdW heterostructure film with a sharp interface between Fe5- x GeTe2 and graphene. Magnetic and transport studies reveal that the ferromagnetic order persists well above 300 K with a perpendicular magnetic anisotropy. In addition, epitaxial graphene on SiC(0001) continues to exhibit a high electronic quality. These results represent an important advance beyond nonscalable flake exfoliation and stacking methods, thus marking a crucial step toward the implementation of ferromagnetic 2D materials in practical applications.

Simultaneous Terahertz Pulse Generation and Manipulation with Spintronic Coding Surface

AbstractThe utilization of spintronic terahertz (THz) emitters has a significant influence on broadband coherent spectroscopy and imaging at THz frequencies. By using femtosecond light to irradiate the spintronic heterostructures, spin currents from the ultrafast demagnetization effect can be transformed into charge currents through the inverse spin Hall effect, leading to the emission of THz waves. In this work, through the incorporation of sequential and inverse deposition of W‐Co20Fe60B20‐Pt heterostructure films, control is gained over the spin currents and THz waveforms, enabling it to achieve a 180° phase difference across a broad frequency spectrum while efficiently radiating THz waves. This, in turn, allows it to control the spatial phase of THz radiation. To test the device's capabilities, lithography‐based devices capable of focusing, producing vortexes, and dividing beams are manufactured. This investigation aims to advance the development of THz pulse sources while providing essential support for cutting‐edge technologies such as THz spectroscopy, high‐resolution imaging, and high‐speed communications.

Electrodeposited NiFe2O4/Cu2O heterostructure thin films with enhanced photocurrent generation

In comparison with single-phase materials, heterostructures have been known for superior water splitting applications. In this study, Cu2O and NiFe2O4 are chosen to fabricate thin film heterostructures. Cu2O is electrodeposited at 60 °C for 5 min on ITO-coated glass substrates using three-electrode system. After deposition, the phase formation is confirmed using powder x-ray diffraction studies. The NiFe2O4 (NFO) thin films are deposited using RF sputtering method at room temperature for 2 h on Cu2O/ITO substrates to obtain NFO/Cu2O/ITO Type-II heterostructure. The scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) cross-sectional images show that the thickness of NFO layer is 120 nm and Cu2O layer is 1.5 µm. The photocurrent density of Cu2O on ITO is 0.08 ± 0.002 mA/cm2, and it increased to 0.12 ± 0.002 mA/cm2 after adding NFO layer on Cu2O film due to Type-II heterojunction formation.

Development of Technology for Obtaining Nanosized Heterostructured Films by Ion-Plasma Deposition

The study of films containing narrow-gap semiconductors is a very promising field related to the production of thermal sensors. In this work, we consider the possibility of obtaining the film coatings from silicides of Ba, Na, Ni, Co, Pd, Mn, and P and BaTiO3 using ionplasma methods. The production of film coatings from metal silicides and BaTiO3 on the surface of crystalline silicon and mica and their electronic and X-ray structural characteristics are studied. The dependence of the properties of film coatings on the conditions of the film deposition is determined.

Straddle-type heterostructure films endow titanium implant with NIR photocatalysis property for rapid sterilization

Near-infrared (NIR) light-triggered photocatalysis antibacterial therapy has attracted significant attention. Herein, we designed a straddle-type heterostructure film of ZnS/Ag2S nanorod on the titanium implant, which showed excellent NIR photocatalytic ability. Under NIR, the electrons of Ag2S cascaded jump to ZnS conduction band (CB), and the electron of ZnS was half-jumped to Ag2S valence band (VB). The VB of Ag2S acted as a consumption platform for the holes of Ag2S and the electrons of ZnS, improving photocatalytic efficiency. To prove the feasibility of this mechanism, another straddle-type heterostructure of ZnS/Bi2S3 with similar energy band structure was fabricated, and its NIR photocatalytic ability was also distinctly enhanced. Furthermore, the ZnS/Ag2S heterostructure films rapidly removed bacteria in vitro and in vivo under the NIR irradiation. This work innovatively discovered NIR photocatalytic effect of the straddle-type heterostructure, which complemented the design of heterostructures in photocatalysis.

In-situ growth pH-adjusted iodine defects engineering BiOI film on 3D-printed polymer substrate for efficient organic pollutant and microorganism purification

Although BiOI has been constructed on FTO or metals to overcome the application shortcomings of powdered photocatalyst, but BiOI film with customizable size and shape will be more suitable for purification environments. In this study, 3D-printed polymer models-likes carbon nanotube, graphene ball, and metal–organic framework are exampled to act as substrates. Compared with the traditional heterostructure film fabricated at complicated temperature and pressure, we report a facile route to synthesize the iodine-defect engineering BiOI film on 3D-printed polymer, under mild room temperature and pressure through only adjusting BiOI solution pH value. The produced iodine vacancies can act as traps to facilitate the separation of electron-holes carriers. Additionally, a self-converted LED device enhances the utilized efficiency of irradiated light. This work reveals good purification efficiency on ca. 99.67% degradation rate towards RhB and >99.99% inactivation rate against E. coli and S. aureus in 1 or 3 h because of the O2−, OH and h+ redox.

C/Sb2Te3 phase-change heterostructure films with low resistance drift for multilevel phase change memories

Multilevel storage and resistance drift are two challenges in phase-change memories. Here, we report that [C(5 nm)/Sb2Te3(12 nm)]5 phase-change heterostructure film has multilevel phase change properties and low resistance drift. The addition of carbon broke the Sb2Te3 bond and formed new C-Sb and C-Te bonds. The reliability of phase-change heterostructure was demonstrated by transmission electron microscopy. The amorphous resistance drift index of C/Sb2Te3 film was reduced effectively which may be caused by the structure relaxation. In addition, PCM devices based on C/Sb2Te3 phase-change heterostructure films also confirmed the potential of multilevel storage. This research provided a new method to realize multilevel phase-change memories with low resistance drift.

High-performance omnidirectional self-powered photodetector constructed by CsSnBr3/ITO heterostructure film

Omnidirectional photodetectors attract enormous attention due to their prominent roles in optical tracking systems and omnidirectional cameras. However, it is still a challenge for the construction of high-performance omnidirectional photodetectors where the incident light can be effectively absorbed in multiple directions and the photo-generated carriers can be effectively collected. Here, a high-performance omnidirectional self-powered photodetector based on the CsSnBr3/indium tin oxide (ITO) heterostructure film was designed and demonstrated. The as-fabricated photodetector exhibited excellent self-powered photodetection performance, showing responsivity and detectivity up to 35.1 ​mA/W and 1.82 ​× ​1010 Jones, respectively, along with the smart rise/decay response time of 4 ​ms/9 ​ms. Benefitting from the excellent photoelectric properties of the CsSnBr3 film as well as the ability of the CsSnBr3/ITO heterostructure to efficiently separate and collect photo-generated carriers, the as-fabricated photodetector also exhibited excellent omnidirectional self-powered photodetection performance. All the results have certified that this work finds an efficient way to realize high-performance omnidirectional self-powered photodetectors.