Thin Film Heterostructures Research Articles

Strain induced optoelectronic properties of two dimensional MnPSe3/WS2 heterostructure

A series of first-principles calculations using Kohn–Sham density functional theory have been used to study MnPSe3/WS2 heterostructures. The Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional has been chosen as the exchange–correlation potential because it gives energy gaps accurately. Five possible atomic stackings were considered to find most stable configuration for a heterostructure. Interestingly, all of the five configurations exhibit a maximum deviation in the binding energy equal to 47 meV which strongly indicates realization of the heterostructures. The calculated energy band gap (2.04 eV) of MnPSe3/WS2 heterostructures is smaller (larger) than an isolated layer of MnPSe3 (WS2). We simulated the role of (i) bi-axial strain, and (ii) interlayer spacing on the stability and electronic properties for pre-identified most stable configuration. Tuning of the energy band gap from 2.04 to 1.86 eV is achievable for case (i) while retaining stability of the system. However, in case (ii) band gaps can vary from 2.04 to 1.47 eV and the stability of the system decreases exponentially when following expansion or compression along the c-axis. Further, the effect of strain on valence and conduction band edges has been investigated in terms of band alignment with respect to vacuum level for cases (i) and (ii). To understand the optical features for the most stable configuration, absorption coefficient has been calculated using the frequency dependent real and imaginary parts of the dielectric functions. These calculations show an improved absorption capacity over the constituent layers. Our results may motivate experimentalists involved in developing efficient thin film heterostructure based optoelectronic devices.

Tunable Shortwave Infrared and Midwave Infrared Optoelectronics in Germanium/Germanium Tin Core/Shell Nanowires

Semiconductor nanowire(NW)-based optoelectronic devices can exhibit superior performances in comparison to their thin film counterparts, as a result of their improved electrical and optical properties. For example, the light-matter interaction in nanowires is enhanced due to the high surface-volume ratio and the light confinement effect resulting from the resonant cavity formed by the nanowire. The enhanced light absorption when using a nanowire geometry can be exploited to increase the responsivity of nanowire-based photodetectors. Light detection and emission at near-IR wavelengths (NIR, 0.8-1.5 μm) can be tailored via strain engineering using Ge-based NW devices.[1] Furthermore, by incorporating Sn in the Ge lattice a direct band gap can be achieved across the short-wave-IR (SWIR, 1.5-3.0 μm) and mid-IR (MIR, 3-8 μm) wavelength range.[2] Despite the equilibrium solubility of Sn in Ge being limited to ~1at.%, non-equilibrium growth methods recently developed in a chemical vapor deposition (CVD) reactor demonstrated a Sn content of 18 at.% with a room-temperature photoluminescence emission up to 4.0 μm [3]. Similarly, when moving to the nanoscale a Sn incorporation well above 10 at.% with a direct band gap emission was demonstrated using Ge/GeSn core/shell NWs.[4]In this presentation, we will discuss the opto-electronic properties of Ge and Ge/GeSn core/shell NWs grown in a CVD reactor using a Ge or Si (111) substrate. The structural properties of the NWs were evaluated by combining Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) in order to understand the nanowire growth direction, crystalline properties as well as Sn distribution uniformity in the shell of the nanowires. Photoluminescence, absorption and Raman measurements will elucidate the effect of strain on the MIR direct bandgap emission/absorption of the GeSn shell.Finally, wewill discuss the electrical characterization of individual Ge and GeSn NW photodetectors. Our devices are fabricated by Electro-Beam Photolithography (EBL) based on metal-semiconductor-metal (M-S-M) structure to address the dependence of the photocurrent under illumination at different SWIR-MIR wavelengths. The time response and transport properties of Ge and Ge/GeSn core/shell NW Field Effect Transistor (FET) in back-gated structure are compared with their counterparts of conventional thin film heterostructures. References Pilon, FT Armand, et al. "Lasing in strained germanium microbridges." Nature communications1 (2019): 1-8.Assali, S., J. Nicolas, and O. Moutanabbir. "Enhanced Sn incorporation in GeSn epitaxial semiconductors via strain relaxation." Journal of Applied Physics2 (2019): 025304.Assali, S., et al. "Atomically uniform Sn-rich GeSn semiconductors with 3.0–3.5 μ m room-temperature optical emission." Applied Physics Letters25 (2018): 251903.Assali, S., et al. "Growth and optical properties of direct band gap Ge/Ge0. 87Sn0. 13 core/shell nanowire arrays." Nano letters3 (2017): 1538-1544.

Boosted photoresponsivity using silver nanoparticle decorated TiO2 nanowire/reduced graphene oxide thin-film heterostructure

Here, we report on the fabrication and use of a silver (Ag) nanoparticle (NP) decorated TiO2 nanowire (NW)/reduced graphene oxide (RGO) thin-film (TF) heterostructure as a UV detector, using a controlled method called the glancing angle deposition technique. Transmission electron microscope images show Ag NPs (size 7–13 nm) covering the entire surface of the TiO2 NWs. A high absorption as well as photoluminescence for the Ag NP-TiO2 NW/RGO TF sample reveals the generation of a large number of electron–hole pairs compared to bare TiO2 NW. The resulting plasmonic UV photodetector from the Ag NP-TiO2 NW/RGO TF exhibits a rectification ratio of 5039 (+10 V) and responsivity of 1760 A W−1 at 350 nm light (with power density as low as 0.58 µW cm−2). Moreover, the device shows fast response speed (rise time of 157 ms and fall time of 488 ms) with detectivity and noise equivalent power of 6.659 × 1013 Jones and 51 fW, respectively. The enhanced plasmonic field and high scattering of light, along with the high mobility RGO layer at the bottom, result in the superior performance of the device.

Role of oxygen partial pressure on structure and properties of sputtered transparent conducting films of La-doped BaSnO3

Single crystal film of La doped BaSnO3 (LBSO) has been reported with excellent conductivity and transparency but in order to improve its applicability, it is important to grow polycrystalline LBSO films on inexpensive substrate. A series of polycrystalline LBSO thin films of ~570 nm in thickness are grown on quartz substrate by radio frequency magnetron sputtering at different oxygen pressures varying from 0 to 0.13 Pa. Both carrier concentration and mobility of the films seem to be decreasing with increasing oxygen pressure. The estimated values of mobility, carrier concentration and conductivity are 5.21 cm2/V s, 9.1 × 1019 cm−3 and 2.8 × 102 Ω−1 cm−1, respectively, with optical transmittance of 68% for the film deposited at lowest oxygen partial pressure (0.01 Pa). The optical transmittance of the films improves significantly upto 82% with increasing oxygen pressure to 0.13 Pa. The suitable condition for deposited films is observed at 0.05 Pa in terms of transmittance (~80%) and conductivity (0.67 × 102 Ω−1 cm−1) which is almost 8 times superior to previously reported conductivity (9 Ω−1 cm−1) for polycrystalline LBSO films and comparable to the conductivity (102 Ω−1 cm−1) of the hetero-structured LBSO thin films. Overall, understanding of changes in microstructure, electrical and optical properties of thin film by varying oxygen pressure have been reported effectively. The LBSO films prepared in the current work could be further utilized in TCO applications.

Large area, patterned growth of 2D MoS2 and lateral MoS2–WS2 heterostructures for nano- and opto-electronic applications

The patterned growth of transition metal dichalcogenides (TMDs) and their lateral heterostructures is paramount for the fabrication of application-oriented electronics and optoelectronics devices. However, the large scale patterned growth of TMDs remains challenging. Here, we demonstrate the synthesis of patterned polycrystalline 2D MoS2 thin films on device ready SiO2/Si substrates, eliminating any etching and transfer steps using a combination of plasma enhanced atomic layer deposition (PEALD) and thermal sulfurization. As an inherent advantage of ALD, precise thickness control ranging from a monolayer to few-layered MoS2 has been achieved. Furthermore, uniform films with exceptional conformality over 3D structures are obtained. Finally, the approach has been leveraged to obtain in-plane lateral heterostructures of 2D MoS2 and WS2 thin films over a large area which opens up an avenue for their direct integration in future nano- and opto-electronic device applications.

Electrochemical performance of Bi2Te3 heterostructure thin film and Cu7Te4 nanocrystals on undoped and In3+-doped WO3 films for energy storage applications

We demonstrated the synthesis of undoped and In3+-doped WO3 as an electron acceptor for energy storage applications, by utilizing the electrochemical S2− insertion/extraction process at the heterostructure of rhombohedral Bi2Te3 thin films and hexagonal Cu7Te4 nanocrystals. The cyclic voltammetry of heterostructured electrodes with and without In3+ doping both showed Faradic pseudo-capacitance behavior based on the oxidation and reduction processes. The largest exchange current density of 3.43 mA/cm2 was obtained for the heterojunction-structured-Bi2Te3 thin films and Cu7Te4 nanocrystals with In3+ doping in the WO3 electrode. This implies more favorable hydrogen evolution reaction kinetics and higher electrocatalytic activity at the anode. The highest specific capacity of 90.2 mA h/g was obtained at a scan rate of 10 mV/s, with the power density reaching 1.7 kW/kg at the highest energy density value of 18.85 Wh/kg for the In3+-doped electrode. The overall results revealed the inherent properties of the new electrode materials, as well as their potential use in energy storage devices or in future electrochemical energy conversion and storage applications involving hydrogen (or oxygen) evolution reactions.

Heteromolecular Bilayers on a Weakly Interacting Substrate: Physisorptive Bonding and Molecular Distortions of Copper-Hexadecafluorophthalocyanine.

Heteromolecular bilayers of π-conjugated organic molecules on metals, considered as model systems for more complex thin film heterostructures, are investigated with respect to their structural and electronic properties. By exploring the influence of the organic-metal interaction strength in bilayer systems, we determine the molecular arrangement in the physisorptive regime for copper-hexadecafluorophthalocyanine (F16CuPc) on Au(111) with intermediate layers of 5,7,12,14-pentacenetetrone and perylene-3,4,9,10-tetracarboxylic diimide. Using the X-ray standing wave technique to distinguish the different molecular layers, we show that these two bilayers are ordered following their deposition sequence. Surprisingly, F16CuPc as the second layer within the heterostructures exhibits an inverted intramolecular distortion compared to its monolayer structure.

Microstructure and Defect Study in Thin Film Heterostructure Materials

Deformation twins and phase interface are important planar defects and microstructures that greatly influence the overall performance of a material system. In multi-layer thin-film heterostructures, their effect is more manifest due to the small dimension of thin films and their influence on the growth of multi-layer structures. This article reviews the recent progress in microstructure and defects observed in thin film heterostructures, serving as a guideline for future research in this field. The multilayer thin-film heterostructures studied here were grown by pulsed laser deposition technique. Microstructures and defects were investigated by Transmission Electron Microscopy.

Asymmetric Lattice Disorder Induced at Oxide Interfaces

AbstractControl of order–disorder phase transitions is a fundamental materials science challenge, underpinning the development of energy storage technologies such as solid oxide fuel cells and batteries, ultra‐high temperature ceramics, and durable nuclear waste forms. At present, the development of promising complex oxides for these applications is hindered by a poor understanding of how interfaces affect lattice disordering processes and defect transport. Here, the evolution of local disorder in ion‐irradiated La2Ti2O7/SrTiO3 thin film heterostructures is explored using a combination of high‐resolution scanning transmission electron microscopy, position‐averaged convergent beam electron diffraction, electron energy loss spectroscopy, and ab initio simulations. Highly non‐uniform lattice disordering driven by asymmetric oxygen vacancy formation across the interface is observed. Theory calculations indicate that this asymmetry results from differences in the polyhedral connectivity and vacancy formation energies of the two interface components, suggesting ways to manipulate lattice disorder in functional oxide heterostructures.

Influence of low energy Ag ion irradiation for formation of Bi2Se3 phase from Bi/GeSe2 heterostructure thin films

The manuscript reports on the influence of 40 keV Ag –ve ion bombardment with different fluences on the microstructural and optical properties of thermally evaporated Bi/GeSe2 bilayer thin films. Two different fluences (5 × 1014 ions cm−2 and 1 × 1015 ions cm−2) of Ag –ve ions were used to irradiate the thin films that changed the microstructure and optical properties as studied by different spectroscopic methods like X-ray diffraction method (XRD), Energy dispersive X-ray spectroscopy (EDS), Field emission scanning electron microscopy (FESEM), Atomic force microscopy (AFM), Raman spectroscopy, and UV–Vis spectroscopy. The evolution of topological Bi2Se3 phase occurs after ion irradiated diffusion of Bi into GeSe2 matrix. The optical parameters as calculated from the transmission spectra infers the indirect allowed transition with reduction of Eg on ion irradiation. The various optical parameters like absorption coefficient (α), optical energy gap (Eg), Tauc parameter (B1/2), Urbach energy (Ee), extinction coefficient (k), refractive index (n) were modified with ion irradiation. The surface morphology is being changed after irradiation as probed by AFM and FESEM. The Raman spectra support the formation of Bi2Se3 phase with irradiation. The obtained results have been explained on the basis of increase in band tailing of valence band due to defect states caused by the irradiation.

Linear and nonlinear optical properties change in Ag/GeS heterostructure thin films by thermal annealing and laser irradiation

Linear and nonlinear optical properties change in Ag/GeS heterostructure thin films by thermal annealing and laser irradiation

Oxygen diffusion barriers for epitaxial thin-film heterostructures with highly conducting SrMoO3 electrodes

Transition metal perovskite oxide SrMoO3 with a Mo4+ 4d2 electronic configuration exhibits a room-temperature resistivity of 5.1 μΩcm in a single-crystal form and, therefore, is considered a prominent conducting electrode material for all-oxide microelectronic devices. Stabilization of the unfavorable Mo4+ valence state in SrMoO3 thin films necessitates reductive growth conditions that are often incompatible with a highly oxidative environment necessary to grow epitaxial heterostructures with fully oxygenated functional layers (e.g., tunable dielectric BaxSr1−xTiO3). Interestingly, only a few unit cells of the perovskite titanate capping layers SrTiO3, BaTiO3, and Ba0.5Sr0.5TiO3 act as an efficient oxygen barrier and minimize SrMoO3 oxidation into electrically insulating SrMoO4 in the broad range of the thin-film growth parameters. The Mo valence state in SrMoO3, determined by x-ray photoelectron spectroscopy, is used to analyze oxygen diffusion through the capping layers. The lowest level of oxygen diffusion is observed in Ba0.5Sr0.5TiO3. A Ba0.5Sr0.5TiO3 film with a thickness of only 6 unit cells preserves the Mo4+ oxidation state in the SrMoO3 underlayer up to the oxygen partial pressure of 8 mTorr at the temperature of 630 °C. Results, therefore, indicate that SrMoO3 films covered with atomically thin Ba0.5Sr0.5TiO3 remain conducting in an oxygen environment and can be integrated into all-oxide thin-film heterostructures with other functional materials.

Giant voltage generating microcantilevers based on Ba0.85Ca0.15Zr0.1Ti0.9O3 and Co76Fe14Ni4Si5B for next-generation energy harvesters

Magnetoelectric thin-film heterostructures with piezoelectric Ba0.85Ca0.15Zr0.1Ti0.9O3 and magnetostrictive Co76Fe14Ni4Si5B are fabricated. Very high ME coupling coefficients of 8 V/(cm Oe) and ~5.8 V/(cm Oe) are observed for BCZT-MG-BCZT and MG-BCZT-MG trilayers at sub resonance. Micro cantilevers of multilayers with total thickness of 130 µm are also fabricated. The microcantilever of BCZT-MG-BCZT showed an enhanced resonance at a frequency of 840 Hz with MECC as high as ~1457 V/(cm Oe). These structures can be effectively employed as an active component in energy harvesters, sensors, and transducers due to their exceptional ME responses in the resonant and sub-resonant frequencies.

Nonlocal accumulation, chemical potential, and Hall effect of skyrmions in Pt/Co/Ir heterostructure

Magnetic skyrmion is a swirling topological spin texture behaving as an individual particle. It shows a gyro-motion similarly to that of a charged particle under a magnetic field, being led to the transverse shift to the electric current, i.e., skyrmion Hall effect. With the open boundaries of a sample, this results in an accumulation of skyrmions on one side and their depletion on the other side. Here we demonstrate experimentally that this effect propagates non-locally over tens of micrometers even where the electric current is absent, when the narrow wires bridge bar-shaped Pt/Co/Ir heterostructure thin film systems. This nonlocality can be understood in terms of the “chemical potential” gradient for the skyrmion bubble induced by the skyrmion Hall effect in the nonequilibrium steady state under the electric current. The present result shows that the skyrmion Hall effect acts as the skyrmion pump and the thermodynamic concepts can be applied to the aggregate of skyrmion bubbles.

Large Spin Hall Magnetoresistance in Antiferromagnetic α−Fe2O3/Pt Heterostructures

We investigate the spin Hall magnetoresistance (SMR) at room temperature in thin film heterostructures of antiferromagnetic, insulating, (0001)-oriented alpha-Fe2O3 (hematite) and Pt. We measure their longitudinal and transverse resistivities while rotating an applied magnetic field of up to 17T in three orthogonal planes. For out-of-plane magnetotransport measurements, we find indications for a multidomain antiferromagnetic configuration whenever the field is aligned along the film normal. For in-plane field rotations, we clearly observe a sinusoidal resistivity oscillation characteristic for the SMR due to a coherent rotation of the Neel vector. The maximum SMR amplitude of 0.25% is, surprisingly, twice as high as for prototypical ferrimagnetic Y3Fe5O12/Pt heterostructures. The SMR effect saturates at much smaller magnetic fields than in comparable antiferromagnets, making the alpha-Fe2O3/Pt system particularly interesting for room-temperature antiferromagnetic spintronic applications.

Evaluation of the heterostructure ITO/BiVO4 under blue monochromatic light irradiation for photoelectrochemical application

In this paper, the semiconductor material BiVO4 was obtained by an adapted process of solution combustion synthesis, using poly(ethylene glycol) (PEG 6000) as an additional stabilizing agent, and deposited on indium-doped tin oxide (ITO) substrate, by the dip-coating deposition process, to build an ITO/BiVO4 thin film heterostructure, which can be used as photoanode in photoelectrochemical (PEC) cell. The ITO/BiVO4 photoanode has its performance evaluated by linear sweep voltammetry (LSV), chronoamperometry, and electrochemical impedance spectroscopy (EIS) techniques, under blue monochromatic light, provided by an InGaN LED source. The LSV curve shows that the photoactivity of the photoanode presents a drastic jump in the current density under illumination and negligible dark current density. Reproducibility of the electrode photoactivity is observed under light-chopped illumination. The decay profile of photocurrent suggests that despite of charge carriers recombination process occurring in the ITO/BiVO4 electrode, it still presents good photoelectrocatalytic efficiency. Additionally, the long-term current stability indicates that the current density stays stable, without considerable decay, for at least one hour. The steady-state photocurrent density obtained is equal 91 µA cm− 2. EIS results showed that under illumination, the charge transfer resistance (Rct) is considerably lower than the dark condition. The PEC performance evaluated for discoloration reaction in rhodamine B (RhB) and methylene blue (MB) shows that the photoelectrochemical system is quite efficient.

The synergistic effect of heterostructured dissimilar metal–organic framework thin films on adsorption properties

Two dissimilar metal–organic frameworks are synthesized as heterostructured thin films that show higher storage capacity than both homo-phases and present up-growing adsorption ability with increasing the size of volatile organic compounds.

Exchange bias in La0.7Sr0.3CrO3/La0.7Sr0.3MnO3/La0.7Sr0.3CrO3 heterostructures

In the recent past, heterostructures of magnetic oxide thin films have attracted a great deal of research excitement due to very interesting physical properties such as antiferromagnetic interlayer coupling, tunable exchange-bias, interfacial driven magnetic properties and high mobility electron gas across the interfaces. In this work, we report on the comprehensive magnetic properties observed from the heterostructures of (2 unit cells) La0.7Sr0.3CrO3/(8 unit cells) La0.7Sr0.3MnO3/(2 unit cells) La0.7Sr0.3CrO3, which are epitaxially deposited on SrTiO3 substrate by plasma-assisted oxide molecular beam epitaxy. Using SQUID magnetometer, the magnetic properties are studied when the magnetic field was applied both in plane and out of plane. The Curie temperature of this structure is found to be at 290 K. Most significantly, at 2 K, we observed a complete up/down shift (along magnetization axis) of hysteresis loop when the sample was cooled under a magnetic field of ± 5000 Oe in the in-plane configuration. We believe that the strong antiferromagnetic (super) exchange coupling of Mn-Cr across the two interfaces is responsible for the observed exchange bias. We will present and discuss our in-detailed experimental findings collected on this heterostructure as a function of temperature and magnetic field.

실리콘 기판 상 바나듐 이산화물 및 알루미늄 질화물 이종 구조 박막에서의 근적외선 레이저 펄스 기반 가역적인 전류 스위칭

In this paper, we demonstrated a reversible current switching in a two-terminal device based on a vanadium dioxide(VO₂) and aluminium nitride(AlN) heterostructure thin film grown on a silicon(Si) substrate using near-infrared laser pulses. The fabricated VO₂/AlN device has a phase transition temperature ∼10K higher than conventional VO₂ devices grown on sapphire substrates. Current switching operation of up to 50mA was possible at various pulse repetition rates in the device with smaller dimensions owing to the increased phase transition temperature, and the average switching contrast was calculated as ∼9634. In particular, the average rising time of the switched current was measured to be ∼36ms, and the falling time was less than 10ms, which is a significantly improved result. Due to the high phase transition temperature and fast switching response, the fabricated device is expected to be beneficially applied to laser-assisted current switching.

Flexible ultrahigh energy storage density in lead-free heterostructure thin-film capacitors

Flexible Ba2Bi4Ti5O18 and BiFe0.93Mn0.07O3/Ba2Bi4Ti5O18 heterostructure thin-film capacitors were deposited onto LaNiO3 buffered fluorophlogopite mica substrates using a cost-effective all-solution chemical solution deposition method. The Ba2Bi4Ti5O18 film showed a high recoverable energy storage density (Ure) of 41.2 J/cm3 and efficiency (η) of 79.1%. The BiFe0.93Mn0.07O3/Ba2Bi4Ti5O18 film showed improved energy storage properties with an ultrahigh Ure of 52.6 J/cm3 and η of 75.9% due to its enhanced breakdown field strength and polarization. Meanwhile, both films showed good mechanical flexibility, excellent fatigue endurance up to 5 × 108 cycles, and excellent thermal stability over a wide temperature range from room temperature to 160 °C. These results indicate that the lead-free, flexible Ba2Bi4Ti5O18 and BiFe0.93Mn0.07O3/Ba2Bi4Ti5O18 heterostructure thin film capacitors show promise in the field of flexible electronics.