Zinc Oxide Substrates Research Articles

Isolation of Single Donors in ZnO.

The shallow donor in zinc oxide (ZnO) is a promising semiconductor spin qubit with optical access. Single indium donors are isolated in a commercial ZnO substrate using plasma focused ion beam (PFIB) milling. Quantum emitters are identified optically by spatial and frequency filtering. The indium donor assignment is based on the optical bound exciton transition energy and magnetic dependence. The emission stability of these single donors in terms of both intensity and frequency, alongside their transition linewidths less than twice the lifetime limit, highlight the promise of single In donors as optically accessible spin qubits. The optical stability of single donors after FIB fabrication is promising for optical device integration required for scalable quantum technologies based on single donors in direct band gap semiconductors.

Interaction of Glass Powder with Al Powder and Zinc Oxide in Aluminum Paste

By analyzing the interaction of different glass powders with Al powder and Zinc oxide, the effect of the wetting property of glass powders on the surface morphology of aluminum paste and the adhesion between aluminum paste and Zinc oxide substrate is discussed. The effect of wetting property for different glass powders on Al and Zinc oxide is analyzed by a high-temperature contact angle tester, and the contact angle-temperature and extension radius-temperature curves are determined during the wetting process of the glass powders. The microstructure of the cross-section of the glass powders and of the substrate, and the surface morphology of the aluminum pastes are analyzed by a scanning electron microscope. Adhesion between the aluminum paste and the Zinc oxide substrate is analyzed by a vertical tensile strength meter. The results show that the wetting property of glass powder is an important factor affecting the adhesion and surface morphology of the paste, and it plays a role in preventing excessive oxidation of aluminum paste during sintering at high temperatures.

Hexagonal-shaped graphene quantum plasmonic nano-antenna sensor

In this manuscript, a hexagonal-shaped graphene quantum plasmonic nanopatch antenna sensor is designed and investigated on silicon dioxide, zinc oxide and silicon substrates for quantum plasmonic biosensing applications. The optical properties of graphene are demonstrated using Kubo modeling to analyze the plasmon resonance characteristics of the nanopatch antenna. Nano-circuit modeling of the hexagonal-shaped graphene nano-antenna is proposed and validated using CST simulations. The parametric analysis of the hexagonal-shaped nanopatch antenna is performed using design parameters such as R (radius of the hexagon), Tp (thickness of the hexagon) and µc (chemical potential of graphene) to obtain optimum characteristics suitable for quantum plasmonic sensing applications. The study demonstrates that the proposed hexagonal-shaped nano-antenna exhibits gain of 4.9 dBi, 2.46 dBi, 14.99 dBi, 8.25 dBi, 5.15 dBi, 10.87 dBi and 2.4 dBi at 29.87 THz, 30 THz, 35 THz, 113.5 THz, 132.5 THz, 85 THz and 24 THz, respectively. The field enhancement factors observed at these frequencies are 794, 779, 584, 255, 234, 654 and 217, respectively.

A molecular dynamics study of the effects of velocity and diameter on the impact behavior of zinc oxide nanoparticles

Molecular dynamics simulations of particle impact have been conducted for a ceramic with mixed ionic-covalent bonding. For these simulations, individual zinc oxide (ZnO) nanoparticles (NPs) were impacted onto a ZnO substrate to observe the effects of impact velocity (1500–3500 m s−1) and particle diameter (10, 20, and 30 nm) on particle deformation and film formation mechanisms that arise during the micro-cold spray process for producing films. The study shows that a critical impact velocity range exists, generally between 1500 and 3000 m s−1, for sticking of the NP to the substrate. Results suggest that solid-state amorphization-induced viscous flow is the primary deformation mechanism present during impact. Decreasing particle diameter and increasing impact velocity results in an increased degree of amorphization and higher local temperatures within the particle. The impact behavior of mixed ionic-covalent bonded ZnO is compared to the behavior of previously studied ionic and covalent materials.

A High-Performance Antibacterial Nanostructured ZnO Microfluidic Device for Controlled Bacterial Lysis and DNA Release.

In this work, the antibacterial properties of nanostructured zinc oxide (ZnO) surfaces are explored by incorporating them as walls in a simple-to-fabricate microchannel device. Bacterial cell lysis is demonstrated and quantified in such a device, which functions due to the action of its nanostructured ZnO surfaces in contact with the working fluid. To shed light on the mechanism responsible for lysis, E. coli bacteria were incubated in zinc and nanostructured ZnO substrates, as well as the here-investigated ZnO-based microfluidic devices. The unprecedented killing efficiency of E. coli in nanostructured ZnO microchannels, effective after a 15 min incubation, paves the way for the implementation of such microfluidic chips in the disinfection of bacteria-containing solutions. In addition, the DNA release was confirmed by off-chip PCR and UV absorption measurements. The results indicate that the present nanostructured ZnO-based microfluidic chip can, under light, achieve partial inactivation of the released bacterial DNA via reactive oxygen species-mediated oxidative damage. The present device concept can find broader applications in cases where the presence of DNA in a sample is not desirable. Furthermore, the present microchannel device enables, in the dark, efficient release of bacterial DNA for downstream genomic DNA analysis. The demonstrated potential of this antibacterial device for tailored dual functionality in light/dark conditions is the main novel contribution of the present work.

Finite Element Analysis of SAW Sensor with ZnO Substrate for Dichloromethane (DCM) Gas Detection

A SAW gas sensor based on Zinc Oxide (ZnO) piezoelectric substrate is simulated and evaluated for the detection of the dichloromethane (DCM) volatile organic compound (VOC). The study is performed based on the finite element method (FEM) using COMSOL Multiphysics software. The obtained device response using the ZnO substrate is compared to the one using the typical lithium niobate (LiNbO3) piezoelectric substrate. A thin film of polyisobutylene (PIB) membrane is selected to act as the sensing layer. The obtained results reveal a linear behaviour of the resonance frequency downshift (i.e., the sensor sensitivity) versus the investigated gas concentrations varying from 10 ppm to 100 ppm of DCM gas. Additionally, the sensor response is investigated by applying several thicknesses of PIB ranging from 0.3 μm to 1.0 μm. The observed sensor response shows less dependence on the PIB thickness using the ZnO substrate than the LiNbO3 one.

A free base porphyrin as an effective modifier of the cathode interlayer for organic solar cells

Herein, we demonstrate the co-optimization of power conversion efficiency (PCE) and air stability of the organic solar cells (OSCs) by free porphyrin-based buffer of zinc oxide (ZnO) cathode. By combining first-principle calculations and experimental measurements, we investigated the adsorption behaviors and working mechanism of free base porphyrin (TPP) and zinc porphyrin (ZnTPP) on ZnO cathode. The N atoms of TPP are capable of forming Zn—N coordination with the Zn atom of ZnO substrate, thereby generating interfacial dipoles and reducing the work function of ITO/ZnO cathode, which is beneficial for the charge transfer in the OSCs. More importantly, the large adsorption energy between ZnO and TPP, as well as the good compatibility between TPP and the organic layer, enables TPP to act as a “molecular glue” between the inorganic interface and the organic active layers, which improves not only the PCE but also the stability of the devices under high humidity air environment. In contrast, the already coordinated porphyrin ZnTPP has no such positive effects on the device performance when used as ZnO buffer. The results are of great significance for the study of the working mechanism of interlayer buffers in OSCs, and are also of guidance for designing the buffer molecules.

Robust mica perovskite photoelectric resistive switching memory

Metal halide perovskites have attracted considerable attention for use in flexible resistive random access memory (RRAM), due to their good photoelectric regulation, high ON/OFF ratios, and low fabrication costs. Flexible conductive substrates play a crucial role in improving RRAM device performance. Herein, mica/silver nanowires welded with aluminum-doped zinc oxide (mica/AgNWs@AZO) substrates with high-temperature resistance, high flexibility, high conductivity, and good stability have been successfully fabricated. The average sheet resistance 3.5 Ω sq−1 of the conductive mica substrate is 68% lower than that of a commercial PET/ITO, and it remains stable below 13.1 Ω sq−1 under 200 °C. The maximum conductivity of the mica/AgNWs@AZO substrate can reach 58 S/m after 64 h of tensile stress bending at a radius of 20 mm. Perovskite CsPbBr3 nanocrystal (NC) RRAM is constructed on the mica/AgNWs@AZO substrate. The ON/OFF ratio 103 of the device in light is 102 times higher than that in dark under 5000 bending cycles. Flexible perovskite RRAM is a promising candidate for next-generation-logic, adaptive, non-volatile memory devices.

High-Performance SAW Device Based on Zinc-Oxide Substrate With Electric Field Regulating Graphene Film Conductivity for Signal Amplifier

In this study, a high-performance surface acoustic wave (SAW) device based on a multi-layer graphene amplifier is proposed, which is mainly composed of a zinc-oxide (ZnO) substrate, an interdigital transducer (IDT) input, a graphene sensing layer, metal electrodes and a fork finger transducer output. The sensor uses graphene’s unique band structure and the electron transport properties of the high mobility of the carrier with extremely small temperature influence to amplify the signal of the SAW caused by the sensing signal, thereby improving the sensitivity of the SAW sensor. The influence of graphene variable conductivity controlled by the uniform electric field on SAW amplifier devices in the near field is studied and analyzed. A small size surface acoustic wave device is fabricated with microelectromechanical system (MEMS) technology. The results show that the resonant frequency of the sensor is about 72 MHz, and the maximum amplification performance is 36 dB/cm. It is found that the SAW amplifier proposed in ZnO piezoelectric crystals exhibits superior performance in graphene-based SAW amplifiers.

Mg-Doped ZnO Nanoparticles with Tunable Band Gaps for Surface-Enhanced Raman Scattering (SERS)-Based Sensing.

Semiconductors have great potential as surface-enhanced Raman scattering (SERS) substrates due to their excellent physiochemical properties. However, they provide low signal enhancements relative to their plasmonic counterparts, which necessitates innovation in their synthesis and application. Substitutional atomic doping is proposed to improve SERS enhancement by controlling electronic properties, such as the band gap. In this work, zinc oxide (ZnO) nanoparticles were synthesized by co-precipitation and doped with magnesium (Mg) at concentrations ranging from 2–10%. Nanoparticle morphology and size were obtained by scanning electron microscopy (SEM). Elemental composition and chemical states were determined using X-ray photoelectron spectroscopy (XPS). Optical properties were obtained with a UV-vis spectrophotometer, while a Raman spectrometer was used to acquire Raman signal enhancements. Stability was assessed by UV-vis spectroscopy, while cytotoxicity was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The results showed that the absorption edge of Mg-doped ZnO nanoparticles was red-shifted compared to pure ZnO nanoparticles. The band gap decreased (3.3–3.01 eV) with increasing Mg doping, while the highest Raman enhancement was observed at 2% doping. No significant cytotoxic effects were observed at low concentrations (3–12 μg/mL). Overall, this study provides evidence for the tunability of ZnO substrates and may serve as a platform for applications in molecular biosensing.

Enhanced Broadband Metamaterial Absorber Using Plasmonic Nanorods and Muti-Dielectric Layers Based on ZnO Substrate in the Frequency Range from 100 GHz to 1000 GHz

A broadband thin film plasmonic metamaterial absorber nanostructure that operates in the frequency range from 100 GHz to 1000 GHz is introduced and analyzed in this paper. The structure consists of three layers: a 200 nm thick gold layer that represents the ground plate (back reflector), a dielectric substrate, and an array of metallic nanorods. A parametric study is conducted to optimize the structure based on its absorption property using different materials, gold (Au), aluminum (Al), and combined Au, and Al for the nanorods. The effect of different dielectric substrates on the absorption is examined using silicon dioxide (SiO2), aluminum oxide (Al2O3), titanium dioxide (TiO2), and a combination of these three materials. This was followed by the analysis of the effect of the distribution of Al, and Au nanorods and their dimensions on the absorption. The zinc oxide (ZnO) layer is added as a substrate on top of the Au layer to enhance the absorption in the microwave range. The optimized structure achieved more than 80% absorption in the ranges 100–280 GHz, 530–740 GHz and 800–1000 GHz. The minimum optimized absorption is more than 65% in the range 100 GHz to 1000 GHz.

Silver Nanorods Array on the Zinc Oxide Thin Film Deposited by Hydrothermal Methods for Surface-Enhanced Raman Scattering

The wide application of surface-enhanced Raman spectroscopy (SERS) is based on adaptable substrates, which are primarily limited to rough precious metals and colloidal nanoparticle materials. A novel method to enhance surface Raman scattering is present. This technique is reliant on the local surface plasmon resonance phenomena, in which incident light can be coupled to the plasma at the interface, resulting in a strong electric field. The field can propagate from the surface of the metal–dielectric interface, so adjacent molecules will experience more intense Raman scattering. The physical enhancement method was adopted; silver is deposited on the surface of different pH rough zinc oxide thin film, deposited by hydrothermal methods using the above principle, considerably improving the surface Raman scattering signal. Comparing the enhancement effects of zinc oxide substrates prepared in different pH environments on the Raman effect, the optimal acid–base environment was found, and the corresponding enhancement factors were calculated.

Low-Temperature Hydrothermal Growth of ZnO Nanowires on AZO Substrates for FACsPb(IBr)3 Perovskite Solar Cells.

Electron and hole transport layers (ETL and HTL) play an essential role in shaping the photovoltaic performance of perovskite solar cells. While compact metal oxide ETL have been largely explored in planar n-i-p device architectures, aligned nanowires or nanorods remain highly relevant for efficient charge extraction and directional transport. In this study, we have systematically grown ZnO nanowires (ZnO NWs) over aluminum-doped zinc oxide (AZO) substrates using a low-temperature method, hydrothermal growth (HTG). The main growth parameters were varied, such as hydrothermal precursors concentrations (zinc nitrate hexahydrate, hexamethylenetetramine, polyethylenimine) and growing time, in order to finely control NW properties (length, diameter, density, and void fraction). The results show that ZnO NWs grown on AZO substrates offer highly dense, well-aligned nanowires of high crystallinity compared to conventional substrates such as FTO, while demonstrating efficient FACsPb(IBr)3 perovskite device performance, without the requirement of conventional compact hole blocking layers. The device performances are discussed based on NW properties, including void fraction and aspect ratio (NW length over diameter). Finally, AZO/ZnO NW-based devices were fabricated with a recent HTL material based on a carbazole moiety (Cz–Pyr) and compared to the spiro-OMeTAD reference. Our study shows that the Cz–Pyr-based device provides similar performance to that of spiro-OMeTAD while demonstrating a promising stability in ambient conditions and under continuous illumination, as revealed by a preliminary aging test.

Polypyrrole Decorated Flower-like and Rod-like ZnO Composites with Improved Microwave Absorption Performance.

In this study, zinc oxide (ZnO)/polypyrrole (PPy) composites with flower- and rod-like structures were successfully fabricated by in situ polymerization and the hydrothermal method and used as microwave absorption (MWA) materials. The surface morphologies, crystal structures, and electromagnetic features of the as-prepared samples were measured by field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and vector network analyzer (VNA). The results show that the conductive polymer PPy was successfully decorated on the surface of ZnO substrates. The MWA ability of flower- and rod-like ZnO/PPy composites is significantly enhanced after introduction of PPy. Rod-like ZnO/PPy composites exhibited superior MWA properties than those of flower-like ZnO/PPy. The former achieved a minimum reflection loss (RLmin) of −59.7 dB at 15.8 GHz with a thickness of 2.7 mm, and the effective absorption bandwidth (EAB, RL < −10 dB) covered 6.4 GHz. PPy addition and stacked structure of rod-like ZnO/PPy composites can effectively improve the dielectric properties, form multiple reflections of incident electromagnetic waves, and generate an interfacial polarization effect, resulting in improved MWA properties of composite materials.

Excited States Calculations of MoS2@ZnO and WS2@ZnO Two-Dimensional Nanocomposites for Water-Splitting Applications

Transition metal dichalcogenide (TMD) MoS2 and WS2 monolayers (MLs) deposited atop of crystalline zinc oxide (ZnO) and graphene-like ZnO (g-ZnO) substrates have been investigated by means of density functional theory (DFT) using PBE and GLLBSC exchange-correlation functionals. In this work, the electronic structure and optical properties of studied hybrid nanomaterials are described in view of the influence of ZnO substrates thickness on the MoS2@ZnO and WS2@ZnO two-dimensional (2D) nanocomposites. The thicker ZnO substrate not only triggers the decrease of the imaginary part of dielectric function relatively to more thinner g-ZnO but also results in the less accumulated charge density in the vicinity of the Mo and W atoms at the conduction band minimum. Based on the results of our calculations, we predict that MoS2 and WS2 monolayers placed at g-ZnO substrate yield essential enhancement of the photoabsorption in the visible region of solar spectra and, thus, can be used as a promising catalyst for photo-driven water splitting applications.

Charge transfer mechanism of AZO-ZnO photoanode based on impedance study for solar cell application

• Studied the effect of growth temperature on the length and defect of ZnO NR. • Charge transfer mechanism of NRs was investigated using electrochemical analysis. • Obtained current density of 0.82 mA/cm 2 and photoconversion efficiency of 0.53 %. • Working mechanism of the NR-based cell was explained using a band diagram. Charge transfer mechanism in ZnO nanorods grown on aluminium doped zinc oxide substrates using a single step hydrothermal method was investigated as a function of ZnO nanorod (NR) growth temperature/nanorod’s length. Band-to-band transition and the defect state transition in the prepared nanorods was confirmed using photoluminescence spectroscopy. The increase in active sites up to an optimum growth temperature/nanorod’s length results in an increase of current density and photoconversion efficiency of the prepared NR. But with the further increase in the latter, the current density decreases due to the recombination of electrons. Nanorod grown at the optimized condition exhibited a current density of 0.82 mA/cm 2 and a photoconversion efficiency η of 0.53 %. Electrochemical impedance spectroscopy and open-circuit photovoltage decay (OCPVD) measurement were employed to determine the charge transfer resistance R ct , double layer capacitance ( C dl ) and the recombination time τ of zinc oxide nanorods of various length. The nanorod prepared at the optimized condition of 140 °C having an average length of 2.4 μm had superior current density and the better charge transfer mechanism. The study confirmed that this was due to the low charge transfer resistance R ct = 1300 Ω value and better recombination time τ = 2.38 s for the sample, which makes ZnO nanorods a promising candidate to be used as a photoanode in quantum dot sensitized solar cells.

Theoretical Investigation of the Prospect to Tailor ZnO Electronic Properties with VP Thin Films.

The atomic and electronic structure of vanadium phosphide one- to four-atomic-layer thin films and their composites with zinc oxide substrate are modelled by means of quantum chemistry. Favorable vanadium phosphide to ZnO orientation is defined and found to remain the same for all the structures under consideration. The electronic structure of the composites is analyzed in detail. The features of the charge and spin density distribution are discussed.

Femtosecond Laser-Pulse-Induced Surface Cleavage of Zinc Oxide Substrate.

The induction of surface cleavage along the crystalline structure of a zinc oxide substrate (plane orientation: 0001) by femtosecond laser pulses (wavelength: 1030 nm) has been reported; a scanning electron microscope image of the one-pulse (pulse energy: 6–60 μJ) irradiated surface shows very clear marks from broken hexagons. This cleavage process differs from the general laser-induced melt process observed on the surfaces of narrower-bandgap semiconductors and other metal materials. This phenomenon is discussed using a multi-photon absorption model, and the pulse-energy dependence of the cleavage depth (less than 3 μm) is quantitatively analyzed. Laser-induced cleavage is found not to occur under multi-pulse irradiation; when more than four pulses are irradiated upon the same spot, the general laser-induced melt process becomes dominant. This cleavage–melt shift is considered to be caused by the enhancement of absorption due to the initial pulses, which is supported by our measurement of cathodoluminescence.

Critical role of additive-induced molecular interaction on the operational stability of perovskite light-emitting diodes

Summary Despite rapid improvements in efficiency and brightness of perovskite light-emitting diodes (PeLEDs), the poor operational stability remains a critical challenge hindering their practical applications. Here, we demonstrate greatly improved operational stability of high-efficiency PeLEDs, enabled by incorporating dicarboxylic acids into the precursor for perovskite depositions. We reveal that the dicarboxylic acids efficiently eliminate reactive organic ingredients in perovskite emissive layers through an in situ amidation process, which is catalyzed by the alkaline zinc oxide substrate. The formed stable amides prohibit detrimental reactions between the perovskites and the charge injection layer underneath, stabilizing the perovskites and the interfacial contacts and ensuring the excellent operational stability of the resulting PeLEDs. Through rationally optimizing the amidation reaction in the perovskite emissive layers, we achieve efficient PeLEDs with a peak external quantum efficiency of 18.6% and a long half-life time of 682 h at 20 mA cm−2, presenting an important breakthrough in PeLEDs.

Enhanced external quantum efficiency of III-nitride micro-light-emitting diodes using vertical and transparent package

In this work, 40 × 40 μm2 blue InGaN micro-light-emitting diodes (μLEDs) with transparent and vertical package was first demonstrated by using either double-side polished zinc oxide (ZnO) or sapphire substrate as a transparent submount. The performance of the vertical and conventional packages was compared, where the devices packaged vertically resulted in smaller blueshift in peak wavelength with increasing drive current due to the higher junction temperature. Moreover, devices packaged vertically with the sapphire submount offered 19% and 32% greater light output power at 20 and 100 A cm−2, respectively, and 18% improvement in maximum external quantum efficiency (EQE) than devices with conventional package. Finally, the peak EQE of 58% was achieved from the μLED packaged vertically using a sapphire submount.