Atomic Layer Deposition Of Zinc Oxide Research Articles

Atomic layer deposited zinc oxide thin film on pencil graphite for DNA sensor applications

Atomic Layer Deposition (ALD) enables precise thin-film deposition on electrode substrates for electrochemical sensors. In this work, we present the first example of ALD grown zinc oxide (ZnO) deposition on pencil graphite surfaces for deoxyribonucleic acid (DNA) sensory applications, including its detection and DNA damage investigation. For DNA sensing studies, the use of highly productive materials is essential. In this context, the ZnO modified pencil graphite electrodes (ZnO/PGEs) exhibited good electrochemical properties that make them a suitable substrate. ZnO films were characterized using scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. The DNA recognition capability of the thin film coated electrodes was tested by using differential pulse voltammetry (DPV), which showed a linear response ranging from 1 mg L−1 to 200 mg L−1 based on the oxidation of guanine (G) with a limit of detection value (LOD) of 0.53 mg L−1 (n = 3). In addition to this, impedimetric monitoring of oxidative DNA damage was performed in the presence of copper(II)/hydrogen peroxide (Cu(II)/H2O2) reagents, and protection studies were conducted in the presence of ascorbic acid. ZnO thin film-based electrodes exhibited good sensor performance in terms of sensitivity, stability, and reproducibility.

Bulk/Interface Defects Engineering and Comparative Performance Analysis of p‐Si/n‐CdS/ALD‐ZnO Heterojunction Solar Cell

Herein, the role of bulk/interface defects and their impact on the performance of novel solar cell device structure p‐Si/n‐CdS/ALD‐ZnO (atomic layer deposited zinc oxide) heterojunction solar cells are shown. To calculate all important parameters and connect both types of defects with the performance of the solar cell, a theoretical model to simulate using well developed, established, and globally popular SCAPS‐1D simulation tool is developed. The different types of optimized simulation parameters that improved the performance of the solar cell have been calculated using bulk defects (p‐Si absorber), interfacial defects (p‐Si/n‐CdS interface), emitter layer (n‐CdS) thickness, and window layer (ALD‐ZnO) thickness. A further effect of incident radiation on the quantum efficiency and the spectral response has been plotted along with the I–V characteristics of the proposed solar cell. Based on the proposed simulation and comparing with the existing experimental and simulation results for similar combinations of the solar cell, this detailed study suggests that the highest efficiency η = 19.97%, fill factor = 83.37% with open circuit voltage = 635.3 mV, and short circuit current = 37.71 mA cm−2 can be achieved. Finally, the obtained performance parameters are best in class with the tabulated existing ones.

Transparent Multi-Level NAND Flash Memory and Circuits Based on ZnO Thin Film Transistor

A simple compatible process is developed to fabricate NAND flash memory and driving logic circuits simultaneously based on atomic layer deposition zinc oxide thin film transistors (ZnO TFTs), in which the active layer and the floating gate layer both are ZnO thin films. The flash memory exhibits excellent memory properties, including large memory window (9.8 V), long retention performance and even multi-level data (2 bits) writing and reading ability. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1}\times {4}$ </tex-math></inline-formula> NAND flash array is designed and tested to verify its storage function. A novel modulated enhancement/flash (E/F) inverter is proposed and used on the logic circuits. Finally, a fully transparent flash system with NAND memory cell and driving logic circuits is realized successfully, which has great potential for application of 3D integrated circuits, transparent or flexible electronics.

Atomic-layer-deposited Al-doped zinc oxide as a passivating conductive contacting layer for n+-doped surfaces in silicon solar cells

Stacks consisting of an ultrathin SiO 2 coated with atomic-layer deposited (ALD) zinc oxide (ZnO) and aluminum oxide (Al 2 O 3 ) have been shown to yield state-of-the-art passivation of n -type crystalline silicon surfaces. The distinguishing aspect of this novel passivation stack is the very conductive nature of the passivating ZnO layer. In this work, it is demonstrated that such a stack can provide additional functionalities relevant for silicon solar cells. Specifically, it is shown that the conductive and transparent stacks can passivate textured and n + -diffused silicon surfaces and that they can form an Ohmic contact to n + -diffused surfaces with a low contact resistivity, provided the ZnO is Al-doped. The Al 2 O 3 capping layer has previously been shown to be crucial in the passivation mechanism by preventing the effusion of hydrogen during annealing. Here, it is demonstrated to enable a significant improvement in both the transparency and lateral conductivity of the ZnO upon annealing as well, up to a level typically only attainable by In-based transparent conductive oxides. It is furthermore shown that the passivation of the stacks is thermally stable up to 500–600 o C, depending on the preparation method for the interfacial SiO 2 . Together, these properties make the presented stack an interesting building block for crystalline silicon solar cells, with possibilities for integration as passivating front contact in Passivated Emitter and Rear Cell (PERC)-like solar cells, e.g. as bottom cell top contact in silicon-perovskite tandem cells, as well as a conductive hydrogenation source for poly-Si passivating contacts. • SiO 2 /ALD ZnO:Al/Al 2 O 3 stacks yield excellent passivation of n -type, textured c -Si. • Contact resistivities as low as 15 mΩcm 2 on n + -doped silicon surfaces were obtained. • Doping of the c-Si and ZnO:Al is crucial for obtaining a low contact resistivity. • ALD ZnO:Al can be made highly conductive and transparent by capping and annealing. • The stack has potential in PERC, poly-Si contact and c -Si/perovskite tandem cell.

Enhanced Electrochemical Performance of Supercapacitors via Atomic Layer Deposition of ZnO on the Activated Carbon Electrode Material.

Fabricating electrical double-layer capacitors (EDLCs) with high energy density for various applications has been of great interest in recent years. However, activated carbon (AC) electrodes are restricted to a lower operating voltage because they suffer from instability above a threshold potential window. Thus, they are limited in their energy storage. The deposition of inorganic compounds’ atomic layer deposition (ALD) aiming to enhance cycling performance of supercapacitors and battery electrodes can be applied to the AC electrode materials. Here, we report on the investigation of zinc oxide (ZnO) coating strategy in terms of different pulse times of precursors, ALD cycles, and deposition temperatures to ensure high electrical conductivity and capacitance retention without blocking the micropores of the AC electrode. Crystalline ZnO phase with its optimal forming condition is obtained preferably using a longer precursor pulse time. Supercapacitors comprising AC electrodes coated with 20 cycles of ALD ZnO at 70 °C and operated in TEABF4/acetonitrile organic electrolyte show a specific capacitance of 23.13 F g−1 at 5 mA cm−2 and enhanced capacitance retention at 3.2 V, which well exceeds the normal working voltage of a commercial EDLC product (2.7 V). This work delivers an additional feasible approach of using ZnO ALD modification of AC materials, enhancing and promoting stable EDLC cells under high working voltages.

Fermi-Level Engineering of Atomic Layer-Deposited Zinc Oxide Thin Films for a Vertically Stacked Inverter

We report here atomic layer-deposited ZnO FETs and an effective electron doping method based on Al2O3 layer for high-performance transistors and its circuit application. Through the atomic layer deposition, an ultrathin and flat ZnO film (5 nm) has been deposited successfully where our ZnO FETs initially show n-type enhancement-mode transfer characteristics. The threshold voltage and the electron field-effect mobility of the device are 42 V and 2.8 cm2 V–1 s–1, respectively. After the deposition of the top Al2O3 layer, our ZnO FETs exhibit depletion-mode transfer characteristics with enhanced mobility. The threshold voltage (Vth) shifts to −38 V and the electron field-effect mobility increases by a factor of 2. Analyzed by a four-point probe and Hall and temperature-variable current–voltage measurements, Al2O3-induced doping is considered the main reason for the noticeable changes by minimizing the trap states in our ZnO films. Furthermore, a vertically stacked low-voltage n-type ZnO inverter was successfully fabricated utilizing the enhancement- and depletion-mode ZnO FETs with a voltage gain of ∼1.5 at low supplied voltage. We thus conclude that the atomic layer-deposited ZnO FETs with Al2O3-induced doping offers practical benefits for the high-performance transistors and its circuit applications.

Preparation of multifunctional drug sustained-release system by atomic layer deposition of ZnO in mesoporous titania coating

In previous studies, it has been proven that properties of titanium mesoporous (MP) coatings have a strong bond to substrates and excellent anti-stripping property, thus making it ideal for clinical implants. Also, the high porosity and specific surface area of MP material make it excellent for drug loading and sustained release. However, compared with untreated titanium, the bioactivity of MP samples does not have a significant improvement. In this study, we deposited zinc oxide (ZnO) into/on MP structures using atomic layer deposition (ALD) technology, which would significantly improve the biological activity of MP material while maintaining its structures. The fluorescence results showed that the porosity and drug loading capacity had little change after 10 ALD cycles (MP-ALD10), but decreased significantly after 30 ALD cycles (MP-ALD30). Cell results showed that with the increase of ALD cycle (from 0 to 50), the cytocompatibility of the corresponding materials increased first and then decreased: the optimal proliferation and differentiation of MC3T3-E1 cells were observed in MP-ALD10 and MP-ALD30 groups, respectively. Moreover, it was found that the antibacterial properties of different MP samples against Escherichia coli and Staphylococcus aureus gradually enhanced with the increase of ZnO (MP < MP-ALD10 < MP-ALD30 < MP-ALD50). Overall, the study proved that 10 cycles of ZnO deposition significantly enhanced the bioactivity of MP without affecting its structure, drug-loading and drug-releasing properties, thus making MP-ALD10 more suitable for the development of drug-device combined titanium implants than MP.

Room Temperature Atomic Layer Deposition of ZnO Observed By in Situ IR Absorption Spectroscopy

Zinc oxide (ZnO) is an attractive material for flexible electronics since it has various merits of nontoxicity, wide bandgap, low resistivity, and a high optical transmittance. The ZnO deposition has been intensively studied as transparent conductive films for the liquid crystal displays and thin film solar cells. Furthermore, ZnO has been used as buffer layers for gas barrier films on organic electronics devices. The ZnO deposition has been already reported by DC magnetron sputtering, chemical vapor deposition (CVD), and metal organic CVD (MOCVD). However, it was difficult to control the film thickness with a nanometer precision. In addition, these require high-temperature treatments exceeding 300 ºC, which might be problems for organic electronics and micromachines. To achieve the room temperature growth with a nanometer scale precision, we developed RT atomic layer deposition (ALD). In this study, we report a new RT ALD with dimethyl zinc (DMZ) and an oxidation gas of plasma excited humidified Ar. We used an in-situ multiple-internal-reflection IR absorption spectroscopy (MIR-IRAS) equipped ALD system to investigate the saturation behavior in precursor adsorption and oxidization. We determined injection conditions of the precursor and oxidization gas for the RT ALD based on the IRAS experiment. The RT ALD of ZnO was performed to confirm the ZnO formation on a silicon substrate. In figure 1, we show ZnO thicknesses as a function of ALD cycle which were measured by spectroscopic ellipsometry. The growth per cycle was estimated as 0.046 nm/cycle. We evaluate its composition by using X-ray photoelectron spectroscopy and confirmed that it was fully oxidized. We assume that the deposited film was amorphous from the X-ray diffraction pattern. In addition, we discuss the reaction mechanism in this ALD with Langmuir equation fitting applied to the saturation curve plotted from the result of IR absorption spectroscopy. We depict the surface reaction scheme of the ZnO RT ALD in this paper. Acknowledgment; This work was partly supported by JST-CREST Grant Number JPMJCR14F3, Japan. It was also partly supported by JSPS KAKENHI Grant Numbers 15H03536 and 16K17494. Figure 1 Growth thicknesses of ZnO as a function of the ALD cycle number. Figure 1

Preparation and Characterization of Microsphere ZnO ALD Coating Dedicated for the Fiber-Optic Refractive Index Sensor.

We report the fabrication of a novel fiber-optic sensor device, based on the use of a microsphere conformally coated with a thin layer of zinc oxide (ZnO) by atomic layer deposition (ALD), and its use as a refractive index sensor. The microsphere was prepared on the tip of a single-mode optical fiber, on which a conformal ZnO thin film of 200 nm was deposited using an ALD process based on diethyl zinc (DEZ) and water at 100 °C. The modified fiber-optic microsphere was examined using scanning electron microscopy and Raman spectroscopy. Theoretical modeling has been carried out to assess the structure performance, and the performed experimental measurements carried out confirmed the enhanced sensing abilities when the microsphere was coated with a ZnO layer. The fabricated refractive index sensor was operating in a reflective mode of a Fabry–Pérot configuration, using a low coherent measurement system. The application of the ALD ZnO coating enabled for a better measurement of the refractive index of samples in the range of the refractive index allowed by the optical fiber. The proof-of-concept results presented in this work open prospects for the sensing community and will promote the use of fiber-optic sensing technologies.

A revisit to atomic layer deposition of zinc oxide using diethylzinc and water as precursors

Nanophase zinc oxide (ZnO) has been widely studied as an important multifunctional material in many applications. Atomic layer deposition (ALD) is a unique thin-film synthesis technique, featuring its extreme uniformity, unrivaled conformal coverage, low deposition temperature, and precise controllability. Using diethylzinc (DEZ) and water as precursors, ALD has been reported previously for growing nanophase ZnO thin films. However, the growth characteristics and the resultant ZnO crystallinity have not been well characterized and understood. To this end, we revisited the ALD process of ZnO using DEZ and water. Through employing a suite of advanced characterization techniques, we systematically addressed the growth characteristics, morphological changes, and the crystallinity evolution of ZnO along with growth temperature in the range of 30–250 °C. The growth characteristics of the ALD ZnO films were investigated using in situ quartz crystal microbalance (QCM), scanning electron microscopy, atomic force microscopy, and synchrotron-based X-ray reflectivity. The crystallinity of the ALD ZnO films was determined using synchrotron-based X-ray diffraction and high-resolution transmission electron microscopy. In addition, through further analyzing QCM data, we proposed the adsorption-limited surface reaction for ALD ZnO growth with the temperature-dependent number of –OH surface group reacting with one DEZ molecule. Thus, this study contributes to offer new and deep insights on the fundamental ALD process of ZnO.

Surface Passivated Zinc Oxide (ZnO) Nanorods by Atomic Layer Deposition of Ultrathin ZnO Layers for Energy Device Applications

Chemically stoichiometric and electrically low-resistive high-quality zinc oxide (ZnO) nanostructures have been developed by surface passivation with atomic layer deposited ZnO layers. The impacts of homogeneous ZnO layer growth and its thickness on the physical properties ZnO nanorods were investigated. Vertically aligned ZnO nanorod structures were synthesized by two-step process, and the surface passivation was performed by atomic layer deposition ZnO at low temperatures. Surface passivated ZnO nanorods exhibit excellent improvement in crystallinity, chemical stoichiometry, optical, and electrical properties. Further, the surface passivated structures show significant enhancement in water-oxidation performance (nearly 3 orders of magnitude, i.e., μA → mA) with greatly reduced overpotentials. These investigations emphasize that surface passivation of hydrothermally grown ZnO nanostructures with the homogeneous materials can significantly enhance the structural and optical quality along with their device...

Anti-irreversible fouling of precisely-designed PVDF-ZnO membrane: Effects of ion strength and co-existing cations

In this work, the atomic layer deposition-zinc oxide (ALD-ZnO) modified membrane was fabricated and the effects of ionic strength, co-existing Ca2+ and Mg2+ on its fouling potential were systematically investigated. Results showed excellent anti-irreversible fouling performance of PVDF-ZnO modified membrane with co-existing cations. Attractively, the values of declined membrane flux dropped by 25.7%, 25.9% and 22.3% after ZnO modification in the presence of 50 mM NaCl, 1.0 mM Ca2+ and 1.0 mM Mg2+, respectively. Besides, Ca2+ was prone to cause membrane fouling than Mg2+. Furthermore, fitting of multistage filtration models revealed that membrane fouling was ascribed to dynamic adsorption initially, followed by surface and pores deposition when filtrating BSA with or without Mg2+. However, the modified membrane experienced reverse process with higher ionic strength or Ca2+ addition due to BSA molecular cluster. Moreover, the reduced repulsive energy induced by charge screening and calcium bridging resulted in slight aggravation of membrane fouling. Interestingly, the flux of PVDF-ZnO fouled membrane was easily recovered after physical cleaning. These findings provided deep insight into practical application of ALD modified membrane in wastewater remediation.

Atomic layer deposition of ZnO on carbon black as nanostructured anode materials for high-performance lithium-ion batteries

Although zinc oxide (ZnO), a low-cost and naturally abundant material, has a high theoretical specific capacity of 987 mA h g-1 for hosting lithium ions, its application as an anode material has been hindered by its rapid capacity fading, mainly due to a large volume change (around 228%) upon repeated charge-discharge cycles. Herein, using carbon black (CB) powder as a support, ZnO-carbon black (denoted as ZnO-CB) nanocomposites were successfully fabricated using the atomic layer deposition (ALD) method. This method was able to produce strong interfacial molecular bindings between ZnO nanoclusters and the carbon surface that provide stable and robust electrical contact during lithiation and delithiation processes, as well as ZnO nanoclusters rich in oxygen vacancies (OVs) for faster Li-ion transport. Overall, the nanocomposites were able to deliver a high discharge specific capacity of 2096 mA h g-1ZnO at 100 mA g-1 and stable cyclic stability with a specific capacity of 1026 mA h g-1ZnO maintained after 500 cycles. The composites also have excellent rate capability, and a reversible capacity at a high 1080 mA h g-1ZnO at 2000 mA g-1. The facile but unique synthesis method demonstrated in this work for producing nanostructures rich in OVs and nanocomposites with strong coupling via interfacial molecular bindings could be extended to the synthesis of other oxide based anode materials and therefore could have general significance for developing high energy density lithium ion batteries.

Incomplete elimination of precursor ligands during atomic layer deposition of zinc-oxide, tin-oxide, and zinc-tin-oxide.

For atomic layer deposition (ALD) of doped, ternary, and quaternary materials achieved by combining multiple binary ALD processes, it is often difficult to correlate the material properties and growth characteristics with the process parameters due to a limited understanding of the underlying surface chemistry. In this work, in situ Fourier transform infrared (FTIR) spectroscopy was employed during ALD of zinc-oxide, tin-oxide, and zinc-tin-oxide (ZTO) with the precursors diethylzinc (DEZ), tetrakis(dimethylamino)tin (TDMASn), and H2O. The main aim was to investigate the molecular basis for the nucleation delay during ALD of ZTO, observed when ZnO ALD is carried out after SnO2 ALD. Gas-phase FTIR spectroscopy showed that dimethylamine, the main reaction product of the SnO2 ALD process, is released not only during SnO2 ALD but also when depositing ZnO after SnO2, indicating incomplete removal of the ligands of the TDMASn precursor from the surface. Transmission FTIR spectroscopy performed during ALD on SiO2 powder revealed that a significant fraction of the ligands persist during both SnO2 and ZnO ALD. These observations provide experimental evidence for a recently proposed mechanism, based on theoretical calculations, suggesting that the elimination of precursor ligands is often not complete. In addition, it was found that the removal of precursor ligands by H2O exposure is even less effective when ZnO ALD is carried out after SnO2 ALD, which likely causes the nucleation delay in ZnO ALD during the deposition of ZTO. The underlying mechanisms and the consequences of the incomplete elimination of precursor ligands are discussed.

Interfacial stabilizing effect of ZnO on Si anodes for lithium ion battery

Silicon nanoparticles with atomic layer deposited zinc oxide (ZnO) coating show significantly improved electrochemical performance mainly because of enhanced mechanical integrity and stablized interface. These ZnO coated Si nanoparticles demonstrate stable cycling with a reversible capacity of 1500mAh/g over 260 cycles. With ZnO protected interface, these electrodes can achieve stable cycling with mass loading as high as 1.4mg/cm2. In-situ structural characterization is performed to illuminate the stabilizing mechanism of the ZnO coating during cycling. It is confirmed that the coating is mechanically robust to remain intact even though Si expands inside, and a battery electrode made of this Si/ZnO structure will undergo minimal structural damage upon cycling.

Temperature and thickness dependence of the sensitivity of nitrogen dioxide graphene gas sensors modified by atomic layer deposited zinc oxide films

The Chemical Vapor Deposition (CVD) grown graphene nitrogen dioxide (NO2) gas sensors modified by zinc oxide (ZnO) thin films via atomic layer deposition (ALD) were fabricated and their sensitivity dependence on the temperature and ZnO film thickness was investigated.

The growth behavior and properties of atomic layer deposited zinc oxide films using hydrogen peroxide (H2O2) and ozone (O3) oxidants

Two types of zinc oxide (ZnO) films were grown by thermal atomic layer deposition (ALD), each using hydrogen peroxide and ozone gas oxidants. Diethylzinc (DEZ) was used as the zinc precursor for all experiments. The use of hydrogen peroxide oxidant resulted in elevated growth rates by approximately 70% at relatively low temperatures below 200°C, in comparison with films grown using ozone gas. It is suggested that the use of hydrogen peroxide induces the formation of hydroxyl compounds on top of the growing film between each ALD cycle, which promotes better surface adsorption of the DEZ precursor molecules, thus enhancing the surface reaction rate. On the other hand, ozone-assisted growth is rather close to a thermally activated process, where the growth rate is observed to increase gradually with substrate temperature. At a relatively low growth temperature of 150°C, the electrical resistivity of the ZnO films grown using hydrogen peroxide was lower than the films grown using ozone, by approximately three orders of magnitude. The free carrier density was observed to be the major parameter affecting the resistivity, the latter decreasing with growth temperature. The differences in electron mobility and concentration were correlated to the microstructure and atomic bonding states examined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

Reducing Friction Force of Si Material by Means of Atomic Layer-Deposited ZnO Films

With excellent lubricating property, zinc oxide (ZnO) films are promising candidates to act as protective coatings in Si-based microelectromechanical system devices for the purpose of decreasing friction forces of silicon (Si) material. In this paper, the nanotribological behavior of ZnO films prepared by atomic layer deposition on a Si (100) substrate is investigated by an atomic force microscope. The ZnO films have various thicknesses ranging from 10.0 to 182.1 nm. With the increase of film thickness, the root-mean-square roughness of the films increases, while the ratio of hardness to Young’s modulus (H/E) decreases. Due to their large surface roughness, the thick ZnO films are low in adhesion force. The friction force of the ZnO films is smaller than that of the Si (100) substrate and is greatly influenced by their adhesion force and mechanical property. In a low-load condition, the friction force is dominated by the adhesion force, and thus, the friction force of the ZnO films decreases as film thickness increases. While in a high-load condition, the friction force is dominated by plowing. Films with higher H/E possess smaller friction force, and thus, the friction force increases with the decreasing film thickness.

High sensitive formaldehyde graphene gas sensor modified by atomic layer deposition zinc oxide films

Zinc oxide (ZnO) thin films with various thicknesses were fabricated by Atomic Layer Deposition on Chemical Vapor Deposition grown graphene films and their response to formaldehyde has been investigated. It was found that 0.5 nm ZnO films modified graphene sensors showed high response to formaldehyde with the resistance change up to 52% at the concentration of 9 parts-per-million (ppm) at room temperature. Meanwhile, the detection limit could reach 180 parts-per-billion (ppb) and fast response of 36 s was also obtained. The high sensitivity could be attributed to the combining effect from the highly reactive, top mounted ZnO thin films, and high conductive graphene base network. The dependence of ZnO films surface morphology and its sensitivity on the ZnO films thickness was also investigated.

Effect of Partial Pressure of Precursors on Atomic Layer Deposited Zinc Oxide Films as TCO Material in Solar Cell Application

Zinc Oxide (ZnO) films were deposited by Atomic Layer Deposition (ALD) using Diethylzinc and a combination of Water and Ozone as the precursores. Electrical conductivity of ALD grown ZnO films, under low field, were studied with varied partial pressure of the constituent reactants. Supressing the oxygen vacancy by introducing O3 during the reaction increase the resistivity of the films by couple of orders of magnitude. UV-Vis spectroscopy measurement showed the films to be transparent giving a room for its application as a TCO in solar cell.