Showing papers on "Atomic layer deposition published in 2021"

Atomic-Scale Layer-by-Layer Deposition of FeSiAl@ZnO@Al2O3 Hybrid with Threshold Anti-Corrosion and Ultra-High Microwave Absorption Properties in Low-Frequency Bands.

Abstract: Developing highly efficient magnetic microwave absorbers (MAs) is crucial, and yet challenging for anti-corrosion properties in extremely humid and salt-induced foggy environments. Herein, a dual-oxide shell of ZnO/Al2O3 as a robust barrier to FeSiAl core is introduced to mitigate corrosion resistance. The FeSiAl@ZnO@Al2O3 layer by layer hybrid structure is realized with atomic-scale precision through the atomic layer deposition technique. Owing to the unique hybrid structure, the FeSiAl@ZnO@Al2O3 exhibits record-high microwave absorbing performance in low-frequency bands covering L and S bands with a minimum reflection loss (RLmin) of -50.6 dB at 3.4 GHz. Compared with pure FeSiAl (RLmin of -13.5 dB, a bandwidth of 0.5 GHz), the RLmin value and effective bandwidth of this designed novel absorber increased up to ~ 3.7 and ~ 3 times, respectively. Furthermore, the inert ceramic dual-shells have improved 9.0 times the anti-corrosion property of FeSiAl core by multistage barriers towards corrosive medium and obstruction of the electric circuit. This is attributed to the large charge transfer resistance, increased impedance modulus |Z|0.01 Hz, and frequency time constant of FeSiAl@ZnO@Al2O3. The research demonstrates a promising platform toward the design of next-generation MAs with improved anti-corrosion properties.

Atomic layer deposition of ZnO on SnO2 nanospheres for enhanced formaldehyde detection

Abstract: Heterostructures of metal oxide semiconductors have a great promise for chemical gas sensors due to the peculiar properties at the heterointerface. In this work, a highly sensitive and selective gas sensor for detecting formaldehyde is reported based on SnO2/ZnO heterospheres designed by atomic layer deposition (ALD). The electronic properties at the SnO2/ZnO heterointerface can be modulated by optimizing the loading of ZnO through changing ALD cycles. Gas sensing tests indicate that the ZnO ALD significantly improved the sensor properties including higher responses, faster response-recovery dynamics and better selectivity. The response of the SnO2/ZnO sensor to 1 ppm formaldehyde (Ra/Rg = 9.7) shows 4 times enhancement compared to pristine SnO2 at a working temperature of 200 °C. ZnO ALD of 10 cycles leads to the best response and recovery dynamics (12 and 24 s), and that of 15 ALD cycles results in the highest response (Ra/Rg = 38.2) to 20 ppm formaldehyde. The SnO2/ZnO sensor also registers a low detection limit of 70 ppb, which allows for reliable detection of sub-ppm formaldehyde. The remarkable sensor performances indicate the ALD surface engineering is promising for the design of new materials for reliable detection of harmful molecules.

Atomic/molecular layer deposition for energy storage and conversion.

Abstract: Energy storage and conversion systems, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting, have played vital roles in the reduction of fossil fuel usage, addressing environmental issues and the development of electric vehicles. The fabrication and surface/interface engineering of electrode materials with refined structures are indispensable for achieving optimal performances for the different energy-related devices. Atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques, the gas-phase thin film deposition processes with self-limiting and saturated surface reactions, have emerged as powerful techniques for surface and interface engineering in energy-related devices due to their exceptional capability of precise thickness control, excellent uniformity and conformity, tunable composition and relatively low deposition temperature. In the past few decades, ALD and MLD have been intensively studied for energy storage and conversion applications with remarkable progress. In this review, we give a comprehensive summary of the development and achievements of ALD and MLD and their applications for energy storage and conversion, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting. Moreover, the fundamental understanding of the mechanisms involved in different devices will be deeply reviewed. Furthermore, the large-scale potential of ALD and MLD techniques is discussed and predicted. Finally, we will provide insightful perspectives on future directions for new material design by ALD and MLD and untapped opportunities in energy storage and conversion.

Long-life lithium-sulfur batteries with high areal capacity based on coaxial CNTs@TiN-TiO2 sponge

Abstract: Rational design of heterostructures opens up new opportunities as an ideal catalyst system for lithium polysulfides conversion in lithium-sulfur battery. However, its traditional fabrication process is complex, which makes it difficult to reasonably control the content and distribution of each component. In this work, to rationally design the heterostructure, the atomic layer deposition is utilized to hybridize the TiO2-TiN heterostructure with the three-dimensional carbon nanotube sponge. Through optimizing the deposited thickness of TiO2 and TiN layers and adopting the annealing post-treatment, the derived coaxial sponge with uniform TiN-TiO2 heterostructure exhibits the best catalytic ability. The corresponding lithium-sulfur battery shows enhanced electrochemical performance with high specific capacity of 1289 mAh g−1 at 1 C and capacity retention of 85% after 500 cycles at 2 C. Furthermore, benefiting from the highly porous structure and interconnected conductive pathways from the sponge, its areal capacity reaches up to 21.5 mAh cm−2. It is challenging to optimize catalytic heterostructures for lithium sulfur (Li-S) batteries. Here, authors prepare nanometer-scale TiN-TiO2 heterostructures via atomic layer deposition on carbon nanotube sponge to realize stable Li-S batteries with high areal capacity and improved rate capability.

Achieving a Low-Voltage, High-Mobility IGZO Transistor through an ALD-Derived Bilayer Channel and a Hafnia-Based Gate Dielectric Stack.

Abstract: Ultrahigh-resolution displays for augmented reality (AR) and virtual reality (VR) applications require a novel architecture and process. Atomic-layer deposition (ALD) enables the facile fabrication of indium-gallium zinc oxide (IGZO) thin-film transistors (TFTs) on a substrate with a nonplanar surface due to its excellent step coverage and accurate thickness control. Here, we report all-ALD-derived TFTs using IGZO and HfO2 as the channel layer and gate insulator, respectively. A bilayer IGZO channel structure consisting of a 10 nm base layer (In0.52Ga0.29Zn0.19O) with good stability and a 3 nm boost layer (In0.82Ga0.08Zn0.10O) with extremely high mobility was designed based on a cation combinatorial study of the ALD-derived IGZO system. Reducing the thickness of the HfO2 dielectric film by the ALD process offers high areal capacitance in field-effect transistors, which allows low-voltage drivability and enhanced carrier transport. The intrinsic inferior stability of the HfO2 gate insulator was effectively mitigated by the insertion of an ALD-derived 4 nm Al2O3 interfacial layer between HfO2 and the IGZO film. The optimized bilayer IGZO TFTs with HfO2-based gate insulators exhibited excellent performances with a high field-effect mobility of 74.0 ± 0.91 cm2/(V s), a low subthreshold swing of 0.13 ± 0.01 V/dec, a threshold voltage of 0.20 ± 0.24 V, and an ION/OFF of ∼3.2 × 108 in a low-operation-voltage (≤2 V) range. This promising result was due to the synergic effects of a bilayer IGZO channel and HfO2-based gate insulator with a high permittivity, which were mainly attributed to the effective carrier confinement in the boost layer with high mobility, low free carrier density of the base layer with a low VO concentration, and HfO2-induced high effective capacitance.

Rational design of ordered porous SnO2/ZrO2 thin films for fast and selective triethylamine detection with humidity resistance

Abstract: Current gas sensors based on metal oxide semiconductors still suffer greatly from the poor selectivity and low tolerance to the high relative humidity (RH) Herein, we report a highly selective and humidity-resistant gas sensor based on SnO2/ZrO2 porous thin films with a three-dimensionally ordered microstructure (3DOM) The 3DOM ZrO2 fabricated by a template method serves as a hydrophobic layer and SnO2 deposited on ZrO2 by atomic layer deposition (ALD) acts as the transducer layer Gas sensing tests reveal the SnO2/ZrO2 sensor has a decent response to triethylamine (TEA), a highly toxic and flammable chemical widely used in industry The sensor exhibits an ultrafast response and recovery (∼ 1 s) speed to 20 ppm TEA at an optimum operating temperature of 190 °C When the RH increases from 50 % to 90 %, the response of SnO2/ZrO2 sensor shows a minor decrease of 18 %, which to our best knowledge surpasses the existing reports on TEA detection under high RH The humidity resistance is attributed to continuous 3DOM ZrO2 layers, which forms an air hydrophobic layer to suppress water adsorption Furthermore, the SnO2/ZrO2 sensor also possesses superior selectivity, long-time stability and a low detection limit of 40 ppb, thereby endowing a potential toward practical TEA detection

Water treatment based on atomically engineered materials: Atomic layer deposition and beyond

Abstract: Summary Global water stress and challenges for producing sufficient supplies of fit-for-purpose water are amplifying. Atomically engineered interfaces are emerging as a powerful tool in the fabrication of advanced water treatment materials. Atomic layer deposition (ALD) and recently developed related methods, such as sequential infiltration synthesis (SIS), offer a tremendously diverse library of chemistries for interface functionalization. Thickness, stoichiometry, and physicochemical properties can be manipulated with precision. We review their fundamental physical chemistry and processing factors. ALD/SIS engineering strategies, including direct deposition, growth with intermediate layers, and secondary treatment are presented with realization of efficient water treatment. We lay out a pathway to establishing an ALD/SIS-based universal functionalization platform for water treatment, including sensitization strategies, in situ regulation, secondary reactions, and simulation/machine learning. We also provide a perspective on ALD/SIS-based interface engineering via synergy with other widely used interface engineering techniques to develop facile, versatile, and energy-efficient strategies for tackling increasingly complex water challenges.

Recent advances in the growth of gallium oxide thin films employing various growth techniques- A review

Abstract: Gallium oxide (Ga2O3) is rapidly emerging as a material of choice for the development of solar blind photodetectors and power electronic devices which are particularly suitable in harsh environment applications, owing to its wide bandgap and extremely high Baliga figure of merit (BFOM). The Ga2O3 based devices show robustness against chemical, thermal and radiation environments. Unfortunately, the current Ga2O3 technology is still not mature for commercial usage., Thus, extensive research on the growth of various polymorph of Ga2O3 materials has been carried out. This article aims to provide an overview of the current understanding of epitaxial growth of different phases of Ga2O3 by various growth techniques including pulsed laser deposition (PLD), molecular beam epitaxy (MBE), metal-organic chemical vapour deposition (MOCVD), sputtering, mist chemical vapour deposition (Mist CVD) and atomic layer deposition (ALD).The review also investigates the factors such as the growth temperature, pressure, carrier gas, III/V ratio, substrate as well as doping which would influence the synthesis and the stability of meta stable phases of Ga2O3. In addition, a through discussion of growth window is also provided using phase diagrams for aforementioned epitaxial deposition methods.

Chemical and Electronic Modulation via Atomic Layer Deposition of NiO on Porous In2O3 Films to Boost NO2 Detection.

Abstract: To achieve high sensitivity under low-temperature operation is currently a challenge for metal oxide semiconductor gas sensors. In this work, a unique NiO-functionalized macroporous In2O3 thin film is designed by atomic layer deposition (ALD), which demonstrates great potential in electronic sensors for detecting NO2 at low temperature. This strategy allows for efficient engineering of the oxygen vacancy concentration and the formation of p-n heterojunctions in the hybrid In2O3/NiO thin films, which has been found to greatly impact the surface chemical and electrical properties of the sensing films. The sensor based on the optimized In2O3/NiO films exhibits a very high response of 532.2 to 10 ppm NO2, which is 26 times higher than that of the In2O3, at a relatively low operating temperature of 145 °C. In addition, an ultralow detection limit of ca. 6.9 ppb has been obtained, which surpasses most reports based on metal oxide sensors. Mechanistic investigations disclose that the improved sensor properties are resultant from the paramount surface active sites and high carrier concentration enabled by the oxygen vacancies, while excessive NiO ALD leads to a decreased sensor response due to the formed p-n heterojunctions.

Scaled Atomic-Layer-Deposited Indium Oxide Nanometer Transistors With Maximum Drain Current Exceeding 2 A/mm at Drain Voltage of 0.7 V

Abstract: In this work, we demonstrate scaled back-end-of-line (BEOL) compatible indium oxide (In2O3) transistors by atomic layer deposition (ALD) with channel thickness (Tch) of 1.0-1.5 nm, channel length (Lch) down to 40 nm, and equivalent oxide thickness (EOT) of 2.1 nm, with record high drain current of 2.0 A/mm at VDS of 0.7 V among all oxide semiconductors. Enhancement-mode In2O3 transistors with ID over 1.0 A/mm at VDS of 1 V are also achieved by controlling the channel thickness down to 1.0 nm at atomic layer scale. Such high current density in a relatively low mobility amorphous oxide semiconductor is understood by the formation of high density 2D channel beyond $4\times 10^{13}$ /cm2 at HfO2/In2O3 oxide/oxide interface.

Single atom catalysts by atomic diffusion strategy

Abstract: The depletion of energy and increasing environmental pressure have become one of the main challenges in the world today Synthetic high-efficiency catalysts bring hope for efficient conversion of energy and effective treatment of pollutants, especially, single-atom catalysts (SACs) are promising candidates Herein, we comprehensively summarizes the atomic diffusion strategy, which is considered as an effective method to prepare a series of SACs According to the different diffusion forms of the precursors, we review the synthesis pathways of SACs from three aspects: gas diffusion, solid diffusion and liquid diffusion The gaseous diffusion method mainly discusses atomic layer deposition (ALD) and chemical vapor deposition (CVD), both of which carry out gas phase mass transfer at high temperatures The solid-state diffusion method can be divided into nanoparticle transformation into single atoms and solid atom migration Liquid diffusion mainly describes the electrochemical method and the molten salt method We hope this review can trigger the rational design of SACs

Fe2O3-sensitized SnO2 nanosheets via atomic layer deposition for sensitive formaldehyde detection

Abstract: Metal oxide semiconductor (MOS) nanostructures have been widely explored for formaldehyde sensors. The low surface chemical and electronic properties of pure MOS, however, greatly limits the sensor functions. In this work, Fe2O3-sensitized SnO2 nanosheets are designed via atomic layer deposition (ALD) to realize high performance formaldehyde detection. By varying the ALD cycles, the influence of different Fe2O3 loading on the sensing performance of SnO2 nanosheets is revealed. It is found that Fe2O3 ALD can greatly boost the sensing performance and the SnO2 nanosheets with 20 Fe2O3 ALD cycles exhibits the best response (Ra/Rg = 4.5) and fast response and recovery dynamics (9 and 34 s) to 20 ppm formaldehyde at a relative low temperature of 220 °C. The sensor based on SnO2/Fe2O3 also displays good selectivity to formaldehyde as well as the reliable stability and low limit of detection (LOD). This work will shed some light to design efficient MOS heterostructures for detection of formaldehyde.

6.2 W/Mm and Record 33.8% PAE at 94 GHz From N-Polar GaN Deep Recess MIS-HEMTs With ALD Ru Gates

Abstract: This letter reports on the $W$ -band power performance of N-polar GaN deep recess MIS–high electron mobility transistors (HEMTs) using a new atomic layer deposition (ALD) ruthenium (Ru) gate metallization process. The deep recess structure is utilized to control the DC-RF dispersion and increase the conductivity in the access regions. The ALD Ru effectively fills the narrow T-gate stems aiding realization of shorter gate lengths with lower gate resistance than in prior work. In this work, the gate length was scaled down to 48 nm, resulting in the demonstration of a record high 8.1-dB linear transducer gain measured at 94 GHz by load pull. This increased gain has enabled a record 33.8% power-added efficiency (PAE) with an associated output power density ( $P_{\mathrm {O}}$ ) of 6.2 W/mm.

Atomic Design and Fine-Tuning of Subnanometric Pt Catalysts to Tame Hydrogen Generation

Abstract: The rational synthesis of subnanocatalysts with controllable electronic and atomic structures remains a challenge to break the limits of traditional catalysts. Here, we report the atomic-level prec...

Preparation of hexagonal nanoporous Al2O3/TiO2/TiN as a novel photodetector with high efficiency

Abstract: The unique optical properties of metal nitrides enhance many photoelectrical applications. In this work, a novel photodetector based on TiO2/TiN nanotubes was deposited on a porous aluminum oxide template (PAOT) for light power intensity and wavelength detection. The PAOT was fabricated by the Ni-imprinting technique through a two-step anodization method. The TiO2/TiN layers were deposited by using atomic layer deposition and magnetron sputtering, respectively. The PAOT and PAOT/TiO2/TiN were characterized by several techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray (EDX). The PAOT has high-ordered hexagonal nanopores with dimensions ~ 320 nm pore diameter and ~ 61 nm interpore distance. The bandgap of PAOT/TiO2 decreased from 3.1 to 2.2 eV with enhancing absorption of visible light after deposition of TiN on the PAOT/TiO2. The PAOT/TiO2/TiN as photodetector has a responsivity (R) and detectivity (D) of 450 mAW-1 and 8.0 × 1012 Jones, respectively. Moreover, the external quantum efficiency (EQE) was 9.64% at 62.5 mW.cm-2 and 400 nm. Hence, the fabricated photodetector (PD) has a very high photoelectrical response due to hot electrons from the TiN layer, which makes it very hopeful as a broadband photodetector.

Impact of vacancies and impurities on ferroelectricity in PVD- and ALD-grown HfO2 films

Abstract: We investigate the emerging chemical states of TiN/HfO2/TiN capacitors and focus especially on the identification of vacancies and impurities in the ferroelectric HfO2 layers, which are produced either by physical vapor deposition (PVD) or atomic layer deposition (ALD). Depending on the specific growth conditions, we identify different mechanisms of oxygen vacancy formation. Corresponding spectral features are consistently observed for all HfO2- and TiN-related core levels by hard x-ray photoelectron spectroscopy (HAXPES). In ALD-grown samples, we find spectral signatures for the electronic interaction between oxygen vacancies and nitrogen impurities. By linking the HAXPES results to electric field cycling experiments on the TiN/HfO2/TiN capacitors, we discuss possible formation mechanisms and stabilization of the ferroelectric HfO2 phase directly related to specific PVD or ALD conditions.

Enhancement-Mode Atomic-Layer-Deposited In 2 O 3 Transistors With Maximum Drain Current of 2.2 A/mm at Drain Voltage of 0.7 V by Low-Temperature Annealing and Stability in Hydrogen Environment

Abstract: In this article, we demonstrate atomic-layer-deposited (ALD) indium oxide (In2O3) transistors with a record high drain current of 2.2 A/mm at ${V}_{DS}$ of 0.7 V among oxide semiconductor transistors with the enhancement-mode operation. The impact of back-end-of-line (BEOL) compatible low-temperature annealing is systematically studied on these highly scaled In2O3 transistors with channel length ( ${L}_{ch}$ ) down to 40 nm, channel thickness ( ${T}_{ch}$ ) down to 1.2 nm, and equivalent oxide thickness (EOTs) of 2.1 nm, at annealing temperatures from 250 °C to 350 °C in N2, O2, and forming gas (FG, 96% N2/4% H2) environments. Annealing in all different environments is found to significantly improve the performance of ALD In2O3 transistors, resulting in enhancement-mode operation, high mobility, reduced bulk and interface trap density ( $\text{D}_{it}$ as low as $6.3\times 10^{11}$ cm $^{-2}\cdot $ eV−1), and nearly ideal subthreshold slope (SS) of 63.8 mV/dec. Remarkably, the ALD In2O3 devices are found to be stable in hydrogen environment, being less affected by the well-known hydrogen doping issue in indium–gallium–tin-oxide (IGZO). Therefore, low-temperature ALD In2O3 transistors are highly compatible with the hydrogen-rich environment in BEOL fabrication processes.