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The growing need for increasingly miniaturized devices has placed high importance and demands on nanofabrication technologies with high-quality, low temperatures, and low-cost techniques. In the past few years, the development and recent advances in atomic layer deposition (ALD) processes boosted interest in their use in advanced electronic and nano/microelectromechanical systems (NEMS/MEMS) device manufacturing. In this context, non-thermal plasma (NTP) technology has been highlighted because it allowed the ALD technique to expand its process window and the fabrication of several nanomaterials at reduced temperatures, allowing thermosensitive substrates to be covered with good formability and uniformity. In this review article, we comprehensively describe how the NTP changed the ALD universe and expanded it in device fabrication for different applications. We also present an overview of the efforts and developed strategies to gather the NTP and ALD technologies with the consecutive formation of plasma-assisted ALD (PA-ALD) technique, which has been successfully applied in nanofabrication and surface modification. The advantages and limitations currently faced by this technique are presented and discussed. We conclude this review by showing the atomic layer etching (ALE) technique, another development of NTP and ALD junction that has gained more and more attention by allowing significant advancements in plasma-assisted nanofabrication.

Resistive random-access memory devices with atomic layer deposition HfO 2 and radio frequency sputtering TiO x as resistive switching layers were fabricated successfully. Low-power characteristic with 1.52 μW set power (1 μA@1.52 V) and 1.12 μW reset power (1 μA@1.12 V) was obtained in the HfO 2 /TiO x resistive random-access memory (RRAM) devices by controlling the oxygen content of the TiO x layer. Besides, the influence of oxygen content during the TiO x sputtering process on the resistive switching properties would be discussed in detail. The investigations indicated that “soft breakdown” occurred easily during the electrical forming/set process in the HfO 2 /TiO x RRAM devices with high oxygen content of the TiO x layer, resulting in high resistive switching power. Low-power characteristic was obtained in HfO 2 /TiO x RRAM devices with appropriately high oxygen vacancy density of TiO x layer, suggesting that the appropriate oxygen vacancy density in the TiO x layer could avoid “soft breakdown” through the whole dielectric layers during forming/set process, thus limiting the current flowing through the RRAM device and decreasing operating power consumption.

This article reviews and assesses recent progress in atomic layer deposition (ALD) and highlights how the field of ALD is expanding into new applications and inspiring new vapor-based chemical reaction methods. ALD is a unique chemical process that yields ultra-thin film coatings with exceptional conformality on highly non-uniform and non-planar surfaces, often with subnanometer scale control of the coating thickness. While industry uses ALD for high-κ dielectrics in the manufacturing of electronic devices, there is growing interest in low-temperature ALD and ALD-inspired processes for newer and more wide-ranging applications, including integration with biological and synthetic polymer structures. Moreover, the conformality and nanoscale control of ALD film thickness makes ALD ideal for encapsulation and nano-architectural engineering. Articles in this issue of MRS Bulletin present details of several growing interest areas, including the extension of ALD to new regions of the periodic table, and molecular layer deposition and vapor infiltration for synthesis of organic-based thin films. Articles also discuss ALD for nanostructure engineering and ALD for energy applications. A final article shows how the challenge of scaling ALD for high rate nanomanufacturing will push advances in plasma, roll-to-roll, and atmospheric pressure ALD.

In this work, hafnium oxide (HfO 2 ) thin films are deposited on p-type Si substrates by remote plasma atomic layer deposition on p-type Si at 250 °C, followed by a rapid thermal annealing in nitrogen. Effect of post-annealing temperature on the crystallization of HfO 2 films and HfO 2 /Si interfaces is investigated. The crystallization of the HfO 2 films and HfO 2 /Si interface is studied by field emission transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy. The experimental results show that during annealing, the oxygen diffuse from HfO 2 to Si interface. For annealing temperature below 400 °C, the HfO 2 film and interfacial layer are amorphous, and the latter consists of HfO 2 and silicon dioxide (SiO 2 ). At annealing temperature of 450-550 °C, the HfO 2 film become multiphase polycrystalline, and a crystalline SiO 2 is found at the interface. Finally, at annealing temperature beyond 550 °C, the HfO 2 film is dominated by single-phase polycrystalline, and the interfacial layer is completely transformed to crystalline SiO 2 .

Artificial synapses are the fundamental of building a neuron network for neuromorphic computing to overcome the bottleneck of the von Neumann system. Based on a low-temperature atomic layer deposition process, a flexible electrical synapse was proposed and showed bipolar resistive switching characteristics. With the formation and rupture of ions conductive filaments path, the conductance was modulated gradually. Under a series of pre-synaptic spikes, the device successfully emulated remarkable short-term plasticity, long-term plasticity, and forgetting behaviors. Therefore, memory and learning ability were integrated to the single flexible memristor, which are promising for the next-generation of artificial neuromorphic computing systems.

In this study, films of gallium oxide (Ga 2 O 3 ) were prepared through remote plasma atomic layer deposition (RP-ALD) using triethylgallium and oxygen plasma. The chemical composition and optical properties of the Ga 2 O 3 thin films were investigated; the saturation growth displayed a linear dependence with respect to the number of ALD cycles. These uniform ALD films exhibited excellent uniformity and smooth Ga 2 O 3 –GaN interfaces. An ALD Ga 2 O 3 film was then used as the gate dielectric and surface passivation layer in a metal–oxide–semiconductor high-electron-mobility transistor (MOS-HEMT), which exhibited device performance superior to that of a corresponding conventional Schottky gate HEMT. Under similar bias conditions, the gate leakage currents of the MOS-HEMT were two orders of magnitude lower than those of the conventional HEMT, with the power-added efficiency enhanced by up to 9 %. The subthreshold swing and effective interfacial state density of the MOS-HEMT were 78 mV decade –1 and 3.62 × 10 11  eV –1 cm –2 , respectively. The direct-current and radio-frequency performances of the MOS-HEMT device were greater than those of the conventional HEMT. In addition, the flicker noise of the MOS-HEMT was lower than that of the conventional HEMT.

Zirconia is a promising material for dental implants; however, an appropriate surface modification procedure has not yet been identified. Atomic layer deposition (ALD) is a nanotechnology that deposits thin films of metal oxides or metals on materials. The aim of this study was to deposit thin films of titanium dioxide (TiO ), aluminum oxide (Al O ), silicon dioxide (SiO ), and zinc oxide (ZnO) on zirconia disks (ZR-Ti, ZR-Al, ZR-Si, and ZR-Zn, respectively) using ALD and evaluate the cell proliferation abilities of mouse fibroblasts (L929) and mouse osteoblastic cells (MC3T3-E1) on each sample. Zirconia disks (ZR; diameter 10 mm) were fabricated using a computer-aided design/computer-aided manufacturing system. Following the ALD of TiO , Al O , SiO , or ZnO thin film, the thin-film thickness, elemental distribution, contact angle, adhesion strength, and elemental elution were determined. The L929 and MC3T3-E1 cell proliferation and morphologies on each sample were observed on days 1, 3, and 5 (L929) and days 1, 4, and 7 (MC3T3-E1). The ZR-Ti, ZR-Al, ZR-Si, and ZR-Zn thin-film thicknesses were 41.97, 42.36, 62.50, and 61.11 nm, respectively, and their average adhesion strengths were 163.5, 140.9, 157.3, and 161.6 mN, respectively. The contact angle on ZR-Si was significantly lower than that on all the other specimens. The eluted Zr, Ti, and Al amounts were below the detection limits, whereas the total Si and Zn elution amounts over two weeks were 0.019 and 0.695 ppm, respectively. For both L929 and MC3T3-E1, the cell numbers increased over time on ZR, ZR-Ti, ZR-Al, and ZR-Si. Particularly, cell proliferation in ZR-Ti exceeded that in the other samples. These results suggest that ALD application to zirconia, particularly for TiO deposition, could be a new surface modification procedure for zirconia dental implants.

Inverse oxide/metal model systems are frequently used to investigate catalytic structure-function relationships at an atomic level. By means of a novel atomic layer deposition process, growth of single-site Fe 1 O x on a Pt(111) single crystal surface was achieved, as confirmed by scanning tunneling microscopy (STM). The redox properties of the catalyst were characterized by synchrotron radiation based ambient pressure X-ray photoelectron spectroscopy (AP-XPS). After calcination treatment at 373 K in 1 mbar O 2 the chemical state of the catalyst was determined as Fe 3+ . Reduction in 1 mbar H 2 at 373 K demonstrates a facile reduction to Fe 2+ and complete hydroxylation at significantly lower temperatures than what has been reported for iron oxide nanoparticles. At reaction conditions relevant for preferential oxidation of CO in H 2 (PROX), the catalyst exhibits a Fe 3+ state (ferric hydroxide) at 298 K while re-oxidation of iron oxide clusters does not occur under the same condition. CO oxidation proceeds on the single-site Fe 1 (OH) 3 through a mechanism including the loss of hydroxyl groups in the temperature range of 373 to 473 K, but no reaction is observed on iron oxide clusters. The results highlight the high flexibility of the single iron atom catalyst in switching oxidation states, not observed for iron oxide nanoparticles under similar reaction conditions, which may indicate a higher intrinsic activity of such single interfacial sites than the conventional metal-oxide interfaces. In summary, our findings of the redox properties on inverse single-site iron oxide model catalyst may provide new insights into applied Fe-Pt catalysis.

Atomic layer deposition (ALD) has emerged as a promising method for surface modification of functional nanoparticles, enabling the versatile applications in energy, catalysis, and human health. The self‐limiting surface chemistry of ALD allows not only the coating of ultrathin and conformal films but also the decoration of nanoparticle surfaces with specific nanoclusters under appropriate processing conditions. In particle ALD, one of the major challenges lies in the strong cohesive force causing nanoparticle agglomerates or aggregates, which requires their homogeneous dispersion. This review provides an overview on the developments and advancements of particle ALD, covering both reactor designs and applications. The fundamentals of ALD are first reviewed, followed by the reactor designs including fluidized bed reactors, rotating bed reactors, and atmospheric‐pressure continuous spatial ALD reactors. Among them, the basics of particle fluidization are concisely outlined to establish a foundation for understanding fluidized bed reactors. The advantages and disadvantages of various reactor designs are compared and analyzed. Subsequently, the applications of ALD‐modified nanoparticles are reviewed, with a focus on energy, catalysis, biomedicine, and cosmetics. Finally, the progress and applications of ALD modification for functional nanoparticles are summarized, and the perspectives in the field are proposed. In this review, the fundamentals, main challenges, and reactor configurations spanning temporal atomic layer deposition (ALD) to spatial ALD have been systematically reviewed. Furthermore, applications of surface modification using particle ALD in the fields of energy, catalysis, luminescence, and human health are introduced. This review aims to assist researchers to rapidly grasp the development of particle ALD and its emerging trends.

For advanced Cu interconnect technology, Co films have been widely investigated to serve as the liner and seed layer replacement because of a better wettability to Cu than Ta. In this article, the Co films are grown by plasma-enhanced atomic layer deposition using Co(EtCp) 2 as a precursor, and the influences of process parameters on the characteristics of the Co films are elaborately investigated. The results indicate that the process window is 125–225 °C with a growth rate of ~ 0.073 Å/cycle. That is to say, the connection of Et group to Cp ligand can enable a stable film growth at 125 °C, while the corresponding temperature must be higher than 200 °C in terms of Co(Cp) 2 and Co(MeCp) 2 . The deposited films contain N and O elements besides dominant Co and C. Furthermore, the prolongation of the NH 3 pulse time significantly enhances the conductivity of the Co film and a low resistivity of 117 μΩ cm can be achieved with a NH 3 pulse time of 40 s. The root mean square roughness shows a smaller variation with the deposition temperature and maintains a low value of ~ 0.3 nm, indicative of a flat Co film.