Atomic Layer Deposition Technology Research Articles

Wetting behavior of stainless-steel surface with zinc oxide nanorod coatings: modulations in nanorod alignment through atomic layer deposition.

This study investigated the hydrophobic-hydrophilic characteristics of zinc oxide (ZnO) nanorod coatings for potential biomedical applications. We examined the effects of different alignments of ZnO nanorods on the wetting and mechanical characteristics of the coatings.
ZnO seed layers were prepared on stainless-steel plates using atomic layer deposition (ALD) at five different temperatures ranging from 50 to 250 ℃. The ZnO nanorod coatings were then deposited on these seed layers through chemical bath deposition. The polycrystalline structure of the seed layers and the morphology of the nanorods were analyzed using grazing incidence angle X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Mechanical and wetting properties of the nanorod coatings were examined using nanoindentation and water-droplet tests. The seed layers produced at 50 and 250 ℃ showed stronger (0 0 2) peaks than the other layers. ZnO nanorods on these seed layers exhibited greater vertical orientation and lower water contact angles indicating a more hydrophilic surface. Additionally, vertically oriented nanorod coatings demonstrated greater elastic modulus and hardness than those of oblique nanorods. Our findings indicate that ALD technology can be used to control the spatial arrangement of ZnO nanorods and optimize the hydrophobic-hydrophilic and mechanical properties of coating surfaces.&#xD.

Efforts of implementing ultra‐flexible thin‐film encapsulation for optoelectronic devices based on atomic layer deposition technology

AbstractFlexible, wearable electronics are the future of electronics. Although organic photovoltaic devices have the advantages of high efficiency, low cost, and flexibility, they face the problem of failure due to the effects of water vapor in the environment. Therefore, the development of encapsulation films with outstanding mechanical and encapsulation properties is the key to realizing wearable devices. This review provides an overview of the development of thin‐film encapsulation (TFE), the application of TFE in the field of optoelectronics, recent advances in the field of flexible encapsulation with TFE using atomic layer deposition technology, and an outlook on future trends in the field of flexible encapsulation with TFE using atomic layer deposition technology.

Precision Interface Engineering of CuNi Alloys by Powder ALD Toward Better Thermoelectric Performance

AbstractThe main bottleneck in obtaining high‐performance thermoelectric (TE) materials is identified as how to decouple the strong interrelationship between electrical and thermal parameters. Herein, a precise interface modification approach based on the powder atomic layer deposition (ALD) technology is presented to enhance the performance of CuNi alloys. ZnO and Al2O3 layers as well as their combinations are deposited on the surface of powders, typically in 10–100 ALD cycles, and their effects on the TE performance of bulks is thoroughly investigated. The enhancement of the Seebeck coefficient, caused by the energy filtering effect, compensates for the electrical conductivity deterioration due to the low electrical conductivity of oxide layers. Furthermore, the oxide layers may significantly increase the phonon scattering. Therefore, to reduce the resistivity of coating layer, a multilayer structure is deposited on the surface of powders by inserting Al2O3 into ZnO. The accurate microstructure characterization shows that the Al atoms diffused into ZnO and realized the doping effect after pressing. Al diffusion has the potential to increase the electrical conductivity and complexity of coating layers. Compared to pure CuNi, zT increases by 128% due to the decrease in resistivity and stronger phonon scattering in phase boundaries.

A restricted dynamic surface self-reconstruction toward high-performance of direct seawater oxidation

The development of highly efficient electrocatalysts for direct seawater splitting with bifunctionality for inhibiting anodic oxidation reconstruction and selective oxygen evolution reactions is a major challenge. Herein, we report a direct seawater oxidation electrocatalyst that achieves long-term stability for more than 1000 h at 600 mA/cm2@η600 and high selectivity (Faraday efficiency of 100%). This catalyst revolves an amorphous molybdenum oxide layer constructed on the beaded-like cobalt oxide interface by atomic layer deposition technology. As demonstrated, a new restricted dynamic surface self-reconstruction mechanism is induced by the formation a stable reconstructed Co-Mo double hydroxide phase interface layer. The device assembled into a two-electrode flow cell for direct overall seawater electrolysis maintained at 1 A/cm2@1.93 V for 500 h with Faraday efficiency higher than 95%. Hydrogen generation rate reaches 419.4 mL/cm2/h, and the power consumption (4.62 KWh/m3 H2) is lower than that of pure water (5.0 KWh/m3 H2) at industrial current density.

Mitigating the Environmental Impact by Synthesis of Adsorbents from Aluminium-Containing Waste

Abstract Purpose To develop effective adsorbents and carriers for removing harmful impurities from waste, due to the shortage of natural bauxite for alumina production. Methods To determine the influence of various impurities present in the waste—spent alumina adsorbent (SAA) on the characteristics of adsorbents for chlorine-containing compounds, samples with a different content of V, Ti and Na have been synthesized. Properties of adsorbents based on a commercial alumina and extensively treated SAA, both types undergoing impregnation with sodium hydroxide and sodium vanadate, have been compared. Alumina adsorbents and alumina-kaolin-borate catalyst carriers with the Ti content of ca. 0.2% were prepared by atomic layer deposition (ALD) of TiCl4 on the ready granules, while introduction of large quantities of titania have been performed by addition of ground alumina-titania carrier waste into the extrusion paste. Adsorption of steam, tetrachloroethylene and hydrochloric acid has been investigated. Results and Conclusions It was found that the adsorption capacity for water vapor reached 43.6 g H2O/100 g SA and 38.9 g H2O/100 g AN-2, while after ALD modification it decreased by ca. 1 and 35%, respectively and with the introduction of SA-Ti(15.0) with the same amount of titanium by ca. 35%. Modification of AN-2 with sodium vanadate at about 0.3% Na and 0.4% V had no effect on water adsorption; while as the concentration of sodium introduced by impregnation with NaOH increased, the adsorption ability deteriorated. Modification of AN-2 and SA using ALD technology sharply diminished efficiency of adsorption of water vapors, tetrachlorethylene and hydrochloric acid. By adsorption of a mixture simulating reforming exhaust gases, formation of chlorinated oligomers on AKB, AN-2 and SA was established. NaOH modification effectively suppressed oligomerization; thus SAA-based adsorbents containing more than 5% Na can be used for drying and purification of reforming exhaust gases, as the most effective, cheapest and resource-saving option. Graphical Abstract

Novel Strategy for High Efficient and Stable Perovskite Solar Cells through Atomic Layer Deposition.

The perovskite material has demonstrated conceivable potential as an absorbing material of solar cells. Although the power conversion efficiency of the device based on perovskite has rapidly come to 26%, there are still many factors that affect the further improvement of the photoelectric conversion efficiency. Interface defects are the dominating concern that influence carrier transportation and stability. Here, we report a novel strategy where B2O3 is deposited on the fresh perovskite film by atomic layer deposition technology. The organic atmosphere during atomic layer deposition can effectively regulate the crystallization kinetics of perovskites and promote crystal growth. The B2O3 adsorbed on the perovskite light-absorption layer can effectively reduce the electropositive defects on the surface of the perovskite, such as uncoordinated Pb2+ and I vacancies due to the electron-donating properties of the side O atoms in B2O3. Consequently, the power conversion efficiency of the perovskite solar cell after B2O3 treatment increases to 21.78% from 18.89%. Simultaneously, B2O3 can improve the stability of devices.

Preparation of high-performance large-area perovskite solar cells by atomic layer deposition of metal oxide buffer layer

Perovskite solar cells have been widely recognized as the most promising new-type photovoltaic device due to its power conversion efficiency rapidly increasing from 3.8% to over 26% in merely fifteen years. However, the high performances are achieved mainly on small area cells with an active area lower than 0.1 cm<sup>2</sup>. When enlarging the active area of perovskite solar cells, the efficiency falls dramatically. So, how to reduce the gap between performances of small area cells and large area cells gradually becomes a critical point in the path towards the commercialization of perovskite photovoltaic technology. Herein, a strategy of pre-growing thin layer of TiO<sub>2</sub> on a rough FTO substrate by atomic layer deposition method before spin-coating SnO<sub>2</sub> nanoparticles is proposed. Due to the inherent conformal film growth mode of atomic layer deposition, the FTO substrate can be completely covered by TiO<sub>2</sub>, thus preventing the direct contact between local protrusions of FTO and perovskite layer and impeding the current leakage phenomenon, which can be verified by the measurements from X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy, and further proved by the dark current measurement. By using this method, the repeatability and consistency of the small area cell fabrication technology on the same substrate are improved obviously. The improved electron transport process revealed by photoluminescence results and incident light management process revealed by external quantum efficiency results also brings about better solar cell performances. More importantly, highly efficient 0.5 cm<sup>2</sup> large area perovskite solar cells are fabricated through optimization of TiO<sub>2</sub> thickness. When growing 200 cycles TiO<sub>2</sub> (~9 nm in thickness) by using atomic layer deposition technology, the champion large area perovskite solar cell possesses a power conversion efficiency as high as 24.8% (certified 24.65%). The device performances also show excellent repeatability between different fabrication batches. The perovskite solar cell with TiO<sub>2</sub> buffer layer grown by the atomic layer deposition method can still retain over 95% of its initial efficiency after having been stored in a nitrogen atmosphere for 1500 h. The technique proposed in this paper can be helpful in manufacturing perovskite solar cell modules in the realistic photovoltaic market and can be extended to the large area fabrication of other perovskite optoelectronic devices such as light emitting diode, laser and detector.

Precision Interface Engineering of CuNi Alloys by Powder ALD Toward High Thermoelectric Performance

The main bottleneck in obtaining high-performance thermoelectric (TE) materials has been identified as how to decouple the strong interrelationship between electrical and thermal parameters. Herein, we present a precise interface modification approach based on the powder Atomic Layer Deposition (pALD) technology to enhance the performance of CuNi alloys. Single-layer ZnO and Al2O3 layers have been deposited on the surface of powders, typically in 10-100 cycles, and their effect on the TE performance of bulks has been thoroughly investigated. A standard model is proposed and experimentally confirmed to build the relationship between the ALD oxide cycle numbers and Zn and Al content, which could be easily adapted to other pALD processes. The enhancement of the Seebeck coefficient, caused by the energy filtering effect, compensates the electrical conductivity deterioration due to the low electrical conductivity of oxide layers. Furthermore, the oxide layers may significantly increase the phonon scattering. Therefore, to reduce the resistivity of coating layers, a multiple-layer structure is deposited on the surface of powders by inserting Al2O3 into ZnO is constructed on. The atom probe tomography shows that after pressing, the Al atoms diffused into ZnO and realized the doping effect. Al diffusion has the potential to increase the electrical conductivity and complexity of coating layers. In comparison to pure CuNi, zT increased by 227.6% as a result of the decrease in resistivity and stronger phonon scattering in phase boundaries. The study demonstrates that ALD-based interface modification may be a versatile method for decoupling TE parameters and precisely modifying phase boundaries, which is practical for other thermoelectric materials.

Effect of Surface Pretreatment to Reduce the Incubation Period of Iridium Thin Films Grown by ALD on the Oxide Surface

Iridium (Ir) has low figure of merit(×λ) and high melting temperature properties, so it has been recently spotlighted as a very important copper (Cu) alternative interconnect material in next-generation semiconductor devices. In particular, in the case of depositing a thin film using atomic layer deposition (ALD) technology, it can be expected to deposit extremely thin film with conformal, uniform and excellent step coverage characteristics even in a very complex structure or a trench structure of several nm dimension due to the inherent self-limiting characteristic of ALD. In this regard, ALD-Ir is considered as one of the most suitable metallization process for the application of advanced semiconductor interconnects. Therefore, considerable efforts have been conducted to develop a reliable ALD-Ir process having improved film qualities. And, ALD-Ir process with excellent thin film properties such as low electrical resistivity and negligible oxygen impurities was recently reported using Tricarbonyl (1,2,3-η)-1,2,3-tri(tert-butyl)-cyclopropenyl iridium (C18H27IrO3 or TICP) precursor and oxygen [1]. However, in the case of this TICP precursor, it was difficult to deposit extremely thin and continuous Ir films on the hydroxyl-terminated oxide layer due to its long incubation delay.Therefore, in this study, a method for depositing a very thin, uniform and continuous ALD-Ir thin film with low resistivity even on oxide materials was explored by reducing the incubation period and promoting nucleation using various surface pretreatment conditions. In addition, the nucleation behavior as well as film properties of ALD-Ir on the oxide material were systemically compared and analyzed according to the surface pretreatment conditions, and finally, ALD-Ir thin film with excellent properties on the oxide surface was obtained.

Stepwise Growth of Crystalline MoS2 in Atomic Layer Deposition

Transition metal dichalcogenides (TMDCs) are layered materials in which each layer is weakly bound by van der Waals forces. TMDCs have interesting intrinsic properties, including high mobility and excellent electrostatic controllability, even at monolayer thickness. Hence, they have emerged as promising materials for widespread applications in nanoelectronics, optoelectronics, gas sensors, etc. The aforementioned properties of TMDCs are significantly affected by the structuralquality and crystallinity. Accordingly, scalable techniques have been sought for synthesizing well-crystallized TMDCs.Atomic layer deposition (ALD) is considered a promising growth technique for transition metal dichalcogenides (TMDCs) because it ensures uniformity and homogeneity of the TMDC grains. However, the poor crystallinity of ALD-grown TMDCs remains a critical challenge. Although crystallinity depends on the growth mechanism, the growth behavior of crystalline TMDCs in ALD is unclear. We investigated the growth behavior of highly crystallized molybdenum disulfide (MoS2) by ALD at 650 oC with an extra pulse of remote H2 plasma. Growth at high temperatures using the activated species aided surface diffusion of the adsorbates. The ALD process facilitates repeated growth and saturation of MoS2, unlike the normal ALD of 3D bulk materials, where the film thickness monotonically increases with the number of ALD cycles. This unique behavior resulted from the evolution of the basal plane without dangling bonds. On the basal plane, MoS2 lateral growth dominates vertical growth, and prolonged incubation is required for nucleation on the basal plane. The grain size is small (up to two monolayers) because of the limited mobility on SiO2, and the grains of the third layer grow to a few hundred nanometers. These findings provide insights into the development of ALD technology for application to high-quality TMDCs.

Atomic layer deposition mechanism of hafnium dioxide using hafnium precursor with amino ligands and water

As a unique nanofabrication technology, atomic layer deposition (ALD) has been widely used for the preparation of various materials in the fields of microelectronics, energy and catalysis. Hafnium dioxide (HfO2), as an excellent high-κ oxide, is widely used as a substitute gate dielectric for conventional SiO2 in field effect transistor devices. Currently, HfO2 high-κ gate dielectric in MOSFET devices was prepared via ALD technology using tetrakis(dimethylamino)hafnium(IV) (Hf(NMe2)4, TDMAHf) and water (H2O) as the precursors. In this work, the complicated surface reaction mechanism of HfO2 H2O-based ALD using Hf(NMe2)4 was investigated using density functional theory calculations. In the TDMAHf reaction, the dimethylamino group of the precursor was eliminated by ligand exchange reaction with the hydroxyl group on the surface. Subsequently, a second dimethylamino group of TDMAHf could further be eliminated by another hydroxyl group on the surface. In the H2O reaction, ligand exchange reactions and coupling reactions could both occur. By the ligand exchange reactions, water molecule could react with the dimethylamino group on the surface. Simultaneously, the hydroxyl and amino groups could also react with neighboring hydroxyl groups to eliminate dimethylamine and water molecules via the coupling reactions. All these insights into the complicated surface reaction mechanism of H2O-based ALD could promote the further development of ALD chemistry and materials.

Advanced two-objective optimization of thickness and large-area homogeneity of ZnO ultrathin films deposited by atomic layer deposition

Semiconductor thin films and coatings have become one of the most relevant research fields due to their significant applications in priority energy-related technologies such as solar cells, photocatalysts, and smart windows. Since all these fields are conceived as tools to fight against the effects of climate change, a real impact requires the successful deposition of semiconductor films on large-area substrates such as windows, panels, pipes, and containers, to give rise to photoactive components suitable for buildings, industries, cars, and parks. However, scalability remains one of the major issues in almost all methodologies known for the deposition of semiconductor films, irrespective of the phase approach used, i.e., either from vapor- or liquid-phase. Here, a mathematical metamodel was applied to simulate the atomic layer deposition (ALD) of zinc oxide (ZnO) ultrathin films (a versatile photoactive material in energy-related research) and optimized their thickness and homogeneity over the whole area of 8 in.-diameter Si wafers. Knowing all ALD parameters that define the quality and properties of the deposited films, we delimitated a set of four metamodel-inputs (zinc precursor dose, purge, and the inner and outer carrier gas flows) based on literature review, expertise, costs, and reactor design aspects specific to the deposition of ZnO. The average thickness and homogeneity of the films were established as the two outputs of the metamodel, which were the object of optimization. Using advanced iterative procedures, we carried out three rounds of experiments that lead us to a set of ALD parameters to deposit a ZnO ultrathin film with an average thickness of 11.38 nm that leads to a deposition rate of 1.9 Å/cycle, which represents 90% of the highest reported value for ZnO by ALD (2.1 Å/cycle). The homogeneity over the whole 8 in.-diameter wafer reached 2.61 nm, which represents the smoothest distribution of thickness values in the entire deposited area. Given the origin of the limits constraining this optimization procedure, our results hold promise in supporting the transition from the laboratory-level synthesis of thin-film-based optoelectronic devices to their large-scale production. This could ultimately help to circumvent the difficulties faced in scaling the ALD technology and enable alternative deposition methodologies such as thermal ALD, otherwise inaccessible to the production chain.

Atomically dispersed Pt to boost adjacent frustrated Lewis pair for 2,6‐diamino‐3,5‐dinitropyridine hydrogenation

AbstractAchieving atomic‐level control over local environment of metal oxide to boost catalytic activity is challenging yet significant for heterogeneous hydrogenations. Herein, we propose anchoring atomically dispersed Pt species onto indium oxide using a precisely conditioned atomic layer deposition (ALD) technology to manipulate the local electronic properties of In2O3 toward enhanced hydrogenation of 2,6‐diamino‐3,5‐dinitropyridine (DADNP) to 2,3,5,6‐tetraaminopyridine (TAP). Experimental and theoretical studies unravel that the isolated Pt atoms localize the electron density surrounding them and thus activate the adjacent frustrated Lewis pair for hydrogen activation. In addition, the adsorption of DADNP is enhanced by such regulation, while that of TAP is suppressed on the Pt1‐In2O3 catalyst. The as‐synthesized Pt1‐In2O3 catalyst thus exhibits 91.7% of TAP selectivity at 100% conversion of DADNP, demonstrating remarkably improved catalytic performances as compared with the In2O3 catalyst for DADNP hydrogenation.

Experimental Investigation of Electrochemical Capacitive Responses versus Pore Geometries through Artificial Nanotubes.

Electrochemical supercapacitors have attracted significant attention due to their large capacity, high-power output, and long cycle life. However, despite extensive studies and advancements in developing highly porous electrode materials, little quantitative research on the impact of pore geometry on electrochemical responses has been conducted. This paper presents the first quantitative investigation of the relationship between electrochemical capacitive responses and pore geometries at the nanoscale. To achieve this, we constructed a uniform cylindrical pore array with controllable pore diameter and depth by using anodized aluminum oxide (AAO) to serve as a template and atomic layer deposition (ALD) technology for TiN conductive layer decoration. Our findings reveal that, at the nanoscale, increasing the specific surface area through pore diameter and depth does not proportionally increase the capacitive response, even at low scan rates. Meanwhile, we observe a critical pore parameter (170/5000 nm, diameter/depth), where the specific capacitance density and characteristic frequency dramatically decrease with a further increase in the pore aspect ratio. These results indicate that blindly pursuing the absolute specific surface area of the electrode material is not advisable. Instead, optimal pore geometry should be designed based on the desired operational conditions, and this work may serve as valuable guidance.

Atomic layer deposition of TiO2 nanolayer coated Vectran fabrics with enhanced UV-blocking performance and structural colors

Vectran fabrics are widely employed as the key material for the manufacturing of stratospheric airship. Nonetheless, Vectran faber would decompose due to the UV aging during the prolonged flying process. Herein, atomic layer deposition (ALD) technology was introduced to coat TiO2 nanolayers on the surface of Vectran fabrics. Titanium isopropoxide liquid was employed as the Ti source precursor throughout the deposition process. Compared with sol-gel vacuum infiltration technic, ALD modified Vectran yarns possessed higher surface uniformity, better UV blocking performance and lower density. Notably, thickness of the TiO2 nanocoating prepared through the ALD method was adjustable, which can optimize the UV resistance of Vectran yarn without significantly affect its density. Additionally, the nanolayer interface can induce structural coloration on the Vectran strand via diffraction phenomena. These outstanding merits endow ALD technic a promising choice to modify the surface of Vectran fiber used as the skin of stratospheric airships.

Suppressed Ion Migration in FA-Rich Perovskite Photovoltaics through Enhanced Nucleation of Encapsulation Interface.

With excellent homogeneity, compactness and controllable thickness, atomic layer deposition (ALD) technology is widely used in perovskite solar cells (PSCs). However, residual organic sources and undesired reactions pose serious challenges to device performance as well as stability. Here, ester groups of poly(ethylene-co-vinyl acetate) are introduced as a reaction medium to promote the nucleation and complete conversion of tetrakis(dimethylamino)tin(IV) (TDMA-Sn). Through simulations and experiments, it is verified that ester groups as Lewis bases can coordinate with TDMA-Sn to facilitate homogeneous deposition of ALD-SnOx , which acts as self-encapsulated interface with blocking properties against external moisture as well as internal ion migration. Meanwhile, a comprehensive evaluation of the self-encapsulated interface reveals that the energy level alignment is optimized to improve the carrier transport. Finally, the self-encapsulated device obtains a champion photovoltaic conversion efficiency (PCE) of 22.06% and retains 85% of the initial PCE after being stored at 85 °C with relative humidity of 85% for more than 800 h.

Material manufacturing from atomic layer

Atomic scale engineering of materials and interfaces has become increasingly important in material manufacturing. Atomic layer deposition (ALD) is a technology that can offer many unique properties to achieve atomic-scale material manufacturing controllability. Herein, we discuss this ALD technology for its applications, attributes, technology status and challenges. We envision that the ALD technology will continue making significant contributions to various industries and technologies in the coming years.

PdRh-functionalized porous In2O3 films to boost NO2 detection at room temperature and mechanistic insights by DFT

To achieve high and fast response at room temperature (RT) has long been a challenge for metal oxide semiconductors (MOS) sensors. Compared to single-metal functionalization, dual-metal modification of MOS offers a viable avenue to high-performance RT sensors. Herein, we employ atomic layer deposition (ALD) technology to deposit Pd and Rh metals on porous In2O3 thin films and investigate their sensitization effects on the NO2 sensing properties. Notably, the Pd/Rh catalysts enable the In2O3 sensor to have a remarkable 13-fold response (31.2) to 10 ppm NO2 at RT compared to that (2.4) of pure In2O3, which is superior to those reported In2O3-based sensors. Meanwhile, the In2O3/Pd/Rh sensor has a very fast response speed of 6.6 s and a low detection limit of 62 ppb. Density functional theory (DFT) calculations reveal that the Pd/Rh catalysts dramatically improve the interaction and charge transfer between NO2 and In2O3. This work will further promote the exploration of RT sensor sensitization strategy.

Measuring Temporal Variation of Concentration of ALD Precursor TEMAZ in Process Chamber Using UV Absorption Method

Atomic layer deposition (ALD) is becoming increasingly important to realize high-accurate atomic-scale deposition processes in semiconductor industry, where device dimensions approach atomic scale with the advances of the miniaturization. Basically, ALD is a process of forming a film using self-limited cyclic reactions, where precursor gas, purging gas, reaction gas, and purging gas are introduced sequentially [1]. To realize high-quality ALD with high-throughput, the reaction cycle should be shortened. However, this may cause incomplete gas replacement due to residual gas, resulting in the degradation in process quality. To develop high-quality ALD, precise control of temporal and spatial distribution of these gases is required. Although the total gas pressure in the chamber was usually measured as process monitor, partial pressure, or concentration of precursor as well as reaction gas was not be measured so far. This makes it impossible to evaluate gas replacement characteristics in the chamber, despite its importance for developing ALD technology.Our group developed a high-sensitivity, real-time, compact gas concentration sensor using UV light absorption method for the supply system of organometallic gases having UV absorption [2]. The gas concentration can be estimated from the UV absorption using Lambert-Beer law. Recently, to develop a new process monitoring tool in ALD, we apply this technique to in-situ measurement of precursor gas in the chamber. In this study, temporal variation of concentration of Tetrakis(ethylmethylamino)zirconium (TEMAZ) in cyclic introduction of TEMAZ and purging Ar gas was evaluated. Here, TEMAZ is widely used as a Zr precursor in ALD for zirconia films deposition, mainly in DRAM fabrication [3].Fig. 1 shows a schematic diagram of the experimental system used in this study. TEMAZ was supplied by a bubbling method. At the downstream of the TEMAZ tank, upstream pressure controller (UPCUS) was equipped to control the pressure in the tank to be constant. An inner diameter of a test chamber was 200 mm, and TEMAZ and purging Ar were supplied using a shower plate installed at the upside of the chamber. A densitometer using UV absorption method consisted of an UV light emitting part and an UV photometer, and these were placed at opposite side of the chamber. UV light with a wavelength of 250 nm, which corresponds to the absorption of TEMAZ, was used. Two densitometers (hereafter denoted as UVH and UVL) were set at 10mm and 60mm below the shower plate, respectively. A pressure gauge was also set at 10mm below the shower plate to measure total pressure in the chamber. In the measurement, the valve operation and data acquisition were conducted by a computer with a sampling period of 10 ms.Fig. 2(a) shows time evolution of chamber pressure and absorbance of UVH (which approximately proportional to TEMAZ partial pressure) in the case that TEMAZ and purging Ar were introduced alternatively every second for 50 times. TEMAZ was supplied to the chamber with diluted Ar (100 sccm) with a TEMAZ concentration of 2000 ppm. Purging Ar flow rate was 1500 sccm. In Fig. 2(b), extended graph of Fig. 2(a) for time range from 90 to 96 s were shown. It is clearly found that behavior of UVH signal and the chamber pressure was different, where UVH absorbance signal increased at TEMAZ introduction, and rapidly decreased when Ar purge started whereas the chamber pressure increased due to the Ar introduction. Such behavior cannot be obtained only from the pressure measurement.Fig. 3 compares UVH and UVL absorbance signals for 1 cycle of TEMAZ and purging Ar introductions. It can be seen that UVH absorbance began to increase at approximately 80.2 s (0.2 s after the TEMAZ introduction), and UHL absorbance began to increase with a delay at approximately 80.6 s (0.6 s after the TEMAZ introduction). This suggested that down flow of TEMAZ could be observed.The results demonstrated validity of the UV absorption method to evaluate temporal and spatial distribution of precursor gas, and this technology will greatly contribute to developing future ALD technology.[1] R. W. Johnson et al., Materials today, 17 (2014) 236.[2] H. Ishii et al., Jpn. J. Appl. Phys., 58 (2019) SBBL04.[3] S. K. Kim and C. S. Hwang, Electrochem. Solid-State Lett., 11 (2008) G9. Figure 1

Emerging Atomic Layer Deposition Technology toward High‐k Gate Dielectrics, Energy, and Photocatalysis Applications

The precise design and efficient development of nanoscale materials at the atomic level has enabled high‐end renewable energy storage, conversion devices, and large‐scale environmental governance equipment. Atomic layer deposition (ALD) is a new vapor‐phase technology for precise surface thin‐film preparation, and is outstanding with self‐limiting reactions, large deposition area, adjustable film composition, film uniformity, angstrom thickness control, and low temperature. With these characteristics, ALD plays an important role in many industry and research fields. This review briefly introduces the principle, main technical advantages, and applications of ALD, including high‐k gate dielectrics, solar cells, fuel cells, and photocatalysis. The progress of the ALD technology in preparation and application of photocatalyst is emphatically reviewed, and the large‐scale application of ALD in photocatalytic thin‐film materials is prospected.