Atomic Layer Deposition Research Articles

Effect of oxygen plasma treatment on the properties of ALD hafnium oxide films

In this work, we studied the effect of processing hafnium oxide samples prepared by atomic layer deposition in a gas discharge plasma of a mixture of argon and oxygen in a ratio of 1:10. It has been shown that such treatment preserves the amorphous structure of the film and reduces the content of oxygen vacancies in the film. This is important for the use of the film in the gate dielectric of a transistor. Processing in plasma leads to a change in its properties, namely: an increase in density and refractive index, as well as a decrease in the intensity of emission bands that are associated with an oxygen vacancy. The plasma temperature and ion energy were determined from the argon emission spectra. The activation energy for the diffusion of oxygen ions in hafnium oxide films has been calculated to be 0.43 eV.

Janus Electronic Devices with Ultrathin High-κ Gate Dielectric Directly Integrated on 1T'-MoTe2.

Integrating high-quality dielectrics with two-dimensional (2D) transition metal chalcogenides (TMDCs) is crucial for high-performance electronics. However, the lack of dangling bonds on 2D material surfaces complicates direct dielectric deposition. We propose using atomic layer deposition (ALD) to integrate ultrathin high-κ dielectric directly on 1T'-MoTe2 surfaces, facilitating the creation of high-performance back-gated field-effect transistors (FETs). Exploiting 1T'-MoTe2's natural oxidation in ambient conditions, we directly deposit dense and uniform HfO2 dielectric films below 5 nm, achieving an equivalent oxide thickness (EOT) of 0.97 nm. The resulting back-gate transistors, with a monolayer MoSSe on HfO2/1T'-MoTe2, show a current on/off ratio over 105 and operate at low voltages (<1 V), indicating high gating efficiency and a charge carrier mobility of 2.93 cm2V-1s-1. Additionally, we demonstrate a 6 × 5 bottom-gated array of MoSSe transistors using all-1T'-MoTe2 electrodes, achieving an 86.7% sample yield. Our approach also enables the creation of various integrated logic circuits such as inverters, NAND, and NOR gates. This research offers a feasible method for integrating high-κ dielectric films using industrially compatible ALD processes, providing excellent thickness control, uniformity, and scalability for 2D electronic devices.

Directing SEI formation on Si-based electrodes using atomic layer deposition.

The design of artificial solid eletroctrolyte interphase is an important task to minimize capacity losses in Li-ion batteries. Herein, TiO2 created through atomic layer deposition was used as an artificial SEI on Si nanoparticles. Such coating led to substantial improvement of cycling stability when evaluated with FEC-free electrolyte.

Advanced Nested Coaxial Thin-Film ZnO Nanostructures Synthesized by Atomic Layer Deposition for Improved Sensing Performance

We report a new synthesis method for multiple-walled nested thin-film nanostructures by combining hydrothermal growth methods with atomic layer deposition (ALD) thin-film technology and sacrificial films, thereby increasing the surface-to-volume ratio to improve the sensing performance of novel ZnO gas sensors. Single-crystal ZnO nanorods serve as the core of the nanostructure assembly and were synthesized hydrothermally on fine-grained ALD ZnO seed films. Subsequently, the ZnO core nanotubes were coated with alternating sacrificial coaxial 3D wrap-around ALD Al2O3 films and ALD ZnO films. Basically, the center nanorod was coated with an ALD 3D wrap-around Al2O3 sacrificial layer to realize a nested coaxial ZnO thin-film nanotube. To increase the surface-to-volume ratio of the nested multiple-film nanostructure, both the front and backside of the nested coaxial ZnO films must be exposed by selectively removing the intermittent Al2O3 sacrificial films. The selective removal of the sacrificial films exposes the front and backside of the free-standing ZnO films for interaction with target gases during sensing operation while steadily increasing the surface-to-volume ratio. The sensing response of the novel ZnO gas sensor architecture with nested nanotubes achieved a maximum 150% enhancement at low temperature compared to a conventional ZnO nanorod sensor.

Covering a 1280–1495 nm (215 nm) wideband high-gain bismuth-doped fiber amplifier with only 1240 nm pumping

In this study, two bismuth-doped fibers were fabricated by atomic layer deposition (ALD) combined with modified chemical vapor deposition (MCVD) technology. For a dual-pump amplification configuration, 1240 and 1310 nm pumping the BDF simultaneously, when the 1240 nm pump power changes, it has little impact on the gain. The 1310 nm pump wavelength overlaps with the emission range of bismuth active centers associated with phosphorus (BACs-P), potentially suppressing its excitation. The experiment reveals that the emission range of BACs associated with silicon (BACs-Si) overlaps the absorption range of BACs-P, indicating that BACs likely exist for their reabsorption properties. Furthermore, enhancing the reabsorption properties can increase the luminescent intensity of BACs-Si in the 1420 nm region with only a 1240 nm pump. The gain of peaks at 1340 and 1420 nm exceeds 31.5 dB at a −23 dBm input signal. Notably, the gain within the 1280–1495 nm range exceeded 15 dB, achieving a bandwidth of 215 nm. This holds significant promise for applications in artificial intelligence, autonomous driving, and other fields with high-capacity communication demands.

Eliminating chemo-mechanical degradation of lithium solid-state battery cathodes during >4.5 V cycling using amorphous Nb2O5 coatings.

Lithium solid-state batteries offer improved safety and energy density. However, the limited stability of solid electrolytes (SEs), as well as irreversible structural and chemical changes in the cathode active material, can result in inferior electrochemical performance, particularly during high-voltage cycling (>4.3 V vs Li/Li+). Therefore, new materials and strategies are needed to stabilize the cathode/SE interface and preserve the cathode material structure during high-voltage cycling. Here, we introduce a thin (~5 nm) conformal coating of amorphous Nb2O5 on single-crystal LiNi0.5Mn0.3Co0.2O2 cathode particles using rotary-bed atomic layer deposition (ALD). Full cells with Li4Ti5O12 anodes and Nb2O5-coated cathodes demonstrate a higher initial Coulombic efficiency of 91.6% ± 0.5% compared to 82.2% ± 0.3% for the uncoated samples, along with improved rate capability (10x higher accessible capacity at 2C rate) and remarkable capacity retention during extended cycling (99.4% after 500 cycles at 4.7 V vs Li/Li+). These improvements are associated with reduced cell polarization and interfacial impedance for the coated samples. Post-cycling electron microscopy analysis reveals that the Nb2O5 coating remains intact and prevents the formation of spinel and rock-salt phases, which eliminates intra-particle cracking of the single-crystal cathode material. These findings demonstrate a potential pathway towards stable and high-performance solid-state batteries during high-voltage operation.

High performance AlGaN/GaN MISHEMTs using N2O treated TiO2 as the gate dielectric

High performance AlGaN/GaN MISHEMTs using N₂O treated TiO₂ as the gate dielectric

Monolith Catalyst Design by Combining 3D Printing and Atomic Layer Deposition: Toward Green Palladium‐Catalyzed Cross‐Coupling Reactions

Monolith Catalyst Design by Combining 3D Printing and Atomic Layer Deposition: Toward Green Palladium‐Catalyzed Cross‐Coupling Reactions

Synthesis of High‐Surface‐Area Alumina using Carbon Templating and Liquid Phase Atomic Layer Deposition

Synthesis of High‐Surface‐Area Alumina using Carbon Templating and Liquid Phase Atomic Layer Deposition

Atomic layer deposition of ultrathin nitride films for enhanced carrier lifetimes and photoluminescence in CdTe/MgCdTe double heterostructures

This work evaluates the passivation effectiveness of ultrathin nitride layers (SiNx, AlN, and TiN) deposited via atomic layer deposition on CdTe/MgCdTe double heterostructures for solar cell applications. Time-resolved photoluminescence and photoluminescence measurements revealed enhanced carrier lifetimes and reduced surface recombination, indicating improved passivation effectiveness. These results underscore the potential of SiNx as a promising passivation material to improve the efficiency of CdTe solar cells.

Polarization-insensitive bifocal metalenses by combining nanoimprint lithography and atomic layer deposition in the visible spectrum

Multifocal lenses are essential components for microscopy, spectroscopic detection, and optical trapping. Benefiting from the unprecedented capability of metasurfaces in light control, metalenses are able to provide multi-foci functionality with a more compact footprint, making them attractive alternatives to traditional bulky lenses. However, current manufacturing techniques encounter some challenges, including low throughput, high cost, and limited patterning areas. Here, we demonstrate the wafer-scale, low-cost, and high-throughput production of polarization-insensitive bifocal metalenses at a wavelength of 450 nm by combining nanoimprint lithography and atomic layer deposition. The nanoimprint process is simplified by using the imprinted resin itself as meta-atoms, which exhibit high aspect ratios (∼10:1) and small critical dimensions (∼90 nm). The effective refractive index of the meta-atoms is increased through atomic layer deposition of the high-index TiO2 film, providing 0–1.5π sufficient phase coverage. Metalenses with diameters of 480 μm are fabricated on the silica substrate, exhibiting two diffraction-limited focal spots along the optical axis. Moreover, the fabricated metalenses demonstrate the polarization-insensitive feature under various polarization states. The fabrication process presented in this Letter paves the way for large-scale and low-cost production of versatile metasurfaces operating in the visible or shorter spectrum.

Substrate induced composition change during Ge2Sb2Te5 atomic layer deposition and study of initial reactions on SiO2 surface

Ge2Sb2Te5 (GST) is a well-known phase change material used in nonvolatile memory devices, photonics, and nonvolatile displays. This study investigates the impact of precursor sequence during atomic layer deposition (ALD) of GST from GeCl2.C4H8O2, SbCl3, and Te[(CH3)3Si]2 on Si/SiO2 substrates, focusing on growth per cycle, morphology, and composition along with initial precursor reactions on the substrate. We found that while thick layers approach stoichiometric Ge2Sb2Te5, a Ge-rich interfacial layer is initially formed, regardless of the binary ALD sequence used to start the deposition (GeTe vs Sb2Te3). Starting the ALD process with the GeTe-Sb2Te3 sequence results in a higher Ge content near the GST/SiO2 interface compared to the Sb2Te3-GeTe sequence. To understand these phenomena, we examine the initial precursor reactions on the SiO2 substrate by total reflection x-ray fluorescence spectrometry. The analysis reveals that SbCl3 exhibits lower reactivity with the SiO2 substrate than GeCl2.C4H8O2, and not all Ge adspecies react with the Te[(CH3)3Si]2 precursors. Additionally, the impact of the initial SiO2 surface on deposition extends over several ALD cycles, as the SiO2 surface only gradually gets covered by GST due to island growth. These processes contribute to the formation of a Ge-rich GST layer at the interface, irrespective of the precursor pulse sequence. These insights from the study may contribute to optimizing the initial deposition stages of GST and other ternary ALD processes to enable better composition control and enhanced device performance.

Impact of CaO-Modified γ-Al2O3 Support on CO Oxidation Activity of Pt/LaFeO3 Catalyst.

In this study, we prepared Pt/29.3 wt % LaFeO3 on a commercial carrier of γ-Al2O3 by inserting a CaO interlayer between LaFeO3 and γ-Al2O3 (i.e., Pt/LaFeO3/CaO/γ-Al2O3) via atomic layer deposition. With the interaction between CaO and LaFeO3, the Pt supported on LaFeO3/CaO/γ-Al2O3 demonstrated diverse dispersion characteristics, with regions showing well-dispersed Pt particles of approximately 2 nm, while others displayed some larger Pt nanoparticles. Interestingly, after redox treatments, the CO adsorption over Pt/LaFeO3/CaO/γ-Al2O3 was significantly attenuated, and high-resolution transmission electron microscope analysis on the Pt surface revealed the presence of FeOx layers covering the Pt. Postoxidation, a thick FeOx layer was generated on Pt, leading to the inertness of the catalyst toward CO oxidation. However, after reduction, a thinner FeOx layer (approximately two atomic layers) developed on Pt, which facilitated the oxidation of CO through the Pt-FeOx interface.

Atomic Layer Deposition of ZnO on CsPbBr3 Perovskite Nanocrystals: Surface-Dependent Mechanistic Insights.

In this study, we investigate the atomic layer deposition (ALD) process on all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) to introduce an inorganic electron transport layer (ETL) in light-emitting diode (LED) devices. Two types of CsPbBr3 PNCs were synthesized with oleate (OA) and oleylammonium (OLA) ligands on the surface. We found that CsPbBr3 PNCs with Cs oleate surfaces experienced severe photoluminescence (PL) quenching after the ALD process, while those with oleylammonium bromide surfaces did not show any significant PL drop. Transmission electron microscopy and X-ray photoelectron spectroscopy revealed that significant Pb metal formation and Ruddlesden-Popper planar faults, linked to uncoordinated Pb2+ ion defects, were generated in CsPbBr3 PNCs terminated with Cs oleate after ALD ZnO. Finally, we fabricated LEDs using PNCs with an ALD ZnO process to introduce inorganic ZnMgO nanoparticles as the ETL. The devices processed with ALD exhibited superior luminance and external quantum efficiency compared to those without the ALD process. This research provides crucial insights into the surface-dependent chemistry of PNCs and the surface-dependent performance of perovskite-based optoelectronic devices.

Amorphous Doped Indium Tin Oxide Thin‐Films by Atomic Layer Deposition.Insights into Their Structural, Electronic and Device Reliability

AbstractThin semiconducting films of magnesium doped indium‐ and tin oxide are prepared by thermal atomic layer deposition (ALD). The metal oxide films are deposited at 200 °C from the precursors trimethylindium, tetrakis(dimethylamido)tin, bis(ethylcyclopentadienyl)magnesium and water as oxidant. These thin‐films are observed to be amorphous by electron microscopy and X‐ray diffraction. However, they exhibited a near‐range atomic order with correlation lengths of up to 10 Å, as demonstrated by high energy total scattering at grazing incidence employing synchrotron radiation. Even minor alterations in composition reveal a significant impact on the thin‐film transistor (TFT) device parameters, due to magnesium's high oxygen binding capability and its ability to inhibit the formation of oxygen vacancies, resulting in a decrease of free charge carriers in the material. Stability tests indicate a device degradation after storage in ambient conditions due to water adsorption on the surface, which could be reversed by an additional annealing step which qualify the films as robust. This studie demonstrate the possibility of employing minor amounts of high band gap oxides such as MgO to manipulate and control the electric behavior of the active channel layer performance in inorganic TFT devices.

Nanometer-thick TiO2 channel thin film transistors as radical monitors for plasma enhanced atomic layer deposition

Nanometer-thick-TiO2-channel thin-film transistors (TFTs) are examined as oxidizing-agent monitors for room-temperature atomic layer deposition (RTALD). RTALD is a plasma-based process using plasma-excited humidified argon where OH radicals oxidize the precursor-gas adsorbed surface. In the TFT, the anatase TiO2 channel, with a thickness of 16 nm, is attached to a 300 nm thick gate capacitor of SiO2, while the channel surface is exposed to the ALD ambient. A heavily doped n-type Si substrate attached to the gate SiO2 is used as the gate electrode. The gate width and length are 1000 and 60 μm, respectively. When the TFT is installed in the RTALD chamber, the drain-current waveform is recorded in the course of the metal organic gas adsorption, evacuation of the residual gas, oxidization, and evacuation. In the present study, three kinds of metal organic (MO) precursors, tetrakis(dimethyl)amino titanium, tris(dimethyl)amino silane, and trimethyl aluminum are examined. The drain current exhibits strong responses upon the exposure of the plasma excited humidified argon. This suggests that OH radicals in the plasma might oxidize the adsorbed MO precursors to produce the OH moieties, where the surface polarization of OH moieties might enhance channel conductivity. The experimental results suggest the applicability of the present TFT as a plasma monitor in RTALD.

Toward Commercial-Scale Perovskite Solar Cells: The Role of ALD-SnO2 Buffer Layers in Performance and Stability.

Hybrid organic-inorganic perovskite solar cells (PSCs) have shown significant potential in photovoltaic applications due to their superior optoelectronic properties. However, the conventional electron transport layer (ETL) of C60 in PSCs poses challenges such as incomplete coverage and metal diffusion, leading to reduced performance and stability. This work explores the efficacy of atomic layer deposition (ALD) of SnO2 as an interlayer between C60 and electrode to enhance the performance and stability of devices. Devices with varying SnO2 thicknesses were fabricated, revealing that a 15 nm ALD-SnO2 layer optimally improved the power conversion efficiency (PCE) to 23.85%, compared to the 22.86% achieved with a BCP layer. Moreover, the SnO2-based devices exhibited superior open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF). Modules (30 × 30 cm) with ALD-SnO2 demonstrated notable enhancements in efficiency and uniformity, suggesting the potential for scalable commercial applications. Photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) analyses confirmed the improved charge extraction and reduced recombination with the SnO2 buffer layer. This research indicates that ALD-SnO2 is a promising interlayer candidate for PSCs, providing a pathway toward higher efficiency and stability in perovskite solar technology.

Biocompatibility and antibacterial properties of medical stainless steel and titanium modified by alumina and hafnia films prepared by atomic layer deposition

New methods for producing surfaces with suitable biocompatible properties are desirable due to increasing demands for biomedical devices. Stainless steel 316 L and cp- titanium specimens were coated with thin films of alumina and hafnia deposited using the atomic layer deposition method at two temperatures, 180 and 260 °C. The morphology of the films was analysed using scanning electron microscopy, and their surface energies were determined based on drop contact angle measurements. Biocompatibility assays performed using mesenchymal stem cells were evaluated by incubating the specimens and then exposing their extracts to the cells or directly seeding cells on the specimen surfaces. No detrimental effect was noticed for any of the specimens. Antibacterial properties were tested by directly incubating the specimens with the bacteria Staphylococcus aureus. Overall, our data show that all prepared films were biocompatible. Alumina films deposited on cp-titanium at 260 °C outperform the other prepared and tested surfaces regarding antiadhesive properties, which could be related to their low surface energy.

Study on the fabrication of high-quality hafnium oxide thin films using spatial rotated atomic layer deposition and supercritical fluids treatment

This study explores the experimental outcomes and discussions surrounding the deposition of high-quality hafnium oxide (HfO2) thin films using spatial rotated atomic layer deposition (SRALD). The primary objective was to enhance the efficiency of ALD processes while maintaining film quality comparable to conventional methods. The SRALD system, developed by Kudos Nano Technology, was employed to deposit HfO2 films over a four-step process. Following deposition, the films underwent high-pressure annealing and supercritical fluids treatment, which are known for reducing thermal budgets. The key findings revealed that high-pressure annealing resulted in a significant reduction in the leakage current by up to 50%, while supercritical fluids treatment improved the dielectric constant of the films, reaching values as high as 23. These treatments also contributed to enhancing the uniformity and density of the films, as confirmed by cross-sectional transmission electron microscopy and x-ray reflectometry analyses. The electrical properties of the resulting metal–insulator–semiconductor capacitors were thoroughly investigated, demonstrating a marked improvement in capacitance-voltage characteristics with minimal hysteresis.

Nondispersive ultraviolet monitoring of pulsed H2S gas delivery

This article describes time-resolved optical measurements of H2S partial pressure and mass flow in a pulsed gas delivery system approximating injection conditions encountered during atomic layer deposition. A high-speed nondispersive ultraviolet (NDUV) gas analyzer design is employed for in-line H2S detection in a gas delivery line with flowing carrier gas. An in-place analyzer calibration performed in a reference cell yields an H2S detection limit of ≈1.4 Pa (at 22 °C) at a sampling rate of 1 kHz. Flow measurements performed on the delivery line are used to evaluate the effects of adjustable delivery parameters on the time-dependent injection system output. Short pulse widths exhibit partial pressure transients attributed to flow development within the different volumes of the delivery system. After ≈1.0 s of injection, steady-state flow is established across flow elements. A partial pressure of H2S in the delivery line is found to vary linearly with upstream H2S pressure, consistent with choked flow. A stronger scaling of partial pressure is evident when the flow coefficient of the downstream metering valve is adjusted. Estimated steady-state H2S flow rates in the range of 0.05–0.21 mg/s are observed within a limited range of valve flow coefficients. However, further increases in the flow coefficient do not result in increased flow, likely due to conductance limitations in downstream flow system components. The utility of NDUV absorption measurements for high-pressure pulsed gas delivery systems is discussed.