Atomic Layer Deposition Reaction Research Articles

Correction to “Pyroelectric Heat Detection for Calibrated Measurement of Atomic Layer Deposition Reaction Heat”

Correction to “Pyroelectric Heat Detection for Calibrated Measurement of Atomic Layer Deposition Reaction Heat”

Shear Bond Strength to Enamel, Mechanical Properties and Cellular Studies of Fiber-Reinforced Composites Modified by Depositing SiO2 Nanofilms on Quartz Fibers via Atomic Layer Deposition.

Poor interfacial bonding between the fibers and resin matrix in fiber-reinforced composites (FRCs) is a significant drawback of the composites. To enhance the mechanical properties of FRC, fibers were modified by depositing SiO2 nanofilms via the atomic layer deposition (ALD) technique. This study aims to evaluate the effect of ALD treatment of the fibers on the mechanical properties of the FRCs. The quartz fibers were modified by depositing different cycles (50, 100, 200, and 400) of SiO2 nanofilms via the ALD technique and FRCs were proposed from the modified fibers. The morphologies, surface characterizations of nanofilms, mechanical properties, and cytocompatibility of FRCs were systematically investigated. Moreover, the shear bond strength (SBS) of FRCs to human enamel was also evaluated. The SEM and SE results showed that the ALD-deposited SiO2 nanofilms have good conformality and homogeneity. According to the results of FTIR and TGA, SiO2 nanofilms and quartz fiber surfaces had good chemical combinations. Three-point bending tests with FRCs showed that the deposited SiO2 nanofilms effectively improved FRCs' strength and Group D underwent 100 deposition cycles and had the highest flexural strength before and after aging. Furthermore, the strength of the FRCs demonstrated a crescendo-decrescendo tendency with SiO2 nanofilm thickness increasing. The SBS results also showed that Group D had outstanding performance. Moreover, the results of cytotoxicity experiments such as cck8, LDH and Elisa, etc., showed that the FRCs have good cytocompatibility. Changing the number of ALD reaction cycles affects the mechanical properties of FRCs, which may be related to the stress relaxation and fracture between SiO2 nanofilm layers and the built-up internal stresses in the nanofilms. Eventually, the SiO2 nanofilms could enhance the FRCs' mechanical properties and performance to enamel by improving the interfacial bonding strength, and have good cytocompatibility.

Al2O3 atomic layer deposition on a porous matrix of carbon fibers (FiberForm) for oxidation resistance

Atomic layer deposition (ALD) was used to coat a porous matrix of carbon fibers known as FiberForm with Al2O3 to improve oxidation resistance. Static trimethylaluminum (TMA) and H2O exposures for Al2O3 ALD were used to obtain the uniform coating of this high porosity material. The carbon surfaces were initially functionalized for Al2O3 ALD by exposure to sequential exposures of nitrogen dioxide and TMA. A gravimetric model was developed to predict the mass gain per cycle under conditions when the ALD reactions reached saturation during each reactant exposure. The uniformity of the Al2O3 ALD coating on FiberForm was confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) analysis. The SEM, EDS, and gravimetric models were all consistent with a uniform Al2O3 ALD coating on the porous carbon fiber network when the ALD reactions reached saturation on the entire surface area. In contrast, the profile of the Al2O3 ALD coating on the FiberForm was also characterized using undersaturation conditions when the ALD reactions did not reach saturation throughout the FiberForm sample. Based on comparisons with results from models for ALD in porous substrates, these Al2O3 coverage profiles were consistent with diffusion-limited Al2O3 ALD. Oxidation of the FiberForm and the Al2O3 ALD-coated FiberForm was also investigated by thermogravimetric analysis (TGA). TGA revealed that a 50 nm thick Al2O3 coating deposited using 400 Al2O3 ALD cycles enhanced the oxidation resistance. The Al2O3 ALD coating increased the oxidation onset temperature by ∼200 °C from 500 to 700 °C. The oxidation of the FiberForm removed carbon and left the Al2O3 ALD coating behind as a white “skeleton” that preserved the shape of the original FiberForm sample. The Al2O3 ALD coating also decreased the oxidation rate of the FiberForm by ∼30%. The oxidation rate of the Al2O3 ALD-coated FiberForm samples was constant and independent of the thickness of the Al2O3 ALD coating. This behavior suggested that the oxidation is dependent on the competing O2 diffusion into the FiberForm and CO2 diffusion out of the FiberForm.

Investigation of Electrochemical Stability of ALD Grown Li3PO4 Thin Films and Its Application in High‐Voltage PEO‐based All‐Solid‐State Lithium Batteries

AbstractIn lithium batteries, the interface between electrolytes and electrodes with optimized structural stability and fast charge transfer kinetics plays a pivotal role in achieving overall cycle and rate performance. Introducing a uniform interfacial layer that conducts Li+ ions while insulating electrons, through atomic layer deposition (ALD) of lithium compounds, has shown promise in facilitating lithium ion transport and enhancing interface stability. However, synthesizing lithium compounds with both robust chemical stability and a broad electrochemical window using ALD poses challenges due to the difficulty of obtaining desired products under specific ALD reaction conditions. In this study, this challenge by investigating Li3PO4 is addressed, a compound grown by ALD that exhibits a noteworthy property: the in situ formation of a more stable LiPO3 phase under high applied voltage. The LiPO3 phase possesses an extended theoretical stability window (LiPO3: 2.48‐5.00 V versus Li3PO4: 0.69‐4.21 V), and its emergence substantially enhances the electrochemical performance of all‐solid‐state lithium batteries based on polyethylene oxide (PEO). This work not only presents experimental evidence of the in situ transformation of the interfacial layer but also offers a pragmatic approach to realizing all‐solid‐state lithium batteries with elevated energy density, emphasizing safety and stability considerations.

Performance Improvement of Proton Ceramic Fuel Cells through Surface Treatment of Cobalt Oxide Nanoparticles on Perovskite Oxide

Ceramic fuel cells, such as solid oxide fuel cells (SOFCs) have attracted substantial attention as next-generation power generators. However, SOFCs exhibit high activation energy required for ion conduction (0.8–1 eV), which considerably increases the resistance upon decreasing the driving temperature. Therefore, the operating temperature of a typical SOFC is 800 °C or higher. However, such high-temperature driving conditions are associated to several challenges, such as heat-induced cell-structure deformation , rapid degradation of the material due to bonding stress, and the need for an insulation structure to prevent energy loss. Therefore, efforts have been made to lower the operating temperatures. Common methods use proton-conductive ceramics for proton-ceramic fuel cells (PCFCs). Unlike SOFCs, where the oxide ions pass through the electrolyte, in PCFC, protons pass through the electrolyte. Given that the activation energy (0.3–0.5 eV) of proton conduction is lower than that of oxide ions, most proton-conductive ceramics have very high ion conductivity at a lower temperature than oxygen-conductive ceramics. Therefore, compared with SOFCs, PCFCs exhibit a relatively high performance in the temperature range of 600 °C or less. As described above, efforts have been made to lower the driving temperature by promoting the oxygen reduction reaction (ORR) at the cathode, as well as by changing the ion transferred from the electrolyte.PrBa0.5Sr0.5Co2xFexO5+δ (PBSCF), a typical co-doping (Sr on the A-site and Fe on the B-site) cathode material, formed rapid oxygen diffusion and surface oxygen exchange through crystalline channels. However, most perovskite oxides, including PBSCF, exhibit poor chemical surface stability in high-temperature oxidation environments. In particular, Sr aggregation is considered a major reason for cathode degradation; however, the exact mechanism of this phenomenon has not yet been elucidated and a solution has not yet been established. Currently, it is known that elements such as Ba and Sr are larger size than other elements. During the stretch compression process inside the lattice, they are pushed out via the strain effect; moreover, the electrostatic phenomenon between the oxygen vacancies and cations may be an additional reason. Surface-treatment techniques are suitable for suppressing these phenomena. Through surface coating, the secondary phases generated by Ba and Sr aggregation may be suppressed to prevent electrode degradation. In addition, surface treatment technology is used to increase the catalytic activity of the cathode. Among the various surface treatment techniques, atomic layer deposition (ALD) is a surface thin-film coating technology suitable for ceramic cell electrodes. ALD proceeds in a chemical manner, such as chemical vapor deposition; however, it has several advantages. This may limit the deposition thickness per cycle to less than that of the atomic layer units through self-limiting reaction characteristics during material synthesis. In addition, the ALD reaction proceeded at the same rate along the surface of the substrate, which enabled uniform coating along a complex surface shape. Therefore, it may be considered an effective process to uniformly deposit a surface film and material inside a porous ceramic cell electrode structure.Herein, we attempted to improve electrode performance by applying ALD CoOx to a porous PBSCF cathode surface. CoOx has gained popularity as a high-performance electrochemical catalyst owing to its excellent ORR performance, low cost, and high chemical stability. As a result, we confirmed that the ohmic and polarization resistances were reduced by approximately 50 % and 34 %, respectively, at 600 °C by treating with CoOx, and through this, we confirmed a performance improvement of approximately 32 %. In addition, the inhibition of Ba or Sr segregation was confirmed through long-term testing. These results show that CoOx acts as an ORR catalyst in a PBSCF cathode with a perovskite structure and that ALD is a suitable method for coating porous cathode structures. In addition, H2O as a by-product of the cathode generates an oxygen reduction reaction in PBSCF, and a large amount of OH- is generated. As the number of oxygen vacancies increased, the movement of active oxygen species and electrons was promoted. This further improves the reaction with the catalyst by facilitating movement to the catalyst surface via overall electron migration and the overall spillover effect.

Resolving the Heat Generated from ZrO2 Atomic Layer Deposition Surface Reactions

AbstractIn situ pyroelectric calorimetry and spectroscopic ellipsometry were used to investigate surface reactions in atomic layer deposition (ALD) of zirconium oxide (ZrO2). Calibrated and time‐resolved in situ ALD calorimetry provides new insights into the thermodynamics and kinetics of saturating surface reactions for tetrakis(dimethylamino)zirconium(IV) (TDMAZr) and water. The net ALD reaction heat ranged from 0.197 mJ cm−2 at 76 °C to 0.155 mJ cm−2 at 158 °C, corresponding to an average of 4.0 eV/Zr at all temperatures. A temperature dependence for reaction kinetics was not resolved over the range investigated. The temperature dependence of net reaction heat and distribution among metalorganic and oxygen source exposure is attributed to factors including growth rate, equilibrium surface hydroxylation, and the extent of the reaction. ZrO2‐forming surface reactions were investigated computationally using DFT methods to better understand the influence of surface hydration on reaction thermodynamics.

Resolving the Heat Generated from ZrO2 Atomic Layer Deposition Surface Reactions.

In situ pyroelectric calorimetry and spectroscopic ellipsometry were used to investigate surface reactions in atomic layer deposition (ALD) of zirconium oxide (ZrO2 ). Calibrated and time-resolved in situ ALD calorimetry provides new insights into the thermodynamics and kinetics of saturating surface reactions for tetrakis(dimethylamino)zirconium(IV) (TDMAZr) and water. The net ALD reaction heat ranged from 0.197 mJ cm-2 at 76 °C to 0.155 mJ cm-2 at 158 °C, corresponding to an average of 4.0 eV/Zr at all temperatures. A temperature dependence for reaction kinetics was not resolved over the range investigated. The temperature dependence of net reaction heat and distribution among metalorganic and oxygen source exposure is attributed to factors including growth rate, equilibrium surface hydroxylation, and the extent of the reaction. ZrO2 -forming surface reactions were investigated computationally using DFT methods to better understand the influence of surface hydration on reaction thermodynamics.

Alternative surface reaction route in the atomic layer deposition of NbN thin films for reduced resistivity

Transition metal nitride thin films such as TiN are necessary as conducting electrodes in memory and transistor devices. Due to their high work function (> 4.7 eV), NbN thin films have recently attracted attention to replace TiN thin films as capacitor electrodes using atomic layer deposition (ALD) process in dynamic random access memories (DRAMs) to reduce leakage currents in the capacitors. Unfortunately, the NbN ALD process using NbCl5 and NH3 as the Nb precursor and nitrogen source resulted in a high resistivity (> 500 μΩ·cm) despite its low bulk resistivity (∼10 μΩ·cm at 300 K) because of the residual Cl impurity (> 5%) within the NbN film. In this study, an alternative ALD surface reaction pathway is proposed by introducing H2S gas pulses between the NbCl5 and NH3 pulse steps to lower the Cl impurity concentration. Using the alternative ALD reaction, the residual Cl concentration was reduced below 1.5% (decrease by > 50%) at the specific ALD deposition temperature of 673 K. Finally, this reaction produced a greater decrease in the resistivity (> 30%) of NbN thin films than the conventional NbN ALD at 673 K.

Substantial lifetime enhancement for Si-based photoanodes enabled by amorphous TiO2 coating with improved stoichiometry

Amorphous titanium dioxide (TiO2) film coating by atomic layer deposition (ALD) is a promising strategy to extend the photoelectrode lifetime to meet the industrial standard for solar fuel generation. To realize this promise, the essential structure-property relationship that dictates the protection lifetime needs to be uncovered. In this work, we reveal that in addition to the imbedded crystalline phase, the presence of residual chlorine (Cl) ligands is detrimental to the silicon (Si) photoanode lifetime. We further demonstrate that post-ALD in-situ water treatment can effectively decouple the ALD reaction completeness from crystallization. The as-processed TiO2 film has a much lower residual Cl concentration and thus an improved film stoichiometry, while its uniform amorphous phase is well preserved. As a result, the protected Si photoanode exhibits a substantially improved lifetime to ~600 h at a photocurrent density of more than 30 mA/cm2. This study demonstrates a significant advancement toward sustainable hydrogen generation.

Ionic Liquid-Mediated Route to Atomic Layer Deposition of Tin(II) Oxide via a C-C Bond Cleavage Ligand Modification Mechanism.

Atomic layer deposition (ALD) is a technologically important method to grow thin films with high conformality and excellent thickness control from vapor phase precursors. The development of new thermal ALD processes can be limited by precursor reactivity and stability: reaction temperature and precursor design are among the few variables available to achieve higher reactivity in gas-phase reactions, unlike in solution synthesis, where the use of solvent and/or a catalyst can promote a desired reaction. To bridge this synthesis gap between vapor-phase and solution-phase, we demonstrate the use of an ultrathin coating layer of a vapor phase-compatible solvent─an ionic liquid (IL)─on our growth substrate to perform ALD of SnO. Successful SnO deposition is achieved using tin acetylacetonate and water, a process that otherwise would require a stronger counter-reactant such as ozone. The presence of the layer of IL allows a solvent-mediated reaction mechanism to take place on the growth substrate surface. We report a growth per cycle of 0.67 Å/cycle at a deposition temperature of 100 °C in an IL comprising 1-ethyl-3-methylimidazolium hydrogen sulfate. Characterization of the ALD films confirms the SnO film composition, and 1H and 13C NMR are used to probe the solvent-mediated ALD reaction, suggesting a solvent-mediated addition-elimination-type mechanism which breaks a C-C bond in acetylacetonate to form acetone and acetate. Density functional theory calculations show that the IL solvent is beneficial to the proposed solvent-mediated mechanism by lowering the C-C bond cleavage energetics of acetylacetonate compared to the vapor phase. A general class of ligand modification reactions for thermal ALD is thus introduced in this work.

Reaction mechanism of atomic layer deposition of zirconium oxide using zirconium precursors bearing 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. As a high-κ gate dielectric to replace SiO2, zirconium oxide (ZrO2) has been prepared through the ALD method for microelectronic devices. In this work, through density functional theory calculations, the possible reaction pathways of ZrO2 ALD using tetrakis(dimethylamino)zirconium (TDMAZ) and water as the precursors were explored. The whole ZrO2 ALD reaction could be divided into two sequential reactions, TDMAZ and H2O reactions. In the TDMAZ reaction on the hydroxylated surface, the dimethylamino group of TDMAZ could be directly eliminated by substitution and ligand exchange reactions with the hydroxyl group on the surface to form dimethylamine (HN(CH3)2). In the H2O reaction with the aminated surface, the reaction process is much more complex than the TDMAZ reaction. These reactions mainly include ligand exchange reactions between the dimethylamino group of TDMAZ and H2O and coupling reactions for the formation of the bridged products and the by-product of H2O or HN(CH3)2. These insights into surface reaction mechanism of ZrO2 ALD can provide theoretical guidance for the precursor design and improving ALD preparation of other oxides and zirconium compounds, which are based ALD reaction mechanism.

(Invited) Investigating Surface Reaction Thermodynamics: In Situ Calorimetry for Atomic Layer Deposition

Atomic layer deposition (ALD) is comprised of sequential self-limiting surface reactions that are inherently sensitive to the surface chemistry of the substrate and the reactivity of the chosen precursors. In order to better understand ALD processes and direct their future development we must investigate the fundamental mechanisms of ALD reactions. This is commonly done using a combination of computational modeling and experimental investigations using techniques like spectroscopic ellipsometry and IR spectroscopy. We present pyroelectric calorimetry for ALD as an in situ technique to measure the time resolved heat generation from ALD reactions. This provides a new dimension of thermodynamic and kinetic reaction data.As an experimental technique, pyroelectric calorimetry measures ALD reactions on realistic surfaces as opposed to idealized models. We have designed and constructed custom calorimeters that are compatible with typical ALD process parameters. These calorimeters have been calibrated with a thermal resolution down to 0.1 μJ/cm2 and a temporal resolution of 50ns. To put this in perspective for an ALD reaction, this corresponds to about 0.1% of the heat evolved in the trimethylaluminum (TMA) and water ALD process and about 104 faster than our measurement of the TMA half reaction. The temporal resolution of our calorimeters is orders of magnitude faster than most complementary in situ analysis techniques including ellipsometry, IR spectroscopy, quartz crystal microgravimetry, and mass spectrometry. This time resolution provides information on precursor flow dynamics and reaction kinetics.Pyroelectric calorimetry was used to investigate the TMA and water half reactions for ALD Al2O3 along with in situ spectroscopic ellipsometry thickness measurements and Rutherford backscattering spectrometry (RBS) composition analysis. This enabled comparisons of the change in thickness with the amount of heat generated as each half reaction saturates. Atomic growth rates calculated form RBS were used to calculate the heat generated on a per-atom basis. These results were then compared with proposed reaction mechanisms and energy changes from density functional theory (DFT) computational modeling.Measurements of reaction and adsorption heats can also be used to compare and evaluate different precursors and inhibitor molecules for ALD growth inhibition in area-selective ALD. We investigated how the thermodynamics of adsorption can guide our choice of precursor-inhibitor pairs when using small molecule inhibitors that rely on competitive adsorption and chemical passivation to prevent ALD growth. Pyroelectric calorimetry offers new insight into what drives and limits ALD reactions and provides many opportunities for future investigations.

Enhanced Performance of LiFePO4 Cathodes Protected By Atomic Layer Deposited Ultrathin Alumina Films

The LiFePO4 (LFP) cathode has a theoretical specific capacity of 170 mAh/g. This material is stable, safe, and environmentally benign. Li-ion batteries with LFP cathodes have a long cycle life with excellent charging/discharging performance. In our contribution, we show that the surface modification of the LFP cathode using ultrathin alumina films grown by atomic layer deposition (ALD) can improve Li-ions charge transfer and rate performance of the Li-ion in half-cell configuration with the LFP cathode.We used two types of LFP cathodes in our study with Li-metal as an anode in a half cell configuration. The first LFP electrode had a thickness of 25 μm and consisted of particles of 0.5 - 1 μm in size [1], while the second one (commercial NANOMYTE BE-60E (NEI Corp.)) had a thickness of 70 μm and the average LFP particle size was 2 μm.Ultrathin Al2O3 films were grown on LFP cathodes by ALD at 100 °C using trimethylaluminum (TMA) and water vapors. Due to the self-saturation surface-limited nature of the ALD reaction, even substrates of highly complex morphology can be uniformly coated, where the limitation is the reach of the precursor vapor molecules. The thickness of the ALD layers depends linearly on the number of ALD cycles and ranges from 0.5 to 2 nm for 5 to 20 cycles.Galvanostatic charging/discharging experiments were performed to evaluate the rate capability of the electrodes. Pristine and Al2O3 coated LFP electrodes were laser cut to 18 mm diameter circular electrodes, inserted in the electrochemical test cells PAT-Cell (EL-CELL), and tested using PAT-Tester-x-8 analyzer. LFP with Al2O3 protecting layers was compared to the pristine LFP electrode.For the LFP cathode with the thickness of 25 μm the pristine sample saturates at the specific capacity of 32 mAh/g at 1.8 c-rate, while for the electrode treated with 5 and 20 cycles of Al2O3 the specific capacity dropped to 80 and 60 mAh/g, respectively. The electrodes protected by Al2O3 film always exhibited better rate capability than the pristine sample.A more detailed analysis of the performance was accomplished for the NANOMYTE electrodes. A specific discharge capacity of 160 mAh/g at a c-rate of 0.2 was achieved for both pristine and Al2O3-protected electrodes. Two supercycles with the c-rate 0.2, 0.5, and 1 were applied to the samples. The specific capacity of the pristine LFP electrode dropped from 160 mAh/g for the c-rate 0.2 to about 90 mAh/g at the c-rate 1, while the electrode which was protected by 5 cycles of Al2O3 exhibited a capacity of 120 mAh/g.Investigation of the rate capability fading using electrochemical impedance spectroscopy revealed a gradual increase of the Nyquist plot semicircle diameter as a function of cycles. According to the equivalent circuit model, the semicircle diameter corresponds to the charge transfer at the solid/electrolyte interface. The charge transfer resistance at the solid/electrolyte interface increases with charge/discharge cycling. The charge transfer resistance of the pristine electrode increased more steeply than that of the electrode with 5 cycles of Al2O3. Improvement of the charge transfer resistance of the LFP electrode covered by thin Al2O3 film can be explained by the formation of the Li3.4Al2O3 phase upon lithiation. The diffusivity of the Li ions in the Li3.4Al2O3 phase is several orders of magnitude higher than that of in the Al2O3 film [2]. The results obtained by electrochemical characterization are compared to the X-ray photoelectron spectroscopy performed on samples before and after galvanostatic charging/discharging measurements.[1] A. Fedorkova et al., J. Power Sources 195 (2010) 3907.[2] S. C. Jung et al., J. Phys. Chem. Lett. 4 (2013) 2681.

Adsorption selectivity of TiCl4 precursor on Pt surfaces for atomic layer deposition via density functional theory

There is an interest in atomic layer deposition as a tool for precise catalyst design and synthesis, due to advantages such as uniform coating, excellent step coverage, and control of thin-film thickness at the atomic level. Using selective atomic layer deposition on platinum-based nanoparticle catalysts improves or maintains catalytic performance, and also improves sintering resistance under high-temperature and -pressure conditions through fine control of the surface. In this study, we used density functional theory to elucidate the mechanism of the initial TiCl4 half-cycle reaction for TiO2 formation on the surface of Pt nanoparticles, and the deposition characteristics according to the crystal properties. In the surface reaction, TiCl4 is adsorbed on Pt (111), (100), and (211) surfaces containing an –OH functional group, and the reaction proceeds through formation of a Pt−O−TiCl3 complex followed by HCl. The chemical adsorption of TiCl4 to the Pt−OH surface has an energy between −2.44 and −2.76 eV, thus providing a highly stable chemical bond. The activation energy of the TiCl4 half-cycle reaction on the surface of Pt nanoparticles is 1.15 – 1.24 eV, in the order Pt (211) > (100) > (111). Via electronic structure analysis of TiCl4-adsorbed Pt nanoparticles, we confirmed that the Pt (111) surface is a favorable pathway for the release of HCl, enhancing its response to the surface reaction. This study provides a quantitative understanding of the selective atomic layer deposition reaction of the precursor TiCl4 on Pt catalyst surfaces. As theoretical understanding of the deposition process improves, we expect that it will become possible to design precursor materials and process conditions applicable to the specifications required by various industries.

Resolving the Heat of Trimethylaluminum and Water Atomic Layer Deposition Half-Reactions.

Atomic layer deposition (ALD) is a surface synthesis technique that is characterized by self-limiting reactions between gas-phase precursors and a solid substrate. Although ALD processes have been demonstrated that span the periodic table, a greater understanding of the surface chemistry that affords ALD is necessary to enable greater precision, including area- and site-selective growth. We offer new insight into the thermodynamics and kinetics of the trimethylaluminum (TMA) and H2O ALD half-reactions with calibrated and time-resolved in situ pyroelectric calorimetry. The half-reactions produce 3.46 and 2.76 eV/Al heat, respectively, which is greater than the heat predicted by computational models based on crystalline Al2O3 substrates and closely aligned with the heat predicted by standard heats of formation. The pyroelectric thin-film calorimeter offers submillisecond temporal resolution that uniquely and clearly resolves precursor delivery and reaction kinetics. Both half-reactions are observed to exhibit multiple kinetic rates, with average TMA half-reaction rates at least 2 orders of magnitude faster than the H2O half-reaction kinetics. Comparing the experimental heat with published computational literature and additional first-principles modeling highlights the need to refine our models and mechanistic understanding of even the most ubiquitous ALD reactions.

Application of Adaptive PID Temperature Control Algorithm under Spatial Thermal Model of ALD Reaction Chamber

The study aims to expand the application of the proportion integral derivative (PID) algorithm and improve the practical application of the PID algorithm to the atomic layer deposition (ALD) process. First, the ALD process is analyzed, and the application method of the PID algorithm is determined. Second, the research conditions of the PID algorithm based on the ALD process are designed. Finally, the temperature control operation of the PID algorithm in the ALD reaction chamber is modeled and experimentally studied under different research conditions. The results show that temperature significantly impacts the reaction chambers of stainless steel and aluminum. When the heating temperature increases, the temperature of the stainless steel chamber will also change, and the maximum difference between the chamber and the heating temperature is about 33°C. In contrast, the temperature of the aluminum chamber varies little with the heating temperature. The maximum difference between the chamber temperature and heating temperature is about 350°C, which shows that the temperature of the stainless steel chamber is better controlled and is more practical under the same temperature conditions. The pressure change has little effect on the temperature change of the reaction chamber of the two materials. The temperature curves of the two chambers show that the PID temperature control system can be used normally and has strong practicability. The study provides technical support for improving the PID temperature control system and the rational use of the PID temperature control algorithm in the ALD process.

Ambient pressure x-ray photoelectron spectroscopy setup for synchrotron-based in situ and operando atomic layer deposition research.

An ambient pressure cell is described for conducting synchrotron-based x-ray photoelectron spectroscopy (XPS) measurements during atomic layer deposition (ALD) processes. The instrument is capable of true in situ and operando experiments in which it is possible to directly obtain elemental and chemical information from the sample surface using XPS as the deposition process is ongoing. The setup is based on the ambient pressure XPS technique, in which sample environments with high pressure (several mbar) can be created without compromising the ultrahigh vacuum requirements needed for the operation of the spectrometer and the synchrotron beamline. The setup is intended for chemical characterization of the surface intermediates during the initial stages of the deposition processes. The SPECIES beamline and the ALD cell provide a unique experimental platform for obtaining new information on the surface chemistry during ALD half-cycles at high temporal resolution. Such information is valuable for understanding the ALD reaction mechanisms and crucial in further developing and improving ALD processes. We demonstrate the capabilities of the setup by studying the deposition of TiO2 on a SiO2 surface by using titanium(IV) tetraisopropoxide and water as precursors. Multiple core levels and the valence band of the substrate surface were followed during the film deposition using ambient pressure XPS.

A Study on the Effect of Base‐Reactant in Low‐Temperature Atomic Layer Deposition of Zinc Oxide

During the low‐temperature atomic layer deposition (ALD) process, residual carbon from the unreacted ligand of precursors causes deterioration in the properties of grown materials. Herein, a simple approach using a base solution as a reactant to reduce residual carbon and improve the low‐temperature ALD reaction is proposed. NaOH dissolved in H2O is used as the reactant base solution and diethyl zinc is used as a reactant. The effects of the base‐reactant on the ZnO film growth are analyzed using X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), photoluminescence (PL), and thin‐film transistor (TFT) measurements. The crystallinity, grain size, and Zn and O contents of the ZnO thin films gradually increased as the concentration of NaOH increased (0, 10, 20, and 30 wt%). Residual carbon occupying Zn sites is reduced as NaOH concentrations increased. The unintended heavily doped state induced by the residual carbon during the low‐temperature ALD process is improved, and the ZnO TFT device fabricated with the NaOH/H2O solution also shows improvements in its field‐effect mobility and the on/off current ratio. This simple approach, using the base solution as the reactant during the low‐temperature ALD process, effectively improves the quality of the grown film with low carbon impurities.

Pyroelectric Heat Detection for Calibrated Measurement of Atomic Layer Deposition Reaction Heat

Pyroelectric Heat Detection for Calibrated Measurement of Atomic Layer Deposition Reaction Heat

Modelling the Growth and Etch of Thin Film Metal Oxides

HfO2 and ZrO2 are two high-k materials that are crucial in semiconductor devices. Atomic level control of material processing is required for fabrication of thin films of these materials at nanoscale device sizes. Atomic layer deposition (ALD) and thermal atomic layer etching (ALE) allow fabrication of ultra-thin films for semiconductor device processing. ALD is a well-known metal oxide thin film deposition technique in which metal and oxygen containing precursors are added sequentially to the reactor to ensure self-limiting precursor adsorption and reaction to enable a high level of control over film thickness. Thermal ALE, which is a relatively modern technique, uses self-limiting fluorination (using hydrogen fluoride exposure) and subsequent ligand exchange reactions at elevated temperatures to remove up to a monolayer of the metal oxide material. This modern approach for controlled etching is the reverse of ALD and removes only the fluorinated layer.Given that it is difficult to investigate ALD and ALE reactions directly using experimental techniques, first-principles-based atomic-level simulations using density functional theory (DFT) can give deep insights into the precursor chemistry and the reactions that drive the deposition and etch of different materials. This contribution presents first principles density functional theory modelling to examine the growth and etch of thin films of HfO2 and ZrO2. Concerning the ALD reaction, the adsorption mechanism of precursors TDMAHf and TDMAZr are studied at the bare and hydroxylated surfaces of HfO2 and ZrO2 respectively. Stable OH coverages of 0.50 ML and 0.63 ML on the surfaces of HfO2 and ZrO2 were found respectively. Ligand loss from the metal precursor can be achieved by protonation from the OH terminated surface of both metal oxides. Concerning the ALE reaction, HF exposures on the surfaces of HfO2 and ZrO2 are studied. HF coverages ranging from 1.0 ± 0.3 to 17.0 ± 0.3 HF/nm2 are investigated and a mixture of molecularly and dissociatively adsorbed HF molecules is present at higher coverages. Theoretical etch rates of -0.61 ± 0.02 Å /cycle for HfO2 and -0.57 ± 0.02 Å /cycle ZrO2 were calculated using maximum coverages of 7.0 ± 0.3 and 6.5 ± 0.3 M-F bonds/nm2 respectively (M = Hf, Zr).