Artificial intelligence in atomic layer deposition

All solid-state ion layers has an ever-growing interest in order to accomplish on-chip energy storage devices. As such, lithium-ion synaptic transistor to build artificial neural networks, integrated area-enhanced capacitors and lithium-ion microbatteries for energy supply are suitable candidates fulfilling energy-efficient devices. Atomic layer deposition (ALD) is one of the most promising techniques for manufacturing ultrathin layers for lithium-ion devices with exceptional capabilities to enable conformal growth at atomic scale. In this area, in situ diagnostics has become of vital importance for the growth process understanding especially on view of the air-sensitivity character of lithium ultra-thin layers.The purpose of this work is to present an in situ spectroscopic ellipsometry (SE) study of ALD thin films used on the fabrication of lithium-ion devices. We will consider several aspects of ALD ultrathin films growth, such as film thickness, saturation curves and initial films nucleation. We shall compare in situ SE results with those of ex situ diagnostics such as XRR (x-ray reflectometry) and XPS (x-ray photoelectron spectroscopy).We focus on the characterization of 10-100 nm thin lithium phosphate electrolyte with and without nitrogen doping deposited at ALD temperature range 300-350°C using LiHMDS-TMPO and LiHMDS-DEPA precursors, respectively. On the other hand, the realization of silicon integrated lithium ionic devices requires the implementation of essential barrier films to prevent Li-ion into the Si substrate. We will explore here the ability of titanium nitride depositions to act as lithium-ion diffusion barriers. TiN deposition (10-20 nm thin) by ALD process (350°C-400°C) uses TiCl4 and NH3 precursors.First, we investigate the growth process of LiPO, LiPON and TiN intrinsic layers deposited using thermal ALD. Secondly, we apply in situ and ex situ diagnostics on exemplary LiPO/LiPON deposited on top of the 10 nm ALD TiN film (Figure 1: Monitoring of LiPON thickness vs deposition time using in-situ Ellipsometry). The film thickness deduced from in situ SE measurements was corroborated by thickness measurements with XRR technique (Figure 2: Evolution of LiPON thickness vs ALD cycles using Ellipsometry and SE characterization techniques). Ex situ SE was used most often for WiW uniformity evaluating (Figure 3: 8” Wafer thickness mapping of ALD LiPON layers (a: 10nm TiN film; b: 17nm LiPON film). The preliminary results underline the fact that ALD growth rate and nucleation of lithium electrolyte and titanium nitride obviously depends on the ALD process parameters (temperature, pulse and purge times, number of cycles) but on the substrate nature (silicon, thermal oxide, and metallic). In situ and ex situ diagnostics highlight that initial film growth of lithium electrolytes and TiN layers strongly depends on the precursors kind used in the ALD process and the substrate material employed. Figure 1

We report the development of an atomic layer deposition (ALD) process for depositing titanium dioxide (TiO 2 ) nanofilms onto porous activated carbon (AC) electrodes to enhance the electrochemical performance of supercapacitors. This study investigates previously unexplored aspects of the ALD process, including the influence of precursor pulse duration and film thickness on the deposition behavior within complex porous AC structures. The deposited TiO 2 nanofilms were amorphous and exhibited excellent uniformity and conformality across the AC surface. Electrochemical measurements revealed a combination of surface redox and intercalation-type pseudocapacitance, with surface redox reactions identified as the dominant energy storage mechanism. An optimal balance between accessible surface area and film thickness was achieved at 60 ALD cycles, corresponding to a TiO 2 film thickness of approximately 2.3 nm. Under these conditions, the specific capacitance of TiO 2 -coated supercapacitors exceeded that of bare AC electrodes, owing to the additional pseudocapacitance contributed by the TiO 2 layer. These findings demonstrate an effective strategy for utilizing ALD to engineer advanced electrode materials for high-performance supercapacitors. • Interfacial decoration of TiO 2 nanofilms on AC supercapacitors via ALD technique. • Highly uniform and conformal TiO 2 nanofilms observed in SEM/cross-sectional TEM. • The TiO 2 /AC demonstrate higher capacitance during extensive charge-discharge cycles. • New insights on next generation supercapacitors based TiO 2 ALD-coated AC electrodes.

From the Ground Up-Materials Science in Singapore.

The nearly unmatched conformality of Atomic Layer Deposition (ALD) renders it a powerful deposition technique for applications such as catalysis where high surface areas are critical, or for protective coatings on complex 3D surfaces such as powders or porous materials. In the last decade, ALD for energy storage has come into view. Advances in technology have pushed the requirements of energy storage devices, leading to novel lithium-ion battery (LIB) concepts such as 3D-structured electrodes, thin-film electrode and the combination of both. These concepts enable high-power and high-energy integrateable batteries, but require a conformal deposition technique for the current collectors, electrodes, solid electrolytes and interfacial coatings alike. Besides 3D structuring, materials design of the LIB electrodes is paramount to achieve higher power and higher energy densities, beyond traditional electrode materials such as LiCoO2, and LiMnO2which are limited to volumetric capacities of 550-700mAh/cm³. Traditionally, the main focus of materials development for batteries has been on crystalline compounds. However, several indications exist that higher energy and power density can be found in amorphous materials. ALD is not only excellently suited to deposit conformal films, but also able to grow high-quality amorphous films at low deposition temperatures, enabling the study of amorphous thin-film electrodes. In this work, ALD of vanadium oxides for applications as lithium-ion electrodes is envisioned. Vanadium oxides were amongst the first materials to be studied as LIB cathodes, but were never commercialised. V2O5 is a well-known LIB electrode, but the rather low volumetric energy density (when storing one lithium) or poor cyclability (when storing 2-3 lithium ions) have prevented its large-scale commercialisation in the past. Here, we demonstrate the ALD deposition of amorphous and crystalline V2O5, and two ‘flavours’ of amorphous VO2, from a single vanadium precursor (Tetrakis[ethylmethylamino] vanadium). We demonstrate the crystallisation of these films into crystalline films in the Wadsley series, and are able to unravel the influence of initial ALD process, atmosphere, temperature and substrate on the crystallization and oxidation of the VO2 films. With this in mind, we are able to obtain phase-pure crystalline vanadium oxides in the whole Wadsley series (VO2–V6O13–V4O9–V3O7–V2O5), which show very high energy densities up to more than double that of typical bulk cathodes (1380mAh/cm³ for V4O9). The amorphous initial states (amorphous VO2 and V2O5) are often not considered due to their lack of a clearly defined electrode potential. However, building on the nature of ALD to grow high-purity amorphous films, these were also investigated here. It was found that, besides also having very high capacities, their kinetics are excellent. Finally, the best candidates were examined on an ALD Pt-coated silicon micropillar array as 3D-structured thin-film electrodes. The 20x surface enhancement of the micropillar substrate enhanced the footprint capacity of the 40nm films from approximately 2-5µAh/cm² to 40-100µAh/cm², with the highest capacity for amorphous VO2(>100µAh/cm² for the 40nm film), while at the same time maintaining the excellent thin-film kinetics of the planar films, in effect simultaneously demonstrating the potential of ALD to deposit 3D thin-film electrodes as well as a tool to study amorphous and crystalline films. In conclusion, a wide range of crystalline and amorphous vanadium oxides were demonstrated from a single vanadium-precursor based ALD process. All films were examined as potential lithium-ion battery electrodes, and showed promise of very high volumetric capacities. In particular, the amorphous films and the crystalline VO2 (B) not only displayed very high capacities, but also excellent kinetics, enabling both high-energy and high-power electrodes. Figure 1

Incorporating intermittent renewable energy sources into the power grid will require large amounts of grid-scale energy storage. Electrochemical batteries are a versatile and scalable energy storage option and, hence, Li-ion batteries have been widely adopted to store excess wind and solar energy [1]. Li-ion batteries, however, have a relatively low energy density and serious safety concerns. An alternative electrochemical battery option lies with zinc-air batteries. This technology uses lower cost materials and is overall much safer. Furthermore, zinc-air batteries have a much larger theoretical energy density than Li-ion batteries [2]. The major impediment to wide-scale adoption of zinc-air batteries is the low energy efficiency because of the poor reaction kinetics at the air electrode. Both the charge and discharge reactions at the air electrode are sluggish and require the use of catalysts to obtain practicable performance. However, many catalysts active towards the charge reaction are not active towards the discharge reaction, and vice versa. The development of a catalyst active towards both the charge and discharge reactions, known as a bifunctional catalyst, is therefore a high priority [3]. Furthermore, catalysts employed in zinc-air batteries often show instability, with performance degradation evident after a few cycles. Ultimately, a highly stable bifunctional zinc-air battery catalyst is of the utmost importance.The aim of this work is to develop highly stable bifunctional catalysts for zinc-air batteries using atomic layer deposition (ALD). With ALD, extremely conformal catalyst coatings can be deposited directly on the air electrode of a zinc-air battery. The self-limiting surface reactions of ALD ensure that electrode porosity is maintained while maximizing the total coating surface area [4]. Since ALD operates in the gas phase, catalytic coatings can be deposited deep within the pores of the air electrode. This will help maintain the three-phase boundary necessary for the discharge reaction and ultimately improve the stability of a zinc-air battery [5]. To create a bifunctional catalyst, two ALD processes, one for manganese oxide and another for iron oxide, is combined into one ALD supercycle, depositing a mixed manganese-iron oxide. Since manganese oxide is a well-established discharge catalyst [6], and iron oxide demonstrates activity towards the charge reaction [7], this mixed manganese-iron oxide exhibits bifunctional activity in a zinc-air battery. An optimized supercycle process will be discussed and full-cell battery test results showcased. Specifically, the bifunctional efficiency of a zinc-air battery can be improved by more than 10% by using the mixed manganese-iron oxide catalyst. In addition, the high stability of the manganese-iron oxide catalyst is demonstrated, where bifunctional efficiency can be maintained at over 95% of the initial value over 200 cycles. Materials characterization of the mixed manganese-iron oxide, deposited through ALD, is also included.[1] L. Trahey, F. R. Brushett, N. P. Balsara, G. Ceder, L. Cheng, Y. M. Chiang, N. T. Hahn, B. J. Ingram, S. D. Minteer, J. S. Moore, K. T. Mueller, L. F. Nazar, K. A. Persson, D. J. Siegel, K. Xu, K. R. Zavadil, V. Srinivasan, and G. W. Crabtree, “Energy Storage Emerging: A Perspective from the Joint Center for Energy Storage Research,” Proc. Natl. Acad. Sci. U. S. A., vol. 117, no. 23, pp. 12550–12557, 2020.[2] J. Fu, R. Liang, G. Liu, A. Yu, Z. Bai, L. Yang, and Z. Chen, “Recent Progress in Electrically Rechargeable Zinc – Air Batteries,” Adv. Mater., vol. 31, no. 31, p. 1805230, 2019.[3] E. Davari and D. G. Ivey, “Bifunctional electrocatalysts for Zn – air batteries,” Sustain. Energy Fuels, vol. 2, no. 1, pp. 39–67, 2018.[4] C. Detavernier, J. Dendooven, S. Pulinthanathu Sree, K. F. Ludwig, and J. A. Martens, “Tailoring nanoporous materials by atomic layer deposition,” Chem. Soc. Rev., vol. 40, no. 11, pp. 5242–5253, 2011.[5] M. P. Clark, M. Xiong, K. Cadien, and D. G. Ivey, “High Performance Oxygen Reduction/Evolution Electrodes for Zinc − Air Batteries Prepared by Atomic Layer Deposition of MnOx,” ACS Appl. Energy Mater., vol. 3, no. 1, pp. 603–313, 2020.[6] M. P. Clark, T. Muneshwar, M. Xiong, K. Cadien, and D. G. Ivey, “Saturation Behavior of Atomic Layer Deposition MnOx from Bis(Ethylcyclopentadienyl) Manganese and Water: Saturation Effect on Coverage of Porous Oxygen Reduction Electrodes for Metal-Air Batteries,” ACS Appl. Nano Mater., vol. 2, no. 1, pp. 267–277, 2019.[7] M. Labbe, M. P. Clark, Z. Abedi, A. He, K. Cadien, and D. G. Ivey, “Atomic layer deposition of iron oxide on a porous carbon substrate via ethylferrocene and an oxygen plasma,” Surf. Coatings Technol., vol. 421, p. 127390, 2021.

NiO thin films have attracted tremendous attention owing to their outstanding chemical stability, good magnetic and catalytic properties1. It is also considered an efficient electrocatalyst for water oxidation, and is one of the few p-type semiconductive oxides with optical transparency due to its wide bandgap of 3.6 eV. Furthermore, NiO films can control high and low conductive states under an external electric field, which is very useful for developing resistance-switching random-access memory devices2.NiO films have been prepared by different deposition techniques, including sputtering, sol-gel, pulsed laser deposition, spray pyrolysis, and chemical vapor deposition (CVD), atomic layer deposition (ALD). Among these, ALD is a powerful technique to grow thin conformal films with fine-tuning of both composition and thickness. The commonly used nickel precursors for ALD process are Ni(Cp)2, Ni(MeCp)2, Ni(EtCp)2, Ni(dmamp)2, Ni(dmamb)2, Ni(acac)2, Ni(apo)2, Ni(dmg)2, Ni(thd)2, and Ni(amd)2 in combination with ozone, water, hydrogen peroxide, or oxygen plasma1. However, ALD of NiO is not well developed yet. The major disadvantages associated with these nickel precursors are low volatility, thermal instability, and poor reactivity or narrow ALD window. Some of these precursors are expensive or very difficult to synthesize. The aforementioned situations indicate that developing a new ALD process for the NiO film with new precursors is pertinent.In this work, we explored different Ni-precursors such as Ni ketoiminates, Ni(ipki)2 and Ni(eeki)2 (their synthesis has been proposed earlier3), and Alanis, provided by Air Liquide. These different reactants combined with different oxygen sources (H2O and O3) resulted in high-quality NiO thin films. Surface analyses indicate NiO films are stoichiometric. They are uniform and exhibit a columnar morphology as determined by TEM (Fig.1a). From the growth characteristics, it is found that the Ni precursors have a strong effect on the GPC. Similarly, the oxygen source affects GPC but it also influences the morphology of the layer leading to significant roughness variations (observed by XRR and AFM). The use of H2O can also result in a nucleation delay. Polycrystalline films are observed when the reaction temperature reaches 125°C, and the crystallinity is further enhanced with deposition temperature (Fig.1b). After comprehensive optimization of the ALD process with Alanis precursor, it has been possible to reach one of the highest growth rate of 1.5 Å/cy, which is nearly seven times higher than that obtained with Ni(EtCp)2 based reaction with the same ALD reactor and having a wide temperature window (100 to 175 °C) with ozone. The same precursor also reacted well with water, giving a GPC of 0.9 Å with an initial nucleation delay. With the use of Ni-ketoiminates, the growth rate could be enhanced considerably with a GPC of 0.7 Å in combination with O3 at a higher temperature.The NiO layers were subsequently used as catalysts for water photooxidation in alkaline medium. The electrochemical properties are better when compared to layers grown by PVD. References Y. Zhang, L. Du, X. Liu, and Y. Ding, A high growth rate atomic layer deposition process for nickel oxide film preparation using a combination of nickel (II) diketonate-diamine and ozone, App. Surf. Sci., 2019, 481, 138-143.H.L. Lu, G. Scarel, X.L. Li, M. Fanciulli, Thin MnO and NiO films grown using atomic layer deposition from ethylcyclopentadienyl type of precursors, J. Cryst. Growth, 2008, 310, 5464-5468.3. D. Zywitzki, D.H. Taffa, L. Lamkowski, M. Winter, D. Rogalla, M. Wark, and A. Devi, Tuning coordination geometry of nickel ketoiminates and its influence on thermal characteristics for chemical vapour deposition of nanostructured NiO electrocatalysts, Inorg. Chem., 2020,59, 14, 10059-10070. Figure 1

Review: 2454 refs.

Atomic layer deposition (ALD) of lithium (Li)-based thin films has aroused significant interest in recent years. Promising applications are Li-ion thin-film batteries (TFBs), protective particle coatings, interface model systems, and neuromorphic computing [1,2]. Here, we demonstrate high footprint capacities and excellent high-rate performance of Li4Ti5O12 (LTO) fabricated by ALD for three-dimensional (3D) solid-state TFBs to power upcoming energy-autonomous sensor systems.The simultaneous increase of power and energy density of full-cell 3D TFBs by coating the battery layer stack over microstructured substrates was recently demonstrated [3]. The required conformal, pinhole-free deposition, and stoichiometric control of nanometer-thin films on highly structured surfaces are only accessible via ALD. The vapor-phase technique based on sequential, self-limiting surface reactions is well understood. However, the direct deposition of Li-based anodes remains challenging [1].In previous studies, we developed a thermal three-step ALD process for Li-containing mixed oxides on 200 mm silicon wafers [4, 5]. Lithium-tert-butoxide (LTB) and lithium hexamethyldisilazide (LiHMDS) were proven as suitable precursors, forming high-quality spinel LTO with low impurities after rapid thermal processing. The excellent electrochemical behavior of ALD LTO with LiHMDS was examined and linked to the film texture [5].In this work, we optimize the LTO ALD process with LTB towards high-capacity 3D TFBs and evaluate the electrochemical performance for the first time. A process with tetrakis (dimethylamino) titanium (TDMAT) and H2O at 300 °C was developed, leading to a saturated growth per cycle of 1.06 Å cycle-1 for 7 s LTB pulses. An ALD temperature window between 240 and 320 °C was identified. The effect of the substrate on the initial growth and crystallization behavior was investigated. To overcome the crystallization-inhibiting effect of the titanium nitride current collector, we introduced an ultrathin AlOx interlayer.Planar ALD LTO films with various thicknesses of up to 75 nm were manufactured, increasing the footprint capacity from 1.5 to 4.3 μAh cm-2. We observed a higher surface capacity contribution due to an increased roughness and an inferior C-rate performance with increasing film thickness. 50 nm LTO films demonstrate the optimum energy and power density. A footprint capacity of 1.95 μAh cm-2, corresponding to 67 % of the initial capacity, was achieved at 50 C with an average Coloumb efficiency of 99.9975 %.Next, we evaluate ALD LTO films as 3D TFB anodes for the first time. The conformality of the ALD process on microstructured substrates was improved by extending the LTB pulse and purge times. The purge time is the key factor enabling a step coverage of 70 % for holes with an aspect ratio of 10:1. The 3D samples with an area-enhancement factor (AEF) of 9 coated with 50 nm LTO obtained a footprint capacity of 20.2 μAh cm-2 at 1 C. The significant capacity enhancement of 6.9 compared to planar samples is according to the conformality. The remarkable high-power capability of 3D LTO is demonstrated with 7.75 μAh cm-2 at extreme currents of 5 mA cm-2. A capacity retention of 97.4 % after 500 cycles at 1 mA cm-2 shows the high-rate cyclability. The superior high-rate performance of ALD LTO compared to other 3D anode materials illustrates the enormous potential for realizing high-energy and high-power on-chip 3D TFBs.

Supercapacitors are a kind of energy storage device that lie between traditional capacitors and batteries, characterized by high power density, long cycle life, and rapid charging and discharging capabilities. The energy storage mechanism of supercapacitors mainly includes electrical double-layer capacitance and pseudocapacitance. In addition to constructing multi-level pore structures to increase the specific surface area of electrode materials, defect engineering is essential for enhancing electrochemical active sites and achieving additional extrinsic pseudocapacitance. Therefore, developing a simple and efficient method for defect engineering is essential. Atomic layer deposition (ALD) technology enables precise control over thin film thickness at the atomic level through layer-by-layer deposition. This capability allows the intentional introduction of defects, such as vacancies, heteroatom doping, or misalignment, at specific sites within the material. The ALD process can regulate the defects in materials without altering the overall structure, thereby optimizing both the electrochemical and physical properties of the materials. Its self-limiting surface reaction mechanism also ensures that defects and doping sites are introduced uniformly across the material surface. This uniform defect distribution is particularly profitable for high surface area electrodes in supercapacitor applications, as it promotes consistent performance across the entire electrode. This review systematically summarizes the latest advancements in defect engineering via ALD technology in supercapacitors, including the enhancement of conductivity and the increase of active sites in supercapacitor electrode materials through ALD, thereby improving specific capacitance and energy density of the supercapacitor device. Furthermore, we discuss the underlying mechanisms, advantages, and future directions for ALD in this field.

Ever since the introduction of iron phosphate as a Li-ion battery (LIB) electrode by Sony in 1991, phosphates have played an important role in various research fields. One advantage for the use of phosphates in for example LIB’s is the strong covalency in the metal-oxygen-phosphorus bonds allowing for a high structural and thermal stability. Next to this, the strong interaction between the metal atom and the phosphate anion allow for these materials to operate at a higher potential than their oxide counterparts[1]. Nevertheless, the energy density of an iron phosphate electrode is still limited, which is why the use of nickel and cobalt phosphate as electrode materials (operating at a much higher potential) is currently actively being investigated. Apart from their use as LIB electrodes, these phosphates have also shown to be of interest for a variety of other applications, such as e.g. electrocatalysis.With these applications in mind, the research towards the deposition of these materials also becomes increasingly important. The use of atomic layer deposition (ALD) has for example already allowed for the deposition of a series of metal phosphates, including iron[2] and cobalt phosphate[3]. An ALD process for the deposition of nickel phosphate is however still missing. In this work, a new plasma-enhanced ALD process (PE-ALD) was developed towards the deposition of a nickel phosphate. The process is based on earlier reported process, combining a TMP plasma (TMP*) with an oxygen plasma (O2*) and a metal precursor. When using nickelocene as the metal precursor in this work, saturated growth of an amorphous nickel phosphate was observed at a substrate temperature of 300°C, with a growth per cycle of 0.2 nm/cycle (figure 1). Using XPS, the nickel is thought to be built in with an oxidation state of 2+ while the position of the oxygen and phosphorus peak agree with the formation of a phosphate-like material.This material was then electrochemically characterised as a LIB electrode, together with cobalt phosphate (using a previously reported ALD process[3]). Both materials unfortunately did not result in the high energy (approximately at a potential of 5 V vs. Li+/Li) electrochemical activity that was expected, but did show activity at a lower voltage window (figure 2). The reason for this is expected to be due to the 2+ oxidation state of nickel (and cobalt) in the as-deposited material, while a 3+ oxidation state would be needed for the high energy redox peak to appear. Nevertheless, besides the observation of an electrochemically active nature (at a low voltage) for both materials, this work can help in the research towards enabling the higher energy variant of these phosphates (i.e. by further fine-tuning the proposed ALD processes) and/or other potential applications for these specific materials (such as electrocatalysis, for which the cobalt phosphate used in this work has already shown to result in beneficial behaviour).[1] Masquelier, C., & Croguennec, L. (2013). ChemInform : Polyanionic (Phosphates, Silicates, Sulfates) Frameworks as Electrode Materials for Rechargeable Li (or Na) Batteries. Cheminform, 44(40), no-no. doi: 10.1002/chin.201340216[2] Dobbelaere, T., Mattelaer, F., Dendooven, J., Vereecken, P., & Detavernier, C. (2016). Plasma-Enhanced Atomic Layer Deposition of Iron Phosphate as a Positive Electrode for 3D Lithium-Ion Microbatteries. Chemistry Of Materials, 28(10), 3435-3445. doi: 10.1021/acs.chemmater.6b00853[3] Rongé, J., Dobbelaere, T., Henderick, L., Minjauw, M., Sree, S., & Dendooven, J. et al. (2019). Bifunctional earth-abundant phosphate/phosphide catalysts prepared via atomic layer deposition for electrocatalytic water splitting. Nanoscale Advances, 1(10), 4166-4172. doi: 10.1039/c9na00391f Figure 1

Recent experimental research efforts on developing functional nanostructured III-nitride and metal-oxide materials via low-temperature atomic layer deposition (ALD) will be reviewed. Ultimate conformality, a unique propoerty of ALD process, is utilized to fabricate core-shell and hollow tubular nanostructures on various nano-templates including electrospun nanofibrous polymers, self-assembled peptide nanofibers, metallic nanowires, and multi-wall carbon nanotubes (MWCNTs). III-nitride and metal-oxide coatings were deposited on these nano-templates via thermal and plasma-enhanced ALD processes with thickness values ranging from a few mono-layers to 40 nm. Metal-oxide materials studied include ZnO, TiO2, HfO2, ZrO2, and Al2O3. Standard ALD growth recipes were modified so that precursor molecules have enough time to diffuse and penetrate within the layers/pores of the nano-template material. As a result, uniform and conformal coatings on high-surface area nano-templates were demonstrated. Substrate temperatures were kept below 200C and within the self-limiting ALD window, so that temperature-sensitive template materials preserved their integrity III-nitride coatings were applied to similar nano-templates via plasma-enhanced ALD (PEALD) technique. AlN, GaN, and InN thin-film coating recipes were optimized to achieve self-limiting growth with deposition temperatures as low as 100C. BN growth took place only for >350C, in which precursor decomposition occured and therefore growth proceeded in CVD regime. III-nitride core-shell and hollow tubular single and multi-layered nanostructures were fabricated. The resulting metal-oxide and III-nitride core-shell and hollow nano-tubular structures were used for photocatalysis, dye sensitized solar cell (DSSC), energy storage and chemical sensing applications. Significantly enhanced catalysis, solar efficiency, charge capacity and sensitivity performance are reported. Moreover, core-shell metal-oxide and III-nitride materials showed promise to be used in applications where flexibility is critical like functional membranes, textile and flexible electronic applications.

Atomic layer deposition (ALD) processes for the growth of ZrO2 and TiO2 were developed using novel precursors. The novel processes were based on cycloheptatrienyl (CHT, -C7H7) – cyclopentadienyl (Cp, -C5H5) compounds of Zr and Ti, offering improved thermal stability and purity of the deposited oxide films. The CpMeZrCHT/O3 ALD process yielded high growth rate (0.7–0.8 Å/cycle) over a wide growth temperature range (300–450 °C) and diminutive impurity levels in the deposited polycrystalline films. Growth temperatures exceeding 400 °C caused partial decomposition of the precursor. Low capacitance equivalent thickness (0.8 nm) with low leakage current density was achieved. In the case of Ti, the novel precursor, namely CpTiCHT, together with ozone as the oxygen source yielded films with low impurity levels and a strong tendency to form the desired rutile phase upon annealing at rather low temperatures. In addition, the thermal stability of the CpTiCHT precursor is higher compared to the usually applied ALD precursors of Ti. The introduction of this new ALD precursor family offers a basis for further improving the ALD processes of group 4 oxide containing thin films for a wide range of applications.

Operating pressure influences over micro trenches in exposure time introduced atomic layer deposition

Our laboratory is developing new chemical precursors for the growth of electropositive metal and element thin films by atomic layer deposition (ALD). We are also interested in processes that exhibit area selective growth. ALD has many current applications in copper metallization, diffusion barriers, liners, and transistor fabrication. Thermal ALD is often preferred because plasmas can afford low conformal coverage due to radical recombination on the walls of deep and narrow features. There has been extensive progress in the thermal ALD of copper and noble metal films in recent years, because the positive electrochemical potentials allow relatively easy reduction of precursor ions to the metals. Thermal ALD approaches to most other metals and elements in the periodic table are not well developed, due to the negative electrochemical potentials of the ions and a current lack of ALD co-reagents that can convert the ions to the metals or elements. Herein, we will describe the thermal ALD growth of electropositive metals such as nickel, cobalt, aluminium, and others. The ALD of nickel and cobalt metal films has been achieved using precursors containing diazadienyl ligands (precursors 1 and 2). These precursors enable the deposition of cobalt and nickel metal films at temperatures below 200 °C and use alkylamines as benign co-reagents. Growth rates are high (0.60 Å/cycle for nickel, 0.98 Å/cycle for cobalt), high purity, low resistivity metal films are obtained, and the films have low rms roughnesses. The processes exhibit inherent selective growth on metal substrates such as platinum, ruthenium, and copper. By contrast, no growth is observed on insulating substrates. We will also overview a new thermal ALD process for the growth of aluminum metal films. This process entails treatment of surface-bound AlCl3 with a thermally stable, volatile aluminium hydride co-reagent. The growth rate for the aluminium metal ALD process is high, and high purity, low resistivity aluminium metal films are obtained. Prospects for the area selective growth of aluminum metal films will be presented. These examples demonstrate that ALD processes can be enabled for electropositive metals through careful design of precursors and chemistry. Moreover, many of the metal ALD processes exhibit area selective growth. Figure 1

Plasma Atomic Layer Deposition (ALD) enables the deposition of a wide variety of materials, with nanometre-scale resolution and precision. Self-limiting growth is a keystone characteristic of ALD processes but limits deposition rate. Long cycle times and low growth per cycle (GPC) impose practical limits on how thick ALD films can be grown. In the field of Quantum Technology (QT), superconducting nanolayers are required for use in Single-Photon Detectors (SPDs), superconducting qubits and interconnects for quantum computing.1 Some superconducting interconnects benefit from non-planar connectivity to control qubits,2 and 3D architectures are key for scaling larger arrays of qubits.3 The deposition of high-quality materials on high aspect ratio Through-Silicon Via (TSV) interconnects is essential but difficult to achieve by conventional sputter techniques. Superconducting nitrides in some QT applications demand relatively thick films (>50 nm), and this poses a new challenge for ALD: to maintain desirable film characteristics and grow thick layers much faster. Here we present recent developments from our new R&D ALD platform: PlasmaPro ASP.The design of the remote, RF-driven plasma source has been optimised to deliver quick, repeatable plasma doses to the substrate with minimal plasma damage. The chamber size, pumping and precursor delivery have been carefully considered to enable efficient ALD of many materials. For multiple materials, we have demonstrated a reduction of cycle times. For example, rates of >25 nm/h for NbN and TiN which is about 3x faster than previously reported. Importantly, these materials retain excellent film properties. NbN showed excellent electrical resistivity (four-point probe), conformality (100% on 8:1 trench), and superconducting transition temperature (Tc) >11 K for <10 nm thick films – a key regime for SPDs. NbN and TiN crystallinity, film stress and film composition will be discussed. Furthermore, many other applications will benefit from this fast plasma ALD. We will also present plasma Al2O3 for power electronics which has been deposited on substrates of up to 200 mm in diameter with a less than one second ALD cycle time. As the needs of emerging quantum technologies and other applications change and continue to push process and film performance, production and research will benefit from high-quality, low damage, conformal films by fast, remote plasma ALD.