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Nanoscale patterning of inorganics is crucial for the fabrication of advanced electronic, photonic, and energy devices. The emerging sequential infiltration synthesis (SIS) method fabricates nanofeatures by block-selective vapor-phase growth in block copolymer templates with tunable patterns. Yet, SIS has been demonstrated mainly for Al2O3 and a few other metal oxides, while deriving metal nanostructures from a single SIS process is a challenge. Here, we present SIS of the Ru metal in polystyrene-block-polymethyl methacrylate (PS-b-PMMA) templates without any pretreatment, using alternating infiltration of RuO4 and H-2. RuO4 interacts selectively and strongly with the aromatic C=C and C-H groups in PS, leaving the PMMA domains inert. Density functional theory calculations corroborate that the PS-RuO4 interaction is energetically favorable, with a calculated interaction energy of -1.65 eV, whereas for PMMA-RuO4, the calculated energy of -0.05 eV indicates an unfavorable interaction. Morphological analysis on the di-BCP after the RuO4-H-2 process indicates an increase in contrast as a function of SIS cycles and templated Ru incorporation. The crystalline nature of the Ru deposits is confirmed using grazing incidence wide-angle X-ray scattering. Plasma-aided removal of the organic components yields Ru nanolines with lateral dimensions of ca 20 nm. We further highlight the broad potential of RuO4 as a reactant for SIS by generating RuO2 nanopatterns via alternating RuO4 and methanol infiltration.

Atomic layer deposition (ALD) of ruthenium dioxide (RuO2) thin films using metalorganic precursors and O-2 can be challenging because the O-2 dose needs to be precisely tuned and significant nucleation delays are often observed. Here, we present a low-temperature ALD process for RuO2 combining the inorganic precursor ruthenium tetroxide (RuO4) with alcohols. The process exhibits immediate linear growth at 1 angstrom/cycle when methanol is used as a reactant at deposition temperatures in the range of 60-120 degrees C. When other alcohols are used, the growth per cycle increases with an increasing number of carbon atoms in the alcohol chain. Based on X-ray photoelectron spectroscopy (XPS) and conventional X-ray diffraction, the deposited material is thought to be amorphous RuO2. Interestingly, pair distribution function (PDF) analysis shows that a structural order exists up to 2-3 nm. Modeling of the PDF suggests the presence of Ru nanocrystallites within a predominantly amorphous RuO2 matrix. Thermal annealing to 420 degrees C in an inert atmosphere crystallizes the films into rutile RuO2. The films are conductive, as is evident from a resistivity value of 230 mu Omega.cm for a 20 nm film grown with methanol, and the resistivity decreased to 120 mu Omega.cm after crystallization. Finally, based on in situ mass spectrometry, in situ infrared spectroscopy, and in vacuo XPS studies, an ALD reaction mechanism is proposed, involving partial reduction of the RuO2 surface by the alcohol followed by reoxidation of the surface by RuO4 and concomitant deposition of RuO2.

Atomic layer deposition (ALD) typically employs metal precursor and co-reactant pulses to deposit thin films in a layer-by-layer fashion. While conventional ABAB-type ALD sequences implement only two functionalities, namely a metal source and ligand exchange agent, additional functionalities have emerged, including etching and reduction agents. Herein, we construct gas phase sequences – coined as ALD+ – with complexities reaching beyond classic ABAB-type ALD by freely combining multiple functionalities within irregular pulse schemes, e.g. ABCADC. The possibilities of such combinations are explored as a smart strategy to tailor bimetallic thin film and nanoparticle (NP) properties. By doing so, we demonstrate that bimetallic thin films can be tailored with target thickness and through the full compositional range, whilst the morphology can be flexibly modulated from thin films to NPs by shuffling the pulse sequence. These complex pulse schemes are expected to be broadely applicable, but are here explored for Pd-Ru bimetallic thin films and NPs.

CO2-assisted propane dehydrogenation has been studied on Pt-Sn/MgAl2O4 catalysts with support surface area of ~ 127 m2/g or ~ 5 m2/g, 3 wt% Pt and a Pt/Sn molar ratio of 3/1. In situ XAS was employed to track the dynamic changes occurring to the catalyst in presence of a reductive (H2) or oxidative (CO2) atmosphere. Reduction leads to the formation of a Pt-Sn alloy, the active compound for propane dehydrogenation. Oxidation by CO2 led to the loss of the Pt-Sn alloy due to firstly oxidation of Sn to SnO and subsequent oxidation of SnO to SnO2. The electronic and structural properties of the catalyst were determined by modelling of the EXAFS data. The Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) method was used in conjunction with the XAS data to determine the amount of Sn present in the Pt-Sn alloy phase and the phase of the alloy itself: after a single step reduction 42% of all Sn goes into Pt3Sn alloy, participating in the reaction, with the remainder being SnOx. The percentage of Sn going into the Pt3Sn alloy increased after 10 H2/O2 redox cycles to 72%. A combination of in-situ XAS with CO2-PDH activity data covering CO2:C3H8 ratios from 0.25:1 to 1:1 allowed to show that CO2 helps to improve conversion of propane by means of the reverse water gas shift reaction, wherein the product H2 generated from PDH reacts with feed CO2 to shift the equilibrium towards products. The reaction performed better at lower ratios of CO2:C3H8. Increasing ratios of CO2:C3H8 induced faster deactivation of the catalyst by the oxidation of Sn to SnOx, leading to loss of Pt-Sn alloy. Suppression of carbon accumulation occurred by means of the reverse Boudouard reaction with the carbon formed during PDH. As possible reaction network for the entire CO2-PDH reaction, a combination of Langmuir-Hinshelwood (L-H) and the Mars-van Krevelen mechanism (MvK) was proposed. The MvK steps were the oxidation of Sn to SnO by CO2, which would then subsequently react with the H2 and C generated from PDH that takes place on Pt sites by the L-H mechanism, to go back to the Pt3Sn alloy.

Lithium (Li) metal is an attractive anode material with high capacity (3860 mAh g−1) and low potential (−3.04 V vs. standard hydrogen electrode) that shows highly promising for applications requiring high energy density. However, the low electrochemical potential of Li metal makes it extremely reactive and inevitably forming a native oxidized layer in the ambient environment and repeatedly being consumed when exposed to liquid electrolytes. It is therefore beneficial to replace the poorly controlled native passivation layer with a tailored artificial SEI to improve interface management between Li and electrolyte and enhance the stability of Li metal battery. Here, we use an integrated glovebox-atomic layer deposition (ALD)- X-ray photoelectron spectroscopy (XPS) setup to in-situ investigating the pristine Li surface and the surface composition after Ar, H2, O2, N2 and NH3 plasma treatment processes. We find that the pristine Li foil is naturally being covered with a native oxidized layer, which is mainly composed of LiOH, Li2O and Li2CO3. These investigated plasmas can efficiently remove the oxidized layer from the Li metal surface, in which metallic Li surface is obtained after Ar or H2 plasma treatments, where Ar plasma is more efficient. While O2 plasma treatment produces a Li2O layer, and N2 or NH3 plasma treatment leads to a Li3N (including a certain amount of LiON) layer on the Li surface. When employing the representative metallic Li (by Ar plasma treatment), Li2O layer coated Li (by O2 plasma treatment) and Li3N layer coated Li (by N2 plasma treatment) foils as electrodes in symmetric Li metal batteries, the Li3N coated Li electrode exhibits much higher stability than that of metallic and Li2O layer coated Li foils. Improved electrochemical performance has also been achieved in LiMn2O4 (LMO)||Li full cells using Li anode with Li3N protective coating layer. Our work reveals the detailed process of surface engineering of Li metal anodes with plasma treatments by in vacuo XPS, which may also be extended to other gas-treatment or plasma-treatment for stabilization of high energy density Li metal anodes and other metal-based anodes.

In this work, the use of ruthenium tetroxide (RuO4) as a co-reactant for atomic layer deposition (ALD) is reported. The role of RuO4 as a co-reactant is twofold: it acts both as an oxidizing agent and as a Ru source. It is demonstrated that ALD of a ternary Ru-containing metal oxide (i.e. a metal ruthenate) can be achieved by combining a metalorganic precursor with RuO4 in a two-step process. RuO4 is proposed to combust the organic ligands of the adsorbed precursor molecules while also binding RuO2 to the surface. As a proof of concept two metal ruthenate processes are developed: one for aluminum ruthenate, by combining trimethylaluminum (TMA) with RuO4; and one for platinum ruthenate, by combining MeCpPtMe3 with RuO4. Both processes exhibit self-limiting surface reactions and linear growth as a function of the number of ALD cycles. The observed saturated growth rates are relatively high compared to what is usually the case for ALD. At 100 degrees C sample temperature, growth rates of 0.86 nm per cycle and 0.52 nm per cycle are observed for the aluminum and platinum ruthenate processes, respectively. The TMA/RuO4 process results in a 1 : 1 Al to Ru ratio, while the MeCpPtMe3/RuO4 process yields a highly Ru-rich composition with respect to Pt. Carbon, hydrogen and fluorine impurities are present in the thin films with different relative amounts for the two investigated processes. For both processes, the as-deposited films are amorphous.

Complex surface reactions between TMA and TMP result in an amorphous, polymerized lithium phosphate.

ALD of a Y2O3 coating layer on Li metal anodes can effectively suppress Li dendrite growth, leading to a uniform plating–stripping process in Li metal batteries with more stable performance and prolonged lifespan.

The world of flexible devices has brought the interest to combine ALD and MLD films. However, direct ALD on MLD can suffer from stability/growth issues. Utilising O2 plasma, their compatibility can be enhanced, providing a more effective stacking.

Controlled surface functionalization with azides to perform on surface "click chemistry" is desired for a large range of fields such as material engineering and biosensors. In this work, the stability of an azido-containing self-assembled monolayer in high vacuum is investigated using in situ Fourier transform infrared spectroscopy. The intensity of the antisymmetric azide stretching vibration is found to decrease over time, suggesting the degradation of the azido-group in high vacuum. The degradation is further investigated at three different temperatures and at seven different nitrogen pressures ranging from 1 x 10(-6) mbar to 5 x 10(-3) mbar. The degradation is found to increase at higher temperatures and at lower nitrogen pressures. The latter supporting the theory that the degradation reaction involves the decomposition into molecular nitrogen. For the condition with the highest degradation detected, only 63% of azides is found to remain at the surface after 8 h in vacuum. The findings show a significant loss in control of the surface functionalization. The instability of azides in high vacuum should therefore always be considered when depositing or postprocessing azido-containing layers.

Surface-modified nanoporous silica films offer attractive features for analyte-specific gas detection applications. Here we demonstrate the integration of highly porous silica-alumina films on silicon nanophotonic chips and their performance in selective NH3 detection. Prototype sensors with microporous as well as mesoporous silica films were assembled. The incorporation of aluminum in trace amount needed to generate acid sites was achieved during film deposition or using postsynthesis atomic layer deposition. Silicon photonic micro-ring resonators functionalized with both techniques demonstrated a selective response to NH3 relative to CO2. Furthermore, the response was rapid and reversible. The role of preadsorbed water vapor on the reversible nature of the sensor is also investigated. Experimental observations indicate that water vapor preadsorbed on the films leads to fast sensor recovery while maintaining selectivity toward NH3. This could be attributed to the relatively less strong and still selective binding of NH3 on protonated water molecules preadsorbed on the surface acid sites. The potential of modified nanoporous films for portable and low-cost NH3 sensing on optical chips demonstrated here can be exploited in health care as well as industrial applications.

The effects of applying an alumina (Al2O3) coating by atomic layer deposition, with a thickness of about similar to 1 nm, on two PtGa catalysts (PtGa/MgAl2O4 and Pt/MgGaAlO) were explored for the propane dehydrogenation reaction (PDH). The combined application of small angle X-ray scattering (SAXS) and X-ray absorption spectroscopy (XAS) was employed on the samples to gain insight into the effect of this coating on catalyst stability. The coating restricted the mobility of surface metal nanoparticles, thereby preventing sintering of the catalyst. On the PtGa/MgAl2O4 catalyst, the presence of the coating hindered the alloy formation between Pt and Ga, while it did not negatively affect the formation of an alloy for the Pt/MgGaAlO catalyst as the Ga is delivered from the support. The SAXS and XAS findings were reflected in the PDH activity tests. The alumina-coated PtGa/MgAl2O4 performed worse than its uncoated counterpart due to the limited alloy formation in the presence of the coating. The coated and uncoated Pt/MgGaAlO catalysts were tested for PDH after 1, 5, and 10 H-2/O-2 redox cycles to see the effect of the coating on activity and stability. In general, the coating reduces the total amount of carbon formation, and the rate of deactivation for the coated sample is slower than for the uncoated counterpart. A higher thickness of coating led to reduced activity due to increased blockage of active sites but at the same time drastically reduced total carbon formation at similar conversions. The coated and uncoated Pt/MgGaAlO samples were then subjected to another 30 redox cycles (40 in total) and subsequently examined with HAADF STEM. Through particle size distribution of STEM images, it is determined that the coating reduced the extent of sintering of the sample. The direct correlation between increased coating thickness and lower extent of sintering of the surface metal nanoparticles was confirmed.

Oxidative modification of graphene-based materials is an attractive route to functional materials. The use of strong oxidants to achieve surface modification of the carbon often leads to poor uniformity and limited reproducibility. Photocatalytic oxidation is a milder method. In this work, graphite is surface oxidized using an anatase thin photocatalytic film with a thickness of 22.5 nm facing the graphite surface to be oxidized. The high UV light transparency (95%) of the supported titania film simplified the experimental setup. The titania thin film was prepared using atomic layer deposition (ALD). Excellent oxidation uniformity and reaction reproducibility are achieved. By avoiding the use of chemical reagents there is no chemical contamination. Graphite photo-oxidation with the titania film prepared with ALD is much faster than with a powdery photocatalyst. The photocatalytic process runs efficiently with air containing water vapor. High resolution scanning electron microscopy (HRSEM), Raman and X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) confirmed the formation of hydroxyl, epoxy and carbonyl functional groups. ALD is a suitable method for thin film preparation rendering this photocatalytic process suitable for scale-up and automation. Photocatalytically oxidized graphite (POG) electrodes are a potential application.

We report on thin-film coatings and catalyst nanoparticles both deposited by atomic layer deposition (ALD) on silicon (Si) photocathodes that simultaneously enhance their performance and stability. Regarding thin-film coatings, we scan various materials (SiO2, TiO2 and Al2O3) appropriate for the electrical passivation of Si surface defects, which result in high minority carrier lifetimes (up to 100 μs). However, these passivating layers seem to act as a barrier for the photogenerated carriers obstructing them from participating in the hydrogen evolution reaction, thus limiting the onset potential (Von). Regarding platinum (Pt) nanoparticles, two deposition approaches are followed based on using different co-reactants during the ALD process, i.e. an O2 pulse or a N2-plasma pulse, with the latter resulting in a higher Von (505 mV). By combining thin-film SiO2 coatings of various thicknesses deposited on top of ALD Pt nanoparticles, a synergetic effect of performance and stability enhancement is observed, with Von values reaching 525 mV. Finally, by systematically studying the Si photocathodes in a day/night cycle operation and using the case of electroless deposited Pt nanoparticles as a benchmark, the N2-plasma deposited Pt nanoparticles coated by ultra-thin SiO2 film show an enhanced stability (85 h-4 days/night cycles).

A method to obtain full mass over charge (m/z), time-resolved quadruple mass spectrometry (QMS) spectra of an atomic layer deposition (ALD) cycle is proposed. This method allows one to circumvent the limitations of traditional approaches for obtaining QMS information in ALD as all m/z values can be simultaneously screened for the formation of reaction products in an efficient way. As a proof of concept, this method was applied to the trimethylaluminum (TMA)-water process. This process has been studied extensively over the past decades. Besides the expected formation of CH4, formation of gaseous HOAl(CH3)2 during the water pulse is observed, revealing a secondary reaction pathway for the water. The reaction energy and Gibbs free energy for different reactions are investigated computationally using density functional theory calculations and confirm that the secondary reaction pathway is thermodynamically allowed for certain surface conditions.

Atomic layer deposition (ALD) of boron-containing films has been mainly studied for use in two-dimensional materials and for B doping of Si. Furthermore, lithium-containing borates show great promi...

There is a growing interest in photonic integrated circuits for biophotonic applications. Here, we present such a circuit operating in the ultraviolet that allows us to implement super-resolved label-free structured illumination on yeast cells.

The spectro-kinetic characterization of complex catalytic materials, i.e. relating the observed reaction kinetics to spectroscopic descriptors of the catalyst state, presents a fundamental challenge with a potentially significant impact on various chemical technologies. We propose to reconcile the kinetic characteristics available from temporal analysis of products (TAP) pulse-response kinetic experiments with the spectroscopic data available from ambient pressure X-ray photoelectron spectroscopy (AP-XPS), using atomic layer deposition (ALD) to synthesize multicomponent model surfaces on 2D and 3D supports. The accumulated surface exposure to a key reactant (total number of collisions) is used as a common scale within which the results from the two techniques can be rigorously compared for microscopically-equivalent surfaces. This approach is illustrated by proof-of-principle TAP and AP-XPS experiments with PtIn/MgO/SiO2 catalysts for alkane dehydrogenation at 800 K. Similarly to industrially-relevant Pt-based bimetallic catalysts on high-surface area supports, the initial period of coke accumulation on the surface resulted in gradually decreased conversion and increased selectivity towards propylene. We were able to monitor the process of coke deposition with both AP-XPS and TAP. The evolution of the C 1s photoelectron spectra is aligned on the common exposure scale with the evolution of the coke amounts deposited per Pt site during a multi-pulse TAP experiment. Moreover, TAP provided quantitative kinetic descriptors of propane consumption and product mean residence time within this common exposure scale. The challenges and opportunities presented by this novel tandem methodology are discussed in the context of catalysis research.

A plasma-enhanced ALD process has been developed to deposit nickel phosphate. The process combines trimethylphosphate (TMP) plasma with oxygen plasma and nickelocene at a substrate temperature of 300 degrees C. Saturation at a growth per cycle of approximately 0.2 nm per cycle is observed for both the TMP plasma and nickelocene, while a continuous decrease in the growth per cycle is found for the oxygen plasma. From ERD, a stoichiometry of Ni-3(P0.8O3.1)(2) is measured, but by adding additional oxygen plasma after nickelocene, the composition of Ni-3(P0.9O3.7)(2) becomes even closer to stoichiometric Ni-3(PO4)(2). The as-deposited layer resulting from the process without the additional oxygen plasma is amorphous but can be crystallized into Ni2P or crystalline Ni-3(PO4)(2) by annealing under a hydrogen or helium atmosphere, respectively. The layer deposited with the additional oxygen plasma shows two X-ray diffraction peaks indicating the formation of crystalline Ni-3(PO4)(2) already during the deposition. The resulting PE-ALD deposited nickel phosphate layers were then electrochemically studied and compared to PE-ALD cobalt and iron phosphate. All phosphates need electrochemical activation at low potential first, after which reversible redox reactions are observed at a potential of approximately 2.5 V vs. Li+/Li. A relatively high capacity and good rate behavior are observed for both nickel and cobalt phosphate, which are thought to originate from either a conversion type reaction or an alloying reaction.

Atomic layer deposition (ALD) of noble metals is an attractive technology potentially applied in nanoelectronics and catalysis. Unlike the combustion-like mechanism shown by other noble metal ALD processes, the main palladium (Pd) ALD process using palladium(ii)hexafluoroacetylacetonate [Pd(hfac)2] as precursor is based on true reducing surface chemistry. In this work, a thorough investigation of plasma-enhanced Pd ALD is carried out by employing this precursor with different plasmas (H2*, NH3*, O2*) and plasma sequences (H2* + O2*, O2* + H2*) as co-reactants at varying temperatures, providing insights in the co-reactant and temperature dependence of the Pd growth per cycle (GPC). At all temperatures, films grown with only reducing co-reactants contain a large amount of carbon, while an additional O2* in the co-reactant sequence helps to obtain Pd films with much lower impurity concentrations. Remarkably, in situ XRD and SEM show an abrupt release of the carbon impurities during annealing at moderate temperatures in different atmospheres. In vacuo XPS measurements reveal the remaining species on the as-deposited surface after every exposure. Links are established between the particular surface termination prior to the precursor pulse and the observed differences in GPC, highlighting hydrogen as the key growth facilitator and carbon and oxygen as growth inhibitors. The increase in GPC with temperature for ALD sequences with H2* or NH3* prior to the precursor pulse is explained by an increase in the amount of hydrogen species that reside on the Pd surface which are available for reaction with the Pd(hfac)2 precursor.

Atomic layer deposition (ALD) is a vacuum technology for the deposition of a small number of atoms on surfaces. Its use in catalysis is growing. Here, we explored the use of ALD for introducing acid and metal sites in zeolites for performing bifunctional catalysis. Plasma-enhanced ALD involving cyclic exposure of a sample to tris(2,2,6,6-tetramethyl-3,5-heptanedionato)gallium (Ga(TMHD)3) vapor and O2 plasma (Ga-ALD) was used for introducing acid sites. Interestingly, Ga-ALD was found to cause preferential deposition of Pt nanoparticles via incipient wetness impregnation on the edges of COK-14 crystal plates, in contrast to previously published results on Al-ALD. Benefiting from the optimum proximity between the Ga acid and Pt metal sites, it is shown here that Ga-ALD is a way to introduce sufficient acidity into all-silica zeolite COK-14 for obtaining bifunctional catalytic behavior. Hydrogenation–dehydrogenation activity in bifunctional catalysts is typically provided by trace amounts of platinum dispersed on the zeolite. Pt-ALD was applied for finely dispersing platinum on ZSM-5 zeolite. Pt-ALD involved alternating exposure to the trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe3) precursor and ozone. The Pt-ALD method proved to be an efficient way to uniformly disperse ultra-small Pt nanoparticles onto the zeolite. The bifunctional catalytic behavior of ALD-functionalized zeolites was confirmed in the hydroconversion of the n-decane model molecule.

The atomic layer deposition (ALD) of yttrium oxide (Y2O3) is investigated using the liquid precursor Y(EtCp)2(iPr-amd) as the yttrium source with thermal (H2O) and plasma-enhanced (H2O plasma and O2 plasma) processes, respectively. Saturation is confirmed for the growth of the Y2O3 films with each investigated reactant with a similar ALD window from 150 to 300 °C, albeit with a different growth rate. All of the as-deposited Y2O3 films are pure and smooth and have a polycrystalline cubic structure. The as-deposited Y2O3 films are hydrophobic with water contact angles >90°. The water contact angle gradually increased and the surface free energy gradually decreased as the film thickness increased, reaching a saturated value at a Y2O3 film thickness of ∼20 nm. The hydrophobicity was retained during post-ALD annealed at 500 °C in static air for 2 h. Exposure to polar and nonpolar solvents influences the Y2O3 water contact angle. The reported ALD process for Y2O3 films may find potential applications in the field of hydrophobic coatings.

Pt doped semiconducting metal oxides and Pt metal clusters embedded in an oxide matrix are of interest for applications such as catalysis and gas sensing, energy storage and memory devices. Accurate tuning of the dopant level is crucial for adjusting the properties of these materials. Here, a novel atomic layer deposition (ALD) based method for doping Pt into In2O3 in specific, and metals in metal oxides in general, is demonstrated. This approach combines alternating exposures of Pt and In2O3 ALD processes in a single ‘supercycle’, followed by supercycle repetition leading to multilayered nanocomposites. The atomic level control of ALD and its conformal nature make the method suitable for accurate dopant control even on high surface area sup-ports. Oxidation state, local structural environment and crystalline phase of the embedded Pt dopants were obtained by means of X-ray characterization methods and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In addition, this approach allows characterization of the nucleation stages of metal ALD processes, by stacking those states multiple times in an oxide matrix. Regardless of experimental conditions, a few Pt ALD cycles leads to the formation of oxidized Pt species due to their highly dispersed nature, as proven by X-ray absorption spectroscopy (XAS). Grazing-incidence small-angle X-ray scattering (GISAXS) and high-resolution scanning transmission electron microscopy, combined with energy dispersive X-ray spectroscopy (HR-STEM/EDXS) show that Pt is evenly distributed in the In2O3 metal oxide matrix without the formation of clusters. For a larger number of Pt ALD cycles, typ. > 10, the oxidation state gradually evolves towards fully metallic, and metallic Pt clusters are obtained within the In2O3 metal oxide matrix. This work reveals how tuning of the ALD supercycle approach for Pt doping allows controlled engineering of the Pt compositional and structural configuration within a metal oxide matrix.

Since the introduction of lithium iron phosphate (LFP) as an electrode material for Li-ion batteries (LIB’s), metal phosphates in general have become increasingly important. The strong covalency of the P-O bonds typically results in a very good thermal and structural stability, which is one of the main reasons for the success of LFP as a LIB electrode. However, the applications of these metal phosphates are multi-fold. Apart from LIB’s, they have been proven to be promising towards e.g. electrocatalytic water splitting, biocompatible coatings or even as protective coatings for luminescent materials. With these applications in mind, the research towards the deposition of these materials also becomes increasingly important. Atomic Layer Deposition (ALD) has emerged as a deposition technique with unique nanotailoring capabilities compared to conventional methods, particularly owing to its high thickness and compositional control. Down-scaling micro-electronic devices according to Moore’s law has already increased interest in the unique capabilities ALD can offer. However, in addition to using ALD for the fabrication of such devices, it can also offer a unique way to create model systems to gain a fundamental insight for a broad range of applications. From this it can be seen why the combination of both research fields, i.e. ALD of metal phosphates, is gaining a lot of interest over the past years. Since the first metal phosphate has been deposited in 1969, a big challenge has been to find a suitable phosphate precursor. Today, the most popular choice proves to be trimethyl phosphate, i.e. TMP. It has allowed for the deposition of a variety of phosphates (e.g. aluminium phosphate, lithium phosphate, iron phosphate, etc.), but more research is required to further extent this research field. To stimulate this research, a comprehensive study on the currently (un)available literature is needed. It would e.g. allow to get a better understanding on the effect of different phosphate precursors and/or various reaction mechanisms during ALD can be better understood, as well as the potential applications of these materials (such as lithium ion battery applications). As such a study on ALD of metal phosphates was so far not yet available, we hope that this work can create a view that is of interest towards various scientific fields, and help to guide future thin film researchers.

Thirty years after the release of the first commercial lithium-ion battery, capacity fading due to complex ageing mechanisms remains one of the major concerns in lithium-ion battery research. Lithium-ion battery cathodes age due to phenomena as transition metal dissolution, electrolyte oxidation and volume expansions.[1] To suppress these effects, a protective coating can be applied to the cathode’s surface to avoid direct contact with the liquid electrolyte. Many studies exist in literature, showing the protective effect of conformal and pinhole-free Atomical Layer Deposited (ALD) coatings. However, the inorganic coatings deposited by ALD are rigid and will crack upon volume expansion of the cathode.[2] Molecular Layer Deposition (MLD) offers the same benefits as ALD but can be used to deposit hybrid inorganic/organic flexible films that can accommodate potential volume expansions of the cathode. To our knowledge, apart from ‘metalcones’ i.e. MLD films grown using a metal containing precursor and an alcohol, MLD films remain to be explored as protective and flexible coatings for lithium-ion batteries.[3] In this work, hybrid MLD titanium carboxylate thin films are deposited using tetrakis(dimethylamido)titanium (TDMAT) and various dicarboxylic acid precursors: oxalic acid, malonic acid, succinic acid, glutaric acid and 3,6-dioxaoctanedioic acid. The latter containing two ethylene oxide units per molecule, potentially increasing the lithium-ion conductivity.[4] The growth of the titanium carboxylate MLD processes is studied using in situ ellipsometry at a substrate temperature of 100 °C and 160 °C. Only the TDMAT/oxalic acid process is found to display good saturation behavior, while a parasitic CVD component is present during the TDMAT pulse for the other processes. The structure of the as-deposited films is physically characterized using Fourier Transform IR spectroscopy (FTIR) and X-Ray Photoelectron Spectroscopy (XPS), confirming the successful deposition of titanium carboxylate films. The films are found to be stable in air up to 50 days as shown by FTIR. This is in contrast to many metalcone MLD films which are considered to be air sensitive as the organic backbone degrades upon air exposure. In addition, FTIR, X-Ray Reflectivity (XRR) and X-Ray Fluorescence (XRF) measurements show that the titanium carboxylate films remain intact upon immersion into a solution of 1 M LiClO4 in propylene carbonate, the liquid electrolyte used for electrochemical characterization. The electrochemical properties of a 5 nm TDMAT/oxalic acid, TDMAT/3,6-dioxaoctanedioic acid and TDMAT/glycerol film (conventional titanicone film [5]) are tested on top of three ideal electrode systems: anatase TiO2, TiN and LiMnO2 (LMO). The titanium carboxylate films are observed to have little to no effect on the lithium-ion kinetics of the TiO2 electrode system compared to the uncoated electrode. This is in contrast to the titanicone film displaying a detrimental effect on the kinetics. All films are observed to effectively suppress electrolyte oxidation when exposing the TiN electrode system to elevated potentials. On the LMO electrode an activation step is necessary for all films, after which a good lithium-ion mobility through the titanium carboxylate films is observed without the severe irreversible reactions detected in the potential profile for the titanicone films. Overall, the explorative tests on thin film electrodes in this work indicate that the electrochemical properties of the titanium carboxylate films seem promising candidates as protective and flexible coating of lithium-ion battery cathodes. [1] Vetter, J., Novák, P., Wagner, M. R., Veit, C., Möller, K. C., Besenhard, J. O., ... & Hammouche, A. (2005). Ageing mechanisms in lithium-ion batteries. Journal of power sources, 147(1-2), 269-281. [2] Ban, C., & George, S. M. (2016). Molecular layer deposition for surface modification of lithium‐ion battery electrodes. Advanced Materials Interfaces, 3(21), 1600762. [3] Zhao, Y., Zhang, L., Liu, J., Adair, K., Zhao, F., Sun, Y., ... & Sun, X. (2021). Atomic/molecular layer deposition for energy storage and conversion. Chemical Society Reviews, 50(6), 3889-3956. [4] Xue, Z., He, D., & Xie, X. (2015). Poly (ethylene oxide)-based electrolytes for lithium-ion batteries. Journal of Materials Chemistry A, 3(38), 19218-19253. [5] Van de Kerckhove, K., Mattelaer, F., Deduytsche, D., Vereecken, P. M., Dendooven, J., & Detavernier, C. (2016). Molecular layer deposition of “titanicone”, a titanium-based hybrid material, as an electrode for lithium-ion batteries. Dalton Transactions, 45(3), 1176-1184.

TiO2 thin films deposited by atomic layer deposition (ALD) at low temperatures (2 parts is known to alter phase transitions and to stabilize crystalline phases. In this work, we have developed low-temperature ALD super-cycles to introduce Al2O3 into TiO2 thin films and photonic crystals. The aluminum oxide content was adjusted by varying the TiO2:Al2O3 internal loop ratio within the ALD super-cycle. Both thin films and inverse opal photonic crystal structures were subjected to thermal treatments ranging from 200 to 1200 °C and were characterized by in- and ex-situ X-ray diffraction, spectroscopic ellipsometry, and spectroscopic reflectance measurements. The results show that the introduction of alumina affects the crystallization and phase transition temperatures of titania as well as the optical properties of the inverse opal photonic crystals (iPhC). The thermal stability of the titania iPhCs was increased by the alumina introduction, maintaining their photonic bandgap even after heat treatment at 900 °C and outperforming the pure titania, with the best results being achieved with the super-cycles corresponding to an estimated alumina content of 26 wt.%., TiO2 thin films deposited by atomic layer deposition (ALD) at low temperatures (lower than 100 °C) are, in general, amorphous and exhibit a smaller refractive index in comparison to their crystalline counterparts. Nonetheless, low-temperature ALD is needed when the substrates or templates are based on polymeric materials, as the deposition has to be performed below their glass transition or melting temperatures. This is the case for photonic crystals generated via ALD infiltration of self-assembled polystyrene templates. When heated up, crystal phase transformations take place in the thin films or photonic structures, and the accompanying volume reduction as well as the burn-out of residual impurities can lead to mechanical instability. The introduction of cation doping (e.g., Al or Nb) in bulk TiO2 parts is known to alter phase transitions and to stabilize crystalline phases. In this work, we have developed low-temperature ALD super-cycles to introduce Al2O3 into TiO2 thin films and photonic crystals. The aluminum oxide content was adjusted by varying the TiO2:Al2O3 internal loop ratio within the ALD super-cycle. Both thin films and inverse opal photonic crystal structures were subjected to thermal treatments ranging from 200 to 1200 °C and were characterized by in- and ex-situ X-ray diffraction, spectroscopic ellipsometry, and spectroscopic reflectance measurements. The results show that the introduction of alumina affects the crystallization and phase transition temperatures of titania as well as the optical properties of the inverse opal photonic crystals (iPhC). The thermal stability of the titania iPhCs was increased by the alumina introduction, maintaining their photonic bandgap even after heat treatment at 900 °C and outperforming the pure titania, with the best results being achieved with the super-cycles corresponding to an estimated alumina content of 26 wt.%.

Surface enhanced Raman spectroscopy (SERS) and stimulated Raman spectroscopy (SRS) are well established techniques capable of boosting the strength of Raman scattering. The combination of both techniques (surface enhanced stimulated Raman spectroscopy, or SE-SRS) has been reported using plasmonic nanoparticles. In parallel, waveguide enhanced Raman spectroscopy has been developed using nanophotonic and nanoplasmonic waveguides. Here, we explore SE-SRS in nanoplasmonic waveguides. We demonstrate that a combined photothermal and thermo-optic effect in the gold material induces a strong background signal that limits the detection limit for the analyte. The experimental results are in line with theoretical estimates. We propose several methods to reduce or counteract this background., SCOPUS: ar.j, info:eu-repo/semantics/published

Electric-field-controlled magnetism can boost energy efficiency in widespread applications. However, technologically, this effect is facing important challenges: mechanical failure in strain-mediated piezoelectric/magnetostrictive devices, dearth of room-temperature multiferroics, or stringent thickness limitations in electrically charged metallic films. Voltage-driven ionic motion (magneto-ionics) circumvents most of these drawbacks while exhibiting interesting magnetoelectric phenomena. Nevertheless, magneto-ionics typically requires heat treatments and multicomponent heterostructures. Here we report on the electrolyte-gated and defect-mediated O and Co transport in a Co3O4 single layer which allows for room-temperature voltage-controlled ON-OFF ferromagnetism (magnetic switch) via internal reduction/oxidation processes. Negative voltages partially reduce Co3O4 to Co (ferromagnetism: ON), resulting in graded films including Co- and O-rich areas. Positive bias oxidizes Co back to Co3O4 (paramagnetism: OFF). This electric-field-induced atomic-scale reconfiguration process is compositionally, structurally, and magnetically reversible and self-sustained, since no oxygen source other than the Co3O4 itself is required. This process could lead to electric-field-controlled device concepts for spintronics., Financial support by the European Research Council (SPINPORICS 2014-Consolidator Grant, Agreement No. 648454), the Spanish Government (Projects MAT2017-86357-C3-1-R and associated FEDER), the Generalitat de Catalunya (2017-SGR-292) and the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 665919 is acknowledged. E.P. is grateful to MINECO for the “Ramon y Cajal” contract (RYC-2012-10839). The ICN2 is funded by the CERCA programme/Generalitat de Catalunya. ICN2 also acknowledges the support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295). Work at UCD is supported by the US NSF (DMR1610060 and ECCS-1611424).

We demonstrate far-field UV structured illumination implemented with in-tegrated aluminum oxide (AlOx) waveguide gratings. Based on simulation and experi-mental results, we discuss the performances of two AlO x waveguide gratings operating at λ = 360nm.

Alucones are one of the best-known films in the Molecular Layer Deposition (MLD) field. In this work, we prove that alucone/Al2O3 nanolaminate synthesis can be successfully performed by alternating alucone MLD growth with static O2 plasma exposures. Upon plasma treatment, only the top part of the alucone is densified into Al2O3, while the rest of the film remains relatively unaltered. X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS) depth profiling show that the process yields a bilayer structure, which remains stable in air. Fourier-transform infrared spectroscopy (FTIR) measurements show that Al2O3 features are generated after plasma treatment, while the original alucone features remain, confirming that plasma treatment results in a bilayer structure. Also, an intermediate carboxylate is created in the interface. Calculations of Al atom density during plasma exposure point towards a partial loss of Al atoms during plasma treatment, in addition to the removal of the glycerol backbone. The effect of different process parameters has been studied. Densification at the highest temperature possible (200 °C) has the best alucone preservation without hindering its thermal stability. In addition, operating at the lowest plasma power is found the most beneficial for the film, but there is a threshold that must be surpassed to achieve successful densification. About 70% of the original alucone film thickness can be expected to remain after densification, but thicker films may result in more diffuse interfaces. Additionally, this process has also been successfully performed in multilayers, showing real potential for encapsulation applications.

The increasing interest in atomic layer deposition (ALD) of Pt for the controlled synthesis of supported nanoparticles for catalysis demands an in-depth understanding of the nucleation controlled growth behaviour. We present an in situ investigation of Pt ALD on planar Si substrates, with native SiO2, by means of X-ray fluorescence (XRF) and grazing incidence small-angle X-ray scattering (GISAXS), using a custom-built synchrotron-compatible high-vacuum ALD setup and focusing on the thermal Pt ALD process, comprising (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) and O-2 gas at 300 degrees C. The evolution in key scattering features provides insights into the growth kinetics of Pt deposits from small nuclei to isolated islands and coalesced worm-like structures. An analysis approach is introduced to extract dynamic information on the average real space parameters, such as Pt cluster shape, size, and spacing. The results indicate a nucleation stage, followed by a diffusion-mediated particle growth regime that is marked by a decrease in average areal density and the formation of laterally elongated Pt clusters. Growth of the Pt nanoparticles is thus not only governed by the adsorption of Pt precursor molecules from the gas-phase and subsequent combustion of the ligands, but is largely determined by adsorption of migrating Pt species on the surface and diffusion-driven particle coalescence. Moreover, the influence of the Pt precursor dose on the particle nucleation and growth is investigated. It is found that the precursor dose influences the deposition rate (number of Pt atoms per cycle), while the particle morphology for a specific Pt loading is independent of the precursor dose used in the ALD process. Our results prove that combining in situ GISAXS and XRF provides an excellent experimental strategy to obtain new fundamental insights about the role of deposition parameters on the morphology of Pt ALD depositions. This knowledge is vital to improve control over the Pt nucleation stage and enable efficient synthesis of supported nanocatalysts.

We report the phase and size-controlled synthesis of Fe–Pt nanoalloys, prepared via a two-step synthesis procedure. The first step is the deposition of bilayers consisting of iron oxide and Pt films of desired thicknesses using atomic layer deposition, followed by a temperature-programmed reduction treatment of the film under H2/N2 atmosphere. This method enables the phase pure synthesis of all three Fe–Pt alloy phases, namely Fe3Pt, FePt, and FePt3, as revealed by in situ x-ray diffraction and x-ray fluorescence measurements. It is also demonstrated that by changing the total thickness of the bilayers while keeping the Pt/(Pt + Fe) atomic ratio constant, the size of the resulting bimetallic nanoparticles can be tuned, as confirmed by scanning electron microscopic measurements.

Supported nanoparticles are commonly applied in heterogeneous catalysis. The catalytic performance of these solid catalysts is, for a given support, dependent on the nanoparticle size, shape, and composition, thus necessitating synthesis techniques that allow for preparing these materials with fine control over those properties. Such control can be exploited to deconvolute their effects on the catalyst’s performance, which is the basis for knowledge-driven catalyst design. In this regard, bottom-up synthesis procedures based on colloidal chemistry or atomic layer deposition (ALD) have proven successful in achieving the desired level of control for a variety of fundamental studies. This review aims to give an account of recent progress made in the two aforementioned synthesis techniques for the application of controlled catalytic materials in gas-phase catalysis. For each technique, the focus goes to mono- and bimetallic materials, as well as to recent efforts in enhancing their performance by embedding colloidal templates in porous oxide phases or by the deposition of oxide overlayers via ALD. As a recent extension to the latter, the concept of area-selective ALD for advanced atomic-scale catalyst design is discussed.

Inherent substrate selectivity is reported for the thermal RuO4 (ToRuS)/H-2 gas atomic layer deposition (ALD) process on H-terminated Si (Si-H) versus SiO2. In situ spectroscopic ellipsometry (SE) detected Ru growth from the first cycle on blanket Si-H, whereas on blanket SiO2, 60 cycles were needed to detect growth. Area-selective growth was evaluated on a patterned substrate with 1-10 mu m wide Si H lines separated by 10 mu m wide SiO2 regions. Ex situ planar scanning electron microscopy and cross-sectional high resolution transmission electron microscopy measurements showed that a smooth, continuous Ru film of 4.5 nm could be deposited on Si-H, with no Ru detected on SiO2. The proposed mechanism behind the inherent substrate selectivity is the oxidation of the Si-H surface by RuO, which was confirmed by in vacuo X-ray photoelectron spectroscopy (XPS) experiments. A methodology to enhance the nucleation of the RuO4/H-2 gas process on oxide substrates is also reported. In situ SE and in vacuo XPS experiments show that the nucleation delay on SiO2 can be completely removed by exposing the surface to trimethylaluminum (TMA) just before the start of the ALD process. We found evidence that the TMA pulse makes the oxide surface reactive toward RuO4, by introduction of surface methyl groups, which can be combusted by RuO4. As TMA is known to be reactive toward many oxide substrates, this methodology presents a way to achieve Ru metallization of virtually any surface. Therefore, one can either (i) use the RuO4/H-2 gas process to coat nonoxidized surfaces selectively with Ru or (ii) use TMA-priming by which one can bypass the selectivity and coat a wide variety of surfaces nonselectively with Ru.

Molecular layer deposition (MLD) offers the deposition of ultrathin and conformal organic or hybrid films which have a wide range of applications. However, some critical potential applications require a very specific set of properties. For application as desiccant layers in water barrier films, for example, the films need to exhibit water uptake and swelling and be overcoatable. For application as a backbone for a solid composite electrolyte for lithium ions on the other hand, the films need to be stable against lithium and need to be transformable from a hybrid MLD film to a porous metal oxide film. Magnesium-based MLD films, called "magnesicone", are promising on both these aspects, and thus, an MLD process is developed using Mg(MeCp)(2) as a metal source and ethylene glycol (EG) or glycerol (GL) as organic reactants. Saturated growth could be achieved at 2 to 3 angstrom/cycle in a wide temperature window from 100 to 250 degrees C. The resulting magnesicone films react with ambient air and exhibit water uptake, which is in the case of the GL-based films associated with swelling (up to 10%) and in the case of EG-based magnesicone with Mg(CO)(3) formation, and are overcoatable with an ALD of Al2O3. Furthermore, by carefully tuning the annealing rate, the EG-grown films can be made porous at 350 degrees C. Hence, these functional tests demonstrate the potential of magnesicone films as reactive barrier layers and as the porous backbone of lithium ion composite solid electrolytes, making it a promising material for future applications.

The development of active and stable earth-abundant catalysts for hydrogen and oxygen evolution is one of the requirements for successful production of solar fuels. Atomic Layer Deposition (ALD) is a proven technique for conformal coating of structured (photo)electrode surfaces with such electrocatalyst materials. Here, we show that ALD can be used for the deposition of iron and cobalt phosphate electrocatalysts. A PE-ALD process was developed to obtain cobalt phosphate films without the need for a phosphidation step. The cobalt phosphate material acts as a bifunctional catalyst, able to also perform hydrogen evolution after either a thermal or electrochemical reduction step. ispartof: Nanoscale Advances vol:1 issue:10 pages:4166-4172 ispartof: location:England status: published

The thermal and plasma-enhanced atomic layer deposition (ALD) growth of titanium oxide using an alkylamine precursor - tetrakis(dimethylamino)titanium (TDMAT) - was investigated. The surface species present during both the precursor and co-reactant pulse were studied with in situ reflection mid-IR spectroscopy (FTIR) and in vacuo X-ray photoelectron spectroscopy (XPS). The thermal process using H2O vapor proceeds through a typical ligand exchange reaction mechanism. The plasma-enhanced ALD processes using H2O-plasma or O2-plasma exhibit an additional decomposition and combustion reaction mechanism. After the plasma exposure, imine (N[double bond, length as m-dash]C) and isocyanate (N[double bond, length as m-dash]C[double bond, length as m-dash]O) surface species were observed by in situ FTIR. In addition, nitrites (NOx) were detected using in vacuo XPS during the O2-plasma process. This study presents the importance of the use of in situ FTIR and in vacuo XPS as complementary techniques to learn more about the ALD reaction mechanism. While in situ FTIR is very sensitive to changes of chemical bonds at the surface, exact identification and quantification could only be done with the aid of in vacuo XPS.

The aluminum precursor plays a crucial role in the Al2O3 ALD process. To date, trimethylaluminum (TMA) is one of the most widely used precursors in experimental and theoretical studies. However, its application at industrial scale can pose safety risks since it is pyrophoric and extremely reactive with water. Aluminum alkoxides offer a promising alternative, but have received far less attention. A combined theoretical and experimental investigation is carried out on the Al2O3 ALD process using aluminum triisopropoxide (ATIP) as a prototypical example of Al-alkoxide precursors. The experimental results pointed out that the thermal ALD process using ATIP and water has a maximal growth per cycle (GPC) of 1.8 A/cycle at temperatures of 150 to 175 °C. On the basis of the in situ mass spectrometry analysis and DFT calculations, the formation of the alumina film mainly occurs during the water pulse by ligand exchange reactions between water and adsorbed precursors, while during the ATIP pulse only adsorption of ...