Atomic layer deposition (ALD) of ruthenium dioxide (RuO2) thin films using metalorganic precursors and O2 can be challenging because the O2 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 Å/cycle when methanol is used as a reactant at deposition temperatures in the range of 60–120 °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 °C in an inert atmosphere crystallizes the films into rutile RuO2. The films are conductive, as is evident from a resistivity value of 230 μΩ·cm for a 20 nm film grown with methanol, and the resistivity decreased to 120 μΩ·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.

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 H2. 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-H2 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.

Metal nanoparticle (NP) sintering is a prime cause of catalyst degradation, limiting its economic lifetime and viability. To date, sintering phenomena are interrogated either at the bulk scale to probe averaged NP properties or at the level of individual NPs to visualize atomic motion. Yet, “mesoscale” strategies which bridge these worlds can chart NP populations at intermediate length scales but remain elusive due to characterization challenges. Here, a multi‐pronged approach is developed to provide complementary information on Pt NP sintering covering multiple length scales. High‐resolution scanning electron microscopy (HRSEM) and Monte Carlo simulation show that the size evolution of individual NPs depends on the number of coalescence events they undergo during their lifetime. In its turn, the probability of coalescence is strongly dependent on the NP's mesoscale environment, where local population heterogeneities generate NP‐rich “hotspots” and NP‐free zones during sintering. Surprisingly, advanced in situ synchrotron X‐ray diffraction shows that not all NPs within the small NP sub‐population are equally prone to sintering, depending on their crystallographic orientation on the support surface. The demonstrated approach shows that mesoscale heterogeneities in the NP population drive sintering and mitigation strategies demand their maximal elimination via advanced catalyst synthesis strategies.

Bimetallic nanoparticles (BMNPs) are frontrunners in various fields including heterogeneous catalysis, medicinal applications, and medical imaging. Tailoring their properties requires adequate control over their structure and composition, which still presents a non-trivial endeavor. We present a flexible strategy to deposit phase-controlled BMNPs by vapor-phase "titration" of a secondary metal to a pre-deposited monometallic nanoparticle (NP) host. The strategy is exemplified for archetypal Pt−Sn BMNPs but transferrable to other BMNPs which alloy noble and non-noble metals. When exposing Pt NPs on a SiO 2 support to discrete TDMASn (tetrakis(dimethylamino)tin) vapor pulses from 150 to 300 °C, TDMASn selectively decomposes on Pt NPs. This leads to saturated infiltration of Sn into Pt NPs through reactive solid-state diffusion, resulting in the formation of Pt−Sn BMNPs with phase/composition control via the substrate temperature. An additional H 2 pulse after each TDMASn pulse removes the surface ligands and excess Sn on the surface as SnH 4 , preserving the small sizes of the pre-deposited Pt NPs. This approach provides a single-step, selective "vapor-phase conversion" of Pt NPs into Pt x Sn y BMNPs with great potential for catalysis. Hereto, a proof of concept is provided by converting wet impregnated Pt NPs into Pt−Sn BMNPs on high surface area supports.

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Area selective atomic layer deposition (AS‐ALD) is an interesting bottom‐up approach due to its self‐aligned fabrication potential. Ruthenium dioxide (RuO2) is an important material for several applications, including microelectronics, demanding area selective processing. Herein, it is shown that ALD of RuO2 using methanol and RuO4 as reactants results in uninhibited continuous growth on SiO2, whereas there is no deposition on polymethyl methacrylate (PMMA) blanket films even up to 200 ALD cycles, resulting in around 25 nm of selective RuO2 deposition on SiO2. The excellent selectivity of the process is verified with X‐ray photoelectron spectroscopy, X‐ray fluorescence, and scanning transmission electron microscopy. AS‐ALD is possible at deposition temperatures as low as 60 °C, with an area selective window from 60 to 120 °C. The deposition of RuO2 using other coreactants namely ethanol and isopropanol in combination with RuO4 increases the process's growth rate while maintaining selectivity. Testing different polymer thin films such as poly(ethylene terephthalate glycol), (poly(lauryl methacrylate)‐co‐ethylene glycol dimethacrylate), polystyrene, and Kraton reveals an important relationship between polymer structure and the applicability of such polymers as mask layers. Finally, the developed method is demonstrated by selectively depositing RuO2 on patterned SiO2/PMMA samples, followed by PMMA removal, resulting in RuO2 nanopatterns.

Atomic layer deposition (ALD) typically employs metal precursors 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 the 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 films 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, while the morphology can be flexibly modulated from thin films to NPs by shuffling the pulse sequence. These complex pulse schemes are expected to be broadly applicable but are here explored for Pd−Ru bimetallic thin films and NPs.

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