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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