The deposition of Pd and Pt nanoparticles by atomic layer deposition (ALD) has been studied extensively in recent years for the synthesis of nanoparticles for catalysis. For these applications, it is essential to synthesize nanoparticles with well-defined sizes and a high density on large-surface-area supports. Although the potential of ALD for synthesizing active nanocatalysts for various chemical reactions has been demonstrated, insight into how to control the nanoparticle properties (i.e. size, composition) by choosing suitable processing conditions is lacking. Furthermore, there is little understanding of the reaction mechanisms during the nucleation stage of metal ALD. In this work, nanoparticles synthesized with four different ALD processes (two for Pd and two for Pt) were extensively studied by transmission electron spectroscopy. Using these datasets as a starting point, the growth characteristics and reaction mechanisms of Pd and Pt ALD relevant for the synthesis of nanoparticles are discussed. The results reveal that ALD allows for the preparation of particles with control of the particle size, although it is also shown that the particle size distribution is strongly dependent on the processing conditions. Moreover, this paper discusses the opportunities and limitations of the use of ALD in the synthesis of nanocatalysts.

Graphene is a two dimensional material with extraordinary properties, which make it an interesting material for many optical and electronic devices. The integration of graphene in these devices often requires the deposition of thin dielectric layers on top of graphene. Atomic layer deposition (ALD) is the method of choice to deposit these layers due to its ability to deposit ultra‐thin, high quality films with sub‐monolayer thickness control. ALD on graphene however, is a challenge due to the lack of reactive surface sites on graphene. This leads to the selective growth on grain boundaries, wrinkles and defect sites present in the graphene. In this review an overview of the different methods to achieve uniform deposition of ALD on graphene is presented. The advantages and disadvantages of each method are discussed from the perspective of ALD together with the opportunities for further research. Special emphasis is given to the recent advancements in the understanding of the ALD process conditions and their influence on the deposition uniformity on graphene. Particularly, improving the quality of the dielectric layers deposited by ALD while maintaining the pristine properties of graphene, will prove vital for the device integration of graphene.

The solar energy conversion efficiency of photoelectrochemical (PEC) devices is usually limited by poor interface energetics, limiting the onset potential, and light reflection losses. Here, a three‐pronged approach to obtain excellent performance of an InP‐based photoelectrode for water reduction is presented. First, a buried p–n+ junction is fabricated, which shifts the valence band edge favorably with respect to the hydrogen redox potential. Photoelectron spectroscopy substantiates that the shift of the surface photovoltage is mainly determined by the buried junction. Second, a periodic array of InP nanopillars is created at the surface of the photoelectrode to substantially reduce the optical reflection losses. This device displays an unprecedented photocathodic power‐saved efficiency of 15.8% for single junction water reduction. Third, a thin TiO2 protection layer significantly increases the stability of the InP‐based photoelectrode. Careful design of the interface energetics based on surface photovoltage spectroscopy allows obtaining a PEC cell with stable record performance in water reduction.

A novel method to form ultrathin, uniform Al2O3 layers on graphene using reversible hydrogen plasma functionalization followed by atomic layer deposition (ALD) is presented. ALD on pristine graphene is known to be a challenge due to the absence of dangling bonds, leading to nonuniform film coverage. We show that hydrogen plasma functionalization of graphene leads to uniform ALD of closed Al2O3 films down to 8 nm in thickness. Hall measurements and Raman spectroscopy reveal that the hydrogen plasma functionalization is reversible upon Al2O3 ALD and subsequent annealing at 400 °C and in this way does not deteriorate the graphene’s charge carrier mobility. This is in contrast with oxygen plasma functionalization, which can lead to a uniform 5 nm thick closed film, but which is not reversible and leads to a reduction of the charge carrier mobility. Density functional theory (DFT) calculations attribute the uniform growth on both H2 and O2 plasma functionalized graphene to the enhanced adsorption of trimethylaluminum (TMA) on these surfaces. A DFT analysis of the possible reaction pathways for TMA precursor adsorption on hydrogenated graphene predicts a binding mechanism that cleans off the hydrogen functionalities from the surface, which explains the observed reversibility of the hydrogen plasma functionalization upon Al2O3 ALD.

Integrating metals and metal oxides with graphene is key in utilizing its extraordinary material properties that are ideal for nanoelectronic and catalyst applications. Atomic layer deposition (ALD) has become a key technique for depositing ultrathin, conformal metal(oxide) films. ALD of metal(oxide) films on graphene, however, remains a genuine challenge due to the chemical inertness of graphene. In this study we address this issue by combining first-principles density functional theory (DFT) simulations with ALD experiments. The focus is on the Pt ALD on graphene, as this hybrid system is very promising for solar and fuel cells, hydrogen technologies, microreactors, and sensors. Here we elucidate the surface reactions underpinning the nucleation stage of Pt ALD on pristine, defective and functionalized graphenes. The employed reaction mechanism clearly depends on (a) the available surface groups on graphene, and (b) the ligands accompanying the metal centre in the precursor. DFT calculations also indicate that graphene oxide (GO) can afford a stronger adsorption of MeCpPtMe, unlike Pt(acac), as compared to bare (non-functionalized) graphene, suggesting that GO monolayers are effective Pt ALD seed layers. Confirming the latter, we evince that wafer-scale, continuous Pt films can indeed be grown on GO monolayers using a thermal ALD process with MeCpPtMe and O gas. Besides, the current in-depth atomistic insights are of practical use for understanding similar ALD processes of other metals and metal oxides on graphene.