In this work, we have quantitatively elucidated the source of the hydrogen content in the atomic layer deposition of Al2O3 at different temperatures (80–220 °C), by replacing the H2O precursor with heavy water (D2O) to use as a tracer and discern between the H coming from the unreacted metal precursor ligands and that from the unreacted −OD (hydroxyl) groups coming from the (heavy) water. The main source of impurities arises from the unreacted hydroxyl groups (−OD), reaching ∼18 atom % of deuterium at a deposition temperature of 80 °C. Reconsidering carefully our own and literature experimental data, we concluded that the generally accepted mechanism of steric hindering by monodentate Al­(CH3)2 adsorbates (dimethylaluminum) cannot be solely responsible for the retention of hydroxyls during atomic layer deposition (ALD). On this regard, we propose two additional mechanisms that can lead to sterically hinder hydroxyl groups which will then remain unreacted in the film: surface rehydroxylation resulting in the reconfiguration of bidentate or tridentate adsorbates into monodentate adsorbates and hindered subsurface hydroxyl groups during the (heavy) water pulse and the hydroxylation of sterically hindered dissociated methyl chemisorbed species. Based on these three steric hindrance mechanisms, we constructed a growth model that consists of the initial chemisorption configurations of trimethyl-aluminum molecules with the alumina surface and the subsequent reconfiguration of the resulting adsorbates into a monodentate configuration that consequently leads to sterically hindered hydroxyl groups. The fraction of AlOx adsorbates arranged in monodentate and bidentate configurations entails a specific number of O/Al atoms and unreacted hydroxyl groups inside the film. This model was able to explain the deuterium content, the O/Al ratio, and the density obtained from Rutherford back-scattering and heavy ion elastic recoil detection analysis measurements. Furthermore, this model was able to predict more accurately the growth per cycle to what has been reported to be the ALD window of alumina. Our findings will spur further detailed investigations of the reaction and growth modes in ALD films.

An effective postgrowth electrical tuning, via an oxygen releasing method, to enhance the content of non-noble metals in deposits directly written with gas-assisted focused-electron-beam-induced deposition (FEBID) is presented. It represents a novel and reproducible method for improving the electrical transport properties of Co-C deposits. The metal content and electrical properties of Co-C-O nanodeposits obtained by electron-induced dissociation of volatile Co(CO) precursor adsorbate molecules were reproducibly tuned by applying postgrowth annealing processes at 100 °C, 200 °C, and 300 °C under high-vacuum for 10 min. Advanced thin film EDX analysis showed that during the annealing process predominantly oxygen is released from the Co-C-O deposits, yielding an atomic ratio of Co:C:O = 100:16:1 (85:14:1) with respect to the atomic composition of as-written Co:C:O = 100:21:28 (67:14:19). In-depth Raman analysis suggests that the amorphous carbon contained in the as-written deposit turns into graphite nanocrystals with size of about 22.4 nm with annealing temperature. Remarkably, these microstructural changes allow for tuning of the electrical resistivity of the deposits over 3 orders of magnitude from 26 mΩ cm down to 26 μΩ cm, achieving a residual resistivity of ρ/ρ = 0.56, close to the value of 0.53 for pure Co films with similar dimensions, making it especially interesting and advantageous over the numerous works already published for applications such as advanced scanning-probe systems, magnetic memory, storage, and ferroelectric tunnel junction memristors, as the graphitic matrix protects the cobalt from being oxidized under an ambient atmosphere.

Direct writing utilizing a focused electron beam constitutes an interesting alternative to resist-based techniques, as it allows for precise and flexible growth onto any conductive substrate in a single-step process. One important challenge, however, is the identification of appropriate precursors which allow for deposition of the material of choice, e.g., for envisaged applications in nano-optics. In this regard the coinage metal silver is of particular interest since it shows a relatively high plasma frequency and, thus, excellent plasmonic properties in the visible range. By utilizing the precursor compound AgOMeBu, direct writing of silver-based nanostructures via local electron beam induced deposition could be realized for the first time. Interestingly, the silver deposition was strongly dependent on electron dose; at low doses of 30 nC/μm a dominant formation of pure silver crystals was observed, while at higher electron doses around 10 nC/μm large carbon contents were measured. A scheme for the enhanced silver deposition under low electron fluxes by an electronic activation of precursor dissociation below thermal CVD temperature is proposed and validated using material characterization techniques. Finally, the knowledge gained was employed to fabricate well-defined two-dimensional deposits with maximized silver content approaching 75 at. %, which was achieved by proper adjustment of the deposition parameters. The corresponding deposits consist of plasmonically active silver crystallites and demonstrate a pronounced Raman signal enhancement of the carbonaceous matrix.

Controlled deposition of thin conformal oxide films on carbon nanotubes (CNTs) by atomic layer deposition (ALD) for applications in solar energy and photocatalysis is still challenging, as the early stages of nucleation and subsequent growth are not yet well understood. In this work, we employed ALD to grow TiO2 on multiwalled carbon nanotubes (MW-CNTs). The effects of deposition temperature (120–240 °C), number of ALD cycles (20–750), and surface pretreatment of the MW-CNTs with oxygen plasma on the morphology and crystallinity of the TiO2 were systematically studied using transmission electron microscopy (TEM). By tuning the deposition conditions, controllable nucleation and growth of TiO2 on CNTs was achieved. In particular, high-quality crystalline anatase conforming to the CNTs was obtained with an ALD growth temperature as low as 200 °C. Direct observation using aberration-corrected atomic-resolution TEM imaging at 120 keV revealed an island structure of crystalline TiO x at the very early stage of nucleation, followed by coalesced growth of crystalline anatase at this temperature. The study also paves the way to understand the interface between the two materials on an atomic level.

We applied the core-shell concept to an urchin-inspired ZnO nanowire photoanode building block as a means to increase the electron transport and reduce recombination between nanowire and electrolyte. Dye-sensitized solar cells (DSSCs) were prepared, for the first time, from arrays of urchin-like ZnO nanowire building blocks covered with a thin layer of anatase TiO2 by atomic layer deposition (ALD). An increase in the cell open-circuit voltage (VOC) and