Atomic layer deposition (ALD) is a cyclic process which relies on sequential self-terminating reactions between gas phase precursor molecules and a solid surface. The self-limiting nature of the chemical reactions ensures precise film thickness control and excellent step coverage, even on 3D structures with large aspect ratios. At present, ALD is mainly used in the microelectronics industry, e.g. for growing gate oxides. The excellent conformality that can be achieved with ALD also renders it a promising candidate for coating porous structures, e.g. for functionalization of large surface area substrates for catalysis, fuel cells, batteries, supercapacitors, filtration devices, sensors, membranes etc. This tutorial review focuses on the application of ALD for catalyst design. Examples are discussed where ALD of TiO(2) is used for tailoring the interior surface of nanoporous films with pore sizes of 4-6 nm, resulting in photocatalytic activity. In still narrower pores, the ability to deposit chemical elements can be exploited to generate catalytic sites. In zeolites, ALD of aluminium species enables the generation of acid catalytic activity.

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The basic unit of information in filamentary-based resistive switching memories is physically stored in a conductive filament. Therefore, the overall performance of the device is indissolubly related to the properties of such filament. In this Letter, we report for the first time on the three-dimensional (3D) observation of the shape of the conductive filament. The observation of the filament is done in a nanoscale conductive-bridging device, which is programmed under real operative conditions. To obtain the 3D-information we developed a dedicated tomography technique based on conductive atomic force microscopy. The shape and size of the conductive filament are obtained in three-dimensions with nanometric resolution. The observed filament presents a conical shape with the narrow part close to the inert-electrode. On the basis of this shape, we conclude that the dynamic filament-growth is limited by the cation transport. In addition, we demonstrate the role of the programming current, which clearly influences the physical-volume of the induced conductive filaments.

Atomic layer deposition (ALD) of TiO2 thin films using Ti isopropoxide and tetrakis-dimethyl-amido titanium (TDMAT) as two kinds of Ti precursors and water as another reactant was investigated. TiO2 films with high purity can be grown in a self-limited ALD growth mode by using either Ti isopropoxide or TDMAT as Ti precursors. Different growth behaviors as a function of deposition temperature were observed. A typical growth rate curve-increased growth rate per cycle (GPC) with increasing temperatures was observed for the TiO2 film deposited by Ti isopropoxide and H2O, while surprisingly high GPC was observed at low temperatures for the TiO2 film deposited by TDMAT and H2O. An energetic model was proposed to explain the different growth behaviors with different precursors. Density functional theory (DFT) calculation was made. The GPC in the low temperature region is determined by the reaction energy barrier. From the experimental results and DFT calculation, we found that the intermediate product stability after the ligand exchange is determined by the desorption behavior, which has a huge effect on the width of the ALD process window.

Efficient CO transformation from a waste product to a carbon source for chemicals and fuels will require reaction conditions that effect its reduction. We developed a "super-dry" CH reforming reaction for enhanced CO production from CH and CO We used Ni/MgAlO as a CH-reforming catalyst, FeO/MgAlO as a solid oxygen carrier, and CaO/AlO as a CO sorbent. The isothermal coupling of these three different processes resulted in higher CO production as compared with that of conventional dry reforming, by avoiding back reactions with water. The reduction of iron oxide was intensified through CH conversion to syngas over Ni and CO extraction and storage as CaCO CO is then used for iron reoxidation and CO production, exploiting equilibrium shifts effected with inert gas sweeping (Le Chatelier's principle). Super-dry reforming uses up to three CO molecules per CH and offers a high CO space-time yield of 7.5 millimole CO per second per kilogram of iron at 1023 kelvin.

A systematic study of the thermally induced reaction of 20 transition metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, and Cu) with Ge substrates was carried out in order to identify appropriate contact materials in Ge-based microelectronic circuits. Thin metal films, nominally 30nm thick, were sputter deposited on both amorphous Ge and crystalline Ge(001). Metal-Ge reactions were monitored in situ during ramp anneals at 3°Cs−1 in an atmosphere of purified He using time-resolved x-ray diffraction, diffuse light scattering, and resistance measurements. These analyses allowed the determination of the phase formation sequence for each metal-Ge system and the identification of the most promising candidates—in terms of sheet resistance and surface roughness—for their use as first level interconnections in microelectronic circuits. A first group of metals (Ti, Zr, Hf, V, Nb, and Ta) reacted with Ge only at temperatures well above 450°C and was prone to oxidation. Another set (Cr, Mo, Mn, Re, Rh, Ru, and Ir) did not form low resistivity phases (<130μΩcm) whereas no reaction was observed in the case of W even after annealing at up to 1000°C. We found that Fe, Co, Ni, Pd, Pt, and Cu were the most interesting candidates for microelectronic applications as they reacted at relatively low temperatures (150–360°C) to form low resistivity phases (22–129μΩcm). Among those, two monogermanides, NiGe and PdGe, exhibited the lowest resistivity values (22–30μΩcm) and were stable over the widest temperature window during ramp anneals. In passing, we note that Cu, Ni, and Pd were the most effective in lowering the crystallization temperature of amorphous Ge, by up to 290°C for our typical ramp anneals at 3°Cs−1.

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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 electrolytegated and defect-mediated O and Co transport in a Co 3 O 4 single layer which allows for room-temperature voltage-controlled ON−OFF ferromagnetism (magnetic switch) via internal reduction/oxidation processes. Negative voltages partially reduce Co 3 O 4 to Co (ferromagnetism: ON), resulting in graded films including Co-and O-rich areas. Positive bias oxidizes Co back to Co 3 O 4 (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 Co 3 O 4 itself is required. This process could lead to electric-field-controlled device concepts for spintronics.