This review provides an overview of area-selective thin film deposition (ASD) with a primary focus on vapor-phase thin film formation via chemical vapor deposition (CVD) and atomic layer deposition (ALD). Areaselective deposition has been successfully implemented in microelectronic processes, but most approaches to date rely on high-temperature reactions to achieve the desired substrate sensitivity. Continued size and performance scaling of microelectronics, as well as new materials, patterning methods, and device fabrication schemes are seeking solutions for new low-temperature (<400 °C) ASD methods for dielectrics, metals, and organic thin films. To provide an overview of the ASD field, this article critically reviews key challenges that must be overcome for ASD to be successful in microelectronics and other fields, including descriptions of current process application needs. We provide an overview of basic mechanisms in film nucleation during CVD and ALD and summarize current known ASD approaches for semiconductors, metals, dielectrics, and organic materials. For a few key materials, selectivity is quantitatively compared for different reaction precursors, giving important insight into needs for favorable reactant and reaction design. We summarize current limitations of ASD and future opportunities that could be achieved using advanced bottom-up atomic scale processes.

Atomic layer deposition (ALD) is a technique capable of producing ultrathin conformal films with atomic level control over thickness. A major drawback of ALD is its low deposition rate, making ALD less attractive for applications that require high throughput processing. An approach to overcome this drawback is spatial ALD, i.e., an ALD mode where the half-reactions are separated spatially instead of through the use of purge steps. This allows for high deposition rate and high throughput ALD without compromising the typical ALD assets. This paper gives a perspective of past and current developments in spatial ALD. The technology is discussed and the main players are identified. Furthermore, this overview highlights current as well as new applications for spatial ALD, with a focus on photovoltaics and flexible electronics.

Hybrid organic-inorganic polymer thin films of the form (-O-Zn-O-C 2 H 4 -) n have been deposited from diethyl zinc and ethylene glycol using molecular layer deposition (MLD) over a range of substrate temperatures between 100 and 170 °C. Infrared transmission confirms that the films consist of Zn-O and ethylene-oxide units. In analogy with known alucone polymers of the form (-O-Al-O-R-) n , the zinc-based hybrid material is an example of a "zincone" polymer. In situ quartz crystal microbalance analysis indicated that the sequential surface reactions of diethyl zinc and ethylene glycol are sufficiently self-limiting and saturating to enable well-controlled MLD growth. Quantitative analysis of in situ quartz crystal microbalance and film thickness results indicate that ethylene glycol molecules can undergo a "double reaction" where the OH groups on both ends of the diol react with available Zn-C 2 H 5 surface sites to produce a relatively inert bridging alkane. The mass uptake per MLD cycle during Zn-hybrid film deposition decreases with increasing reaction temperature. Infrared transmission spectroscopy also shows that Zn-organic hybrid films are stable in dry air. However, the as-deposited ZnO-hybrid material could be hydrolyzed by H 2 O (for example, in ambient) resulting in films consisting of zinc oxide and zinc hydroxide with some carbon remnants. Spectroscopic ellipsometry indicates the thickness of hydrolyzed films increases linearly with reaction cycles, and scanning probe and transmission electron microscopy images show the hydrolyzed ZnO-hybrid film coating is uniform and conformal. The transmission electron micrographs also show the hydrolyzed Zn-hybrid films contain nanoscale porosity. These results suggest new pathways to fabricate organic-inorganic hybrid materials, including metalorganic framework structures.

Artificial photosynthesis and the production of solar fuels could be a key element in a future renewable energy economy providing a solution to the energy storage problem in solar energy conversion. We describe a hybrid strategy for solar water splitting based on a dye sensitized photoelectrosynthesis cell. It uses a derivatized, core-shell nanostructured photoanode with the core a high surface area conductive metal oxide film--indium tin oxide or antimony tin oxide--coated with a thin outer shell of TiO 2 formed by atomic layer deposition. A "chromophore-catalyst assembly" 1, [(PO 3 H 2 ) 2 bpy) 2 Ru(4-Mebpy-4-bimpy)Rub(tpy)(OH 2 )] 4+ , which combines both light absorber and water oxidation catalyst in a single molecule, was attached to the TiO 2 shell. Visible photolysis of the resulting core-shell assembly structure with a Pt cathode resulted in water splitting into hydrogen and oxygen with an absorbed photon conversion efficiency of 4.4% at peak photocurrent.P hotosynthesis uses the energy of the sun with water as the reducing agent to drive the reduction of carbon dioxide to carbohydrates with oxygen as a coproduct through a remarkably complex process. At photosystem II, a subsystem imbedded in the thylakoid membrane where O 2 is produced, light absorption, energy migration, electron transfer, proton transfer, and catalysis are all used in multiple stepwise chemical reactions which are carefully orchestrated at the molecular level (1, 2).Photosynthesis solves the problem of energy storage by biomass production but with low solar efficiencies, typically <1%. In artificial photosynthesis with solar fuels production, the goal is similar but the targets are either hydrogen production from water splitting, Eq. 1, or reduction of carbon dioxide to a carbon-based fuel, Eq. 2 (3, 4). Different strategies for solar fuels have evolved (5, 6). In one, direct bandgap excitation of semiconductors creates electron-hole pairs which are then used to drive separate halfreactions for water oxidation (2H 2 O → O 2 + 4H + + 4e − ) and water/proton reduction (2H + + 2e − → H 2 ) (7-9).Here, we report a hybrid strategy for solar water splitting, the dye sensitized photoelectrosynthesis cell (DSPEC). It combines the electron transport properties of semiconductor nanocrystalline thin films with molecular-level reactions (10). In this approach, a chromophore-catalyst molecular assembly acts as both light absorber and catalyst. It is bound to the surface of a "core-shell," nanostructured, transparent conducting oxide film. The core structure consists of a nanoparticle film of either tin-doped indium oxide (nanoITO), or antimony-doped tin oxide (nanoATO), deposited on a fluoride-doped tin oxide (FTO) glass substrate. The shell consists of a conformal TiO 2 nanolayer applied by atomic layer deposition (ALD). The resulting "photoanode," where water oxidation occurs, is connected to a Pt cathode for proton reduction to complete the water splitting cell. A diagram for the photoanode in the DSPEC device is shown in Fig. 1. It illustrates...

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