Area-selective atomic layer deposition is a key technology for modern microelectronics as it eliminates alignment errors inherent to conventional approaches by enabling material deposition only in specific areas. Typically, the selectivity originates from surface modifications of the substrate that allow or block precursor adsorption. The control of the deposition process currently remains a major challenge as the selectivity of the no-growth areas is lost quickly. Here, we show that surface modifications of the substrate strongly manipulate the surface diffusion. The selective deposition of TiO2 on poly (methyl methacrylate) and SiO2 yields localized nanostructures with tailored aspect ratios. Controlling the surface diffusion allows to tune such nanostructures as it boosts the growth rate at the interface of the growth and no-growth areas. Kinetic Monte-Carlo calculations reveal that species move from high to low diffusion areas. Further, we identify the catalytic activity of TiCl4 during the formation of carboxylic acid on poly (methyl methacrylate) as the reaction mechanism responsible for the loss of selectivity, and show that process optimization leads to higher selectivity. Our work enables the precise control of areaselective atomic layer deposition on the nanoscale, and offers new strategies in area-selective deposition processes by exploiting surface diffusion effects.

Thin, porous films of WO3 were fabricated by solution-based synthesis via spin-coating using polyethylene glycol (PEG), a block copolymer (PIB50-b-PEO45), or a combination of PEG and PIB50-b-PEO45 as structure-directing agents. The influence of the polymers on the composition and porosity of WO3 was investigated by microwave plasma atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and gas sorption analysis. The electrochromic performance of the WO3 thin films was characterized with LiClO4 in propylene carbonate as electrolyte. To analyze the intercalation of the Li+ ions, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy were performed on films in a pristine or reduced state. The use of PEG led to networks of micropores allowing fast reversible electrochromic switching with a high modulation of the optical transmittance and a high coloration efficiency. The use of PIB50-b-PEO45 provided isolated spherical mesopores leading to an electrochromic performance similar to compact WO3, only. Optimum characteristics were obtained in films which had been prepared in the presence of both, PEG and PIB50-b-PEO45, since WO3 films with mesopores were obtained that were interconnected by a microporous network and showed a clear progress in electrochromic switching beyond compact or microporous WO3.

No abstract

The ongoing miniaturization of semiconductor devices renders charge‐carrier transport along interfaces increasingly important. The characteristic length scales in state‐of‐the‐art semiconductor technology span only a few nanometers. Consequently, charge‐carrier transport inevitably occurs directly at interfaces between adjacent layers rather than being confined to a single material. Herein, charge‐carrier diffusion is systematically studied in prototypical active layer systems, namely, in type‐I direct‐gap quantum wells and in type‐II heterostructures. The impact of internal interfaces are revealed in detail as charge‐carrier diffusion takes place much closer to or even across the internal interfaces in type‐II heterostructures. Type‐I quantum wells and type‐II heterostructures exhibit comparable diffusion rates given similar inhomogeneous exciton linewidths. Consequently, the changes in the structural quality of the interfaces are responsible for changes in diffusion and charge‐carrier transport along interfaces rather than the existence of the interfaces themselves.