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Atomic layer deposition (ALD), a layer-by-layer controlled method to synthesize ultrathin materials, provides various merits over other techniques such as precise thickness control, large area scalability and excellent conformality. Here we demonstrate the possibility of using ALD growth on top of suspended 2D materials to fabricate nanomechanical resonators. We fabricate ALD nanomechanical resonators consisting of a graphene/MoS2 heterostructure. Using atomic force microscope indentation and optothermal drive, we measure their mechanical properties including Young's modulus, resonance frequency and quality factor, showing a lower energy dissipation compared to their exfoliated counterparts. We also demonstrate the fabrication of nanomechanical resonators by exfoliating an ALD grown NbS2 layer. This study exemplifies the potential of ALD techniques to produce high-quality suspended nanomechanical membranes, providing a promising route towards high-volume fabrication of future multilayer nanodevices and nanoelectromechanical systems.

Recently, stacks consisting of an ultrathin SiO2 coated with atomic-layer-deposited (ALD) Al-doped zinc oxide (ZnO:Al) have been shown to yield state-of-the-art passivation of n-type crystalline silicon surfaces and provide low contact resistivities to n+-doped Si and poly-Si surfaces. Key for achieving good surface passivation are an intentionally-grown SiO2 interlayer, an aluminum oxide (Al2O3) capping layer and a post-deposition anneal, whereas n-type doping of the ZnO is required to achieve a low contact resistivity. In this work, we present the latest results and insights obtained for this contact stack. This includes a study of the minimum required thicknesses of both the ZnO and the Al2O3 capping layer to achieve a high passivation level after post-deposition anneal. Also, we provide details on how to remove the Al2O3 capping layer selectively from the ZnO:Al after the post-deposition anneal using a pH-controlled wet-etch, such that the ZnO:Al can be contacted by a metal. Whereas previous work was based on lab-scale temporal ALD, in this work we highlight the industrialization potential by demonstrating that these layers can be prepared by spatial ALD, yielding good passivation levels on both undiffused n-type and n+-diffused c-Si surfaces. Finally, we demonstrate the capability of ALD to deposit ZnO:Al layers selectively on oxidized regions of an otherwise HF-last treated c-Si surface. Such area-selective deposition opens up potential pathways for local, self-aligned contact formation. Altogether, this work provides valuable insights into the working mechanism and practical aspects of ZnO:Al-based passivating contacts.

The scalable and conformal synthesis of two-dimensional (2D) transition metal dichalcogenide (TMDC) heterostructures is a persisting challenge for their implementation in next-generation devices. In this work, we report the synthesis of nanometer-thick 2D TMDC heterostructures consisting of TiSx-NbSx on both planar and 3D structures using atomic layer deposition (ALD) at low temperatures (200−300 °C). To this end, a process was developed for the growth of 2D NbSx by thermal ALD using (tert-butylimido)-tris-(diethylamino)-niobium (TBTDEN) and H2S gas. This process complemented the TiSx thermal ALD process for the growth of 2D TiSx-NbSx heterostructures. Precise thickness control of the individual TMDC material layers was demonstrated by fabricating multilayer (5-layer) TiSx-NbSx heterostructures with independently varied layer thicknesses. The heterostructures were successfully deposited on large-area planar substrates as well as over a 3D nanowire array for demonstrating the scalability and conformality of the heterostructure growth process. The current study demonstrates the advantages of ALD for the scalable synthesis of 2D heterostructures conformally over a 3D substrate with precise thickness control of the individual material layers at low temperatures. This makes the application of 2D TMDC heterostructures for nanoelectronics promising in both BEOL and FEOL containing high-aspect-ratio 3D structures.

Transparent conductive oxides form an important group of materials that combine high conductivity with high transparency. In this context, the authors designed an atomic layer deposition process for Nb-doped TiO2. The presented process enables accurate control over both the position and concentration of the Nb dopants. The as-deposited films become crystalline (brookite) and low resistive (4.3 × 10−3 Ω cm) upon a postdeposition anneal with temperatures as low as 300 °C. Variations in annealing ambient and temperature yielded resistivity changes over four orders of magnitude and significant changes in the sub-bandgap absorption of light. Next to doping, annealing is therefore shown to be a powerful tool in controlling electrical and optical properties of TiO2:Nb.

Two-dimensional transition metal dichalcogenides (2D-TMDs) are an exciting class of new materials. Their ultrathin body, optical band gap and unusual spin and valley polarization physics make them very promising candidates for a vast new range of (opto-)electronics and catalysis applications. So far, most experimental work on 2D-TMDs has been performed on exfoliated flakes made by the ‘Scotch tape’ technique. The major next challenge is the large-area synthesis of 2D-TMDs with control over their properties by a technique that ultimately can be used in industry. This article will focus on ALD for large-area 2D-TMD synthesis for application in (opto-)electronics and catalysis and will highlight the precise control over the thickness, morphology, composition and phase of the 2D-TMDs that can be obtained by ALD.

Dielectric metasurfaces based on amorphous silicon (a-Si) nanodisks are interesting for nanophotonic applications due to the high refractive index and mature/low temperature fabrication of a-Si. The investigated metasurfaces consist of a-Si nanodisk arrays embedded in a transparent film. The diameter-dependent optical properties of the nanodisk Mie resonators have been investigated by finite-difference time-domain (FDTD) simulations and spectrally-resolved reflectivity and transmission measurements. Well-ordered substrate-free a-Si nanodisk arrays were fabricated and characterized with regard to their broadband anti-reflection properties when placed on a crystalline silicon (c-Si) surface, and reflectivity/ transmission properties when embedded in a polydimethylsiloxane (PDMS) film. Our results confirm broadband anti-reflection when placed on silicon, while the optical characteristics of the nanodisks embedded in PDMS are shown to be potentially useful for color/NIR filter applications as well as for coloring on the micro/nanoscale. under the terms of the OSA Open Access Publishing Agreement, QC 20210826