Gas-phase 3D printing of functional materials

Our paper has been accepted for publication in Advanced Materials Technologies (IF > 5).

This work shows that Spatial Atomic Layer Deposition (SALD) indeed represents an ideal platform for area-selective deposition of functional materials by proper design and miniaturization of close-proximity SALD heads. In particular, the potential offered by 3D printing is used to fabricate low-cost customized close-proximity heads, which can be easily designed and modified to obtain different deposition areas, free-form patterns, and even complex multimaterial structures. We also demonstrated that by designing a miniaturized head with circular concentric gas channels, 3D printing of functional materials can be performed with nanometric resolution in Z. This constitutes a new gas-phase 3D printing approach. Because the process is based on ALD reactions, conformal and continuous thin films of functional materials can be printed at low temperatures and with high deposition rate in the open air. Our approach represents a new versatile way of printing functional materials and devices with spatial and topological control, thus extending the potential of SALD and ALD in general, and opening a new avenue in the field of area-selective deposition of functional materials. This paper is the fruit of a great collaboration with LMGP team in Grenoble, France.

Optimization of precursor exposure using Comsol Multiphysics simulation for the case of Spatial Atomic Layer Deposition (SALD) in order to obtain high-quality films as well as to improve the process efficiency.

Our paper has been accepted for publication in Chemical Engineering Journal (IF > 10).

Here, we present a study on how to control the precursor exposure, a critical parameter in Spatial Atomic Layer Deposition (SALD), for the deposition of ZnO films using a close-proximity, open-air SALD approach. A simple physical model supported by Comsol Multiphysics simulations has been developed to study the effect of the substrate velocity as well as the precursor concentration in the carrier gas on film growth rate. We found that the precursor entrainment by the moving substrate induces an asymmetric precursor concentration profile that remarkably affects the obtained growth per cycle (GPC). Also, we show that the mass density and structural properties of the deposited films closely depend on the film growth rate. For instance, fast growth does not always produce dense films. Indeed, a compromise between the growth rate and the precursor consumption should be considered to obtain both good process efficiency and high-quality films. Our findings are particularly relevant for using SALD in large-scale coating applications, in which high deposition rate and good coating density should be obtained with a minimal ALD precursor consumption.

Tuning the Photocatalytic Activity of TiO2 Nanoparticles by Ultrathin SiO2 Films Grown by Low-Temperature Atmospheric Pressure Atomic Layer Deposition

Our paper has been accepted for publication in Applied Surface Science (IF > 6).

We employed atomic layer deposition (ALD) to deposit ultrathin SiO2 layers on P25 TiO2 nanoparticles to fabricate TiO2/SiO2 core/shell nanostructures. The ALD process carried out in a fluidized bed reactor working at atmospheric pressure using TiCl4 and H2O as precursors, enabling the deposition of SiO2 at 100 °C with the ability to control the thickness at the sub-nanometer level. By controlling the thickness of the SiO2 in a very narrow range, i.e., below 2 nm, the photocatalytic activity of TiO2 can be tuned. In particular, an enhancement was obtained for the SiO2 layers with a thickness of below 1.4 nm, in which the layer with a thickness of about 0.7 nm exhibited the highest photocatalytic activity; for the layers thicker than 1.4 nm, the photocatalytic activity was strongly suppressed. The photocatalytic activity enhancement and the degradation mechanism of RhB by the TiO2 /SiO2 photocatalysts were investigated by combining X-ray photoelectron spectroscopy, UV-Vis absorption spectroscopy, photoluminescence spectroscopy and the aid of charge carrier and radical scavengers. Our findings have revealed an improvement of photogenerated charge separation due to the SiO2 coating and the dominating role of hydroxyl radicals in the degradation of RhB.

Schematic representation of our custom head integrating both the precursor injector and the atmospheric plasma generator

Breaking news: our paper has been accepted for publication in Chemistry of Materials (IF > 10).

In this work, we present a low-temperature, open-air process based on spatial atomic layer deposition (SALD) that yields high purity SiO2 films at temperatures down to room temperature. The films were obtained by operating our SALD system in CVD mode (i.e. allowing precursor crosstalk), using an oxygen plasma in combination with Trivinylmethoxysilane. 3D printing was employed to fabricate custom heads integrating both the precursor injector and the atmospheric plasma generator. Our results show that conformal, pinhole-free SiO2 thin films can be deposited by our atmospheric plasma-enhanced spatial chemical vapor deposition (APE-SCVD) approach at low temperatures (RT – 180 °C) on different substrates, including silicon wafers, micro-glass slides, or even on polymeric substrates with a high growth rate up to 2 – 5 nm/min. Even though the deposition of SiO2 was carried out at low temperatures in the open air using a metalorganic precursor, no contamination from SiNx or SiCx, was observed by FTIR and XPS measurements. Our results open the door to the low-temperature, fast printing of Si-based devices. This work was done in collaboration with Dr. David Muñoz-Rojas in LMGP, University Grenoble Alpes, France.

Scanning Electron Microscope images of ZnO/CdS NRs (a) and ZnO/Au/CdS NRs (b); and Transmission Electron Microscope images of ZnO/Au/CdS (c & d).

Our new paper has been accepted for publication in Chemical Communications (IF > 6).

In this work, omnidirectional Au nanoparticle-embedded ZnO/CdS core/shell heterostructures were fabricated on ITO substrates for photoelectrochemical water-splitting photoelectrodes by combining electrospinning, hydrothermal treatment, photoreduction and chemical bath deposition. The obtained omnidirectional heterostructures harvested solar light efficiently, provided good electrical conductivity, and enhanced the charge transfer between CdS and ZnO that eventually enhanced photoconversion efficiency.

On the 19th September 2019, ALD Research Group was officially founded!

On the photo from the left to the right, Dr. Vu Van Truong, Dr. Dang The Hung, Dr. Bui Van Hao, Dr. Vu Ngoc Hai and Dr. Dao Van Duong, the leaders of potential research groups receive Establishment Decision from President of Phenikaa University, Prof. Dr. Pham Thanh Huy.

The 2019 Best Thesis Prize of French Chemical Society (the solid state chemistry division ) has been awarded to Viet Huong Nguyen.

His PhD was performed in the laboratory LMGP, and CEA-INES, France on the development of transparent electrodes by vacuum-free and low-cost deposition methods for photovoltaic applications. The thesis manuscript is available online from here.

Congratulations, Dr. Viet Huong Nguyen!