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New Atomic Layer Deposition Route for Boron Nitride Thin Films – ALaDiN

Fabrication of efficient BN-based structures for environmental applications

A new ALD approach for BN is developed based on the chemical route of polymer-derived ceramics. It consists of 2 steps: (1) ALD deposition of a pre-polymer film with a controlled thickness, (2) post-treatment to convert the ALD deposit into BN. This process allows the fabrication of Van der Waals BN/C heterostructures as well as highly crystallized BN nanostructures. The latter have proven to be very interesting for water purification.

Development of an alternative ammonia-free process for depositing boron nitride films with atomic-level control of the thickness

Renewable clean energy and environment are two of the most major concerns for the coming decades. Carbon-based nanostructured materials are leading materials due to their outstanding chemical and physical properties. Less investigated hexagonal boron nitride (BN)-based nanostructures such as nanotubes and nanosheets, which are structural analogues of their carbon counterparts, are very attractive materials for energy and environmental applications due to their high chemical and thermal stability, hydrophobicity and surface charge. Fabrication of BN nanomaterials requires reliable synthesis method that allows controlling their structure, dimensionalities and properties. Even though several approaches are available, few of them permit an atomic tuning of the thickness and the BN deposition on various supports. Among the different fabrication processes, atomic layer deposition (ALD) is one of the most attractive techniques due to its simplicity, reproducibility, high conformity of the obtained films and control of the deposited thickness at the atomic scale. A few ALD processes have been reported in the literature for the deposition of BN, however none of them allows obtaining directly an h-BN film of very good crystalline quality. Moreover, they often require the use of corrosive compounds such as ammonia. It therefore appears necessary to develop a new process for the preparation of thin films and nano-/hetero-structures of h-BN. The ALaDiN project aims to develop a new ammonia-free ALD process for the fabrication of h-BN films on various substrates. The elaboration of highly crystallized h-BN films is motivated, among other things, by the exploration of h-BN/carbon Van der Waals (VdW) heterostructures, which have a strong application potential.

Atomic layer deposition (ALD) is the technique of choice for the fabrication of thin films and complex nanostructured materials due to its simplicity as well as the reproducibility and high homogeneity of the deposits. It allows a control of the film thickness at the atomic scale. In order to avoid the use of ammonia and to limit the deposition temperature, a new two-step ALD process, based on the polymer-derived ceramics route, has been developed. It consists of (1) the growth layer by layer of a so-called preceramic BN films, onto various substrates, at low temperature, and then (2) to its densification into pure BN by annealing process. Ultra-thin homogeneous films of stoichiometric BN are thus produced in a reproducible manner both on flat and highly structured substrates. The first low temperature step enables using polymer template and fabricating various BN nanostructures.

Based on the PDCs route, a new two-step ALD process for BN, without ammonia, has been reported for the first time: (1) from trichloroborazine (TCB) and hexamethyldisilazane (HMDS), ALD deposition at 80 °C of a polyborazine film with controlled thickness followed by (2) a post-treatment to convert the preceramic film into pure BN. Homogeneous and uniform quasi-stoichiometric BN films (B/N=0.95) were reproducibly fabricated. Any chlorinated impurity is detected, while they content a very low amount of Si impurity (0.4at%) related to the chain terminations of the preceramic. BN layers can be deposited on both planar substrates such as Si wafers and highly structured substrates such as SiO2 particles and carbon nanotubes (CNTs) as well as polycarbonate (PC) membranes and polyacrylonitrile (PAN) fibres, used as templates. This two-step approach is an important step towards the controlled fabrication of complex h-BN nano-/hetero-structures. Indeed, despite the annealing step, the low deposition temperature allows the use of polymeric templates not accessible by other ALD processes for BN.
Several BN structures have thus been ALD fabricated using TCB and HMDS: heterostructures and nanostructures from inorganic and polymer nanomaterials, respectively, as substrates/templates. In particular, 1D VdW heterostructures such as carbon nanotubes coated with h-BN were obtained. Crystallized h-BN is directly deposited on non-functionalized single and multi-walled carbon nanotubes, maintaining their intrinsic properties.
Using this new process, unwoven textiles made of boron nitride nanotubes with controllable dimensions, i.e. internal diameter and wall thickness, were fabricated from polymer template. These BN textiles have proven to be excellent absorber and effective filters for organic compounds, useful for purifying polluted water. Easy to handle, stable in air and in acidic and basic environments, they are renewable and thus reusable. BN-Carbon nanostructures have also been developed and are under study.

The controlled fabrication of 1D h-BN/C VdW heterostructures is an important challenge. In line with the spectacular improvement and emergence of new physical properties in 2D VdW heterostructures, the curvature and confinement effects provided by the reduced dimensionality of 1D VdW heterostructures make them highly attractive. These new 1D materials are of particular interest for applications ranging from sensing and quantum optics, to biological labeling. While BN/C hetero-nanotubes have already been reported in the literature, their synthesis is generally poorly controlled in terms of either crystallinity or dimensionality. The ALD of BN based on the PDCs route thus presents a strong potential for the controlled elaboration of this kind of VdW heterostructures, allowing the study of their structural and physical properties, especially their optical properties. This work is carried out within the collaborative ANR HeteroBN-C project which is in line with the ALaDiN one.
The developed ALD process for BN will be reused to synthesize BN layers with controlled crystallinity on various substrates, within a European project. The later aims at fabricate resistive switching devices, magnetic tunnel junctions and spin injection tunnel barriers.

The obtained results within the ALaDiN project have been disseminated to the scientific community via 3 scientific articles in international journals and oral communications in several national and international conferences (9). In addition, 6 invited talks have been given.
Scientific articles
W. Hao, C. Marichy, C. Journet, A. Brioude, “A Novel two-step ammonia-free atomic layer deposition approach of boron nitride”, ChemNanoMat, 2017, 3, 656-663.
W. Hao, C. Marichy, A. Brioude, “Promising properties of ALD boron nitride nanotube mat for water purification”, Environmental science. Nano., 2017, 4, 2311-2320
B. Matsoso, W. Hao, Y. Li, V. Vuillet-a-Ciles, V. Garnier, P. Steyer, B. Toury, C. Marichy, C. Journet, “Synthesis of hexagonal boron nitride 2D layers using polymer derived ceramics route and derivatives” Journal of Physics: Materials, 2020, 3, 034002.
Invited talks
1. C. Marichy, W. Hao, V. Salles, A. Brioude, “Combination of ALD and PDCs routes for BN nanostructures”, workshop on Hybrid materials by ALD/MLD, 23, 24 janvier 2017, San Sebastian, Espagne.
2. C. Marichy, W. Hao, A. Brioude, “Atomic layer deposition of boron nitride material”, 12th International conference on ceramic materials and components for energy and environmental application (CMCEE2018), 22-27 juillet 2018, Singapour, Singapour
3. C. Marichy, W. Hao, A. Brioude, “Atomic layer deposition of boron nitride material”, Matériaux 2018, 19-23 novembre 2018, Strasbourg, France
4. C. Marichy, W. Hao, C. Journet, A. Brioude, “Fabrication of BN membranes: environmental applications”, ALD 2020 – 20th international conference on the atomic layer deposition. 29 Juin-1er Juillet 2020, Virtual Meeting (initialement Gand, Belgique).
5. W. Hao, T. Saboo, C. Journet, C. Marichy, “ALD of Boron Nitride by Polymer derived ceramics chemistry”, ALD 2021 – 21th international conference on the atomic layer deposition. 28-30 Juin 2021, Virtual Meeting (initialement Tampa, USA).
6. W. Hao, C. Journet, C. Marichy, “ALD of hexagonal Boron Nitride: towards h-BN/Carbon Van der Waals 1D heterostructures”, 240th ECS Fall Meeting. 11-15 octobre 2021, Virtual Meeting (initialement Orlando, USA).

The scientific interest for h-BN material is growing every year due to its potential use in various domains such as microelectronic. The presented project aims to develop and study a new atomic layer deposition (ALD) approach for boron nitride very thin films. Indeed, the few existing ALD processes being mostly based on ammonia and/or halide precursors, new ALD approach using alternative precursors is proposed to avoid corrosive and/or irritant reactant and by-product as well as to improve the film quality especially in term of crystallinity. Regarding an eventual industrial application, low energy consumption and environmentally friendly process is sought after. The polymer derived ceramics route will thus be transposed to ALD. No process combining these two synthetic routes has been reported up to now. Elaboration of well crystallized h-BN ultra-thin films is motivated among others by further study of BN/graphene heterostructures, which are highly promising in microelectronics.

Project coordinator

Madame Catherine Marichy (Laboratoire des Multimatériaux et Interfaces)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LMI Laboratoire des Multimatériaux et Interfaces

Help of the ANR 220,287 euros
Beginning and duration of the scientific project: October 2016 - 36 Months

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