Atomic Layer Deposition of Amorphous Thin Films in Surface Modification and Protection for Electrochemical and Electronic Applications PDF Download

Author: Yutao Dong
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Languages : en
Pages : 0

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Book Description
Atomic layer deposition (ALD) is a powerful manufacturing approach for amorphous thin film growth. With the advantages of excellent conformity, pinhole-free and concise thickness control, ALD has been widely applied in many energy systems, including batteries, catalysts and photoelectrochemical (PEC) cells, to achieve surface modification and good protection performance. In this dissertation, a series of works will be exhibited to discuss ALD amorphous film coating on batteries electrode and separator, semiconductor photoelectrodes, demonstrating its enormous prospects to enable stable performance in electrochemical systems. Chapter 1 is an overview of photoelectrochemistry and ALD technique to provide principal background to inspire our ALD amorphous film studies in electrochemical systems. ALD protective coatings on batteries electrodes and semiconductor photoelectrodes have been reviewed to illustrate the advantage of homogenous amorphous ALD film. Structure inhomogeneity and chemical composition impurities in ALD amorphous film are discussed to present unsolved problems to optimize ALD amorphous film properties. Chapter 2 discusses the development of bioresorbable zinc anode coated by ALD amorphous Al2O3 film. With the protective ALD Al2O3 protective shell, the zinc anode filament exhibited directional dissolution behavior with a tunable lifetime and output, providing an effective pathway toward bioresorbable transient batteries powering biomedical implantable devices. Chapter 3 exhibited the surface modification performance of ALD amorphous Al2O3 film on ferroelectric P(VDF-TrFE) film, severing as dendrite-suppression separator in aqueous rechargeable zinc ions batteries. The separator surface hydrophilicity is largely improved with the ferroelectric properties maintained after ALD amorphous Al2O3 coating, generating uniform zinc ions diffusion during plating/stripping cycling. This works depicts ALD amorphous film modified ferroelectric film as promising separator candidates in aqueous rechargeable batteries systems. Chapter 4 discusses the ALD amorphous film protection on Si photoanode and reveals the detrimental role of unreacted Cl ligands to film stability in PEC water splitting. In addition to crystalline phase, the residual Cl impurities can become the weak point of ALD amorphous TiO2 film due to local high hole conductivity and discontinuous Ti-O-Ti networks. Furthermore, post-ALD in-situ water treatment approach is demonstrated to effectively decouple the ALD reaction completeness from crystallization. The as-processed TiO2 film has a much lower residual Cl concentration and thus an improved film stoichiometry, while its uniform amorphous phase is well preserved. Thus, this water-treated ALD amorphous TiO2 film enabled record-high protection stability with high photocurrent density, demonstrating a significant advancement toward sustainable hydrogen generation. Inspired by the stoichiometry influence on ALD amorphous TiO2 film properties, the residual ligands in plasmas-enhanced chemical vapor deposition (PECVD) amorphous silicon nitride (SiNx) film are also investigated and demonstrated to largely affect the film mechanical properties in Chapter 5. The high residual N-H ligands from the NH3 precursor induces excessive tensile strain at the SiNx/Si wafer interface and consequently aggravates SiNx film crack formation. With a long-soak pretreatment, residual H ligands are effectively reduced to achieve homogenous chemical composition in both thin and thick long-soak SiNx film. As a result, the crack number and the remaining crack length are substantially reduced in contrast to the original SiNx film. This work further demonstrates the crucial role of residual ligands on internal strain regulation and points out a pathway to achieve crack-free PECVD SiNx films in industrial manufacturing. Chapter 6 provides summaries of ALD amorphous film applications in electrochemical system and concludes the film stoichiometry influence on amorphous film chemical/mechanical stability. Based on the substantial performance enhancement with improved stoichiometry, promising research outlooks have been proposed for ALD amorphous film optimization.