Precursor Chemistry Research Articles

Electrodeposition of cobalt-manganese oxide selective coatings for solar-thermal applications

Solar absorber coatings are the heart of solar-thermal power systems and their desired properties intimately depend on the operational temperature. Specifically for medium to high temperature applications, the systems require a thermally-stable selective coating with optimal optical properties. Black metal mixed oxides with the spinel crystal structure are interesting prospects as a new family of selective absorber materials. In this work we report on the indirect electrodeposition of a spinel black oxide of the type MnxCo3-xO4, using a nitrate solution; the electrochemical reduction of nitrate results in the formation of surface hydroxide leading to the co-precipitation of Co and Mn hydroxides, and the resulting mainly amorphous film is subsequently converted to the spinel material by sintering. The optimal precursor chemistry and electrodeposition conditions were obtained using a combinatorial method employing the Hull cell. After optimization and thermal annealing, spinel MnxCo3-xO4 films (x ≈ 0.7) with solar absorptance of α = 89.5% and thermal emittance of ε = 14.9% (at 100 °C) were obtained, illustrating their promising optical properties. The thermal stability of the coatings at medium and high temperatures (250 °C and 560 °C), as well as under harsh accelerated weathering conditions, was found to be excellent. The scalability of the electrodeposition method was confirmed by deposition onto a stainless steel tube.

Combustion kinetics of alternative jet fuels, Part-I: Experimental flow reactor study

A comprehensive collection of technical aviation fuels enabled an experimental and numerical study on detailed combustion chemistry and pollutant formation presented in a series of 3 interlinking parts. Part-I: Experimental Flow Reactor Study focuses on the characterization of 42 technical jet fuels and provides experimental speciation data for model development presented in Part-II: Model and Surrogate Strategy. Model validation based on the presented technical fuels here is presented in Part-III: Model Application on Technical Jet Fuels.The fuels investigated in this study cover a broad range of approved SAFs (Sustainable Aviation Fuels), candidates for approval, and technical products outside the present ASTM-D7566 specification and is completed by reference fuels (ASTM-D1655). This includes SAF components such as HEFA (Hydroprocessed Esters and Fatty Acids), ATJ (Alcohol-To-Jet), SIP (Synthesized Iso-Paraffins), and Fischer-Tropsch-products as well as their blends.A systematic investigation of the soot precursor chemistry by analyzing the influence of the complex chemical fuel composition on the intermediate species pool is presented. The experimental set-up consists of an atmospheric flow reactor with coupled molecular-beam mass spectrometer (MBMS). Quantitative evolution of combustion reaction intermediates is recorded for fuel-rich (Φ = 1.2) and fuel-lean (Φ = 0.8) conditions at intermediate temperatures up to 1200 K including small intermediate species (e.g. ethylene, butene) and soot precursor species (e.g. benzene, naphthalene, phenanthrene).A general systematic dependency of the soot precursor concentration on the degree of unsaturation (Index of Hydrogen Deficiency) or the hydrogen content, respectively, is demonstrated. Furthermore, larger soot precursor concentrations depend on the naphthalene content of the fuel.

Modelling the Growth and Etch of Thin Film Metal Oxides

HfO2 and ZrO2 are two high-k materials that are crucial in semiconductor devices. Atomic level control of material processing is required for fabrication of thin films of these materials at nanoscale device sizes. Atomic layer deposition (ALD) and thermal atomic layer etching (ALE) allow fabrication of ultra-thin films for semiconductor device processing. ALD is a well-known metal oxide thin film deposition technique in which metal and oxygen containing precursors are added sequentially to the reactor to ensure self-limiting precursor adsorption and reaction to enable a high level of control over film thickness. Thermal ALE, which is a relatively modern technique, uses self-limiting fluorination (using hydrogen fluoride exposure) and subsequent ligand exchange reactions at elevated temperatures to remove up to a monolayer of the metal oxide material. This modern approach for controlled etching is the reverse of ALD and removes only the fluorinated layer.Given that it is difficult to investigate ALD and ALE reactions directly using experimental techniques, first-principles-based atomic-level simulations using density functional theory (DFT) can give deep insights into the precursor chemistry and the reactions that drive the deposition and etch of different materials. This contribution presents first principles density functional theory modelling to examine the growth and etch of thin films of HfO2 and ZrO2. Concerning the ALD reaction, the adsorption mechanism of precursors TDMAHf and TDMAZr are studied at the bare and hydroxylated surfaces of HfO2 and ZrO2 respectively. Stable OH coverages of 0.50 ML and 0.63 ML on the surfaces of HfO2 and ZrO2 were found respectively. Ligand loss from the metal precursor can be achieved by protonation from the OH terminated surface of both metal oxides. Concerning the ALE reaction, HF exposures on the surfaces of HfO2 and ZrO2 are studied. HF coverages ranging from 1.0 ± 0.3 to 17.0 ± 0.3 HF/nm2 are investigated and a mixture of molecularly and dissociatively adsorbed HF molecules is present at higher coverages. Theoretical etch rates of -0.61 ± 0.02 Å /cycle for HfO2 and -0.57 ± 0.02 Å /cycle ZrO2 were calculated using maximum coverages of 7.0 ± 0.3 and 6.5 ± 0.3 M-F bonds/nm2 respectively (M = Hf, Zr).

(Invited) Chemical Modulation of Precursor Reactivity for Systematic Synthesis of High-Quality Quantum Dots

With their size-dependent electronic properties, solution processability, and synthetic tunability, quantum dots (QDs) have been heavily studied for fundamental research and commercial applications. The performance of QD-based devices and QD probes are greatly affected by their size distribution and structural quality. To date, extensive studies have investigated size control, allowing us to grow QDs with less than a single monolayer difference in their size variation. In contrast, high quality QD growth is achieved mostly by trial-and-error and a reaction condition optimized for a specific QD system cannot be adapted to QDs of different sizes or materials. To address this critical gap in QD synthesis, we first identified the key parameters contributing to the structural quality of QDs and examined how they affect QD growth. Our study shows that the reaction temperature governs the instability of the QD surface and the level of lattice relaxation, while precursor reactivity impacts the reaction kinetics at the surface as well as satellite particle formation. Systematic optimization of growth conditions requires independent tuning of these two parameters. Unfortunately, conventional precursors do not allow temperature-independent modulation of their reactivity, requiring new precursors to be synthesized for different reaction conditions. This approach is inherently low throughput and labor-intensive.To enable temperature-independent modulation of precursor reactivity, we designed a new sulfur precursor that has a reactivity that can be chemically tuned in a predictable manner. The additives used for this reaction are commercially available, making the new chemistry highly accessible. The new precursor chemistry represents a new paradigm for QD growth: chemically-induced precursor conversion. We show that the new precursor allows systematic growth of high quality QDs of various sizes and materials for both core-only and core-shell QDs. Moreover, a close examination of the growth results provided invaluable insight into the nanoparticle growth process, enabling logical tuning of the reaction condition. We also show that this new precursor chemistry employs completely different reaction mechanisms for nucleation and growth. By effectively separating growth and nucleation even at a high concentration of precursors, the new precursor allows heat-up-based growth of high quality shells that are comparable to those created by the injection method. Our study inspires the design of other precursors to systematically grow high quality nanocrystals and achieve the heat-up-based growth of high quality shells, a highly economical and scalable approach for large-scale synthesis.

Characterization of functionalized coatings prepared from pulsed plasma polymerization

Material assembly based on elastomer part and metallic substrate has been widely used in many industrial sectors. However, the adhesion between the two materials requests specific processes and adhesives. Plasma technology is an interesting way to prepare the assembly since the plasma polymer layers used for the adhesive joint can bear different reactive chemical functions toward the elastomer. Three different plasma coatings are synthesized from acetylene, acrylic acid, and maleic anhydride plasma because of their respective chemical functions able to open the carbon-carbon double bond of the elastomer (rubber, fluoroelastomer). For such a purpose, fine-tuning of plasma parameters was essential to preserve the precursor chemistry and to avoid any degradation. Pulsed plasma discharge was selected, plasma parameters defined thanks to the design of experiment. The different plasma polymers were characterized by FTIR, XPS and NEXAFS spectroscopies and surface energy measurement.

Origin of minerals in åkermanite-rich patch texture and oxygen isotopic evolution of compact Type A Ca-Al-rich inclusions from the Northwest Africa 7865 CV chondrite

We report the in-situ oxygen isotopic distributions corresponding to the petrographic-mineralogical observation on a compact Type A (CTA) Ca-Al-rich inclusion (CAI), KU-N-02, from a reduced CV3 chondrite, Northwest Africa 7865. The CTA has an igneous texture and mainly consists of spinel, melilite, and Al-Ti-rich clinopyroxene (fassaite). Oxygen isotopic compositions of the constituent minerals plot along the carbonaceous chondrite anhydrous mineral line. The spinel grains are poikilitically enclosed in the melilite and fassaite and are uniformly 16O-rich (Δ17O = approximately − 23‰). The fassaite is texturally classified into two types: blocky fassaite and intergranular fassaite. The blocky fassaite crystals exhibit growth zoning as they change from Ti-rich to Ti-poor along the inferred directions of crystal growth from core to rim, while the oxygen isotopic compositions change from 16O-poor (Δ17O = approximately − 6‰) to 16O-rich (Δ17O = approximately − 23‰) with crystal growth. The intergranular fassaite crystals exist between the melilite crystals and exhibit variable Ti abundance and oxygen isotopic compositions. Additionally, their relationships between Ti contents and oxygen isotopic composition are similar to those of the blocky fassaite. The melilite grains are homogeneously 16O-poor (Δ17O = approximately − 2‰), irrespective of their åkermanite (Åk) content. Each melilite grain generally exhibits growth zoning with increasing Åk contents from core to rim, although the melilite contains Åk-rich patches within single crystal. Åk-rich patches often include two types of fassaite: small blebby crystals attached to spinel crystals and round crystals. The oxygen isotopic compositions of the Åk-rich patch and blebby fassaite are 16O-poor (Δ17O = approximately − 2‰), similar to that of the host melilite. On the other hand, the round fassaite exhibits significant variation in oxygen isotopic compositions ranging from Δ17O = −23‰ to − 4‰, which are different from those of the host melilite. These petrographic textures and oxygen isotopic variations indicate the presence of a solid precursor with variable oxygen isotopic compositions for the CTA. The spinel and round fassaite grains are relicts of the precursor that melted in the 16O-poor nebular gas, resulting in the crystallization of the host melilite from the 16O-poor melt. The Åk-rich patches and blebby fassaite crystallized from melts trapped by the growing host melilite crystals. The blocky and intergranular fassaite crystallized after the melilite did, and the oxygen isotopic composition of the melt changed to 16O-rich during the crystallization process, suggesting that the oxygen isotopic composition of the surrounding nebular gas could be varied. The inferred oxygen isotopic evolution for CTA is consistent with those inferred for Type B CAIs, suggesting that coarse-grained igneous CAIs formed in a similar nebular environment regardless of precursor chemistry.

Role of the Precursor Composition in the Synthesis of Metal Ferrite Nanoparticles.

Ternary oxide nanoparticles have attracted much interest because of their intriguing properties, which are not exhibited by binary oxide nanoparticles. However, the synthesis of ternary oxide nanoparticles is not trivial and requires a fundamental understanding of the complicated precursor chemistry that governs the formation mechanism. Herein, we investigate the role of the chemical composition of precursors in the formation of ternary oxide nanoparticles via a combination of mass spectrometry, electron microscopy with elemental mapping, and thermogravimetric analysis. Mn2+, Co2+, and Ni2+ ions easily form bimetallic-oxo clusters with Fe3+ ions with a composition of MFe2O(oleate)6 (M = Mn, Co, Ni). The use of clusters as precursors leads to the successful synthesis of monodisperse metal ferrite nanoparticles (MFe2O4). On the contrary, zinc- or copper-containing complexes are formed independently from iron-oxo clusters in the precursor synthesis. The mixture of complexes without a bimetallic-oxo core yields a mixture of two different nanoparticles. This study reveals the importance of the precursor composition in the synthesis of ternary oxide nanoparticles.

Effect of PAA-induced surface etching on the adhesion properties of ZnO nanostructured films

Zinc oxide - polymer interfaces are known to exhibit interesting properties regarding molecular adhesion. This work is aimed at the investigation of the effect of the morphology and surface chemistry on the macroscopic adhesion of a model epoxy-based adhesive to nanorod (ZnO NR) and nanocrystalline (ZnO NC) ZnO-modified surfaces. Both ZnO films have been prepared using hydrothermal synthesis on hot-dip galvanized steel (HDG) surfaces by varying the precursor chemistry in order to control the film morphology. Poly (acrylic acid) (PAA) was used to improve the interfacial adhesion by modifying the morphology and surface chemistry of ZnO nanostructured films. The strong interaction of PAA from a dilute and neutral aqueous solution with the ZnO nanocrystallites was shown to significantly improve the interfacial adhesion by means of a nanoetching process. It was shown that the wet peel-forces correlate well with the considered morphology and surface chemistry.

Tunable SiO2 to SiOxCyH films by ozone assisted chemical vapor deposition from tetraethylorthosilicate and hexamethyldisilazane mixtures

Silica and silica-based materials with tunable functionalities are frequently encountered in low-k material applications, porous membranes, and microelectonic devices. In the present study, an innovative O2/O3 assisted CVD process for the deposition of such films at moderate temperature is presented, based on a dual precursor chemistry from hexamethyldisilazane (HMDS) and tetraethyl orthosilicate (TEOS). Films with tunable carbon content were obtained through variation of the HMDS flow ratio. A comprehensive FT-IR study reveals the transition of the material from a SiOxCyH type film containing -CH3 moieties, to a methyl-free SiOx film with the increase of the temperature. At the same time the water contact angle of 81.0° at 400 °C is decreased to 52.8° at 550 °C, related to the absence of methyl moieties in the latter. Ion beam analysis (IBA) confirms the lack of carbon in the films when deposition temperatures are equal to or exceed 500 °C. The resistance to liquid corrosion is investigated as a function of the deposition temperature; SiOx type films present a low Pliskin etching rate of 15 Å.s−1, with this value increasing to 60 Å.s−1 for the SiOxCy:CH3 films produced at the lower temperatures. It is found that the addition of HMDS to a TEOS chemistry can be utilized to modulate the film composition from SiOx to SiOxCyH and by such, tune the film functional properties, in particular its etching rate, opening the way to the development of new sacrificial films.

Rapid Annealing of Perovskite Solar Cells through Intense Pulsed Light

The perovskite solar technology has managed a fair amount of excitement since it was first introduced nearly ten years ago by Miyasaka’s group. The efficiency of small devices has increased rapidly from the 3.8% reported by Miyasaka to well over 20%. The efficiency now stands near that of the market dom,inated crystalline silicon solar cell, and the durability has been demonstrated for upwards of 1,000 hours. The organo-metal halide perovskite that is the core layer of the perovskite solar cell can be deposited using simple solution phase processes at low temperatures. The materials tend to have very high defect tolerances and hence have long excited charge carrier lifetimes. The excitement in the research and manufacturing communities’ centers around the simplicity of the device fabrication. Other layers within the stack also lead to simple solution phase deposition and low temperature processing.The deposition of the perovskite material generally involves a precursor chemistry that undergoes evaporation and crystallization. The crystallization typically involves thermal energy often at temperatures less than 100 oC. The activation energy of the organo-metal halide perovskite crystallization is very low especially when compared to that of amorphous silicon. Thus annealing is typically accomplished using low temperatures conduction (hot plates); however, several studies using radiative processes inducing much higher temperatures have also been established.These radiative processes include the intense pulsed light process (IPL). The IPL process involves the absorption of light energy into a thin film from an intense rapid pulse with a broad spectrum that can cover large areas. A thin film with absorptivity within the spectrum of light will absorb the energy, which is then rapidly transformed into thermal energy. The technology has been utilized in processing polymers, metals, metal oxides and semiconductors since the 1970’s and was recently reviewed specifically for materials in the photovoltaic technologies. The advantage of this technique for plastic substrates is that it can initiate very high temperatures within a thin film without damage to the underlying substrate.In this work we will describe the intense pulsed light process as it relates to the annealing of perovskite solar cells on plastic substrates on a roll-to-roll manufacturing line. The work will include the description of careful control of the IPL process parameters and the impact on the crystallization of the perovskite layer. The talk will concentrate on the tuning the IPL parameters to fit into high speed roll-to-roll applications. The films are characterized using UV-Vis spectroscopy, x-ray diffraction and scanning electron microscopy. Finally, devices built on the roll-to-roll platform will be discussed.

Hierarchical Structures from Nanocrystalline Colloidal Precursors within Hybrid Perovskite Thin Films: Implications for Photovoltaics

Originating from stochastic nanocrystalline colloidal precursors with differential chemical compositions, crystalline thin films exhibit hierarchical structures originating at the crystallographic level and scaling up to mesoscale structures, manifested within their nanocrystalline morphology and mesoscale topology. We interlink morphogenetic signatures within thin films to differential precursor chemistry and explain the cooperative impact of structure-defining inorganic and organic counterparts on perovskite hybrids. Understanding the effect of chemical species on the structural characteristics of thin films and leveraging complex assembly processes present facile routes to tuning multiscale morphologies in thin films, pertinent for engineering functional performance metrics within thin-film perovskite photovoltaics.

Controllable modulation of precursor reactivity using chemical additives for systematic synthesis of high-quality quantum dots

The optical and electronic performance of quantum dots (QDs) are affected by their size distribution and structural quality. Although the synthetic strategies for size control are well established and widely applicable to various QD systems, the structural characteristics of QDs, such as morphology and crystallinity, are tuned mostly by trial and error in a material-specific manner. Here, we show that reaction temperature and precursor reactivity, the two parameters governing the surface-reaction kinetics during growth, govern the structural quality of QDs. For conventional precursors, their reactivity is determined by their chemical structure. Therefore, a variation of precursor reactivity requires the synthesis of different precursor molecules. As a result, existing precursor selections often have significant gaps in reactivity or require synthesis of precursor libraries comprising a large number of variants. We designed a sulfur precursor employing a boron-sulfur bond, which enables controllable modulation of their reactivity using commercially available Lewis bases. This precursor chemistry allows systematic optimization of the reaction temperature and precursor reactivity using a single precursor and grows high-quality QDs from cores of various sizes and materials. This work provides critical insights into the nanoparticle growth process and precursor designs, enabling the systematic preparation of high-quality QD of any sizes and materials.

Tert-butoxides as precursors for atomic layer deposition of alkali metal containing thin films

Alkali metal containing materials have become increasingly attractive in a world hunting for sustainable energy materials and green functional devices. Lithium- and sodium battery technology, lead-free piezo- and ferroelectric devices, and record-breaking alkali doped tandem perovskite solar cells are among the applications where alkali metal-containing thin films get increasing attention. Atomic layer deposition (ALD) is one of the enabling thin film deposition techniques that offer chemical and geometrical versatility to realize the implementation of such thin films on an applicable scale. The drawback has until recently been a lack of available precursor chemistry that offers self-limiting growth that is fundamental to ALD. The alkali metal tert-butoxides have been shown to exhibit the necessary properties to facilitate saturating growth for Li-, Na-, K-, and Rb-containing compounds. However, the behavior of the tert-butoxides in ALD-growth has been considered difficult to unravel, with processes exhibiting limited control and low reproducibility. Very little has been reported on trends in reaction mechanisms as the mass of the alkali metal increases. Herein, we summarize the existing literature on the use of alkali metal tert-butoxides as precursors in ALD. We consider differences in the structure and behavior of the tert-butoxides as the alkali metal cation becomes heavier. In addition, we present precursor synthesis routes and key information on precursor structure, stability, and mechanistic behavior. Finally, we provide the first ever report of Cs-containing films by ALD to complement previous work on its lighter counterparts.

Editorial: Biographical Memoirs, Volume 69

Editorial: Biographical Memoirs, Volume 69

Understanding the precursor chemistry for one-step deposition of mixed cation perovskite solar cells by methylamine route

Upscaling perovskite solar cell fabrication is one of the key challenges in the pathway for commercialization. The slow evaporation of frequently used solvents (DMF or DMSO) limits the fast perovskite layer crystallization, hindering their implementation in large scale deposition methods. Alternatively, methylamine-based precursors have demonstrated rapid crystallization, leading to uniform and specular films. Nonetheless, their application has been limited to MAPbI3 perovskites with limited efficiency and stability. In this work, we report the requirements for stabilizing α-phase of mixed cation perovskites with high amount of formamidinium by using a methylamine-based precursor. We found that even though, there are many methods for incorporating the methylamine (MA) in precursors or films; the MA content determines stabilization of the α-phase and therefore the viscous-solution route is the only method to incorporate high amounts of MA. At low amounts of MA, perovskite tend to crystallize in 1D dimensional FA3(MA)PbI5 phases due to the incomplete solvation of the PbI6− clusters. In contrast, high MA ratio induces a full solvation of the clusters, leading to a rapid crystallization and a full stabilization of the active 3D α-phase. These results open a window in the development and understanding of new precursors for the fabrication of high efficient, stable and scalable perovskite devices.

Paul O'Brien. 22 January 1954—16 October 2018

Paul O'Brien, known affectionately as ‘POB’, was one of the most imaginative and creative materials chemists of his generation. He brought a deep understanding and knowledge of classical coordination chemistry to bear on routes to thin films and nanoparticles of technologically important materials, particularly metal chalcogenides. His development of molecular precursor chemistry as a method to produce very high quality materials safely, inexpensively and on a large scale laid the foundations for the successful technological exploitation of quantum dots. Paul had a compendious knowledge of science, particularly inorganic chemistry, and was passionate about the exploitation of science and engineering to improve society, both in the UK and around the world, most notably in Africa. He was a wonderful raconteur, and a great counsellor to his many friends, and a source of endless jokes (many of them bad). His greatest passion was science, yet somehow he also found time for other interests, including reading, hill-walking and camping, theatre and football. Paul was diagnosed with glioblastoma multiforme on his sixty-fourth birthday in January 2018, and this led to his retirement in July 2018 and his appointment as Emeritus Professor at the University of Manchester. He approached his illness with his usual scientific curiosity and optimism. He passed away peacefully with his beloved wife Kym by his side.

Nanocrystal Precursor Incorporating Separated Reaction Mechanisms for Nucleation and Growth to Unleash the Potential of Heat-up Synthesis.

A heat-up method for quantum dots (QDs) synthesis holds distinctive benefits for large-scale production with its simplicity, scalability, and high reproducibility. Its applications, however, have been limited because it inevitably yields a strong overlap between the nucleation and the growth stages. We addressed this long-standing problem by introducing a precursor having separated reaction paths for nucleation and growth. Unlike existing precursors, which employ a shared intermediate for both reactions, 9-mercapto-9-borabicyclo[3.3.1]nonane (BBN-SH) induces growth via surface-assisted conversion and drives nucleation via cluster formation in solution. Furthermore, this precursor chemistry embeds an efficient mechanism to suppress nucleation during growth. As such, BBN-SH allows heat-up-based growth of high-quality shells that are comparable to those created by the injection method. It is also notable that BBN-SH-based heat-up synthesis shows mitigated sensitivity to temperature fluctuation; therefore, it is highly suitable for industrial-scale reactions. We established a simple, scalable, and economic scheme for core/shell QDs by streamlining quantitative core synthesis and heat-up-based shell growth and showed that the scheme produces QDs of comparable quality to those produced by the traditional method. Here, we introduce a precursor that drives a distinctive mode of nanoparticle growth. We anticipate our study to inspire the design of other precursors and unleash the full potential of heat-up synthesis.

Effect of Multilayer versus Monolayer Dodecanethiol on Selectivity and Pattern Integrity in Area-Selective Atomic Layer Deposition.

Monolayer and multilayer dodecanethiols (DDT) can be assembled onto a copper surface from the vapor phase depending on the initial oxidation state of the copper. The ability of the copper-bound dodecanethiolates to block atomic layer deposition (ALD) and the resulting behavior at the interfaces of Cu/SiO2 patterns during area-selective ALD (AS-ALD) are compared between mono- and multilayers. We show that multilayer DDT is ∼7 times more effective at blocking ZnO ALD from diethylzinc and water than is monolayer DDT. Conversely, monolayer DDT exhibits better performance than does multilayer DDT in blocking of Al2O3 ALD from trimethylaluminum and water. Investigation into interfacial effects at the interface between Cu and SiO2 on Cu/SiO2 patterns reveals both a gap at the SiO2 edges and a pitch size-dependent nucleation delay of ZnO ALD on SiO2 regions of multilayer DDT-coated patterns. In contrast, no impact on ZnO ALD is observed on the SiO2 regions of monolayer DDT-coated patterns. We also show that these interfacial effects depend on the ALD chemistry. Whereas an Al2O3 film grows on the TaN diffusion barrier of a DDT-treated Cu/SiO2 pattern, the ZnO film does not. These results indicate that the structure of the DDT layer and the ALD precursor chemistry both play an important role in achieving AS-ALD.

LiF by atomic layer deposition—Made easy

Lithium fluoride (LiF) is an integral part of UV optics. Recently, it has also gained attention for its role in the solid-electrolyte interphase on the anode of lithium-ion batteries. Atomic layer deposition (ALD) is the preferred tool for synthesizing conformal and pin-hole free LiF thin films, especially on high aspect ratio structures. Present routes to deposit LiF by ALD are based on HF or HF-pyridine as the fluorine source, requiring strict safety precautions. Other routes involve TiF4 or WF6, resulting in inclusions of Ti or W impurities in the resulting films. Herein, we present a new route to deposit LiF by ALD, using lithium tert-butoxide (LiOtBu) and NH4F as precursors. The process yields uniform films over a broad temperature range (150–300 °C), with a growth per cycle of 50.9 pm/cycle (225 °C). The films are free from any nitrogen contamination from the NH4F precursor. This process provides a facile route for high purity LiF thin films with the use of less harmful precursor chemistry.

Discovering Biomass Structural Determinants Defining the Properties of Plant-Derived Renewable Carbon Fiber

SummaryTraditional lignocellulosic feedstock research has focused on biomass characteristics essential for improving saccharification efficiency, yet the key biomass features underlying high-quality renewable lignin materials remain unknown. Nevertheless, modern biorefinery cannot achieve sustainability and cost-effectiveness unless the lignin stream can be valorized. We hereby addressed these scientific gaps by investigating biomass characteristics defining lignin-based carbon materials properties. Lignin from eight sorghum samples with diverse characteristics was fabricated into carbon fibers (CFs). Remarkably, only lignin uniformity was found to define CF mechanical performance, highlighting the new structure-property relationship. Contrarily, lignin content and composition did not impact on carbon material properties. Mechanistic study by XRD and Raman spectroscopy revealed that higher lignin uniformity enhanced CF microstructures, in particular, turbostratic carbon content. The study for the first time highlighted lignin uniformity as an important biomass structure determinant for renewable products, which opened up new avenues for feedstock design toward diverse products enabling sustainable and cost-effective bioeconomy.