Precursor Vapor Research Articles

Atomic layer deposition of nanofilms on porous polymer substrates: Strategies for success

Atomic layer deposition (ALD) is a versatile technique for engineering the surfaces of porous polymers, imbuing the flexible, high-surface-area substrates with inorganic and hybrid material properties. Previously reported enhancements include fouling resistance, electrical conductance, thermal stability, photocatalytic activity, hydrophilicity, and oleophilicity. However, there are many poorly understood phenomena that introduce challenges in applying ALD to porous polymers. In this paper, we address five common challenges and ways to overcome them: (1) entrapped precursor, (2) embrittlement, (3) film fracture, (4) deformation, and (5) pore collapse. These challenges are often interrelated and can exacerbate one another. To investigate these phenomena, we applied various ALD chemistries to porous polymers including polyethersulfone, polysulfone, polyvinylidene fluoride, and polycarbonate track-etched membranes. Reaction-diffusion modeling revealed why certain precursors and processing conditions result in embrittling subsurface material growth, entrapment of unreacted precursors, and nongrowth. We quantify the limits of ALD processing temperatures that are dictated by thermal expansion mismatch and can lead to fractured ALD films. The results herein allow us to make recommendations to avoid, mitigate, or overcome the difficulties encountered when performing ALD and plasma-enhanced ALD on porous polymers. We intend this article to serve as a “lessons learned” guide informed by previous experience to provide a better understanding of the difficulties and limitations of ALD on porous polymers and knowledge-based guidelines for successful depositions. This knowledge can accelerate future research and help experimentalists navigate and troubleshoot as they expose porous polymers to reactive precursor vapors.

Molecular Mechanisms of Aerosol Nucleation: from CLOUD Chamber Experiments to Field Observations

Atmospheric aerosol particles contribute to over four million premature deaths annually and play a critical role in modulating Earth’s climate. Most atmospheric particles and more than 50% of the cloud condensation nuclei are formed through a secondary process named new particle formation involving unique precursor vapors. This article summarizes current knowledge of how new atmospheric particles form, based on experiments at the CERN CLOUD chamber. While the role of sulfuric acid has long been known, other vapors like highly oxygenated organic molecules and iodine oxoacids are also important, along with stabilizers like ammonia, amines, and ions from cosmic rays. We explain how findings from CLOUD experiments help us understand particle formation in various atmospheric conditions and improve air quality and climate models.

Precursor Vapor Pressure Estimation and Precise QCM Measurement for ALD Process Development with Ideal ALD Characteristics

Atomic Layer Deposition (ALD) produces thin films by alternately supplying precursors and reaction gases. In this process, a film with one atomic layer or fewer is formed in a single cycle. By properly controlling the number of cycles, the film thickness can be precisely controlled and reproducible film formation is possible. This technology is widely used in the production of semiconductor integrated circuits (ULSIs). The amount of growth per cycle is called GPC, and it is well known that GPC remains constant over a temperature range known as the ALD Window, within which ideal ALD film-formation characteristics can be obtained. Therefore, a wide ALD window is important for constructing an easy-to-use ALD process. The GPC is constant in the ALD Window because the coverage factor of the chemisorbed precursor is nearly unity. Therefore, it is necessary to consider the conditions under which saturated chemisorption occurs during the adsorption process of the precursor. The surface coverage factor depends on the adsorption constant K and precursor concentration C according to the "Langmuir-Hinshelwood equation," as shown below.θ=KC/(1+KC)If the product of the adsorption equilibrium constant K and the precursor concentration C is large (e.g., 100 or more), the coverage factor θ is almost constant at unity, even at different substrate surface temperatures; that is, even if the values of K differ slightly, or even if the concentration C differs slightly between the center and the edge of the wafer. This is the main reason for the good thickness reproducibility and uniformity of the ALD process.We developed a method to precisely estimate the precursor concentration, that is, the saturated vapor pressure, using quantum chemical calculations (the Modified COSMO-SAC method). This allowed us to identify compounds that could be supplied at appropriate concentrations as ALD precursors. This vapor pressure estimation is also effective for constructing the Atomic Layer Etching (ALE) process.The adsorption equilibrium constant K of the precursor can be determined by quantum chemical calculations; however, this is time-consuming and computationally expensive. For the synthesized precursor compounds, the adsorption equilibrium constant K can be easily determined experimentally using precise Quartz Crystal Microbalance (QCM) measurements. As QCM is very sensitive to the temperature change, we have specially made “AT cut” Quartz Crystal which is insensitive to the temperature fluctuation at the desired temperature. The combination of a custom-made oscillation circuit for the above AT cut crystal and a frequency counter enables measurement of weight change with a sensitivity of 0.3 ng/cm2 or less and measurement of weight change over time due to adsorption or reaction with high time resolution of 20 points/sec. We combined these calculations with experiments to develop ALD systems that exhibit ideal ALD properties.

The annual cycle and sources of relevant aerosol precursor vapors in the central Arctic during the MOSAiC expedition

Abstract. In this study, we present and analyze the first continuous time series of relevant aerosol precursor vapors from the central Arctic (north of 80° N) during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. These precursor vapors include sulfuric acid (SA), methanesulfonic acid (MSA), and iodic acid (IA). We use FLEXPART simulations, inverse modeling, sulfur dioxide (SO2) mixing ratios, and chlorophyll a (chl a) observations to interpret the seasonal variability in the vapor concentrations and identify dominant sources. Our results show that both natural and anthropogenic sources are relevant for the concentrations of SA in the Arctic, but anthropogenic sources associated with Arctic haze are the most prevalent. MSA concentrations are an order of magnitude higher during polar day than during polar night due to seasonal changes in biological activity. Peak MSA concentrations were observed in May, which corresponds with the timing of the annual peak in chl a concentrations north of 75° N. IA concentrations exhibit two distinct peaks during the year, namely a dominant peak in spring and a secondary peak in autumn, suggesting that seasonal IA concentrations depend on both solar radiation and sea ice conditions. In general, the seasonal cycles of SA, MSA, and IA in the central Arctic Ocean are related to sea ice conditions, and we expect that changes in the Arctic environment will affect the concentrations of these vapors in the future. The magnitude of these changes and the subsequent influence on aerosol processes remains uncertain, highlighting the need for continued observations of these precursor vapors in the Arctic.

Role of Organic Vapor Precursors in Secondary Organic Aerosol Formation: Concurrent Observations of IVOCs and VOCs in Guangzhou

AbstractSecondary organic aerosol (SOA) formed through the atmospheric transformation of organic vapors constitutes a significant portion of fine particulate matter or PM2.5. While recent laboratory studies underscore the importance of intermediate‐volatility organic compounds (IVOCs) as key precursors to SOA, field observations that recognize the role of both volatile organic compounds (VOCs) and IVOCs in SOA formation remain scarce. In this study, we conducted concurrent measurements of VOCs and IVOCs in ambient air at urban and suburban sites in Guangzhou during a PM2.5 pollution event in winter 2021. The results reveal that between 12:00–15:00 local time, the photochemically adjusted initial concentrations of VOCs at both sites were approximately 7 times higher than that of IVOCs. However, the SOA formation potential (SOAFP) of primary hydrocarbon IVOCs exceeded that of VOCs by over 3–4 times. Receptor modeling results further indicated that while ship emissions contributed to less than 10% of the C2–C22 primary hydrocarbons concentration (VOCs + primary carbonaceous IVOCs), they accounted for the most significant source (approximately 40%) of SOA formation. This study highlights the substantial role of IVOCs in SOA formation and emphasizes the importance of future PM2.5 pollution control measures targeting major IVOCs contributors, such as ship emissions in harbor cities.

Ag/CNT Catalyst Synthesized by Plasma-Enhanced Atomic Layer Deposition for Anion Exchange Membrane Fuel Cells

Anion exchange membrane fuel cells (AEMFCs) have recently gained attention as a viable alternative to proton exchange membrane fuel cells (PEMFC), offering the potential for high output without relying on expensive platinum (Pt) catalysts. PEMFCs operate in an acidic environment characterized by a high concentration of H+, necessitating the use of platinum-based catalysts to ensure both performance and stability in such conditions. In contrast, AEMFCs operate in an alkaline environment (OH-), affording the use of high-performance catalysts like silver (Ag), which is sensitive to acidity. Moreover, the cost of Ag is approximately 1/50 of Pt, offering significant cost advantages for fuel cell commercialization. Atomic layer deposition (ALD) has garnered substantial attention as a valuable technique for crafting high-performance nano-catalysts. ALD's self-limiting nature, based on the sequential exposure of vaporized precursors and reactants, enables precise control over catalyst size and composition. In this study, we employed plasma-enhanced ALD (PEALD) to fabricate cutting-edge AEMFC cathodes comprised of carbon nanotubes (CNTs) adorned with Ag. This approach yielded impressive results, achieving an AEMFC output exceeding 300 mW cm-2 or more than 2 W mgAg -1 at 65 °C with a CNT cathode featuring an exceedingly low Ag loading of less than 0.15 mg cm-2. Notably, this represents the world's highest reported Ag-AEMFC performance to date. The Ag-decorated cathode created through ALD played a pivotal role in significantly reducing resistance in the polarization region, a major contributor to overall energy losses in AEMFCs. Additionally, when evaluating the durability of the Ag-decorated CNT anode in an alkaline environment, we observed excellent long-term stability. In this presentation, we will discuss a more detailed exploration of the relationship between AEMFC performance, featuring ALD-fabricated Ag-CNT catalysts, and the intricate catalyst structure.

HfTiO4 transparent thick film phosphors activated with Eu3+, Dy3+, and Tb3+ ions

Hafnium (Hf)-based double oxides show promise as high-efficiency scintillators due to large effective atomic numbers and high relative density. However, the preparation of these scintillation crystals is challenging due to their high melting points and incongruent melting behavior. In the present study, we demonstrated that the chemical vapor deposition (CVD) of single-phase HfTiO4 films on quartz glass substrate was successfully deposited at temperatures ranging from 973 to 988 K, with a TiO2 molar ratio in the precursor vapor of 25–45 mol% TiO2. The deposition rate of HfTiO4 reached 36 µm h−1. The films exhibited an in-line transmittance of 78 % relative to the raw glass substrate at a wavelength of 600 nm. When activated with Eu3+, Dy3+, and Tb3+ ions, the HfTiO4 films displayed red, yellow, and green photoluminescence emissions originated from the 4f–4f transitions of each trivalent rare-earth ion under ultraviolet light irradiation. HfTiO4 exhibited no intrinsic background emission, suggesting that the addition of a selected activator could yield a phosphor with the desired emission color range.

Comparative Ablation Behaviors of 2D Needled C/SiC and C/SiC-ZrC Composites

To investigate the effect of ZrC on the ablative properties of C/SiC composites in a high-temperature environment, the oxidative ablation of C/SiC and C/SiC-ZrC composites at high-temperatures was examined through ablation tests. In this study, two ceramic matrix composites, C/SiC and C/SiC-ZrC, were prepared by chemical vapor deposition and precursor impregnation pyrolysis. The ablation properties of the materials were tested and analyzed using an oxyacetylene flame to simulate a high-temperature environment. The results revealed that the line ablation rate of C/SiC-ZrC was 8.48% and 20.81% lower than that of C/SiC at 30 s and 60 s, respectively. At the same ablation time, the depth of the crater resulting from erosion of the C/SiC material by the high-temperature airflow was deeper than that of C/SiC-ZrC. The traces of the fibers subjected to erosion were more prominent. In a longitudinal comparison, the mass ablation rate of C/SiC-ZrC material decreased with the increase in time, while the line ablation rate initially increased rapidly and then decreased. From 30 s to 90 s of ablation, the line ablation rate and mass ablation rate decreased by 55.62% and 89.5%, respectively. The overall trend for both rates was a decrease with the increase in time. Under the same ablation time, the ablation rate of C/SiC-ZrC was generally lower than that of C/SiC. This is because the generated molten ZrO2 was more viscous and denser than SiO2, effectively blocking oxidizing gases from penetrating the interior of the material. The molten ZrO2 provided better protection for the substrate in the high-temperature environment.

Tuning Nanopores in Tubular Ceramic Nanofiltration Membranes with Atmospheric-Pressure Atomic Layer Deposition: Prospects for Pressure-Based In-Line Monitoring of Pore Narrowing

Atomic layer deposition (ALD) is known for its unparalleled control over layer thickness and 3D conformality and could be the future technique of choice to tailor the pore size of ceramic nanofiltration membranes. However, a major challenge in tuning and functionalizing a multichannel ceramic membrane is posed by its large internal pore volume, which needs to be evacuated during ALD cycling. This may require significant energy and processing time. This study presents a new reactor design, operating at atmospheric pressure, that is able to deposit thin layers in the pores of ceramic membranes. In this design, the reactor wall is formed by the industrial tubular ceramic membrane itself, and carrier gas flows are employed to transport the precursor and co-reactant vapors to the reactive surface groups present on the membrane surface. The layer growth for atmospheric-pressure ALD in this case proceeds similarly to that for state-of-the-art vacuum-based ALD. Moreover, for membrane preparation, this new reactor design has three advantages: (i) monolayers are deposited only at the outer pore mouths rather than in the entire bulk of the porous membrane substrate, resulting in reduced flow resistances for liquid permeation; (ii) an in-line gas permeation method was developed to follow the layer growth in the pores during the deposition process, allowing more precise control over the finished membrane; and (iii) expensive vacuum components and cleanroom environment are eliminated. This opens up a new avenue for ceramic membrane development with nano-scale precision using ALD at atmospheric pressure.

Sublimation-based wafer-scale monolayer WS2 formation via self-limited thinning of few-layer WS2.

Atomically-thin monolayer WS2 is a promising channel material for next-generation Moore's nanoelectronics owing to its high theoretical room temperature electron mobility and immunity to short channel effect. The high photoluminescence (PL) quantum yield of the monolayer WS2 also makes it highly promising for future high-performance optoelectronics. However, the difficulty in strictly growing monolayer WS2, due to its non-self-limiting growth mechanism, may hinder its industrial development because of the uncontrollable growth kinetics in attaining the high uniformity in thickness and property on the wafer-scale. In this study, we report a scalable process to achieve a 4 inch wafer-scale fully-covered strictly monolayer WS2 by applying the in situ self-limited thinning of multilayer WS2 formed by sulfurization of WOx films. Through a pulsed supply of sulfur precursor vapor under a continuous H2 flow, the self-limited thinning process can effectively trim down the overgrown multilayer WS2 to the monolayer limit without damaging the remaining bottom WS2 monolayer. Density functional theory (DFT) calculations reveal that the self-limited thinning arises from the thermodynamic instability of the WS2 top layers as opposed to a stable bottom monolayer WS2 on sapphire above a vacuum sublimation temperature of WS2. The self-limited thinning approach overcomes the intrinsic limitation of conventional vapor-based growth methods in preventing the 2nd layer WS2 domain nucleation/growth. It also offers additional advantages, such as scalability, simplicity, and possibility for batch processing, thus opening up a new avenue to develop a manufacturing-viable growth technology for the preparation of a strictly-monolayer WS2 on the wafer-scale.

Impact of desert dust on new particle formation events and the cloud condensation nuclei budget in dust-influenced areas

Abstract. Detailed knowledge on the formation of new aerosol particles in the atmosphere from precursor gases, and their subsequent growth, commonly known as new particle formation (NPF) events, is one of the largest challenges in atmospheric aerosol science. High pre-existing particle loadings are expected to suppress the formation of new atmospheric aerosol particles due to high coagulation and condensation (CS) sinks. However, NPF events are regularly observed in conditions with high concentrations of pre-existing particles and even during intense desert dust intrusions that imply discrepancies between the observations and theory. In this study, we present a multi-site analysis of the occurrence of NPF events under the presence of desert dust particles in dust-influenced areas. Characterization of NPF events at five different locations highly influenced by desert dust outbreaks was done under dusty and non-dusty conditions using continuous measurements of aerosol size distribution in both fine and coarse size fractions. Contrary to common thought, our results show that the occurrence of NPF events is highly frequent during desert dust outbreaks, showing that NPF event frequencies during dusty conditions are similar to those observed during non-dusty conditions. Furthermore, our results show that NPF events also occur during intense desert dust outbreaks at all the studied sites, even at remote sites where the amounts of precursor vapours are expected to be low. Our results show that the condensation sink associated with coarse particles (CSC) represents up to the 60 % of the total CS during dusty conditions, which highlights the importance of considering coarse-fraction particles for NPF studies in desert-dust-influenced areas. However, we did not find a clear pattern of the effect of desert dust outbreaks on the strength of NPF events, with differences from site to site. The particle growth rate (GR) did not present a clear dependence on the CS during dusty and non-dusty conditions. This result, together with the fact that desert dust has different effects on the growth and formation rates at each site, suggests different formation and growth mechanisms at each site between dusty and non-dusty conditions, probably due to differences in precursor vapours' origins and concentrations as well as changes in the oxidative capacity of pre-existing particles and their effectiveness acting as CS. Further investigation based on multiplatform measurement campaigns and chamber experiments with state-of-the-art gaseous and particulate physical and chemical properties measurements is needed to better understand the role of catalyst components present in desert dust particles in NPF. Finally, our results reveal a significant impact of NPF events on the cloud condensation nuclei (CCN) budget during desert dust outbreaks at the studied sites. Therefore, since desert dust contributes to a major fraction of the global aerosol mass load, and since there is a foreseeable increase in the frequency, duration and intensity of desert dust episodes due to climate change, it is imperative to improve our understanding of the effect of desert dust outbreaks on NPF and the CCN budget for better climate change prediction.

Enhancing growth of high-quality two-dimensional CsPbBr3 flakes on sapphire substrate by direct chemical vapor deposition method

Two-dimensional (2D) cesium lead halide (CsPbBr3) nanoflakes have attracted significant attention due to their exceptional optoelectronic properties. Herein, the direct chemical vapor deposition (CVD) method was employed to synthesize high-quality single-crystalline 2D CsPbBr3 flakes on a sapphire substrate using PbBr2 and CsBr precursors. The study offers a comprehensive analysis of the reaction mechanisms involved, including precursor vaporization, transport, decomposition, and subsequent reactions. These factors play a crucial role in modifying the growth process and achieving the desired properties of CsPbBr3 flakes on the sapphire substrate. Additionally, a detailed investigation was conducted into the position-dependent and power-dependent photoluminescence (PL) properties of CsPbBr3flakes on sapphire substrates. The results of this study contribute to the expanding knowledge base regarding the growth of 2D perovskite materials. Moreover, they open up avenues for future research and development in the field of advanced optoelectronics.

Process intensification of microplasma nanoparticle synthesis enabled by gas flow design

The wide range of practical uses for nanometer-size metal particles has motivated many lab-scale aerosol synthesis processes. It is well known that the aggregation dynamics of aerosol particles impose a trade-off between particle size and concentration: methods that achieve sub-10 nm particles without aggregation are generally limited by low concentration and low flow rates of order 100 cm3/min. Thus, the intensification of aerosol nanoparticle synthesis and its development for industrial use remains a unique and important manufacturing challenge. We present a microplasma reactor system that has been developed to improve process intensification and reliability. The system utilizes an atmospheric pressure DC microplasma to synthesize iron-carbon particles from a ferrocene vapor precursor. The microplasma incorporates a novel focusing technique using a spatial gradient in gas composition to stabilize short-term fluctuations in performance, achieving an iron yield of up to 0.93. We identify the build-up of deposits between the plasma electrodes as the primary cause of reduced performance over time, and eliminate this build-up by indirectly supplying ferrocene to avoid dissociation in this region of the reactor. Further, we show that the design and conditions downstream of the microplasma have a similar influence on the final particle size distribution as those of the microplasma itself. By tuning the coupled process variables of both the microplasma and this downstream region, we synthesize aerosols with mean diameter from 2 to 7 nm and number concentration of 2 to 8×109 #/cm3 at the system outlet.

J-GAIN v1.1: a flexible tool to incorporate aerosol formation rates obtained by molecular models into large-scale models

Abstract. New-particle formation from condensable gases is a common atmospheric process that has significant but uncertain effects on aerosol particle number concentrations and aerosol–cloud–climate interactions. Assessing the formation rates of nanometer-sized particles from different vapors is an active field of research within atmospheric sciences, with new data being constantly produced by molecular modeling and experimental studies. Such data can be used in large-scale climate and air quality models through parameterizations or lookup tables. Molecular cluster dynamics modeling, ideally benchmarked against measurements when available for the given precursor vapors, provides a straightforward means to calculate high-resolution formation rate data over wide ranges of atmospheric conditions. Ideally, the incorporation of such data should be easy, efficient and flexible in the sense that same tools can be conveniently applied for different data sets in which the formation rate depends on different parameters. In this work, we present a tool to generate and interpolate lookup tables of formation rates for user-defined input parameters. The table generator primarily applies cluster dynamics modeling to calculate formation rates from an input quantum chemistry data set defined by the user, but the interpolator may also be used for tables generated by other models or data sources. The interpolation routine uses a multivariate interpolation algorithm, which is applicable to different numbers of independent parameters, and gives fast and accurate results with typical interpolation errors of up to a few percent. These routines facilitate the implementation and testing of different aerosol formation rate predictions in large-scale models, allowing the straightforward inclusion of new or updated data without the need to apply separate parameterizations or routines for different data sets that involve different chemical compounds or other parameters.

Explaining apparent particle shrinkage related to new particle formation events in western Saudi Arabia does not require evaporation

Abstract. The majority of new particle formation (NPF) events observed in Hada Al Sham, western Saudi Arabia, during 2013–2015 showed an unusual progression where the diameter of a newly formed particle mode clearly started to decrease after the growth phase. Many previous studies refer to this phenomenon as aerosol shrinkage. We will opt to use the term decreasing mode diameter (DMD) event, as shrinkage bears the connotation of reduction in the sizes of individual particles, which does not have to be the case. While several previous studies speculate that ambient DMD events are caused by evaporation of semivolatile species, no concrete evidence has been provided, partly due to the rarity of the DMD events. The frequent occurrence and large number of DMD events in our observations allow us to perform statistically significant comparisons between the DMD and the typical NPF events that undergo continuous growth. In our analysis, we find no clear connection between DMD events and factors that might trigger particle evaporation at the measurement site. Instead, examination of air mass source areas and the horizontal distribution of anthropogenic emissions in the study region leads us to believe that the observed DMD events could be caused by advection of smaller, less-grown particles to the measurement site after the more-grown ones. Using a Lagrangian single-particle growth model, we confirm that the observed particle size development, including the DMD events, can be reproduced by non-volatile condensation and thus without evaporation. In fact, when considering increasing contributions from a semivolatile compound, we find deteriorating agreement between the measurements and the model. Based on these results, it seems unlikely that evaporation of semivolatile compounds would play a significant role in the DMD events at our measurement site. In the proposed non-volatile explanation, the DMD events are a result of the observed particles having spent an increasing fraction of their lifetime in a lower-growth environment, mainly enabled by the lower precursor vapor concentrations further away from the measurement site combined with decreasing photochemical production of condensable vapors in the afternoon. Correct identification of the cause of the DMD events is important as the fate and the climate relevance of the newly formed particles heavily depend on it – if the particles evaporated, their net contribution to larger and climatically active particle sizes would be greatly reduced. Our findings highlight the importance of considering transport-related effects in NPF event analysis, which is an often overlooked factor in such studies.

A systematical investigation of layer growth rate, impurity level and morphology evolution in TiO2 thin films grown by ALD between 100 and 300 °C

TiO2 thin films prepared by atomic layer deposition (ALD) have attracted great attention due to the widespread application of the oxide as a promising charge storage material for lithium or proton batteries. In this work, we study TiO2 film grown on Si substrates by atomic layer deposition with tetrakis (dimethylamino) titanium as metal precursor (TDMAT) and water vapour as an oxidant. The chemical composition and impurity content of the film as a function of growth temperature is studied by Ion Beam Analysis (IBA). D2O (99.8%) was used as oxidant to study the film growth to distinguish between hydrogen atoms originating from the water oxidant or the metal precursor. Combining ellipsometry with Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA) reveals film density as a function of growth temperature. Atomic force microscopy (AFM) was used to characterize the film surface structure. By investigating the structural and compositional range of ALD TiO2 films will open the new opportunities of application.

Controllable and universal anisotropic vapor–solid growth of vertical 2D metal chalcogenide nanoflakes with enhanced photoelectric and electrocatalytic properties

Epitaxial growth and subsequent processing of 2D materials are mostly confined to xy plane parallel to the substrate. Introducing another degree of freedom, i.e., the vertical direction perpendicular to the base plane, is very intriguing, as the resulting vertically aligned 2D materials will intuitively have a high aspect ratio, anisotropic structure, and abundant edge sites, holding great promise in field emission, photoelectronics, piezoelectricity, clean energy catalysis, etc. However, the key factors governing the spatially anisotropic growth to selectively obtain vertically or horizontally aligned 2D nanoflakes remain elusive. Herein, we report a controllable and general strategy to vertically grow representative 2D metal chalcogenide materials, including but not limited to SnS, SnSe, Bi2Se3, MoO3, and MoS2 nanoflakes, via a rapid heating–cooling process on various optional substrates. The rapid heating–cooling process allows rapid desublimation and nucleation of highly-supersaturated precursor vapor, leading to ultrafast growth of vertically aligned nanoflakes with exposed side surfaces and edges. As an example, the vertically grown SnS nanoflakes exhibit anisotropic spectroscopic features, superior photoelectric properties and enhanced electrocatalytic performances for the nitrate reduction and CO2 reduction reactions. This work provides a feasible approach to controllably synthesize versatile vertically aligned 2D metal chalcogenide nanoflakes on various substrates, which can advance the mechanistic understanding of anisotropic growth and physicochemical properties of 2D materials towards photoelectric devices and clean energy conversion.

Detecting nuclear spins in an organosilane monolayer using nitrogen-vacancy centers for analysis of precursor self-assembly on diamond surface

We demonstrated the correlation spectroscopy of organosilane monolayers using an ensemble of shallow nitrogen-vacancy centers as the quantum sensor. Several types of organosilane monolayers were grown directly on the diamond surface by exposing the surface to a silane precursor vapor. The feasibility of detecting 1H and 19F in the monolayer was examined by correlation spectroscopy measurements. The effect of the magnetic dipole–dipole interaction on the peak width was also discussed by comparing the spectrum of the monolayer with that of surface-attached 1H and that of immersion oil. The results highlight the feasibility of nitrogen-vacancy centers as the spin probe for physicochemical analyses of monolayers grown on the diamond surface.

Direct-Patterning ZnO Deposition by Atomic-Layer Additive Manufacturing Using a Safe and Economical Precursor.

Area-selective atomic layer deposition (AS-ALD) is a bottom-up nanofabrication method delivering single atoms from a molecular precursor. AS-ALD enables self-aligned fabrication and outperforms lithography in terms of cost, resistance, and equipment prerequisites, but it requires pre-patterned substrates and is limited by insufficient selectivity and finite choice of substrates. These challenges are circumvented by direct patterning with atomic-layer additive manufacturing (ALAM) - a transfer of 3D-printing principles to atomic-layer manufacturing where a precursor supply nozzle enables direct patterning instead of blanket coating. The reduced precursor vapor consumption in ALAM as compared with ALD calls for the use of less volatile precursors by replacing diethylzinc used traditionally in ALD with bis(dimethylaminopropyl)zinc, Zn(DMP)2 . The behavior of this novel ZnO ALAM process follows that of the corresponding ALD in terms of deposit quality and growth characteristics. The temperature window for self-limiting growth of stoichiometric, crystalline material is 200-250°C. The growth rates are 0.9Å per cycle in ALD (determined by spectroscopic ellipsometry) and 1.1Å per pass in ALAM (imaging ellipsometry). The preferential crystal orientation increases with temperature, while energy-dispersive X-ray spectroscopic and XPS show that only intermediate temperatures deliver stoichiometric ZnO. A functional thin-film transistor is created from an ALAM-deposited ZnO line and characterized.

Chitosan-coated iron oxide nanoparticles obtained by laser pyrolysis

The structural and magnetic properties of iron oxide nanoparticles (NPs) synthesized by laser pyrolysis, as well as their chitosan-stabilized aqueous suspensions were studied in regards to the ratio between O2 and Ar. During the synthesis, the flow of Fe(CO)5 precursor vapors and C2H4 sensitizer molecules was kept constant, while the ratio between O2 and Ar in the reactive mixture was increased (1:4, 1:2, 1:1, and 2:1). The formation of small particles (under 4 nm in size) was observed at lower O2 concentrations, whereas their mean crystallite size increased to ∼14 nm for those formed from the richest O2 content, which also induced the formation of particles with the highest magnetization saturation (101.4 emu/g). Maghemite and/or magnetite phases were identified as the main components in all samples, while a small amount of α iron/iron carbides presence was detected with the exception of sample obtained at 1:1 O2 to Ar ratio. The formation of these minor phases reveals the interplay between oxidative and reductive processes which depend on O2 content and C2H4 reactivity at different temperatures. After chitosan loading, all aqueous suspensions presented excellent stability (zeta potential values over 76 mV). Moreover, the samples stabilized using low polymer concentration (0.05 g/l) displayed relatively low hydrodynamic sizes (110–125 nm).