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A method and device for reducing ice and frost on a surface comprising a wettable pattern on a surface. The pattern is wetted with water which is frozen into ice to create overlapping hygroscopic that cover the surface.
Abstract not provided.
Key features of syntheses, involving the quaternary ammonium passivation of CsPbBr 3 nanocrystals (NCs), include stable, reproducible and large (often near-unity) emission quantum yields (QYs). The archetypical example involves didodecyl dimethyl ammonium (DDDMA + ) passivated CsPbBr 3 NCs where robust QYs stem from interactions between DDDMA + and NC surfaces. Despite widespread adoption of this synthesis, specific ligand-NC surface interactions responsible for large DDDMA + -passivated NC QYs have not been fully established. Multidimensional nuclear magnetic resonance experiments now reveal a new DDDMA + -NC surface interaction, beyond established “tightly-bound” DDDMA + interactions, which strongly affects observed emission QYs. Depending upon the existence of this new DDDMA + coordination, NC QYs vary broadly between 60% and 85%. More importantly, these measurements reveal surface passivation through unexpected didodecyl ammonium (DDA + ) that works in concert with DDDMA + , to produce near unity (i.e. >90%) QYs.
The ligand-nanocrystal boundaries of colloidal quantum dots (QDs) mediate the primary energy and electron transfer processes that underpin photochemical and photocatalytic transformations at their surfaces. We use mid-infrared transient absorption spectroscopy to reveal the influence that ligand structure and bonding to nanocrystal surfaces have on the changes of the excited state surface chemistry of this boundary in PbS QDs and the corresponding impact on charge transfer processes between nanocrystals. We demonstrate that oleate ligands undergo marked changes in their bonding to surfaces in the excitonic excited states of the nanocrystals, indicating that oleate passivated PbS surfaces undergo significant structural changes following photoexcitation. These changes can impact the surface mobility of the ligands and the ability of redox shuttles to approach the nanocrystal surfaces to undergo charge transfer in photocatalytic reactions. In contrast, markedly different transient vibrational features are observed in iodide/mercaptoproprionic acid passivated PbS QD films that result from charge transfer between neighboring nanocrystals and localization of holes at the nanocrystal surfaces near MPA ligands. This ability to distinguish the influence that excitonic excited states vs charge transfer processes have on the surface chemistry of the ligand-nanocrystal boundary lays the groundwork for exploration of how this boundary can be understood and controlled for the design of nanocrystalline materials tailored for specific applications in solar energy harvesting and photocatalytic reactions.
Li 4 Ti 5 O 12 /LiMn 2 O 4 (LTO/LMO) chemistry was evaluated as a potential candidate for behind-the-meter storage (BTMS) applications. Its long-term cycle performance at 45 °C was tested using ethylene carbonate (EC) and propylene carbonate (PC) solvent electrolytes. Over 1000 cycles, LTO/LMO cells exhibited ~80% capacity retention and Coulombic efficiency higher than 99.96%. Electrochemical test results showed the major degradation mode of LTO/LMO cells arises from continuous electrolyte decomposition at the LTO anode and loss of Li inventory. EC and PC electrolytes created distinct surface layers, where the EC reduction products were more effective in passivating the LTO electrode surface. Dissolution and migration of Mn from the cathode was probed as Mn 2+ species distributed throughout the surface layer at the anode. By utilizing a prelithiated LTO electrode, the LTO/LMO cell performance was significantly enhanced with EC electrolyte. On the other hand, PC electrolyte resulted in accelerated electrolyte decomposition at the lithiated LTO surface due to the lack of surface passivation. Thus, mitigating parasitic reactions at the LTO electrode is the key to developing successful LTO/LMO cells.
Methods for fabricating thin, high-aspect-ratio Ge nanostructures from high-quality, single-crystalline Ge substrates are provided. Also provided are grating structures made using the methods. The methods utilize a thin layer of graphene between a surface of a Ge substrate, and an overlying resist layer. The graphene passivates the surface, preventing the formation of water-soluble native Ge oxides that can result in the lift-off of the resist during the development of the resist.
GaAs(111)B are commercially available substrates widely used for the growth of van der Waals chalcogenide films. Wafer-scale, high-quality crystalline films can be deposited on GaAs(111)B substrates using molecular beam epitaxy. However, two obstacles persist in the use of GaAs(111)B: first, the surface dangling bonds make it challenging for the growth of van der Waals materials; second, the As-terminated surface is prone to aging in air. This study investigated a thermal treatment method for deoxidizing GaAs(111)B substrates while simultaneously passivating the surface dangling bonds with Se. By optimizing the treatment parameters, we obtained a flat and completely deoxidized platform for subsequent film growth, with highly reproducible operations. Furthermore, through first-principle calculations, we find that the most energetically favorable surface of GaAs(111)B after Se passivation consists of 25% As atoms and 75% Se atoms. Finally, we discovered that the common storage method using food-grade vacuum packaging cannot completely prevent substrate aging, and even after thermal treatment, aging still affects subsequent growth. Therefore, we recommend using N2-purged containers for better preservation.
Niobium metal occupies nearly 100% of the volume of a typical 2D transmon device. While the aluminum Josephson junction is of utmost importance, maintaining quantum coherence across the entire device means that pair-breaking in Nb leads, capacitive pads, and readout resonators can be a major source of decoherence. The established contributors are surface oxides and hydroxides, as well as absorbed hydrogen and oxygen. Metal encapsulation of freshly grown surfaces with non-oxidizing metals, preferably without breaking the vacuum, is a successful strategy to mitigate these issues. While the positive effects of encapsulation are undeniable, it is important to understand its impact on the macroscopic behavior of niobium films. We present a comprehensive study of the bulk superconducting properties of Nb thin films encapsulated with gold and palladium/gold, and compare them to those of bare Nb films. Magneto-optical imaging, magnetization, resistivity, and London and Campbell penetration depth measurements reveal significant differences in encapsulated samples. Both sputtered, and epitaxial Au-capped films exhibit the highest residual resistivity ratio and superconducting transition temperature, as well as the lowest upper critical field, London penetration depth, and critical current. These results are in good agreement with the microscopic theory of anisotropic normal and superconducting states of Nb. We conclude that pair-breaking in the bulk of niobium films, driven by disorder throughout the film rather than just at the surface, is a significant source of quantum decoherence in transmons. We also conclude that gold capping not only passivates the surface but also affects the properties of the entire film, significantly reducing the scattering rate due to defects likely induced by surface diffusion if the film is not protected immediately after fabrication.
Electrochemical interfaces are dynamic systems, evolving based on their local environment and reactant surface structures. The electrode-electrolyte interface in Li-ion batteries can be protective, limiting parasitic reactions with the electrolyte to passivate the surface [1]. Additionally, this interphase has an impact on the Li-ion transport through that layer based on its composition, bonding environment, and thickness. These parameters are challenging to collect and may vary depending on the electrode surface site investigated relative to its spatial position in a coin cell. This study will detail a multiscale cryogenic electron microscopy approach where millimeter-scale cross-sections through the coin cell batteries were made using a cryogenic stage within a fs-laser plasma focused ion beam (laser PFIB) with complementary energy dispersive X-ray spectroscopy able to detect variations in the composition at electrode interfaces [2]. Microscale cross-sectioning and lamella sample preparation of battery electrodes was conducted at the Center for Integrated Nanotechnologies using a Ga-ion focused ion beam (FIB) with air-free and cryo-transfer [3], followed by nanoscale mapping of composition and bonding within the CEI through cryo-scanning transmission electron microscopy (cryo-STEM) electron energy loss spectroscopy [4]. This multiscale approach enabled identification of millimeter-scale features of a battery stack with visualization of degradation in electrodes such as cracks in cathode particles, gas evolution, and SEI evolution; microscale interfacial characteristics, such as heterogeneity in the SEI or barrier layer and identification of electrolyte networks to the electrode surfaces; and nanoscale measurement of the CEI thickness, mapping of transition metal bonding within the cathode particles to identify loss of active materials, and identification of beneficial electrolyte additives incorporated into the CEI structure. This multiscale approach allows for a statistical understanding of the primary mechanisms and parasitic degradation pathways that impact performance by limiting the ion transport pathways within Li+ batteries.
We report an order and disorder combined corrosion morphology of dual-phase Ni-based alloy in the passive state. After galvanostatic polarization in the passive region, the surface of the γ(Ni) phase presents amorphous feature while that of the γ′(Ni 3 Al) phase maintains crystalline. The variations in weight percentages of Ni (50.19% → 3.80%), Co (19.24% → 0.65%), Ta (0.85% → 21.19%), and W (5.73% → 43.79%) of γ surface are evident, whereas the composition of γ′ surface is nearly unchanged. The passive film comprises $W^{6+}_{ox}$, $Ta^{5+}_{ox}$, $Cr^{3+}_{ox}$, $Co^{8/3+}_{ox}$, $Ni^{2+}_{hy}$, and $Co^{2+}_{hy}$, and it shows stronger protection effect on the γ phase.
The presence of unreacted lead iodide in organic-inorganic lead halide perovskite solar cells is widely correlated with an increase in power conversion efficiency. We investigate the mechanism for this increase by identifying the role of surfaces and interfaces present between methylammonium lead iodide perovskite films and excess lead iodide. We show how type I and II band alignments arising under different conditions result in either passivation of surface defects or hole injection. Through first-principles simulations of solid-solid interfaces, we find that lead iodide captures holes from methylammonium lead iodide and modulates the formation of defects in the perovskite, affecting recombination. Using surface-sensitive optical spectroscopy techniques, such as transient reflectance and time-resolved photoluminescence, we show how excess lead iodide affects the diffusion and surface recombination velocity of charge carriers in methylammonium lead iodide films. Our coupled experimental and theoretical results elucidate the role of excess lead iodide in perovskite solar cells.
A significant enhancement in the Menshutkin S N 2 reaction between 1-methylimidazole (MeIm) and methyl thiocyanate (MeSCN) is observed when the reaction is confined in the nanoscale silica pores of MCM41 and SBA15. The experiments in the silica pores are conducted without surrounding bulk reaction mixture. The influences of temperature, pore radius, and surface chemistry on the kinetics of the confined reaction are analyzed with time-dependent infrared spectroscopy, molecular dynamics simulations, and ab initio calculations. The rate constant of the pseudo-first order reaction increases with decreasing pore size, and the activation energy is found to decrease by 5.6 kJ/mol in the smallest pore studied (2.8 nm) relative to the bulk reaction. The rate constant dependence on pore size is accurately described by a two-state model in which molecules within the 4.6 Å interfacial layer experience a 2.4-fold rate constant increase relative to those reacting at the bulk rate further away from the interface. The removal of polar silanol groups from the silica surface via passivation with trimethylsilyl chloride results in bulk-like kinetics despite a reduction in the pore diameter, demonstrating the role of silanols as catalytic sites. Here, electronic structure calculations of the energy profile on a model silica surface confirm that silanol groups, particularly those of the vicinal type, can reduce the activation energy and reaction endothermicity through the donation of hydrogen bonds to the reactant, transition state, and product complexes.
Graphene-like layered transition metal carbides, nitrides, or carbonitrides, called MXenes, obey the stoichiometric formula of M n+1 X n T x , where M is an early transition metal such as scandium (Sc), n is a natural number, X is C, N, or CN, and T x is a functional group such as –O, –F, or –OH that passivates the surface of the MXene. The electronic structure of bare Sc 2 C and functionalized Sc 2 CT x MXenes are explored by performing first-principles density functional theory (DFT) calculations. The bare Sc 2 C is metallic, but less stable than its passivated structure. The Sc 2 C MXene has an interlayer 2D electron gas not bound to Sc or C atoms but free to move, making it an electride. DFT calculations show that functionalization can open an energy gap in Sc 2 CT x MXenes. The size and type (direct versus indirect) of the bandgap vary with the functional groups, which provides a means for opening and tuning of the band gap.
Abstract Materials can passivate by forming surface films when placed in aqueous media. However, these films may or may not be stable, and their stability can be predicted by a metric called the Pilling-Bedworth Ratio (PBR). In this article, we extend PBR to predict passivation protectiveness of multi-component materials. We then evaluate this PBR (ePBR)’s effectiveness by comparing its predictions against experimental studies of 21 multi-element materials of diverse chemistries, with agreement for 17 of the materials. Finally, we encode the methodology to compute ePBR in a web-application to predict the protectiveness of 140,000+ materials in the Materials Project database.
As lithium-ion batteries approach their theoretical limits for energy density, magnesium-ion batteries are emerging as a promising next-generation energy storage technology. However, progress in magnesium-ion battery research has been stymied by a lack of available high capacity cathode materials that can reversibly insert magnesium ions. Vanadium Oxide (V 2 O 5 ) has emerged as one of the more promising candidate cathode materials, owing to its high theoretical capacity, facile synthesis methods, and relatively high operating voltage. This review focuses on the outlook of hydrated V 2 O 5 structures as a high capacity cathode material for magnesium-ion batteries. In general, V 2 O 5 structures exhibit poor experimental capacity for magnesium-ion insertion due to sluggish magnesium-ion insertion kinetics and poor electronic conductivity. However, several decades ago, it was discovered that the addition of water to organic electrolytes significantly improves magnesium-ion insertion into V 2 O 5 . This review clarifies the various mechanisms that have been used to explain this observation, from charge shielding to proton insertion, and offers an alternative explanation that examines the possible role of structural hydroxyl groups on the V 2 O 5 surface. While the mechanism still needs to be further studied, this discovery fueled new research into V 2 O 5 electrodes that incorporate water directly as a structural element. The most promising of these hydrated V 2 O 5 materials, many of which incorporate conductive additives, nanostructured architectures, and thin film morphologies, are discussed. Ultimately, however, these hydrated V 2 O 5 structures still face a significant barrier to potential applications in magnesium-ion batteries. During full cell electrochemical cycling, these hydrated structures tend to leach water into the electrolyte and passivate the surface of the magnesium anode, leading to poor cycle life and low capacity retention. Recently, some promising strides have been made to remedy this problem, including the use of artificial solid electrolyte interphase layers as an anode protection scheme, but a call to action for more anode protection strategies that are compatible with trace water and magnesium metal is required.
As a metal that can occur in nature in the elemental form, copper (Cu) has been used by humans since ca. 8000 BC. With most properties matching those of Ag and Au, Cu has played a more significant role in commercial applications owing to its much higher (the 25th among all elements) abundance in Earth’s crust and thus more affordable price. In addition to its common use as a conductor of heat and electricity, it is a constituent of various metal alloys for hardware, coins, strain gauges, and thermocouples. Bulk Cu is also widely utilized as a building material. When downsized to the nanoscale, Cu and Cu-based structures have found widespread use in applications ranging from electronics to optoelectronics, plasmonics, catalysis, sensing, and biomedicine. Besides Ag and Au, for example, Cu is another metal known for its localized surface plasmon resonance (LSPR) in the visible and near-infrared regions when prepared as nanocrystals. As a potential replacement for indium–tin oxide (ITO) films, polymer coatings containing Cu nanowires are strong candidates for the fabrication of transparent and flexible electrodes key to touchscreen display and related applications. The commercial catalysts for water–gas shift and gas detoxification reactions are also based on Cu nanoparticles. Most recently, Cu nanocrystals have attracted considerable interest for their superior selectivity toward hydrocarbons and multicarbon species during the electrochemical reduction of CO 2 . The success of all these applications critically depends on our ability to control the shape and surface structure of the nanocrystals. Relative to Ag and Au, it is more challenging to generate Cu-based nanocrystals using colloidal methods due to its lower reduction potential and greater vulnerability to oxidation. Here, in this account, we discuss recent progress in the colloidal synthesis of Cu nanocrystals with controlled shapes for plasmonic, biomedical, and catalytic applications. With glucose serving as a reducing agent, Cu nanocrystals bearing a twinned or single-crystal structure can be synthesized using an aqueous system with the assistance of hexadecylamine (HDA). In this synthetic protocol, HDA not only passivates the surface to protect the nanocrystals from oxidation but also manipulates the reduction kinetics of Cu(II) precursor through coordination and an increase of solution pH. Typical products include nanocubes and penta-twinned nanowires whose surfaces are dominated by {100} facets. When seeds produced either in situ or ex situ are introduced, Cu-based nanocrystals featuring a singly twinned, core–shell, or Janus structure can be readily synthesized. Aside from segmented structures, Cu-based alloys with various noble metals can be synthesized through coreduction or a galvanic replacement reaction with preformed Cu nanocrystals. By controlling the size and/or shape of Cu nanocrystals, their LSPR peaks can be tuned into the near-infrared region, making them promising candidates for optical imaging contrast enhancement and photothermal treatment. The inclusion of the 64 Cu isotope makes them immediately useful in positron emission tomography and thus image-guided therapy. The surface structure, elemental distribution, and valence state of Cu-based nanocrystals can all be tailored to augment their electrocatalytic performance. It is hoped that this Account will inspire more studies into the development of rational methods capable of producing Cu-based nanocrystals with diverse and well-controlled shapes, internal structures, and compositions for a broader range of applications.
Polycrystalline silicon on silicon oxide (poly-Si/SiO x ) passivating contacts can be used for ultra-high-efficiency interdigitated back contact (IBC) monocrystalline silicon solar cells. We evaluate the use of intrinsic poly-Si for the region that isolates the p- and n-type fingers at the back side of IBC devices. To mitigate shunt across the isolation region between the doped p- and n-type fingers, we demonstrate self-aligned subtractive processing by etching the poly-Si in the isolation region using SF6 plasma followed by etching in a tetramethylammonium hydroxide (TMAH) solution. After removal of the poly-Si, the isolation region was passivated with SiN x and Al 2 O 3 , which resulted in an 11.7% increase in the fill factor in a 19.8% efficient device. Furthermore, we evaluate the limitations of this device through Suns-V oc analysis and simulations using SunSolve and Quokka3 solar cell simulation software. Through Quokka3, we show that the most significant efficiency losses come from junction recombination current (J 02 ) in the isolation region between doped fingers. We predict that the cell efficiency can be most improved with reduced J 02 through better isolation of heavily doped fingers by etching the isolation region deeper into the bulk or through enhanced surface chemical passivation in this region.
The atomistic-level mechanism for the chemical passivation of the monocrystalline Si (c-Si) surface with thermally annealed Al 2 O 3 was studied using in situ infrared spectroscopy and photoconductance decay measurements. Al 2 O 3 was deposited on high-lifetime, float-zone c-Si substrates using atomic layer deposition (ALD) from trimethylaluminum (TMA), and H 2 O or O 3 . Surface-sensitive attenuated total reflection Fourier transform infrared spectroscopy was used to monitor the c-Si/Al 2 O 3 interface, as well as the bulk of the Al 2 O 3 film during the entire process. Our results show that some surface Si–H bonds are preserved after the ALD of Al 2 O 3 on H-terminated Si. During the annealing step at 400 °C, restructuring occurs at the c-Si/Al 2 O 3 interface to form interfacial SiO x . Isotope labeling was used to differentiate interfacial SiD bonds on the c-Si surface from H incorporated in Al 2 O 3 . Within the sensitivity of our infrared setup (~10 13 cm –2 ), we did not observe any net migration of atomic H or D from Al 2 O 3 to the c-Si/Al 2 O 3 interface. To isolate the effects of chemical and field-effect passivation of Al 2 O 3 thin films, we carried out surface passivation studies on c-Si/SiO 2 /Al 2 O 3 stacks. We also annealed these stacks in different atmospheres to test the influence of annealing atmospheres on the chemical passivation of c-Si by Al 2 O 3 and observed that O 2 -containing atmosphere led to the best surface chemical passivation.