Interfacial Growth of Large Area Single-Crystalline Silver Sheets Through Ambient Microdroplets

The creation of micrometer-sized sheets of silver at the air-water interface by direct deposition of electrospray-generated silver ions (Ag+) on an aqueous dispersion of reduced graphene oxide (RGO), in ambient conditions, is reported. In the process of electrospray deposition (ESD), an electrohydrodynamic flow is created in the aqueous dispersion, and the graphene sheets assemble, forming a thin film at the air-water interface. The deposited Ag+ coalesce to make single-crystalline Ag sheets on top of this assembled graphene layer. Fast neutralization of Ag+ forming atomic Ag, combined with their enhanced mobility on graphene surfaces, presumably facilitates the growth of larger Ag clusters. Moreover, restrictions imposed by the interface drive the crystal growth in 2D. By controlling the precursor salt concentration, RGO concentration, deposition time, and ion current, the dimensionality of the Ag sheets can be tuned. These Ag sheets are effective substrates for surface-enhanced Raman spectroscopy (SERS), as demonstrated by the successful detection of methylene blue at nanomolar concentrations.

Honeycomb ZrCo Intermetallic for High Performance Hydrogen and Hydrogen Isotope Storage

Hydrogen isotope storage materials are of great significance for controlled nuclear fusion, which is promising to provide unlimited clean and dense energy. Conventional storage materials of micrometer-sized polycrystalline ZrCo alloys prepared by the smelting method suffer from slow kinetics, pulverization, disproportionation, and poor cycling stability. Here, we synthesize a honeycomb-structured ZrCo composed of highly crystalline submicrometer ZrCo units using electrospray deposition and magnesiothermic reduction. Compared with conventional ones, honeycomb ZrCo does not require activation and exhibits more than 1 order of magnitude increase in kinetic property. Owing to low defects and low stress, the anti-disproportionation ability and cycling stability of honeycomb ZrCo are also obviously higher than those of conventional ZrCo. Moreover, the interfacial stress (due to hydrogenation/dehydrogenation) as a function of particle radius is established, quantitatively elucidating that small-sized ZrCo reduces stress and pulverization. This study points out a direction for the structural design of ZrCo alloy with high-performance hydrogen isotope storage.

Solution-Synthesized Extended Graphene Nanoribbons Deposited by High-Vacuum Electrospray Deposition

Solution-synthesized graphene nanoribbons (GNRs) facilitate various interesting structures and functionalities, like nonplanarity and thermolabile functional groups, that are not or not easily accessible by on-surface synthesis. Here, we show the successful high-vacuum electrospray deposition (HVESD) of well-elongated solution-synthesized GNRs on surfaces maintained in ultrahigh vacuum. We compare three distinct GNRs, a twisted nonplanar fjord-edged GNR, a methoxy-functionalized "cove"-type (or also called gulf) GNR, and a longer "cove"-type GNR both equipped with alkyl chains on Au(111). Nc-AFM measurements at room temperature with submolecular imaging combined with Raman spectroscopy allow us to characterize individual GNRs and confirm their chemical integrity. The fjord-GNR and methoxy-GNR are additionally deposited on nonmetallic HOPG and SiO2, and fjord-GNR is deposited on a KBr(001) surface, facilitating the study of GNRs on substrates, as of now not accessible by on-surface synthesis.

Fabrication of a New, Low-Cost, and Environment-Friendly Laccase-Based Biosensor by Electrospray Immobilization with Unprecedented Reuse and Storage Performances

The fabrication of enzyme-based biosensors has received much attention for their selectivity and sensitivity. In particular, laccase-based biosensors have attracted a lot of interest for their capacity to detect highly toxic molecules in the environment, becoming essential tools in the fields of white biotechnology and green chemistry. The manufacturing of a new, metal-free, laccase-based biosensor with unprecedented reuse and storage capabilities has been achieved in this work through the application of the electrospray deposition (ESD) methodology as the enzyme immobilization technique. Electrospray ionization (ESI) has been used for ambient soft-landing of laccase enzymes on a carbon substrate, employing sustainable chemistry. This study shows how the ESD technique can be successfully exploited for the fabrication of a new promising environment-friendly electrochemical amperometric laccase-based biosensor, with storage capability up to two months without any particular care and reuse performance up to 63 measurements on the same electrode just prepared and 20 measurements on the one-year-old electrode subjected to redeposition. The laccase-based biosensor has been tested for catechol detection in the linear range 2-100 μM, with a limit of detection of 1.7 μM, without interference from chrome, cadmium, arsenic, and zinc and without any memory effects.

Imaging the Single-Electron Ln-Ln Bonding Orbital in a Dimetallofullerene Molecular Magnet

Chemically robust single-molecule magnets (SMMs) with sufficiently high blocking temperatures T_B are among the key building blocks for the realization of molecular spintronic or quantum computing devices. Such device applications require access to the magnetic system of a SMM molecule by means of electronic transport, which primarily depends on the interaction of magnetic orbitals with the electronic states of the metallic electrodes. Scanning tunneling microscopy in combination with ab initio calculations allows to directly address the unoccupied component of the single-electron molecular orbital that mediates the ferromagnetic exchange coupling between two 4f ions within a lanthanide endohedral dimetallofullerene deposited on a graphene surface. The single-electron metal-metal bond provides a direct access to the molecule's magnetic system in the transport experiments, paving the way for investigation and controlled manipulation of the spin system of individual dimetallofullerene SMMs, essential for molecular spintronics.

Electrospray Deposition of Cellulose Nanofibers on Paper: Overcoming the Limitations of Conventional Coating

While the potential of cellulose nanofibers to enhance the mechanical and barrier properties of paper is well-known, there are many uncertainties with respect to how to apply them. In this study, we use not only bulk addition of micro-/nanofibers and bar coating with oxidized nanofibers, but also a combination of these and, as a novel element, electrospray deposition of nanofiber dispersions. Characterization involved testing the strength of uncoated and coated paper sheets, their resistance to air flow, their Bendtsen roughness, and their apparent density, plus visualization of their surface and cross-sections by scanning electron microscopy. As expected, bulk addition to the unrefined pulp was sufficient to attain substantial strengthening, but this enhancement was limited to approximately 124%. Following this, surface addition by bar coating improved air resistance, but not strength, since, as applying nanocellulose at high consistency was technically unfeasible, this was performed several times with detrimental drying stages in between. However, replacing bar coating with electrospraying helped us overcome these apparent limitations, producing enhancements in both barrier and tensile properties. It is concluded that electrosprayed nanofibers, owing to their uniform deposition and favorable interactions, operate as an effective binder between fibers (and/or fines).

Exceptionally High Blocking Temperature of 17 K in a Surface-Supported Molecular Magnet

Single-molecule magnets (SMMs) are among the most promising building blocks for future magnetic data storage or quantum computing applications, owing to magnetic bistability and long magnetic relaxation times. The practical device integration requires realization of 2D surface assemblies of SMMs, where each magnetic unit shows magnetic relaxation being sufficiently slow at application-relevant temperatures. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism, it is shown that sub-monolayers of Dy₂ @C₈₀ (CH₂ Ph) dimetallofullerenes prepared on graphene by electrospray deposition exhibit magnetic behavior fully comparable to that of the bulk. Magnetic hysteresis and relaxation time measurements show that the magnetic moment remains stable for 100 s at 17 K, marking the blocking temperature T_B(100) , being not only in excellent agreement with that of the bulk sample but also representing by far the highest one detected for a surface-supported single-molecule magnet. The reported findings give a boost to the efforts to stabilize and address the spin degree of freedom in molecular magnets aiming at the realization of SMM-based spintronic units.

Influence of electrospray deposition on C60 molecular assemblies

Maintaining clean conditions for samples during all steps of preparation and investigation is important for scanning probe studies at the atomic or molecular level. For large or fragile organic molecules, where sublimation cannot be used, high-vacuum electrospray deposition is a good alternative. However, because this method requires the introduction into vacuum of the molecules from solution, clean conditions are more difficult to be maintained. Additionally, because the presence of solvent on the surface cannot be fully eliminated, one has to take care of its possible influence. Here, we compare the high-vacuum electrospray deposition method to thermal evaporation for the preparation of C60 on different surfaces and compare, for sub-monolayer coverages, the influence of the deposition method on the formation of molecular assemblies. Whereas the island location is the main difference for metal surfaces, we observe for alkali halide and metal oxide substrates that the high-vacuum electrospray method can yield single isolated molecules accompanied by surface modifications.

High-Efficiency Electrospray Deposition Method for Nonconductive Substrates: Applications of Superhydrophobic Coatings

When highly insulating materials are used as substrates for electronic devices, manufacturing yields become worse, and electronic components are often damaged due to undissipated electrostatic charges on such substrates. In the case of electrospray deposition, the problem of undissipated charges is particularly vexing. If charges accumulated on the substrate are not properly compensated, a repulsive force is generated against the incoming charged droplets, which negatively affects the uniformity and deposition rate of the coating layer. In order to overcome this limitation, we demonstrated a new electrospray method, which can significantly increase the deposition efficiency even in the presence of accumulated charges on nonconductive substrates. A highly reliable superhydrophobic layer was uniformly deposited on highly insulating substrates, including printed circuit board (PCB), polyester (PET), and polyimide (PI) substrates.

Multifunctional Nafion/CeO2 Dendritic Structures for Enhanced Durability and Performance of Polymer Electrolyte Membrane Fuel Cells

The development of a novel approach to achieve high-performance and durable fuel cells is imperative for the further commercialization of proton-exchange (or polymer electrolyte) membrane fuel cells (PEMFCs). In this work, multifunctional dendritic Nafion/CeO₂ structures were introduced onto the cathode side of the interface between a membrane and a catalyst layer through electrospray deposition. The dendritic structures enlarged the interfacial contact area between the membrane and the catalyst layer and formed microscale voids between the catalyst layer and gas diffusion medium. This improved the PEMFC performance through the effective utilization of the catalyst and enhanced mass transport of the reactant. Especially, under low-humidity conditions, the hygroscopic effect of CeO₂ nanoparticles also boosted the power density of PEMFCs. In addition to the beneficial effects on the efficiency of the PEMFC, the incorporation of CeO₂, widely known as a radical scavenger, effectively mitigated the free-radical attack on the outer surface of the membrane, where chemical degradation is initiated by radicals formed during PEMFC operation. These multifunctional effects of the dendritic Nafion/CeO₂ structures on PEMFC performance and durability were investigated using various in situ and ex situ measurement techniques.

Antibacterial and Osteogenic Activity of Titania Nanotubes Modified with Electrospray-Deposited Tetracycline Nanoparticles

The nanotubular surface of titanium implants is known to have superior osteogenic activity but is also vulnerable to failure because of induced bacterial attachment and consequent secondary infection. Here, the problem was attempted to be solved by depositing nanosized tetracycline (TC)-loaded particles in poly(lactic-co-glycolic acid) on titania nanotubes (TNTs) using the electrospray deposition method. The antibacterial effect of the newly formed TNT surface was considered using the common pathogen Staphylococcus aureus. Maintenance of the biocompatibility and osteogenic characteristics of TNTs has been tested through cytotoxicity tests and osteogenic gene expression/extra-cellular matrix mineralization, respectively. The results showed that TNTs were successfully formed by anodization, and the characterization of TC deposited on the TNTs was controlled by varying the spraying parameters such as particle size and coating time. The TC nanoparticle-coated TNTs showed antibacterial activity against Staphylococcus aureus and biocompatibility with MC3T3-E1 pre-osteoblasts, while the osteogenic activity of the TNT structure was preserved, as demonstrated by osteocalcin and osteopontin gene expression, as well as Alizarin red staining. Hence, this study concluded that the electrosprayed TC coating of TNTs is a simple and effective method for the formation of bactericidal implants that can maintain osteogenic activity.

Self-Limiting Electrospray Deposition for the Surface Modification of Additively Manufactured Parts

Electrospray deposition (ESD) is a spray coating process that utilizes a high voltage to atomize a flowing solution into charged microdroplets. These self-repulsive droplets evaporate as they travel to a target substrate, depositing the solution solids. Our previous research investigated the conditions necessary to minimize charge dissipation and deposit a thickness-limited film that grows in area over time through self-limiting electrospray deposition. Such sprays possess the ability to conformally coat complex three-dimensional (3D) objects without changing the location of the spray needle or orientation of the object. This makes them ideally suited for the postprocessing of materials fabricated through additive manufacturing (AM), opening a paradigm of independent bulk and surface functionality. Having demonstrated 3D coating with film thickness in the range of 1-50 μm on a variety of conductive objects, in this study, we employed model substrates to quantitatively study the technique's limits with regard to geometry and scale. Specifically, we examined the effectiveness of thickness-limited ESD for coating recessed features with gaps ranging from 50 μm to 1 cm, as well as the ability to coat surfaces hidden from the line-of-sight of the spray needle. This was then extended to the coating of hydrogel structures printed by AM, demonstrating that coating could be conducted even into the body of the structures as a means to create hydrophobic surfaces without affecting the absorption-driven humidity response. Further, these coatings were robust enough to create superhydrophobicity in the entire structure, causing it to resist immersion in water.

Stable and Efficient Green Perovskite Nanocrystal-Polysilazane Films for White LEDs Using an Electrospray Deposition Process

We successfully fabricated a stable, efficient, and easy-to-use CsPbBr₃ perovskite nanocrystal (PeNC)-embedded inorganic polymer film through an encapsulation step with a Si-N/Si-O-based polysilazane (PSZ) matrix via the electrospray (e-spray) deposition of a silazane (SZ) oligomer-decorated PeNC solution. To eliminate Pb²⁺ defect sites that are generated when the ligands are peeled from the PeNC surface, surface passivation of the Lewis acid/base adduct is possible by coupling the SZ oligomer (the donor of lone pairs) with Pb²⁺ sites (the acceptor of lone pairs). With the addition of the SZ oligomer, the photoluminescence quantum yield of photodegraded CsPbBr₃ PeNC was recovered and increased by 2.35-fold whereas the stability was improved significantly from an untreated CsPbBr₃ PeNC solution. During the e-spray deposition process, SZ-treated CsPbBr₃ PeNC solution droplets can react with atmospheric moisture to polymerize and form a Si-N/Si-O network encapsulant via a sol-gel reaction. The resultant CsPbBr₃-PSZ films showed improved stability levels under most environmental conditions, including air storage, blue light exposure, UV exposure, thermal exposure, and water immersion. The optimum CsPbBr₃-PSZ film-covered blue light-emitting diode (LED) showed good performance capabilities, with a luminous efficacy (LE) of 85.9 lm/W and color-by-blue conversion efficiency (CE) of 60.1%. Furthermore, this easy-to-use CsPbBr₃-PSZ film can be employed to realize a remote-type white-by-blue LED by combining it with red emissive K₂SiF₆:Mn⁴⁺/silicone film. The LE and CE rates of the white LED were 71.0 lm/W and 50.8%, respectively, at a correlated color temperature of 9334 K, with only an 8% drop in the LE for long-term operation of 100 h. This result indicates that e-spray deposition is a simple fabrication process by which to create stable and efficient PeNC films from an unstable PeNC solution using a rapid sol-gel reaction between droplets and moisture from the air.

Bulk-Like Magnetic Signature of Individual Fe4H Molecular Magnets on Graphene

Single-molecule magnets (SMMs) incorporate key properties that make them promising candidates for the emerging field of spintronics. The challenge to realize ordered SMM arrangements on surfaces and at the same time to preserve the magnetic properties upon interaction with the environment is a crucial point on the way to applications. Here we employ inelastic electron tunneling spectroscopy (IETS) to address the magnetic properties in single Fe₄ complexes that are adsorbed in a highly ordered arrangement on graphene/Ir(111). We are able to substantially reduce the influence of both the tunneling tip and the adsorption environment on the Fe₄ complex during the measurements by using appropriate tunneling parameters in combination with the flat-lying Fe₄H derivative and a weakly interacting surface. This allows us to perform noninvasive IETS studies on these bulky molecules. From the measurements we identify intermultiplet spin transitions and determine the intramolecular magnetic exchange interaction constant on a large number of molecules. Although a considerable scattering of the exchange constant values is observed, the distribution maximum is located at a value that coincides with that of the bulk. Our findings confirm a retained molecular magnetism of the Fe₄H complex at the local scale and evaluate the influence of the environment on the magnetic exchange interaction.

Electrical Field Guided Electrospray Deposition for Production of Gradient Particle Patterns

Our previous work demonstrated the uniform particle pattern formation on the substrates using electrical field guided electrospray deposition. In this work, we reported for the first time the fabrication of gradient particle patterns on glass slides using an additional point, line, or bar electrode based on our previous electrospray deposition configuration. We also demonstrated that the polydimethylsiloxane (PDMS) coating could result in the formation of uniform particle patterns instead of gradient particle patterns on glass slides using the same experimental setup. Meanwhile, we investigated the effect of experimental configurations on the gradient particle pattern formation by computational simulation. The simulation results are in line with experimental observations. The formation of gradient particle patterns was ascribed to the gradient of electric field and the corresponding focusing effect. Cell patterns can be formed on the particle patterns deposited on PDMS-coated glass slides. The formed particle patterns hold great promise for high-throughput screening of biomaterial-cell interactions and sensing.

Uniaxial 2D Superlattice of Fe4 Molecular Magnets on Graphene

We demonstrate that electrospray deposition enables the fabrication of highly periodic self-assembled arrays of Fe₄H single molecule magnets on graphene/Ir(111). The energetic positions of molecular states are probed by means of scanning tunneling spectroscopy, showing pronounced long- and short-ranged spatial modulations, indicating the presence of both locally varying intermolecular as well as adsorption-site dependent molecule-substrate interactions. From the magnetic field dependence of the X-ray magnetic circular dichroism signal, we infer that the magnetic easy axis of each Fe₄H molecule is oriented perpendicular to the sample surface and that after the deposition the value of the uniaxial anisotropy is identical to the one in bulk. Our findings therefore suggest that the observed interaction of the molecules with their surrounding does not modify the molecular magnetism, resulting in a two-dimensional array of molecular magnets that retain their bulk magnetic properties.

Toward Tailored All-Spin Molecular Devices

Molecular based spintronic devices offer great potential for future energy-efficient information technology as they combine ultimately small size, high-speed operation, and low-power consumption. Recent developments in combining atom-by-atom assembly with spin-sensitive imaging and characterization at the atomic level have led to a first prototype of an all-spin atomic-scale logic device, but the very low working temperature limits its application. Here, we show that a more stable spintronic device could be achieved using tailored Co-Salophene based molecular building blocks, combined with in situ electrospray deposition under ultrahigh vacuum conditions as well as control of the surface-confined molecular assembly at the nanometer scale. In particular, we describe the tools to build a molecular, strongly bonded device structure from paramagnetic molecular building blocks including spin-wires, gates, and tails. Such molecular device concepts offer the advantage of inherent parallel fabrication based on molecular self-assembly as well as an order of magnitude higher operation temperatures due to enhanced energy scales of covalent through-bond linkage of basic molecular units compared to substrate-mediated coupling schemes employing indirect exchange coupling between individual adsorbed magnetic atoms on surfaces.

Highly Ordered Surface Self-Assembly of Fe₄ Single Molecule Magnets

Single molecule magnets (SMMs) have attracted considerable attention due to low-temperature magnetic hysteresis and fascinating quantum effects. The investigation of these properties requires the possibility to deposit well-defined monolayers or spatially isolated molecules within a well-controlled adsorption geometry. Here we present a successful fabrication of self-organized arrays of Fe4 SMMs on hexagonal boron nitride (h-BN) on Rh(111) as template. Using a rational design of the ligand shell optimized for surface assembly and electrospray as a gentle deposition method, we demonstrate how to obtain ordered arrays of molecules forming perfect hexagonal superlattices of tunable size, from small islands to an almost perfect monolayer. High-resolution low temperature scanning tunneling microscopy (STM) reveals that the Fe4 molecule adsorbs on the substrate in a flat geometry, meaning that its magnetic easy axis is perpendicular to the surface. By scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations, we infer that the majority- and minority-spin components of the spin-split lowest unoccupied molecular orbital (LUMO) can be addressed separately on a submolecular level.

CdSe/ZnS quantum dot thin film formation by an electrospray deposition process for light-emitting devices

About 30 nm quantum-dot thin films are formed by electrospray deposition (ESD) process and quantum-dot-light-emitting-diodes (QD-LEDs) are demonstrated. Maximum brightness of 23 000 cd m(-2) and current efficiency of 5.9 cd A(-1) are achieved with the ESD process. The ESD process can be a potential solution for large area quantum dot layers with simple and flexible control.

Large-area freestanding graphene paper for superior thermal management

Large-area freestanding graphene papers (GPs) are fabricated by electrospray deposition integrated with a continuous roll-to-roll process. Upon mechanical compaction and thermal annealing, GPs can achieve a thermal conductivity of as high as 1238.3-1434 W m(-1) K(-1) . The super-thermally conductive GPs display an outstanding heat-spread ability and are more efficient in removing hot spots than Cu and Al foils.