Bringing Electrochemical Three-Dimensional Printing to the Nanoscale

A Tutorial for Scanning Electrochemical Cell Microscopy (SECCM) Measurements: Step-by-Step Instructions, Visual Resources, and Guidance for First Experiments

Scanning electrochemical cell microscopy (SECCM) produces nanoscale-resolution electrochemical maps of electrode surfaces using the meniscus at the tip of an electrolyte-filled nanopipette as a mobile electrochemical cell. While the use and range of applications of SECCM have grown rapidly since its introduction, the pathway to performing SECCM measurements can be daunting to those without direct access to expert users. This work fills this expertise gap by providing a step-by-step guide to performing one's first SECCM experiments, including troubleshooting strategies, videos/images, suggested parameters and experimental systems, and representative data (of both successful experiments and common problems). No background in SECCM is assumed and fundamentals are clearly explained at each stage with a rationale for the experimental steps provided. This work provides an entry point for the uninitiated to understand and use this powerful nanoscale electrochemical characterization technique.

Droplet-Confined Electroplating for Nanoscale Additive Manufacturing: Current Control of the Initial Stages of Growth of Copper Nanowires

Droplet-confined electrodeposition enables a precise deposition of three-dimensional, nanoscopic, and high purity metal structures. It aspires to fabricate intricate microelectronic devices, metamaterials, plasmonic structures, and functionalized surfaces. Yet, a major handicap of droplet-confined electrodeposition is the current lack of control over the process, which is owed to its dynamic nature and the nanoscopic size of the involved droplets. The deposition current offers itself as an obvious and real-time window into the deposition and needs to be analyzed operando. Nucleation and growth dynamics are evaluated systematically. Our results indicate different deposition regimes and link the current to both morphology and volume of deposited copper. This allows for optimized electroplating strategies and calibration of the slicing algorithms necessary for a controlled deposition of 3D structures with different solvents. The potential of selecting appropriate solvents further readies this novel technique for the reliable deposition of functional structures with submicron resolution.

On the Resolution Limit of Electrohydrodynamic Redox 3D Printing

Additive manufacturing (AM) will empower the next breakthroughs in nanotechnology by combining unmatched geometrical freedom with nanometric resolution. Despite recent advances, no micro-AM technique has been able to synthesize functional nanostructures with excellent metal quality and sub-100 nm resolution. Here, significant breakthroughs in electrohydrodynamic redox 3D printing (EHD-RP) are reported by directly fabricating high-purity Cu (>98 at.%) with adjustable voxel size from >6µm down to 50 nm. This unique tunability of the feature size is achieved by managing in-flight solvent evaporation of the ion-loaded droplet to either trigger or prevent the Coulomb explosion. In the first case, the landing of confined droplets on the substrate allows the fabrication of high-aspect-ratio 50 nm-wide nanopillars, while in the second, droplet disintegration leads to large-area spray deposition. It is discussed that the reported pillar width corresponds to the ultimate resolution achievable by EHD printing. The unrivaled feature size and growth rate (>100 voxel s-1) enable the direct manufacturing of 30 µm-tall atom probe tomography (APT) tips that unveil the pristine microstructure and chemistry of the deposit. This method opens up prospects for the development of novel materials for 3D nano-printing.

Engineering the Hot-Spots in Au-Ag Alloy Nanoparticles through Meniscus-Confined 3D Printing for Microplastic Detection

The escalating concern surrounding microplastic (MP) pollution necessitates urgent attention and the development of rapid techniques for quantifying extremely low concentrations. Surface-enhanced Raman spectroscopy (SERS) has emerged as a promising method due to its simplicity, high sensitivity, and rapid quantification capabilities. Herein, the efficacy of gold-silver alloy nanoparticles (3DPAu-Ag) substrates for detecting poly(methyl methacrylate) (PMMA) and polystyrene (PS) MPs is investigated. The 3DPAu-Ag SERS substrates are fabricated using the meniscus-confined electrochemical 3D printing (MC-E3DP) process, employing a nozzle of 0.8 mm size with 2.5 V potential at a printing speed of 0.4 mm s-1. The proposed SERS substrates exhibit exceptional sensitivity and are capable of detecting PMMA concentrations as low as 0.2 μg mL-1 and PS concentrations of 1.2 μg mL-1 within the ranges of 1-103 μg mL-1 and 10-104 μg mL-1, respectively. Remarkable enhancement factors (EFs) of up to 3.2 × 104 for PMMA and 9.3 × 103 for PS are achieved, underscoring the substrates' effectiveness. Furthermore, the investigation demonstrates outstanding uniformity and reproducibility of the 3DPAu-Ag substrates, with relative standard deviation (RSD) values of only 4.1 and 6.4%, respectively, across 31 and 5 measurements. Additionally, a minimal 17% decrease in the initial SERS signal value after 5 weeks highlights the substrates' high stability. This not only highlights the superior quality of the substrates but also positions them ahead of previously reported works in the literature. Moreover, this study also comes up with a plausible mechanism for MPs SERS detection facilitated by the 3DPAu-Ag substrates, offering insights into the underlying processes. Overall, 3DPAu-Ag substrates show promise for sensitive, stable MP detection, which is crucial for environmental monitoring.

Advances in 3D printing for the repair of tympanic membrane perforation: a comprehensive review

Tympanic membrane perforation (TMP) is one of the most common conditions in otolaryngology worldwide, and hearing damage caused by inadequate or prolonged healing can be distressing for patients. This article examines the rationale for utilizing three-dimensional (3D) printing to produce scaffolds for repairing TMP, compares the advantages and disadvantages of 3D printed and bioprinted grafts with traditional autologous materials and other tissue engineering materials in TMP repair, and highlights the practical and clinical significance of 3D printing in TMP repair while discussing the current progress and promising future of 3D printing and bioprinting. There is a limited number of reviews specifically dedicated to 3D printing for TMP repair. The majority of reviews offer a general overview of the applications of 3D printing in the broader realm of tissue regeneration, with some mention of TMP repair. Alternatively, they explore the biopolymers, cells, and drug molecules utilized for TMP repair. However, more in-depth analysis is needed on the strategies for selecting bio-inks that integrate biopolymers, cells, and drug molecules for tympanic membrane repair.

Five years of scanning electrochemical cell microscopy (SECCM): new insights and innovations

Scanning electrochemical cell microscopy (SECCM) is a nanopipette-based technique which enables measurement of localised electrochemistry. SECCM has found use in a wide range of electrochemical applications, and due to the wider uptake of this technique in recent years, new applications and techniques have been developed. This minireview has collected all SECCM research articles published in the last 5 years, to demonstrate and celebrate the recent advances, and to make it easier for SECCM researchers to remain well-informed. The wide range of SECCM applications is demonstrated, which are categorised here into electrocatalysis, electroanalysis, photoelectrochemistry, biological materials, energy storage materials, corrosion, electrosynthesis, and instrumental development. In the collection of this library of SECCM studies, a few key trends emerge. (1) The range of materials and processes explored with SECCM has grown, with new applications emerging constantly. (2) The instrumental capabilities of SECCM have grown, with creative techniques being developed from research groups worldwide. (3) The SECCM research community has grown significantly, with adoption of the SECCM technique becoming more prominent.

Silicon-photonics-enabled chip-based 3D printer

Imagine if it were possible to create 3D objects in the palm of your hand within seconds using only a single photonic chip. Although 3D printing has revolutionized the way we create in nearly every aspect of modern society, current 3D printers rely on large and complex mechanical systems to enable layer-by-layer addition of material. This limits print speed, resolution, portability, form factor, and material complexity. Although there have been recent efforts in developing novel photocuring-based 3D printers that utilize light to transform matter from liquid resins to solid objects using advanced methods, they remain reliant on bulky and complex mechanical systems. To address these limitations, we combine the fields of silicon photonics and photochemistry to propose the first chip-based 3D printer. The proposed system consists of only a single millimeter-scale photonic chip without any moving parts that emits reconfigurable visible-light holograms up into a simple stationary resin well to enable non-mechanical 3D printing. Furthermore, we experimentally demonstrate a stereolithography-inspired proof-of-concept version of the chip-based 3D printer using a visible-light beam-steering integrated optical phased array and visible-light-curable resin, showing 3D printing using a chip-based system for the first time. This work demonstrates the first steps towards a highly-compact, portable, and low-cost solution for the next generation of 3D printers.

The Roles of Microprobe in Localized Electrodeposition: Electrolyte Localized Transport and Force-Displacement Sensitivity

Facing the rapid development of 6G communication, long-wave infrared metasurface and biomimetic microfluidics, the performance requirements for microsystems based on metal tiny structures are gradually increasing. As one of powerful methods for fabrication metal complex microstructures, localized electrochemical deposition microadditive manufacturing technology can fabricate copper metal micro overhanging structures without masks and supporting materials. In this study, the role of the microprobe cantilever (MC) in localized electrodeposition was studied. The MC can be used for precise deposition with electrolyte localized transport function and high accuracy force-displacement sensitivity. To prove this, the electrolyte flow was simulated when the MC was in bending or normal state. The simulation results can indicate the influence of turbulent flow on the electrolyte flow velocity and the pressure at the end of the pyramid. The results show that the internal flow velocity increased by 8.9% in the bending probe as compared with normal. Besides, this study analyzed the force-potential sensitivity characteristics of the MC. Using the deformation of the MC as an intermediate variable, the model of the probe tip displacement caused by the growth of the deposit and the voltage value displayed by the photodetector was mathematically established. In addition, the deposition of a single voxel was simulated by simulation process with the simulated height of 520 nm for one voxel, and the coincidence of simulation and experimental results was 93.1%. In conclusion, this method provides a new way for localized electrodeposition of complex microstructures.

Aerosol Jet Printing Conductive 3D Microstructures from Graphene Without Post-Processing

Three-dimensional (3D) graphene microstructures have the potential to boost performance in high-capacity batteries and ultrasensitive sensors. Numerous techniques have been developed to create such structures; however, the methods typically rely on structural supports, and/or lengthy post-print processing, increasing cost and complexity. Additive manufacturing techniques, such as printing, show promise in overcoming these challenges. This study employs aerosol jet printing for creating 3D graphene microstructures using water as the only solvent and without any post-print processing required. The graphene pillars exhibit conductivity immediately after printing, requiring no high-temperature annealing. Furthermore, these pillars are successfully printed in freestanding configurations at angles below 45° relative to the substrate, showcasing their adaptability for tailored applications. When graphene pillars are added to humidity sensors, the additional surface area does not yield a corresponding increase in sensor performance. However, graphene trusses, which add a parallel conduction path to the sensing surface, are found to improve sensitivity nearly 2×, highlighting the advantages of a topologically suspended circuit construction when adding 3D microstructures to sensing electrodes. Overall, incorporating 3D graphene microstructures to sensor electrodes can provide added sensitivity, and aerosol jet printing is a viable path to realizing these conductive microstructures without any post-print processing.

Effect of Magnetic Field on Maskless Localized Electrodepositing Three-Dimensional Microstructure of Nano Nickel Crystals

In the intricate process of maskless localized electrodeposition (MLED) for fabricating three-dimensional microstructures, specifically nickel micro-columns with an aspect ratio of 7:1, magnetic fields of defined strength were employed, oriented both parallel and anti-parallel to the electric field. The aim was to achieve nanocrystalline microstructures and elevated deposition rates. A detailed comparative analysis was conducted to examine the volumetric deposition rate, surface morphology, and grain size of the MLED nickel crystal 3D microstructures, both in the absence and presence of the two magnetic field directions, facilitated by a self-assembled experimental setup. The results indicate that the anti-parallel magnetic field significantly boosts the volumetric deposition rate to a notable 19,050.65 μm3/s and refines the grain size, achieving an average size of 24.82 nm. Conversely, the parallel magnetic field is found to enhance the surface morphology of the MLED nickel crystal 3D microstructure.

Solid-State Nanopores for Biomolecular Analysis and Detection

Advances in nanopore technology and data processing have rendered DNA sequencing highly accessible, unlocking a new realm of biotechnological opportunities. Commercially available nanopores for DNA sequencing are of biological origin and have certain disadvantages such as having specific environmental requirements to retain functionality. Solid-state nanopores have received increased attention as modular systems with controllable characteristics that enable deployment in non-physiological milieu. Thus, we focus our review on summarizing recent innovations in the field of solid-state nanopores to envision the future of this technology for biomolecular analysis and detection. We begin by introducing the physical aspects of nanopore measurements ranging from interfacial interactions at pore and electrode surfaces to mass transport of analytes and data analysis of recorded signals. Then, developments in nanopore fabrication and post-processing techniques with the pros and cons of different methodologies are examined. Subsequently, progress to facilitate DNA sequencing using solid-state nanopores is described to assess how this platform is evolving to tackle the more complex challenge of protein sequencing. Beyond sequencing, we highlight the recent developments in biosensing of nucleic acids, proteins, and sugars and conclude with an outlook on the frontiers of nanopore technologies.

Flexible Carbon Nanotube-Epitaxially Grown Nanocrystals for Micro-Thermoelectric Modules

Flexible thermoelectric materials have attracted increasing interest because of their potential use in thermal energy harvesting and high-spatial-resolution thermal management. However, a high-performance flexible micro-thermoelectric device (TED) compatible with the microelectronics fabrication process has not yet been developed. Here a universal epitaxial growth strategy is reported guided by 1D van der Waals-coupling, to fabricate freestanding and flexible hybrids comprised of single-wall carbon nanotubes and ordered (Bi,Sb)2 Te3 nanocrystals. High power factors ranging from ≈1680 to ≈1020 µW m-1 K-2 in the temperature range of 300-480 K, combined with a low thermal conductivity yield a high average figure of merit of ≈0.81. The fabricated flexible micro-TED module consisting of two p-n couples of freestanding thermoelectric hybrids has an unprecedented open circuit voltage of ≈22.7 mV and a power density of ≈0.36 W cm-2 under ≈30 K temperature difference, and a net cooling temperature of ≈22.4 K and a heat absorption density of ≈92.5 W cm-2 .

Aptamer Conformational Dynamics Modulate Neurotransmitter Sensing in Nanopores

Aptamers that undergo conformational changes upon small-molecule recognition have been shown to gate the ionic flux through nanopores by rearranging the charge density within the aptamer-occluded orifice. However, mechanistic insight into such systems where biomolecular interactions are confined in nanoscale spaces is limited. To understand the fundamental mechanisms that facilitate the detection of small-molecule analytes inside structure-switching aptamer-modified nanopores, we correlated experimental observations to theoretical models. We developed a dopamine aptamer-functionalized nanopore sensor with femtomolar detection limits and compared the sensing behavior with that of a serotonin sensor fabricated with the same methodology. When these two neurotransmitters with comparable mass and equal charge were detected, the sensors showed an opposite electronic behavior. This distinctive phenomenon was extensively studied using complementary experimental techniques such as quartz crystal microbalance with dissipation monitoring, in combination with theoretical assessment by the finite element method and molecular dynamic simulations. Taken together, our studies demonstrate that the sensing behavior of aptamer-modified nanopores in detecting specific small-molecule analytes correlates with the structure-switching mechanisms of individual aptamers. We believe that such investigations not only improve our understanding of the complex interactions occurring in confined nanoscale environments but will also drive further innovations in biomimetic nanopore technologies.

Untapped Potential of Deep Eutectic Solvents for the Synthesis of Bioinspired Inorganic-Organic Materials

Since the discovery of deep eutectic solvents (DESs) in 2003, significant progress has been made in the field, specifically advancing aspects of their preparation and physicochemical characterization. Their low-cost and unique tailored properties are reasons for their growing importance as a sustainable medium for the resource-efficient processing and synthesis of advanced materials. In this paper, the significance of these designer solvents and their beneficial features, in particular with respect to biomimetic materials chemistry, is discussed. Finally, this article explores the unrealized potential and advantageous aspects of DESs, focusing on the development of biomineralization-inspired hybrid materials. It is anticipated that this article can stimulate new concepts and advances providing a reference for breaking down the multidisciplinary borders in the field of bioinspired materials chemistry, especially at the nexus of computation and experiment, and to develop a rigorous materials-by-design paradigm.

Localised polymerisation of acrylamide using single-barrel scanning electrochemical cell microscopy

Single-barrel scanning electrochemical cell microscopy has been adapted for polymerisation of acrylamide in droplet cells formed at gold electrode surfaces. Localised electrochemical atom transfer radical polymerisation enables controlled synthesis and deposition of polyacrylamide or synthesis of polyacrylamide brushes from initiator-functionalised electrode surfaces.

Nanoelectrochemistry in electrochemical phase transition reactions

Electrochemical phase transition is important in a range of processes, including gas generation in fuel cells and electrolyzers, as well as in electrodeposition in battery and metal production. Nucleation is the first step in these phase transition reactions. A deep understanding of the kinetics, and mechanism of the nucleation and the structure of the nuclei and nucleation sites is fundamentally important. In this perspective, theories and methods for studying electrochemical nucleation are briefly reviewed, with an emphasis on nanoelectrochemistry and single-entity electrochemistry approaches. Perspectives on open questions and potential future approaches are also discussed.

Beginner's Guide to Micro- and Nanoscale Electrochemical Additive Manufacturing

Electrochemical additive manufacturing is an advanced microfabrication technology capable of producing features of almost unlimited geometrical complexity. A unique combination of the capacity to process conductive materials, design freedom, and micro- to nanoscale resolution offered by these electrochemical techniques promises tremendous opportunities for a multitude of future applications spanning microelectronics, sensing, robotics, and energy storage. This review aims to equip readers with the basic principles of electrochemical 3D printing at the small length scale. By describing the basic principles of electrochemical additive manufacturing technology and using the recent advances in the field, this beginner's guide illustrates how controlling the fundamental phenomena that underpin the print process can be used to vary dimensions, morphology, and microstructure of printed structures.

Impact of nanodroplets on cone-textured surfaces

Molecular dynamics simulations have been performed to study the dynamics of nanodroplets impacting on a flat superhydrophobic surface and surfaces covered with nanocone structures. We present a panorama of nanodroplet behaviors for a wide range of impact velocities and different cone geometrics, and develop a model to predict whether a nanodroplet impacting onto cone-textured surfaces will touch the underlying substrate during impact. The advantages and disadvantages of applying nanocone structures to the solid surface are revealed by the investigations into restitution coefficient and contact time. The effects of nanocone structures on droplet bouncing dynamics are probed using momentum analysis rather than conventional energy analysis. We further demonstrate that a single Weber number is inadequate for unifying the dynamics of macroscale and nanoscale droplets on cone-textured surfaces, and propose a combined dimensionless number to address it. The extensive findings of this study carry noteworthy implications for engineering applications, such as nanoprinting and nanomedicine on functional patterned surfaces, providing fundamental support for these technologies.

Filament Growth and Related Instabilities during Adsorbate Suppressed Electrodeposition

Anisotropic growth of a single filament on a microelectrode is demonstrated by galvanostatic electrodeposition in a bistable passive-active critical system. Specifically, a Cu filament is formed by disruption of a passivating polyether-halide bilayer triggered by metal deposition with positive feedback guiding highly localized deposition. For macroscale electrodes, complex passive-active Turing patterns develop, while for micrometer-sized electrodes, bifurcation is frustrated and a single active zone develops, which is reinforced by hemispherical transport. As deposition proceeds, hemispherical symmetry is broken with lateral propagation of a single filament while an increasing fraction of the applied current supports expansion of the passive sidewall area that eventually leads to termination of anisotropic growth. Different polyether suppressors alter the dynamic range between passive and active growth that determines the shape and extent of filament formation. The impact of electrode area, geometry, and applied current on morphological evolution was also briefly examined. The results highlight the utility of appropriately scaled microelectrodes in the study of growth instabilities during breakdown of additive suppressed layers in critical electrodeposition systems.

3D Nanolithography by Means of Lipid Ink Spreading Inhibition

While patterning 2D metallic nanostructures are well established through different techniques, 3D printing still constitutes a major bottleneck on the way to device miniaturization. In this work a fluid phase phospholipid ink is used as a building block for structuring with dip-pen nanolithography. Following a bioinspired approach that relies on ink-spreading inhibition, two processes are presented to build 2D and 3D metallic structures. Serum albumin, a widely used protein with an innate capability to bind to lipids, is the key in both processes. Covering the sample surface with it prior to lipid writing, anchors lipids on the substrate, which ultimately allows the creation of highly stable 3D lipid-based scaffolds to build metallic structures.

Additive manufacturing of Zn with submicron resolution and its conversion into Zn/ZnO core-shell structures

Electrohydrodynamic redox 3D printing (EHD-RP) is an additive manufacturing (AM) technique with submicron resolution and multi-metal capabilities, offering the possibility to switch chemistry during deposition "on-the-fly". Despite the potential for synthesizing a large range of metals by electrochemical small-scale AM techniques, to date, only Cu and Ag have been reproducibly deposited by EHD-RP. Here, we extend the materials palette available to EHD-RP by using aqueous solvents instead of organic solvents, as used previously. We demonstrate deposition of Cu and Zn from sacrificial anodes immersed in acidic aqueous solvents. Mass spectrometry indicates that the choice of the solvent is important to the deposition of pure Zn. Additionally, we show that the deposited Zn structures, 250 nm in width, can be partially converted into semiconducting ZnO structures by oxidation at 325 °C in air.

In Vivo Penetrating Microelectrodes for Brain Electrophysiology

In recent decades, microelectrodes have been widely used in neuroscience to understand the mechanisms behind brain functions, as well as the relationship between neural activity and behavior, perception and cognition. However, the recording of neuronal activity over a long period of time is limited for various reasons. In this review, we briefly consider the types of penetrating chronic microelectrodes, as well as the conductive and insulating materials for microelectrode manufacturing. Additionally, we consider the effects of penetrating microelectrode implantation on brain tissue. In conclusion, we review recent advances in the field of in vivo microelectrodes.

Intermediate Valence Ion-Mediated Electrodeposition Process

The assembly of biomolecules and ions (e.g., biomineralization process) generates many intricate structures in nature. However, human beings' control over the assembly processes of ions is in its infant stage compared with nature. Here, it is reported that the intermediate valence metal ions in the electrolyte can influence the growth speed of certain crystal facets and in turn adjust the shape of the electrodeposits created by anodic electrodeposition. This is because the intermediate valence metal ions (e.g., Pb²⁺ , Mn²⁺ , etc.) can be oxidized by the electrochemically oxidized high valence ions (e.g., Ag²⁺ and Ag³⁺ ). Therefore, the concentration of the electrochemically oxidized high valence ions can be controlled by the intermediate valence ions, affecting the growth kinetics of the electrodeposits. Taking the anodic electrodeposition of Ag₇ O₈ NO₃ as an example, the role of intermediate valence ions in tailoring the shape of the Ag₇ O₈ NO₃ electrodeposits is demonstrated. Moreover, the growth location of the second-order structure can be controlled by the intermediate valence metal ions. Additionally, the designed complex microarchitectures starting from certain crystal facets to form hollow nanoframes can be selectively etched. The control capability over the electrochemical assembly process of metal ions is significantly strengthened by introducing intermediate valence ions into the electrolyte.

Micro 3D printing of a functional MEMS accelerometer

Microelectromechanical system (MEMS) devices, such as accelerometers, are widely used across industries, including the automotive, consumer electronics, and medical industries. MEMS are efficiently produced at very high volumes using large-scale semiconductor manufacturing techniques. However, these techniques are not viable for the cost-efficient manufacturing of specialized MEMS devices at low- and medium-scale volumes. Thus, applications that require custom-designed MEMS devices for markets with low- and medium-scale volumes of below 5000-10,000 components per year are extremely difficult to address efficiently. The 3D printing of MEMS devices could enable the efficient realization and production of MEMS devices at these low- and medium-scale volumes. However, current micro-3D printing technologies have limited capabilities for printing functional MEMS. Herein, we demonstrate a functional 3D-printed MEMS accelerometer using 3D printing by two-photon polymerization in combination with the deposition of a strain gauge transducer by metal evaporation. We characterized the responsivity, resonance frequency, and stability over time of the MEMS accelerometer. Our results demonstrate that the 3D printing of functional MEMS is a viable approach that could enable the efficient realization of a variety of custom-designed MEMS devices, addressing new application areas that are difficult or impossible to address using conventional MEMS manufacturing.

Unraveling the Structural Sensitivity of CO2 Electroreduction at Facet-Defined Nanocrystals via Correlative Single-Entity and Macroelectrode Measurements

The conversion of CO₂ into value-added products is a compelling way of storing energy derived from intermittent renewable sources and can bring us closer to a closed-loop anthropogenic carbon cycle. The ability to synthesize nanocrystals of well-defined structure and composition has invigorated catalysis science with the promise of nanocrystals that selectively express the most favorable sites for efficient catalysis. The performance of nanocrystal catalysts for the CO₂ reduction reaction (CO₂RR) is typically evaluated with nanocrystal ensembles, which returns an averaged system-level response of complex catalyst-modified electrodes with each nanocrystal likely contributing a different (unknown) amount. Measurements at single nanocrystals, taken in the context of statistical analysis of a population, and comparison to macroscale measurements are necessary to untangle the complexity of the ever-present heterogeneity in nanocrystal catalysts, achieve true structure-property correlation, and potentially identify nanocrystals with outlier performance. Here, we employ environment-controlled scanning electrochemical cell microscopy to isolate and investigate the electrocatalytic CO₂RR response of individual facet-defined gold nanocrystals. Using correlative microscopy approaches, we conclusively demonstrate that {110}-terminated gold rhombohedra possess superior activity and selectivity for CO₂RR compared with {111}-terminated octahedra and high-index {310}-terminated truncated ditetragonal prisms, especially at low overpotentials where electrode kinetics is anticipated to dominate the current response. The methodology framework described here could inform future studies of complex electrocatalytic processes through correlative single-entity and macroscale measurement techniques.

Nanoscale electrochemical 3D deposition of cobalt with nanosecond voltage pulses in an STM

To explore a minimal feature size of <100 nm with electrochemical additive manufacturing, we use a strategy originally applied to microscale electrochemical machining for the nanoscale deposition of Co on Au. The concept's essence is the localization of electrochemical reactions below a probe during polarization with ns-long voltage pulses. As shown, a confinement that exceeds that predicted by a simple model based on the time constant for one-dimensional double layer charging enables a feature size of <100 nm for 2D patterning. We further indirectly verify the potential for out-of-plane deposition by tracking growth curves of high-aspect-ratio deposits. Importantly, we report a lack of anodic stability of Au tips used for patterning. As an inert probe is the prerequisite for controlled structuring, we experimentally verify an increased resistance of Pt probes against degradation. Consequently, the developed setup and processes show a path towards reproducible direct 2D and 3D patterning of metals at the nanoscale.

Electrochemical 3D printing of Ni-Mn and Ni-Co alloy with FluidFM

Additive manufacturing can realize almost any designed geometry, enabling the fabrication of innovative products for advanced applications. Local electrochemical plating is a powerful approach for additive manufacturing of metal microstructures; however, previously reported data have been mostly obtained with copper, and only a few cases have been reported with other elements. In this study, we assessed the ability of fluidic force microscopy to produce Ni-Mn and Ni-Co alloy structures. Once the optimal deposition potential window was determined, pillars with relatively smooth surfaces were obtained. The printing process was characterized by printing rates in the range of 50-60 nm s^-1. Cross-sections exposed by focused ion beam showed highly dense microstructures, while the corresponding face scan with energy-dispersive x-ray spectroscopy spectra revealed a uniform distribution of alloy components.