The infrared optical response of noble metals is traditionally considered perfect electrical conductor (PEC)-like due to the noble metals’ exceptionally large electron concentrations, and thus large (and negative) real permittivity. While PEC-like behavior is ideal for a broad range of applications, for instance mirrors, gratings, and wavelength- (and macro-) scale resonators and antennas, the utility of noble metals for nanoscale (sub-diffraction-limit) physics at long wavelengths is limited. However, in ultra-low volume (dilute) metal films, such as those with nanometer-scale thicknesses or lithographic dilution (subwavelength perforation), the thin films’ sheet conductivity is massively reduced, enabling light to penetrate and interact with the films much more efficiently. This avails the infrared of a host of opportunities for noble-metal-based plasmonics, with the potential for nanoscale (deep subwavelength) confinement and strong light-matter interaction, otherwise prohibited with noble metals in this wavelength range. In this perspective, we review the recent advances in dilute metal films for near- and mid-infrared photonics and plasmonics, and discuss the advantageous properties of these optical thin films for potential applications in sensors, detectors, sources, and nonlinear and quantum optics.

ABSTRACT In natural circulation loops (NC loops), flow initiation is driven by the difference between the heat source and the heat sink density variations. Given that the flow rates within these loops are lower than those in forced convection channels, surface characteristics can significantly influence the flow. No heat transfer studies have been found that describe the effects of UV‐irradiated PDMS surface modifications in NC loops. The study focuses on evaluating the thermal performance of surface‐modified natural circulation mini‐loops with a hydraulic diameter of 3 mm. The impact of surface modifications at the mini‐loop heater section, under different power inputs (10, 15, and 20 W) and temperatures at the heat sink (20°C and 30°C), is investigated. The performance of 0.01 and 0.02 vol.% Al 2 O 3 and SiO 2 nanofluids was measured and compared with that of D.I. water. The initial experiment involved a channel with untreated polydimethylsiloxane (PDMS) coating on the heater section (contact angle of 86.2 ± 2.7°). Subsequently, the experiment was repeated with a vacuum UV (VUV)‐treated PDMS coating (contact angle of 2.7 ± 2.1°). The heat transfer coefficient within the heater section was estimated using a nonintrusive interferometric technique. The thermal performance of a 3 mm hydraulic diameter mini‐loop with dilute metal oxide nanofluids was compared with deionized water (D.I. water), and the results were validated against Vijayan's correlation. Figure of Merit (FOM) analysis indicated that, for the designed mini‐loop, 0.02 vol.% alumina nanofluid exhibited the best performance. At 10 W and 283 K, the surface‐tuned heater section with 0.02 vol.% alumina nanofluid demonstrated a 12.42 ± 1.6% enhancement in the local heat transfer coefficient. However, the Nusselt number increment was only 5.39 ± 1.7%. The high wettability of the heater section hinders the slip flow. The rise in the thermal conductivity of the basefluid due to nanoparticle addition also reduces the Nusselt number. The surface effects being comparable with the buoyancy forces, the Reynolds number inside the loop is lower.

The traditional Gouy–Chapman–Stern theory has been effective in explaining the behavior of dilute electrolytes in the electrical double layer but falls short when it comes to describing how ions behave at the metal/electrolyte interface. This is because it overlooks key factors such as the molecular structure of water at the interface and the effects of electron screening in the metal. To address these gaps, we revisit ion adsorption at the metal/electrolyte interface. The approach combines the method of images with a field-theoretic framework for dilute electrolytes and metals described by the Thomas–Fermi model. Nonlocal polarization correlations in water are described by a first-order gradient expansion in the Landau free energy functional. Unlike earlier approaches that relied on the “specular reflection approximation,” our method provides a less constrained way to handle the complex electrostatic boundary conditions at the interface. Analyzing the behavior of a test charge near the interface, an electrostatic energy minimum is found. This minimum depends on the metal’s screening properties and the overall potential drop across the double layer. In addition, the alignment of water dipoles at the interface creates an asymmetry in the energy experienced by positively and negatively charged ions. Finally, we derived an expression for the electrosorption isotherm by describing both the distribution of the electrostatic potential and the lateral interactions between charges along the interface. Our findings highlight how the structure of interfacial water can drive processes such as underpotential deposition by creating favorable electrostatic conditions for ion adsorption.

Designing highly active and cost-effective electrocatalysts for the alkaline hydrogen oxidation reaction (HOR) is critical for advancing anion-exchange membrane fuel cells (AEMFCs). While dilute metal alloys have demonstrated substantial potential in enhancing alkaline HOR performance, there has been limited exploration in terms of rational design, controllable synthesis, and mechanism study. Herein, we developed a series of dilute Pd-Ni alloys, denoted as x% Pd-Ni, based on a trace-Pd decorated Ni-based coordination polymer through a facile low-temperature pyrolysis approach. The x% Pd-Ni alloys exhibit efficient electrocatalytic activity for HOR in alkaline media. Notably, the optimal 0.5 % Pd-Ni catalyst demonstrates high intrinsic activity with an exchange current density of 0.055 mA cm-2, surpassing that of many other alkaline HOR catalysts. The mechanism study reveals that the strong synergy between Pd single atoms (SAs)/Pd dimer and Ni substrate can modulate the binding strength of proton (H)/hydroxyl (OH), thereby significantly reducing the activation energy barrier of a decisive reaction step. This work offers new insights into designing advanced dilute metal or single-atom-alloys (SAAs) for alkaline HOR and potentially other energy conversion processes.

Abstract Designing highly active and cost‐effective electrocatalysts for the alkaline hydrogen oxidation reaction (HOR) is critical for advancing anion‐exchange membrane fuel cells (AEMFCs). While dilute metal alloys have demonstrated substantial potential in enhancing alkaline HOR performance, there has been limited exploration in terms of rational design, controllable synthesis, and mechanism study. Herein, we developed a series of dilute Pd−Ni alloys, denoted as x% Pd−Ni, based on a trace‐Pd decorated Ni‐based coordination polymer through a facile low‐temperature pyrolysis approach. The x% Pd−Ni alloys exhibit efficient electrocatalytic activity for HOR in alkaline media. Notably, the optimal 0.5 % Pd−Ni catalyst demonstrates high intrinsic activity with an exchange current density of 0.055 mA cm−2, surpassing that of many other alkaline HOR catalysts. The mechanism study reveals that the strong synergy between Pd single atoms (SAs)/Pd dimer and Ni substrate can modulate the binding strength of proton (H)/hydroxyl (OH), thereby significantly reducing the activation energy barrier of a decisive reaction step. This work offers new insights into designing advanced dilute metal or single‐atom‐alloys (SAAs) for alkaline HOR and potentially other energy conversion processes.

The mechanism of superconductivity in materials with aborted ferroelectricity and its emergence out of a dilute metallic phase in systems like doped SrTiO_{3} is an outstanding issue in condensed matter physics. This dilute metal has anomalous properties that are both similar and different to those found in the normal state of other unconventional superconductors. For instance, T^{2} resistivity can be found at densities that are too small to allow current decay through electron-electron scattering. We have investigated the optical properties of the dilute metallic phase in doped SrTiO_{3} using THz time-domain spectroscopy. At low frequencies the THz response exhibits a Drude-like form as expected for typical metal-like conductivity. We observed the frequency and temperature dependencies to the low energy scattering rate Γ(ω,T)∝(ℏω)^{2}+(pπk_{B}T)^{2} expected in a conventional Fermi liquid. However, we find the lowest known p values of 0.39-0.72. As p is 2 in a canonical Fermi liquid and existing models based on energy dependent elastic scattering bound p from below to 1, our observation lies outside current explanation. Our data also give insight into the high temperature regime and show that the temperature dependence of the resistivity derives in part from strong T dependent mass renormalizations.

Electroreduction of CO2 into liquid fuels is a compelling strategy for storing intermittent renewable energy. Here, we introduce a family of facet-defined dilute copper alloy nanocrystals as catalysts to improve the electrosynthesis of n-propanol from CO2 and H2O. We show that substituting a dilute amount of weak-CO-binding metals into the Cu(100) surface improves CO2-to-n-propanol activity and selectivity by modifying the electronic structure of catalysts to facilitate C1-C2 coupling while preserving the (100)-like 4-fold Cu ensembles which favor C1-C1 coupling. With the Au0.02Cu0.98 champion catalyst, we achieve an n-propanol Faradaic efficiency of 18.2 ± 0.3% at a low potential of -0.41 V versus the reversible hydrogen electrode and a peak production rate of 16.6 mA·cm-2. This study demonstrates that shape-controlled dilute-metal-alloy nanocrystals represent a new frontier in electrocatalyst design, and precise control of the host and minority metal distributions is crucial for elucidating structure-composition-property relationships and attaining superior catalytic performance.

Abstract Biological ion channels use the synergistic effects of various strategies to realize highly selective ion sieving. For example, potassium channels use functional groups and angstrom‐sized pores to discriminate rival ions and enrich target ions. Inspired by this, we constructed a layered crystal pillared by crown ether that incorporates these strategies to realize high Li+ selectivity. The pillared channels and crown ether have an angstrom‐scale size. The crown ether specifically allows the low‐barrier transport of Li+. The channels attract and enrich Li+ ions by up to orders of magnitude. As a result, our material sieves Li+ out of various common ions such as Na+, K+, Ca2+, Mg2+ and Al3+. Moreover, by spontaneously enriching Li+ ions, it realizes an effective Li+/Na+ selectivity of 1422 in artificial seawater where the Li+ concentration is merely 25 μM. We expect this work to spark technologies for the extraction of lithium and other dilute metal ions.

Biological ion channels use the synergistic effects of various strategies to realize highly selective ion sieving. For example, potassium channels use functional groups and angstrom-sized pores to discriminate rival ions and enrich target ions. Inspired by this, we constructed a layered crystal pillared by crown ether that incorporates these strategies to realize high Li+ selectivity. The pillared channels and crown ether have an angstrom-scale size. The crown ether specifically allows the low-barrier transport of Li+ . The channels attract and enrich Li+ ions by up to orders of magnitude. As a result, our material sieves Li+ out of various common ions such as Na+ , K+ , Ca2+ , Mg2+ and Al3+ . Moreover, by spontaneously enriching Li+ ions, it realizes an effective Li+ /Na+ selectivity of 1422 in artificial seawater where the Li+ concentration is merely 25 μM. We expect this work to spark technologies for the extraction of lithium and other dilute metal ions.

Magnetic nanomaterials are sought to provide new functionalities for applications ranging from information processing and storage to energy generation and biomedical imaging. MXenes are a rapidly growing family of two-dimensional transition metal carbides and nitrides with versatile chemical and structural diversity, resulting in a variety of interesting electronic and optical properties. However, strategies for producing MXenes with tailored magnetic responses remain underdeveloped and challenging. Herein, we incorporate elemental Ni and Co into Ti3C2Tx MXene by mixing with dilute metal chloride solutions. We achieve a uniform distribution of Ni and Co, confirmed by X-ray fluorescence (XRF) mapping with nanometer resolution, with Ni and Co concentrations of approximately 2 and 7 at% relative to the Ti concentration. The magnetic susceptibility of these Ni- and Co-incorporated Ti3C2Tx MXenes is one to two orders of magnitude larger than pristine Ti3C2Tx, illustrating the potential for dilute metal incorporation to enhance linear magnetic responses at room temperature.

Surface e-precipitation (SEP) is a largely unknown in separation electrochemical technique that uniquely combines the kinetic advantage of chemical precipitation with the advantages of conventional surface-based separation techniques such as electrodeposition/electrowinning (e-deposition), electrosorption, and adsorption. This work explores the potential of SEP in recovering valuable elements and removing toxic elements from mining water of a polysulfide ore origin. Without employing any reagent, in a simple batch-type laboratory setup with a carbon electrode, SEP alone or in combination with e-deposition can concentrate groups of dilute (20–30 mg/L) and ultradilute (<2 mg/L) valuable metals such as Zn, Al, Cu, Co, Ni, and rare earth elements (REE) vs gangue metals such as Mn, Fe, and an excess of Ca and Mg by an order of magnitude at highly competitive rate and energy consumption values which can reach 0.25 m3/(kg carbon ⋅ min) and 0.02 kWh/m3, respectively. The recovery and relative content of the concentrated metals can be controlled by the method design and operational variables such as applied potential, retention time (water treatment rate), and the number of stages. The uptake of Zn and Cu by SEP and e-deposition, respectively, is compared in mining waters and synthetic sulfate solutions. This comparison reveals that the ionic matrix of mining water promotes SEP but inhibits e-deposition. The comparison with the chemical precipitation at similar pH and reaction time shows that SEP has higher selectivity but lower recovery. These results demonstrate that SEP is a promising novel approach to valorizing and decontaminating acid mine drainage (AMD), process water, and metal-loaded wastewater.

The temperature dependence of the phase space for electron-electron (e-e) collisions leads to a T-square contribution to electrical resistivity of metals. Umklapp scattering is identified as the origin of momentum loss due to e-e scattering in dense metals. However, in dilute metals like lightly doped strontium titanate, the origin of T-square electrical resistivity in the absence of umklapp events is yet to be pinned down. Here, by separating electron and phonon contributions to heat transport, we extract the electronic thermal resistivity in niobium-doped strontium titanate and show that it also displays a T-square temperature dependence. Its amplitude correlates with the T-square electrical resistivity. The Wiedemann-Franz law strictly holds in the zero-temperature limit, but not at finite temperature, because the two T-square prefactors are different by a factor of ≈3, like in other Fermi liquids. Recalling the case of ^{3}He, we argue that T-square thermal resistivity does not require umklapp events. The approximate recovery of the Wiedemann-Franz law in the presence of disorder would account for a T-square electrical resistivity without umklapp.

In this study, interaction of dilute metal chloride solutes in molten eutectic LiCl-KCl was studied via equilibrium potential measurements. Open circuit potential (OCP) was measured between a pure iron rod and a Ag/AgCl reference electrode with concentration of FeCl2 varying from 0.2–1 mol% at 530 °C. The Nernst equation was used to calculate activity coefficient of FeCl2 based on OCP. Measurements were made in LiCl-KCl-FeCl2 with and without additions of 0.5 mol% CsCl, NaCl, and LaCl3. The activity coefficient of FeCl2 was found to be unaffected by these small concentrations of CsCl, LaCl3, and NaCl. However, there was observed evidence that the activity coefficient of FeCl2, above 0.8 mol% Fe, may be affected by the presence of LaCl3 at higher concentrations beginning around 0.5 mol% La. Over the full range of conditions tested, the activity coefficient of FeCl2 in molten LiCl-KCl ranged from 2.95 × 10−5 to 1.01 × 10−4.

Colloidal single-walled carbon nanotubes (SWCNTs) offer a promising platform for the nanoscale engineering of molecular recognition. Optical sensors have been recently designed through the modification of noncovalent corona phases (CPs) of SWCNTs through a phenomenon known as corona phase molecular recognition (CoPhMoRe). In CoPhMoRe constructs, DNA CPs are of great interest due to the breadth of the design space and our ability to control these molecules with sequence specificity at scale. Utilizing these constructs for metal ion sensing is a natural extension of this technology due to DNA's well-known coordination chemistry. Additionally, understanding metal ion interactions of these constructs allows for improved sensor design for use in complex aqueous environments. In this work, we study the interactions between a panel of 9 dilute divalent metal cations and 35 DNA CPs under the most controlled experimental conditions for SWCNT optical sensing to date. We found that best practices for the study of colloidal SWCNT analyte responses involve mitigating the effects of ionic strength, dilution kinetics, laser power, and analyte response kinetics. We also discover that SWCNT with DNA CPs generally offers two unique sensing states at pH 6 and 8. The combined set of sensors in this work allowed for the differentiation of Hg2+, Pb2+, Cr2+, and Mn2+. Finally, we implemented Hg2+ sensing in the context of portable detection within fish tissue extract, demonstrating nanomolar level detection.

SrTiO3, a quantum paralectric, displays a detectable phonon thermal Hall effect (THE). Here, we show that the amplitude of the THE is extremely sensitive to stoichiometry. It drastically decreases upon substitution of a tiny fraction of Sr atoms with Ca, which stabilizes the ferroelectric order. It drastically increases by an even lower density of oxygen vacancies, which turn the system to a dilute metal. The enhancement in the metallic state exceeds by far the sum of the electronic and the phononic contributions. We explain this observation as an outcome of three features: 1) Heat is mostly transported by phonons; 2) the electronic Hall angle is extremely large; and 3) there is substantial momentum exchange between electrons and phonons. Starting from Herring's picture of phonon drag, we arrive to a quantitative account of the enhanced THE. Thus, phonon drag, hitherto detected as an amplifier of thermoelectric coefficients, can generate a purely thermal transverse response in a dilute metal with a large Hall angle. Our results reveal a hitherto-unknown consequence of momentum-conserving collisions between electrons and phonons.

Superconductivity in low carrier density metals challenges the conventional electron-phonon theory due to the absence of retardation required to overcome Coulomb repulsion. Here we demonstrate that pairing mediated by energy fluctuations, ubiquitously present close to continuous phase transitions, occurs in dilute quantum critical polar metals and results in a dome-like dependence of the superconducting Tc on carrier density, characteristic of non-BCS superconductors. In quantum critical polar metals, the Coulomb repulsion is heavily screened, while the critical transverse optical phonons decouple from the electron charge. In the resulting vacuum, long-range attractive interactions emerge from the energy fluctuations of the critical phonons, resembling the gravitational interactions of a chargeless dark matter universe. Our estimates show that this mechanism may explain the critical temperatures observed in doped SrTiO3. We provide predictions for the enhancement of superconductivity near polar quantum criticality in two- and three-dimensional materials that can be used to test our theory.

Industrial ammonia synthesis through the Haber–Bosch process operated under harsh reaction conditions leaves ample room for improvement through material design. Designing a catalyst with high activity and low cost is considered as the key to enable large-scale operation under mild conditions. In this work, dilute metal alloys are studied using density functional theory (DFT) calculations and microkinetic modeling to investigate their catalytic performance for ammonia synthesis. Thermochemical scaling relations developed between reaction intermediates and Brønsted–Evans–Polanyi (BEP) relations developed for *N2 dissociation and *NHx hydrogenation form the basis of microkinetic simulations of reaction rates. A degree of rate control analysis shows that the overall reaction is rate-controlled by either *N2 dissociation or *NH2 hydrogenation, resulting in a volcano plot for single-atom alloys (SAAs) with Nb-doped Ag(111) SAA siting at the volcano peak. The BEP relationship for N2 dissociation derived on dimer alloys is closer to the ideal limit in comparison to that obtained on SAAs, leading to higher activities of dimer alloys for ammonia synthesis. Among the dimer alloys, Mo2/Ag(111) is not only more active than the commercial Ru catalysts but also very stable under real reaction conditions and could potentially be used in industrial processes.

Sr2+ and Ba2+ salts induced conformational structure of sodium polyacrylate PAA investigated by molecular dynamics simulations

Correlation governs the impurity (Ti, Zr, Hf) diffusion in face−centered cubic iridium through first−principles calculation

Insights about inductively coupled plasma optical emission spectroscopy interferences of major rare earth elements in complex e-waste feeds