Interfacial Density Research Articles

Cuttlefish-Bone-Derived Hybrid Composite Scaffolds for Bone Tissue Engineering

Current investigations into the fabrication of innovative biomaterials that stimulate cartilage development result from increasing interest due to emerging bone defects. In particular, the investigation of biomaterials for musculoskeletal therapies extensively depends on the development of various hydroxyapatite (HA)/sodium alginate (SA) composites. Cuttlefish bone (CFB)-derived composite scaffolds for hard tissue regeneration have been effectively illustrated in this investigation using a hydrothermal technique. In this, the HA was prepared from the CFB source without altering its biological properties. The as-developed HA nanocomposites were investigated through XRD, FTIR, SEM, and EDX analyses to confirm their structural, functional, and morphological orientation. The higher the interfacial density of the HA/SA nanocomposites, the more the hardness of the scaffold increased with the higher applied load. Furthermore, the HA/SA nanocomposite revealed a remarkable antibacterial activity against the bacterial strains such as E. coli and S. aureus through the inhibition zones measured as 18 mm and 20 mm, respectively. The results demonstrated a minor decrease in cell viability compared with the untreated culture, with an observed percentage of cell viability at 97.2% for the HA/SA nanocomposites. Hence, the proposed HA/SA scaffold would be an excellent alternative for tissue engineering applications.

Characterization of the triphenylmethane dye (Patent Blue V)-modified Al/p-Si diode

The sol-gel spin coating method, an easily applicable, low-temperature, and inexpensive method, was used to grow Patent Blue V (PBV) organic thin films placed between metal and semiconductor. Atomic force microscope images were taken to reveal the morphological structure of the resulting organic film. FTIR, NMR, and UV-Vis measurements were taken to investigate the chemical features and optical structure of the PBV molecule. Using the traditional I-V, Cheung, and Norde methods of the produced Al/PBV/p-Si diode structure, ideality factor (n), barrier height (Φb), series resistance (Rs), and interfacial density of states (Nss) parameters were calculated. The differences between the results obtained with these methods arise from calculating the I-V characteristic of the methods from different regions. The ideality value of n for the produced diodes is much greater than one (n > > 1). Deviating the calculated n value from 1 indicates possible mechanisms, such as generation-recombination effect, organic PBV layer, and interfacial states. It was observed that the electronic parameters of the Al/p-Si conventional junction can be controlled using an organic PBV interlayer.Graphical abstract

Interactions between Per- and Polyfluoroalkyl Substances (PFAS) at the Water-Air Interface.

Per- and polyfluoroalkyl substances (PFAS)─so-called "forever chemicals"─contaminate the drinking water of about 100 million people in the U.S. alone and are inefficiently removed by standard treatment techniques. A key property of these compounds that underlies their fate and transport and the efficacy of several promising remediation approaches is that they accumulate at the water-air interface. This phenomenon remains incompletely understood, particularly under conditions relevant to natural and treatment systems where water-air interfaces often carry significant loads of other organic contaminants or natural organic matter. To understand the impact of organic loading on PFAS adsorption, we carried out molecular dynamics simulations of PFAS at varying interfacial densities. We find that adsorbed PFAS form strong mutual interactions (attraction between perfluoroalkyl chains and electrostatic interactions among charged head groups) that give rise to ordered interfacial coatings. These interactions often involve near-cancellation of hydrophobic attraction and Coulomb repulsion. Our findings explain an apparent paradox whereby PFAS adsorption isotherms often suggest minimal mutual interactions while simultaneously displaying a high sensitivity to the composition and density of interfacial coatings. Consideration of the compounds present with PFAS at the interface has the potential to allow for more accurate predictions of fate and transport and the design of more efficient remediation approaches.

Gas-Liquid Interface of Aqueous Solutions of Surface Active Aromatic Molecules Studied Using Extreme Ultraviolet Laser Photoelectron Spectroscopy and Molecular Dynamics Simulation.

We investigated the gas-liquid interface of aqueous solutions containing phenol and related aromatic compounds using extreme ultraviolet laser photoelectron spectroscopy and molecular dynamics simulations. The interfacial densities of protonated and deprotonated forms of phenol, aniline, and 4-nitrophenol were found to be primarily determined by their surface affinities and exhibit similar concentration dependences to their respective bulk densities. Despite the distinct interfacial orientations of their permanent dipole moments, these compounds monotonically decreased the surface potential at higher concentrations. The exception was sodium phenolate, whose surface potential first increased and then decreased with increasing concentration. This behavior is attributed to the opposing effects of the electric double layer formed by Na+ and phenolate ions at the gas-liquid interface and the induced electronic polarization of phenolate.

Boron-doped diamond MOSFETs operating at temperatures up to 400°C

The boron-doped diamond (B-diamond) metal-oxide–semiconductor field–effect transistors (MOSFETs) are fabricated and characterized at operating temperatures up to 400°C. The SiO2 serves as the gate oxide insulator, while the Ti/Pt bilayer is employed as the gate contact metal. As the operating temperature rises from room temperature (RT) to 400°C, the absolute drain current maximum for the B-diamond MOSFET increases from 3.9 μA mm−1 to 177.4 μA mm−1. Conversely, the on-resistance decreases significantly from 1469.8 kΩ mm to 16.5 kΩ mm. The on/off ratio for the MOSFET at RT is 1.9 × 105, which increases to over 5.0 × 106 at temperatures exceeding 100°C. The threshold voltage exhibits a decreasing trend, though it deviates from this trend at 300°C. The subthreshold voltage and extrinsic transconductance maximum show increasing trends from 113 mV dec−1 to 299 mV dec−1 and from 0.9 μS mm−1 to 23.1 μS mm−1, respectively. The interfacial trapped charge density is found to be stable in the range of 8.0 × 1011–2.3 × 1012 eV−1 cm−2.

Theoretical evaluation of the realizable power conversion efficiency and the possible scheme for hole-transport-layer-free carbon-cathode CsPbI2Br solar cells

Abstract Hole-transport-layer (HTL)-free carbon-cathode CsPbI2Br solar cells have gained notable attention because of the good balance between light absorption and improved stability, as well as the cost advantage. However, the power conversion efficiency (PCE) experimentally realized for the related solar cells of < 16% is necessarily improved for possible practical application. In this study, the impact of the interfacial defect density between CsPbI2Br and the carbon cathode that is one of the most pivotal factors influencing the PCE improvement is studied, and meanwhile a feasible scheme using a thin AlOx passivation layer to block electrons and allow hole tunneling is proposed. The PCE of 19.68% is predicted for HTL-free carbon-cathode CsPbI2Br solar cells.

Nonpolar P-type Conjugated Small Molecules Enable High-Performance Organic Photodetectors for Potential Application in Optical Wireless Communication.

The high responsivity and broad spectral sensitivity of organic photodetectors (OPDs) present a bright future of commercialization. However, the relatively high dark current density still limits its development. Herein, two novel nonpolar p-type conjugated small molecules, NSN and NSSN, are synthesized as interface layers to enhance the performance of the OPDs, which not only can tune energy alignments and increase the reverse charge injection barrier but also can reduce the interfacial trap density. Moreover, benefiting from the smoother surface morphology and enhanced conductivity, the NSN exhibited superior charge transport and collection properties. Consequently, the OPD with NSN achieved a dark current density of 0.37 nA cm-2 and a high specific detectivity of 2.77 × 1013 Jones at -2 V. More importantly, the optimized OPDs can be successfully integrated into optical communication systems, demonstrating precise digital signal communication without obvious distortion, showing promising application potential in the wireless transmission system.

High-power ultrasonic spot welding of copper to type 304L austenitic stainless steel

The demand for a robust welding technique capable of joining copper and steel is driven by their extensive application across various industrial sectors. Addressing the limitations of current welding methods, this study explores the effectiveness of ultrasonic welding in joining commercially pure copper to type 304L stainless steel. The effects of different welding parameters on the characteristics of the welded joints were investigated. The results demonstrate the successful welding of the two metals without inserting an interlayer despite the metallurgical immiscibility of copper and iron. The interfacial bond density and the joint strength were found to increase with the applied welding energy. A joint strength of approximately 80% of the base copper strength was obtained. Transmission electron microscopy (TEM) analysis unveiled a well-bonded interface with excellent continuity between the two metals. A diffusion layer containing nano-sized chromium-rich oxide or intermetallic compound particles was observed. It was noticed that copper penetrated the partially disrupted chromium-rich oxide layer reaching and developing intimate contact with the newly uncoated stainless steel surface. A synergy of mechanical interlocking and solid-state metallurgical adhesion was revealed for the bonding mechanism in addition to potential metallurgical interactions at the interface.

Optical Detection of Proteins Using Microgel-Stabilized Pickering Liquid Crystal-in-Water Emulsions.

Herein, we present a novel liquid crystal (LC)-based sensing platform utilizing microgel-stabilized Pickering LC droplets dispersed in water for simple and label-free detection of proteins in an aqueous environment. This could be achieved by tailoring the surface of 4-cyano-4'-pentylbiphenyl (5CB) LC droplets dispersed in aqueous medium through the interfacial adsorption of poly(N-isopropylacrylamide) (PNIPAM) microgel particles, followed by the introduction of model surfactants, such as anionic sodium dodecyl sulfate and cationic dodecyltrimethylammonium bromide. These surfactant/microgel complex-coated LC droplets underwent a configurational transition from radial-to-bipolar under a polarized optical microscope, upon exposure to model proteins, namely bovine serum albumin and lysozyme. This transition stemmed from the interfacial adsorption of proteins, which was facilitated by their strong interaction with the preadsorbed microgel particles and surfactant molecules. The adsorption of proteins led to the disruption of the interfacial packing density of surfactant molecules, inducing a switch from homeotropic-to-planar surface anchoring of LCs within the droplets. In addition to providing remarkable Pickering stability to the LC droplets, the microgel coating significantly enhanced the sensitivity of the resulting emulsions to proteins. The dose-response behavior and detection limit of these modified LC droplets were strongly influenced by the microgel concentration, surfactant charge, pH of the medium, and the types of proteins. Notably, the droplets exhibited heightened responsiveness under conditions that favor attractive interactions between the proteins and interfacial surfactant molecules. Thus, this study opens avenues for engineering Pickering LC-based biosensors to discern biomolecular interactions, thereby facilitating various interfacial and sensing applications.

Research on Total Ionizing Dose Effect of double-trench SiC MOSFET

In this article, the impact of <sup>60</sup>Co-γ ray irradiation on double trench SiC metal–oxide–semiconductor field-effect transistors (MOSFETs) was investigated under different condiation. First, the effect of the total ionizing dose(TID) on the electrical performance of the device at different gate bias voltages was carried out. The results indicate that at 150 krad (Si) irradiation dose, the threshold voltage of the device after irradiation decreases by 3.28 V and 2.36 V for gate voltages of +5 V and -5 V bias, respectively, whereas the threshold voltage of the device after irradiation decreases by only 1.36 V for a gate voltage of 0 V bias. The threshold voltage of the device after irradiation drifts in the negative direction, and the degradation of the electrical performance is especially obvious under the positive gate bias. This is attributed to the increase in the number of charges trapped in the oxide layer. Meanwhile, room temperature annealing experiments were performed on the irradiated devices for 24, 48 and 168 hours. The shallow oxide trap charges generated by irradiation annealed at room temperature, while the deep oxide trap charges and interface trap charges were difficult to recover at room temperature, resulting in an increase in the threshold voltage of the devices after annealing, indicating that the electrical properties of the devices could be partially recovered after annealing at room temperature. In order to characterise the effect of <sup>60</sup>Co-γ ray irradiation on the interfacial state defect density of the devices, low frequency noise (1/<i>f</i>) tests were performed at different doses and different gate bias voltages. The 1/<i>f</i> low frequency noise test revealed that, under different bias voltages, the presence of oxide trap charges induced inside the oxide layer of the device after irradiation and the interfacial trap charges generated at the SiO<sub>2</sub>/SiC interface increased the irradiated defect density inside the device. This resulted in an increase of 4-9 orders of magnitude in the normalized power spectral density of the drain current noise of the irradiated device.To further obtain the irradiation damage mechanism of the device, a numerical simulation study was carried out using the TCAD simulation tool, and the results revealed that a large number of oxide trap charges induced by irradiation in the oxide layer cause an increase in the electric field strength in the gate oxide layer close to the trench side, which leads to a negative drift of the threshold voltage of the device and affects the performance of the device. The results of this paper can provide important theoretical references for the radiation effect mechanism and radiation reinforcement design of double trench SiC MOSFET devices.

Enhancement of performance and reliability in MOSFETs via high-pressure microwave annealing

This study introduces a novel approach to enhance the electrical and reliability characteristics of metal-oxide-semiconductor transistors (MOSFETs) through high-pressure microwave annealing (HPMWA) as a post-metallization annealing (PMA) technique. HPMWA effectively passivates traps by supplying energy in the form of both heat and microwaves, thereby offering key advantages such as low-temperature processing (≤350 °C), rapid volumetric heating, and material selectivity. These factors collectively lead to significant improvements in interface quality, resulting in superior device performance, including a low subthreshold slope (65.7 mV/dec), high on/off ratio (6.64 × 107), and elevated field-effect mobility (110.4 cm2/V s), compared to devices treated with conventional thermal annealing methods. The findings are experimentally validated by measuring interfacial trap density and positive bias stability. Consequently, HPMWA emerges as a crucial process for future semiconductor applications that require low-temperature processing, particularly in flexible electronics and back-end-of-line integration.

Microstructure evolution and thermoelectric behaviour of directionally solidified Bi2Te3–Ga2Te3 eutectic alloy

Abstract Thermoelectric (TE) materials are known for efficiently converting thermal to electrical energy, and vice versa. Multiphase TEs offer better freedom to tune the TE properties of such materials by varying individual phase fractions, microstructural morphology, interface density controls, etc. These controlled changes in microstructural features can be achieved by directional solidification. Bi2Te3-Ga2Te3 based TEs have been reported with enhanced TE performance. In the present study, alloys with a combination of these phases were developed using a eutectic composition from the pseudo-binary phase diagram of Bi2Te3–Ga2Te3. The alloys were fabricated using the vertical Bridgman method with three different solidification velocities (V), namely 1000 (E1), 200 (E2) and 10 (E3) μm s−1, at a constant temperature gradient of 35 K cm−1 at the solid/liquid interface. Microstructural features show a significant change in the morphology and the interlamellar spacing between two adjacent Ga2Te3 lamellae in alloys E1, E2 and E3. In addition, x-ray diffraction patterns suggest changes in the lattice parameters of Bi2Te3 and Ga2Te3 for all alloys. Significant change in the macrotexture of the different alloys was observed along the growth direction. The highest power factor of 1.6 mW mK−2 was recorded for alloy E2 at room temperature. Alloy E2 shows the highest figure of merit among all the alloys investigated (0.38 at room temperature), attributed to the highest S value of 201.7 μV K−1 at room temperature. In addition, the total thermal conductivity of all alloys was around 1.33 W mK−1 at 307 K, while alloy E1 has the smallest lattice and bipolar thermal conductivity.

A Tale of Two Tails: Tail Ordering of Stoichiometric 1:1 DTAB:SDS Pairs Adsorbed at the Oil-Water Interface.

Cationic:anionic surfactant mixtures adsorbed at an oil-water interface stabilize foams in the presence of oil, making them essential to the oil, gas, and firefighting industries. The oil tolerance of foams stabilized by surfactant mixtures, relative to pure (unmixed) cationic and anionic surfactants, results from the mixtures' enhanced flexibility in tailoring the physicochemical properties of the interface. To judiciously employ these mixtures, it is necessary to characterize the structure-function property relationship of their surfactant monolayers that lend to oil-tolerant/intolerant foams. In this work, we employ interfacial tensiometry and vibrational sum frequency spectroscopy to determine the composition (surfactant population and cationic:anionic ratio) and the structure (surfactant alkyl tail conformation) of monolayers prepared at the oil-water interface by 1:1 DTAB:SDS (dodecyltrimethylammonium bromide:sodium dodecyl sulfate) mixtures. We show that the interfacial surfactant density of 1:1 DTAB:SDS mixtures greatly exceeds that of pure DTAB and SDS at similar concentrations up to and beyond their respective critical micelle concentration. The enhanced interfacial adsorption of these mixtures is due to the adsorption of stoichiometric 1:1 DTAB:SDS surfactant pairs that form through the attractive electrostatic interactions between surfactant headgroups. We find that these paired surfactants preferentially adsorb at the interface, causing the interfacial DTAB:SDS ratio to be nearly 1:1. Additionally, we find that the SDS tail is more conformationally ordered than the DTAB tail, even though they are expected to be conformationally identical along the entire tail, since they are likely conjoined through van der Waals interactions. This leads to the conclusion that the surfactant pairs are in a staggered arrangement at the interface. These findings help to uncover molecular factors that contribute to the enhanced oil tolerance, and in some cases oil intolerance, of foams stabilized by cationic:anionic surfactant mixtures.

Toward the Use of Composite Cathode with Significantly High Interfacial Area Density for Solid-State Li–S Batteries

Toward the Use of Composite Cathode with Significantly High Interfacial Area Density for Solid-State Li–S Batteries

Ex-situ observation of ferrite grain growth behavior in a welded 9Cr-1Mo-V-Nb steel during aging at 740 °C

It has recently been reported that ferrite grains coarsened to several hundred micrometers were occasionally observed in long-term serviced 9Cr-1Mo-V-Nb steel welds. To clarify the factors that cause ferrite grain growth in martensite during high-temperature exposure, alternating aging heat treatment and observation of the same field of view was performed using a welded 9Cr-1Mo-V-Nb steel. Such ex-situ observations revealed that the rapid grain growth of ferrite by consuming martensite occurred in the weld metal during aging at 740 °C. In the test material used in this study, some δ-ferrite grains were observed in the weld metal near the fusion line. In the region where δ-ferrite grains were observed, the concentrations of austenite-forming elements such as Mn and Ni were locally decreased in the matrix due to dilution by the base metal, promoting δ-ferrite retention after welding. Ex-situ observation indicated that no significant grain growth of δ-ferrite occurred during aging. Therefore, it was suggested that a new ferrite grain formation followed by rapid grain growth consuming martensite occurred during aging. The elastic strain energy density of the dislocations PMdis and the interfacial energy density PMsurf in martensite can affect the driving force for ferrite grain growth by consuming martensite. Based on the evaluation results for PMdis and PMsurf after 500 h of aging, PMsurf was considered to be the main driving force for ferrite grain growth. Although the ferrite-formation process could not be directly observed, it is possible that ferrite was formed by the recrystallization of martensite through the bulging mechanism.

Electrodeposition for Metal Recovery from Spent Batteries: Strategies for Improving Selectivity

Selective recovery of critical metals such as cobalt and nickel at a molecular level is crucial for the sustainable recycling of Li-ion batteries. However, the similarity in reduction potentials between these metals presents a significant challenge for achieving selectivity during electrodeposition, particularly for elements like cobalt and nickel (with E°Co = −0.277 V and E°Ni = −0.250 V vs SHE). In this presentation, we introduce a key strategy aimed at controlling selectivity toward either cobalt or nickel during potential-dependent electrodeposition. Initially, manipulating the electrolyte composition to introduce an excess of chloride ions enables precise control over speciation, leading to the distinct formation of anionic cobalt chloride complexes (CoCl42-) while keeping nickel predominantly in its cationic form ([Ni(H2O)5Cl]+) within an aqueous electrolyte. This forms the basis for potential-dependent selectivity. Additionally, regulating the interfacial charge density through electrode functionalization further fine-tunes selectivity by controlling the diffusion coefficient of the target ions. Moreover, we demonstrate the effectiveness of temperature-dependent control in achieving selectivity, resulting in a Ni/Co ratio exceeding 100. Unlike traditional selective electrodeposition methods, where the extended enrichment of one metal on the solid surface adversely impacts dynamic selectivity due to concentration change in the bulk electrolyte, our innovative approach guarantees high-purity and high-recovery metal extraction even during prolonged electrodeposition. This study presents a hopeful prospect for selective electrodeposition as a proficient separation method in battery recycling procedures.

Enhancing Interfacial Capacitance Using Anionic Amphiphiles in Ionic Liquid Electrolyte Blends

The acceleration of climate change due to carbon emissions has generated an imminent need to transition towards renewable energy sources. However, the intermittent nature of renewable sources like wind or solar energy necessitates breakthroughs in energy storage devices that can rapidly charge and discharge. This demand creates a new role for high power density supercapacitors. While supercapacitors can quickly discharge electricity, they are limited by low energy densities. This limitation in energy density has generated research interest into charge storage mechanisms at interfaces and new types of supercapacitor electrolytes. An ideal supercapacitor electrolyte has a wide electrochemical stability window and high capacitance to maximize the energy density. Ionic liquids (ILs) show potential for this role with their wide electrochemical stability windows, nonflammability, and nonvolatility. Problematically, strong ion correlations present in ILs result in low capacitances. I will discuss our work aimed at tuning ionic correlations in binary IL blends to provide pathways towards higher energy density capacitive interfaces. We show how the addition of surface-active amphiphilic anions weakens these correlations increasing the interfacial charge density and capacitance of these IL blends. Notably, we find that mixing surface-active amphiphilic anions with nonamphiphilic ILs doubles the capacitance at negative surfaces. We hypothesize that polarity-dictated anion-anion van der Waals interactions serve to weaken IL cation-anion interactions and ultimately drive molecular assembly at negative surfaces, increasing capacitance. I will also present our complementary investigations of non-amphiphilic binary IL mixtures and provide spectroscopic insight into bulk ion correlations within these systems. Our study ultimately paves the path towards fundamental investigations into the chemical nature of additives in ionic liquid blends to boost performance within next-generation supercapacitors.

(Invited) Common Practical Challenges in Characterization of Wide-Bandgap Semiconductors

For the past decade, Sandia National Laboratories has been at the forefront of research in vertical gallium nitride power semiconductor devices. Prime examples of this are the demonstration of a world record > 6 kV GaN pn diode, as well as the first demonstration of a > 1.2 kV vertical GaN trench MOSFET with a HfO2 gate dielectric. In the past six years, Sandia has worked on a program funded by the Department of Energy’s Vehicle Technologies Office to develop vertical GaN power semiconductors for next-generation vehicle electrification. This talk focuses on the challenges and cycles of learning from that program as they relate to the characterization and development of wide bandgap (WBG) power semiconductors.Many of the conventional characterization techniques used for WBG semiconductors were developed for Si-based electronics in the latter half of the 20th century and were later adapted to WBG semiconductors. As the understanding of WBG semiconductors evolves over time, it becomes necessary to reevaluate these techniques for sources of error and to provide modifications and alternate methods which adapt to the nuances of the material being evaluated. One such example of this is the challenge in extracting the density of interface traps (DIT ) in a WBG metal oxide semiconductor (MOS) capacitor. We will explore some of the nuances in extracting DIT for a WBG semiconductor compared to silicon. In addition, we propose a method of visual qualification of the shape of the DIT vs. [EC-ET] curve which can be used to assess the accuracy of the extraction.Reducing channel resistance for MOSFETs is a key factor in improving performance and has an especially large impact for GaN or SiC vertical devices rated at 1700 V or below. A large contributing element to high channel resistance comes from low channel mobilities which are often reported as low as 15-30 cm2/V·s for SiC, but have been reported as high as 200 cm2/V·s for GaN. A common and basic technique for extracting mobility in SiC planar devices is to use fatFET structures which are long channel devices where the channel resistance becomes the dominant contributor to total device resistance, and hence provides an accurate method for extracting channel mobility. For trench MOSFETs, making a long channel device is not a viable option due to the channel orientation, hence it becomes challenging to find a good approach for extracting channel mobility. One method sometimes used to extract mobility is the transconductance method. We will discuss this method and the inaccuracy of this technique for extracting channel mobility in trench MOSFETs. In our study, the transconductance technique underestimates channel mobility by as much as 33% and the error is associated with the additional series resistance. We will discuss this issue and as well as alternate approaches to extracting mobility.Another challenge we report on concerns the extraction of contact resistivity and the limitations of various techniques. Using the circular transmission line model (CTLM) for extracting contact resistivity has several challenges related to the thickness of the semiconductor film below the contact, the correction factor approximation, and the error for extremely low resistivity contacts. For thick films, alternative methods like the Cox and Strack [1] method are significantly more area efficient. Understanding the limitations of these techniques helps set boundaries on our interpretation of data and is key in providing accurate information on contact resistivity. References R. H. Cox and H. Strack, Solid-State Electron. 10 (12), 1213 (1967). This work was supported by the Electric Drivetrain Consortium managed by Susan Rogers of DOE’s Vehicle Technologies Office. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Engineering the Coherent Phonon Transport in Polar Ferromagnetic Oxide Superlattices.

Artificial superlattices composed of perovskite oxides serves as an essential platform for engineering coherent phonon transport by redefining the lattice periodicity, which strongly influences the lattice-coupled phase transitions in charge and spin degrees of freedom. However, previous methods of manipulating phonons have been limited to controlling the periodicity of superlattice, rather than utilizing complex mutual interactions that are prominent in transition metal oxides. In this study onoxide superlattices composed of ferromagnetic metallic SrRuO3 and quantum paraelectric SrTiO3, phonon modulation by controlling the geometry of superlattice in atomic-scale precision is realized, demonstrating the coherent phonon engineering using structural and magnetic phase transitions. By modulating the interface density, coherent-incoherent crossover of the phonon transport at room temperature is observed, which is coupled with a change in interfacial structural continuity. Upon cooling, the close relation between phonon transport and multiple phase transitions is identified. In particular, the enhancement of the polar state in SrTiO3 layer at ≈200K leads to the weakening of phonon coherence and a further reduction of thermal conductivity in superlattices compared to the bulk limit. These findings provide a guide to developing future thermoelectric nanodevices by engineering the coherence of phonons via the design of complex oxide heterostructures.

Self‐Assembled Monolayer Dyes for Contact‐Passivated and Stable Perovskite Solar Cells

AbstractSurface modification of transparent conductive oxides (TCOs) with carbazole‐based self‐assembled monolayers (SAMs) is an effective method toward the formation of highly efficient hole‐selective contacts, enabling the fabrication of high‐performance perovskite solar cells (PSCs). However, the lack of long‐term structural and performance stability of the TCO/SAM/perovskite stack endangers the market entry of PSCs. Here, it is demonstrated that these challenges can be overcome by employing dyes as multi‐functional SAMs, simultaneously facilitating charge transport, passivating interfacial defects, and acting as a “molecular adhesive” layer, preserving structural integrity of the contact stack. Particularly, the surface modification of ITO with a dye (N719) monolayer is shown to create a hole‐selective contact for the fabrication of p–i–n PSCs with power conversion efficiencies reaching 24%. The N719 SAM‐based PSCs have also shown superior stability compared to state‐of‐the‐art PSCs incorporating carbazole SAMs and polyarylamine hole‐selective contacts by preserving ≈90% of their initial PCE under continuous light and thermal stress tests for 1000 h. The robustness of the ITO/N719/perovskite stack is attributed to its low interfacial trap density, UV resilience and strong adhesion capability. These findings place dye SAMs as a promising alternative for improving the performance of next‐generation photovoltaics.