Additive-Assisted Hydrothermal Growth Enabling Defect Passivation and Void Remedy in Antimony Selenosulfide Solar Cells.

Antimony selenosulfide (Sb2(S,Se)3) has recently emerged as a promising light-absorbing material, attributed to its tunable photovoltaic properties, low toxicity, and robust environmental stability. However, despite these advantages, the current record efficiency for Sb2(S,Se)3 solar cells significantly lags behind their Shockley-Queisser limit, especially when compared to other well-established chalcogenide-based thin-film solar cells, such as CdTe and Cu(In,Ga)Se2. This underperformance primarily arises from the formation of unfavorable defects, predominately located at deep energy levels, which act as recombination centers, thereby limiting the potential for performance enhancement in Sb2(S,Se)3 solar cells. Specifically, deep-level defects, such as sulfur vacancy (VS), have a lower formation energy, leading to severe non-radiative recombination and compromising device performance. To address this challenge, thioacetamide (TA), a sulfur-containing additive is introduced, into the precursor solution for the hydrothermal deposition of Sb2(S,Se)3. This results indicate that the incorporation of TA helps in passivating deep-level defects such as sulfur vacancies and in suppressing the formation of large voids within the Sb2(S,Se)3 absorber. Consequently, Sb2(S,Se)3 solar cells, with reduced carrier recombination and improved film quality, achieved a power conversion efficiency of 9.04%, with notable improvements in open-circuit voltage and fill factor. This work provides deeper insights into the passivation of deep-level donor-like VS defects through the incorporation of a sulfur-containing additive, highlighting pathways to enhance the photovoltaic performance of Sb2(S,Se)3 solar cells.

Manipulating Nanoparticle Aggregates Regulates Receptor-Ligand Binding in Macrophages.

The receptor-ligand interactions in cells are dynamically regulated by modulation of the ligand accessibility. In this study, we utilize size-tunable magnetic nanoparticle aggregates ordered at both nanometer and atomic scales. We flexibly anchor magnetic nanoparticle aggregates of tunable sizes over the cell-adhesive RGD ligand (Arg-Gly-Asp)-active material surface while maintaining the density of dispersed ligands accessible to macrophages at constant. Lowering the accessible ligand dispersity by increasing the aggregate size at constant accessible ligand density facilitates the binding of integrin receptors to the accessible ligands, which promotes the adhesion of macrophages. In high ligand dispersity, distant magnetic manipulation to lift the aggregates (which increases ligand accessibility) stimulates the binding of integrin receptors to the accessible ligands available under the aggregates to augment macrophage adhesion-mediated pro-healing polarization both in vitro and in vivo. In low ligand dispersity, distant control to drop the aggregates (which decreases ligand accessibility) repels integrin receptors away from the aggregates, thereby suppressing integrin receptor-ligand binding and macrophage adhesion, which promotes inflammatory polarization. Here, we present "accessible ligand dispersity" as a novel fundamental parameter that regulates receptor-ligand binding, which can be reversibly manipulated by increasing and decreasing the ligand accessibility. Limitless tuning of nanoparticle aggregate dimensions and morphology can offer further insight into the regulation of receptor-ligand binding in host cells.

Magnetic Control and Real-Time Monitoring of Stem Cell Differentiation by the Ligand Nanoassembly.

Native extracellular matrix (ECM) exhibits dynamic change in the ligand position. Herein, the ECM-emulating control and real-time monitoring of stem cell differentiation are demonstrated by ligand nanoassembly. The density of gold nanoassembly presenting cell-adhesive Arg-Gly-Asp (RGD) ligand on Fe3 O4 (magnetite) nanoparticle in nanostructures flexibly grafted to material is changed while keeping macroscale ligand density invariant. The ligand nanoassembly on the Fe3 O4 can be magnetically attracted to mediate rising and falling ligand movements via linker stretching and compression, respectively. High ligand nanoassembly density stimulates integrin ligation to activate the mechanosensing-assisted stem cell differentiation, which is monitored via in situ real-time electrochemical sensing. Magnetic control of rising and falling ligand movements hinders and promotes the adhesion-mediated mechanotransduction and differentiation of stem cells, respectively. These rising and falling ligand states yield the difference in the farthest distance (≈34.6 nm) of the RGD from material surface, thereby dynamically mimicking static long and short flexible linkers, which hinder and promote cell adhesion, respectively. Design of cytocompatible ligand nanoassemblies can be made with combinations of dimensions, shapes, and biomimetic ligands for remotely regulating stem cells for offering novel methodologies to advance regenerative therapies.

Large and Externally Positioned Ligand-Coated Nanopatches Facilitate the Adhesion-Dependent Regenerative Polarization of Host Macrophages.

Macrophages can associate with extracellular matrix (ECM) demonstrating nanosequenced cell-adhesive RGD ligand. In this study, we devised barcoded materials composed of RGD-coated gold and RGD-absent iron nanopatches to show various frequencies and position of RGD-coated nanopatches with similar areas of iron and RGD-gold nanopatches that maintain macroscale and nanoscale RGD density invariant. Iron patches were used for substrate coupling. Both large (low frequency) and externally positioned RGD-coated nanopatches stimulated robust attachment in macrophages, compared with small (high frequency) and internally positioned RGD-coated nanopatches, respectively, which mediate their regenerative/anti-inflammatory M2 polarization. The nanobarcodes exhibited stability in vivo. We shed light into designing ligand-engineered nanostructures in an external position to facilitate host cell attachment, thereby eliciting regenerative host responses.

In Situ Magnetic Control of Macroscale Nanoligand Density Regulates the Adhesion and Differentiation of Stem Cells.

Developing materials with remote controllability of macroscale ligand presentation can mimic extracellular matrix (ECM) remodeling to regulate cellular adhesion in vivo. Herein, we designed charged mobile nanoligands with superparamagnetic nanomaterials amine-functionalized and conjugated with polyethylene glycol linker and negatively charged RGD ligand. We coupled negatively a charged nanoligand to a positively charged substrate by optimizing electrostatic interactions to allow reversible planar movement. We demonstrate the imaging of both macroscale and in situ nanoscale nanoligand movement by magnetically attracting charged nanoligand to manipulate macroscale ligand density. We show that in situ magnetic control of attracting charged nanoligand facilitates stem cell adhesion, both in vitro and in vivo, with reversible control. Furthermore, we unravel that in situ magnetic attraction of charged nanoligand stimulates mechanosensing-mediated differentiation of stem cells. This remote controllability of ECM-mimicking reversible ligand variations is promising for regulating diverse reparative cellular processes in vivo.

Self-Passivation of 2D Ruddlesden-Popper Perovskite by Polytypic Surface PbI2 Encapsulation.

Two-dimensional Ruddlesden-Popper (2D RP) halide perovskites, C2MAn-1PbnI3n+1 (C = bulky ammonium cation; MA = methylammonium) with low n-members (n < 5), have been garnering sensational attention for photovoltaic and optoelectronic applications because of the long carrier diffusion lengths, long-term stability, and tunable bandgap. Yet, the surface modification of 2D RP under kinetic particle irradiation, such as light or electron irradiation, is ambiguous, even though it is imperative to elucidate long-stabilized conversion efficiency. Herein, we present molecular-scale observations of dynamic surface reconstruction of BA2MA2Pb3I10 (n = 3) 2D RP induced by the electron beam. The surface dynamics reveal lateral growth of polytypic PbI2 with 3R, 4H, and 2H structures at the edge and surface of the 2D perovskite, accompanied by simultaneous annihilation at the other edges. Local radiolysis occurs dominantly by the internal energy increase of electron momentum transfer, which triggers a sequential layer-by-layer degradation into PbI2. In situ observation of the polytypic PbI2 growth at the whole surface and edges of 2D RP under electron irradiation elucidates how the outer PbI2 self-passivation can protect inner 2D RP, causing longer operando stability.

Unconventional Defects in a Quasi-One-Dimensional KMn6Bi5.

Quasi-one-dimensional (Q1D) structures comprising a compact array of indefinitely long 1D nanowires (NWs) are scarce, especially in a bulk device-scale showing metallic and semiconducting behaviors along different axes. Unlike plentiful observations of nature of defects in three-/two-dimensional materials, there is a notable paucity of such reports in Q1D. Herein we present unconventional motific defects and their properties in a bulk Q1D KMn6Bi5 crystal, in which an individual NW motif acts as one body. We discovered motific inter- and intra-NW defects, such that a linear set of 1D motifs are displaced. Stress generates two domains with altered inter-NW spacings and a Bi-Mn solid solution grain, leading to a local bulk plasmon shift due to NW array reconfiguration as well as atomic rearrangement. The observation of such exotic defects and associated phenomena in this Q1D may provide guidance on overall defect mechanism in other Q1D systems and their collective anisotropic properties.

Remote Control of Heterodimeric Magnetic Nanoswitch Regulates the Adhesion and Differentiation of Stem Cells.

Remote, noninvasive, and reversible control over the nanoscale presentation of bioactive ligands, such as Arg-Gly-Asp (RGD) peptide, is highly desirable for temporally regulating cellular functions in vivo. Herein, we present a novel strategy for physically uncaging RGD using a magnetic field that allows safe and deep tissue penetration. We developed a heterodimeric nanoswitch consisting of a magnetic nanocage (MNC) coupled to an underlying RGD-coated gold nanoparticle (AuNP) via a long flexible linker. Magnetically controlled movement of MNC relative to AuNP allowed reversible uncaging and caging of RGD that modulate physical accessibility of RGD for integrin binding, thereby regulating stem cell adhesion, both in vitro and in vivo. Reversible RGD uncaging by the magnetic nanoswitch allowed temporal regulation of stem cell adhesion, differentiation, and mechanosensing. This physical and reversible RGD uncaging utilizing heterodimeric magnetic nanoswitch is unprecedented and holds promise in the remote control of cellular behaviors in vivo.

Unique [Mn6Bi5]- Nanowires in KMn6Bi5: A Quasi-One-Dimensional Antiferromagnetic Metal.

We report a new quasi-one-dimensional compound KMn6Bi5 composed of parallel nanowires crystallizing in a monoclinic space group C2/ m with a = 22.994(2) Å, b = 4.6128(3) Å, c = 13.3830(13) Å and ß = 124.578(6)°. The nanowires are infinite [Mn6Bi5]- columns each of which is composed of a nanotube of Bi atoms acting as the cladding with a nanorod of Mn atoms located in the central axis of the nanotubes. The nanorods of Mn atoms inside the Bi cladding are stabilized by Mn-Mn bonding and are defined by distorted Mn-centered cluster icosahedra of Mn13 sharing their vertices along the b axis. The [Mn6Bi5]- nanowires are linked with weak internanowire Bi-Bi bonds and charge balanced with K+ ions. The [Mn6Bi5]- nanowires were directly imaged by high-resolution transmission electron microscopy and scanning transmission electron microscopy. Magnetic susceptibility studies show one-dimensional characteristics with an antiferromagnetic transition at ∼75 K and a small average effective magnetic moment (1.56 µB/Mn for H ∥ b and 1.37 µB/Mn for H ⊥ b) of Mn from Curie-Weiss fits above 150 K. Specific heat measurements reveal an electronic specific heat coefficient γ of 6.5(2) mJ K-2(mol-Mn)-1 and a small magnetic entropy change Δ Smag ≈ 1.6 J K-1 (mol-Mn)-1 across the antiferromagnetic transition. In contrast to a metallic resistivity along the column, the resistivity perpendicular to the column shows a change from a semiconducting behavior at high temperatures to a metallic one at low temperatures, indicating an incoherent-to-coherent crossover of the intercolumn tunneling of electrons.

Remote Manipulation of Ligand Nano-Oscillations Regulates Adhesion and Polarization of Macrophages in Vivo.

Macrophages play crucial roles in various immune-related responses, such as host defense, wound healing, disease progression, and tissue regeneration. Macrophages perform distinct and dynamic functions in vivo, depending on their polarization states, such as the pro-inflammatory M1 phenotype and pro-healing M2 phenotype. Remote manipulation of the adhesion of host macrophages to the implants and their subsequent polarization in vivo can be an attractive strategy to control macrophage polarization-specific functions but has rarely been achieved. In this study, we grafted RGD ligand-bearing superparamagnetic iron oxide nanoparticles (SPIONs) to a planar matrix via a long flexible linker. We characterized the nanoscale motion of the RGD-bearing SPIONs grafted to the matrix, in real time by in situ magnetic scanning transmission electron microscopy (STEM) and in situ atomic force microscopy. The magnetic field was applied at various oscillation frequencies to manipulate the frequency-dependent ligand nano-oscillation speeds of the RGD-bearing SPIONs. We demonstrate that a low oscillation frequency of the magnetic field stimulated the adhesion and M2 polarization of macrophages, whereas a high oscillation frequency suppressed the adhesion of macrophages but promoted their M1 polarization, both in vitro and in vivo. Macrophage adhesion was also temporally regulated by switching between the low and high frequencies of the oscillating magnetic field. To the best of our knowledge, this is the first demonstration of the remote manipulation of the adhesion and polarization phenotype of macrophages, both in vitro and in vivo. Our system offers the promising potential to manipulate host immune responses to implanted biomaterials, including inflammation or tissue reparative processes, by regulating macrophage adhesion and polarization.

Doping against the native propensity of MoS2: degenerate hole doping by cation substitution.

Layered transition metal dichalcogenides (TMDs) draw much attention as the key semiconducting material for two-dimensional electrical, optoelectronic, and spintronic devices. For most of these applications, both n- and p-type materials are needed to form junctions and support bipolar carrier conduction. However, typically only one type of doping is stable for a particular TMD. For example, molybdenum disulfide (MoS2) is natively an n-type presumably due to omnipresent electron-donating sulfur vacancies, and stable/controllable p-type doping has not been achieved. The lack of p-type doping hampers the development of charge-splitting p-n junctions of MoS2, as well as limits carrier conduction to spin-degenerate conduction bands instead of the more interesting, spin-polarized valence bands. Traditionally, extrinsic p-type doping in TMDs has been approached with surface adsorption or intercalation of electron-accepting molecules. However, practically stable doping requires substitution of host atoms with dopants where the doping is secured by covalent bonding. In this work, we demonstrate stable p-type conduction in MoS2 by substitutional niobium (Nb) doping, leading to a degenerate hole density of ∼ 3 × 10(19) cm(-3). Structural and X-ray techniques reveal that the Nb atoms are indeed substitutionally incorporated into MoS2 by replacing the Mo cations in the host lattice. van der Waals p-n homojunctions based on vertically stacked MoS2 layers are fabricated, which enable gate-tunable current rectification. A wide range of microelectronic, optoelectronic, and spintronic devices can be envisioned from the demonstrated substitutional bipolar doping of MoS2. From the miscibility of dopants with the host, it is also expected that the synthesis technique demonstrated here can be generally extended to other TMDs for doping against their native unipolar propensity.

Spatial variation of available electronic excitations within individual quantum dots.

Quantum dots (QDs) allow for manipulation of the position and energy levels of electrons at sub-10 nm length scales through control of material chemistry, size, and shape. It is known from optical studies that the bandgap of semiconductor QDs increases as their size decreases due to the narrowing of the quantum confinement potential. The mechanism of quantum confinement also indicates that the localized properties within individual QDs should depend on their shape in addition to their size, but direct observations of this effect have proven challenging due to the limited spatial resolution of measurement techniques at this scale and the ability to remove contributions from the surroundings. Here we present experimental evidence of spatial variations in the lowest available electron transition energy within a series of single electrically isolated QDs due to a dome-shaped geometry, measured using electron energy-loss spectroscopy in a (scanning) transmission electron microscope [(S)TEM-EELS]. We observe a consistent increase in the energy onset of electronic excitations from the lateral center of the dot toward the edges, which we attribute purely to shape. This trend is in qualitative agreement with a simple quantum simulation of the local density of states in a dome-shaped QD.

Functionalized soft nanoporous materials through supramolecular assembly of end-functionalized polymer blends.

Supramolecular assembly through complementary interaction between molecular subgroups belonging to phase-separating polymer species offers a great opportunity, not only for constructing nanoscale soft templates reminiscent of conventional block copolymer morphologies, but also for tailoring surface properties by facile removal of one of the structure components by cleaving complementary interactions. Herein we report the fabrication of a novel, organic, nanoporous film through supramolecular assembly of two complementarily, end-interacting, mono-end-functionalized polymers under solvent annealing. The film of end-functionalized polymer blends under solvent annealing yielded phase-separated nanodomains that resemble nanoscopically ordered structures of block copolymers, but that are more advantageous due to easily cleavable and exchangeable links between the phase-separated domains. The removal of one of the components of the precursor structure formed from the end-functionalized polymers through cleavage of complementary interactions allowed us to fabricate mono- or multilayered nanoporous structures in which the chemically useful end-functionalities of the remnant polymers are rich on the surface of the pores. The resultant, organic, nanoporous films with tailored surface functionality offer a useful platform for various chemical and biological applications.

Atomic layer deposition of lead sulfide quantum dots on nanowire surfaces.

Quantum dots provide unique advantages in the design of novel optoelectronic devices owing to the ability to tune their properties as a function of size. Here we demonstrate a new technique for fabrication of quantum dots during the nucleation stage of atomic layer deposition (ALD) of PbS. Islands with sub-10 nm diameters were observed during the initial ALD cycles by transmission electron microscopy, and in situ observations of the coalescence and sublimation behavior of these islands show the possibility of further modifying the size and density of dots by annealing. The ALD process can be used to cover high-aspect-ratio nanostructures, as demonstrated by the uniform coating of a Si nanowire array with a single layer of PbS quantum dots. Photoluminescence measurements on the quantum dot/nanowire composites show a blue shift when the number of ALD cycles is decreased, suggesting a route to fabricate unique three-dimensional nanostructured devices such as solar cells.

Elucidating and Mitigating High-Voltage Degradation Cascades in Cobalt-Free LiNiO2 Lithium-Ion Battery Cathodes.

LiNiO2 (LNO) is a promising cathode material for next-generation Li-ion batteries due to its exceptionally high capacity and cobalt-free composition that enables more sustainable and ethical large-scale manufacturing. However, its poor cycle life at high operating voltages over 4.1 V impedes its practical use, thus motivating efforts to elucidate and mitigate LiNiO2 degradation mechanisms at high states of charge. Here, a multiscale exploration of high-voltage degradation cascades associated with oxygen stacking chemistry in cobalt-free LiNiO2 , is presented. Lattice oxygen loss is found to play a critical role in the local O3-O1 stacking transition at high states of charge, which subsequently leads to Ni-ion migration and irreversible stacking faults during cycling. This undesirable atomic-scale structural evolution accelerates microscale electrochemical creep, cracking, and even bending of layers, ultimately resulting in macroscopic mechanical degradation of LNO particles. By employing a graphene-based hermetic surface coating, oxygen loss is attenuated in LNO at high states of charge, which suppresses the initiation of the degradation cascade and thus substantially improves the high-voltage capacity retention of LNO. Overall, this study provides mechanistic insight into the high-voltage degradation of LNO, which will inform ongoing efforts to employ cobalt-free cathodes in Li-ion battery technology.

Dynamic Ligand Screening by Magnetic Nanoassembly Modulates Stem Cell Differentiation.

In native microenvironment, diverse physical barriers exist to dynamically modulate stem cell recruitment and differentiation for tissue repair. In this study, nanoassembly-based magnetic screens of various sizes are utilized, and they are elastically tethered over an RGD ligand (cell-adhesive motif)-presenting material surface to generate various nanogaps between the screens and the RGDs without modulating the RGD density. Large screens exhibiting low RGD distribution stimulate integrin clustering to facilitate focal adhesion, mechanotransduction, and differentiation of stem cells, which are not observed with small screens. Magnetic downward pulling of the large screens decreases the nanogaps, which dynamically suppress the focal adhesion, mechanotransduction, and differentiation of stem cells. Conversely, magnetic upward pulling of the small screens increases the nanogaps, which dynamically activates focal adhesion, mechanotransduction, and differentiation of stem cells. This regulation mechanism is also shown to be effective in the microenvironment in vivo. Further diversifying the geometries of the physical screens can further enable diverse modalities of multifaceted and safe unscreening of the distributed RGDs to unravel and modulate stem cell differentiation for tissue repair.

Submolecular Ligand Size and Spacing for Cell Adhesion.

Cell adhesion occurs when integrin recognizes and binds to Arg-Gly-Asp (RGD) ligands present in fibronectin. In this work, submolecular ligand size and spacing are tuned via template-mediated in situ growth of nanoparticles for dynamic macrophage modulation. To tune liganded gold nanoparticle (GNP) size and spacing from 3 to 20 nm, in situ localized assemblies of GNP arrays on nanomagnetite templates are engineered. 3 nm-spaced ligands stimulate the binding of integrin, which mediates macrophage-adhesion-assisted pro-regenerative polarization as compared to 20 nm-spaced ligands, which can be dynamically anchored to the substrate for stabilizing integrin binding and facilitating dynamic macrophage adhesion. Increasing the ligand size from 7 to 20 nm only slightly promotes macrophage adhesion, not observed with 13 nm-sized ligands. Increasing the ligand spacing from 3 to 17 nm significantly hinders macrophage adhesion that induces inflammatory polarization. Submolecular tuning of ligand spacing can dominantly modulate host macrophages.

Controllable Nonclassical Conductance Switching in Nanoscale Phase-Separated (PbI2 )1- x (BiI3 )x Layered Crystals.

Layered 2D (PbI2 )1- x (BiI3 )x materials exhibit a nonlinear dependence in structural and charge transport properties unanticipated from the combination of PbI2 and BiI3 . Within (PbI2 )1- x (BiI3 )x crystals, phase integration yields deceptive structural features, while phase boundary separation leads to new conductance switching behavior observed as large peaks in current during current-voltage (I-V) measurements (±100 V). Temperature- and time-dependent electrical measurements demonstrate that the behavior is attributed to ionic transport perpendicular to the layers. High-resolution transmission electron microscopy reveals that the structure of (PbI2 )1- x (BiI3 )x is a "brick wall" consisting of two phases, Pb-rich and Bi-rich. These brick-like features are 10s nm a side and it is posited that iodide ion transport at the interfaces of these regions is responsible for the conductance switching action.

Realization of Wafer-Scale 1T-MoS2 Film for Efficient Hydrogen Evolution Reaction.

The octahedral structure of 2D molybdenum disulfide (1T-MoS2 ) has attracted attention as a high-efficiency and low-cost electrocatalyst for hydrogen production. However, the large-scale synthesis of 1T-MoS2 films has not been realized because of higher formation energy compared to that of the trigonal prismatic phase (2H)-MoS2 . In this study, a uniform wafer-scale synthesis of the metastable 1T-MoS2 film is performed by sulfidation of the Mo metal layer using a plasma-enhanced chemical vapor deposition (PE-CVD) system. Thus, plasma-containing highly reactive ions and radicals of the sulfurization precursor enable the synthesis of 1T-MoS2 at 150 °C. Electrochemical analysis of 1T-MoS2 shows enhanced catalytic activity for the hydrogen evolution reaction (HER) compared to that of previously reported MoS2 electrocatalysts 1T-MoS2 does not transform into stable 2H-MoS2 even after 1000 cycles of HER. The proposed low-temperature synthesis approach may offer a promising solution for the facile production of various metastable-phase 2D materials.

Remote Control of Time-Regulated Stretching of Ligand-Presenting Nanocoils In Situ Regulates the Cyclic Adhesion and Differentiation of Stem Cells.

Native extracellular matrix (ECM) can exhibit cyclic nanoscale stretching and shrinking of ligands to regulate complex cell-material interactions. Designing materials that allow cyclic control of changes in intrinsic ligand-presenting nanostructures in situ can emulate ECM dynamicity to regulate cellular adhesion. Unprecedented remote control of rapid, cyclic, and mechanical stretching ("ON") and shrinking ("OFF") of cell-adhesive RGD ligand-presenting magnetic nanocoils on a material surface in five repeated cycles are reported, thereby independently increasing and decreasing ligand pitch in nanocoils, respectively, without modulating ligand-presenting surface area per nanocoil. It is demonstrated that cyclic switching "ON" (ligand nanostretching) facilitates time-regulated integrin ligation, focal adhesion, spreading, YAP/TAZ mechanosensing, and differentiation of viable stem cells, both in vitro and in vivo. Fluorescence resonance energy transfer (FRET) imaging reveals magnetic switching "ON" (stretching) and "OFF" (shrinking) of the nanocoils inside animals. Versatile tuning of physical dimensions and elements of nanocoils by regulating electrodeposition conditions is also demonstrated. The study sheds novel insight into designing materials with connected ligand nanostructures that exhibit nanocoil-specific nano-spaced declustering, which is ineffective in nanowires, to facilitate cell adhesion. This unprecedented, independent, remote, and cytocompatible control of ligand nanopitch is promising for regulating the mechanosensing-mediated differentiation of stem cells in vivo.