Solution-phase Process Research Articles

Self-Aligning Nanojunctions for Integrated Single-Molecule Circuits.

Robust, high-yield integration of nanoscale components such as graphene nanoribbons, nanoparticles, or single-molecules with conventional electronic circuits has proven to be challenging. This difficulty arises because the contacts to these nanoscale devices must be precisely fabricated with angstrom-level resolution to make reliable connections, and at manufacturing scales this cannot be achieved with even the highest-resolution lithographic tools. Here we introduce an approach that circumvents this issue by precisely creating nanometer-scale gaps between metallic carbon electrodes by using a self-aligning, solution-phase process, which allows facile integration with conventional electronic systems with yields approaching 50%. The electrode separation is controlled by covalently binding metallic single-walled carbon nanotube (mCNT) electrodes to individual DNA duplexes to create mCNT-DNA-mCNT nanojunctions, where the gap is precisely matched to the DNA length. These junctions are then integrated with top-down lithographic techniques to create single-molecule circuits that have electronic properties dominated by the DNA in the junction, have reproducible conductance values with low dispersion, and are stable and robust enough to be utilized as active, high-specificity electronic biosensors for dynamic single-molecule detection of specific oligonucleotides, such as those related to the SARS-CoV-2 genome. This scalable approach for high-yield integration of nanometer-scale devices will enable opportunities for manufacturing of hybrid electronic systems for a wide range of applications.

One-pot synthesis of heterostructured CsPbBr3/PdSe nanowires with excellent humidity stability.

Lead halide perovskite nanowires (NWs) have garnered increasing attention owing to their unique properties, including axial carrier transportation, low pumping thresholds, and polarized emission. However, their intrinsic instability significantly limits their applications. In this study, heterostructured CsPbBr3/PbSe NWs with a diameter of 10 nm and lengths ranging from several to tens of microns were successfully synthesized via a one-pot solution-phase process. Photoluminescence measurements revealed that the CsPbBr3/PbSe NWs emitted green fluorescence with a narrow width of 16 nm and a high photoluminescence quantum yield (PLQY) of 37.6%. The obtained CsPbBr3/PbSe NWs underwent anion exchange with I- ion precursors to transform into CsPbBr3-xIx/PbSe, but not with Cl- ion precursors. Remarkably, these heterostructured CsPbBr3/PbSe NWs remained stable when immersed in water or exposed to air for several months, demonstrating excellent humidity stability. This study offers an effective approach for preparing stable CsPbBr3 NWs and fosters their future applications in optoelectronic devices.

Zinc‐Imidazolate Films as an All‐Dry Resist Technology

AbstractMotivated by the drawbacks of solution phase processing, an all‐dry resist formation process is presented that utilizes amorphous zinc‐imidazolate (aZnMIm) films deposited by atomic/molecular layer deposition (ALD/MLD), patterned with electron beam lithography (EBL), and developed by novel low temperature (120 °C) gas phase etching using 1,1,1,5,5,5‐hexafluoroacetylacetone (hfacH) to achieve well‐resolved 22 nm lines with a pitch of 30 nm. The effects of electron beam irradiation on the chemical structure and hfacH etch resistance of aZnMIm films are investigated, and it is found that electron irradiation degrades the 2‐methylimidazolate ligands and transforms aZnMIm into a more dense material that is resistant to etching by hfacH and has a C:N:Zn ratio effectively identical to that of unmodified aZnMIm. These findings showcase the potential for aZnMIm films to function in a dry resist technology. Sensitivity, contrast, and critical dimensions of the patterns are determined to be 37 mC cm−2, 0.87, and 29 nm, respectively, for aZnMIm deposited on silicon substrates and patterned at 30 keV. This work introduces a new direction for solvent‐free resist processing, offering the prospect of scalable, high‐resolution patterning techniques for advanced semiconductor fabrication processes.

Tunable Sulfur Incorporation into Atomic Layer Deposition Films Using Solution Anion Exchange

Metal sulfide and oxysulfide thin films deposited by atomic layer deposition (ALD) are important functional materials for a range of applications including solar cells, catalysts, and electronic devices. However, ALD of sulfur-containing films typically requires H2S, a toxic, corrosive, and flammable gas. To circumvent these challenges, we propose a method of tuning sulfur incorporation into ALD films by first growing a metal oxide, using CuOx as a model system, followed by a solution-phase sulfur anion-exchange process. By controlling the reaction time, solution molarity, and temperature, we demonstrate tunable sulfur incorporation into the films, which is described using a coupled reaction-diffusion model. The evolution of the film crystallinity, composition, and morphology was quantified as a function of the anion-exchange process parameters. Conformal anion exchange on a ZnO@TiO2@CuO core–shell–shell nanowire is shown, demonstrating the ability to maintain the conformality of the initial ALD process on high-aspect-ratio structures. Additionally, area-selective anion exchange was performed on micro-patterned substrates, illustrating a pathway toward device fabrication. Finally, the electrical properties of the converted films were evaluated, indicating a tunable reduction in sheet resistance of up to 4 orders of magnitude. In the future, the combination of ALD and anion-exchange chemistry can be used to incorporate sulfur without the need for H2S gas, while maintaining the atomically precise and conformal properties of the original ALD process.

A Universal Perovskite Nanocrystal Ink for High-Performance Optoelectronic Devices.

Semiconducting lead halide perovskite nanocrystals (PNCs) are regarded as promising candidates for next-generation optoelectronic devices due to their solution processability and outstanding optoelectronic properties. While the field of light-emitting diodes (LEDs) and photovoltaics (PVs), two prime examples of optoelectronic devices, has recently seen a multitude of efforts toward high-performance PNC-based devices, realizing both devices with high efficiencies and stabilities through a single PNC processing strategy has remained a challenge. In this work, diphenylpropylammonium (DPAI) surface ligands, found through a judicious ab-initio-based ligand search, are shown to provide a solution to this problem. The universal PNC ink with DPAI ligands presented here, prepared through a solution-phase ligand-exchange process, simultaneously allows single-step processed LED and PV devices with peak electroluminescence external quantum efficiency of 17.00% and power conversion efficiency of 14.92% (stabilized output 14.00%), respectively. It is revealed that a careful design of the aromatic rings such as in DPAI is the decisive factor in bestowing such high performances, ease of solution processing, and improved phase stability up to 120days. This work illustrates the power of ligand design in producing PNC ink formulations for high-throughput production of optoelectronic devices; it also paves a path for "dual-mode" devices with both PV and LED functionalities.

PEG-Infiltrated Polyoxometalate Frameworks with Flexible Form-Factors.

We present the synthesis of metal oxide frameworks composed of the Preyssler anion, [NaP5W30O110]14–, bridged with transition-metal cations and infiltrated with polyethylene glycol. The frameworks can be dissolved in water to form freestanding rigid or flexible films or gels. Powder X-ray diffraction shows that all form-factors maintain the short-range order of the original crystals. Raman spectroscopy reveals that, similar to hydrogels, the macroscopic mechanical properties of these composites are dependent on the water content and the extent of hydrogen-bonding within the water network. The understanding gained from these studies facilitates solution-phase processing of polyoxometalate frameworks into flexible form factors.

Facile Morphology and Porosity Regulation of Zeolite ZSM-5 Mesocrystals with Synergistically Enhanced Catalytic Activity and Shape Selectivity

The morphology and mesoporosity of zeolite are two vital properties to determine its performance in diverse applications involving adsorption and catalysis; while it remains a big challenge for the synthesis and regulation of zeolites with exceptional morphology/porosity only through inorganic-ions-based modification. Herein, by simply optimizing the alkali metal type (K+ or Na+), as well as alkali/water ratio and crystallization temperature, the zeolite ZSM-5 mesocrystals with diverse mesostructures are simply and controllably prepared via fine-tuning the crystallization mechanism in an organotemplate-free, ions-mediated seed-assisted system. Moreover, the impacts of these key parameters on the evolution of seed crystals, the development and assembly behavior of aluminosilicate species and the solution-phase process during zeolite crystallization are investigated by means of directional etching in NH4F or NaOH solutions. Except for the morphology/mesoporosity modulation, their physical and chemical properties, such as particle size, microporosity, Si/Al ratio and acidity, can be well maintained at a similar level. As such, the p/o-xylene adsorption and catalytic performance of o-xylene isomerization are used to exhaustively evaluate the synergistically enhanced catalytic activity and shape selectivity of the obtained products. This work demonstrates the possibility of effectively constructing novel zeolite mesostructures by simply altering parameters on simple ions-controlled crystallization and provides good models to inspect the impacts of mesoporosity or morphology on their catalytic performances.

Mass production of self-passivated perovskite microlaser particles by solution-phase processing for gas sensors

Developing mass-productive and high-performance microlaser particles (MLPs) by cost-effective approaches is highly promising for MLP-based optoelectronic applications, which remains a daunting challenge. Herein, we develop a novel solution-phase technique to realize the halide perovskite-based MLPs in a scalable manner. By regulating the dynamic process of crystallization in a two-step spin-coating procedure, the large-scale CsPbBr3 microcrystals are acquired. Importantly, the solution-processed CsPbBr3 microcrystals exhibit much stronger emission than the ones prepared by the chemical vapor deposition method, which is attributed to the low carrier trap density by the formation of a self-passivated and bromine-rich surface. These CsPbBr3 microcrystals with inverted pyramid morphology are demonstrated to support the whispering-gallery mode lasing, featuring low pump threshold and high Q-factor. Moreover, the technologically important single-mode lasing is achieved from the sub-5 μm-sized MLPs, thanks to the superior optical property. Eventually, the laser-emission-based gas sensor is demonstrated. These results represent a significant step toward scalable MLPs and related applications.

2D Colloids: Size- and Shape-Controlled 2D Materials at Fluid-Fluid Interfaces.

Advances in synthesis of model 3D colloidal particles with exotic shapes and physical properties have enabled discovery of new 3D colloidal phases not observed in atomic systems, and simulations and quasi-2D studies suggest 2D colloidal systems have an even richer phase behavior. However, a model 2D (one-atom-thick) colloidal system has yet to be experimentally realized because of limitations in solution-phase exfoliation of 2D materials and other 2D particle fabrication technologies. Herein, we use a photolithography-based methodology to fabricate size- and shape-controlled monolayer graphene particles, and then transfer the particles to an air-water interface to study their dynamics and self-assembly in real-time using interference reflection microscopy. Results suggest the graphene particles behave as "hard" 2D colloidal particles, with entropy influencing the self-assembled structures. Additional evidence suggests the stability of the self-assembled structures manifests from the edge-to-edge van der Waals force between 2D particles. We also show graphene discs with diameters up to 50 μm exhibit significant Brownian motion under optical microscopy due to their low mass. This work establishes a facile methodology for creating model experimental systems of colloidal 2D materials, which will have a significant impact on our understanding of fundamental 2D physics. Finally, our results advance our understanding of how physical particle properties affect the interparticle interactions between monolayer 2D materials at fluid-fluid interfaces. This information can be used to guide the development of scalable synthesis techniques (e.g., solution-phase processing) to produce bulk suspensions of 2D materials with desired physical particle properties that can be used as building blocks for creating thin films with desired structures and properties via interfacial film assembly.

Crack-Free Conjugated PbS Quantum Dot–Hole Transport Layers for Solar Cells

Colloidal quantum dots (QDs) benefit from solution-phase processing and band-gap tuning for their application in solar cell development. Today’s QD solar cells rely on solid-state ligand exchange (...

PbS Colloidal Quantum Dot Inks for Infrared Solar Cells.

SummaryInfrared PbS colloidal quantum dot (CQD)-based materials receive significant attention because of its unique properties. The PbS CQD ink that originates from ligand exchange of CQDs is highly potential for efficient and stable infrared CQD solar cells (CQDSCs) using low-temperature solution-phase processing. In this review, we present a comprehensive overview of CQD inks for the development of efficient infrared solar cells, which can effectively harvest the photons from the infrared wavelength region of the solar spectrum, including the importance of infrared absorbers for solar cells, the unique properties of CQDs, ligand-exchange determined CQD inks, and related photovoltaic performance of CQDSCs. Finally, we present a brief conclusion, and the possible challenges and opportunities of the CQD inks are discussed in-depth to further develop highly efficient and stable infrared solar cells.

Vapor Deposition of Functional Porous Polymer Membranes

The fabrication of porous polymer membranes is currently dominated by solution-phase processing techniques. We recently developed a versatile solventless method to deposit porous polymer membranes. In this paper, we will review the mechanism that governs the fabrication process, the advantages and capabilities of the technique, and potential applications for these membranes. In the fabrication process, low substrate temperatures are used to transition the monomer vapor into solid microstructures which are then polymerized using a thermally cleavable vapor-phase initiator. This paper covers the effect of processing parameters such as time and temperature on the molecular weight distribution of the polymer and the porosity of the membranes. We will discuss several methods for patterning and cross-linking the membranes, and we will demonstrate that asymmetric membranes with varying chemical functionalities and thicknesses can be fabricated. Finally, we will review potential applications for these membranes.

Mild route to metal carbides

A mild solution-phase process for making transition-metal carbides could help the low-cost materials replace expensive noble-metal catalysts in some industrial processes (J. Am. Chem. Soc. 2020, DOI: 10.1021/jacs.9b11238). Nanoparticles of transition-metal carbides are known to be active catalysts that can convert carbon dioxide to carbon monoxide, hydrocarbons, and other valuable compounds. The carbides are usually prepared via carburization, a process in which metals or metal oxides are heated in a furnace together with a carbon source and hydrogen, sometimes at temperatures above 800 °C. Because the harsh conditions make it difficult to control particle size and morphology, which affect catalytic performance, carbides are rarely used as catalysts. In addition, unlike metal and semiconductor nanoparticles, which can be made with exquisite control thanks to years of intense research, metal carbides are rarely studied. Noah Malmstadt and Richard L. Brutchey of the University of Southern California and cow...

Photodeposition of Pd onto Colloidal Au Nanorods by Surface Plasmon Excitation.

A protocol is described to photocatalytically guide Pd deposition onto Au nanorods (AuNR) using surface plasmon resonance (SPR). Excited plasmonic hot electrons upon SPR irradiation drive reductive deposition of Pd on colloidal AuNR in the presence of [PdCl4]2-. Plasmon-driven reduction of secondary metals potentiates covalent, sub-wavelength deposition at targeted locations coinciding with electric field "hot-spots" of the plasmonic substrate using an external field (e.g., laser). The process described herein details a solution-phase deposition of a catalytically-active noble metal (Pd) from a transition metal halide salt (H2PdCl4) onto aqueously-suspended, anisotropic plasmonic structures (AuNR). The solution-phase process is amenable to making other bimetallic architectures. Transmission UV-vis monitoring of the photochemical reaction, coupled with ex situ XPS and statistical TEM analysis, provide immediate experimental feedback to evaluate properties of the bimetallic structures as they evolve during the photocatalytic reaction. Resonant plasmon irradiation of AuNR in the presence of [PdCl4]2- creates a thin, covalently-bound Pd0 shell without any significant dampening effect on its plasmonic behavior in this representative experiment/batch. Overall, plasmonic photodeposition offers an alternative route for high-volume, economical synthesis of optoelectronic materials with sub-5 nm features (e.g., heterometallic photocatalysts or optoelectronic interconnects).

Photochemically Induced Phase Change in Monolayer Molybdenum Disulfide.

Monolayer transition metal dichalcogenide (TMDs) are promising candidates for two-dimensional (2D) ultrathin, flexible, low-power, and transparent electronics and optoelectronics. However, the performance of TMD-based devices is still limited by the relatively low carrier mobility and the large contact resistance between the semiconducting 2D channel material and the contact metal electrodes. Phase-engineering in monolayer TMDs showed great promise in enabling the fabrication of high-quality hetero-phase structures with controlled carrier mobilities and heterojunction materials with reduced contact resistance. However, to date, general methods to induce phase-change in monolayer TMDs either employ highly-hostile organometallic compounds, or have limited compatibility with large-scale, cost-effective device fabrication. In this paper, we report a new photochemical method to induce semiconductor to metallic phase transition in monolayer MoS2 in a benign chemical environment, through a bench-top, cost-effective solution phase process that is compatible with large-scale device fabrication. It was demonstrated that photoelectrons produced by the band-gap absorption of monolayer MoS2 have enough chemical potential to activate the phase transition in the presence of an electron-donating solvent. This novel photochemical phase-transition mechanism advances our fundamental understanding of the phase transformation in 2D transition metal dichalcogenides (TMDs), and will open new revenues in the fabrication of atomically-thick metal-semiconductor heterostructures for improved carrier mobility and reduced contact resistance in TMD-based electronic and optoelectronic devices.

Deposition of β-Polyfluorene by Resonant Infrared Matrix-Assisted Pulsed Laser Evaporation

Emulsion-based, resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) was used to deposit thin films of polyfluorene (PFO) with semi-crystalline phase domains (β-PFO), which has been performed, previously, only by solution phase processing. Various target emulsion recipes were studied, with emphasis on the primary solvent choice, emulsion mixing time, secondary solvent concentration, or total water concentration. The emulsified particle size for each recipe was compared using dynamic light scattering. Additionally, elevated growth temperature of the substrate was considered for controlling film formation. The surface quality of films was determined by atomic force microscopy, and β-PFO concentration was monitored using photoluminescence or UV–visible absorbance spectroscopy. Importantly, in contrast to solution-based deposition of β-PFO in thin films, emulsion-based RIR-MAPLE demonstrated the ability to increase β-PFO content without degrading, simultaneously, the surface properties of the films. This initial result helps establish the ability of RIR-MAPLE to control and promote semi-crystalline phases in polymer films.

Fluorination Effects on Indacenodithienothiophene Acceptor Packing and Electronic Structure, End-Group Redistribution, and Solar Cell Photovoltaic Response.

Indacenodithienothiophene (IDTT)-based postfullerene electron acceptors, such as ITIC (2,2'-[[6,6,12,12-tetrakis(4-hexylphenyl)-6,12-dihydrodithieno[2,3- d:2',3'- d']-s-indaceno[1,2- b:5,6- b']dithiophene-2,8-diyl]-bis[methylidyne(3-oxo-1 H-indene-2,1(3 H)-diylidene)]]bis[propanedinitrile]), have become synonymous with high power conversion efficiencies (PCEs) in bulk heterojunction (BHJ) polymer solar cells (PSCs). Here we systematically investigate the influence of end-group fluorination density and positioning on the physicochemical properties, single-crystal packing, end-group redistribution propensity, and BHJ photovoltaic performance of a series of ITIC variants, ITIC- nF ( n = 0, 2, 3, 4, and 6). Increasing n from 0 → 6 contracts the optical bandgap, but only marginally lowers the LUMO for n > 4. This yields enhanced photovoltaic short-circuit current density and good open-circuit voltage, so that ITIC-6F achieves the highest PCE of the series, approaching 12% in blends with the PBDB-TF donor polymer. Single-crystal diffraction reveals that the ITIC- nF molecules cofacially interleave with ITIC-6F having the shortest π-π distance of 3.28 Å. This feature together with ZINDO-level computed intermolecular electronic coupling integrals as high as 57 meV, and B3LYP/DZP-level reorganization energies as low as 147 meV, rival or surpass the corresponding values for fullerenes, ITIC-0F, and ITIC-4F, and track a positive correlation between the ITIC- nF space-charge limited electron mobility and n. Finally, a heretofore unrecognized solution-phase redistribution process between the 2-(3-oxo-indan-1-ylidene)-malononitrile-derived end-groups (EGs) of IDTT-based NFAs, i.e., EG1-IDTT-EG1 + EG2-IDTT-EG2 ⇌ 2 EG1-IDTT-EG2, with implications for the entire ITIC PSC field, is identified and mechanistically characterized, and the effects on PSC performance are assessed.

Phage antibody library screening for the selection of novel high-affinity human single-chain variable fragment against gastrin receptor: an in silico and in vitro study.

As a membrane G protein coupled receptors (GPCRs) family, gastrin/cholecystokinin-2 receptor (CCK2R) plays a key role in the initiation and development of gastric cancer. Targeting CCK2R by immunotherapeutics such as single-chain variable fragments (scFvs) may provide an effective treatment modality against gastric cancer. Thus, the main objective of this study was to isolate scFvs specific to CCK2R. To isolate scFvs specific to the CCK2R, we capitalized on a semi-synthetic diverse phage antibody library (PAL) and a solution-phase biopanning process. The library was panned against a biotinylated peptide of the second extracellular loop (ECL2) of CCK2R. After four rounds of biopanning, the selected soluble scFv clones were screened by enzyme-linked immunosorbent assay (ELISA) and examined for specific binding to the peptide. The selected scFvs were purified using immobilized metal affinity chromatography (IMAC). The binding affinity and specificity of the scFvs were examined by the surface plasmon resonance (SPR), immunoblotting and flow cytometry assays and molecular docking using ZDOCK v3.0.2. Ten different scFvs were isolated, which displayed binding affinity ranging from 0.68 to 8.0 (nM). Immunoblotting and molecular docking analysis revealed that eight scFvs were able to detect the denatured form of CCK2R protein. Of the isolated scFvs, two scFvs showed high-binding affinity to the human gastric adenocarcinoma AGS cells. Based on our findings, a couple of the selected scFvs showed markedly high-binding affinity to immobilized CCK2R peptide and CCK2R-overexpressing AGS cells. Therefore, these scFvs are proposed to serve as targeting and/or treatment agents in the diagnosis and immunotherapy of CCK2R-positive tumors. Graphical abstract ᅟ.

Multi-scale modeling of early-stage morphology in solution-processed polycrystalline thin films.

A model is introduced for treating early-stage nucleation, growth kinetics, and mesoscale domain structure in submonolayer polycrystalline films prepared by solution-phase processing methods such as spin casting, dip coating, liquid-based printing, and related techniques. The model combines a stochastic treatment of nucleation derived from classical nucleation theory with deterministic computation of the spatiotemporal dynamics of the monomer concentration landscape by numerical solution of the two-dimensional diffusion equation, treating nuclei as monomer sinks. Results are compared to experimental measurements of solution-processed submonolayer tetracene films prepared using a vapor-liquid-solid deposition technique. Excellent agreement is observed with most major kinetic and structural film characteristics, including the existence of distinct induction, nucleation, and growth regimes, the onset time for nucleation, the number of domains formed per unit area, and the micron- to millimeter-scale spacing statistics of those domains. The model also provides a detailed description the dynamically-evolving monomer concentration landscape during film formation as well as quantities derived from it, such as time- and position-dependent domain nucleation and growth rates.

High performance, flexible and renewable nano-biocomposite artificial muscle based on mesoporous cellulose/ ionic liquid electrolyte membrane

A flexible nano-biocomposite artificial muscle based on a mesoporous renewable cellulose/ionic liquid (IL-Cel) electrolyte membrane with high porosity of 91.31% was developed in this paper. The IL-Cel electrolyte membrane, fabricated by a solution-phase separation process, exhibited absolute advantages in flexibility and ion transfer efficiency, so IL-Cel regenerated actuators exhibited significant enhancement in the deflection displacement and force, which were 4 and 2 times greater than traditional DMAC/Li-dissolved cellulose (Dm-Cel)-based actuators. Good flexibility (from the tensile test) and low surface resistance (within 100 Ω, from SEM) were also attained by actuators composed of an IL-Cel electrolyte membrane without regenerated substances (from FT-IR and XRD). Actuators with a solid-state electric double layer capacitor using multi-wall carbon nanotubes as electrodes and [Emim]Ac-Cel as the polymer electrolyte, exhibited the highest specific capacitance of 890 mF g−1 at 20 mV s−1, a lower internal resistance (0.098 Ω g−1) at range of 105 Hz–0.01 Hz, and the lowest power density (149 W kg−1) at 10 A g−1. Results indicated that cathode deflection was achieved by the action of van der Waals force and anion volumetric strain. These findings suggest that the developed mesoporous IL-Cel based actuators hold great promise in the further study of high-performance actuators.