Ultrathin Lamella Research Articles

Enhancing strength-conductivity synergy in an ultrathin lamellar-structured W[sbnd]Cu composite prepared by freeze-casting and infiltration

One of the key strategies to enhance the performance of composites is the implementation of a lamellar structure, which has demonstrated remarkable success. In this study, an ultrathin lamellar WCu composite was fabricated using a combination of freeze-casting and infiltration techniques. Compared to the homogeneous WCu composite, the aligned structure in this composite provides continuous conductive channels for electrons, reducing interface scattering. Additionally, the ultrathin lamellae offer exceptional load-bearing capacity. These synergistic effects result in both superior strength and enhanced electrical conductivity. This innovative design strategy for WCu composites presents promising potential for advancing the development of next-generation composite materials.

Bending-driven patterning of solid inclusions in lipid membranes: Colloidal assembly and transitions in elastic 2D fluids.

Biological or biomimetic membranes are examples within the larger material class of flexible ultrathin lamellae and contoured fluid sheets that require work or energy to impose bending deformations. Bending elasticity also dictates the interactions and assembly of integrated phases or molecular clusters within fluid lamellae, for instance enabling critical cell functions in biomembranes. More broadly, lamella and other thin fluids that integrate dispersed objects, inclusions, and phases behave as contoured 2D colloidal suspensions governed by elastic interactions. To elucidate the breadth of interactions and assembled patterns accessible through elastic interactions, we consider the bending elasticity-driven assembly of 1-10 μm solid plate-shaped Brownian domains (the 2D colloids), integrated into a fluid phospholipid membrane (the 2D fluid). Here, the fluid membranes of giant unilamellar vesicles, 20-50 μm in diameter, each contain 4-100 monodisperse plate-domains at an overall solid area fraction of 17 ± 3%. Three types of reversible plate arrangements are found: persistent vesicle-encompassing quasi-hexagonal lattices, persistent closely associated chains or concentrated lattices, and a dynamic disordered state. The interdomain distances evidence combined attractive and repulsive elastic interactions up to 10 μm, far exceeding the ranges of physio-chemical interactions. Bending contributions are controlled through membrane slack (excess area) producing, for a fixed composition, a sharp cooperative multibody transition in plate arrangement, while domain size and number contribute intricacy.

Indium-zinc-oxide thin films produced by low-cost chemical solution deposition: Tuning the microstructure, optical and electrical properties with the processing conditions

Indium-zinc-oxide (IZO) films were prepared by spin coating an ethanol-ethylene-glycol precursor solution with a Zn/(In + Zn) ratio of 0.36 on glass. The effects of temperature on the structure, microstructure, electrical, and optical properties of the IZO thin films were investigated by thermal analysis, Fourier-transform infrared spectroscopy, X-ray diffraction, electron and atomic-force microscopy, X-ray photoelectron spectroscopy and variable-angle spectroscopic ellipsometry. The prepared IZO thin films heated at 500, 600, and 700 °C in air were transparent, without long-range ordering, and with an RMS surface roughness of less than 1 nm. The lowest electrical resistivity at room temperature, 0.0069 Ωcm, was observed for the 115-nm-thick IZO thin film heated at 600 °C in air and subsequently post-annealed in Ar/H2. The thin film exhibited a microstructure characterized by grains typically 20 nm in size and had no organic residues. This film exhibits uniaxial optical anisotropy due to its ultra-thin lamellae with a high electron density. The ordinary refractive index was fitted as a Tauc-Lorentz-Urbach function, which is typical of an indirect absorption edge occurring in amorphous semiconductor materials. The principal absorption peak with an onset at about 2.8 eV and a Tauc gap energy of ∼2.6 eV is similar to those observed for In2O3. The described process of chemical solution deposition and subsequent curing is promising for the low-cost fabrication of IZO thin films for transparent electronics, and can be used to tune the structure and microstructure of IZO thin films, as well as their electrical and optical properties.

Like-Charge PISA: Polymerization-Induced Like-Charge Electrostatic Self-Assembly.

We report the use of l-aspartic acid chiral ionic hydrogen bonds to drive liquid-liquid phase separation (LLPS) and precision two-dimensional electrostatic self-assembly in photo-RAFT aqueous polymerization-induced self-assembly (photo-PISA). Homopolymerization can yield salt-resistant, 3 nm ultrafine fibril-structured 5 nm ultrathin lamellae via LLPS, a left-to-right-handed chirality transition, and a droplets-to-lamellae transition. Like-charge block copolymerization leads to supercharged yet identical fibril-structured ultrathin lamellae, also, via LLPS, the left-to-right chirality transition and the droplets-to-lamellae transition. Ultrafine structures maintain intactness upon the seeded polymerization of the oppositely charged monomer. This work demonstrates that amino acid chiral ionic hydrogen bonds are powerful for the precision synthesis of salt-resistant ultrathin membrane nanomaterials.

Structurally optimized MXene-based photocatalytic membrane to achieve self-cleaning properties and enhanced removal for small molecule from wastewater

Membrane contamination not only reduces the efficacy of separation; but also increases the cost due to frequent application of cleaning agents and shortens membrane life. Therefore, we had constructed a new membrane that could be effectively used to solve the pollution problem. In this work, MXene nanosheets with ultra-thin lamellae have been fabricated by chemical etching, followed by the inclusion of oxygen-doped graphite-phase carbon nitride (OCN) photocatalyst with porous structure. The vacuum-assisted device was utilized to synthesize MXene@OCN/Polyethersulfone (MX-OCN) photocatalytic composite membrane possessing self-cleaning ability. The thickness, average surface roughness and the embedding structure of the MX-OCN composite membranes were found to change significantly, leading to the permeability of the MX-OCN membrane up to 1313 L·m−2·h−1·bar−1. The interlayer sieving and photocatalysis provided the MX-OCN membrane a high removal ratio for the contaminants like: Congo red: 98 %, Trolybenzene blue: 96 %, Tetracycline hydrochloride: 83 %. During self-cleaning the composite membrane maintained a removal ratio of 94 % and high for CR after 4 cycles, thus effectively alleviating the problem of membrane pollution. Density function theory calculation (DFT) showed that O atom doping could enhance the charge density and reduce the band gap width, which would be more favorable to the photocatalytic activity.

Coacervate-Assisted Polymerization-Induced Self-Assembly of Chiral Alternating Copolymers into Hierarchical Bishell Capsules with Sub-5nm Ultrathin Lamellae.

Hierarchical self-assembly of synthetic polymers in solution represents one of the sophisticated strategies to replicate the natural superstructures which lay the basis for their superb functions. However, it is still quite challenging to increase the degree of complexity of the as-prepared assemblies, especially in a large scale. Liquid-liquid phase separation (LLPS) widely exists in cells and is assumed to be responsible for the formation of many cellular organelles without membranes. Herein, through integrating LLPS with the polymerization-induced self-assembly (PISA), a coacervate-assisted PISA (CAPISA) methodology to realize the one-pot and scalable preparation of hierarchical bishell capsules (BCs) from nanosheets with ultrathin lamellae phase (sub-5nm), microflakes, unishell capsules to final BCs in a bottom-up sequence is presented. Both the self-assembled structure and the dynamic formation process of BCs have been disclosed. Since CAPISA has combined the advantages of coacervates, click chemistry, interfacial reaction and PISA, it is believed that it will become a promising option to fabricate biomimetic polymer materials with higher structural complexity and more sophisticated functions.

Tissue-Engineered Corneal Endothelial Sheets Using Ultrathin Acellular Porcine Corneal Stroma Substrates for Endothelial Keratoplasty.

Tissue-engineered cornea endothelial sheets (TECES), created using a biocompatible thin and transparent carrier with corneal endothelial cells, could alleviate the shortage of donor corneas and provide abundant functional endothelial cells. In our previous clinical trials, the effectiveness and safety of the acellular porcine corneal stroma (APCS) applied in lamellar keratoplasty have been confirmed. In this study, we optimized the method to cut APCS into multiple 20 μm ultrathin lamellae by a cryostat microtome and investigated the feasibility of TECES by seeding rabbit corneal endothelial cells (RCECs) on ultrathin APCS. Cell adhesion, proliferation, and functional gene expression of RCECs on tissue-culture plastic and APCS of different thicknesses were compared. The results indicated that ultrathin lamellae were superior in increasing cell viability and maintaining cell functions. Analyzing with histology, electron microscopy, and immunofluorescence, we found that RCECs cultured on 20 μm ultrathin APCS for 5 days grew into a confluent monolayer with a density of 3726 ± 223 cells/mm2 and expressed functional biomarkers Na+/K+-ATPase and zonula occludens. After 14 days, RCECs formed an early stage of Descemet's membrane-like structure by synthesizing collagen IV and laminin. Human corneal endothelial cells were also used to further validate the supportive effect of ultrathin APCS on cells. The resulting constructs were flexible and tough enough to implant into rabbits' anterior chambers through small incisions. TECES adhered to the posterior corneal stroma, and the thickness of cornea gradually reduced to normal after grafting. These results indicate that the ultrathin APCS can serve as a tissue engineering carrier and might be a suitable alternative for endothelial cells expansion in endothelial keratoplasty.

Manually prepared lamellae for Descemet stripping endothelial keratoplasty (Pachy-DSEK): comparison of four dissection depths.

This study aimed to compare four depths of manual dissection for the preparation of Descemet stripping endothelial keratoplasty lamellae. Eye bank corneas were randomized into four groups according to dissection depths: Pachy-100 (incision depth = central corneal thickness-safety margin of 100 µm), Pachy-50 (safety margin of 50 µm), Pachy-0 (no safety margin), and Pachy+50 (incision depth = central corneal thickness + 50 µm). All endothelial lamellae were prepared using a standardized method of manual dissection (Pachy-DSEK). The central, paracentral (3.0-mm zone), and peripheral (6.0-mm zone) lamella thicknesses and incision depths were measured by optical coherence tomography. The 3.0-mm and 6.0-mm zone central-to-peripheral thickness ratios were calculated. Endothelial perforation occurred only in the Pachy+50 group (n=3, 30%). Central lamella's thickness in Pachy-100, Pachy-50, Pachy-0, and Pachy+50 groups measured 185 ± 42 µm, 122 ± 29 µm, 114 ± 29 µm, and 58 ± 31 µm, respectively (p<0.001). The overall 3.0- and 6.0-mm C/P ratios were 0.97 ± 0.06 and 0.92 ± 0.14, respectively. Preoperative donor characteristics were not correlated with most thickness outcomes. The planned incision depth correlated significantly with most lamella's thickness parameters (p<0.001). The overall thickness of the lamella negatively correlated with the planned incision depth (p<0.001, r=-0.580). The best outcome was found in the Pachy-0 group, as 75% of the lamellae measured <130 µm and there was no endothelial perforation. By using a standardized method of dissection, most manually prepared lamellae presented a planar shape. Setting the incision depth to the central corneal thickness did not result in endothelial perforation and a high percentage of ultrathin lamellae was achieved.

Two-dimensional polymerization-induced electrostatic self-assembly via a C12-polyelectrolyte lamellar template.

We present a template strategy for precision synthesis of "complex coacervates-in-dodecyl atmosphere" ultrathin lamellae possessing exceptional shape-preservation and charge-tolerance properties.

Nano-scale compositional oscillation and phase intergrowth in Cu2S0.5Se0.5 and their role in thermal transport

Solid solution alloying is a promising strategy to establish high performance thermoelectrics. By alloying different elements, phase structures and phase compositions may vary accompanied by appearance of variety of interesting microstructures including mass fluctuation, lattice strain, nano-scale defects and spinodal decomposition, all of which may greatly influence the electrical and specifically the thermal transport of the material. In the present study, atomic structures of Cu2S0.5Se0.5 solid solution have been examined by using atom-resolved electron microscopy in order to investigate the structure-correlated physical insights for the abnormal thermal transport in this solid solution. Then the exceptional intergrowth nanostructures were observed. The solid solution consists of two high symmetrical phases, i.e. the hexagonal and cubic phase, which alternately intergrow to form highly oriented ultra-thin lamellae of nano or even, unit cell scales. The compositional oscillation in Se/S atomic ratio during alloying is responsible for the phase stability and intergrowth nanostructures. The unique binary phase intergrowth nanostructures make great contribution to the ultra-low lattice thermal conductivity comparable to glass and extremely short phonon mean free path of only 1.04 Å, peculiar continuous hexagonal-to-cubic structural transformation without a critical transition temperature and its corresponding abnormal changes of thermal characters with temperatures. The present study further evokes the unlimited possibilities and potentials for tailoring nanostructures by alloying for improved thermoelectric performance.

The 2D petaloid MoS2 lamellas modified cubic CaTiO3 nanocomposites towards photocatalytic hydrogen production enhancement

The 2D petaloid MoS2 lamellas modified CaTiO3 nanocomposites are fabricated via a simple two-step hydrothermal method. There, the as-prepared MoS2/CaTiO3 nanocomposites exhibit a remarkable photocatalytic HER enhancement of about ∼30 folds than the unmodified CaTiO3 and a decent photocatalytic stability, which can be mainly ascribed to the modification of the MoS2 lamellas, there, the MoS2 with lower Fermi level can capture the photoelectron for improving the charge carriers transferring, and the ultrathin lamellas nanostructure can provide sufficient HER active sites and shorten reaction time to improve the photocatalytic HER performance and stability.

The 2D nickel‑molybdenum bimetals sulfide synergistic modified hollow cubic CdS towards enhanced photocatalytic water splitting hydrogen production

The 2D(two-dimension) nickel‑molybdenum bimetals sulfide synergistic modified hollow cubic CdS is fabricated by the continuous chemical precipitation, vulcanized and hydrothermal methods, there, the hollow cubic CdS is vulcanized from the CdCO3 and then the 2D Ni-Mo-S lamellas grow on the surface of the CdS. Evaluated by the photocatalytic hydrogen production, the photocatalytic performance of the CdS/Ni-Mo-S exhibits an obvious enhancement of about ~80 folds than the single CdS. Studied by the electrochemical measurements, the main reasons for the HER(hydrogen evolution reaction) enhancement are ascribed to that the Pt-like behavior bimetals Ni-Mo-S can quickly accept and transfer-diffuse the photo-generated electrons to water, the 2D ultrathin lamellas can provide sufficient HER active sites and shorten the transferring time, and the hollow nanostructure can increase the solar utilization.

Colloidal Stable PIC Vesicles and Lamellae Enabled by Wavelength-Orthogonal Disulfide Exchange and Polymerization-Induced Electrostatic Self-Assembly

Block copolymer nanoparticles have been widely used for advanced materials. However, the stabilization is challenging. Herein, we present a method for convenient yet reliable synthesis of stabilized polyion complex (PIC) nanometer-sized spheres and micrometer-sized ultrathin lamellae and vesicles by taking advantage of the wavelength orthogonality of UV-induced disulfide exchange and visible light-initiated polymerization-induced electrostatic self-assembly (PIESA). Disulfide-containing PIC vesicles are synthesized at scale using this PIESA, undergoing a small sphere-to-larger sphere-to-lamella-to-vesicle transition. As such, surface-neutralized and surface-charged micrometer-sized vesicles can be achieved. UV irradiation of the vesicles (5.0 mg/mL in water) in ambient air induces very fast exchange reaction of locally confined/enriched disulfide motifs, leading to cross-linking, shape transition, and cystamine salt release in 4 min. As such, cross-linked PIC spheres, lamellae, and vesicles can be achieve...

Synthesis of isomorphous MFI nanosheet zeolites for supercritical catalytic cracking of n-dodecane

The isomorphous MFI nanosheet zeolites (MFI (M), M=Al, Ga, and Fe) were synthesized hydrothermally and characterized by XRD, SEM, TEM, N2 adsorption-desorption, NH3-TPD, FTIR and pyridine-absorbed FTIR. The MFI nanosheet zeolites with higher surface area, large mesoporous, ultrathin lamella structure and different acidity strength were applied in the catalytic cracking of n-dodecane and their catalytic activity on the gas generation rate, product selectivity, carbon deposition and heat sink were determined. The gas generation rates of the MFI nanosheet zeolites were higher than that of ZSM-5 zeolite and bare tube. More light alkenes generated over the MFI nanosheet zeolites, and their deactivation rates were lower than that of ZSM-5 zeolite due to the special mesoporous and lamella structure which could prevent the deactivation resulting from pore blocking by carbon deposition. The heat sinks of the n-dodecane cracking at 550°C under 4MPa were 2865kJ/kg for MFI-Al, 3040kJ/kg for MFI-Ga and 2735kJ/kg for MFI-Fe which were all higher than that of ZSM-5 zeolite (2542kJ/kg) and bare tube (2175kJ/kg). At 600°C, the heat sinks for MFI-Al, MFI-Ga and MFI-Fe reached to 3124, 3384 and 3221kJ/kg, respectively. Besides, from the cracking results of the MFI nanosheet zeolites, it can be concluded that the decrease of acidity strength by Ga substitution showed positive effect on the catalytic cracking of n-dodecane.

Generation of isentropic compression by use of multi-layer composite flyer and its influence on system thermodynamics: A simulation study

Recently the possibility of achieving quasi-isentropic compression using functionally graded materials, in both gas gun and explosive driven systems was explored by hydro-dynamic simulations. In the current paper, we show that multi-layered composite flyer with progressively increasing shock impedances, referred to as graded density impactor (GDI), has the potential to enable increased flexibility in suitably tailoring the applied-pressure profiles, further relaxing constraints on the thermodynamic path of compressed material. Present simulation study pertaining to constant velocity impact of GDI reveals that linear ramp pulses of different pressure rise times, with comparable peak values can be realized only by changing the layer thicknesses of a particular GDI. We report generation of three different slope ramp pulses by five layer GDI made of PMMA, Al, Ti, Cu and Ta with different set of thicknesses obtained by genetic algorithm based optimization technique. Generation of long duration (μs) isentropic pressures using discrete GDI is a significant step, since it is devoid of fabrication difficulties of ultra-thin lamellae of FGM. Signatures of isentropic compression of a thin Cu target under different slope ramp loadings are identified from basic thermodynamic aspects in terms of temperature rise and entropy production. It is shown that that extent of entropy increase is closely related to the slope of ramping pulse. Further, a physical model has been constructed to determine approximate time profile of pressure pulse generated by equal layer-width GDI.

Improved Focused Ion Beam Target Preparation of (S)TEM Specimen—A Method for Obtaining Ultrathin Lamellae

Specimen quality is vital to (scanning) transmission electron microscopy (TEM) investigations. In particular, thin specimens are required to obtain excellent high-resolution TEM images. Conventional focused ion beam (FIB) preparation methods cannot be employed to reliably create high quality specimens much thinner than 20 nm. We have developed a method for in situ target preparation of ultrathin TEM lamellae by FIB milling. With this method we are able to routinely obtain large area lamellae with coplanar faces, thinner than 10 nm. The resulting specimens are suitable for low kV TEM as well as scanning TEM. We have demonstrated atomic resolution by Cs-corrected high-resolution TEM at 20 kV on a FIB milled Si specimen only 4 nm thick; its amorphous layer measuring less than 1 nm in total.

FIB Target Preparation for 20 kV STEM - A Method for Obtaining Ultra-Thin Lamellas

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Nanoimprint lithography stamp modification utilizing focused ion beams

Nanoimprint lithography (NIL) has been established as a high-throughput technique to fabricate sub-25-nm patterns at a low cost. The fabrication of NIL templates with features in the submicrometer range is currently a bottleneck of the NIL technology. The replication of errors on NIL templates places a major challenge on the reusability of templates. Focused ion beam (FIB) technology is employed to modify prestructured NIL templates. In this work, repair strategies for NIL stamps are discussed. Excess material from stamps has been removed by ion milling. Nanoscale trenches and ultrathin lamellas fabricated with a focused ion beam and their corresponding imprints are presented. It has been confirmed that commercial UV-NIL stamps can be modified by FIB milling and imprinted line patterns were successfully replicated by UV-NIL using the repaired templates. Furthermore, the potential of three-dimensional NIL templates structured by FIB was evaluated. Three-dimensional imprints with features down to 80nm with good structure conformity to the template were demonstrated. The capabilities and limitations of FIB as repair technology for NIL stamps are discussed.

Molecular dynamics simulation of plastic deformation of nanotwinned copper

The plastic deformation of polycrystalline Cu with ultrathin lamella twins has been studied using molecular dynamics simulations. The results of uniaxial tensile deformation simulation show that the abundance of twin boundaries provides obstacles to dislocation motion, which in consequence leads to a high strain hardening rate in the nanotwinned Cu. We also show that the twin lamellar spacing plays a vital role in controlling the strengthening effects, i.e., the thinner the thickness of the twin lamella, the harder the material. Additionally, twin boundaries can act as dislocation nucleation sites as they gradually lose coherency at large strain. These results indicate that controlled introduction of nanosized twins into metals can be an effective way of improving strength without suppression tensile ductility.

Leukocyte polarization in cell migration and immune interactions.

Cell migration plays a key role in a wide variety of biological phenomena. This process is particularly important for leukocyte function and the inflammatory response. Prior to migration leukocytes undergo polarization, with the formation of a lamellipodium at the leading edge and a uropod at the trailing edge. This cell shape allows them to convert cytoskeletal forces into net cell-body displacement. Leukocyte chemoattractants, including chemokines, provide directional cues for leukocyte motility, and concomitantly induce polarization. Chemoattractant receptors, integrins and other adhesion molecules, cytoskeletal proteins and intracellular regulatory molecules change their cellular localization during cell polarization. A complex system of signal transduction molecules, including tyrosine kinases, lipid kinases, second messengers and members of the Rho family of small GTPases is thought to regulate the cytoskeletal rearrangements underlying leukocyte polarization and migration. The elucidation of the mechanisms and signals that control this complex reorganization will lead to a better understanding of critical questions in cell biology of leukocyte migration and polarity.