Growth Of Bilayers Research Articles

Supramolecular Assemblies in Active Motor-Filament Systems: Micelles, Bilayers, and Foams

Active matter systems evade the constraints of thermal equilibrium, leading to the emergence of intriguing collective behavior. A paradigmatic example is given by motor-filament mixtures, where the motion of motor proteins drives alignment and sliding interactions between filaments and their self-organization into macroscopic structures. After defining a microscopic model for these systems, we derive continuum equations, exhibiting the formation of active supramolecular assemblies such as micelles, bilayers, and foams. The transition between these structures is driven by a branching instability, which destabilizes the orientational order within the micelles, leading to the growth of bilayers at high microtubule densities. Additionally, we identify a fingering instability, modulating the shape of the micelle interface at high motor densities. We study the role of various mechanisms in these two instabilities, such as contractility, active splay, and anchoring, allowing for generalization beyond the system considered here. Published by the American Physical Society 2024

Development of ATP-modified CoFe2O4@ZIF-8@ZIF-67 core–shell nanozyme for sensitive colorimetric detection of dopamine

Core-shell nanostructures (NSs) are a type of nanozyme broadly used in various fields due to their significant physicochemical advantages. In the present study, the CoFe2O4@ZIF-8@ZIF-67 core–shell were fabricated by a consecutive two-step synthesis method, including hydrothermal for CoFe2O4 metal spinel and epitaxial solvothermal growth of ZIFs bilayers on the metal spinel NSs. The core–shell surface was modified using ATP inspired by the active site of the natural peroxidase enzyme. The nanocomposites were characterized by XRD, FT-IR, SEM, EDX, and Dot-mapping techniques. The peroxidase-like activity of the ATP/CoFe2O4@ZIF-8@ZIF-67 was assessed by a colorimetric method. Modified nanocomposite displayed desirable peroxidase mimetic activity and could enzymatically generate hydroxyl radicals from H2O2 and oxidize TMB. The high catalytic activity of ATP-modified nanocomposite and its ability to oxidize TMB provides a rapid and sensitive platform for the colorimetric detection of dopamine. Dopamine consumes hydroxyl radicals, prevents TMB oxidation, and causes a color change in the detection solution, which the naked eye can recognize. The presented colorimetric test provided an excellent LOD for dopamine (0.4 µM) with a good linear range (0.2–18 µM) and selectivity, which was prosperously applied to dopamine assay in serum blood samples.

Quasi van der Waals Epitaxy of Rhombohedral-Stacked Bilayer WSe2 on GaP(111) Heterostructure.

The growth of bilayers of two-dimensional (2D) materials on conventional 3D semiconductors results in 2D/3D hybrid heterostructures, which can provide additional advantages over more established 3D semiconductors while retaining some specificities of 2D materials. Understanding and exploiting these phenomena hinge on knowing the electronic properties and the hybridization of these structures. Here, we demonstrate that a rhombohedral-stacked bilayer (AB stacking) can be obtained by molecular beam epitaxy growth of tungsten diselenide (WSe2) on a gallium phosphide (GaP) substrate. We confirm the presence of 3R-stacking of the WSe2 bilayer structure using scanning transmission electron microscopy (STEM) and micro-Raman spectroscopy. Also, we report high-resolution angle-resolved photoemission spectroscopy (ARPES) on our rhombohedral-stacked WSe2 bilayer grown on a GaP(111)B substrate. Our ARPES measurements confirm the expected valence band structure of WSe2 with the band maximum located at the Γ point of the Brillouin zone. The epitaxial growth of WSe2/GaP(111)B helps to understand the fundamental properties of these 2D/3D heterostructures, toward their implementation in future devices.

Area-Selective Growth of Two-Dimensional Mono- And Bilayer WS2 for Field Effect Transistors

Herein, we propose a novel approach for area-selective tunable growth of uniform monolayer or bilayer WS2 on dielectric substrates through in situ conversion of a predeposited W metal pad to WOx initially and then to WS2 mono- and bilayers. Compared with the various transfer methods that have been used previously for multilayer stacking, this direct-growth method has the advantages of producing cleaner interfaces and the capability of growing tunable layers on target substrates, thereby making it more suitable for manufacturing processes. The WS2 bilayer displayed uniform optical properties, with the atomic arrangement between layers having an AA stacking order that are supposed to have higher mobility. We adopted these WS2 monolayers and bilayers in field-effect transistors. Accordingly, this approach for highly area-selective growth of transition metal dichalcogenide monolayers and bilayers with metal pads and their in situ conversion appears to provide effective platforms for further device applications.

Designed growth of large bilayer graphene with arbitrary twist angles.

The production of large-area twisted bilayer graphene (TBG) with controllable angles is a prerequisite for proceeding with its massive applications. However, most of the prevailing strategies to fabricate twisted bilayers face great challenges, where the transfer methods are easily stuck by interfacial contamination, and direct growth methods lack the flexibility in twist-angle design. Here we develop an effective strategy to grow centimetre-scale TBG with arbitrary twist angles (accuracy, <1.0°). The success in accurate angle control is realized by an angle replication from two prerotated single-crystal Cu(111) foils to form a Cu/TBG/Cu sandwich structure, from which the TBG can be isolated by a custom-developed equipotential surface etching process. The accuracy and consistency of the twist angles are unambiguously illustrated by comprehensive characterization techniques, namely, optical spectroscopy, electron microscopy, photoemission spectroscopy and photocurrent spectroscopy. Our work opens an accessible avenue for the designed growth of large-scale two-dimensional twisted bilayers and thus lays the material foundation for the future applications of twistronics at the integration level.

Selective Growth and Robust Valley Polarization of Bilayer 3R-MoS2.

Noncentrosymmetric transition-metal dichalcogenides, particularly their 3R polymorphs, provide a robust setting for valleytronics. Here, we report on the selective growth of monolayers and bilayers of MoS2, which were acquired from two closely but differently oriented substrates in a chemical vapor deposition reactor. It turns out that as-grown bilayers are predominantly 3R-type, not more common 2H-type, as verified by microscopic and spectroscopic characterization. As expected, the 3R bilayer showed a significantly higher valley polarization compared with the centrosymmetric 2H bilayer, which undergoes efficient interlayer scattering across contrasting valleys because of their vertical alignment of the K and K' points in momentum space. Interestingly, the 3R bilayer showed even higher valley polarization compared with the monolayer counterpart. Moreover, the 3R bilayer reasonably maintained its valley efficiency over a very wide range of excitation power density from ∼0.16 kW/cm2 to ∼0.16 MW/cm2 at both low and room temperatures. These observations are rather surprising because valley dephasing could be more efficient in the bilayer via both interlayer and intralayer scatterings, whereas only intralayer scattering is allowed in the monolayer. The improved valley polarization of the 3R bilayer can be attributed to its indirect-gap nature, where valley-polarized excitons can relax into the valley-insensitive band edge, which otherwise scatter into the contrasting valley to effectively cancel out the initial valley polarization. Our results provide a facile route for the growth of 3R-MoS2 bilayers that could be utilized as a platform for advancing valleytronics.

A Study of the Effects of Plasma Surface Treatment on Lipid Bilayers Self-Spreading on a Polydimethylsiloxane Substrate under Different Treatment Times.

Plasma-treated poly(dimethylsiloxane) (PDMS)-supported lipid bilayers are used as functional tools for studying cell membrane properties and as platforms for biotechnology applications. Self-spreading is a versatile method for forming lipid bilayers. However, few studies have focused on the effect of plasma treatment on self-spreading lipid bilayer formation. In this paper, we performed lipid bilayer self-spreading on a PDMS surface with different treatment times. Surface characterization of PDMS treated with different treatment times is evaluated by AFM and SEM, and the effects of plasma treatment of the PDMS surface on lipid bilayer self-spreading behavior is investigated by confocal microscopy. The front-edge velocity of lipid bilayers increases with the plasma treatment time. By theoretical analyses with the extended-DLVO modeling, we find that the most likely cause of the velocity change is the hydration repulsion energy between the PDMS surface and lipid bilayers. Moreover, the growth behavior of membrane lobes on the underlying self-spreading lipid bilayer was affected by topography changes in the PDMS surface resulting from plasma treatment. Our findings suggest that the growth of self-spreading lipid bilayers can be controlled by changing the plasma treatment time.

A total‐Lagrangian material point method for coupled growth and massive deformation of incompressible soft materials

AbstractA total‐Lagrangian material point method (TLMPM) with a mixed formulation is proposed in this article for the mechanical analysis of incompressible soft materials coupling the mass growth and massive deformation. In this work, the growth‐induced large deformation behavior is handled within the framework of the material point method (MPM) based on the multiplicative decomposition of deformation gradient. To overcome the volumetric locking caused by the incompressibility of soft materials, a weak‐form equation for hydrostatic pressure is implemented into a mixed MPM framework. To deal with the massive deformation caused by growth, the total‐Lagrangian formulation is further introduced into the mixed MPM. The TLMPM discretized via the B‐spline basis functions is then developed in the proposed solution procedure. The efficiency and accuracy of the proposed method are demonstrated by several representative two‐ and three‐dimensional numerical examples with large deformation such as the free growth of blocks and constrained growth of rings. The challenging problems including the volumetric growth of bilayers with complex geometry and the strain‐driven growth of skin are further investigated using the proposed TLMPM to illustrate its ability for evaluating the growth phenomena and behaviors as observed in nature and engineering.

Strain-Induced Growth of Twisted Bilayers during the Coalescence of Monolayer MoS2 Crystals

Tailoring the grain boundaries (GBs) and twist angles between two-dimensional (2D) crystals are two crucial synthetic challenges to deterministically enable envisioned applications such as moiré excitons, emerging magnetism, or single-photon emission. Here, we reveal how twisted 2D bilayers can be synthesized from the collision and coalescence of two growing monolayer MoS2 crystals during chemical vapor deposition. The twisted bilayer (TB) moiré angles are found to preserve the misorientation angle (θ) of the colliding crystals. The shapes of the TB regions are rationalized by a kink propagation model that predicts the GB formed by the coalescing crystals. Optical spectroscopy measurements reveal a θ-dependent long-range strain in crystals with stitched grain boundaries and a sharp (θ > 20°) threshold for the appearance of TBs, which relieves this strain. Reactive molecular dynamics simulations explain this strain from the continued growth of the crystals during coalescence due to the insertion of atoms at unsaturated defects along the GB, a process that self-terminates when the defects become saturated. The simulations also reproduce atomic-resolution electron microscopy observations of faceting along the GB, which is shown to arise from the growth-induced long-range strain. These facets align with the axes of the colliding crystals to provide favorable nucleation sites for second-layer growth of a TB with twist angles that preserve the misorientation angle θ. This interplay between strain generation and aligned nucleation provides a synthetic pathway for the growth of TBs with deterministic angles.

Controllable Epitaxial Growth of MoSe2 Bilayers with Different Stacking Orders by Reverse-Flow Chemical Vapor Deposition.

The stacking order plays a critical role in the electronic and optical properties of two-dimensional materials. It is however of great challenge to achieve large-size and homogeneous bilayer crystals with precisely controlled stacking orders. Here, we demonstrate an optimized chemical vapor deposition strategy to grow MoSe2 bilayers with controlled AA or AB stacking sequences. Reverse gas flow effectively suppresses the random nucleation centers, leading to uniform growth of the second layer of MoSe2 on the first monolayer. A customized temperature profile selectively activates the growth of the MoSe2 bilayer with different stacking orders: the AA stacking MoSe2 bilayer tends to form at 810 °C, and the AB stacking MoSe2 bilayer prefers to grow at a higher temperature of 860 °C. A series of characterization methods confirm that MoSe2 bilayers with different stacking orders exhibit distinct crystal structures and physical properties. Our results demonstrate a robust and effective route for the controllable synthesis of transition metal dichalcogenide bilayers, which will benefit the development of two-dimensional materials and van der Waals heterostructures.

Tailoring nanostructured surfaces with plasmonic/magnetic multifunctional response

In this work, we present an innovative way to functionalize large surfaces combining both plasmonic and magnetic nanoparticles on a substrate, by the growth of bilayers and a subsequent single annealing. In particular, we show here the formation of Au and γ-Fe2O3 nanoparticles using this route. Thermal treatments promote the nanostructuration of the film plus a partial oxidation of Fe to form ferrimagnetic oxides. For this purpose, annealing conditions and the structure of the bilayer must be selected to achieve an optimal nanostructuration, avoiding the full oxidation of Fe to form antiferromagnetic hematite.

The discrete nature of inhomogeneity: the initial stages and local configurations of TiOPc during bilayer growth on Ag(111).

The operation of organic optoelectronic devices relies notably on the bulk properties of compound molecular species, but even more so on the influence of interfaces thereof since it is at the interface where elemental electronic processes take place. Their identification and characterization thereby requires that these critical sections of a device are well defined and can be prepared with low defect density. In this context titanyl phthalocyanine (TiOPc) arises as an excellent candidate that reveals the formation of a stable bilayer structure with a characteristic "up-down" molecular arrangement that optimizes the dipole-dipole interaction within the bilayer. In our experimental study, long-range ordered TiOPc bilayers have been grown on Ag(111) surfaces and analyzed using infrared absorption spectroscopy and scanning tunneling microscopy. By monitoring the prominent Ti[double bond, length as m-dash]O stretching mode in IRAS and identifying local configurations in STM, a microscopic model for the growth of TiOPc bilayers on Ag(111) is suggested. We demonstrate that defect structures within these bilayers lead to characteristic vibrational signatures which react sensitively to the local environment of the molecules. Thermal desorption spectroscopy reveals a high thermal stability of the TiOPc bilayer up to 500 K, which is attributed to hydrogen bonds between oxygen of the titanyl unit and the hydrogen rim of phthalocyanines in the second layer, in addition to contributions arising from the oppositely oriented axial dipole moments and the ubiquitous van der Waals interactions.

When the Sequence of Thin Film Deposition Matters: Examination of Organic-on-Organic Heterostructure Formation Using Molecular Beam Techniques and in Situ Real Time X-ray Synchrotron Radiation

We have examined the growth of bilayers and superlattices of pentacene and perylene derivatives (PTCDI-Cn) using in situ real time X-ray synchrotron radiation techniques and ex situ atomic force microscopy. We find that the growth of PTCDI-Cn layers on 1 monolayer (ML) of pentacene is initially 2D layer-by-layer (LbL), eventually transitioning to a mode of growth that is more 3D after several monolayers have been deposited. We find that the extent of 2D LbL growth depends on the length of the alkyl end chains, Cn: the smoothest films are formed with PTCDI-C5, while the roughest are formed with PTCDI-C13. These observations reflect a difference in the Ehrlich–Schwoebel barrier for step-edge crossing with alkyl end-chain length. When the sequence of deposition is reversed, we observe spectacular changes in the evolution of surface roughness for the growth of pentacene thin films on 1 ML of PTCDI-Cn. The growth is immediately 3D, while still remaining crystalline. The morphology of these thin films indicates...

Amphiphilic Nanoparticles Control the Growth and Stability of Lipid Bilayers with Open Edges.

Molecular amphiphiles self-assemble in polar media to form ordered structures such as micelles and vesicles essential to a broad range of industrial and biological processes. Some of these architectures such as bilayer sheets, helical ribbons, and hollow tubules are potentially useful but inherently unstable owing to the presence of open edges that expose the hydrophobic bilayer core. Here, we describe a strategy to stabilize open bilayer structures using amphiphilic nanoparticle surfactants that present mixtures of hydrophilic and hydrophobic ligands on their surface. We observe that these particles bind selectively to the open edge of bilayer membranes to stabilize otherwise transient amphiphile assemblies. We show how such particles can precisely control the size of lipid tubules, how they can inhibit the formation of undesirable assemblies such as gallstone precursors, and how they can stabilize free-floating lipid microdiscs.

Amphiphilic Nanoparticles Control the Growth and Stability of Lipid Bilayers with Open Edges

AbstractMolecular amphiphiles self‐assemble in polar media to form ordered structures such as micelles and vesicles essential to a broad range of industrial and biological processes. Some of these architectures such as bilayer sheets, helical ribbons, and hollow tubules are potentially useful but inherently unstable owing to the presence of open edges that expose the hydrophobic bilayer core. Here, we describe a strategy to stabilize open bilayer structures using amphiphilic nanoparticle surfactants that present mixtures of hydrophilic and hydrophobic ligands on their surface. We observe that these particles bind selectively to the open edge of bilayer membranes to stabilize otherwise transient amphiphile assemblies. We show how such particles can precisely control the size of lipid tubules, how they can inhibit the formation of undesirable assemblies such as gallstone precursors, and how they can stabilize free‐floating lipid microdiscs.

Kinetics of monolayer and bilayer nanoparticle film formation during electrophoretic deposition

The kinetics of electrophoretic deposition are studied for the growth of monolayers and bilayers of ∼10 nm iron oxide nanoparticles. The net deposited nanoparticle film is measured as a function of time for five voltages through analysis of scanning electron microcopy images of the films. The collected data suggest that films deposited at different voltages have different kinetic behaviours. Additionally, we observe monolayer and bilayer growth separately, from which we assert that the initiation of the bilayer may be the source of variation in kinetic behaviour.

In Situ Growth of Cellular Two-Dimensional Silicon Oxide on Metal Substrates

Crystalline hexagonally ordered silicon oxide layers with a thickness of less than a nanometer are grown on transition metal surfaces in an in situ electron microscopy experiment. The nucleation and growth of silica bilayers and monolayers, which represent the thinnest possible ordered structures of silicon oxide, are monitored in real time. The emerging layers show structural defects reminiscent of those in graphene and can also be vitreous. First-principles calculations provide atomistic insight into the energetics of the growth process. The interplay between the gain in silica-metal interaction energy due to their epitaxial match and energy loss associated with the mechanical strain of the silica network is addressed. The results of calculations indicate that both ordered and vitreous mono/bilayer structures are possible, so that the actual morphology of the layer is defined by the kinetics of the growth process.

Multicomponent Interstitial Diffusion in and Thermodynamic Characteristics of the Interstitial Solid Solution ε-Fe3(N,C)1+x : Nitriding and Nitrocarburizing of Pure α-Iron

A series of gas nitriding and gas nitrocarburizing experiments was performed at 823 K (550 °C) to investigate the growth kinetics of e-Fe3(N,C)1+x /γ′-Fe4N1-z -double layers on pure α-iron substrates. The growth rate and composition of the (sub)layers were determined by (sub)layer-thickness measurements using light optical microscopy and electron-probe microanalyses (EPMA), respectively. Models for the growth of bilayers into a substrate, controlled by the interstitial diffusion of two elements (N and C), were applied to the experimental data to determine the intrinsic diffusion coefficients of N and C in e-Fe3(N,C)1+x as well as the self-diffusion coefficient of N in γ′-Fe4N1−z . For e-Fe3(N,C)1+x , it was found that the four components of the diffusion matrix, \( D_{\text{NN}}^{\varepsilon } ,\,D_{\text{CC}}^{\varepsilon } ,\,D_{\text{NC}}^{\varepsilon } \) and \( D_{\text{CN}}^{\varepsilon } \), are all positive. The significant values of the off-diagonal diffusivities \( D_{\text{NC}}^{\varepsilon } \) and \( D_{\text{CN}}^{\varepsilon } \) indicate profound interaction of both interstitial species. Thereby, additional information is obtained about the thermodynamic properties of the e phase in the ternary Fe-N-C system.

Growth of Metallic-Insulator Bilayers Yields Interfacial Region Exhibiting High-Tc Superconductivity

Growth of Metallic-Insulator Bilayers Yields Interfacial Region Exhibiting High-<i>T</i>_c Superconductivity

In situ stress evolution during sputter deposition of Cu∕Co bilayers and multilayers

The stress evolution of Cu∕Co bilayers and multilayers sputtered onto oxidized Si(100) (SiOx) substrates has been studied by in situ substrate curvature measurements with the thickness of the individual layers ranging from 3 to 10 nm. In order to understand the stress developing during deposition, we investigated the microstructure of single layers and bilayers by scanning electron microscopy as well as of the multilayers by cross-section transmission electron microscopy. The growth of Cu and Co on SiOx substrates proceeds by the Volmer-Weber mechanism. Due to the lower mobility, Co layers exhibit a finer grain morphology compared to Cu. The stress evolution and morphology of the first Cu∕Co or Co∕Cu bilayer are still influenced by the SiOx substrates and differ from that of subsequent bilayers. The metal on metal growth of subsequent bilayers is discussed in terms of the surface energies of Cu and Co, respectively. Accordingly, Cu wets Co and Co forms three-dimensional (3D) islands on Cu. After a transition region of 5−10 bilayers, a steady state with respect to the evolution of stress and morphology is reached. In both, the Cu and Co layers, the lattice mismatch gives rise to stress during deposition of the first monolayers.