Automated Buildup of Biomimetic Films in Cell Culture Microplates for High‐Throughput Screening of Cellular Behaviors

An automatic method is established for layer‐by‐layer (LbL) assembly of biomimetic coatings in cell culture microplates using a commercial liquid‐handling robot. Highly homogeneous thin films are formed at the bottom of each microwell. The LbL film‐coated microplates are compatible with common cellular assays, using microplate readers and automated microscopes. Cellular adhesion is screened on crosslinked and peptide‐functionalized LbL films and stem cell differentiation in response to increasing doses of bone morphogenetic proteins (2, 4, 7, 9). This method paves the way for future applications of LbL films in cell‐based assays for regenerative medicine and high‐throughput drug screening.     

功能性层层组装厚膜

层层组装是一种基于物质交替沉积而制备复合膜的方法,可以实现膜的结构和组成的精确调控。层层组装通常被认为是超薄膜的构筑方法。与超薄膜相比,微米或亚微米的厚膜更容易实现高的负载、微纳复合结构的调控、多功能集成以及赋予膜更高的稳定性。以作者的研究结果为基础,阐明TN用大尺度的构筑基元,包括聚合物复合物、大尺度的无机粒子以及聚集的粒子,可以方便地实现微米厚度的层层组装膜的快速构筑。以快速构筑的厚膜为功能载体,实现了层层组装膜的自修复、高负载、细胞可控粘附及多功能集成。进一步,将层层组装厚膜从基底上剥离制备了自支持膜,拓展了层层组装膜的功能。     

Hybrid organic-inorganic nanostructures fabricated from layer-by-layer self-assembled multilayers of hyperbranched polyglycerols and phosphorus dendrimers

Multilayer thin films of cationic phosphorous dendrimers and anionic hyperbranched polyglycerols were fabricated by electrostatic layer-by-layer (LbL) self-assembly (SA). The film formation was monitored by surface plasmon resonance (SPR) spectroscopy and UV-visible spectroscopy, and it was found that the stepwise, alternating deposition results in a linear growth up to four bilayers. Hybrid organic-TiO2 nanostructures were generated by exposing the supramolecular multilayers to TiCl4 precursors. The amounts of TiO2 incorporated inside the scaffolds could be tuned by controlling the porosity of the multilayers with the addition of a small amount of salts. The resulting hybrid films exhibit characteristic photoluminescence (PL) properties.     

Drug delivery: Layer‐By‐Layer‐Assembled Capsules and Films for Therapeutic Delivery (Small 17/2010)

Polymeric materials formed via layer‐by‐layer (LbL) assembly have promise for use as drug delivery vehicles. These multilayered materials, both as capsules and thin films, can encapsulate a high payload of toxic or sensitive drugs, and can be readily engineered and functionalized with specific properties. This review highlights important and recent studies that advance the use of LbL‐assembled materials as therapeutic devices. It also seeks to identify areas that require additional investigation for future development of the field. A variety of drug‐loading methods and delivery routes are discussed. The biological barriers to successful delivery are identified, and possible solutions to these problems are discussed. Finally, state‐of‐the‐art degradation and cargo release mechanisms are also presented.     

Tape-Casting Li0.34La0.56TiO3 Ceramic Electrolyte Films Permit High Energy Density of Lithium-Metal Batteries

Ceramic oxide electrolytes are outstanding due to their excellent thermostability, wide electrochemical stable windows, superior Li-ion conductivity, and high elastic modulus compared to other electrolytes. To achieve high energy density, all-solid-state batteries require thin solid-state electrolytes that are dozens of micrometers thick due to the high density of ceramic electrolytes. Perovskite-type Li_0.34La_0.56TiO₃ (LLTO) freestanding ceramic electrolyte film with a thickness of 25 µm is prepared by tape-casting. Compared to a thick electrolyte (>200 µm) obtained by cold-pressing, the total Li ionic conductivity of this LLTO film improves from 9.6 × 10⁻⁶ to 2.0 × 10⁻⁵ S cm⁻¹. In addition, the LLTO film with a thickness of 25 µm exhibits a flexural strength of 264 MPa. An all-solid-state Li-metal battery assembled with a 41 µm thick LLTO exhibits an initial discharge capacity of 145 mAh g⁻¹ and a high capacity retention ratio of 86.2% after 50 cycles. Reducing the thickness of oxide ceramic electrolytes is crucial to reduce the resistance of electrolytes and improve the energy density of Li-metal batteries.     

A Chemical Route to Monolithic Integration of Crystalline Oxides on Semiconductors

This work demonstrates the growth of crystalline SrTiO₃ (STO) directly on germanium via a chemical method. After thermal deoxidation, the Ge substrate is transferred in vacuo to the deposition chamber where a thin film of STO (2 nm) is deposited by atomic layer deposition (ALD) at 225 °C. Following post‐deposition annealing at 650 °C for 5 min, the STO film becomes crystalline with epitaxial registry to the underlying Ge (001) substrate. Thicker STO films (up to 15 nm) are then grown on the crystalline STO seed layer. The crystalline structure and orientation are confirmed via reflection high‐energy electron diffraction, X‐ray diffraction, and transmission electron microscopy. Electrical measurements of a 15‐nm thick epitaxial STO film on Ge show a large dielectric constant (k ≈ 90), but relatively high leakage current of ≈10 A/cm² for an applied field of 0.7 MV/cm. To suppress the leakage current, an aluminum precursor is cycled during ALD growth to grow crystalline Al‐doped STO (SrTi_1‐x­Al_xO_3‐δ) films. With sufficient Al doping (≈13%), the leakage current decreases by two orders of magnitude for an 8‐nm thick film. The current work demonstrates the potential of ALD‐grown crystalline oxides to be explored for advanced electronic applications, including high‐mobility Ge‐based transistors.     

Epitaxial PbZrxTi1−xO3 Ferroelectric Bilayers with Giant Electromechanical Properties

Giant electromechanical response viaferroelastic domain switching is achieved in epitaxial (001) ferroelectric tetragonal (T) PbZr_0.3Ti_0.7O₃/rhombohedral (R) PbZr_0.55Ti_0.45O₃ bilayers, grown on La_0.67Sr_0.33MnO₃ buffered SrTiO₃ substrates. X‐ray diffraction and transmission electron microscopy show that the domain structure of the T films is tuned as a function of its thickness, from a fully a₁/a₂‐domains (30 nm thick T layer) to a three domain stress‐free c/a₁/c/a₂ polytwin state (100 nm thick T layer). A large switchable polarization is found up to 65 μC cm⁻². Quantitative piezoelectric force microscopy reveals enhanced piezoelectric coefficients, with d₃₃ coefficients ranging from 250 to 350 pm V⁻¹, which is up to seven times higher than the nominal PbZr_xTi_1−xO₃ thin film values. These are attributed to the motion of nanoscale ferroelastic domains. Fatigue testing proves that these domains are reversible and repeatable up to 10⁷ cycles. In‐situ X‐ray synchrotron measurements reveal that the ferroelastic domain switching is promoted by a pulsating strain effect imposed by the R layer. The study reports a fundamental understanding of the origin of giant piezoelectric coefficients in epitaxial ferroelectric bilayers.     

Fabrication of graphene thin films based on layer-by-layer self-assembly of functionalized graphene nanosheets

In this study, we present a facile means of fabricating graphene thin films via layer-by-layer (LbL) assembly of charged graphene nanosheets (GS) based on electrostatic interactions. To this end, graphite oxide (GO) obtained from graphite powder using Hummers method is chemically reduced to carboxylic acid-functionalized GS and amine-functionalized GS to perform an alternate LbL deposition between oppositely charged GSs. Specifically, for successful preparation of positively charged GS, GOs are treated with an intermediate acyl-chlorination reaction by thionyl chloride and a subsequent amidation reaction in pyridine, whereby a stable GO dispersibility can be maintained within the polar reaction solvent. As a result, without the aid of additional hybridization with charged nanomaterials or polyelectrolytes, the oppositely charged graphene nanosheets can be electrostatically assembled to form graphene thin films in an aqueous environment, while obtaining controllability over film thickness and transparency. Finally, the electrical property of the assembled graphene thin films can be enhanced through a thermal treatment process. Notably, the introduction of chloride functions during the acyl-chlorination reaction provides the p-doping effect for the assembled graphene thin films, yielding a sheet resistance of 1.4 kΩ/sq with a light transmittance of 80% after thermal treatment. Since the proposed method allows for large-scale production as well as elaborate manipulation of the physical properties of the graphene thin films, it can be potentially utilized in various applications, such as transparent electrodes, flexible displays and highly sensitive biosensors.     

Deposition from an r.f. induction source of aluminum-copper alloys onto laminated polyimide substrates

A physical vapor deposition process with an r.f. induction vapor source was developed to deposit an aluminum-copper alloy 11.2 μm thick onto laminated polyimide substrates. The average thickness uniformity (the standard deviation divided by the average thickness), which was obtained using a beta backscatter technique, was approximately 1% for these deposits. The Al-0.3 wt.% Cu vapor charge resulted in a copper content in the deposit of 0.12 wt.%. The copper showed no preferential deposition pattern, as related to the surface of the laminate and its dispersion throughout the deposit. The resistivity of the aluminum-copper deposits was 3.0 μΩ cm and was stable from one deposition run to another. Also the resistivity was not related to the geometry of the domed substrate. The density of the aluminum-copper film 11.2 μm thick was within 1% of the theoretical density, and the film adhesion to the polyimide exceeded that required for post-deposition operations and handling. The deposited films exhibited a specular reflectance of above 90% using a source of wavelength 632.8 nm and had a grain size of 0.6 μm throughout the deposit.     

Self-Limiting Assembly Approaches for Nanoadditive Manufacturing of Electronic Thin Films and Devices

Most electronics consist of functional thin films with tens of nanometer thicknesses. It is usually challenging to control the growth of these thin films using conventional solution-based approaches. Nanoadditive manufacturing, a method to deposit electronically desired molecules, polymers, or nanomaterials in a layer-by-layer (LbL) fashion, has emerged as a promising technique for the precise control of film growth and device fabrication. Here, basic principles of nanoadditive manufacturing approaches with self-limiting characteristics are summarized with a particular focus on Langmuir–Blodgett assembly and LbL assembly. Additively manufactured electronic thin films with properties of conductors, semiconductors, and dielectrics are reviewed, followed by a discussion of their application in various electronics, such as field-effect transistors, sensors, memory devices, photodetectors, light-emitting diodes, and electrochromic devices. Finally, challenges and future developments of these approaches are proposed. The resulting analysis reveals promising opportunities of nanoadditive manufacturing for the solution-based fabrication of electronic devices.     

Abscheidung optisch,elektrisch und akustisch wirksamer Schichten mit dem Doppel‐Ring‐Magnetron

Numerous applications in optics, electronics and sensor technology require thin dielectric films. Conventionally they are deposited by evaporation, activated evaporation, rf‐sputtering or CVD‐techniques. This paper describes the deposition of such films using reactive Pulse Magnetron Sputtering. This technology not only enables a tenfold deposition rate compared to the conventional techniques but also offers new possibilities for influencing film growth. For example it is possible to alter film composition during deposition and hence to deposit complete optical systems without interruption of the plasma process. Furthermore the energetic bombardment of the growing film can be controlled in a wide range by the pulse mode and the pulse parameters. This can be used to either deposit very dense films by strong energetic bombardment or to deposit films at low thermal load onto temperature sensitive substrates. Examples of film deposition for laser optics, electrical insulation applications and surface acoustic wave devices show how these new technological possibilities advantageously can be used for creating innovative layer systems. Film deposition is carried out in stationary mode using a Double Ring Magnetron. This type of magnetron ensures film thickness uniformity better than ± 1 % on 8” substrates by the superposition of the thickness distributions of two concentric discharges.     

Layer‐by‐Layer Hydrogen‐Bonded Polymer Films: From Fundamentals to Applications

Recent years have seen increasing interest in the construction of nanoscopically layered materials involving aqueous‐based sequential assembly of polymers on solid substrates. In the booming research area of layer‐by‐layer (LbL) assembly of oppositely charged polymers, self‐assembly driven by hydrogen bond formation emerges as a powerful technique. Hydrogen‐bonded (HB) LbL materials open new opportunities for LbL films, which are more difficult to produce than their electrostatically assembled counterparts. Specifically, the new properties associated with HB assembly include: 1) the ease of producing films responsive to environmental pH at mild pH values, 2) numerous possibilities for converting HB films into single‐ or two‐component ultrathin hydrogel materials, and 3) the inclusion of polymers with low glass transition temperatures (e.g., poly(ethylene oxide)) within ultrathin films. These properties can lead to new applications for HB LbL films, such as pH‐ and/or temperature‐responsive drug delivery systems, materials with tunable mechanical properties, release films dissolvable under physiological conditions, and proton‐exchange membranes for fuel cells. In this report, we discuss the recent developments in the synthesis of LbL materials based on HB assembly, the study of their structure–property relationships, and the prospective applications of HB LbL constructs in biotechnology and biomedicine.     

Exponential growth of LBL films with incorporated inorganic sheets

The fastest growth pattern of layer-by-layer (LBL) assembled films is exponential LBL (e-LBL), which has both fundamental and practical importance. It is associated with "in-and-out" diffusion of flexible polymers and thus was considered to be impossible for films containing clay sheets with strong barrier function, preventing diffusion. Here, we demonstrate that e-LBL for inorganic sheets is possible in a complex tricomponent film of poly(ethyleneimine) (PEI), poly(acrylic acid) (PAA), and Na(+)-montmorillonite (MTM). This system displayed clear e-LBL patterns in terms of both initial accumulation of materials and unusually thick individual bilayers later in the deposition process with film thicknesses reaching 200 microm for films composed of 200 pairs of layers. Successful incorporation of MTM layers was observed by scanning electron microscopy and thermo-gravimetric analysis. Surprisingly, the growth rate was found to be nearly identical in films with and without clay layers, which suggests fast permeation/reptation of polyelectrolytes between the nanosheets during the "in-and-out" diffusion of polymer. In considering these findings, e-LBL growth property is expected for a wide array of available inorganic nanoscale components and have a potential to greatly expand the e-LBL field and LBL field altogether. The large thickness and rapid growth of the films affords fast preparation of nanostructured materials which is essential for multiple practical applications ranging from optical devices to ultrastrong composites.     

Cobalt Nanoparticle Arrays made by Templated Solid‐State Dewetting

Self‐assembled cobalt particle arrays are formed by annealing, which cause agglomeration (dewetting) of thin Co films on oxidized silicon substrates that are topographically prepatterned with an array of 200‐nm‐period pits. The Co nanoparticle size and uniformity are related to the initial film thickness, annealing temperature, and template geometry. One particle per 200‐nm‐period pit is formed from a 15‐nm film annealed at 850 °C; on a smooth substrate, the same annealing process forms particles with an average interparticle distance of 200 nm. Laser annealing enables templated dewetting of 5‐nm‐thick films to give one particle per pit. Although the as‐deposited films exhibit a mixture of hexagonal close‐packed and face‐centered cubic (fcc) phases, the ordered cobalt particles are predominantly twinned fcc crystals with weak magnetic anisotropy. Templated dewetting is shown to provide a method for forming arrays of nanoparticles with well‐controlled sizes and positions.     

Influence of the deposition pressure on the preparation of μc-Si:H thin films in hot-wire-assisted MWECR-CVD system

Considering the important influence of the deposition pressure on the growth of thin films, such as deposition rate, crystalline volume fraction and density, etc., and based on the analysis of the advantages and disadvantages on the mono-pressure method, we proposed a new method of high- and low-pressure combination to prepare hydrogenated microcrystalline silicon (μc-Si:H) films, i.e. at first we used high pressure to deposit film in 2 min in order to minish the thickness of incubation layer from the amorphous phase transition to crystalline phase, and then used low pressure to deposit film in 18 min to improve the density and decrease the oxidation of the film. The experimental results showed that using this new method the thin film with high crystalline volume fraction of 61% and low light-induced degradation ratio of 5.6% at 210 min was obtained, and meanwhile, it also possessed higher density and better photoelectronic properties than mono-pressure method.     

A Layer‐by‐Layer ZnO Nanoparticle–PbS Quantum Dot Self‐Assembly Platform for Ultrafast Interfacial Electron Injection

Absorbent layers of semiconductor quantum dots (QDs) are now used as material platforms for low‐cost, high‐performance solar cells. The semiconductor metal oxide nanoparticles as an acceptor layer have become an integral part of the next generation solar cell. To achieve sufficient electron transfer and subsequently high conversion efficiency in these solar cells, however, energy‐level alignment and interfacial contact between the donor and the acceptor units are needed. Here, the layer‐by‐layer (LbL) technique is used to assemble ZnO nanoparticles (NPs), providing adequate PbS QD uptake to achieve greater interfacial contact compared with traditional sputtering methods. Electron injection at the PbS QD and ZnO NP interface is investigated using broadband transient absorption spectroscopy with 120 femtosecond temporal resolution. The results indicate that electron injection from photoexcited PbS QDs to ZnO NPs occurs on a time scale of a few hundred femtoseconds. This observation is supported by the interfacial electronic‐energy alignment between the donor and acceptor moieties. Finally, due to the combination of large interfacial contact and ultrafast electron injection, this proposed platform of assembled thin films holds promise for a variety of solar cell architectures and other settings that principally rely on interfacial contact, such as photocatalysis.     

Preparation and properties of thin ZnS:Cu films phosphors

Thin films of ZnS and ZnS:Cu were prepared by an original metalorganic chemical vapour deposition (MOCVD) method under atmospheric pressure onto a glass substrate heated up to 230–250 °C. The film thickness varied from 0.6 to 1 μm. The thin films were doped with Cu and Cl by the thermal treatment during 1 h at 600 °C at atmospheric pressure in the blend composed of a ZnS powder with Cu and Cl compounds. These films were used for fabrication of the thin film electroluminescent (TFEL) devices with a conventional double insulating structure. The structural properties were investigated by use of X-ray diffraction (XRD) techniques and atomic force microscopy (AFM). Electroluminescent (EL) spectra, electrical and EL characteristics were investigated. The EL spectra and characteristics as well as structural parameters depend on the growth conditions and significantly modified after the annealing. Blue color emission with brightness of 10 cd m^− 2 under a sine wave excitation at 60 V and 5 kHz was obtained. The degradation behavior of the TFEL devices with ZnS:[Cu, Cl] films fabricated using an original non-vacuum methods of deposition and annealing is the same as that of commercial thin film phosphor.     

Microstructure characterization of microcrystalline silicon thin films deposited by very high frequency plasma-enhanced chemical vapor deposition by spectroscopic ellipsometry

We applied ex situ spectroscopic ellipsometry (SE) on silicon thin films across the a-Si:H/μc-Si:H transition deposited using different hydrogen dilutions at a high pressure by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). The optical models were based on effective medium approximation (EMA) and effective to estimate the thickness of the amorphous incubation layer and the volume fractions of amorphous, microcrystalline phase and void in μc-Si:H thin films. We obtained an acceptable data fit and the SE results were consistent with that from Raman spectroscopy and atomic force microscopy (AFM). We found a thick incubation layer in μc-Si:H thin films deposited at a high rate of ~ 5 Å/s and this microstructure strongly affected their conductivity.     

The role of the Zn buffer layers in the structural and photoluminescence properties of ZnO films on Zn buffer layers deposited by RF magnetron sputtering

Highly c-axis oriented ZnO thin films were grown on Si (100) substrates with Zn buffer layers. Effects of the Zn buffer layer thickness on the structural and optical qualities of ZnO thin films were investigated for the ZnO films with the buffer layers 90, 110, and 130 nm thick using X-ray diffraction (XRD), photoluminescence (PL) and atomic force microscopy (AFM) analysis techniques. It was confirmed that the quality of a ZnO thin film deposited by RF magnetron sputtering was substantially improved by using a Zn buffer layer. The highest ZnO film quality was obtained with a Zn buffer layer 110 nm thick. The surface roughness of the ZnO thin film increases as the Zn buffer layer thickness increases.     

Immobilization of liposomes in nanostructured layer-by-layer films containing dendrimers

Artificial vesicles or liposomes composed of lipid bilayers have been widely exploited as building blocks for artificial membranes, in attempts to mimic membrane interaction with drugs and proteins and to investigate drug delivery processes. In this study we report on the immobilization of liposomes of 1,2-dipalmitoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol)] (Sodium Salt) (DPPG) in layer-by-layer (LbL) films, alternated with poly(amidoamine) G4 (PAMAM) dendrimer layers. The average size of the liposomes in solution was 120 nm as determined by dynamic light scattering, with their spherical shape being inferred from scanning electron microscopy (SEM) in cast films. LbL films containing up to 20 PAMAM/DPPG bilayers were assembled onto glass and/or silicon wafer substrates. The growth of the multilayers was achieved by alternately immersing the substrates into the PAMAM and DPPG solutions for 5 and 10 min, respectively. The formation of PAMAM/DPPG liposome multilayers and its ability to interact with BSA were confirmed by Fourier transform infrared spectroscopy (FTIR). The structural features and film thickness were obtained using X-ray diffraction and surface plasmon resonance (SPR).