Ultrathin Multilayer Films Research Articles

Out-of-plane single-mode photonic microcantilevers for integrated nanomechanical sensing platform

We have studied the optomechanical performance of optical microcantilevers fabricated with integrated waveguides for the on-chip and real-time detection of biorecognition events. The nanomechanical photonic device consists of an optical microcantilever with on-chip integrated waveguides for both coupling the light and detecting the microcantilever response. The photonic device was designed to reach a high sensitivity with a low deflection noise density (DND) of only 0.13fm/Hz. The BioMEMS transducer is embedded into a proper designed PMMA/PDMS microfluidic header and connected to a flow delivery system to study the response of the fully-integrated device under physiological conditions. As a proof of concept, we have studied the photonic microcantilever bending during consecutive formation of ultrathin polyelectrolyte multilayer films (electrostatic binding) and during biofunctionalization and biorecognition of the human growth hormone. The read-out platform was developed based on a single laser-single acquisition channel. To avoid the effect of external factors such as device positioning or temperature fluctuations, an automatized light coupling system keeps on tracking the laser beam focused into an input waveguide, increasing the required reproducibility needed for BioMEMS devices and paving the way for a potential portable multichannel sensor platform.

Bombardment induced ion transport - part IV: ionic conductivity of ultra-thin polyelectrolyte multilayer films.

The dependence of the ionic conductance of ultra-thin polyelectrolyte multilayer (PEM) films on the temperature and the number of bilayers has been investigated by the recently developed low energy bombardment induced ion transport (BIIT) method. To this end multilayers of alternating poly(sodium 4-styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) layers were deposited on a metal electrode and subsequently bombarded by a low energy potassium ion beam. Ions are transported through the film according to the laws of electro-diffusion towards a grounded backside electrode. They are neutralized at the interface between the polymer film and the metal electrode. The detected neutralization current scales linearly with the acceleration potential of the ion beam indicating Ohmic behavior for the (PAH/PSS)x multilayer, where x denotes the number of bilayers. The conductance exhibits a non-monotonic dependence on the number of bilayers, x. For 2 ≤ x ≤ 8 the conductance increases non-linearly with the number of bilayers. For x ≥ 8 the conductance decreases with increasing number of bilayers. The variation of the conductance is rationalized by a model accounting for the structure dependence of the conductivity. The thinnest sample for which the conductance has been measured is the single bilayer reflecting properties dominated by the interface. The activation energy for the ion transport is 0.49 eV.

Construction of a carbon fiber based layer-by-layer (LbL) assembly – a smart approach towards effective EMI shielding

Construction of ultrathin multilayer polymer nanocomposite films with tailor-made properties have been achieved to suppress incoming EM radiation with 52 dB shielding effectiveness at 18 GHz.

‘One-component’ ultrathin multilayer films based on poly(vinyl alcohol) as stabilizing coating for phenytoin-loaded liposomes

Ultrathin “one-component” multilayer polymeric films for potential biomedical applications were designed based on polyvinyl alcohol,—a non-toxic, fully degradable synthetic polymer. Good uniformity of the obtained film and adequate adsorption properties of the polymeric layers were achieved by functional modification of the polymer, which involved synthesis of cationic and anionic derivatives. Synthesized polymers were characterized by FTIR, NMR spectroscopy, dynamic light scattering measurements and elemental analysis. The layer by layer assembly technique was used to build up a multilayer film and this process was followed using UV–Vis spectroscopy and ellipsometry. The morphology and thickness of the obtained multilayered film material was evaluated by atomic force microscopy (AFM). Preliminary studies on the application of the obtained multilayer film for coating of liposomal nanocarriers containing phenytoin, an antiarrhythmic drug, were performed. The coating effectively stabilizes liposomes and the effect increases with an increasing number of deposited layers until the polymeric film reaches the optimal thickness. The obtained release profiles suggest that bilayer-coated liposomes release phenytoin less rapidly than uncoated ones. The cytotoxicity studies performed for all obtained nanocarriers confirmed that none of them has negative effect on cell viability. All of the performed experiments suggest that liposomes coated with ultrathin film obtained from PVA derivatives can be attractive drug nanocarriers.

Preparation and characterization of polyelectrolyte/silver multilayer films on PET substrates and its antibacterial property

Silver nanoparticles (AgNPs) were synthesized by a chemical reduction method that reduced silver nitrate with sodium borohydride. Hydrolysis of poly(ethylene terephthalate) (PET) in concentrated alkaline solution produced a carboxyl‐enriched surface. The ultrathin multilayer films were fabricated by sequential adsorption of the positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged AgNPs colloid solution on PET substrates by an layer‐by‐layer (LBL) self‐assembly technique. The multilayer film growth process on PET substrates was monitored by UV–vis absorption spectroscopy. The surface morphology and chemical composition of the multilayer film was characterized by field emission scanning electron microscope (FESEM), scanning probe microscope (SPM), and X‐ray photoelectron spectroscopy (XPS). The results showed that the AgNPs were uniformly dispersed on the PET film as metallic silver state. The surface wettability of multilayer film was investigated using sessile drop method. The results suggest that the PET films after assembled 10‐bilayer PDDA/AgNPs multilayer films exhibits good antibacterial property. POLYM. COMPOS., 36:1161–1168, 2015. © 2015 Society of Plastics Engineers

Broadband nonlinear optical response in multi-layer black phosphorus: an emerging infrared and mid-infrared optical material.

Black phosphorous (BP), the most thermodynamically stable allotrope of phosphorus, is a high-mobility layered semiconductor with direct band-gap determined by the number of layers from 0.3 eV (bulk) to 2.0 eV (single layer). Therefore, BP is considered as a natural candidate for broadband optical applications, particularly in the infrared (IR) and mid-IR part of the spectrum. The strong light-matter interaction, narrow direct band-gap, and wide range of tunable optical response make BP as a promising nonlinear optical material, particularly with great potentials for infrared and mid-infrared opto-electronics. Herein, we experimentally verified its broadband and enhanced saturable absorption of multi-layer BP (with a thickness of ~10 nm) by wide-band Z-scan measurement technique, and anticipated that multi-layer BPs could be developed as another new type of two-dimensional saturable absorber with operation bandwidth ranging from the visible (400 nm) towards mid-IR (at least 1930 nm). Our results might suggest that ultra-thin multi-layer BP films could be potentially developed as broadband ultra-fast photonics devices, such as passive Q-switcher, mode-locker, optical switcher etc.

The Application of Assembled Inorganic and Organic Hybrid Nanoarchitecture of Prussian Blue/Polymers/Graphene in Glucose Biosensing

By using graphene as a spacer, multilayer ultrathin films composed of Prussian blue nanoparticles and glucose oxidase have been fabricated on a glass carbon electrode via electrostatic layer-by-layer (LbL) assembly technique to construct glucose biosensors. This work demonstrated the capability of graphene as the spacer to form electrochemically functionalized inorganic and organic hybrid nanoarchitecture. The buildup and electrochemical properties of the multilayer nanoarchitecture were investigated by UV–Vis spectroscopy, atomic force microscopy technique and cyclic voltammetry, respectively. It was found that the developed glucose biosensor allowed rapid and sensitive determination of glucose. The amperometric response exhibited a linear correlation to glucose concentration over a range from 0.1 to 6.5 mM and the response time and detection limit were determined to be 2 s and 6 μM, respectively. It can be expected that the combination of useful graphene and versatile LbL technique could develop more efficient and more advanced biosensing devices.

Photocrosslinked ultrathin anionic polysaccharide supports for accelerated growth of human mesenchymal stem cells.

Properties of cell culture supports obtained from ultrathin multilayer films containing anionic natural polysaccharides (PSacs) and a synthetic polycation were studied. Supports were prepared via a layer-by-layer (LbL) self-assembly deposition method. Polymers used were: heparin (Hep), chondroitin sulphate (CS), hyaluronic acid (HA), and ι-carrageenan (Car) as polyanions, and diazoresin (DR) as a polycation. PSac layers were crosslinked with DR layers by irradiation with UV light absorbed by DR resin. DR/PSac films are very efficient cell culture growth supports as found from experiments with human mesenchymal stem cells (hMSCs). Irradiation of the films resulted in changing zeta potential of outermost layers of both DR and PSac to more negative values, and in increased film hydrophobicity, as found from the contact angle measurements. Photocrosslinking of the supports led to their increased stability. The supports allow for obtaining intact cell monolayers faster than when typical polystyrene tissue culture plates are used. Moreover, these monolayers spontaneously detach permitting formation of new cell layers on these surfaces relatively early during culture, compared to cells cultured on commonly used tissue culture plastic.

Multilayered poly(p-phenylenevinylene)/reduced graphene oxide film: an efficient organic current collector in an all-plastic supercapacitor.

This article describes the preparation, using layer-by-layer deposition techniques, of an all-solid-state flexible in-plane supercapacitor based on a poly(ethylene terephthalate) (PET) substrate, laminated with two strata of ultrathin multilayer films composed of 30 polyaniline (PANi)/reduced graphene oxide (RGO) bilayers and 30 poly(p-phenylenevinylene) (PPV)/RGO bilayers. The influence of the (PPV/RGO)30 stratum on the electrochemical properties of the (PANi/RGO)30/(PPV/RGO)30 film (denoted P30) (d = 90.1 nm) supported on a PET was evaluated and compared to the corresponding influence of the (PANi/RGO)53 film (denoted P53) (d = 91.5 nm). The volumetric capacitance of P30 at a discharge current of 20 A/cm(3) (957 F/cm(3)) was much higher than that obtained from P53 (733 F/cm(3)), indicating that the (PPV/RGO)30 film performed well as a current collector. Furthermore, an all-solid-state flexible in-plane EC assembled with P30 electrodes in parallel mode (denoted EC30) exhibited an outstanding volumetric capacitance (152 F/cm(3) at 20 A/cm(3)) with a high energy density (9.4 mW h/cm(3)) and power density (6.5 W/cm(3)), compared to EC53 (assembled with P53). The electron-transfer resistance of the P30 electrode corresponded to only 59% of the P53's value (1.53 vs 2.60 kΩ cm(2)). The high capacitance of EC30 was attributed to the low internal resistance of P30, which resulted from the presence of additional in-plane electrical pathways in the electrode. The enhanced transport led to 85% capacitance retention by EC30 (69% for EC53) after a 1000 charge/discharge cycles test. The series resistance variations (ΔR/R0) of EC30 also indicated good electromechanical durability in the device, with a 5.0% increase in the resistance (contrasted with a 10.8% increase in EC53) over 1000 bending cycles at a minimum radius of 5 mm. The excellent electrochemical properties of EC30 may potentially meet the requirements for miniaturized electrodes in the manufacture of flexible, lightweight, mechanically durable microelectronic applications.

Application of longitudinal generalized magneto-optical ellipsometry in magnetic ultrathin films

The longitudinal generalized magneto-optical ellipsometry (GME) method is extended to the measurement of three-layer ultrathin magnetic films. In this work, the theory of the reflection matrix is introduced into the GME measurement to obtain the reflective matrix parameters of ultrathin multilayer magnetic films with different thicknesses. After that, a spectroscopic ellipsometry is used to determine the optical parameter and the thickness of every layer of these samples, then the magneto-optical coupling constant of the multilayer magnetic ultrathin film can be obtained. After measurements of a series of ultrathin Fe films, the results show that the magneto-optical coupling constant Q is independent of the thickness of the magnetic film. The magneto-optical Kerr rotations and ellipticity are measured to confirm the validity of this experiment. Combined with the optical constants and the Q constant, the Kerr rotations and ellipticity are calculated in theory. The results show that the theoretical curve fits very well with the experimental data.

Acetate-intercalated Ni–In layered double hydroxides with low infrared emissivity: Synthesis, delamination and restacked to form the multilayer films

The low-emissive membrane materials have potential applications in infrared detecting technologies. Herein, we report a novel LDHs film with low infrared emissivity, which was based on the deposition of the exfoliated LDH nanosheets. The monodispersed hexagonal plate-like particles of Ni–In–CO32− LDHs were prepared by coprecipitation method with hydrothermal treatment under optimized conditions. In order to exfoliate the LDHs into nanosheets, acetate-intercalated Ni–In LDHs were prepared by anion-exchange of Ni–In–CO32− LDHs. The as-prepared acetate-intercalated LDHs exhibited excellent delaminating behavior in water and unilamellar nanosheets were easily obtained. The resulting positive-charged nanosheets were assembled onto quartz substrates to produce the multilayer films. The infrared emissivity values of all the samples were characterized. It was found that the incorporation of Ni2+ and In3+ in the host layer significantly reduced the infrared emissivity value. Moreover, the value was further reduced by the fabrication of multilayer ultrathin films, which can be ascribed to the dense orderly structure and smooth surface morphology.

Layer-by-layer self-assembly of ultrathin multilayer films composed of magnetite/reduced graphene oxide bilayers for supercapacitor application

This article describes electrochemical properties of layer-by-layer self-assembled multilayer films composed of magnetite nanoparticle (Fe3O4 NP) and chemically reduced graphene oxide (RGO) for supercapacitor application. The thickness of the Fe3O4/GO bilayer was determined by optical ellipsometry to be 6.53±0.17nm, which agreed well with the sum of the independently measured thickness for each Fe3O4 (5.61±0.14nm) and GO (0.91±0.1nm) layer component. Each layer was found to be deposited uniformly and regularly. Fe3O4/RGO multilayer film was obtained by reducing a Fe3O4/GO film using hydrazine. The multilayer film yielded a minimum resistance of 1.0×104Ω/sq (2.8S/cm) for a film with approximately 50 bilayers. The electrodes fabricated from 30 Fe3O4/RGO bilayers exhibited excellent capacitive performances with a maximum specific gravimetric capacitance (151F/g) at a current density of 0.9A/g.

The extended magneto optic method to explore the Longitude Magneto Optic Kerr effect of the ultrathin magnetic film grown on optic uniaxial substrate

A general method to solve the Magneto optic effect of the multilayer ultrathin films grown on the optic uniaxial crystal substrate has been developed by using a new boundary matrix. Based on this method, we can apply the magneto optic to any magnetic ultrathin film grown on uniaxial substrate as long as we choose a proper coordinate system. The formula for longitude Magneto Optical Kerr effect is derived to find out the influence of the optic properties of the uniaxial crystal on the magneto optic characteristics of multilayer system. A numerical simulation was carried out to find out the relation between Kerr rotation and optic properties of substrate. The result can be used to select the best suitable substrate on which the sample grown.

Layer‐by‐layer assembled hydrogel nanocomposite film with a high loading capacity

ABSTRACTThe layer‐by‐layer assembly technique is a method that widely used in the preparation of nanostructured multilayer ultrathin films. We fabricated a hydrogel nanocomposite film by alternating the deposition of a core–shell poly[(dimethylimino)(2‐hydroxy‐1,3‐propanedily) chloride] (PDMIHPC)–laponite solution and poly(acrylic acid). The growth of the deposition procedure was proven by ultraviolet–visible spectroscopy and spectroscopic ellipsometry. The surface morphology of the films was observed by scanning electron microscopy. The films could reversibly load and release methylene blue (MB) dye, which was used as an indicator. It took about 4.5 h to reach loading equilibrium at pH 9.0. The loading capacity of the film for MB was as large as 4.48 μg/cm2 per bilayer because of the introduction of the core–shell PDMIHPC–laponite as a film component. Nearly 90% of MB was released at pH 3.0 or in a 300 mM NaCl solution within 2.5 h. The loading and release processes were greatly influenced by the ionic strength and pH value of the MB solution. The hydrogel nanocomposite film showed good pH‐triggered loading‐release reversibility and suggested potential applications in controlled drug‐delivery systems and smart materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39352.

Illustrating the Processability of Magnetic Layered Double Hydroxides: Layer-by-Layer Assembly of Magnetic Ultrathin Films

We report the preparation of single-layer layered double hydroxide (LDH) two-dimensional (2D) nanosheets by exfoliation of highly crystalline NiAl-NO3 LDH. Next, these unilamellar moieties have been incorporated layer-by-layer (LbL) into a poly(sodium 4-styrenesulfonate)/LDH nanosheet multilayer ultrathin film (UTF). Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible light (UV-vis), and X-ray diffraction (XRD) profiles have been used to follow the uniform growth of the UTF. The use of a magnetic LDH as the cationic component of the multilayered architecture enables study of the resulting magnetic properties of the UTFs. Our magnetic data show the appearance of spontaneous magnetization at ∼5 K, thus confirming the effective transfer of the magnetic properties of the bulk LDH to the self-assembled film that displays glassy-like ferromagnetic behavior. The high number of bilayers accessible-more than 80-opens the door for the preparation of more-complex hybrid multifunctional materials that combine magnetism with the physical properties provided by other exfoliable layered inorganic hosts.

A Method for Fabricating an Ultrathin Multilayer Film Composed of Poly(p‐phenylenevinylene) and Reduced Graphene Oxide on a Plastic Substrate for Flexible Optoelectronic Applications

AbstractThe photoconductive properties of a uniform ultrathin multilayer film composed of alternating poly(p‐phenylene vinylene) (PPV) and reduced graphene oxide (RGO) layers, fabricated on a poly(ethylene terephthalate) (PET) sheet are reported. The assembly of the two electron‐rich layer components on the temperature‐sensitive substrate is realized using a layer‐by‐layer‐deposition technique under mild conditions and HI/H2O vapor treatment at 100 °C. This protocol is established to simultaneously convert the layer components to their conjugated counterparts, PPV and RGO in the multilayer films, whose total thicknesses shrinks to 50% of their original values due to lattice contraction. Furthermore, the surface roughness decreases significantly, in contrast to the results obtained from general chemical treatments. The PET sheets coated with (PPV/RGO)15 films exhibit a photocurrent of 115 μA at an illumination intensity of 1.1 mW and a photoresponsivity of 111.1 mA W−1 at an illumination intensity of 0.5 mW; these are among the best values yet achieved in carbon‐based materials. The establishment of a method for fabricating (PPV/RGO) films on a temperature‐sensitive transparent flexible sheet is crucial for the development of organic‐based portable electronic devices.

Magnetic-stress-assisted damping of magnetization precession in multilayered metallic films

Micromagnetic dynamics of spin relaxation in multilayered metallic films of stacked microelectronic devices is modeled by a modified Landau–Lifshitz–Gilbert equation with a newly introduced form of damping torque owing its origin to coupling between precessing magnetization-vector and stress-tensor of combined intrinsic and extrinsic magnetic anisotropy. Based on the magnetization energy loss equation, the exponential relaxation time as a function of precession frequency and angle of applied rf-field is obtained, depending upon two parameters of intrinsic and extrinsic damping torques acting on precessing magnetization. It is shown that theoretically obtained from the Gabor uncertainty relation the FMR linewidth, originating from the above magnetic-stress-assisted damping of magnetization precession, provides proper account for the empirical non-linear linewidth-vs-frequency curves deduced from recent in-plane FMR measurements on multilayered ultrathin films of ferromagnetic metals.

Highly Stable Graphene‐Based Multilayer Films Immobilized via Covalent Bonds and Their Applications in Organic Field‐Effect Transistors

AbstractHighly stable graphene oxide (GO)‐based multilayered ultrathin films can be covalently immobilized on solid supports through a covalent‐based method. It is demonstrated that when (3‐aminopropyl) trimethoxysilane (APTMS), which works as a covalent cross‐linking agent, and GO nanosheets are assembled in an layer‐by‐layer (LBL) manner, GO nanosheets can be covalently grafted on the solid substrate successfully to produce uniform multilayered (APTMS/GO)N films over large‐area surfaces. Compared with conventional noncovalent LBL films constructed by electrostatic interactions, those assembled using this covalent‐based method display much higher stability and reproducibility. Upon thermal annealing‐induced reduction of the covalent (APTMS/GO)N films, the obtained reduced GO (RGO) films, (APTMS/RGO)N, preserve their basic structural characteristics. It is also shown that the as‐prepared covalent (APTMS/RGO)N multilayer films can be used as highly stable source/drain electrodes in organic field‐effect transistors (OFETs). When the number of bilayers of the (APTMS/RGO)N film exceeds 2 (ca. 2.7 nm), the OFETs based on (APTMS/RGO)N electrodes display much better electrical performance than devices based on 40 nm Au electrodes. The covalent protocol proposed may open up new opportunities for the construction of graphene‐based ultrathin films with excellent stability and reproducibility, which are desired for practical applications that require withstanding of multistep post‐production processes.

Luminescent Layer by Layer Thin Films Based on Polyoxometalate and Poly(amidoamine) Dendrimer

Ultrathin multilayer films containing polyoxometalate (POM) K11[Eu(PW11O39)2] (Eu(PW11)2) and poly(amidoamine) (PAMAM) dendrimer were prepared using layer-by-layer (LBL) assembly method in the present work. The stable multilayer films were assembled by alternate adsorption of negatively charged POM and positively charged PAMAM from their aqueous dispersions. The growth of the muhilayer films is regular．The proposed novel immobilized method exhibited good stability and the photoluminescent behavior of films at room temperature was investigated to show the Eu3+ charaeteristic emission pattern，which is important for practical application.

Covalent molecular assembly: Construction of ultrathin multilayer films by a two-dimensional fabrication method

A two-dimensional fabrication method was employed to assemble ultrathin multilayer films with specific three-dimensional structures by making use of interlayer and intralayer covalent bonding. The films were assembled in a layer-wise fashion on a silicon surface using bi- and multi-functional molecules as building blocks and strengthened by lateral cross-linking. The fabrication process could be controlled at the sub-nano-scale with the roughness of the surface after deposition of each layer within 0.2nm. The film showed better resistance to harsh environments than randomly cross-linked or linearly linked films of comparable thickness. The combination of covalent LbL assembly and lateral cross-linking has significant potential as a method of fabrication for assembling nano-structures for a variety of applications.