Silica nanowires fabricated with layer-by-layer self-assembled nanoparticles

In this paper we demonstrate an approach to fabricate silica nanowires by combining "top-down" e-beam lithography and "bottom-up" layer-by-layer (LbL) nano self-assembly techniques. The simple and low-cost LbL self-assembly technique is used to grow silica nanoparticle thin film, while the e-beam lithography based lift-off technique is implemented to pattern the self-assembled thin film to nanometer scale. The silica nanowires fabricated by this method have an average width of 90 nm, while the minimum width obtained is 63 nm. Our experimental results indicate a new approach to fabricate nanowires that can be used in nanoelectronic devices and circuits.     

基于PDMS纳米粒子改性的热模压技术

介绍了一种采用纳米SiO2、TiO2改性聚二甲基硅氧烷(PDMS)的方法,研究了两种纳米材料SiO2、TiO2添加的比例对热压效果的影响及优化条件,并分析了其改性后的热膨胀系数及杨氏模量的变化,以及其改性后热压效果的提高进行了初步分析,最后用改性的PDMS材料,快速成型来制造热压模具,热压制作聚甲基丙烯酸甲酯(PMMA)微流控芯片。与常用的金属模具(如镍模具)相比,此方法具有脱模容易,工艺周期短,难度低,重复性好,价格低等优点。     

Investigation on replication of microfluidic channels by hot embossing

In this study, effects of embossing temperature, time, and force on production of a microfluidic device were investigated. Polymethyl methacrylate (PMMA) substrates were hot embossed by using a micromilled aluminum mold. The process parameters were altered to observe the variation of replication rate in width and depth as well as symmetry of the replicated microfluidic channels. Analysis of variance (ANOVA) on the experimental results indicated that embossing temperature was the most important process parameter, whereas embossing time and force have less impact. One distinguishing aspect of this study is that, the channels were observed to be skewed to either side of the channel depending on the location of the protrusions on the mold. The mechanism of the skewness was investigated by finite element analysis and discussed in detail. Results showed that the skewness depends on the flow characteristics of the material and could be reduced by increasing the embossing temperature. The best replication rates were obtained at parameter settings of 115°C, 10?kN, and 8?min for the molds with minimum 56?µm wide features of 120?µm depth. We also showed that the fabricated channels could be successfully sealed by solvent-assisted thermo-compressive bonding at 85°C under 5.5?kN force.     

Transferring vertically aligned carbon nanotubes onto a polymeric substrate using a hot embossing technique for microfluidic applications

We explored the hot embossing method for transferring vertically aligned carbon nanotubes (CNTs) into microfluidic channels, fabricated on poly-methyl-methacrylate (PMMA). Patterned and unpatterned CNTs were synthesized by microwave plasma-enhanced chemical vapour deposition on silicon to work as a stamp. For hot embossing, 115°C and 1 kN force for 2 min were found to be the most suitable parameters for the complete transfer of aligned CNTs on the PMMA microchannel. Raman and SEM studies were used to analyse the microstructure of CNTs before and after hot embossing. The PMMA microparticles with dimensions (approx. 10 µm in diameter) similar to red blood cells were successfully filtered using laminar flow through these microfluidic channels. Finally, a microfluidic-based point-of-care device for blood filtration and detection of bio-molecules is drawn schematically.     

Fabrication of a microfluidic system for capillary electrophoresis using a two-stage embossing technique and solvent welding on poly(methyl methacrylate) with water as a sacrificial layer

Methods for fabricating poly(methyl methacrylate) microchips using a novel two-stage embossing technique and solvent welding to form microchannels in microfluidic devices are presented. The hot embossing method involves a two-stage process to create the final microchip design. In its simplest form, a mold made of aluminum is fabricated using CNC machining to create the desired microchannel design. In this work, two polymer substrates with different glass transition temperatures (Tg), polyetherimide (PEI) and poly(methyl methacrylate) (PMMA), were used to make the reusable secondary master and the final chip. First, the aluminum mold was used to emboss the PEI, a polymeric substrate with Tg approximately 216 degrees C. The embossed PEI was then used as a secondary mold for embossing PMMA, a polymeric substrate with a lower Tg ( approximately 105 degrees C). The resulting PMMA substrate possessed the same features as those of the aluminum mold. Successful feature transfer from the aluminum mold to the PMMA substrate was verified by profilometry. Bonding of the embossed layer and a blank PMMA layer to generate the microchip was achieved by solvent welding. The embossed piece was first filled with water that formed a solid sacrificial layer when frozen. The ice layer prevented channel deformation when the welding solvent (dichloroethane) was applied between the two chips during bonding. Electrophoretic separations of fluorescent dyes, rhodamine B (Rh B) and fluorescein (FL), were performed on PMMA microchips to demonstrate the feasibility of the fabrication process for microreplication of useful devices for separations. The PMMA micro-chip was tested under an electric field strength of 705 V cm-1. Separations of the test mixture of Rh B and FL generated 55 500 and 66 300 theoretical plates/meter, respectively.     

Polymeric optofluidic Fabry-Perot sensor by direct laser machining and hot embossing

We present a polymeric-based Fabry-Perot optofluidic sensor fabricated by combining direct laser machining and hot embossing. This technique provides a more elegant solution to conventional hot embossing by increasing the production rate, improving the reproducibility, and further reducing the cost, providing a large working area and flexibility in design modification and customization. As a proof of concept, a Fabry-Perot (F-P) optofluidic sensor was fabricated in polymethyl methacrylate (PMMA) from a micromachined stamp. The experimental results of the sensor agree well with analytical calculations and show a sensitivity of 2.13×10?3 RIU/nm for fluid refractive index change.     

Preparation of highly filled super-paramagnetic PMMA-magnetite nano composites using the solution method

The effect of super-paramagnetism is limited to magnetite particles at the nano scale [1–5]. Agglomerated particles exceeding a diameter of 20 nm do not show super-paramagnetism any longer. To transfer this special nano property to a bulk material it is necessary to ensure maximum dispersion of the fine particles within the polymer matrix. The focus of this paper is on the production process for super-paramagnetic magnetite PMMA nano composite material. The polymer PMMA is highly filled up to 50 mass-% with magnetite particles. The solution process uses a stabilized magnetic fluid, in which the polymer is dissolved. This solution/dispersion is atomized and dried in a spray tower to produce a fine powder of composite material. This powder is characterized (SAXS, XRD, VSM, AGM) and further processed e.g. in an injection moulding machine to manufacture structural parts. The structural parts still show super-paramagnetic properties.     

Metal-oxide-Semiconductor capacitors fabricated by layer-by-layer nanoassembly and microfabrication

Metal oxide semiconductor (MOS) capacitors were fabricated by electrostatic layer-by-layer self-assembly (LbL-SA) combined with a modified lift-off technique. The MOS capacitors were built on both n-type and p-type silicon substrates. The numbers of silicon dioxide (SiO2) nanoparticle layers were varied to characterize the electrical performance of MOS capacitors. Unlike the conventional process, LbL-SA allows us to deposit the thin films for a semiconductor device with a lower temperature, lower cost, and shorter processing time. The stability of the silica insulation layers was also investigated. Atomic force microscopy (AFM) served to monitor the film quality of the self-assembled thin films.     

Nanostructuring titania by embossing with polymer molds made from anodic alumina templates

We demonstrate a method for embossing titania sol--gel precursor with poly(methyl methacrylate) (PMMA) molds to make thin films of titania that have dense arrays of 35--65 nm diameter pores, whose features are 1 order of magnitude smaller than those previously demonstrated for sol--gel molding. We show that the high modulus of PMMA is necessary to preserve small features with high aspect ratios on the mold for nanopatterning. The molds are prepared by thermally infiltrating PMMA into anodic alumina templates, whose pore dimensions and depths are adjustable by varying anodization conditions. The difficulties associated with mold release from a master are avoided by wet etching the template. These titania films, and others made with other semiconductors, could be useful for photovoltaic, photocatalytic, and sensing applications where nanostructuring of surfaces with controlled dimensions are essential.     

Multifunctional iron and iron oxide nanoparticles in silica

Iron and iron oxide nanoparticles in silica layers deposited by sol–gel techniques on Si wafers were formed and studied. It was shown that multifunctional nanoparticles of different iron oxides possessing various physical properties can be fabricated by means of post-growth annealing of (SiO₂:Fe)/SiO₂/Si samples in various atmospheres. The hematite, maghemite, and iron nanoparticles were found to be dominant upon annealing the samples in air, argon, and hydrogen atmosphere, respectively. The physical properties of produced hybrid structures were studied by Raman and FT-IR spectroscopy, spectroscopic ellipsometry, AFM, and magnetic measurements. The sol–gel technique with subsequent annealing procedure is demonstrated to be an effective method for the formation of multifunctional hybrid structures composed of iron or iron oxide nanoparticles in silica matrix.     

Modification of BN nanosheets and their thermal conducting properties in nanocomposite film with polysiloxane according to the orientation of BN

A facile technique was developed to modify boron nitride (BN) nanosheets with iron oxides in order to fabricate highly-oriented polysiloxane/BN nanosheet composite films and their thermal properties were evaluated according to the orientation of BN. The surfaces of the BN nanosheets were modified with iron oxide nano particles by chemical vapor deposition, and their one-dimensional arrangement with variation of BN content was controlled under a magnetic field. The homogeneous suspension of BN nanosheets and pre-polymers of polysiloxane was cast on a glass spacer, and subjected to a magnetic field before the mixture was crosslinked. X-ray diffraction, transmission electron microscopy, and superconducting quantum interference device measurements were employed to identify the phases and amounts of iron oxide nano particles deposited on the BN nanosheets. The results revealed that the modified BN nanosheets were aligned either horizontally or vertically to the film plane, depending on the direction of magnetic flux with high anisotropy. The transmittance and thermal conductivity of the nano composite films were improved due to the orientation of the BN nanosheets inside the polymer matrix.     

基于局部溶解性激活的聚合物微流控芯片超声波键合

利用低于临界振幅下的超声波作用在聚合物上仅产生表面热的特点,结合PMMA在异丙醇(IPA)中的温变溶解特性,提出了一种基于局部溶解性激活的超声波聚合物微流控芯片键合方法.理论分析表明当超声振幅小于临界振幅时,只有器件接触表面产生局部表面热,而且在70℃附近IPA对PMMA的溶解性才具有良好的激活作用.在试验研究中,利用精密加工法和热压法制作了带面接触式导能筋结构和80μm×80μm微通道的PMMA微流控芯片基片.在超声振幅为13μm、键合时间8 s、键合压力300 N的条件下进行了键合试验.结果表明,芯片拉伸强度达2.25 MPa,微通道的承压能力超过800 kPa,键合后导能筋无熔融,微沟道变形率小于2%,键合时间仅为8s.该方法的键合强度和键合效率明显高于传统的键合方法,而微结构的变形率却较小,故可作为一种具有产业化前景的聚合物MEMS器件快速封接方法.     

3D Fabrication of Fully Iron Magnetic Microrobots

Biocompatibility and high responsiveness to magnetic fields are fundamental requisites to translate magnetic small‐scale robots into clinical applications. The magnetic element iron exhibits the highest saturation magnetization and magnetic susceptibility while exhibiting excellent biocompatibility characteristics. Here, a process to reliably fabricate iron microrobots by means of template‐assisted electrodeposition in 3D‐printed micromolds is presented. The 3D molds are fabricated using a modified two‐photon absorption configuration, which overcomes previous limitations such as the use of transparent substrates, low writing speeds, and limited depth of field. By optimizing the geometrical parameters of the 3D molds, metallic structures with complex features can be fabricated. Fe microrollers and microswimmers are realized that demonstrate motion at ≈20 body lengths per second, perform 3D motion in viscous environments, and overcome higher flow velocities than those of “conventional 3D printed helical microswimmers.” The cytotoxicity of these microrobots is assessed by culturing them with human colorectal cancer (HCT116) cells for four days, demonstrating their good biocompatibility characteristics. Finally, preliminary results regarding the degradation of iron structures in simulated gastric acid liquid are provided.     

Liquid PMMA: A High Resolution Polymethylmethacrylate Negative Photoresist as Enabling Material for Direct Printing of Microfluidic Chips

Polymethymethacrylate (PMMA) is one of the most important thermoplasts and a commonly used material in microsystem fabrication, for example, microfluidics owning mainly to its optical transparency, biocompatibility, low autofluorescence, and low cost. However, being a thermoplastic material PMMA is typically structured using industrial replication techniques making PMMA unsuitable for rapid prototyping. The fact that neither material nor processing technique can be directly transferred from laboratory to industrial state makes the research‐to‐business conversion often extremely difficult in microfluidics since material properties have a major impact on the final system behavior. This paper presents “Liquid PMMA,” a fast curing viscous PMMA prepolymer which can be used as a negative photoresist and directly structured using ultraviolet or visible light with tens of micron resolution and smooth surfaces. Using this technique microfluidic chips in PMMA can be fabricated within minutes. The cured Liquid PMMA parts show the same high optical transparency, low autofluorescence, and surface properties like commercial PMMA. In this way, microfluidic chips can be rapidly developed and optimized on the laboratory scale in the same material which is later on used on the industrial scale.

     

Intercalative poly(carbazole) precursor electropolymerization within hybrid nanostructured titanium oxide ultrathin films

A protocol for nanostructuring and electropolymerization of a hybrid semiconductor polycarbazole-titanium oxide ultrathin film is described. Ultrathin (<100 nm) films based on polycarbazole precursor polyelectrolytes and titanium oxide (TiOx) have been fabricated by combining the layer-by-layer (LbL) and surface sol-gel layering techniques. Film growth was followed and confirmed through UV-vis spectroscopy, ellipsometry and quartz crystal microbalance with dissipation (QCM-D). Subsequent anodic electrochemical oxidation of the carbazole pendant units afforded a conjugated polymer network (CPN) film within intercalating TiOx layers of cross-linked and π-conjugated carbazole units. Cyclic voltammetry (CV), UV-vis, and fluorescence spectroscopy measurements confirmed this process. The LbL-driven polyelectrolyte deposition process resulted in a quantified electrochemical response, proportional to the number of layers, while the TiOx acted as a dielectric spacer limiting electron transfer kinetics and attenuating energy transfer in fluorescence. Electro-optical properties were compared with other polycarbazole thin film materials with respect to bandgap energy (Eg). The straightforward protocol in film nanostructuring and barrier/dielectric properties of the inorganic oxide slab (denoted here as, TiOx) should enable applications in organic light-emitting diodes (OLEDs), dielectric mirrors, planar waveguides, and photovoltaic devices for these hybrid ultrathin films.     

Synthesis,self-assembly,and characterization of PEG-coated iron oxide nanoparticles as potential MRI contrast agent

Aim: Investigated the self-assembly and characterization of novel antifouling polyethylene glycol (PEG)-coated iron oxide nanoparticles as nanoprobes for magnetic resonance imaging (MRI) contrast agent. Method: Monodisperse oleic acid-coated superparamagnetic iron oxide cores are synthesized by thermal decomposition of iron oleate. The self-assembly behavior between iron oxide cores and PEG-lipid conjugates in water and their characteristics are confirmed by transmission electron microscope, X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, and vibrating sample magnetometer. Result: Dynamic light scattering shows superparamagnetic iron oxide nanoparticles coated with PEG are stable in water for pH of 3–10 and ionic strengths up to 0.3 M NaCl, and are protein resistant in physiological conditions. Additionally, in vitro MRI study demonstrates the efficient magnetic resonance imaging contrast characteristics of the iron oxide nanoparticles. Conclusion: The result indicates that the novel antifouling PEG-coated superparamagnetic iron oxide nanoparticles could potentially be used in a wide range of applications such as biotechnology, MRI, and magnetic fluid hyperthermia.     

Fabrication of magnetic nanodot arrays for patterned magnetic recording media

Fabrication processes of arrayed magnetic nanodots for the use of patterned magnetic recording media were reviewed. One candidate for the patterned media is ordered assemble of magnetic nanoparticles, and the other is patterned magnetic thin films fabricated using various micro/nano scale machining processes. For the formation of patterned masks and molds, lithography processes as well as self-organized pattern formation are utilized. For the deposition processes of magnetic dots, electrochemical deposition processes were widely used. These fabrication processes are reviewed mainly from recent reports. The recording systems for the patterned media including probe-type-recording are also overviewed.     

Multilayer self-assembly of TiO₂ nanoparticles and polyaniline-grafted-chitosan copolymer (CPANI) for photocatalysis

A photocatalytic thin film of TiO? nanoparticles and polyaniline-grafted-chitosan (CPANI) was fabricated by layer-by-layer (LbL) approach. The growth of the self-assembly of polymer nanocomposite was monitored by UV-vis spectroscopy and the thin film morphology was analyzed from scanning electron microscopy (SEM). Poly(styrene sulfonate) (PSS) was used as a bridging layer between TiO? nanoparticles and CPANI. Incorporation of CPANI within the LbL self-assembly of polymer nanocomposites enhanced the dye degradation ability of the thin film. These results indicate that the presence of CPANI improves the adsorption of dye in the self-assembly. The effect of surface area and the amount of catalyst was also examined. The reusability of the thin films for dye degradation study ensures the stability of the self-assembly.     

Polymer-ultrathin graphite sheet-polymer composite structured flexible nonvolatile bistable organic memory devices

We present data, which were obtained before bending and after bending, for the electrical bistabilities, memory stabilities, and memory mechanisms of three-layer structured flexible bistable organic memory (BOM) devices, which were fabricated utilizing the ultrathin graphite sheets (UGS) sandwiched between insulating poly(methylmethacrylate) (PMMA) polymer layers. The UGS were formed by transferring UGS (about 30 layers) and using a simple spin-coating technique. Transmission electron microscopy (TEM) measurements were performed to investigate the microstructural properties of the PMMA/UGS/PMMA films. Current-voltage (I-V) measurements were carried out to investigate the electrical properties of the BOM devices containing the UGS embedded in the PMMA polymer. Current-time (I-t) and current-cycle measurements under flat and bent conditions were performed to investigate the memory stabilities of the BOM devices. The memory characteristics of the BOM maintained similar device efficiencies after bending and were stable during repeated bendings of the BOM devices. The mechanisms for these characteristics of the fabricated BOM are described on the basis of the I-V results.     

Photonic stop band effect in ZnO inverse photonic crystal

Three-dimensional photonic crystals are fabricated using inward-growing self-assembly technique from polymethyl methacrylate (PMMA) colloids. Their air voids are infiltrated with zinc oxide (ZnO) by sol-gel method and the PMMA template is removed by the two independent processes of heat treatment and wet chemical method resulting in ZnO inverse photonic crystal. The inversion is confirmed from the structural characterization. In X-ray diffraction (XRD) experiment, the ZnO inverse photonic crystals obtained by both the techniques do not show any signature of single-crystalline ZnO. The inverse photonic crystals obtained by chemical method are further heated at different temperatures and XRD confirms crystalline nature of ZnO for temperature treatment at 400 °C. Laser-induced emission studies on ZnO inverse photonic crystals are carried out at two different excitation wavelengths. Excitation with 355 nm enables the observation of the stop band effect for emission at 45° from the inverse crystal obtained by the inexpensive chemical method.