Two- and three-dimensional micro/nanostructure patterning of CdS-polymer nanocomposites with a laser interference technique and in situ synthesis

Two-?and three-dimensional (2D and 3D) micro/nanostructures of CdS-polymer nanocomposites have been successfully patterned, combining photopolymerization via a laser four-beam interference technique with in situ synthesis of CdS nanoparticles in the patterned polymer matrix. The morphology and optical properties of CdS nanoparticles in polymer matrices have been confirmed using TEM, XRD, FTIR, UV-vis absorption and fluorescence spectroscopy. Laser irradiation time and film thickness are certified to be the key factors for the control of the micro/nanostructures. With thickening film, the fabricated microstructures of CdS-polymer nanocomposites were dramatically changed from 2D rods to 3D networks which were composed of nanofibres, nanometre-scale walls and micrometre-scale rods. These kinds of 2D and 3D micro/nanostructures could be expected as potential applications in the development of nanotechnology, such as nanomedical systems, micro-fluidic chips, nanoreactors and micro/nanopurification or separation systems.     

High‐Throughput Near‐Field Optical Nanoprocessing of Solution‐Deposited Nanoparticles

The application of nanoscale electrical and biological devices will benefit from the development of nanomanufacturing technologies that are high‐throughput, low‐cost, and flexible. Utilizing nanomaterials as building blocks and organizing them in a rational way constitutes an attractive approach towards this goal and has been pursued for the past few years. The optical near‐field nanoprocessing of nanoparticles for high‐throughput nanomanufacturing is reported. The method utilizes fluidically assembled microspheres as a near‐field optical confinement structure array for laser‐assisted nanosintering and nanoablation of nanoparticles. By taking advantage of the low processing temperature and reduced thermal diffusion in the nanoparticle film, a minimum feature size down to ≈100 nm is realized. In addition, smaller features (50 nm) are obtained by furnace annealing of laser‐sintered nanodots at 400 °C. The electrical conductivity of sintered nanolines is also studied. Using nanoline electrodes separated by a submicrometer gap, organic field‐effect transistors are subsequently fabricated with oxygen‐stable semiconducting polymer.     

Patterned dispersion of nanoparticles in hydrogels using microfluidics

Uniform dispersions of nanoparticles in polymers have received increasing attention for optical applications, and patterned dispersions could enhance the potential applications. Methods for achieving patterned dispersions of nanoparticles in polymers are limited. However, microfluidics represents one technique that holds promise for this application. To demonstrate proof-of-concept, model samples of fluorescent polystyrene nanoparticles dispersed in hydrogels were chosen. High fidelity staircase patterns were produced, imaged using fluorescence microscopy and quantified using image analysis software. The results demonstrate the suitability of microfluidics for creating patterned dispersions of nanoparticles in polymers and establishes the foundation for enabling optical applications.     

Electric field imprinting of sub-micron patterns in glass-metal nanocomposites

We demonstrate that the dissolution of 10?nm metal nanoparticles localized in the subsurface layer of silicate glass by static electric field can be employed to alter the optical density and surface profile of the glass-metal composite with spatial resolution of 200?nm. The developed technique, which can be referred to as electric field imprinting (EFI), offers an attractive alternative to conventional micro-?and nano-pattering techniques.     

Large-scale assembly of colloidal nanoparticles and fabrication of periodic subwavelength structures

This paper reports a simple and scalable spin-coating technique for assembling 70?nm silica nanoparticles into non-close-packed colloidal crystals over a large area. The thickness of the shear-aligned colloidal crystals can be controlled from hundreds of layers to a single monolayer by adjusting the spin-coating conditions. We further demonstrate that the spin-coated colloidal monolayers can be used as structural templates to pattern sub-100?nm pillar arrays directly on silicon substrates. The resulting subwavelength-structured pillar arrays exhibit excellent broadband antireflective and superhydrophobic properties, which are promising for developing self-cleaning antireflection coatings for crystalline silicon solar cells. This bottom-up approach enables large-scale production of periodic nanostructures with resolution beyond the optical diffraction limit that have important technological applications ranging from high-density data storage and optoelectronics to biological sensing and subwavelength optics.     

Formation and field emission of patterned zinc oxide-adhering graphene cathodes

Large scale zinc oxide (ZnO)-adhering patterned graphene cathodes were realized by using spin-coating technique, and their field emission characteristics were investigated. The graphene sheets edges are extracted from the hybrid cathode to form emission centers, leading to high field enhancement and low threshold field. The ZnO film improves the interface contact and adhesion of graphene sheets with the electrode and acts as negative feedback resistive layer, which contributes to the uniformity and long-time stability. Our study opens up avenues for application of graphene sheets in field emission device utilizing efficient, large scale, pattern and low-cost technology.     

Study and Application of Controlled Vortex Dynamics in?Patterned YBCO Films

Quantitative imaging of the local magnetic field and of current density distribution in superconductors (with microscopic resolution over macroscopic length scales) is achieved by means of the Magneto-Optical Imaging technique with an indicator film. We exploit this technique to study the vortex arrangement and the corresponding supercurrent distribution in high temperature superconducting YBa₂Cu₃O_7?x films. Several patterned superconducting films were studied, either non-simply connected structures, which imply macroscopic flux quantization, and superconductors whose local properties were tailored by means of confined heavy-ion irradiation. Moreover, by means of electrical transport measurements coupled with the real-time imaging of the magnetic pattern, it is directly shown how the local current distribution in patterned superconductors is affected by the electrical transport both in the Meissner and in the vortex regimes. The relevance of a controlled and localized dissipation induced by the confined vortex motion in tailored superconducting films is demonstrated for direct applications of this phenomenology to superconducting devices, such as magnetic field and photon detectors.     

Brownian motion in a designer force field: dynamical effects of negative refraction on nanoparticles

Photonic crystals (PC) have demonstrated unique features that have renewed the fields of classical and quantum optics. Although holding great promises, associated mechanical effects have proven challenging to observe. We demonstrate for the first time that one of the most salient properties of PC, namely negative refraction, can induce specific forces on metal nanoparticles. By integrating a periodically patterned metal film in a fluidic cell, we show that near-field optical forces associated with negatively refracted surface plasmons are capable of controlling particle trajectories. Coupling particle motions to PC band structures draws new approaches and strategies for parallel and high resolution all-optical control of particle flows with applications for micro- and nanofluidic systems.     

Lithographically patterned magnetic calorimeter X-ray detectors with integrated SQUID readout

We describe the design, fabrication and performance of a fully lithographically patterned magnetic microcalorimeter X-ray detector. The detector is fabricated on the same chip as a low-noise SQUID that measures the change in the magnetic sensor film's magnetization as the film is heated by absorbed X-rays. Our proof-of-principle detectors use a 100 μm×100 μm–2 μm paramagnetic Au:Er film coupled to a low-noise on-chip SQUID via a meandering superconducting pickup loop that also provides the magnetic field bias to the film. Absorption of 6 keV X-rays in the film causes heating on the order of 1 mK with a decay time of 1 ms or less, the fastest reported using a magnetic calorimeter. However, the resolution is currently poor due to poor Au:Er film properties and non-optimized coupling to the SQUID. We describe the design and fabrication of this device and present measurements of the heat capacity, decay time constant and effective thermal conductance of the microcalorimeter as a function of temperature. Because the SQUID and calorimeter are lithographically patterned on the same substrate, this technology can be readily applied to the fabrication of arrays of multiplexed magnetic microcalorimeter detectors.     

Density-controlled, solution-based growth of ZnO nanorod arrays via layer-by-layer polymer thin films for enhanced field emission

A simple, scalable, and cost-effective technique for controlling the growth density of ZnO nanorod arrays based on a layer-by-layer polyelectrolyte polymer film is demonstrated. The ZnO nanorods were synthesized using a low temperature (T = 90?°C), solution-based method. The density-control technique utilizes a polymer thin film pre-coated on the substrate to control the mass transport of the reactant to the substrate. The density-controlled arrays were investigated as potential field emission candidates. The field emission results revealed that an emitter density of 7?nanorods?μm(-2) and a tapered nanorod morphology generated a high field enhancement factor of 5884. This novel technique shows promise for applications in flat panel display technology.     

Composite nanowire-based probes for magnetic resonance force microscopy

We present a nanowire-based methodology for the fabrication of ultrahigh sensitivity and resolution probes for atomic resolution magnetic resonance force microscopy (MRFM). The fabrication technique combines electrochemical deposition of multifunctional metals into nanoporous polycarbonate membranes and chemically selective electroless deposition of optical nanoreflector onto the nanowire. The completed composite nanowire structure contains all the required elements for an ultrahigh sensitivity and resolution MRFM sensor with (a) a magnetic nanowire segment providing atomic resolution magnetic field imaging gradients as well as large force gradients for high sensitivity, (b) a noble metal enhanced nanowire segment providing efficient scattering cross-section from a sub-wavelength source for optical readout of nanowire vibration, and (c) a nonmagnetic/nonplasmonic nanowire segment providing the cantilever structure for mechanical detection of magnetic resonance.     

Fabrication of sticky and slippery superhydrophobic surfaces via spin-coating silica nanoparticles onto flat/patterned substrates

Silica nanoparticles were spin-coated onto a flat/patterned (regular pillar-like) substrate to enhance the surface roughness. The surface was further modified by a self-assembled fluorosilanated monolayer. The advancing/receding contact angle and sliding angle measurements were performed to determine the wetting behavior of a water droplet on the surface. It is interesting to find that a transition from a Wenzel surface to a sticky superhydrophobic surface is observed due to the spin-coating silica nanoparticles. A slippery superhydrophobic surface can be further obtained after secondary spin-coating with silica nanoparticles to generate a multi-scale roughness structure. The prepared superhydrophobic substrates should be robust for practical applications. The adhesion between the substrate and nanoparticles is also examined and discussed.     

Lithography-free sub-100 nm nanocone array antireflection layer for low-cost silicon solar cell

A high-density and -uniformity sub-100 nm surface-oxidized silicon nanocone forest structure is created and integrated onto the existing texturization microstructures on a photovoltaic device surface by a one-step high-throughput plasma-enhanced texturization method. We suppressed the broadband optical reflection on chemically textured grade-B silicon solar cells for up to 70.25% through this nanomanufacturing method. The performance of the solar cell is improved with the short-circuit current increased by 7.1%, fill factor increased by 7.0%, and conversion efficiency increased by 14.66%. Our method demonstrates the potential to improve the photovoltaic device performance with low-cost and high-throughput nanomanufacturing technology.     

3D characterization of microstructured poly(methacrylic acid) thin films via Mach-Zehnder interference microscopy

We demonstrate the adaption of a further developed Mach-Zehnder interference (MZI) microscope for the rapid 3D characterization of transparent microstructured polymer thin films. In order to quantify the accuracy of the Mach-Zehnder interferometer, comparative film thickness measurements of photolithographically patterned poly(methacrylic acid) polymer brushes are performed employing two alternative techniques: white light profilometry (WIM) and atomic force microscopy (AFM). When the refractive index of the polymer brushes is calculated from MZI data, we obtain a good agreement with results received from an independent method (ellipsometry).In contrast to surface probing techniques such as AFM or WIM, Mach-Zehnder interferometry is a transmitted light method that measures both surface height profiles and refractive index distributions. MZI thus enables the quantification of film homogeneity with respect to height and density variations at the lateral resolution of a refraction limited microscope. We conclude that MZI is an adequate tool for the rapid and non-destructive characterization of structured polymer thin films. This method should be particularly useful for production quality control of microstructured polymer thin films which possess great potential in electronic device fabrication and biotechnology.     

Evidence for intergranular tunnelling in polyaniline passivated α-Fe nanoparticles

Nanoparticles are of immense importance both from the fundamental and application points of view. They exhibit quantum size effects which are manifested in their improved magnetic and electric properties. Mechanical attrition by high energy ball milling (HEBM) is a top down process for producing fine particles. However, fineness is associated with high surface area and hence is prone to oxidation which has a detrimental effect on the useful properties of these materials. Passivation of nanoparticles is known to inhibit surface oxidation. At the same time, coating polymer film on inorganic materials modifies the surface properties drastically. In this work a modified set-up consisting of an RF plasma polymerization technique is employed to coat a thin layer of a polymer film on Fe nanoparticles produced by HEBM. Ball-milled particles having different particle size ranges are coated with polyaniline. Their electrical properties are investigated by measuring the dc conductivity in the temperature range 10-300?K. The low temperature dc conductivity (I-V) exhibited nonlinearity. This nonlinearity observed is explained on the basis of the critical path model. There is clear-cut evidence for the occurrence of intergranular tunnelling. The results are presented here in this paper.     

条纹图形Heusler合金CoFeMnSi薄膜的制备及其磁特性研究

以CoFeMnSi作为研究对象,对其进行图形化设计,以研究图形化CoFeMnSi薄膜的磁学特性。利用感光溶胶-凝胶法和激光干涉法制得条纹图形ZrO2薄膜,之后利用磁控溅射法在其表面溅射沉积CoFeMnSi,以达到制得图形化CoFeMnSi磁性薄膜的目的,并对其表面形貌和磁学特性进行了表征。采用金相显微镜分析验证CoFeMnSi薄膜继承了ZrO2的条纹图形结构,条纹图形周期约为2μm;面内磁性测量显示薄膜398 kA/m磁场下的磁化强度与外磁场和条纹夹角θ呈180°周期性变化关系,且磁化强度介于390~440 kA/m;利用CoFeMnSi平膜面内磁化强度及面外磁化强度与外加磁场方向的变化关系,解释了条形薄膜磁化强度的θ角度依赖关系;采用磁力显微镜观察到磁畴结构形态为蜂窝状,磁畴尺寸大约1~2μm。     

Characterization of Combinatorial Polymer Blend Composition Gradients by FTIR Microspectroscopy

A new FTIR technique was developed for characterizing thin polymer films used in combinatorial materials science. Fourier transform infrared microspectroscopy mapping technique was used to determine the composition of polymer blend gradients. Composition gradients were made from poly(L-lactic acid) (PLLA) and poly(D,L-lactic acid) (PDLLA) in the form of thin films (6 cm × 2 cm) deposited on IR reflective substrates. Three composition gradient films were prepared and characterized. The results demonstrate the reproducibility and feasibility of a new, high-throughput approach for preparing and characterizing polymer composition gradients. The combination of composition gradient film technology and automated nondestructive FTIR microspectroscopy makes it possible to rapidly and quantitatively characterize polymer composition gradients for use in combinatorial materials science.     

Field enhancement and large optical nonlinearity in Ag nanocomposite polymer film

We report a simple in situ synthesis for Ag nanocomposite polymer film. The extinction spectrum and the distribution of the local field intensities for Ag nanoparticles are performed by means of the dipole discrete approximation. The local field intensity is enhanced over 20 times to that of the incident light at the peak wavelength of the extinction spectrum. Nonlinear optical measurements, performed by using the Z-scan techniques, are presented afterwards. Giant enhancement of nonlinear optical responses is found for Ag/PMMA film compared with pure PMMA (polymethyl methacrylate) film. The nonlinear refractive index γ of the Ag/PMMA film is measured to be 3.708 × 10^?2 cm² GW^?1. The enhanced optical properties are due to the surface plasmon resonance of Ag nanoparticles. These results are in agreement with the previous field calculations. Analyzed with respect to Stegeman figures of merit, Ag/PMMA nonlinear polymer film shows promise for practical use in ultrafast optical devices.     

Parallel patterning of nanoparticles via electrodynamic focusing of charged aerosols

The development of nanodevices that exploit the unique properties of nanoparticles will require high-speed methods for patterning surfaces with nanoparticles over large areas and with high resolution. Moreover, the technique will need to work with both conducting and non-conducting surfaces. Here we report an ion-induced parallel-focusing approach that satisfies all requirements. Charged monodisperse aerosol nanoparticles are deposited onto a surface patterned with a photoresist while ions of the same polarity are introduced into the deposition chamber in the presence of an applied electric field. The ions accumulate on the photoresist, modifying the applied field to produce nanoscopic electrostatic lenses that focus the nanoparticles onto the exposed parts of the surface. We have demonstrated that the technique could produce high-resolution patterns at high speed on both conducting (p-type silicon) and non-conducting (silica) surfaces. Moreover, the feature sizes in the nanoparticle patterns were significantly smaller than those in the original photoresist pattern.     

High-density silver nanoparticle film with temperature-controllable interparticle spacing for a tunable surface enhanced Raman scattering substrate

The formation of high-density silver nanoparticles and a novel method to precisely control the spacing between nanoparticles by temperature are demonstrated for a tunable surface enhanced Raman scattering substrates. The high-density nanoparticle thin film is accomplished by self-assembling through the Langmuir-Blodgett (LB) technique on a water surface and transferring the particle monolayer to a temperature-responsive polymer membrane. The temperature-responsive polymer membrane allows producing a dynamic surface enhanced Raman scattering substrate. The plasmon peak of the silver nanoparticle film red shifts up to 110 nm with increasing temperature. The high-density particle film serves as an excellent substrate for surface-enhanced Raman spectroscopy (SERS), and the scattering signal enhancement factor can be dynamically tuned by the thermally activated SERS substrate. The SERS spectra of Rhodamine 6G on a high-density silver particle film at various temperatures is characterized to demonstrate the tunable plasmon coupling between high-density nanoparticles.