Three-dimensional micropatterns of well-aligned carbon nanotubes produced by photolithography

Three-dimensional micropatterns of well-aligned carbon nanotubes were prepared on photolithographically prepatterned substrates by pyrolysis of iron(II) phthalocyanine (FePc) under an Ar/H2 atmosphere at 800-1100 degrees C. The photopatterning was achieved by photolithographic cross-linking of a chemically amplified photoresist layer spin-cast on a quartz plate or a silicon wafer, coupled with solution development. Owing to an appropriate surface characteristic, the patterned photoresist layer was found in this case to support aligned carbon nanotube growth by pyrolysis of FePc, as were the photoresist-free substrate surfaces. The difference in chemical nature between the surface areas covered and uncovered by the photoresist film, however, caused a region-specific growth of the nanotubes with different tubular lengths and packing densities, leading to the formation of three-dimensional aligned nanotube patterns suitable for various device applications.     

The residual pattern of double thin-film over-etching for the fabrication of continuous patterns with dimensions varying from 50 nm to millimeters over a large area

Attempts at heavy edge over-etching of a single thin film under a photoresist to leave behind a residual smaller patterned line as a mask for nanostructure fabrication frequently fail due to detachment of the photoresist above it. We have accordingly developed a technique named 'residual pattern of double thin-film over-etching' (RDTO) to obtain a nanoscale residual pattern of the bottom thin film after extensive edge over-etching. When Au and Cr were used as the top and bottom thin films, respectively, heavy over-etching of Cr for use as a mask for nanopatterning of the underlying silicon substrate was feasible. Three patterns were fabricated for demonstration of the RDTO technique, and nanopatterns with linewidths as small as 50?nm were obtained. More importantly, our technique allows the fabrication of a single pattern with feature dimensions that vary continuously from a few tens of nanometers to a few millimeters at different positions. In addition, we have developed simple models to analyze the hydrodynamic and surface tension effects during the over-etching procedure to show the feasibility of RDTO. This technique will find diverse applications in micro-?and nano-fluidics, lab-on-a-chip nano-arrays and biomedical engineering.     

Electrophoretic deposition of ZnO nanoparticles, from micropatterns to substrate coverage

We report on an electrophoretic deposition (EPD) method that is suited for the preparation of both ZnO thin films and micropatterns. By applying small DC voltages between a Cu electrode and a conductive Si substrate, submersed in a suspension of ZnO quantum dots, we can cover entire substrates with ZnO layers of a tuneable thickness ranging from a few monolayers to 200?nm. The deposition occurs selectively at the cathode, which indicates that the ZnO particles have a positive charge. Atomic force microscopy was used to study the influence of the deposition voltage, time, and the quantum dot concentration on the final layer thickness. By using lithographically patterned Si substrates, the same technique enables the formation of ZnO micropatterns of variable thickness with dimensions down to 5?μm. This is done by depositing a ZnO layer on a Si substrate that is covered with a patterned, developed photoresist. After EPD, the resist is removed by submersing the substrate in the appropriate solvent without damaging the ZnO deposit. This illustrates the robustness of the layers obtained by EPD.     

Double-shot inkjet printing of donor-acceptor-type organic charge-transfer complexes: Wet/nonwet definition and its use for contact engineering

We developed the double-shot inkjet printing technique for manufacturing the uniform polycrystalline thin films of organic charge-transfer complexes with a well-defined patterning on the substrate surfaces. The technique utilizes the wet/nonwet surface modification to confine the intermixed droplets of individually-printed donor and acceptor inks in a predefined area, which results in the picoliter-scale instantaneous complex formation. By the method, we obtained synthetic-metal patterned deposits of tetrathiafulvalene-tetracyanoquinodimethane with smooth thickness distribution and highly c-axis orientation, where the preference for the 1:1 complex formation is clearly demonstrated. We also discuss the use of the patterned deposits for the contact engineering of organic thin-film transistors.     

Patterned structures fabricated on chalcogenide phase-change thin films by laser direct writing

In laser direct writing technology, the pattern is usually written in a photoresist. In this work, we use the chalcogenide phase change thin films as the laser direct writing materials, and patterned structures with different shapes and sizes were directly written with different laser wavelengths. Compared with traditional photoresist materials, the patterned structures can be directly formed in the chalcogenide phase change thin films without developing and etching procedures, and also can be directly written with different laser wavelengths. By tuning the laser parameters precisely, patterned structures with different sizes and shapes could be obtained as well. The analysis indicates that the formation mechanism of the patterned structure is mainly due to the volume expansion caused by material vaporization and the interior of the patterned structure is hollow with some solid leavings, and the chalcogenide phase change thin films are very good candidate materials for patterned structure formation.     

Carbon electrode fabrication from pyrolyzed parylene C

Carbon electrodes coupled with electrochemical detection have been used extensively for the investigation of biogenic amines. Herein we report the fabrication and characterization of carbonaceous electrodes prepared from pyrolyzed parylene C (PPC) films. High-aspect ratio carbonaceous microelectrodes have been prepared by masking PPC coated pipets with an insulating parylene C film. PPC thin film electrodes were characterized electrochemically, spectroscopically, and with electron microscopy. The procedures described here offer a route to fabrication of thin film carbon electrodes that can be patterned and produced in parallel. These electrodes are similar to carbon electrodes derived from pyrolyzed photoresist films but do not require spin-coating or lithography and can readily coat three-dimensional surfaces.     

Method for patterning various nanomaterials: electrochemical deposition of patterned Ni thin films and their utilization as a strippable mask

We report an interesting approach for preparing micropatternings of nanomaterials, such as carbon nanotubes and TiO(2) nanoparticles. In the method, exfoliation of electrodeposited Ni thin films was the key process. After patterning indium thin oxide (ITO) plates with an insulating photoresist by conventional photolithography, Ni was electrodeposited on only the exposed ITO areas. The resulting substrates were evenly covered with nanomaterials by a drop cast method. By exfoliating the electrodeposited Ni thin films from the substrates, patterned nanomaterial films were formed.     

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.     

Atomic layer deposition on phase-shift lithography generated photoresist patterns for 1D nanochannel fabrication

A versatile, low-cost, and flexible approach is presented for the fabrication of millimeter-long, sub-100 nm wide 1D nanochannels with tunable wall properties (wall thickness and material) over wafer-scale areas on glass, alumina, and silicon surfaces. This approach includes three fabrication steps. First, sub-100 nm photoresist line patterns were generated by near-field contact phase-shift lithography (NFC-PSL) using an inexpensive homemade borosilicate mask (NFC-PSM). Second, various metal oxides were directly coated on the resist patterns with low-temperature atomic layer deposition (ALD). Finally, the remaining photoresist was removed via an acetone dip, and then planar nanochannel arrays were formed on the substrate. In contrast to all the previous fabrication routes, the sub-100 nm photoresist line patterns produced by NFC-PSL are directly employed as a sacrificial layer for the creation of nanochannels. Because both the NFC-PSL and the ALD deposition are highly reproducible processes, the strategy proposed here can be regarded as a general route for nanochannel fabrication in a simplified and reliable manner. In addition, the fabricated nanochannels were used as templates to synthesize various organic and inorganic 1D nanostructures on the substrate surface.     

Detection of tumor markers using single-walled carbon nanotube field effect transistors

We have developed a biosensor capable of detecting carcinoembryonic antigen (CEA) markers using single-walled carbon nanotube field effect transistors (SWNT-FETs). These SWNT-FETs were fabricated using nanotubes produced by a patterned catalyst growth technique, where the top contact electrodes were generated using conventional photolithography. For biosensor applications, SU-8 negative photoresist patterns were used as an insulation layer. CEA antibodies were employed as recognition elements to specific tumor markers, and were successfully immobilized on the sides of a single-walled carbon nanotube using CDI-Tween 20 linking molecules. The binding of tumor markers to these antibody-functionalized SWNT-FETs was then monitored continuously during exposure to dilute CEA solutions. The observed sharp decrease in conductance demonstrates the possibility of realizing highly sensitive, label-free SWNT-FET-based tumor sensors.     

图案化In2O3:Sn薄膜制备及显影剂对图案制备的影响研究

功能薄膜的图案化是微电子加工中不可或缺的工序,目前已经成为制约我国微型化集成电路发展的关键因素。本研究以制备低成本且高质量的图案化In₂O₃:Sn薄膜为目的,摒弃常规且工艺复杂的干法刻蚀或湿法刻蚀的研究思路,转而向一种化学修饰的溶胶凝胶技术探索。利用化学修饰后的纳米级溶质颗粒的紫外感光特性,以及曝光前后溶质颗粒在有机溶剂中发生的溶解度变化,通过溶胶凝胶工艺成膜,后经曝光、显影、热处理等工序,形成图案化的In₂O₃:Sn薄膜。重点探索了显影剂配方对薄膜图案制备的影响规律。该方法去除了包含光刻胶制备、剥离以及刻蚀等一系列复杂工序,薄膜图案化制备简单且质量较高,是一种新的值得继续探究并广泛推广的薄膜图案化技术。     

Fabrication and photoelectrochemical characteristics of the patterned CdS microarrays on indium tin oxide substrates

In an effort to investigate the extraordinary photoelectrochemical characteristics of nanostructured CdS thin films in promising photovoltaic device applications, the patterned CdS microarrays with different feature sizes (50, 130, and 250 μm in diameter) were successfully fabricated on indium tin oxide (ITO) glass substrates using the chemical bath deposition method. The ultraviolet lithography process was employed for fabricating patterned octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) as the functional organic thin layer template. The results show that the regular and compact patterned CdS microarrays had been deposited onto ITO glass surfaces, with clear edges demarcating the boundaries between the patterned CdS region and substrate under an optimal depositing condition. The microarrays consisted of pure nanocrystalline CdS with average crystallite size of about 10.7 nm. The photocurrent response and the optical adsorption of the patterned CdS microarray thin films increased with the decrease of the feature size, which was due to the increased CdS surface area, as well as the increased optical path length within the patterned CdS thin films, resulting from multiple reflection of incident light. The resistivity values increase with the increase of feature size, due to the increase of the relative amount of gaps between CdS microarrays with increasing the feature size of patterned CdS microarrays.     

基于碳膜的柔性神经微电极阵列加工

为了实现长期安全有效的神经电刺激,避免电极腐蚀情况,提出了一种基于热解光刻胶形成碳膜作为导电材料的柔性视网膜神经微电极阵列．首先,通过高温热解图形化的光刻胶形成导电碳膜,然后利用光敏性聚酰亚胺（Durimide 7510）作为基底材料,通过光刻结合转膜、键合和牺牲层腐蚀技术,实现了具有柔性特征的碳膜神经微电极阵列．实验结果显示这种碳膜电极的电荷存储能力达到6．625mC／cm2．是金电极的12．4倍,显示了良好的电化学稳定性和电荷注入能力,有利于其长期植入和安全有效地工作,可应用于新一代人工视网膜系统的构建．     

Fabrication of mid-infrared frequency-selective surfaces by soft lithography

We describe the fabrication of large areas (4 cm(2)) of metallic structures or aperture elements that have ~100-350-nm linewidths and act as frequency-selective surfaces. These structures are fabricated with a type of soft lithography-near-field contact-mode photolithography-that uses a thin elastomeric mask having topography on its surface and is in conformal contact with a layer of photoresist. The mask acts as an optical element to create minima in the intensity of light delivered to the photoresist. Depending on the type of photoresist used, lines of, or trenches in, photoresist are formed on the substrate by exposure, development, and lift-off. These surfaces act as bandpass or bandgap filters in the infrared.     

Electroanalytical performance of carbon films with near-atomic flatness

Physicochemical and electrochemical characterization of carbon films obtained by pyrolyzing a commercially available photoresist has been performed. Photoresist spin-coated on to a silicon wafer was pyrolyzed at 1,000 degrees C in a reducing atmosphere (95% nitrogen and 5% hydrogen) to produce conducting carbon films. The pyrolyzed photoresist films (PPF) show unusual surface properties compared to other carbon electrodes. The surfaces are nearly atomically smooth with a root-mean-square roughness of <0.5 nm. PPF have a very low background current and oxygen/carbon atomic ratio compared to conventional glassy carbon and show relatively weak adsorption of methylene blue and anthraquinone-2,6-disulfonate. The low oxygen/carbon ratio and the relative stability of PPF indicate that surfaces may be partially hydrogen terminated. The pyrolyzed films were compared to glassy carbon (GC) heat treated under the same conditions as pyrolysis to evaluate the electroanalytical utility of PPF. Heterogeneous electron-transfer kinetics of various redox systems were evaluated. For Ru(NH3)6(3+/2+), Fe(CN)6(3-/4-), and chlorpromazine, fresh PPF surfaces show electron-transfer rates similar to those on GC, but for redox systems such as Fe3+/2+, ascorbic acid, dopamine, and oxygen, the kinetics on PPF are slower. Very weak interactions between the PPF surface and these redox systems lead to their slow electron-transfer kinetics. Electrochemical anodization results in a simultaneous increase in background current, adsorption, and electron-transfer kinetics. The PPF surfaces can be chemically modified via diazonium ion reduction to yield a covalently attached monolayer. Such a modification could help in the preparation of low-cost, high-volume analyte-specific electrodes for diverse electroanalytical applications. Overall, pyrolysis of the photoresist yields an electrode surface with properties similar to a very smooth version of glassy carbon, with some important differences in surface chemistry.     

Patterning of catalysts for the selective growth of carbon nanotubes using laser irradiation of nickel nitrate

We developed a simple method to produce patterned catalysts for the growth of carbon nanotubes (CNTs) on Si substrate using laser irradiation of Ni nitrate. We found that Ni nitrate can easily be decomposed into Ni oxide by KrF laser irradiation and that unexposed Ni nitrate can be removed using deionized (DI) water. Once we obtained patterned Ni oxide, we were able to synthesize multi-walled CNTs using a conventional thermal CVD. This new method does not require any photoresist or vacuum processes. Not only is the method compatible with low-temperature and large-area fabrication, it also significantly reduces the total processing steps required for conventional lithographic patterning technology. A detailed investigation of the decomposition process of this patterned catalyst and the microstructure of the patterned multi-walled CNTs was carried out using IR, SEM and TEM.     

Development of RF-MEMS switch on PCB substrates with polyimide planarization

This paper describes an improved manufacturing technology for the fabrication of radio frequency (RF) microelectromechanical systems switches on a laminated printed circuit board (PCB). The process simplifies the fabrication process without sacrificing the RF performance of switches on the PCB. The proposed process patterns a 17.5-/spl mu/m-thick copper layer on the PCB; as a result, the surface becomes highly nonplanarized. Polyimide is then used to planarize the PCB's patterned copper layer. The use of polyimide for planarization has not only made the fabrication process simpler, but it has also reduced the formation of voids in the photoresist sacrificial layer where metallic membrane is deposited and patterned. The switches fabricated with this technology demonstrate a low insertion loss (less than 0.06 dB at 10 GHz) and good isolation (less than 20 dB at 10 GHz).     

Nanostructured biointerfaces

Colloidal lithography is used to create nanostructured interfaces suitable for studying and interacting with cellular biosystems. Large areas of patterned surface can be produced. We investigate the use of plasma etching for transfer of the pattern of individual colloidal particles into the substrates to create short-range ordered arrays of topographic and/or chemical nanostructures. Colloidal masks perform differently to traditional photoresist masks and local redeposition of material around the particle has significant impact on the resultant structures. The colloidal particles can be reshaped to allow the fabrication of flat-topped structures. Topographic and chemical nanostructures can be used to template the self assembly of macromolecules. The phase separation of thin films of PS-PMMA symmetric block copolymers above nanostructure sites is aligned at the surface nanostructure by topographic features. PLL-PEG assembly at alkanethiol-modified nanoscale chemical patterns of gold/silicon allows the production of nanoscale protein patterns. Patterns of ferritin 100 nm in diameter are demonstrated.     

Patterning of various silicon structures via polymer lithography and catalytic chemical etching

We demonstrate a facile fabrication of a rich variety of silicon patterns with different length scales by combining polymer lithography and a metal-assisted chemical etching method. Several types of polymer patterns were fabricated on silicon substrates, and silver layers were deposited on the patterned silicon surfaces and used to etch the silicon beneath. Various silicon patterns including topographic lines, concentric rings, and square arrays were created at a micro-?and nanoscale after etching the silicon and subsequent removal of the patterned polymer masks. Alternatively, the arrays of sub-30?nm silicon nanowires were produced by a chemical etching of the silicon wafer which was covered with highly ordered polystyrene-block-polyvinylpyridine (PS-b-PVP) micellar films. In addition, silicon nanohole arrays were also generated by etching with hexagonally packed silver nanoparticles that were prepared using PS-b-PVP block copolymer templates.     

Photoconductive optically driven deformable membrane under high-frequency bias: fabrication, characterization, and modeling

The fabrication and characterization of an optically addressable deformable mirror for a spatial light modulator are described. Device operation utilizes an electrostatically driven pixelated aluminized polymeric membrane mirror supported above an optically controlled photoconductive GaAs substrate. A 5 mum thick grid of patterned photoresist supports the 2 mum thick aluminized Mylar membrane. A conductive ZnO layer is placed on the backside of the GaAs wafer. Similar devices were also fabricated with InP. A standard Michelson interferometer is used to measure mirror deformation data as a function of illumination, applied voltage, and frequency. The device operates as an impedance distribution between two cascaded impedances of deformable membrane substrate, substrate, and electrode. An analysis of device's operation under several bias conditions, which relates membrane deformation to operating parameters, is presented.