Traditional Lithography Methods Research Articles

Fabrication of hierarchical nanostructures using binary colloidal nanosphere assembly

In this paper, we investigate the self-assembly of hierarchical nanostructures using monodispersed nanospheres with two different diameters. Our approach is to use a two-step method where the assembly of larger 200 nm nanospheres is used to direct the assembly of smaller 50 nm particles. This self-assembly technique is based on Langmuir–Blodgett assembly and has low equipment cost when compared with traditional lithography methods. We examine the effects of substrate surface treatment, solution concentration ratio, and spin speeds on the quality of the hierarchical assembly. The fabricated samples are examined using optical and scanning electron microscopy to investigate assembly yield. Various defect types are identified and mitigated by process control. The ability to create more complex assembly can result in smaller features and can enhance the performance of photonics and nanostructured surfaces.

Flexible Tactile Sensor Based on Patterned Ag-Nanofiber Electrodes through Electrospinning.

The growing demand for intelligent equipment has greatly inspired the development of flexible devices. Thus, disparate flexible multifunctional devices, including pressure sensitive flexible/stretchable displays, have drawn worldwide research attention. Electrodes maintaining conductivity and mechanical strength against deformations are indispensable components in all prospective applications. In this work, a flexible pressure mapping sensor array is developed based on patterned Ag-nanofibers (Ag-NFs) electrode through electrospinning and lithography. The metallic Ag layer is sputtered onto the electrospinning polyvinyl alcohol (PVA) NFs. A uniform and super conductive electrode layer with outstanding mechanical performance is thus formed after dissolving PVA. Followed by the traditional lithography method, a patterned electrode array (4 × 4 sensors) is obtained. Based on the newly developed triboelectric nanogenerator (TENG) technology, a flexible pressure-mapping sensor with excellent stability towards bending deformations is further demonstrated. Moreover, a letter “Z” is successfully visualized by this pressure sensor array, encouraging more human–machine interactive implementations, such as multi-functional tactile screens.

Lithography via electrospun fibers with quantitative morphology analysis

Electrospun fibers have been used to enhance material properties, as drug delivery devices, and for physical filtration systems. However, the use of electrospinning as a viable method for lithographic patterning and subsequent pattern transfer has not been demonstrated. As with traditional lithography methods, feature position and size are critical to the performance and repeatability of resultant structures. The placement of electrospun fibers is driven by the electrostatic field strength. In the present research, the electrostatic field strength between the spinneret (capillary) and the substrate (collection electrode) is controlled by modifying the voltage applied to two electrodes on or adjacent to the substrate. Such manipulation modifies the applied electrostatic field, creating a stronger field strength directed at one electrode as compared to the other. The fiber will preferentially be directed to the electrode along the path of highest field strength, resulting in deposition to the desired electrode. Two methods to control the voltage applied to the two electrodes during electrospinning are presented: (1) electronic control of the applied electrode voltage and (2) electromechanical control of the applied electrode voltage. The use of an electromechanical commutator resulted in an increase in deposition (and associated lithographic write) speed. Both methods of voltage control result in the deposition of aligned fibers onto the substrate. Additional studies examine the relationship between shape of the electrodes and subsequent alignment achieved. Image analysis quantifying image analysis via fast Fourier transform is used to quantify fiber alignment. Resultant fibers are used to transfer the fiber pattern into an underlying silicon substrate via lift-off and subsequent plasma etching. Results demonstrate the potential of electrospun fiber masks for future use in the economical fabrication of electronic and optical devices where nanoscale features over large areas are suitable.

Graphene processing using electron beam assisted metal deposition and masked chemical vapor deposition growth

The fabrication of graphene devices can be challenging due to exposure to harsh chemicals and mechanical wear such as ultrasonication used for cleaning in photolithography and metal deposition. Common graphene processing methods often damage fragile graphene sheets and can ruin the device during fabrication. The authors report a facile method to overcome many of these challenges, which is specifically compatible with graphene grown by chemical vapor deposition (CVD). Using e-beam assisted metal deposition to deposit fine platinum features, electrodes can be deposited directly on graphene while still on the copper foil used as the catalyst during the CVD growth. The graphene and electrodes are then transferred to an insulating substrate, without further processing. This method preserves the graphene/metal interface from exposure to harsh chemicals used in traditional lithography methods, and avoids many of the conventional processing steps, which can cause unwanted doping, and damage or destroy the graphene. The authors observe an increase in Raman D-mode in the graphene under the Pt deposit, which suggests that the deposition method facilitates chemisorption by slightly abrading the surface of graphene surface during deposition. Using e-beam assisted electrode deposition in conjunction with masked CVD graphene growth on copper, the authors show the feasibility of fabricating complete graphene devices without subjecting the graphene to lithography, plasma etching, metal lift-off steps, or even shadow mask processing.

Preparation of a Superhydrophobic and Peroxidase-like Activity Array Chip for H2O2 Sensing by Surface-Enhanced Raman Scattering.

In this paper, we propose a novel and simple method for preparing a dual-biomimetic functional array possessing both superhydrophobic and peroxidase-like activity that can be used for hydrogen peroxide (H2O2) sensing. The proposed method is an integration innovation that combines the above two properties and surface-enhanced Raman scattering (SERS). We integrated a series of well-ordered arrays of Au points (d = 1 mm) onto a superhydrophobic copper (Cu)/silver (Ag) surface by replicating an arrayed molybdenum template. Instead of using photoresists and the traditional lithography method, we utilized a chemical etching method (a substitution reaction between Cu and HAuCl4) with a Cu/Ag superhydrophobic surface as the barrier layer, which has the benefit of water repellency. The as-prepared Au points were observed to possess peroxidase-like activity, allowing for catalytic oxidation of the chromogenic molecule o-phenylenediamine dihydrochloride (OPD). Oxidation was evidenced by a color change in the presence of H2O2, which allows the array chip to act as an H2O2 sensor. In this study, the water repellency of the superhydrophobic surface was used to fabricate the array chip and increase the local reactant concentration during the catalytic reaction. As a result, the catalytic reaction occurred when only 2 μL of an aqueous sample (OPD/H2O2) was placed onto the Au point, and the enzymatic product, 2,3-diaminophenazine, showed a SERS signal distinguishable from that of OPD after mixing with 2 μL of colloidal Au. Using the dual-biomimetic functional array chip, quantitative analysis of H2O2 was performed by observing the change in the SERS spectra, which showed a concentration-dependent behavior for H2O2. This method allows for the detection of H2O2 at concentrations as low as 3 pmol per 2 μL of sample, which is a considerable advantage in H2O2 analysis. The as-prepared substrate was convenient for H2O2 detection because only a small amount of sample was required in each analysis. Highly sensitive detection was realized using SERS. Therefore, this chip was shown to exhibit significant potential for applications in bioanalysis.