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Fabrication and Classification of Nanomaterials
Published in Vladimir I. Gavrilenko, Optics of Nanomaterials, 2019
The procedure for preparing ordered silica microspheres asymmetrically coated with Ag nanoparticles and Ag nanoparticle-doped polymer voids can be outlined in the following way (Sun and Yang, 2006). First, a single layer of close-packed silica microspheres is transferred onto the surface of a polydimethylsiloxane (PDMS) stamp by using the lift-up soft lithography technique. After depositing Ag nanoparticles on the microspheres by chemical reduction (Sun and Yang, 2006), the silica microspheres are asymmetrically coated with Ag nanoparticles, which can be transferred onto another substrate by a ICP technique. By etching away the silica microspheres with hydrofluoric acid, ordered Ag nanoparticle-doped polymer voids are finally obtained. Left panel in Fig. 1.12 is an SEM image of ordered silica microspheres asymmetrically coated with Ag nanoparticles on the PDMS stamp. The silica microspheres are uniformly coated with Ag nanoparticles and also adopt an ordered hexagonal array. Because of the uniformity of the Ag nanoparticles and the ordered arrays of the composite microspheres, these ordered microspheres can be used as substrates for surface-enhanced Raman scattering (SERS). Right panel in Fig. 1.12 is the SEM image of the ordered Ag-nanoparticle-doped polymer voids. The silica microspheres are etched away.
Synthesis of Nanomaterials
Published in Rajendra Kumar Goyal, Nanomaterials and Nanocomposites, 2017
Nanoimprint lithography: There are four different types of NIL, which includes thermal (or hot) NIL, UV NIL, soft lithography, and roll-to-roll nanoimprint. Soft stamp imprinting is more popular than the hard one because it has an intimate contact with the surface, which can fulfill large-area imprinting. The most recent roll-to-roll NIL has gained popularity for volume fabrication. Although NIL has wide applications in nanodevices, biomedicine, organic devices, etc., there are many issues to overcome, such as mold fabrication and inspection, defects controlling, alignment, and overlay. It can provide nanoscale resolution of patterning, because it is not limited by the diffraction limit, the scattering effects, and the secondary electrons. NIL is a promising technology for producing 2-D or 3-D structures with sub-50-nm half-pitch features. The direct NIL process with a polydimethylsiloxane (PDMS) stamp has successfully produced silver line patterns in the range of 200–300 nm, and the combined NIL and liftoff process successfully produced silver line patterns in the range of 15–60 nm. The process has advantages of low cost, high-replication reliability, and relatively high-throughput production. The NIL is suitable for the fabrication of electronic devices such as organic light emitting diodes (OLEDs), printed circuit boards, solar cells, active matrix OLEDs (AMOLEDs), printed capacitors, and chemical sensors [30,31].
Carbon Nanotube–Based Electrochemical Biosensors
Published in Li Jun, Wu Nianqiang, Biosensors Based on Nanomaterials and Nanodevices, 2017
Soft-lithographic techniques, including the micro-contact printing and micro-molding, have also been used to prepare micropatterns of VA-CNTs [5]. The micro-contact printing process involves transferring monolayers of alkylsiloxane onto a quartz substrate in a patterned region by using a PDMS (polydimethylsiloxane) elastomer stamp (Figure 11.3a) while the micro-molding method [26] allows the formation of polymer patterns in the non-PDMS stamp region (Figure 11.3b). Compared with photolithographic patterning, the softlithography could lead to micropatterns of a resolution down to submicron and provide possibility to produce micro-/nanopatterns on curved surfaces [27,28] and even flexible substrates [26,29–33].
MEMS enabled suspended silicon waveguide platform for long-wave infrared modulation applications
Published in International Journal of Optomechatronics, 2022
Xinmiao Liu, Qifeng Qiao, Bowei Dong, Weixin Liu, Cheng Xu, Siyu Xu, Guangya Zhou
The membrane transfer printing process is done using a manual micropositioner under an optical microscope with micro-meter level alignment accuracy as shown in Figure 3(b). Before the transfer printing process, the Polydimethylsiloxane (PDMS) stamp retriever with microstructure pyramids is made with a reusable mould. The PDMS is made by mixing elastomer and the curing agent at a ratio of 5:1 to allow sufficient hardness to withstand mechanical deformation and avoid stiction during the transfer process. Once mixing up the solution and pour onto the mould for full immersion, the petri dish is put into the vacuum chamber to extract all the air trapped inside the PDMS mixture. The mixture is then taken out and heated at 60 °C on a hot plate for 2 h, before natural aging in ambient air for at least 24 h on a flat surface. The reusable mould is made from SiO2 with pyramid shape etching holes (first dry etched on SiO2 layer then isotropically wet etched Si substrate) covered with SU-8 photoresist on top, and a large square shape pattern is exposed and developed that defines the PDMS mould base. The square pattern size is set to 2500*2500 µm, which is slightly larger than the Si device membrane size. It should be noted that the stamp size should be made in accordance with membrane size, and while theoretically Si membrane can be as large as the whole chip, due to transfer process variation on chip flatness and alignment accuracy, the unevenly distributed load between Si membrane and stamp could cause local stiction and tear of the membrane. For a larger-scale membrane transfer, the membrane thickness should be increased and an automatic pick-up process using a commercial wafer bonder could be adopted. In this way, the stress in the transfer thin film could be alleviated, and tearing failure could be avoided, thus enabling the large-scale manufacturing.