For functional nanowire based electronics fabrication, conventionally, combination of complex multiple steps, such as (1) chemical vapor deposition (CVD) growth of nanowire, (2) harvesting of nanowire, (3) manipulation and placement of individual nanowires, and (4) integration of nanowire to circuit are necessary. Each step is very time consuming, expensive, and environmentally unfriendly, and only a very low yield is achieved through the multiple steps. As an alternative to conventional complex multistep approach, original findings are presented on the first demonstration of rapid, one step, digital selective growth of nanowires directly on 3D micro/nanostructures by developing a novel approach; laser induced hydrothermal growth (LIHG) without any complex integration of series of multiple process steps such as using any conventional photolithography process or CVD. The LIHG process can grow nanowires by scanning a focused laser beam as a local heat source in a fully digital manner to grow nanowires on arbitrary patterns and even on the non‐flat, 3D micro/nano structures in a safer liquid environment, as opposed to a gas environment. The LIHG process can greatly reduce the processing lead time and simplify the nanowire‐based nanofabrication process by removing multiple steps for growth, harvest, manipulation/placement, and integration of the nanowires. LIHG process can grow nanowire directly on 3D micro/nano structures, which will be extremely challenging even for the conventional nanowire integration processes. LIHG does not need a vacuum environment to grow nanowires but can be performed in a solution environment which is safer and cheaper. LIHG can also be used for flexible substrates such as temperature‐sensitive polymers due to the low processing temperature. Most of all, the LIHG process is a digital process that does not require conventional vacuum deposition or a photolithography mask.
We develop a digital direct writing method for ZnO NW micro-patterned growth on a large scale by selective laser decomposition of zinc acetate. For ZnO NW growth, by replacing the bulk heating with the scanning focused laser as a fully digital local heat source, zinc acetate crystallites can be selectively activated as a ZnO seed pattern to grow ZnO nanowires locally on a larger area. Together with the selective laser sintering process of metal nanoparticles, more than 10,000 UV sensors have been demonstrated on a 4 cm × 4 cm glass substrate to develop all-solution processible, all-laser mask-less digital fabrication of electronic devices including active layer and metal electrodes without any conventional vacuum deposition, photolithographic process, premade mask, high temperature and vacuum environment.
We introduce laser growth of iron oxide micro and nanorods by the photothermal chemical liquid growth method at low temperature, ambient pressure, and solution environment. By focusing a 532 nm continuous-wave laser on a Pt substrate immersed in iron oxide precursor solution, vertically aligned iron oxide micro- and nanorods are successfully fabricated with the length up to >100 μm, whereas the length can be easily controlled by changing the laser power or the illumination time. It is also found that the direction of the laser ray determines the growth direction of the iron oxide micro- and nanorods, which is the property that makes this process suitable for the fabrication of complex 3D structures as confirmed by making an iron oxide junction and kinked iron oxide microrod structure. Moreover, the resultant iron oxide microrod is applied as a microtemplate for the growth of nanostructure to show that this process can be further integrated to other 3D structures to achieve trans-scale hierarchical structures.
Exploration of the electronics solely composed of bottom-up synthesized nanowires has been largely limited due to the complex multistep integration of diverse nanowires. We report a single-step, selective, direct, and on-demand laser synthesis of a hierarchical heterogeneous nanowire-on-nanowire structure (secondary nanowire on the primary backbone nanowire) without using any conventional photolithography or vacuum deposition. The highly confined temperature rise by laser irradiation on the primary backbone metallic nanowire generates a highly localized nanoscale temperature field and photothermal reaction to selectively grow secondary branch nanowires along the backbone nanowire. As a proof-of-concept for an all-nanowire electronics demonstration, an all-nanowire UV sensor was successfully fabricated without using conventional fabrication processes.
We demonstrate ZnO nanowire based UV sensor by laser-induced hydrothermal growth of ZnO nanowire. By inducing a localized temperature rise using focused laser, ZnO nanowire array at~15 μm size consists of individual nanowires with~8 μm length and 200~400 nm diameter is readily synthesized on gold electrode within 30 min at the desired position. The laser-induced growth process is consecutively applied on two different points to bridge the micron gap between the electrodes. The resultant photoconductive ZnO NW interconnections display 2~3 orders increase in the current upon the UV exposure at a fixed voltage bias. It is also confirmed that the amount of photocurrent can be easily adjusted by changing the number of ZnO NW array junctions. The device exhibits clear response to the repeated UV illumination, suggesting that this process can be usefully applied for the facile fabrication of low-cost UV sensor array.
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