Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting....

Polymers for 3D Printing and Customized Additive Manufacturing

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

3D printing technology has attracted much attention due to its high potential in scientific and industrial applications. As an outstanding 3D printing technology, two-photon polymerization (TPP) microfabrication has been applied in the fields of micro/nanophotonics, micro-electromechanical systems, microfluidics, biomedical implants and microdevices. In particular, TPP microfabrication is very useful in tissue engineering and drug delivery due to its powerful fabrication capability for precise microstructures with high spatial resolution on both the microscopic and the nanometric scale. The design and fabrication of 3D hydrogels widely used in tissue engineering and drug delivery has been an important research area of TPP microfabrication. The resolution is a key parameter for 3D hydrogels to simulate the native 3D environment in which the cells reside and the drug is controlled to release with optimal temporal and spatial distribution in vitro and in vivo. The resolution of 3D hydrogels largely depends on the efficiency of TPP initiators. In this paper, we will review the widely used photoresists, the development of TPP photoinitiators, the strategies for improving the resolution and the microfabrication of 3D hydrogels.

Two-photon polymerization microfabrication of hydrogels: an advanced 3D printing technology for tissue engineering and drug delivery

Ultrafast laser nanostructuring of photopolymers: a decade of advances

High-throughput fabrication techniques for generating arbitrarily complex three-dimensional structures with nanoscale features are desirable across a broad range of applications. Two-photon lithography (TPL)–based submicrometer additive manufacturing is a promising candidate to fill this gap. However, the serial point-by-point writing scheme of TPL is too slow for many applications. Attempts at parallelization either do not have submicrometer resolution or cannot pattern complex structures. We overcome these difficulties by spatially and temporally focusing an ultrafast laser to implement a projection-based layer-by-layer parallelization. This increases the throughput up to three orders of magnitude and expands the geometric design space. We demonstrate this by printing, within single-digit millisecond time scales, nanowires with widths smaller than 175 nanometers over an area one million times larger than the cross-sectional area.

Scalable Submicrometer Additive Manufacturing

Amino-terminated ionic liquid assisted multiphoton photoreduction (IL-MPR) was developed for the direct writing of subwavelength gold nanostructures in AuCl4- ions aqueous solution by femtosecond laser It was revealed that the carbon chain length was crucial for morphology and size control of gold nanostructures A 228 nm width of gold nanostructure, which was beyond the optical diffraction limit, was fabricated by the matching between IL and the power and scanning speed of the laser beam The measured conductivity is of the same order as that of bulk gold Furthermore, we successfully fabricated a U-shaped terahertz planar metamaterial whose spectral response is consistent with the theoretical expectation The IL-MPR nanofabrication protocol is expected to play an important role in the fabrication of fine metallic micro/nanostructures for applications in microelectromechanical systems, nanoelectronics and nanophotonics

Femtosecond direct laser writing of gold nanostructures by ionic liquid assisted multiphoton photoreduction

The present invention discloses a phosphorus-doped zinc oxide film preparation method, and belongs to the technical field of zinc oxide film preparation The method comprises that: zinc source-containing gas and oxygen source-containing gas are introduced into an atomic layer deposition device, a zinc oxide film grows on the surface of a silicon substrate in the reaction chamber of the atomic layer deposition device, phosphorus source-containing gas and oxygen source-containing gas are introduced into the atomic layer deposition device, and phosphorus-oxygen bond grow on the zinc oxide film surface According to the present invention, doping of phosphorus atoms in the zinc oxide film can be easily achieved, and the prepared film has characteristics of controllable doping layer, high uniformity and complete performance

Phosphorus-doped zinc oxide film preparation method

We have investigated the photoinitiating properties of the photoinitiator 3,6-bis[2-(4-nitrophenyl)-ethynyl]-9-(4-methoxy-benzyl)-carbazole (BNMBC), which has an intramolecular radical quenching group "p-methoxybenzyl," in the substrate lines fabrication of two-photon induced photopolymerization (TPIP). Another photoinitiator 3,6-bis[2-(4-nitrophenyl)-ethynyl]-9-benzyl-carbazole (BNBC) with similar chemical structure but not radical quenching group was studied for comparison. Their photopolymerization properties were studied with resins in which BNBC and BNMBC were used as photoinitiators with a molar ratio of 0.02%, respectively. The linewidth of polymer lines fabricated by TPIP of the photoresist that contained BNMBC could be decreased to 65% of those using BNBC. Besides, we introduced a radical quencher, phenyl methyl ether (PhOCH3), to BNBC and further studied the photopolymerization properties by using BNBC, BNBC/PhOCH3 and BNMBC as photoinitiators with a molar ratio of 0.1%. The results further indicated that BNMBC was effective to confine the radical diffusion in polymerization due to the radical quenching effect of moiety. This intramolecular radical quenching moiety exhibited more effective confining effect of radical diffusion compared to the intermolecular radical quencher PhOCH3. Furthermore, arbitrary complex three-dimensional (3D) microstructure was achieved using the photoresist with photoinitiator BNMBC. The approach could open up broad prospect for improving the resolution in TPIP.

Two-photon induced photopolymerization using photoinitiator with an intramolecular radical quenching moiety for nanolithography.

The invention discloses a method for preparing a double-acceptor co-doped zinc oxide thin film through atomic layer deposition. The method includes the steps: placing a substrate in a reaction chamber of an atomic layer deposition device; carrying out multi-component composite deposition, wherein the composite deposition includes before zinc source deposition, introducing P doping source deposition for one time and oxygen source deposition for one time, and then introducing nitrogen doping source deposition for one time; and carrying out cyclic deposition of the multi-component complex, and thus obtaining the N-P double-acceptor co-doped zinc oxide thin film prepared through the atomic layer deposition. According to the method for preparing the double-acceptor co-doped zinc oxide thin film through the atomic layer deposition, the ALD technology is utilized, during the zinc oxide thin film growth process, co-doping of a whole thin film structure is completed, and the N-P double-acceptor co-doping is achieved. The preparation process is simple, the deposition and doping processes are easy to control, and the prepared co-doped zinc oxide thin film is beneficial for p-type doping of the zinc oxide thin film and improvement of the stability of p-type electrical properties.

Method for preparing double-acceptor co-doped zinc oxide thin film through atomic layer deposition

The present invention discloses a preparation method for a co-doped zinc oxide film through atomic layer deposition. The preparation method comprises: placing a substrate in an ALD reaction chamber, heating the substrate and the chamber pipeline, and sequentially carrying out multi-component composite deposition, wherein the composite deposition comprises respectively introducing one doped deposition of a doped element Zr-containing doped source, second zinc source deposition, two nitrogen doped source depositions and two oxygen source depositions after first zinc source deposition to form N-Zr-N co-doping, wherein the deposition sequence of the nitrogen doped source deposition and the oxygen source deposition is that the oxygen source deposition and the nitrogen doped source deposition are sequentially performed, and the deposition sequence of the doped element Zr-containing doped source deposition and the second zinc source deposition is that the second zinc source deposition and the doped element Zr-containing doped source deposition are sequentially performed. With the method, the in situ donor-acceptor co-doping can be performed on the zinc oxide film so as to increase the doping amount of the acceptor element and promote the p type conversion of the zinc oxide film.

Preparation method for co-doped zinc oxide film through atomic layer deposition

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