2,792 research outputs found
Nanoscale precision of 3D polymerisation via polarisation control
A systematic analysis of polarization effects in a direct write femtosecond
laser 3D lithography is presented. It is newly shown that coupling between
linear polarization of the writing light electric field and temperature
gradient can be used to fine-tune feature sizes in structuring of photoresists
at a nanoscale. The vectorial Debye focusing is used to simulate polarization
effects and a controlled variation up to 20% in the linewidth is shown
experimentally for the identical axial extent of the polymerised features. The
revealed mechanisms are relevant for a wide range of phenomena of light-matter
interaction at tight focusing in laser-tweezers and in plasmonic or dielectric
sub-wavelength focusing where strong light intensity and thermal gradients
coexist.Comment: 15 pages, 3 figure
A fully integrated high-Q Whispering-Gallery Wedge Resonator
Microresonator devices which posses ultra-high quality factors are essential
for fundamental investigations and applications. Microsphere and microtoroid
resonators support remarkably high Q's at optical frequencies, while planarity
constrains preclude their integration into functional lightwave circuits.
Conventional semiconductor processing can also be used to realize
ultra-high-Q's with planar wedge-resonators. Still, their full integration with
side-coupled dielectric waveguides remains an issue. Here we show the full
monolithic integration of a wedge-resonator/waveguide vertically-coupled system
on a silicon chip. In this approach the cavity and the waveguide lay in
different planes. This permits to realize the shallow-angle wedge while the
waveguide remains intact, allowing therefore to engineer a coupling of
arbitrary strength between these two. The precise size-control and the
robustness against post-processing operation due to its monolithic integration
makes this system a prominent platform for industrial-scale integration of
ultra-high-Q devices into planar lightwave chips.Comment: 6 pages, 4 figure
Rapid and mask-less laser-processing technique for the fabrication of microstructures in polydimethylsiloxane
We report a rapid laser-based method for structuring polydimethylsiloxane (PDMS) on the micron-scale. This mask-less method uses a digital multi-mirror device as a spatial light modulator to produce a given spatial intensity pattern to create arbitrarily shaped structures via either ablation or multi-photon photo-polymerisation in a master substrate, which is subsequently used to cast the complementary patterns in PDMS. This patterned PDMS mould was then used for micro-contact printing of ink and biological molecules
Chiral microstructures (spirals) fabrication by holographic lithography
We present an optical interference model to create chiral microstructures
(spirals) and its realization in photoresist using holographic lithography. The
model is based on the interference of six equally-spaced circumpolar linear
polarized side beams and a circular polarized central beam. The pitch and
separation of the spirals can be varied by changing the angle between the side
beams and the central beam. The realization of the model is carried out using
the 325 nm line of a He-Cd laser and spirals of sub-micron size are fabricated
in photoresist.Comment: 6 page
Efficient synthesis of Vitamin D3 in a 3D ultraviolet photochemical microreactor fabricated using an ultrafast laser
Large-scale, high-precision, and high-transparency microchannels hold great
potential for developing high-performance continuous-flow photochemical
reactions. We demonstrate ultrafast laser-enabled fabrication of 3D
microchannel reactors in ultraviolet (UV) grade fused silica which exhibit high
transparency under the illumination of UV light sources of wavelengths well
below 300 nm with excellent mixing efficiency. With the fabricated glass
microchannel reactors, we demonstrate continuous-flow UV photochemical
synthesis of vitamin D3 with low power consumption of the UV light sources
Three-dimensional femtosecond laser nanolithography of crystals
Nanostructuring hard optical crystals has so far been exclusively feasible at
their surface, as stress induced crack formation and propagation has rendered
high precision volume processes ineffective. We show that the inner chemical
etching reactivity of a crystal can be enhanced at the nanoscale by more than
five orders of magnitude by means of direct laser writing. The process allows
to produce cm-scale arbitrary three-dimensional nanostructures with 100 nm
feature sizes inside large crystals in absence of brittle fracture. To showcase
the unique potential of the technique, we fabricate photonic structures such as
sub-wavelength diffraction gratings and nanostructured optical waveguides
capable of sustaining sub-wavelength propagating modes inside yttrium aluminum
garnet crystals. This technique could enable the transfer of concepts from
nanophotonics to the fields of solid state lasers and crystal optics.Comment: Submitted Manuscript and Supplementary Informatio
FABRICATION OF MAGNETIC TWO-DIMENSIONAL AND THREE-DIMENSIONAL MICROSTRUCTURES FOR MICROFLUIDICS AND MICROROBOTICS APPLICATIONS
Micro-electro-mechanical systems (MEMS) technology has had an increasing impact on industry and our society. A wide range of MEMS devices are used in every aspects of our life, from microaccelerators and microgyroscopes to microscale drug-delivery systems. The increasing complexity of microsystems demands diverse microfabrication methods and actuation strategies to realize. Currently, it is challenging for existing microfabrication methods—particularly 3D microfabrication methods—to integrate multiple materials into the same component. This is a particular challenge for some applications, such as microrobotics and microfluidics, where integration of magnetically-responsive materials would be beneficial, because it enables contact-free actuation. In addition, most existing microfabrication methods can only fabricate flat, layered geometries; the few that can fabricate real 3D microstructures are not cost efficient and cannot realize mass production.
This dissertation explores two solutions to these microfabrication problems: first, a method for integrating magnetically responsive regions into microstructures using photolithography, and second, a method for creating three-dimensional freestanding microstructures using a modified micromolding technique. The first method is a facile method of producing inexpensive freestanding photopatternable polymer micromagnets composed NdFeB microparticles dispersed in SU-8 photoresist. The microfabrication process is capable of fabricating polymer micromagnets with 3 µm feature resolution and greater than 10:1 aspect ratio. This method was used to demonstrate the creation of freestanding microrobots with an encapsulated magnetic core. A magnetic control system was developed and the magnetic microrobots were moved along a desired path at an average speed of 1.7 mm/s in a fluid environment under the presence of external magnetic field. A microfabrication process using aligned mask micromolding and soft lithography was also developed for creating freestanding microstructures with true 3D geometry. Characterization of this method and resolution limits were demonstrated. The combination of these two microfabrication methods has great potential for integrating several material types into one microstructure for a variety of applications
Optically Micro-fabricated Linear and Freeform 3-D Extracellular Matrix Scaffolds for Tissue Engineering
This work was aimed at advancing multi-photon excited, freeform fabrication technology with nano-scale and sub-micron precision as an enabler for tissue engineers to investigate cellular response to a biomimetic, bio-active extracellular matrix. We demonstrated that sub-micron and micron scale Collagen and Fibronectin structures can be fabricated via multi-photon excited photochemistry using a modified Benzophenone dimer and Rose Bengal while maintaining the biomimetic ECM structures’ bioactivity.
We confirmed that three-photon excitation produces significantly smaller features at comparable excitation wavelengths as a consideration to better approach focal adhesion size.
Bioactivity of MPE cross-linked FN and Collagens I and II was established via immunofluorescence and fibroblast adhesion. Additionally, the relative rates of degradation in these cross-linked matrices are consistent with the known activities of these enzymes.
Morphology measurements of fibroblasts grown on these proteins include log(Area), Perimeter, Area/Perimeter2 were considered as proxies for cell response. Fibroblast perimeters are statistically different when associated with the Collagen I microenvironment. Among fibroblasts grown on MPE structures of Collagen I, Fibronectin, BSA and the BSA Monolayer, the stress fiber distributions on Collagen I (all fiber lengths) are highly significantly different (p \u3c 1x10-4) than the distribution of stress fibers of cells on BSA Lines. This suggests contact guidance only for cells on BSA Lines but yet a combination of contact guidance and chemical signaling (RGD) with cells on Collagen I Lines. This supports additional overall orientation findings based on fibroblasts’ fitted ellipse major axis direction for Collagens I, II and Fibronectin.
Stress fiber distribution on BSA Monolayer differed significantly from those on BSA structures (p = 0.01). This underscores the effects of pure contact guidance alone provided by the BSA fibers compared to the combined contact guidance and ECM cues provided by the FN, and collagen structures.
A method similar to rapid prototyping or three-dimensional printing was accomplished to resolve cellular response at the submicron level by fabricating biomimetic, bioactive extracellular matrices in a freeform three-dimensional (3D) manner. To the best of our knowledge, simultaneous 3D spatial and chemical control of collagen scaffold synthesis at the micrometer and sub-micrometer size scales has not been fully demonstrated
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