Digital micromirror devices for laser-based manufacturing

Digital Micromirror Devices (DMDs), containing arrays of around one million individually-controllable ~10µm square mirrors, provide an extremely cost-effective and practical method to modulate the spatial beam profile of a pulsed laser source for both additive and subtractive laser processing and printing. When demagnified by a factor of ~100 in one dimension (hence ~10,000 in area) a ~1mJ/cm2 laser pulse reflected from the mirrors on the DMD surface that are switched to the 'on' position, attains a fluence of ~10J/cm2 at the workpiece, which is more than sufficient to ablate most materials of interest to the laser-manufacturing community. More familiar in the context of high values of magnification by the laser projection industry, reversing the role to use them for equally high values of demagnification opens up a wealth of possibilities for ablation, multiphoton polymerization, security marking and fabrication of features that perhaps surprisingly can be well below the wavelength of the laser used. Of key relevance is that very high-resolution patterning can be achieved by a single laser pulse, and step-and-repeat processes, when combined with the refresh rates of the DMD pattern that are currently at the 30kHz level, open up the possibility of processing areas of up to 1cm2 per second with micron-scale resolution where each ~100µm x 100µm area patterned per pulse can display arbitrary pixelated content. We will discuss the application of DMD-baser laser processing to the following areas of interest to the laser-manufacturing community

Nanomaterial structure determination using XUV diffraction

Diffraction using coherent XUV radiation is used to study the structure of nanophotonic materials, in this case an ordered array of 196nm spheres. Crystal structure and defects are visible, and the nanomaterial dielectric constant determined

Restoring Urban and Human Microbiotas

Humans harbour communities of coevolved microbiota known as ‘old friends’ and together we form ‘holobionts’ – multi-cellular organisms teeming with microbes that perform many critical functions for their host. These microbiota are important for our healthy physiological and immunological development, and disturbances to them can result in disease states such as chronic inflammatory conditions. The absence of certain microbes from the human body has been linked to chronic conditions, such as asthma or anxiety, and more broadly to the state of inflammation in our brain, lungs, gut, and skin. Modern processes, such as the state of our industrial food system, loss of biodiversity, and increasing urbanisation, are causing a loss of exposure to these coevolved microbiota that have been linked to the proliferation of many diseases worldwide. Urbanisation is one of the most widespread impacts, due to human demographic changes and limited exposure to biodiversity, but urban ecological restoration is a way to provide exposure to these ‘old friends’ in urban settings. A key focus of this thesis is to explore the potential of ecological restoration in urban green spaces to restore beneficial microbial diversity. The proceeding chapters empirically explore the interplay between environmental microbial diversity, the diversity of vegetation communities used in urban ecological restoration, and microbial interactions with humans in green spaces. In Chapter 1, we reviewed the literature relating to the nexus of microbially-mediated health (in humans, other animals, and plants), urbanisation, and restoration ecology. In Chapter 2, we investigated the effect of native revegetation on restoring urban soil microbiota to a remnant state in an Australian city. We found that revegetation of complex biodiverse vegetation states supported soil microbial communities that were more similar to remnant vegetation blocks, compared to those of low biodiversity urban spaces such as lawns, vacant lots, and parklands. However, urban vegetation communities can vary widely across the Earth. Therefore, in Chapter 3, we investigated the broader relationship between urban vegetation complexity and soil microbiota in multiple cities. Here, we found that high vegetation complexity (typically defined by higher structural, functional, and species diversity) was generally associated with unique microbial communities when compared to low vegetation complexity. Lastly, in Chapter 4, we investigated the effect of native revegetation on restoring disturbed microbial communities of human skin. We found that natively revegetated green space had a stronger effect on restoring human skin microbial communities than sports field (turf) green space and that staying indoors had no effect on restoring skin microbiota. These findings have implications for the application of biodiversity management in public, private, and educational spaces. However, future work needs to focus beyond the microbial ecology and cover the physiological and immunological responses of children using ecologically restored green space and on the potential risks (e.g., zoonotic spill-over) of increasing urban biodiversity interaction with high population densities.Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 202

Multi-shot laser ablation and digital micromirror device mask translation for sub-diffraction-limit machining resolution

Digital Micromirror Devices (DMDs) can offer rapidly generated, bespoke intensity modulation masks for image-projection-based laser-machining. Recent work has shown repeatable sub-micron feature patterning [1], with proposed applications in the medical sciences and photonics. While DMDs can offer rapid patterning, with ~32kHz switching speeds available [2], they are not yet efficient reflectors at <300nm, thus limiting machining resolution to the diffraction limit at the near-visible wavelengths and above

Transfer pricing: strategies, practices, and tax minimization

Using a survey of tax executives from multinational corporations, we document that some firms set their transfer pricing strategy to minimize tax payments, but more firms focus on tax compliance. We estimate that a firm focusing on minimizing taxes has a GAAP effective tax rate that is 6.6 percentage points lower and generates about $43 million more in tax savings, on average, than a firm focusing on tax compliance. Available COMPUSTAT data on sample firms confirm our survey‐based inferences. We also find that transfer pricing‐related tax savings are greater when higher foreign income, tax haven use, and R&D activities are combined with a tax minimization strategy. Finally, compliance‐focused firms report lower FIN 48 tax reserves than tax‐minimizing firms, consistent with the former group using less uncertain transfer pricing arrangements. Collectively, our study provides direct evidence that multinational firms have differing internal priorities for transfer pricing, and that these differences are strongly related to the taxes reported by these firms.First author draf

Femtosecond laser-induced patterned transfer of intact semiconductor and polymer thin films via a digital micromirror device

The laser-induced forward transfer (LIFT) of thin films is an attractive technique to deposit materials on a size scale that can span nanometres to millimeters. During LIFT, the energy of a laser pulse is absorbed in a small volume of a thin film (donor) causing an explosive expansion which is used to propel a portion of the donor away from the carrier substrate and transfer it onto a receiver substrate as shown in Fig.1(a). Ultrashort laser systems can limit laser damage to remaining areas of the donor usually present using laser systems with longer (nanosecond) pulse widths

Simultaneous patterning and deposition of thin films via femtosecond laser-induced transfer using a digital micromirror device for spatial pulse shaping

The forward and backward femtosecond laser-induced transfer of thin films in an intact state with good adhesion, via a digital micromirror array acting as a dynamic object mask for spatial beam shaping is presented

Nanohybrid Membrane Synthesis with Phosphorene Nanoparticles: A Study of the Addition, Stability and Toxicity

Phosphorene is a promising candidate as a membrane material additive because of its inherent photocatalytic properties and electrical conductance which can help reduce fouling and improve membrane properties. The main objective of this study was to characterize structural and morphologic changes arising from the addition of phosphorene to polymeric membranes. Here, phosphorene was physically incorporated into a blend of polysulfone (PSf) and sulfonated poly ether ether ketone (SPEEK) doping solution. Protein and dye rejection studies were carried out to determine the permeability and selectivity of the membranes. Since loss of material additives during filtration processes is a challenge, the stability of phosphorene nanoparticles in different environments was also examined. Furthermore, given that phosphorene is a new material, toxicity studies with a model nematode, Caenorhabditis elegans, were carried out to provide insight into the biocompatibility and safety of phosphorene. Results showed that membranes modified with phosphorene displayed a higher protein rejection, but lower flux values. Phosphorene also led to a 70% reduction in dye fouling after filtration. Additionally, data showed that phosphorene loss was negligible within the membrane matrix irrespective of the pH environment. Phosphorene caused toxicity to nematodes in a free form, while no toxicity was observed for membrane permeates