Laser-assisted transfer for rapid additive micro-fabrication of electronic devices

Laser-based micro-fabrication techniques can be divided into the two broad categories of subtractive and additive processing. Subtractive embraces the well-established areas of ablation, drilling, cutting and trimming, where the substrate material is post-processed into the desired final form or function. Additive describes a manufacturing process that most recently has captured the news in terms of 3-d printing, where materials and structures are assembled from scratch to form complex 3-d objects. While most additive 3-d printing methods are purely aimed at fabrication of structures, the ability to deposit material on the micron-scale enables the creation of functional, e.g. electronic or photonic, devices [1]. Laser-induced forward transfer (LIFT) is a method for the transfer of functional thin film materials with sub-micron to few millimetre feature sizes [2,3]. It has a unique advantage as the materials can be optimised beforehand in terms of their electrical, mechanical or optical properties. LIFT allows the intact transfer of solid, viscous or matrix-embedded films in an additive fashion. As a direct-write method, no lithography or post-processing is required and does not add complexity to existing laser machining systems, thus LIFT can be applied for the rapid and inexpensive fabrication or repair of electronic devices. While the technique is not limited to a specific range of materials, only a few examples show transfer of inorganic semiconductors. So far, LIFT demonstration of materials such as silicon [4,5] have undergone melting, and hence a phase transition process during the transfer which may not be desirable, compromising or reducing the efficiency of a resulting device. Here, we present our first results on the intact transfer of solid thermoelectric semiconductor materials on a millimetre scale via nanosecond excimer laser-based LIFT. We have studied the transfer and its effect on the phase and physical properties of the printed materials and present a working thermoelectric generator as an example of such a device. Furthermore, results from initial experiments to transfer silicon onto polymeric substrates in an intact state via a Ti:sapphire femtosecond laser are also shown, which illustrate the utility of LIFT for printing micron-scale semiconductor features in the context of flexible electronic applications

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

Very high gain single pass two-beam coupling in 'blue' Rh:BaTiO₃

Two-beam coupling has been studied at red and near-infrared wavelengths in "blue" Rh:BaTiO3. High amplification, of the order of 20,000 - 37,000, of a weak signal beam, has been measured. Rh:BaTiO3 exhibits strong intensity-dependent absorption and transmission behaviour and this effect is considered when fitting theoretical plots to the experimental data

Laser-induced forward transfer of thermoelectric materials on polymer and glass substrates

Laser-induced forward transfer (LIFT) is a laser-assisted direct write method that has been used to print a range of solids and rheological fluids. The donor that is to be printed is previously deposited onto a transparent support substrate that is usually referred to as a carrier. A highly energetic short-pulsed laser beam imaged through the transparent carrier onto the donor results in the forward transfer of a donor pixel onto a receiver substrate placed either in contact or a few microns apart. Solid films can be transferred with minimal change in their crystal and domain structure via LIFT

Molecular dynamics simulations of the shock response of the energetic materials pentaerythritol tetranitrate and hexahydro-1,3,5-trinitro-1,3,5-s-triazine

Dissertation supervisor: Prof. Thomas D. Sewell.Includes vita.Energetic materials are the key active ingredients in explosive formulations. Understanding the response of energetic materials is vital for the design of safe and reliable explosives. It is a challenge to experimentally study the initial events that lead to detonation in these materials. Classical mechanics based computer simulations are a useful method for the study of these initial chemical and physical events. This research focuses on the shock response of two energetic materials: pentaerythritol tetranitrate (PETN) and hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX). Computer simulations were used to study how the shock response of single crystals of PETN varies based on the orientation of the crystal relative to the shock wave. Thermo-mechanical properties were calculated for the shocks along two different orientations to quantify the difference in response. In RDX, the potential of voids to act as nucleation sites for detonation was studied. The magnitude of energy localization from void collapse as function of shock strength was studied for three different shock strengths.Includes bibliographical references

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

Characterisation of the porous structure of Gilsocarbon graphite using pycnometry, cyclic porosimetry and void-network modeling

file: :C$$:/pdf/1-s2.0-S000862231400164X-main.pdf:pdfThe cores of the fourteen Advanced Gas-cooled nuclear Reactors (AGRs) within the UK comprise Gilsocarbon graphite, a manufactured material surrounded predominantly by CO2 at high pressure and temperature to provide heat exchange. The intense ionising radiation within the reactors causes radiolytic oxidation, and the resulting mass loss is a primary factor in determining reactor lifetime. The void structure of the porous Gilsocarbon graphite affects the permeability and diffusion of the carbon dioxide, and the sites of oxidation. To model this void structure, the porosities and densities of ten virgin Gilsocarbon graphite samples have been measured by powder and helium pycnometry. For comparison, results are also presented for highly ordered pyrolytic graphite (HOPG), and a fine-grained Ringsdorff graphite. Samples have been examined at a range of magnifications by electron microscopy. Total porosities and percolation characteristics have been measured by standard and cyclic mercury porosimetry up to an applied mercury pressure of 400MPa. Inverse modelling of the cyclic intrusion curves produces simulated void structures with characteristics which closely match those of experiment. Void size distributions of the structures are presented, together with much Supplementary Information. The simulated void networks provide the bases for future simulations of the radiolytic oxidation process itself

The Athletic Identity of Collegiate Athletic Trainers: A Descriptive Study

Context: Empirical and anecdotal evidence suggest that many athletic trainers were former athletes and select the profession due to its affiliation with sport. Qualitative research has indicated that collegiate athletic trainers may have a strong athletic identity, but the concept of athletic identity has not been quantified in this population. Objective: To quantitatively asses the athletic identity of collegiate athletic trainers and determine if group differences exist. Design: Cross-sectional observational study. Setting: Collegiate clinical setting. Patients and other participants: A total of 257 (n = 93 (37%) males, n = 162 (63%) females) athletic trainers employed in the collegiate setting were included in data analysis. Main outcome measure(s): Data were collected via a web-based survey platform which was designed to measure athletic identity. Demographic information was analyzed for frequency and distribution. Mann-Whitney U tests and Kruskal-Wallis tests were calculated to determine if group differences existed. Results: The large majority of participants (90%) self-identified as having participated in organized sport yet scored moderately on the athletic identity measurement scale (22.9 ± 7.9). There were no sex differences in overall athletic identity (p = .446), but females did have higher levels of negative affectivity (p = .045) than males. Testing also revealed group differences based on current employment setting for social identity (p = .020), with NCAA Division I scores less than Division II, III, and NAIA. NCAA Division III exclusivity (p = .030) was lower than NCAA Division II and NAIA. Conclusions: It appears that components of athletic identity vary based on the employment setting of collegiate athletic trainers and may have a relationship to the number of hours worked in the summer. The moderate athletic identity scores of collegiate athletic trainers are comparable to former athletes who selected career paths outside of sport. This may indicate adaptive career decision processes