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

Proceedings of the first International Conference on Veterinary Behavioural Medicine

Abstrac

Microbial diversity in sediments and gas hydrates associated with cold seeps in the Gulf of Mexico

A molecular phylogenetic approach was used to characterize the composition of microbial communities from two gas hydrate sedimentary systems in the Gulf of Mexico. Nucleic acids were extracted from three distinct locales on surface breaching gas hydrate mounds, i.e., sediment overlaying gas hydrate, sediment/hydrate interface and sediment-free hydrate, and from three sediment depths, i.e., 0-2, 6-8 and 10-12 cm, in Beggiatoa sp. mat-associated sediments located several meters from exposed gas hydrate. Samples were collected from a research submersible (water depth 550-575 m) during two research cruises aboard the R/V Seward Johnson I and II funded by the NSF Life in Extreme Environments program. The 16S rRNA gene and 16S rRNA were amplified using PCR and reverse transcription-PCR, respectively, from DNA and RNA extracted from the total microbial community. The primers targeted microorganisms at the domain-specific, i.e., Bacteria and Archaea, and group-specific, i.e., sulfate-reducing bacteria (SRB) and putative anaerobic methane-oxidizing (ANME) archaea, level. Sequence analysis of the Bacteria clones revealed that the microbial communities were primarily dominated by Deltaproteobacteria. Other Proteobacteria classes, including Epsilon- and Gammaproteobacteria, represented a large fraction of the total microbial community isolated from the sediment overlying hydrate sample and the metabolically active fraction of the 0-2 cm sediment depth sampled from the Beggiatoa sp. mat-associated sediments. Sequence analysis indicated the majority of the archaeal clones were most closely related to Methanosarcinales, Methanomicrobiales and distinct lineages within the ANME groups. Several novel lineages were identified including a fourth ANME-2 clade, i.e., ANME-2D, and three clades with no closely related previously sequenced 16S rRNA gene clones or isolates, i.e., Unclassified Bacteria groups 1 and 2 and Unclassified Euryarchaeota. These studies represent the first 16S rRNA gene and 16S rRNA phylogenetic-based description of microbial communities extant in sediment-free gas hydrate and in methane-rich hydrate-associated and Beggiatoa sp.-associated sediments from a hydrocarbon seep region in the Gulf of Mexico.Ph.D.Committee Chair: Patricia Sobecky; Committee Member: Frank Loeffler; Committee Member: Joseph Montoya; Committee Member: Roger Wartell; Committee Member: Thomas DiChristin

Time-resolved imaging of flyer dynamics for femtosecond laser-induced backward transfer of solid polymer thin films

AbstractWe have studied the transfer regimes and dynamics of polymer flyers from laser-induced backward transfer (LIBT) via time-resolved shadowgraphy. Imaging of the flyer ejection phase of LIBT of 3.8μm and 6.4μm thick SU-8 polymer films on germanium and silicon carrier substrates was performed over a time delay range of 1.4–16.4μs after arrival of the laser pulse. The experiments were carried out with 150fs, 800nm pulses spatially shaped using a digital micromirror device, and laser fluences of up to 3.5J/cm2 while images were recorded via a CCD camera and a spark discharge lamp. Velocities of flyers found in the range of 6–20m/s, and the intact and fragmented ejection regimes, were a function of donor thickness, carrier and laser fluence. The crater profile of the donor after transfer and the resulting flyer profile indicated different flyer ejection modes for Si carriers and high fluences. The results contribute to better understanding of the LIBT process, and help to determine experimental parameters for successful LIBT of intact deposits

Haemophilus influenzae type b reemergence after combination immunization

An increase in Haemophilus influenzae type b (Hib) in British children has been linked to the widespread use of a diphtheria/tetanus/acellular pertussis combination vaccine (DTaP-Hib). We measured anti-polyribosyl-ribitol phos- phate antibody concentration and avidity before and after a Hib booster in 176 children 2–4 years of age who had received 3 doses of DTP-Hib (either DT whole cell pertus- sis-Hib or DTaP-Hib) combination vaccine in infancy. We also measured pharyngeal carriage of Hib. Antibody con- centrations before and avidity indices after vaccination were low (geometric mean concentration 0.46μg/mL, 95% confidence interval [CI] 0.36–0.58; geometric mean avidity index 0.16, 95% CI 0.14–0.18) and inversely related to the number of previous doses of DTaP-Hib (p = 0.02 and p<0.001, respectively). Hib was found in 2.1% (95% CI 0.7%–6.0%) of study participants. Our data support an association between DTaP-Hib vaccine combinations and clinical Hib disease through an effect on antibody concen- tration and avidit

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 &lt;300nm, thus limiting machining resolution to the diffraction limit at the near-visible wavelengths and above

Characterization of Microbial Population Shifts during Sample Storage

The objective of this study was to determine shifts in the microbial community structure and potential function based on standard Integrated Ocean Drilling Program (IODP) storage procedures for sediment cores. Standard long-term storage protocols maintain sediment temperature at 4°C for mineralogy, geochemical, and/or geotechnical analysis whereas standard microbiological sampling immediately preserves sediments at −80°C. Storage at 4°C does not take into account populations may remain active over geologic time scales at temperatures similar to storage conditions. Identification of active populations within the stored core would suggest geochemical and geophysical conditions within the core change over time. To test this potential, the metabolically active fraction of the total microbial community was characterized from IODP Expedition 325 Great Barrier Reef sediment cores prior to and following a 3-month storage period. Total RNA was extracted from complementary 2, 20, and 40 m below sea floor sediment samples, reverse transcribed to complementary DNA and then sequenced using 454 FLX sequencing technology, yielding over 14,800 sequences from the six samples. Interestingly, 97.3% of the sequences detected were associated with lineages that changed in detection frequency during the storage period including key biogeochemically relevant lineages associated with nitrogen, iron, and sulfur cycling. These lineages have the potential to permanently alter the physical and chemical characteristics of the sediment promoting misleading conclusions about the in situ biogeochemical environment. In addition, the detection of new lineages after storage increases the potential for a wider range of viable lineages within the subsurface that may be underestimated during standard community characterizations

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