Laser drilling of via micro-holes in single-crystal semiconductor substrates using a 1070 nm fibre laser with millisecond pulse widths

Micro-machining of semiconductors is relevant to fabrication challenges within the semiconductor industry. For via holes for solar cells, laser drilling potentially avoids deep plasma etching which requires sophisticated equipment and corrosive, high purity gases. Other applications include backside loading of cold atoms into atom chips and ion traps for quantum physics research, for which holes through the semiconductor substrate are needed. Laser drilling, exploiting the melt ejection material removal mechanism, is used industrially for drilling hard to machine materials such as superalloys. Lasers of the kind used in this work typically form holes with diameters of 100’s of microns and depths of a few millimetres in metals. Laser drilling of semiconductors typically uses short pulses of UV or long wavelength IR to achieve holes as small as 50 microns. A combination of material processes occurs including laser absorption, heating, melting, vaporization with vapour and dust particle ejection and resolidification. An investigation using materials with different fundamental material parameters allows the suitability of any given laser for the processing of semiconductors to be determined. We report results on the characterization of via holes drilled using a 2000 W maximum power 1070 nm fibre laser with 1-20 ms pulses using single crystal silicon, gallium arsenide and sapphire. Holes were characterised in cross-section and plan view. Significantly, relatively long pulses were effective even for wide bandgap substrates which are nominally transparent at 1070 nm. Examination of drilled samples revealed holes had been successfully generated in all materials via melt ejection

Successful elimination of factor VIII inhibitor using cyclosporin A

No abstract available

Using in situ management to conserve biodiversity under climate change

This is the final version of the article. Available from Wiley via the DOI in this record.The accepted author manuscript version of this article is in ORE at http://hdl.handle.net/10871/18829Successful conservation will increasingly depend on our ability to help species cope with climate change. While there has been much attention on accommodating or assisting range shifts, less has been given to the alternative strategy of helping species survive climate change through in situ management.Here we provide a synthesis of published evidence examining whether habitat management can be used to offset the adverse impacts on biodiversity of changes in temperature, water availability and sea-level rise. Our focus is on practical methods whereby the local environmental conditions experienced by organisms can be made more suitable.Many studies suggest that manipulating vegetation structure can alter the temperature and moisture conditions experienced by organisms, and several demonstrate that these altered conditions benefit species as regional climatic conditions become unsuitable. The effects of topography on local climatic conditions are even better understood, but the alteration of topography as a climate adaptation tool is not ingrained in conservation practice. Trials of topographic alteration in the field should therefore be a priority for future research.Coastal systems have the natural capacity to keep pace with climate change, but require sufficient sediment supplies and space for landward migration to do so. There is an extensive literature on managed realignment. While the underlying rationale is simple, successful implementation requires careful consideration of elevation and past land use. Even with careful management, restored habitats may not attain the physical and biological attributes of natural habitats. Synthesis and applications. The recent literature provides a compelling case that some of the adverse effects of climate change can be offset by appropriate management. However, much of the evidence for this is indirect and too few studies provide empirical tests of the long-term effectiveness of these management interventions. It is clear from the existing evidence that some techniques have a higher risk of failure or unexpected outcomes than others and managers will need to make careful choices about which to implement. We have assessed the strength of evidence of these approaches in order to demonstrate to conservation professionals the risks involved.A.J.S. was funded by a NERC grant, ref: NE/L00268X/1

Laser drilling of micro-holes in single crystal silicon, indium phosphide and indium antimonide using a continuous wave (CW) 1070 nm fibre laser with millisecond pulse widths

The laser micro-drilling of “thru” holes, also known as via holes, in Si, InP and InSb semiconductor wafers was studied using millisecond pulse lengths from an IPG Laser Model YLR-2000 CW multimode 2 kW Ytterbium Fibre Laser and a JK400 (400 W) fibre laser, both with 1070 nm wavelength. The flexibility of this laser wavelength and simple pulsing scheme were demonstrated for semiconductor substrates of narrow (InSb Eg 0.17 eV) and wide (InP Eg 1.35 eV)) room-temperature bandgap, Eg, with respect to the photon energy of 1.1 eV. Optical microscopy and cross-sectional analysis were used to quantify hole dimensions and the distribution of recast material for all wafers and, for silicon, any microcracking for both (100) and (111) single crystal surface Si wafer orientations. It was found that the thermal diffusivity was not a sufficient parameter for predicting the relative hole sizes for the Si, InP and InSb single crystal semiconductors studied. Detailed observations for Si showed that, between the threshold energies for surface melting and the irradiance for drilling a “thru” hole from the front surface to rear surface, there was a range of irradiances for which micro-cracking occurred near the hole circumference. The directionality and lengths of these microcracks were studied for the (100) and (111) orientations and possible mechanisms for formation were discussed, including the Griffith criterion for microcracks and the failure mechanism of fatigue usually applied to welding of metals. For Si, above the irradiance for formation of a thru-hole, few cracks were observed. Future work will compare similar observations and measurements in other narrow- and wide-bandgap semiconductor wafer substrates. We demonstrated one application of this laser micro-drilling process for the micro-fabrication of a thru hole precisely-located in the centre of a silicon-based atom chip which had been patterned using semiconductor lithographic techniques. The end-user application was a source of magneto-optically trapped (MOT) cold atoms of Rubidium (87Rb) for portable quantum sensing

[Accepted Manuscript] Optimizing tubal ligation service delivery: a prospective cohort study to measure the task-sharing experience of Marie Stopes International Ethiopia.

The Ethiopian government implements a progressive task-sharing policy for health services as a strategy to address shortages of highly skilled providers and increase access to critical services, such as family planning. Since 2009, Marie Stopes International Ethiopia has trained health officers to provide tubal ligations, a permanent method of family planning, as part of its task-sharing strategy. The objectives of this research were to evaluate task-sharing tubal ligations to health officers at Marie Stopes International Ethiopia, specifically: (a) to investigate safety, as measured by the proportion of major adverse events; (b) to evaluate the feasibility, as measured by adherence to the standard tubal ligation procedure protocol and (c) to investigate acceptability to clients of the tubal ligation procedure provided by health officers. We established a prospective cohort of women aged  ≥18 years presenting for tubal ligation at Marie Stopes International Ethiopia sites in three regions in Ethiopia (March-May 2014). Data on adverse events (incomplete procedure, pain, bleeding, infection, perforation) were collected intra-operatively; peri-operatively (1-h post-procedure); and post-operatively (7 days post-procedure). To measure feasibility, 65% of procedures were selected for 'audit', where a nurse observed and scored health officers adherence to standard protocol using an 18-item checklist. To assess acceptability, women were asked about their satisfaction with the procedure. In total, 276 women were enrolled in the study. 97.5% of procedures took place in rural settings. All participants were followed up 7 days post-procedure (100% response rate). The overall proportion of major adverse events was 3% (95% CI 1-6%). The most frequent adverse event was 'failure to complete the TL' (2.2%, n = 6). The average score on protocol adherence was 96.9%. Overall, 98.2% (n = 271) of clients would recommend the procedure to a friend. Findings from this study, indicating safety, feasibility and acceptability, are consistent with the existing literature, which indicate safety and acceptability for task-sharing tubal ligations, and other methods of contraception with non-physician health providers. This study adds to scant literature on task-sharing tubal ligations in rural and low-resource settings.<br/

Laser drilling of microholes in single crystal silicon using continuous wave (CW) 1070 nm fiber lasers with millisecond pulse widths

The laser microdrilling of via holes in Si semiconductor wafers was studied using 1 ms pulses from an Yb fibre laser with 1070 nm wavelength. Optical microscopy and cross‑sectional analysis were used to quantify hole dimensions, the distribution of recast material and any microcracking for both (100) and (111) single crystal surface semiconductor wafer orientations. The flexibility of this laser wavelength and simple pulsing scheme were demonstrated for a range of semiconductor substrates of narrow and wide bandgap including InSb, GaSb, InAs, GaAs, InP and sapphire. Detailed observations for Si showed that, between the threshold energies for surface melting and the irradiance for drilling a “thru” hole from the front surface to rear surface, there was a range of irradiances for which microcracking occurred near the hole circumference. The directionality and lengths of these microcracks were studied for the (100) and (111) orientations and possible mechanisms for formation were discussed, including the Griffith criterion for microcracks and the failure mechanism of fatigue usually applied to welding of metals. Above the irradiance for formation of a thru hole, few cracks were observed. Future work will compare similar observations and measurements in other narrow- and wide-bandgap semiconductor wafer substrates

Regional Invasive Species & Climate Change Management Challenge: Forest Pest Risk is Heating Up

Insect pests and pathogens, and climate change, each threaten forest health. But what happens when the two are combined? Climate change brings pests to new areas, makes pests more damaging, reduces trees’ defenses to pests, and can alter how forests recover after pest disturbance. Strategies for managing the combined impacts of forest pests and climate change include preventing new pest introductions, resisting pest spread by treating individual trees and diversifying forest stands, promoting more resilient forests that can rebound from pests, and helping forests transition to a state better adapted to our future climate

Comparison of Approaches for Measuring and Predicting the Viscosity of Ternary Component Aerosol Particles

Measurements of the water activity-dependent viscosity of aerosol particles from two techniques are compared, specifically from the coalescence of two droplets in holographic optical tweezers (HOT) and poke-and-flow experiments on particles deposited onto a glass substrate. These new data are also compared with the fitting of dimer coagulation, isolation, and coalescence (DCIC) measurements. The aerosol system considered in this work are ternary mixtures of sucrose-citric acid-water and sucrose-NaNO3-water, at varying solute mass ratios. Results from HOT and poke-and-flow are in excellent agreement over their overlapping range of applicability (∼103–107 Pa s); fitted curves from DCIC data show variable agreement with the other two techniques because of the sensitivity of the applied modeling framework to the representation of water content in the particles. Further, two modeling approaches for the predictions of the water activity-dependent viscosity of these ternary systems are evaluated. We show that it is possible to represent their viscosity with relatively simple mixing rules applied to the subcooled viscosity values of each component or to the viscosity of the corresponding binary mixtures

Hidden Symmetries and their Consequences in t2gt_{2g} Cubic Perovskites

The five-band Hubbard model for a $d$ band with one electron per site is a model which has very interesting properties when the relevant ions are located at sites with high (e. g. cubic) symmetry. In that case, if the crystal field splitting is large one may consider excitations confined to the lowest threefold degenerate $t_{2g}$ orbital states. When the electron hopping matrix element ($t$) is much smaller than the on-site Coulomb interaction energy ($U$), the Hubbard model can be mapped onto the well-known effective Hamiltonian (at order $t^{2}/U$) derived by Kugel and Khomskii (KK). Recently we have shown that the KK Hamiltonian does not support long range spin order at any nonzero temperature due to several novel hidden symmetries that it possesses. Here we extend our theory to show that these symmetries also apply to the underlying three-band Hubbard model. Using these symmetries we develop a rigorous Mermin-Wagner construction, which shows that the three-band Hubbard model does not support spontaneous long-range spin order at any nonzero temperature and at any order in $t/U$ -- despite the three-dimensional lattice structure. Introduction of spin-orbit coupling does allow spin ordering, but even then the excitation spectrum is gapless due to a subtle continuous symmetry. Finally we showed that these hidden symmetries dramatically simplify the numerical exact diagonalization studies of finite clusters.Comment: 26 pages, 3 figures, 520 KB, submitted Phys. Rev.