Cathodoluminescence-based nanoscopic thermometry in a lanthanide-doped phosphor

Crucial to analyze phenomena as varied as plasmonic hot spots and the spread of cancer in living tissue, nanoscale thermometry is challenging: probes are usually larger than the sample under study, and contact techniques may alter the sample temperature itself. Many photostable nanomaterials whose luminescence is temperature-dependent, such as lanthanide-doped phosphors, have been shown to be good non-contact thermometric sensors when optically excited. Using such nanomaterials, in this work we accomplished the key milestone of enabling far-field thermometry with a spatial resolution that is not diffraction-limited at readout. We explore thermal effects on the cathodoluminescence of lanthanide-doped NaYF$_4$ nanoparticles. Whereas cathodoluminescence from such lanthanide-doped nanomaterials has been previously observed, here we use quantitative features of such emission for the first time towards an application beyond localization. We demonstrate a thermometry scheme that is based on cathodoluminescence lifetime changes as a function of temperature that achieves $\sim$ 30 mK sensitivity in sub-$\mu$m nanoparticle patches. The scheme is robust against spurious effects related to electron beam radiation damage and optical alignment fluctuations. We foresee the potential of single nanoparticles, of sheets of nanoparticles, and also of thin films of lanthanide-doped NaYF$_4$ to yield temperature information via cathodoluminescence changes when in the vicinity of a sample of interest; the phosphor may even protect the sample from direct contact to damaging electron beam radiation. Cathodoluminescence-based thermometry is thus a valuable novel tool towards temperature monitoring at the nanoscale, with broad applications including heat dissipation in miniaturized electronics and biological diagnostics.Comment: Main text: 30 pages + 4 figures; supplementary information: 22 pages + 8 figure

Atomic Control : a crystallography simulator

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.Includes bibliographical references (p. 51).AtomicControl is a software package designed to aid in the teaching of crystallography and x-ray diffraction concepts to materials science students. It has the capability to create an arbitrary crystal structure based on the user's specification of a space group and atomic coordinates. It also can generate a simulated powder diffractogram based on the user's generated crystal. The program is fully interactive and allows the user to view the effects of changes to lattice and atoms in a 3D visualization of the crystal. AtomicControl's x-ray diffraction patterns have been shown to match well with experimental data, proving the validity of the algorithm. AtomicControl is available online.by Edward S. Barnard.S.B

MOE11 Emittance Growth from the Thermalization of Space-Charge Nonuniformities

Beams injected into a linear focusing channel typically have some degree of space-charge nonuniformity. In general, injected particle distributions with systematic charge nonuniformities are not equilibria of the focusing channel and launch a broad spectrum of collective modes. These modes can phase-mix and have nonlinear wave-wave interactions which, at high space-charge intensities, results in a relaxation to a more thermal-like distribution characterized by a uniform density profile. This thermalization can transfer self-field energy from the initial space-charge nonuniformity to the local particle temperature, thereby increasing beam phase space area (emittance growth). In this paper, we employ a simple kinetic model of a continuous focusing channel and build on previous work that applied system energy and charge conservation quantify emittance growth associated with the collective thermalization of an initial azimuthally symmetric, rms matched beam with a radial density profile that is hollowed or peaked. This emittance growth is shown to be surprisingly modest even for high beam intensities with significant radial structure in the initial density profile.Comment: Paper MOE11, XX International Linac Conference, Monterey, CA 21-25 August 2000 3 pages, 3 figure

Electrically driven photon emission from individual atomic defects in monolayer WS2.

Quantum dot-like single-photon sources in transition metal dichalcogenides (TMDs) exhibit appealing quantum optical properties but lack a well-defined atomic structure and are subject to large spectral variability. Here, we demonstrate electrically stimulated photon emission from individual atomic defects in monolayer WS2 and directly correlate the emission with the local atomic and electronic structure. Radiative transitions are locally excited by sequential inelastic electron tunneling from a metallic tip into selected discrete defect states in the WS2 bandgap. Coupling to the optical far field is mediated by tip plasmons, which transduce the excess energy into a single photon. The applied tip-sample voltage determines the transition energy. Atomically resolved emission maps of individual point defects closely resemble electronic defect orbitals, the final states of the optical transitions. Inelastic charge carrier injection into localized defect states of two-dimensional materials provides a powerful platform for electrically driven, broadly tunable, atomic-scale single-photon sources

LSST: Comprehensive NEO Detection, Characterization, and Orbits

(Abridged) The Large Synoptic Survey Telescope (LSST) is currently by far the most ambitious proposed ground-based optical survey. Solar System mapping is one of the four key scientific design drivers, with emphasis on efficient Near-Earth Object (NEO) and Potentially Hazardous Asteroid (PHA) detection, orbit determination, and characterization. In a continuous observing campaign of pairs of 15 second exposures of its 3,200 megapixel camera, LSST will cover the entire available sky every three nights in two photometric bands to a depth of V=25 per visit (two exposures), with exquisitely accurate astrometry and photometry. Over the proposed survey lifetime of 10 years, each sky location would be visited about 1000 times. The baseline design satisfies strong constraints on the cadence of observations mandated by PHAs such as closely spaced pairs of observations to link different detections and short exposures to avoid trailing losses. Equally important, due to frequent repeat visits LSST will effectively provide its own follow-up to derive orbits for detected moving objects. Detailed modeling of LSST operations, incorporating real historical weather and seeing data from LSST site at Cerro Pachon, shows that LSST using its baseline design cadence could find 90% of the PHAs with diameters larger than 250 m, and 75% of those greater than 140 m within ten years. However, by optimizing sky coverage, the ongoing simulations suggest that the LSST system, with its first light in 2013, can reach the Congressional mandate of cataloging 90% of PHAs larger than 140m by 2020.Comment: 10 pages, color figures, presented at IAU Symposium 23

Long-Range Exciton Diffusion in Two-Dimensional Assemblies of Cesium Lead Bromide Perovskite Nanocrystals

F\"orster Resonant Energy Transfer (FRET)-mediated exciton diffusion through artificial nanoscale building block assemblies could be used as a new optoelectronic design element to transport energy. However, so far nanocrystal (NC) systems supported only diffusion length of 30 nm, which are too small to be useful in devices. Here, we demonstrate a FRET-mediated exciton diffusion length of 200 nm with 0.5 cm2/s diffusivity through an ordered, two-dimensional assembly of cesium lead bromide perovskite nanocrystals (PNC). Exciton diffusion was directly measured via steady-state and time-resolved photoluminescence (PL) microscopy, with physical modeling providing deeper insight into the transport process. This exceptionally efficient exciton transport is facilitated by PNCs high PL quantum yield, large absorption cross-section, and high polarizability, together with minimal energetic and geometric disorder of the assembly. This FRET-mediated exciton diffusion length matches perovskites optical absorption depth, opening the possibility to design new optoelectronic device architectures with improved performances, and providing insight into the high conversion efficiencies of PNC-based optoelectronic devices

Aortic haemostasis and resuscitation: advanced resuscitative endovascular balloon occlusion of the aorta for non-compressible torso haemorrhage and reversal of haemorrhage-induced traumatic cardiac arrest in a swine model

Trauma is the leading cause of death in young people in the UK and US. Non-compressible torso haemorrhage (NCTH) is a major cause of potentially survivable trauma death. A large proportion of these patients are in traumatic cardiac arrest (TCA) on arrival at hospital, and survival rates after haemorrhagic TCA are extremely low. The limited data available suggest that closed chest compressions (CPR) are ineffective, and may be harmful, in haemorrhagic TCA. Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) has shown promise in the setting of NCTH, although its utility in haemorrhagic TCA is unknown. Selective Aortic Arch Perfusion (SAAP) is an experimental intervention that has the potential to resuscitate haemorrhagic TCA, but it has not been compared to CPR or REBOA. The aim of this research was to evaluate SAAP against other interventions for the management of haemorrhagic TCA. A large swine (70-90 kg) translational model of TCA secondary to NCTH and a controlled arterial haemorrhage was developed to answer hypotheses in three parts. First, a comparison of 60 minute survival between CPR, REBOA, SAAP with oxygenated lactated Ringer’s solution (SAAP-LR), and SAAP with oxygenated fresh whole blood (SAAP-FWB), followed by surgical control and a three-hour critical care period; second, in a more severe model of TCA, comparison of SAAP-LR and SAAP-FWB, and an evaluation of extra-corporeal life support (ECLS) to mitigate the effects of aortic occlusion; and third, a translational paradigm of escalating endovascular intervention, from REBOA to SAAP, to ECLS. In Part One, 40 animals were allocated to four groups; SAAP-FWB inferred a significant 60 minute survival advantage (90.0%, 95%CI 59.6-99.5) over CPR (10.0%, 95%CI 0.5-40.4), REBOA (0.0%, 95%CI 0.0-27.8), and SAAP-LR (30.0%, 95%CI 10.8-60.3), p<0.001. SAAP-FWB and CPR were observed to resuscitate cardiac electrical asystole; both of these are novel findings, but no asystolic animals survived to the end of the protocol. In Part Two, ECLS after SAAP catheter removal demonstrated a significant three-hour survival advantage over non-ECLS historical controls, p<0.05. The translational paradigm of escalating endovascular intervention was shown to be a feasible and efficacious method of resuscitating swine in haemorrhagic TCA in Part Three. A novel swine donor pool supplied >700 units of FWB for the experiments, and was an effective way of obtaining large volumes of blood product whilst reducing overall animal use. Ventricular fibrillation was observed in animals in the SAAP-FWB group, and further development of the technique is needed prior to clinical implementation. SAAP-FWB is capable of resuscitating swine in haemorrhagic cardiac electrical asystole, and infers a superior short-term survival compared to intervention with CPR, REBOA, and SAAP-LR, but further data are needed to ensure normocalcaemia during infusion of citrated blood products. ECLS has been demonstrated to prolong survival in the setting of cardiopulmonary dysfunction secondary to TCA and intra-aortic balloon occlusion. An escalating paradigm of endovascular intervention is a feasible and efficacious method of resuscitating large swine in haemorrhagic TCA that is translatable to clinical practice