Engineering topics
Tan, K.
Publications and source records attributed to Tan, K..
Rapid desolvation-triggered domino lattice rearrangement in a metal-organic framework
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Broadband quadrature-squeezed vacuum and nonclassical photon number correlations from a nanophotonic device
We report demonstrations of both quadrature-squeezed vacuum and photon number difference squeezing generated in an integrated nanophotonic device. Squeezed light is generated via strongly driven spontaneous four-wave mixing below threshold in silicon nitride microring resonators. The generated light is characterized with both homodyne detection and direct measurements of photon statistics using photon number–resolving transition-edge sensors. We measure 1.0(1) decibels of broadband quadrature squeezing (~4 decibels inferred on-chip) and 1.5(3) decibels of photon number difference squeezing (~7 decibels inferred on-chip). Nearly single temporal mode operation is achieved, with measured raw unheralded second-order correlations g (2) as high as 1.95(1). Multiphoton events of over 10 photons are directly detected with rates exceeding any previous quantum optical demonstration using integrated nanophotonics. These results will have an enabling impact on scaling continuous variable quantum technology.
Quenching of photoluminescence in a Zn-MOF sensor by nitroaromatic molecules
We uncover the exact mechanisms that lead to a quenching of the photoluminescence in a Zn-based metal organic framework (MOF) material upon nitroaromatic molecule adsorption. We present evidence based on ab initio simulations, coupled with in situ IR spectroscopy and photoluminescence measurements, showing that quenching occurs as the result of a shift of the lowest unoccupied orbital from the MOF host to the guest molecule. Our results provide a mechanistic understanding of quenching of photoluminescence in MOFs and are of importance for chemical sensing applications, where they aid the design of novel MOFs with increased sensing selectivity.
Structures of riboswitch RNA reaction states by mix-and-inject XFEL serial crystallography
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Chemistry in confined spaces: reactivity of the Zn-MOF-74 channels
Using infrared spectroscopy combined with ab initio methods we study reactions of H2O and CO inside the confined spaces of Zn-MOF-74 channels. Our results show that, once the water dissociation reaction H2O → OH + H takes place at the metal centers, the addition of 40 Torr of CO at 200 °C starts the production of formic acid via OH + H + CO → HCO2H. Our detailed analysis shows that the overall reaction H2O + CO → HCO2H takes place in the confinement of MOF-74 without an external catalyst, unlike the same reaction on flat surfaces. This discovery has several important consequences: it opens the door to a new set of catalytic reactions inside the channels of the MOF-74 system, it suggests that a recovery of the MOF's adsorption capacity is possible after it has been exposed to water (which in turn stabilizes its crystal structure), and it produces the important industrial feedstock formic acid.
Systematic non-LTE study of the −2.6 ≤ [Fe/H] ≤ 0.2 F and G dwarfs in the solar neighborhood. I. Stellar atmosphere parameters
We present atmospheric parameters for 51 nearby F and G dwarf and subgiant stars uniformly distributed over the −2.60<[Fe/H]<+0.20 metallicity range that is suitable for the Galactic chemical evolution research. Lines of iron in the two ionization stages, Fe i and Fe ii, were used to derive a homogeneous set of effective temperatures, surface gravities, iron abundances, and microturbulence velocities. Our spectroscopic analyses took advantage of employing high-resolution (R ≥ 60,000) Shane/Hamilton and Canada–France–Hawaii Telescope/ESPaDOnS observed spectra and non-LTE (NLTE) line formation for Fe i and Fe ii in the classical one-dimensional model atmospheres. The spectroscopic method was tested in advance with the 20 benchmark stars, for which there are multiple measurements of the infrared flux method effective temperature and their Hipparcos parallax error is less than 10%. We found NLTE abundances from lines of Fe i and Fe ii to be consistent within 0.06 dex for every benchmark star, when applying a scaling factor of S{sub H} = 0.5 to the Drawinian rates of inelastic Fe+H collisions. The obtained atmospheric parameters were checked for each program star by comparing its position in the log g–T{sub eff} plane with the theoretical evolutionary track of given metallicity and α-enhancement in the Yi et al. grid. Our final effective temperatures lie exactly in between the T{sub IRFM} scales of Alonso et al. and Casagrande et al., with a mean difference of +46 and −51 K, respectively. NLTE leads to higher surface gravity compared with that for LTE. The shift in log g is smaller than 0.1 dex for stars with [Fe/H] ⩾−0.75, T{sub eff} ≤ 5750 K, or log g ≥ 4.20. NLTE analysis is crucial for the very metal-poor turnoff and subgiant stars, for which the shift in log g between NLTE and LTE can be up to 0.5 dex. The obtained accurate atmospheric parameters will be used in the forthcoming papers to determine NLTE abundances of important astrophysical elements from lithium to europium and to improve observational constraints on the chemodynamical models of the Galaxy evolution.