Pyrene emission from monolayers 'clicked' onto quartz

A series of quartz surfaces were modifed with a series of crosslinkers and functional groups in order to obtain an azide-terminated monolayer, which was then used to immobilize pyrene onto the surface via alkyne-azide \click" chemistry. During the course of the immobilization, different ratios of tert-butyl diphenyl chlorosilane were used to control the distribution and hence the photophysical properties of the pyrene on the surface. The preparative surface reactions and photophysical properties were investigated with contact angle, X-ray photoelectron spectroscopy, UV-visible absorption and emission spectroscopy. High surface coverage was achieved of just under 1molecule per nm2. At this coverage all emission from the pyrene was in the form of excimer emission. Excimer emission dominated at all surface coverages greater than 0.45 molecules per nm2. Below this coverage the monomer emission could also be observed. The conclusions that can be drawn are important for understanding the interactions of neighboring molecules in molecular monolayers. Our results suggest that at high surface coverage a substantial number of the pyrene molecules are already close enough to their neighbors that pairs of them can be directly excited to form excimer with no requirement for diffusion. This can be stated because the long wavelength end of the pyrene absorption and excitation spectra show a broad tail that is assigned to a charge transfer band resulting from an electron being directly transferred from a ground state pyrene to a neighboring pyrene molecule. Furthermore, absorption spectra shifts also indicate that the pyrene molecules undergo some interactions on the surface when they are closely packed

Transient absorption spectroscopy on spiropyran monolayers using nanosecond pump–probe Brewster angle reflectometry

Self-assembled monolayers of 11-(3’,3’-dimethyl-6,8-dinitrospiro[chromene-2,2’-indoline]-1’-yl) undecanoic acid (amphiphilic spiropyran) at the air–water interface are studied using Brewster angle reflectometry. Transient kinetics of the spiropyran to merocyanine conversion are recorded in a UV-pump, VIS-probe configuration. By varying the probe wavelength using an optical parametric oscillator, we are able to reconstruct absorption spectra of intermediate states with a time-resolution of 10 nanoseconds, limited by the temporal convolution of the two laser pulses. After UV irradiation, spiropyran converts to merocyanine in two stages. The first occurs within a timescale of several tens of nanoseconds and is heavily convoluted with the system response time, whereas the second stage occurs over a few hundred nanoseconds. During the rise time there is a small red shift in the transient absorption spectrum of ∼20 nm. We assign the red shift and the slower kinetics to the isomerization of a merocyanine isomer cis about the central methine bond to those that are trans about the same bond

Nanoscale mapping of optically inaccessible bound-states-in-the-continuum

Bound-states-in-the-continuum (BIC) is an emerging concept in nanophotonics with potential impact in applications, such as hyperspectral imaging, mirror-less lasing, and nonlinear harmonic generation. As true BIC modes are non-radiative, they cannot be excited by using propagating light to investigate their optical characteristics. In this paper, for the 1st time, we map out the strong near-field localization of the true BIC resonance on arrays of silicon nanoantennas, via electron energy loss spectroscopy with a sub-1-nm electron beam. By systematically breaking the designed antenna symmetry, emissive quasi-BIC resonances become visible. This gives a unique experimental tool to determine the coherent interaction length, which we show to require at least six neighboring antenna elements. More importantly, we demonstrate that quasi-BIC resonances are able to enhance localized light emission via the Purcell effect by at least 60 times, as compared to unpatterned silicon. This work is expected to enable practical applications of designed, ultra-compact BIC antennas such as for the controlled, localized excitation of quantum emitter

Silicon Nanoantenna Mix Arrays for a Trifecta of Quantum Emitter Enhancements

Dielectric nanostructures have demonstrated optical antenna effects due to Mie resonances. Preliminary investigations on dielectric nanoantennas have been carried out for a trifecta of enhancements, i.e., simultaneous enhancements in absorption, emission directionality and radiative decay rates of quantum emitters. However, these investigations are limited by fragile substrates or low Purcell factor, which is extremely important for exciting quantum emitters electrically. In this paper, we present a Si mix antenna array to achieve the trifecta enhancement of ~1200 fold with a Purcell factor of ~47. The antenna design incorporates ~10 nm gaps within which fluorescent molecules strongly absorb the pump laser energy through a resonant mode. In the emission process, the antenna array increases the radiative decay rates of the fluorescence molecules via Purcell effect and provides directional emission through a separate mode. This work could lead to novel CMOS compatible platforms for enhancing fluorescence for biological and chemical applications.Comment: 20 pages, 4 figure

Raman mapping glucose metabolites during human mesenchymal stem cell adipogenesis

Raman mapping was used to determine the lipid distribution inside human mesenchymal stem cells during induced adipogenesis by monitoring C-H stretching bands of the fats inside the lipid droplets. By incorporating deuterated glucose into the cell culture medium during induction it was possible to distinguish whether or not downstream metabolites, either in lipid droplets or in the cytoplasm, had been formed before or after the adipogenic cascade, because C-D stretching bands are 1/√2 shifted compared to the C-H bands. Thus, metabolites formed after the initiation of the process displayed both C-H and C-D stretching bands and so were forming during induced adipogenesis rather than prior to it. With the ability to distinguish small putative lipid drops formed by the induction of adipogenesis from those pre-formed in the cell, it was possible to analyze spectral changes occurring in the droplets at the earliest stages of adipogenesis. There were two key findings. Firstly, Raman spectra of lipid droplets evolved over time, suggesting that their composition at the early stages was not the same as at the later stages. Secondly, it was apparent that the proportion of unsaturated fats in droplets was higher at early stages than it was at later stages, suggesting that unsaturated fats arrive in the droplets faster than saturated ones

Tunneling through a multigrain system: deducing the sample topology from the nonlinear conductance

We study a current transport through a system of a few grains connected with tunneling links. The exact solution is given for an arbitrarily connected double-grain system with a shared gate in the framework of the orthodox model. The obtained result is generalized for multigrain systems with strongly different tunneling resistances. We analyse the large-scale nonlinear conductance and demonstrate how the sample topology can be unambiguously deduced from the spectroscopy pattern (differential conductance versus gate-bias plot). We present experimental data for a multigrain sample and reconstruct the sample topology. A simple selection rule is formulated to distinguish samples with spectral patterns free from spurious disturbance caused by recharging of some grains nearby. As an example, we demonstrate experimental data with additional peaks in the spectroscopy pattern, which can not be attributed to coupling to additional grains. The described approach can be used to judge the sample topology when it is not guaranteed by fabrication and direct imaging is not possible.Comment: 13 pages (including 8 figures

Transient Brewster angle reflectometry of spiropyran monolayers

Brewster angle reflectometry has been developed as a tool for determining the absorbance and refractive index changes in molecular monolayers containing spiropyran. The method is sensitive to changes in both the real and imaginary parts of the refractive index in the monolayers. It was used to monitor the conversion of spiropyran to merocyanine and the reversal of this reaction when the molecules were immobilised on quartz using silane coupling. An analytical solution of Fresnel formula allowed the transient reflectometry data to be converted into transient absorption information. Absorbances of transients as low as ~10-6 were possible using the current apparatus with a single laser pulse transient measurement. It was found that spiropyran photoconverted to merocyanine with an efficiency of ~0.1. The photochemical reversion of converted merocyanine to spiropyran occurred with efficiencies of 0.03–0.2 and this was probably site dependent. It was found that the thermal conversion from merocyanine to spiropyran was slow and even after 10 min there was no significant thermal reversion. This measurement was possible because the real part of the refractive index of the monolayer could be monitored with time using an off-resonance probe at a wavelength where the merocyanine did not absorb light meaning that the probe did not photobleach the sample. Thus our method also provides a non-intrusive method for probing changes in molecules in thin films

Mortality of Children Born on Early Gestational Age: is it the Impassable Barrier or the Reserve for Reducing the Infants Mortality?

The problem of premature infants is well recognized in Russia and all over the world. The article discusses the mortality level and structure of extremely premature infant during 2015–2019. The aim of the study was to identify significant cause-effect relations for high mortality of premature infants and infants with extremely low body weight (ELBW) according to reports from obstetric departments, pediatric outpatient clinics, children's hospitals, statistical agencies, queries results from Territorial Compulsory Medical Insurance Fund (TCMIF) in Saint Petersburg and Russian Association of Human Reproduction (RAHR). The main demographic indices are presented by the Petrostat association. Russian Federal State Statistics Service (Rosstat) forms provided by the Center for Analysis and Prediction of Maternal and Child Health of the Saint Petersburg Health care Committee (No. 32 “Information on medical care for pregnant women, women in labour and new mothers” (approved by order of Rosstat No. 591 of 27.11.2015); No. 19 “Information on children with disabilities” registered in children's clinics (approved by order of Rosstat No. 866 of 27.12.2016); No. 14 “Information on the activities of medical facilities units providing inpatient medical care” (approved by order of Rosstat No. 723 of 05.12.2014); No. 30 “Information on the medical facility” (approved by order of Rosstat No. 483 of 03.08.2018 “On the approval of statistical tools for the organization of federal statistical observation in the field of healthcare by the Ministry of Health of the Russian Federation”) presented by Saint Petersburg Medical Informational and Analytical Center (MIAC)), and answers from TCMIF in Saint Petersburg and RARCH have been investigated. The authors have analyzed the fertility and mortality rates of premature infants, the group of children with ELBW has been established. High mortality levels have been revealed in the first weeks of life (22–23), they were mainly associated with infectious processes. The authors associate the premature delivery increase with the widespread implementation of assisted reproductive technology (ART). ART can be performed either via compulsory medical insurance funds, or other non-government sources. The assumption was proposed that there are possible violations of ART indications, contraindications, and the number of procedures. The ART efficacy is difficult to estimate as well due to insufficient information provided by Rosstat report form No. 32. The need of implementation of the new statistical form that will cover the data on the of ART administration, the possibility of efficacy estimation of modern invasive methods for infertility treatment and mandatory submission of reports about the use of these methods by medical facilities is discussed

Reconstraction of 3D object models from vectorised engineering drawings

In this paper, the problem of 3D-object model reconstruction from engineering drawing projections is analysed, and its main stages are shown. Image vectorisation and entity recognition is mentioned briefly, the main focus being editing or the parameterisation of vectorised drawings and 3D object model reconstruction from vectorised ED projections. Vectorised drawing, as a rule, do not exactly correspond to sizes and other features (touching, parallelity, perpendicularly, symmetry, collinearity, etc.) being available on the initial drawing, and this ED vector model is not suitable for direct use in CAD systems. That is why the parameterisation stage is introduced and considered in detail. An algorithm for 3D-object reconstruction from the vectorised and parameterised drawing is proposed. The algorithm is based on the detection of volumetric solid-state object components (primitives), and performing theoretic-set operations with the components. Practical experience in realising these stages is show

Giant field effect in self-assembled metallo-organic nanoscale networks

Three-terminal devices have been produced by self-assembly of chemically stabilized gold clusters of 5–7 nm in diameter in a nanogap between the source and drain electrodes on top of an electrostatic gate made of oxidized aluminium. The conductivity of the devices with the agglomerates of clusters, self-assembled in the gap, was modulated substantially by the electric field of the gate. The effect is attributed to the mechanical deformation of the organic tunneling barriers between the gold clusters under the influence of Coulomb forces. A peculiar interplay between the mechanical deformations caused by the gate and the source-drain voltages leads to unusual current-voltage characteristics of the devices. A phenomenological theory based on these ideas has been developed