Stroboscopic Space Tag for Optical Time-Resolved Measurements with a Charge Coupled Device Detector

AbstractInvestigations of magnetically ordered phases on the femtosecond timescale have provided significant insights into the influence of charge and lattice degrees of freedom on the magnetic sub-system. However, short-range magnetic correlations occurring in the absence of long-range order, for example in spin-frustrated systems, are inaccessible to many ultrafast techniques. Here, we show how time-resolved resonant inelastic X-ray scattering (trRIXS) is capable of probing such short-ranged magnetic dynamics in a charge-transfer insulator through the detection of a Zhang–Rice singlet exciton. Utilizing trRIXS measurements at the O K-edge, and in combination with model calculations, we probe the short-range spin correlations in the frustrated spin chain material CuGeO3 following photo-excitation, revealing a strong coupling between the local lattice and spin sub-systems.

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A time-domain phase diagram of metastable states in a charge ordered quantum material

Nature Communications ◽

10.1038/s41467-021-22646-7 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Jan Ravnik ◽

Michele Diego ◽

Yaroslav Gerasimenko ◽

Yevhenii Vaskivskyi ◽

Igor Vaskivskyi ◽

...

Keyword(s):

Phase Diagram ◽

Time Domain ◽

Metastable States ◽

Scanning Tunneling ◽

Photon Density ◽

Tunneling Microscopy ◽

Equilibrium Conditions ◽

Time Resolved ◽

A Charge ◽

Non Equilibrium

AbstractMetastable self-organized electronic states in quantum materials are of fundamental importance, displaying emergent dynamical properties that may be used in new generations of sensors and memory devices. Such states are typically formed through phase transitions under non-equilibrium conditions and the final state is reached through processes that span a large range of timescales. Conventionally, phase diagrams of materials are thought of as static, without temporal evolution. However, many functional properties of materials arise as a result of complex temporal changes in the material occurring on different timescales. Hitherto, such properties were not considered within the context of a temporally-evolving phase diagram, even though, under non-equilibrium conditions, different phases typically evolve on different timescales. Here, by using time-resolved optical techniques and femtosecond-pulse-excited scanning tunneling microscopy (STM), we track the evolution of the metastable states in a material that has been of wide recent interest, the quasi-two-dimensional dichalcogenide 1T-TaS2. We map out its temporal phase diagram using the photon density and temperature as control parameters on timescales ranging from 10−12 to 103 s. The introduction of a time-domain axis in the phase diagram enables us to follow the evolution of metastable emergent states created by different phase transition mechanisms on different timescales, thus enabling comparison with theoretical predictions of the phase diagram, and opening the way to understanding of the complex ordering processes in metastable materials.

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Synthesis and Photobehavior of a NewDehydrobenzoannulene-Based HOF with Fluorine Atoms: From Solution to Single Crystals Observation

International Journal of Molecular Sciences ◽

10.3390/ijms22094803 ◽

2021 ◽

Vol 22 (9) ◽

pp. 4803

Author(s):

Eduardo Gomez ◽

Ichiro Hisaki ◽

Abderrazzak Douhal

Keyword(s):

Charge Transfer ◽

Single Crystals ◽

Parent Compound ◽

Time Resolved ◽

Strong Basis ◽

Triplet Structure ◽

Carboxylic Groups ◽

Potential Applications ◽

A Charge ◽

Further Development

Hydrogen-bonded organic frameworks (HOFs) are the focus of intense scientific research due their potential applications in science and technology. Here, we report on the synthesis, characterization, and photobehavior of a new HOF (T12F-1(124TCB)) based on a dehydrobenzoannulene derivative containing fluorine atoms (T12F-COOH). This HOF exhibits a 2D porous sheet, which is hexagonally networked via H-bonds between the carboxylic groups, and has an interlayers distance (4.3 Å) that is longer than that of a typical π–π interaction. The presence of the fluorine atoms in the DBA molecular units largely increases the emission quantum yield in DMF (0.33, T12F-COOH) when compared to the parent compound (0.02, T12-COOH). The time-resolved dynamics of T12F-COOH in DMF is governed by the emission from a locally excited state (S1, ~ 0.4 ns), a charge-transfer state (S1(CT), ~ 2 ns), and a room temperature emissive triplet state (T1, ~ 20 ns), in addition to a non-emissive triplet structure with a charge-transfer character (T1(CT), τ = 0.75 µs). We also report on the results using T12F-ester. Interestingly, FLIM experiments on single crystals unravel that the emission lifetimes of the crystalline HOF are almost twice those of the amorphous ones or the solid T12F-ester sample. This shows the relevance of the H-bonds in the photodynamics of the HOF and provides a strong basis for further development and study of HOFs based on DBAs for potential applications in photonics.

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Spectroscopic flat-fields can be used for precision CCD gain and noise tests

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2020.54 ◽

2021 ◽

Vol 38 ◽

Author(s):

J. Gordon Robertson

Keyword(s):

Ccd Camera ◽

Matched Pair ◽

Optical Fibres ◽

Charge Coupled Device ◽

Small Areas ◽

Flat Field ◽

Basic Parameters ◽

The Mean ◽

A Charge ◽

Analogue To Digital

Abstract One of the basic parameters of a charge coupled device (CCD) camera is its gain, that is, the number of detected electrons per output Analogue to Digital Unit (ADU). This is normally determined by finding the statistical variances from a series of flat-field exposures with nearly constant levels over substantial areas, and making use of the fact that photon (Poisson) noise has variance equal to the mean. However, when a CCD has been installed in a spectroscopic instrument fed by numerous optical fibres, or with an echelle format, it is no longer possible to obtain illumination that is constant over large areas. Instead of making do with selected small areas, it is shown here that the wide variation of signal level in a spectroscopic ‘flat-field’ can be used to obtain accurate values of the CCD gain, needing only a matched pair of exposures (that differ in their realisation of the noise). Once the gain is known, the CCD readout noise (in electrons) is easily found from a pair of bias frames. Spatial stability of the image in the two flat-fields is important, although correction of minor shifts is shown to be possible, at the expense of further analysis.

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The role of spin in the degradation of organic photovoltaics

Nature Communications ◽

10.1038/s41467-020-20601-6 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Ivan Ramirez ◽

Alberto Privitera ◽

Safakath Karuthedath ◽

Anna Jungbluth ◽

Johannes Benduhn ◽

...

Keyword(s):

Transient Absorption ◽

Bulk Heterojunction ◽

Critical Factor ◽

Model Systems ◽

Transient Absorption Spectroscopy ◽

Triplet States ◽

Paramagnetic Resonance ◽

Time Resolved ◽

A Charge

AbstractStability is now a critical factor in the commercialization of organic photovoltaic (OPV) devices. Both extrinsic stability to oxygen and water and intrinsic stability to light and heat in inert conditions must be achieved. Triplet states are known to be problematic in both cases, leading to singlet oxygen production or fullerene dimerization. The latter is thought to proceed from unquenched singlet excitons that have undergone intersystem crossing (ISC). Instead, we show that in bulk heterojunction (BHJ) solar cells the photo-degradation of C60 via photo-oligomerization occurs primarily via back-hole transfer (BHT) from a charge-transfer state to a C60 excited triplet state. We demonstrate this to be the principal pathway from a combination of steady-state optoelectronic measurements, time-resolved electron paramagnetic resonance, and temperature-dependent transient absorption spectroscopy on model systems. BHT is a much more serious concern than ISC because it cannot be mitigated by improved exciton quenching, obtained for example by a finer BHJ morphology. As BHT is not specific to fullerenes, our results suggest that the role of electron and hole back transfer in the degradation of BHJs should also be carefully considered when designing stable OPV devices.

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