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Fraction of Rare-Earth (Sm/Nd)-Lanthanum Ferrite-Based Perovskite Ferroelectric and Magnetic Nanopowders
摘要： Multiferroic compound, especially LaFeO3-based perovskite nanopowders that exhibit robust simultaneous ferromagnetism and ferroelectricity, are widely investigated and applied in different applications. In this work, we report the synthesis and characterization pertaining to fraction of rare-earth (Sm/Nd)-substituted lanthanum ferrite based perovskite nanopowders via solid-state technique. The multiferroic phenomenon is the fundamental approach to combine both the ferromagnetic and ferroelectric properties in a single system. Reduction in crystallite size, as well as some lattice distortion effects, are included to show the possibilities of tuning the lattice structure, electrical, optical as well as the magnetic properties which are closely connected to the ferroelectric behavior and magnetism. At room temperature, the ferroelectric behavior of La0.9(Sm/Nd)0.1FeO3 exhibiting a P-E hysteresis loop became more and more pronounced, indicating the electrical leakage is greatly reduced. The canted antiferromagnetic hysteresis loop shows that the rare-earth (Sm/Nd) ion can significantly affect the magnetic parameters of the materials.
关键词： Lanthanum ferrite,x-ray diffraction,optical and magnetic properties,solid-state reaction,ferroelectric,UV–Vis spectroscopy
更新于2025-09-23 15:23:52
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Metal-Organic Frameworks as Hosts for Fluorinated Azobenzenes: A Path Towards Quantitative Photoswitching with Visible Light
摘要： Fifteen new photochromic hybrid materials were synthesized by gas phase loading of fluorinated azobenzenes, namely ortho-tetrafluoroazobenzene (tF-AZB), 4H,4H'-octafluoroazobenzene (oF-AZB), and perfluoroazobenzene (pF-AZB), into the pores of the well-known metal-organic frameworks MOF-5, MIL-53(Al), MIL-53(Ga), MIL-68(Ga), and MIL-68(In). Their composition was analysed by elemental (CHNS) and DSC/TGA analysis. For pF-AZB0.34@MIL-53(Al) a structural model based on high-resolution synchrotron powder diffraction data was developed and the host-guest and guest-guest interactions were elucidated from this model. These interactions of O-H…F and π…π type were confirmed by significant shifts of the O-H frequencies in loaded and unloaded MOFs of the MIL-53 and MIL-68 series. Most remarkably, all of the synthesized F-AZB@MOF systems can be switched with visible light and some of them show almost quantitative (> 95 %) photo-isomerization between its E and Z forms with no significant fatigue after repeated switching cycles.
关键词： azobenzene,fluorinated derivatives,solid state switching,metal-organic frameworks,photochromism
更新于2025-09-23 15:23:52
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Gain and noise in GaAs/AlGaAs avalanche photodiodes with thin multiplication regions
摘要： Avalanche photodiodes based on GaAs/AlGaAs with separated absorption and multiplication regions (SAM-APDs) will be discussed in terms of capacitance, response to light (gain and noise) and time response. The structures have been fabricated by molecular beam epitaxy introducing a δ p layer doped with carbon to separate the multiplication and the absorption regions. The thickness of the latter layer defines the detection efficiency and the time resolution of the structure, which in turn allows tailoring the device for specific scientific applications. Within the multiplication region a periodic modulation of the bandgap is obtained by growing alternating nanometric layers of AlGaAs and GaAs with increasing Al content; this staircase structure enables the tuning of the bandgap and subsequently provides a well-defined charge multiplication. The use of such staircase hetero-junctions enhances electron multiplication and conversely reduces — at least in principle — the impact of the noise associated to hole multiplication, which should result in a decreased overall noise, when compared to p-i-n diodes composed by a single material. The first part of this paper focuses on the electrical characteristics of the grown structure and on the comparison with the simulated behaviour of such devices. In addition, gain and noise measurements, which have been carried out on these devices by utilizing photons from visible light to hard X-rays, will be discussed and will be compared to the results of a nonlocal history-dependent model specifically developed for staircase APDs.
关键词： X-ray detectors,Solid state detectors,Avalanche-induced secondary effects
更新于2025-09-23 15:23:52
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Exploration of structural, vibrational and spectroscopic properties of self-activated orthorhombic double molybdate RbEu(MoO4)2 with isolated MoO4 units
摘要： RbEu(MoO4)2 is synthesized by the two-step solid state reaction method. The crystal structure of RbEu(MoO4)2 is defined by Rietveld analysis in space group Pbcn with cell parameters a=5.13502(5), b=18.8581(2) and c=8.12849(7) ?, V=787.13(1) ?3, Z=4 (RB=0.86%). This molybdate possesses its phase transition at 817 K and melts at 1250K. The Raman spectra were measured with the excitation at l =1064 and 514.5nm. The photoluminescence spectrum is evaluated under the excitation at 514.5nm. The absolute domination of hypersensitive 5D0(cid:1)7F2 transition is observed. The ultranarrow 5D0(cid:1)7F0 transition in RbEu(MoO4)2 is positioned at 580.2nm being 0.2nm blue shifted, with respect to that in Eu2(MoO4)3.
关键词： Rietveld refinement,rubidium europium molybdate,Raman luminescence,solid state reaction,DSC
更新于2025-09-23 15:23:52
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Shock synthesis of Sr2Si5N8:Eu2+ phosphor
摘要： A new approach to synthesise the red-emitting nitridosilicate phosphor Sr2Si5N8:Eu2+ using shock waves is described. The solid state reaction of a mixture of Si3N4, Sr3N2 and EuN was induced using a detonation-driven shock wave apparatus. The obtained products consist of Sr2Si5N8:Eu2+ with a purity of 80–89 %, containing 7–9 % of SrSi7N10 and 4–11 % α-Si3N4, according to Rietveld analyses. Crystallites with sizes of 240–310 nm are formed, yielding particles of 2–3 μm grain size. The luminescence properties are similar to conventionally produced Sr2Si5N8:Eu2+ phosphors.
关键词： High-pressure,Phosphors,Luminescence,Solid state reaction
更新于2025-09-23 15:23:52
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Assignment of NMR resonances of protons covalently bound to photochemically active cofactors in photosynthetic reaction centers by 13C–1H photo-CIDNP MAS-J-HMQC experiment
摘要： Modified versions of through-bond heteronuclear correlation (HETCOR) experiments are presented to take advantage of the light-induced hyperpolarization that occurs on 13C nuclei due to the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect. Such 13C–1H photo-CIDNP MAS-J-HMQC and photo-CIDNP MAS-J-HSQC experiments are applied to acquire the 2D 13C–1H correlation spectra of selectively 13C-labeled photochemically active cofactors in the frozen quinone-blocked photosynthetic reaction center (RC) of the purple bacterium Rhodobacter (R.) sphaeroides wild-type (WT). Resulting spectra contain no correlation peaks arising from the protein backbone, which greatly simplifies the assignment of aliphatic region. Based on the photo-CIDNP MAS-J-HMQC NMR experiment, we obtained assignment of selective 1H NMR resonances of the cofactors involved in the electron transfer process in the RC and compared them with values theoretically predicted by density functional theory (DFT) calculation as well as with the chemical shifts obtained from monomeric cofactors in the solution. We also compared proton chemical shifts obtained by photo-CIDNP MAS-J-HMQC experiment under continuous illumination with the ones obtained in dark by classical cross-polarization (CP) HETCOR. We expect that the proposed approach will become a method of choice for obtaining 1H chemical shift maps of the active cofactors in photosynthetic RCs and will aid the interpretation of heteronuclear spin-torch experiments.
关键词： MAS-J-HSQC,Solid-state photo-CIDNP,HETCOR,MAS-J-HMQC,Bacterial reaction center
更新于2025-09-23 15:23:52
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The efficient photodesorption of nitric oxide (NO) ices
摘要： The study and quantification of UV photon-induced desorption of frozen molecules furthers our understanding of the chemical evolution of cold interstellar regions. Nitric oxide (NO) is an important intermediate species in both gas-phase and solid-phase chemical networks. In this work, we present quantitative measurements of the photodesorption of a pure NO ice. We used the tunable monochromatic synchrotron light of the DESIRS beamline of the SOLEIL facility near Paris to irradiate NO ices in the 6–13.6 eV range and measured desorption by quadrupole mass spectrometry. We find that NO photodesorption is very efficient, its yield being around 10?2 molecule per incident photon for UV fields relevant to the diffuse and dense interstellar medium. We discuss the extrapolation of our results to an astrophysical context and we compare photodesorption of NO to previously studied molecules.
关键词： methods: laboratory: solid state,ISM: abundances,ultraviolet: ISM,astrochemistry,ISM: molecules,molecular processes
更新于2025-09-23 15:23:52
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Controlling the emission and absorption spectrum of a quantum emitter in a dynamic environment
摘要： We study the emission spectrum and absorption spectrum of a quantum emitter when it is driven by various pulse sequences. We consider the Uhrig sequence of nonequidistant πx pulses, the periodic sequence of πxπy pulses and the periodic sequence of πz pulses (phase kicks). We find that, similar to the periodic sequence of πx pulses, the Uhrig sequence of πx pulses has emission and absorption that are, with small variations, analogous to those of the resonance fluorescence spectrum. In addition, while the periodic sequence of πz pulses produces a spectrum that is dependent on the detuning between the emitter and the pulse carrier frequency, the Uhrig sequence of nonequidistant πx pulses and the periodic sequence of πxπy pulses have spectra with little dependence on the detuning as long as it stays moderate along with the number of pulses. This implies that they can also, similar to the previously studied periodic sequence of πx pulses, be used to tune the emission or absorption of quantum emitters to specific frequencies, to mitigate inhomogeneous broadening and to enhance the production of indistinguishable photons from emitters in the solid state.
关键词： spectral diffusion,emission/absorption spectrum,solid state emitter,pulse-driven emitter
更新于2025-09-23 15:23:52
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Experimental performance of a highly-innovative low-noise charge-sensitive preamplifier with integrated range-booster
摘要： Integrated charge-sensitive preamplifiers suffer from a reduced available dynamic range respect to discrete-type equivalents. This is due to the limits on maximum supply voltages that modern scaled technologies can tolerate. In this work we present a low-noise low-power integrated charge-sensitive preamplifier (CSP) for solid-state detectors. This device is equipped with an integrated range-booster that can enhance the spectroscopic range of the preamplifier by more than one order of magnitude, enabling high-resolution spectroscopy even if the preamplifier is in deep saturation condition. If the input signals from the detector are under the natural saturation threshold (40 MeV), the preamplifier works in an usual linear way, producing at the output the typical exponential signals. With proper filtering a resolution of approximately 1 keV is achievable. When a large signal from the detector saturates the preamplifier, a sensing circuit detects the saturation and switches the operation mode of the CSP to the “fast-reset mode”. In this mode a constant and controlled current generator discharges the input node of the preamplifier until the normal operating point is reached. Meanwhile an auxiliary circuit similar to a TAC (Time-to-Amplitude converter) retrieves the energy of the signal that caused saturation. Although the natural dynamic range of the CSP is 40 MeV, the fast-reset mode enables for high-resolution spectroscopy (under 0.2% FWHM) up to several hundreds of MeV (700 MeV typically). One issue in this kind of circuits is the dependence of the energy measured with the TAC circuit on the baseline value of the CSP before the “fast-reset event” [5]. As a solution to this problem we propose a correction algorithm implemented inside the TAC block in the form of an analog circuit. On a test-bench a series of large 3 pC charge signals is injected in the input node of the preamplifier through a test capacitor. Before these events, residual charges ranging from 0 to 0.56 pC produce non-zero baseline voltages at the output of the CSP. The TAC with correction not only retrieves correctly the energy of the main event, but also rejects the baseline voltages, leaving the energy measurement unaffected. The fluctuations of the flat-top voltage in the signals produced by the auxiliary TAC circuit due to the different baseline voltages are under the 0.6% of the total signal amplitude.
关键词： Front-end electronics for detector readout,VLSI circuits,Analogue electronic circuits,Electronic detector readout concepts (solid-state)
更新于2025-09-23 15:23:52
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Achievable noise performance of spectroscopic prototype DEPFET detectors
摘要： A new generation of spectroscopic X-ray DEPFET detectors has been produced in the course of the detector development for the Wide Field Imager (WFI) of Athena. These devices served to perform a detailed analysis of the noise composition, which was enabled by the development of appropriate test algorithms. A result of the analysis is the distinction of different components, which sum up to the total noise. In particular the contribution of shot noise, white noise and 1/f noise to the readout noise is determined as well as the signal noise caused by the generation of charge carriers. The resulting parametrization enables the adaptation and optimization of operation modes to given purposes. The studied prototype detectors included 64×64 pixels with a linear gate design and provided an excellent noise, below 1.6 e?ENC at a readout time faster than 10 μs/pixel and a temperature of -80 ?C in rolling-shutter operation. This performance is enabled by an extended signal integration time. A further noise reduction is prevented by the signal noise, caused by charge carrier generation. In order to demonstrate the low noise properties of the DEPFET transistor, the measurement conditions were adapted and a noise of 0.95 e?ENC was measured at the expense of the sensor size — by operating only parts of the sensor in window mode — and dynamic range — by using the Al Kα line at about 1.49 keV for calibration.
关键词： Imaging spectroscopy,Solid state detectors,Instrumental noise,X-ray detectors and telescopes
更新于2025-09-23 15:23:52