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Nano Letters Jun 2024Upon the interaction of light with metals, nonthermal electrons are generated with intriguing transient behavior. Here, we present femtosecond hot electron probing in a...
Upon the interaction of light with metals, nonthermal electrons are generated with intriguing transient behavior. Here, we present femtosecond hot electron probing in a noveloptical pump/plasmon probe scheme. With this, we probed ultrafast interband and intraband dynamics with 15 nm interface selectivity, observing a two-component-decay of hot electron populations. Results are in good agreement with a three-temperature model of the metal; thus, we could attribute the fast (∼100 fs) decay to the thermalization of hot electrons and the slow (picosecond) decay to electron-lattice thermalization. Moreover, we could modulate the transmission of our plasmonic channel with ∼40% depth, hinting at the possibility of ultrafast information processing applications with plasmonic signals.
PubMed: 38833525
DOI: 10.1021/acs.nanolett.4c01669 -
Nanoscale Jun 2024Understanding molecular film growth on substrates and the ultrafast electron dynamics at their interface is crucial for advancing next-generation organic electronics. We...
Understanding molecular film growth on substrates and the ultrafast electron dynamics at their interface is crucial for advancing next-generation organic electronics. We have focused on studying the ultrafast photoexcited electron dynamics in nanoscale organic crystals of an aromatic molecule, pentacene, on a two-dimensional material of graphite substrate. Through the use of time-resolved two-photon photoelectron emission microscopy (2P-PEEM), we have visualized the ultrafast lateral evolution of photoexcited electrons. By resonantly tuning the incident photon to excite pentacene molecules, polarization-dependent 2P-PEEM has revealed that pentacene nanocrystals (sub- to several μm) on the substrate exhibit a preferential orientation, in which a molecular π-orbital contacts the substrate in a "lying flat" orientation, facilitating electron transfer to the substrate. The time-resolved 2P-PEEM captures the motion of excited electrons in a femto- to pico-second timescale, clearly imaging the ultrafast charge transfer and lateral expansion two-dimensionally on the graphite substrate. Moreover, we found that the lying-flat molecular orientation of pentacene nanocrystals is transformable into a "standing-up" one through gentle heating up to 50 °C. These experimental insights using time-resolved 2P-PEEM will be highly valuable in enhancing the photofunctionalities of organic electronic devices by controlled molecular deposition.
PubMed: 38832543
DOI: 10.1039/d4nr00720d -
Scientific Reports Jun 2024The silicon suboxide SiOx (x < 2.0) offers promising industrial application possibilities ranging from electrodes in lithium-ion batteries, which are used widely in...
The silicon suboxide SiOx (x < 2.0) offers promising industrial application possibilities ranging from electrodes in lithium-ion batteries, which are used widely in electrical vehicles and portable devices to sensing applications. Therefore, a low cost, environmental friendly and high performance silicon oxide materials are required for an appropriate operation of any electronic gadget. In this work, we report on the physical and electrical properties of a suboxide layer of up to 1 μm, which was grown on silicon during the formation of a dielectric layer, namely the ammonium silicon hexafluoride. It is a stable oxide exhibiting light emission from 400 to 1700 nm offering scalable and cost-effective large area processing capability. The measurement results reveal interesting properties, which are required to be understood clearly before proceeding with any suitable application. The results have been analyzed using state-of-the-art physical and electrical characterization techniques such as ellipsometry, AFM, SEM, FTIR, photoluminescence lifetime and resistive switching measurements to determine structural, optical and electrical properties. At 300 K the carrier lifetime measurements reveal the lifetime values ranging from about few tens of picosecond up to 4500 picoseconds. Scanning probe analysis indicate a surface roughness of about 30 Å. Resistive memory forming was observed also in these layers at relatively low power thresholds. We provide a comprehensive description of the physical and electrical properties in order to clarify the origin of the observed features. The wavelength dependent real and the imaginary dielectric functions provided useful insights on optical properties. A lookout is given for the possible applications of this special SiOx dielectric oxide layer.
PubMed: 38830980
DOI: 10.1038/s41598-024-63377-1 -
Physical Chemistry Chemical Physics :... Jun 2024Bridged triarylamines, so-called N-heterotriangulenes (N-HTAs) are promising organic semiconductors for applications in optoelectronic devices. Thereby the electronic...
Bridged triarylamines, so-called N-heterotriangulenes (N-HTAs) are promising organic semiconductors for applications in optoelectronic devices. Thereby the electronic structure at organic/metal interfaces and within thin films as well as the electronically excited states dynamics after optical excitation is essential for the performance of organic-molecule-based devices. Here, we investigated the energy level alignment and the excited state dynamics of a N-HTA derivative adsorbed on Au(111) by means of energy- and time-resolved two-photon photoemission spectroscopy. We quantitatively determined the energetic positions of several occupied and unoccupied molecular (transport levels) and excitonic states (optical gap) in detail. A transport gap of 3.20 eV and an optical gap of 2.58 eV is determined, resulting in an exciton binding energy of 0.62 eV. With the first time-resolved investigation on a N-HTA compound we gained insights into the exciton dynamics and resolved processes on the femtosecond to picosecond timescale.
PubMed: 38819930
DOI: 10.1039/d4cp01713g -
The Journal of Craniofacial Surgery May 2024This study aims to evaluate the use of 755-nm picosecond alexandrite laser with a focus lens array to treat facial pores.
OBJECTIVES
This study aims to evaluate the use of 755-nm picosecond alexandrite laser with a focus lens array to treat facial pores.
METHODS
Laser treatment was performed on 129 patients between January 2021 and October 2022. VISIA imaging system was used for photographic assessments, the total average number and pore index was calculated, the physicians' assessment score and patient satisfaction score were collected, and the incidence of disadvantage effects was also documented.
RESULTS
The mean patient age was 35.2±6.4 years (21-45 y). The total average number of facial pores was 1614.1±412.8, and the total average number decreased to 1262.6±356.2 three months after the last treatment. The pretreatment baseline of pore index was 26.1±4.5, while the pore index was 21.3±3.7 three months after the last treatment. The physicians' assessment score was 2.7 on the 0-to-4 scale, and patient satisfaction score was 3.5 on the 1-to-5 scale. There were no adverse events, such as hyperkeratosis, scarring, and hypo-or hyperpigmentation.
CONCLUSIONS
755-nm picosecond alexandrite laser with a focus lens array was safe and effective in the treatment of facial pores with relatively few unanticipated adverse events.
LEVEL OF EVIDENCE
Level IV-observational study without controls.
PubMed: 38819149
DOI: 10.1097/SCS.0000000000010379 -
Journal of Cosmetic Dermatology May 2024
PubMed: 38813826
DOI: 10.1111/jocd.16416 -
Chemphyschem : a European Journal of... May 2024Vibrational-mode-selective modulation of electronic excitation is conducted with a synchronized femtosecond (fs) visible (vis) pulse and a picosecond (ps) infrared (IR)...
Vibrational-mode-selective modulation of electronic excitation is conducted with a synchronized femtosecond (fs) visible (vis) pulse and a picosecond (ps) infrared (IR) pulse. The mechanism of modulation of vibrational and vibronic relaxation behavior of excited state is investigated with ultrafast vis/IR, IR/IR, and vis-IR/IR transient spectroscopy, optical gating experiments and theoretical calculations. An organic molecule, 4'-(N,N-dimethylamino)-3-methoxyflavone (DMA3MHF) is chosen as the model system. Upon 1608 cm-1 excitation, the skeleton stretching vibration of DMA3MHF is energized, which can significantly increase the Franck-Condon factor for electronic transition, facilitate the radiative decay and promote emission from vibrational excited states. As results, a remarkable enhancement and a slight blueshift in fluorescence are observed. The mode-selective modulation of electronic excitation is not limited in luminescence or photophysics. It is expected to be widely applicable in tuning many photochemical processes.
PubMed: 38807346
DOI: 10.1002/cphc.202400335 -
Chemistry (Weinheim An Der Bergstrasse,... May 2024Urea is believed to have been essential to the synthesis of prebiotic nucleotides and thereby the RNA or DNA of the first lifeforms. Models suggesting that life began in...
Urea is believed to have been essential to the synthesis of prebiotic nucleotides and thereby the RNA or DNA of the first lifeforms. Models suggesting that life began in wet-dry cycles around shallow aquatic ponds imply that reactants such as urea were exposed to deep ultraviolet irradiation from the young sun. Detrimental photodissociation of urea induced by deep UV excitation potentially challenges these models. We here follow the primary deep ultraviolet photochemistry of aqueous urea. The data show that urea is barely excited at 200 nm due to weak ultraviolet absorption. The likelihood of photodissociation is further reduced by strong intra-molecular coupling of the CN and CO stretch vibrations accompanied by an efficient dissipation of the excitation energy to the surrounding water molecules mitigated by urea-water hydrogen bonds. We find that 54±5 % of the excited urea molecules dissociate. Reactions between the photoproducts and surrounding solvent molecules form carbamic acid or the carbamate anions within 0.6 ps. The molecules that do not dissociate return to the electronic ground state in 2 ps. Interestingly, the photodissociation processes of urea in the aqueous phase is different from earlier reported reactions observed following the VUV photolysis of urea in noble gas matrices and highlight the potential influence of water on the prebiotic photochemistry.
PubMed: 38804868
DOI: 10.1002/chem.202400728 -
ChemPlusChem May 2024Ultrafast spectroscopy can be used to study dynamic processes on femtosecond to nanosecond timescales, but is typically used for photoinduced processes. Several...
Ultrafast spectroscopy can be used to study dynamic processes on femtosecond to nanosecond timescales, but is typically used for photoinduced processes. Several materials can induce ultrafast temperature rises upon absorption of femtosecond laser pulses, in principle allowing to study thermally activated processes, such as (catalytic) reactions, phase transitions, and conformational changes. Gold-silica core-shell nanoparticles are particularly interesting for this, as they can be used in a wide range of media and are chemically inert. Here we computationally model the temporal and spatial temperature profiles of gold nanoparticles with and without silica shell in liquid and gas media. Fast rises in temperature within tens of picoseconds are always observed. This is fast enough to study many of the aforementioned processes. We also validate our results experimentally using a poly(urethane-urea) exhibiting a temperature-dependent hydrogen bonding network, which shows local temperatures above 90 ◦C are reached on this timescale. Moreover, this experimentally shows the hydrogen bond breaking in such polymers occurs within tens of picoseconds.
PubMed: 38804190
DOI: 10.1002/cplu.202400134 -
Photochemistry and Photobiology May 2024Light emission from organoboron compounds of Schiff bases is found to depend strongly on their chemical structure. Two of these compounds (OB1 and OB2), which contain a...
Light emission from organoboron compounds of Schiff bases is found to depend strongly on their chemical structure. Two of these compounds (OB1 and OB2), which contain a benzene ring between the Schiff base moieties, exhibit weak fluorescence in methanol, with marked viscosity dependence. Fluorescence lifetimes of these compounds are in picosecond timescale, as determined by femtosecond optical gating (FOG). A significant enhancement in fluorescence intensity and lifetime is observed at 77 K, indicating the operation of an activated nonradiative process. Using fluorescence lifetime imaging microscopy (FLIM), OB1 and OB2 are shown to be potential membrane probes. The third (OB3), which is devoid of this benzene ring, exhibits relatively stronger fluorescence with nanosecond lifetimes at room temperature. No viscosity dependence is observed in this case. The emission spectrum at 77 K is markedly more intense and exhibits an additional red shifted structured feature, which persists for a few seconds. Hence, OB3 seems to have greater promise not only as fluorescent probe but also for light harvesting. The marked improvement of the light emission properties of OB3 compared with OB1 and OB2 is likely to serve as a pointer for the design of Schiff base-derived organoboron luminophores with diverse potential applications.
PubMed: 38801138
DOI: 10.1111/php.13965