We experimentally studied the formation of CH-(A) radicals in butane seeded plasma generated with chirp-controlled ultrashort laser pulses (∼760 μJ/pulse, 890 nm, 1 kHz, 8 fs). The focused beam with high peak intensity (∼1014-1016 W/cm2) caused Coulomb explosion (CE). The time-dependent emission spectra were observed with the Fourier-transform Visible spectroscopy (FTVis) step-scan method. The average signal intensity decreased with the chirp in the Ar+ > C2 > H-α ∼ CH-(A) order, with a plateau for CH-(A) in the -200 to -100 fs2 range. The short rise time of the CH-(A) emission signal, the monoexponential emission decay and the nearly constant rotational and vibrational temperatures of the CH-(A) radicals (∼3000 and ∼3800 K) all support their potential formation as a primary product (<120 fs) or in other photodissociation, neutralization processes before collisions of the fragments (<2 ns). Our TDDFT calculations predict that CH and many other fragments can be formed beyond CE at ∼7 × 1014 W/cm2 intensity. The average charge of CH (+0.6) and its relative abundance (0.5%) support the formation of detectable CH-(A) within 120 fs. Suitable optical gating techniques and measurement of the temporal evolution of the electron density in plasma could elucidate the relative importance of the different formation pathways of the CH-(A) radicals in the first nanosecond after CE.

This chapter discusses the basis of magnetism in magnetic nanoparticles (MNPs), including the principal relaxation mechanisms (Néel and Brownian relaxation). A special emphasis is giving on the physical consequences of applying magnetic pulses, including the release of sound from formulations containing magnetic nanoparticles that can be utilized for triggered drug delivery.

Fragmentation dynamics in the Coulomb explosion of hydrocarbons, specifically methane, ethane, propane, and butane, are investigated using time-dependent density functional theory (TDDFT) simulations. The goal of this work is to elucidate the distribution of fragments generated under laser-driven Coulomb explosion conditions. Detailed analysis reveals the types of fragments formed, their respective charge states, and the optimal laser intensities required for achieving various fragmentations. Our results indicate distinct fragmentation patterns for each hydrocarbon, correlating with the molecular structure and ionization potential. Additionally, we identify the laser parameters that maximize fragmentation efficiency, providing valuable insights for experimental setups. This research advances our understanding of Coulomb explosion mechanisms and offers a foundation for further studies in controlled molecular fragmentation.

In this work, temperature dependent transient absorption spectroscopy measurements are presented on gallium-alloyed CdSe/ZnS core-shell nanoparticles between 30 and 130 degrees C. To our knowledge, temperature dependent measurements in these systems have been reported only in a few papers, although all processes related to carrier recombination are affected by temperature. For these experiments, gallium-alloyed CdSe/ZnS QD samples were used with nominal doping percentages of 2.5%, 7.5%, 15%. The experimental results show that the transient absorption decay is faster for the pristine CdSe/ZnS samples than in the gallium-alloyed samples at all temperatures. It is assumed that Ga-alloying promotes the formation of trions in the samples by introducing occupied impurity levels within the bandgap of CdSe. The resulting Coulomb blockade will, in turn, prolong the hot-electron relaxation process. By variation of the temperature, the distribution of charge carriers in the different recombination channels can be altered to accelerate recombination in the Ga-alloyed samples at higher temperatures. These measurements demonstrated their usefulness for observing the redistribution of charge carriers among different relaxation pathways.

2D transition metal dichalcogenides are an attractive family of materials in the field of electronics and optoelectronics. They are excellent candidates for sensitive photodetectors, light harvesting devices (photovoltaics, photocatalysts or photoelectrodes), lasers or non-linear optical devices. All these applications rely on light-matter interactions, which processes will ultimately decide the efficiency of the derived devices. Understanding carrier dynamics and the interaction of various exotic quasi-particles (excitons, trions) in these materials is of paramount importance to design better performing devices. Pump-probe transient absorption/reflection spectroscopy (TAS/TRS) is a powerful technique to study photophysical processes involved in charge carrier generation and recombination on the ultrafast timescale. In MoS2 photoelectrodes after light excitation different types of excitons are generated, and their decay can be monitored with these techniques. Coupling electrochemical techniques with these ultrafast methods, allows to probe the decay of the excited state in these materials under working conditions. In this manner the effect of trap state filling [1] or the effect of charge extraction [2] on the charge carrier dynamics of photoelectrochemical systems can be revealed. In my presentation I will show ultrafast spectroelectrochemical measurements on ITO/MoS2 photoelectrodes and reveal how the decay of excitons are influenced by the applied electrochemical bias. By comparing results from TAS/TRS spectroscopy the separation of carrier dynamics on the surface and bulk of these systems can be performed. These measurements reveal that the dissociation of excitons occurs at the ITO/MoS2 interface, resulting in a long living exciton population on the surface of these samples. Charging/discharging studies carried out in these systems reveal that the trap states involved in the dissociation of excitons in these systems can be permanently filled. The electrochemical filling of these trap states allows the tuning of the excited state lifetime of these systems, which can aid the better design of photoelectrochemical devices based on MoS2. References [1] ACS Energy Lett. 2019, 4, 3, 702–708 [2] J. Am. Chem. Soc. 2018, 140, 1, 86–89

We measured the exciton dynamics in van der Waals heterojunctions of transition metal dichalcogenides (TMDCs) and organic semiconductors (OSs). TMDCs and OSs are semiconducting materials with rich and highly diverse optical and electronic properties. Their heterostructures, exhibiting van der Waals bonding at their interfaces, can be utilized in the field of optoelectronics and photovoltaics. Two types of heterojunctions, MoS2-pentacene and WSe2-pentacene, were prepared by layer transfer of 20 nm pentacene thin films as well as MoS2 and WSe2 monolayer crystals onto Au surfaces. The samples were studied by means of transient absorption spectroscopy in the reflectance mode. We found that A-exciton decay by hole transfer from MoS2 to pentacene occurs with a characteristic time of 21 ± 3 ps. This is slow compared to previously reported hole transfer times of 6.7 ps in MoS2-pentacene junctions formed by vapor deposition of pentacene molecules onto MoS2 on SiO2. The B-exciton decay in WSe2 shows faster hole transfer rates for WSe2-pentacene heterojunctions, with a characteristic time of 7 ± 1 ps. The A-exciton in WSe2 also decays faster due to the presence of a pentacene overlayer; however, fitting the decay traces did not allow for the unambiguous assignment of the associated decay time. Our work provides important insights into excitonic dynamics in the growing field of TMDC-OS heterojunctions.

Affordable fossil-free ammonia synthesis will enable high-yield sustainable crop production for a growing world population while preserving the planet and making the best use of water and land. Simple technology amenable to intermittent operation using renewable energy will be made available through step catalysis activating dinitrogen at atmospheric pressure by nitride formation. Project objectives: (1) At the single particle level, quantify and analyze N2 activation by doped or alloyed manganese macroscopic- and nano particles at atmospheric pressure, (2) Quantify and analyze ammonia synthesis from doped or alloyed metal nitride particles when contacting them with hydrogen at atmospheric pressure, and (3) Integrate experimental data and atomic-level computational models to predict the behavior of metal alloys in nitrogen activation and subsequent ammonia synthesis.

The efficiency of terahertz (THz) pulse generation improves at longer driving wavelengths. For this reason, the use of mid-infrared (MIR) sources is more advantageous compared to visible or near-infrared systems. In this work, we investigate how single-color and two-color schemes of MIR pulses with few-cycle pulse durations compare in producing THz pulses. The results reveal that as the duration of the driving pulses decreases, the second harmonic generation crystal can be omitted from the system. Our numerical study pinpointed three regions where the optimal pulse parameters are fundamentally different for the most efficient THz pulse generation. The first is the two-color approach, where the two-color scheme is dominant at 3.2 optical cycles and over. The second is the single-color approach, where the single-color scheme becomes dominant at 1.7 optical cycles and below. Therefore, it simplifies the traditional two-color scheme for THz pulse generation. There is also a third transitional region where the two-color scheme still prevails, but the sign of the relative phase between the input pulses becomes important. Considering the effect of the relative phase and the carrier to envelope phase (CEP) effect on the THz pulse generation, the results have shown that as the pulse duration become shorter, the role of the CEP becomes important for efficient THz generation. By measuring the efficiency of the THz generation in this optical arrangement, quantifying the CEP becomes possible, which could become an important experimental tool for few-cycle, MIR laser technology.

The direct one-pot synthesis of γ-Fe2O3 nanoparticles (NPs) has been demonstrated through a facile inductive heating method.

The generation of terahertz pulses from two-color mid-infrared pulses is numerically investigated. The central wavelength of the fundamental laser pulse is varied from 2.15 µm up to 15.15 µm resulting the most efficient THz generation at 14.30 µm.

Dual-site models were constructed to represent manganese nitride (Mn4N)-supported Ni3 and Fe3 clusters for NH3 synthesis. Density functional theory calculations produced an energy barrier of approximately 0.55 eV for N-N bond activation at the interfacial nitrogen vacancy sites (Nv); also, the hydrogenation and removal of interfacial N is promoted by earth-abundant Ni and Fe metals. Steady-state microkinetic modeling revealed that the turnover frequencies of NH3 production follow an order of Fe3@Mn4N ≈ Ni3@Mn4N > Mn4N > Fe ≫ Ni. Moreover, we present clear evidence that, before NH3 formation, NH migrates from Nv onto the metallic sites. Using N binding energy (BEN) and the transition-state energy of N2 activation (ETS) as descriptors, we concluded that the beneficial effects owing to interfacial Nv sites are the most pronounced when BEN is either too strong or too weak while ETS is high; otherwise, excessive Nv sites may hinder catalyst performance.

Terahertz pulse generation from one- and two-color laser pulses in the mid-infrared spectral range are investigated numerically. The results show, that the one-color (two-color) method is more effective under (over) 1.5 optical cycles.

Microporation techniques facilitate the passive transport of molecules into cells via mechanical, electrical, or magnetic simulation. In this work, a combinatorial microporation technique is demonstrated utilizing small superparamagnetic particles and inhomogeneous magnetic pulses. This microporation technique is applied to facilitate the transport of a model therapeutic agent (doxorubicin) into the U937 cancer cell line. This work demonstrates that the drug transport of doxorubicin to the U-937 cancer line increases by 75% when the cells are exposed to only a few inhomogeneous magnetic pulses. The increased transport resulted in more effective destruction of the cancer cells demonstrating that the technique can be utilized to increase the effectiveness of common cancer drugs. The results also demonstrate that the presence of the magnetic particles or the presence of the magnetic fields does not show significant effect on cell viability in the presence of cancer drugs.

Inductive heating synthesis is an emerging technique with the potential to displace the hot-injection synthesis method to prepare colloidal particles very rapidly with a narrow size distribution, controlled size, and high crystallinity. In this work, the inductive heating synthesis is applied to produce a short-temperature jump to mimic conditions like the hot-injection method to prepare traditional iron and iron oxide nanoparticles (IONPs) in the 3-11 nm size range within various solvents, precursors, and reaction time conditions. Moreover, this inductive heating technique can be used under unique experimental conditions not available for hot-injection reactions. These conditions include the use of very high initial monomer concentrations. Considering benefits over conventional methods, the inductive heating technique has the potential to provide an industrial level scale-up synthesis. The magnetization of these particles is consistent with the magnetization of the particles from the literature.

Manganese (Mn) nitrides are important nitrogen (N) carriers for small-scale intermittent ammonia (NH3) synthesis. However, only 3 similar to 8 % of lattice N are converted into NH3. In this study, the geometric and electronic structures of well-defined Mn4N and Mn2N lattices were altered using transition metal heteroatoms (Cr, Fe, Co, Ni, Mo) to understand the driving force behind lattice N diffusion and extraction. Density Functional Theory (DFT) revealed that the binding of early hydrogenation product (NH) follows a linear relationship with lattice N over a wide range of close-packed surfaces. But, the binding of NH2 and NH3 are more sensitive to the geometric and electronic structures. Further, the chemical bonding can be quantitatively characterized with the covalency derived from Crystal Orbital Hamiltonian Population (COHP). In the Eley Rideal-Mars van Krevelan pathway, the overall NH3 formation free energy (Delta GNH3 ) and lattice N diffusion barrier (Ea ) are the respective thermodynamic and kinetic determining factors. Aided by a rate-determining step (RDS) model, Mn4N modified with Fe, Co, Ni single-atom dopants all show enhanced rates for NH3 formation.

Broadband terahertz radiation can be efficiently produced by mixing laser pulses of different colors in the mid-infrared (MIR) and longwave-infrared (LWIR) spectral region. In this paper, we report on a numerical investigation of ultrashort terahertz pulse generation from plasmas created in nitrogen gas by two-color laser pulses with the fundamental laser pulse wavelength between 2.15 and 15.15 µm, in order to explore the efficiency of the terahertz pulse generation process. The results show that the electron acceleration efficiency increases monotonically with the fundamental laser pulse wavelength. The most intense terahertz pulse generation is observed at 12.30 µm with four optical-cycle laser pulses with 2.5 GW peak power. The results show that the terahertz pulse generation with a MIR laser is one order of magnitude and with a LWIR laser is two orders of magnitude more efficient than the terahertz pulse generation with Ti:Sapphire lasers using the exact same pulse parameters. The terahertz pulse generation efficiency is also known to be very sensitive to the relative phase between the components of the two-color laser pulses. One of the most useful tools to control the relative phase and optimize the terahertz pulse intensity is thin dielectric plates. It has been shown that alkaline halides and alkaline earth halides have suitable optical properties for the relative phase control for efficient terahertz pulse generation in the MIR spectral range.

Magnetic nanoparticle-assisted drug release from liposomes is an important way to enhance the functionality/usefulness of liposomes. This work demonstrates an approach how to integrate magnetic nanoparticles with liposomes with the assistance of gold–thiol chemistry. The gold coated magnetic particles cover the thiolated liposomes from the outside, which removes the competition of the drug molecules and the triggering magnetic particles to free the inner space of the liposomes when compared to previous magneto liposome formulations. The liposome consists of dipalmitoyl phosphatidylcholine (DPPC) combined with distearoylphosphatidylcholine (DSPC) in addition to regular cholesterol or cholesterol-PEG-SH. Permeability assays and electron microscopy images show efficient coupling between the liposomes and nanoparticles in the presence of thiol groups without compromising the functionality of the liposomes. The nanoparticles such as gold nanoparticles, gold coated iron oxide nanoparticles and bare iron oxide nanoparticles are added following the model drug encapsulation. The efficient coupling between the gold coated nanoparticles (NPs) and the thiolate liposomes is evidenced by the shift in transition temperature of the thiolated liposomes. The addition of magnetically triggerable nanoparticles externally makes the entire interior of liposomes available for drug loading. The drug release efficiencies of these liposomes/NPs complexes were compared under exposure to pulsed magnetic fields. The results indicate up to 20% of the drug can be released in short time, which is comparable in efficiency to previous studies performed when magnetic NPs were located inside liposomes. Interestingly, the liposomes were found to exhibit variations in release efficiency based on different dilution media which is attributed to an osmotic pressure effect on liposomal stability.

In this publication, the generation of terahertz pulses from two-color mid-infrared pulses is investigated in ambient air by numerical simulations. In these simulations, the central wavelength of the fundamental laser pulse is varied from 1.6 µm up to 10 µm. As expected, the results show that the ionization efficiency decreases at longer wavelengths, while the electron acceleration efficiency increases, resulting the highest THz pulse generation around 8.2-8.5 µm. At the 8.2-8.5 µm the generated THz electric field peak intensity is hundred times more compared to the Ti:Sapphire lasers, which are the most commonly used lasers for this type of THz generation. We show that optimal phase control between the second harmonics and the fundamental pulse can be achieved with the help of thin plates of barium, calcium and lithium fluorides.