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In this paper, we consider a class of k-order (3 ≤ k ≤ 5) backward differentiation formulas (BDF-k) for the molecular beam epitaxial (MBE) model without slope selection. Convex splitting technique along with k-th order Douglas-Dupont regularization term τ n k (− Δ) k D _ k ϕ n ( D _ k represents a truncated BDF-k formula) is added to the numerical schemes to ensure unconditional energy stability. The stabilized convex splitting BDF-k (3 ≤ k ≤ 5) methods are unique solvable unconditionally. Then the modified discrete energy dissipation laws are established by using the discrete gradient structures of BDF-k (3 ≤ k ≤ 5) formulas and processing k-th order explicit extrapolations of the concave term. In addition, based on the discrete energy technique, the L 2 norm stability and convergence of the stabilized BDF-k (3 ≤ k ≤ 5) schemes are obtained by means of the discrete orthogonal convolution kernels and the convolution type Young inequalities. Numerical results are carried out to verify our theory and illustrate the validity of the proposed schemes. [ABSTRACT FROM AUTHOR]

At the CERN-ISOLDE radioactive ion beam facility, thick targets are irradiated using a beam of 1.4-GeV protons. One of ISOLDE's key features is the large choice of ion source types and target materials available, enabling us to select the ideal combination for optimal intensity and purity of the isotopes requested by ISOLDE users. The ever-increasing demands in terms of isotope production yield, beam purity, and overall reliability of the employed systems are driving the continuous development efforts. Over the past few years, CERN has invested heavily in facilities and infrastructure that facilitate ongoing developments required for ISOLDE. A dedicated offline laboratory (Offline 2) has been recently equipped with high repetition rate nanosecond tunable lasers required for scheme development and developments of specialized laser ion source types such as VADLIS, LIST and PI-LIST. Moreover, it hosts a twin setup of the ISOLDE RFQ cooler and buncher (ISCOOL), which is envisaged to be used for studies of molecular beam creation and breakup, as well as the development of improved RFQ services and operational modes. For material development, particularly for nanostructured materials, the new nano laboratory has just been commissioned and will enable the production and development of nano actinide targets for ISOLDE. In this contribution we describe the infrastructure required for target and ion source developments, highlight recent efforts and experimental results on both target material development and ion source development, and provide an outlook on what to expect in the near future. [ABSTRACT FROM AUTHOR]

ISOLDE's Offline 2 laboratory has been upgraded to facilitate development for the production and study of molecular ion beams. New gas injection systems have been implemented for both molecular formation in the ion source and in the radio-frequency quadrupole ion trap used for beam preparation. MagneToF detectors and time-resolved single ion counting data acquisition have been implemented for low intensity beams and studies of laser-atom or laser-molecule interactions. We present a study of the formation and ionization of BaF + using the upgraded facility. • ISOLDE's Offline 2 mass separator facility has been upgraded for studies of molecular ion beams. • High-power laser light interacts with molecules to ionize and dissociate. • Barium and barium fluoride ions are ionized using laser light at 355 nm. [ABSTRACT FROM AUTHOR]

The use of radioactive molecules for fundamental physics research is a developing interdisciplinary field limited dominantly by their scarce availability. In this work, radioactive molecular ion beams containing actinide nuclei extracted from uranium carbide targets are produced via the Isotope Separation On-Line technique at the CERN-ISOLDE facility. Two methods of molecular beam production are studied: extraction of molecular ion beams from the ion source, and formation of molecular ions from the mass-separated ion beam in a gas-filled radio-frequency quadrupole ion trap. Ion currents of U + , UO 1−3 +, UC 1−3 +, UF 1−4 +, UF 1,2 O 1,2 + are reported. Metastable tantalum and uranium fluoride molecular ions are identified. Formation of UO 1−3 +, U(OH) 1−3 +, UC 1−3 +, UF 1,2 O 1,2 + from mass-separated beams of U + , UF 1,2 + with residual gas is observed in the ion trap. The effect of trapping time on molecular formation is presented. [ABSTRACT FROM AUTHOR]

Linear gas stopping cells have been used for nearly two decades to slow down projectile fragments at the National Superconducting Cyclotron Laboratory, now the Facility for Rare Isotope Beams, for experiments with low-energy and reaccelerated beams. In order to efficiently stop and rapidly extract light to medium-mass fast ions, a cyclotron gas-stopper has been constructed. It uses a cyclotron-type magnet and a helium-gas filled stopping chamber to slow down the injected beam. RF ion guides transport the stopped ions to the center of the magnet and axially through the bore before acceleration to < 60 keV. Following successful offline tests, the cyclotron stopper was moved to an experimental vault and connected to a new momentum–compression beam line. Beam transport to and into the cyclotron stopper was tested with stable beams. Using 46K fragments, the first successful stopping and extraction of a high-energy beam with the cyclotron stopper was demonstrated. [ABSTRACT FROM AUTHOR]

The under-construction FRIB-EDM 3 -instrument was designed to study polar radioactive molecules (such as RaF) in transparent cryogenic solids by laser spectroscopy. The instrument is divided into a frontend- and a backend section. The frontend accepts an aqueous sample from isotope harvesting and provides a mass-separated molecular ion beam in an ultra-high vacuum environment. In the backend, the ions are guided into alkali-metal vapor and the resulting neutrals are co-deposited in a solid argon matrix to perform laser spectroscopy. This work addresses the frontend of the instrument. The efficient ionization of harvested radioisotopes from aqueous samples is achieved with a spray-ionization method. Subsequently, the molecular ion beam is analyzed by mass-to-charge ratio by a quadrupole mass filter. To verify the feasibility of the approach, numerical simulations with the COMSOL and SIMION packages have been conducted. While the former was applied to study transport in ion funnels, the latter was used to investigate ion beam transmission through the lower pressure sections. Following promising simulation results, a first experimental setup is under construction. [ABSTRACT FROM AUTHOR]

• Influence of Sb/Se ratio of Sb 2 Se 3 films were investigated. • Sb 2 Se 3 films with different compositions fabricated by CMBD method from separate sources of Sb and Se. • The Se content in the solid phase is directly proportional to the Se content in the vapour phase during the growth process. • Sb 2 Se 3 thin films with micro-sized crystal grains exhibit (hk 1) preferential orientation at the stoichiometric composition. Sb x Se y thin-films were obtained by chemical-molecular beam deposition (CMBD) on soda-lime glass from Sb and Se precursors. By the precise control of the Sb/Se ratio, Sb 2 Se 3 thin films with stoichiometric composition were successfully obtained. The elemental and phase composition, as well as the crystal structure of Sb x Se y thin-films, were studied by energy-dispersive X-ray microanalysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy and atomic force microscopy. The optical bandgap of the films was determined from the absorption spectra acquired by a spectrophotometer. The physical properties of Sb x Se y thin films with different compositions were investigated. [ABSTRACT FROM AUTHOR]

• Deposition technology for antimony sulfide selenide (Sb 2 (S x Se 1-x) 3) thin films. • Sb 2 (S x Se 1-x) 3 thin films obtained by the chemical molecular beam deposition method. • Band gap of Sb 2 (S x Se 1-x) 3 was 1.2–1.36 eV by varying S/(S +Se) ratio from 0.03 to 0.08. • Changing the ratio shifts peaks toward a higher 2θ angle (+0.15°). Antimony sulfide selenide, Sb 2 (S x Se 1-x) 3 (x = 0–1), is a tunable bandgap compound that combines the advantages of antimony sulfide (Sb 2 S 3) and antimony selenide (Sb 2 Se 3). This material shows great potential as a light-absorbing material for low-cost, low-toxicity, and highly stable thin-film solar cells. In this study, Sb 2 (S x Se 1-x) 3 thin films were deposited by chemical-molecular beam deposition on soda-lime glass substrates using antimony (Sb), selenium (Se), and sulfur (S) precursors at a substrate temperature of 420 °C. By independently controlling the source temperatures of Sb, Se, and S, Sb 2 (S x Se 1-x) 3 thin films with varying component ratios were obtained. Scanning electron microscopy revealed significant changes in the surface morphology of the films depending on the elemental ratio of [S]/([S]+[Se]). Crystallites shaped like cylindrical microrods with d = 0.5–2 µm diameter and l = 3–5 µm length were grown at a certain angle on the substrate. X-ray diffraction patterns showed peaks corresponding to the orthorhombic structures of Sb 2 Se 3 , Sb 2 S 3 and their ternary compounds Sb 2 (S x Se 1-x) 3. The optical characterization revealed a high absorption coefficient of 105 cm−1 in the visible and near-infrared light regions. The band gap of the compounds changed almost linearly from 1.2 eV to 1.36 eV with a change in the ratio of elements [S]/([S]+[Se]) from 0.03 to 0.08. [ABSTRACT FROM AUTHOR]

• Ln-mediated dehydrogenation of ethylamine where Ln = La and Ce. • Vibrationally resolved ionization spectra and precise adiabatic ionization energies of Ln(NCH 2 CH 3). • Spin-orbit coupling of Ce(NCH 2 CH 3). • Plausible reaction pathways for the formation of Ln(NCH 2 CH 3). Ln (Ln = La and Ce) atom reactions with ethylamine are conducted in a pulsed laser vaporization supersonic molecular beam source. Dehydrogenation and association metal-containing species are observed with time-of-flight mass spectrometry, and the dehydrogenated Ln ethylimido species in the formula Ln(NC 2 H 5) are characterized by single-photon mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical calculations. The theoretical calculations include density functional theory for both Ln species and a scalar relativity correction, electron correlation, and spin-orbit coupling through multiconfiguration quasi-degenerate second-order perturbation theory for the Ce species. The MATI spectrum of lanthanum ethylimido La(NCH 2 CH 3) has a single vibronic band system from the ionization of the doublet ground state with the La 6s1 configuration, whereas that of the cerium ethylimido Ce(NCH 2 CH 3) displays two vibronic band system from the ionization of the two lowest-energy spin-orbit coupling states with the Ce 4f16s1 configuration. Both Ln ethylimido complexes are formed by the thermodynamically and kinetically favorable concerted dehydrogenation of the amino group. Two additional isomers of Ln(NC 2 H 5) include a four-membered metallacycle Ln(NHCH 2 CH 2) from the dehydrogenation of the amino and methyl groups and a three-membered cycle Ln(NHCHCH 3) from the dehydrogenation of the amino and methylene groups. The cyclic isomers are not observed experimentally as they are not populated under the experimental conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

We present Raman spectroscopy of the polycrystalline Si and Ge films formed by molecular beam deposition on a dielectric substrate. Structural properties of the poly– films have been studied by XRD and TEM. The Raman spectra of poly– Si films demonstrate both a downward shift and an asymmetrical broadening of the vibrational band near 520 cm−1, while only a symmetrical broadening of the band at 300 cm−1 is observed in the spectra of poly– Ge. The Raman line shape has been modeled within the framework of phonon confinement theory, taking into account the sizes of coherent scattering domains estimated using XRD and the influence of extended defects on peak broadening. Phonon dispersion and density of phonon states have been simulated using density functional theory. It has been found that grain boundaries, rather than other extended defects such as twins (multiple twins, twin boundaries), lead to significant changes in phonon dispersion and density of phonon states. • Asymmetrical broadening of the main band is observed in the Raman spectra of poly-Si. • Symmetrical broadening of the main band is observed in the Raman spectra of poly-Ge. • Phonon confinement theory is used to model asymmetrical Raman band broadening. • Phonon confinement is associated with grain boundaries rather than twins. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dissociation of 0.5–1.9 eV supersonic CH 3 Cl molecules on Cu 2 O(111). • Cl as the dominant adsorbed species coming from the dissociative scattering of CH 3 Cl. • Identification of the adsorbed species using SR-XPS. • Comparison of the reactivity between bulk Cu 2 O(111) and precursor Cu-oxide grown on Cu(111). To examine the elementary steps of the Rochow-Müller process we placed copper oxides, viz., Cu 2 O(111) and the bulk Cu 2 O precursor "29"-structure on Cu(111), under supersonic molecular beams (SSMB) of CH 3 Cl. The SSMB energies range from 0.5-1.9 eV. We employed X-ray photoemission spectroscopy (XPS) in conjunction with synchrotron radiation (SR) to determine the resulting adsorbed species present. We identified two reaction paths, viz., Reaction I and Reaction II. Reaction I involves dissociative adsorption of CH 3 Cl. In Reaction II, CH 3 Cl also dissociates, but with Cl as the dominant adsorbed species (higher than that of adsorbed carbonaceous species, as observed for Reaction I). For the incident energies and exposure conditions considered, we found Reaction II as the dominant reaction path for CH 3 Cl reaction on both Cu 2 O(111) and the "29"-structure on Cu(111). [ABSTRACT FROM AUTHOR]

Lipid peroxidation, a self-propagating chain reaction that oxydates lipid molecules, contributes to harmful effects of ionizing radiation. A decrease in peroxidation at higher dose rates could play a role in the FLASH sparing effect. We explored how lipid peroxidation induced by FLASH (>100 Gy/s) and conventional (CONV, <0.2 Gy/s) radiation depends on lipid concentration and content of polyunsaturated fatty acids (PUFA). Additionally, we investigated the correlation between the lipid peroxidation and the main beam parameters characterizing pulsed electron beams, namely the dose per pulse (DR p) and the average dose rate (DR av). We employed phosphatidylcholine (PC) liposomes as a model of biological membranes. Suspensions of liposomes containing different proportions of linoleic acid (LA) were prepared at various concentrations and irradiated at FLASH and CONV dose rates. Additionally, the liposomes were exposed to beams characterized by diverse combinations of DR p and DR av. The extent of lipid peroxidation was assessed by monitoring oxygen consumption (ΔpO 2) and measuring the yield of malondialdehyde (MDA), and in certain instances, of lipid peroxides (LOOH). Regardless of the radiation dose, liposome concentration or LA content, ΔpO 2 and the yield of MDA were significantly lower for FLASH than for CONV irradiation. Increase in the proportion of readily oxidizable LA in the lipid had negative effect on the MDA yield but correlated positively with ΔpO 2 and LOOH yield. Exposing liposomes to beams operating at different pulse repetition frequencies, while keeping the total dose and DR p constant, resulted in markedly different ΔpO 2 and MDA yields. In contrast, DR av was found to exhibit stable correlation with both MDA yield and ΔpO 2. Irradiation at FLASH dose rates produces lower yield of lipid peroxidation in PUFA-containing artificial PC membranes than CONV irradiation under all tested conditions. Time-averaged dose rate, in contrast to pulse dose rate, was the critical parameter determining the level of lipid peroxidation induced by pulsed electron beams. • Lipid peroxidation after FLASH is decreased compared to CONV regardless of lipid concentration and proportion of PUFA. • Main determinant of lipid peroxidation yield for pulsed electron beams is average dose rate. • Lipid peroxidation yield is poorly correlated with pulse dose rate/dose per pulse. • Under irradiation, lipids with lower PUFA content consume less oxygen but yield more MDA. [ABSTRACT FROM AUTHOR]

An advanced radio-frequency quadrupole (RFQ) ion cooler was developed for accelerator mass spectrometry to use element-selective laser photodetachment and ion-molecule reactions for isobar suppression. The system will be installed as a central part of the new Anion Laser Isobar Separator (ALIS) at the 6 MV AMS system of CologneAMS. The new RFQ design intends to solve the technical challenge of the deceleration and trapping of heavy molecular ion beams with high emittance. Therefore, an elliptical injection electrode was developed to slow down the ions far away from the central entrance aperture. A new and easy-to-manufacture guide-field assembly was developed. For this purpose, diagonally-split cylindrical surface electrodes are capacitively coupled to a core rod that is carrying the RF signal. Consequently, only low DC voltages are needed to create a gradually changing potential in the longitudinal direction. The RFQ and the acceleration electrodes are installed in a self-aligned structure. [ABSTRACT FROM AUTHOR]

Proanthocyanidin (PAC) is recognized as a potent natural antioxidant that prevents various diseases. As societal awareness increases, eco-friendly and efficient natural product extraction technologies are gaining more attention. In this study, an electron beam irradiation (EBI) coupled with ultrasound-assisted natural deep eutectic solvents (NADES) extraction method was developed to enable the green and highly efficient extraction of PAC from walnut green husk (WGH). NADES, prepared with choline chloride and ethylene glycol, demonstrated excellent extraction capacity and storage stability for PAC. Molecular dynamics simulations elucidated the high compatibility between NADES and PAC, attributed mainly to a higher SASA value (207.85 nm2), a greater number of hydrogen bonds (330.99), an extended hydrogen bonding lifetime (4.54 ps), and lower inter-molecular interaction energy. Based on these findings, the optimal conditions (13 kGy EBI, 42 mL/g liquid-solid ratio, 38 °C extraction temperature, 70 min extraction time) resulted in a maximum PAC extraction yield of 56.34 mg/g. Notably, this yield was 32.93 % higher than that observed in samples not treated with EBI and ultrasound-assisted extraction (UAE). Analysis of tissue morphology, extract functional groups and thermal behavior suggested a possible mechanism for the synergistically enhanced PAC extraction by the EBI-NADES-UAE method. Additionally, the PAC extracted using the NADES by the EBI coupled with ultrasound-assisted method exhibited outstanding antioxidant activity (comparable to Vc), digestive enzyme inhibition (IC50: 17–0.61 mg/mL), and anti-glycation capacity (IC50: 86.49 μg/mL). Overall, this work provided a green and efficient strategy for PAC extraction from WGH, elucidated the extraction mechanism and bioactivities, and offered valuable insights for potential industrial applications. [Display omitted] • Turning walnut green husk, an agricultural waste, into high-value healthcare products • NADES exhibited excellent efficiency in green extraction of proanthocyanidins • Molecular dynamics simulation revealed the mechanism of efficient extraction by NADES • Electron beam irradiation and ultrasonic-assisted showed synergistic effect during extraction. • PAC extracted by BEI-NADES-UAE method exhibited excellent antioxidant, enzyme inhibitor and anti-glycation activities. [ABSTRACT FROM AUTHOR]

• Ensemble effects dominate over electronic effects for many systems. • Examples for CuPd, AuPd and PdZn. • Test for such effects combine the use of monodentate and bidentate adsorbates. In this paper the geometric ("ensemble") and electronic ("ligand") effects of alloying on surface reactivity and catalysis are considered. The effect of alloying on the behaviour of Pd, both in single crystal form, and as a nanoparticulate catalyst is discussed. The first case concerns Pd alloyed with Cu, and here the reactivity with formic acid and ethanol is modified by the presence of Cu. However, both Cu and Pd maintain their elemental integrity for the reactions, and it is shown that the main alloying effect is one of dilution of Pd atoms, rather than by global electronic factors such as d-band shifting and filling. Similarly, when Pd is alloyed with Au, then the adsorption characteristics (sticking probability and uptake) for CO, O 2 , ethene and acetaldehyde are dominated by changes in the surface arrangement of the two atoms. Au mainly acts as an adsorption blocker, but to different degrees depending upon the nature of the adsorbing molecule and its demand for particular ensemble sizes. Finally, nanoparticulate Pd is considered, and the effect of alloying on high pressure methanol synthesis from CO 2 and H 2 is outlined. Pd on its own is not very selective, instead it mainly produces CO and methane. However, by supporting on oxides such as ZnO, Ga 2 O 3 and In 2 O 3 and by reducing in hydrogen, the Pd forms alloys, which then results in high selectivity to methanol. Again, this is ascribed to the dilution of the Pd ensembles at the surface, which are the cause of methane production. [Display omitted] [ABSTRACT FROM AUTHOR]

Effect of bubble shape on the terminal velocity of bubbles of three sizes (aspect ratio increased by frother addition and higher liquid medium viscosity). [Display omitted] • Bubble terminal velocity and aspect ratio are linked; corresponding maxima/minima reached at the same time. • Bubbles smaller than 5 mm rise in pure liquids with mobile surfaces and spherical and oblate spheroidal shapes. • Bubbles smaller than 5 mm rise in highly contaminated solutions with rigid surfaces and spherical shapes. • Models to predict bubble terminal velocities as a function of size do not produce reliable results. • Models to predict bubble terminal velocity must consider bubble shape parameters to work. Minerals flotation is a process that involves the formation of a population of bubbles to produce a concentrate by selective capture and separation of particles of valuable hydrophobic minerals on the surface of bubbles. The bubble rising velocity is a crucial piece of information for developing operating and control strategies, and for estimating metallurgical performance of flotation circuits. Bubble rising velocities depend on their size and on the physicochemical characteristics of the surrounding liquid medium. Velocities in pure liquids are the largest possible because gas-liquid interfaces remain clean and fully mobile allowing circulation of the gas phase, but when surfactants and ions from soluble mineral species are present (contaminated liquid), which is the case in minerals flotation, a molecular arrangement of adsorbed molecules develops on the surface of the bubbles. This structure reduces bubble surface mobility as internal gas circulation is restricted, velocity is reduced, and shape evolves from oblate spheroidal to spherical. Models proposed to predict the terminal velocity of bubbles have been devised, in general, for working at two extreme sets of conditions: bubbles rising either with fully mobile surfaces in pure liquids, or with rigid surfaces in highly contaminated liquids. The purpose of this work was the assessment of bubble velocity predictions of models that have been used in flotation applications; a data set of simultaneous measurement of velocity and shape of rising single bubbles under a broad set of conditions relevant for minerals flotation was used. The results demonstrated that bubble velocity and aspect ratio were intrinsically linked, and for bubbles of the same size, consistent trends between terminal velocity and aspect ratio that included measurements in frother and polymer solutions. Measurements in solutions of four frothers showed, as expected, significantly different terminal-velocity reduction trends as the frother concentrations were increased. This was considered as a demonstration that the frother molecular structure and the extent of equilibrium coverage were frother dependent. Model assessment demonstrated that prediction of terminal velocities was not possible for contaminated solutions with frother concentrations below the levels that get bubble surfaces fully covered. The measurements collected in this work were used to develop an empirical model for predicting bubble velocities as a function of aspect ratio; the comparison of measured and predicted velocities had a correlation coefficient of 0.9987. [ABSTRACT FROM AUTHOR]

Adsorption process is proposed to be determined by such two successively coupling steps as a transport of adsorbate molecules into system by free convection and a formation of collision-complexes by surface complexing, whose kinetic rate equation can be expressed by a product of exponential monotonous with logistic growth function and quite well experimentally validated by three different adsorption systems. [Display omitted] • Non-linearly coupling molecular transport with surface complexing step leads to a new adsorption kinetic equation. • This equation is suitable for three kinds of adsorption system in vacuum basket, dynamic basket and fixed bed. • Its kinetic parameters can be characterized by molecular motions. Inspired by reaction molecular dynamics together with chain reaction theory, physical adsorption process is proposed to be determined by two successively coupling steps, such as a transport of adsorbate molecules into adsorption system in a free convection velocity and a formation of collision-complex between surface and activated adsorbate molecule in a surface complexing velocity. This leads to establish a new kinetic equation by a product of exponential monotonic and logistic growth functions equal to adsorption extent ratio, which can be quite well validated experimentally by both uptake curves in vacuum or dynamic basket and breakthrough curves from fixed bed for adsorption of benzene vapor by micro-porous carbon. Molecular transport step is an ideal flow with a rate constant of the free convection velocity over the system size; whereas, surface complexing step depends not only on a rate constant of the surface complexing velocity over the apparent free path basically around carbon granular size, but also on its initial surface complex density distribution. The activated adsorbate growth probability is less than unity and equal to the ratio of surface complexing over free convection velocity, both of which are almost nearly proportional to the adsorbate concentration relative to adsorption capacity. [ABSTRACT FROM AUTHOR]

We propose a monolayer actively tunable dual-frequency switch in the terahertz (THz) range based on photosensitive silicon (PSi) metamaterial. The designed unit cell consists of hollow cross-shaped slots and four L-shaped slots made of a perfect electric conductor (PEC), with PSi embedded in both the cross-shaped and four L-shaped slots of identical dimensions. The PEC serves as the dielectric substrate. By varying the intensity of the pump beam to adjust the conductivity of the PSi, tuning of the transmittance at the resonant frequencies of the entire structure is achieved, enabling the switch to function in both ON and OFF states. Under vertical incidence of THz waves in the range of 1 THz to 3 THz, in the absence of pump beam, the PSi is in an insulating state with a conductivity of approximately 1 S/m. The proposed terahertz dual-frequency switch is in the ON state, with transmittances of 97.0% at the first resonance frequency (f 1 = 1.736 THz) and 98.3% at the second resonance frequency (f 2 = 2.176 THz), and group delays of 4.397 ps and 2.540 ps, respectively. When the pump beam intensity is 294.6 μj/cm2, the PSi is in a metallic state with a conductivity of approximately 1 × 105 S/m. The switch is in the OFF state, with zero transmittance in the range of 1 THz to 3 THz and a group delay of 0.327 ps. The calculated modulation degrees of amplitude at f 1 and f 2 for this terahertz dual-frequency switch are both 100%, demonstrating a high-performance switch. The two resonant frequencies f 1 and f 2 of the terahertz dual-frequency switch are generated by weakly coupled superposition between the embedded cross-shaped and four L-shaped PSi resonators (CSPR and FLSPR), exhibiting polarization-insensitive characteristics under vertical incidence of THz waves. We believe that this compact structure of terahertz metamaterial dual-frequency switch holds great application prospects in terahertz filtering, slow light devices, terahertz modulation, and the future 6G communication field. • We propose a monolayer actively tunable dual-frequency switch based on photosensitive silicon metamaterial operates within the frequency range of 1 THz to 3 THz. • It exhibits polarization-insensitive characteristics under vertically incident terahertz waves. • This device achieves high-performance tuning of transmittance at the first resonance frequency (f 1 = 1.736 THz) and the second resonance frequency (f 2 = 2.176 THz), with a range from 97.0% to 0 and 98.3% to 0, respectively (corresponding to the ON and OFF states). • Moreover, it demonstrates the 100% modulation degrees of amplitude, making it a high-performance switch. [ABSTRACT FROM AUTHOR]

Since the mechanism underlying real-time acquisition of mechanical strength during laser-induced skin wound fusion remains unclear, and collagen is the primary constituent of skin tissue, this study investigates the structural and mechanical alterations in collagen at temperatures ranging from 40 °C to 60 °C using various spectroscopic techniques and molecular dynamics calculations. The COMSOL Multiphysics coupling is employed to simulate the three-dimensional temperature field, stress-strain relationship, and light intensity distribution in the laser thermal affected zone of skin wounds during dual-beam laser welding process. Raman spectroscopy, synchronous fluorescence spectroscopy and circular dichroism measurement results confirm that laser energy activates biological activity in residues, leading to a transformation in the originally fractured structure of collagen protein for enhanced mechanical strength. Molecular dynamics simulations reveal that stable hydrogen bonds form at amino acid residues within the central region of collagen protein when the overall temperature peak around the wound reaches 60 °C, thereby providing stability to previously fractured skin incisions and imparting instantaneous strength. However, under a 55 °C system, Type I collagen ensures macrostructural stability while activating biological properties at amino acid bases to promote wound healing function; this finding aligns with experimental analysis results. The COMSOL simulation outcomes also correspond well with macroscopic morphology after laser welding samples, confirming that by maintaining temperatures between 55 °C–60 °C during laser welding of skin incisions not only can certain instantaneous mechanical strength be achieved but irreversible thermal damage can also be effectively controlled. It is anticipated that these findings will provide valuable insights into understanding the healing mechanism for laser-welded skin wounds. • Spectroscopic and computational investigation elucidates Collagen Reconstruction Mechanism in Skin Wound through Dual-Beam Laser Welding. • By synchronizing fluorescence spectroscopy, circular dichroism spectroscopy, and Raman spectroscopy, it has been confirmed that the optimal temperature threshold for laser welding of skin wounds is between 55 and 60 °C . This temperature range allows for instantaneous tensile strength and activates the biological activity of collagen protein amino acid functional groups. • The collagen reconstruction during the laser welding of skin wounds involves hydrophobic interactions and hydrogen bond formation, thereby explaining the mechanism behind the instantaneous tensile strength acquisition. • The results obtained from COMSOL indicate that under 60 °C, photothermal effect induces a concave deformation within thermal affected zone, leading to significant stress and strain. [ABSTRACT FROM AUTHOR]

Pulsed beams containing O and O 2 with incident velocities of ∼7900 m s−1 were directed at a carbon fiber preform network (FiberForm) at temperatures in the range, 1023–1823 K, and the products that scattered from the network were detected with a rotatable mass spectrometer as a function of their velocities and scattering angles. A beam containing pure Ar atoms was also directed at the network, allowing multiple-bounce effects in the absence of reaction to be characterized. Scattered O, O 2 , and Ar exhibited the dynamical characteristics of impulsive (non-thermal) scattering and thermal desorption (TD). On the other hand, CO and CO 2 exhibited only TD dynamics. The fluxes of all products were quantified as a function of sample temperature and, for two focus temperatures, as a function of scattering angle. CO was the dominant reactive product. A temperature dependent hysteresis in the CO flux was quantified, and a comparison was made between the hysteresis on the carbon fiber network and on a planar vitreous carbon surface. The new results may be used to increase the fidelity of oxygen-carbon ablation models for hypersonic flight. [Display omitted] [ABSTRACT FROM AUTHOR]

The present study evaluated whether different concentrations of albumin would influence the immediate or long-term bond strength of adhesive systems to dentin. Human third molars (N = 90) were sectioned at the dentin-enamel junction to obtain middle dentin occlusal surfaces. After sectioning into discs, the molars were restored with resin composite (Filtek Z250, 3 M/ESPE) by using an etch-and-rinse (Adper Scotchbond Multi-Purpose, 3 M/ESPE) or a self-etch (Clearfil SE Bond, Kuraray) adhesive system. The specimens were then sectioned into beams and stored in artificial saliva containing albumin in regular (100 μg/mL; SA100) or elevated (700 μg/mL; SA700) concentration—both concentrations simulated the range in which this enzyme may be present clinically, depending on the patient's periodontal condition. Beams from the control group (CO) were kept in artificial saliva with no addition of albumin. Half of the beams from each group were stored for 24 h, and the remainder, for 12 months. Then, the microtensile bond strength test was performed, and the failure mode was analyzed (adhesive, cohesive, or mixed). Bond strength data were submitted to the generalized linear model, followed by the Tukey tests, and failure modes were compared using chi-square tests (α = 5%). There were no significant interactions, but there was a significant effect between the albumin concentration (p = 0.015) and the time factor (p = 0.016). The beams stored in SA700 had significantly lower bond strength in comparison with the CO beams, regardless of the adhesive system. At 12 months, the bond strength decreased significantly for all groups. SA700 caused a significant increase in the adhesive failures after 12 months (p = 0.005). It was concluded that the bond strength of both adhesive systems was impaired by the albumin concentration aging. [ABSTRACT FROM AUTHOR]

A combination of simulation and experimentation is employed to explore the influence of the non-uniformity of energy distribution in nanosecond PSEB on the target ablation. Firstly, A spatiotemporally distributed heat source model is built using Monte Carlo computational method and an ablation phase transition model is established using molecular dynamics method. The results reveal the time evolution of multiple cavities in the sub-surface region, as well as the temperature and stress field distributions with electron beam irradiation. Phase explosion formation and lattice structure changes in the steel target during the ablation process is found for the first time. The PSEB modified AISI1045 steel samples is experimentally conducted. The characterization results show the changes in the crystal structure within AISI1045 steel, which is attributed to the formation of an amorphous layer resulting from grain refinement and structural defects, as well as the combined effects of thermal elastic stress waves, shock thermal stress waves and temperature gradient distribution. The experimentally obtained crystal phase changes are consistent with the simulation results, confirming the accuracy and validity of the modelling. The findings of this study provide a molecular-scale explanation for the formation of unique morphology and micro-structures during the PSEB ablated metal target. [ABSTRACT FROM AUTHOR]

The Velocity Slice Imaging technique has revolutionized charged particle-molecule interaction studies in general and electron-molecule interaction studies in particular. Multiple electrostatic lens assemblies are often used in spectrometers for resolving low kinetic energy fragments. In a crossed-beam experiment with an effusive molecular beam as a target, the background gas forms a strong extended source of ions where the charged particle beam is used as a projectile without focusing. This extended source creates artefacts on the momentum images as we try to magnify them beyond a certain size. Here, we present a systematic study of this effect on momentum imaging in the low-energy-electron molecule collisions as an example and the solutions to address this issue by background subtraction with suitable magnification. Additionally, we demonstrated that a supersonic molecular beam target helps minimize these artefacts in the image magnification by reducing the background signal. These systematic findings may bring valuable insight into the investigation of low kinetic energy release processes involving electron impact, ion impact, and merge beam experiments with large interaction volumes where high magnification is essential. [Display omitted] • Systematic study of the effect of the static gas background on the momentum images. • Assessment of the image magnification limitation for the momentum spectrometers. • Suppressing the background restores the spectrometer's magnification capability. • Challenging for low cross-section processes like Dissociative Electron Attachment. [ABSTRACT FROM AUTHOR]

А 3D CFD model coupled with wave optics model for laser beam propagation is used to calculate the performance of a hydrocarbon-free K end pumped flowing-gas diode pumped alkali amplifier (DPAA). The K DPAA efficiency and output beam quality were calculated as a function of various parameters and the results were compared with those calculated for end pumped Rb DPAA with hydrocarbon-free buffer gas. For moderate pump intensity, both the efficiency and beam quality deteriorate at low gas velocity. The efficiency strongly depends on the pressure of the buffer helium, reaching a maximum at pressure close to atmospheric and falling with a further increase in pressure. The maximum efficiency of the K DPAA (∼0.45) is approximately 4 times higher than that of the Rb one, achieved at the same optimal pump power of 5 kW. Addition of CH 4 to the He buffer in the K DPAA decreases the amplifier efficiency and reduces the beam quality. [ABSTRACT FROM AUTHOR]

The pyrolysis of three-component surrogate fuel for jet fuel has been studied experimentally in flow reactor using synchrotron photoionization and molecular beam mass spectrometry techniques with temperature range of 850–1150 K. Alkenes are the most abundant products in the decomposition process. Other important intermediates such as alkanes, alkynes, polycyclic aromatic hydrocarbons were also identified and quantified. Detailed kinetic reaction model involving 462 species and 3170 reactions have been developed by validating against the measured results as well as oxidation data reported previously with reasonable predictions. Detailed rate of production and sensitivity analysis indicated T135MCH mainly decay through demethylation and H-abstraction reactions. Moreover, n-propylbenzene consumption is more sensitive to CH 3 than H, while n-dodecane and T135MCH prefer H radical. The reactions between fuel and fuel-derived radicals show limited effect on surrogate fuel consumption. Reactivity changes of NPB and NC 12 H 26 were investigated through the comparison of fuel conversion ratio. The coupling effect was displayed via the common and important sensitive reactions which are related to the H and CH 3 radicals. Present experimental data and reaction model will contribute to a better understanding of combustion behavior of 3C surrogate fuel. Thus, the results of present work could contribute to comprehensive investigation of jet fuel combustion properties. [ABSTRACT FROM AUTHOR]

Recent investigations illustrated that clustering of hydrocarbons by radical-chain reaction (CHRCR) mechanism provides key mechanistic steps for the rapid synthesis of polycyclic aromatic hydrocarbons (PAHs) and soot. Resonance-stabilized radicals (RSRs) play critical roles in this mechanism, and non-benzene first-ring species have attracted considerable attention as precursors of larger aromatic hydrocarbons. C 7 H 7 RSRs, such as benzyl, tropyl, vinyl-cyclopentadienyl, are particularly stable and are thus quite important in the growth of PAHs. The addition of vinylacetylene to propargyl radical, a prototypical CHRCR reaction, provides a facile route to C 7 H 7 RSRs. We have directly investigated the reaction of propargyl and vinylacetylene in isomer-resolved elementary experiments by synchrotron vacuum ultra-violet photoionization molecular beam mass spectrometry (SVUV-PI-MBMS). In good agreement with theoretical predictions, vinyl-cyclopentadienyl is found to be the major product of vinylacetylene and propargyl reaction while benzyl is minor. This work demonstrates a feasible CHRCR pathway, not proceeding through benzene, for PAH formation. [ABSTRACT FROM AUTHOR]

Identification of species in the gaseous phase of hydride materials and their mixtures (e.g. LiBH 4 –MgH 2) is crucial for understanding the reactional mechanisms and diffusion kinetics of hydrogen across the different interfaces of phase segregation. This phase separation makes the characterization by conventional gas analysis techniques complicated and some analytical information could not be accessible. To overcome this surface/interface related issue, the study of the evolution of the gas phase emitted by the complex hydrides during ball-milling is considered. In this respect, an experimental set-up is designed by coupling a milling reactor with a mass spectrometer through a capillary tubing and an effusion Knudsen cell. A gas flow study (from molecular to viscous regimes) is performed in order to propose a suitable architecture of the entire device (ball-mill, capillary tubing, pipes, effusion cell compartment and pumping system) compatible with the mass spectrometric detection in terms of effused flow and molecular beam. Simulation of the flows and definition of their regimes nature at each stage of the pipes and vessels system is addressed as function of geometric parameters, upstream pressures, and pumping capacity on the downstream side (effusion cell). The study highlights the advantage of using a capillary tubing for the connection and ensure an optimal detection. Different working pressure conditions are demonstrated and associated to its length, meanwhile the diameter of the capillary has been demonstrated to be too sensitive to be varied. Image 1 • Hydrogenation processes depend on the solid-state interface/surfaces. • Evolution of the gas phase during the course of milling is considered. • A milling reactor is coupled to mass spectrometer through a capillary tubing. • An optimized architecture is proposed based on flow calculation. • This original device may allow advanced characterization of hydrogen materials. [ABSTRACT FROM AUTHOR]

1-butene is an important intermediate in combustion of various hydrocarbon fuels and oxygenated biofuels (e.g., butanol). Understanding its oxidation chemistry can help improve ignition and combustion process in advanced engines and provide better emission control. This work addresses a discrepancy between experiments and simulations in 1-butene oxidation at low temperatures, wherein simulations with AramcoMech 3.0 model show greater fuel reactivity than experiments. To further explore 1-butene low temperature reaction pathways from 550 to 910 K, experiments were conducted in three jet-stirred reactors: two coupled to time-of-flight molecular beam mass spectrometers with synchrotron vacuum ultraviolet radiation as the photoionization source, and one coupled to gas chromatography mass spectrometer. Isomeric structure identification, comprehensive species datasets, and reactor cross examinations are provided by the combination of three experiments. The identified isomer-resolved species provide evidence of various 1-butene low temperature reaction pathways. For example, the identification of propanal confirms the Waddington reaction pathway. The kinetic model over-predicts fuel reactivity in the low temperature regime (550–700 K). Updating the rate coefficients of key reactions in the Waddington pathways, e.g., forward and reverse isomerization of hydroxyl-butyl-peroxide to butoxyl-peroxide and Waddington decomposition of butoxyl-peroxide reduces the discrepancies. The role of rate constant updates in each step of the Waddington pathway is evaluated and discussed to provide directions for future model development. [ABSTRACT FROM AUTHOR]

• The conductivity of Sb x Se y films was studied as a function of the vapor phase mixture of Sb and Se. • The conductivity was varied in the wide range of 10−5–102 (Ohm × cm)−1. • The obtained results were explained by the formation of intrinsic point defects. Antimony selenide (Sb 2 Se 3) has been developed as attractive, non-toxic and earth-abundant solar absorber candidate among the thin-film photovoltaic devices. The growth of Sb x Se y thin films, by atmospheric pressure chemical molecular beam deposition (CMBD) method, from separate Sb and Se precursors has been reported. The conductivity of the films was investigated as a function of the vapor phase mixture of Sb and Se. By the precise control of the Sb/Se ratio we succeeded in obtaining stoichiometric Sb 2 Se 3 films. It is also found out that we can control the conductivity by deliberately introducing the deviation from the stoichiometry. The conductivity was varied in the wide range of 10−5 ÷ 102 (Ohm × cm)−1 and samples had p- and n-type conductivity depending on Sb/Se ratio. The obtained results were explained by the formation of intrinsic point defects. [ABSTRACT FROM AUTHOR]

Purpose: Small animal irradiation is crucial to the investigation of radiobiological mechanisms. The paradigm of clinical radiation therapy is trending toward high-precision, stereotactic treatment. However, translating this scheme to small animal irradiation is challenging owing to the lack of high-quality image guidance. To overcome this obstacle, we developed a multimodality image guided precision radiation platform.Methods and Materials: The platform consists of 4 modules: x-ray computed tomography (CT), bioluminescence tomography (BLT), fluorescence molecular tomography (FMT), and radiation therapy. CT provides animal anatomy and material density for radiation dose calculation, as well as body contour for BLT and FMT reconstruction. BLT and FMT provide tumor localization to guide radiation beams and molecular activity to evaluate treatment outcome. Furthermore, we developed a Monte Carlo-based treatment planning system (TPS) for 3-dimensional dose calculation, calibrated it using radiochromic films sandwiched in a water-equivalent phantom, and validated it using in vivo dosimeters surgically implanted into euthanized mice (n = 4). Finally, we performed image guided irradiation on mice bearing orthotopic breast and prostate tumors and confirmed radiation delivery using γH2AX histology.Results: The Monte Carlo-based TPS was successfully calibrated by benchmarking simulation dose against film measurement. For in vivo dosimetry measured in the euthanized mice, the average difference between the TPS calculated dose and measured dose was 3.86% ± 1.12%. Following the TPS-generated treatment plan, we successfully delivered 20 Gy dose to an animal bearing an orthotopic prostate tumor using 4 BLT-guided radiation beams and 5 Gy dose to an animal bearing an orthotopic breast tumor using a single FMT-guided radiation beam. γH2AX histology presented significantly more DNA damage in irradiated tumors and thus validated the dose delivery accuracy.Conclusions: Combined with Monte Carlo TPS, this multimodality CT/BLT/FMT image guided small animal radiation platform can specifically localize tumors, accurately calculate dose distribution, precisely guide radiation delivery, and molecularly evaluate treatment response. It provides an advanced toolset for radiobiology and translational cancer research. [ABSTRACT FROM AUTHOR]

• Growth of Sb 2 Se 3 films on Si/SiO 2 (1 0 0) substrate using molecular beam evaporation. • The surface morphology and compositional analysis using EDS and WDS technique. • Determination of band-gaps and Urbach energies using K-M formalism and Tauc's plot. • Blue shift of Raman peaks due to the point defects caused by the loss of Se. • Red shift of band gaps with the increase of evaporation temperature. Antimony selenide (Sb 2 Se 3) is a promising material for thin-film solar-cells due to its attractive optoelectronic properties with the desirable band gap. In the present work, four different Sb 2 Se 3 films were grown on Si/SiO 2 (1 0 0) substrates at ambient temperature using ultra-high vacuum molecular beam evaporation technique and different evaporation temperatures. The compositional analysis with the help of wavelength-dispersive X-ray spectroscopy measurements demonstrate that there is a loss of Se in the as-deposited samples. However, the X-ray diffraction study indicates that the as-deposited films are nanocrystalline in nature, with average crystallite size slightly increasing with the evaporation temperature. The blue shift of Raman peaks with the increase of evaporation temperature indicates the possibility of the presence of small amount of compressive strain in the crystal lattice and it appears because of the anion vacancy (V Se) due to the loss of Se. The obtained band gap value ranges from 1.075 eV to 1.21 eV, which indicate that the as-deposited nanocrystalline Sb 2 Se 3 films are suitable for application in thin-film photovoltaic solar-cells. The tuning of the band-gap with the evaporation temperature opens a new road to optimize the device efficiency for the low-cost thin-film photovoltaics. [ABSTRACT FROM AUTHOR]

The oxidation of benzaldehyde (A1CHO) at atmospheric pressure in a jet-stirred reactor at equivalence ratios of 0.4 and 2.0 within 475–900 K was studied. The intermediates and products were identified by synchrotron radiation photoionization and molecular beam mass spectrometry. Compared with previous studies, 29 species such as HCHO, CH 3 O, H 2 O 2 , ketene, furan, 2,4-cyclopentadiene-1-one (C 5 H 4 O), furfural, o-benzoquinone, 1,4-benzenediol and 1,4-cyclohex-2-enedione were newly detected. A kinetic model, involving 376 species and 2163 reactions was proposed, which reasonably predicted the experimental value. Rate-of-production analysis shows that H-abstractions reactions involving H atoms, OH, CH 3 , HO 2 and phenoxy radicals dominate the consumption of A1CHO. The decarbonylation reactions and ring opening reactions have a certain contribution to the promotion of oxidation process. Phenoxy radicals, phenol and C 5 H 4 O are one of the most significant intermediates for A1CHO oxidation. Sensitivity analysis shows that A1CHO+OH=A1CO+H 2 O and H 2 O 2 (+M) =OH+OH(+M) are among the most sensitive reactions to promote the consumption of A1CHO at both conditions while the reaction A1OH+O 2 =A1O+HO 2 has strong inhibiting effect. A1CHO is more difficult to produce benzene compared with benzyl alcohol oxidation while is easier to generate phenol at the same condition. These results will enrich the understanding the oxidation mechanism and soot formation of A1CHO as a potential aromatic fuel. [ABSTRACT FROM AUTHOR]

New families of nonnegative biquadratic forms that have 8, 9 or 10 real zeros in P 2 × P 2 are constructed. These are the first examples with 8, 9 or 10 real zeros. It is known that nonnegative biquadratic forms with finitely many real zeros can have at most 10 zeros; our examples show that the upper bound is obtained. Such biquadratic forms define positive linear maps on real symmetric 3 × 3 matrices that are not completely positive. Our constructions are explicit, and moreover we are able to determine which of the examples are extremal. We extend the examples to positive maps on complex matrices and find families of extreme rays in the cone of positive maps. [ABSTRACT FROM AUTHOR]

SnTe (1 0 0) single-domain thin films have been previously grown on GaAs substrates by molecular beam epitaxy but obtaining excellent crystallinity can be difficult. In this paper, ZnTe buffer layers are introduced to improve the crystallinity of SnTe films. The effects of the molecular beam flux ratio (J Te / J Sn) and growth temperature (T g) on the crystallinity are investigated to achieve high-quality layers. The surface morphology and electrical properties of the SnTe thin films are also evaluated in addition to the conventional X-ray diffraction (XRD)measurements. The crystallographic properties of the grown samples are shown to be significantly improved by introducing a ZnTe buffer layer. XRD (θ –2 θ) full width at half maximum of the lowest value obtained so far is about 0.14°. It is also found that lowering J Te / J Sn to 0.6 results in a reduced growth rate, and an increased growth temperature (T g = 220 °C) promotes the migration of atoms at the growth front. Both effects contribute to improvement in the crystallographic quality, including the layer surface smoothness. The cross-sectional transmission electron microscopy observation of the sample indicates the abrupt interface formation with different lattice structures. It is also found that low growth temperatures (below 200 °C) are not favorable for the SnTe layer growth, which is confirmed by the surface morphology. [ABSTRACT FROM AUTHOR]

It was demonstrated recently that the W 1 + ∞ algebra contains commutative subalgebras associated with all integer slope rays (including the vertical one). In this paper, we realize that every element of such a ray is associated with a generalized W ˜ algebra. In particular, the simplest commutative subalgebra associated with the rational Calogero Hamiltonians is associated with the W ˜ algebras studied earlier. We suggest a definition of the generalized W ˜ algebra as differential operators in variables p k basing on the matrix realization of the W 1 + ∞ algebra, and also suggest an unambiguous recursive definition, which, however, involves more elements of the W 1 + ∞ algebra than is contained in its commutative subalgebras. The positive integer rays are associated with W ˜ algebras that form sets of Ward identities for the WLZZ matrix models, while the vertical ray associated with the trigonometric Calogero-Sutherland model describes the hypergeometric τ -functions corresponding to the completed cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dissociation of 0.7–1.9 eV supersonic CH3Cl molecules on Cu(1 1 1) • Cl as the dominant adsorbed species coming from the dissociative scattering of CH3Cl. • Identification of the adsorbed species using SR-XPS. • The threshold kinetic energy of the dissociative reaction depending on the crystal. • surface orientation. To study the elementary steps in the Rochow-Müller process, we bombarded Cu(1 1 1) and Cu(4 1 0) with 0.7–1.9 eV supersonic molecular beams (SSMB) of CH 3 Cl. We then identified the corresponding adsorbed species using X-ray photoemission spectroscopy (XPS) in conjunction with synchrotron radiation (SR). We found Cl as the dominant adsorbed species (much higher than that of adsorbed carbonaceous species) coming from the dissociative scattering of CH 3 Cl. We also found that the threshold kinetic energy of the reaction depends on the crystal surface orientation. [ABSTRACT FROM AUTHOR]

• The Zn x Sn 1−x Se films have orthorhombic and cubic structures depending on composition. • The films were found to have a direct optical band gap (Eg) value of 1.0–2.1 eV depending on the composition. • The films showed p- and n-type conductivity depending on the composition. We have fabricated Zn x Sn 1−x Se (ZTSe) films for the first time. Samples were fabricated by chemical molecular beam deposition method at atmospheric pressure in hydrogen flow. ZnSe and SnSe powders with 99.999% purity were used as precursors. The temperature of precursors varied in the range of (850–950) °C. Films were deposited at substrate temperature of (500–600) °C. Borosilicate glass was used as a substrate. We have studied ZTSe films by EDS, XRD and SEM. The samples had orthorhombic and cubic structures depending on composition. Results of EDS have shown that stoichiometric composition of samples moved to ZnSe side by increasing with substrate temperature. SEM pictures have shown that samples had polycrystalline structure. The grain size varied in the range of (2–15) µm. The grain size of samples increased from (2–5) µm to (15–20) µm for substrate temperatures of 500 °C and 550 °C respectively. While, at a substrate temperature of 600 °C the grain size decreased up to (3–5) µm, possibly, because of increasing of ZnSe content. XRD analysis has shown that samples have ZnSe, SnSe, Se and Sn phases. The band gap of samples varied in the range of 1.0–2.0 eV depending on the film compositions. An inversion of the conductivity type was found: samples fabricated at 500 °C and 550 °C performed of p-type conductivity; while samples fabricated at 600 °C showed n-type conductivity. [ABSTRACT FROM AUTHOR]

Pyrolysis study of iso-propylbenzene (IPB) at 30 and 760 torr was carried out by using synchrotron photoionization and molecular beam mass spectrometry techniques. 0.5%IPB was diluted by helium and heated to 798–1148 K in a flow tube. Styrene was the most abundant aromatic intermediate at both pressures. Several polycyclic aromatics were only observed at 760 torr, such as 2-ethenyl-1, 4-dimethyl-benzene, fluorene, anthracene, phenanthrene, 2-methyl-anthracene and pyrene, while fulvene, 1, 3-cyclohexadiene, and 5-ethenylidene-1, 3-cyclopentadiene were only detected at 30 torr. A detail mechanism involving 306 species and 1990 reactions was developed by updating ipso-addition and unimolecular dissociation reactions of IPB as well as reactions related to styrene, indene and naphthalene. The mechanism could predict the pyrolysis of IPB and production of other intermediates well. Rate-of-production analysis shows that the formations of 2-phenethyl, 1-iso-phenylpropyl and 2-iso-phenylpropyl radicals are the main consumption reactions of IPB independent of pressure. Sensitivity analysis indicates that the unimolecular dissociation of IPB forming 2-phenethyl radical is the most significant promoting reaction at both pressures. H-abstraction reaction forming 1-iso-phenylpropyl radical tends to play a significant inhibiting effect on IPB consumption at 30 torr, while the most inhibiting reaction is self-combination of methyl radicals at 760 torr. Compared to n-propylbenzene experiments reported by Liu et al. (Combustion and Flame, 191 (2018) 53–65) and Yuan et al. (Combustion and Flame,186 (2017) 178–192.), IPB tends to produce larger quantities of benzene, styrene and indene under pyrolysis and oxidation conditions. These results will improve the understanding of the combustion and soot formation of IPB as a potential aviation surrogate fuel. [ABSTRACT FROM AUTHOR]

Herein, the interfacial properties of new three-dimensional (3D) configurations of metallic carbon, namely T6 and T14, incorporated to different polymer matrices (T6 and T14@polymers) are studied using molecular dynamics (MD) simulations. The effects of two types of shape models for T6 and T14, i.e. beam- and plate-like models, various square cross-sectional areas for the reinforcements, pull-out velocity and polymer structure on the interaction energy and pull-out force of final system are investigated. The results reveal that the interfacial resistance of the system is improved by imposing a high pull-out velocity to the nanofillers. For each pull-out velocity, the effect of beam-like T6 and T14@polycarbonate (beam-like T6 and T14@PC) on increasing average pull-out force is more remarkable than that of similar models surrounded by polypropylene (PP). The beam- and plate-like structures@polymers possess the lowest and highest interfacial resistance, respectively. As the aspect ratio (length-to-width ratio) of nanofillers changes from the lowest value to the highest one, the average pull-out force decreases. The average pull-out force of plate-like T6@polymers is higher than their plate-like T14 counterparts. Besides, higher absolute values of interaction energy in plate-like T6 and T14@polymers in comparison with others imply that the load-carrying capacity from the surrounding matrix to the plate-like nanofillers is significantly increased. Image 1 • Studying the interfacial properties of T6 and T14 structures incorporated to different polymer matrices (T6 and T14@polymers) using MD simulations • Using two types of configurations for T6 and T14 (beam- and plate-like models) • Investigating effects of square cross-sectional areas for the reinforcements, pull-out velocity and polymer structure on the pull-out force and interaction energy [ABSTRACT FROM AUTHOR]

• Theoretical sticking probability of O 2 dissociation on Cu(100) is found non-activated. • Topology of the potential energy surface is very open in entrance channels. • Direct dissociation mechanism dominates the dynamics. • Choice of the functional used in DFT calculations could solve the experiment/theory difference. The dynamics of O 2 dissociative chemisorption on Cu(100) is studied by means of quasi-classical dynamics simulation making use of a 6-dimensional potential energy surface based on density functional theory (DFT) calculations. The sticking probability is found in reasonable agreement with experiment above 0.3 eV collision energy. However, theory fails at capturing the activated behaviour experimentally evidenced for lower energies. While molecular beam experiments exhibit an energetic threshold in the sticking curve, simulations show a high dissociation probability at collision energies below this threshold. Present calculations suggest that this discrepancy is due to dynamics governed by a direct dissociation mechanism steming from several barrierless reaction paths associated with an indirect dissociation mechanism governed by dynamic trapping. These direct and indirect components are strongly related to the structure of the PES questioning the reliability of the DFT calculations and the choice of the functional used. Beyond the question of the DFT accuracy, this theoretical work addresses the still open question of experiments/theory comparison for systems involving O 2 and metal surfaces such as Cu(100). [ABSTRACT FROM AUTHOR]

We have conducted beam-surface scattering experiments with the intent of identifying the reaction mechanisms that are relevant to the ablation of carbon by N atoms at surface temperatures relevant to hypersonic flight. A pulsed molecular beam containing N and N 2 with translational energies of 460 and 808 kJ mol-1, respectively, was directed at a vitreous carbon surface held at temperatures in the range 1023–1923 K. Time-of-flight distributions were collected for scattered products with fixed incidence and final angles of θ i = θ f = 45°. Inelastically scattered N and N 2 and reactively scattered CN were the only products observed. The scattering dynamics of N and N 2 were independent of surface temperature and were indicative of purely impulsive scattering. The scattering dynamics of CN suggested that this reaction product is formed by a mechanism that occurs in thermal equilibrium with the surface – i.e., a Langmuir-Hinshelwood mechanism. The reaction probability to produce CN has an Arrhenius temperature dependence with an activation energy of 207 kJ mol-1. The relevance of the current results to the hypersonic ablation of carbon in the presence of dissociated air is discussed. Image 1086731 [ABSTRACT FROM AUTHOR]

In the paper, the processes occurring during low-temperature growth of non-hydrogenated amorphous Si and polycrystalline Si films on multilayer Si 3 N 4 /SiO 2 /c-Si substrates from molecular beams under conditions of ultrahigh vacuum are studied in detail. Diffusion of hydrogen atoms from a dielectric layer into the growing film is shown to accompany the growth of a silicon film on a Si 3 N 4 layer deposited by CVD or on a SiO 2 layer obtained by thermal oxidation of a silicon wafer. The process of hydrogen migration from the dielectric substrates into the silicon film is studied using FTIR spectroscopy. The reduction of IR absorption at the bands related to the N H bonds vibrations and the increase of IR absorption at the bands relating to the Si N bonds vibrations in IR spectra demonstrate that hydrogen atoms leave Si 3 N 4 layer during Si deposition from a molecular beam. The absorption band assigned to the valence vibrations of the Si H bond at ∼2100 cm–1 emerging in IR spectra obtained at samples deposited both on Si 3 N 4 and SiO 2 layers indicates the accumulation of hydrogen atoms in silicon films. The difference in chemical potentials of hydrogen atoms in the dielectric layer and the silicon film explains the transfer of hydrogen atoms from the Si 3 N 4 or SiO 2 layer into the growing silicon film. [ABSTRACT FROM AUTHOR]

Non-evaporable getter (NEG) coatings are widely used in vacuum chambers of particle accelerators. Vacuum solutions group at STFC Daresbury Laboratory is continuously developing and optimising the NEG coatings are for various applications and vacuum chamber geometries. The pumping properties of the NEG coatings are characterised by sticking probability and pumping capacity. Initial sticking probability of the NEG coated tube can be measured by gas injection at one end of the tube and partial pressure measurements at either sides, P 1 and P 2 respectively. This requires the NEG coating facility to be modelled with the Test Particle Monte-Carlo (TPMC) method to obtain the pressure ratio R = P 1 / P 2 as a function of sticking probability, R (α), for each type and geometry of the with each of the NEG coated tubes. The purpose of TPMC modelling reported in this paper was to find R (α) for the NEG coating evaluation facility with a sample in a form of the 0.5-m long NEG coated tubes with inner diameters of 5, 7, 9 and 38 mm. Furthermore, the effect of RGA2 location was also studied. It has been demonstrated that the RGA2 location could significantly (from a few percent up to a factor 3.1) affect the pressure ratio R (α). The effect of pressure measurement errors on calculated sticking probability was studied for Δ R / R = 10, 20 and 50%. The sticking probability accuracy varies: Δ α / α = 0.04–0.5 for Δ R / R = 10%, Δ α / α = 0.07–0.8 for Δ R / R = 20% and Δ α / α = 0.23–2.0 for Δ R / R = 50%. • Modelling the RGA reading in TPMC model in case of molecular beaming effect is shown. • Location and orientation of RGA can significantly affect the RGA reading. • Highest sensitivity for the pressure ratio measurement are found. • The error for the pressure ratio measurements has been estimated. [ABSTRACT FROM AUTHOR]

Abstract Organosilicon compounds are surprising in the diversity of their applications as a result of the enormous diversity in their structure. Of particular interest are the self-assembling possibilities of silsesquioxane molecules leading to the formation of thin films with thicknesses not exceeding tens of nanometers. To date, only cases of self-organization of molecules with a strongly asymmetrical shape have been known. This study is aimed at obtaining confirmation of self-organization of silsesquioxane molecules in which the π-stacking interaction between arranged spherically symmetrical aromatic rings leads to the formation of a new smectic phase not observed for bulk material. For this purpose, the morphology of growth and the structure of thin octasilsesquioxane layers substituted either with vinyl or phenyl groups was compared. Due to the use of molecular beam technique for thin-film deposition under ultra-high vacuum conditions, any undesirable external influences as well as those associated with the solvent were avoided. The main measurement techniques were the X-Ray Reflectometry and Atomic Force Microscopy, which provided the final proof of the key role of aromatic rings in the self-assembly of these spherically symmetrical molecules. Graphical abstract Unlabelled Image Highlights • Comparison of the structure and growth morphology of Vi-T 8 and Ph-T 8 thin films deposited by PVD technique. • Surface vicinity and the reduced dimensionality is not sufficient to induce new crystalline phases in the thin films. • The dispersive and electrostatic interaction between phenyl rings play a key role in the new smectic phase formation. • Direct observation of the self-organization induced by π-stacking for the spherically symmetric molecules. [ABSTRACT FROM AUTHOR]

Highlights from the article: • The effusion cell provides molecules along the normal to the effusion orifice that travel to the ion source with a very small solid angle - generally <10 SP -2 sp sr - and the main part of the molecular beam - >98% and about 2 steradian - goes in the thermal shields and in the furnace. This feature is directly related to the size of the field aperture which is usually rather large in conventional mass spectrometers (about 5-7 mm) compared to the effusion orifice in order to be sure to catch any gaseous species at the initial loading of the Knudsen cell furnace in the mass spectrometer followed by pumping and heating up to the convenient temperature for the first detection of vapors before centering the effusion orifice. Ionic intensity profiles obtained when centering the effusion orifices may also be performed during the experiment to check either the reliability of the initial centering (especially when using multiple cells) or the modifications in the effusion orifice environment i.e. the surface vaporizations. Graph: Fig. 8 Surface vaporization around the effusion orifice edge as analyzed with a slit scanning the molecular beam perpendicularly to its normal to the orifice on the trajectory of molecules.

Free jet expansion sampling mass spectrometry is a valuable tool for identifying high temperature vapor species formed in a 1 bar process. The system at NASA Glenn consists of four differentially pumped vacuum chambers. A Pt/20Rh entrance nozzle from the 1 bar process to a rapidly pumped chamber creates the free jet expansion. This is followed by a skimmer and thus an intense supersonic molecular beam is formed and directed to a quadrupole mass spectrometer. An unobstructed path to the mass spectrometer allows direct identification of condensable and non-condensable vapor species formed at 1 bar while preserving their chemical and dynamic integrity. This system has been very valuable for identification of metal hydroxides and oxyhydroxides which would not have been seen in a low pressure system. We discuss studies of Si(OH) 4 , Al(OH) 3 , TaO(OH) 3 , B(OH) 3 , and CrO 2 (OH) 2 vapors. [ABSTRACT FROM AUTHOR]

Highlights • Interdigitated type-I and type-II quantum dots are grown by molecular beam epitaxy. • Type-I InAs/GaAs and type-II GaSb/GaAs quantum dots are utilized. • The interdigitated quantum dots are incorporated into a heterojunction solar cell. • By comparing with the homojunction cell, V OC is improved by 20.6%. Abstract Interdigitated quantum dots, which are multiple stacks of type-I InAs/GaAs quantum dots and type-II GaSb/GaAs quantum dots, are grown using molecular beam epitaxy. By incorporating the interdigitated quantum dots into a p - i - n AlGaAs/GaAs heterojunction solar cell structure, we demonstrate a photovoltaic effect with a 20.6% improvement in open-circuit voltage, when compared to that of another cell incorporating the same quantum dots but with a p - i - n GaAs homojunction architecture. A transmission electron microscopy is performed to analyze strain-induced defects created in the multi-stack quantum dot structures. The heterojunction solar cell incorporating the interdigitated quantum dots realized in this work would find potential applications in high-efficiency single-junction intermediate band solar cells operating under concentrated sunlight. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Spatial separation of pyrrole and pyrrole(H 2 O) from other species in a molecular beam. • Our experimental findings are supported by simulations. • Pure sample of pyrrole(H 2 O) clusters. Abstract We demonstrate the spatial separation of pyrrole and pyrrole(H 2 O) clusters from the other atomic and molecular species in a supersonically-expanded beam of pyrrole and traces of water seeded in high-pressure helium gas. The experimental results are quantitatively supported by simulations. The obtained pyrrole(H 2 O) cluster beam has a purity of ∼ 100 %. The extracted rotational temperature of pyrrole and pyrrole(H 2 O) from the original supersonic expansion is T rot = 0.8 ± 0.2 K, whereas the temperature of the deflected, pure-pyrrole(H 2 O) part of the molecular beam corresponds to T rot ≈ 0.4 K. [ABSTRACT FROM AUTHOR]

Abstract A fluorescent biosensing strategy based on three helix molecular beacons (tMBs) for simultaneous simple and rapid detection of HIV related genes was developed. This tMBs contain outer loop sequences and fluorescent probes. The outer loop sequences consist of target capture sequences (cDNA) and the stems can lock the fluorescent probes (P). Initially, the probes were tethered to display weak fluorescence signals in the tMBs. Once the target DNAs opened loops, the stems of tMBs were dehybridized which resulted in turning on the fluorescence. By applying tMBs fluorescent switch detection strategy, the fluorescence response at 484 nm and 367 nm were corresponding to thioflavin (THT) and 2-aminopurine (2-AP) respectively with high selectivity and sensitivity. The detection limits were calculated to be 227 pM for HIV-1 and 352 pM for HIV-2, respectively. As a general detection model for multiple species, the proposed strategy exhibits outstanding analytical performance such as simple, low-cost, and high anti-interference capability, which provides a new and ultrasensitive biosensing platform for multiple DNAs simultaneous detection in biomedical research and early clinical diagnosis. [ABSTRACT FROM AUTHOR]