Imaging Extreme Ultraviolet Radiation Using Nanodiamonds with Nitrogen-Vacancy Centers.

Extreme ultraviolet (EUV) radiation with wavelengths of 10-121 nm has drawn considerable attention recently for its use in photolithography to fabricate nanoelectronic chips. This study demonstrates, for the first time, fluorescent nanodiamonds (FNDs) with nitrogen-vacancy (NV) centers as scintillators to image and characterize EUV radiations. The FNDs employed are ∼100 nm in size; they form a uniform and stable thin film on an indium-tin-oxide-coated slide by electrospray deposition. The film is nonhygroscopic and photostable and can emit bright red fluorescence from NV0 centers when excited by EUV light. An FND-based imaging device has been developed and applied for beam diagnostics of 50 nm and 13.5 nm synchrotron radiations, achieving a spatial resolution of 30 µm using a film of ∼1 µm thickness. The noise equivalent power density is 29 µW/(cm2 Hz1/2) for the 13.5 nm radiation. The method is generally applicable to imaging EUV radiation from different sources.

Time-resolved X-ray reflection phases of the nearly forbidden Si(222) reflection under laser excitation.

The covalent electron density, which makes Si(222) measurable, is subject to laser excitation. The three-wave Si(222)/(13 {\overline 1}) diffraction at 7.82 keV is used for phase measurements. It is found that laser excitation causes a relative phase change of around 4° in Si(222) in the first 100 ps of excitation and this is gradually recovered over several nanoseconds. This phase change is due to laser excitation of covalent electrons around the silicon atoms in the unit cell and makes the electron density deviate further from the centrosymmetric distribution.

Triplet vs πσ* state mediated N-H dissociation of aniline.

UV-excited aromatic molecules with N-H/O-H moieties often possess an important nonradiative relaxation pathway, from an optically bright ππ* state to a dark dissociative πσ* state. We apply a new time-selected photofragment translational spectroscopy method to disclose a previously unknown triplet-mediated N-H dissociation of aniline prevented by the multiphoton dissociative ionization in conventional methods. We further determined the branching fractions of aniline dissociated in the πσ*, triplet, and ground states at 248 nm. Additionally, we selectively captured the population changes in the singlet and triplet states with ionization from different laser wavelengths, 355 or 266 nm, in time-resolved photoion yields. The combination of experimental data enables us to uniquely determine the relative ionization cross sections of the singlet and triplet states at an ionization laser wavelength of 266 nm and allows us to extensively measure the rate constants of intersystem crossing and the branching fractions at various excitation wavelengths.

Excited-state dissociation dynamics of phenol studied by a new time-resolved technique.

Phenol is an important model molecule for the theoretical and experimental investigation of dissociation in the multistate potential energy surfaces. Recent theoretical calculations [X. Xu et al., J. Am. Chem. Soc. 136, 16378 (2014)] suggest that the phenoxyl radical produced in both the X and A states from the O-H bond fission in phenol can contribute substantially to the slow component of photofragment translational energy distribution. However, current experimental techniques struggle to separate the contributions from different dissociation pathways. A new type of time-resolved pump-probe experiment is described that enables the selection of the products generated from a specific time window after molecules are excited by a pump laser pulse and can quantitatively characterize the translational energy distribution and branching ratio of each dissociation pathway. This method modifies conventional photofragment translational spectroscopy by reducing the acceptance angles of the detection region and changing the interaction region of the pump laser beam and the molecular beam along the molecular beam axis. The translational energy distributions and branching ratios of the phenoxyl radicals produced in the X, A, and B states from the photodissociation of phenol at 213 and 193 nm are reported. Unlike other techniques, this method has no interference from the undissociated hot molecules. It can ultimately become a standard pump-probe technique for the study of large molecule photodissociation in multistates.

High-resolution light-scattering imaging with two-dimensional hexagonal illumination patterns: system implementation and image reconstruction formulations.

Structured illumination microscopy (SIM) was recently adapted to coherent imaging, named structured oblique-illumination microscopy (SOIM), to improve the contrast and resolution of a light-scattering image. Herein, we present high-resolution laterally isotropic SOIM imaging with 2D hexagonal illuminations. The SOIM is implemented in a SIM fluorescence system based on a spatial-light modulator (SLM). We design an SLM pattern to generate diffraction beams at 0° and ± 60.3° simultaneously to form a 2D hexagonal illumination, and undertake calculations to obtain optimal SLM shifts at 19 phases to yield a reconstructed image correctly. Beams of linear and circular polarizations are used to show the effect of polarization on the resolution improvement. We derive the distributions of the electric field of the resultant hexagonal patterns and work out the formulations of the corresponding coherent-scattering imaging for image reconstruction. The reconstructed images of gold nanoparticles (100 nm) confirm the two-fold improvement of resolution and reveal the effect of polarization on resolving adjacent nanoparticles. To demonstrate biological applications, we present the cellular structures of a label-free fixed HeLa cell with improved contrast and resolution. This work enables one to perform high-resolution dual-mode - fluorescence and light-scattering - imaging in a system, and is expected to broaden the applications of SOIM.

Direct infrared observation of hydrogen chloride anions in solid argon.

To facilitate direct spectroscopic observation of hydrogen chloride anions (HCl-), electron bombardment of CH3Cl diluted in excess Ar during matrix deposition was used to generate this anion. Subsequent characterization were performed by IR spectroscopy and quantum chemical calculations. Moreover the band intensity of HCl- decays slowly when the matrix sample is maintained in the dark for a prolonged time. High-level ab inito calculation suggested that HCl- is only weakly bound. Atom-in-molecule charge analysis indicated that both atoms of HCl- are negatively charged and the Cl atom is hypervalent.

Advantage of spatial map ion imaging in the study of large molecule photodissociation.

The original ion imaging technique has low velocity resolution, and currently, photodissociation is mostly investigated using velocity map ion imaging. However, separating signals from the background (resulting from undissociated excited parent molecules) is difficult when velocity map ion imaging is used for the photodissociation of large molecules (number of atoms ≥ 10). In this study, we used the photodissociation of phenol at the S1 band origin as an example to demonstrate how our multimass ion imaging technique, based on modified spatial map ion imaging, can overcome this difficulty. The photofragment translational energy distribution obtained when multimass ion imaging was used differed considerably from that obtained when velocity map ion imaging and Rydberg atom tagging were used. We used conventional translational spectroscopy as a second method to further confirm the experimental results, and we conclude that data should be interpreted carefully when velocity map ion imaging or Rydberg atom tagging is used in the photodissociation of large molecules. Finally, we propose a modified velocity map ion imaging technique without the disadvantages of the current velocity map ion imaging technique.

Is energy pooling necessary in ultraviolet matrix-assisted laser desorption/ionization?

RATIONALE: Energy pooling has been suggested as the key process for generating the primary ions during ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI). In previous studies, decreases in fluorescence quantum yields as laser fluence increased for 2-aminobenzoic acid, 2,5-dihydroxybenzoic acid (2,5-DHB), and 3-hydroxypicolinic acid were used as evidence of energy pooling. This work extends the research to other matrices and addresses whether energy pooling is a universal property in UV-MALDI. METHODS: Energy pooling was investigated in a time-resolved fluorescence experiment by using a short laser pulse (355 nm, 20 ps pulse width) for excitation and a streak camera (1 ps time resolution) for fluorescence detection. RESULTS: The excited-state lifetime of 2,5-DHB decreased with increases in laser fluence. This suggests that a reaction occurs between two excited molecules, and that energy pooling may be one of the possible reactions. However, the excited-state lifetime of 2,4,6-trihydroxyacetophenone (THAP) did not change with increases in laser fluence. The upper limit of the energy pooling rate constant for THAP is estimated to be approximately 100-500 times smaller than that of 2,5-DHB. CONCLUSIONS: The small energy pooling rate constant for THAP indicates that the potential contribution of the energy pooling mechanism to the generation of THAP matrix primary ions should be reconsidered.

Fluorescence spectroscopy of UV-MALDI matrices and implications of ionization mechanisms.

Matrix-assisted laser desorption ionization (MALDI) has been widely used in the mass analysis of biomolecules; however, there are a lot of debates about the ionization mechanisms. Previous studies have indicated that S1-S1 annihilation might be a key process in the generation of primary ions. This study investigates S1-S1 annihilation by examining the time-resolved fluorescence spectra of 12 matrices. No S1-S1 annihilation was observed in six of these matrices (3-hydroxy-picolinic acid, 6-aza-2-thiothymine, 2,4-dihydroxy-acetophenone, 2,6-dihydroxy-acetophenone, 2,4,6-trihydroxy-acetophenone, and ferulic acid). We observed two matrix molecules reacting in an electronically excited state (S1) in five of these matrices (2,5-dihydroxybenzoic acid, α-cyano-4-hydroxycinnamic acid, 2,5-dihydroxy-acetophenone, 2,3-dihydroxybenzoic acid, and 2,6-dihydroxybenzoic acid), and S1-S1 annihilation was a possible reaction. Among these five matrices, no S1-S1 annihilation was observed for 2,3-dihydroxybenzoic acid in typical peak power region of nanosecond laser pulses in MALDI, but a very small value of reaction rate constant was observed only in the high peak power region. The excited-state lifetime of sinapinic acid was too short to determine whether the molecules reacted in an electronically excited state. No correlation was observed between the ion generation efficiency of MALDI and S1-S1 annihilation. The results indicate that the proposal of S1-S1 annihilation is unnecessary in MALDI and energy pooling model for MALDI ionization mechanism has to be modified.

Water Plays Multifunctional Roles in the Intervening Formation of Secondary Organic Aerosols in Ozonolysis of Limonene: A Valence Photoelectron Spectroscopy and Density Functional Theory Study.

Although water may affect aqueous aerosol chemistry, how it intervenes in the formation of secondary organic aerosols (SOAs) at the molecular level remains elusive. Ozonolysis of limonene is one of the most important sources of indoor SOAs. Here, we report the valence electronic properties of limonene aerosols and SOAs derived from limonene ozonolysis (Lim-SOAs) via aerosol vacuum ultraviolet photoelectron spectroscopy, with a focus on the effects of water on Lim-SOAs. The first vertical ionization energy of limonene aerosols is measured to be 8.79 ± 0.07 eV. While water significantly increases the total photoelectron yield of Lim-SOAs, three photoelectron features attributable to Lim-SOAs each exhibit distinct dependence on the fraction of water in aerosols, implying that different formation pathways and molecular origins are involved in the formation of Lim-SOAs. Combined with density functional theory calculation and mass spectrometry measurements, this study reveals that water, particularly the water dimer, enhances the formation of Lim-SOAs by altering the ozonolysis energetics and pathways by intervening in its Criegee chemistry, acting as both a catalyst and a reactant. The atmospheric implication is discussed.

Far-UV spectroscopy of mono- and multilayer hexagonal boron nitrides.

Hexagonal boron nitrides (hBNs) have a very high luminescence efficiency and are promising materials for deep-UV emitters. Although intense deep-UV emissions have been recorded in various forms of hBN excited by photons or energetic electrons, information on the electronic structure of the conduction band has been derived mainly from theoretical works. Therefore, there is a lack of high-resolution absorption data in the far-UV region. In this study, the far-UV absorption spectra of chemical-vapor-deposition-grown mono- and multilayer hBNs were recorded at 10 and 298 K. In addition to the previously reported band at 6.10 eV, two absorption bands at 6.82 and 8.86 eV were observed for the first time in thin-film hBN. Furthermore, excitation of the hBN thin film samples with 6.89-eV photons revealed intense emission peaks at 6.10 (mono) and 5.98 (multi) eV with a bandwidth of ∼0.7 eV. Comparing the absorption and photoluminescence data, we believe that both direct and indirect transitions occur in the radiative processes.

A novel six-rhodopsin system in a single archaeon.

Microbial rhodopsins, a diverse group of photoactive proteins found in Archaea, Bacteria, and Eukarya, function in photosensing and photoenergy harvesting and may have been present in the resource-limited early global environment. Four different physiological functions have been identified and characterized for nearly 5,000 retinal-binding photoreceptors, these being ion transporters that transport proton or chloride and sensory rhodopsins that mediate light-attractant and/or -repellent responses. The greatest number of rhodopsins previously observed in a single archaeon had been four. Here, we report a newly discovered six-rhodopsin system in a single archaeon, Haloarcula marismortui, which shows a more diverse absorbance spectral distribution than any previously known rhodopsin system, and, for the first time, two light-driven proton transporters that respond to the same wavelength. All six rhodopsins, the greatest number ever identified in a single archaeon, were first shown to be expressed in H. marismortui, and these were then overexpressed in Escherichia coli. The proteins were purified for absorption spectra and photocycle determination, followed by measurement of ion transportation and phototaxis. The results clearly indicate the existence of a proton transporter system with two isochromatic rhodopsins and a new type of sensory rhodopsin-like transducer in H. marismortui.

Coherent anti-Stokes Raman scattering microscopy using a single-pass picosecond supercontinuum-seeded optical parametric amplifier.

We have demonstrated coherent anti-Stokes Raman scattering (CARS) microscopy with a single-pass picosecond supercontinuum-seeded optical parametric amplifier (SCOPA). The SCOPA was pumped by a frequency-doubled picosecond passively mode-locked Nd:YVO(4) laser, and was seeded by a supercontinuum light source. Compared with the conventional experimental setups of CARS microscopy, our exposition is substantially simpler because the pump and Stokes lasers are overlapped in the SCOPA automatically and thus steered into a microscope coherently. The feasibility of this novel light source to CARS imaging was illustrated by acquiring the fundamental and overtone CARS images of the aromatic C-H stretching mode of polystyrene beads and an image of the pharynx of a C. elegans of the aliphatic C-H stretching mode.

Ion dissociation of hydrazoic acid investigated by synchrotron-radiation-based photoionization mass spectrometry.

We report mass resolved photoionization yield spectra of a molecular-beam cooled sample of HN(3) using photoionization mass spectrometry based on high-resolution monochromatized synchrotron radiation. Spectra are reported at mass-to-charge ratios of 14(N(+)), 15(NH(+)), 29(N(2)H(+)), 42(N(3)(+)), and 43(HN(3)(+)) in the region of each ionization threshold. The thresholds observed here are all lower than the previously reported ones obtained with electron impact ionization, which were the only ones available in the literature prior to this work. The appearance energies can be used to evaluate four key thermochemical quantities of relevance to HN(3): D(0)(H-N(3)), D(0)(N-N(2)), D(0)(N-H), and IE(NH). We observe the appearance energy of the parent ion (HN(3)(+)) to be 10.56 +/- 0.02 eV, somewhat below the reported ionization energies derived from photoelectron spectroscopy. Great care was taken to evaluate the importance of vibrational hot bands to the photoionization yield spectra. This experiment also provides a lower limit to the proton affinity of N(2) allowing us to bracket this quantity with improved certainty: 119.3 kcal/mol

Spectra of atomic sulfur 1D in transitions to autoionizing Rydberg states in the region of 75,800-89,500 cm(-1).

We recorded photoionization spectra of sulfur atoms in transitions from state (1)D in the range of 75,800-89,500 cm(-1). Dissociation of CS(2) after photolysis at 193 nm produced these sulfur atoms in a singlet excited state; they were then ionized with synchrotron radiation (NSRRC, beamline U9CGM) at resolution of up to 3 cm(-1) and detected with a quadruple mass filter. Rydberg series 3s(2)3p(3)((2)D(3/2)(0))nd[3/2] and 3s(2)3p(3)((2)D(5/2)(0))ns[5/2] with n extending to 16 and 32, respectively, to limit (2)D(0) are assigned. New Rydberg series 3s(2)3p(3)((2)D(3/2)(0))nd[1/2](1), ((2)D(5/2)(0))nd[5/2], and ((2)D(3/2)(0))nd[5/2] with n from 5-9 for the former two series and 7-13 for the latter are assigned. A new Rydberg line at 85 335 cm(-1) is assigned to 3s(2)3p(3)((2)D(3/2)(0))6d (1)P.

Interfacial Solvation and Surface pH of Phenol and Dihydroxybenzene Aqueous Nanoaerosols Unveiled by Aerosol VUV Photoelectron Spectroscopy.

Although the significance of aqueous interfaces has been recognized in numerous important fields, it can be even more prominent for nanoscaled aqueous aerosols because of their large surface-to-volume ratios and prevalent existence in nature. Also, considering that organic species are often mixed with aqueous aerosols in nature, a fundamental understanding of the electronic and structural properties of organic species in aqueous nanoaerosols is essential to learn the interplay between water and organic solutes under the nanoscaled size regime. Here, we report for the first time the vacuum ultraviolet photoelectron spectroscopy of phenol and three dihydroxybenzene (DHB) isomers including catechol, resorcinol, and hydroquinone in the aqueous nanoaerosol form. By evaluating two photoelectron features of the lowest vertical ionization energies originated from the b1(π) and a2(π) orbitals for phenolic aqueous nanoaerosols, their interfacial solvation characteristics are unraveled. Phenolic species appear to reside primarily on/near the aqueous nanoaerosol interface, where they appear only partially hydrated on the aqueous interface with the hydrophilic hydroxyl group more solvated in water. An appreciable proportion of phenol is found to coexist with phenolate at/near the nanoaerosol interface even under a high bulk pH of 12.0, indicating that the nanoaerosol interface exhibits a composition distribution and pH drastically different from those of the bulk. The surface pH of phenol-containing aqueous nanoaerosols is found to be ∼2.2 ± 0.1 units more acidic than that of the bulk interior, as measured at the bulk pH of 12.0. From the photoelectron spectra of DHB aqueous nanoaerosols, the effects of numbers/arrangements of -OH groups are assessed. This study shows that the hydration extents, pH values, deprotonation status, and numbers/relative arrangements of -OH groups are crucial factors affecting the ionization energies of phenolic aqueous nanoaerosols and thus their redox-based activities. The multifaceted implications of the present study in the aerosol science, atmospheric/marine chemistry, and biological science are also addressed.

Molecular Basis of the Antioxidant Capability of Glutathione Unraveled via Aerosol VUV Photoelectron Spectroscopy.

Glutathione (GSH), the most abundant nonenzymatic antioxidant in living systems, actively scavenges various exogenous/endogenous oxidizing species, defending important biomolecules against oxidative damages. Although it is well established that the antioxidant activity of GSH originates from the cysteinyl thiol (-SH) group, the molecular origin that makes the thiol group of GSH a stronger reducing agent than other thiol-containing proteins is unclear. To gain insights into the molecular basis underlying GSH's superior antioxidant capability, here we report, for the first time, the valence electronic structures of solvated GSH in the aqueous aerosol form via the aerosol vacuum ultraviolet photoelectron spectroscopy technique. The pH-dependent electronic evolution of GSH is obtained, and the possible correlations between GSH and its constituting amino acids are interrogated. The valence band maxima (VBMs) for GSH aqueous aerosols are found at 7.81, 7.61, 7.52, and 5.51 ± 0.10 eV at a pH of 1.00, 2.74, 7.00, and 12.00, respectively, which appear to be lower than the values of their corresponding hybrid counterparts collectively contributed from the three isolated constituting amino acids of GSH. An additional photoelectron feature is observed for GSH aqueous aerosols at pH = 12.00, where the thiol group on its Cys residue becomes deprotonated and the relatively well-separated feature allows its vertical ionization energy (VIE) to be determined as 6.70 ± 0.05 eV. Compared to a VIE of 6.97 ± 0.05 eV obtained for a similar thiolate feature observed previously for isolated Cys aqueous aerosols ( Su et al. VUV Photoelectron Spectroscopy of Cysteine Aqueous Aerosols: A Microscopic View of Its Nucleophilicity at Varying pH Conditions . J. Phys. Chem. Lett. 2015 , 6 , 817 - 823 ), a 0.27 eV reduction in the VIE is found for GSH, indicating that the outermost electron corresponding to the nonbonding electron on the thiolate group can be removed more readily from the GSH tripeptide than that from Cys alone. The possible origins underlying the decrease in the VBM of GSH with respect to that of each corresponding hybrid counterpart and the decrease in the VIE of the thiolate feature of GSH with respect to that of the isolated Cys are discussed, providing hints to understand the superior antioxidant capability of GSH from a molecular level.

VUV Photoelectron Spectroscopy of Cysteine Aqueous Aerosols: A Microscopic View of Its Nucleophilicity at Varying pH Conditions.

Cysteine (Cys) is unique due to its highly reactive thiol group. It often regulates the biological function of proteins by acting as the redox site. Despite its biological significance, however, the valence electronic structure of Cys under the aqueous environments remains unavailable. Here, we report the VUV photoelectron spectroscopy of Cys aqueous aerosols via a newly built aerosol VUV photoelectron spectroscopy apparatus. The photoelectron spectra of Cys show distinct band shapes at varying pH conditions, reflecting the altered molecular orbital characters when its dominating form changes. The ionization energy of Cys is determined to be 8.98 ± 0.05 eV at low pH. A new feature at a binding energy of 6.97 ± 0.05 eV is observed at high pH, suggesting that the negative charge on the thiolate group becomes the first electron to be removed upon ionization. This work implies that when Cys is involved in redox processes, the charge transfer mechanism may be entirely altered under different pH conditions.

Entry-level skill competency : a comparison of head nurses expectations and new graduates perceptions.

The purpose of this study was to compare the differences between head nurses expectations and new graduates perceptions of the entry-level skill competency. Subjects included 147 new graduates and 126 head nurses from four schools of nursing and their affiliated medical centers located in northern, central and southern Taiwan. The results showed that among 213 skills, 153 skills were reported by over 60% of head nurses to be performed precisely under clinical settings. In contrast to the graduates perceptions, over 60% of the graduates had confidence to perform only 82 skills precisely. The percentage of head nurses expectation and the perception of the graduates in skills that were reported to be performed precisely in clinical situations were significantly different in 145 skills (68%). For seventy-six skill items there was congruence between the percentage of head nurses expectations and new graduates perceptions. The percentage of the head nurses expectation were higher than the graduates perception in 55 skills. On the other hand, for 14 skills the percentage of graduates who perceived themselves as being able to perform them precisely was significantly higher than the percentage of head nurses. The results can be applied to improve nursing skills teaching and students pre-job preparation.

[Community care for a foreign bride who had attempted suicide].

Cultural maladjustment of foreign brides is an important social problem. In order to elucidate effective community nursing intervention, a 27 year-old Indonesian bride who had attempted suicide was adopted as a subject presented. In four months of community nursing care, the client's cooperation was won the client's and family's knowledge of suicide was improved, the client's coping skills were improved, communication between the couple was improved and the client's social interaction was improved, and religious tension with the family was moderated. The client's attitude was changed from rejecting to accepting. There was no suicide attempt in the subsequent 6 months and the client's ability to use social resources was significantly improved.