Surface-state parameters from very low energy electron reflection data

A parametric form of the amplitude of elastic reflection of very low energy electrons is derived. The amplitude expression conforms to the results of an earlier analysis of a simple case of electron reflection called the quasi two-beam case. The parameters in the amplitude expression refer to: (1) the surface states of the crystal; (2) the band structure of the substrate crystal; and (3) absorption (inelastic scattering) in the energy range of the experiment The amplitude expression also includes parameters relating to (4) the behavior of the amplitude at infinity and at negative energy.The amplitude expression is used to parameterize existing experimental results for nickel (001) and for the surface formed by adsorption of sodium on nickel (001) to form the centered (2 × 2) structure. The parameterization employs previously-computed values of parameters relating to the nickel band structure [category (2) above], and parameters in categories (1), (3) and (4) are adjusted to fit the electron-reflection data. In the case of the sodium-covered surface it is shown that the shape of the intensity-energy curve and the general level of intensity relative to that for clean nickel depends critically on the surface-state parameters. Two surface states are needed to fit the intensity data The values of the surface-state parameters are: location relative to vacuum level: 2.5 ± 0.1, 6.9 ± 0.2eV; width: 4.2 ± 0.4, 7.5 ± 1.0eV. The classification and significance of surface-state resonances is discussed briefly.     

The application of quasi-phase-matched parametric light sources to practical infrared chemical sensing systems

Quasi-phase-matched (QPM) materials allow the generation of spectroscopically useful infrared radiation in an efficient and broadly tunable format. Here, we describe several applications of QPM-based light sources to remote and local chemical sensing. The remote systems are gas imagers that employ a fiber-pumped continuous-wave optical parametric oscillator or a microlaser-pumped, diode-seeded optical parametric amplifier as the illumination source. Technology described for local sensing includes a cavity ring down spectrometer that employs a novel optical parametric generator–amplifier to achieve ≥350 cm^-1 of contiguous tuning and a long-wave infrared light source based on QPM GaAs. In each case the use of QPM materials in conjunction with effective pump sources instills simplicity and ruggedness into the sensing systems. Received: 15 April 2002 / Revised version: 6 June 2002 / Published online: 12 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-925/294-2595, E-mail: tjkulp@sandia.gov RID="**" ID="**"Present address: Corning Inc., Corning, NY 14831, USA RID="*" ID="*"Present address: Corning Inc., Corning, NY 14831, USA RID="**" ID="**"Present address: Blue Leaf Networks, Sunnyvale, CA 94086, USA RID="***" ID="***"Present address: Sandia National Laboratories, Albuquerque, NM 87185, USA     

Species specific isotope dilution for the accurate and SI traceable determination of arsenobetaine and methylmercury in cuttlefish and prawn

Methods based on species specific isotope dilution were developed for the accurate and SI traceable determination of arsenobetaine (AsBet) and methylmercury (MeHg) in prawn and cuttlefish tissues by LC-MS/MS and SPME GC-ICPMS. Quantitation of AsBet and MeHg were achieved by using a ¹³C-enriched AsBet spike (NRC CRM CBET-1) and an enriched spike of Me¹⁹⁸Hg (NRC CRM EMMS-1), respectively, wherein analyte mass fractions in enriched spikes were determined by reverse isotope dilution using natural abundance AsBet and MeHg primary standards. Purity of these primary standards were characterized by quantitative ¹H-NMR with the use of NIST SRM 350b benzoic acid as a primary calibrator, ensuring the final measurement results traceable to SI. Validation of employed methods of ID LC-MS/MS and ID SPME GC-ICPMS was demonstrated by analysis of several biological CRMs (DORM-4, TORT-3, DOLT-5, BCR-627 and BCR-463) with satisfying results.     

Identification of compound classes in soil and peat fulvic acids as observed by electrospray ionization tandem mass spectrometry

Soil and peat fulvic acids obtained from the International Humic Substances Society were fractionated by their solubility in methanol and analyzed by electrospray ionization tandem mass spectrometry. Precursor and product ion experiments produced mass spectra that indicated the presence of benzene, phenol, dihydroxy benzene, furan and thiophene carboxylic acids. Standards were used to substantiate the fragmentation patterns observed in the product ion spectra of the fulvic acid samples. This study makes significant progress into the direct identification of individual compounds in humic substances using a non-degradation technique.     

Low energy electron diffraction beam profiles and phase transition at Si(111)-7 X 7 surface

Angular profiles of low energy electron diffraction (LEED) beams from Si(111)-7 × 7 are measured for various crystal temperatures T near the phase transition with apparent critical temperature T_c ≈ 1140 K. From analyses of the profiles it is concluded that (1) long range superstructure order persists for T up to at least 50 K above T_c and (2) with increasing T the correlation length characterizing the short-range order peaks for T ≈ T_c ? 100 K and decreases rapidly for T >T_c. Conclusion (1) is discussed with reference to a dislocation network model of Si(111)-7 × 7 reconstruction.     

Block copolymer‐directed synthesis of porous anatase for lithium‐ion battery electrodes

A templating method is developed to produce porous nanocrystalline anatase materials for negative electrodes in lithium‐ion batteries (LIBs). Amphiphilic diblock copolymers are used to generate template films with phase‐separated internal structure. Subsequent swelling with acidified titanium(IV) bis(ammonium lactato) dihydroxide (TALH) solution yielded structured hybrid films. Upon heating, the formation of TiO₂ nanocrystals is induced, resulting in a three‐dimensional mesoporous structure directed by the bulk morphology of the polymer template. In comparison to commercial nanosized anatase, the structured anatase shows significant performance improvements in lithium‐ion coin cell batteries in terms of capacity, stability, and rate capability. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1890–1896     

Valonea Tannin: Tyrosinase Inhibition Activity,Structural Elucidation and Insights into the Inhibition Mechanism

Valonea tannin is a natural product readily extracted from acorn shells that has been suggested to have potential skin whitening properties. This study investigated the tyrosinase inhibition activity of extracted valonea tannin and the associated structure–function activity. Nuclear magnetic resonance spectroscopy and molecular weight analysis with gel permeation chromatography revealed that valonea tannin could be characterized as a hydrolysable tannin with galloyl, hexahydroxydiphenoyl and open formed-glucose moieties and an average molecular weight of 3042 ± 15 Da. Tyrosinase inhibition assays demonstrated that valonea tannin was 334 times more effective than gallic acid and 3.4 times more effective than tannic acid, which may relate to the larger molecular size. Kinetic studies of the inhibition reactions indicated that valonea tannin provided tyrosinase inhibition through mixed competitive–uncompetitive way. Stern–Volmer fitted fluorescence quenching analysis, isothermal titration calorimetry analysis and in silico molecule docking showed valonea tannin non-selectively bound to the surface of tyrosinase via hydrogen bonds and hydrophobic interactions. Inductively coupled plasma-optical emission spectroscopy and free radical scavenging assays indicated the valonea tannin had copper ion chelating and antioxidant ability, which may also contribute to inhibition activity. These results demonstrated the structure–function activity of valonea tannin as a highly effective natural tyrosinase inhibitor that may have commercial application in dermatological medicines or cosmetic products.