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Articles you may be interested in Combining high mass resolution and velocity imaging in a time-of-flight ion spectrometer using pulsed fields and an electrostatic lens Rev. Sci. Instrum. 78, 083104 (2007); A pulsed Laval nozzle apparatus with laser ionization mass spectroscopy for direct measurements of rate coefficients at low temperatures with condensable gases Rev. High-resolution ion mobility measurements for silicon cluster anions and cations Abstract. Mass spectrometry is powerful tool for environmental and atmospheric chemistry analysis. Modern mass spectrometers demonstrate low detection limits, high sensitivity, and high resolving power. However, such high performance is not always enough to identify ambient ion clusters due to the clusters braking at the atmospheric pressure-to-vacuum interface of mass spectrometer. This study presents a high resolution ion mobility spectrometer-time-of-flight mass spectrometer (IMS-TOF) in the CLOUD experiment. This combination of orthogonal analytical techniques allows obtaining structural information in addition to mass-to-charge separation.

We report on a band structure calculation and de Haas-van Alphen measurements of KFe 2 As 2 . Three cylindrical Fermi surfaces are found. Effective masses of electrons range from 6 to 18m e , m e being the free electron mass. Remarkable discrepancies between the calculated and observed Fermi surface areas and the large mass enhancement (&3) highlight the importance of electronic correlations in determining the electronic structures of iron pnicitide superconductors. The discovery of superconductivity at T c ¼ 26 K in LaFeAs (O,F) 1) has given rise to intense experimental and theoretical efforts to elucidate the superconducting pairing mechanism and symmetry in iron pnictide superconductors (see ref. 2 for a recent review). Since the development of realistic theories of the mechanism requires detailed knowledge of the Fermi surface (FS), experimental determination of the FS is highly desirable.Accordingly, many angle-resolved photoemission spectroscopy (ARPES) studies have been performed.2) Their results show some level of agreement in the FS and band dispersion with conventional band structure calculations and moderate mass renormalization due to many-body effects. On the other hand, measurements of de Haas-van Alphen (dHvA) or other quantum oscillations, which are bulk probes and allow accurate determination of the FS cross sections and effective masses m à , are rather limited. dHvA measurements performed on the FeP compounds LaFePO 3,4) and SrFe 2 P 2 5) have shown that band shifts of up to $0:1 eV are necessary to bring band structure calculations into agreement with experiments and that the enhancement of effective masses over band ones is about two. Since high T c 's are found only in FeAs compounds, dHvA studies of FeAs compounds are more desired. However, because of the structural/magnetic phase transitions, measurements on the alkaline-earth 122 parent compounds AFe 2 As 2 (A ¼ Ca, Sr, and Ba) [6][7][8] have observed only small FS pockets, which makes it difficult to draw an overall picture of the electronic structures of these compounds. Very recently, dHvA measurements have been performed on BaFe 2 (As 1Àx P x ) 2 for 0:41 x 1. 9) As one goes from x ¼ 1 to 0.41, where T c $ 25 K, the electron FS's shrink and the mass enhancement factor increases from $2 to $4.KFe 2 As 2 is an end member of the high-T c binary alloy (Ba 1Àx K x )Fe 2 As 2 with the ThCr 2 Si 2 structure and has T c $ 3 K.10,11) The low-temperature resistivity exhibits a clear T 2 dependence with a large coefficient of A ¼ 0:026 m cm/K 2 , 12) and specific heat measurements have found correspondingly large Sommerfeld coefficients: exp ¼ 69 or 93 mJ/(K 2 Ámol-f.u.) (f.u. = formula unit) for poly or single crystals, respectively. 13,14) These indicate the existence of moderately large electron correlations.75 As nuclear quadrupole resonance measurements have shown that spin fluctuations (SF's) are much suppressed (compared with the optimally doped compound).13) The first ARPES measurement 15) found and hole FS's at the À point in the Bri...

Employing a hybrid density functional theory, we reveal the origin of the large absorption coefficient in BaSi 2 , which is roughly two to eighty times larger at ħω % E g = 0.5 eV than other conventional absorbers such as Si, GaAs, CdTe, CuInSe 2 , and Cu 2 ZnSnS 4 . This is explained on the basis of the electronic band structure of BaSi 2 , whereby the lowest conduction band (CB) has a small dispersion, owing to the localized Ba-d states, resulting in flat bands. Consequently, these flat bands contribute to a wide range of optical absorption in the low-energy region and lead to high optical activity in BaSi 2 .

Optical and electrical properties of polycrystalline orthorhombic BaSi2 prepared by arc melting in Ar atmosphere were investigated. The optical absorption spectra measured at room temperature showed that indirect and direct absorption edges were 1.15 and 1.25 eV, respectively. The activation energy estimated from temperature dependence of the resistivity was 1.10 eV. These results agreed well with a calculated band structure of the orthorhombic BaSi2 by first principles calculation using density functional theory.

We report on a barium disilicide (BaSi2) system as a potential absorber material for thin-film solar cells within the density functional theory framework by using advanced methods like GW and BSE and elucidate the first report on the molecular orbital diagram and defect physics in BaSi2.

We have completely determined the Fermi surface in KFe2As2 via de Haas-van Alphen (dHvA) measurements. Fundamental frequencies ǫ, α, ζ, and β are observed in KFe2As2. The first one is attributed to a hole cylinder near the X point of the Brillouin zone, while the others to hole cylinders at the Γ point. We also observe magnetic breakdown frequencies between α and ζ and suggest a plausible explanation for them. The experimental frequencies show deviations from frequencies predicted by band structure calculations. Large effective masses up to 19 me for B c have been found, me being the free electron mass. The carrier number and Sommerfeld coefficient of the specific heat are estimated to be 1.01 -1.03 holes per formula unit and 82 -94 mJmol −1 K −2 , respectively, which are consistent with the chemical stoichiometry and a direct measure of 93 mJmol −1 K −2 [H. Fukazawa et al., J. Phys. Soc. Jpn. 80SA, SA118 (2011)]. The Sommerfeld coefficient is about 9 times enhanced over a band value, suggesting the importance of low-energy spin and/or orbital fluctuations, and places KFe2As2 among strongly correlated metals. We have also performed dHvA measurements on Ba0.07K0.93Fe2As2 and have observed the α and β frequencies.

A ternary silicide Ca(Al0.5,Si0.5)2 was prepared by Ar arc melting. Powder x-ray diffraction measurement indicates that it has the AlB2-type structure with lattice constants of a=4.1905(5) and c=4.3992(8) Å, where Si and Al atoms are arranged in the disordered honeycomb lattice and Ca atoms are intercalated between them. The silicide is isostructural with a superconductor MgB2. Electrical resistivity and dc magnetization measurements revealed that it is a superconductor with a TC of 7.7 K.