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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 .