Articles you may be interested inFirst storage of ion beams in the Double Electrostatic Ion-Ring Experiment: DESIREE Rev. Sci. Instrum. 84, 055115 (2013); 10.1063/1.4807702 Upgrade of the MIT Linear Electrostatic Ion Accelerator (LEIA) for nuclear diagnostics development for Omega, Z and the NIF Rev. Sci. Instrum. 83, 043502 (2012); 10.1063/1.3703315 The double electrostatic ion ring experiment: A unique cryogenic electrostatic storage ring for merged ion-beams studies Rev. Sci. Instrum. 82, 065112 (2011);An electrospray ion source has been coupled to an accelerator that injects ions into an electrostatic heavy-ion storage ring. Since the dc ion current produced by electrospray ionization is low (ϳ10 6 ions/s), ions are accumulated in a cylindrical ion trap filled with a helium buffer gas. The ions are collisionally damped in the buffer gas and confined to the central trap region by a rf field. Extraction from the trap occurs within a few microseconds and after acceleration through 22 kV, the ions of interest are selected by a magnet according to their mass to charge ratio. The ion bunch is subsequently injected into the ring. Both positive and negative ions have been stored, with masses ranging over 3 orders of magnitude (ϳ10 2 -10 4 Da). From a pickup signal in the ring, the number of ions in a bunch is estimated to be of the order of 10 3 -10 4 when the accumulation time is 0.1 s. Our first measurements show that we can store a sufficient number of ions to study the decay of metastable ions and to determine relative destruction cross sections. The technique could be useful to probe conformers differing only in size. Furthermore, our setup can be used for spectroscopic measurements of the ion-photon interaction such as the excitation of ͓Cytochrome cϩ17H] 17ϩ protein ions with 532 nm photons.

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We have developed a lithography-free, all-dry process for fabricating graphene devices using an ultrathin quartz filament as a shadow mask to avoid possible contamination of graphene during lithographic process. This technique was used to prepare devices for electrical transport as well as planar tunnel junction studies of n-layer graphene (nLG), with n = 1, 2, 3 and higher. We observed localization behavior and an apparent reduction of density of states (DOS) near the Fermi energy in nLG.There has been a flurry of recent work 1,2 on films of 1-layer graphene (1LG), motivated by the pioneering work of Geim and coworkers 3 and Kim and coworkers 4 . Surprisingly, 1LG was found to host a two-dimensional electron gas with a band structure featuring zero effective mass 5 . Two types of unconventional integer quantum Hall effects (IQHE) were observed in 1LG 1,2 and in 2-layer graphene (2LG) 6 devices, respectively. Theoretical calculation indicates that n-layer graphene (nLG) with n > 2 are also interesting 5 .The highest mobility reported for 1LG devices is around 10,000 cm 2 /Vs at high gate voltages 2 , which is remarkable. However, it may not be sufficiently high to allow the observation of certain physical phenomena, such as fractional quantum Hall effect (FQHE). So far, all graphene devices reported in the literature were prepared by e-beam lithography. Multiple steps are required to pattern a device, including coating with organic materials, which may subject the graphene to possible contamination and add unwanted disorder to the device. It is therefore desirable to pursue alternative graphene device fabrication. Using ultrathin quartz filaments as shadow masks, we have developed a method to fabricate graphene devices, aiming at raising the mobility of the devices. Our method is lithography-free, all dry, and simple to implement. Devices fabricated were measured using a DC technique with a typical excitation current of 1 µA in a dip probe in which the sample was cooled by direct contact with 4 He liquid or gas.Two methods have been used to create graphene samples -exfoliation either mechanically in air 7 or chemically in solutions 8 , and thermal decomposition of SiC 9 . Our nLG flakes were created by mechanical exfoliation in air from freshly cleaved highly oriented pyrolytic graphite (HOPG) 10 . Heavily N-doped silicon with a 300-nm-thick thermally grown SiO 2 top layer was used as substrates. Thin graphene flakes were

C60(2-) and C70(2-) dianions have been produced by electrospray of the monoanions and subsequent electron pickup in a Na vapor cell. The dianions were stored in an electrostatic ring and their decay by electron emission was measured up to 1 s after injection. While C70(2-) ions are stable on this time scale, except for a small fraction of the ions which have been excited by gas collisions, most of the C60(2-) ions decay on a millisecond time scale, with a lifetime depending strongly on their internal temperature. The results can be modeled as decay by electron tunneling through a Coulomb barrier, mainly from thermally populated triplet states about 120 meV above a singlet ground state. At times longer than about 100 ms, the absorption of blackbody radiation plays an important role for the decay of initially cold ions. The tunneling rates obtained from the modeling, combined with WKB estimates of the barrier penetration, give a ground-state energy 200+/-30 meV above the energy of the monoanion plus a free electron and a ground-state lifetime of the order of 20 s.

We have developed an experimental technique that allows us to study the physics of short lived molecular dianions in the gas phase. It is based on the formation of monoanions via electrospray ionization, acceleration of these ions to keV energies, and subsequent electron capture in a sodium vapor cell. The dianions are stored in an electrostatic ion storage ring in which they circulate with revolution times on the order of 100 micros. This enables lifetime studies in a time regime covering five orders of magnitude, 10(-5)-1 s. We have produced dianions of 7,7,8,8-tetracyano-p-quinodimethane and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-p-quinodimethane (TCNQ-F(4)) and measured their lifetimes with respect to electron autodetachment. Our data indicate that most of the dianions were initially formed in electronically excited states in the electron transfer process. Two levels of excitation were identified by spectroscopy on the dianion of TCNQ-F(4), and the absorption spectrum was compared with spectra obtained from spectroelectrochemistry of TCNQ-F(4) in acetonitrile solution.

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