Superconducting Tunnel Junction Detectors for Mass Spectrometry

Ohkubo, M.,Zen, N.,Kitazume, T.,Ukibe, M.,Shiki, S.,Koike, M. The Korean Superconductivity Society 2012 Progress in superconductivity Vol.14 No.2

With conventional mass spectrometry (MS), ions are separated according to mass/charge (m/z) ratios. We must speculate the z values to obtain the m values. Superconducting tunnel junction (STJ) detectors can solve this problem, and true mass spectrometry becomes possible instead of m/z spectrometry. The STJ detectors were installed in MS instruments with a variety of ion sources. As an example, we report fragmentation analysis of a non-covalent protein complex of hemoglobin.

Superconducting Tunnel Junction Detectors for Mass Spectrometry

M. Ohkubo,N. Zen,T. Kitazume,S. Shiki,M. Ukibe,M. Koike 한국초전도학회 2012 Progress in superconductivity Vol.14 No.2

With conventional mass spectrometry (MS), ions are separated according to mass/charge (m/z) ratios. We must speculate the z values to obtain the m values. Superconducting tunnel junction (STJ) detectors can solve this problem, and true mass spectrometry becomes possible instead of m/z spectrometry. The STJ detectors were installed in MS instruments with a variety of ion sources. As an example, we report fragmentation analysis of a non-covalent protein complex of hemoglobin.

Photoinduced Electron Transfer from a Tetrathiafulvalene-Calix[4]pyrrole to a Porphyrin Carboxylate within a Supramolecular Ensemble

Davis, Christina M.,Kawashima, Yuki,Ohkubo, Kei,Lim, Jong Min,Kim, Dongho,Fukuzumi, Shunichi,Sessler, Jonathan L. American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.25

<P>A supramolecular assembly is formed upon mixing millimolar concentrations of a <I>tetrakis</I>-tetrathiafulvalene calix[4]pyrrole (TTF-C4P) and a porphyrin tetraethylammonium carboxylate salt in benzonitrile (PhCN). The TTF-C4P binds to the carboxylate moiety of the porphyrin with a 1:1 stoichiometry and a binding constant of 6.3 × 10<SUP>4</SUP> M<SUP>–1</SUP> in this solvent at 298 K. Laser photoexcitation of the supramolecular complex results in formation of the triplet charge-separated (CS) state composed of a radical cation of the TTF-C4P receptor and the radical anion of the porphyrin carboxylate. These processes and the resulting states were characterized by means of transient absorption and electron spin resonance (ESR) spectroscopies. The rate constants corresponding to the forward and backward intramolecular electron-transfer (ET) processes were determined to be 2.1 × 10<SUP>4</SUP> and 3.6 × 10<SUP>2</SUP> s<SUP>–1</SUP>, respectively. The rate constants of intermolecular forward and backward electron transfer were also determined to be 4.4 × 10<SUP>8</SUP> and 9.8 × 10<SUP>8</SUP> M<SUP>–1</SUP> s<SUP>–1</SUP>, respectively. The electronic coupling constant (<I>V</I>), 1.2 × 10<SUP>–2</SUP> cm<SUP>–1</SUP>, and the reorganization energy (λ), 0.76 eV, for back electron transfer were evaluated from the temperature dependence of the rate constants of intramolecular electron transfer. The small <I>V</I> value indicates little spin-forbidden interaction between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and substantiates the long-lived CS lifetime. These results were corroborated by density function theory (DFT) calculations, which provided support for the conclusion that the HOMO and LUMO, located on a TTF moiety of the TTF-C4P and the porphyrin core, respectively, have little interaction though space.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-25/jp504087b/production/images/medium/jp-2014-04087b_0014.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp504087b'>ACS Electronic Supporting Info</A></P>

Introduction to IEC Standardization for Superconducting Sensors and Detectors

M. Ohkubo 한국초전도학회 2012 Progress in superconductivity Vol.14 No.2

Superconducting sensors and detectors have been applied to many fields or beginning to enter the maturing stage. The applications spread over a wide range of fields such as radio telescope, medical examination, quantum information,contamination inspection, materials analysis, etc. For users of the superconducting devices as well as developers, we have to avoid confusion of naming, graphical circuit symbols, and measurement methods for device performance. We are trying to formulate international standards under the International Electrotechnical Commission - Technical Committee 90(IEC-TC90), which is responsible for superconductivity. The sensors and detectors to be considered are divided into two groups: coherent sensors (SQUID, SIS mixers, etc.) and direct detectors (TES, STJ, MKID, SSPD, etc.).

Introduction to IEC Standardization for Superconducting Sensors and Detectors

Ohkubo, M. The Korean Superconductivity Society 2012 Progress in superconductivity Vol.14 No.2

Superconducting sensors and detectors have been applied to many fields or beginning to enter the maturing stage. The applications spread over a wide range of fields such as radio telescope, medical examination, quantum information, contamination inspection, materials analysis, etc. For users of the superconducting devices as well as developers, we have to avoid confusion of naming, graphical circuit symbols, and measurement methods for device performance. We are trying to formulate international standards under the International Electrotechnical Commission - Technical Committee 90 (IEC-TC90), which is responsible for superconductivity. The sensors and detectors to be considered are divided into two groups: coherent sensors (SQUID, SIS mixers, etc.) and direct detectors (TES, STJ, MKID, SSPD, etc.).

Analysis of Wide-gap Semiconductors with Superconducting XAFS Apparatus

S. Shiki,N. Zen,M. Koike,M. Ukibe,Y. Kitajima,S. Nagamachi,M. Ohkubo,N. Matsubayashi 한국초전도학회 2012 Progress in superconductivity Vol.14 No.2

Fluorescent yield X-ray absorption fine structure (XAFS) spectroscopy is useful for analyzing local structure of specific elements in matrices. We developed an XAFS apparatus with a 100-pixel superconducting tunnel junction (STJ) detector array with a high sensitivity and a high resolution for light-element dopants in wide-gap semiconductors. An STJ detector has a pixel size of 100 μm square, and an asymmetric layer structure of Nb(300 nm)-Al(70 nm)/AlOx/Al(70 nm)-Nb(50 nm). The 100-pixel STJ array has an effective area of 1 mm2. The XAFS apparatus with the STJ array detector was installed in BL-11A of High Energy Accelerator Research Organization, Photon Factory (KEK PF). Fluorescent X-ray spectrum for boron nitride showed that the average energy resolution of the 100-pixels is 12 eV in full width half maximum for the N-K line, and The C-K and N-K lines are separated without peak tail overlap. We analyzed the N dopant atoms implanted into 4H-SiC substrates at a dose of 300 ppm in a 200 nm-thick surface layer. From a comparison between measured X-ray Absorption Near Edge Structure (XANES) spectra and ab initio FEFF calculations, it has been revealed that the N atoms substitute for the C site of the SiC lattice.

Superconducting Strip Ion Detectors for Time-of-flight Mass Spectrometer

N. Zen,K. Suzuki,S. Shiki,M. Ukibe,M. Koike,A. Casaburi,M. Ejrnaes,R. Cristiano,M. Ohkubo 한국초전도학회 2012 Progress in superconductivity Vol.14 No.2

Superconducting detectors are promising as ion detectors for time-of-flight mass spectrometers (TOF MS). They can achieve mass-independent detection efficiency even for macromolecular bombardments, because output signals are produced through the deposited kinetic energy at ion impact instead of secondary electron emission that is the ion detection mechanism of conventional microchannel plate (MCP) detectors or secondary electron multipliers (SEM). Among the superconducting detectors, the superconducting strip ion detectors (SSIDs), which consist of several hundreds of superconducting lines with a width of a few hundreds nm and a thickness of a few tens of nm, have a fast response time of less than 1 ns. Inherently, the response time of SSIDs is determined by kinetic inductance, so that it was difficult to realize a fast SSID with a large detection area. However, we succeeded in realizing the detector size up to 5×5 mm2 without response time degradation by using a parallel configuration.

Analysis of Wide-gap Semiconductors with Superconducting XAFS Apparatus

Shiki, S.,Zen, N.,Matsubayashi, N.,Koike, M.,Ukibe, M.,Kitajima, Y.,Nagamachi, S.,Ohkubo, M. The Korean Superconductivity Society 2012 Progress in superconductivity Vol.14 No.2

Fluorescent yield X-ray absorption fine structure (XAFS) spectroscopy is useful for analyzing local structure of specific elements in matrices. We developed an XAFS apparatus with a 100-pixel superconducting tunnel junction (STJ) detector array with a high sensitivity and a high resolution for light-element dopants in wide-gap semiconductors. An STJ detector has a pixel size of $100{\mu}m$ square, and an asymmetric layer structure of Nb(300 nm)-Al(70 nm)/AlOx/Al(70 nm)-Nb(50 nm). The 100-pixel STJ array has an effective area of $1mm^2$. The XAFS apparatus with the STJ array detector was installed in BL-11A of High Energy Accelerator Research Organization, Photon Factory (KEK PF). Fluorescent X-ray spectrum for boron nitride showed that the average energy resolution of the 100-pixels is 12 eV in full width half maximum for the N-K line, and The C-K and N-K lines are separated without peak tail overlap. We analyzed the N dopant atoms implanted into 4H-SiC substrates at a dose of 300 ppm in a 200 nm-thick surface layer. From a comparison between measured X-ray Absorption Near Edge Structure (XANES) spectra and ab initio FEFF calculations, it has been revealed that the N atoms substitute for the C site of the SiC lattice.

Superconducting Strip Ion Detectors for Time-of-flight Mass Spectrometer

Zen, N.,Suzuki, K.,Shiki, S.,Ukibe, M.,Koike, M.,Casaburi, A.,Ejrnaes, M.,Cristiano, R.,Ohkubo, M. The Korean Superconductivity Society 2012 Progress in superconductivity Vol.14 No.2

Superconducting detectors are promising as ion detectors for time-of-flight mass spectrometers (TOF MS). They can achieve mass-independent detection efficiency even for macromolecular bombardments, because output signals are produced through the deposited kinetic energy at ion impact instead of secondary electron emission that is the ion detection mechanism of conventional microchannel plate (MCP) detectors or secondary electron multipliers (SEM). Among the superconducting detectors, the superconducting strip ion detectors (SSIDs), which consist of several hundreds of superconducting lines with a width of a few hundreds nm and a thickness of a few tens of nm, have a fast response time of less than 1 ns. Inherently, the response time of SSIDs is determined by kinetic inductance, so that it was difficult to realize a fast SSID with a large detection area. However, we succeeded in realizing the detector size up to $5{\times}5mm^2$ without response time degradation by using a parallel configuration.

Electroreduction and Acid–Base Properties of Dipyrrolylquinoxalines

Fu, Zhen,Zhang, Min,Zhu, Weihua,Karnas, Elizabeth,Mase, Kentaro,Ohkubo, Kei,Sessler, Jonathan L.,Fukuzumi, Shunichi,Kadish, Karl M. American Chemical Society 2012 The journal of physical chemistry. A, Molecules, s Vol.116 No.41

<P>The electroreduction and acid–base properties of dipyrrolylquinoxalines of the form H<SUB>2</SUB>DPQ, H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>), and H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB>2</SUB> were investigated in benzonitrile (PhCN) containing 0.1 M tetra-<I>n</I>-butylammonium perchlorate (TBAP). This study focuses on elucidating the complete electrochemistry, spectroelectrochemistry, and acid–base properties of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> (<I>n</I> = 0, 1, or 2) in PhCN before and after the addition of trifluoroacetic acid (TFA), tetra-<I>n</I>-butylammonium hydroxide (TBAOH), tetra-<I>n</I>-butylammonium fluoride (TBAF), or tetra-<I>n</I>-butylammonium acetate (TBAOAc) to solution. Electrochemical and spectroelectrochemical data provide support for the formation of a monodeprotonated anion after disproportionation of a dipyrrolylquinoxaline radical anion produced initially. The generated monoanion is then further reduced in two reversible one-electron-transfer steps at more negative potentials in the case of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>) and H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB>2</SUB>. Electrochemically monitored titrations of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> with OH<SUP>–</SUP>, F<SUP>–</SUP>, or OAc<SUP>–</SUP> (in the form of TBA<SUP>+</SUP>X<SUP>–</SUP> salts) give rise to the same monodeprotonated H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> produced during electroreduction in PhCN. This latter anion can then be reduced in two additional one-electron-transfer steps in the case of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>) and H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB>2</SUB>. Spectroscopically monitored titrations of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> with X<SUP>–</SUP> show a 1:2 stoichiometry and provide evidence for the production of both [H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB>]<SUP>−</SUP> and XHX<SUP>–</SUP>. The spectroscopically measured equilibrium constants range from log β<SUB>2</SUB> = 5.3 for the reaction of H<SUB>2</SUB>DPQ with TBAOAc to log β<SUB>2</SUB> = 8.8 for the reaction of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB>2</SUB> with TBAOH. These results are consistent with a combined deprotonation and anion binding process. Equilibrium constants for the addition of one H<SUP>+</SUP> to each quinoxaline nitrogen of H<SUB>2</SUB>DPQ, H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>), and H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB>2</SUB> in PhCN containing 0.1 M TBAP were also determined via electrochemical and spectroscopic means; this gave rise to log β<SUB>2</SUB> values ranging from 0.7 to 4.6, depending upon the number of nitro substituents present on the H<SUB>2</SUB>DPQ core. The redox behavior of the H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> compounds of the present study were further analyzed through comparisons with simple quinoxalines that lack the two linked pyrrole groups, i.e., Q(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> where <I>n</I> = 0, 1, or 2. It is concluded that the pyrrolic substituents play a critical role in regulating the electrochemical and spectroscopic features of DPQs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcafh/2012/jpcafh.2012.116.issue-41/jp3074706/production/images/medium/jp-2012-074706_0017.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp3074706'>ACS Electronic Supporting Info</A></P>